Editas Medicine (EDIT) 10-K 26 Feb 20 2019 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2019	Feb. 14, 2020	Jun. 28, 2019
Document and Entity Information
Document Type	10-K
Document Annual Report	true
Document Transition Report	false
Document Period End Date	Dec. 31, 2019
Entity File Number	001-37687
Entity Registrant Name	EDITAS MEDICINE, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	46-4097528
Entity Address, Address Line One	11 Hurley Street
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02141
City Area Code	617
Local Phone Number	401-9000
Title of 12(b) Security	Common Stock
Trading Symbol	EDIT
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 1,222,233,659
Entity Common Stock, Shares Outstanding		54,875,392
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Central Index Key	0001650664
Amendment Flag	false

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 238,183	$ 134,776
Marketable securities	218,957	234,179
Accounts receivable	418	30
Prepaid expenses and other current assets	6,286	5,791
Total current assets	463,844	374,776
Property and equipment, net	10,887	40,232
Right-of-use assets	28,761
Restricted cash and other non-current assets	5,393	5,378
Total assets	508,885	420,386
Current liabilities:
Accounts payable	5,843	5,327
Accrued expenses	22,120	12,813
Deferred revenue, current	23,514	15,712
Operating lease liabilities	5,804
Other current liabilities	2,682	2,048
Total current liabilities	59,963	35,900
Operating lease liabilities, net of current portion	23,277
Deferred revenue, net of current portion	163,207	115,614
Construction financing lease obligation, net of current portion		32,417
Other non-current liabilities	1	293
Total liabilities	246,448	184,224
Commitments and contingencies (see Note 8)
Stockholders' equity
Preferred stock, $0.0001 par value per share: 5,000,000 shares authorized; no shares issued or outstanding
Common stock, $0.0001 par value per share: 195,000,000 shares authorized; 54,553,798 and 49,028,907 shares issued, and 54,355,798 and 48,758,951 shares outstanding at December 31, 2019 and December 31, 2018, respectively	5	5
Additional paid-in capital	811,546	652,464
Accumulated other comprehensive income (loss)	107	(29)
Accumulated deficit	(549,221)	(416,278)
Total stockholders' equity	262,437	236,162
Total liabilities and stockholders' equity	$ 508,885	$ 420,386

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
Consolidated Balance Sheets
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized	195,000,000	195,000,000
Common stock, shares issued	54,553,798	49,028,907
Common stock, shares outstanding	54,355,798	48,758,951

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Consolidated Statements of Operations
Collaboration and other research and development revenues	$ 20,531	$ 31,937	$ 13,728
Revenue type	us-gaap:ServiceMember	us-gaap:ServiceMember	us-gaap:ServiceMember
Operating expenses:
Research and development	$ 96,898	$ 90,654	$ 83,159
General and administrative	64,555	55,010	50,502
Total operating expenses	161,453	145,664	133,661
Operating loss	(140,922)	(113,727)	(119,933)
Other income (expense), net
Other (expense) income, net	(137)	328	587
Interest income (expense), net	7,313	3,445	(978)
Total other income (expense), net	7,176	3,773	(391)
Net loss	(133,746)	(109,954)	(120,324)
Net loss attributable to common stockholders	$ (133,746)	$ (109,954)	$ (120,324)
Net loss per share attributable to common stockholders, basic and diluted	$ (2.68)	$ (2.33)	$ (2.98)
Weighted-average common shares outstanding, basic and diluted	49,983,329	47,097,735	40,323,631

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Consolidated Statements of Comprehensive Loss
Net loss	$ (133,746)	$ (109,954)	$ (120,324)
Other comprehensive loss:
Unrealized gain (loss) on marketable securities	136	47	(76)
Comprehensive loss	$ (133,610)	$ (109,907)	$ (120,400)

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock2017 March Offering	Common Stock2017 December Offering	Common StockAt The Market Offering One	Common StockAt The Market Offering Two	Common Stock	Additional Paid-In Capital2017 March Offering	Additional Paid-In Capital2017 December Offering	Additional Paid-In CapitalAt The Market Offering One	Additional Paid-In CapitalAt The Market Offering Two	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive (Loss) Income	2017 March Offering	2017 December Offering	At The Market Offering One	At The Market Offering Two	Total
Balance, beginning of period at Dec. 31, 2016					$ 4					$ 320,129	$ (185,526)						$ 134,607
Balance, beginning of period (in shares) at Dec. 31, 2016					35,818,131
Statement of Stockholders' Equity (Deficit)
Issuance of common stock from public offering, net of issuance costs						$ 96,685	$ 57,223						$ 96,685	$ 57,223
Issuance of common stock from public offering, net of issuance costs (in shares)	4,600,000	2,265,500
Issuance of common stock for repayment of notes payable										14,823							14,823
Issuance of common stock for repayment of notes payable (in shares)					750,617
Exercise of stock options										1,768							1,768
Exercise of stock options (in shares)					272,210
Vesting of employee restricted common stock and common stock subject to repurchase																	8,085
Vesting Of Employee Restricted Common Stock And Common Stock Subject To Repurchase (in shares)					801,502
Stock-based compensation expense										23,374							15,289
Unrealized loss on marketable securities												$ (76)					(76)
Net loss											(120,324)						(120,324)
Balance, end of period at Dec. 31, 2017					$ 4					514,002	(305,850)	(76)					208,080
Balance, end of period (in shares) at Dec. 31, 2017					44,507,960
Statement of Stockholders' Equity (Deficit)
Issuance of common stock from public offering, net of issuance costs			$ 1					$ 48,493	$ 28,387						$ 48,494	$ 28,387
Issuance of common stock from public offering, net of issuance costs (in shares)			1,429,205	1,107,000
Issuance of common stock for repayment of notes payable										22,030							22,030
Issuance of common stock for repayment of notes payable (in shares)					636,526
Issuance of common stock for asset purchase agreement										1,942							1,942
Issuance of common stock for asset purchase agreement (in shares)					56,099
Exercise of stock options										10,328							10,328
Exercise of stock options (in shares)					749,294
Vesting of restricted common stock awards (in shares)					72,000
Vesting of employee restricted common stock and common stock subject to repurchase										4							4
Vesting Of Employee Restricted Common Stock And Common Stock Subject To Repurchase (in shares)					174,595
Stock-based compensation expense										26,598							26,598
Purchase of common stock under benefit plan										680							680
Purchase of common stock under benefit plan (in shares)					26,272
Unrealized loss on marketable securities												47					47
Net loss											(109,954)						(109,954)
Balance, end of period at Dec. 31, 2018					$ 5					652,464	(416,278)	(29)					236,162
Balance, end of period (in shares) at Dec. 31, 2018					48,758,951
Statement of Stockholders' Equity (Deficit)
Cumulative effect adjustment for adoption of new accounting guidance											(474)						(474)
Issuance of common stock from public offering, net of issuance costs								$ 116,356							$ 116,356
Issuance of common stock from public offering, net of issuance costs (in shares)			4,341,428
Exercise of stock options										14,863							14,863
Exercise of stock options (in shares)					1,120,186
Vesting of restricted common stock awards (in shares)					99,919
Stock-based compensation expense										27,243							27,243
Purchase of common stock under benefit plan										620							620
Purchase of common stock under benefit plan (in shares)					35,314
Unrealized loss on marketable securities												136					136
Net loss											(133,746)						(133,746)
Balance, end of period at Dec. 31, 2019					$ 5					$ 811,546	(549,221)	$ 107					262,437
Balance, end of period (in shares) at Dec. 31, 2019					54,355,798
Statement of Stockholders' Equity (Deficit)
Cumulative effect adjustment for adoption of new accounting guidance											$ 803						$ 803

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
2017 March Offering
Stock issuance costs			$ 0.6
2017 December Offering
Stock issuance costs			$ 1.7
At The Market Offering One
Stock issuance costs	$ 0.2	$ 0.1
At The Market Offering Two
Stock issuance costs		$ 0.6

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flow from operating activities
Net loss	$ (133,746)	$ (109,954)	$ (120,324)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	27,243	26,598	23,364
Depreciation	2,830	3,254	2,683
Non-cash research and development expenses		14,442	14,500
Non-cash investment in equity securities		(3,667)
Other non-cash items, net	(2,928)	(3,268)	(300)
Changes in operating assets and liabilities:
Accounts receivable	(388)	649	(591)
Prepaid expenses and other current assets	(495)	(3,410)	(596)
Right-of-use assets	(9,300)
Other non-current assets	(15)	(92)	2
Accounts payable	274	1,780	(1,515)
Accrued expenses	9,485	4,042	(8,334)
Deferred revenue	55,395	22,889	81,707
Operating lease liabilities	9,324
Other current and non-current liabilities	1,652	1,030	(13)
Net cash used in operating activities	(40,669)	(45,707)	(9,417)
Cash flow from investing activities
Purchases of property and equipment	(6,167)	(4,754)	(2,059)
Proceeds from the sale of equipment	102	37	15
Purchases of marketable securities	(342,183)	(459,370)	(375,266)
Proceeds from maturities of marketable securities	360,500	411,000	193,500
Net cash provided by (used in) investing activities	12,252	(53,087)	(183,810)
Cash flow from financing activities
Proceeds from offering of common stock, net of issuance costs	116,341	76,789	154,143
Proceeds from exercise of stock options	14,863	10,328	1,755
Payments on construction financing lease obligation		(857)	(764)
Issuances of common stock under benefit plans	620	680
Payments of notes payable			(600)
Net cash provided by financing activities	131,824	86,940	154,534
Net increase (decrease) in cash, cash equivalents, and restricted cash	103,407	(11,854)	(38,693)
Cash, cash equivalents, and restricted cash, beginning of period	136,395	148,249	186,942
Cash, cash equivalents, and restricted cash, end of period	239,802	136,395	148,249
Supplemental disclosure of cash and non-cash activities:
Right-of-use assets obtained in exchange of operating lease obligations	19,461
Cash paid in connection with operating lease liabilities	5,970
Fixed asset additions included in accounts payable and accrued expenses	728	659	623
Offering expenses included in accounts payable and accrued expenses	$ 15	92	235
Reclassification of liability for common stock subject to repurchase		4	11
Issuance of common stock for repayment of notes payable		22,030	$ 14,823
Issuance of common stock for asset acquisition		$ 1,942

Nature of Business

Nature of Business	12 Months Ended
	Dec. 31, 2019
Nature of Business
Nature of Business	1. Nature of Business Editas Medicine, Inc. (the “Company”) is a leading, clinical stage genome editing company dedicated to developing potentially transformative genomic medicines to treat a broad range of serious diseases. The Company was incorporated in the state of Delaware in September 2013. Its principal offices are in Cambridge, Massachusetts. Since its inception, the Company has devoted substantially all of its efforts to business planning, research and development, recruiting management and technical staff, and raising capital. The Company has primarily financed its operations through various equity financings, payments received under a research collaboration with Juno Therapeutics, a wholly-owned subsidiary of the Bristol-Myers Squibb Company (“Juno Therapeutics”), and payments received under a strategic alliance and option agreement with Allergan Pharmaceuticals International Limited (together with its affiliates, “Allergan”) The Company is subject to risks common to companies in the biotechnology industry, including but not limited to, risks of failure of preclinical studies and clinical trials, the need to obtain marketing approval for any drug product candidate that it may identify and develop, the need to successfully commercialize and gain market acceptance of its product candidates, dependence on key personnel, protection of proprietary technology, compliance with government regulations, development by competitors of technological innovations and ability to transition from pilot-scale manufacturing to large-scale production of products. Liquidity As of December 31, 2019, the Company has raised an aggregate of $444.8 million in net proceeds through the sale of shares of its common stock in public offerings and at-the-market offerings. In March 2018, the Company entered into a sales agreement with Cowen and Company, LLC (“Cowen”), under which the Company from time to time could issue and sell shares of its common stock through Cowen in at-the-market offerings for aggregate gross sales proceeds of $150.0 million (the “March 2018 ATM Program”). Through December 31, 2019, the Company sold an aggregate of 5,448,428 shares of its common stock pursuant to the March 2018 ATM Program at a weighted-average price of $27.53 per share for gross proceeds of $150.0 million. The Company paid Cowen a 3% cash commission on the gross sales price per share of its common stock sold under the March 2018 ATM Program. No shares of common stock remain available for sale under the March 2018 ATM Program. ​ The Company has incurred annual net operating losses in every year since its inception. The Company expects that its existing cash, cash equivalents and marketable securities at December 31, 2019 and anticipated interest income will enable it to fund its operating expenses and capital expenditure requirements for at least 24 months following the date of this Annual Report on Form 10-K. The Company had an accumulated deficit of $549.2 million at December 31, 2019, and will require substantial additional capital to fund its operations. The Company has never generated any product revenue. There can be no assurance that the Company will be able to obtain additional debt or equity financing or generate product revenue or revenues from collaborative partners, on terms acceptable to the Company, on a timely basis or at all. The failure of the Company to obtain sufficient funds on acceptable terms when needed could have a material adverse effect on the Company’s business, results of operations, and financial condition.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2019
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Principles of Consolidation The accompanying consolidated financial statements include the accounts of Editas Medicine, Inc. and its wholly owned subsidiary, Editas Securities Corporation, which is a Delaware subsidiary created to buy, sell and hold securities. All intercompany transactions and balances have been eliminated. Basis of Presentation The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”). Reclassification Certain prior period amounts have been reclassified for consistency with the current period presentation. These reclassifications had no effect on previously reported results of operations. Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates, which include, but are not limited to, estimates related to revenue recognition, accrued expenses, stock-based compensation expense, research and development expenses and deferred tax valuation allowances. The Company bases its estimates on historical experience and other market-specific or relevant assumptions that it believes to be reasonable under the circumstances. Actual results may differ from those estimates or assumptions. Fair Value of Financial Instruments ASC Topic 820, Fair Value Measurement ASC 820 identifies fair value as the exchange price representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As a basis for considering market participant assumptions in fair value measurements, ASC 820 establishes a three-tier fair value hierarchy that distinguishes between the following: ● Level 1 – Quoted market prices in active markets for identical assets or liabilities. ● Level 2 – Inputs other than Level 1 inputs that are either directly or indirectly observable, such as quoted market prices, interest rates, and yield curves. ● Level 3 – Unobservable inputs developed using estimates of assumptions developed by the Company, which reflect those that a market participant would use. To the extent that the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. The carrying amounts reflected in the consolidated balance sheets for cash and cash equivalents, restricted cash, marketable securities, accounts receivable, prepaid expenses and other current assets, accounts payable, accrued expenses, and other current liabilities approximate their fair values, due to their short-term nature. The Company believes that the carrying value of the notes payable approximates their fair value based on Level 3 inputs including a quoted rate. Cash, Cash Equivalents, and Restricted Cash The Company considers all highly liquid investments purchased with original maturities of 90 days or less at acquisition to be cash equivalents. Cash and cash equivalents include cash held in banks and amounts held in money market funds and U.S. government-backed securities. The Company has restricted cash of $1.6 million held in the form of a letter of credit, as collateral for the Company’s corporate headquarters. The restricted funds are maintained in a traditional bank account. The following table presents cash, cash equivalents, and restricted cash as reported on the consolidated balance sheets that equal the total amounts on the consolidated statements of cash flows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ As of December 31, ​ ​ 2019 ​ 2018 ​ 2017 Cash and cash equivalents ​ $ 238,183 ​ $ 134,776 ​ $ 146,630 Restricted cash included in "Restricted cash and other non-current assets" ​ ​ 1,619 ​ ​ 1,619 ​ ​ 1,619 Total cash, cash equivalents, and restricted cash ​ $ 239,802 ​ $ 136,395 ​ $ 148,249 ​ Marketable Securities The Company classifies marketable securities with a remaining maturity when purchased of greater than three months and less than one year from the balance sheet date as current. Marketable securities with a remaining maturity date greater than one year are classified as non-current. The Company classifies all of its marketable securities as available-for-sale securities. Available-for-sale securities are carried at fair value with the unrealized gains and losses included in other comprehensive loss as a component of stockholders’ equity until realized. Any premium or discount arising at purchase is amortized and/or accreted to interest income and/or expense over the life of the of the underlying security. Realized gains and losses are included in other income (expense). If any adjustment to fair value reflects a decline in value of the investment, the Company considers all available evidence to evaluate the extent to which the decline is “other-than-temporary.” To determine whether an impairment is other-than-temporary, the Company considers whether it has the ability and intent to hold the investment until a market price recovery and considers whether evidence indicating the cost of the investment is recoverable outweighs evidence to the contrary. The Company does not intend to sell the investments and it is not likely that the Company will be required to sell the investments before recovery of their amortized cost bases, which may be maturity. Corporate Equity Securities The Company records investments in privately issued corporate equity securities that do not have readily determinable fair values at cost and adjusts for changes in observable prices minus impairment. Each reporting period the Company adjusts the carrying value of these investments if it observes that additional shares have been issued in an orderly transaction between market participants resulting in a price increase or decrease per share. Additionally, each reporting period the Company reviews these investments for impairment considering all available information to conclude whether an impairment exists. Changes in measurement for all corporate equity investments are recognized in “Other income (expense),” net in the Company’s consolidated statements of operations. Accounts Receivable The Company makes judgments as to its ability to collect outstanding receivables and provides an allowance for receivables when collection becomes doubtful. Provisions are made based upon a specific review of all significant outstanding invoices and the overall quality and age of those invoices not specifically reviewed. The Company's receivables primarily relate to amounts reimbursed under its collaboration agreements. The Company believes that credit risk associated with its collaborations partners is not significant. To date, the Company has not had any write-offs of bad debt, and the Company did not have an allowance for doubtful accounts as of December 31, 2019 and 2018. Property and Equipment Property and equipment consists of computers, laboratory equipment, furniture and office equipment, and leasehold improvements and is stated at cost, less accumulated depreciation. Maintenance and repairs that do not improve or extend the lives of the respective assets are expensed to operations as incurred, while costs of major additions and betterments are capitalized. Depreciation is calculated over the estimated useful lives of the assets using the straight-line method. The Company capitalizes laboratory equipment used for research and development if it has alternative future use in research and development or otherwise. ​ ​ ​ ​ ​ Asset: Estimated Useful life Lab equipment 5 years ​ Computer equipment and software 3 years ​ Furniture and equipment 5 years ​ Leasehold improvements Shorter of useful life or remaining lease term ​ ​ Impairment of Long-lived Assets The Company evaluates long-lived assets for potential impairment when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparing the book values of the assets to the expected future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book values of the assets exceed their fair value. The Company has not recognized any impairment losses from inception through December 31, 2019. Profit-Sharing Arrangements The Company considers the nature and contractual terms of the arrangements and assesses whether such arrangements involve a joint operating activity pursuant to which the Company is an active participant and is exposed to significant risks and rewards with respect to such arrangement. If the Company is an active participant and is exposed to significant risks and rewards with respect to such arrangement, the Company accounts for such arrangement as a collaboration under ASC Topic 808, Collaborative Arrangements Payments received from a collaboration partner to which this policy applies are recorded as contra-expense in the applicable period and may include development costs or patent expense reimbursements. The Company classifies payments made under the cost sharing provisions of such arrangements as a component of research and development expenses to reflect the joint risk sharing nature of such profit-sharing arrangements. The Company classifies payments owed or receivables recorded as other current liabilities or prepaid expenses and other current assets, respectively, in the Company’s consolidated balance sheets. Revenue Recognition To date, the Company has primarily earned revenue under the collaboration and license agreement with Juno Therapeutics and the strategic alliance with Allergan. The Company recognizes revenue in accordance with ASC Topic 606, Revenue from Contracts with Customers that are within the scope of ASC 606, under which the Company licenses, may license or grants an option to license rights to certain of the Company’s product candidates and performs research and development services in connection with such arrangements. The terms of these arrangements typically include payment of one or more of the following: non-refundable, up-front fees; reimbursement of research and development costs; development, clinical, regulatory and commercial sales milestone payments; and royalties on net sales of licensed products. Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine the appropriate amount of revenue to be recognized for arrangements determined to be within the scope of ASC 606, the Company performs the following five steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect consideration it is entitled to in exchange for the goods or services it transfers to the customer. The promised goods or services in the Company’s arrangements typically consist of a license, or option to license, rights to the Company’s intellectual property or research and development services. The Company provides options to additional items in such arrangements, which are accounted for as separate contracts when the customer elects to exercise such options, unless the option provides a material right to the customer. Performance obligations are promised goods or services in a contract to transfer a distinct good or service to the customer and are considered distinct when (i) the customer can benefit from the good or service on its own or together with other readily available resources and (ii) the promised good or service is separately identifiable from other promises in the contract. In assessing whether promised good or services are distinct, the Company considers factors such as the stage of development of the underlying intellectual property, the capabilities of the customer to develop the intellectual property on its own or whether the required expertise is readily available and whether the goods or services are integral or dependent to other goods or services in the contract. The Company estimates the transaction price based on the amount expected to be received for transferring the promised goods or services in the contract. The consideration may include fixed consideration or variable consideration. At the inception of each arrangement that includes variable consideration, the Company evaluates the amount of potential payment and the likelihood that the payments will be received. The Company utilizes either the most likely amount method or expected value method to estimate the amount expected to be received based on which method best predicts the amount expected to be received. The amount of variable consideration that is included in the transaction price may be constrained and is included in the transaction price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized will not occur in a future period. The Company’s contracts often include development and regulatory milestone payments that are as assessed under the most likely amount method and constrained if it is probable that a significant revenue reversal would occur. Milestone payments that are not within the Company’s control or the licensee’s control, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. At the end of each reporting period, the Company re-evaluates the probability of achievement of such development and clinical milestones and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect collaboration and other research and development revenues in the period of adjustment. For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from any of the Company’s collaboration or strategic alliance arrangements. The Company allocates the transaction price based on the estimated standalone selling price. The Company must develop assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company utilizes key assumptions to determine the stand-alone selling price, which may include other comparable transactions, pricing considered in negotiating the transaction and the estimated costs. Variable consideration is allocated specifically to one or more performance obligations in a contract when the terms of the variable consideration relate to the satisfaction of the performance obligation and the resulting amounts allocated are consistent with the amounts the Company would expect to receive for the satisfaction of each performance obligation. The consideration allocated to each performance obligation is recognized as revenue when control is transferred for the related goods or services. For performance obligations which consist of licenses and other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. The Company receives payments from its customers based on billing schedules established in each contract. Up-front payments and fees are recorded as deferred revenue upon receipt or when due until the Company performs its obligations under these arrangements. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional. ​ In connection with the Company’s adoption of ASC 606, the Company has included the following financial statement line items for comparability purposes for the year ended December 31, 2018 (in thousands, except per share data): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, 2018 ​ As reported under Topic 606 ​ Balances without adoption of ASC 606 ​ Effect of Change Collaboration and other research and development revenues $ 31,937 ​ $ 33,993 ​ $ (2,056) Operating loss $ (113,727) ​ $ (111,671) ​ $ (2,056) Net loss attributable to common stockholders $ (109,954) ​ $ (107,898) ​ $ (2,056) Net loss per share attributable to common stockholders, basic and diluted $ (2.33) ​ $ (2.29) ​ $ (0.04) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Prior to ASC 606 Adoption Revenue for the year ended December 31, 2017 was recognized in accordance with ASC Topic 605, Revenue Recognition ● Persuasive evidence of an arrangement exists; ● Delivery has occurred or services have been rendered; ● The seller’s price to the buyer is fixed or determinable; and ● Collectability is reasonably assured. Amounts received prior to satisfying the revenue recognition criteria were recorded as deferred revenue. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified in current liabilities. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue, net of current portion. The Company evaluated multiple-element arrangements based on the guidance in ASC Topic 605-25, Revenue Recognition Multiple-Element Arrangements Options were considered substantive if, at the inception of the arrangement, the Company was at risk as to whether the collaboration partner will choose to exercise the option. Factors that the Company considered in evaluating whether an option is substantive include the cost to exercise the option, the overall objective of the arrangement, the benefit the collaborator might obtain from the arrangement without exercising the option and the likelihood the option will be exercised. When an option was considered substantive, the Company does not consider the option or item underlying the option to be a deliverable at the inception of the arrangement and the associated option fees are not included in allocable consideration, assuming the option is not priced at a significant and incremental discount. Conversely, when an option is not considered substantive, the Company would consider the option, including other deliverables contingent upon the exercise of the option, to be a deliverable at the inception of the arrangement and a corresponding amount would be included in allocable arrangement consideration. In addition, if the price of the option includes a significant incremental discount, the discount would be included as a deliverable at the inception of the arrangement. The consideration received under the arrangement that is fixed or determinable was then allocated among the separate units of accounting using the relative selling price method. The Company determined the estimated selling price for units of accounting within each arrangement using vendor-specific objective evidence (“VSOE”) of selling price, if available, third-party evidence (“TPE”) of selling price if VSOE is not available, or best estimate of selling price (“BESP”) if neither VSOE nor TPE is available. Determining the BESP for a unit of accounting required significant judgment. In developing the BESP for a unit of accounting, the Company considered applicable market conditions and relevant entity-specific factors, including factors that were contemplated in negotiating the agreement with the customer and estimated costs. The Company validated the BESP for units of accounting by evaluating whether changes in the key assumptions used to determine the BESP had a significant effect on the allocation of arrangement consideration between multiple units of accounting. The Company recognized arrangement consideration allocated to each unit of accounting when all of the revenue recognition criteria in ASC 605 are satisfied for that particular unit of accounting. In the event that a deliverable does not represent a separate unit of accounting, the Company recognized revenue from the combined unit of accounting over the Company’s contractual or estimated performance period for the undelivered elements, which is typically the term of the Company’s research and development obligations. If there is no discernible pattern of performance or objectively measurable performance measures do not exist, then the Company recognized revenue under the arrangement on a straight-line basis over the period the Company is expected to complete its performance obligations. Conversely, if the pattern of performance in which the service is provided to the customer can be determined and objectively measurable performance measures exist, then the Company recognized revenue under the arrangement using the proportional performance method. Revenue recognized is limited to the lesser of the cumulative amount of payments received or the cumulative amount of revenue earned, as determined using the straight-line method or proportional performance method, as applicable, as of the period ending date. At the inception of an arrangement that includes milestone payments, the Company evaluated whether each milestone was substantive and at risk to both parties on the basis of the contingent nature of the milestone. This evaluation includes an assessment of whether: (1) the consideration is commensurate with either the Company’s performance to achieve the milestone or the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from its performance to achieve the milestone, (2) the consideration relates solely to past performance and (3) the consideration is reasonable relative to all of the deliverables and payment terms within the arrangement. The Company evaluated factors such as the scientific, clinical, regulatory, commercial, and other risks that must be overcome to achieve the particular milestone and the level of effort and investment required to achieve the particular milestone in making this assessment. There was considerable judgment involved in determining whether a milestone satisfies all of the criteria required to conclude that a milestone is substantive. Milestones that are not considered substantive were recognized as earned if there are no remaining performance obligations or over the remaining period of performance, assuming all other revenue recognition criteria are met. ​ Research and Development Expenses Research and development expenses are charged to expense as incurred in performing research and development activities. The costs include employee-related expenses including salaries, benefits, and stock-based compensation expense, costs of funding research performed by third parties that conduct research and development and preclinical and clinical activities on the Company’s behalf, the cost of purchasing lab supplies and non-capital equipment used in preclinical and clinical activities and in manufacturing preclinical and clinical study materials, consultant fees, facility costs including rent, depreciation, and maintenance expenses, and fees for acquiring and maintaining licenses under third party licensing agreements, including any sublicensing or success payments made to the Company’s licensors. In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. If the actual timing of the performance of services or the level of effort varies from the Company’s estimate, the accrual or prepaid is adjusted accordingly. The Company defers and capitalizes non-refundable advance payments made by the Company for research and development activities until the related goods are received or the related services are performed. In circumstances where amounts have been paid in excess of costs incurred, the Company records a prepaid expense. In-process Research and Development Assets In-process research and development assets that are acquired in a transaction that does not qualify as a business combination under GAAP and that do not have an alternative future use are expensed in the period in which the assets are acquired. Patent Costs The Company expenses patent and patent application costs and related legal costs for the prosecution and maintenance of such patents and patent applications, including patents and patent applications the Company in-licenses, as incurred and classifies such costs as general and administrative expenses in the accompanying consolidated statements of operations. Construction Financing Lease Obligation Beginning in 2016, the Company began recording certain estimated construction costs incurred and reported to the Company by a landlord as an asset and corresponding construction financing lease obligation on the Company’s consolidated balance sheets because the Company was deemed to be the owner of the building during the construction period for accounting purposes. In each reporting period, the landlord estimated and reported to the Company the costs incurred to date and provided supporting invoices for the Company to review. The Company periodically met with the landlord and its construction manager to review the estimates and observe construction progress prior to recording such amounts. Construction was completed in October 2016 and the Company considered the requirements for sale-leaseback accounting treatment, which included an evaluation of whether all risks of ownership had transferred back to the landlord as evidenced by a lack of continuing involvement in the lease property. The Company determined that the arrangement did not qualify for sale lease-back accounting treatment, the building asset will remain on the Company’s consolidated balance sheet at its historical cost, and such asset would be depreciated over its estimated useful life of thirty years. Effective January 1, 2019, the Company adopted Accounting Standards Update (“ASU”) No. 2016-02, Leases ​ ​ ​ ​ ​ As of ​ January 1, 2019 Property and equipment, net $ 32,627 Other current liabilities $ (1,014) Construction financing lease obligation, net of current portion $ (32,417) Accumulated deficit $ 803 ​ Leases The Company accounts for leases in accordance with ASC 842. At the inception of an arrangement the Company determines whether the arrangement contains a lease. If a lease is identified in an arrangement, the Company recognizes a right-of-use asset and liability on its balance sheet and determines whether the lease should be classified as a finance or operating lease. The Company does not recognize assets or liabilities for leases with lease terms of less than 12 months. Lease payments for short-term leases are recorded to operating expense on a straight-line basis over the lease term and variable lease payments are recorded in the period in which the obligation for those payments is incurred. A lease qualifies as a finance lease if any of the following criteria are met at the inception of the lease: (i) there is a transfer of ownership of the leased asset to the Company by the end of the lease term, (ii) the Company holds an option to purchase the leased asset that it is reasonably certain to exercise, (iii) the lease term is for a major part of the remaining economic life of the leased asset, (iv) the present value of the sum of lease payments equals or exceeds substantially all of the fair value of the leased asset, and (v) the nature of the leased asset is specialized to the point that it is expected to provide the lessor no alternative use at the end of the lease term. All other leases are recorded as operating leases. Finance and operating lease assets and liabilities are recognized at the lease commencement date based on the present value of the lease payments over the lease term using the discount rate implicit in the lease. If the rate is not readily determinable, the Company utilizes its incremental borrowing rate at the lease commencement date. Operating lease assets are further adjusted for prepaid or accrued lease payments. Operating lease payments are expensed using the straight-line method as an operating expense over the lease term. Finance lease assets are amortized to depreciation expense using the straight-line method over the shorter of the useful life of the related asset or the lease term. Finance lease payments are bifurcated into (i) a portion that is recorded as imputed interest expense and (ii) a portion that reduces the finance liability associated with the lease. The Company does not separate lease and non-lease components when determining which lease payments to include in the calculation of its lease assets and liabilities. Variable lease payments are expensed as incurred. If a lease includes an option to extend or terminate the lease, the Company reflects the option in the lease term if it is reasonably certain it will exercise the option. Stock-based Compensation Expense The Company’s stock-based compensation program grant awards which have included stock options, restricted stock awards (“RSAs”), restricted stock unit awards (“RSUs”), a market-based option award, and shares issued under the Company’s 2015 employee stock purchase plan (“ESPP”). The Company accounts for stock-based compensation awards in accordance with ASC Topic 718, Compensation—Stock Compensation using the Black-Scholes option-pricing model. The fair value of the Company’s RSAs and RSUs is based on market value of the Company’s common stock on the date of grant. For awards subject to service-based vesting conditions, the Company recognizes the stock-based compensation expense on a straight-line basis over the requisite service period. If an employee or non-employee service requirement is concluded to be non-substantive, the stock-based compensation expense would be expensed immediately. Forfeitures are recorded as they occur. Prior to 2019, the Company accounted for stock-based payments issued to non-employees in accordance with ASC Topic 505-50, Equity Based Payments to Non-Employees For stock options granted to employees and to members of the Company’s board of directors for their services on the board of directors, the Company estimates the grant date fair value of each option award using the Black-Scholes option-pricing model. The Black-Scholes option pricing model requires the input of certain subjective assumptions, including (1) the expected stock price volatility, (2) the calculation of expected term of the award, (3) the risk-free interest rate, and (4) the expected dividend yield. Because there had been no public market for the Company’s common stock prior to its initial public offering, there was a lack of company-specific historical and implied volatility data. Accordingly, the Company based its estimates of expected volatility on the historical volatility of a group of similar c

