Cara Therapeutics (CARA) 10-Q 6 Nov 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Nov. 01, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Trading Symbol	CARA
Entity Registrant Name	Cara Therapeutics, Inc.
Entity Central Index Key	1,346,830
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Common Stock, Shares Outstanding		39,446,757

Condensed Balance Sheets

Condensed Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 96,729	$ 9,388
Marketable securities	109,348	83,181
Income tax receivable	539	731
Other receivables	193	123
Prepaid expenses	4,218	1,635
Restricted cash, current	361
Total current assets	211,388	95,058
Property and equipment, net	908	1,177
Restricted cash	408	769
Total assets	212,704	97,004
Current liabilities:
Accounts payable and accrued expenses	14,003	8,506
Current portion of deferred revenue	29,242
Total current liabilities	43,245	8,506
Deferred revenue, non-current	18,300
Deferred lease obligation	1,629	1,718
Commitments and contingencies (Note 15)
Stockholders’ equity:
Preferred stock; $0.001 par value; 5,000,000 shares authorized at September 30, 2018 and December 31, 2017, zero shares issued and outstanding at September 30, 2018 and December 31, 2017
Common stock; $0.001 par value; 100,000,000 shares authorized at September 30, 2018 and December 31, 2017, 39,389,515 shares and 32,662,255 shares issued and outstanding at September 30, 2018 and December 31, 2017, respectively	39	33
Additional paid-in capital	423,180	307,158
Accumulated deficit	(273,702)	(220,341)
Accumulated other comprehensive income (loss)	13	(70)
Total stockholders’ equity	149,530	86,780
Total liabilities and stockholders’ equity	$ 212,704	$ 97,004

Condensed Balance Sheets (Paren

Condensed Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
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	$ 0.001	$ 0.001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	39,389,515	32,662,255
Common stock, shares outstanding	39,389,515	32,662,255

Condensed Statements of Compreh

Condensed Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue:
Total revenue	$ 5,062		$ 7,936	$ 911
Operating expenses:
Research and development	22,303	$ 9,151	52,732	36,948
General and administrative	3,227	3,805	10,609	8,877
Total operating expenses	25,530	12,956	63,341	45,825
Operating loss	(20,468)	(12,956)	(55,405)	(44,914)
Other income	1,002	367	1,780	788
Loss before benefit from income taxes	(19,466)	(12,589)	(53,625)	(44,126)
Benefit from income taxes	66	145	264	178
Net loss	$ (19,400)	$ (12,444)	$ (53,361)	$ (43,948)
Net loss per share:
Basic and Diluted	$ (0.51)	$ (0.38)	$ (1.54)	$ (1.43)
Weighted average shares:
Basic and Diluted	38,034,216	32,591,550	34,696,835	30,729,752
Other comprehensive income (loss), net of tax of $0:
Change in unrealized gains (losses) on available-for- sale marketable securities	$ 70	$ 53	$ 83	$ 37
Total comprehensive loss	(19,330)	$ (12,391)	(53,278)	(43,911)
License and Milestone Fees [Member]
Revenue:
Total revenue	5,029		7,903	530
Collaborative Revenue [Member]
Revenue:
Total revenue				313
Clinical Compound Revenue [Member]
Revenue:
Total revenue	$ 33		$ 33	$ 68

Condensed Statements of Compr_2

Condensed Statements of Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Other comprehensive income (loss), tax	$ 0	$ 0	$ 0	$ 0

Condensed Statements of Stockho

Condensed Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Follow-on Public Offering [Member]	Common Stock [Member]	Common Stock [Member]Follow-on Public Offering [Member]	Additional Paid-In Capital [Member]	Additional Paid-In Capital [Member]Follow-on Public Offering [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance, Value at Dec. 31, 2016	$ 50,725		$ 27		$ 212,866		$ (162,171)	$ 3
Balance, Shares at Dec. 31, 2016			27,296,863
Sale of common stock, net of underwriting discounts and commissions and offering expenses, Value		$ 86,224		$ 5		$ 86,219
Sale of common stock, net of underwriting discounts and commissions and offering expenses, Shares				5,117,500
Stock-based compensation expense	4,046				4,046
Modification of equity awards	474				474
Shares issued upon exercise of stock options, Value	1,516		$ 1		1,515
Shares issued upon exercise of stock options, Shares			194,122
Cumulative effect adjustment upon adoption of ASU 2016-09					45		(45)
Net loss	(43,948)						(43,948)
Other comprehensive income	37							37
Balance, Value at Sep. 30, 2017	99,074		$ 33		305,165		(206,164)	40
Balance, Shares at Sep. 30, 2017			32,608,485
Balance, Value at Dec. 31, 2017	86,780		$ 33		307,158		(220,341)	(70)
Balance, Shares at Dec. 31, 2017			32,662,255
Sale of common stock, net of underwriting discounts and commissions and offering expenses, Value		$ 92,077		$ 5		$ 92,072
Sale of common stock, net of underwriting discounts and commissions and offering expenses, Shares				5,175,000
Sale of common stock under license agreement, Value	14,556		$ 1		14,555
Sale of common stock under license agreement, Shares			1,174,827
Stock-based compensation expense	5,759				5,759
Shares issued upon exercise of stock options, Value	3,636				3,636
Shares issued upon exercise of stock options, Shares			377,433
Net loss	(53,361)						(53,361)
Other comprehensive income	83							83
Balance, Value at Sep. 30, 2018	$ 149,530		$ 39		$ 423,180		$ (273,702)	$ 13
Balance, Shares at Sep. 30, 2018			39,389,515

Condensed Statements of Stock_2

Condensed Statements of Stockholders' Equity (Parenthetical) - Follow-on Public Offering [Member] - Common Stock [Member] - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Sale of common stock, per share	$ 19	$ 18
Underwriting discounts and commissions and offering expenses	$ 6,248	$ 5,891

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Operating activities
Net loss	$ (53,361)	$ (43,948)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Stock-based compensation expense	5,759	4,046
Modification of equity awards		474
Depreciation and amortization	318	370
Amortization/accretion of available-for-sale marketable securities	(1,177)	(356)
Realized loss (gain) on sale of available-for-sale marketable securities	32	(4)
Realized gain on sale of property and equipment		(41)
Deferred rent costs	(89)	131
Deferred revenue	47,542
Changes in operating assets and liabilities:
Income tax receivable	192	147
Other receivables	(70)	(10)
Prepaid expenses	(2,583)	38
Accounts payable and accrued expenses	5,497	(4,261)
Net cash provided by (used in) operating activities	2,060	(43,414)
Investing activities
Proceeds from maturities of available-for-sale marketable securities	85,500	65,406
Proceeds from sale of available-for-sale marketable securities	28,250	5,730
Purchases of available-for-sale marketable securities	(138,689)	(115,745)
Purchases of property and equipment	(49)	(58)
Proceeds from sale of property and equipment		41
Net cash used in investing activities	(24,988)	(44,626)
Financing activities
Proceeds from sale of common stock in a follow-on public offering, net of issuance costs	92,077	86,224
Proceeds from the sale of common stock under license agreement	14,556
Proceeds from the exercise of stock options	3,636	1,516
Net cash provided by financing activities	110,269	87,740
Net increase (decrease) in cash, cash equivalents and restricted cash	87,341	(300)
Cash, cash equivalents and restricted cash at beginning of period	10,157	13,561
Cash, cash equivalents and restricted cash at end of period	$ 97,498	$ 13,261

Business

Business	9 Months Ended
	Sep. 30, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Business	1. Business Cara Therapeutics, Inc., or the Company, is a clinical-stage biopharmaceutical corporation formed on July 2, 2004. The Company is focused on developing and commercializing new chemical entities designed to alleviate pruritus and pain by selectively targeting kappa opioid receptors. The Company’s primary activities to date have been organizing and staffing the Company, developing its product candidates, including conducting preclinical studies and clinical trials of CR845/difelikefalin-based product candidates and raising capital. As of September 30, 2018, the Company had raised aggregate net proceeds of approximately $383,200 from several rounds of equity financing, including its initial public offering, or IPO, which closed in February 2014 and three follow-on public offerings of common stock, which closed in July 2018, April 2017 and August 2015, and the issuance of convertible preferred stock and debt prior to the IPO. The Company had also received approximately $88,900 under its license agreements for CR845/difelikefalin, primarily with Vifor Fresenius Medical Care Renal Pharma Ltd., or VFMCRP, Maruishi Pharmaceutical Co. Ltd., or Maruishi, and Chong Kun Dang Pharmaceutical Corp., or CKDP, and an earlier product candidate for which development efforts ceased in 2007. Additionally, in May 2018, the Company received net proceeds of $14,556 from the issuance and sale of 1,174,827 shares of the Company’s common stock to Vifor (International) Ltd., or Vifor, in connection with the Company’s license agreement with VFMCRP (see Note 10, Collaborations and Licensing Agreements As of September 30, 2018, the Company had unrestricted cash and cash equivalents and marketable securities of $206,077 and an accumulated deficit of $273,702. The Company has incurred substantial net losses and negative cash flows from operating activities in nearly every fiscal period since inception and expects this trend to continue for the foreseeable future. The Company recognized net losses of $19,400 and $12,444 for the three months ended September 30, 2018 and 2017, respectively, and $53,361 and $43,948 for the nine months ended September 30, 2018 and 2017, respectively, and had net cash provided by (used in) operating activities of $2,060 and $(43,414) for the nine months ended September 30, 2018 and 2017, respectively. The Company is subject to risks common to other life science companies including, but not limited to, uncertainty of product development and commercialization, lack of marketing and sales history, development by its competitors of new technological innovations, dependence on key personnel, market acceptance of products, product liability, protection of proprietary technology, ability to raise additional financing, and compliance with Food and Drug Administration, or FDA, and other government regulations. If the Company does not successfully commercialize any of its product candidates, it will be unable to generate recurring product revenue or achieve profitability.

Basis of Presentation

Basis of Presentation	9 Months Ended
	Sep. 30, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Basis of Presentation	2. Basis of Presentation The unaudited interim condensed financial statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission, or SEC. Accordingly, they do not include all information and disclosures necessary for a presentation of the Company’s financial position, results of operations and cash flows in conformity with generally accepted accounting principles in the United States of America, or GAAP. In the opinion of management, these unaudited interim financial statements reflect all adjustments, consisting primarily of normal recurring accruals, necessary for a fair presentation of results for the periods presented. Certain amounts in the prior year’s condensed financial statements have been reclassified to conform to the current-year presentation due to the adoption of certain accounting standards (see Note 2, Accounting Pronouncements Recently Adopted: ASU 2016-18, Statement of Cash Flows (Topic 230), Restricted Cash . Use of Estimates The preparation of financial statements in conformity with GAAP requires the Company to make estimates and assumptions that affect the reported amounts of assets and liabilities, and disclosure of contingent assets and liabilities, as of the date of the financial statements as well as the reported amounts of revenues and expenses during the reporting period. Actual results could differ materially from the Company’s estimates and assumptions. Significant estimates include the fair value of marketable securities that are classified as level 2 of the fair value hierarchy, useful lives of fixed assets, the periods over which certain revenues will be recognized, including licensing and collaborative revenue recognized from non-refundable up-front and milestone payments, the determination of prepaid research and development, or R&D, clinical costs and accrued research projects, the amount of non-cash compensation costs related to share-based payments to employees and non-employees and the periods over which those costs are expensed and the likelihood of realization of deferred tax assets. Significant Accounting Policies There have been no material changes to the significant accounting policies previously disclosed in Note 2 to the Financial Statements in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017, except for the recent adoption of new accounting pronouncements as disclosed below. Accounting Pronouncements Recently Adopted Revenue Recognition On January 1, 2018, the Company adopted Accounting Standards Update, or ASU, 2014-09, Revenue from Contracts with Customers (Topic 606) Collaboration and Licensing Agreements Revenue Recognition) The Company has entered into agreements to license its intellectual property, or IP, related to CR845/difelikefalin to develop, manufacture and/or commercialize drug products. These agreements typically contain multiple performance obligations, including licenses of IP and R&D services. Payments to the Company under these agreements may include nonrefundable license fees, payments for research activities, payments based upon the achievement of certain milestones and royalties on any resulting net product sales. The Company identifies agreements as contracts that create enforceable rights and obligations when the agreement is approved by the parties, identifies the rights of the parties and the payment terms, has commercial substance and it is probable that the Company will collect the consideration to which it will be entitled in exchange for the goods and services that will be transferred to the customer. The counterparty is considered to be a customer when it has contracted with the Company to obtain goods and services that are the output of the Company’s ordinary activities (i.e., development of pharmaceutical products) in exchange for consideration. A performance obligation is a promise to transfer distinct goods or services to a customer. Performance obligations that are both capable of being distinct and distinct within the context of the contract are considered to be separate performance obligations. Performance obligations are capable of being distinct if the counterparty is able to benefit from the good or service on its own or together with other resources that are readily available to it. Performance obligations are distinct within the context of the contract when each performance obligation is separately identifiable from each other; i.e., the Company is not using the goods or services as inputs to produce or deliver the combined output or outputs specified by the customer; one or more of the goods or services does not significantly modify or customize one of the other goods or services in the contract; and goods or services are not highly interdependent or not highly interrelated. Performance obligations that are not distinct are accounted for as a single performance obligation over the period that goods or services are transferred to the customer. The determination of whether performance obligations in a contract are distinct may require significant judgment. The transaction price is the amount of consideration that the Company expects to be entitled to in exchange for transferring promised goods or services to the customer based on the contract terms at inception of a contract. There is a constraint on inclusion of variable consideration related to licenses of IP, such as milestone payments or sales-based royalty payments, in the transaction price if there is uncertainty at inception of the contract as to whether such consideration will be recognized in the future because it is probable that there will be a significant reversal of revenue in the future when the uncertainty is resolved. The determination of whether or not it is probable that a significant reversal of revenue will occur in the future depends on the likelihood and magnitude of the reversal. Factors that could increase the likelihood or magnitude of a reversal of revenue include (a) the susceptibility of the amount of consideration to factors outside the entity’s influence, such as the outcome of clinical trials, the timing of initiation of clinical trials by the counterparty and the approval of drug product candidates by regulatory agencies, (b) situations in which the uncertainty is not expected to be resolved for a long period of time, and (c) level of the Company’s experience in the field. When it becomes probable that events will occur, for which variable consideration was constrained at inception of the contract, the Company allocates the related consideration to the separate performance obligations in the same manner as described below. At inception of a contract, the Company allocates the transaction price to the distinct performance obligations based upon their relative standalone selling prices. Standalone selling price is the price at which an entity would sell a promised good or service separately to a customer. The best evidence of standalone selling price is an observable price of a good or service when sold separately by an entity in similar circumstances to similar customers. Since the Company typically does not have such evidence, it estimates standalone selling price so that the amount that is allocated to each performance obligation equals the amount that the Company expects to receive for transferring goods or services. The methods that the Company uses to make such estimates include (1) the adjusted market assessment approach, under which the Company forecasts and analyzes CR845/difelikefalin in the appropriate market, the phase of clinical development as well as considering recent similar license arrangements within the same phase of clinical development, therapeutic area, type of agreement, etc. and (2) the expected cost of satisfying the performance obligations plus a margin, or the expected cost plus a margin approach. The Company recognizes revenue when, or as, it satisfies a performance obligation by transferring a promised good or service to a customer and the customer obtains control of the good or service. Revenue related to the grant of a license that is a distinct performance obligation and that is deemed to be functional IP is recognized at the point in time that the Company has the right to payment for the license, the customer has legal title to the license and can direct the use of the license (for example, to grant sublicenses), the customer has the significant risks and rewards of ownership of the license and the customer has accepted the asset (license) by signing the license agreement. Recognition of revenue related to R&D services that are a distinct performance obligation or that are combined with granting of a license as a single performance obligation is deferred at inception of a contract and is recognized as those services are performed based on the costs incurred as a percentage of the estimated total costs to be incurred to complete the performance obligation. Milestone payments are considered to be variable consideration and are not included in the transaction price at inception of the contract if it is uncertain that the milestone will be achieved. Rather, when it becomes probable that the milestone will be achieved and, therefore, there will not be a significant reversal of revenue in future periods, the respective amount to be earned is included in the transaction price, allocated to the distinct performance obligations based on their relative standalone selling price and recognized as revenue, as described above. Sales milestones and sales-based royalty payments related to a license of IP are recognized as revenue when the respective sales occur. Other Accounting Pronouncements Recently Adopted In August 2018, the SEC adopted amendments to certain disclosure requirements in Securities Act Release No. 33-10532, Disclosure Update and Simplification As of January 1, 2018, the Company adopted ASU No. 2017-09, Compensation – Stock Compensation (Topic 718) - Scope of Modification Accounting Stock-based Compensation As of January 1, 2018, the Company adopted ASU Business Combinations (Topic 805), Clarifying the Definition of a Business, , As of January 1, 2018, the Company adopted ASU No. 2016-18, Statement of Cash Flows (Topic 230), Restricted Cash Restricted Cash Accounting Pronouncements Not Yet Adopted In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement In June 2018, the FASB issued ASU No. 2018-07, Compensation—Stock Compensation (Topic 718) Improvements to Nonemployee Share-Based Payment Accounting In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) Commitments and Contingencies Leases (Topic 842): Targeted Improvements

