Achillion Pharmaceuticals 10-Q 7 Nov 19 2019 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2019	Nov. 01, 2019
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Entity Registrant Name	ACHILLION PHARMACEUTICALS INC
Entity Central Index Key	0001070336
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		140,046,647
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	false
Title of 12(b) Security	Common Stock, Par Value $0.001 per share
Trading Symbol	ACHN
Security Exchange Name	NASDAQ
Entity File Number	001-33095
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	52-2113479
Entity Address, Address Line One	1777 Sentry Parkway West
Entity Address, Address Line Two	Building 14, Suite 200
Entity Address, City or Town	Blue Bell
Entity Address, State or Province	PA
Entity Address, Postal Zip Code	19422
City Area Code	215
Local Phone Number	709-3040
Document Quarterly Report	true
Document Transition Report	false

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 43,567	$ 49,829
Marketable securities	110,121	221,148
Restricted cash	152
Accounts and other receivables	236	350
Prepaid expenses and other current assets	3,764	4,053
Total current assets	157,840	275,380
Marketable securities	75,274
Fixed assets, net	949	2,137
Operating lease right of use asset	2,265
Other assets	14	189
Restricted cash		152
Total assets	236,342	277,858
Current liabilities:
Accounts payable	3,144	2,335
Accrued expenses	13,710	9,363
Current portion of operating lease liability	754
Current portion of long-term debt		131
Total current liabilities	17,608	11,829
Long-term portion of operating lease liability	1,518
Other long-term liabilities		17
Total liabilities	19,126	11,846
Commitments and contingencies (Note 11)
Stockholders’ equity:
Common Stock, $0.001 par value; 300,000 and 200,000 shares authorized at September 30, 2019 and December 31, 2018, respectively; 139,891 and 138,716 shares issued and outstanding at September 30, 2019 and December 31, 2018, respectively	140	139
Additional paid-in capital	947,747	938,998
Accumulated deficit	(730,894)	(672,926)
Accumulated other comprehensive income (loss)	223	(199)
Total stockholders’ equity	217,216	266,012
Total liabilities and stockholders’ equity	$ 236,342	$ 277,858

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Common Stock, par value	$ 0.001	$ 0.001
Common Stock, shares authorized	300,000,000	200,000,000
Common Stock, shares issued	139,891,000	138,716,000
Common Stock, shares outstanding	139,891,000	138,716,000

Statements of Comprehensive Los

Statements of Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Operating expenses
Research and development	$ 14,993	$ 12,842	$ 45,744	$ 37,915
General and administrative	6,061	4,447	16,326	17,924
Restructuring charges (Note 4)	0	75	655	1,900
Total operating expenses	21,054	17,364	62,725	57,739
Loss from operations	(21,054)	(17,364)	(62,725)	(57,739)
Other income (expense)
Interest income	1,473	1,484	4,775	4,093
Interest expense	(2)	(4)	(18)	(25)
Net loss	$ (19,583)	$ (15,884)	$ (57,968)	$ (53,671)
Basic and diluted net loss per share (Note 5)	$ (0.14)	$ (0.12)	$ (0.42)	$ (0.39)
Total comprehensive loss (Note 9)	$ (19,653)	$ (15,673)	$ (57,546)	$ (53,490)
Weighted average number of shares used in computing basic and diluted net loss per share	139,589	138,586	139,025	138,344

Statements of Stockholders' Equ

Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Balances at Dec. 31, 2017	$ 324,515	$ 138	$ 927,420	$ (602,654)	$ (389)
Balances (in shares) at Dec. 31, 2017		137,894
Net loss	(20,588)			(20,588)
Other comprehensive income (loss)	(296)				(296)
Stock compensation	2,335		2,335
Issuance of common stock upon exercise of stock options	1,304		1,304
Issuance of common stock upon exercise of stock options (in shares)		446
Balances at Mar. 31, 2018	307,270	$ 138	931,059	(623,242)	(685)
Balances (in shares) at Mar. 31, 2018		138,340
Balances at Dec. 31, 2017	324,515	$ 138	927,420	(602,654)	(389)
Balances (in shares) at Dec. 31, 2017		137,894
Net loss	(53,671)
Balances at Sep. 30, 2018	280,506	$ 139	936,900	(656,325)	(208)
Balances (in shares) at Sep. 30, 2018		138,589
Balances at Mar. 31, 2018	307,270	$ 138	931,059	(623,242)	(685)
Balances (in shares) at Mar. 31, 2018		138,340
Net loss	(17,199)			(17,199)
Other comprehensive income (loss)	266				266
Stock compensation	3,550		3,550
Issuance of common stock upon exercise of stock options	570	$ 1	569
Issuance of common stock upon exercise of stock options (in shares)		206
Issuance of common stock under the employee stockpurchase plan	102		102
Issuance of common stock under the employee stock purchase plan (in shares)		40
Balances at Jun. 30, 2018	294,559	$ 139	935,280	(640,441)	(419)
Balances (in shares) at Jun. 30, 2018		138,586
Net loss	(15,884)			(15,884)
Other comprehensive income (loss)	211				211
Stock compensation	1,611		1,611
Issuance of common stock upon exercise of stock options	9		9
Issuance of common stock upon exercise of stock options (in shares)		3
Balances at Sep. 30, 2018	280,506	$ 139	936,900	(656,325)	(208)
Balances (in shares) at Sep. 30, 2018		138,589
Balances at Dec. 31, 2018	266,012	$ 139	938,998	(672,926)	(199)
Balances (in shares) at Dec. 31, 2018		138,716
Net loss	(18,959)			(18,959)
Other comprehensive income (loss)	320				320
Stock compensation	1,566		1,566
Balances at Mar. 31, 2019	248,939	$ 139	940,564	(691,885)	121
Balances (in shares) at Mar. 31, 2019		138,716
Balances at Dec. 31, 2018	266,012	$ 139	938,998	(672,926)	(199)
Balances (in shares) at Dec. 31, 2018		138,716
Net loss	$ (57,968)
Issuance of common stock upon exercise of stock options (in shares)	1,142
Balances at Sep. 30, 2019	$ 217,216	$ 140	947,747	(730,894)	223
Balances (in shares) at Sep. 30, 2019		139,891
Balances at Mar. 31, 2019	248,939	$ 139	940,564	(691,885)	121
Balances (in shares) at Mar. 31, 2019		138,716
Net loss	(19,426)			(19,426)
Other comprehensive income (loss)	172				172
Stock compensation	1,588		1,588
Issuance of common stock upon exercise of stock options	291		291
Issuance of common stock upon exercise of stock options (in shares)		103
Issuance of common stock under the employee stockpurchase plan	79		79
Issuance of common stock under the employee stock purchase plan (in shares)		32
Balances at Jun. 30, 2019	231,643	$ 139	942,522	(711,311)	293
Balances (in shares) at Jun. 30, 2019		138,851
Net loss	(19,583)			(19,583)
Other comprehensive income (loss)	(70)				(70)
Stock compensation	1,707		1,707
Issuance of common stock upon exercise of stock options	3,519	$ 1	3,518
Issuance of common stock upon exercise of stock options (in shares)		1,040
Balances at Sep. 30, 2019	$ 217,216	$ 140	$ 947,747	$ (730,894)	$ 223
Balances (in shares) at Sep. 30, 2019		139,891