Cash Equivalents, Marketable Se

Cash Equivalents, Marketable Securities and Equity Securities	12 Months Ended
	Dec. 31, 2019
Cash Equivalents, Marketable Securities and Equity Securities
Cash Equivalents, Marketable Securities and Equity Securities	3. Cash Equivalents, Marketable Securities and Equity Securities Cash equivalents, marketable securities and equity securities consisted of the following at December 31, 2019 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross ​ Gross ​ ​ ​ ​ Amortized ​ Unrealized ​ Unrealized ​ Fair December 31, 2019 ​ Cost ​ Gains ​ Losses ​ Value Cash equivalents and marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 230,201 ​ $ — ​ $ — ​ $ 230,201 U.S. Treasuries ​ ​ 71,348 ​ ​ 20 ​ ​ — ​ ​ 71,368 Government agency securities ​ ​ 155,484 ​ ​ 87 ​ ​ — ​ ​ 155,571 Equity securities included in other non-current assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Corporate equity securities ​ ​ 3,667 ​ ​ — ​ ​ — ​ ​ 3,667 Total ​ $ 460,700 ​ $ 107 ​ $ — ​ $ 460,807 ​ Cash equivalents, marketable securities and equity securities consisted of the following at December 31, 2018 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross ​ Gross ​ ​ ​ ​ Amortized ​ Unrealized ​ Unrealized ​ Fair December 31, 2018 ​ Cost ​ Gains ​ Losses ​ Value Cash equivalents and marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 130,049 ​ $ — ​ $ — ​ $ 130,049 U.S. Treasuries ​ ​ 208,754 ​ ​ — ​ ​ (24) ​ ​ 208,730 Government agency securities ​ ​ 29,940 ​ ​ — ​ ​ (5) ​ ​ 29,935 Equity securities included in other non-current assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Corporate equity securities ​ ​ 3,667 ​ ​ — ​ ​ — ​ ​ 3,667 Total cash equivalents and marketable securities ​ $ 372,410 ​ $ — ​ $ (29) ​ $ 372,381 ​ At December 31, 2019, the Company held three securities that were in an unrealized loss position. The aggregate fair value of securities held by the Company in an unrealized loss position for less than 12 months at December 31, 2019 was $26.6 million, and there were no securities held by the Company in an unrealized loss position for more than 12 months. As of December 31, 2019, the Company did not intend to sell, and was not more likely than not required to sell, the debt securities in an unrealized loss position before recovery of their amortized cost bases. Furthermore, the Company has determined that there were no material changes in the credit risk of the debt securities. As a result, the Company determined it did not hold any securities with any other-than-temporary impairment as of December 31, 2019. There were no realized gains or losses on available-for-sale securities during the years ended December 31, 2019 or 2018. ​

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2019
Fair Value Measurements
Fair Value Measurements	4. Fair Value Measurements Assets measured at fair value on a recurring basis as of December 31, 2019 were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Quoted Prices Significant ​ ​ ​ ​ ​ ​ ​ in Active ​ Other ​ Significant ​ ​ ​ ​ ​ Markets for ​ Observable ​ Unobservable ​ ​ December 31, ​ Identical Assets ​ Inputs ​ Inputs Financial Assets ​ 2019 ​ (Level 1) ​ (Level 2) ​ (Level 3) Cash equivalents: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 230,201 ​ $ 230,201 ​ $ — ​ $ — U.S. Treasuries ​ ​ 7,982 ​ ​ 7,982 ​ ​ — ​ ​ — Marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Treasuries ​ ​ 63,386 ​ ​ 63,386 ​ ​ — ​ ​ — Government agency securities ​ ​ 155,571 ​ ​ 155,571 ​ ​ — ​ ​ — Restricted cash and other non-current assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Corporate equity securities ​ ​ 3,667 ​ ​ — ​ ​ 3,667 ​ ​ — Money market funds ​ ​ 1,619 ​ ​ 1,619 ​ ​ — ​ ​ — Total financial assets ​ $ 462,426 ​ $ 458,759 ​ $ 3,667 ​ $ — ​ Assets and liabilities measured at fair value on a recurring basis as of December 31, 2018 were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Quoted Prices Significant ​ ​ ​ ​ ​ ​ ​ in Active ​ Other ​ Significant ​ ​ ​ ​ ​ Markets for ​ Observable ​ Unobservable ​ ​ December 31, ​ Identical Assets ​ Inputs ​ Inputs Financial Assets ​ 2018 ​ (Level 1) ​ (Level 2) ​ (Level 3) Cash and cash equivalents: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 130,049 ​ $ 130,049 ​ $ — ​ $ — U.S. Treasuries ​ ​ 4,487 ​ ​ 4,487 ​ ​ — ​ ​ — Marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Treasuries ​ ​ 204,243 ​ ​ 204,243 ​ ​ — ​ ​ — Government agency securities ​ ​ 29,935 ​ ​ 29,935 ​ ​ — ​ ​ — Restricted cash and other non-current assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Corporate equity securities ​ ​ 3,667 ​ ​ — ​ ​ 3,667 ​ ​ ​ Money market funds ​ ​ 1,619 ​ ​ 1,619 ​ ​ — ​ ​ — Total financial assets ​ $ 374,000 ​ $ 370,333 ​ $ 3,667 ​ $ — ​ There were no transfers between fair value measurement levels during the years ended December 31, 2019 or 2018.

Property and Equipment, net

Property and Equipment, net	12 Months Ended
	Dec. 31, 2019
Property and Equipment, net
Property and Equipment, net	5. Property and Equipment, Net Property and equipment, net consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ As of ​ ​ December 31, ​ 2019 2018 Laboratory equipment ​ $ 14,571 ​ $ 10,892 Construction-in-progress ​ ​ 1,336 ​ ​ — Leasehold improvements ​ 1,042 ​ 289 Computer equipment ​ 858 ​ 733 Furniture and office equipment ​ 166 ​ ​ 166 Software ​ ​ 118 ​ ​ 118 Building ​ ​ — ​ ​ 35,167 Total property and equipment ​ 18,091 ​ 47,365 Less: accumulated depreciation ​ (7,204) ​ (7,133) Property and equipment, net ​ $ 10,887 ​ $ 40,232 ​ The Company recorded $2.8 million, $3.3 million and $2.7 million in depreciation expense during the years ended December 31, 2019, 2018 and 2017, respectively. ​ See Note 7, “Leases” for additional information regarding ASC 842 adoption including derecognition of the building.

Accrued Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2019
Accrued Expenses
Accrued Expenses	6. Accrued Expenses Accrued expenses consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ As of ​ ​ December 31, ​ 2019 2018 Sublicensing and success payment expenses ​ $ 11,416 ​ $ 3,750 Employee related expenses ​ ​ 4,971 ​ ​ 5,201 Intellectual property and patent related fees ​ ​ 3,725 ​ ​ 1,939 Professional service expenses ​ 674 ​ 475 Process and platform development expenses ​ ​ 735 ​ ​ 1,044 Other expenses ​ 599 ​ 404 Total ​ $ 22,120 ​ $ 12,813 ​