Available-for-Sale Marketable S

Available-for-Sale Marketable Securities	9 Months Ended
	Sep. 30, 2018
Investments Debt And Equity Securities [Abstract]
Available-for-Sale Marketable Securities	3. Available-for-Sale Marketable Securities As of September 30, 2018 and December 31, 2017, the Company’s available-for-sale marketable securities consisted of money market funds and debt securities issued by the U.S. Treasury, U.S. government-sponsored entities and by investment grade institutions. The following tables summarize the Company's available-for-sale marketable securities by major type of security as of September 30, 2018 and December 31, 2017: As of September 30, 2018 Gross Unrealized Type of Security Amortized Cost Gains Losses Estimated Fair Value Money market funds $ 51,428 $ 27 $ — $ 51,455 U.S. Treasury securities 2,996 — — 2,996 U.S. government agency obligations 2,592 — — 2,592 Corporate bonds 10,933 1 (5 ) 10,929 Commercial paper 41,386 1 (11 ) 41,376 Total available-for-sale marketable securities $ 109,335 $ 29 $ (16 ) $ 109,348 As of December 31, 2017 Gross Unrealized Type of Security Amortized Cost Gains Losses Estimated Fair Value Money market funds $ 39,988 $ — $ (37 ) $ 39,951 U.S. government agency obligations 7,799 — (5 ) 7,794 Corporate bonds 15,919 — (12 ) 15,907 Commercial paper 19,545 — (16 ) 19,529 Total available-for-sale marketable securities $ 83,251 $ — $ (70 ) $ 83,181 All available-for-sale marketable securities are classified in the Company’s Condensed Balance Sheets as Marketable securities. The Company classifies its marketable debt securities based on their contractual maturity dates. As of September 30, 2018 As of December 31, 2017 Contractual maturity Amortized Cost Fair Value Amortized Cost Fair Value Less than one year $ 57,907 $ 57,893 $ 43,263 $ 43,230 During the nine months ended September 30, 2018, the Company sold shares of a money market fund, that is classified as an available-for-sale marketable security, with a total fair value of $28,250. The cost of the money market fund shares that were sold was determined by specific identification. The sales of the shares of the money market fund resulted in a realized loss of $32. The following tables show the fair value of the Company's available-for-sale marketable securities that have unrealized losses and that are deemed to be only temporarily impaired, aggregated by investment category and length of time that the individual investments have been in a continuous unrealized loss position. As of September 30, 2018 Less than 12 Months 12 Months or Greater Total Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Corporate bonds $ 10,929 $ (5 ) $ — $ — $ 10,929 $ (5 ) Commercial paper 41,376 (11 ) — — 41,376 (11 ) Total $ 52,305 $ (16 ) $ — $ — $ 52,305 $ (16 ) As of December 31, 2017 Less than 12 Months 12 Months or Greater Total Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Money market funds $ 39,951 $ (37 ) $ — $ — $ 39,951 $ (37 ) U.S. government agency obligations 7,794 (5 ) — — 7,794 (5 ) Corporate bonds 15,907 (12 ) — — 15,907 (12 ) Commercial paper 19,031 (16 ) — — 19,031 (16 ) Total $ 82,683 $ (70 ) $ — $ — $ 82,683 $ (70 ) As of September 30, 2018 and December 31, 2017, the Company held a total of 26 out of 31 positions and 30 out of 31 positions, respectively, that were in an unrealized loss position, none of which had been in an unrealized loss position for 12 months or greater. Based on the Company’s review of these securities, the Company believes that the cost basis of its available-for-sale marketable securities is recoverable and that, therefore, it had no other-than-temporary impairments on these securities as of September 30, 2018 and December 31, 2017. The Company does not intend to sell these debt securities before maturity and the Company believes it is not more likely than not that it will be required to sell these securities before the recovery of their amortized cost basis, which may be maturity.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
Accumulated Other Comprehensive Income (Loss)	4. Accumulated Other Comprehensive Income (Loss) The following table summarizes the changes in accumulated other comprehensive income (loss), or AOCI, net of tax, from unrealized gains (losses) on available-for-sale marketable securities, the Company's only component of AOCI, for the nine months ended September 30, 2018 and September 30, 2017. Total Accumulated Other Comprehensive Income (Loss) Balance, December 31, 2017 $ (70 ) Other comprehensive income before reclassifications 51 Amount reclassified from accumulated other comprehensive loss 32 Net current period other comprehensive income 83 Balance, September 30, 2018 $ 13 Balance, December 31, 2016 $ 3 Other comprehensive income before reclassifications 41 Amount reclassified from accumulated other comprehensive income (4 ) Net current period other comprehensive income 37 Balance, September 30, 2017 $ 40 The reclassifications out of AOCI and into net loss were as follows: Three Months Ended September 30, Nine Months Ended September 30, Affected Line Item in the Statements of Component of AOCI 2018 2017 2018 2017 Operations Unrealized gains (losses) on available- for-sale marketable securities $ (17 ) $ — $ (32 ) $ 4 Other income — — — — Benefit from income taxes $ (17 ) $ — $ (32 ) $ 4 The amounts reclassified out of AOCI into net loss were determined by specific identification.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	5. Fair Value Measurements As of September 30, 2018 and December 31, 2017, the Company’s financial instruments consisted of cash and cash equivalents, available-for-sale marketable securities, restricted cash, accounts payable and accrued liabilities. The fair values of cash and cash equivalents, restricted cash, accounts payable and accrued liabilities approximate their carrying values due to the short-term nature of these financial instruments. Available-for-sale marketable securities are reported on the Company’s Condensed Balance Sheets as Marketable Securities at their fair values, based upon pricing of securities with the same or similar investment characteristics as provided by third-party pricing services, as described below. Current accounting guidance defines fair value, establishes a framework for measuring fair value in accordance with ASC section 820, and requires certain disclosures about fair value measurements. The valuation techniques included in the guidance are based on observable and unobservable inputs. Observable inputs reflect readily obtainable data from independent sources, while unobservable inputs reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability and are developed based on the best information available in the circumstances. The Company classifies its investments in a fair value hierarchy that is intended to increase consistency and comparability in fair value measurements and related disclosures. The fair value hierarchy is divided into three levels based on the source of inputs as follows: • Level 1 – Observable inputs – quoted prices in active markets for identical assets and liabilities. • Level 2 – Observable inputs other than the quoted prices in active markets for identical assets and liabilities – such as quoted prices for similar instruments, quoted prices for identical or similar instruments in inactive markets, or other inputs that are observable or can be corroborated by observable market data. • Level 3 – Unobservable inputs – includes amounts derived from valuation models where one or more significant inputs are unobservable and require the Company to develop relevant assumptions. Valuation Techniques - Level 2 Inputs The Company estimates the fair values of its financial instruments categorized as level 2 in the fair value hierarchy, including U.S. Treasury securities, U.S. government agency obligations, corporate bonds, commercial paper and money market funds with similar underlying investments, by taking into consideration valuations obtained from third-party pricing services. The pricing services use industry standard valuation models, including both income- and market-based approaches, 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, benchmark yields, issuer credit spreads, benchmark securities, and other observable inputs. The Company obtains a single price for each financial instrument and does not adjust the prices obtained from the pricing service. The Company validates the prices provided by its third-party pricing services by reviewing their pricing methods, obtaining market values from other pricing sources and comparing them to the share prices presented by the third-party pricing services. After completing its validation procedures, the Company did not adjust or override any fair value measurements provided by its third-party pricing services as of September 30, 2018 or December 31, 2017. The following tables summarize the Company’s financial assets measured at fair value on a recurring basis as of September 30, 2018 and December 31, 2017. Fair value measurement as of September 30, 2018: Financial assets Quoted prices in Significant other Significant active markets for observable unobservable identical assets inputs inputs Type of Instrument Total (Level 1) (Level 2) (Level 3) Cash and cash equivalents: Money market fund and checking accounts $ 96,729 $ 96,729 $ — $ — Available-for-sale marketable securities: Money market funds 51,455 — 51,455 — U.S. Treasury securities 2,996 — 2,996 — U.S. government agency obligations 2,592 — 2,592 — Corporate bonds 10,929 — 10,929 — Commercial paper 41,376 — 41,376 — Restricted cash: Commercial money market account 769 769 — — Total financial assets $ 206,846 $ 97,498 $ 109,348 $ — Fair value measurement as of December 31, 2017: Financial assets Quoted prices in Significant other Significant active markets for observable unobservable identical assets inputs inputs Type of Instrument Total (Level 1) (Level 2) (Level 3) Cash and cash equivalents: Money market fund and checking accounts $ 9,388 $ 9,388 $ — $ — Available-for-sale marketable securities: Money market fund 39,951 — 39,951 — U.S. government agency obligations 7,794 — 7,794 — Corporate bonds 15,907 — 15,907 — Commercial paper 19,529 — 19,529 — Restricted cash: Commercial money market account 769 769 — — Total financial assets $ 93,338 $ 10,157 $ 83,181 $ — There were no purchases, sales or maturities of Level 3 financial assets and no unrealized gains or losses related to Level 3 available-for-sale marketable securities for the nine months ended September 30, 2018. There were no transfers of financial assets between Levels 1, 2, or 3 classifications during the nine months ended September 30, 2018.

Restricted Cash

Restricted Cash	9 Months Ended
	Sep. 30, 2018
Receivables [Abstract]
Restricted Cash	6. Restricted Cash The Company is required to maintain a stand-by letter of credit as a security deposit under its lease for its office space in Stamford, Connecticut (refer to Note 15, Commitments and Contingencies The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the Condensed Balance Sheets that sum to the total of the same such amounts shown in the Condensed Statements of Cash Flows. September 30, 2018 December 31, 2017 Cash and cash equivalents $ 96,729 $ 9,388 Restricted cash, current assets 361 — Restricted cash, long-term assets 408 769 Total cash, cash equivalents, and restricted cash shown in the Condensed Statements of Cash Flows $ 97,498 $ 10,157

Prepaid Expenses

Prepaid Expenses	9 Months Ended
	Sep. 30, 2018
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Prepaid Expenses	7. Prepaid expenses As of September 30, 2018, prepaid expenses were $4,218, consisting of $3,466 of prepaid R&D clinical costs, $505 of prepaid insurance and $247 of other prepaid costs. As of December 31, 2017, prepaid expenses were $1,635, consisting of $1,287 of prepaid R&D clinical costs, $124 of prepaid insurance, and $224 of other prepaid costs.

