Cara Therapeutics (CARA) 10-Q8 Nov 212021 Q3 Quarterly reportFinancial data

Company Profile

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2021	Nov. 04, 2021
Document And Entity Information [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
Document Transition Report	false
Entity File Number	001-36279
Entity Registrant Name	CARA THERAPEUTICS, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	75-3175693
Entity Address, Address Line One	4 Stamford Plaza
Entity Address, Address Line Two	107 Elm Street
Entity Address, Address Line Three	9th Floor
Entity Address, City or Town	Stamford
Entity Address, State or Province	CT
Entity Address, Postal Zip Code	06902
City Area Code	203
Local Phone Number	406-3700
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	CARA
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		53,458,679
Entity Central Index Key	0001346830
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Amendment Flag	false

Condensed Balance Sheets

Condensed Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 22,991	$ 31,683
Marketable securities	121,203	149,242
Income tax receivable	697	1,507
Other receivables	20,350	557
Prepaid expenses	6,258	12,076
Total current assets	171,499	195,065
Operating lease right-of-use assets	3,310	4,279
Marketable securities, non-current	49,221	70,565
Property and equipment, net	654	840
Restricted cash	408	408
Total assets	225,092	271,157
Current liabilities:
Accounts payable and accrued expenses	13,812	16,881
Operating lease liabilities, current	1,716	1,602
Total current liabilities	15,528	18,483
Operating lease liabilities, non-current	2,373	3,673
Commitments and contingencies (Note 15)
Stockholders' equity:
Preferred stock; $0.001 par value; 5,000,000 shares authorized at September 30, 2021 and December 31, 2020, zero shares issued and outstanding at September 30, 2021 and December 31, 2020
Common stock; $0.001 par value; 100,000,000 shares authorized at September 30, 2021 and December 31, 2020, 50,175,988 shares 49,872,213 shares issued and outstanding at September 30, 2021 and December 31, 2021, respectively	50	50
Common stock subscribed in Vifor stock purchase, or Private Offering; $0.001 par value; 3,282,391 shares at September 30, 2021	3
Additional paid-in capital	699,482	641,195
Stock subscription receivable	(44,969)
Accumulated deficit	(447,376)	(392,317)
Accumulated other comprehensive income	1	73
Total stockholders' equity	207,191	249,001
Total liabilities and stockholders' equity	$ 225,092	$ 271,157

Condensed Balance Sheets (Paren

Condensed Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
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	50,175,988	49,872,213
Common stock, shares outstanding	50,175,988	49,872,213
Common stock, shares subscribed but unissued par value	$ 0.001
Common stock, shares subscribed but unissued	3,282,391

Condensed Statements of Compreh

Condensed Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenue:
Total revenue	$ 20,272	$ 9,266	$ 22,207	$ 22,993
Operating expenses:
Research and development	15,514	21,067	59,870	80,711
General and administrative	5,882	5,219	17,898	15,187
Total operating expenses	21,396	26,286	77,768	95,898
Operating loss	(1,124)	(17,020)	(55,561)	(72,905)
Other income, net	111	379	502	1,970
Loss before benefit from income taxes	(1,013)	(16,641)	(55,059)	(70,935)
Benefit from income taxes	0	132	0	436
Net Loss	$ (1,013)	$ (16,509)	$ (55,059)	$ (70,499)
Net Loss per share:
Basic and Diluted	$ (0.02)	$ (0.35)	$ (1.10)	$ (1.51)
Weighted average shares:
Basic and Diluted	50,114,710	46,885,424	50,031,615	46,803,659
Other comprehensive income (loss), net of tax of $0:
Change in unrealized gains (losses) on available-for-sale marketable securities	$ 6	$ (272)	$ (72)	$ 193
Total comprehensive loss	(1,007)	(16,781)	(55,131)	(70,306)
License and Milestone Fees
Revenue:
Total revenue	20,031	9,257	21,223	22,377
Collaborative Revenue
Revenue:
Total revenue			706
Clinical Compound Revenue
Revenue:
Total revenue	$ 241	$ 9	$ 278	$ 616

Condensed Statements of Compr_2

Condensed Statements of Comprehensive Income (Loss) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
CONDENSED STATEMENTS OF COMPREHENSIVE LOSS
Other comprehensive loss, tax	$ 0	$ 0	$ 0	$ 0