Statements of Cash Flows

Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities
Net loss	$ (57,968)	$ (53,671)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	868	858
Non-cash stock-based compensation	4,861	7,496
Premium on purchases of marketable securities	(378)	(59)
Amortization of (discount) premium on marketable securities	(1,875)	(166)
Loss on disposal of fixed assets	381
Impairment of fixed assets	128
Changes in operating assets and liabilities:
Accounts and other receivables	114	(22)
Prepaid expenses and other assets	464	(477)
Accounts payable	815	(3,630)
Operating lease right-of-use asset	790
Operating lease liability	(783)
Accrued expenses	4,327	(590)
Other liabilities	(17)	(49)
Net cash used in operating activities	(48,273)	(50,310)
Cash flows from investing activities
Purchases of fixed assets	(177)	(468)
Purchases of marketable securities	(188,727)	(173,029)
Proceeds from sale of fixed assets	2
Maturities of marketable securities	227,155	214,749
Net cash provided by investing activities	38,253	41,252
Cash flows from financing activities
Proceeds from exercise of stock options	3,810	1,883
Proceeds from sale of common stock under Employee Stock Purchase Plan	79	102
Repayments of debt	(131)	(132)
Net cash provided by financing activities	3,758	1,853
Net decrease in cash and cash equivalents	(6,262)	(7,205)
Cash, cash equivalents and restricted cash, beginning of period	49,981	43,648
Cash, cash equivalents and restricted cash, end of period	43,719	36,443
Supplemental disclosure of cash flow information
Cash paid for interest	18	26
Supplemental disclosure of non-cash activities
Purchases of fixed assets in accounts payable and accrued expenses	11	$ 11
Operating lease right-of-use asset and liability (non-cash adoption balances)	1,889
Noncash change in right of use asset and liability from remeasurement of existing leases and addition of new lease	$ 1,166

Nature of the Business

Nature of the Business	9 Months Ended
	Sep. 30, 2019
Nature Of Business [Abstract]
Nature of the Business	1. Nature of the Business Achillion Pharmaceuticals, Inc. (the “Company”) was incorporated on August 17, 1998 in Delaware. The Company is a clinical-stage biopharmaceutical company focused on advancing its oral factor D inhibitors into late-stage development and commercialization. Each of the product candidates in the Company’s factor D portfolio was discovered in the Company’s laboratories and is wholly owned by the Company. The Company is focusing its product development activities on complement-mediated diseases where there are no approved therapies or significant unmet medical needs persist despite existing therapies. The Company is currently advancing novel orally administered small molecules from its platform that target complement factor D, an essential protein of the alternative pathway. The Company believes that the alternative pathway plays a critical role in a number of disease conditions including the therapeutic areas of hematology, nephrology, ophthalmology and neurology. Initially the Company is targeting paroxysmal nocturnal hemoglobinuria (“PNH”), a blood disorder, and C3 glomerulopathy (“C3G”) and immune complex membranoproliferative glomerulonephritis (“IC-MPGN”), two related rare diseases affecting the kidney. The Company plans to expand its drug development efforts into additional indications where it believes an overactive alternative pathway plays an important role in disease pathogenesis. The Company incurred net losses of $19,583 and $15,884 for the three months ended September 30, 2019 and 2018 On October 15, 2019, the Company entered into an Agreement and Plan of Merger (the “Merger Agreement”) with Alexion Pharmaceuticals, Inc., a Delaware corporation (“Alexion”) and Beagle Merger Sub, Inc., a Delaware corporation and wholly owned subsidiary of Alexion (“Merger Sub”), pursuant to which, among other things and subject to the satisfaction or waiver of specified conditions, Merger Sub will merge with and into the Company (the “Merger”), with the Company surviving the Merger as a direct wholly owned subsidiary of Alexion. The Company expects to complete the Merger in the first half of 2020. However, the exact timing of completion of the Merger is subject to closing conditions specified in the Merger Agreement, many of which are outside of the Company’s control. Based on the Company’s current development plan, whether the proposed Merger is consummated or not, the Company believes that its existing cash, cash equivalents and marketable securities will be sufficient to meet its current projected operating requirements for at least the next 12 months from the issuance of these financial statements. However, the Company’s future capital requirements may change and will depend upon numerous factors, including but not limited to: • changes in the likelihood or timing of the consummation of the proposed Merger; • the scope, progress, results and costs of drug discovery, nonclinical development, laboratory testing and clinical trials for the Company’s product candidates; • the Company’s ability to enter into and the terms and timing of any collaborations, licensing or other arrangements that it may establish; • the number of future product candidates that the Company pursues and their development requirements; • the outcome, timing and costs of seeking regulatory approvals; • the costs of commercialization activities for any of the Company’s product candidates that receive marketing approval to the extent such costs are not the responsibility of any collaborators, including the costs and timing of establishing product sales, marketing, distribution and manufacturing capabilities; • subject to receipt of marketing approval, revenue, if any, received from commercial sales of the Company’s product candidates; • the Company’s headcount growth and associated costs as, and when, it seeks to expand its clinical development capabilities and establish a commercial infrastructure; • the costs involved in preparing, filing, prosecuting, maintaining, enforcing and defending patent and other intellectual property rights and defending against intellectual property-related claims; • the Company’s ability to raise debt or equity capital, including any changes in the credit or equity markets that may impact its ability to obtain capital in the future; • the costs associated with, and the outcome of, lawsuits against the Company, if any; • the Company’s acquisition and development of new technologies and product candidates; and • competing technological and market developments, including those currently unknown to the Company.

