Editas Medicine (EDIT) 10-Q 7 Aug 19 2019 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2019	Aug. 01, 2019
Document and Entity Information
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Jun. 30, 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 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 Common Stock, Shares Outstanding		49,515,328
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Entity Central Index Key	0001650664
Amendment Flag	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 210,605	$ 134,776
Marketable securities	107,325	234,179
Accounts receivable	12	30
Prepaid expenses and other current assets	6,298	5,791
Total current assets	324,240	374,776
Property and equipment, net	8,530	40,232
Right-of-use asset	17,477
Restricted cash and other non-current assets	5,378	5,378
Total assets	355,625	420,386
Current liabilities:
Accounts payable	3,981	5,327
Accrued expenses	8,169	12,813
Deferred revenue, current	56,036	15,712
Operating lease liability	3,648
Other current liabilities	1,033	2,048
Total current liabilities	72,867	35,900
Operating lease liability, net of current portion	13,784
Deferred revenue, net of current portion	75,911	115,614
Construction financing lease obligation, net of current portion		32,417
Other non-current liabilities	1	293
Total liabilities	162,563	184,224
Commitments and contingencies (see note 7)
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; 49,175,122 and 49,028,907 shares issued, and 48,923,122 and 48,758,951 shares outstanding at March 31, 2019 and December 31, 2018, respectively	5	5
Additional paid-in capital	671,522	652,464
Accumulated other comprehensive income (loss)	45	(29)
Accumulated deficit	(478,510)	(416,278)
Total stockholders' equity	193,062	236,162
Total liabilities and stockholders' equity	$ 355,625	$ 420,386

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2019	Dec. 31, 2018
Condensed 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	49,432,039	49,028,907
Common stock, shares outstanding	49,241,093	48,758,951

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Condensed Consolidated Statements of Operations
Collaboration and other research and development revenues	$ 2,330	$ 7,372	$ 4,399	$ 11,299
Revenue type	us-gaap:ServiceMember	us-gaap:ServiceMember	us-gaap:ServiceMember	us-gaap:ServiceMember
Operating expenses:
Research and development	$ 23,565	$ 32,718	$ 39,408	$ 54,017
General and administrative	14,414	14,311	31,903	28,498
Total operating expenses	37,979	47,029	71,311	82,515
Operating loss	(35,649)	(39,657)	(66,912)	(71,216)
Other income, net:
Other (expense) income, net	(68)	154	(111)	336
Interest income, net	1,931	780	3,988	1,219
Total other income, net	1,863	934	3,877	1,555
Net loss	$ (33,786)	$ (38,723)	$ (63,035)	$ (69,661)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.69)	$ (0.82)	$ (1.29)	$ (1.50)
Weighted-average common shares outstanding, basic and diluted	49,070,574	46,952,059	48,955,043	46,474,685

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Condensed Consolidated Statements of Comprehensive Loss
Net Loss	$ (33,786)	$ (38,723)	$ (63,035)	$ (69,661)
Other comprehensive income (loss):
Unrealized gain (loss) on marketable debt securities	16	53	74	77
Comprehensive loss	$ (33,770)	$ (38,670)	$ (62,961)	$ (69,584)

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive (Loss) Income	Other Accumulated Deficit	Total
Balance, beginning of period at Dec. 31, 2017	$ 4	$ 514,002	$ (76)	$ (305,850)	$ 208,080
Balance, beginning 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 of $0.1 million		48,493			48,493
Issuance of common stock from public offering, net of issuance costs of $0.1 million (in shares)	1,429,205
Issuance of common stock for repayment of notes payable		9,530			9,530
Issuance of common stock for repayment of notes payable (in shares)	305,909
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		4,328			4,328
Exercise of stock options (in shares)	305,408
Vesting of restricted common stock units and awards		652			652
Vesting of restricted common stock units and awards (in shares)	107,114
Stock-based compensation expense		5,878			5,878
Unrealized gain on marketable securities			24		24
Net loss				(30,939)	(30,939)
Balance, end of period at Mar. 31, 2018	$ 4	584,825	(52)	(337,263)	247,514
Balance, end of period (in shares) at Mar. 31, 2018	46,711,695
Balance, beginning of period at Dec. 31, 2017	$ 4	514,002	(76)	(305,850)	208,080
Balance, beginning of period (in shares) at Dec. 31, 2017	44,507,960
Statement of Stockholders' Equity (Deficit)
Net loss					(69,661)
Balance, end of period at Jun. 30, 2018	$ 5	607,310	1	(375,986)	231,330
Balance, end of period (in shares) at Jun. 30, 2018	47,352,753
Statement of Stockholders' Equity (Deficit)
Cumulative effect adjustment for adoption of new accounting guidance				(474)	(474)
Balance, beginning of period at Mar. 31, 2018	$ 4	584,825	(52)	(337,263)	247,514
Balance, beginning of period (in shares) at Mar. 31, 2018	46,711,695
Statement of Stockholders' Equity (Deficit)
Issuance of common stock for repayment of notes payable	$ 1	12,500			12,501
Issuance of common stock for repayment of notes payable (in shares)	330,617
Exercise of stock options		2,597			2,597
Exercise of stock options (in shares)	192,687
Vesting of restricted common stock units and awards		677			677
Vesting of restricted common stock units and awards (in shares)	103,481
Purchase of common stock under benefit plan		362			362
Purchase of common stock under benefit plan (in shares)	14,273
Stock-based compensation expense		6,349			6,349
Unrealized gain on marketable securities			53		53
Net loss				(38,723)	(38,723)
Balance, end of period at Jun. 30, 2018	$ 5	607,310	1	(375,986)	231,330
Balance, end of period (in shares) at Jun. 30, 2018	47,352,753
Balance, beginning of period at Dec. 31, 2018	$ 5	652,464	(29)	(416,278)	236,162
Balance, beginning of period (in shares) at Dec. 31, 2018	48,758,951
Statement of Stockholders' Equity (Deficit)
Exercise of stock options		1,533			1,533
Exercise of stock options (in shares)	146,171
Vesting of restricted common stock units and awards		410			410
Vesting of restricted common stock units and awards (in shares)	18,000
Stock-based compensation expense		7,445			7,445
Unrealized gain on marketable securities			58		58
Net loss				(29,249)	(29,249)
Balance, end of period at Mar. 31, 2019	$ 5	661,852	29	(444,724)	217,162
Balance, end of period (in shares) at Mar. 31, 2019	48,923,122
Balance, beginning of period at Dec. 31, 2018	$ 5	652,464	(29)	(416,278)	$ 236,162
Balance, beginning of period (in shares) at Dec. 31, 2018	48,758,951
Statement of Stockholders' Equity (Deficit)
Exercise of stock options (in shares)					423,430
Net loss					$ (63,035)
Balance, end of period at Jun. 30, 2019	$ 5	671,522	45	(478,510)	193,062
Balance, end of period (in shares) at Jun. 30, 2019	49,241,093
Statement of Stockholders' Equity (Deficit)
Cumulative effect adjustment for adoption of new accounting guidance				803	803
Balance, beginning of period at Mar. 31, 2019	$ 5	661,852	29	(444,724)	217,162
Balance, beginning of period (in shares) at Mar. 31, 2019	48,923,122
Statement of Stockholders' Equity (Deficit)
Exercise of stock options		2,894			2,894
Exercise of stock options (in shares)	277,259
Vesting of restricted common stock units and awards		410			410
Vesting of restricted common stock units and awards (in shares)	24,486
Purchase of common stock under benefit plan		283			283
Purchase of common stock under benefit plan (in shares)	16,226
Stock-based compensation expense		6,083			6,083
Unrealized gain on marketable securities			16		16
Net loss				(33,786)	(33,786)
Balance, end of period at Jun. 30, 2019	$ 5	$ 671,522	$ 45	$ (478,510)	$ 193,062
Balance, end of period (in shares) at Jun. 30, 2019	49,241,093