Condensed Statements of Stockho

Condensed Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock [Member]Common Stock [Member]	Common Stock [Member]Common Stock Subscribed in Private Offering [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Stock Subscription Receivable [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total
Balance, Value at Dec. 31, 2019			$ 47	$ 587,223		$ (400,727)	$ 170	$ 186,713
Balance, Shares at Dec. 31, 2019			46,720,225
Stock-based compensation expense				2,846				2,846
Shares issued upon exercise of stock options, value				75				75
Shares issued upon exercise of stock options, shares			7,500
Net Loss						(28,922)		(28,922)
Other comprehensive income (loss)							(238)	(238)
Balance, Value at Mar. 31, 2020			$ 47	590,144		(429,649)	(68)	160,474
Balance, Shares at Mar. 31, 2020			46,727,725
Balance, Value at Dec. 31, 2019			$ 47	587,223		(400,727)	170	186,713
Balance, Shares at Dec. 31, 2019			46,720,225
Net Loss								(70,499)
Other comprehensive income (loss)							193
Balance, Value at Sep. 30, 2020			$ 47	598,663		(471,226)	363	127,847
Balance, Shares at Sep. 30, 2020			46,892,552
Balance, Value at Mar. 31, 2020			$ 47	590,144		(429,649)	(68)	160,474
Balance, Shares at Mar. 31, 2020			46,727,725
Stock-based compensation expense				2,993				2,993
Shares issued upon exercise of stock options, value				201				201
Shares issued upon exercise of stock options, shares			16,846
Shares issued upon vesting of restricted stock units, value				1,625				1,625
Shares issued upon vesting of restricted stock units, shares			119,834
Net Loss						(25,068)		(25,068)
Other comprehensive income (loss)							703	703
Balance, Value at Jun. 30, 2020			$ 47	594,963		(454,717)	635	140,928
Balance, Shares at Jun. 30, 2020			46,864,405
Stock-based compensation expense				3,305				3,305
Shares issued upon exercise of stock options, value				395				395
Shares issued upon exercise of stock options, shares			28,147
Net Loss						(16,509)		(16,509)
Other comprehensive income (loss)							(272)	(272)
Balance, Value at Sep. 30, 2020			$ 47	598,663		(471,226)	363	127,847
Balance, Shares at Sep. 30, 2020			46,892,552
Balance, Value at Dec. 31, 2020	$ 50			641,195		(392,317)	73	249,001
Balance, Shares at Dec. 31, 2020	49,872,213
Stock-based compensation expense				2,744				2,744
Shares issued upon exercise of stock options, value				688				688
Shares issued upon exercise of stock options, shares	45,035
Shares issued upon vesting of restricted stock units, value				1,388				1,388
Shares issued upon vesting of restricted stock units, shares	109,419
Net Loss						(23,301)		(23,301)
Other comprehensive income (loss)							(61)	(61)
Balance, Value at Mar. 31, 2021	$ 50			646,015		(415,618)	12	230,459
Balance, Shares at Mar. 31, 2021	50,026,667
Balance, Value at Dec. 31, 2020	$ 50			641,195		(392,317)	73	249,001
Balance, Shares at Dec. 31, 2020	49,872,213
Net Loss								(55,059)
Other comprehensive income (loss)							(72)
Common stock shares subscribed but unissued at Sep. 30, 2021		$ 3						$ 3
Common stock, shares subscribed but unissued (shares) at Sep. 30, 2021		3,282,391						3,282,391
Balance, Value at Sep. 30, 2021	$ 50			699,482	$ (44,969)	(447,376)	1	$ 207,191
Balance, Shares at Sep. 30, 2021	50,175,988
Balance, Value at Mar. 31, 2021	$ 50			646,015		(415,618)	12	230,459
Balance, Shares at Mar. 31, 2021	50,026,667
Stock-based compensation expense				3,376				3,376
Shares issued upon exercise of stock options, value				293				293
Shares issued upon exercise of stock options, shares	25,494
Shares issued upon vesting of restricted stock units, value				100				100
Shares issued upon vesting of restricted stock units, shares	36,000
Net Loss						(30,745)		(30,745)
Other comprehensive income (loss)							(17)	(17)
Balance, Value at Jun. 30, 2021	$ 50			649,784		(446,363)	(5)	203,466
Balance, Shares at Jun. 30, 2021	50,088,161
Subscription of common stock in Vifor stock purchase, value		$ 3		44,966	(44,969)
Subscription of common stock in Vifor stock purchase, shares		3,282,391
Stock-based compensation expense				3,487				3,487
Shares issued upon exercise of stock options, value				339				339
Shares issued upon exercise of stock options, shares	43,825
Shares issued upon vesting of restricted stock units, value				906				906
Shares issued upon vesting of restricted stock units, shares	44,002
Net Loss						(1,013)		(1,013)
Other comprehensive income (loss)							6	6
Common stock shares subscribed but unissued at Sep. 30, 2021		$ 3						$ 3
Common stock, shares subscribed but unissued (shares) at Sep. 30, 2021		3,282,391						3,282,391
Balance, Value at Sep. 30, 2021	$ 50			$ 699,482	$ (44,969)	$ (447,376)	$ 1	$ 207,191
Balance, Shares at Sep. 30, 2021	50,175,988

Condensed Statements of Stock_2

Condensed Statements of Stockholders' Equity (Parenthetical)	Sep. 30, 2021$ / shares
CONDENSED STATEMENTS OF STOCKHOLDERS' EQUITY
Share Price	$ 15.23