Leases

Leases	12 Months Ended
	Dec. 31, 2019
Leases
Leases	7. Leases ​ Leases ​ ​ ​ ​ ​ ​ ​ ​ ​ As of ​ December 31, ​ January 1, ​ 2019 2019 Right-of-use assets $ 28,761 ​ $ 19,461 Operating lease liabilities, current $ (5,804) ​ $ (3,848) Operating lease liabilities, noncurrent $ (23,277) ​ $ (15,909) ​ ​ ​ ​ ​ ​ ​ Year Ended Maturity of lease liabilities: December 31, 2019 2020 $ 8,150 2021 $ 8,041 2022 $ 7,848 2023 $ 7,279 2024 $ 3,484 Thereafter $ 290 Total minimum lease payments $ 35,092 Less: imputed interest $ (6,011) Total operating lease liabilities at December 31, 2019 $ 29,081 ​ ​ Hurley Street In 2016, the Company entered into a lease agreement for 59,783 square feet of office and laboratory space located on Hurley Street in Cambridge, Massachusetts. The term of the lease began on October 1, 2016 and continues until October 2023. In connection with the lease and as a security deposit, the Company deposited with the landlord a letter of credit in the amount of approximately $1.6 million. Subject to the terms of the lease and certain reduction requirements specified therein, the $1.6 million security deposit may decrease over time. The letter of credit, which is collateralized by the Company, is recorded in restricted cash and other non-current assets in the accompanying consolidated balance sheets as of December 31, 2019 and December 31, 2018. The Company subleased approximately 10,000 square feet of the Hurley Street premises pursuant to a sublease, which commenced in February 2017 and terminated in June 2018. ​ One Main ​ ​ over the term of the lease.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2019
Commitments and Contingencies
Commitments and Contingencies	8. Commitments and Contingencies The Company is a party to a number of license agreements under which the Company licenses patents, patent applications and other intellectual property from third parties. As such, the Company is obligated to reimburse licensors for various costs including upfront licenses fees, annual license fees, certain licensor expense reimbursements, success payments, research funding payments, and milestones triggerable upon certain development, regulatory, and commercial events as well as royalties on future products. These contracts are generally cancellable, with notice, at the Company’s option and do not have significant cancellation penalties. Broad Sponsored Research Agreement In June 2018, the Company entered into a sponsored research agreement (the “Sponsored Research Agreement”) with The Broad Institute, Inc. (“Broad”). The Sponsored Research Agreement provides for Broad to conduct research useful or relevant to genome editing in the field of genomic medicines for the prevention or treatment of human disease with funding from the Company. Under the Sponsored Research Agreement, Broad granted to the Company an exclusive right of first negotiation for licenses from Broad with respect to patentable inventions developed by Broad in the course of the sponsored research, subject to certain limitations and retained rights (“Sponsored Invention Licenses”). Under the Sponsored Research Agreement, the Company is obligated to make Market Cap Research Funding payments in the event the Company’s market capitalization reaches specified thresholds ranging from a mid-nine digit dollar amount to a low-eleven digit dollar amount or Company Sale Research Funding payments in the event of a Company sale for consideration ranging from a mid-nine digit dollar amount to a low-eleven digit dollar amount. In connection with entering into the Sponsored Research Agreement, the Company confirmed that the first two research payments of $5.0 million and $7.5 million, respectively, were due and payable to Broad. In connection with the Initial Research Payments, the Company issued promissory notes to Broad that it settled in common stock in June 2018. The $12.5 million in research funding expense was recorded to research and development expenses during the year ended December 31, 2018. The Company fully settled the outstanding principal and accrued interest on the Initial Research Notes by issuing 330,617 shares of common stock to Broad in June 2018. Other than the Initial Research Payments, the Company is not required to make additional Research Funding Payments if the Company, whether directly or through its affiliates or sublicensees, is not researching, developing, or commercializing products based on or incorporating inventions exclusively licensed to the Company from Broad under Sponsored Invention Licenses or based on or incorporating CRISPR technology owned, co-owned, or controlled by Broad and otherwise licensed to the Company, subject to certain exclusions (an “Applicable Product” and such exemption from payment, the “Funding Exemption”). In the event that the Company, whether directly or through its affiliates or sublicensees, later resumes research, development, or commercialization of an Applicable Product within a specified period of time, any Research Funding Payment that was not paid to Broad as a result of the Funding Exemption shall become payable. Under the Sponsored Research Agreement, the Company is obligated to pay up to $125.0 million to Broad in Research Funding, inclusive of the Initial Research Payments, and in no event shall the aggregate amount of all Research Funding Payments exceed such amount. Unless the Company has undergone a change in control, Market Cap Research Funding is payable by the Company in cash, common stock, or in the form of promissory notes, which may be settled in shares of common stock at the election of the Company. Following a change in control of the Company, Company Sale Research Funding is required to be made in cash. The Sponsored Research Agreement is terminable by each party upon the occurrence of specified bankruptcy events of the other party and otherwise will continue in effect until the later of the expenditure of all Research Funding Payments by Broad and such time as the Company has no further rights of first negotiation for Sponsored Invention Licenses, unless otherwise mutually agreed between the parties. Cas9-I License Agreement In October 2014, the Company entered into an agreement (the “Cas9-I License Agreement”) with Broad and the President and Fellows of Harvard College (“Harvard”) to license certain patent rights owned or co-owned by, or among, Broad, the Massachusetts Institute of Technology (“MIT”), and Harvard (collectively, the “Institutions”). Consideration for the granting of the license included the payment of an upfront license issuance fee of $0.2 million and the issuance of 561,531 shares of the Company’s common stock. The Institutions are collectively entitled to receive clinical and regulatory milestone payments totaling up to $14.8 million in the aggregate per licensed product approved in the United States, European Union, and Japan for the treatment of a human disease that afflicts at least a specified number of patients in the aggregate in the United States. If the Company undergoes a change of control during the term of the license agreement, the clinical and regulatory milestone payments will be increased by a certain percentage in the mid-double digits. The Company is also obligated to make additional payments to the Institutions, collectively, of up to an aggregate of $54.0 million upon the occurrence of certain sales milestones per licensed product for the treatment of a human disease that afflicts at least a specified number of patients in the aggregate in the United States. The Institutions are collectively entitled to receive clinical and regulatory milestone payments totaling up to $4.1 million in the aggregate per licensed product approved in the U.S. and at least one jurisdiction outside the U.S. for the treatment of a human disease based on certain criteria. The Company is also obligated to make additional payments to the Institutions, collectively, of up to an aggregate of $36.0 million upon the occurrence of certain sales milestones per licensed product for the treatment of a rare disease meeting certain criteria. The Institutions are entitled to receive from the Company nominal annual license fees and a mid-single digit percentage royalties on net sales of products for the prevention or treatment of human disease and ranging from low single digit to high single digit percentage royalties on net sales of other products and services, made by the Company, its affiliates, or its sublicensees. The royalty percentage depends on the product and service, and whether such licensed product or licensed service is covered by a valid claim within the certain patent rights that the Company licenses from the Institutions. Cpf1 License Agreement In December 2016, the Company entered into the Cpf1 License Agreement with Broad, for specified patent rights (the “Cpf1 Patent Rights”) related primarily to Cas12a (formerly known as Cpf1) compositions of matter and their use for gene editing. Concurrently with entering into the Cpf1 License Agreement, the Company, Broad, and Harvard amended and restated the Cas9-I License Agreement as described below and the Company and Broad entered into the Cas9-II License Agreement for specified patent rights (the “Cas9-II Patent Rights”) related primarily to certain Cas9 compositions of matter and their use for genome editing. The Company paid an upfront fee in aggregate of $16.5 million under these agreements which was recorded in research and development expenses during 2016. The upfront fee was fully settled in 2017, partially by issuing 479,270 shares of common stock. Pursuant to the Cpf1 License Agreement, Broad, on behalf of itself, Harvard, MIT, Wageningen, and the University of Tokyo (“UTokyo” and, together with Broad, Harvard, Massachusetts Institute of Technology (“MIT”), and Wageningen University (“Wageningen”),(the “Cpf1 Institutions”) granted the Company an exclusive, worldwide, royalty-bearing, sublicensable license to the Cpf1 Patent Rights, to make, have made, use, have used, sell, offer for sale, have sold, export and import products in the field of the prevention or treatment of human disease using gene therapy, editing of genetic material, or targeting of genetic material, subject to certain limitations and retained rights (collectively, the “Cpf1 Exclusive Field”), as well as a non-exclusive, worldwide, royalty-bearing sublicensable license to the Cpf1 Patent Rights for all other purposes, subject to certain limitations and retained rights. The Company is obligated to use commercially reasonable efforts to research, develop, and commercialize products in the Cpf1 Exclusive Field. The Company is also required to achieve certain development milestones within specified time periods for products covered by the Cpf1 Patent Rights, with Broad having the right to terminate the Cpf1 License Agreement if the Company fails to achieve these milestones within the required time periods. Broad and Wageningen are collectively entitled to receive clinical and regulatory milestone payments totaling up to $20.0 million in the aggregate per licensed product approved in the United States, European Union, and Japan for the prevention or treatment of a human disease that afflicts at least a specified number of patients in the aggregate in the United States. The Company is also obligated to make additional payments to Broad and Wageningen, collectively, of up to an aggregate of $54.0 million upon the occurrence of certain sales milestones per licensed product for the prevention or treatment of a human disease that afflicts at least a specified number of patients in the aggregate in the United States. Broad and Wageningen are collectively entitled to receive clinical and regulatory milestone payments totaling up to $6.0 million in the aggregate per licensed product approved in the United States, European Union and Japan for the prevention or treatment of a human disease that afflicts fewer than a specified number of patients in the aggregate in the United States or a specified number of patients per year in the United States (an “Ultra-Orphan Disease”). The Company is also obligated to make additional payments to Broad and Wageningen, collectively, of up to an aggregate of $36.0 million upon the occurrence of certain sales milestones per licensed product for the prevention or treatment of an Ultra-Orphan Disease. Broad and Wageningen, collectively, are entitled to receive, on a product-by-product and country-by-country basis, mid single-digit percentage royalty on net sales of licensed products for the prevention or treatment of human disease, and royalties on net sales of other licensed products and licensed services, made by the Company, its affiliates, or its sublicensees. The royalty percentage depends on the product and service, and whether such licensed product or licensed service is covered by a valid claim within the Cpf1 Patent Rights. If the Company is legally required to pay royalties to a third party on net sales of the Company’s products because such third party holds patent rights that cover such licensed product, then the Company can credit up to a specified percentage of the amount paid to such third party against the royalties due to Broad and Wageningen in the same period. Such credit may not exceed 50% of the applicable royalties paid by the Company to the applicable third party. The Company’s obligation to pay royalties will expire on a product-by-product and country-by-country basis upon the later of the expiration of the last to expire valid claim of the Cpf1 Patent Rights that covers each licensed product or service in each country or the tenth anniversary of the date of the first commercial sale of the licensed product or licensed service. If the Company sublicenses any of the Cpf1 Patent Rights to a third party, Broad and Wageningen, collectively, have the right to receive sublicense income, depending on the stage of development of the products or services in question at the time of the sublicense. Under the Cpf1 License Agreement, Broad and Wageningen are also entitled, collectively, to receive success payments in the event the Company’s market capitalization reaches specified thresholds (the “Cpf1 Market Cap Success Payments”) or a Company sale for consideration in excess of those thresholds (the “Cpf1 Company Sale Success Payments” and, collectively with the Cpf1 Market Cap Success Payments, the “Cpf1 Success Payments”). The Cpf1 Success Payments payable to Broad and Wageningen are triggered when the Company’s market capitalization reaches certain amounts ranging from $750.0 million to $10.0 billion for a specified period of time, and collectively the Cpf1 Success Payments will not exceed, in aggregate, $125.0 million, which maximum amount would be payable only if the Company reaches a market capitalization threshold of $10.0 billion and has at least one product candidate covered by a claim of a patent right licensed to the Company under either the Cpf1 License Agreement or the Cas9-I License Agreement that is or was the subject of a clinical trial pursuant to development efforts by the Company or any Company affiliate or sublicensee. The Cpf1 Market Cap Success Payments are payable by the Company in cash or in the form of promissory notes. Following a change in control of the Company, Cpf1 Market Cap Success Payments are required to be made in cash. Cpf1 Company Sale Success Payments are payable solely in cash. The Company triggered the first and second Cpf1 Success Payments during 2017 when the Company’s market capitalization reached $750 million and $1.0 billion, respectively. The Company issued promissory notes for both Success Payments that were settled in 271,347 shares and 150,606 shares of common stock in August 2017 and January 2018, respectively. Unless terminated earlier, the term of the Cpf1 License Agreement will expire on a country-by-country basis, upon the expiration of the last to expire valid claim of the Cpf1 Patent Rights in such country. The Company has the right to terminate the Cpf1 License Agreement at will upon four months’ written notice to Broad. Either party may terminate the Cpf1 License Agreement upon a specified period of notice in the event of the other party’s uncured material breach of a material obligation, such notice period varying depending on the nature of the breach. Broad may terminate the Cpf1 License Agreement immediately if the Company challenges the enforceability, validity, or scope of any Cpf1 Patent Right or assist a third party to do so, or in the event of the Company’s bankruptcy or insolvency. Amendment and Restatement of Cas9-I License Agreement In December 2016, the Company amended and restated the Cas9-I License Agreement (such agreement, as amended, the “Amended and Restated Cas9-I License Agreement”) to exclude additional fields from the scope of the exclusive license previously granted to the Company, to make the exclusive license to three targets become non-exclusive, subject to the limitation that each of Broad and Harvard would only be permitted to grant a license to only one third party at a time with respect to each such target within the field of the exclusive license, and to revise certain provisions relating to the rights of Harvard and Broad to grant further licenses under specified circumstances to third parties that wish to develop and commercialize products that target a particular gene and that otherwise would fall within the scope of the exclusive license under this agreement, so that Harvard and Broad together would have rights substantially similar to the equivalent rights possessed by Broad under the Cpf1 License Agreement to designate gene targets for which the designating institution, whether alone or together with an affiliate or third party, has an interest in researching and developing products that would otherwise be covered by rights licensed by Harvard and/or Broad to the Company under this agreement, the Cpf1 License Agreement or the Cas9-II License Agreement. In March 2017, the Company and Harvard and Broad further amended the Amended and Restated Cas9-I License Agreement to (i) grant an exclusive license from Broad to the Company with respect to certain patent rights that The Rockefeller University (“Rockefeller”) has or may have rights in and to and for which Rockefeller has, under a certain inter-institutional agreement that Broad and Rockefeller entered into in February 2017, appointed Broad as sole and exclusive agent for the purposes of licensing and (ii) provide to Rockefeller certain rights, including with respect to patent enforcement, indemnification, insurance, confidentiality, reservation of certain rights, and publicity, that are generally consistent with those granted to Broad, Harvard, MIT and the Howard Hughes Medical Institute under the Amended and Restated Cas9-I License Agreement. Cas9-II License Agreement Pursuant to the Cas9-II License Agreement, Broad, on behalf of itself, MIT, Harvard, and the University of Iowa Research Foundation, granted the Company an exclusive, worldwide, royalty bearing sublicensable license to certain of the Cas9-II Patent Rights as well as a non-exclusive, worldwide, royalty-bearing sublicensable license to all of the Cas9-II Patent Rights, in each case on terms substantially similar to the licenses granted to the Company under the Cpf1 License Agreement except, among other things, for the following commitment amounts. Under the Cas9-II License Agreement, the Company will pay an upfront license fee in a low seven digit dollar amount and will have to pay an annual license maintenance fee. The Company is obligated to pay clinical and regulatory milestone payments per licensed product approved in the United States, European Union and Japan for the prevention or treatment of a human disease that afflicts at least a specified number of patients in the aggregate in the United States totaling up to $3.7 million in the aggregate, and sales milestone payments for any such licensed product totaling up to $13.5 million in the aggregate. In addition, the Company is obligated to pay clinical and regulatory milestone payments totaling up to $1.1 million in the aggregate per licensed product approved in the United States and the European Union or Japan for the prevention or treatment of a human disease that afflicts fewer than a specified number of patients in the United States, plus sales milestone payments of up to $9.0 million for any such licensed product. Consistent with the Cpf1 License Agreement, the licensors are entitled to royalties on net sales of products for the prevention or treatment of human disease and other products and services made by the Company, its affiliates, or its sublicensees. Royalties due under other license agreements are creditable against these royalties up to a specified amount in the same period. Lastly, Broad is entitled to receive success payments if the Company’s market capitalization reaches specified thresholds ascending from $1.0 billion to $9.0 billion or upon a sale of the Company for consideration in excess of those thresholds. The potential success payments range from a low seven digit dollar amount to a low eight digit dollar amount and will not exceed, in aggregate, $30.0 million, which maximum amount would be owed only if the Company reaches a market capitalization threshold of $9.0 billion and has at least one product candidate covered by a claim of a patent right licensed to the Company under either the Cas9-I License Agreement or the Cas9-II License Agreement that is or was the subject of a clinical trial pursuant to development efforts by the Company or any Company affiliate or sublicensee. The Company triggered the first Success Payment under the Cas9-II License Agreement during the fourth quarter of 2017 when the Company’s market capitalization reached $1.0 billion, which the Company settled by issuing 75,303 shares of its common stock in January 2018. Licensor Expense Reimbursement The Company is obligated to reimburse to Broad and Harvard for expenses incurred by each of them associated with the prosecution and maintenance of the patent rights that the Company licenses from them pursuant to the license agreement by and among the Company, Broad and Harvard, including the interference and opposition proceedings involving patents licensed to the Company under the license agreement, and other license agreements between the Company and Broad. As such, the Company anticipates that it has a substantial commitment in connection with these proceedings until such time as these proceedings have been resolved, but the amount of such commitment is not determinable. The Company incurred an aggregate of $13.5 million, $14.2 million and $18.2 million in expense during the years ended December 31, 2019, 2018 and 2017, respectively, for such reimbursement. Litigation The Company is not a party to any litigation and did not have contingency reserves established for any litigation liabilities as of December 31, 2019 or 2018.