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Parenthetical) $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)
Initial Public Offering
Stock issuance costs	$ 0.1

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flow from operating activities
Net loss	$ (63,035)	$ (69,661)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	14,348	13,552
Depreciation	1,321	1,535
Non-cash research and development expense		14,442
Non-cash investment in equity securities		(3,667)
Other non-cash items, net	(1,959)	(1,098)
Changes in operating assets and liabilities:
Accounts receivable	18	317
Prepaid expenses and other current assets	301	(1,414)
Right-of-use asset	1,984
Other non-current assets		(92)
Accounts payable	(1,459)	984
Accrued expenses	(4,627)	2,032
Deferred revenue	621	3,877
Operating lease liability	(2,325)
Other current and non-current liabilities	3
Net cash used in operating activities	(54,809)	(39,193)
Cash flow from investing activities
Purchases of property and equipment	(2,231)	(2,401)
Proceeds from the sale of equipment	36	5
Purchases of marketable securities	(106,569)	(224,465)
Proceeds from maturities of marketable securities	235,500	196,000
Net cash provided by investing activities	126,736	(30,861)
Cash flow from financing activities
Proceeds from offering of common stock, net of issuance costs		48,471
Proceeds from exercise of stock options	3,619	6,925
Issuances of common stock under benefit plans	283	362
Payments on construction financing lease obligation		(410)
Net cash provided by financing activities	3,902	55,348
Net increase in cash and cash equivalents	75,829	(14,706)
Cash, cash equivalents and restricted cash, beginning of period	136,395	148,249
Cash, cash equivalents and restricted cash, end of period	212,224	133,543
Supplemental disclosure of cash and non-cash activities:
Fixed asset additions included in accounts payable and accrued expenses	96	371
Receivable of proceeds from exercise of stock options	808
Cash paid in connection with operating lease liabilities	3,089
Right-of-use assets obtained in exchange of operating lease obligations	$ 19,461
Reclassification of liability for common stock subject to repurchase		4
Issuance of common stock for settlement of success payments (see note 7)		22,030
Issuance of common stock for asset acquisition		1,942
Adjustment to deferred revenue for revenue adoption		474
Offering costs included in accounts payable and accrued expenses		$ 22

Nature of Business

Nature of Business	6 Months Ended
	Jun. 30, 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, Inc., a Celgene company that is a wholly-owned subsidiary of Celgene Corporation (“Juno Therapeutics”), and payments received under a strategic alliance and option agreement with Allergan Pharmaceuticals International Limited (“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 June 30, 2019, the Company has raised an aggregate of $328.3 million in net proceeds through the sale of shares of its common stock in public offerings. 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 June 30, 2019 and anticipated interest income will enable it to fund its operating expenses and capital expenditure requirements for at least the next 24 months following the date of this Quarterly Report on Form 10-Q. The Company had an accumulated deficit of $478.5 million at June 30, 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	6 Months Ended
	Jun. 30, 2019
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies ​ Unaudited Interim Financial Information ​ The condensed consolidated financial statements of the Company included herein have been prepared, without audit, pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”). Certain information and footnote disclosures normally included in financial statements prepared in accordance with generally accepted accounting principles in the United States of America (“GAAP”) have been condensed or omitted from this report, as is permitted by such rules and regulations. Accordingly, these condensed consolidated financial statements should be read in conjunction with the financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2018 (the “Annual Report”). ​ The unaudited condensed consolidated financial statements include the accounts of Editas Medicine, Inc. and its wholly owned subsidiary, Editas Securities Corporation. All intercompany transactions and balances of the subsidiary have been eliminated in consolidation. In the opinion of management, the information furnished reflects all adjustments, all of which are of a normal and recurring nature, necessary for a fair presentation of the results for the reported interim periods. The Company considers events or transactions that occur after the balance sheet date but before the financial statements are issued to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure. The three months ended June 30, 2019 and 2018 are referred to as the second quarter of 2019 and 2018, respectively. The results of operations for interim periods are not necessarily indicative of results to be expected for the full year or any other interim period. ​ Summary of Significant Accounting Policies ​ The Company’s significant accounting policies are described in Note 2, “Summary of significant accounting policies,” to the consolidated financial statements included in the Annual Report. There have been no material changes to the significant accounting policies previously disclosed in the Annual Report other than as noted below. ​ Recent Accounting Pronouncements –Adopted ​ Leases ​ Effective January 1, 2019, the Company adopted Accounting Standards Update (“ASU”) No. 2016-02, Leases ​ 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. The Company elected the modified-retrospective transition method, 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 Accounting Standards Codification (“ASC”) 840, Leases which allows the Company to reassess the lease term as it was not relevant to the Company’s leases. As of June 30, 2019, the Company had only operating leases and has recorded the $17.5 million asset balance and $17.4 million liability balance in right-of-use assets and operating lease liabilities, respectively, in the condensed consolidated balance sheet as of June 30, 2019. The Company has finalized changes to its controls to support lease accounting and related disclosures under the new standard. Stock-Based Compensation Effective January 1, 2019, the Company adopted ASU No. 2018-07, Compensation – Stock Compensation: Improvements to Nonemployee Share-Based Payment Accounting Compensation – Stock Compensation Equity-Based Payments to Non-Employees ​ Recent Accounting Pronouncements – Issued But Not Yet Adopted ​ 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 (Topic 326): Measurement of Credit Losses on Financial Instruments