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
Condensed Statements of Cash Flows - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Operating activities
Net loss	$ (55,059)	$ (70,499)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	12,001	10,770
Depreciation and amortization	186	147
Amortization expense component of lease expense	969	496
Amortization of available-for-sale marketable securities, net	590	28
Realized gain on sale of available-for-sale marketable securities	(39)	(126)
Realized gain on sale of property and equipment	(70)
Deferred revenue		(21,751)
Changes in operating assets and liabilities:
Income tax receivable	810	(436)
Other receivables	(19,793)	509
Prepaid expenses	5,818	(1,391)
Accounts payable and accrued expenses	(3,069)	(4,608)
Operating lease liabilities	(1,186)	(714)
Net cash used in operating activities	(58,842)	(87,575)
Investing activities
Proceeds from maturities of available-for-sale marketable securities	134,220	119,895
Proceeds from redemptions of available-for-sale marketable securities, at par	13,500	22,035
Proceeds from sale of available-for-sale marketable securities	10,029	23,148
Purchases of available-for-sale marketable securities	(108,989)	(21,016)
Proceeds from sale of property and equipment	70
Purchases of property and equipment		(182)
Net cash provided by investing activities	48,830	143,880
Financing activities
Proceeds from the exercise of stock options	1,320	671
Net cash provided by financing activities	1,320	671
Net (decrease) increase in cash, cash equivalents and restricted cash	(8,692)	56,976
Cash, cash equivalents and restricted cash at beginning of period	32,091	18,713
Cash, cash equivalents and restricted cash at end of period	23,399	$ 75,689
Noncash investing and financing activities
Stock subscription receivable from Vifor	$ 44,969

Business

Business	9 Months Ended
Business	Sep. 30, 2021
Basis of Presentation
Business	1. Business Cara Therapeutics, Inc., or the Company, is an early commercial-stage biopharmaceutical company formed on July 2, 2004. The Company is focused on developing and commercializing new chemical entities designed to alleviate pruritus by selectively targeting peripheral kappa opioid receptors. The Company’s primary activities to date have been organizing and staffing the Company, developing its product candidates and raising capital. On August 23, 2021, the Company received U.S. Food and Drug Administration, or FDA, approval for KORSUVA TM As of September 30, 2021, the Company had raised aggregate net proceeds of approximately $519,600 from several rounds of equity financing, including its initial public offering, or IPO, which closed in February 2014 and four follow-on public offerings of common stock, which closed in July 2019, July 2018, April 2017 and August 2015, respectively, and the issuance of convertible preferred stock and debt prior to the IPO. The Company had also earned approximately $224,100 under its license agreements for CR845/difelikefalin, primarily with Vifor (International) Ltd., or Vifor, 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. In October 2021, the Company received net proceeds of $44,969 from the issuance and sale of 3,282,391 shares of the Company’s common stock to Vifor in connection with U.S. regulatory approval for KORSUVA injection in August 2021 (see Notes 9, Stockholders’ Equity Subsequent Events Collaboration and Licensing Agreements As of September 30, 2021, the Company had unrestricted cash and cash equivalents and marketable securities of $193,415 and an accumulated deficit of $447,376. 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 $1,013 and $16,509 for the three months ended September 30, 2021 and 2020, respectively, and $55,059 and $70,499 for the nine months ended September 30, 2021 and 2020, respectively, and had net cash used in operating activities of $58,842 and $87,575 for the nine months ended September 30, 2021 and 2020, 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 FDA and other government regulations. If the Company does not successfully commercialize KORSUVA injection or 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
Basis of Presentation	Sep. 30, 2021
Basis of Presentation
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. The results of operations for interim periods are not necessarily indicative of the results for the full year. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted from this report, as is permitted by SEC rules and regulations; however, the Company believes that the disclosures are adequate to make the information presented not misleading. The condensed balance sheet data as of December 31, 2020 were derived from audited financial statements, but do not include all disclosures required by GAAP. These unaudited interim condensed financial statements should be read in conjunction with the audited financial statements and accompanying notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020. 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. The more significant estimates include the fair value of marketable securities that are classified as level 2 of the fair value hierarchy, 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, the incremental borrowing rate used in lease calculations and the likelihood of realization of deferred tax assets. The ongoing COVID-19 pandemic has interrupted business operations across the globe. Estimates and assumptions about future events and their effects cannot be determined with certainty and therefore require the exercise of judgment. As of the date of issuance of these condensed financial statements, the Company is not aware of any specific event or circumstance that would require the Company to update its estimates, assumptions and judgments or revise the reported amounts of assets and liabilities or the disclosure of contingent assets and liabilities. These estimates, however, may change as new events occur and additional information is obtained, and are recognized in the condensed financial statements as soon as they become known. Actual results could differ materially from the Company’s estimates and assumptions. 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, 2020, except for the recent adoption of new accounting pronouncements as disclosed below. Accounting Pronouncements Recently Adopted In December 2019, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, No. 2019-12, Income Taxes (Topic 740) of legal entities that are not subject to tax; and (iv) enacted changes in tax laws in interim periods. The amendments in ASU 2019-12 are effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020. The amendments in ASU 2019-12 related to separate financial statements of legal entities that are not subject to tax should be applied on a retrospective basis for all periods presented. The amendments related to changes in ownership of foreign equity method investments or foreign subsidiaries should be applied on a modified retrospective basis through a cumulative-effect adjustment to retained earnings as of the beginning of the fiscal year of adoption. The amendments related to franchise taxes that are partially based on income should be applied on either a retrospective basis for all periods presented or a modified retrospective basis through a cumulative-effect adjustment to retained earnings as of the beginning of the fiscal year of adoption. All other amendments should be applied on a prospective basis. The Company adopted ASU 2019-12 on January 1, 2021 and it did not have a material effect on its results of operations, financial position, and cash flows due to the full valuation allowance recorded.