Collaboration and Profit-Sharin

Collaboration and Profit-Sharing Agreements	12 Months Ended
	Dec. 31, 2019
Collaboration and Profit-Sharing Agreements
Collaboration and Profit-Sharing Agreements	9. Collaboration and Profit-Sharing Agreements Collaboration Revenue ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the year ended December 31, 2019 Balance at December 31, 2018 ​ Additions ​ Deductions ​ Balance at Accounts receivable $ 30 ​ $ 418 ​ $ (30) ​ $ 418 Contract liabilities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Deferred revenue $ 131,326 ​ $ 75,500 ​ $ (20,105) ​ $ 186,721 ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ Year Ended Revenue recognized in the period from: December 31, 2019 Amounts included in deferred revenue at the beginning of the period $ 4,715 ​ $ 11,448 Performance obligations satisfied in previous periods $ 1,261 ​ $ 2,455 ​ Juno Therapeutics Collaboration Agreement In May 2015, the Company entered into a collaboration and license agreement (the “Collaboration Agreement”) with Juno Therapeutics and in May 2018 the Company and Juno Therapeutics entered into an amended and restated collaboration and license agreement (the Collaboration Agreement, as amended and restated, the “2018 Amended Collaboration Agreement”). The collaboration was initially focused on the research and development of engineered T cells with chimeric antigen receptors and T cell receptors that have been genetically modified to recognize and kill other cells. In November 2019 (the “Amendment Date”), the Company amended and restated the 2018 Amended Collaboration and entered into a license agreement (the 2018 Amended Collaboration Agreement, as amended and restated, and collectively with the license agreement, the “2019 Amended Collaboration Agreement”) to focus on the research, development, and commercialization of autologous and allogenic alpha-beta T cell medicines for the treatment of all diseases, subject to certain exceptions. 2018 Amended Collaboration Agreement ​ Pursuant to the 2018 Amended Collaboration Agreement, the Company and Juno Therapeutics were pursuing research in accordance with a mutually agreed upon research plan across four research areas. The 2018 Amended Collaboration Agreement increased the scope of the research plan from three to four research areas. The Company’s research and development responsibilities under the research plan were related to generating genome editing reagents that modify gene targets selected by Juno Therapeutics. Except with respect to the Company’s obligations under the mutually agreed upon research plan, Juno Therapeutics had sole responsibility, at its own cost, for the worldwide research, development, manufacturing and commercialization of products within each of the four research areas for the diagnosis, treatment or prevention of any cancer in humans through the use of engineered T-cells, excluding the diagnosis, treatment or prevention of medullary cystic kidney disease 1 (the “Exclusive Field”). The initial term of the research program commenced on May 26, 2015 and continued for five years ending on May 26, 2020 (the “Initial Research Program Term”). Under the terms of the Collaboration Agreement, the Company granted to Juno Therapeutics during the Initial Research Program Term a nonexclusive research license solely for the purpose of conducting specific research related activities as defined by the research plan. Pursuant to the terms of the 2018 Amended Collaboration Agreement, the license rights granted to Juno Therapeutics were expanded to incorporate the fourth research area (together, the initial research license granted per the terms of the Collaboration Agreement and the incremental research license granted per the terms of the 2018 Amended Collaboration Agreement, the “Research License”). The Company granted to Juno Therapeutics exclusive worldwide development and commercialization licenses in the Exclusive Field, specifically as it relates to certain targets or products selected by Juno Therapeutics in each of the four research areas. Furthermore, for two of the original research areas under the terms of the Collaboration Agreement, the Company granted to Juno Therapeutics a non-exclusive worldwide license to use certain genome editing reagents that were created under the agreement in all fields outside the Exclusive Field (“the Non-Exclusive Field”) specifically as it relates to certain targets selected by Juno Therapeutics, if the genome editing reagents were previously incorporated into an investigational new drug application filed by Juno Therapeutics in the Exclusive Field (together, the license in the Exclusive Field and the license in the Non-Exclusive Field are referred to as the “Development and Commercialization License” for each particular research area). Under the terms of the Collaboration Agreement, the Company received a $25.0 million up-front, non-refundable, non-creditable cash payment. In connection with the entry into the 2018 Amended Collaboration Agreement, the Company received an additional $5.0 million up-front, non-refundable, non-creditable cash payment. In addition, Juno Therapeutics was obligated to pay to the Company research and development funding over the Initial Research Program Term across the four research areas consisting primarily of funding for up to a specified maximum number of full-time equivalents personnel each year. Consistent with the terms of the Collaboration Agreement, under the terms of the 2018 Amended Collaboration Agreement, there was no incremental compensation due to the Company with respect to the Development and Commercialization License granted to Juno Therapeutics associated with the first target or product, as applicable, designated by Juno Therapeutics within each of the four research areas. However, for two of the research areas Juno Therapeutics had the option to purchase up to three additional Development and Commercialization Licenses associated with other gene targets for an additional fee of $2.5 million per target. In addition, Juno Therapeutics would have been required to make certain milestone payments to the Company upon the achievement of specified development, regulatory and commercial events. Royalties would have been paid on a licensed product-by-product and country-by-country basis from the date of the first commercial sale of each product in a country until the expiration date. The Company achieved two $2.5 million development milestones under the Collaboration Agreement resulting from technical progress in a research program in each of May 2016 and July 2017. The Company also achieved two additional $2.5 million development milestones under the 2018 Amended Collaboration Agreement resulting from technical progress in a research program in May 2018. The Company evaluated the 2018 Amended Collaboration Agreement in accordance with the provisions of ASC 606. The Company accounted for the amendment resulting from the 2018 Amended Collaboration Agreement as a modification to the original contract and not as a separate contract. The Company identified the following performance obligations under the modified arrangement: (i) Research License and the related research and development services during the Initial Research Program Term (the “Research License and Related Services”), (ii) four material rights related to the first Development and Commercialization Licenses related to each of the four research areas (each, a “First Development and Commercialization License Material Right”) and (iii) six material rights related to the option to purchase up to three additional Development and Commercialization Licenses for two of the research areas (each, an “Additional Development and Commercialization License Material Right”). The rights to be conveyed to Juno Therapeutics pursuant to each of the Development and Commercialization Licenses extend exclusively to an individual target or product, as applicable; therefore, control is deemed to be transferred upon the designation by Juno Therapeutics of the specific target or product, as applicable, whereupon the license becomes effective upon Juno Therapeutics exercising their option. Through the date of the 2018 Amended Collaboration Agreement, the Company had recognized approximately $12.3 million of revenue associated with the Research License and Related Services which was excluded from the modification date transaction price. The total transaction price associated with the remaining consideration based on the 2018 Amended Collaboration Agreement was determined to be $40.7 million, consisting of: (i) $30.0 million in upfront payments (ii) $2.9 million of remaining research and development funding and (iii) $7.7 million of milestones payments received by the Company that were not yet recognized as revenue. The Company utilized the most likely amount method to determine the amount of research and development funding to be received. The outstanding milestones payments were fully constrained. The transaction price was allocated to the performance obligations based on the relative estimated standalone selling prices of each performance obligation or, in the case of certain variable consideration, to one or more performance obligations. The transaction price allocated to the Research License and Related Services was $10.7 million. The Company recognized revenue related to amounts allocated to the Research License and Related Services as the underlying services were performed using a proportional performance model. The Company measured proportional performance based on full time employee hours relative to projected full time employee hours to complete the research services which best reflects the progress towards satisfaction of the performance obligation. The remaining transaction price of $30.0 million was allocated to the material rights. Revenue related to each of the material rights would have been recognized upon the earlier of when the respective options were exercised or when the respective options lapse. None of the options associated with the material rights had been exercised or had lapsed prior to the execution of the 2019 Amended Collaboration Agreement . 2019 Amended Collaboration Agreement ​ one ​ ​ The development and commercialization licenses granted to Juno Therapeutics are subject to the terms and conditions of a license agreement that was entered into on the same day as the 2019 Amended Collaboration Agreement. Pursuant to the license agreement, Juno Therapeutics must use commercially reasonable efforts and meet certain regulatory and commercial diligence requirements. The license agreement provided that the Company would manufacture clinical grade materials through a Phase 1 clinical trial if requested by Juno Therapeutics at an incremental cost to be negotiated by the parties. Per the termination provisions of the license agreement, Juno Therapeutics has the right to terminate the agreement either on a licensed product-by-product basis or in its entirety for any reason at any time upon ninety days prior written notice. If Juno Therapeutics terminates the license agreement without cause, the exclusive licenses granted to Juno Therapeutics automatically revert back to the Company. ​ On a product-by-product basis, the Company is eligible to receive up to $27.5 million in development milestones and $107.5 million in regulatory milestones. The Company is also eligible to receive up to an aggregate of $60.0 million for the first two licensed products to reach certain sales milestones. The Company is entitled to a high-single digit to low double-digit percentage of royalties on net sales of licensed products, subject to reductions in certain circumstances, through the later of the expiration of the patent(s) related to the licensed products or six years post-first commercial sale of such licensed products. ​ The Company received a $70.0 million up-front, non-refundable, non-creditable cash payment in connection with the execution of the 2019 Amended Collaboration Agreement. The Company also received an additional $0.5 million for the first development and commercialization license (the “First 2019 Development and Commercialization License”) which was delivered to Juno Therapeutics at the onset of the arrangement. ​ The Company evaluated the 2019 Amended Collaboration Agreement and concluded that the collaboration agreement and licensing agreement qualify as a contract with a customer under ASC 606 as one combined arrangement. The contract modification was accounted for on a prospective basis as if it were a termination of the existing contract and the creation of a new contract since the promised goods and services were distinct from the goods and services that were transferred on or before the effective date of the amendment. ​ The Company has identified the following performance obligations under the 2019 Amended Collaboration Agreement: (i) First 2019 Development and Commercialization License and (ii) seventeen material rights for additional development and commercialization licenses for other Programs. The Company also evaluated the (i) the research license, (ii) contract term extensions, (iii) clinical supply arrangement, (iv) participation by employees on the oversight committee, alliance and technology transfer teams and (v) certain intellectual property rights and concluded that none of these met the definition of a performance obligation as a result of the promise being quantitively and qualitatively immaterial in the context of the arrangement or the promise did not convey a material right to Juno Therapeutics. The Company also concluded that there was not an implicit promise to perform research and development services. ​ As of Amendment Date and December 31, 2019, the total transaction price was approximately $102.5 million comprised of the following: (i) $70.0 million amendment fee, (ii) $0.5 million related to the exercise fee for the First 2019 Development and Commercialization License and (iii) $32.0 million in remaining deferred revenue balance that was not recognized pursuant to the 2018 Amended Collaboration Agreement. The Company utilizes the most likely amount method to estimate any development and regulatory milestone payments to be received as well as extension term fees. As of December 31, 2019, there were no milestones or extension term fees included in the transaction price. The Company considers the stage of development and the risks associated with the remaining development required to achieve the milestone, as well as whether the achievement of the milestone is outside the control of the Company or Juno Therapeutics. The outstanding milestone payments and extension term fees were fully constrained as of December 31, 2019, as a result of the uncertainty of whether any of the milestones will be achieved or the term would be extended. The Company has determined that any commercial milestones and sales-based royalties will be recognized when the related sales occurs. The Company reevaluates the transaction price at the end of each reporting period and as uncertain events are resolved or other changes in circumstances occur. ​ The Company concluded that rights and attributes of each of the development and commercialization licenses are identical for both the license granted at inception and the licenses that may be issued in the future upon exercise of the associated option. Each development and commercialization license is differentiated only by the Program to which it relates. The Company has considered the early stage of the science and the uncertainty of success and concluded that the probability of scientific success and opt-in is equal amongst all Programs. In addition, each Program is multi-functional, and a combination of Programs can be utilized in the development of a product candidate. As such, the Company concluded that the standalone selling price of each material right is the same. The Company will recognize the transaction price allocated to each material right when the material right is exercised, lapsed or expired. ​ During the year ended December 31, 2019, the Company recognized $6.2 million of the $102.5 million transaction price upon delivery of the First 2019 Development and Commercialization License and deferred the remaining $96.3 million allocated to the material rights. As of December 31, 2019, the $96.3 million was classified as long-term in the accompanying consolidated balance sheets. ​ During the year ended December 31, 2019 and 2018, the Company incurred $11.3 million and $1.7 million in sublicense fees owed to certain of the Company’s licensors in connection with the 2019 Amended Collaboration Agreement and 2018 Amended Collaboration Agreement, respectively, which the Company recorded as research and development expenses during such periods. The sublicense fee owned in connection with the 2019 Amended Collaboration Agreement is fully accrued in the consolidated balance sheet as of December 31, 2019. ​ Allergan Pharmaceuticals Strategic Alliance and Profit-Sharing Agreement ​ In March 2017, the Company entered into a Strategic Alliance and Option Agreement with Allergan to discover, develop, and commercialize new gene editing medicines for a range of ocular disorders (the “Allergan Agreement”). Over a seven-year research term, Allergan will have an exclusive option to exclusively license from the Company up to five collaboration development programs for the treatment of ocular disorders (each, a “CDP”), including the Company’s Leber congenital amaurosis 10 (“LCA10”) program and the related experimental therapeutic EDIT-101 to treat LCA10 (the “LCA10 Program”). Under the Allergan Agreement, the Company will use commercially reasonable efforts to develop at least five CDPs and deliver preclinical results and data meeting specified criteria with respect to each CDP (each, an “Option Package,” and such criteria, the “Option Package Criteria”) to Allergan. The list of proposed targets that may be subject to a CDP may be amended from time to time by mutual agreement of the Company and Allergan. The Company is responsible for the preparation and delivery of a written development plan for each particular CDP setting forth the discovery and research activities to be conducted which is subject to the approval of the alliance steering committee that was formed under the Allergan Agreement, comprised of three members from each of the Company and Allergan (the “Steering Committee”). The Company will maintain primary responsibility for the development efforts under each CDP. The Company is responsible for all research and development costs prior to the achievement of the Option Package Criteria. Allergan will have the ability for a defined period of time (“Initial Option Period”) to exercise an option (each, an “Option”) to obtain a worldwide right and license to the Company’s background intellectual property and the Company’s interest in the CDP intellectual property to develop, commercialize, make, have made, use, offer for sale, sell, and import any gene editing therapy product that results from such CDP during the term of the Allergan Agreement (a “Licensed Product”) in any category of human diseases and conditions other than the diagnosis, treatment or prevention of any cancer in humans through the use of engineered T-cells and subject to specified other limitations. Allergan has the option to extend the Initial Option Period and require the Company to perform additional research and development services, subject to the payment of additional consideration. After exercise of an Option with respect to a CDP, with the exception of any CDP’s where the Company has exercised its profit-sharing option, Allergan will be responsible for all development, manufacturing, and commercialization activities in connection with licensed products arising from such CDP, other than with respect to the LCA10 Program, if LCA10 is designated as a CDP. In July 2018, Allergan exercised its Option with respect to the LCA10 Program. In connection with such exercise, Allergan paid the Company $15.0 million. Following such exercise, the Company exercised its Profit-Share Election, as defined below, with respect to the LCA10 Program. Following such election, the LCA10 Program became subject to a Profit-Sharing Arrangement, as defined below, and the Company and an affiliate of Allergan entered into a separate profit-sharing agreement with respect to the Profit-Sharing Arrangement for the LCA10 Program in February 2019. The initial term of the Allergan Agreement commenced on March 14, 2017 and continues for seven years ending on March 14, 2024 (the “Research Term”). If the Company has not delivered an Option Package, which includes the results and data from the CDP, for five CDPs that satisfy the Option Package Criteria, then the Research Term will automatically extend by one-year increments until such obligation is satisfied, up to a maximum of ten years from March 2017. The activities under the Allergan Agreement during the Research Term will be governed by the Steering Committee. The Steering Committee will review and monitor the direction of the development plan, evaluate and determine which targets are selected to become CDP, establish the Option Package Criteria for each CDP and evaluate the achievement of such criteria as well as oversee the development and commercialization activities after Allergan has licensed a CDP. Under the terms of the Allergan Agreement, the Company received a $90.0 million up-front, non-refundable, non-creditable cash payment related to the Company’s research and development costs for Option Packages for at least five CDPs and for reimbursement of the Company’s past out of pocket costs with respect to the prosecution and defense of patents that it owns and in-licenses. Allergan has the option to purchase at least five development and commercialization licenses associated with CDPs that have satisfied the Option Package Criteria. The option exercise fee during the Initial Option Period is $15.0 million per CDP. If Allergan elects to extend the Initial Option Period, Allergan is required to pay an additional fee of $5.0 million to extend the option, at which point the Company is required to perform additional research services. If Allergan elects to exercise its option to a development and commercialization license after extending the Initial Option Period, Allergan must pay the Company the option exercise fee of $22.5 million, plus specified costs incurred by the Company in connection with the additional development work. Following the exercise by Allergan of an Option with respect to a CDP, Allergan would be required to make certain milestone payments to the Company upon the achievement of specified development, product approval and launch and commercial events, on a CDP by CDP basis. On a CDP by CDP basis, for the first product in the first field to achieve the associated event, the Company is eligible to receive up to an aggregate of $42.0 million for development milestone payments and $75.0 million for product approval and launch milestone payments, in each case, for an indication in the field per CDP. In addition, the Company is eligible to receive additional development and product approval and launch milestone payments for subsequent products developed within two additional fields. The Company is also eligible for up to $90.0 million in sales milestone payments on a CDP by CDP basis, associated with aggregate worldwide sales. Certain product approval milestones are subject to certain reductions under specified circumstances, including for payments required to be made by Allergan to obtain certain third party intellectual property rights. In December 2018, the Company received a $25.0 million payment from Allergan in connection with the acceptance of the IND for the LCA10 Program, the Company’s experimental therapeutic generated under the LCA10 Program (the “LCA-10 Program Milestone Payment”). With respect to the LCA10 Program, and up to one other CDP of the Company’s choosing, following the exercise by Allergan of its Option to such programs the Company will have the right to elect to participate in a profit-sharing arrangement with Allergan in the United States, on terms mutually agreed by the Company and Allergan and subject to a right of Allergan to reject such election under certain circumstances, under which the Company and Allergan would share equally in net profits and losses on specific terms to be agreed between the Company and Allergan, in lieu of Allergan paying royalties on net sales of any applicable Licensed Products in the United States, and in such event Allergan’s milestone payment obligations would be reduced, with the Company being eligible to receive development and product approval and launch milestone payments up to a low nine-digit amount in the aggregate and further sales milestone payments up to a high-eight digit amount in the aggregate, subject to reduction under certain circumstances (such right, the “Profit-Share Election,” and such arrangement, a “Profit-Sharing Arrangement”). If the Company elects to participate in a Profit-Sharing Arrangement, which it has for the LCA10 Program, the Company is obligated to reimburse Allergan for half of the United States development costs incurred by Allergan with respect to the applicable CDP, and Allergan will retain control of all development and commercialization activities for the applicable Licensed Products. In addition, to the extent there is any Licensed Product, the Company would be entitled to receive tiered royalty payments of high single digits based on a percentage of net sales of such Licensed Product, subject to certain reductions under specified circumstances, and the Company will remain obligated to pay all license fees, milestone payments, and royalties due to its upstream licensors based on Allergan’s exercise of its license rights with respect to Licensed Products. However, if a Licensed Product is subject to a Profit-Sharing Arrangement the royalties will only be paid on ex-U.S. net sales. Royalties are due on a Licensed Product by Licensed Product and country by country basis from the date of the first commercial sale of each Licensed Product in a country until the later of: (i) the tenth anniversary of the first commercial sale of such Licensed Product in such country, (ii) the expiration date in such country of the last to expire valid claim within the licensed intellectual property covering the manufacture, use or sale of such Licensed Product in such country and (iii) the expiration of an exclusive legal right granted by the regulatory authority in such country to market and sell such Licensed Product. Unless earlier terminated, the Allergan Agreement will terminate upon (i) the expiration of the Research Term, if Allergan does not exercise an Option, (ii) on a Licensed Product-by-Licensed Product and country-by-country basis, on the date of the expiration of all payment obligations under the Allergan Agreement with respect to such Licensed Product in such country or (iii) in its entirety upon the expiration of all payment obligations with respect to the last Licensed Product in all countries, unless terminated earlier due to the early termination provisions. Either party may terminate the Allergan Agreement if the other party has materially breached or defaulted in the performance of any of its material obligations and such breach or default continues after the specified cure period. During the Research Term, Allergan will have the right to terminate the Allergan Agreement on a CDP by CDP basis in the event of a change in control of the Company or for all CDPs, provided that Allergan will not have any right to exercise an Option for any CDPs following such termination. After the exercise of an Option, Allergan will have the right, at its sole discretion, to terminate the Allergan Agreement, on a CDP by CDP basis, upon 90 days’ written notice. The Company may terminate the Allergan Agreement in the event that Allergan brings, assumes, or participates in, or knowingly, willfully or recklessly assists in bringing a dispute or challenge against the Company related to its intellectual property. Lastly, Allergan may terminate the Allergan Agreement with respect to a CDP if a safety concern, as specified in the Allergan Agreement, arises. Termination of the Allergan Agreement for any reason will not release either party from any liability which, at the time of such termination, has already accrued to the other party or which is attributable to a period prior to such termination. In addition, termination of the Allergan Agreement will not preclude either party from pursuing any rights and remedies it may have under the agreement or at law or in equity with respect to any breach of the Allergan Agreement. If Allergan terminates the Allergan Agreement as a result of the Company’s uncured material breach or default, then: (i) the licenses and rights conveyed to Allergan will continue as set forth in the agreement for any CDP Allergan has already licensed and (ii) Allergan’s obligations related to milestones and royalties will continue as set forth in the agreement. If the Allergan Agreement is terminated for any other reason, then the options and licenses conveyed to Allergan under the agreement will terminate. Under the Allergan Agreement, the Company has identified a single performance obligation that includes (i) the research and development services during the Research Term (the “Allergan R&D Services”), and (ii) Steering Committee services during the Research Term (the “ASC Services”). The Company has concluded that the Allergan R&D Services is not distinct from the ASC Services during the Research Term. The Steering Committee provides oversight and management of the overall Allergan Agreement, and the members of the Steering Committee from the Company have specialized industry knowledge, particularly as it relates to genome editing technology. The Steering Committee is meant to facilitate the early stage research being performed and coordinate the activities of both the Company and Allergan. Further, the Steering Committee services are critical to the selection of a CDP, the ongoing evaluation of a CDP and the development and evaluation of the Option Package Criteria. Accordingly, the Company’s participation on the Steering Committee is essential to Allergan receiving value from the Allergan R&D Services and as such, the ASC Services along with the Allergan R&D Services are considered one performance obligation (the “CDP Services”). In addition, the Company has concluded that the option to purchase five development and commercialization licenses is considered a marketing offer as the options did not provide any discounts or other rights that would be considered a material right in the arrangement. As of January 1, 2018, the date of the initial application of ASC 606 by the Company, the total transaction price was determined to be $90.0 million, consisting solely of the upfront non-refundable, non-creditable cash payment. The Company also utilized the most likely amount method to estimate any development and regulatory milestone payments to be received. As of January 1, 2018, there were no milestones included in the transaction price. The milestones were fully constrained due to the significant uncertainties surrounding such payments. The Company considered the stage of development and the risks associated with the remaining development required to achieve the milestone, as well as whether the achievement of the milestone is outside the control of the Company or Allergan. Upon achievement of the EDIT-101 Milestone Payment, $25.0 million was added to the transaction price in November 2018. As of December 31, 2019, the total transaction price is $115.0 million. The remaining milestone payments were fully constrained, as a result of the uncertainty as to whether any of the milestones would be achieved, as of December 31, 2019. The Company has determined that any commercial milestones and sales-based royalties will be recognized when the related sales occur and therefore have also been excluded from the transaction price. The Company re-evaluates the transaction price at the end of each reporting period and as uncertain events are resolved or other changes in circumstances occur. The Company recognizes revenue related to the CDP Services as the underlying services are performed using a proportional performance model. The Company measures proportional performance based on full time employee hours relative to projected full time employee hours to complete the research service. During the year ended December 31, 2019, the Company recognized revenue As part of the Profit-Sharing Arrangement, the Company and an affiliate of Allergan will equally split U.S. profit

Preferred Stock

Preferred Stock	12 Months Ended
	Dec. 31, 2019
Preferred Stock
Preferred Stock	10. Preferred Stock On February 8, 2016, the Company filed a restated certificate of incorporation with the Secretary of State of the State of Delaware. The restated certificate amended and restated the Company’s certificate of incorporation in its entirety to, among other things increase the authorized number of shares of common stock to 195,000,000 shares, eliminate all references to the previously existing series of preferred stock, and authorize 5,000,000 shares of undesignated preferred stock that may be issued from time to time by the Company’s board of directors in one or more series. As of December 31, 2019

Common Stock

Common Stock	12 Months Ended
	Dec. 31, 2019
Common Stock
Common Stock	11. Common Stock The voting, dividend, and liquidation rights of the holders of the common stock are subject to and qualified by the rights, powers, and preferences of holders of the preferred stock that may be issued from time to time. The common stock had the following characteristics as of December 31, 2019: Voting The holders of shares of common stock are entitled to one vote for each share of common stock held at any meeting of stockholders and at the time of any written action in lieu of a meeting. Dividends The holders of shares of common stock are entitled to receive dividends, if and when declared by the Company’s board of directors. Cash dividends may not be declared or paid to holders of shares of common stock until all unpaid dividends on the redeemable convertible preferred stock have been paid in accordance with their terms. No dividends have been declared or paid by the Company since its inception. 2013 Stock Incentive Plan In September 2013, the board of directors adopted the 2013 Stock Incentive Plan, which was subsequently amended (as amended, the “2013 Plan”), which provides for the grant of incentive stock options and nonqualified stock options or other awards including restricted stock awards, unrestricted stock awards, and restricted stock units to the Company’s employees, officers, directors, advisors, and consultants for the purchase of up to 1,057,692 shares of the Company’s common stock, which has been amended several times, and as of July 2015, a total of 6,317,769 shares were reserved. The terms of stock awards agreements, including vesting requirements, are determined by the board of directors and are subject to the provisions of the 2013 Plan. The stock options granted to employees generally vest over a four-year period and expire ten years from the date of grant. Certain awards contain performance based vesting criteria. There has only been one such award to date. Certain options provide for accelerated vesting in the event of a change in control, as defined in the applicable options. Awards granted to non-employee consultants generally vest monthly over a period of one 2015 Stock Incentive Plan The Company’s board of directors adopted and the Company’s stockholders approved the 2015 stock incentive plan (the “2015 Plan”), which became effective immediately prior to the effectiveness of the registration statement related to the IPO. The 2015 Plan provides for the grant of incentive stock options, nonstatutory stock options, restricted stock awards, restricted stock units, stock appreciation rights and other stock-based awards. The Company’s employees, officers, directors and consultants and advisors are eligible to receive awards under the 2015 Plan. The number of shares reserved for issuance under the 2015 Plan is subject to further increases for (a) any additional shares of the Company’s common stock subject to outstanding awards under the 2013 Plan that expire, terminate, or are otherwise surrendered, cancelled, forfeited, or repurchased by the Company at their original issuance price pursuant to a contractual repurchase right and (b) annual increases, to be added as of the first day of each fiscal year, from January 1, 2017 until, and including, January 1, 2026, equal to the lowest of 2,923,076 shares of common stock, 4% of the number of shares of common stock outstanding on such first day of the fiscal year in question and an amount determined by the Company’s board of directors. In January 2020, the shares under the 2015 Plan were increased by 2,182,151 shares pursuant to the annual increase described in the prior sentence. 2015 Employee Stock Purchase Plan The Company’s board of directors adopted and the Company’s stockholders approved the 2015 employee stock purchase plan (the “2015 ESPP”), which became effective upon the closing of the IPO. The number of shares reserved for issuance under the 2015 ESPP is subject to annual increases, to be added as of the first day of each fiscal year, from January 1, 2017 until, and including, January 1, 2026, in an amount equal to the least of (a) 769,230 shares of common stock, (b) 1% of the total number of shares of common stock outstanding on the first day of the applicable year, and (c) an amount determined by the board of directors. The first offering under the 2015 ESPP opened on December 1, 2017. In January 2020, the shares under the 2015 ESPP Plan were increased by 545,537 shares pursuant to the annual increase described in the prior sentence. Inducement Awards From time to time the Company’s board of directors approves inducement awards to certain employees outside of the existing equity compensation plans in connection with such employees commencing employment with the Company. Inducement awards are typically a service-based option or a restricted stock unit and are subject to the Company’s typical vesting terms and the employee’s continued service relationship with the Company through the applicable vesting dates. In January 2020, the Company’s board of directors approved an inducement grant to the Company’s recently hired Chief Financial Officer, including an option to purchase up to 120,000 shares of the Company’s common stock and an award of 20,000 restricted stock units. Shares Reserved for Future Issuance ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ 2019 2018 Shares reserved for outstanding stock option awards under the 2013 Stock Incentive Plan, as amended ​ 312,342 873,373 Shares reserved for outstanding stock option awards under the 2015 Stock Incentive Plan ​ 4,254,357 ​ 3,709,225 Shares reserved for outstanding inducement stock option award ​ 175,000 ​ 107,188 Remaining shares reserved, but unissued, for future awards under the 2015 Stock Incentive Plan ​ 4,061,357 ​ 3,233,031 Remaining shares reserved, but unissued, for future awards under the 2015 Employee Stock Purchase Plan 1,630,199 ​ 1,175,224 ​ 10,433,255 9,098,041 ​

