0001564590-20-049771 | 10-Q | XBRL Viewer

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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2020	Oct. 30, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Entity Registrant Name	ORCHARD THERAPEUTICS PLC
Current Fiscal Year End Date	--12-31
Entity Central Index Key	0001748907
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Common Stock, Shares Outstanding		97,749,444
Entity Shell Company	false
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Incorporation, State or Country Code	X0
Entity Address, Address Line One	108 Cannon Street
Entity Address, City or Town	London
Entity Address, Postal Zip Code	EC4N 6EU
City Area Code	44
Local Phone Number	(0) 203 808-8286
Document Quarterly Report	true
Document Transition Report	false
Entity File Number	001-38722
Entity Emerging Growth Company	false
Entity Tax Identification Number	00-0000000
Entity Address, Country	GB
Title of 12(b) Security	American Depositary Shares, each representing one ordinary share, nominal value £0.10 per share
Trading Symbol	ORTX
Security Exchange Name	NASDAQ

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 41,161	$ 19,053
Marketable securities	160,183	305,937
Trade receivables	3,183	1,442
Prepaid expenses and other current assets	11,537	8,530
Research and development tax credit receivable, current	18,047	14,934
Total current assets	234,111	349,896
Non-current assets:
Operating lease right-of-use-assets	30,476	19,415
Property and equipment, net	4,912	7,596
Research and development tax credit receivable	12,440	13,710
Restricted cash	4,266	4,264
Other assets	12,110	4,400
Total assets	298,315	399,281
Current liabilities:
Accounts payable	5,861	11,984
Accrued expenses and other current liabilities	23,135	37,980
Operating lease liabilities	8,990	5,892
Notes payable, current	2,778
Total current liabilities	40,764	55,856
Notes payable, long-term	22,199	24,699
Operating lease liabilities, net of current portion	24,162	15,320
Other long-term liabilities	4,123	4,213
Total liabilities	91,248	100,088
Commitments and contingencies (see Note 12)
Shareholders’ equity:
Ordinary shares, £0.10 nominal value	12,426	12,331
Additional paid-in capital	763,229	738,481
Accumulated other comprehensive income	3,432	2,042
Accumulated deficit	(572,020)	(453,661)
Total shareholders’ equity	207,067	299,193
Total liabilities and shareholders’ equity	$ 298,315	$ 399,281

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - £ / shares	Sep. 30, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Ordinary Shares, Nominal Value	£ 0.10	£ 0.10

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Product sales, net	$ 1,998	$ 1,918	$ 2,595	$ 1,918
Revenue, Product and Service [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember
Costs and operating expenses:
Cost of product sales	$ 667	$ 614	$ 858	$ 614
Cost, Product and Service [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember
Research and development	$ 14,678	$ 28,493	$ 71,082	$ 86,464
Selling, general and administrative	12,956	14,223	48,760	38,687
Total costs and operating expenses	28,301	43,330	120,700	125,765
Loss from operations	(26,303)	(41,412)	(118,105)	(123,847)
Other income (expense):
Interest income	534	2,169	2,906	5,519
Interest expense	(572)	(660)	(1,753)	(905)
Other income (expense), net	5,510	972	(2,223)	(1,146)
Total other income (expense), net	5,472	2,481	(1,070)	3,468
Net loss before income tax	(20,831)	(38,931)	(119,175)	(120,379)
Income tax benefit	541	2,194	816	2,373
Net loss	(20,290)	(36,737)	(118,359)	(118,006)
Other comprehensive income (loss)
Foreign currency translation adjustment	(5,310)	(613)	1,334	995
Unrealized gain (loss) on marketable securities	(308)	178	56	286
Total other comprehensive income (loss)	(5,618)	(435)	1,390	1,281
Total comprehensive loss	$ (25,908)	$ (37,172)	$ (116,969)	$ (116,725)
Net loss per share, basic and diluted	$ (0.20)	$ (0.38)	$ (1.19)	$ (1.29)
Weighted average number of ordinary shares outstanding, basic and diluted	99,664,616	97,817,847	99,255,370	91,553,803

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net loss	$ (118,359)	$ (118,006)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	1,558	1,213
Non-cash share-based compensation	21,221	13,753
Impairment of long-lived assets	5,650
Non-cash interest expense	378	180
Non-cash consideration for licenses	791
Amortization of Strimvelis loss provision	(2,018)	(2,921)
Amortization of premium (discount) on marketable securities	465	(559)
Other non-cash adjustments	650	(3,314)
Changes in operating assets and liabilities:
Trade receivables	(1,750)	(543)
Research and development tax credit receivable	(2,423)	(12,390)
Prepaid expenses, other current assets and other assets	(2,680)	(6,286)
Operating leases, right-of-use assets	4,253	2,123
Accounts payable, accrued expenses and other current liabilities	(16,166)	3,520
Other long-term liabilities		(1,465)
Operating lease liabilities	(6,010)	(514)
Net cash used in operating activities	(114,440)	(125,209)
Cash flows from investing activities:
Proceeds from sales and maturities of marketable securities	221,538	43,249
Purchases of marketable securities	(76,203)	(373,080)
Payment of construction deposit	(10,000)
Receipt of funds from construction deposit	1,876
Purchases of property and equipment	(2,551)	(1,528)
Net cash provided by (used in) investing activities	134,660	(331,359)
Cash flows from financing activities:
Issuance of debt from credit facility, net of debt issuance costs paid		24,473
Proceeds from share options and ESPP shares	2,831	1,741
Issuance of ADSs in follow-on offering, net of underwriters' discount		130,257
Payment of offering costs		(605)
Net cash provided by financing activities	2,831	155,866
Effect of exchange rate changes on cash, cash equivalents, and restricted cash	(941)	708
Net increase (decrease) in cash, cash equivalents and restricted cash	22,110	(299,994)
Cash, cash equivalents, and restricted cash, beginning of period	23,317	339,681
Cash, cash equivalents, and restricted cash, end of period	45,427	39,687
Supplemental disclosure of non-cash investing and financing activities
Property and equipment included in accounts payable and accrued expenses	15	29
Shares issued as part of license agreement	791
Supplemental disclosure of cash flow information:
Cash paid for taxes	2,375
Cash paid for interest	1,374	$ 726
Lease assets obtained in exchange for new operating lease liabilities	$ 17,486

Condensed Consolidated Statements Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Ordinary Shares	Additional Paid-in Capital	Accumulated Other Comprehensive Income	Accumulated Deficit
Balance at Dec. 31, 2018	$ 311,338	$ 10,924	$ 587,490	$ 3,163	$ (290,239)
Balance, Shares at Dec. 31, 2018		85,865,557
Share-based compensation expense	3,821		3,821
Exercise of share options	4		4
Exercise of share options, Shares		1,471
Other comprehensive income (loss)	3,051			3,051
Net loss	(30,739)				(30,739)
Balance at Mar. 31, 2019	287,475	$ 10,924	591,315	6,214	(320,978)
Balance, Shares at Mar. 31, 2019		85,867,028
Balance at Dec. 31, 2018	311,338	$ 10,924	587,490	3,163	(290,239)
Balance, Shares at Dec. 31, 2018		85,865,557
Other comprehensive income (loss)	1,281
Net loss	(118,006)
Balance at Sep. 30, 2019	339,744	$ 12,277	731,268	4,444	(408,245)
Balance, Shares at Sep. 30, 2019		96,517,534
Balance at Mar. 31, 2019	287,475	$ 10,924	591,315	6,214	(320,978)
Balance, Shares at Mar. 31, 2019		85,867,028
Share-based compensation expense	4,630		4,630
Exercise of share options	573	$ 69	504
Exercise of share options, Shares		532,889
Issuance of ESPP shares	693	$ 8	685
Issuance of ESPP shares, Shares		60,335
Issuance of ADSs in initial (follow-on) public offering, net of issuance costs	129,651	$ 1,233	128,418
Issuance of ADSs in initial (follow-on)public offering, net of issuance costs, Shares		9,725,268
Other comprehensive income (loss)	(1,335)			(1,335)
Net loss	(50,530)				(50,530)
Balance at Jun. 30, 2019	371,157	$ 12,234	725,552	4,879	(371,508)
Balance, Shares at Jun. 30, 2019		96,185,520
Share-based compensation expense	5,302		5,302
Exercise of share options	457	$ 43	414
Exercise of share options, Shares		332,014
Other comprehensive income (loss)	(435)			(435)
Net loss	(36,737)				(36,737)
Balance at Sep. 30, 2019	339,744	$ 12,277	731,268	4,444	(408,245)
Balance, Shares at Sep. 30, 2019		96,517,534
Balance at Dec. 31, 2019	299,193	$ 12,331	738,481	2,042	(453,661)
Balance, Shares at Dec. 31, 2019		96,923,729
Share-based compensation expense	9,479		9,479
Exercise of share options	1,438	$ 30	1,408
Exercise of share options, Shares		230,836
Other comprehensive income (loss)	5,013			5,013
Net loss	(50,569)				(50,569)
Balance at Mar. 31, 2020	264,554	$ 12,361	749,368	7,055	(504,230)
Balance, Shares at Mar. 31, 2020		97,154,565
Balance at Dec. 31, 2019	$ 299,193	$ 12,331	738,481	2,042	(453,661)
Balance, Shares at Dec. 31, 2019		96,923,729
Exercise of share options, Shares	607,167
Other comprehensive income (loss)	$ 1,390
Net loss	(118,359)
Balance at Sep. 30, 2020	207,067	$ 12,426	763,229	3,432	(572,020)
Balance, Shares at Sep. 30, 2020		97,659,771
Balance at Mar. 31, 2020	264,554	$ 12,361	749,368	7,055	(504,230)
Balance, Shares at Mar. 31, 2020		97,154,565
Share-based compensation expense	6,079		6,079
Exercise of share options	670	$ 27	643
Exercise of share options, Shares		214,299
Issuance of ESPP shares	432	$ 7	425
Issuance of ESPP shares, Shares		53,462
Ordinary shares issued as part of license agreements	791	$ 10	781
Ordinary shares issued as part of license agreements, Shares		75,413
Other comprehensive income (loss)	1,995			1,995
Net loss	(47,500)				(47,500)
Balance at Jun. 30, 2020	227,021	$ 12,405	757,296	9,050	(551,730)
Balance, Shares at Jun. 30, 2020		97,497,739
Share-based compensation expense	5,663		5,663
Exercise of share options	291	$ 21	270
Exercise of share options, Shares		162,032
Other comprehensive income (loss)	(5,618)			(5,618)
Net loss	(20,290)				(20,290)
Balance at Sep. 30, 2020	$ 207,067	$ 12,426	$ 763,229	$ 3,432	$ (572,020)
Balance, Shares at Sep. 30, 2020		97,659,771

Condensed Consolidated Statements Shareholders' Equity (Unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Jun. 30, 2019	Sep. 30, 2019
Statement Of Stockholders Equity [Abstract]
Issuance of ADSs in initial (follow-on)public offering, net of issuance costs	$ 620	$ 605

Nature of the Business

9 Months Ended

Sep. 30, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Nature of the Business

1. Nature of the Business

Orchard Therapeutics plc (the “Company”) is a global gene therapy leader dedicated to transforming the lives of people affected by rare diseases through the development of innovative, potentially curative gene therapies. The Company’s ex vivo autologous gene therapy approach utilizes genetically modified blood stem cells and seeks to correct the underlying cause of disease in a single administration. The Company’s gene therapy product candidate pipelines span multiple therapeutic areas where the disease burden on children, families and caregivers is immense and current treatment options are limited or do not exist.

The Company is a public limited company incorporated pursuant to the laws of England and Wales. The Company has American Depositary Shares (ADSs) registered with the U.S. Securities and Exchange Commission (the “SEC”) and has been listed on the Nasdaq Global Select Market since October 31, 2018. The Company’s ADSs each represent one ordinary share of the Company.

The Company is subject to risks and uncertainties common to development-stage companies in the biotechnology industry. There can be no assurance that the Company’s research and development will be successfully initiated or completed, that adequate protection for the Company’s technology will be obtained, that any products developed will obtain necessary government regulatory approval or that any products, if approved, will be commercially viable. The Company operates in an environment of rapid scientific and technological innovation and substantial competition from pharmaceutical and biotechnology companies. In addition, the Company is dependent upon the services of its employees, consultants and service providers. Even if the Company’s product development efforts are successful in gaining regulatory approval, it is uncertain when, if ever, the Company will realize significant revenue from product sales.

The Company is subject to risks associated with the COVID-19 pandemic. In an effort to halt the outbreak of COVID-19, a number of countries, including the United States, United Kingdom and Italy where the Company operates, have placed significant restrictions on travel. While some COVID-19 restrictions have been relaxed, limitations on travel and other social distancing measures have had an effect on the Company’s preclinical and clinical activities and regulatory timelines. Any prolonged material disruptions to the Company’s employees, suppliers, contract manufacturers, vendors, patients, government sponsored funding programs or the Company’s marketable securities could impact operating results and could lead to impairments. To date the Company has recorded impairments on long-lived assets that are due to a combination of a corporate restructuring and COVID-19 market impacts (see Note 8).

Through September 30, 2020, the Company funded its operations primarily with proceeds from the sale of convertible preferred shares and ADSs in the Company’s initial public offering (“IPO”) and a subsequent follow-on offering, as well as with certain grant and reimbursement payments and a drawdown on its credit facility, described in note 6 below. The Company has incurred recurring losses since its inception. As of September 30, 2020, the Company had an accumulated deficit of $572.0 million. The Company expects to continue to generate operating losses for the foreseeable future. The Company expects that its cash, cash equivalents, and marketable securities on hand as of September 30, 2020 of $201.3 million, will be sufficient to fund its operations and capital expenditure requirements through at least the next twelve months.