Available-for-Sale Marketable S

Available-for-Sale Marketable Securities	9 Months Ended
Available-for-Sale Marketable Securities	Sep. 30, 2021
Investments Debt And Equity Securities [Abstract]
Available-for-Sale Marketable Securities	3. Available-for-Sale Marketable Securities As of September 30, 2021 and December 31, 2020, the Company’s available-for-sale marketable securities consisted of debt securities issued by the U.S. Treasury, U.S. government-sponsored entities and investment grade institutions as well as municipal bonds. The following tables summarize the Company’s available-for-sale marketable securities by major type of security as of September 30, 2021 and December 31, 2020: As of September 30, 2021 Gross Unrealized Estimated Fair Type of Security Amortized Cost Gains Losses Value U.S. Treasury securities $ 10,067 $ 3 $ — $ 10,070 U.S. government agency obligations 17,046 3 (5) 17,044 Corporate bonds 46,920 17 (23) 46,914 Commercial paper 78,452 6 (4) 78,454 Municipal bonds 17,938 19 (15) 17,942 Total available-for-sale marketable securities $ 170,423 $ 48 $ (47) $ 170,424 As of December 31, 2020 Gross Unrealized Estimated Fair Type of Security Amortized Cost Gains Losses Value U.S. Treasury securities $ 20,710 $ 41 $ (1) $ 20,750 U.S. government agency obligations 22,125 4 (1) 22,128 Corporate bonds 49,080 61 (23) 49,118 Commercial paper 116,139 5 (17) 116,127 Municipal bonds 11,680 12 (8) 11,684 Total available-for-sale marketable securities $ 219,734 $ 123 $ (50) $ 219,807 The following tables summarize the fair value and gross unrealized losses of the Company’s available-for-sale marketable securities by investment category and disaggregated by the length of time that individual debt securities have been in a continuous unrealized loss position as of September 30, 2021 and December 31, 2020: As of September 30, 2021 Less than 12 Months 12 Months or Greater Total Gross Gross Gross Fair Unrealized Fair Unrealized Fair Unrealized Value Losses Value Losses Value Losses U.S. government agency obligations $ 9,495 $ (5) $ — $ — $ 9,495 $ (5) Corporate bonds 24,488 (23) — — 24,488 (23) Commercial paper 25,976 (4) — — 25,976 (4) Municipal bonds 7,319 (15) — — 7,319 (15) Total $ 67,278 $ (47) $ — $ — $ 67,278 $ (47) As of December 31, 2020 Less than 12 Months 12 Months or Greater Total Gross Gross Gross Fair Unrealized Fair Unrealized Fair Unrealized Value Losses Value Losses Value Losses U.S. Treasury securities $ 12,682 $ (1) $ — $ — $ 12,682 $ (1) U.S. government agency obligations 2,500 (1) — — 2,500 (1) Corporate bonds 23,553 (23) — — 23,553 (23) Commercial paper 68,897 (17) — — 68,897 (17) Municipal bonds 6,259 (8) — — 6,259 (8) Total $ 113,891 $ (50) $ — $ — $ 113,891 $ (50) As of September 30, 2021 and December 31, 2020, no allowance for credit losses were recognized on the Company’s available-for-sale debt securities as no portion of the unrealized losses associated with those securities were due to credit losses. The information that the Company considered in reaching the conclusion that an allowance for credit losses was not necessary is as follows: As of September 30, 2021 and December 31, 2020, the Company held a total of 26 out of 59 positions and 30 out of 59 positions, respectively, that were in an unrealized loss position, none of which had been in an unrealized loss position for 12 months or greater. Unrealized losses individually and in aggregate were not considered to be material for each respective period. 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. U.S. government agency obligations. positions for its U.S. government agency obligations that were in unrealized loss positions as of September 30, 2021. Corporate bonds, commercial paper, and municipal bonds. grade status. The contractual terms of these investments do not permit the issuer to repay principal at a price less than the amortized cost bases of the investments, which is equivalent to the par value on the maturity date. The Company expects to recover the entire amortized cost bases of these securities on the maturity date. The Company does not intend to sell these investments, and it is not more likely than not that the Company will be required to sell these investments, before recovery of their amortized cost bases. The Company held 10 out of 20 positions for its corporate bonds, 7 out of 19 positions for its commercial paper, and 6 out of 12 positions for its municipal bonds, that were in unrealized loss positions as of September 30, 2021. The Company classifies its marketable debt securities based on their contractual maturity dates. As of September 30, 2021, the Company’s marketable debt securities mature at various dates through September 2024. The amortized cost and fair values of marketable debt securities by contractual maturity were as follows. As of September 30, 2021 As of December 31, 2020 Contractual maturity Amortized Cost Fair Value Amortized Cost Fair Value Less than one year $ 121,189 $ 121,203 $ 149,164 $ 149,242 One year to three years 49,234 49,221 70,570 70,565 Total $ 170,423 $ 170,424 $ 219,734 $ 219,807 All available-for-sale marketable securities are classified as Marketable securities, current or Marketable securities, non-current depending on the contractual maturity date of the individual available-for-sale security. Other income, net includes interest and dividends, accretion/amortization of discounts/premiums, realized gains and losses on sales of securities and credit loss expense due to declines in the fair value of securities, if any. The cost of securities sold is based on the specific identification method. During the three and nine months ended September 30, 2021, the Company sold certain shares of its available-for-sale debt securities with a total fair value of $1,000 and $10,029, respectively, which resulted in no realized gains or losses for the three months ended September 30, 2021, and $39 of realized gains for the nine months ended September 30, 2021, respectively. During the three and nine months ended September 30, 2020, the Company sold certain shares of its available-for-sale debt securities with a total fair value of $12,471 and $23,148, respectively, which resulted in realized gains of $66 and $126 for the three and nine months ended September 30, 2020, respectively. As of September 30, 2021 and December 31, 2020, accrued interest receivables on our available-for-sale debt securities were $318 and $311, respectively.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	9 Months Ended
Accumulated Other Comprehensive Income (Loss)	Sep. 30, 2021
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), net of tax, from unrealized gains (losses) on available-for-sale marketable securities, the Company’s only component of accumulated other comprehensive income (loss), for the nine months ended September 30, 2021 and September 30, 2020. Total Accumulated Other Comprehensive Income (Loss) Balance, December 31, 2020 $ 73 Other comprehensive loss before reclassifications (33) Amount reclassified from accumulated other comprehensive income (39) Net current period other comprehensive loss (72) Balance, September 30, 2021 $ 1 Balance, December 31, 2019 $ 170 Other comprehensive income before reclassifications 319 Amount reclassified from accumulated other comprehensive income (126) Net current period other comprehensive income 193 Balance, September 30, 2020 $ 363 Amounts reclassified out of accumulated other comprehensive income (loss) into net loss are determined by specific identification. The reclassifications out of accumulated other comprehensive income (loss) and into net loss were as follows: Three Months Ended Nine Months Ended Affected Line Item in the Component of Accumulated Other September 30, September 30, Condensed Statements of Comprehensive Income (Loss) 2021 2020 2021 2020 Comprehensive Income (Loss) Unrealized gains (losses) on available-for-sale marketable securities: Realized gains on sales of securities $ — $ 66 $ 39 $ 126 Other income, net Income tax effect — — — — Benefit from income taxes Realized gains on sales of securities, net of tax $ — $ 66 $ 39 $ 126