Accounts Payable and Accrued Ex

Accounts Payable and Accrued Expenses	9 Months Ended
	Sep. 30, 2018
Payables And Accruals [Abstract]
Accounts Payable and Accrued Expenses	8. Accounts Payable and Accrued Expenses Accounts payable and accrued expenses consist of the following: September 30, 2018 December 31, 2017 Accounts payable $ 2,638 $ 3,829 Accrued research projects 8,978 2,356 Accrued professional fees 253 384 Accrued compensation and benefits 2,011 1,864 Accrued other 123 73 Total $ 14,003 $ 8,506

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
Stockholders' Equity	9. Stockholders’ Equity On April 5, 2017, the Company closed an underwritten follow-on offering for 5,117,500 shares of its common stock, . The Company received net proceeds This offering was made p On May 17, 2018, the Company issued 1,174,827 shares of its common stock to Vifor in connection with the license agreement entered into with VFMCRP (refer to Note 10, Collaboration and Licensing Agreements On July 18, 2018, the Company entered into an underwriting agreement with Jefferies LLC and Merrill Lynch, Pierce, Fenner & Smith Incorporated, as representatives of the several underwriters named therein, relating to the issuance and sale by the Company of up to 5,175,000 shares of its common stock, On July 23, 2018, the Company closed the offering, including the full exercise of the underwriters’ option to purchase 675,000 additional shares of common stock. The Company .

Collaboration and Licensing Agr

Collaboration and Licensing Agreements	9 Months Ended
	Sep. 30, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Collaboration and Licensing Agreements	10. Collaboration and Licensing Agreements Vifor Fresenius Medical Care Renal Pharma Ltd. On May 17, 2018, the Company entered into a license agreement, or the VFMCRP Agreement, with VFMCRP under which the Company granted VFMCRP an exclusive, royalty-bearing license, or the VFMCRP License, to seek regulatory approval to commercialize, import, export, use, distribute, offer for sale, promote, sell and otherwise commercialize CR845/difelikefalin injection, or the Licensed Product, for all therapeutic uses to prevent, inhibit or treat itch associated with pruritus in hemodialysis and peritoneal-dialysis patients, or the Field, worldwide (excluding the United States, Japan and South Korea), or the Territory. VFMCRP cannot perform development activities on their own unless specifically allocated to VFMCRP by the Joint Development Committee, or JDC, and Joint Steering Committee, or JSC. The Company’s membership on the JSC or JDC is at its sole discretion and is not its obligation. The Company is responsible, at its own cost, to undertake clinical and non-clinical development, or the R&D services. The Company is also responsible to provide all content and subject matter expertise required for registration with the European Medicines Agency, or EMA, in the European Union, or the EU, that will be needed by VFMCRP for such registration, including participation in regulatory meetings, as needed. If third-party costs incurred by the Company with respect to its clinical development for the EMA registration exceed $20,000, such excess costs will be shared equally by the Company and VFMCRP. VFMCRP will contribute, at its own cost, its clinical development expertise as reasonably useful for such development activities, such as preparing the clinical results that the Company presents to it in a format acceptable to the EMA to obtain marketing approval in the EU. The Company has identified two performance obligations under ASC 606: (1) granting of the VFMCRP License and (2) the R&D services. The Company has determined that these two performance obligations are not capable of being distinct (i.e., do not have standalone value for VFMCRP) because VFMCRP cannot benefit (derive potential cash flows) from either one on its own or together with other resources that are readily available to it since VFMCRP is relying on the Company’s expertise in investigating chronic kidney disease-associated pruritus, or CKD-aP, and its know-how obtained from multiple years of pre-clinical and clinical development, and years of interactions with the FDA which other companies or CROs would not have. The VFMCRP License does not provide benefit to VFMCRP until and unless the Company conducts the pivotal clinical trials and other supportive trials in CKD-aP to gather sufficient clinical data for VFMCRP to obtain marketing approval in the Territory. Furthermore, VFMCRP does not have the right to perform development activities on its own unless specifically allocated by the JDC or JSC. The two identified performance obligations are also not distinct within the context of the contract, (i.e., are not separately identifiable from each other) because of the nature of the promise within the context of the contract. The nature of the promise is to transfer a combined deliverable to VFMCRP based on the agreement (to support the ability of VFMCRP to commercialize the Licensed Product) and the Company determined that the VFMCRP License and the R&D services are inputs rather than a transfer of each of these goods and services individually. In addition, the two identified performance obligations are highly interrelated and interdependent because satisfaction of both performance obligations is required for VFMCRP to derive benefit from the VFMCRP Agreement for commercialization of the Licensed Product in the Territory. Therefore, the two performance obligations are not distinct from each other and are accounted for as a single performance obligation. Upon entry into the VFMCRP Agreement, VFMCRP made a non-refundable, non-creditable $50,000 upfront payment to the Company and Vifor purchased 1,174,827 shares of the Company’s common stock, or the Vifor Shares, for $20,000 at a price of $17.024 per share, which represents a premium over a pre-determined average closing price of the Company’s common stock. The purchase of the Company’s common stock was governed by a separate stock purchase agreement. The excess of the stock purchase price over the cost of the Vifor Shares at the closing price of the Company’s common stock on the purchase date of $5,444 was added to the upfront payment for accounting purposes. The Company is eligible to receive from VFMCRP regulatory and commercial milestone payments in the aggregate of up to $470,000, consisting of up to $30,000 in regulatory milestones and up to $440,000 in tiered commercial milestones, all of which are sales-related. The Company is also eligible to receive tiered double-digit royalty payments based on annual net sales, as defined in the VFMCRP Agreement, of CR845/difelikefalin injection in the Licensed Territories. The Company retains full commercialization rights for CR845/difelikefalin injection for the treatment of CKD-aP in the United States except in the dialysis clinics of Fresenius Medical Care North America, or FMCNA, where VFMCRP and the Company will promote CR845/difelikefalin injection under a profit-sharing arrangement (subject to the terms and conditions of the VFMCRP Agreement) based on net FMCNA clinic sales recorded by the Company. At inception of the VFMCRP Agreement, there was significant uncertainty as to whether marketing approval would be obtained in the Territory for the Licensed Product. Therefore, at that time, there was a significant probability that any potential revenue from sales of the Licensed Product that would be included in the transaction price would be reversed when the uncertainty is resolved. Consequently, any sales royalties and sales milestones are constrained from the transaction price at inception of the VFMCRP Agreement and will be recognized as revenue if, and when, such sales transactions occur in the future. At inception of the VFMCRP Agreement, the transaction price of $55,444 was allocated entirely to the one combined performance obligation, as described above, and was initially recorded as deferred revenue. License and milestone revenue will be recognized proportionately as the R&D services are conducted (i.e., prior to submission of an NDA). The license also requires VFMCRP to promote and take orders in the U.S. for sale by the Company to FMC U.S. Dialysis Clinics and allows VFMCRP to grant sub-licenses, which, in certain cases, requires the Company’s prior written consent. The Company retains the rights to import, distribute, promote, sell and otherwise commercialize the Licensed Product outside of the Field and outside of the Territory. The Company retains the rights to make and have made the Licensed Product in the Territory for commercial sale by VFMCRP in the Field in or outside the Territory and for supply of Licensed Product to VFMCRP under the terms of a supply agreement, or the Supply Agreement. The supply price will be the Company’s cost of goods sold, as calculated under U.S. GAAP, plus an agreed upon margin. The Supply Agreement will co-terminate with the VFMCRP Agreement. In regards to a supply agreement, the VFMCRP Agreement only includes a requirement for the Company to negotiate in good faith with VFMCRP. After the execution of the VFMCRP Agreement, a separate agreement to supply them with the Licensed Product would be entered into, although the Company has no obligation to execute a supply agreement. In the event that the parties fail to enter into a Supply Agreement or if the Company fails to provide Licensed Product on a timely basis, VFMCRP has the right to manufacture or have manufactured the Licensed Product in and outside the Territory. The Supply Agreement will be accounted for as a customer option that is not a material right because the selling price of the Licensed Product under the Supply Agreement is the Company’s cost of goods sold plus an agreed upon margin, which is commensurate with the “cost of goods sold plus” model that the Company would charge other parties under similar agreements (the standalone selling price) and not at a discount. Therefore, the sale of clinical compound to VFMCRP is not a performance obligation under the VFMCRP Agreement but rather the Supply Agreement is a separate agreement from the VFMCRP Agreement. The only performance obligation under the Supply Agreement is the delivery of the Licensed Product to VFMCRP for commercialization. Revenue from the sale of the Licensed Product to VFMCRP will be recognized as Clinical Supply revenue in the Company’s Statements of Comprehensive Loss as sales of the Licensed Product occur. As of September 30, 2018, no supply agreement has been entered into between the Company and VFMCRP. The VFMCRP Agreement terminates upon the expiration of all royalty terms with respect to the Licensed Products, which expire on a Product-by-Product and country-by-country basis, at the latest of (a) the expiration of all patent rights licensed to VFMCRP covering such Licensed Product; (b) the expiration of all regulatory and data exclusivity applicable to such Licensed Product in such country and (c) the tenth anniversary of the first commercial sale of such Product in such country. The VFMCRP Agreement may be terminated earlier by either party for material breach that is not cured within 60 days, bankruptcy by either party and by both parties upon mutual written consent. The Company may terminate the VFMCRP Agreement if VFMCRP challenges the validity of any licensed patent rights, except if such patent challenge results from the Company’s action against VFMCRP for infringement of any licensed patent in the Territory. In addition, upon the earlier of (1) the acceptance for filing of an NDA covering Licensed Product filed with the FDA (after completion of the Phase 3 program) or (2) the third anniversary of the Effective Date, the VFMCRP Agreement may be terminated by VFMCRP in its entirety or with respect to any countries within the Territory upon written notice to the Company. Such termination will be effective twelve months following the date of such notice. If the VFMCRP Agreement terminates early for any reason stated above, VFMCRP’s licenses will terminate, VFMCRP’s rights to use the Company’s confidential information and the Company’s know-how will revert to the Company and VFMCRP will assign and transfer to the Company all right, title and interest in all regulatory applications (IND’s and NDA’s), regulatory approval applications and regulatory approvals in the Territory covering Licensed Product. Maruishi Pharmaceutical Co., Ltd. In April 2013, the Company entered into a license agreement with Maruishi, or the Maruishi Agreement, under which the Company granted Maruishi an exclusive license to develop, manufacture, and commercialize drug products containing CR845/difelikefalin for acute pain and/or uremic pruritus in Japan. Maruishi has the right to grant sub-licenses in Japan, which entitles the Company to receive sub-license fees, net of prior payments made by Maruishi to the Company. Under the Maruishi Agreement, the Company and Maruishi are required to use commercially reasonable efforts, at their own expense, to develop, obtain regulatory approval for and commercialize CR845/difelikefalin in the United States and Japan, respectively. In addition, the Company provided Maruishi specific clinical development services for CR845/difelikefalin used in Maruishi’s field of use. Under the Maruishi Agreement, the Company identified two performance obligations in accordance with ASC 606: (1) the license; and (2) the R&D services specific to the uremic pruritus field of use (specified as Phase 1 and proof-of-concept clinical trials), both of which were determined to have standalone value. The Company determined that these performance obligations had standalone value due to the fact that Maruishi obtained the right to develop the compound on its own and the Company was specifically contracted to perform specific R&D services as noted above. The Company believes that these early stage R&D services performed by the Company did not require any specific expertise or know-how, but rather could have been completed by outside third parties, therefore providing standalone value to Maruishi. In March 2017, Maruishi entered into a sub-license agreement with Kissei Pharmaceutical Co. Ltd. for the development and sales/marketing of CR845/difelikefalin (called MR13A9 by Maruishi) for the treatment of uremic pruritus in dialysis patients in Japan. Consequently, for the nine months ended September 30, 2017, the Company recognized revenue of $843 related to the sub-license fee. The Company allocated the amount of the sub-license fee to each of the two identified performance obligations in the same proportion as the upfront license fee that the Company received at inception of the Maruishi Agreement. Accordingly, $530 was recognized as license and milestone fees revenue and $313 was recognized as collaborative revenue. During the three and nine months ended September 31, 2018, the Company recognized clinical compound revenue of $33 from the sale of clinical compound to Maruishi. During the nine months ended September 30, 2017, the Company recognized clinical compound revenue of $68 from the sale of clinical compound to Maruishi. There were no sales of clinical compound during the three months ended September 30, 2017. The Company incurred R&D expense related to the Maruishi Agreement of $30, consisting of cost of clinical compound, during the three and nine months ended September 30, 2018. The Company incurred R&D expense related to the Maruishi Agreement of $61, consisting of cost of clinical compound, during the nine months ended September 30, 2017. The Company did not incur any R&D expense for clinical compound during the three months ended September 30, 2017. Chong Kun Dang Pharmaceutical Corporation In April 2012, the Company entered into a license agreement, or the CKDP Agreement, with Chong Kun Dang Pharmaceutical Corporation, or CKDP, in South Korea, under which the Company granted CKDP an exclusive license to develop, manufacture and commercialize drug products containing CR845/difelikefalin in South Korea. The Company and CKDP are each required to use commercially reasonable efforts, at their respective expense, to develop, obtain regulatory approval for and commercialize CR845/difelikefalin in the United States and South Korea, respectively. The Company identified the granting of the license as its only performance obligation under the CKDP Agreement. Under the terms of the CKDP Agreement, the Company is eligible to receive milestone payments upon the achievement of defined clinical and regulatory events as well as tiered royalties, with percentages ranging from the high single digits to the high teens, based on net sales of products containing CR845/difelikefalin in South Korea, if any, and share in any sub-license fees.