The Company will seek additional funding through private or public equity financings, debt financings, collaborations, strategic alliances and marketing, distribution or licensing arrangements, or any combination thereof. The Company may not be able to obtain financing on acceptable terms, or at all, and the Company may not be able to enter into collaborations or other arrangements. The terms of any financing may adversely affect the holdings or the rights of the Company’s shareholders and ADS holders. The future viability of the Company is dependent on its ability to raise additional capital to finance its operations. If the Company is unable to obtain funding, the Company will be forced to delay, reduce or eliminate some or all of its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects, or the Company may be unable to continue operations. Although management continues to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all.

Basis of Presentation and Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2020

Accounting Policies [Abstract]

Basis of Presentation and Summary of Significant Accounting Policies

2. Basis of Presentation and Summary of Significant Accounting Policies

Basis of presentation

The condensed consolidated interim financial statements of the Company are unaudited and have been prepared in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”) for interim financial reporting and in accordance with Regulation S-X, Rule 10-01. Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete financial statements. Any reference in these notes to applicable guidance is meant to refer to the authoritative U.S. GAAP as found in the Accounting Standards Codification (“ASC”), and Accounting Standards Update (“ASU”), of the Financial Accounting Standards Board (“FASB”). All intercompany accounts and transactions between the Company and its subsidiaries have been eliminated upon consolidation.

The accompanying unaudited condensed consolidated interim financial statements should be read in conjunction with the audited consolidated financial statements and accompanying notes included in the Company’s Annual Report on Form 10-K filed with the SEC on February 27, 2020 (the “Annual Report”). The condensed consolidated balance sheet as of December 31, 2019 was derived from audited consolidated financial statements included in the Company’s Annual Report but does not include all disclosures required by U.S. GAAP.

Certain information and footnote disclosures normally included in financial statements prepared in accordance with U.S. GAAP have been condensed or omitted from these interim financial statements. However, these interim financial statements include all adjustments, consisting only of normal recurring adjustments, which are, in the opinion of the Company’s management, necessary to fairly state the results of the interim period. The interim results are not necessarily indicative of results to be expected for the full year.

Use of estimates

The preparation of condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of revenue and expenses during the reporting periods. Significant estimates and assumptions reflected in these condensed consolidated financial statements include, but are not limited to, the accrual for research and development expenses, the research and development tax credit receivable, share-based compensation, operating lease assets and liabilities, and income taxes. The full extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s business, results of operations and financial condition, including sales, expenses, reserves and allowances, manufacturing, clinical trials, research and development costs and employee-related costs, will depend on future developments that are highly uncertain, including as a result of new information that may emerge concerning COVID-19 and the actions taken to contain it or treat COVID-19, as well as the economic impact on local, regional, national and international customers and markets. The Company has made estimates of the impact of COVID-19 within the Company’s financial statements and there may be changes to those estimates in future periods. As of the date of issuance of these unaudited condensed consolidated financial statements, the Company is not aware of any specific event or circumstance that would require the Company to update estimates, judgments or revise the carrying value of any assets or liabilities. Actual results may differ from these estimates.

Foreign currency

The reporting currency of the Company is the U.S. dollar. The Company has determined the functional currency of the parent company, Orchard Therapeutics plc, is the U.S. dollar because it predominantly raises finances and expends cash in U.S. dollars. The functional currency of the Company’s subsidiary operations is the applicable local currency. Transactions in foreign currencies are translated into the functional currency of the subsidiary in which they occur at the foreign exchange rate in effect on the date of the transaction. Monetary assets and liabilities denominated in foreign currencies at the balance sheet date are translated into the functional currency of the relevant subsidiary at the foreign exchange rate in effect on the balance sheet date. Non-monetary assets and liabilities denominated in foreign currencies that differ from the functional currency are translated into the functional currency at the exchange rates prevailing at the date of the transaction. The Company recorded realized and unrealized foreign currency transaction gains of $5.9 million and $1.0 million for the three months ended September 30, 2020 and 2019, respectively. The Company recorded realized and unrealized foreign currency transaction losses of $1.5 million and $1.1 million for the nine months ended September 30, 2020 and 2019, respectively. These amounts are included in other income (expense) in the condensed consolidated statements of operations and comprehensive loss.

The results of operations for subsidiaries, the functional currency of which is not the U.S. dollar, are translated at an average rate for the period in which this rate approximates to the foreign exchange rates ruling at the dates of the transactions and the balance sheets of these subsidiaries are translated at foreign exchange rates prevailing at the balance sheet date. Exchange differences arising from this translation of foreign operations are reported as an item of other comprehensive loss.

Cash and cash equivalents

The Company considers all highly liquid investments purchased with original maturities of 90 days or less at acquisition to be cash equivalents.

Marketable debt securities

Marketable securities consist of investments with original maturities greater than ninety days. The Company has classified its investments with maturities beyond one year as short term, based on their highly liquid nature and because such marketable securities represent the investment of cash that is available for current operations. The Company considers its investment portfolio of investments as available-for-sale. Accordingly, these investments are recorded at fair value, which is based on quoted market prices or other observable inputs. Unrealized gains and losses are recorded as a component of other comprehensive income (loss). Realized gains and losses are determined on a specific identification basis and are included in other income (loss). Amortization and accretion of discounts and premiums is also recorded in other income (loss).

When the fair value is below the amortized cost of the asset an estimate of expected credit losses is made, and is limited to the amount by which fair value is less than amortized cost. The credit-related impairment amount is recognized in net income; the remaining impairment amount and unrealized gains are reported as a component of accumulated other comprehensive income (loss) in shareholders’ equity. Credit losses are recognized through the use of an allowance for credit losses account and subsequent improvements in expected credit losses are recognized as a reversal of the allowance account. If the Company has the intent to sell the security or it is more likely than not that the Company will be required to sell the security prior to recovery of its amortized cost basis the allowance for credit loss is written off and the excess of the amortized cost basis of the asset over its fair value is recorded in net income.

United Kingdom research and development tax credit

As a company that carries out extensive research and development activities, the Company seeks to benefit from two U.K. research and development tax relief programs, the Small and Medium-sized Enterprises research and development tax credit (“SME”) program and the Research and Development Expenditure (“RDEC”) program. Qualifying expenditures largely comprise employment costs for research staff, consumables and certain internal overhead costs incurred as part of research projects for which the Company does not receive income.

Based on criteria established by U.K. HM Revenue and Customs (“HMRC”), management of the Company expects a proportion of expenditures being incurred in relation to its pipeline research, clinical trials management and manufacturing development activities to be eligible for research and development tax credits for the 2020 fiscal year. The Company has qualified under the more favorable SME regime for the year ended December 31, 2019 and expects to qualify under the SME regime for the year ending December 31, 2020.

The RDEC and SME credits are not dependent on the Company generating future taxable income or on the ongoing tax status or tax position of the Company. The Company has assessed its research and development activities and expenditures to determine which activities and expenditures are likely to be eligible under the research and development incentive program described above. At each period end, the Company estimates the reimbursement available to the Company based on available information at the time.

The Company recognizes credits from the research and development incentives when the relevant expenditure has been incurred and there is reasonable assurance that the reimbursement will be received. Such credits are accounted for as reductions in research and development expense. The following table below outlines the changes to the research and development tax credit receivable, including amounts recognized as an offset to research and development expense during the period, for the periods ended September 30, 2020 and 2019 (in thousands):

	Three Months Ended September 30,						Nine Months Ended September 30,
	2020			2019			2020			2019
Balance at beginning of period	$	32,729		$	20,325		$	28,644		$	10,585
Recognition of credit claims as offset to research and development expense		10,104			2,712			17,169			12,651
Receipt of credit claims		(13,558	)		(152	)		(14,573	)		(152	)
Foreign currency translation		1,212			(657	)		(753	)		(856	)
Balance at end of period	$	30,487		$	22,228		$	30,487		$	22,228

During the three months ended September 30, 2020, the Company recorded $5.8 million of additional tax credits related to a change in estimate associated with its U.K research and development tax credit receivable claim for fiscal year 2019 ($4.8 million) and estimate of our 2020 claim through June 30, 2020 ($1.0 million). The change in estimate was based on the results of a tax credit analysis associated with the Company’s qualified projects and research and development expenditures completed during the quarter to finalize the 2019 U.K. tax return. This amount was recorded as an offset to research and development expense. As of September 30, 2020, the Company’s tax incentive receivable from the U.K. government was $30.5 million, of which $18.1 million was classified as current and $12.4 million was classified as noncurrent. As of December 31, 2019, the Company’s tax incentive receivable from the U.K. government was $28.6 million, of which $14.9 million was classified as current, and $13.7 million was classified as noncurrent.

Restricted cash and construction deposits

Cash and cash equivalents that are restricted as to withdrawal or use under the terms of certain contractual agreements are recorded as restricted cash on the Company’s condensed consolidated balance sheet. The Company has an outstanding letter of credit for $3.0 million associated with a lease, and is required to hold this amount in a standalone bank account, as of September 30, 2020 and December 31, 2019. The Company is also contractually required to maintain cash collateral accounts associated with corporate credit cards and other leases in the amount of $1.3 million at September 30, 2020, and December 31, 2019.

The Company includes the restricted cash balance in cash and cash equivalents when reconciling beginning-of-period and end-of-period total amounts shown on the condensed consolidated statements of cash flows The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported in the condensed consolidated balance sheet that sum to the total of the amounts reported in the unaudited condensed consolidated statement of cash flows:

	September 30,		December 31,
	2020		2019
	(in thousands)
Cash and cash equivalents	$	41,161	$	19,053
Restricted cash		4,266		4,264
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	$	45,427	$	23,317

The Company also has $8.1 million in an escrow account associated with the construction of the Company’s leased facility in Fremont, California, which the Company has ceased construction and build-out of and intends to consider its options relating to the lease, including subleasing the facility. Subject to the terms of the lease and reduction provisions, this amount may be decreased to nil over time upon qualifying construction expenditure, or will be returned in late 2022 to the extent funds are not used. The Company deposited $10.0 million into the account in the first quarter of 2020 and has received $1.9 million in receipts from the escrow funds for work performed to date. Of the $8.1 million remaining in the escrow account, $2.3 million is classified within other prepaid expenses and other current assets and $5.8 million is classified within other assets on the condensed consolidated balance sheet based on the timing of when the Company expects to receive the cash from the escrow agent.

Product sales

The Company’s product sales of Strimvelis are currently distributed exclusively at the San Raffaele Hospital in Milan, Italy. San Raffaele Hospital will purchase and pay for Strimvelis and submit a claim to the payer. The Company’s contracted sales with San Raffaele Hospital contain a single performance obligation and the Company recognizes revenue from product sales when the Company has satisfied its performance obligation by transferring control of Strimvelis to San Raffaele Hospital. Control of the product generally transfers upon the completion of the scheduled Strimvelis treatment. The Company’s product sales represent total net product sales of Strimvelis. The Company evaluated the variable consideration under Accounting Standards Codification (ASC) 606, Revenue from Contracts with Customers, and there is currently no variable consideration included in the transaction price for Strimvelis. Costs to manufacture and deliver the product and those associated with administering the therapy are included in cost of product sales. As the product is sold in direct relation to a scheduled treatment, the Company estimates that there is limited risk of product return, including the risk of product expiration.

Research and development costs

Research and development costs are expensed as incurred. Research and development expenses consist of costs incurred in performing research and development activities, including salaries, share-based compensation and benefits, facilities costs, depreciation, third-party license fees, certain milestone payments, and external costs of outside vendors engaged to conduct preclinical and clinical development activities and clinical trials, as well as costs to develop a manufacturing process, perform analytical testing and manufacture clinical trial materials. Non-refundable prepayments for goods or services that will be used or rendered for future

research and development activities are recorded as prepaid expenses. Such amounts are recognized as an expense as the goods are delivered or the related services are performed, or until it is no longer expected that the goods will be delivered, or the services rendered. In addition, funding from research grants is recognized as an offset to research and development expense on the basis of costs incurred on the research program. Royalties to third parties associated with research grants will be accrued when they become probable.

Research agreement costs and accruals

The Company has entered into various research and development contracts. These agreements are cancelable, and related costs are recorded as research and development expenses as incurred. When billing terms under these contracts do not coincide with the timing of when the work is performed, the Company is required to make estimates of outstanding obligations as of period end to those third parties. Any accrual estimates are based on a number of factors, including the Company’s knowledge of the progress towards completion of the research and development activities, invoicing to date under the contracts, communication from the research institution or other companies of any actual costs incurred during the period that have not yet been invoiced, and the costs included in the contracts. Significant judgments and estimates may be made in determining the accrued balances at the end of any reporting period. Actual results could differ from the estimates made by the Company. The historical accrual estimates made by the Company have not been materially different from the actual costs.

Share-based compensation

The Company measures share-based awards granted to employees and directors based on the fair value of the shares and options on the date of the grant and recognizes compensation expense for those awards over the requisite service period, which is the vesting period of the respective award. Forfeitures are accounted for as they occur.