Stock-based Compensation

Stock-based Compensation	12 Months Ended
	Dec. 31, 2019
Stock-based Compensation
Stock-based Compensation	12. Stock-Based Compensation Total compensation cost recognized for all stock-based compensation awards in the consolidated statements of operations was as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ ​ 2019 ​ 2018 ​ 2017 Research and development ​ $ 13,538 ​ $ 14,734 ​ $ 15,131 General and administrative ​ 13,705 ​ 11,864 ​ 8,243 Total stock-compensation expense ​ $ 27,243 ​ $ 26,598 ​ $ 23,374 ​ Restricted Stock and Restricted Stock Unit Awards ​ The following table summarizes restricted stock and restricted stock unit awards activity for the instruments discussed above as of December 31, 2018 and 2019 is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ Average ​ ​ ​ ​ Grant Date ​ ​ ​ ​ Fair Value ​ ​ Shares ​ Per Share Unvested restricted stock and restricted stock unit awards as of December 31, 2018 270,000 ​ $ 28.05 Issued 498,425 ​ $ 22.00 Vested ​ (99,919) ​ $ 26.52 Forfeited (87,098) ​ $ 21.51 Unvested restricted stock and restricted stock unit awards as of December 31, 2019 581,408 ​ $ 24.03 ​ The expense related to restricted stock and restricted stock unit awards granted to employees and non-employees was $4.7 million and $1.6 million, respectively, for the year ended December 31, 2019. The expense related to restricted stock and restricted stock unit awards granted to employees and non-employees was $0 million and $2.4 million, respectively, for the year ended December 31, 2018. The expense related to restricted stock and restricted stock unit awards granted to employees and non-employees was $0.5 and $4.1 million, respectively, for the year ended December 31, 2017. As of December 31, 2019, the Company had $4.3 million and $4.5 million in unrecognized stock-based compensation expense related to its employee and non-employee unvested restricted stock and restricted stock unit awards which is expected to be recognized over a remaining weighted average vesting period of 1.8 years and 2.7 years, respectively. Stock Options The following is a summary of stock option activity for the year ended December 31, 2019: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted Average Remaining Aggregate Intrinsic ​ ​ Shares ​ Exercise Price ​ Contractual Life ​ Value (in thousands) Outstanding at December 31, 2018 4,689,786 ​ $ 23.80 ​ 7.9 ​ $ 20,686 Granted 1,793,247 ​ $ 24.04 ​ ​ ​ ​ ​ Exercised (1,120,186) ​ $ 13.27 ​ ​ ​ ​ ​ Cancelled ​ (1,004,556) ​ $ 28.96 ​ ​ ​ ​ ​ Outstanding at December 31, 2019 4,358,291 ​ $ 25.40 ​ 7.4 ​ $ 26,060 Exercisable at December 31, 2019 1,994,417 ​ $ 24.26 ​ 6.1 ​ $ 15,747 ​ The stock options granted during the year ended December 31, 2019 include an option granted to the Company’s Chief Executive Officer to purchase 250,000 shares of the Company’s common stock that contains market-based vesting provisions. ​ Using the Black-Scholes option pricing model, the weighted average fair value of options containing service-based vesting granted to employees and directors during the years ended December 31, 2019, 2018, and 2017 was $15.67, $24.91 and $16.07, respectively. The expense related to options containing service-based vesting granted to employees and directors was $18.1 million, $19.9 million and $12.3 million for the years ended December 31, 2019, 2018, and 2017, respectively. The fair value of each service-based vesting option issued to employees and directors was estimated at the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ ​ 2019 ​ ​ 2018 ​ ​ 2017 Expected volatility 73.8 % ​ 77.5 % ​ 77.8 % Expected term (in years) 6.25 ​ ​ 6.25 ​ ​ 6.25 ​ Risk free interest rate 2.0 % ​ 2.9 % ​ 2.1 % Expected dividend yield — ​ ​ — ​ ​ — ​ ​ There were no options granted to persons other than employees and directors during the years ended December 31, 2019, 2018 and 2017. ​ As of December 31, 2019, the Company had unrecognized stock-based compensation expense related to its employee service-based stock options and market-based stock options of $34.5 million and $2.9 million which the Company expects to recognize over a remaining weighted average vesting period of 2.8 years and 1.5 years, respectively.

401(k) Savings Plan

401(k) Savings Plan	12 Months Ended
	Dec. 31, 2019
401(k) Savings Plan
401(k) Savings Plan	13. 401(k) Savings Plan The Company has a defined-contribution savings plan under Section 401(k) of the Internal Revenue Code of 1986, as amended (the “401(k) Plan”). The 401(k) Plan covers all employees who meet defined minimum age and service requirements, and allows participants to defer a portion of their annual compensation on a pretax basis. Effective in 2017, the Company will provide a 200% match of employee contributions up to a limit on the Company’s contributions of the lesser of $6,000 and 3% of the employee’s salary. The Company made $0.8 million, $0.7 million and $0.5 million in contributions to the 401(k) Plan for the years ended December 31, 2019, 2018 and 2017, respectively. ​

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2019
Income Taxes
Income Taxes	14. Income Taxes ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ ​ 2019 ​ ​ 2018 ​ 2017 Income tax computed at federal statutory tax rate ​ 21.0 % ​ 21.0 % ​ 34.0 % State taxes, net of federal benefit ​ 5.2 % ​ 6.4 % ​ 5.9 % General business credit carryovers ​ 2.8 % ​ 4.4 % ​ 2.5 % Stock Options ​ (2.2) % ​ 0.7 % ​ (1.2) % Non-deductible expenses ​ (0.1) % ​ (0.1) % ​ (0.9) % Federal tax rate reduction ​ — % ​ — % ​ (24.7) % Change in valuation allowance ​ (26.7) % ​ (32.4) % ​ (15.6) % ​ ​ — % ​ — % ​ — % ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ ​ 2019 ​ 2018 Deferred tax assets: ​ ​ ​ ​ ​ ​ Net operating loss carryforwards ​ $ 50,511 ​ $ 20,302 Tax credit carryforwards ​ ​ 13,767 ​ 10,059 Accrued expenses ​ ​ 2,219 ​ 3,099 Capitalized patent costs ​ ​ 39,070 ​ 33,101 Lease liabilities ​ ​ 7,879 ​ ​ — Deferred revenue ​ ​ 31,880 ​ ​ 34,039 Construction financing lease obligation ​ ​ — ​ ​ 9,100 Other ​ ​ 7,865 ​ 8,347 Total deferred tax assets ​ 153,191 ​ 118,047 Less valuation allowance ​ (144,540) ​ (109,091) Net deferred tax assets ​ 8,651 ​ 8,956 Deferred tax liabilities: ​ (8,651) ​ (8,956) Depreciation and amortization ​ ​ (859) ​ ​ (8,956) Right-of-use assets ​ ​ (7,792) ​ ​ — Net deferred taxes ​ $ — ​ $ — ​ ​ The Company has incurred net operating losses (“NOL”) since inception. At December 31, 2019 and 2018, the Company had federal net operating loss carryforwards of $185.4 million and $74.7 million, respectively. Of the amount as of December 31, 2019, $110.0 million will carryforward indefinitely while $75.4 million will expire beginning in 2033 and will continue to expire through 2037. As of December 31, 2019, and 2018, the Company also had state net operating loss carryforwards of approximately $183.3 million and $73.1 million, respectively, which may be available to offset future income tax liabilities and will expire beginning in 2035 and will continue to expire through 2039. ​ Under the provisions of the Internal Revenue Code of 1986, as amended (the “Code”), the NOL and tax credit carryforward are subject to review and possible adjustment by the Internal Revenue Service and state tax authorities. NOL and tax credit carryforwards may become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant shareholders over a three-year period in excess of 50%, as defined under Sections 382 and 383 of the Code, respectively, as well as other similar state provisions. The Company conducted an analysis under Section 382 to determine if historical changes in ownership through December 31, 2018 would limit or otherwise restrict its ability to utilize its NOL and research and development credit carryforwards. As a result of this analysis, the Company does not believe there are any significant limitations on its ability to utilize these carryforwards. However, future changes in ownership occurring after December 31, 2018 could affect the limitation in future years, and any limitation may result in expiration of a portion of the NOL or research and development credit carryforwards before utilization. Management has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets, which principally comprise of NOL carryforwards, research and development credit carryforwards and capitalized license and patent costs. The Company’s management has determined that it is more likely than not that the Company will not recognize the benefits of its federal and state deferred tax assets, and as a result, a valuation allowance of $144.5 million and $109.1 million has been established at December 31, 2019 and 2018, respectively. The increase in the valuation allowance of $35.4 million for the year ended December 31, 2019 was primarily due to current period pre-tax losses incurred and research tax credits generated. The Company applies ASC 740 related to accounting for uncertainty in income taxes. The Company’s reserves related to income taxes are based on a determination of whether, and how much of, a tax benefit taken by the Company in its tax filings or positions is more likely than not to be realized following resolution of any potential contingencies present related to the tax benefit. At December 31, 2019 and 2018, the Company had no unrecognized tax benefits. Interest and penalty charges, if any, related to unrecognized tax benefits would be classified as income tax expense in the accompanying statements of operations. The Company has not as yet conducted a study of its research and development credit carry forwards. This study may result in an adjustment to the Company’s research and development credit carryforwards; however, until a study is completed and any adjustment is known, no amounts are being presented as an uncertain tax position. A full valuation allowance has been provided against the Company’s research and development credits, and if an adjustment is required, this adjustment would be offset by an adjustment to the valuation allowance. Thus, there would be no impact to the consolidated balance sheets or statements of operations if an adjustment were required. The Company files income tax returns in the U.S. federal tax jurisdiction, the Massachusetts state jurisdiction, the California state jurisdiction and the Colorado state jurisdiction. Since the Company is in a loss carryforward position, the Company is generally subject to examination by the U.S. federal, state and local income tax authorities for all tax years in which a loss carryforward is available. The Company did not have any international operations as of December 31, 2019. There are no federal or state audits in process.

Net Loss per Share

Net Loss per Share	12 Months Ended
	Dec. 31, 2019
Net Loss per Share
Net Loss per Share	15. Net Loss per Share Basic net loss per common share is calculated by dividing the net loss attributable to common stockholders by the weighted average number of shares of common stock outstanding during the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted average number of shares of common stock and potentially dilutive securities outstanding for the period determined using the treasury stock and if converted methods. Contingently issuable shares are included in the calculation of basic loss per share as of the beginning of the period in which all the necessary conditions have been satisfied. Contingently issuable shares are included in diluted loss per share based on the number of shares, if any, that would be issuable under the terms of the arrangement if the end of the reporting period was the end of the contingency period, if the results are dilutive. For purposes of the diluted net loss per share calculation, stock options are considered to be common stock equivalents, but they were excluded from the Company’s calculation of diluted net loss per share allocable to common stockholders because their inclusion would have been anti-dilutive. Therefore, basic and diluted net loss per share applicable to common stockholders was the same for all periods presented. The following common stock equivalents were excluded from the calculation of diluted net loss per share allocable to common stockholders because their inclusion would have been anti-dilutive: ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ 2019 2018 Unvested restricted common stock 581,408 270,000 Outstanding stock options 4,358,291 4,689,786 Total 4,939,699 4,959,786 ​ The table above reflects restricted stock issued upon exercise of unvested stock options as exercised on the dates that the shares are no longer subject to repurchase.

Related-Party Transactions

Related-Party Transactions	12 Months Ended
	Dec. 31, 2019
Related-Party Transactions
Related-Party Transactions	16. Related-Party Transactions The Company received $0.4 million and $0.8 million in rent and facility-related fees from a related party during the years ended December 31, 2018 and 2017, respectively, in connection with subleasing a portion of its headquarters and no rent or facility-related payments were received from this related party during the year ended December 31, 2019. During the years ended December 31, 2018 and 2017, the Company paid a related party $0.8 million and $0.3 million, respectively, in connection with certain research and development expenses. The Company did not make any payments to this related party during the year ended December 31, 2019.

Selected Quarterly Financial Da

Selected Quarterly Financial Data	12 Months Ended
	Dec. 31, 2019
Selected Quarterly Financial Data
Selected Quarterly Financial Data	17. Selected Quarterly Financial Data (unaudited) – The following table contains selected quarterly financial information from 2019 and 2018. The Company believes that the following information reflects all normal recurring adjustments necessary for a fair statement of the information for the periods presented. The operating results for any quarter are not necessarily indicative of results for any future period. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ March 31, 2019 ​ June 30, 2019 ​ September 30, 2019 ​ December 31, 2019 ​ ​ (in thousands, except per share data) Total collaboration and other research and development revenues $ 2,069 ​ $ 2,330 ​ $ 3,848 ​ $ 12,284 Total operating expenses ​ 33,331 ​ ​ 37,979 ​ ​ 38,436 ​ ​ 51,707 Total other income (expense), net ​ 2,013 ​ ​ 1,863 ​ ​ 1,647 ​ ​ 1,653 Net loss $ (29,249) ​ $ (33,786) ​ $ (32,941) ​ $ (37,770) Net loss applicable to common stockholders $ (29,249) ​ $ (33,786) ​ $ (32,941) ​ $ (37,770) Net loss per share applicable to common stockholders — basic and diluted $ (0.60) ​ $ (0.69) ​ $ (0.66) ​ $ (0.74) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ March 31, 2018 ​ June 30, 2018 ​ September 30, 2018 ​ December 31, 2018 ​ ​ (in thousands, except per share data) Total collaboration and other research and development revenues $ 3,927 ​ $ 7,372 ​ $ 14,519 ​ $ 6,119 Total operating expenses ​ 35,486 ​ ​ 47,029 ​ ​ 30,777 ​ ​ 32,372 Total other income (expense), net ​ 620 ​ ​ 934 ​ ​ 1,020 ​ ​ 1,199 Net loss $ (30,939) ​ $ (38,723) ​ $ (15,238) ​ $ (25,054) Net loss applicable to common stockholders $ (30,939) ​ $ (38,723) ​ $ (15,238) ​ $ (25,054) Net loss per share applicable to common stockholders — basic and diluted $ (0.67) ​ $ (0.82) ​ $ (0.32) ​ $ (0.52) ​