Recent Accounting Pronouncement

Recent Accounting Pronouncements	9 Months Ended
	Sep. 30, 2019
New Accounting Pronouncements And Changes In Accounting Principles [Abstract]
Recent Accounting Pronouncements	2. Recent Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-02 “Leases—Topic 842” (“ASU No. 2016-02”). ASU No. 2016-02 requires the recognition of lease assets and lease liabilities by lessees for all leases greater than one year in duration and classified as operating leases under United States generally accepted accounting principles (“U.S. GAAP”). ASU No. 2016-02 is effective for fiscal years beginning after December 15, 2018, and for interim periods within those fiscal years. In July 2018, the FASB issued ASU No. 2018-10, “Codification Improvements to Topic 842, Leases” (“ASU No. 2018-10”), and ASU No. 2018-11, “Leases (Topic 842): Targeted Improvements” (“ASU No. 2018-11”), both of which clarify and enhance the certain amendments made in ASU No. 2016-02 and were adopted in conjunction with ASU No. 2016-02. The Company adopted Topic 842 as of January 1, 2019 under the modified retrospective transition and elected the package of practical expedients. The Company determined that its operating lease commitments were subject to the new standard and recognized a $1,900 right-of-use asset and a $1,900 operating lease liability upon its adoption of ASU No. 2016-02. In August 2018, FASB issued ASU No. 2018-13, “Fair Value Measurement (Subtopic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement” (“ASU No. 2018-13”) which modifies the disclosure requirements on fair value measurements. The amendments related to changes in unrealized gains and losses, the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements, and the narrative description of measurement uncertainty should be applied prospectively for only the most recent interim or annual period presented in the initial year of adoption. All other amendments should be applied retrospectively to all periods presented upon their effective date. ASU No. 2018-13 is effective for fiscal years beginning after December 15, 2019 and interim periods within those fiscal years. Early adoption is permitted. The Company does not believe ASU No. 2018-13 will have a material effect on its financial position and results of operations.

Basis of Presentation

Basis of Presentation	9 Months Ended
	Sep. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Basis of Presentation	3. Basis of Presentation The accompanying unaudited financial statements of the Company should be read in conjunction with the audited financial statements and notes as of and for the year ended December 31, 2018 included in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission (the “SEC”) on March 7, 2019. The accompanying financial statements have been prepared in accordance with U.S. GAAP for interim financial information, in accordance with the instructions to Form 10-Q and the guidance in Article 10 of Regulation S-X. Accordingly, since they are interim financial statements, the accompanying financial statements do not include all of the information and disclosures required by U.S. GAAP for complete financial statements. In the opinion of the Company, the accompanying unaudited financial statements contain all adjustments, consisting of only normal recurring adjustments, necessary for a fair statement of its financial position as of September 30, 2019, and its results of operations for the three and nine months ended September 30, 2019 and 2018, stockholders’ equity for the three and nine months ended September 30, 2019 and 2018 and cash flows for the nine months ended September 30, 2019 and 2018. The balance sheet as of December 31, 2018 was derived from audited annual financial statements but does not contain all of the footnote disclosures from the annual financial statements. Interim results are not necessarily indicative of results for a full year. The preparation of financial statements in accordance with U.S. GAAP requires management to make estimates and assumptions that affect amounts reported in the financial statements and notes thereto.

Restructuring Plan

Restructuring Plan	9 Months Ended
	Sep. 30, 2019
Restructuring And Related Activities [Abstract]
Restructuring Plan	4. Restructuring Plan In January 2019 and February 2018, the Company implemented restructuring plans that reduced employee headcount. The restructuring plans were implemented following an initial strategic assessment of the Company’s portfolio and continued evaluation of the Company’s operations to optimize its structure. Further, the Company opened an office in and recently changed its principal address to Blue Bell, Pennsylvania which provides the Company with access to the talent in that geographic area, and it is evaluating and optimizing the location of its functional areas. In connection with these restructurings, the Company offered individuals whose employment was terminated a severance package that included severance pay, continuation of benefits and outplacement services. Restructuring costs during the three months ended September 30, 2019 and 2018 were $0 and $75, respectively. Restructuring costs during the nine months ended September 30, 2019 and 2018 were $655 and $1,900, respectively. Of these amounts, $181 related to non-cash stock-based compensation and the remainder were cash payments. All amounts relating to the restructurings have been paid.

Earnings (Loss) Per Share

Earnings (Loss) Per Share	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Earnings (Loss) Per Share	5. Earnings (Loss) Per Share Basic earnings (loss) per share (“EPS”) is calculated in accordance with Accounting Standards Codification (“ASC”) 260, “Earnings Per Share,” by dividing net income or loss attributable to common stockholders by the weighted average common stock outstanding. Diluted EPS is calculated by adjusting weighted average common shares outstanding for the dilutive effect of common stock options and warrants. In periods in which a net loss is recorded, no effect is given to potentially dilutive securities, since the effect would be antidilutive. Securities that could potentially dilute basic EPS in the future were not included in the computation of diluted EPS because to do so would have been antidilutive. The calculations of basic and diluted net loss per share are as follows: Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Net loss (numerator) $ (19,583 ) $ (15,884 ) $ (57,968 ) $ (53,671 ) Weighted-average shares, in thousands (denominator) 139,589 138,586 139,025 138,344 Basic and diluted net loss per share $ (0.14 ) $ (0.12 ) $ (0.42 ) $ (0.39 ) Potentially dilutive securities outstanding consists solely of outstanding stock options. The Company had stock options outstanding to purchase 14,979 and 15,569 shares of common stock, respectively, as of September 30, 2019 and 2018, respectively.