Cash Equivalents, Marketable Se

Cash Equivalents, Marketable Securities and Equity Securities	6 Months Ended
	Jun. 30, 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 June 30, 2019 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross ​ Gross ​ ​ ​ ​ Amortized ​ Unrealized ​ Unrealized ​ Fair June 30, 2019 ​ Cost ​ Gains ​ Losses ​ Value Cash equivalents and marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 210,605 ​ $ — ​ $ — ​ $ 210,605 U.S. Treasuries ​ ​ 59,851 ​ ​ 20 ​ ​ — ​ ​ 59,871 Government agency securities ​ ​ 47,429 ​ ​ 25 ​ ​ — ​ ​ 47,454 Equity securities included in other non-current assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Corporate equity securities ​ ​ 3,667 ​ ​ — ​ ​ — ​ ​ 3,667 Total ​ $ 321,552 ​ $ 45 ​ $ — ​ $ 321,597 ​ 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 ​ $ 372,410 ​ $ — ​ $ (29) ​ $ 372,381 ​ At June 30, 2019, the Company held two 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 June 30, 2019 was $9.0 million, and there were no securities held by the Company in an unrealized loss position for more than 12 months. Pursuant to the adoption of ASU No. 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities , the Company records changes in the fair value of its investments in corporate equity securities to “Other (expense) income, net” in the Company’s condensed consolidated statements of operations. The Company records unrealized gains (losses) on available-for-sale debt securities as a component of accumulated other comprehensive income (loss) until such gains and losses are realized. ​ As of June 30, 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 marketable securities with any other-than-temporary impairment as of June 30, 2019. ​ There were no realized gains or losses on available-for-sale securities during the six months ended June 30, 2019 or 2018.

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2019
Fair Value Measurements
Fair Value Measurements	4. Fair Value Measurements ​ Assets measured at fair value on a recurring basis as of June 30, 2019 were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Quoted Prices Significant ​ ​ ​ ​ ​ ​ ​ in Active ​ Other ​ Significant ​ ​ ​ ​ ​ Markets for ​ Observable ​ Unobservable ​ ​ June 30, ​ Identical Assets ​ Inputs ​ Inputs Financial Assets ​ 2019 ​ (Level 1) ​ (Level 2) ​ (Level 3) Cash equivalents: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 210,605 ​ $ 210,605 ​ $ — ​ $ — Marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Treasuries ​ ​ 59,871 ​ ​ 59,871 ​ ​ — ​ ​ — Government agency securities ​ ​ 47,454 ​ ​ 47,454 ​ ​ — ​ ​ — Restricted cash and other non-current assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Corporate equity securities ​ ​ 3,667 ​ ​ — ​ ​ 3,667 ​ ​ — Money market funds ​ ​ 1,619 ​ ​ 1,619 ​ ​ — ​ ​ — Total financial assets ​ $ 323,216 ​ $ 319,549 ​ $ 3,667 ​ $ — ​ Assets 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 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 six months ended June 30, 2019.

Accrued Expenses

Accrued Expenses	6 Months Ended
	Jun. 30, 2019
Accrued Expenses
Accrued Expenses	5. Accrued Expenses ​ Accrued expenses consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ As of ​ ​ June 30, ​ December 31, ​ 2019 2018 Intellectual property and patent related fees ​ $ 2,952 ​ $ 1,939 Employee related expenses ​ ​ 2,727 ​ ​ 5,201 Professional service expenses ​ ​ 1,026 ​ ​ 475 Process and platform development expenses ​ ​ 700 ​ ​ 1,044 Sublicensing and success payment expenses ​ ​ 412 ​ ​ 3,750 Other expenses ​ 352 ​ 404 Total accrued expenses ​ $ 8,169 ​ $ 12,813 ​

Property and Equipment, net

Property and Equipment, net	6 Months Ended
	Jun. 30, 2019
Property and Equipment, net
Property and Equipment, net	6. Property and Equipment, net ​ Property and equipment, net consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ As of ​ ​ June 30, ​ December 31, ​ 2019 2018 Laboratory equipment ​ $ 12,501 ​ $ 10,892 Computer equipment ​ ​ 733 ​ ​ 733 Construction-in-progress ​ ​ 456 ​ ​ — Leasehold improvements ​ 289 ​ 289 Furniture and office equipment ​ ​ 166 ​ ​ 166 Software ​ 118 ​ 118 Building ​ ​ — ​ ​ 35,167 Total property and equipment ​ 14,263 ​ 47,365 Less: accumulated depreciation ​ (5,733) ​ (7,133) Property and equipment, net ​ $ 8,530 ​ $ 40,232 ​

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2019
Commitments and Contingencies
Commitments and Contingencies	7. Commitments and Contingencies ​ Leases ​ 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. The Company has the option to extend the lease for an additional five-year term at market-based rates. The base rent payments commenced in November 2016 and continue through the term of the lease and are subject to increases over the term of the lease. 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. ​ . ​ ​ ​ ​ ​ ​ 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 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of ​ June 30, ​ January 1, ​ 2019 2019 Right-of-use asset $ 17,477 ​ $ 19,461 Lease liability, current $ (3,648) ​ $ (3,848) Lease liability, noncurrent $ (13,784) ​ $ (15,909) ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended ​ June 30, 2019 Operating lease costs $ 1,421 ​ $ 2,842 Variable lease costs $ 261 ​ $ 528 Total lease costs $ 1,682 ​ $ 3,370 ​ ​ ​ ​ ​ ​ ​ Six Months Ended Maturity of lease liabilities: ​ June 30, 2019 2019 $ 2,293 2020 $ 5,620 2021 $ 4,761 2022 $ 4,470 2023 $ 3,802 Thereafter $ — Total minimum lease payments $ 20,946 Less: imputed interest $ (3,514) Total operating lease liabilities at June 30, 2019 $ 17,432 ​ The above table excludes $0.6 million of legally binding minimum lease payments for leases executed but not yet commenced as of June 30, 2019. Commencement occurred in July 2019. ​ ​ Licensor Expense Reimbursement ​ The Company is obligated to reimburse The Broad Institute, Inc. (“Broad”) and the President and Fellows of Harvard College (“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. During the three and six months ended June 30, 2019, the Company recognized $3.5 million and $6.9 million in expense for such reimbursement, respectively. During the three and six months ended June 30, 2018, the Company recognized $3.5 million and $8.0 million in expense for such reimbursement, respectively. ​ Success Payments ​ In 2016, the Company entered into patent license agreements with each of The General Hospital Corporation, d/b/a Massachusetts General Hospital (“MGH”), and Broad (collectively, the “2016 License Agreements”). Pursuant to the terms of the 2016 License Agreements, the Company is required to make certain success payments to MGH, Broad and Wageningen University (“Wageningen” and such payments, collectively, the “Success Payments”), payable in cash or, at the Company’s election, common stock in the case of MGH or, in the case of Broad and Wageningen, promissory notes payable in cash or, at the Company’s election subject to certain conditions, common stock of the Company. The Success Payments are payable, if and when, the Company’s market capitalization reaches specified thresholds for a specific period of time or upon a sale of the Company for consideration in excess of those thresholds (collectively, the “Payment Conditions”). ​ The Success Payments were historically accounted for under the provisions of ASC 505-50. Effective January 1, 2019, the Company adopted ASU 2018-07, which expands the scope of ASC 718 and superseded ASC 505-50. In accordance with ASC 718, the Company will recognize a Success Payment when it becomes probable that the Payment Conditions will be met. However, the Company has the right to terminate any of the 2016 License Agreements at will upon written notice. Absent any of the Payment Conditions being achieved prior to termination, the Company would not be obligated to pay any Success Payments. As such, the Company will recognize the expense and liability associated with each Success Payment when it is probable that the amounts will become due. The Company records this expense as a research and development expense in its condensed consolidated statements of operations. ​ Research Funding Payments ​ In June 2018, the Company entered into a sponsored research agreement (the “Sponsored Research Agreement”) with Broad. Pursuant to the terms of the Sponsored Research Agreement, the Company is required to make certain research funding payments to Broad, payable by promissory note, cash or common stock. Under the Sponsored Research Agreement, the Company is obligated to make payments of research funding to Broad 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 (“Market Cap Research Funding”) or a Company sale for consideration ranging from a mid-nine digit dollar amount to a low-eleven digit dollar amount (“Company Sale Research Funding” and, collectively with the Market Cap Research Funding, the “Research Funding Payments”). In connection with entering into the Sponsored Research Agreement, the Company confirmed that the first two Research Funding Payments of $5.0 million and $7.5 million were due and payable to Broad (the “Initial Research Payments”). ​ 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 developed under the Sponsored Research Agreement and exclusively licensed to the Company from Broad or based on or incorporating CRISPR technology owned, co-owned, or controlled by Broad and otherwise licensed to the Company, subject to certain exclusions. The Research Funding Payments were historically accounted for under the provisions of ASC Topic 505-50. Effective January 1, 2019, the Company adopted ASU 2018-07, which expands the scope of ASC 718 and superseded ASC 505-50. Under ASC 718, the Company will recognize the expenses and liability associated with each Research Funding Payment when it is probable that the amounts will become due. The Company records this expense as a research and development expense in its statements of operations. ​ In June 2018, in connection with the Company’s entry into the Sponsored Research Agreement and the trigger of the Initial Research Payments, the Company issued promissory notes in an aggregate principal amount of $12.5 million to Broad (the “Initial Research Notes”) bearing interest at a rate of 4.8% per annum, except with respect to $7.5 million of the principal, which would not start accruing interest until November 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. ​ Litigation ​ The Company is not a party to any litigation and did not have contingency reserves established for any litigation liabilities as of June 30, 2019 or December 31, 2018.