Fair Value Measurements

Fair Value Measurements	9 Months Ended
Fair Value Measurements	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	5. Fair Value Measurements As of September 30, 2021 The valuation techniques used by the Company 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 municipal bonds, 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, 2021 The following tables summarize the Company’s financial assets measured at fair value on a recurring basis as of September 30, 2021 Fair value measurement as of September 30, 2021 Quoted prices in Significant other Significant Financial assets 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 funds and checking accounts $ 22,991 $ 22,991 $ — $ — Available-for-sale marketable securities: U.S. Treasury securities 10,070 — 10,070 — U.S. government agency obligations 17,044 — 17,044 — Corporate bonds 46,914 — 46,914 — Commercial paper 78,454 — 78,454 — Municipal bonds 17,942 — 17,942 — Restricted cash: Commercial money market account 408 408 — — Total financial assets $ 193,823 $ 23,399 $ 170,424 $ — Fair value measurement as of December 31, 2020: Quoted prices in Significant other Significant Financial assets 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 funds and checking accounts $ 31,683 $ 31,683 $ — $ — Available-for-sale marketable securities: U.S. Treasury securities 20,750 — 20,750 — U.S. government agency obligations 22,128 — 22,128 — Corporate bonds 49,118 — 49,118 — Commercial paper 116,127 — 116,127 — Municipal bonds 11,684 — 11,684 — Restricted cash: Commercial money market account 408 408 — — Total financial assets $ 251,898 $ 32,091 $ 219,807 $ — 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 during the three and nine months ended September 30, 2021 and 2020, respectively September 30, 2021 and 2020, respectively