Comprehensive loss

Comprehensive loss includes net loss as well as other changes in shareholders’ equity that result from transactions and economic events other than those with shareholders. Reclassifications from other comprehensive loss to income from the sale of investments are not material. The components of accumulated other comprehensive income (loss) are detailed as follows (in thousands):

	Currency Translation			Unrealized Gain (Loss) on Investments			Accumulated Other Comprehensive Income (Loss)
Balance at December 31, 2019	$	1,776		$	266		$	2,042
Other comprehensive (loss) income, net of tax		6,034			(1,021	)		5,013
Balance at March 31, 2020	$	7,810		$	(755	)	$	7,055
Other comprehensive (loss) income, net of tax	$	610		$	1,385			1,995
Balance at June 30, 2020	$	8,420		$	630		$	9,050
Other comprehensive (loss) income, net of tax		(5,310	)		(308	)		(5,618	)
Balance at September 30, 2020	$	3,110		$	322		$	3,432

Leases

The Company determines if an arrangement is a lease at contract inception. Operating lease assets represent a right to use an underlying asset for the lease term and operating lease liabilities represent an obligation to make lease payments arising from the lease. Operating lease liabilities with a term greater than one year and their corresponding right-of-use assets are recognized on the balance sheet at the commencement date of the lease based on the present value of lease payments over the expected lease term. Certain adjustments to the right-of-use asset may be required for items such as initial direct costs paid or incentives received. The Company made an accounting policy election to not record a right-of-use asset or lease liability for leases with a term of one year or less. To date, the Company has not identified any material short-term leases, either individually or in the aggregate.

As the Company’s leases do not provide an implicit rate, the Company utilized the appropriate incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis over a similar term as the lease an amount equal to the lease payments in a similar economic environment. The Company estimated the incremental borrowing rate based on the Company’s currently outstanding credit facility as inputs to the analysis to calculate a spread, adjusted for factors that reflect the profile of secured borrowing over the expected term of the lease.

The components of a lease should be split into three categories: lease components (e.g., land, building, etc.), non-lease components (e.g., common area maintenance, utilities, performance of manufacturing services, purchase of inventory, etc.), and non-components (e.g., property taxes, insurance, etc.). Then the fixed contract consideration (including any related to non-components) must be allocated based on fair values to the lease components and non-lease components. Although separation of lease and non-lease components is required, certain practical expedients are available to entities. Entities electing the practical expedient would not separate lease and non-lease components. Rather, they would account for each lease component and the related non-lease component together as a single component. The Company has elected not to apply the practical expedient and with respect to its lease of manufacturing space at a contract manufacturing organization, the Company has allocated the consideration between the lease and non-lease components of the contract based on the respective fair values of the lease and non-lease components. The Company calculated the fair value of the lease and non-lease components using financial information readily available as part of its master services arrangement and other representative data indicative of fair value.

Impairment of long-lived assets

Long-lived assets consist of property and equipment and operating lease right-of-use assets. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset group to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset group are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset group over its fair value, as determined in accordance with the related accounting literature.

Strimvelis loss provision

As part of the GSK transaction (as defined in Note 10), the Company is required to maintain commercial availability of Strimvelis in the European Union until such time that an alternative gene therapy is available (see Note 10). Strimvelis is not currently expected to generate sufficient cash flows to overcome the costs of maintaining the product and certain regulatory commitments; therefore, the Company initially recorded a liability associated with the loss contract of $18.4 million in 2018. The Company recognizes the amortization of the loss provision on a diminishing balance basis based on the actual net loss incurred associated with the Strimvelis program during each period and the expected future net losses to be generated until such time as Strimvelis is no longer commercially available. The amortization of the provision is recorded as a credit to research and development expense. The Company has made an estimate of the expected future losses associated with Strimvelis and will adjust this estimate as facts and circumstances change regarding the commercial availability and costs of maintaining and selling Strimvelis. The Company does not update the accrued loss provision for any subsequent adjustment of the future losses; however, the timing of recognizing the amortization of what was originally recorded is adjusted for the updated future losses. The following table below outlines the changes to the Strimvelis loss provision for the periods ended September 30, 2020 and 2019 (in thousands):

	Three Months Ended September 30,					Nine Months Ended September 30,
	2020		2019			2020			2019
Balance at beginning of period	$	4,392	$	7,817		$	6,790		$	10,339
Amortization of loss provision		—		(330	)		(2,018	)		(2,921	)
Foreign currency translation		191		(247	)		(189	)		(178	)
Balance at end of period	$	4,583	$	7,240		$	4,583		$	7,240

Of the balance as of September 30, 2020 noted in the table above, $0.9 million is classified as current, and $3.7 million is classified as non-current.

Net income (loss) per share

Basic net income (loss) per share is computed by dividing the net income (loss) by the weighted average number of ordinary shares outstanding for the period. Diluted net income (loss) is computed by adjusting net income (loss) based on the potential impact of dilutive securities. Diluted net income (loss) per share is computed by dividing the diluted net income (loss) by the weighted average number of ordinary shares outstanding for the period, including potential dilutive ordinary shares. For purpose of this calculation, outstanding options and unvested restricted shares are considered potential dilutive ordinary shares. Since the Company was in a loss position for all periods presented, basic net loss per share is the same as diluted net loss per share for all periods as the inclusion of all potential ordinary share equivalents outstanding would have been anti-dilutive.

The following securities, presented based on amounts outstanding at each period end, are considered to be ordinary share equivalents, but were not included in the computation of diluted net loss per ordinary share because to do so would have been anti-dilutive:

	As of September 30,
	2020		2019
Share options		11,980,433		10,384,608
Unvested restricted share units		867,574		596,922
		12,848,007		10,981,530

Recent Accounting Pronouncements

Recently adopted accounting pronouncements

In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) (“ASU 2016-02”), which sets out the principles for the recognition, measurement, presentation and disclosure of leases for both parties to a contract (i.e., lessees and lessors). ASU 2016-02 supersedes the lease guidance under FASB ASC Topic 840, Leases, resulting in the creation of FASB ASC Topic 842, Leases (“ASC 842”). As we are no longer an emerging growth company as of December 31, 2019, ASC 842 became effective for us in 2019, as of January 1, 2019. During the nine months ended September 30, 2019, while the Company was an emerging growth company, ASC 840 was applied to leases. The Company’s previously reported consolidated cash flow statement for the nine months ended September 30, 2019 has been recast to reflect adoption of ASC 842 effective January 1, 2019. The following table summarizes the impact of the adoption to the Company’s operating cash flows in the previously issued condensed consolidated statement of cash flows. There was no impact to the condensed consolidated statement of comprehensive loss for the nine months ended September 30, 2019 as a result of the adoption of ASC 842. The table also includes other presentation adjustments within operating cash flows made to conform to current period presentation (in thousands):

	As previously reported			ASC 842 adjustments			Other presentation adjustments			As recast
Cash flows from operating activities:
Net loss	$	(118,006	)	$	—		$	—		$	(118,006	)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation		1,213			—			—			1,213
Non-cash share-based compensation		13,753			—			—			13,753
Impairment of long-lived assets		—			—			—			—
Non-cash interest expense		—			—			180			180
Non-cash considerations for licenses and milestones		—			—			—
Amortization of Strimvelis loss provision		(2,921	)		—			—			(2,921	)
Amortization of premium (discount) on marketable securities		—			—			(559	)		(559	)
Other non-cash adjustments		(3,693	)		—			379			(3,314	)
Changes in operating assets and liabilities:
Trade receivables		(2,937	)		—			2,394			(543	)
Research and development tax credit receivable		(12,390	)		—			—			(12,390	)
Prepaid expenses, current assets and other assets		(3,548	)		(344	)		(2,394	)		(6,286	)
Operating leases, right-of-use assets		-			2,123			—			2,123
Accounts payable, accrued expenses and other current liabilities		3,676			(156	)		—			3,520
Other long-term liabilities		(356	)		(1,109	)		—			(1,465	)
Operating lease liabilities		—			(514	)		—			(514	)
Net cash used in operating activities	$	(125,209	)	$	—		$	—		$	(125,209	)

In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”), which requires entities to record expected credit losses for certain financial instruments, including trade receivables, as an allowance that reflects the entity's current estimate of credit losses expected to be incurred. For available-for-sale debt securities in unrealized loss positions, the new standard requires allowances to be recorded instead of reducing the amortized cost of the investment. The new standard became effective for us on January 1, 2020. This guidance did not have a significant impact on the Company’s consolidated financial statements and related disclosures. The Company has a U.K. research and development tax credit receivable and trade receivables that are subject to this guidance. The Company has assessed whether it believes there is a current estimate of credit loss expected to be recorded for these receivables and concluded that any amount would not be significant and therefore the Company has not recorded any credit loss allowance for these receivables.

Fair Value Measurements and Marketable Debt Securities

9 Months Ended

Sep. 30, 2020

Fair Value Disclosures [Abstract]

Fair Value Measurements and Marketable Debt Securities

3. Fair Value Measurements and Marketable Debt Securities

The following tables present information about the Company’s financial assets that have been measured at fair value as of September 30, 2020 and indicate the fair value of the hierarchy of the valuation inputs utilized to determine such fair value. In general, fair values determined by Level 1 inputs utilize quoted prices (unadjusted) in active markets for identical assets or liabilities. Fair value determined by Level 2 inputs utilize observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted market prices in markets that are not active or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities. Fair values determined by Level 3 inputs are unobservable data points for the asset or liability, and include situations where there is little, if any, market activity for the asset or liability. During the three months and nine months ended September 30, 2020, there were no transfers between Level 1 and Level 2 financial assets.

The following table summarizes the Company’s cash equivalents and marketable debt securities as of September 30, 2020, in thousands:

	Fair Value Measurements at September 30, 2020 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents
Money market funds	$	5,610	$	—	$	—	$	5,610
U.S government securities		—		7,000		—		7,000
Corporate bonds				1,503
Commercial paper		—		1,000		—		1,000
Total cash equivalents		5,610		9,503		—		13,610
Marketable securities
U.S. government securities		—		3,000		—		3,000
Corporate bonds		—		132,399		—		132,399
Commercial paper		—		24,784		—		24,784
Total marketable securities		—		160,183		—		160,183
Total	$	5,610	$	169,686	$	—	$	173,793

The following table summarizes the Company’s cash equivalents and marketable debt securities as of December 31, 2019, in thousands:

	Fair Value Measurements at December 31, 2019 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents
Money market funds	$	202	$	—	$	—	$	202
U.S. government securities		—		3,159		—		3,159
Commercial paper		—		9,792		—		9,792
Total cash equivalents	$	202	$	12,951	$	—	$	13,153
Marketable securities
Corporate bonds	$	—	$	259,900	$	—	$	259,900
Commercial paper		—		46,037		—	$	46,037
Total marketable securities	$	—	$	305,937	$	—	$	305,937
Total	$	202	$	318,888	$	—	$	319,090

The carrying amount reflected in the condensed consolidated balance sheets for research and development tax incentive receivable, trade receivables, accounts payable, and accrued expenses approximate fair value due to their short-term maturities. The carrying value of the Company’s outstanding notes payable approximates fair value (a Level 2 fair value measurement), reflecting interest rates currently available to the Company.

Marketable Debt Securities

The following table summarizes the Company’s marketable debt securities as of September 30, 2020, in thousands:

	September 30, 2020
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Credit Losses		Fair Value
U.S. government securities	$	10,000	$	—	$	—		$	—	$	10,000
Corporate bonds		133,586		334		(18	)		—		133,902
Commercial paper		25,778		7		(1	)		—		25,784
Total	$	169,364	$	341	$	(19	)	$	—	$	169,686

The following table summarizes the Company’s marketable securities as of December 31, 2019, in thousands:

	December 31, 2019
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
U.S. government securities	$	3,159	$	—	$	—		$	3,159
Corporate bonds		259,669		285		(54	)		259,900
Commercial paper		55,794		42		(7	)		55,829
Total	$	318,622	$	327	$	(61	)	$	318,888

The following table summarizes the Company’s available-for-sale debt securities by contractual maturity, as of September 30, 2020 and December 31, 2019, in thousands:

	September 30, 2020		December 31, 2019
Due in one year	$	150,590	$	250,490
Due after one year through three years		19,096		68,398
Total	$	169,686	$	318,888

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Property and Equipment, Net

9 Months Ended

Sep. 30, 2020

Property Plant And Equipment [Abstract]

Property and Equipment, Net

4. Property and Equipment, Net

Property and equipment, net consisted of the following, in thousands:

	September 30,			December 31,
	2020			2019
Property and equipment:
Lab equipment	$	4,695		$	6,377
Leasehold improvements		2,441			1,839
Furniture and fixtures		299			508
Office and computer equipment		531			184
Construction-in-process		504			1,848
Property and equipment	$	8,470		$	10,756
Less: accumulated depreciation		(3,558	)		(3,160	)
Property and equipment, net	$	4,912		$	7,596

Depreciation expense was $0.5 million and $0.3 million for the three months ended September 30, 2020 and 2019, respectively. Depreciation expense was $1.6 million and $1.2 million for the nine months ended September 30, 2020 and 2019, respectively. During the second quarter of 2020, the Company took impairment charges of $2.3 million related to construction-in-process and $0.8 million related to laboratory equipment (See Note 8).