Collaboration and License Agree

Collaboration and License Agreements	6 Months Ended
	Jun. 30, 2019
Collaboration and License Agreements
Collaboration and License Agreements	8. Collaboration and License Agreements ​ ​ Collaboration Revenue ​ As of June 30, 2019, the Company’s contract liabilities were primarily related to the Company’s collaboration with Juno Therapeutics and strategic alliance with Allergan. The following table presents changes in the Company’s accounts receivable and contract liabilities for the six months ended June 30, 2019 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the six months ended June 30, 2019 Balance at December 31, 2018 ​ Additions ​ Deductions ​ Balance at June 30, 2019 Accounts receivable $ 30 ​ $ 12 ​ $ (30) ​ $ 12 Contract liabilities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Deferred revenue $ 131,326 ​ $ 5,000 ​ $ (4,379) ​ $ 131,947 ​ During the three and six months ended June 30, 2019, the Company recognized the following collaboration revenue (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended Revenue recognized in the period from: June 30, 2019 Amounts included in deferred revenue at the beginning of the period $ 2,318 ​ $ 4,379 Performance obligations satisfied in previous periods $ — ​ $ — ​ Juno Therapeutics Collaboration Agreement ​ In May 2015, the Company entered into a Collaboration and License Agreement with Juno Therapeutics and in May 2018 the Company and Juno Therapeutics entered into an Amended and Restated Collaboration and License Agreement (collectively, the “Juno Agreement”). ​ ​ ​ Allergan Pharmaceuticals Strategic Alliance and Option Agreement 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”). development and commercialization licenses are 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. In August 2018, Allergan exercised its right to the LCA10 Program and the option fee was recognized as revenue during the three months ended September 30, 2018 when the control transferred to Allergan. ​ During the three and six months ended June 30, 2019, the Company recognized revenue related to the Allergan Agreement of approximately $2.3 million and $4.3 million, respectively. During the three and six months ended June 30, 2018, the Company recognized revenue related to the Allergan Agreement of approximately $2.9 million. As of June 30, 2019 and December 31, 2018, there was $94.9 million and $99.2 million of deferred revenue related to the Allergan Agreement, respectively, of which $72.4 million and $86.4 million is classified as long-term on the condensed consolidated balance sheet, respectively. There were no amounts classified in accounts receivable on the condensed balance sheets related to the Allergan Agreement. ​ The Company and an affiliate of Allergan (together with Allergan, the “Allergan Entities”) agreed to equally split U.S. profits and losses for the LCA10 Program in the United States and to co-develop the LCA10 Program in the United States (the “Profit-Sharing Agreement”). The Company accounts for the Profit-Sharing Arrangement with respect to the LCA10 Program within the scope of ASC Topic 808, Collaborative Arrangements

Stock-based Compensation

Stock-based Compensation	6 Months Ended
	Jun. 30, 2019
Stock-based Compensation
Stock-based Compensation	9 Stock-based Compensation ​ Stock-based compensation expense by classification included in the condensed consolidated statements of operations and comprehensive loss was as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended ​ ​ ​ June 30, ​ June 30, ​ ​ ​ 2019 ​ 2018 2019 2018 Research and development ​ $ 3,853 ​ $ 3,996 ​ $ 7,235 ​ $ 7,906 ​ General and administrative ​ 2,640 ​ 3,028 ​ 7,113 ​ 5,646 ​ Total stock-based compensation expense ​ $ 6,493 ​ $ 7,024 ​ $ 14,348 ​ $ 13,552 ​ ​ Restricted Stock and Restricted Stock Unit Awards ​ Restricted stock awards are subject to repurchase rights. Accordingly, the Company has recorded the proceeds from the issuance of restricted stock awards as a liability in its condensed consolidated balance sheets. The restricted stock liability is reclassified into stockholders’ equity as the restricted stock vests. ​ The following table summarizes restricted stock and restricted stock unit awards activity as of December 31, 2018 and June 30, 2019: ​ ​ ​ ​ ​ ​ ​ ​ ​ 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 400,722 ​ $ 21.52 Vested (42,486) ​ $ 27.09 Forfeited ​ (36,763) ​ $ 21.33 Unvested restricted stock and restricted stock unit awards as of June 30, 2019 591,473 ​ $ 24.11 ​ As of June 30, 2019, the Company had $10.7 million in unrecognized stock-based compensation expense related to unvested restricted stock and unvested restricted stock unit awards. ​ Stock Options ​ The following is a summary of stock option activity for the six months ended June 30, 2019: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted Average Remaining Aggregate Intrinsic ​ ​ Shares ​ Exercise Price ​ Contractual Life (years) ​ Value (in thousands) Outstanding at December 31, 2018 4,689,786 ​ $ 23.80 ​ 7.9 ​ $ 20,686 Granted ​ 653,707 ​ $ 21.55 ​ ​ ​ ​ ​ Exercised ​ (423,430) ​ $ 10.46 ​ ​ ​ ​ ​ Cancelled ​ (467,185) ​ $ 27.84 ​ ​ ​ ​ ​ Outstanding at June 30, 2019 4,452,878 ​ $ 24.31 ​ 7.8 ​ $ 19,365 Exercisable at June 30, 2019 2,220,677 ​ $ 21.21 ​ 6.9 ​ $ 15,108 ​ As of June 30, 2019, the Company had unrecognized stock-based compensation expense related to its employee and director stock options of $32.9 million, which the Company expects to recognize over the remaining weighted average vesting period of 2.41 years. As of June 30, 2019, the Company had unrecognized stock-based compensation expense related to its non-employee stock options of $1.1 million, which the Company expects to recognize over the remaining weighted average vesting period of 0.74 years.