Restricted Cash

Restricted Cash	9 Months Ended
Restricted Cash	Sep. 30, 2021
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 leases for its office space in Stamford, Connecticut (refer to Note 15, Commitments and Contingencies: Leases balance to serve as collateral for the letter of credit issued to the landlord by the bank. As of September 30, 2021, the restricted cash balance for the Stamford Lease was invested in a commercial money market account. As of September 30, 2021 and December 31, 2020, the Company had $408 of restricted cash related to the Stamford Lease in long-term assets. 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, 2021 December 31, 2020 Cash and cash equivalents $ 22,991 $ 31,683 Restricted cash, long-term assets 408 408 Total cash, cash equivalents, and restricted cash shown in the Condensed Statements of Cash Flows $ 23,399 $ 32,091

Prepaid Expenses

Prepaid Expenses	9 Months Ended
Prepaid Expenses	Sep. 30, 2021
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Prepaid Expenses	7. Prepaid expenses As of September 30, 2021, prepaid expenses were $6,258, consisting of $4,098 of prepaid R&D clinical costs, $855 of prepaid insurance and $1,305 of other prepaid costs. As of December 31, 2020, prepaid expenses were $12,076, consisting of $11,286 of prepaid R&D clinical costs, $223 of prepaid insurance, and $567 of other prepaid costs.

Accounts Payable and Accrued Ex

Accounts Payable and Accrued Expenses	9 Months Ended
Accounts Payable and Accrued Expenses	Sep. 30, 2021
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, 2021 December 31, 2020 Accounts payable $ 5,369 $ 4,893 Accrued research projects 3,496 6,194 Accrued compensation and benefits 4,125 4,955 Accrued professional fees and other 822 839 Total $ 13,812 $ 16,881

Stockholders' Equity

Stockholders' Equity	9 Months Ended
Stockholders' Equity	Sep. 30, 2021
Equity [Abstract]
Stockholders' Equity	9. Stockholders’ Equity In August 2021, the Company earned a $50,000 regulatory milestone from Vifor for the purchase of the Company’s common stock at a price of $15.23 per share. As of September 30, 2021, the Company recorded a stock subscription receivable of $44,969 in connection with the U.S. regulatory approval of KORSUVA injection, representing $15.23 per share, as well as license and milestone fees revenue of $5,031 representing the excess of the stock purchase price over the cost of the purchased shares at the closing price of the Company’s common stock on the date of the achievement of the milestone. In October 2021, after the expiration of the requisite waiting period under the Hart-Scott-Rodino Antitrust Improvement Act of 1976, or the HSR Act, the Company received the $50,000 payment and issued 3,282,391 shares of its common stock in connection with U.S. regulatory approval of KORSUVA injection on August 23, 2021 (see Notes 10, Collaboration and Licensing Agreements Subsequent Events In August 2021, as a result of the achievement of certain performance targets, an aggregate of 44,002 performance-based restricted stock units of various executive officers vested and were settled in shares of the Company’s common stock (see Note 13, Stock-Based Compensation In June 2021, as a result of the completion of the one-year vesting period, an aggregate of 36,000 restricted stock units of members of the Board of Directors vested and were settled in shares of the Company’s common stock (see Note 13, Stock-Based Compensation In February and March 2021, as a result of the achievement of certain performance targets, an aggregate of 76,750 performance-based restricted stock units of various executive officers vested and were settled in shares of the Company’s common stock (see Note 13, Stock-Based Compensation In February 2021, as a result of the completion of the first year of the three-year vesting period, an aggregate of 32,669 time-based restricted stock units of various executive officers vested and were settled in shares of the Company’s common stock (see Note 13, Stock-Based Compensation In October 2020, the Company issued 2,939,552 shares of its common stock to Vifor in connection with the license agreement entered into with Vifor (see Note 10, Collaboration and Licensing Agreements In June 2020, as a result of the completion of the one-year vesting period, an aggregate of 24,000 restricted stock units of members of the Board of Directors vested and were settled in shares of the Company’s common stock (see Note 13, Stock-Based Compensation In April and June 2020, as a result of the achievement of certain performance targets, an aggregate of 95,834 restricted stock units of various executive officers vested and were settled in shares of the Company’s common stock (see Note 13, Stock-Based Compensation