Marketable Securities

Marketable Securities	9 Months Ended
	Sep. 30, 2019
Investments Debt And Equity Securities [Abstract]
Marketable Securities	6. Marketable Securities The Company applies the provisions of ASC 820, “Fair Value Measurements and Disclosures,” for financial assets and liabilities measured on a recurring basis which requires disclosure that establishes a framework for measuring fair value and expands disclosures in the financial statements. The guidance requires that fair value measurements be classified and disclosed in one of the three categories: Level 1: Quoted prices in active markets for identical assets and liabilities that the reporting entity has the ability to access at the measurement date; Level 2: Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly; or Level 3: Unobservable inputs. The fair value of the Company’s marketable securities of $185,395 and $221,148 as of September 30, 2019 and December 31, 2018, respectively, is valued based on Level 2 inputs. The Company’s investments consist mainly of U.S. government and agency securities, government-sponsored bond obligations and certain other corporate debt securities. Fair value is determined by taking into consideration valuations obtained from third-party pricing services. The third-party pricing services utilize industry standard valuation models, for which all significant inputs are observable, either directly or indirectly, to estimate fair value. These inputs include reported trades of and broker/dealer quotes on the same or similar securities; issuer credit spreads; benchmark securities; and other observable inputs. The Company has assessed these as Level 2 within the fair value hierarchy of ASC 820. There were no transfers between levels within the hierarchy during the nine months ended September 30, 2019 and 2018. The Company classifies its entire investment portfolio as available for sale as defined in ASC 320, “Debt Securities.” Securities are carried at fair value with the unrealized gains (losses) reported in accumulated other comprehensive income. The unrealized gain (loss) from marketable securities was $ 223 As of September 30, 2019 and December 31, 2018, none of the Company’s investments were determined to be other than temporarily impaired. The following table summarizes the Company’s investments: September 30, 2019 December 31, 2018 Amortized Cost Unrealized Gain Unrealized (Loss) Estimated Fair Value Amortized Cost Unrealized Gain Unrealized (Loss) Estimated Fair Value Commercial Paper $ 19,862 $ 38 $ — $ 19,900 $ 36,235 $ 49 $ (1 ) $ 36,283 Corporate Debt Securities 111,240 167 (7 ) $ 111,400 159,348 5 (238 ) 159,115 Government and Agency Securities 54,070 32 (7 ) 54,095 25,764 — (14 ) 25,750 Total $ 185,172 $ 237 $ (14 ) $ 185,395 $ 221,347 $ 54 $ (253 ) $ 221,148

Accrued Expenses

Accrued Expenses	9 Months Ended
	Sep. 30, 2019
Payables And Accruals [Abstract]
Accrued Expenses	7. Accrued Expenses Accrued expenses consisted of the following: September 30, 2019 December 31, 2018 Accrued compensation $ 3,694 $ 4,397 Accrued research and development expenses 8,467 3,414 Accrued professional expenses 1,270 1,049 Other accrued expenses 279 503 Total $ 13,710 $ 9,363 Accrued research and development expenses are comprised of amounts owed to third-party contract research organizations, clinical investigators, laboratories and data managers for research and development work performed on behalf of the Company.

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	8. Stock-Based Compensation The Company’s Amended and Restated 2015 Stock Incentive Plan (the “2015 Plan”), is administered by the Company’s board of directors and provides for the grant of incentive stock options, nonstatutory stock options, restricted stock, restricted stock units, stock appreciation rights and other stock-based awards. The Company’s officers, employees, consultants, advisors and directors are eligible to receive awards under the 2015 Plan; however, incentive stock options may only be granted to employees. Stock option awards are exercisable for a period determined by the Company, but in no event longer than ten years from the date of the grant. Stock option awards generally vest as to 25% of the shares underlying the option on the first anniversary of the date of grant and as to 6.25% of the shares underlying the option quarterly thereafter for the following three years, subject to continued service. In May 2018, the Company’s stockholders approved an amendment and restatement of the 2015 Plan which included an 8,200 increase to the number of shares of common stock that may be issued pursuant to the 2015 Plan. There were 8,535 shares available to be granted under the 2015 Plan as of September 30, 2019. A summary of the status of the Company’s stock option activity for the nine months ended September 30, 2019 is presented in the table and narrative below: Options Weighted Average Exercise Price Outstanding at January 1, 2019 14,950 $ 5.14 Granted 5,398 2.28 Exercised (1,142 ) 3.34 Cancelled/Forfeited (4,227 ) 6.61 Outstanding at September 30, 2019 14,979 $ 3.83 Options exercisable at September 30, 2019 6,139 $ 5.46 Weighted-average fair value of options granted during the period $ 1.59 The Company utilizes the Black-Scholes option pricing model for determining the estimated fair value for stock-based awards. The Black-Scholes model requires the use of assumptions which determine the fair value of the stock-based awards. The assumptions used to value options granted are as follows: Nine Months Ended September 30, 2019 September 30, 2018 Expected term of option 5.6 - 6.0 years 6.0 years Expected volatility 73% - 82% 79% - 80% Risk free interest rate 1.41% - 2.60% 2.62% - 2.98% Expected dividend yield 0 % 0 % Total compensation expense recorded in the accompanying statements of operations associated with stock option grants made to employees was $1,688 and $1,506 for the three months ended September 30, 2019 and 2018, respectively, and $4,655 and $7,281 for the nine months ended September 30, 2019 and 2018, respectively. Total compensation expense recorded in the accompanying statements of operations associated with stock option grants made to consultants was $0 and $89 for the three months ended September 30, 2019 and 2018, respectively, and $154 and $161 for the nine months ended September 30, 2019 and 2018, respectively. The Company recorded no tax benefit related to these stock options since the Company currently maintains a full valuation allowance on its deferred tax assets. As of September 30, 2019, the intrinsic value of the stock options outstanding was $10,501, of which $1,764 related to vested stock options and $8,737 related to unvested stock options. The intrinsic value of stock options is calculated based on the difference between the exercise prices of the underlying common stock and the quoted stock price of the Company’s common stock as of the reporting date. As of September 30, 2019, the total compensation cost related to unvested stock options not yet recognized in the financial statements was approximately $12,719, net of estimated forfeitures, and the weighted average period over which this amount is expected to be recognized is 2.8 years.