Accrued Expenses and Other Liabilities

9 Months Ended

Sep. 30, 2020

Accrued Liabilities And Other Liabilities [Abstract]

Accrued Expenses and Other Liabilities

5. Accrued Expenses and Other Liabilities

Accrued expenses and other liabilities consisted of the following, in thousands:

	September 30,		December 31,
	2020		2019
Accrued external research and development expenses	$	8,982	$	16,215
Accrued payroll and related expenses, including severance		9,768		12,381
Accrued professional fees		1,087		1,321
Accrued other		2,428		5,069
Strimvelis liability - current portion		870		2,994
Total accrued expenses and other liabilities	$	23,135	$	37,980

Notes Payable

9 Months Ended

Sep. 30, 2020

Debt Disclosure [Abstract]

Notes Payable

6. Notes Payable

In May 2019, as amended in April 2020, the Company entered into a senior term facilities agreement (the “Credit Facility”) with MidCap Financial (Ireland) Limited (“MidCap Financial”), as agent, and additional lenders from time to time (together with MidCap Financial, the “Lenders”), to borrow up to $75.0 million in term loans. To date, the Company has borrowed $25.0 million under an initial term loan. The remaining $50.0 million under the Credit Facility may be drawn down in the form of a second and third term loan, the second term loan being a $25.0 million term loan available no earlier than July 1, 2020 and no later than March 31, 2021 upon submission of certain regulatory filings and evidence of the Company having $100 million in cash and cash equivalent investments; and the third term loan being a $25.0 million term loan available no earlier than July 1, 2020 and no later than September 30, 2021 upon certain regulatory approvals and evidence of the Company having $125 million in cash and cash equivalent investments.

Each term loan under the Credit Facility bears interest at an annual rate equal to 6% plus LIBOR. The Company is required to make interest-only payments on the term loan for all payment dates prior to 24 months following the date of the Credit Facility, unless the third tranche is drawn, in which case for all payment dates prior to 36 months following the date of the Credit Facility. The term loans under the Credit Facility will begin amortizing on either the 24-month or the 36-month anniversary of the Credit Facility (as applicable), with equal monthly payments of principal plus interest to be made by the Borrower to the Lenders in consecutive monthly installments until the Loan Maturity Date. In addition, a final payment of 4.5% is due on the Loan Maturity Date. The Company accrues the final payment amount of $1.1 million associated with the first term loan, to outstanding debt by charges to interest expense using the effective-interest method from the date of issuance through the maturity date.

The Credit Facility includes affirmative and negative covenants. The affirmative covenants include, among others, covenants requiring the Company to maintain their legal existence and governmental approvals, deliver certain financial reports, maintain insurance coverage, maintain property, pay taxes, satisfy certain requirements regarding accounts and comply with laws and regulations. The negative covenants include, among others, restrictions on the Company transferring collateral, incurring additional indebtedness, engaging in mergers or acquisitions, paying dividends or making other distributions, making investments, creating liens, amending material agreements and organizational documents, selling assets, changing the nature of the business and undergoing a change in control, in some cases subject to certain exceptions. The Company is also subject to an ongoing minimum cash financial covenant in which the Company must maintain unrestricted cash in an amount not less than $20.0 million following the utilization of the second term loan and not less than $35.0 million following the utilization of the third term loan.

As of September 30, 2020, and December 31, 2019, notes payable consist of the following (in thousands):

	September 30,			December 31,
	2020			2019
Notes payable, net of issuance costs	$	24,630		$	24,541
Less: current portion		(2,778	)		—
Notes payable, net of current portion	$	21,852		$	24,541
Accretion related to final payment		347			158
Notes payable, long term	$	22,199		$	24,699

As of September 30, 2020, the estimated future principal payments due are as follows (in thousands):

	Aggregate Minimum Payments
2020 (September - December)		—
2021		4,861
2022		8,333
2023		8,334
Thereafter		4,597
Total		26,125
Less current portion		(2,778	)
Less unamortized portion of final payment		(779	)
Less unamortized debt issuance costs		(369	)
Notes payable, long term	$	22,199

During the three and nine months ended September 30, 2020, the Company recognized $0.6 million and $1.8 million of interest expense, respectively, related to the term loan. During the three and nine months ended September 30, 2019 the Company recognized $0.7 million and $0.9 million of interest expense related to the term loan, respectively. The effective annual interest rate as of September 30, 2020 on the outstanding debt under the term loan was approximately 9.4%.

Share-Based Compensation

9 Months Ended

Sep. 30, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Share-Based Compensation

7. Share-Based Compensation

The Company maintains four equity compensation plans; the Orchard Therapeutics Limited Employee Share Option Plan with Non-Employee Sub-Plan and U.S. Sub-Plan (the “2016 Plan”), the Orchard Therapeutics plc 2018 Share Option and Incentive Plan (the “2018 Plan”), the 2018 Employee Share Purchase Plan (the “ESPP”), and the 2020 Inducement Equity Plan (the “Inducement Plan”). The board of directors determined not to make any further awards under the 2016 plan following the Company’s IPO. In August 2020, pursuant to the evergreen provision in the 2018 plan, the Company increased the number of ordinary shares available for issuance under the 2018 plan by 4,846,186. As of September 30, 2020, 6,361,972 shares remained available for issuance under the 2018 Plan, 1,000,000 remained available under the Inducement Plan and 1,525,904 shares remained available for issuance under the ESPP.

Share option activity

The following table summarizes option activity under the plans for nine months ended September 30, 2020:

	Number of Options			Weighted Average Exercise Price
Outstanding at December 31, 2019		12,216,140		$	6.61
Granted		5,629,352			11.63
Exercised		(607,167	)		4.03
Forfeited		(2,572,755	)		10.65
Outstanding at September 30, 2020		14,665,570		$	7.93
Vested and expected to vest, as of September 30, 2020		14,665,570		$	7.93
Exercisable, September 30, 2020		7,053,899		$	5.47

The weighted-average grant date fair value of share options granted during the nine months ended September 30, 2020 was $7.38.

Restricted Share Units

Performance-based restricted share units

The Company has issued performance-based restricted share units (“RSUs”) to certain executives and members of its senior management, with vesting linked to the achievement of three specific regulatory and research and development milestones and one market condition based upon the volume weighted-average price (“VWAP”) of the Company’s ADSs for a certain period. Upon achievement of any of the aforementioned milestones, one third of the RSUs will vest, and the award will become fully vested upon achievement of three of the four performance conditions.

CEO Award

The Company granted 195,000 performance-based RSUs to its Chief Executive Officer, Bobby Gaspar, M.D., Ph.D., in April 2020. The award vests on January 2, 2024 as to 1/3 of the award for each of the first three to occur of four milestones, if each such milestone is achieved by the Company on or before December 31, 2023 and Dr. Gaspar remains continuously employed with the Company through January 2, 2024. The milestones relate to achievement of specific clinical and regulatory milestones.

Time-based restricted share units

Time-based restricted share units generally vest in equal annual installments over a three-year period.

The following table summarizes award activity for all types of restricted share units for the nine months ended September 30, 2020:

	Shares			Weighted Average Grant Date Fair Value
Unvested and outstanding at December 31, 2019		556,422		$	13.58
Granted		426,750			6.42
Vested		—			—
Forfeited		(310,672	)		14.16
Unvested and outstanding at September 30, 2020		672,500		$	8.77

The fair value associated with the performance-based conditions will be recognized when achievement of the milestones becomes probable, if at all. The Company determined that, as of September 30, 2020, none of the regulatory and research and development milestones associated with any outstanding performance-based RSUs were deemed probable. The amount of compensation cost recognized for the three months ended September 30, 2020 and 2019 for the market condition associated with the performance-based RSUs was nil and $0.3 million, respectively. The amount of compensation cost recognized for the nine months ended September 30, 2020 and 2019 for the market condition associated with the performance-based RSUs was $0.3 million and $0.9 million, respectively.

Share-based compensation expense

Share-based compensation expense recorded as research and development and general and administrative expenses is as follows (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2019		2020		2019
Research and development	$	2,617	$	2,071	$	8,398	$	5,041
General and administrative		3,046		3,231		12,823		8,712
Total share-based compensation	$	5,663	$	5,302	$	21,221	$	13,753

During the nine months ended September 30, 2020, the Company recognized $2.7 million of share-based compensation expense to selling, general and administrative expense related to the modification of share option awards associated with the separation of the Company’s former Chief Executive Officer.

As of September 30, 2020, total unrecognized compensation cost related to unvested share option grants was approximately $52.8 million. This amount is expected to be recognized over a weighted average period of approximately 2.7 years. As of September 30, 2020, the total unrecognized compensation cost related to performance-based RSUs is a maximum of $5.4 million, dependent upon achievement of the aforementioned milestones. As of September 30, 2020, the total unrecognized compensation cost related to time-based RSUs was $1.1 million. The expense associated with our performance-based and time-based RSUs is expected to be recognized over a weighted average period of approximately 2.3 years.

Restructuring Charges

9 Months Ended

Sep. 30, 2020

Restructuring And Related Activities [Abstract]

Restructuring Charges

8. Restructuring charges

On May 4, 2020, the Company committed to a new strategic plan and restructuring intended to enable the Company to advance its corporate strategy while reducing overall operating expenses, including ceasing construction and build-out of its Fremont, California manufacturing facility, closing its office in Menlo Park, California, reducing its workforce by approximately 25% across the Company, eliminating a number of future positions expected to be recruited in 2020 and 2021, reducing its investment in the future development for certain programs, and other cost-saving measures (collectively, the “Restructuring”). The workforce reductions took place primarily during the second and third quarters of 2020, and are expected to conclude in the fourth quarter of 2020.

Cash restructuring charges

Accrued restructuring and severance costs are included in Accrued expenses and other current liabilities in the condensed consolidated balance sheet. Activity for the fiscal year are summarized as follows, in thousands:

	Three Months Ended September 30,			Nine Months Ended September 30,
	2020			2020
Balance at beginning of period	$	841		$	—
Charged to expense		(9	)		1,575
Payments made		(511	)		(1,254	)
Balance at end of period	$	321		$	321

There were no restructuring costs during the three and nine months ended September 30, 2019.

During the nine months ended September 30, 2020, $1.2 million of the employee termination benefits has been classified on the condensed consolidated statement of operations as research and development expense and $0.4 million has been classified as selling, general, and administrative expense.

Impairment of long-lived assets

During the second quarter of 2020, the Company also took the following non-cash charges to research and development expense associated with the impairment of construction-in-process associated with the Fremont manufacturing facility, partial impairment of the right-of-use asset for the Fremont manufacturing facility lease (the “Fremont ROU asset”), and a write-down of laboratory equipment from the Company’s Menlo Park, CA facility, in thousands:

	Asset write-downs
Operating lease right-of-use asset	$	2,605
Construction-in-process		2,285
Laboratory equipment		760
Charge included in research and development expense	$	5,650

The Company assessed the Fremont construction-in-process for impairment in May 2020 upon the Restructuring. The construction-in-process related to design costs, and was determined to have no potential future value, and an impairment charge of $2.3 million was taken for the full value of the construction-in-process asset.

The Company assessed the Fremont ROU asset for impairment in May 2020 upon the Restructuring when the carrying value of the asset was $13.8 million. The Fremont ROU asset represented the asset group for the impairment assessment. Upon failing the first step of the long-lived asset impairment model where the undiscounted cash flows were less than the carrying value of the Fremont ROU asset, the Company performed the second step by comparing the fair value of the Fremont ROU asset to its carrying value. The fair value of the Fremont ROU asset is a non-recurring fair value measurement that was measured using a probability-weighted discounted cash flow approach, which estimated the present value of potential sublease income to be generated by the facility, less costs incurred to sublease the facility. The significant assumptions inherent in estimating the various probability weighted scenarios included the undiscounted forecasted sublease income less costs incurred, which included assumptions of the expected income and timing of entering into a future sublease, and a market-participant discount rate that reflects a potential discount rate. The Company selected the assumptions used in the fair value estimate using current market data associated with the potential sublease income and market participant discount rates. The undiscounted cash flows utilized in the fair value estimate ranged from $11.7 million to $19.1 million to be generated over the remainder of the lease term. The market-participant discount rate utilized in the fair value estimate was 4.6%. These assumptions represent level 3 inputs of the fair value hierarchy (see Note 3).

As of the assessment date, the fair value of the Fremont ROU asset was $11.2 million, and the Company recorded a $2.6 million impairment charge related to the asset. The remaining carrying value of the Fremont ROU asset is being amortized over the remaining lease term on a straight-line basis. A triggering event identified for the Fremont ROU asset in future periods could result in additional impairment charges if the estimated fair value of the asset is determined to be lower than the carrying value.

Leases

9 Months Ended

Sep. 30, 2020

Leases [Abstract]

Leases

9. Leases

Embedded operating lease arrangement

The Company is party to a manufacturing agreement for research and development and commercial production with AGC Biologics, S.p.A. (formerly MolMed S.p.A.)(“AGC”) pursuant to which AGC will develop, manufacture and supply certain viral vectors and conduct cell processing activities for certain Company development and commercial programs. A manufacturing agreement with AGC was novated to the Company as part of the GSK Agreement (see Note 10). On July 2, 2020 (the “Effective Date”), the Company entered into a new manufacturing and technology development master agreement with AGC (the “AGC Agreement”) which superseded the novated agreement.

The Company determined that the AGC Agreement contains an embedded lease as it includes provision of manufacturing suites designated for the Company’s exclusive use during the term of the agreement. The AGC Agreement has an initial term of five years, beginning on the Effective Date and ending July 2, 2025. The agreement may be extended for an additional two years by mutual agreement of the Company and AGC. The AGC Agreement contains payments associated with lease and non-lease components. The annual rental payments associated with the lease we considered a lease component and amount to €2.7 million per contract year. The non-lease components of the agreement consist of minimum manufacturing purchase requirements and dedicated manufacturing and development services with an initial annual commitment of €10.4 million. As a result of this agreement, the Company recorded a right-of-use asset in the amount of $13.7 million and lease liability in the amount of $13.7 million for this operating lease as of July 2020, and is recognizing rent expense on a straight-line basis throughout the estimated remaining term of the embedded lease.