Collaboration and Licensing Agr

Collaboration and Licensing Agreements	9 Months Ended
Collaboration and Licensing Agreements	Sep. 30, 2021
Basis of Presentation
Collaboration and Licensing Agreements	Vifor (International) Ltd. In October 2020, the Company entered into a license agreement with Vifor, or the Vifor Agreement, under which the Company granted Vifor an exclusive license solely in the United States to use, distribute, offer for sale, promote, sell and otherwise commercialize CR845/difelikefalin injection for all therapeutic uses relating to the inhibition, prevention or treatment of itch associated with pruritus in hemodialysis and peritoneal dialysis patients in the United States. Under the Vifor Agreement, the Company retains all rights with respect to the clinical development of, and activities to gain regulatory approvals of, CR845/difelikefalin injection in the United States. The Vifor Agreement provides full commercialization rights in dialysis clinics to Vifor in the United States under a profit-sharing arrangement. Pursuant to the profit-sharing arrangement, the Company will generally be entitled to 60% of the net profits (as defined in the Vifor Agreement) from sales of CR845/difelikefalin injection in the United States (excluding sales to Fresenius Medical Center dialysis clinics, compensation for which is governed by the VFMCRP Agreement) and Vifor is entitled to 40% of such net profits, subject to potential temporary adjustment in future years based on certain conditions. Under the Vifor Agreement, in consideration of Vifor’s conduct of the marketing, promotion, selling and distribution of CR845/difelikefalin injection in the United States, the Company will pay a marketing and distribution fee to Vifor based on the level of annual net sales. This fee will be deducted from product sales in calculating the net profits that are subject to the profit-sharing arrangement under the Vifor Agreement. Under the terms of the Vifor Agreement, the Company received from Vifor an upfront payment of $100,000 and an additional payment of $50,000 for the purchase of an aggregate of 2,939,552 shares of the Company’s common stock at a price of $17.0094 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, or the Vifor Stock Purchase Agreement. After U.S. regulatory approval of KORSUVA injection in August 2021, the Company received an additional $50,000 in October 2021 for the purchase of an aggregate of 3,282,391 shares of the Company’s common stock at a price of $15.23 per share, which represents a 20% premium to the 30-day In addition, pursuant to the Vifor Agreement, the Company is eligible to receive payments of up to $240,000 upon the achievement of certain sales-based milestones. The Company retains the rights to make and have made CR845/difelikefalin injection, or the Licensed Product, on a non-exclusive basis, in the United States for commercial sale of the Licensed Product for use in all therapeutic uses to prevent, inhibit or treat itch associated with pruritus in hemodialysis and peritoneal-dialysis patients, or the Field, anywhere in the world and for supply of Licensed Product to Vifor under the terms of a supply agreement, or the Vifor Supply Agreement, which was executed in September 2021. The supply price is the Company’s cost of goods sold, as calculated under GAAP, plus an agreed upon margin. The Vifor Supply Agreement will co-terminate with the Vifor Agreement. The Vifor 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 Vifor 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 commercial supply to Vifor is not a performance obligation under the Vifor Agreement but rather the Vifor Supply Agreement is a separate agreement from the Vifor Agreement. The only performance obligation under the Vifor Supply Agreement is the delivery of the Licensed Product to Vifor for commercialization. Revenue from the sale of the Licensed Product to Vifor will be recognized in the Company’s Condensed Statements of Comprehensive Loss as sales of the Licensed Product occur. There were no sales of Licensed Product to Vifor through September 30, 2021. Vifor Fresenius Medical Care Renal Pharma Ltd. In May 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 the Licensed Product for all therapeutic uses to prevent, inhibit or treat itch associated with pruritus in the Field worldwide (excluding the United States, Japan and South Korea), or the Territory. 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. After U.S. regulatory approval of KORSUVA injection in August 2021, the Company was entitled to receive a $15,000 regulatory milestone payment which was received in October 2021, and was recorded as license and milestone fees revenue for the three and nine months ended September 30, 2021, based on the identification of one combined performance obligation at contract inception. The Company is eligible to receive from VFMCRP additional regulatory and commercial milestone payments in the aggregate of up to $455,000, consisting of up to $15,000 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. 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 VFMCRP Supply Agreement, which was executed in May 2020. The supply price is the Company’s cost of goods sold, as calculated under GAAP, plus an agreed upon margin. The VFMCRP Supply Agreement will co-terminate with the VFMCRP Agreement. The VFMCRP Supply Agreement is accounted for as a customer option that is not a material right because the selling price of the Licensed Product under the VFMCRP 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 commercial supply to VFMCRP is not a performance obligation under the VFMCRP Agreement but rather the VFMCRP Supply Agreement is a separate agreement from the VFMCRP Agreement. The only performance obligation under the VFMCRP 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 in the Company’s Condensed Statements of Comprehensive Loss as sales of the Licensed Product occur. During each of three and nine months ended September 30, 2021, the Company recognized clinical compound revenue of $241 from the sale of clinical compound to VFMCRP and as a result, the Company incurred R&D expense of $228 during these periods. During the nine months ended September 30, 2020, the Company recognized clinical compound revenue of $88 from the sale of clinical compound to VFMCRP and as a result, the Company incurred R&D expense of $79 during this period. There were no sales of clinical compound to VFMCRP during the three months ended September 30, 2020. 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 terms of the Maruishi Agreement, the Company is eligible to receive milestone payments upon the achievement of defined clinical and regulatory events as well as tiered, low double-digit royalties with respect to any sales of the licensed product sold in Japan by Maruishi, if any, and share in any sub-license fees. There were no sales of clinical compound to Maruishi during each of the three months ended September 30, 2021 and 2020. During the nine months ended September 30, 2021 and 2020, the Company recognized clinical compound revenue of $37 and $528, respectively, from the sale of clinical compound to Maruishi, and as a result, the Company incurred R&D expense of $33 and $476, respectively, during these periods. Chong Kun Dang Pharmaceutical Corporation In April 2012, the Company entered into a license agreement, or the CKDP Agreement, with 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