Comprehensive Loss

Comprehensive Loss	9 Months Ended
	Sep. 30, 2019
Comprehensive Income Net Of Tax [Abstract]
Comprehensive Loss	9. Comprehensive Loss The Company reports and presents comprehensive income (loss) in accordance with ASC 220, “Comprehensive Income,” which establishes standards for reporting and display of comprehensive income (loss) and its components in a full set of general purpose financial statements. The objective of the statement is to report a measure of all changes in equity of an enterprise that result from transactions and other economic events of the period other than transactions with owners. The Company’s other comprehensive income (loss) arises from net unrealized gains (losses) on marketable securities. The unrealized gain (loss) from marketable securities was $223 and $(199) at September 30, 2019 and December 31, 2018, respectively.

Leases

Leases	9 Months Ended
	Sep. 30, 2019
Leases [Abstract]
Leases	10. Leases Effective January 1, 2019, the Company adopted ASU No. 2016-02, “Leases (Topic 842)” and the related ASUs that followed (collectively referred to as “Topic 842”). Topic 842 requires the recognition of right of use (“ROU”) lease assets and liabilities by lessees for all leases greater than one year in duration and classified as operating leases under U.S. GAAP. The Company elected the package of practical expedients which allows the Company to apply the transition provision for Topic 842 at its adoption date instead of at the earliest comparative period presented in our financial statements. Therefore, existing leases at January 1, 2019 were recognized and measured but without retrospective application. The Company also elected the short-term lease practical expedient but did not elect the hindsight practical expedient. The impact of Topic 842 on the Company’s balance sheet beginning January 1, 2019 was the recognition of ROU assets and lease liabilities for operating leases. There was no income to the Company’s statement of comprehensive loss or beginning retained earnings related to the adoption of Topic 842. The Company’s operating lease commitments consist of obligations under operating leases for its facilities and office equipment. The Company has leases for its operating facilities in New Haven, Connecticut and Blue Bell, Pennsylvania. The lease agreements require monthly lease payments through September 2022 and November 2022, respectively. In September 2019, the Company modified its existing building lease for its New Haven, CT facilities to exit the majority of its current space early and entered into a lease agreement for new space in the same building in New Haven, CT. The Company does not have any leases that are classified as finance leases. The Company determines if an arrangement is a lease at inception. For purposes of calculating operating lease liabilities, lease terms may include options to extend or terminate the lease when it becomes probable that the Company will exercise the option. As the rate implicit in the lease is generally not readily determinable for the Company’s operating leases, the discount rates used to determine the present value of its lease liability are based on the Company’s incremental borrowing rate at the lease commencement date. The following table summarizes the Company’s lease obligations as of September 30, 2019: Year Ending December 31, Remainder of 2019 $ 288 2020 800 2021 802 2022 638 Total lease payments 2,528 Less: imputed interest (256 ) Total $ 2,272 The following table summarizes the Company’s lease obligations as of December 31, 2018: Year Ending December 31, 2019 $ 1,239 2020 551 2021 322 2022 287 Total $ 2,399 Expense related to the Company’s operating leases is included in operating expenses and was $262 and $235 for the three months ended September 30, 2019 and 2018, respectively, and $858 and $671 for the nine months ended September 30, 2019 and 2018, respectively. As of September 30, 2019, the carrying value of the ROU assets was $2,265 and is separately stated on the Company’s balance sheet. The related short-term and long-term liabilities as of September 30, 2019 were $754 and $1,518, respectively. During the nine months ended September 30, 2019 cash paid for operating leases was $783. As of September 30, 2019, the weighted average remaining lease term was 2.9 years and the weighted average incremental borrowing rate was 7.1%.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2019
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	11. Commitments and Contingencies From time to time, in the ordinary course of business, the Company may be subject to litigation and regulatory examinations as well as information gathering requests, inquiries and/or investigations. The Company is not currently subject to any matters where it believes there is a reasonable possibility that a material loss may be incurred.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Income Taxes	12. Income Taxes During the three months ended June 30, 2019, the Company updated its review of “ownership changes” through December 31, 2018 as defined under Section 382 of the Internal Revenue Code of 1986, as amended. Based on this review, the Company’s federal net operating loss carryforwards increased by $115,366. This increase was recorded with an offsetting valuation allowance during the three months ended September 30, 2019. The Company’s total federal net operating loss carryforwards were determined to be $541,254.