The Company may terminate the AGC Agreement and the use of the exclusive manufacturing suites, with 12-months’ notice, and beginning no earlier than July 2, 2022. AGC may terminate the AGC Agreement with 24-months’ notice. The AGC Agreement provides for an option to reserve one additional exclusive manufacturing suite any time prior to January 1, 2022 for a one-time option fee plus annual rental fee. The AGC Agreement extends until July 2, 2025.

License Agreements

9 Months Ended

Sep. 30, 2020

License Agreements [Abstract]

License Agreements

10. License Agreements

GSK asset purchase and license agreement

In April 2018, the Company completed an asset purchase and license agreement (the “GSK Agreement”) with subsidiaries of GSK to acquire a portfolio of autologous ex vivo gene therapy assets and licenses for rare diseases and option rights on three additional programs in preclinical development from Telethon Foundation and San Raffaele Hospital (“Telethon-OSR”). The portfolio of programs and options acquired consisted of two late-stage clinical gene therapy programs in ongoing registrational trials for MLD and WAS, one earlier stage clinical gene therapy program for TDT, Strimvelis, and option rights exercisable upon completion of clinical proof of concept studies for three additional earlier-stage development programs, which option rights have all subsequently lapsed. The Company accounted for the GSK Agreement as an asset acquisition, since the asset purchase and licensing arrangement did not meet the definition of a business pursuant to ASC 805, Business Combinations, resulting in total consideration of $133.6 million, which was recorded in the second quarter of 2018.

The Company is required to use commercially reasonable efforts to obtain a Priority Review Voucher (“PRV”) from the United States Food and Drug Administration for each of the programs for MLD, WAS and TDT, the first of which GSK retained beneficial ownership over. GSK also has an option to acquire, at a price pursuant to an agreed upon formula, any PRV granted to the Company thereafter for MLD, WAS and TDT. If GSK does not exercise this option to purchase any PRV, the Company may sell the PRV to a third party and must share any proceeds in excess of a specified sale price equally with GSK. As part of the GSK Agreement the Company is also required to use its best endeavors to make Strimvelis commercially available in the European Union until such time as an alternative gene therapy, such as the Company’s OTL-101 product candidate, is commercially available for patients in Italy, and at all times at the San Raffaele Hospital in Milan, provided that a minimum number of patients continue to be treated at this site.

The Company will pay GSK non-refundable royalties and milestone payments in relation to the gene therapy programs acquired and the Company-developed product candidate, OTL-101. The Company will pay a flat mid-single digit percentage royalty on the combined annual net sales of ADA-SCID products, which includes Strimvelis and OTL-101. The Company will also pay tiered royalty rates at a percentage beginning in the mid-teens up to twenty percent for the MLD and WAS products, upon marketing approval, calculated as percentages of aggregate cumulative net sales of the MLD and WAS products, respectively. The Company will pay a tiered royalty at a percentage from the high single-digits to low double-digit for the TDT product, upon marketing approval, calculated as percentages of aggregate annual net sales of the TDT product. These royalties owed to GSK are in addition to any royalties owed to other third parties under various license agreements for the GSK programs. In aggregate, the Company may pay up to £90.0 million in milestone payments upon achievement of certain sales milestones applicable to GSK. The Company’s royalty obligations with respect to MLD and WAS may be deferred for a certain period in the interest of prioritizing available capital to develop each product. The Company’s royalty obligations are subject to reduction on a product-by-product basis in the event of market control by biosimilars and will expire in April 2048. Other than Strimvelis, these royalty and milestone payments were not determined to be probable and estimable at the date of the acquisition and are not included as part of consideration.

Telethon-OSR research and development collaboration and license agreements

In connection with the Company’s entering into the GSK Agreement in April 2018, the Company also acquired and assumed agreements with Telethon Foundation and San Raffaele Hospital, together referred to as Telethon-OSR, for the research, development and commercialization of autologous ex vivo gene therapies for ADA-SCID, WAS, MLD and TDT.

As consideration for the licenses, the Company will be required to make payments to Telethon-OSR upon achievement of certain product development milestones, up to an aggregate of approximately €31.0 million. Additionally, the Company will be required to pay to Telethon-OSR a tiered mid-single to low-double digit royalty percentage on annual sales of licensed products covered by patent rights on a country-by-country basis, as well as a low double-digit percentage of sublicense income received from any certain third-party sublicenses of the collaboration programs.

In May 2019, the Company entered into a license agreement with Telethon-OSR, under which Telethon-OSR granted to the Company an exclusive worldwide license for the research, development, manufacture and commercialization of Telethon-OSR’s ex vivo autologous HSC lentiviral based gene therapy for the treatment of mucopolysaccharidosis type I (“MPS-I”), including the Hurler variant. Under the terms of the agreement, Telethon-OSR received €15.0 million in upfront and milestone payments from the Company upon entering into the agreement, resulting in $17.2 million in in-process research and development expense. The Company is also required to make milestone payments contingent upon certain development, regulatory and commercial milestones are achieved. Additionally, the Company will be required to pay Telethon a tiered mid-single to low-double digit royalty percentage on annual net sales of licensed products.

Oxford BioMedica license, development and supply agreement

In November 2016, and as amended in June 2017, May 2018, July 2018, September 2018, May 2019 and April 2020, the Company entered into an arrangement with Oxford BioMedica plc whereby Oxford BioMedica granted an exclusive intellectual property license to the Company for the purposes of research, development, and commercialization of collaboration products, and whereby Oxford BioMedica will provide process development services (“Oxford BioMedica Development Agreement”). As part of the consideration to rights and licenses granted under the Oxford BioMedica Development Agreement, the Company issued 588,220 ordinary shares to Oxford BioMedica. The Company is also obligated to make certain development milestone payments in the form of issuance of additional ordinary shares if the milestones are achieved. In November 2017, the first milestone was achieved, and the Company was committed to issue another 150,826 ordinary shares, and issued these shares in 2018. In September 2018, the second and fourth milestones were achieved, and the Company issued 150,826 ordinary shares. In April 2020, the fifth milestone was deemed to have been met upon execution of the amended agreement in April 2020, and the Company issued another 75,413 ordinary shares to Oxford BioMedica with a total value of $0.8 million. The Company may also pay low single-digit percentage royalties on net sales of collaborated product generated under the Oxford BioMedica Agreement.

Income Taxes

9 Months Ended

Sep. 30, 2020

Income Tax Disclosure [Abstract]

Income Taxes

11. Income Taxes

Deferred tax assets and deferred tax liabilities are determined based on temporary differences between the financial reporting and tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. A valuation allowance is recorded against deferred tax assets if it is more likely than not that some portion or all of the deferred tax assets will not be realized.

The Company does not recognize a tax benefit for uncertain tax positions unless it is more likely than not that the position will be sustained upon examination by tax authorities, including resolution of any related appeals or litigation processes, based on the technical merits of the position. The tax benefit that is recorded for these positions is measured at the largest amount of cumulative benefit that has greater than a 50 percent likelihood of being realized upon ultimate settlement. Deferred tax assets that do not meet these recognition criteria are not recorded and the Company recognizes a liability for uncertain tax positions that may result in tax payments. If such unrecognized tax benefits were realized and not subject to valuation allowances, the entire amount would impact the tax provision. The Company has not recorded any amounts for unrecognized tax positions as of September 30, 2020 or December 31, 2019.

In response to the COVID-19 pandemic, the Coronavirus Aid, Relief and Economic Security Act (CARES Act) was signed into law in March 2020. The CARES Act lifts certain deduction limitations originally imposed by the Tax Cuts and Jobs Act of 2017 (2017 Tax Act). The CARES Act provides that corporate taxpayers may carryback net operating losses (NOLs) originating during 2018 through 2020 for up to five years to recover taxes paid in prior years, eliminates the 80% of taxable income limitations by allowing corporate entities to fully utilize NOL carryforwards to offset taxable income in 2018, 2019 or 2020. Taxpayers may generally deduct interest up to the sum of 50% of adjusted taxable income plus business interest income (30% limit under the 2017 Tax Act) for tax years beginning January 1, 2019 and 2020. The CARES Act allows taxpayers with alternative minimum tax credits to claim a refund in 2020 for the entire amount of the credits instead of recovering the credits through refunds over a period of years, as originally enacted by the 2017 Tax Act. In addition, the CARES Act raises the corporate charitable deduction limit to 25% of taxable income and makes qualified improvement property generally eligible for 15-year cost-recovery and 100% bonus depreciation. The enactment of the CARES Act did not result in any material adjustments to the Company’s income tax provision for the three months and nine months ended September 30, 2020, or to the Company’s net deferred tax assets as of September 30, 2020.

The Company recorded and income tax benefit of $0.5 million and $2.2 million for the three months ended September 30, 2020 and 2019, respectively, which relates primarily to the Company’s subsidiary operations in Europe and the U.SThe Company recorded income tax benefit of $0.8 million and $2.4 million for the nine months ended September 30, 2020 and 2019, respectively. .

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References + Details

Commitments and Contingencies

9 Months Ended

Sep. 30, 2020

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

12. Commitments and Contingencies

Manufacturing and technology development master agreement with AGC Biologics, S.p.A.

As discussed in Note 9, on July 2, 2020, the Company entered into the AGC Agreement, pursuant to which AGC will develop, manufacture and supply certain viral vectors and conduct cell processing activities for certain Company development and commercial programs. Under the terms of the AGC Agreement, the Company is obligated to pay AGC a minimum product manufacturing commitment of €2.7 million per contract year beginning in 2021 for the term of the AGC Agreement, which may increase to the mid-seven figures per contract year upon the achievement of certain milestones that may require additional manufacturing capacity. Additionally, the Company has committed €10.4 million per contract year for dedicated manufacturing and development resources, of which €2.7 million per contract year is considered a lease component associated with the exclusive manufacturing suites within AGC’s existing facilities (see Note 9). The Company may increase or decrease the usage of dedicated development services on a rolling basis with between six and 12-months’ prior written notice to AGC.

The AGC Agreement has an initial term of five years, beginning on the Effective Date and ending July 2, 2025. The AGC Agreement may be extended for an additional two years by mutual agreement of the Company and AGC. The Company has the right to terminate the AGC Agreement at its discretion upon 12-month’s prior written notice to AGC, and beginning no earlier than July 2, 2022, AGC has the right to terminate the AGC Agreement at its discretion upon 24-month’s prior written notice to the Company. Each party may terminate the AGC Agreement upon prior notice to the other party for an uncured material breach that the breaching party does not cure within the notice period.

Legal proceedings

The Company is not a party to any material litigation and does not have contingency reserves established for any litigation liabilities.

Employee Benefit Plans

9 Months Ended

Sep. 30, 2020

Compensation And Retirement Disclosure [Abstract]

Employee Benefit Plans

13. Employee Benefit Plans

The Company makes contributions to private defined contribution employee benefit plans on behalf of its employees. The Company provides employee contributions of up to six percent of each employee’s annual salary based on the jurisdiction the employees are located. The Company paid $0.3 million and $1.3 million in matching contributions for the three and nine months ended September 30, 2020. The Company paid $0.3 million and $0.9 million in matching contributions for the three and nine months ended September 30, 2019.

- Definition

The entire disclosure for retirement benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
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-Section 55
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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+ Details

Related Party Transactions

9 Months Ended

Sep. 30, 2020

Related Party Transactions

14. Related Party Transactions

GSK

In April 2018, the Company completed the GSK Agreement with subsidiaries of GSK to acquire a portfolio of autologous ex vivo gene therapy assets and licenses, for rare diseases and option rights on three additional programs in preclinical development from Telethon-OSR (See Note 10).

As of September 30, 2020, and December 31, 2019, the Company had accounts payable and accrued expenses due to GSK of $0.2 million and $3.3 million, respectively. During the nine months ended September 30, 2020 the Company entered into a global license agreement with GSK for use of their lentiviral stable cell line technology whereby we recorded $1.3 million of in-process research and development expense associated with upfront payments made to GSK. During the nine months ended September 30, 2020, the Company made $5.8 million in payments on accounts payable due to GSK, and the Company incurred $0.1 million in royalties due to GSK associated with sales of Strimvelis.

Basis of Presentation and Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2020

Accounting Policies [Abstract]

Basis of presentation

Use of estimates

Foreign currency

Cash and cash equivalents

The Company considers all highly liquid investments purchased with original maturities of 90 days or less at acquisition to be cash equivalents.