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2019
Summary of Significant Accounting Policies
Principles of Consolidation	Principles of Consolidation The accompanying consolidated financial statements include the accounts of Editas Medicine, Inc. and its wholly owned subsidiary, Editas Securities Corporation, which is a Delaware subsidiary created to buy, sell and hold securities. All intercompany transactions and balances have been eliminated.
Unaudited Interim Financial Information	Basis of Presentation The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”).
Reclassification	Reclassification Certain prior period amounts have been reclassified for consistency with the current period presentation. These reclassifications had no effect on previously reported results of operations.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates, which include, but are not limited to, estimates related to revenue recognition, accrued expenses, stock-based compensation expense, research and development expenses and deferred tax valuation allowances. The Company bases its estimates on historical experience and other market-specific or relevant assumptions that it believes to be reasonable under the circumstances. Actual results may differ from those estimates or assumptions.
Fair Value of Financial Instruments	Fair Value of Financial Instruments ASC Topic 820, Fair Value Measurement ASC 820 identifies fair value as the exchange price representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As a basis for considering market participant assumptions in fair value measurements, ASC 820 establishes a three-tier fair value hierarchy that distinguishes between the following: ● Level 1 – Quoted market prices in active markets for identical assets or liabilities. ● Level 2 – Inputs other than Level 1 inputs that are either directly or indirectly observable, such as quoted market prices, interest rates, and yield curves. ● Level 3 – Unobservable inputs developed using estimates of assumptions developed by the Company, which reflect those that a market participant would use. To the extent that the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. The carrying amounts reflected in the consolidated balance sheets for cash and cash equivalents, restricted cash, marketable securities, accounts receivable, prepaid expenses and other current assets, accounts payable, accrued expenses, and other current liabilities approximate their fair values, due to their short-term nature. The Company believes that the carrying value of the notes payable approximates their fair value based on Level 3 inputs including a quoted rate.
Cash, Cash Equivalents, and Restricted Cash	Cash, Cash Equivalents, and Restricted Cash The Company considers all highly liquid investments purchased with original maturities of 90 days or less at acquisition to be cash equivalents. Cash and cash equivalents include cash held in banks and amounts held in money market funds and U.S. government-backed securities. The Company has restricted cash of $1.6 million held in the form of a letter of credit, as collateral for the Company’s corporate headquarters. The restricted funds are maintained in a traditional bank account. The following table presents cash, cash equivalents, and restricted cash as reported on the consolidated balance sheets that equal the total amounts on the consolidated statements of cash flows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ As of December 31, ​ ​ 2019 ​ 2018 ​ 2017 Cash and cash equivalents ​ $ 238,183 ​ $ 134,776 ​ $ 146,630 Restricted cash included in "Restricted cash and other non-current assets" ​ ​ 1,619 ​ ​ 1,619 ​ ​ 1,619 Total cash, cash equivalents, and restricted cash ​ $ 239,802 ​ $ 136,395 ​ $ 148,249 ​ Marketable Securities The Company classifies marketable securities with a remaining maturity when purchased of greater than three months and less than one year from the balance sheet date as current. Marketable securities with a remaining maturity date greater than one year are classified as non-current. The Company classifies all of its marketable securities as available-for-sale securities. Available-for-sale securities are carried at fair value with the unrealized gains and losses included in other comprehensive loss as a component of stockholders’ equity until realized. Any premium or discount arising at purchase is amortized and/or accreted to interest income and/or expense over the life of the of the underlying security. Realized gains and losses are included in other income (expense). If any adjustment to fair value reflects a decline in value of the investment, the Company considers all available evidence to evaluate the extent to which the decline is “other-than-temporary.” To determine whether an impairment is other-than-temporary, the Company considers whether it has the ability and intent to hold the investment until a market price recovery and considers whether evidence indicating the cost of the investment is recoverable outweighs evidence to the contrary. The Company does not intend to sell the investments and it is not likely that the Company will be required to sell the investments before recovery of their amortized cost bases, which may be maturity.
Marketable Securities	​
Corporate Equity Securities	Corporate Equity Securities The Company records investments in privately issued corporate equity securities that do not have readily determinable fair values at cost and adjusts for changes in observable prices minus impairment. Each reporting period the Company adjusts the carrying value of these investments if it observes that additional shares have been issued in an orderly transaction between market participants resulting in a price increase or decrease per share. Additionally, each reporting period the Company reviews these investments for impairment considering all available information to conclude whether an impairment exists. Changes in measurement for all corporate equity investments are recognized in “Other income (expense),” net in the Company’s consolidated statements of operations.
Accounts Receivable	Accounts Receivable The Company makes judgments as to its ability to collect outstanding receivables and provides an allowance for receivables when collection becomes doubtful. Provisions are made based upon a specific review of all significant outstanding invoices and the overall quality and age of those invoices not specifically reviewed. The Company's receivables primarily relate to amounts reimbursed under its collaboration agreements. The Company believes that credit risk associated with its collaborations partners is not significant. To date, the Company has not had any write-offs of bad debt, and the Company did not have an allowance for doubtful accounts as of December 31, 2019 and 2018.
Property and Equipment	Property and Equipment Property and equipment consists of computers, laboratory equipment, furniture and office equipment, and leasehold improvements and is stated at cost, less accumulated depreciation. Maintenance and repairs that do not improve or extend the lives of the respective assets are expensed to operations as incurred, while costs of major additions and betterments are capitalized. Depreciation is calculated over the estimated useful lives of the assets using the straight-line method. The Company capitalizes laboratory equipment used for research and development if it has alternative future use in research and development or otherwise. ​ ​ ​ ​ ​ Asset: Estimated Useful life Lab equipment 5 years ​ Computer equipment and software 3 years ​ Furniture and equipment 5 years ​ Leasehold improvements Shorter of useful life or remaining lease term ​ ​ Impairment of Long-lived Assets The Company evaluates long-lived assets for potential impairment when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparing the book values of the assets to the expected future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book values of the assets exceed their fair value. The Company has not recognized any impairment losses from inception through December 31, 2019.
Impairment of Long-lived Assets	​
Profit-Sharing Arrangements	Profit-Sharing Arrangements The Company considers the nature and contractual terms of the arrangements and assesses whether such arrangements involve a joint operating activity pursuant to which the Company is an active participant and is exposed to significant risks and rewards with respect to such arrangement. If the Company is an active participant and is exposed to significant risks and rewards with respect to such arrangement, the Company accounts for such arrangement as a collaboration under ASC Topic 808, Collaborative Arrangements Payments received from a collaboration partner to which this policy applies are recorded as contra-expense in the applicable period and may include development costs or patent expense reimbursements. The Company classifies payments made under the cost sharing provisions of such arrangements as a component of research and development expenses to reflect the joint risk sharing nature of such profit-sharing arrangements. The Company classifies payments owed or receivables recorded as other current liabilities or prepaid expenses and other current assets, respectively, in the Company’s consolidated balance sheets.
Revenue Recognition	Revenue Recognition To date, the Company has primarily earned revenue under the collaboration and license agreement with Juno Therapeutics and the strategic alliance with Allergan. The Company recognizes revenue in accordance with ASC Topic 606, Revenue from Contracts with Customers that are within the scope of ASC 606, under which the Company licenses, may license or grants an option to license rights to certain of the Company’s product candidates and performs research and development services in connection with such arrangements. The terms of these arrangements typically include payment of one or more of the following: non-refundable, up-front fees; reimbursement of research and development costs; development, clinical, regulatory and commercial sales milestone payments; and royalties on net sales of licensed products. Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine the appropriate amount of revenue to be recognized for arrangements determined to be within the scope of ASC 606, the Company performs the following five steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect consideration it is entitled to in exchange for the goods or services it transfers to the customer. The promised goods or services in the Company’s arrangements typically consist of a license, or option to license, rights to the Company’s intellectual property or research and development services. The Company provides options to additional items in such arrangements, which are accounted for as separate contracts when the customer elects to exercise such options, unless the option provides a material right to the customer. Performance obligations are promised goods or services in a contract to transfer a distinct good or service to the customer and are considered distinct when (i) the customer can benefit from the good or service on its own or together with other readily available resources and (ii) the promised good or service is separately identifiable from other promises in the contract. In assessing whether promised good or services are distinct, the Company considers factors such as the stage of development of the underlying intellectual property, the capabilities of the customer to develop the intellectual property on its own or whether the required expertise is readily available and whether the goods or services are integral or dependent to other goods or services in the contract. The Company estimates the transaction price based on the amount expected to be received for transferring the promised goods or services in the contract. The consideration may include fixed consideration or variable consideration. At the inception of each arrangement that includes variable consideration, the Company evaluates the amount of potential payment and the likelihood that the payments will be received. The Company utilizes either the most likely amount method or expected value method to estimate the amount expected to be received based on which method best predicts the amount expected to be received. The amount of variable consideration that is included in the transaction price may be constrained and is included in the transaction price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized will not occur in a future period. The Company’s contracts often include development and regulatory milestone payments that are as assessed under the most likely amount method and constrained if it is probable that a significant revenue reversal would occur. Milestone payments that are not within the Company’s control or the licensee’s control, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. At the end of each reporting period, the Company re-evaluates the probability of achievement of such development and clinical milestones and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect collaboration and other research and development revenues in the period of adjustment. For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from any of the Company’s collaboration or strategic alliance arrangements. The Company allocates the transaction price based on the estimated standalone selling price. The Company must develop assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company utilizes key assumptions to determine the stand-alone selling price, which may include other comparable transactions, pricing considered in negotiating the transaction and the estimated costs. Variable consideration is allocated specifically to one or more performance obligations in a contract when the terms of the variable consideration relate to the satisfaction of the performance obligation and the resulting amounts allocated are consistent with the amounts the Company would expect to receive for the satisfaction of each performance obligation. The consideration allocated to each performance obligation is recognized as revenue when control is transferred for the related goods or services. For performance obligations which consist of licenses and other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. The Company receives payments from its customers based on billing schedules established in each contract. Up-front payments and fees are recorded as deferred revenue upon receipt or when due until the Company performs its obligations under these arrangements. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional. ​ In connection with the Company’s adoption of ASC 606, the Company has included the following financial statement line items for comparability purposes for the year ended December 31, 2018 (in thousands, except per share data): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, 2018 ​ As reported under Topic 606 ​ Balances without adoption of ASC 606 ​ Effect of Change Collaboration and other research and development revenues $ 31,937 ​ $ 33,993 ​ $ (2,056) Operating loss $ (113,727) ​ $ (111,671) ​ $ (2,056) Net loss attributable to common stockholders $ (109,954) ​ $ (107,898) ​ $ (2,056) Net loss per share attributable to common stockholders, basic and diluted $ (2.33) ​ $ (2.29) ​ $ (0.04) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Prior to ASC 606 Adoption Revenue for the year ended December 31, 2017 was recognized in accordance with ASC Topic 605, Revenue Recognition ● Persuasive evidence of an arrangement exists; ● Delivery has occurred or services have been rendered; ● The seller’s price to the buyer is fixed or determinable; and ● Collectability is reasonably assured. Amounts received prior to satisfying the revenue recognition criteria were recorded as deferred revenue. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified in current liabilities. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue, net of current portion. The Company evaluated multiple-element arrangements based on the guidance in ASC Topic 605-25, Revenue Recognition Multiple-Element Arrangements Options were considered substantive if, at the inception of the arrangement, the Company was at risk as to whether the collaboration partner will choose to exercise the option. Factors that the Company considered in evaluating whether an option is substantive include the cost to exercise the option, the overall objective of the arrangement, the benefit the collaborator might obtain from the arrangement without exercising the option and the likelihood the option will be exercised. When an option was considered substantive, the Company does not consider the option or item underlying the option to be a deliverable at the inception of the arrangement and the associated option fees are not included in allocable consideration, assuming the option is not priced at a significant and incremental discount. Conversely, when an option is not considered substantive, the Company would consider the option, including other deliverables contingent upon the exercise of the option, to be a deliverable at the inception of the arrangement and a corresponding amount would be included in allocable arrangement consideration. In addition, if the price of the option includes a significant incremental discount, the discount would be included as a deliverable at the inception of the arrangement. The consideration received under the arrangement that is fixed or determinable was then allocated among the separate units of accounting using the relative selling price method. The Company determined the estimated selling price for units of accounting within each arrangement using vendor-specific objective evidence (“VSOE”) of selling price, if available, third-party evidence (“TPE”) of selling price if VSOE is not available, or best estimate of selling price (“BESP”) if neither VSOE nor TPE is available. Determining the BESP for a unit of accounting required significant judgment. In developing the BESP for a unit of accounting, the Company considered applicable market conditions and relevant entity-specific factors, including factors that were contemplated in negotiating the agreement with the customer and estimated costs. The Company validated the BESP for units of accounting by evaluating whether changes in the key assumptions used to determine the BESP had a significant effect on the allocation of arrangement consideration between multiple units of accounting. The Company recognized arrangement consideration allocated to each unit of accounting when all of the revenue recognition criteria in ASC 605 are satisfied for that particular unit of accounting. In the event that a deliverable does not represent a separate unit of accounting, the Company recognized revenue from the combined unit of accounting over the Company’s contractual or estimated performance period for the undelivered elements, which is typically the term of the Company’s research and development obligations. If there is no discernible pattern of performance or objectively measurable performance measures do not exist, then the Company recognized revenue under the arrangement on a straight-line basis over the period the Company is expected to complete its performance obligations. Conversely, if the pattern of performance in which the service is provided to the customer can be determined and objectively measurable performance measures exist, then the Company recognized revenue under the arrangement using the proportional performance method. Revenue recognized is limited to the lesser of the cumulative amount of payments received or the cumulative amount of revenue earned, as determined using the straight-line method or proportional performance method, as applicable, as of the period ending date. At the inception of an arrangement that includes milestone payments, the Company evaluated whether each milestone was substantive and at risk to both parties on the basis of the contingent nature of the milestone. This evaluation includes an assessment of whether: (1) the consideration is commensurate with either the Company’s performance to achieve the milestone or the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from its performance to achieve the milestone, (2) the consideration relates solely to past performance and (3) the consideration is reasonable relative to all of the deliverables and payment terms within the arrangement. The Company evaluated factors such as the scientific, clinical, regulatory, commercial, and other risks that must be overcome to achieve the particular milestone and the level of effort and investment required to achieve the particular milestone in making this assessment. There was considerable judgment involved in determining whether a milestone satisfies all of the criteria required to conclude that a milestone is substantive. Milestones that are not considered substantive were recognized as earned if there are no remaining performance obligations or over the remaining period of performance, assuming all other revenue recognition criteria are met.
Research and Development Costs	Research and Development Expenses Research and development expenses are charged to expense as incurred in performing research and development activities. The costs include employee-related expenses including salaries, benefits, and stock-based compensation expense, costs of funding research performed by third parties that conduct research and development and preclinical and clinical activities on the Company’s behalf, the cost of purchasing lab supplies and non-capital equipment used in preclinical and clinical activities and in manufacturing preclinical and clinical study materials, consultant fees, facility costs including rent, depreciation, and maintenance expenses, and fees for acquiring and maintaining licenses under third party licensing agreements, including any sublicensing or success payments made to the Company’s licensors. In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. If the actual timing of the performance of services or the level of effort varies from the Company’s estimate, the accrual or prepaid is adjusted accordingly. The Company defers and capitalizes non-refundable advance payments made by the Company for research and development activities until the related goods are received or the related services are performed. In circumstances where amounts have been paid in excess of costs incurred, the Company records a prepaid expense.
In-process Research and Development Assets	In-process Research and Development Assets In-process research and development assets that are acquired in a transaction that does not qualify as a business combination under GAAP and that do not have an alternative future use are expensed in the period in which the assets are acquired.
Patent Costs	Patent Costs The Company expenses patent and patent application costs and related legal costs for the prosecution and maintenance of such patents and patent applications, including patents and patent applications the Company in-licenses, as incurred and classifies such costs as general and administrative expenses in the accompanying consolidated statements of operations.
Construction Financing Lease Obligation	Construction Financing Lease Obligation Beginning in 2016, the Company began recording certain estimated construction costs incurred and reported to the Company by a landlord as an asset and corresponding construction financing lease obligation on the Company’s consolidated balance sheets because the Company was deemed to be the owner of the building during the construction period for accounting purposes. In each reporting period, the landlord estimated and reported to the Company the costs incurred to date and provided supporting invoices for the Company to review. The Company periodically met with the landlord and its construction manager to review the estimates and observe construction progress prior to recording such amounts. Construction was completed in October 2016 and the Company considered the requirements for sale-leaseback accounting treatment, which included an evaluation of whether all risks of ownership had transferred back to the landlord as evidenced by a lack of continuing involvement in the lease property. The Company determined that the arrangement did not qualify for sale lease-back accounting treatment, the building asset will remain on the Company’s consolidated balance sheet at its historical cost, and such asset would be depreciated over its estimated useful life of thirty years. Effective January 1, 2019, the Company adopted Accounting Standards Update (“ASU”) No. 2016-02, Leases ​ ​ ​ ​ ​ As of ​ January 1, 2019 Property and equipment, net $ 32,627 Other current liabilities $ (1,014) Construction financing lease obligation, net of current portion $ (32,417) Accumulated deficit $ 803 ​ Leases The Company accounts for leases in accordance with ASC 842. At the inception of an arrangement the Company determines whether the arrangement contains a lease. If a lease is identified in an arrangement, the Company recognizes a right-of-use asset and liability on its balance sheet and determines whether the lease should be classified as a finance or operating lease. The Company does not recognize assets or liabilities for leases with lease terms of less than 12 months. Lease payments for short-term leases are recorded to operating expense on a straight-line basis over the lease term and variable lease payments are recorded in the period in which the obligation for those payments is incurred. A lease qualifies as a finance lease if any of the following criteria are met at the inception of the lease: (i) there is a transfer of ownership of the leased asset to the Company by the end of the lease term, (ii) the Company holds an option to purchase the leased asset that it is reasonably certain to exercise, (iii) the lease term is for a major part of the remaining economic life of the leased asset, (iv) the present value of the sum of lease payments equals or exceeds substantially all of the fair value of the leased asset, and (v) the nature of the leased asset is specialized to the point that it is expected to provide the lessor no alternative use at the end of the lease term. All other leases are recorded as operating leases. Finance and operating lease assets and liabilities are recognized at the lease commencement date based on the present value of the lease payments over the lease term using the discount rate implicit in the lease. If the rate is not readily determinable, the Company utilizes its incremental borrowing rate at the lease commencement date. Operating lease assets are further adjusted for prepaid or accrued lease payments. Operating lease payments are expensed using the straight-line method as an operating expense over the lease term. Finance lease assets are amortized to depreciation expense using the straight-line method over the shorter of the useful life of the related asset or the lease term. Finance lease payments are bifurcated into (i) a portion that is recorded as imputed interest expense and (ii) a portion that reduces the finance liability associated with the lease. The Company does not separate lease and non-lease components when determining which lease payments to include in the calculation of its lease assets and liabilities. Variable lease payments are expensed as incurred. If a lease includes an option to extend or terminate the lease, the Company reflects the option in the lease term if it is reasonably certain it will exercise the option.
Leases	​
Stock-based Compensation Expense	Stock-based Compensation Expense The Company’s stock-based compensation program grant awards which have included stock options, restricted stock awards (“RSAs”), restricted stock unit awards (“RSUs”), a market-based option award, and shares issued under the Company’s 2015 employee stock purchase plan (“ESPP”). The Company accounts for stock-based compensation awards in accordance with ASC Topic 718, Compensation—Stock Compensation using the Black-Scholes option-pricing model. The fair value of the Company’s RSAs and RSUs is based on market value of the Company’s common stock on the date of grant. For awards subject to service-based vesting conditions, the Company recognizes the stock-based compensation expense on a straight-line basis over the requisite service period. If an employee or non-employee service requirement is concluded to be non-substantive, the stock-based compensation expense would be expensed immediately. Forfeitures are recorded as they occur. Prior to 2019, the Company accounted for stock-based payments issued to non-employees in accordance with ASC Topic 505-50, Equity Based Payments to Non-Employees For stock options granted to employees and to members of the Company’s board of directors for their services on the board of directors, the Company estimates the grant date fair value of each option award using the Black-Scholes option-pricing model. The Black-Scholes option pricing model requires the input of certain subjective assumptions, including (1) the expected stock price volatility, (2) the calculation of expected term of the award, (3) the risk-free interest rate, and (4) the expected dividend yield. Because there had been no public market for the Company’s common stock prior to its initial public offering, there was a lack of company-specific historical and implied volatility data. Accordingly, the Company based its estimates of expected volatility on the historical volatility of a group of similar companies that are publicly traded. The Company calculates historical volatility based on a period of time commensurate with the expected term. The Company computes expected volatility based on the historical volatility of a representative group of companies with similar characteristics to the Company, including their stages of product development and focus on the life science industry. The Company uses the simplified method as prescribed by the Securities and Exchange Commission’s Staff Accounting Bulletin No. 107, Share-Based Payment In 2014, certain of the Company’s stock option agreements allowed for the exercise of unvested awards. The unvested shares were subject to repurchase by the Company if the employees ceased to provide service to the Company, with or without cause. As such, the Company did not treat the exercise of unvested options as a substantive exercise. The Company recorded the proceeds from the exercise of unvested stock options as a liability in the consolidated balance sheets. The liability for unvested common stock subject to repurchase was reclassified into stockholders’ equity as the shares vested. As of June 30, 2018, the early exercise stock options were fully vested. RSAs are subject to repurchase rights. Accordingly, the Company has recorded the proceeds from the issuance of restricted stock as a liability in the consolidated balance sheets. The restricted stock liability is reclassified into stockholders’ equity as the restricted stock vests. ​ If factors change or different assumptions are used, the Company’s stock-based compensation expense could be materially different in the future.
Success Payments, Research Funding Payments and Notes Payables	Success Payments, Research Funding Payments and Notes Payables
Income taxes	Income taxes Income taxes are recorded in accordance with ASC Topic 740, Income Taxes The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is comprised of net loss and other comprehensive income or loss. Comprehensive loss includes net loss as well as other changes in stockholders’ equity that result from transactions and economic events other than those with stockholders. Comprehensive loss currently consists of net loss and changes in unrealized losses on marketable securities.
Concentrations of Credit Risk and Off-Balance Sheet Risk	Concentrations of Credit Risk and Off-Balance Sheet Risk The Company has no financial instruments with off-balance sheet risk such as foreign exchange contracts, option contracts, or other foreign hedging arrangements. Financial instruments that potentially subject the Company to a concentration of credit risk are cash, cash equivalents, marketable securities and receivables owed to the Company from collaboration partners. The Company’s cash, cash equivalents and marketable securities are held in accounts at a financial institution that may exceed federally insured limits. The Company has not experienced any credit losses in such accounts and does not believe it is exposed to any significant credit risk on these funds.
Segment Information	Segment Information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker in deciding how to allocate resources and assess performance. The Company and the Company’s chief operating decision maker, the Company’s Chief Executive Officer, view the Company’s operations and manage the Company’s business as a single operating segment, which is the business of developing and commercializing genome editing technology.
Recent Accounting Pronouncements Adopted And Issued But Not Yet Adopted	Recent Accounting Pronouncements –Adopted Leases As discussed above, the Company adopted ASC 842, using the modified-retrospective transition method, effective January 1, 2019, pursuant to which the Company recognized a cumulative-effect adjustment of $0.8 million to the opening balance of accumulated deficit on January 1, 2019 associated with de-recognizing the net asset balance recorded in property and equipment, net and the offsetting construction financing lease liability related to the Company’s headquarters which was previously accounted for under the built-to-suit guidance in ASC 840, Leases which allows the Company to reassess the lease term as it was not relevant to the Company’s leases. Stock-Based Compensation Expense Effective January 1, 2019, the Company adopted ASU No. 2018-07, Compensation – Stock Compensation: Improvements to Nonemployee Share-Based Payment Accounting ​ Recent Accounting Pronouncements – Issued But Not Yet Adopted In August 2018, the FASB issued ASU No. 2018-13, Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement ​ In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses Measurement of Credit Losses on Financial Instruments ​ In August 2018, the FASB issued ASU No. 2018-15, Intangibles—Goodwill and Other-Internal-Use Software (Topic 350): Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract to all implementation costs incurred after the date of adoption. The Company does not anticipate a material impact on its consolidated financial statements as a result of the adoption of ASU 2018-15.

Summary of significant accoun_3

Summary of significant accounting policies (Tables)	12 Months Ended
	Dec. 31, 2019
Schedule of cash, cash equivalents, and restricted cash	The following table presents cash, cash equivalents, and restricted cash as reported on the consolidated balance sheets that equal the total amounts on the consolidated statements of cash flows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ As of December 31, ​ ​ 2019 ​ 2018 ​ 2017 Cash and cash equivalents ​ $ 238,183 ​ $ 134,776 ​ $ 146,630 Restricted cash included in "Restricted cash and other non-current assets" ​ ​ 1,619 ​ ​ 1,619 ​ ​ 1,619 Total cash, cash equivalents, and restricted cash ​ $ 239,802 ​ $ 136,395 ​ $ 148,249 ​
Schedule of estimated useful lives of property, plant and equipment	​ ​ ​ ​ ​ Asset: Estimated Useful life Lab equipment 5 years ​ Computer equipment and software 3 years ​ Furniture and equipment 5 years ​ Leasehold improvements Shorter of useful life or remaining lease term ​ ​
ASU 2014-09
Schedule of financial statement line items for comparability purposes	In connection with the Company’s adoption of ASC 606, the Company has included the following financial statement line items for comparability purposes for the year ended December 31, 2018 (in thousands, except per share data): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, 2018 ​ As reported under Topic 606 ​ Balances without adoption of ASC 606 ​ Effect of Change Collaboration and other research and development revenues $ 31,937 ​ $ 33,993 ​ $ (2,056) Operating loss $ (113,727) ​ $ (111,671) ​ $ (2,056) Net loss attributable to common stockholders $ (109,954) ​ $ (107,898) ​ $ (2,056) Net loss per share attributable to common stockholders, basic and diluted $ (2.33) ​ $ (2.29) ​ $ (0.04)
ASU 2016-02
Schedule of financial statement line items for comparability purposes	​ ​ ​ ​ ​ As of ​ January 1, 2019 Property and equipment, net $ 32,627 Other current liabilities $ (1,014) Construction financing lease obligation, net of current portion $ (32,417) Accumulated deficit $ 803 ​

Cash Equivalents, Marketable _2

Cash Equivalents, Marketable Securities and Corporate Equity Securities (Tables)	12 Months Ended
	Dec. 31, 2019
Cash Equivalents, Marketable Securities and Equity Securities
Schedule of cash equivalents, marketable securities and corporate equity securities	Cash equivalents, marketable securities and equity securities consisted of the following at December 31, 2019 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross ​ Gross ​ ​ ​ ​ Amortized ​ Unrealized ​ Unrealized ​ Fair December 31, 2019 ​ Cost ​ Gains ​ Losses ​ Value Cash equivalents and marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 230,201 ​ $ — ​ $ — ​ $ 230,201 U.S. Treasuries ​ ​ 71,348 ​ ​ 20 ​ ​ — ​ ​ 71,368 Government agency securities ​ ​ 155,484 ​ ​ 87 ​ ​ — ​ ​ 155,571 Equity securities included in other non-current assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Corporate equity securities ​ ​ 3,667 ​ ​ — ​ ​ — ​ ​ 3,667 Total ​ $ 460,700 ​ $ 107 ​ $ — ​ $ 460,807 ​ Cash equivalents, marketable securities and equity securities consisted of the following at December 31, 2018 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross ​ Gross ​ ​ ​ ​ Amortized ​ Unrealized ​ Unrealized ​ Fair December 31, 2018 ​ Cost ​ Gains ​ Losses ​ Value Cash equivalents and marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 130,049 ​ $ — ​ $ — ​ $ 130,049 U.S. Treasuries ​ ​ 208,754 ​ ​ — ​ ​ (24) ​ ​ 208,730 Government agency securities ​ ​ 29,940 ​ ​ — ​ ​ (5) ​ ​ 29,935 Equity securities included in other non-current assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Corporate equity securities ​ ​ 3,667 ​ ​ — ​ ​ — ​ ​ 3,667 Total cash equivalents and marketable securities ​ $ 372,410 ​ $ — ​ $ (29) ​ $ 372,381

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2019
Fair Value Measurements
Schedule of assets measured at fair value on a recurring basis	Assets measured at fair value on a recurring basis as of December 31, 2019 were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Quoted Prices Significant ​ ​ ​ ​ ​ ​ ​ in Active ​ Other ​ Significant ​ ​ ​ ​ ​ Markets for ​ Observable ​ Unobservable ​ ​ December 31, ​ Identical Assets ​ Inputs ​ Inputs Financial Assets ​ 2019 ​ (Level 1) ​ (Level 2) ​ (Level 3) Cash equivalents: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 230,201 ​ $ 230,201 ​ $ — ​ $ — U.S. Treasuries ​ ​ 7,982 ​ ​ 7,982 ​ ​ — ​ ​ — Marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Treasuries ​ ​ 63,386 ​ ​ 63,386 ​ ​ — ​ ​ — Government agency securities ​ ​ 155,571 ​ ​ 155,571 ​ ​ — ​ ​ — Restricted cash and other non-current assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Corporate equity securities ​ ​ 3,667 ​ ​ — ​ ​ 3,667 ​ ​ — Money market funds ​ ​ 1,619 ​ ​ 1,619 ​ ​ — ​ ​ — Total financial assets ​ $ 462,426 ​ $ 458,759 ​ $ 3,667 ​ $ — ​ Assets and liabilities measured at fair value on a recurring basis as of December 31, 2018 were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Quoted Prices Significant ​ ​ ​ ​ ​ ​ ​ in Active ​ Other ​ Significant ​ ​ ​ ​ ​ Markets for ​ Observable ​ Unobservable ​ ​ December 31, ​ Identical Assets ​ Inputs ​ Inputs Financial Assets ​ 2018 ​ (Level 1) ​ (Level 2) ​ (Level 3) Cash and cash equivalents: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 130,049 ​ $ 130,049 ​ $ — ​ $ — U.S. Treasuries ​ ​ 4,487 ​ ​ 4,487 ​ ​ — ​ ​ — Marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Treasuries ​ ​ 204,243 ​ ​ 204,243 ​ ​ — ​ ​ — Government agency securities ​ ​ 29,935 ​ ​ 29,935 ​ ​ — ​ ​ — Restricted cash and other non-current assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Corporate equity securities ​ ​ 3,667 ​ ​ — ​ ​ 3,667 ​ ​ ​ Money market funds ​ ​ 1,619 ​ ​ 1,619 ​ ​ — ​ ​ — Total financial assets ​ $ 374,000 ​ $ 370,333 ​ $ 3,667 ​ $ — ​