Net Loss per Share

Net Loss per Share	6 Months Ended
	Jun. 30, 2019
Net Loss per Share
Net Loss per Share	10. Net Loss per Share ​ Basic net loss per common share is calculated by dividing the net loss attributable to common stockholders by the weighted by the weighted average number of common shares 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. ​ In connection with at-the-market offerings consummated by the Company during 2018, the Company sold 2,536,205 shares of its common stock. The issuance of these shares resulted in a significant increase in the Company’s weighted-average shares outstanding and is expected to continue to impact the year-over-year comparability of the Company’s net loss per share calculations for the remainder of 2019. ​ 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 June 30, ​ ​ 2019 2018 Unvested restricted stock and restricted stock unit awards ​ 591,473 306,000 Outstanding stock options ​ 4,452,878 5,101,679 Total ​ 5,044,351 5,407,679 ​

Related-Party Transactions

Related-Party Transactions	6 Months Ended
	Jun. 30, 2019
Related-Party Transactions
Related-Party Transactions	11. Related-Party Transactions ​ The Company received $0.4 million in rent and facility-related fees from a related party during the six months ended June 30, 2018 in connection with the Company’s Hurley Street sublease and no rent or facility-related payments were received from this related party during the six months ended June 30, 2019. ​

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2019
Subsequent Events
Subsequent Events	12. Subsequent Events ​ On August 6, 2019, the Company’s Board of Directors appointed Cynthia Collins as President and Chief Executive Officer of the Company, effective August 19, 2019. Ms. Collins previously served as the Company’s interim President and Chief Executive Officer under a consulting agreement. The Company will grant stock options with both time-based and performance-based vesting and a restricted stock unit award subject to time-based vesting pursuant to the terms of the offer letter entered into by the Company and Ms. Collins. ​

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2019
Summary of Significant Accounting Policies
Unaudited Interim Financial Information	Unaudited Interim Financial Information ​ The condensed consolidated financial statements of the Company included herein have been prepared, without audit, pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”). Certain information and footnote disclosures normally included in financial statements prepared in accordance with generally accepted accounting principles in the United States of America (“GAAP”) have been condensed or omitted from this report, as is permitted by such rules and regulations. Accordingly, these condensed consolidated financial statements should be read in conjunction with the financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2018 (the “Annual Report”). ​ The unaudited condensed consolidated financial statements include the accounts of Editas Medicine, Inc. and its wholly owned subsidiary, Editas Securities Corporation. All intercompany transactions and balances of the subsidiary have been eliminated in consolidation. In the opinion of management, the information furnished reflects all adjustments, all of which are of a normal and recurring nature, necessary for a fair presentation of the results for the reported interim periods. The Company considers events or transactions that occur after the balance sheet date but before the financial statements are issued to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure. The three months ended June 30, 2019 and 2018 are referred to as the second quarter of 2019 and 2018, respectively. The results of operations for interim periods are not necessarily indicative of results to be expected for the full year or any other interim period.
Recent Accounting Pronouncements Adopted And Issued But Not Yet Adopted	Recent Accounting Pronouncements –Adopted ​ Leases ​ Effective January 1, 2019, the Company adopted Accounting Standards Update (“ASU”) No. 2016-02, Leases ​ 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. The Company elected the modified-retrospective transition method, 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 Accounting Standards Codification (“ASC”) 840, Leases which allows the Company to reassess the lease term as it was not relevant to the Company’s leases. As of June 30, 2019, the Company had only operating leases and has recorded the $17.5 million asset balance and $17.4 million liability balance in right-of-use assets and operating lease liabilities, respectively, in the condensed consolidated balance sheet as of June 30, 2019. The Company has finalized changes to its controls to support lease accounting and related disclosures under the new standard. Stock-Based Compensation Effective January 1, 2019, the Company adopted ASU No. 2018-07, Compensation – Stock Compensation: Improvements to Nonemployee Share-Based Payment Accounting Compensation – Stock Compensation Equity-Based Payments to Non-Employees ​ Recent Accounting Pronouncements – Issued But Not Yet Adopted ​ 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 (Topic 326): Measurement of Credit Losses on Financial Instruments

Cash Equivalents, Marketable _2

Cash Equivalents, Marketable Securities and Corporate Equity Securities (Tables)	6 Months Ended
	Jun. 30, 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 June 30, 2019 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross ​ Gross ​ ​ ​ ​ Amortized ​ Unrealized ​ Unrealized ​ Fair June 30, 2019 ​ Cost ​ Gains ​ Losses ​ Value Cash equivalents and marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 210,605 ​ $ — ​ $ — ​ $ 210,605 U.S. Treasuries ​ ​ 59,851 ​ ​ 20 ​ ​ — ​ ​ 59,871 Government agency securities ​ ​ 47,429 ​ ​ 25 ​ ​ — ​ ​ 47,454 Equity securities included in other non-current assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Corporate equity securities ​ ​ 3,667 ​ ​ — ​ ​ — ​ ​ 3,667 Total ​ $ 321,552 ​ $ 45 ​ $ — ​ $ 321,597 ​ 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 ​ $ 372,410 ​ $ — ​ $ (29) ​ $ 372,381