Revenue Recognition

Revenue Recognition	9 Months Ended
	Sep. 30, 2018
Revenue Recognition [Abstract]
Revenue Recognition	11. Revenue Recognition The Company currently recognizes revenue in accordance with ASC 606, as amended, for the VFMCRP, Maruishi and CKDP agreements (see Note 10 , Collaboration and Licensing Agreements Contract balances As of September 30, 2018, the Company had deferred revenue, current of $29,242 and deferred revenue, non-current of $18,300 related to the performance obligations from the VFMCRP Agreement and had no balances of receivables or other assets related to the VFMCRP Agreement. There were no balances of receivables, other assets or deferred revenue relating to the Maruishi and CKDP agreements as of September 30, 2018. As of December 31, 2017, the Company had no balances of receivables, other assets or deferred revenue related to the Maruishi and CKDP Agreements. Performance obligations Under the VFMCRP Agreement, the Company’s performance obligations of granting a license to allow VFMCRP to commercialize CR845/difelikefalin injection worldwide, except in the United States, Japan and South Korea, which occurred at inception of the contract in May 2018, and performing R&D services by the Company to obtain sufficient clinical data which will be shared with VFMCRP to allow them to receive regulatory approval to sell CR845/difelikefalin in the licensed territory, are not distinct, and are accounted for as a single performance obligation during the period that the R&D services are rendered (see Note 10, Collaboration and Licensing Agreements The Company’s distinct performance obligations under the Maruishi Agreement include transfer of the license to the Company’s IP, which allowed Maruishi to develop and commercialize CR845/difelikefalin, for acute pain and uremic pruritus indications in Japan, which occurred at inception of the contract in 2013, and performance of R&D services, which occurred from 2013 to 2015, as those services were rendered. The Company agreed to conduct limited work on an oral tablet formulation of CR845/difelikefalin and to conduct Phase 1 and proof-of-concept Phase 2 clinical trials of an intravenous formulation of CR845/difelikefalin to be used to treat patients with uremic pruritus. The Company agreed to transfer the data and information from such development to Maruishi for its efforts to obtain regulatory approval in Japan. These activities are referred to as R&D services. The Company’s only performance obligation under the supply agreement with Maruishi is to deliver clinical compound to Maruishi in accordance with the receipt of purchase orders. If and when the Company enters into a supply agreement with VFMCRP, the Company’s only performance obligation under this supply agreement would be to deliver CR845/difelikefalin injection to VFMCRP in accordance with the receipt of purchase orders. Under the CKDP Agreement, the Company’s only performance obligation is to transfer the license to the Company’s IP related to CR845/difelikefalin, which occurred at inception of the contract in 2012. Upon execution of the VFMCRP Agreement, the Maruishi Agreement and the CKDP Agreement, the Company received a single fixed payment from each counterparty in exchange for granting the respective licenses and performing its other obligations. In addition, each of the counterparties made an equity investment in the Company’s common stock. Transaction price allocated to the remaining performance obligations At inception of the VFMCRP Agreement, the entire transaction price of $55,444 was allocated to the one combined performance obligation, as described above. As of September 30, 2018, $7,903 of that amount was recognized as license and milestone fees revenue based on the percentage of R&D services that had been completed. As of September 30, 2018, there were no remaining performance obligations under either the Maruishi Agreement or the CKDP Agreement, although the Company is eligible to receive milestone payments and sales royalties in the future. Significant judgments In applying ASC 606, as amended, to its three contracts, the Company made the following judgments that significantly affect the timing and amount of revenue recognition: 1. Determination of the number of distinct performance obligations in a contract The VFMCRP Agreement contains one distinct performance obligation, which includes the Company’s two performance obligations to grant a license to VFMCRP and conduct R&D services. Both of those performance obligations are inputs to the promise, within the context of the contract, to transfer a combined output for which VFMCRP has contracted (the ability of VFMCRP to commercialize the Licensed Product) (see Note 10, Collaboration and Licensing Agreements The Maruishi Agreement contains two distinct performance obligations: the granting of the license and the promise to deliver defined R&D services. Under the Maruishi Agreement, the license and the R&D services represent distinct goods or services from each other because Maruishi is able to benefit from the license on its own or together with other resources that are readily available to it (i.e., capable of being distinct). Maruishi’s ability to benefit from the license without the R&D services is indicated by its ability to conduct clinical trials of CR845/difelikefalin on its own and by the provision in the Maruishi Agreement whereby if the Company suspends or discontinues its development activity, the Company will provide information regarding its development efforts up to that point so that Maruishi may continue development and commercialization of the product in Japan. Therefore, the R&D services do not significantly affect Maruishi’s ability to use and benefit from the license. In addition, the Company’s promise in the Maruishi contract to transfer the license is separately identifiable from the promise to provide defined R&D services (i.e., distinct within the context of the contract) because the Company is not using the goods or services as inputs to produce or deliver the combined output or outputs specified by the customer. The combined output specified by Maruishi is its right to conduct development activities related to CR845/difelikefalin in Japan, which could result in regulatory approval in Japan. That right is derived from the Company’s grant of the license. Maruishi is conducting clinical trials on its own and does not require the R&D services provided by the Company. Furthermore, the R&D services do not significantly modify or customize the license and vice versa. Finally, the license and R&D services are not highly interdependent or highly interrelated because the Company is able to fulfill its promise to transfer the initial license independently from its promise to subsequently provide the R&D services, which Maruishi can obtain on its own. The only performance obligation in the CKDP Agreement is the granting of the license. 2. Determination of the transaction price, including whether any variable consideration is included at inception of the contract The transaction price is the amount of consideration that the Company expects to be entitled to in exchange for transferring promised goods or services to the customer. The transaction price must be determined at inception of a contract and may include amounts of variable consideration. However, there is a constraint on inclusion of variable consideration, such as milestone payments or sales-based royalty payments, in the transaction price related to licenses of IP, if there is uncertainty at inception of the contract as to whether such consideration will be recognized in the future (see Note 2, Accounting Pronouncements Recently Adopted: Revenue Recognition The decision as to whether or not it is probable that a significant reversal of revenue will occur in the future, depends on the likelihood and magnitude of the reversal and is highly susceptible to factors outside the entity’s influence (for example, the Company cannot determine the outcome of clinical trials; the Company cannot determine if or when they or the counterparty will initiate or complete clinical trials; and the Company’s ability to obtain regulatory approval is difficult). In addition, the uncertainty is not expected to be resolved for a long period of time (in the order of years) and finally, the Company has limited experience in the field. Therefore, at inception of the VFMCRP Agreement, the Maruishi Agreement and the CKDP Agreement, milestones and sales-based royalty payments were not included in the transaction price based on the factors noted above. Under the VFMCRP Agreement, the single combined performance obligation will be satisfied as the R&D services are rendered and the transaction price, including the upfront payment of $50,000 and the premium on the common stock purchased by VFMCRP of $5,444, will be recognized as revenue as the R&D services are performed based on the costs incurred as a percentage of the estimated total costs to be incurred to complete the performance obligation. The remaining potential consideration was considered to be variable consideration and was constrained at inception of the contract, including regulatory and sales milestones and sales royalties (see Note 10, Collaboration and Licensing Agreements All performance obligations under the Maruishi Agreement and the CKDP Agreement were satisfied by the end of 2015. In the future, any milestone event will be recognized in accordance with Note 2, Accounting Pronouncements Recently Adopted: Revenue Recognition, Under the Maruishi Agreement, the transaction price includes only the non-refundable and non-creditable upfront license fee of $15,337, including the premium of $337 from the sale of Company stock to Maruishi, that was paid to the Company at inception of the contract. The remaining potential consideration was considered to be variable consideration and was constrained at inception of the contract, including an aggregate of up to $10,500, which the Company is eligible to receive upon achievement of clinical development and regulatory milestones, a one-time sales milestone of one billion Yen when a certain sales level is attained; a mid-double-digit percentage of all non-royalty payments received by Maruishi from its sub-licensees, if any; and tiered royalties based on net sales of products containing CR845/difelikefalin in Japan, if any, with minimum royalty rates in the low double digits and maximum royalty rates in the low twenties. Under the CKDP Agreement, the transaction price includes only the non-refundable and non-creditable upfront license fee of $646, including the premium of $83 from the sale of Company stock to CKDP, that was paid to the Company at inception of the contract. The remaining consideration was considered to be variable consideration and was constrained at inception of the contract, including an aggregate of up to $3,750, which the Company is eligible to earn upon achievement of clinical development and regulatory milestones. The Company is also eligible to receive a mid-double-digit percentage of all non-royalty payments received by CKDP from its sub-licensees, if any, and tiered royalties ranging from the high single digits to the high teens based on net sales of products containing CR845/difelikefalin in South Korea, if any. 3. Determination of the estimate of the standalone selling price of performance obligations In order to recognize revenue under ASC 606, as amended, for contracts for which more than one distinct performance obligation has been identified, the Company must allocate the transaction price to the performance obligations based upon their standalone selling prices. The best evidence of standalone selling price is an observable price of a good or service when sold separately by an entity in similar circumstances to similar customers. If such evidence is not available, standalone selling price should be estimated so that the amount that is allocated to each performance obligation equals the amount that the entity expects to receive for transferring goods or services. The Company has identified more than one performance obligation only in the Maruishi Agreement. Since evidence based on observable prices is not available for the performance obligations under the Maruishi Agreement, the Company considered market conditions and entity-specific factors, including those contemplated in negotiating the agreements, as well as certain internally developed estimates. At inception of the Maruishi Agreement, the Company determined the estimate of standalone selling price for the license performance obligation by using the adjusted market assessment approach. Under this method, the Company forecasted and analyzed CR845/difelikefalin in the Japanese market, the phase of clinical development as well as considered recent similar license arrangements within the same phase of clinical development, therapeutic area, type of agreement, etc. To estimate the standalone selling price of the R&D services, the Company forecasted its expected costs of satisfying that performance obligation and added a margin for that service. 4. Determination of the method of allocation of the transaction price to the distinct performance obligations At inception of the Maruishi Agreement, the Company allocated the transaction price of $15,337 between the two performance obligations based on their relative standalone selling prices, determined as described above. The Company determined that the license and the R&D services had estimated standalone selling prices of $10,200 and $6,200, respectively. The resulting percentage allocations were applied to the $15,337 of total transaction price, which resulted in $9,637 being allocated to the license performance obligation, which was recognized immediately as license revenue, while $5,700 was allocated to the R&D services performance obligation. The amount allocated to the R&D services performance obligation was initially recorded as deferred revenue and was recognized as collaborative revenue as the R&D services were provided through July 2015. Since both the VFMCRP Agreement and the CKDP Agreement each contain only one distinct performance obligation, at the inception of each of those agreements, the entire transaction price was allocated to the respective performance obligation. 5. Determination of the timing of revenue recognition for contracts Revenue should be recognized when, or as, an entity satisfies a performance obligation by transferring a promised good or service to a customer; i.e., when the customer obtains control of the good or service. The licenses granted to both Maruishi and CKDP are being accounted for as distinct performance obligations. As discussed below, both licenses relate to functional IP for which revenue is recognized at a point in time – in the case of these two license agreements, the point in time is at inception of the contract because the customer obtained control of the license at that point. The licenses grant Maruishi and CKDP the right to use the Company’s IP relating to CR845/difelikefalin as it existed at the point in time that the licenses were granted. That IP has significant standalone functionality as it provides the customer with the ability to perform a function or task, such as to manufacture CR845/difelikefalin and conduct clinical trials, and is considered to be functional IP. During the license periods, the Company is continuing to develop and advance CR845/difelikefalin by conducting clinical trials. Those development efforts are for its own benefit and do not substantively change the significant standalone functionality of the licensed IP granted to Maruishi or CKDP. Therefore, the Company’s ongoing development efforts do not significantly affect the IP’s utility to which Maruishi or CKDP have rights. Furthermore, if the Company abandons its development efforts, Maruishi or CKDP may still continue to develop CR845/difelikefalin in their respective countries. The R&D services performance obligation under the Maruishi Agreement represents a separate performance obligation. The R&D services were provided to Maruishi by the Company from inception of the agreement in 2013 through the third quarter of 2015, at which time the Company had fulfilled its promise related to the R&D services. Revenue related to the R&D services performance obligation was recognized as services were performed based on the costs incurred as a percentage of the estimated total costs to be incurred to complete the performance obligation. Similarly, under the VFMCRP Agreement, revenue related to the single distinct performance obligation, which includes both granting of the license and performance of the R&D services, will be recognized as the R&D services are performed, based on the costs incurred as a percentage of the estimated total costs to be incurred to complete the performance obligation. The Company expects that the remaining amount of the transaction price that was allocated to the combined performance obligation of $47,542 at September 30, 2018 will be recognized by 2020, as the R&D services are performed, subject to certain development and regulatory uncertainties. 6. Determination of consideration as variable consideration, including factors related to inclusion in the transaction price at inception of the contract and timing of recognition as revenue. The VFMCRP Agreement, the Maruishi Agreement and the CKDP Agreement contain potential payments related to achievement of defined milestone events and royalties upon net sales of future products, which are considered to be variable consideration because of the uncertainty of occurrence of any of those events specified in those agreements at inception of the agreements. Therefore, those potential payments were not included in the transaction price at the inception of the agreements. Revenue related to achievement of milestone events is recognized when the Company has determined that it is probable that a milestone event will be achieved and there will not be a significant reversal of revenue in future periods. Upon probability of achievement of a milestone event, the most likely amount of variable consideration is included in the transaction price. Subsequent changes to the transaction price, after contract initiation, are allocated to the performance obligations in the contract on the same basis as at contract inception. Revenue for variable consideration is recognized in the same manner (point in time or over time) as for the performance obligations to which the payment amounts were allocated. The Maruishi Agreement and the CKDP Agreement specify that certain development milestones will be achieved at pre-specified defined phases of a clinical trial (such as initiation or completion or other pre-specified time during a clinical trial as specified in the agreements). During the nine months ended September 30, 2018 and 2017, no milestone events were probable of occurrence or achieved. Sublicense payments VFMCRP’s, Maruishi’s and CKDP’s right to grant sub-licenses is explicitly stated in their respective license agreements. The amount of any potential sub-license fees to be received by the Company, which is based on a formula, is considered to be variable consideration and is constrained from inclusion in the transaction price at inception of the contract since at that time it was probable that there would be a reversal of such revenue in the future because the Company did not know if a sublicense would be granted in the future. In March 2017, Maruishi entered into a sub-license agreement to the Maruishi Agreement with another pharmaceutical company in Japan for development and sales/marketing of CR845/difelikefalin for the treatment of uremic pruritus in dialysis patients in Japan. The Company first learned that the terms of the sub-license agreement had been finalized less than a month before the sub-licensee publicly announced the agreement. At that time, the Company determined that the sub-license fee would not be constrained from inclusion in the transaction price. Consequently, the Company included the amount of the sub-license fee in the transaction price and recognized revenue of $843 in the same manner as described above for milestone payments. Sales-based Royalty Payments The VFMCRP Agreement, CKDP Agreement and Maruishi Agreement each allow the Company to earn sales-based royalty payments in exchange for a license of intellectual property. In that case, the Company will recognize revenue for a sales-based royalty only when (or as) the later of the following events occurs: a. The subsequent sale or usage occurs. b. The performance obligation Since the sale (item a, above) occurs after the license was delivered (item b, above), the sales-based royalty exception, to exclude such royalty payments from the transaction price, applies to the overall revenue stream. Therefore,