Property and Equipment, net (Ta

Property and Equipment, net (Tables)	12 Months Ended
	Dec. 31, 2019
Property and Equipment, net
Schedule of property and equipment, net	Property and equipment, net consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ As of ​ ​ December 31, ​ 2019 2018 Laboratory equipment ​ $ 14,571 ​ $ 10,892 Construction-in-progress ​ ​ 1,336 ​ ​ — Leasehold improvements ​ 1,042 ​ 289 Computer equipment ​ 858 ​ 733 Furniture and office equipment ​ 166 ​ ​ 166 Software ​ ​ 118 ​ ​ 118 Building ​ ​ — ​ ​ 35,167 Total property and equipment ​ 18,091 ​ 47,365 Less: accumulated depreciation ​ (7,204) ​ (7,133) Property and equipment, net ​ $ 10,887 ​ $ 40,232 ​

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2019
Accrued Expenses
Schedule of accrued expenses	Accrued expenses consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ As of ​ ​ December 31, ​ 2019 2018 Sublicensing and success payment expenses ​ $ 11,416 ​ $ 3,750 Employee related expenses ​ ​ 4,971 ​ ​ 5,201 Intellectual property and patent related fees ​ ​ 3,725 ​ ​ 1,939 Professional service expenses ​ 674 ​ 475 Process and platform development expenses ​ ​ 735 ​ ​ 1,044 Other expenses ​ 599 ​ 404 Total ​ $ 22,120 ​ $ 12,813

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2019
Leases
Summary of leases included on its consolidated balance sheet	​ ​ ​ ​ ​ ​ ​ ​ As of ​ December 31, ​ January 1, ​ 2019 2019 Right-of-use assets $ 28,761 ​ $ 19,461 Operating lease liabilities, current $ (5,804) ​ $ (3,848) Operating lease liabilities, noncurrent $ (23,277) ​ $ (15,909)
Summary of maturities of lease liabilities	​ ​ ​ ​ ​ Year Ended Maturity of lease liabilities: December 31, 2019 2020 $ 8,150 2021 $ 8,041 2022 $ 7,848 2023 $ 7,279 2024 $ 3,484 Thereafter $ 290 Total minimum lease payments $ 35,092 Less: imputed interest $ (6,011) Total operating lease liabilities at December 31, 2019 $ 29,081 ​

Collaboration and License Agree

Collaboration and License Agreements (Tables)	12 Months Ended
	Dec. 31, 2019
Collaboration and Profit-Sharing Agreements
Schedule of accounts receivable and contract liabilities	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the year ended December 31, 2019 Balance at December 31, 2018 ​ Additions ​ Deductions ​ Balance at Accounts receivable $ 30 ​ $ 418 ​ $ (30) ​ $ 418 Contract liabilities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Deferred revenue $ 131,326 ​ $ 75,500 ​ $ (20,105) ​ $ 186,721
Schedule of change in contract assets and contract liabilities	​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ Year Ended Revenue recognized in the period from: December 31, 2019 Amounts included in deferred revenue at the beginning of the period $ 4,715 ​ $ 11,448 Performance obligations satisfied in previous periods $ 1,261 ​ $ 2,455

Common Stock (Tables)

Common Stock (Tables)	12 Months Ended
	Dec. 31, 2019
Common Stock
Schedule of shares reserved for future issuance	​ ​ ​ ​ ​ ​ ​ As of December 31, ​ 2019 2018 Shares reserved for outstanding stock option awards under the 2013 Stock Incentive Plan, as amended ​ 312,342 873,373 Shares reserved for outstanding stock option awards under the 2015 Stock Incentive Plan ​ 4,254,357 ​ 3,709,225 Shares reserved for outstanding inducement stock option award ​ 175,000 ​ 107,188 Remaining shares reserved, but unissued, for future awards under the 2015 Stock Incentive Plan ​ 4,061,357 ​ 3,233,031 Remaining shares reserved, but unissued, for future awards under the 2015 Employee Stock Purchase Plan 1,630,199 ​ 1,175,224 ​ 10,433,255 9,098,041

Stock-based Compensation (Table

Stock-based Compensation (Tables)	12 Months Ended
	Dec. 31, 2019
Stock-based Compensation
Schedule of stock-based compensation expense	Total compensation cost recognized for all stock-based compensation awards in the consolidated statements of operations was as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ ​ 2019 ​ 2018 ​ 2017 Research and development ​ $ 13,538 ​ $ 14,734 ​ $ 15,131 General and administrative ​ 13,705 ​ 11,864 ​ 8,243 Total stock-compensation expense ​ $ 27,243 ​ $ 26,598 ​ $ 23,374 ​
Schedule of changes in unvested restricted stock	​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ Average ​ ​ ​ ​ Grant Date ​ ​ ​ ​ Fair Value ​ ​ Shares ​ Per Share Unvested restricted stock and restricted stock unit awards as of December 31, 2018 270,000 ​ $ 28.05 Issued 498,425 ​ $ 22.00 Vested ​ (99,919) ​ $ 26.52 Forfeited (87,098) ​ $ 21.51 Unvested restricted stock and restricted stock unit awards as of December 31, 2019 581,408 ​ $ 24.03
Schedule of stock option activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted Average Remaining Aggregate Intrinsic ​ ​ Shares ​ Exercise Price ​ Contractual Life ​ Value (in thousands) Outstanding at December 31, 2018 4,689,786 ​ $ 23.80 ​ 7.9 ​ $ 20,686 Granted 1,793,247 ​ $ 24.04 ​ ​ ​ ​ ​ Exercised (1,120,186) ​ $ 13.27 ​ ​ ​ ​ ​ Cancelled ​ (1,004,556) ​ $ 28.96 ​ ​ ​ ​ ​ Outstanding at December 31, 2019 4,358,291 ​ $ 25.40 ​ 7.4 ​ $ 26,060 Exercisable at December 31, 2019 1,994,417 ​ $ 24.26 ​ 6.1 ​ $ 15,747
Schedule of assumptions used to value stock options	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ ​ 2019 ​ ​ 2018 ​ ​ 2017 Expected volatility 73.8 % ​ 77.5 % ​ 77.8 % Expected term (in years) 6.25 ​ ​ 6.25 ​ ​ 6.25 ​ Risk free interest rate 2.0 % ​ 2.9 % ​ 2.1 % Expected dividend yield — ​ ​ — ​ ​ — ​

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2019
Income Taxes
Schedule of reconciliation of effective income tax rate	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ ​ 2019 ​ ​ 2018 ​ 2017 Income tax computed at federal statutory tax rate ​ 21.0 % ​ 21.0 % ​ 34.0 % State taxes, net of federal benefit ​ 5.2 % ​ 6.4 % ​ 5.9 % General business credit carryovers ​ 2.8 % ​ 4.4 % ​ 2.5 % Stock Options ​ (2.2) % ​ 0.7 % ​ (1.2) % Non-deductible expenses ​ (0.1) % ​ (0.1) % ​ (0.9) % Federal tax rate reduction ​ — % ​ — % ​ (24.7) % Change in valuation allowance ​ (26.7) % ​ (32.4) % ​ (15.6) % ​ ​ — % ​ — % ​ — %
Schedule of components of deferred tax assets and liabilities	​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ ​ 2019 ​ 2018 Deferred tax assets: ​ ​ ​ ​ ​ ​ Net operating loss carryforwards ​ $ 50,511 ​ $ 20,302 Tax credit carryforwards ​ ​ 13,767 ​ 10,059 Accrued expenses ​ ​ 2,219 ​ 3,099 Capitalized patent costs ​ ​ 39,070 ​ 33,101 Lease liabilities ​ ​ 7,879 ​ ​ — Deferred revenue ​ ​ 31,880 ​ ​ 34,039 Construction financing lease obligation ​ ​ — ​ ​ 9,100 Other ​ ​ 7,865 ​ 8,347 Total deferred tax assets ​ 153,191 ​ 118,047 Less valuation allowance ​ (144,540) ​ (109,091) Net deferred tax assets ​ 8,651 ​ 8,956 Deferred tax liabilities: ​ (8,651) ​ (8,956) Depreciation and amortization ​ ​ (859) ​ ​ (8,956) Right-of-use assets ​ ​ (7,792) ​ ​ — Net deferred taxes ​ $ — ​ $ —

Net Loss per Share (Tables)

Net Loss per Share (Tables)	12 Months Ended
	Dec. 31, 2019
Net Loss per Share
Schedule of anti-dilutive common stock equivalents	​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ 2019 2018 Unvested restricted common stock 581,408 270,000 Outstanding stock options 4,358,291 4,689,786 Total 4,939,699 4,959,786 ​

Selected Quarterly Financial _2

Selected Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2019
Selected Quarterly Financial Data
Schedule of selected quarterly financial information	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ March 31, 2019 ​ June 30, 2019 ​ September 30, 2019 ​ December 31, 2019 ​ ​ (in thousands, except per share data) Total collaboration and other research and development revenues $ 2,069 ​ $ 2,330 ​ $ 3,848 ​ $ 12,284 Total operating expenses ​ 33,331 ​ ​ 37,979 ​ ​ 38,436 ​ ​ 51,707 Total other income (expense), net ​ 2,013 ​ ​ 1,863 ​ ​ 1,647 ​ ​ 1,653 Net loss $ (29,249) ​ $ (33,786) ​ $ (32,941) ​ $ (37,770) Net loss applicable to common stockholders $ (29,249) ​ $ (33,786) ​ $ (32,941) ​ $ (37,770) Net loss per share applicable to common stockholders — basic and diluted $ (0.60) ​ $ (0.69) ​ $ (0.66) ​ $ (0.74) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ March 31, 2018 ​ June 30, 2018 ​ September 30, 2018 ​ December 31, 2018 ​ ​ (in thousands, except per share data) Total collaboration and other research and development revenues $ 3,927 ​ $ 7,372 ​ $ 14,519 ​ $ 6,119 Total operating expenses ​ 35,486 ​ ​ 47,029 ​ ​ 30,777 ​ ​ 32,372 Total other income (expense), net ​ 620 ​ ​ 934 ​ ​ 1,020 ​ ​ 1,199 Net loss $ (30,939) ​ $ (38,723) ​ $ (15,238) ​ $ (25,054) Net loss applicable to common stockholders $ (30,939) ​ $ (38,723) ​ $ (15,238) ​ $ (25,054) Net loss per share applicable to common stockholders — basic and diluted $ (0.67) ​ $ (0.82) ​ $ (0.32) ​ $ (0.52)

Nature of Business (Details)

Nature of Business (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Liquidity
Accumulated deficit	$ 549,221	$ 549,221	$ 416,278
March 2018 ATM Program
Liquidity
Threshold sale proceeds				$ 150,000
Number of common stock issued	5,448,428
Weighted average price per share	$ 27.53
Gross proceeds	$ 150,000
Number of common stock available for sale	0	0
March 2018 ATM Program | Cowen and Company LLC ("Cowen)
Liquidity
Cash commission paid	3.00%
Public and Market Offering
Liquidity
Aggregate net proceeds		$ 444,800

Summary Of Significant Accoun_4

Summary Of Significant Accounting Policies - Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash, Cash Equivalents, and Restricted Cash
Restricted cash	$ 1,600
Cash and cash equivalents	238,183	$ 134,776	$ 146,630
Restricted cash included in "Restricted cash and other non-current assets"	1,619	1,619	1,619
Total	$ 239,802	$ 136,395	$ 148,249	$ 186,942

Summary Of Significant Accoun_5

Summary Of Significant Accounting Policies - Accounts Receivable (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Accounts Receivable
Bad debt write-offs	$ 0	$ 0
Allowance for doubtful accounts	$ 0	$ 0

Summary Of Significant Accoun_6

Summary Of Significant Accounting Policies - Property And Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property and equipment policy
Estimated useful life	30 years
Impairment losses	$ 0	$ 0	$ 0
Laboratory equipment
Property and equipment policy
Estimated useful life	5 years
Computer equipment and software
Property and equipment policy
Estimated useful life	3 years
Furniture and office equipment
Property and equipment policy
Estimated useful life	5 years

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Derecognition of Balances (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Leases
Property and equipment, net	$ 10,887		$ 40,232
Other current liabilities	2,682		2,048
Construction financing lease obligation, net of current portion			32,417
Accumulated deficit	$ (549,221)		$ (416,278)
Estimated useful life	30 years
ASU 2016-02 | Restatement Adjustment
Leases
Property and equipment, net		$ 32,627
Other current liabilities		(1,014)
Construction financing lease obligation, net of current portion		(32,417)
Accumulated deficit		$ 803

Summary Of Significant Accoun_8

Summary Of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Recent Accounting Pronouncements
Collaboration and other research and development revenues	$ 12,284	$ 3,848	$ 2,330	$ 2,069	$ 6,119	$ 14,519	$ 7,372	$ 3,927	$ 20,531	$ 31,937	$ 13,728
Revenue type									us-gaap:ServiceMember	us-gaap:ServiceMember	us-gaap:ServiceMember
Operating loss									$ (140,922)	$ (113,727)	$ (119,933)
Net Income (Loss) Attributable to Parent	$ (37,770)	$ (32,941)	$ (33,786)	$ (29,249)	$ (25,054)	$ (15,238)	$ (38,723)	$ (30,939)	$ (133,746)	$ (109,954)	$ (120,324)
Net loss per share attributable to common stockholders, basic and diluted									$ (2.68)	$ (2.33)	$ (2.98)
Promissory Notes
Recent Accounting Pronouncements
Interest rate (as a percentage)	4.80%								4.80%
Period of outstanding principal and accrued interest payable									5 months
Accumulated Deficit
Recent Accounting Pronouncements
Net Income (Loss) Attributable to Parent									$ (133,746)	$ (109,954)	$ (120,324)
ASU 2014-09 | As originally reported under Topic 606
Recent Accounting Pronouncements
Collaboration and other research and development revenues										33,993
Operating loss										(111,671)
Net Income (Loss) Attributable to Parent										$ (107,898)
Net loss per share attributable to common stockholders, basic and diluted										$ (2.29)
ASU 2014-09 | Effect of Change
Recent Accounting Pronouncements
Collaboration and other research and development revenues										$ (2,056)
Operating loss										(2,056)
Net Income (Loss) Attributable to Parent										$ (2,056)
Net loss per share attributable to common stockholders, basic and diluted										$ (0.04)

Summary Of Significant Accoun_9

Summary Of Significant Accounting Policies - Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Recent Accounting Pronouncements
Cumulative effect adjustment for adoption of new accounting guidance	$ 803		$ (474)
Total assets	508,885		420,386
Total liabilities	246,448		184,224
Right-of-use assets	28,761	$ 19,461
Lease liability	$ 29,081
Lease, Practical Expedients, Package	true
Lease, Practical Expedient, Use of Hindsight	true
Accumulated Deficit
Recent Accounting Pronouncements
Cumulative effect adjustment for adoption of new accounting guidance	$ 803		$ (474)
ASU 2016-02 | Restatement Adjustment
Recent Accounting Pronouncements
Total assets		32,600
Total liabilities		33,400
Right-of-use assets		19,500
Lease liability		19,700
ASU 2016-02 | Restatement Adjustment | Accumulated Deficit
Recent Accounting Pronouncements
Cumulative effect adjustment for adoption of new accounting guidance		$ 800

Cash Equivalents, Marketable _3

Cash Equivalents, Marketable Securities and Corporate Equity Securities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)item	Dec. 31, 2018USD ($)
Cash Equivalents, Marketable Securities and Equity Securities
Amortized Cost	$ 460,700	$ 372,410
Gross Unrealized Gains	107
Gross Unrealized Losses		(29)
Fair Value	$ 460,807	372,381
Number of securities in an unrealized loss position | item	3
Securities held by the Company in an unrealized loss position for less than 12 months	$ 26,600
Number of securities in an unrealized loss position for more than 12 months | item	0
Realized gains (losses) on available-for-sale securities	$ 0	0
Corporate equity securities
Equity securities included in other non-current assets:
Amortized Cost	3,667	3,667
Fair Value	3,667	3,667
Money market funds
Cash Equivalents, Marketable Securities and Corporate Equity Securities
Amortized Cost	230,201	130,049
Fair Value	230,201	130,049
U.S. Treasuries
Cash Equivalents, Marketable Securities and Corporate Equity Securities
Amortized Cost	71,348	208,754
Gross Unrealized Gains	20
Gross Unrealized Losses		(24)
Fair Value	71,368	208,730
Government agency securities
Cash Equivalents, Marketable Securities and Corporate Equity Securities
Amortized Cost	155,484	29,940
Gross Unrealized Gains	87
Gross Unrealized Losses		(5)
Fair Value	$ 155,571	$ 29,935

Fair Value Measurements - Recur

Fair Value Measurements - Recurring Basis (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)item	Dec. 31, 2018USD ($)item
Financial Assets
Transfers between levels | item	0	0
Corporate equity securities
Financial Assets
Equity securities	$ 3,667	$ 3,667
Money market funds
Financial Assets
Marketable securities	230,201	130,049
U.S. Treasuries
Financial Assets
Marketable securities	71,368	208,730
Government agency securities
Financial Assets
Marketable securities	155,571	29,935
Recurring
Financial Assets
Total financial assets	462,426	374,000
Recurring | U.S. Treasuries
Financial Assets
Marketable securities	63,386	204,243
Recurring | Government agency securities
Financial Assets
Marketable securities	155,571	29,935
Recurring | Corporate equity securities
Financial Assets
Equity securities		3,667
Restricted cash	3,667
Recurring | Money market funds
Financial Assets
Cash and cash equivalents	230,201	130,049
Restricted cash	1,619	1,619
Recurring | U.S. Treasuries
Financial Assets
Cash and cash equivalents	7,982	4,487
Recurring | Level 1
Financial Assets
Total financial assets	458,759	370,333
Recurring | Level 1 | U.S. Treasuries
Financial Assets
Marketable securities	63,386	204,243
Recurring | Level 1 | Government agency securities
Financial Assets
Marketable securities	155,571	29,935
Recurring | Level 1 | Money market funds
Financial Assets
Cash and cash equivalents	230,201	130,049
Restricted cash	1,619	1,619
Recurring | Level 1 | U.S. Treasuries
Financial Assets
Cash and cash equivalents	7,982	4,487
Recurring | Level 2
Financial Assets
Total financial assets	3,667	3,667
Recurring | Level 2 | Corporate equity securities
Financial Assets
Equity securities		$ 3,667
Restricted cash	$ 3,667

Property and Equipment, net (De

Property and Equipment, net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property and equipment disclosures
Total property and equipment	$ 18,091	$ 47,365
Less: accumulated depreciation	(7,204)	(7,133)
Property and equipment, net	10,887	40,232
Depreciation	2,830	3,254	$ 2,683
Laboratory equipment
Property and equipment disclosures
Total property and equipment	14,571	10,892
Construction-in-progress
Property and equipment disclosures
Total property and equipment	1,336
Leasehold improvements
Property and equipment disclosures
Total property and equipment	1,042	289
Computer equipment
Property and equipment disclosures
Total property and equipment	858	733
Furniture and office equipment
Property and equipment disclosures
Total property and equipment	166	166
Software
Property and equipment disclosures
Total property and equipment	$ 118	118
Building
Property and equipment disclosures
Total property and equipment		$ 35,167

Accrued Expenses (Details)

Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accrued Expenses
Sublicensing and success payment expenses	$ 11,416	$ 3,750
Employee related expenses	4,971	5,201
Intellectual property and patent related fees	3,725	1,939
Professional service expenses	674	475
Process and platform development expenses	735	1,044
Other expenses	599	404
Total	$ 22,120	$ 12,813

Leases - Right of Use Asset and

Leases - Right of Use Asset and Lease Liability (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
Leases are included on its condensed consolidated balance sheet
Right-of-use assets	$ 28,761			$ 19,461
Operating lease liabilities, current	(5,804)			(3,848)
Operating lease liabilities, noncurrent	(23,277)			$ (15,909)
Operating lease costs	5,600
Variable lease costs	$ 1,000
Rent expense		$ 1,800	$ 1,200

Leases - Maturities of Lease Li

Leases - Maturities of Lease Liabilities (Details) $ in Thousands	Dec. 31, 2019USD ($)
Maturity of lease liabilities:
2020	$ 8,150
2021	8,041
2022	7,848
2023	7,279
2024	3,484
Thereafter	290
Total minimum lease payments	35,092
Less: imputed interest	(6,011)
Total operating lease liabilities at December 31, 2019	$ 29,081
Weighted average remaining lease term	4 years 2 months 12 days
Weighted average discount rate	8.90%

Leases - Operating Leases (Deta

Leases - Operating Leases (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019ft²	Jan. 31, 2020USD ($)	Feb. 28, 2017ft²	Oct. 01, 2016USD ($)ft²
Hurley Street Lease
Leases
Leased space ( in square feet)				59,783
Security deposit | $				$ 1.6
Lessee, Operating Lease, Existence of Option to Extend [true false]	true
Extended lease option (in years)				5 years
One Main
Leases
Leased space ( in square feet)	31,571
Security deposit | $		$ 0.8
Lessee, Operating Lease, Existence of Option to Extend [true false]	true
Extended lease option (in years)	5 years
Facility Sublease Arrangement
Leases
Leased space ( in square feet)			10,000