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 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 June 30, 2019 were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Quoted Prices Significant ​ ​ ​ ​ ​ ​ ​ in Active ​ Other ​ Significant ​ ​ ​ ​ ​ Markets for ​ Observable ​ Unobservable ​ ​ June 30, ​ Identical Assets ​ Inputs ​ Inputs Financial Assets ​ 2019 ​ (Level 1) ​ (Level 2) ​ (Level 3) Cash equivalents: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 210,605 ​ $ 210,605 ​ $ — ​ $ — Marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Treasuries ​ ​ 59,871 ​ ​ 59,871 ​ ​ — ​ ​ — Government agency securities ​ ​ 47,454 ​ ​ 47,454 ​ ​ — ​ ​ — Restricted cash and other non-current assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Corporate equity securities ​ ​ 3,667 ​ ​ — ​ ​ 3,667 ​ ​ — Money market funds ​ ​ 1,619 ​ ​ 1,619 ​ ​ — ​ ​ — Total financial assets ​ $ 323,216 ​ $ 319,549 ​ $ 3,667 ​ $ — ​ Assets 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 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 ​ $ —

Accrued Expenses (Tables)

Accrued Expenses (Tables)	6 Months Ended
	Jun. 30, 2019
Accrued Expenses
Schedule of accrued expenses	Accrued expenses consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ As of ​ ​ June 30, ​ December 31, ​ 2019 2018 Intellectual property and patent related fees ​ $ 2,952 ​ $ 1,939 Employee related expenses ​ ​ 2,727 ​ ​ 5,201 Professional service expenses ​ ​ 1,026 ​ ​ 475 Process and platform development expenses ​ ​ 700 ​ ​ 1,044 Sublicensing and success payment expenses ​ ​ 412 ​ ​ 3,750 Other expenses ​ 352 ​ 404 Total accrued expenses ​ $ 8,169 ​ $ 12,813 ​

Property and Equipment, net (Ta

Property and Equipment, net (Tables)	6 Months Ended
	Jun. 30, 2019
Property and Equipment, net
Schedule of property and equipment, net	Property and equipment, net consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ As of ​ ​ June 30, ​ December 31, ​ 2019 2018 Laboratory equipment ​ $ 12,501 ​ $ 10,892 Computer equipment ​ ​ 733 ​ ​ 733 Construction-in-progress ​ ​ 456 ​ ​ — Leasehold improvements ​ 289 ​ 289 Furniture and office equipment ​ ​ 166 ​ ​ 166 Software ​ 118 ​ 118 Building ​ ​ — ​ ​ 35,167 Total property and equipment ​ 14,263 ​ 47,365 Less: accumulated depreciation ​ (5,733) ​ (7,133) Property and equipment, net ​ $ 8,530 ​ $ 40,232 ​

Commitments and Contingencies (

Commitments and Contingencies (Tables)	6 Months Ended
	Jun. 30, 2019
Commitments and Contingencies
Summary of derecognition of balances relating to the building, accumulated depreciation and the corresponding construction financing lease on adoption of ASC 842	​ ​ ​ ​ ​ 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
Summary of leases included on its condensed consolidated balance sheet	The Company’s leases are included on its condensed consolidated balance sheet as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ As of ​ June 30, ​ January 1, ​ 2019 2019 Right-of-use asset $ 17,477 ​ $ 19,461 Lease liability, current $ (3,648) ​ $ (3,848) Lease liability, noncurrent $ (13,784) ​ $ (15,909)
Summary of the operating lease costs	The following table contains a summary of the operating lease costs recognized under ASC 842 and other information pertaining to the Company’s operating leases during the three and six months ended June 30, 2019 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended ​ June 30, 2019 Operating lease costs $ 1,421 ​ $ 2,842 Variable lease costs $ 261 ​ $ 528 Total lease costs $ 1,682 ​ $ 3,370
Summary of maturities of lease liabilities	Maturities of the Company’s lease liabilities in accordance with ASC 842 as of June 30, 2019 were as follows (in thousands): ​ ​ ​ ​ ​ ​ Six Months Ended Maturity of lease liabilities: ​ June 30, 2019 2019 $ 2,293 2020 $ 5,620 2021 $ 4,761 2022 $ 4,470 2023 $ 3,802 Thereafter $ — Total minimum lease payments $ 20,946 Less: imputed interest $ (3,514) Total operating lease liabilities at June 30, 2019 $ 17,432

Collaboration and License Agr_2

Collaboration and License Agreements (Tables)	6 Months Ended
	Jun. 30, 2019
Collaboration and License Agreements
Schedule of accounts receivable and contract liabilities	The following table presents changes in the Company’s accounts receivable and contract liabilities for the six months ended June 30, 2019 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the six months ended June 30, 2019 Balance at December 31, 2018 ​ Additions ​ Deductions ​ Balance at June 30, 2019 Accounts receivable $ 30 ​ $ 12 ​ $ (30) ​ $ 12 Contract liabilities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Deferred revenue $ 131,326 ​ $ 5,000 ​ $ (4,379) ​ $ 131,947
Schedule of change in contract assets and contract liabilities	During the three and six months ended June 30, 2019, the Company recognized the following collaboration revenue (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended Revenue recognized in the period from: June 30, 2019 Amounts included in deferred revenue at the beginning of the period $ 2,318 ​ $ 4,379 Performance obligations satisfied in previous periods $ — ​ $ —

Stock-based Compensation (Table

Stock-based Compensation (Tables)	6 Months Ended
	Jun. 30, 2019
Stock-based Compensation
Schedule of stock-based compensation expense	Stock-based compensation expense by classification included in the condensed consolidated statements of operations and comprehensive loss was as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended ​ ​ ​ June 30, ​ June 30, ​ ​ ​ 2019 ​ 2018 2019 2018 Research and development ​ $ 3,853 ​ $ 3,996 ​ $ 7,235 ​ $ 7,906 ​ General and administrative ​ 2,640 ​ 3,028 ​ 7,113 ​ 5,646 ​ Total stock-based compensation expense ​ $ 6,493 ​ $ 7,024 ​ $ 14,348 ​ $ 13,552 ​ ​
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 400,722 ​ $ 21.52 Vested (42,486) ​ $ 27.09 Forfeited ​ (36,763) ​ $ 21.33 Unvested restricted stock and restricted stock unit awards as of June 30, 2019 591,473 ​ $ 24.11
Schedule of stock option activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted Average Remaining Aggregate Intrinsic ​ ​ Shares ​ Exercise Price ​ Contractual Life (years) ​ Value (in thousands) Outstanding at December 31, 2018 4,689,786 ​ $ 23.80 ​ 7.9 ​ $ 20,686 Granted ​ 653,707 ​ $ 21.55 ​ ​ ​ ​ ​ Exercised ​ (423,430) ​ $ 10.46 ​ ​ ​ ​ ​ Cancelled ​ (467,185) ​ $ 27.84 ​ ​ ​ ​ ​ Outstanding at June 30, 2019 4,452,878 ​ $ 24.31 ​ 7.8 ​ $ 19,365 Exercisable at June 30, 2019 2,220,677 ​ $ 21.21 ​ 6.9 ​ $ 15,108

Net Loss per Share (Tables)