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Net Loss Per Share	12. Net Loss Per Share The Company computes basic net income (loss) per share by dividing net income (loss) by the weighted-average number of shares of common stock outstanding. Diluted net income per share includes the potential dilutive effect of common stock equivalents as if such securities were exercised during the period, when the effect is dilutive. Common stock equivalents may include outstanding stock options or restricted stock units, which are included using the treasury stock method when dilutive. For the three and nine months ended September 30, 2018 and 2017, the Company excluded the effects of potentially dilutive shares that were outstanding during those respective periods from the denominator as their inclusion would be anti-dilutive due to the Company’s net losses during those periods. The denominators used in the net loss per share computations are as follows: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Basic: Weighted average common shares outstanding 38,034,216 32,591,550 34,696,835 30,729,752 Diluted: Weighted average common shares outstanding - Basic 38,034,216 32,591,550 34,696,835 30,729,752 Common stock options* — — — — Denominator for diluted net loss per share 38,034,216 32,591,550 34,696,835 30,729,752 * No amounts were considered as their effects would be anti-dilutive. Basic and diluted net loss per share are computed as follows: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Net loss $ (19,400 ) $ (12,444 ) $ (53,361 ) $ (43,948 ) Weighted-average common shares outstanding: Basic and Diluted 38,034,216 32,591,550 34,696,835 30,729,752 Net loss per share, Basic and Diluted $ (0.51 ) $ (0.38 ) $ (1.54 ) $ (1.43 ) As of September 30, 2018 and 2017, 3,780,390 and 3,492,786 stock options, respectively, were outstanding, which could potentially dilute basic earnings per share in the future, but were not included in the computation of diluted net loss per share because to do so would have been anti-dilutive. In addition, 83,791 restricted stock units granted during the three and nine months ended September 30, 2018 were also not included in the computation of diluted net loss per share because to do would have been anti-dilutive (see Note 13, Stock-Based Compensation

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	13. 2014 Equity Incentive The Company’s 2014 Equity Incentive Plan, or the 2014 Plan, is administered by the Company’s Board of Directors or a duly authorized committee thereof, referred to as the Plan administrator. The 2014 Plan provides for the grant of incentive stock options, non-statutory stock options, restricted stock awards, restricted stock unit awards, stock appreciation rights, performance stock awards and other forms of equity compensation, collectively referred to as Stock Awards. Additionally, the 2014 Plan provides for the grant of performance cash awards. Incentive stock options may be granted only to employees. All other awards may be granted to employees, including officers, non-employee directors, and consultants. No incentive stock options may be granted under the 2014 Plan after the tenth anniversary of the effective date of the 2014 Plan. Stock Awards granted under the 2014 Plan vest at the rate specified by the Plan administrator. Initial grants of Stock Awards made to employees and non-employee consultants generally vest as to 25% on the first anniversary of the date of grant and the balance ratably over the next 36 months and subsequent grants vest monthly over a period of four years from the grant date. Stock options initially granted to members of the Company’s Board of Directors vest over a period of three years in equal installments from the date of the grant, subject to the option holder’s continued service as a Director through such date. Subsequent grants to Directors that are made automatically at Annual Meetings of Stockholders vest fully on the first anniversary of the date of grant. The Plan administrator determines the term of Stock Awards granted under the 2014 Plan up to a maximum of ten years. The aggregate number of shares of the Company’s common stock reserved for issuance under the 2014 Plan has automatically increased on January 1 of each year, beginning on January 1, 2015 and will continue to increase on January 1 of each year through and including January 1, 2024, by 3% of the total number of shares of the Company’s capital stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares determined by the Company’s Board of Directors. On January 1, 2018, the aggregate number of shares of common stock that may be issued pursuant to stock awards under the 2014 Plan automatically increased from 3,920,613 to 4,900,481. The maximum number of shares that may be issued pursuant to the exercise of incentive stock options under the 2014 Plan is 30,000,000 shares. Restricted Stock Units During the three and nine months ended September 30, 2018, the Company granted a total of 83,791 restricted stock units to executive officers under the 2014 Plan with a grant date fair value of $20.21 per share. Vesting of the restricted stock units is contingent on the achievement of certain performance targets through the first quarter of 2019, subject to the recipient’s continuous service through the vesting events. The Company has determined that the probability of achievement of the performance targets cannot be determined until they are achieved, and accordingly, the Company intends to recognize compensation expense associated with these awards when, and to the extent, the restricted stock units vest in accordance with achievement of the performance targets. As of September 30, 2018, none of the performance targets had been achieved and, consequently, none of the restricted stock units had vested and no compensation expense has been recognized. Stock Options Under the 2014 Plan, the Company granted 165,000 and 415,000 stock options during the three months ended September 30, 2018 and 2017, respectively, and 897,500 and 1,253,500 stock options during the nine months ended September 30, 2018 and 2017, respectively. The fair values of stock options granted during the three and nine months ended September 30, 2018 and 2017 were estimated as of the dates of grant using the Black-Scholes option pricing model with the following assumptions: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Risk-free interest rate 2.73% - 2.99% 1.87% - 1.97% 2.51% - 2.99% 1.85% - 2.57% Expected volatility 82.6% - 87.6% 81.4% - 81.7% 82.6% - 92.8% 75.3% - 83.3% Expected dividend yield 0% 0% 0% 0% Expected life of employee options (in years) 6.25 6.25 6.25 6.25 Expected life of non-employee options (in years) — — — 10 The weighted-average grant date fair value of options granted to employees, non-employee members of the Company’s Board of Directors for their Board service and non-employee consultants during the three months ended September 30, 2018 and 2017 was $14.51 and $10.00, respectively, and during the nine months ended September 30, 2018 and 2017 was $11.25 and $11.61, respectively. As of September 30, 2018 and 2017, the Company used the Black-Scholes option valuation model with the following ranges of assumptions to re-measure the fair value of all outstanding options that had been granted to non-employee consultants during the vesting period of each tranche in accordance with ASC 505-50: September 30, 2018 2017 Risk-free interest rate 2.06% - 3.02% 1.28% - 2.28% Expected volatility 77.4% - 80.9% 75.2% - 84.0% Expected dividend yield 0% 0% Expected life of non-employee options (in years) 0.26 - 8.44 0.88 - 9.44 The weighted-average fair value of outstanding options that had been granted to non-employee consultants, as re-measured during the vesting period of each tranche in accordance with ASC 505-50, was $20.48 and $8.31 as of September 30, 2018 and 2017, respectively. On January 1, 2017, the Company adopted ASU No. 2016-09, Improvements to Employee Share-Based Payment Accounting During the three and nine months ended September 30, 2018 and 2017, the Company recognized compensation expense in the accompanying Condensed Statements of Comprehensive Loss relating to stock options, as follows: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Research and development $ 901 $ 619 $ 2,401 1,784 General and administrative 918 1,475 3,358 2,736 Total stock option expense $ 1,819 $ 2,094 $ 5,759 $ 4,520 Included in the table above are the following amounts of compensation expense recognized with regard to stock options that were granted to non-employee consultants, including the effect of re-measurement of the fair values of those options, as described above: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Research and development $ 68 $ 9 $ 189 $ 156 General and administrative 13 70 192 103 Total stock option expense $ 81 $ 79 $ 381 $ 259 A summary of stock option award activity related to employees, non-employee members of the Company’s Board of Directors and non-employee consultants as of and for the nine months ended September 30, 2018 is presented below: Number of Shares Weighted Average Exercise Price Outstanding, December 31, 2017 3,492,141 $ 11.75 Granted 897,500 15.12 Exercised (377,433 ) 9.64 Expired (58,395 ) 10.65 Forfeited (173,423 ) 12.12 Outstanding, September 30, 2018 3,780,390 $ 12.76 Options exercisable, September 30, 2018 1,797,351 The Company does not expect to realize any tax benefits from its stock option activity or the recognition of stock-based compensation expense because the Company currently has net operating losses and has a full valuation allowance against its deferred tax assets. Accordingly, no amounts related to excess tax benefits have been reported in cash flows from operations for the nine months ended September 30, 2018 and 2017.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	14. Income Taxes For the three months ended September 30, 2018 and 2017, pre-tax losses were $19,466 and $12,589, respectively, and for the nine months ended September 30, 2018 and 2017, pre-tax losses were $53,625 and $44,126, respectively. The Company recognized a full tax valuation allowance against its deferred tax assets as of September 30, 2018 and December 31, 2017. Upon adoption of ASU 2016-09 on January 1, 2017, the tax benefit related to the exercise of stock options is recognized as a deferred tax asset that is offset by a corresponding valuation allowance. The benefit from income taxes of $66 and $145 for the three months ended September 30, 2018 and 2017, respectively, and $264 and $178 for the nine months ended September 30, 2018 and 2017, respectively relates to state R&D tax credits exchanged for cash pursuant to the Connecticut R&D Tax Credit Exchange Program, which permits qualified small businesses engaged in R&D activities within Connecticut to exchange their unused R&D tax credits for a cash amount equal to 65% of the value of the exchanged credits. On December 22, 2017, the United States enacted the Tax Cuts and Jobs Act, or the Act. The Act, which is also commonly referred to as “U.S. tax reform”, significantly changed U.S. corporate income tax laws by, among other provisions, reducing the maximum U.S. corporate income tax rate from 35% to 21% starting in 2018. In accordance with the reduction in U.S. corporate income tax rate during the period of enactment, the Company reduced its deferred tax assets, which were offset by a corresponding reduction to its valuation allowance. On September 30, 2018 and December 31, 2017, the Company did not have any foreign subsidiaries and the international aspects of the Act are not applicable for the respective periods. On December 22, 2017, Staff Accounting Bulletin 118, or SAB 118, was issued by the SEC due to the complexities involved in accounting for the Act. SAB 118 requires the Company to include in its financial statements a reasonable estimate of the impact of the Act on earnings to the extent such estimate has been determined. Accordingly, the Company’s annual estimated effective tax rate for the year ending December 31, 2018 is based on the reasonable estimate guidance provided by SAB 118. The Company is continuing to assess the impact from the Act and will record adjustments in 2018, if necessary.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2018
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	15. Commitments and Contingencies Contractual obligations and commitments as of September 30, 2018, consisting of future minimum lease payments under the Company’s Stamford lease, were as follows: Payment Due for the Year Ending December 31, 2018 2019 2020 2021 2022 2023 Total Stamford operating lease $ 300 $ 1,215 $ 1,240 $ 1,264 $ 1,288 $ 1,164 $ 6,471 Stamford Operating Lease In December 2015, the Company entered into a lease agreement, or the Stamford Lease, with Four Stamford Plaza Owner LLC, or the Landlord, for office space in Stamford, Connecticut, or the Premises, for the purpose of relocating its headquarters. The initial term of the Stamford Lease commenced in May 2016, or the Commencement Date, and ends in November 2023. The Stamford Lease requires monthly lease payments, including rent escalations and rent holidays, during the initial lease term. The Company began to make rental payments from the Commencement Date. The Company records monthly rent expense on a straight-line basis from March 2016, upon taking possession of the Premises, through November 2023. As of September 30, 2018 and December 31, 2017, the balance of deferred lease obligation, representing the difference between cash rent paid and straight-line rent expense, was $895 and $876, respectively. The Stamford Lease is renewable for one five-year term. As of the Commencement Date, the Stamford landlord had made tenant improvements of approximately $1,094 to the leased premises. Such amount was included in Property and equipment, net and in Deferred lease obligation on the Company’s Balance Sheet on that date. The portion of Deferred lease obligation that is related to tenant improvements is being amortized as a reduction to rent expense over the same term as rent expense. As of September 30, 2018 and December 31, 2017, the balance of Deferred lease obligation related to tenant improvements was $734 and $842, respectively. In connection with the signing of the Stamford Lease, the Company entered into a standby letter of credit agreement for $769, which serves as a security deposit for the Premises. The standby letter of credit is automatically renewed annually through November 2023. This standby letter of credit is secured with restricted cash in a money market account (refer to Note 6, Restricted Cash

Subsequent Event

Subsequent Event	9 Months Ended
	Sep. 30, 2018
Subsequent Events [Abstract]
Subsequent Event	16. Subsequent Event On October 18, 2018, the Company and its then Chief Medical Officer, or CMO, agreed to the transition of the role from CMO to a consultant. On October 22, 2018, the Company and the former CMO entered into a Separation and Consulting Agreement, pursuant to which the former CMO will provide consulting services to the Company for a period of up to nine months. Effective October 22, 2018, a new CMO was appointed by the Company.