Subsequent Event

Subsequent Event	9 Months Ended
	Sep. 30, 2019
Subsequent Events [Abstract]
Subsequent Event	13. Subsequent Event On October 15, 2019, the Company entered into the Merger Agreement with Alexion and Merger Sub, pursuant to which, among other things and subject to the satisfaction or waiver of specified conditions, Merger Sub will merge with and into the Company, with the Company surviving the Merger as a direct wholly owned subsidiary of Alexion. Under the terms of the Merger Agreement, at the time the Merger becomes effective (the “Effective Time”) each share of Company common stock issued and outstanding immediately prior to the Effective Time (other than certain excluded shares as described in the Merger Agreement) will be automatically converted into (i) the right to receive $6.30 in cash, without interest, and (ii) one (1) contractual contingent value right (a “CVR”) pursuant to the CVR agreement that Alexion and a rights agent mutually agreeable to Alexion and the Company will enter into at or prior to the Effective Time. In addition, at the Effective Time, each (i) compensatory option to purchase shares of Company common stock (a “Company Stock Option”) that is then outstanding, unexercised and vested (or which, pursuant to its terms or the terms of a contract in effect on October 15, 2019, shall become vested upon the consummation of the Merger), (ii) unvested Company Stock Option held by a Specified Holder (as defined in the Merger Agreement) (each Company Stock Option held by a Specified Holder, a “Specified Holder Option”) who has, at or prior to the Effective Time, delivered to the Company and not revoked a Non-Competition Agreement (as that term is defined in the Merger Agreement), (iii) unvested Company Stock Option, that is not a Specified Holder Option that is held by an officer or employee of the Company other than a Specified Holder who has, at or prior to the Effective Time, delivered to the Company and not revoked a General Release (as that term is defined in the Merger Agreement), and (iv) Company Stock Option that is then outstanding and unexercised, whether or not vested, that is held by an individual who is not an officer or employee of the Company, which, in each case, has a per share exercise price that is less than the Cash Merger Consideration (each, an “In the Money Option”), will be cancelled and converted into the right to receive both (i) a cash payment equal to (A) the excess, of (x) the Cash Merger Consideration over (y) the exercise price payable per share of Company common stock under such Company Stock Option, multiplied by (B) the total number of shares of Company common stock subject to such In the Money Option immediately prior to the Effective Time (without regard to vesting) and (ii) one CVR for each share of Company common stock subject to such In the Money Option immediately prior to the Effective Time (without regard to vesting). At the Effective Time, each (i) Company Stock Option other than an In the Money Option that is then outstanding, unexercised and vested (or which, pursuant to its terms or the terms of a contract in effect on October 15, 2019, shall become vested upon the consummation of the Merger), (ii) unvested Company Stock Option that is not an In the Money Option that is held by a Specified Holder who has, at or prior to the Effective Time, delivered to the Company and not revoked a Non-Competition Agreement, (iii) unvested Company Stock Option that is not an In the Money Option held by an officer or employee of the Company other than a Specified Holder who has, at or prior to the Effective Time, delivered to the Company and not revoked a General Release, (iv) Company Stock Option other than an In the Money Option that is then outstanding and unexercised, whether or not vested, that is held by an individual who is not an officer or employee of the Company (each, an “Out of the Money Option”), will be cancelled and, except as described below, converted into the right to receive a cash payment, if any, from Alexion with respect to each share of Company common stock subject to the Out of the Money Option upon each Milestone Payment Date (as defined in the CVR Agreement) (each, a “Valuation Point”) which occurs after the Effective Time, equal to (i) the amount by which, as of the Valuation Point, the sum of (x) the Cash Merger Consideration, (y) the amount per share of Company common stock in cash previously paid in respect of any earlier Valuation Points (if any) and (z) the amount per share of Company common stock in cash to be paid at such Valuation Point under the CVR Agreement (collectively, the “Per Share Value Paid”) exceeds the exercise price payable per share of Company common stock under such Out of the Money Option, less (ii) the amount of all payments previously received with respect to such Out of the Money Option. Any Out of the Money Options with an exercise price payable per share of Company common stock equal to or greater than $8.30 and any other Company Stock Options that are not vested as of the effective time and which do not vest pursuant to their respective terms or the terms of a contract in effect on October 15, 2019 that are held by (1) a Specified Holder who has not, at or prior to the Effective Time, delivered to the Company and not revoked a Non-Competition Agreement or (2) an officer or employee of the Company who is not a Specified Holder who has not, at or prior to the Effective Time, delivered to the Company and not revoked a General Release will be cancelled at the Effective Time without any consideration payable therefor. The Merger Agreement includes customary representations, warranties and covenants in the Merger Agreement. The Merger Agreement includes restrictions on the conduct of the Company’s business prior to the completion of the Merger, generally requiring the Company to conduct its business in the ordinary course and subjecting the Company to a variety of specified limitations absent Alexion’s consent. The closing of the Merger is subject to the adoption of the Merger Agreement by the Company’s shareholders and other customary closing conditions. Either the Company or Alexion may terminate the Merger Agreement in certain circumstances, including if (1) the Merger is not completed by April 15, 2020, subject to extension by Alexion in certain circumstances in the event that antitrust approval is not obtained (the “End Date”), (2) a governmental authority of competent jurisdiction has issued a final non-appealable order prohibiting the Merger or any applicable law makes consummation of the Merger illegal, (3) the Company’s stockholders fail to adopt the Merger Agreement, (4) the other party breaches its representations, warranties or covenants in the Merger Agreement in a way that would entitle the party seeking to terminate the Merger Agreement not to consummate the Merger, subject to the right of the breaching party to cure the breach, (5) subject to compliance with specified process and notice requirements, the Company terminates the Merger Agreement in order to enter into an agreement providing for a “Superior Proposal” (as such term is defined in the Merger Agreement), or (6) the Company’s board of directors has changed its recommendation in favor of the Merger. In the event of a termination of the Merger Agreement under certain specified circumstances, including termination by Achillion to enter into an agreement providing for a Superior Proposal, or a termination by Alexion following a change in recommendation by the Company’s board of directors, the Company may be required to pay Alexion a termination fee equal to $20,000,000. In the event of a termination of the Merger Agreement under certain specified circumstances, including failure to complete the merger by April 15, 2020 (or such later date as extended by Alexion) if, at the time of such termination, any necessary antitrust approval has not been obtained, or a final non-appealable order prohibiting the Merger by a governmental authority of competent jurisdiction, Alexion may be required to pay the Company a termination fee equal to (i) $30,000,000 if the Merger Agreement is terminated prior to April 15, 2020, (ii) $40,000,000 if Alexion has extended the End Date and the Merger Agreement is terminated after April 15, 2020 but on or prior to July 15, 2020, (iii) $50,000,000 if Alexion has extended the End Date twice and the Merger Agreement is terminated after July 15, 2020 but on or prior to October 15, 2020 or (iv) $60,000,000 if Alexion has extended the End Date three times and the Merger Agreement is terminated after October 15, 2020. Additional information about the Merger is set forth in the Company’s Current report on Form 8-K filed with the SEC on October 16, 2019, which includes the full text of the Merger Agreement as Exhibit 2.1 thereto.