Net Loss per Share (Tables)	6 Months Ended
	Jun. 30, 2019
Net Loss per Share
Schedule of anti-dilutive common stock equivalents	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 June 30, ​ ​ 2019 2018 Unvested restricted stock and restricted stock unit awards ​ 591,473 306,000 Outstanding stock options ​ 4,452,878 5,101,679 Total ​ 5,044,351 5,407,679 ​

Nature of Business (Details)

Nature of Business (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Liquidity
Accumulated deficit	$ 478,510	$ 416,278
Public and Market Offering
Liquidity
Aggregate net proceeds	$ 328,300

Summary Of Significant Accoun_3

Summary Of Significant Accounting Policies - Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Mar. 31, 2018
Recent Accounting Pronouncements
Cumulative effect adjustment for adoption of new accounting guidance		$ 803			$ (474)
Total assets	$ 355,625			$ 420,386
Total liabilities	162,563			$ 184,224
Right-of-use asset	17,477		$ 19,461
Lease liability	$ 17,432
Lease, Practical Expedients, Package	true
Lease, Practical Expedient, Use of Hindsight	false
Other 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 asset			19,500
Lease liability			19,700
ASU 2016-02 | Restatement Adjustment | Other 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	6 Months Ended		12 Months Ended
	Jun. 30, 2019USD ($)item	Jun. 30, 2018USD ($)	Dec. 31, 2018USD ($)
Cash Equivalents, Marketable Securities and Equity Securities
Amortized Cost	$ 321,552		$ 372,410
Gross Unrealized Gains	45
Gross Unrealized Losses			(29)
Fair Value	$ 321,597		372,381
Number of securities in an unrealized loss position | item	2
Securities held by the Company in an unrealized loss position for less than 12 months	$ 9,000
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	210,605		130,049
Fair Value	210,605		130,049
U.S. Treasuries
Cash Equivalents, Marketable Securities and Corporate Equity Securities
Amortized Cost	59,851		208,754
Gross Unrealized Gains	20
Gross Unrealized Losses			(24)
Fair Value	59,871		208,730
Government agency securities
Cash Equivalents, Marketable Securities and Corporate Equity Securities
Amortized Cost	47,429		29,940
Gross Unrealized Gains	25
Gross Unrealized Losses			(5)
Fair Value	$ 47,454		$ 29,935

Fair Value Measurements - Recur

Fair Value Measurements - Recurring Basis (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2019USD ($)item	Dec. 31, 2018USD ($)
Financial Assets
Transfers between levels | item	0
Corporate equity securities
Financial Assets
Equity securities	$ 3,667	$ 3,667
Money market funds
Financial Assets
Marketable securities	210,605	130,049
U.S. Treasuries
Financial Assets
Marketable securities	59,871	208,730
Government agency securities
Financial Assets
Marketable securities	47,454	29,935
Recurring
Financial Assets
Total financial assets	323,216	374,000
Recurring | U.S. Treasuries
Financial Assets
Marketable securities	59,871	204,243
Recurring | Government agency securities
Financial Assets
Marketable securities	47,454	29,935
Recurring | Corporate equity securities
Financial Assets
Equity securities	3,667	3,667
Recurring | Money market funds
Financial Assets
Cash and cash equivalents	210,605	130,049
Restricted cash	1,619	1,619
Recurring | U.S. Treasuries
Financial Assets
Cash and cash equivalents		4,487
Recurring | Level 1
Financial Assets
Total financial assets	319,549	370,333
Recurring | Level 1 | U.S. Treasuries
Financial Assets
Marketable securities	59,871	204,243
Recurring | Level 1 | Government agency securities
Financial Assets
Marketable securities	47,454	29,935
Recurring | Level 1 | Money market funds
Financial Assets
Cash and cash equivalents	210,605	130,049
Restricted cash	1,619	1,619
Recurring | Level 1 | U.S. Treasuries
Financial Assets
Cash and cash equivalents		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	$ 3,667

Accrued Expenses (Details)

Accrued Expenses (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Accrued Expenses
Intellectual property and patent related fees	$ 2,952	$ 1,939
Employee related expenses	2,727	5,201
Professional service expenses	1,026	475
Process and platform development expenses	700	1,044
Other expenses	352	404
Sublicensing and success payment expenses	412	3,750
Total	$ 8,169	$ 12,813

Property and Equipment, net (De

Property and Equipment, net (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Property and equipment disclosures
Total property and equipment	$ 14,263	$ 47,365
Less: accumulated depreciation	(5,733)	(7,133)
Property and equipment, net	8,530	40,232
Laboratory equipment
Property and equipment disclosures
Total property and equipment	12,501	10,892
Computer equipment
Property and equipment disclosures
Total property and equipment	733	733
Construction-in-progress
Property and equipment disclosures
Total property and equipment	456
Leasehold improvements
Property and equipment disclosures
Total property and equipment	289	289
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

Commitments and Contingencies -

Commitments and Contingencies - Operating Leases (Details) - ft²	Oct. 01, 2016	Jun. 30, 2019	Feb. 28, 2017
Hurley Street Lease
Leases
Leased space ( in square feet)	59,783
Lessee, Operating Lease, Existence of Option to Extend [true false]		true
Extended lease option (in years)	5 years
Estimated useful life	30 years
Facility Sublease Arrangement
Leases
Leased space ( in square feet)			10,000

Commitments and Contingencies_2

Commitments and Contingencies - Derecognition of Balances (Details) $ in Thousands	Jan. 01, 2019USD ($)item	Jun. 30, 2019USD ($)	Dec. 31, 2018USD ($)
Lessee, Lease, Description [Line Items]
Property and equipment, net		$ 8,530	$ 40,232
Other current liabilities		1,033	2,048
Construction financing lease obligation, net of current portion			32,417
Accumulated deficit		$ (478,510)	$ (416,278)
Number of other operating leases for laboratory space | item	2
ASU 2016-02 | Restatement Adjustment
Lessee, Lease, Description [Line Items]
Property and equipment, net	$ 32,627
Other current liabilities	(1,014)
Construction financing lease obligation, net of current portion	(32,417)
Accumulated deficit	$ 803

Commitments and Contingencies_3

Commitments and Contingencies - Right of Use Asset and Lease Liability (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Jan. 01, 2019
Leases are included on its condensed consolidated balance sheet
Right-of-use asset	$ 17,477	$ 19,461
Lease liability, current	(3,648)	(3,848)
Lease liability, noncurrent	$ (13,784)	$ (15,909)

Commitments and Contingencies_4

Commitments and Contingencies - Operating Lease Costs (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Operating Lease Costs
Operating lease costs	$ 1,421	$ 2,842
Variable lease costs	261	528
Total lease costs	$ 1,682	$ 3,370