Basis of Presentation (Policies

Basis of Presentation (Policies)	9 Months Ended
	Sep. 30, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires the Company to make estimates and assumptions that affect the reported amounts of assets and liabilities, and disclosure of contingent assets and liabilities, as of the date of the financial statements as well as the reported amounts of revenues and expenses during the reporting period. Actual results could differ materially from the Company’s estimates and assumptions. Significant estimates include the fair value of marketable securities that are classified as level 2 of the fair value hierarchy, useful lives of fixed assets, the periods over which certain revenues will be recognized, including licensing and collaborative revenue recognized from non-refundable up-front and milestone payments, the determination of prepaid research and development, or R&D, clinical costs and accrued research projects, the amount of non-cash compensation costs related to share-based payments to employees and non-employees and the periods over which those costs are expensed and the likelihood of realization of deferred tax assets.
Significant Accounting Policies	Significant Accounting Policies There have been no material changes to the significant accounting policies previously disclosed in Note 2 to the Financial Statements in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017, except for the recent adoption of new accounting pronouncements as disclosed below.
Recent Accounting Pronouncements	Accounting Pronouncements Recently Adopted Revenue Recognition On January 1, 2018, the Company adopted Accounting Standards Update, or ASU, 2014-09, Revenue from Contracts with Customers (Topic 606) Collaboration and Licensing Agreements Revenue Recognition) The Company has entered into agreements to license its intellectual property, or IP, related to CR845/difelikefalin to develop, manufacture and/or commercialize drug products. These agreements typically contain multiple performance obligations, including licenses of IP and R&D services. Payments to the Company under these agreements may include nonrefundable license fees, payments for research activities, payments based upon the achievement of certain milestones and royalties on any resulting net product sales. The Company identifies agreements as contracts that create enforceable rights and obligations when the agreement is approved by the parties, identifies the rights of the parties and the payment terms, has commercial substance and it is probable that the Company will collect the consideration to which it will be entitled in exchange for the goods and services that will be transferred to the customer. The counterparty is considered to be a customer when it has contracted with the Company to obtain goods and services that are the output of the Company’s ordinary activities (i.e., development of pharmaceutical products) in exchange for consideration. A performance obligation is a promise to transfer distinct goods or services to a customer. Performance obligations that are both capable of being distinct and distinct within the context of the contract are considered to be separate performance obligations. Performance obligations are capable of being distinct if the counterparty is able to benefit from the good or service on its own or together with other resources that are readily available to it. Performance obligations are distinct within the context of the contract when each performance obligation is separately identifiable from each other; i.e., the Company is not using the goods or services as inputs to produce or deliver the combined output or outputs specified by the customer; one or more of the goods or services does not significantly modify or customize one of the other goods or services in the contract; and goods or services are not highly interdependent or not highly interrelated. Performance obligations that are not distinct are accounted for as a single performance obligation over the period that goods or services are transferred to the customer. The determination of whether performance obligations in a contract are distinct may require significant judgment. The transaction price is the amount of consideration that the Company expects to be entitled to in exchange for transferring promised goods or services to the customer based on the contract terms at inception of a contract. There is a constraint on inclusion of variable consideration related to licenses of IP, such as milestone payments or sales-based royalty payments, in the transaction price if there is uncertainty at inception of the contract as to whether such consideration will be recognized in the future because it is probable that there will be a significant reversal of revenue in the future when the uncertainty is resolved. The determination of whether or not it is probable that a significant reversal of revenue will occur in the future depends on the likelihood and magnitude of the reversal. Factors that could increase the likelihood or magnitude of a reversal of revenue include (a) the susceptibility of the amount of consideration to factors outside the entity’s influence, such as the outcome of clinical trials, the timing of initiation of clinical trials by the counterparty and the approval of drug product candidates by regulatory agencies, (b) situations in which the uncertainty is not expected to be resolved for a long period of time, and (c) level of the Company’s experience in the field. When it becomes probable that events will occur, for which variable consideration was constrained at inception of the contract, the Company allocates the related consideration to the separate performance obligations in the same manner as described below. At inception of a contract, the Company allocates the transaction price to the distinct performance obligations based upon their relative standalone selling prices. Standalone selling price is the price at which an entity would sell a promised good or service separately to a customer. The best evidence of standalone selling price is an observable price of a good or service when sold separately by an entity in similar circumstances to similar customers. Since the Company typically does not have such evidence, it estimates standalone selling price so that the amount that is allocated to each performance obligation equals the amount that the Company expects to receive for transferring goods or services. The methods that the Company uses to make such estimates include (1) the adjusted market assessment approach, under which the Company forecasts and analyzes CR845/difelikefalin in the appropriate market, the phase of clinical development as well as considering recent similar license arrangements within the same phase of clinical development, therapeutic area, type of agreement, etc. and (2) the expected cost of satisfying the performance obligations plus a margin, or the expected cost plus a margin approach. The Company recognizes revenue when, or as, it satisfies a performance obligation by transferring a promised good or service to a customer and the customer obtains control of the good or service. Revenue related to the grant of a license that is a distinct performance obligation and that is deemed to be functional IP is recognized at the point in time that the Company has the right to payment for the license, the customer has legal title to the license and can direct the use of the license (for example, to grant sublicenses), the customer has the significant risks and rewards of ownership of the license and the customer has accepted the asset (license) by signing the license agreement. Recognition of revenue related to R&D services that are a distinct performance obligation or that are combined with granting of a license as a single performance obligation is deferred at inception of a contract and is recognized as those services are performed based on the costs incurred as a percentage of the estimated total costs to be incurred to complete the performance obligation. Milestone payments are considered to be variable consideration and are not included in the transaction price at inception of the contract if it is uncertain that the milestone will be achieved. Rather, when it becomes probable that the milestone will be achieved and, therefore, there will not be a significant reversal of revenue in future periods, the respective amount to be earned is included in the transaction price, allocated to the distinct performance obligations based on their relative standalone selling price and recognized as revenue, as described above. Sales milestones and sales-based royalty payments related to a license of IP are recognized as revenue when the respective sales occur. Other Accounting Pronouncements Recently Adopted In August 2018, the SEC adopted amendments to certain disclosure requirements in Securities Act Release No. 33-10532, Disclosure Update and Simplification As of January 1, 2018, the Company adopted ASU No. 2017-09, Compensation – Stock Compensation (Topic 718) - Scope of Modification Accounting Stock-based Compensation As of January 1, 2018, the Company adopted ASU Business Combinations (Topic 805), Clarifying the Definition of a Business, , As of January 1, 2018, the Company adopted ASU No. 2016-18, Statement of Cash Flows (Topic 230), Restricted Cash Restricted Cash Accounting Pronouncements Not Yet Adopted In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement In June 2018, the FASB issued ASU No. 2018-07, Compensation—Stock Compensation (Topic 718) Improvements to Nonemployee Share-Based Payment Accounting In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) Commitments and Contingencies Leases (Topic 842): Targeted Improvements

Available-for-Sale Marketable_2

Available-for-Sale Marketable Securities (Tables)	9 Months Ended
	Sep. 30, 2018
Investments Debt And Equity Securities [Abstract]
Summary of Available-for-Sale Marketable Securities by Major Type of Security	The following tables summarize the Company's available-for-sale marketable securities by major type of security as of September 30, 2018 and December 31, 2017: As of September 30, 2018 Gross Unrealized Type of Security Amortized Cost Gains Losses Estimated Fair Value Money market funds $ 51,428 $ 27 $ — $ 51,455 U.S. Treasury securities 2,996 — — 2,996 U.S. government agency obligations 2,592 — — 2,592 Corporate bonds 10,933 1 (5 ) 10,929 Commercial paper 41,386 1 (11 ) 41,376 Total available-for-sale marketable securities $ 109,335 $ 29 $ (16 ) $ 109,348 As of December 31, 2017 Gross Unrealized Type of Security Amortized Cost Gains Losses Estimated Fair Value Money market funds $ 39,988 $ — $ (37 ) $ 39,951 U.S. government agency obligations 7,799 — (5 ) 7,794 Corporate bonds 15,919 — (12 ) 15,907 Commercial paper 19,545 — (16 ) 19,529 Total available-for-sale marketable securities $ 83,251 $ — $ (70 ) $ 83,181
Schedule of Amortized Cost and Fair Values of Marketable Debt Securities by Contractual Maturity	The Company classifies its marketable debt securities based on their contractual maturity dates. As of September 30, 2018 As of December 31, 2017 Contractual maturity Amortized Cost Fair Value Amortized Cost Fair Value Less than one year $ 57,907 $ 57,893 $ 43,263 $ 43,230
Schedule of Fair Values and Continuous Unrealized Loss Positions of Available-for-Sale Marketable Securities	The following tables show the fair value of the Company's available-for-sale marketable securities that have unrealized losses and that are deemed to be only temporarily impaired, aggregated by investment category and length of time that the individual investments have been in a continuous unrealized loss position. As of September 30, 2018 Less than 12 Months 12 Months or Greater Total Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Corporate bonds $ 10,929 $ (5 ) $ — $ — $ 10,929 $ (5 ) Commercial paper 41,376 (11 ) — — 41,376 (11 ) Total $ 52,305 $ (16 ) $ — $ — $ 52,305 $ (16 ) As of December 31, 2017 Less than 12 Months 12 Months or Greater Total Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Money market funds $ 39,951 $ (37 ) $ — $ — $ 39,951 $ (37 ) U.S. government agency obligations 7,794 (5 ) — — 7,794 (5 ) Corporate bonds 15,907 (12 ) — — 15,907 (12 ) Commercial paper 19,031 (16 ) — — 19,031 (16 ) Total $ 82,683 $ (70 ) $ — $ — $ 82,683 $ (70 )

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Tables)	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
Summary of Changes in Accumulated Other Comprehensive Income (Loss), Net of Tax, from Unrealized Gains (Losses) on Available-for-Sale Marketable Securities	The following table summarizes the changes in accumulated other comprehensive income (loss), or AOCI, net of tax, from unrealized gains (losses) on available-for-sale marketable securities, the Company's only component of AOCI, for the nine months ended September 30, 2018 and September 30, 2017. Total Accumulated Other Comprehensive Income (Loss) Balance, December 31, 2017 $ (70 ) Other comprehensive income before reclassifications 51 Amount reclassified from accumulated other comprehensive loss 32 Net current period other comprehensive income 83 Balance, September 30, 2018 $ 13 Balance, December 31, 2016 $ 3 Other comprehensive income before reclassifications 41 Amount reclassified from accumulated other comprehensive income (4 ) Net current period other comprehensive income 37 Balance, September 30, 2017 $ 40
Schedule of Reclassification Out of Accumulated Other Comprehensive Income	The reclassifications out of AOCI and into net loss were as follows: Three Months Ended September 30, Nine Months Ended September 30, Affected Line Item in the Statements of Component of AOCI 2018 2017 2018 2017 Operations Unrealized gains (losses) on available- for-sale marketable securities $ (17 ) $ — $ (32 ) $ 4 Other income — — — — Benefit from income taxes $ (17 ) $ — $ (32 ) $ 4

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Summary of Financial Assets Measured at Fair Value on Recurring Basis	The following tables summarize the Company’s financial assets measured at fair value on a recurring basis as of September 30, 2018 and December 31, 2017. Fair value measurement as of September 30, 2018: Financial assets Quoted prices in Significant other Significant active markets for observable unobservable identical assets inputs inputs Type of Instrument Total (Level 1) (Level 2) (Level 3) Cash and cash equivalents: Money market fund and checking accounts $ 96,729 $ 96,729 $ — $ — Available-for-sale marketable securities: Money market funds 51,455 — 51,455 — U.S. Treasury securities 2,996 — 2,996 — U.S. government agency obligations 2,592 — 2,592 — Corporate bonds 10,929 — 10,929 — Commercial paper 41,376 — 41,376 — Restricted cash: Commercial money market account 769 769 — — Total financial assets $ 206,846 $ 97,498 $ 109,348 $ — Fair value measurement as of December 31, 2017: Financial assets Quoted prices in Significant other Significant active markets for observable unobservable identical assets inputs inputs Type of Instrument Total (Level 1) (Level 2) (Level 3) Cash and cash equivalents: Money market fund and checking accounts $ 9,388 $ 9,388 $ — $ — Available-for-sale marketable securities: Money market fund 39,951 — 39,951 — U.S. government agency obligations 7,794 — 7,794 — Corporate bonds 15,907 — 15,907 — Commercial paper 19,529 — 19,529 — Restricted cash: Commercial money market account 769 769 — — Total financial assets $ 93,338 $ 10,157 $ 83,181 $ —

Restricted Cash (Tables)

Restricted Cash (Tables)	9 Months Ended
	Sep. 30, 2018
Receivables [Abstract]
Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the Condensed Balance Sheets that sum to the total of the same such amounts shown in the Condensed Statements of Cash Flows. September 30, 2018 December 31, 2017 Cash and cash equivalents $ 96,729 $ 9,388 Restricted cash, current assets 361 — Restricted cash, long-term assets 408 769 Total cash, cash equivalents, and restricted cash shown in the Condensed Statements of Cash Flows $ 97,498 $ 10,157

Accounts Payable and Accrued _2

Accounts Payable and Accrued Expenses (Tables)	9 Months Ended
	Sep. 30, 2018
Payables And Accruals [Abstract]
Schedule of Accounts Payable and Accrued Expenses	Accounts payable and accrued expenses consist of the following: September 30, 2018 December 31, 2017 Accounts payable $ 2,638 $ 3,829 Accrued research projects 8,978 2,356 Accrued professional fees 253 384 Accrued compensation and benefits 2,011 1,864 Accrued other 123 73 Total $ 14,003 $ 8,506