Commitments and Contingencies -

Commitments and Contingencies - Research Funding Payments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2018
Commitments and contingencies
Research and development	$ 96,898	$ 90,654	$ 83,159
Sponsored Research Agreement | Broad
Commitments and contingencies
First research funding amount due and payable	5,000
Second research funding amount due and payable	$ 7,500
Research and development		$ 12,500
Promissory notes issued				$ 125,000

Commitments and Contingencies_2

Commitments and Contingencies - Notes Payable (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Notes Payable
Notes paid in cash		$ 600
Broad | Sponsored Research Agreement
Notes Payable
Promissory notes issued	$ 125,000
Common stock issued	330,617

Commitments and Contingencies_3

Commitments and Contingencies - Other Agreements (Details) - USD ($) $ in Thousands	1 Months Ended				12 Months Ended
	Jan. 31, 2018	Aug. 31, 2017	Dec. 31, 2016	Oct. 31, 2014	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 16, 2016
Research and development					$ 96,898	$ 90,654	$ 83,159
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) | License Patent Rights
Upfront fee				$ 200
Stock issued to licensors				561,531
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) | Cpf1 License Agreement
Research and development			$ 16,500
Common stock issued for settlement	150,606	271,347					479,270
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) | Cpf1 Market Cap Success Payments
Market capitalization							$ 1,000,000	$ 750,000
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) | Cas9-II License Agreement
Common stock issued for settlement	75,303
Market capitalization							$ 1,000,000
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) | Maximum | Cpf1 License Agreement
Royalties credit paid to third party (as a percent)					50.00%
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) | Maximum | Cpf1 Success Payments
Success Payments					$ 10,000,000
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) | Maximum | Cpf1 Market Cap Success Payments
Success Payments					125,000
Market capitalization threshold					10,000,000
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) | Maximum | Cas9-II License Agreement
Success Payments					30,000
Market capitalization threshold					9,000,000
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) | Minimum | Cpf1 Success Payments
Success Payments					750,000
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) | Minimum | Cas9-II License Agreement
Market capitalization threshold					1,000,000
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) | Rare disease | Maximum
Potential liability for future sales milestone payments				$ 36,000
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) | Rare disease | Maximum | Cpf1 License Agreement
Potential liability for future sales milestone payments					36,000
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) | United States Europe And Japan | Maximum | License Patent Rights
Potential liability for future clinical and regulatory milestone payments related to product approval				14,800
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) | United States Europe And Japan | Human disease | Maximum | Cpf1 License Agreement
Potential liability for future clinical and regulatory milestone payments related to product approval					20,000
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) | United States Europe And Japan | Human disease | Maximum | Cas9-II License Agreement
Potential liability for future sales milestone payments					13,500
Potential liability for future clinical and regulatory milestone payments related to product approval									$ 3,700
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) | United States Europe And Japan | Rare disease | Maximum | Cpf1 License Agreement
Potential liability for future clinical and regulatory milestone payments related to product approval					6,000
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) | United States Europe And Japan | Rare disease | Maximum | Cas9-II License Agreement
Potential liability for future sales milestone payments					9,000
Potential liability for future clinical and regulatory milestone payments related to product approval					1,100
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) | United States and one other | Human disease | Maximum | License Patent Rights
Potential liability for future clinical and regulatory milestone payments related to product approval				4,100
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) | UNITED STATES | Human disease | Maximum | License Patent Rights
Potential liability for future sales milestone payments				$ 54,000
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) | UNITED STATES | Human disease | Maximum | Cpf1 License Agreement
Potential liability for future sales milestone payments					$ 54,000

Commitments and Contingencies_4

Commitments and Contingencies - Licensor Expense Reimbursement (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Licensor Expense Reimbursement
Commitments and contingencies
Expense for prosecution and maintenance of patent rights	$ 13.5	$ 14.2	$ 18.2

Collaboration and Profit-Shar_2

Collaboration and Profit-Sharing Agreements - Revenue Recognition (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
Accounts receivable
Accounts receivable, Balance at Beginning of Period	$ 30
Accounts Receivable, Additions	418
Accounts Receivable, Deductions	(30)
Accounts receivable, Balance at End of Period	418
Contract liabilities, deferred Revenue:
Deferred Revenue, Balance at Beginning of Period	131,326
Deferred revenue, Additions	75,500
Deferred revenue, Deductions	(20,105)
Deferred Revenue, Balance at End of Period	$ 186,721

Collaboration and Profit-Shar_3

Collaboration and Profit-Sharing Agreements - Contract Assets and Liability (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2019
Change in contract asset and contract liability balances
Amounts included in deferred revenue at the beginning of the period	$ 4,715	$ 11,448
Performance obligations satisfied in previous periods	$ 1,261	$ 2,455

Collaboration and Profit-Shar_4

Collaboration and Profit-Sharing Agreements - Summary of Agreement (Details) $ in Thousands	1 Months Ended		3 Months Ended								12 Months Ended
	Mar. 31, 2017item	May 31, 2015item	Dec. 31, 2019USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue			$ 186,721				$ 131,326				$ 186,721	$ 131,326
Deferred revenue, current			23,514				15,712				23,514	15,712
Deferred revenue, long-term			163,207				115,614				163,207	115,614
Accounts receivable			418				30				418	30
Revenue recognized			4,715								11,448
Total revenue			12,284	$ 3,848	$ 2,330	$ 2,069	6,119	$ 14,519	$ 7,372	$ 3,927	$ 20,531	$ 31,937	$ 13,728
Revenue type											us-gaap:ServiceMember	us-gaap:ServiceMember	us-gaap:ServiceMember
Research and development											$ 96,898	$ 90,654	$ 83,159
Juno Therapeutics | Collaboration and License Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Agreement term		5 years
Number of additional licenses | item		3
Juno Therapeutics | Amended Collaboration and License Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development											11,300	1,700
Allergan
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of additional licenses | item	2
Allergan | Strategic Alliance
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue			85,600				99,200				85,600	99,200
Deferred revenue, long-term			$ 63,800				$ 86,400				63,800	$ 86,400
Agreement term	7 years
Number of Collaboration Development Programs | item	5
Total revenue											$ 13,600
Revenue type											us-gaap:ServiceMember	us-gaap:ServiceMember
Broad | Sponsored Research Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development												$ 12,500
Beam Therapeutics, Inc | License Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenue											$ 200	$ 4,000
Revenue type											us-gaap:ServiceMember	us-gaap:ServiceMember

Collaboration and Profit-Shar_5

Collaboration and Profit-Sharing Agreements - Summary of Agreements (Details) $ in Millions	1 Months Ended					12 Months Ended		15 Months Ended
	Nov. 30, 2019USD ($)item	Jul. 31, 2018USD ($)	May 31, 2018USD ($)item	Mar. 31, 2017USD ($)item	May 31, 2015USD ($)item	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Jul. 31, 2017USD ($)item
Juno Therapeutics
Allocable arrangement consideration - R&D Services Unit of Accounting						$ 10.7
Allocable arrangement consideration - Material rights						30
Allergan
Number of additional licenses | item				2
One time payment to acquire the license				$ 25
Allergan | Maximum
Potential development milestone payments				42
Potential regulatory and commercial milestone payments				75
Potential commercial milestone payments				$ 90
Collaboration and License Agreement | Juno Therapeutics
Number of research areas | item					3
Agreement term					5 years
Upfront fee received					$ 25
Number of milestones related to technical progress | item								2
Potential fee receivable for each gene target licensed					$ 2.5
Number of additional licenses | item					3
Milestone payment received under license agreement								$ 2.5
Amended Collaboration and License Agreement | Juno Therapeutics
Number of research areas | item			4
Additional upfront fee received			$ 5
Number of milestones related to technical progress | item			2
Milestone payment receivable related to technical progress			$ 2.5
Amended Collaboration Agreement 2019 | Juno Therapeutics
Agreement term	5 years
Extensions | item	2
Extension period	1 year
Potential development milestone payments	$ 27.5
Potential regulatory milestone payments	107.5
Potential licensed products milestone payments	$ 60
Strategic Alliance | Allergan
Agreement term				7 years
Extension period				1 year
Upfront fee received				$ 90
Number of Committee Members | item				3
Option exercise price per CDP				$ 15
Extension fee for Initial Option Period				5
Option exercise price for development and commercialization license				$ 22.5
Contracts Revenue						21.5
Program expense after option exercise						18.6	$ 5.9
Research and development expense							6
Accrued research and development expenses							$ 3.8
Contract termination notice							90 days
Option exercise payment received		$ 15				$ 15
Percentage of share of expenses recognized						50.00%
Strategic Alliance | Allergan | Prepaid expenses and other current assets
Research and development expense						$ 1.8	$ 2.3
Strategic Alliance | Allergan | Other current liabilities
Research and development expense						0.6
Accrued research and development expenses						$ 2.6
Strategic Alliance | Allergan | Maximum
Extension period				10 years
License Agreement | Beam Therapeutics, Inc
Non-cash consideration aggregate fair value received			$ 3.6
Contract termination notice			90 days

Collaboration and Profit-Shar_6

Collaboration and Profit-Sharing Agreements - Accounting Analysis (Details) $ in Thousands	Jan. 02, 2018USD ($)	Nov. 30, 2019USD ($)	Nov. 30, 2018USD ($)	Mar. 31, 2017item	Dec. 31, 2019USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue					$ 186,721				$ 131,326				$ 131,326	$ 186,721	$ 131,326
Collaboration and other research and development revenues					12,284	$ 3,848	$ 2,330	$ 2,069	6,119	$ 14,519	$ 7,372	$ 3,927		20,531	31,937	$ 13,728
Deferred revenue, long-term					163,207				$ 115,614				115,614	163,207	115,614
Juno Therapeutics
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total transaction price													$ 12,300		40,700
Allergan
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of development and commercialization licenses | item				5
Total transaction price	$ 90,000		$ 25,000											115,000
Collaboration and License Agreement | Juno Therapeutics
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Transaction price research and development expenses funding															2,900
Transaction price milestone payment received															7,700
Amended Collaboration and License Agreement | Juno Therapeutics
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Transaction price upfront fee received															30,000
Amended Collaboration Agreement 2019 | Juno Therapeutics
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total transaction price					102,500									102,500
Amendment fee														70,000
Exercise fee														500
Deferred revenue					32,000									32,000
Collaboration and other research and development revenues					6,200
Deferred revenue, long-term					$ 96,300									96,300
Transaction price upfront fee received		$ 70,000
First development and commercialization license payment received		$ 500
License Agreement | Beam Therapeutics, Inc
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total transaction price														3,800
Collaboration and other research and development revenues														$ 200	$ 4,000

Preferred Stock (Details)

Preferred Stock (Details) - shares	Dec. 31, 2019	Dec. 31, 2018	Feb. 08, 2016
Preferred Stock
Authorized common stock	195,000,000	195,000,000	195,000,000
Authorized preferred stock	5,000,000	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0

Common Stock (Details)

Common Stock (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)Voteshares	Dec. 31, 2018USD ($)shares	Dec. 31, 2017USD ($)	Jul. 31, 2015shares
Common Stock, Capital Shares Reserved for Future Issuance	10,433,255	9,098,041
Proceeds from offering of common stock, net of issuance costs | $	$ 116,341	$ 76,789	$ 154,143
Common Stock
Voting rights per share | Vote	1
Dividends, Common Stock | $	$ 0	$ 0	$ 0
Common Stock | Stock options
Common Stock, Capital Shares Reserved for Future Issuance	175,000	107,188
2013 Plan
Common Stock, Capital Shares Reserved for Future Issuance				6,317,769
2013 Plan | Common Stock | Stock options
Common Stock, Capital Shares Reserved for Future Issuance	312,342	873,373
2015 Plan | Common Stock
Common Stock, Capital Shares Reserved for Future Issuance	4,061,357	3,233,031
2015 Plan | Common Stock | Stock options
Common Stock, Capital Shares Reserved for Future Issuance	4,254,357	3,709,225
2015 Employee Stock Purchase Plan
Common Stock, Capital Shares Reserved for Future Issuance	1,630,199	1,175,224

Common Stock - Stock Incentive

Common Stock - Stock Incentive Plan (Details)	Jan. 01, 2020shares	Jan. 31, 2020shares	Dec. 31, 2019item$ / sharesshares	Dec. 31, 2018shares	Jul. 31, 2015shares	Sep. 30, 2013shares
Stock-based compensation disclosures
Shares reserved for future awards			10,433,255	9,098,041
Employee and Consultant Options
Stock-based compensation disclosures
Options granted (in shares)			1,793,247
Restricted Stock
Stock-based compensation disclosures
Shares granted			498,425
Issued (in dollars per share) | $ / shares			$ 22
2013 Plan
Stock-based compensation disclosures
Shares authorized						1,057,692
Shares reserved for future awards					6,317,769
2013 Plan | Consultant Stock Options
Stock-based compensation disclosures
Expiration period			10 years
2013 Plan | Performance based awards
Stock-based compensation disclosures
Number of awards with performance vesting criteria | item			1
2015 Plan | Subsequent Event
Stock-based compensation disclosures
Increase to number of shares authorized	2,182,151
2015 Employee Stock Purchase Plan
Stock-based compensation disclosures
Shares reserved for future awards			1,630,199	1,175,224
2015 Employee Stock Purchase Plan | Subsequent Event
Stock-based compensation disclosures
Increase to number of shares authorized	545,537
Maximum | 2013 Plan | Consultant Stock Options
Stock-based compensation disclosures
Vesting period			4 years
Maximum | 2015 Plan
Stock-based compensation disclosures
Shares reserved for future awards			2,923,076
Percent of shares outstanding reserved for future awards (as a percent)			4.00%
Maximum | 2015 Employee Stock Purchase Plan
Stock-based compensation disclosures
Shares reserved for future awards			769,230
Percent of shares outstanding reserved for future awards (as a percent)			1.00%
Minimum | 2013 Plan | Consultant Stock Options
Stock-based compensation disclosures
Vesting period			1 year
Chief Medical Officer | Stock options | Subsequent Event
Stock-based compensation disclosures
Options granted (in shares)		120,000
Chief Medical Officer | Restricted Stock Units (RSUs) | Subsequent Event
Stock-based compensation disclosures
Shares granted		20,000

Stock-based Compensation - Expe

Stock-based Compensation - Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock-based compensation disclosures
Compensation expense	$ 27,243	$ 26,598	$ 23,374
Research and development
Stock-based compensation disclosures
Compensation expense	13,538	14,734	15,131
General and administrative
Stock-based compensation disclosures
Compensation expense	$ 13,705	$ 11,864	$ 8,243

Stock-based Compensation - Rest

Stock-based Compensation - Restricted Stock and Stock Options (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Changes in unvested stock options
Compensation expense	$ 27,243	$ 26,598	$ 23,374
Chief Executive Officer
Changes in unvested stock options
Granted (in shares)	250,000
Other than employees and directors
Changes in unvested stock options
Granted (in shares)	0	0	0
Employees
Changes in unvested stock options
Compensation expense	$ 4,700
Non-employees
Changes in unvested stock options
Compensation expense	$ 1,600
Restricted Stock
Changes in unvested restricted stock
Unvested restricted shares, beginning of period (in shares)	270,000
Issued (in shares)	498,425
Vested (in shares)	(99,919)
Forfeited (in shares)	(87,098)
Unvested restricted shares, end of period(in shares)	581,408	270,000
Weighted Average Grant Date Fair Value
Balance, beginning of period	$ 28.05
Issued (in dollars per share)	22
Vested (in dollars per share)	26.52
Forfeited (in dollars per share)	21.51
Balance, ending of period	$ 24.03	$ 28.05
Restricted Stock | Employees
Changes in unvested stock options
Period for recognition	1 year 9 months 18 days
Compensation expense		$ 0	$ 500
Unrecognized stock-based compensation expense	$ 4,300
Restricted Stock | Non-employees
Changes in unvested stock options
Period for recognition	2 years 8 months 12 days
Compensation expense		$ 2,400	4,100
Unrecognized stock-based compensation expense	$ 4,500
Employee and Consultant Options
Changes in unvested stock options
Outstanding, beginning of period (in shares)	4,689,786
Granted (in shares)	1,793,247
Exercised (in shares)	(1,120,186)
Cancelled (in shares)	(1,004,556)
Outstanding, end of period (in shares)	4,358,291	4,689,786
Exercisable (in shares)	1,994,417
Outstanding, beginning of period (in dollars per share)	$ 23.80
Granted (in dollars per share)	24.04
Exercised (in dollars per share)	13.27
Cancelled (in dollars per share)	28.96
Outstanding, end of period (in dollars per share)	25.40	$ 23.80
Exercisable (in dollar per share)	$ 24.26
Remaining contractual life	7 years 4 months 24 days	7 years 10 months 24 days
Exercisable, remaining contractual life	6 years 1 month 6 days
Aggregate intrinsic value	$ 26,060	$ 20,686
Exercisable, aggregated intrinsic value	15,747
Intrinsic value of options exercised	$ 14,600	$ 15,900	$ 5,000
Weighted average fair value of options granted (per share)	$ 15.67	$ 24.91	$ 16.07
Employee and Consultant Options | Employees and directors
Changes in unvested stock options
Compensation expense	$ 18,100	$ 19,900	$ 12,300
Employee and Consultant Options | Employees
Changes in unvested stock options
Period for recognition	2 years 9 months 18 days
Unrecognized stock-based compensation expense	$ 3,000
Market-based Stock Options | Employees
Changes in unvested stock options
Period for recognition	1 year 6 months
Unrecognized stock-based compensation expense	$ 2,900

Stock-based Compensation - Assu

Stock-based Compensation - Assumptions (Details) - Employee and Consultant Options - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Employees and directors
Assumptions
Risk free interest rate	2.00%	2.90%	2.10%
Expected term (in years)	6 years 3 months	6 years 3 months	6 years 3 months
Expected volatility	73.80%	77.50%	77.80%
Employees
Assumptions
Unrecognized stock-based compensation expense	$ 3
Period for recognition	2 years 9 months 18 days

401(K) Savings Plan (Details)

401(K) Savings Plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
401(k) Savings Plan
Employer match (as a percent)	200.00%
Maximum employee contributions eligible for matching contributions	$ 6,000
Maximum employee contributions eligible for matching contributions (as a percent)	3.00%
Contributions to the 401(k) Plan	$ 800,000	$ 700,000	$ 500,000

Income Taxes - Effective Income

Income Taxes - Effective Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of income tax rate
Income tax computed at federal statutory tax rate	21.00%	21.00%	34.00%
State taxes, net of federal benefit	5.20%	6.40%	5.90%
General business credit carryovers	2.80%	4.40%	2.50%
Stock Options	(2.20%)	0.70%	(1.20%)
Non-deductible expenses	(0.10%)	(0.10%)	(0.90%)
Federal tax rate reduction			(24.70%)
Change in valuation allowance	(26.70%)	(32.40%)	(15.60%)

Income Taxes - Components of De

Income Taxes - Components of Deferred Tax Assets And Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Net operating loss carryforwards	$ 50,511	$ 20,302
Tax credit carryforwards	13,767	10,059
Accrued expenses	2,219	3,099
Capitalized patent costs	39,070	33,101
Lease liabilities	7,879
Deferred revenue	31,880	34,039
Construction financing lease obligation		9,100
Other	7,865	8,347
Total deferred tax assets	153,191	118,047
Less valuation allowance	(144,540)	(109,091)
Net deferred tax assets	8,651	8,956
Deferred tax liabilities	(8,651)	(8,956)
Deferred tax liabilities - Right-of-use assets	(859)	$ (8,956)
Deferred tax liabilities - depreciation and amortization	$ (7,792)

Income Taxes - Net Operating Lo

Income Taxes - Net Operating Losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Operating Loss Carryforwards [Line Items]
Net operating losses with expiration	$ 75,400
Valuation allowance	144,540	$ 109,091
Change in the valuation allowance	35,400
Unrecognized tax benefits	0	0
Federal
Operating Loss Carryforwards [Line Items]
Net operating losses	185,400	74,700
Net operating losses carryforward indefinitely	110,000
State
Operating Loss Carryforwards [Line Items]
Net operating losses	$ 183,300	$ 73,100

Net Loss per Share (Details)

Net Loss per Share (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Potentially dilutive securities
Anti-dilutive common stock equivalent shares	4,939,699	4,959,786
Restricted Stock
Potentially dilutive securities
Anti-dilutive common stock equivalent shares	581,408	270,000
Stock options
Potentially dilutive securities
Anti-dilutive common stock equivalent shares	4,358,291	4,689,786

Related-Party Transactions (Det

Related-Party Transactions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Rent and facility related fees
Related-Party Transactions
Fees received from related party	$ 0	$ 400	$ 800
Research And Development Expenses [Member]
Related-Party Transactions
Fees paid to related party	$ 0	$ 800	$ 300

Selected Quarterly Financial _3

Selected Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Selected Quarterly Financial Data
Total revenue	$ 12,284	$ 3,848	$ 2,330	$ 2,069	$ 6,119	$ 14,519	$ 7,372	$ 3,927	$ 20,531	$ 31,937	$ 13,728
Total operating expenses	51,707	38,436	37,979	33,331	32,372	30,777	47,029	35,486	161,453	145,664	133,661
Total other income (expense), net	1,653	1,647	1,863	2,013	1,199	1,020	934	620	7,176	3,773	(391)
Net loss	(37,770)	(32,941)	(33,786)	(29,249)	(25,054)	(15,238)	(38,723)	(30,939)	(133,746)	(109,954)	(120,324)
Net loss applicable to common stockholders	$ (37,770)	$ (32,941)	$ (33,786)	$ (29,249)	$ (25,054)	$ (15,238)	$ (38,723)	$ (30,939)	$ (133,746)	$ (109,954)	$ (120,324)
Net loss per share applicable to common stockholders - basic and diluted	$ (0.74)	$ (0.66)	$ (0.69)	$ (0.60)	$ (0.52)	$ (0.32)	$ (0.82)	$ (0.67)