Commitments and Contingencies_5

Commitments and Contingencies - Maturities of Lease Liabilities (Details) $ in Thousands	Jun. 30, 2019USD ($)
Maturity of lease liabilities:
2019	$ 2,293
2020	5,620
2021	4,761
2022	4,470
2023	3,802
Total minimum lease payments	20,946
Less: imputed interest	(3,514)
Total operating lease liabilities at June 30, 2019	17,432
Legally binding minimum lease payments for leases executed but not yet commenced	$ 600
Weighted average remaining lease term	4 years
Weighted average discount rate	9.27%

Commitments and Contingencies_6

Commitments and Contingencies - Licensor Expense Reimbursement (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Licensor Expense Reimbursement
Commitments and contingencies
Expense for prosecution and maintenance of patent rights	$ 3.5	$ 3.5	$ 6.9	$ 8

Commitments and Contingencies_7

Commitments and Contingencies - Research Funding Payments (Details) - Research Funding Payments - Sponsored Research Agreement - Broad $ in Millions	Jun. 30, 2018USD ($)
Commitments and contingencies
First research funding amount due and payable	$ 5
Second research funding amount due and payable	$ 7.5

Commitments and Contingencies_8

Commitments and Contingencies - Notes Payable (Details) - Broad - Sponsored Research Agreement - USD ($) $ in Millions	1 Months Ended
	Jun. 30, 2018	Jun. 30, 2019
Notes Payable
Common stock issued	330,617
Initial Notes
Notes Payable
Promissory notes issued	$ 12.5
Interest rate (as a percentage)	4.80%
Interest free debt instrument		$ 7.5

Collaboration and License Agr_3

Collaboration and License Agreements - Revenue Recognition (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2019USD ($)
Accounts receivable
Accounts receivable, Balance at Beginning of Period	$ 30
Accounts Receivable, Additions	12
Accounts Receivable, Deductions	(30)
Accounts receivable, Balance at End of Period	12
Contract liabilities, deferred Revenue:
Deferred Revenue, Balance at Beginning of Period	131,326
Deferred revenue, Additions	5,000
Deferred revenue, Deductions	(4,379)
Deferred Revenue, Balance at End of Period	$ 131,947

Collaboration and License Agr_4

Collaboration and License Agreements - Contract Assets and Liability (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Change in contract asset and contract liability balances
Amounts included in deferred revenue at the beginning of the period	$ 2,318	$ 4,379

Collaboration and License Agr_5

Collaboration and License Agreements - Summary of Agreement (Details) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Mar. 31, 2017item	Jun. 30, 2019USD ($)	Jun. 30, 2018USD ($)	Jun. 30, 2019USD ($)item	Jun. 30, 2018USD ($)	Dec. 31, 2018USD ($)
Revenue recognized		$ 2,318		$ 4,379
Deferred revenue		131,947		131,947		$ 131,326
Deferred revenue, current		56,036		56,036		15,712
Deferred revenue, long-term		75,911		75,911		115,614
Accounts receivable		12		12		30
Collaboration and License Agreement | Juno Therapeutics
Revenue recognized			$ 3,500		$ 4,500
Deferred revenue		32,000		32,000		32,000
Deferred revenue, current		$ 32,000		$ 32,000		2,800
Strategic Alliance
Percentage of share of expenses recognized		50.00%		50.00%
Strategic Alliance | Allergan
Agreement term	7 years
Number of Collaboration Development Programs | item	5
Number of additional licenses | item				5
Revenue recognized		$ 2,300	$ 2,900	$ 4,300	$ 2,900
Deferred revenue		94,900		94,900		99,200
Deferred revenue, long-term		72,400		72,400		86,400
Accounts receivable		0		0		$ 0
Expenses incurred		$ 3,700		$ 9,000

Stock-based Compensation - Expe

Stock-based Compensation - Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Stock-based compensation disclosures
Compensation expense	$ 6,493	$ 7,024	$ 14,348	$ 13,552
Research and development
Stock-based compensation disclosures
Compensation expense	3,853	3,996	7,235	7,906
General and administrative
Stock-based compensation disclosures
Compensation expense	$ 2,640	$ 3,028	$ 7,113	$ 5,646

Stock-based Compensation - Rest

Stock-based Compensation - Restricted Stock and Stock Options (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Changes in unvested restricted stock
Unvested restricted shares, beginning of period (in shares)			270,000
Issued (in shares)			400,722
Vested (in shares)			(42,486)
Forfeited (in shares)			(36,763)
Unvested restricted shares, end of period(in shares)	591,473		591,473		270,000
Weighted Average Grant Date Fair Value
Balance, beginning of period			$ 28.05
Issued (in dollars per share)			21.52
Vested (in dollars per share)			27.09
Forfeited (in dollars per share)			21.33
Balance, ending of period	$ 24.11		$ 24.11		$ 28.05
Changes in unvested stock options
Compensation expense	$ 6,493	$ 7,024	$ 14,348	$ 13,552
Outstanding, beginning of period (in shares)			4,689,786
Granted (in shares)			653,707
Exercised (in shares)			(423,430)
Cancelled (in shares)			(467,185)
Outstanding, end of period (in shares)	4,452,878		4,452,878		4,689,786
Exercisable (in shares)	2,220,677		2,220,677
Outstanding, beginning of period (in dollars per share)			$ 23.80
Granted (in dollars per share)			21.55
Exercised (in dollars per share)			10.46
Cancelled (in dollars per share)			27.84
Outstanding, end of period (in dollars per share)	$ 24.31		24.31		$ 23.80
Exercisable (in dollar per share)	$ 21.21		$ 21.21
Remaining contractual life			7 years 9 months 18 days		7 years 10 months 24 days
Exercisable, remaining contractual life			6 years 10 months 24 days
Aggregate intrinsic value	$ 19,365		$ 19,365		$ 20,686
Exercisable, aggregated intrinsic value	15,108		$ 15,108
Employees and directors
Changes in unvested stock options
Period for recognition			2 years 4 months 28 days
Unrecognized stock-based compensation expense	32,900		$ 32,900
Non-employees
Changes in unvested stock options
Period for recognition			8 months 26 days
Unrecognized stock-based compensation expense	1,100		$ 1,100
Restricted Stock
Changes in unvested stock options
Unrecognized stock-based compensation expense	$ 10,700		$ 10,700

Net Loss per Share (Details)

Net Loss per Share (Details) - shares	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Potentially dilutive securities
Anti-dilutive common stock equivalent shares	5,044,351	5,407,679
Restricted Stock
Potentially dilutive securities
Anti-dilutive common stock equivalent shares	591,473	306,000
Outstanding stock options
Potentially dilutive securities
Anti-dilutive common stock equivalent shares	4,452,878	5,101,679
At Market Offering
Potentially dilutive securities
Number of common stock issued	2,536,205

Related-party Transactions (Det

Related-party Transactions (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Rent and facility related fees
Related Party Transaction [Line Items]
Fees received from related party	$ 0	$ 0.4