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Computation of Denominators Used in Net Loss per Share	The denominators used in the net loss per share computations are as follows: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Basic: Weighted average common shares outstanding 38,034,216 32,591,550 34,696,835 30,729,752 Diluted: Weighted average common shares outstanding - Basic 38,034,216 32,591,550 34,696,835 30,729,752 Common stock options* — — — — Denominator for diluted net loss per share 38,034,216 32,591,550 34,696,835 30,729,752 * No amounts were considered as their effects would be anti-dilutive.
Computation of Basic and Diluted Net Loss per Share	Basic and diluted net loss per share are computed as follows: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Net loss $ (19,400 ) $ (12,444 ) $ (53,361 ) $ (43,948 ) Weighted-average common shares outstanding: Basic and Diluted 38,034,216 32,591,550 34,696,835 30,729,752 Net loss per share, Basic and Diluted $ (0.51 ) $ (0.38 ) $ (1.54 ) $ (1.43 )

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2018
Summary of Assumptions Used in Black-Scholes Option Pricing Model	The fair values of stock options granted during the three and nine months ended September 30, 2018 and 2017 were estimated as of the dates of grant using the Black-Scholes option pricing model with the following assumptions: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Risk-free interest rate 2.73% - 2.99% 1.87% - 1.97% 2.51% - 2.99% 1.85% - 2.57% Expected volatility 82.6% - 87.6% 81.4% - 81.7% 82.6% - 92.8% 75.3% - 83.3% Expected dividend yield 0% 0% 0% 0% Expected life of employee options (in years) 6.25 6.25 6.25 6.25 Expected life of non-employee options (in years) — — — 10
Summary of Compensation Expense Relating to Stock Options	During the three and nine months ended September 30, 2018 and 2017, the Company recognized compensation expense in the accompanying Condensed Statements of Comprehensive Loss relating to stock options, as follows: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Research and development $ 901 $ 619 $ 2,401 1,784 General and administrative 918 1,475 3,358 2,736 Total stock option expense $ 1,819 $ 2,094 $ 5,759 $ 4,520
Summary of Stock Option Activity	A summary of stock option award activity related to employees, non-employee members of the Company’s Board of Directors and non-employee consultants as of and for the nine months ended September 30, 2018 is presented below: Number of Shares Weighted Average Exercise Price Outstanding, December 31, 2017 3,492,141 $ 11.75 Granted 897,500 15.12 Exercised (377,433 ) 9.64 Expired (58,395 ) 10.65 Forfeited (173,423 ) 12.12 Outstanding, September 30, 2018 3,780,390 $ 12.76 Options exercisable, September 30, 2018 1,797,351
Non-employee Consultants [Member]
Summary of Compensation Expense Relating to Stock Options	Included in the table above are the following amounts of compensation expense recognized with regard to stock options that were granted to non-employee consultants, including the effect of re-measurement of the fair values of those options, as described above: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Research and development $ 68 $ 9 $ 189 $ 156 General and administrative 13 70 192 103 Total stock option expense $ 81 $ 79 $ 381 $ 259
Re-Measurement [Member]
Summary of Assumptions Used in Black-Scholes Option Pricing Model	As of September 30, 2018 and 2017, the Company used the Black-Scholes option valuation model with the following ranges of assumptions to re-measure the fair value of all outstanding options that had been granted to non-employee consultants during the vesting period of each tranche in accordance with ASC 505-50: September 30, 2018 2017 Risk-free interest rate 2.06% - 3.02% 1.28% - 2.28% Expected volatility 77.4% - 80.9% 75.2% - 84.0% Expected dividend yield 0% 0% Expected life of non-employee options (in years) 0.26 - 8.44 0.88 - 9.44

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2018
Commitments And Contingencies Disclosure [Abstract]
Schedule of Contractual Obligations and Commitments Consisting of Future Minimum Lease Payments	Contractual obligations and commitments as of September 30, 2018, consisting of future minimum lease payments under the Company’s Stamford lease, were as follows: Payment Due for the Year Ending December 31, 2018 2019 2020 2021 2022 2023 Total Stamford operating lease $ 300 $ 1,215 $ 1,240 $ 1,264 $ 1,288 $ 1,164 $ 6,471

Business - Additional Informati

Business - Additional Information (Detail) - USD ($) $ in Thousands	Jul. 18, 2018	May 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Nature Of Business [Line Items]
Date of formation					Jul. 2, 2004
Proceeds from equity and debt financing			$ 383,200		$ 383,200
Upfront and milestone payments received in connection with license agreements			88,900		88,900
Proceeds from sale of common stock in connection with license agreement					14,556
Unrestricted cash and cash equivalents and marketable securities			206,077		206,077
Accumulated deficit			273,702		273,702		$ 220,341
Net loss			$ 19,400	$ 12,444	53,361	$ 43,948
Net cash provided by (used in) operating activities					$ 2,060	$ (43,414)
Common Stock [Member]
Nature Of Business [Line Items]
Common stock, shares issued	5,175,000
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member]
Nature Of Business [Line Items]
Proceeds from sale of common stock in connection with license agreement		$ 14,556
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member] | Common Stock [Member]
Nature Of Business [Line Items]
Common stock, shares issued		1,174,827

Available-for-Sale Marketable_3

Available-for-Sale Marketable Securities - Summary of Available-for-Sale Marketable Securities by Major Type of Security (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 109,335	$ 83,251
Gross Unrealized Gains	29
Gross Unrealized Losses	(16)	(70)
Estimated Fair Value	109,348	83,181
Money Market Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	51,428	39,988
Gross Unrealized Gains	27
Gross Unrealized Losses		(37)
Estimated Fair Value	51,455	39,951
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,996
Estimated Fair Value	2,996
U.S. Government Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,592	7,799
Gross Unrealized Losses		(5)
Estimated Fair Value	2,592	7,794
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,933	15,919
Gross Unrealized Gains	1
Gross Unrealized Losses	(5)	(12)
Estimated Fair Value	10,929	15,907
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	41,386	19,545
Gross Unrealized Gains	1
Gross Unrealized Losses	(11)	(16)
Estimated Fair Value	$ 41,376	$ 19,529

Available-for-Sale Marketable_4

Available-for-Sale Marketable Securities - Schedule of Amortized Cost and Fair Values of Marketable Debt Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Investments Debt And Equity Securities [Abstract]
Amortized Cost of marketable debt securities, contractual maturity, Less than one year	$ 57,907	$ 43,263
Fair value of marketable debt securities, contractual maturity, Less than one year	$ 57,893	$ 43,230

Available-for-Sale Marketable_5

Available-for-Sale Marketable Securities - Additional Information (Detail)	9 Months Ended		12 Months Ended
	Sep. 30, 2018USD ($)Position	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)Position
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sale of available-for-sale marketable securities	$ 28,250,000	$ 5,730,000
Realized loss	$ 32,000	$ (4,000)
Number of available-for-sale marketable securities in unrealized loss positions | Position	26		30
Total number of positions | Position	31		31
Other-than-temporary impairments on securities	$ 0		$ 0
Money Market Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sale of available-for-sale marketable securities	28,250,000
Realized loss	$ 32,000

Available-for-Sale Marketable_6

Available-for-Sale Marketable Securities - Schedule of Fair Values and Continuous Unrealized Loss Positions of Available-for-Sale Marketable Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Fair Value	$ 52,305	$ 82,683
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Gross Unrealized Losses	(16)	(70)
Available-for-sale marketable securities, continuous unrealized loss position, Fair Value	52,305	82,683
Available-for-sale marketable securities, continuous unrealized loss position, Gross Unrealized Losses	(16)	(70)
Money Market Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Fair Value		39,951
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Gross Unrealized Losses		(37)
Available-for-sale marketable securities, continuous unrealized loss position, Fair Value		39,951
Available-for-sale marketable securities, continuous unrealized loss position, Gross Unrealized Losses		(37)
U.S. Government Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Fair Value		7,794
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Gross Unrealized Losses		(5)
Available-for-sale marketable securities, continuous unrealized loss position, Fair Value		7,794
Available-for-sale marketable securities, continuous unrealized loss position, Gross Unrealized Losses		(5)
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Fair Value	10,929	15,907
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Gross Unrealized Losses	(5)	(12)
Available-for-sale marketable securities, continuous unrealized loss position, Fair Value	10,929	15,907
Available-for-sale marketable securities, continuous unrealized loss position, Gross Unrealized Losses	(5)	(12)
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Fair Value	41,376	19,031
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Gross Unrealized Losses	(11)	(16)
Available-for-sale marketable securities, continuous unrealized loss position, Fair Value	41,376	19,031
Available-for-sale marketable securities, continuous unrealized loss position, Gross Unrealized Losses	$ (11)	$ (16)

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Loss) - Summary of Changes in Accumulated Other Comprehensive Income (Loss), Net of Tax, from Unrealized Gains (Losses) on Available-for-Sale Marketable Securities (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income Loss [Line Items]
Balance, Value		$ 86,780	$ 50,725
Other comprehensive income before reclassifications		51	41
Amount reclassified from accumulated other comprehensive loss (income)	$ 17	32	(4)
Net current period other comprehensive income (loss)		83	37
Balance, Value	149,530	149,530	99,074
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance, Value		(70)	3
Net current period other comprehensive income (loss)		83	37
Balance, Value	$ 13	$ 13	$ 40

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Income (Loss) - Schedule of Reclassifications Out of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Other income	$ 1,002	$ 367	$ 1,780	$ 788
Benefit from income taxes	(66)	(145)	(264)	(178)
Net of tax	(17)		(32)	4
Accumulated Net Unrealized Investment Gain (Loss) Attributable to Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Other income	(17)		(32)	4
Benefit from income taxes	$ 0	$ 0	$ 0	$ 0

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financial assets
Available-for-sale marketable securities	$ 109,348	$ 83,181
Recurring [Member]
Financial assets
Total financial assets	206,846	93,338
U.S. Government Agency Obligations [Member]
Financial assets
Available-for-sale marketable securities	2,592	7,794
U.S. Government Agency Obligations [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities	2,592	7,794
Corporate Bonds [Member]
Financial assets
Available-for-sale marketable securities	10,929	15,907
Corporate Bonds [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities	10,929	15,907
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring [Member]
Financial assets
Total financial assets	97,498	10,157
Significant Other Observable Inputs (Level 2) [Member] | Recurring [Member]
Financial assets
Total financial assets	109,348	83,181
Significant Other Observable Inputs (Level 2) [Member] | U.S. Government Agency Obligations [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities	2,592	7,794
Significant Other Observable Inputs (Level 2) [Member] | Corporate Bonds [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities	10,929	15,907
Money Market Funds [Member] | Recurring [Member]
Financial assets
Cash and cash equivalents	96,729	9,388
Available-for-sale marketable securities	51,455	39,951
Restricted cash	769	769
Money Market Funds [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring [Member]
Financial assets
Cash and cash equivalents	96,729	9,388
Restricted cash	769	769
Money Market Funds [Member] | Significant Other Observable Inputs (Level 2) [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities	51,455	39,951
U.S. Treasury Securities [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities	2,996
U.S. Treasury Securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities	2,996
Commercial Paper [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities	41,376	19,529
Commercial Paper [Member] | Significant Other Observable Inputs (Level 2) [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities	$ 41,376	$ 19,529

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2018USD ($)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Purchases of financial assets	$ 0
Sales of financial assets	0
Maturities of financial assets	0
Transfer of financial asset into level 3 of fair value	0
Fair value assets level 2 to level 1 transfers	0
Fair value assets level 1 to level 2 transfers	0
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Unrealized gains	0
Unrealized losses	$ 0

Restricted Cash - Additional In

Restricted Cash - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash balance	$ 408	$ 769
Restricted cash in current assets	361
Stamford Lease [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Letter of credit, remaining amount	769
Letter of credit, through the end of lease term	$ 408
Letter of credit, remaining amount date	2019-05
Operating lease, expiration year	2,023
Restricted cash balance	$ 408	$ 769
Restricted cash in current assets	$ 361

Restricted Cash - Schedule of R

Restricted Cash - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Cash And Cash Equivalents [Abstract]
Cash and cash equivalents	$ 96,729	$ 9,388
Restricted cash, current	361
Restricted cash, long-term assets	408	769
Total cash, cash equivalents, and restricted cash shown in the Condensed Statements of Cash Flows	$ 97,498	$ 10,157	$ 13,261	$ 13,561

Prepaid Expenses - Additional I

Prepaid Expenses - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Prepaid expenses	$ 4,218	$ 1,635
Prepaid R&D clinical costs	3,466	1,287
Prepaid insurance	505	124
Other prepaid costs	$ 247	$ 224

Accounts Payable and Accrued _3

Accounts Payable and Accrued Expenses - Schedule of Accounts Payable and Accrued Expenses (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Accounts payable	$ 2,638	$ 3,829
Accrued research projects	8,978	2,356
Accrued professional fees	253	384
Accrued compensation and benefits	2,011	1,864
Accrued other	123	73
Total	$ 14,003	$ 8,506

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Jul. 23, 2018	Jul. 18, 2018	May 17, 2018	Apr. 05, 2017	Sep. 30, 2018	Sep. 30, 2017
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member]
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued			1,174,827
Sale of common stock, per share			$ 17.024
Common Stock [Member]
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued		5,175,000
Common Stock [Member] | Follow-on Public Offering [Member]
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued				5,117,500	5,175,000	5,117,500
Proceeds from issuance of common stock net of underwriting discounts and offering costs	$ 92,077			$ 86,224
Underwriting discounts, commission and offering expenses	$ 6,248			$ 5,891
Sale of common stock, per share		$ 19			$ 19	$ 18
Common Stock [Member] | Underwriter's Over-Allotment [Member]
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued		675,000
Common Stock [Member] | Underwriter's Over-Allotment [Member] | Maximum [Member]
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued	675,000			667,500