Marketable debt securities

United Kingdom research and development tax credit

	Three Months Ended September 30,						Nine Months Ended September 30,
	2020			2019			2020			2019
Balance at beginning of period	$	32,729		$	20,325		$	28,644		$	10,585
Recognition of credit claims as offset to research and development expense		10,104			2,712			17,169			12,651
Receipt of credit claims		(13,558	)		(152	)		(14,573	)		(152	)
Foreign currency translation		1,212			(657	)		(753	)		(856	)
Balance at end of period	$	30,487		$	22,228		$	30,487		$	22,228

Restricted cash and construction deposits

	September 30,		December 31,
	2020		2019
	(in thousands)
Cash and cash equivalents	$	41,161	$	19,053
Restricted cash		4,266		4,264
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	$	45,427	$	23,317

Product sales

Research and development costs

Research agreement costs and accruals

Share-based compensation

Comprehensive loss

	Currency Translation			Unrealized Gain (Loss) on Investments			Accumulated Other Comprehensive Income (Loss)
Balance at December 31, 2019	$	1,776		$	266		$	2,042
Other comprehensive (loss) income, net of tax		6,034			(1,021	)		5,013
Balance at March 31, 2020	$	7,810		$	(755	)	$	7,055
Other comprehensive (loss) income, net of tax	$	610		$	1,385			1,995
Balance at June 30, 2020	$	8,420		$	630		$	9,050
Other comprehensive (loss) income, net of tax		(5,310	)		(308	)		(5,618	)
Balance at September 30, 2020	$	3,110		$	322		$	3,432

Leases

Impairment of long-lived assets

Strimvelis loss provision

	Three Months Ended September 30,					Nine Months Ended September 30,
	2020		2019			2020			2019
Balance at beginning of period	$	4,392	$	7,817		$	6,790		$	10,339
Amortization of loss provision		—		(330	)		(2,018	)		(2,921	)
Foreign currency translation		191		(247	)		(189	)		(178	)
Balance at end of period	$	4,583	$	7,240		$	4,583		$	7,240

Of the balance as of September 30, 2020 noted in the table above, $0.9 million is classified as current, and $3.7 million is classified as non-current.

Net income (loss) per share

	As of September 30,
	2020		2019
Share options		11,980,433		10,384,608
Unvested restricted share units		867,574		596,922
		12,848,007		10,981,530

Recently adopted accounting pronouncements

	As previously reported			ASC 842 adjustments			Other presentation adjustments			As recast
Cash flows from operating activities:
Net loss	$	(118,006	)	$	—		$	—		$	(118,006	)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation		1,213			—			—			1,213
Non-cash share-based compensation		13,753			—			—			13,753
Impairment of long-lived assets		—			—			—			—
Non-cash interest expense		—			—			180			180
Non-cash considerations for licenses and milestones		—			—			—
Amortization of Strimvelis loss provision		(2,921	)		—			—			(2,921	)
Amortization of premium (discount) on marketable securities		—			—			(559	)		(559	)
Other non-cash adjustments		(3,693	)		—			379			(3,314	)
Changes in operating assets and liabilities:
Trade receivables		(2,937	)		—			2,394			(543	)
Research and development tax credit receivable		(12,390	)		—			—			(12,390	)
Prepaid expenses, current assets and other assets		(3,548	)		(344	)		(2,394	)		(6,286	)
Operating leases, right-of-use assets		-			2,123			—			2,123
Accounts payable, accrued expenses and other current liabilities		3,676			(156	)		—			3,520
Other long-term liabilities		(356	)		(1,109	)		—			(1,465	)
Operating lease liabilities		—			(514	)		—			(514	)
Net cash used in operating activities	$	(125,209	)	$	—		$	—		$	(125,209	)

Basis of Presentation and Summary of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2020

Accounting Policies [Abstract]

Summary of Amounts Recognized to Offset Research and Development Expense

The following table below outlines the changes to the research and development tax credit receivable, including amounts recognized as an offset to research and development expense during the period, for the periods ended September 30, 2020 and 2019 (in thousands):

	Three Months Ended September 30,						Nine Months Ended September 30,
	2020			2019			2020			2019
Balance at beginning of period	$	32,729		$	20,325		$	28,644		$	10,585
Recognition of credit claims as offset to research and development expense		10,104			2,712			17,169			12,651
Receipt of credit claims		(13,558	)		(152	)		(14,573	)		(152	)
Foreign currency translation		1,212			(657	)		(753	)		(856	)
Balance at end of period	$	30,487		$	22,228		$	30,487		$	22,228

Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash

The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported in the condensed consolidated balance sheet that sum to the total of the amounts reported in the unaudited condensed consolidated statement of cash flows:

	September 30,		December 31,
	2020		2019
	(in thousands)
Cash and cash equivalents	$	41,161	$	19,053
Restricted cash		4,266		4,264
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	$	45,427	$	23,317

Components of Accumulated Other Comprehensive Income (Loss)

Reclassifications from other comprehensive loss to income from the sale of investments are not material. The components of accumulated other comprehensive income (loss) are detailed as follows (in thousands):

	Currency Translation			Unrealized Gain (Loss) on Investments			Accumulated Other Comprehensive Income (Loss)
Balance at December 31, 2019	$	1,776		$	266		$	2,042
Other comprehensive (loss) income, net of tax		6,034			(1,021	)		5,013
Balance at March 31, 2020	$	7,810		$	(755	)	$	7,055
Other comprehensive (loss) income, net of tax	$	610		$	1,385			1,995
Balance at June 30, 2020	$	8,420		$	630		$	9,050
Other comprehensive (loss) income, net of tax		(5,310	)		(308	)		(5,618	)
Balance at September 30, 2020	$	3,110		$	322		$	3,432

Schedule of Changes in Loss Provision

The following table below outlines the changes to the Strimvelis loss provision for the periods ended September 30, 2020 and 2019 (in thousands):

	Three Months Ended September 30,					Nine Months Ended September 30,
	2020		2019			2020			2019
Balance at beginning of period	$	4,392	$	7,817		$	6,790		$	10,339
Amortization of loss provision		—		(330	)		(2,018	)		(2,921	)
Foreign currency translation		191		(247	)		(189	)		(178	)
Balance at end of period	$	4,583	$	7,240		$	4,583		$	7,240

Securities Excluded in the Computation of Diluted Net Loss Per Ordinary Share

	As of September 30,
	2020		2019
Share options		11,980,433		10,384,608
Unvested restricted share units		867,574		596,922
		12,848,007		10,981,530

Summary of Operating Cash Flows to Current Presentation and Other Presentation Adjustments

The following table summarizes the impact of the adoption to the Company’s operating cash flows in the previously issued condensed consolidated statement of cash flows. There was no impact to the condensed consolidated statement of comprehensive loss for the nine months ended September 30, 2019 as a result of the adoption of ASC 842. The table also includes other presentation adjustments within operating cash flows made to conform to current period presentation (in thousands):

	As previously reported			ASC 842 adjustments			Other presentation adjustments			As recast
Cash flows from operating activities:
Net loss	$	(118,006	)	$	—		$	—		$	(118,006	)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation		1,213			—			—			1,213
Non-cash share-based compensation		13,753			—			—			13,753
Impairment of long-lived assets		—			—			—			—
Non-cash interest expense		—			—			180			180
Non-cash considerations for licenses and milestones		—			—			—
Amortization of Strimvelis loss provision		(2,921	)		—			—			(2,921	)
Amortization of premium (discount) on marketable securities		—			—			(559	)		(559	)
Other non-cash adjustments		(3,693	)		—			379			(3,314	)
Changes in operating assets and liabilities:
Trade receivables		(2,937	)		—			2,394			(543	)
Research and development tax credit receivable		(12,390	)		—			—			(12,390	)
Prepaid expenses, current assets and other assets		(3,548	)		(344	)		(2,394	)		(6,286	)
Operating leases, right-of-use assets		-			2,123			—			2,123
Accounts payable, accrued expenses and other current liabilities		3,676			(156	)		—			3,520
Other long-term liabilities		(356	)		(1,109	)		—			(1,465	)
Operating lease liabilities		—			(514	)		—			(514	)
Net cash used in operating activities	$	(125,209	)	$	—		$	—		$	(125,209	)

Fair Value Measurements and Marketable Debt Securities (Tables)

9 Months Ended

Sep. 30, 2020

Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]

Schedule of Cash Equivalents and Marketable Debt Securities

The following table summarizes the Company’s cash equivalents and marketable debt securities as of September 30, 2020, in thousands:

	Fair Value Measurements at September 30, 2020 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents
Money market funds	$	5,610	$	—	$	—	$	5,610
U.S government securities		—		7,000		—		7,000
Corporate bonds				1,503
Commercial paper		—		1,000		—		1,000
Total cash equivalents		5,610		9,503		—		13,610
Marketable securities
U.S. government securities		—		3,000		—		3,000
Corporate bonds		—		132,399		—		132,399
Commercial paper		—		24,784		—		24,784
Total marketable securities		—		160,183		—		160,183
Total	$	5,610	$	169,686	$	—	$	173,793

The following table summarizes the Company’s cash equivalents and marketable debt securities as of December 31, 2019, in thousands:

	Fair Value Measurements at December 31, 2019 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents
Money market funds	$	202	$	—	$	—	$	202
U.S. government securities		—		3,159		—		3,159
Commercial paper		—		9,792		—		9,792
Total cash equivalents	$	202	$	12,951	$	—	$	13,153
Marketable securities
Corporate bonds	$	—	$	259,900	$	—	$	259,900
Commercial paper		—		46,037		—	$	46,037
Total marketable securities	$	—	$	305,937	$	—	$	305,937
Total	$	202	$	318,888	$	—	$	319,090

Schedule of Marketable Debt Securities

The following table summarizes the Company’s marketable debt securities as of September 30, 2020, in thousands:

	September 30, 2020
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Credit Losses		Fair Value
U.S. government securities	$	10,000	$	—	$	—		$	—	$	10,000
Corporate bonds		133,586		334		(18	)		—		133,902
Commercial paper		25,778		7		(1	)		—		25,784
Total	$	169,364	$	341	$	(19	)	$	—	$	169,686

The following table summarizes the Company’s marketable securities as of December 31, 2019, in thousands:

	December 31, 2019
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
U.S. government securities	$	3,159	$	—	$	—		$	3,159
Corporate bonds		259,669		285		(54	)		259,900
Commercial paper		55,794		42		(7	)		55,829
Total	$	318,622	$	327	$	(61	)	$	318,888

Schedule of Available-for-Sale Debt Securities by Contractual Maturity

The following table summarizes the Company’s available-for-sale debt securities by contractual maturity, as of September 30, 2020 and December 31, 2019, in thousands:

	September 30, 2020		December 31, 2019
Due in one year	$	150,590	$	250,490
Due after one year through three years		19,096		68,398
Total	$	169,686	$	318,888

Property and Equipment, Net (Tables)

9 Months Ended

Sep. 30, 2020

Property Plant And Equipment [Abstract]

Schedule of Property and Equipment, Net

Property and equipment, net consisted of the following, in thousands:

	September 30,			December 31,
	2020			2019
Property and equipment:
Lab equipment	$	4,695		$	6,377
Leasehold improvements		2,441			1,839
Furniture and fixtures		299			508
Office and computer equipment		531			184
Construction-in-process		504			1,848
Property and equipment	$	8,470		$	10,756
Less: accumulated depreciation		(3,558	)		(3,160	)
Property and equipment, net	$	4,912		$	7,596

Accrued Expenses and Other Liabilities (Tables)

9 Months Ended

Sep. 30, 2020

Accrued Liabilities And Other Liabilities [Abstract]

Schedule of Accrued Expenses and Other Liabilities

Accrued expenses and other liabilities consisted of the following, in thousands:

	September 30,		December 31,
	2020		2019
Accrued external research and development expenses	$	8,982	$	16,215
Accrued payroll and related expenses, including severance		9,768		12,381
Accrued professional fees		1,087		1,321
Accrued other		2,428		5,069
Strimvelis liability - current portion		870		2,994
Total accrued expenses and other liabilities	$	23,135	$	37,980

Notes Payable (Tables)

9 Months Ended

Sep. 30, 2020

Debt Disclosure [Abstract]

Summary of Notes Payable

As of September 30, 2020, and December 31, 2019, notes payable consist of the following (in thousands):

	September 30,			December 31,
	2020			2019
Notes payable, net of issuance costs	$	24,630		$	24,541
Less: current portion		(2,778	)		—
Notes payable, net of current portion	$	21,852		$	24,541
Accretion related to final payment		347			158
Notes payable, long term	$	22,199		$	24,699

Summary of Estimated Future Principal Payments Due

As of September 30, 2020, the estimated future principal payments due are as follows (in thousands):

	Aggregate Minimum Payments
2020 (September - December)		—
2021		4,861
2022		8,333
2023		8,334
Thereafter		4,597
Total		26,125
Less current portion		(2,778	)
Less unamortized portion of final payment		(779	)
Less unamortized debt issuance costs		(369	)
Notes payable, long term	$	22,199

Share-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Option Activity

The following table summarizes option activity under the plans for nine months ended September 30, 2020:

	Number of Options			Weighted Average Exercise Price
Outstanding at December 31, 2019		12,216,140		$	6.61
Granted		5,629,352			11.63
Exercised		(607,167	)		4.03
Forfeited		(2,572,755	)		10.65
Outstanding at September 30, 2020		14,665,570		$	7.93
Vested and expected to vest, as of September 30, 2020		14,665,570		$	7.93
Exercisable, September 30, 2020		7,053,899		$	5.47

Summary of Award Activity

The following table summarizes award activity for all types of restricted share units for the nine months ended September 30, 2020:

	Shares			Weighted Average Grant Date Fair Value
Unvested and outstanding at December 31, 2019		556,422		$	13.58
Granted		426,750			6.42
Vested		—			—
Forfeited		(310,672	)		14.16
Unvested and outstanding at September 30, 2020		672,500		$	8.77

Share-based Compensation Expense

Share-based compensation expense recorded as research and development and general and administrative expenses is as follows (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2019		2020		2019
Research and development	$	2,617	$	2,071	$	8,398	$	5,041
General and administrative		3,046		3,231		12,823		8,712
Total share-based compensation	$	5,663	$	5,302	$	21,221	$	13,753