Earnings (Loss) Per Share (Tabl

Earnings (Loss) Per Share (Tables)	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Calculations of Basic and Diluted Net Loss per Share	The calculations of basic and diluted net loss per share are as follows: Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Net loss (numerator) $ (19,583 ) $ (15,884 ) $ (57,968 ) $ (53,671 ) Weighted-average shares, in thousands (denominator) 139,589 138,586 139,025 138,344 Basic and diluted net loss per share $ (0.14 ) $ (0.12 ) $ (0.42 ) $ (0.39 )

Marketable Securities (Tables)

Marketable Securities (Tables)	9 Months Ended
	Sep. 30, 2019
Investments Debt And Equity Securities [Abstract]
Summary of the Investments	The following table summarizes the Company’s investments: September 30, 2019 December 31, 2018 Amortized Cost Unrealized Gain Unrealized (Loss) Estimated Fair Value Amortized Cost Unrealized Gain Unrealized (Loss) Estimated Fair Value Commercial Paper $ 19,862 $ 38 $ — $ 19,900 $ 36,235 $ 49 $ (1 ) $ 36,283 Corporate Debt Securities 111,240 167 (7 ) $ 111,400 159,348 5 (238 ) 159,115 Government and Agency Securities 54,070 32 (7 ) 54,095 25,764 — (14 ) 25,750 Total $ 185,172 $ 237 $ (14 ) $ 185,395 $ 221,347 $ 54 $ (253 ) $ 221,148

Accrued Expenses (Tables)

Accrued Expenses (Tables)	9 Months Ended
	Sep. 30, 2019
Payables And Accruals [Abstract]
Summary of Accrued Expenses	Accrued expenses consisted of the following: September 30, 2019 December 31, 2018 Accrued compensation $ 3,694 $ 4,397 Accrued research and development expenses 8,467 3,414 Accrued professional expenses 1,270 1,049 Other accrued expenses 279 503 Total $ 13,710 $ 9,363

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Stock Option Activity	A summary of the status of the Company’s stock option activity for the nine months ended September 30, 2019 is presented in the table and narrative below: Options Weighted Average Exercise Price Outstanding at January 1, 2019 14,950 $ 5.14 Granted 5,398 2.28 Exercised (1,142 ) 3.34 Cancelled/Forfeited (4,227 ) 6.61 Outstanding at September 30, 2019 14,979 $ 3.83 Options exercisable at September 30, 2019 6,139 $ 5.46 Weighted-average fair value of options granted during the period $ 1.59
Assumptions Used to Value Options Granted	The assumptions used to value options granted are as follows: Nine Months Ended September 30, 2019 September 30, 2018 Expected term of option 5.6 - 6.0 years 6.0 years Expected volatility 73% - 82% 79% - 80% Risk free interest rate 1.41% - 2.60% 2.62% - 2.98% Expected dividend yield 0 % 0 %

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2019
Leases [Abstract]
Summary of Company's Lease Obligations	The following table summarizes the Company’s lease obligations as of September 30, 2019: Year Ending December 31, Remainder of 2019 $ 288 2020 800 2021 802 2022 638 Total lease payments 2,528 Less: imputed interest (256 ) Total $ 2,272
Future Minimum Annual Lease Payments	The following table summarizes the Company’s lease obligations as of December 31, 2018: Year Ending December 31, 2019 $ 1,239 2020 551 2021 322 2022 287 Total $ 2,399

Nature of Business - Additional

Nature of Business - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Nature Of Business [Abstract]
Net loss	$ 19,583	$ 19,426	$ 18,959	$ 15,884	$ 17,199	$ 20,588	$ 57,968	$ 53,671
Accumulated deficit	$ 730,894						$ 730,894		$ 672,926
Merger agreement date							Oct. 15, 2019

Recent Accounting Pronounceme_2

Recent Accounting Pronouncements - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Jan. 01, 2019
Operating Lease, Right-of-Use Asset	$ 2,265
Operating Lease, Liability	$ 2,272
ASU-2016-02
Operating Lease, Right-of-Use Asset		$ 1,900
Operating Lease, Liability		$ 1,900

Restructuring Plan - Additional

Restructuring Plan - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Restructuring And Related Activities [Abstract]
Restructuring cost	$ 0	$ 75	$ 655	$ 1,900
Non-cash stock-based compensation				$ 181

Calculations of Basic and Dilut

Calculations of Basic and Diluted Net Loss per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Earning per share, Basic and diluted
Net loss (numerator)	$ (19,583)	$ (19,426)	$ (18,959)	$ (15,884)	$ (17,199)	$ (20,588)	$ (57,968)	$ (53,671)
Weighted-average shares, in thousands (denominator)	139,589			138,586			139,025	138,344
Basic and diluted net loss per share	$ (0.14)			$ (0.12)			$ (0.42)	$ (0.39)

Earnings (Loss) Per Share - Add

Earnings (Loss) Per Share - Additional Information (Detail) - shares shares in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Employee Stock Option
Stock options outstanding	14,979	15,569

Marketable Securities - Additio

Marketable Securities - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Fair value of marketable securities	$ 185,395	$ 221,148
Unrealized gain (loss) from marketable securities	223	(199)
Fair Value, Inputs, Level 2
Debt Securities, Available-for-sale [Line Items]
Fair value of marketable securities	$ 185,395	$ 221,148

Summary of Investments (Detail)

Summary of Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 185,172	$ 221,347
Unrealized Gain	237	54
Unrealized (Loss)	(14)	(253)
Estimated Fair Value	185,395	221,148
Corporate Debt Securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	111,240	159,348
Unrealized Gain	167	5
Unrealized (Loss)	(7)	(238)
Estimated Fair Value	111,400	159,115
Government and Agency Securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	54,070	25,764
Unrealized Gain	32
Unrealized (Loss)	(7)	(14)
Estimated Fair Value	54,095	25,750
Commercial Paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	19,862	36,235
Unrealized Gain	38	49
Unrealized (Loss)		(1)
Estimated Fair Value	$ 19,900	$ 36,283