Collaboration and Licensing A_2

Collaboration and Licensing Agreements - Additional Information (Detail)	May 17, 2018USD ($)PerformanceObligation$ / sharesshares	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)PerformanceObligation	Sep. 30, 2017USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue from contract with customer		$ 5,062,000		$ 7,936,000	$ 911,000
License and Milestone Fees [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue from contract with customer		5,029,000		7,903,000	530,000
Collaborative Revenue [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue from contract with customer					313,000
Clinical Compound Revenue [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue from contract with customer		33,000		$ 33,000	68,000
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of performance obligations for revenue recognized | PerformanceObligation				2
Non-refundable, non-creditable upfront payment	$ 50,000,000
Common stock, shares issued | shares	1,174,827
Purchase of common stock value	$ 20,000,000
Purchase common stock per share amount | $ / shares	$ 17.024
Closing prices of company common stock description	over a pre-determined average closing price of the Company’s common stock.
Premium from sale of stock	$ 5,444,000
Contract liabilities	$ 55,444,000
Number of combined performance obligations for revenue recognized | PerformanceObligation	1
Number of days to terminate agreement				60 days
Termination notice effective period				12 months
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member] | Maximum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Third-party cost for clinical development	$ 20,000,000
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member] | Maximum [Member] | Regulatory and Commercial Milestones [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable	470,000,000
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member] | Maximum [Member] | Regulatory Milestones [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable	30,000,000
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member] | Maximum [Member] | Tiered Commercial Milestones [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable	$ 440,000,000
Maruishi Pharmaceutical Co., Ltd. [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of performance obligations for revenue recognized | PerformanceObligation				2
Cost of clinical compound related to R&D expense		30,000	$ 0	$ 30,000	61,000
Maruishi Pharmaceutical Co., Ltd. [Member] | Sub-License Fee [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue from contract with customer					843,000
Maruishi Pharmaceutical Co., Ltd. [Member] | License and Milestone Fees [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue from contract with customer					530,000
Maruishi Pharmaceutical Co., Ltd. [Member] | Collaborative Revenue [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue from contract with customer					313,000
Maruishi Pharmaceutical Co., Ltd. [Member] | Clinical Compound Revenue [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue from contract with customer		$ 33,000	$ 0	$ 33,000	$ 68,000

Revenue Recognition - Additiona

Revenue Recognition - Additional Information (Detail) ¥ in Billions	May 17, 2018USD ($)PerformanceObligation	Apr. 30, 2013USD ($)PerformanceObligation	Apr. 30, 2012USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2018USD ($)PerformanceObligationMilestone	Sep. 30, 2017USD ($)Milestone	Dec. 31, 2017USD ($)	Apr. 30, 2013JPY (¥)
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Deferred revenue, current				$ 29,242,000	$ 29,242,000
Deferred revenue, non current				18,300,000	18,300,000
Total revenue				5,062,000	7,936,000	$ 911,000
Remaining performance obligations				0	$ 0
Number of milestone event probable of occurrence or achieved | Milestone					0	0
License and Milestone Fees [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Total revenue				5,029,000	$ 7,903,000	$ 530,000
Royalty [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Revenue from contract with customer					0
VFMCRP Agreement [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Deferred revenue, current				29,242,000	29,242,000
Deferred revenue, non current				18,300,000	18,300,000
Receivables				0	0
Other assets				0	0
Deferred revenue	$ 55,444,000
Number of combined performance obligations for revenue recognized | PerformanceObligation	1
Remaining performance obligations				$ 47,542,000	$ 47,542,000
Number of performance obligations for revenue recognized | PerformanceObligation	2
Upfront payment	$ 50,000,000
Premium from sale of stock	$ 5,444,000
Remaining performance obligation, expected timing of satisfaction, year				2,020	2,020
VFMCRP Agreement [Member] | License and Milestone Fees [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Total revenue					$ 7,903,000
Maruishi and CKDP Agreements [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Receivables				$ 0	0		$ 0
Other assets				0	0		0
Deferred revenue				$ 0	$ 0		$ 0
Maruishi Agreement [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Number of performance obligations for revenue recognized | PerformanceObligation		2			2
Premium from sale of stock		$ 337,000
Upfront non-refundable, non-creditable license fee and premium from sale of stock		15,337,000
Maruishi Agreement [Member] | Clinical Development and Regulatory Milestones [Member] | Maximum [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Remaining potential consideration		10,500,000
Maruishi Agreement [Member] | One-time Sales Milestone [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Remaining potential consideration | ¥								¥ 1
Maruishi Agreement [Member] | License [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Remaining performance obligations		9,637,000
Estimated selling price		10,200,000
Maruishi Agreement [Member] | R&D Services [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Remaining performance obligations		5,700,000
Estimated selling price		$ 6,200,000
CKDP Agreement [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Premium from sale of stock			$ 83,000
CKDP Agreement [Member] | Clinical Development and Regulatory Milestones [Member] | Maximum [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Remaining potential consideration			3,750,000
CKDP Agreement [Member] | License [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Revenue from contract with customer			$ 646,000

Net Loss per Share - Computatio

Net Loss per Share - Computation of Denominators Used in Net Loss per Share (Detail) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Basic:
Weighted average common shares outstanding	38,034,216	32,591,550	34,696,835	30,729,752
Diluted:
Weighted average common shares outstanding - Basic	38,034,216	32,591,550	34,696,835	30,729,752
Common stock options	0	0	0	0
Denominator for diluted net loss per share	38,034,216	32,591,550	34,696,835	30,729,752

Net Loss per Share - Computat_2

Net Loss per Share - Computation of Basic and Diluted Net Loss per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net loss	$ (19,400)	$ (12,444)	$ (53,361)	$ (43,948)
Weighted-average common shares outstanding:
Basic and Diluted	38,034,216	32,591,550	34,696,835	30,729,752
Net loss per share, Basic and Diluted	$ (0.51)	$ (0.38)	$ (1.54)	$ (1.43)

Net Loss per Share - Additional

Net Loss per Share - Additional Information (Detail) - shares	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017
Employee Options [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Anti-dilutive common stock equivalents		3,780,390	3,492,786
Restricted Stock Units [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Anti-dilutive common stock equivalents	83,791	83,791

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail)	Sep. 30, 2018USD ($)PerformanceTarget$ / sharesshares	Sep. 30, 2018USD ($)PerformanceTarget$ / sharesshares	Sep. 30, 2017USD ($)$ / sharesshares	Sep. 30, 2018USD ($)PerformanceTarget$ / sharesshares	Sep. 30, 2017USD ($)$ / sharesshares	Dec. 31, 2015shares	Jan. 01, 2018shares	Dec. 31, 2017shares	Jan. 01, 2017USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense | $		$ 1,819,000	$ 2,094,000	$ 5,759,000	$ 4,520,000
Fair value of options granted | $ / shares		$ 14.51	$ 10	$ 11.25	$ 11.61
Excess tax benefits from stock option activity or stock-based compensation expense recognized in cash flows from operations | $				$ 0	$ 0
ASU 2016-09 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cumulative-effect adjustment to stockholders' equity | $									$ 45,000
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of performance targets achieved | PerformanceTarget	0	0		0
Restricted stock units, vested	0
Compensation expense | $	$ 0
Non-employee Consultants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair values of outstanding options | $ / shares	$ 20.48	$ 20.48	$ 8.31	$ 20.48	$ 8.31
2014 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock options that may be granted after the tenth anniversary of the 2014 Plan				0
Annual increases in number of shares reserved for issuance as a percentage of shares of capital stock outstanding through January 1, 2024						3.00%
Share-based compensation arrangement by share-based payment award, number of shares authorized							4,900,481	3,920,613
Options granted		165,000	415,000	897,500	1,253,500
2014 Equity Incentive Plan [Member] | Share-Based Compensation Award, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of vested shares on first anniversary of grant date				25.00%
2014 Equity Incentive Plan [Member] | Share-based Compensation Award, Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of awards granted				36 months
2014 Equity Incentive Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Term of awards granted				10 years
2014 Equity Incentive Plan [Member] | Maximum [Member] | Incentive Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, number of shares authorized						30,000,000
2014 Equity Incentive Plan [Member] | Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of awards granted				4 years
2014 Equity Incentive Plan [Member] | Board of Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of awards granted				3 years
2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units, granted		83,791		83,791
Restricted stock units, grant date fair value | $ / shares		$ 20.21

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Assumptions Used in Black-Scholes Option Pricing Model (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate, minimum	2.73%	1.87%	2.51%	1.85%
Risk-free interest rate, maximum	2.99%	1.97%	2.99%	2.57%
Expected volatility, minimum	82.60%	81.40%	82.60%	75.30%
Expected volatility, maximum	87.60%	81.70%	92.80%	83.30%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Employee Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life of options (in years)	6 years 3 months	6 years 3 months	6 years 3 months	6 years 3 months
Nonemployee Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life of options (in years)				10 years

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Re-measurement of Assumptions Used in Black-Scholes Option Pricing Model (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate, minimum	2.73%	1.87%	2.51%	1.85%
Risk-free interest rate, maximum	2.99%	1.97%	2.99%	2.57%
Expected volatility, minimum	82.60%	81.40%	82.60%	75.30%
Expected volatility, maximum	87.60%	81.70%	92.80%	83.30%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Nonemployee Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life of options (in years)				10 years
Re-Measurement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate, minimum			2.06%	1.28%
Risk-free interest rate, maximum			3.02%	2.28%
Expected volatility, minimum			77.40%	75.20%
Expected volatility, maximum			80.90%	84.00%
Expected dividend yield			0.00%	0.00%
Re-Measurement [Member] | Nonemployee Options [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life of options (in years)			3 months 3 days	10 months 17 days
Re-Measurement [Member] | Nonemployee Options [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life of options (in years)			8 years 5 months 8 days	9 years 5 months 8 days

Stock-Based Compensation - Su_3

Stock-Based Compensation - Summary of Compensation Expense Relating to Stock Options (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock option expense	$ 1,819	$ 2,094	$ 5,759	$ 4,520
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock option expense	901	619	2,401	1,784
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock option expense	$ 918	$ 1,475	$ 3,358	$ 2,736

Stock-Based Compensation - Su_4

Stock-Based Compensation - Summary of Compensation Expense Recognized With Regard to Stock Options Granted to Non-employee Consultants Including Effect of Re-measurement of Fair Values of Options (Detail) - Non-employee Consultants [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock option expense including effect of re-measurement of fair value	$ 81	$ 79	$ 381	$ 259
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock option expense including effect of re-measurement of fair value	68	9	189	156
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock option expense including effect of re-measurement of fair value	$ 13	$ 70	$ 192	$ 103

Stock-Based Compensation - Su_5

Stock-Based Compensation - Summary of Stock Option Activity (Detail) - 2014 Equity Incentive Plan [Member] - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Options, Outstanding at December 31, 2017			3,492,141
Number of Options, Granted	165,000	415,000	897,500	1,253,500
Number of Options, Exercised			(377,433)
Number of Options, Expired			(58,395)
Number of Options, Forfeited			(173,423)
Number of Options, Outstanding at June 31, 2018	3,780,390		3,780,390
Number of Options, Options exercisable at June 30, 2018	1,797,351		1,797,351
Weighted-Average Exercise Price, Outstanding at December 31, 2017			$ 11.75
Weighted-Average Exercise Price, Granted			15.12
Weighted-Average Exercise Price, Exercised			9.64
Weighted-Average Exercise Price, Expired			10.65
Weighted-Average Exercise Price, Forfeited			12.12
Weighted-Average Exercise Price, Outstanding at June 30, 2018	$ 12.76		$ 12.76

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Pre-tax losses	$ 19,466	$ 12,589	$ 53,625	$ 44,126
Benefit from income taxes	$ 66	$ 145	$ 264	$ 178
Percentage of annual research and development credit for cash			65.00%
Income tax rate			21.00%		35.00%

Commitments and Contingencies -

Commitments and Contingencies - Schedule of Contractual Obligations and Commitments Consisting of Future Minimum Lease Payments (Detail) - Stamford Operating Lease [Member] $ in Thousands	Sep. 30, 2018USD ($)
Operating Leased Assets [Line Items]
2,018	$ 300
2,019	1,215
2,020	1,240
2,021	1,264
2,022	1,288
2,023	1,164
Total	$ 6,471

Commitments and Contingencies_2

Commitments and Contingencies - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	May 31, 2016
Other Commitments [Line Items]
Deferred lease obligation	$ 1,629,000	$ 1,718,000
Stamford Operating Lease [Member]
Other Commitments [Line Items]
Operating Lease, description	The Stamford Lease requires monthly lease payments, including rent escalations and rent holidays, during the initial lease term. The Company began to make rental payments from the Commencement Date. The Company records monthly rent expense on a straight-line basis from March 2016, upon taking possession of the Premises, through November 2023. As of September 30, 2018 and December 31, 2017, the balance of deferred lease obligation, representing the difference between cash rent paid and straight-line rent expense, was $895 and $876, respectively. The Stamford Lease is renewable for one five-year term.
Operating Lease, renewable term	5 years
Operating lease, expiration date	Nov. 30, 2023
Deferred lease obligation	$ 895,000	876,000
Tenant improvement expenses			$ 1,094,000
Stamford Operating Lease [Member] | Standby Letter of Credit [Member]
Other Commitments [Line Items]
Letter of credit, amount	$ 769,000
Operating lease, renewable term description	Automatically renewed annually through November 2023.
Stamford Operating Lease [Member] | Standby Letter of Credit [Member] | Maximum [Member]
Other Commitments [Line Items]
Letter of credit, renewal date	Nov. 30, 2023
Stamford Operating Lease [Member] | Leasehold Improvements [Member]
Other Commitments [Line Items]
Deferred lease obligation	$ 734,000	$ 842,000

Subsequent Event - Additional I

Subsequent Event - Additional Information (Detail)	Oct. 22, 2018
Former CMO [Member] | Maximum [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Consulting services, period of services	9 months