Restructuring Charges (Tables)

9 Months Ended

Sep. 30, 2020

Restructuring And Related Activities [Abstract]

Summary of Cash Restructuring Charges

	Three Months Ended September 30,			Nine Months Ended September 30,
	2020			2020
Balance at beginning of period	$	841		$	—
Charged to expense		(9	)		1,575
Payments made		(511	)		(1,254	)
Balance at end of period	$	321		$	321

Summary of Impairment of Long Lived Assets

	Asset write-downs
Operating lease right-of-use asset	$	2,605
Construction-in-process		2,285
Laboratory equipment		760
Charge included in research and development expense	$	5,650

Nature of the Business - Additional Information (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Accumulated deficit	$ 572,020	$ 453,661
Cash, cash equivalents and marketable securities	$ 201,300

Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Mar. 31, 2020	Dec. 31, 2018
Summary Of Significant Accounting Policies [Line Items]
Foreign currency transaction gain (loss)	$ 5,900,000	$ 1,000,000.0		$ (1,500,000)	$ (1,100,000)
Tax incentive receivable, current	18,047,000			18,047,000		$ 14,934,000
Tax incentive receivable, noncurrent	12,440,000			12,440,000		13,710,000
Proceeds from lines of credit				3,000,000.0		3,000,000.0
Cash collateral associated with corporate credit cards and other leases	1,300,000			1,300,000		1,300,000
Liability associated with the loss contract								$ 18,400,000
Strimvelis loss provision current	900,000			900,000
Strimvelis loss provision non current	3,700,000			3,700,000
Fremont Lease Agreement [Member]
Summary Of Significant Accounting Policies [Line Items]
Escrow deposits related to construction	8,100,000			8,100,000
Deposit in escrow account							$ 10,000,000.0
Receipts from escrow funds				1,900,000
Fremont Lease Agreement [Member] \| Other Current Assets
Summary Of Significant Accounting Policies [Line Items]
Deposit in escrow account	2,300,000			2,300,000
Fremont Lease Agreement [Member] \| Other Noncurrent Assets
Summary Of Significant Accounting Policies [Line Items]
Deposit in escrow account	5,800,000			5,800,000
United Kingdom
Summary Of Significant Accounting Policies [Line Items]
Tax incentive receivable	30,500,000			30,500,000		28,600,000
Tax incentive receivable, current	18,100,000			18,100,000		14,900,000
Tax incentive receivable, noncurrent	12,400,000			12,400,000		13,700,000
Allowance for research and development tax credit receivable and trade receivables	0			0
United Kingdom \| Research and Development Expense
Summary Of Significant Accounting Policies [Line Items]
Foreign currency transaction gain (loss)	1,212,000	$ (657,000)		$ (753,000)	$ (856,000)
Additional tax credits	$ 5,800,000		$ 1,000,000.0			$ 4,800,000

Basis of Presentation and Summary of Significant Accounting Policies - Summary of Amounts recognized to Offset Research and Development Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Summary Of Significant Accounting Policies [Line Items]
Foreign currency transaction gain (loss)	$ 5,900	$ 1,000	$ (1,500)	$ (1,100)
United Kingdom \| Research and Development Expense
Summary Of Significant Accounting Policies [Line Items]
Balance at beginning of period	32,729	20,325	28,644	10,585
Recognition of credit claims as offset to research and development expense	10,104	2,712	17,169	12,651
Receipt of credit claims	(13,558)	(152)	(14,573)	(152)
Foreign currency transaction gain (loss)	1,212	(657)	(753)	(856)
Balance at end of period	$ 30,487	$ 22,228	$ 30,487	$ 22,228

Basis of Presentation and Summary of Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Summary Of Significant Accounting Policies [Abstract]
Cash and cash equivalents	$ 41,161	$ 19,053
Restricted cash	4,266	4,264
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	$ 45,427	$ 23,317	$ 39,687	$ 339,681

Basis of Presentation and Summary of Significant Accounting Policies - Components of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income Loss [Line Items]
Other comprehensive (loss) income, net of tax	$ (5,618)	$ 1,995	$ 5,013	$ (435)	$ (1,335)	$ 3,051	$ 1,390	$ 1,281
Currency Translation
Accumulated Other Comprehensive Income Loss [Line Items]
Stockholders Equity, Beginning Balance	8,420	7,810	1,776				1,776
Other comprehensive (loss) income, net of tax	(5,310)	610	6,034
Stockholders Equity, Ending Balance	3,110	8,420	7,810				3,110
Unrealized Gain (Loss) on Investments
Accumulated Other Comprehensive Income Loss [Line Items]
Stockholders Equity, Beginning Balance	630	(755)	266				266
Other comprehensive (loss) income, net of tax	(308)	1,385	(1,021)
Stockholders Equity, Ending Balance	322	630	(755)				322
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income Loss [Line Items]
Stockholders Equity, Beginning Balance	9,050	7,055	2,042				2,042
Other comprehensive (loss) income, net of tax	(5,618)	1,995	5,013
Stockholders Equity, Ending Balance	$ 3,432	$ 9,050	$ 7,055				$ 3,432

- Definition

Amount after tax and reclassification adjustments of other comprehensive income (loss).

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+ Details

- Definition

Amount of stockholders' equity (deficit), net of receivables from officers, directors, owners, and affiliates of the entity, attributable to both the parent and noncontrolling interests. Amount excludes temporary equity. Alternate caption for the concept is permanent equity.

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-Section 65
-Paragraph 15
-Subparagraph (f)(1)
-URI http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333

Reference 17: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22499-107794

Reference 19: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(g)(1)(ii))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

Reference 20: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 30
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6450520&loc=d3e32583-110901

Reference 21: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 65
-Paragraph 15
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333

Reference 22: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 65
-Paragraph 8
-Subparagraph (d)(2)

Reference 23: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 65
-Paragraph 8
-Subparagraph (d)(3)

+ Details

Basis of Presentation and Summary of Significant Accounting Policies - Schedule of Changes in Loss Provision (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Summary Of Significant Accounting Policies [Abstract]
Balance at beginning of period	$ 4,392	$ 7,817	$ 6,790	$ 10,339
Amortization of loss provision		(330)	(2,018)	(2,921)
Foreign currency translation	191	(247)	(189)	(178)
Balance at end of period	$ 4,583	$ 7,240	$ 4,583	$ 7,240

Basis of Presentation and Summary of Significant Accounting Policies - Securities Excluded in the Computation of Diluted Net Loss Per Ordinary Share (Details) - shares	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common shares attributable to anti-dilutive shares	12,848,007	10,981,530
Share options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common shares attributable to anti-dilutive shares	11,980,433	10,384,608
Unvested Restricted Share Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common shares attributable to anti-dilutive shares	867,574	596,922

Basis of Presentation and Summary of Significant Accounting Policies - Summary of Operating Cash Flows to Current Presentation and Other Presentation Adjustments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net loss			$ (118,359)	$ (118,006)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	$ 500	$ 300	1,558	1,213
Non-cash share-based compensation			21,221	13,753
Impairment of long-lived assets			5,650
Non-cash interest expense			378	180
Amortization of Strimvelis loss provision			(2,018)	(2,921)
Amortization of premium (discount) on marketable securities			465	(559)
Other non-cash adjustments			650	(3,314)
Changes in operating assets and liabilities:
Trade receivables			(1,750)	(543)
Research and development tax credit receivable			(2,423)	(12,390)
Prepaid expenses, current assets and other assets			(2,680)	(6,286)
Operating leases, right-of-use assets			4,253	2,123
Accounts payable, accrued expenses and other current liabilities			(16,166)	3,520
Other long-term liabilities				(1,465)
Operating lease liabilities			(6,010)	(514)
Net cash used in operating activities			$ (114,440)	(125,209)
As Previously Reported
Cash flows from operating activities:
Net loss				(118,006)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation				1,213
Non-cash share-based compensation				13,753
Amortization of Strimvelis loss provision				(2,921)
Other non-cash adjustments				(3,693)
Changes in operating assets and liabilities:
Trade receivables				(2,937)
Research and development tax credit receivable				(12,390)
Prepaid expenses, current assets and other assets				(3,548)
Accounts payable, accrued expenses and other current liabilities				3,676
Other long-term liabilities				(356)
Net cash used in operating activities				(125,209)
ASC 842 Adjustments \| Accounting Standards Update 2016-02
Changes in operating assets and liabilities:
Prepaid expenses, current assets and other assets				(344)
Operating leases, right-of-use assets				2,123
Accounts payable, accrued expenses and other current liabilities				(156)
Other long-term liabilities				(1,109)
Operating lease liabilities				(514)
Other Presentation Adjustments
Adjustments to reconcile net loss to net cash used in operating activities:
Non-cash interest expense				180
Amortization of premium (discount) on marketable securities				(559)
Other non-cash adjustments				379
Changes in operating assets and liabilities:
Trade receivables				2,394
Prepaid expenses, current assets and other assets				$ (2,394)

Fair Value Measurements and Marketable Debt Securities - Additional Information (Details) $ in Thousands	Sep. 30, 2020 USD ($)
Fair Value Disclosures [Abstract]
Fair value of financial assets transfers between level 1 to level 2	$ 0
Fair value of financial assets transfers between level 2 to level 1	$ 0

Fair Value Measurements and Marketable Debt Securities - Schedule of Cash Equivalents and Marketable Debt Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Cash equivalents
Total cash equivalents	$ 13,610	$ 13,153
Marketable securities
Total marketable securities	160,183	305,937
Total	173,793	319,090
Level 1
Cash equivalents
Total cash equivalents	5,610	202
Marketable securities
Total	5,610	202
Level 2
Cash equivalents
Total cash equivalents	9,503	12,951
Marketable securities
Total marketable securities	160,183	305,937
Total	169,686	318,888
Money Market Funds
Cash equivalents
Total cash equivalents	5,610	202
Money Market Funds \| Level 1
Cash equivalents
Total cash equivalents	5,610	202
U.S. Government Securities
Cash equivalents
Total cash equivalents	7,000	3,159
Marketable securities
Total marketable securities	3,000
U.S. Government Securities \| Level 2
Cash equivalents
Total cash equivalents	7,000	3,159
Marketable securities
Total marketable securities	3,000
Corporate Bonds
Marketable securities
Total marketable securities	132,399	259,900
Corporate Bonds \| Level 2
Cash equivalents
Total cash equivalents	1,503
Marketable securities
Total marketable securities	132,399	259,900
Commercial Paper
Cash equivalents
Total cash equivalents	1,000	9,792
Marketable securities
Total marketable securities	24,784	46,037
Commercial Paper \| Level 2
Cash equivalents
Total cash equivalents	1,000	9,792
Marketable securities
Total marketable securities	$ 24,784	$ 46,037

Fair Value Measurements and Marketable Debt Securities - Schedule of Marketable Debt Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	$ 169,364	$ 318,622
Gross Unrealized Gains	341	327
Gross Unrealized Losses	(19)	(61)
Fair Value	169,686	318,888
U.S. Government Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	10,000	3,159
Fair Value	10,000	3,159
Corporate Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	133,586	259,669
Gross Unrealized Gains	334	285
Gross Unrealized Losses	(18)	(54)
Fair Value	133,902	259,900
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	25,778	55,794
Gross Unrealized Gains	7	42
Gross Unrealized Losses	(1)	(7)
Fair Value	$ 25,784	$ 55,829

Fair Value Measurements and Marketable Debt Securities - Schedule of Available-for-Sale Debt Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Due in one year	$ 150,590	$ 250,490
Due after one year through three years	19,096	68,398
Total	$ 169,686	$ 318,888

Property and Equipment, Net - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Property and equipment	$ 8,470	$ 10,756
Less: accumulated depreciation	(3,558)	(3,160)
Property and equipment, net	4,912	7,596
Lab Equipment
Property Plant And Equipment [Line Items]
Property and equipment	4,695	6,377
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment	2,441	1,839
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment	299	508
Office and Computer Equipment
Property Plant And Equipment [Line Items]
Property and equipment	531	184
Construction-In-Process
Property Plant And Equipment [Line Items]
Property and equipment	$ 504	$ 1,848

Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Property Plant And Equipment [Abstract]
Depreciation expense	$ 500	$ 300	$ 1,558	$ 1,213
Impairment charges related to construction-in-process	2,300
Impairment charges related to laboratory equipment	$ 800

Accrued Expenses and Other Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Accrued Liabilities And Other Liabilities [Abstract]
Accrued external research and development expenses	$ 8,982	$ 16,215
Accrued payroll and related expenses, including severance	9,768	12,381
Accrued professional fees	1,087	1,321
Accrued other	2,428	5,069
Strimvelis liability - current portion	870	2,994
Total accrued expenses and other liabilities	$ 23,135	$ 37,980