Accrued Expenses (Detail)

Accrued Expenses (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Accrued Liabilities, Current [Abstract]
Accrued compensation	$ 3,694	$ 4,397
Accrued research and development expenses	8,467	3,414
Accrued professional expenses	1,270	1,049
Other accrued expenses	279	503
Total	$ 13,710	$ 9,363

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($) shares in Thousands, $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	May 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation expense associated					$ 181
Intrinsic value of options outstanding		$ 10,501		$ 10,501
Intrinsic value of options vested		1,764		1,764
Intrinsic value of options unvested		8,737		8,737
Total compensation cost related to stock options not yet recognized		12,719		$ 12,719
Total compensation cost related to stock options not yet recognized, Weighted average period for recognition				2 years 9 months 18 days
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation expense associated		1,688	$ 1,506	$ 4,655	7,281
Consultants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation expense associated		$ 0	$ 89	$ 154	$ 161
2015 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares of common stock authorized	8,200
Shares of common stock available for grant		8,535		8,535
2015 Plan | Quarterly thereafter for the following three years
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options awards, vesting percentage				6.25%
Options vested period				3 years
2015 Plan | On first anniversary of the date of grant
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options awards, vesting percentage				25.00%
2015 Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option awards, expiration period				10 years

Company's Stock Option Activity

Company's Stock Option Activity (Detail) - $ / shares shares in Thousands	9 Months Ended
	Sep. 30, 2019
Options
Outstanding at January 1, 2019	14,950
Stock Options, Granted	5,398
Stock Options, Exercised	(1,142)
Stock Options, Cancelled/Forfeited	(4,227)
Outstanding at September 30, 2019	14,979
Options exercisable at September 30, 2019	6,139
Weighted Average Exercise Price
Weighted Average Exercise Price, Outstanding at January 1, 2019	$ 5.14
Weighted Average Exercise Price, Granted	2.28
Weighted Average Exercise Price, Exercised	3.34
Weighted Average Exercise Price,Cancelled/Forfeited	6.61
Weighted Average Exercise Price, Outstanding at September 30, 2019	3.83
Weighted Average Exercise Price, Options exercisable at September 30, 2019	5.46
Weighted Average Exercise Price, Weighted-average fair value of options granted during the period	$ 1.59

Assumptions Used to Value Optio

Assumptions Used to Value Options Granted (Detail)	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term of option		6 years
Expected dividend yield	0.00%	0.00%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term of option	5 years 7 months 6 days
Expected volatility	73.00%	79.00%
Risk free interest rate	1.41%	2.62%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term of option	6 years
Expected volatility	82.00%	80.00%
Risk free interest rate	2.60%	2.98%

Comprehensive Loss - Additional

Comprehensive Loss - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Comprehensive Income Net Of Tax [Abstract]
Unrealized gain (loss) from marketable securities	$ 223	$ (199)

Leases - Additional Information

Leases - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Leases [Line Items]
Rent expense under operating lease	$ 262	$ 235	$ 858	$ 671
Operating Lease, Right-of-Use Asset	2,265		2,265
Short term liability	754		754
Long term liability	$ 1,518		1,518
Operating lease payments			$ 783
Weighted average remaining lease term	2 years 10 months 24 days		2 years 10 months 24 days
Weighted average incremental borrowing rate	7.10%		7.10%
New Haven Connecticut
Leases [Line Items]
Period of monthly lease payment			Sep. 30, 2022
Blue Bell Pennsylvania
Leases [Line Items]
Period of monthly lease payment			Nov. 30, 2022

Summary of Company's Lease Obli

Summary of Company's Lease Obligations (Detail) $ in Thousands	Sep. 30, 2019USD ($)
Leases [Abstract]
Remainder of 2019	$ 288
2020	800
2021	802
2022	638
Total lease payments	2,528
Less: imputed interest	(256)
Total	$ 2,272

Future Minimum Annual Lease Pay

Future Minimum Annual Lease Payments (Detail) $ in Thousands	Dec. 31, 2018USD ($)
Leases [Abstract]
2019	$ 1,239
2020	551
2021	322
2022	287
Total	$ 2,399

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) $ in Thousands	3 Months Ended
	Sep. 30, 2019USD ($)
Income Tax Disclosure [Abstract]
Increase in federal net operating loss carryforwards	$ 115,366
Operating loss carryforwards	$ 541,254

Subsequent Event - Additional I

Subsequent Event - Additional Information (Detail) - Alexion Pharmaceuticals Incorporation and Beagle Merger Sub Incorporation - Subsequent Event	Oct. 15, 2019USD ($)$ / sharesshares
Subsequent Event [Line Items]
Right to receive cash under terms of merger agreement | $ / shares	$ 6.30
Merger agreement conversion term	Under the terms of the Merger Agreement, at the time the Merger becomes effective (the “Effective Time”) each share of Company common stock issued and outstanding immediately prior to the Effective Time (other than certain excluded shares as described in the Merger Agreement) will be automatically converted into (i) the right to receive $6.30 in cash, without interest, and (ii) one (1) contractual contingent value right (a “CVR”) pursuant to the CVR agreement that Alexion and a rights agent mutually agreeable to Alexion and the Company will enter into at or prior to the Effective Time.
Agreement termination fee	$ 20,000,000
Merger Agreement Terminated Prior to April 15, 2020
Subsequent Event [Line Items]
Agreement termination fee income	30,000,000
Merger Agreement Terminated After April 15, 2020 or Prior to July 15, 2020
Subsequent Event [Line Items]
Agreement termination fee income	40,000,000
Merger Agreement Terminated After July 15, 2020 or Prior to October 15, 2020
Subsequent Event [Line Items]
Agreement termination fee income	50,000,000
Merger Agreement Terminated After October 15, 2020
Subsequent Event [Line Items]
Agreement termination fee income	$ 60,000,000
In the Money Option
Subsequent Event [Line Items]
Number of CVR called by each share of common stock | shares	1
Out of the Money Option
Subsequent Event [Line Items]
Minimum exercise price payable per share of common stock | $ / shares	$ 8.30