Notes Payable - Additional Information (Details) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	May 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Debt Instrument [Line Items]
Line of credit facility agreement date	May 31, 2019
Credit facility maximum borrowings	$ 75,000,000.0
Proceeds from lines of credit				$ 3,000,000.0		$ 3,000,000.0
Credit facility, remaining borrowings	$ 50,000,000.0
Line of credit facility interest payments term	24 months
Line of credit facility amortization term	36 months
Line of credit facility, frequency of payments				monthly payments
Line of credit facility, percentage of final payment	4.50%
Final payment amount	$ 1,100,000
Line of credit facility interest rate description				Each term loan under the Credit Facility bears interest at an annual rate equal to 6% plus LIBOR. The Company is required to make interest-only payments on the term loan for all payment dates prior to 24 months following the date of the Credit Facility, unless the third tranche is drawn, in which case for all payment dates prior to 36 months following the date of the Credit Facility. The term loans under the Credit Facility will begin amortizing on either the 24-month or the 36-month anniversary of the Credit Facility (as applicable), with equal monthly payments of principal plus interest to be made by the Borrower to the Lenders in consecutive monthly installments until the Loan Maturity Date. In addition, a final payment of 4.5% is due on the Loan Maturity Date.
Line of credit facility covenants description				The Company is also subject to an ongoing minimum cash financial covenant in which the Company must maintain unrestricted cash in an amount not less than $20.0 million following the utilization of the second term loan and not less than $35.0 million following the utilization of the third term loan
Term Loan
Debt Instrument [Line Items]
Debt instrument, interest expense		$ 600,000	$ 700,000	$ 1,800,000	$ 900,000
Debt instrument, effective annual interest rate				9.40%
LIBOR
Debt Instrument [Line Items]
Debt instrument, annual interest rate	6.00%
Minimum \| Second Tranche (Term Loan Available from July 1, 2020 to March 31, 2021)
Debt Instrument [Line Items]
Line of credit facility minimum cash financial covenant	$ 20,000,000.0
Minimum \| Third Tranche (Term Loan Available from July 1, 2020 to September 30, 2021)
Debt Instrument [Line Items]
Line of credit facility minimum cash financial covenant	35,000,000.0
Initial Term Loan
Debt Instrument [Line Items]
Proceeds from lines of credit	25,000,000.0
Second Tranche (Term Loan Available from July 1, 2020 to March 31, 2021)
Debt Instrument [Line Items]
Credit facility maximum borrowings	25,000,000.0
Line of Credit Facility, Covenant Terms				upon submission of certain regulatory filings and evidence of the Company having $100 million in cash and cash equivalent investments
Second Tranche (Term Loan Available from July 1, 2020 to March 31, 2021) \| Minimum
Debt Instrument [Line Items]
Cash and cash equivalent investments	100,000,000
Third Tranche (Term Loan Available from July 1, 2020 to September 30, 2021)
Debt Instrument [Line Items]
Credit facility maximum borrowings	25,000,000.0
Line of Credit Facility, Covenant Terms				upon certain regulatory approvals and evidence of the Company having $125 million in cash and cash equivalent investments
Third Tranche (Term Loan Available from July 1, 2020 to September 30, 2021) \| Minimum
Debt Instrument [Line Items]
Cash and cash equivalent investments	$ 125,000,000

Notes Payable - Summary of Notes Payable (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Long Term Notes And Loans [Abstract]
Notes payable, net of issuance costs	$ 24,630	$ 24,541
Less: current portion	(2,778)
Notes payable, net of current portion	21,852	24,541
Accretion related to final payment	347	158
Notes payable, long term	$ 22,199	$ 24,699

Notes Payable - Summary of Estimated Future Principal Payments Due (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Long Term Debt By Maturity [Abstract]
2021	$ 4,861
2022	8,333
2023	8,334
Thereafter	4,597
Total	26,125
Less current portion	(2,778)
Less unamortized portion of final payment	(779)
Less unamortized debt issuance costs	(369)
Notes payable, long term	$ 22,199	$ 24,699

Share-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended		9 Months Ended
	Aug. 31, 2020	Apr. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average grant date fair value of share options granted					$ 7.38
Number of shares granted					426,750
Compensation cost recognized			$ 5,663	$ 5,302	$ 21,221	$ 13,753
Total unrecognized compensation cost of stock option			52,800		$ 52,800
Compensation cost expected to be recognized weighted average period					2 years 8 months 12 days
Total unrecognized compensation cost			5,400		$ 5,400
Selling, General and Administrative Expenses
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Compensation cost recognized					2,700
Performance-based Restricted Share Units ("RSUs")
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Compensation cost recognized				$ 300	$ 300	$ 900
Performance-based Restricted Share Units ("RSUs") \| Chief Executive Officer
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares granted		195,000
Performance-based Restricted Share Units ("RSUs") \| Chief Executive Officer \| Achievement of At Least Three of Four Milestones
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting rights					The award vests on January 2, 2024 as to 1/3 of the award for each of the first three to occur of four milestones, if each such milestone is achieved by the Company on or before December 31, 2023
Time-based Restricted Share Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vest period in annual installments					3 years
Compensation cost expected to be recognized weighted average period					2 years 3 months 18 days
Total unrecognized compensation cost			$ 1,100		$ 1,100
2018 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Remaining shares available for issuance			6,361,972		6,361,972
Increase in ordinary shares available for issuance	4,846,186
2018 ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Remaining shares available for issuance			1,525,904		1,525,904
Inducement Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Remaining shares available for issuance			1,000,000		1,000,000

Share-Based Compensation - Summary of Option Activity (Details) - $ / shares	9 Months Ended
	Sep. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Options, Outstanding at December 31, 2019	12,216,140
Number of Options, Granted	5,629,352
Number of Options, Exercised	(607,167)
Number of Options, Forfeited	(2,572,755)
Number of Options, Outstanding at June 30, 2020	14,665,570
Number of Options, Vested and expected to vest, as of June 30, 2020	14,665,570
Number of Options, Exercisable, June 30, 2020	7,053,899
Weighted Average Exercise Price, Outstanding at December 31, 2019	$ 6.61
Weighted Average Exercise Price, Granted	11.63
Weighted Average Exercise Price, Exercised	4.03
Weighted Average Exercise Price, Forfeited	10.65
Weighted Average Exercise Price, Outstanding at June 30, 2020	7.93
Weighted Average Exercise Price, Vested and expected to vest, as of June 30, 2020	7.93
Weighted Average Exercise Price, Exercisable, June 30, 2020	$ 5.47

Share-Based Compensation - Summary of Award Activity (Details)	9 Months Ended
	Sep. 30, 2020 $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares, Unvested and outstanding at December 31, 2019 \| shares	556,422
Shares, Granted \| shares	426,750
Shares, Forfeited \| shares	(310,672)
Shares, Unvested and outstanding at June 30, 2020 \| shares	672,500
Weighted Average Grant Date Fair Value, Unvested at December 31, 2019 \| $ / shares	$ 13.58
Weighted Average Grant Date Fair Value, Granted \| $ / shares	6.42
Weighted Average Grant Date Fair Value, Forfeited \| $ / shares	14.16
Weighted Average Grant Date Fair Value, Unvested at June 30, 2020 \| $ / shares	$ 8.77

Share-Based Compensation - Share-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total share-based compensation	$ 5,663	$ 5,302	$ 21,221	$ 13,753
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total share-based compensation	2,617	2,071	8,398	5,041
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total share-based compensation	$ 3,046	$ 3,231	$ 12,823	$ 8,712

Restructuring Charges - Additional Information (Details) - USD ($)		1 Months Ended	3 Months Ended			9 Months Ended
	May 04, 2020	May 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Restructuring Cost And Reserve [Line Items]
Restructuring costs			$ (9,000)		$ 0	$ 1,575,000	$ 0
Construction-in-process, impairment charges			2,300,000
Operating lease right-of-use-assets			$ 30,476,000			30,476,000		$ 19,415,000
Research and Development Expense
Restructuring Cost And Reserve [Line Items]
Employee termination benefits						1,200,000
Selling, General and Administrative Expenses
Restructuring Cost And Reserve [Line Items]
Employee termination benefits						$ 400,000
Office Workforce Menlo Park, California
Restructuring Cost And Reserve [Line Items]
Number of positions eliminated, percent	25.00%
Construction-in-process, impairment charges		$ 2,300,000		$ 2,285,000
Operating lease right-of-use-assets		$ 13,800,000
Discount rate		4.60%
Fair value of ROU asset		$ 11,200,000
Right of use asset, impairment charge		2,600,000		$ 2,605,000
Office Workforce Menlo Park, California \| Minimum
Restructuring Cost And Reserve [Line Items]
Undiscounted cash flow estimate		11,700,000
Office Workforce Menlo Park, California \| Maximum
Restructuring Cost And Reserve [Line Items]
Undiscounted cash flow estimate		$ 19,100,000

Restructuring Charges - Summary of Cash Restructuring Charges (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Restructuring And Related Activities [Abstract]
Balance at beginning of period	$ 841,000
Charged to expense	(9,000)	$ 0	$ 1,575,000	$ 0
Payments made	(511,000)		(1,254,000)
Balance at end of period	$ 321,000		$ 321,000

Restructuring Charges - Summary of Impairment of Long Lived Assets (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	May 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2020
Restructuring Cost And Reserve [Line Items]
Construction-in-process		$ 2,300
Laboratory equipment, Asset write-downs		$ 800
Charge included in research and development expense				$ 5,650
Office Workforce Menlo Park, California
Restructuring Cost And Reserve [Line Items]
Operating lease right-of-use asset	$ 2,600		$ 2,605
Construction-in-process	$ 2,300		2,285
Laboratory equipment, Asset write-downs			760
Charge included in research and development expense			$ 5,650

Leases - Additional Information (Details) $ in Thousands, € in Millions	9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2020 EUR (€)	Dec. 31, 2019 USD ($)
Lessee Lease Description [Line Items]
Operating lease right-of-use-assets	$ 30,476		$ 19,415
Operating lease, liability, noncurrent	$ 24,162		$ 15,320
GSK Agreement [Member]
Lessee Lease Description [Line Items]
Operating lease term	5 years	5 years
Lessee, operating lease, option to extend	The agreement may be extended for an additional two years by mutual agreement of the Company and AGC
Lessee, operating Lease, existence of option to extend [true false]	true
Operating lease extended term	2 years
Operating lease right-of-use-assets	$ 13,700
Operating lease, liability, noncurrent	$ 13,700
Operating lease expiration term	Jul. 02, 2025
Lease component manufacturing suites commitment amount per contract year \| €		€ 2.7
Dedicated manufacturing and development resources commitment amount per contract year \| €		€ 10.4

License Agreements - Additional Information (Details) $ in Thousands, € in Millions, £ in Millions	1 Months Ended			3 Months Ended	9 Months Ended
	May 31, 2019 USD ($)	May 31, 2019 EUR (€)	Apr. 30, 2018 Program	Jun. 30, 2018 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2020 EUR (€)	Sep. 30, 2020 GBP (£)	Apr. 30, 2020 USD ($) shares	Dec. 31, 2019 USD ($)	Nov. 30, 2018 shares	Sep. 30, 2018 shares	Nov. 30, 2016 shares
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Ordinary shares value \| $					$ 12,426				$ 12,331
GSK Asset Purchase and License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of additional programs in preclinical development \| Program			3
Number of late-stage clinical gene therapy programs \| Program			2
Number of earlier stage clinical gene therapy program \| Program			1
Number of additional earlier-stage development programs \| Program			3
Total consideration \| $				$ 133,600
Payment of tiered royalty, maximum percentage					20.00%	20.00%	20.00%
Milestone payments payable upon achievement of certain sales milestones						€ 31.0	£ 90.0
Upfront payment description					In May 2019, the Company entered into a license agreement with Telethon-OSR, under which Telethon-OSR granted to the Company an exclusive worldwide license for the research, development, manufacture and commercialization of Telethon-OSR’s ex vivo autologous HSC lentiviral based gene therapy for the treatment of mucopolysaccharidosis type I (“MPS-I”), including the Hurler variant. Under the terms of the agreement, Telethon-OSR received €15.0 million in upfront and milestone payments from the Company upon entering into the agreement, resulting in $17.2 million in in-process research and development expense.
Telethon-OSR License Agreements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront and milestone payments \| €		€ 15.0
In-process research and development expense for upfront and milestone payments \| $	$ 17,200
Oxford BioMedica License, Development and Supply Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Ordinary shares issued \| shares								75,413		150,826	150,826	588,220
Ordinary shares value \| $								$ 800

Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Unrecognized tax positions	$ 0		$ 0		$ 0
Income tax (benefit) expense	$ (541,000)	$ (2,194,000)	$ (816,000)	$ (2,373,000)

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References + Details

Commitments and Contingencies - Additional Information (Details) - Agreement - AGC Biologics - EUR (€) € in Millions	9 Months Ended
	Sep. 30, 2020	Jul. 02, 2020
Other Commitments [Line Items]
Minimum product manufacturing commitment amount per contract year		€ 2.7
Dedicated manufacturing and development resources commitment amount per contract year		10.4
Lease component manufacturing suites commitment amount per contract year		€ 2.7
Initial term of agreement	5 years
Agreement maturity date	Jul. 02, 2025
Agreement extension term	2 years

Employee Benefit Plans - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Compensation And Retirement Disclosure [Abstract]
Maximum annual contribution employer matches per employee, percent			6.00%
Contribution expenses	$ 0.3	$ 0.3	$ 1.3	$ 0.9

Related Party Transactions - Additional Information (Details) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Apr. 30, 2018 Program	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Related Party Transaction [Line Items]
Research and development		$ 14,678	$ 28,493	$ 71,082	$ 86,464
GSK Asset Purchase and License Agreement
Related Party Transaction [Line Items]
Number of additional programs in preclinical development \| Program	3
GSK
Related Party Transaction [Line Items]
Due to related party transactions, accounts payable		$ 200		200
Due to related party transactions, accrued expenses						$ 3,300
Payments on accounts payable				5,800
Royalties incurred				100
GSK \| GSK Asset Purchase and License Agreement
Related Party Transaction [Line Items]
Research and development				$ 1,300