Revenue Recognition	Sep. 30, 2021
Revenue Recognition [Abstract]
Revenue Recognition	11. Revenue Recognition The Company currently recognizes revenue in accordance with FASB Accounting Standards Codification, or ASC, Topic 606, Revenue from Contracts with Customers , Collaboration and Licensing Agreements Contract balances As of September 30, 2021 and December 31, 2020, there were no material balances of receivables, and no other assets or deferred revenue related to the Maruishi and CKDP agreements. As of September 30, 2021, the Company recorded receivables from Vifor and VFMCRP for $20,031 in aggregate ($15,000 from VFMCRP and $5,031 premium related to the Vifor equity issuance) as a result of milestones being achieved during the period, which were included within Other receivables. In addition, the Company recorded a stock subscription receivable for $44,969 as of September 30, 2021 in connection with the U.S. regulatory milestone from Vifor. There were no other assets or deferred revenue related to the Vifor and VFMCRP agreements as of September 30, 2021 and December 31, 2020. Performance obligations Under the Vifor Agreement, the Company’s only performance obligation is granting a license to allow Vifor to commercialize CR845/difelikefalin in the United States, which occurred at inception of the contract in October 2020 (see Note 10, Collaboration and Licensing Agreements 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, were not distinct, and were accounted for as a single performance obligation during the period that the R&D services were 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 (see Note 10, Collaboration and Licensing Agreements 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. The Company’s only performance obligation under the VFMCRP Supply Agreement is 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 (see Note 10, Collaboration and Licensing Agreements Upon execution of the Vifor, VFMCRP, Maruishi and CKDP agreements, 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 Vifor Agreement, the entire transaction price of $111,551 was allocated to the one performance obligation, as described above, and was recognized as license and milestone fees revenue for the year ended December 31, 2020 as the license was granted to Vifor in October 2020. As of September 30, 2021, there were no remaining performance obligations under the Vifor Agreement. The Company is eligible to receive milestone payments in the future. 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, 2021, there were no remaining performance obligations, and the entire transaction price has been recognized as license and milestone fees revenue through December 31, 2020 since R&D services have been completed during 2020. The Company is eligible to receive milestone payments and sales royalties in the future. As of September 30, 2021, there were no remaining performance obligations under either the Maruishi or CKDP agreements, 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 four 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 combined 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 Vifor and CKDP agreements 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. 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 Vifor, VFMCRP, Maruishi and CKDP agreements, milestones and sales-based royalty payments were not included in the transaction price based on the factors noted above. Under the Vifor Agreement, the one performance obligation was satisfied when the license was granted to Vifor in October 2020, and as a result, $111,551 (including the upfront payment of $100,000 and the premium on the common stock purchased by Vifor of $11,551) was recognized as license and milestone fees revenue during the year ended December 31, 2020. The remaining potential consideration was considered to be variable consideration and was constrained at inception of the contract, which includes regulatory and sales milestones (see Note 10, Collaboration and Licensing Agreements Under the VFMCRP Agreement, the single combined performance obligation was satisfied as the R&D services were 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, was recognized as revenue as the R&D services were 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 and CKDP agreements were satisfied by the end of 2015. In the future, any milestone event will be recognized as milestone and license fee revenue and collaboration revenue based upon the relative standalone selling prices of the two performance obligations at inception of the Maruishi Agreement, and as milestone and license fee revenue under the CKDP Agreement. The remaining potential consideration was considered to be variable consideration and was constrained at inception of the contract, including clinical, regulatory and sales milestones, and sales royalties (see Note 10, Collaboration and Licensing Agreements 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 the Vifor, VFMCRP and CKDP agreements 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 Vifor, Maruishi and CKDP were 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 three 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 Vifor, 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 Vifor, Maruishi or CKDP. Therefore, the Company’s ongoing development efforts do not significantly affect the IP’s utility to which Vifor, Maruishi or CKDP have rights. Furthermore, if the Company abandons its development efforts, Vifor, 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, was recognized as the R&D services were performed, based on the costs incurred as a percentage of the estimated total costs to be incurred to complete the performance obligation. As of September 30, 2021, there is no remaining amount of the transaction price to be recognized as license and milestone fees revenue as all R&D services were completed in 2020. 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 Vifor, VFMCRP, Maruishi and CKDP agreements contain potential payments related to achievement of defined milestone events and royalties (excluding Vifor) 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). After U.S. regulatory approval of KORSUVA injection in August 2021, the Company received an additional $50,000 milestone payment in October 2021 from Vifor for the purchase of an aggregate of 3,282,391 shares of the Company’s common stock at a price of $15.23 per share, which represents a 20% premium to the 30-day trailing average price of the Company’s common stock as of the date of the achievement of the milestone. The excess of the stock purchase price over the cost of the purchased shares at the closing price of the Company’s common stock on the date of the achievement of the milestone of $5,031 was included as license and milestone fees revenue for the three and nine months ended September 30, 2021, as the variable consideration was deemed probable upon the FDA approval in August 2021. After U.S. regulatory approval of KORSUVA injection in August 2021, the Company received a $15,000 milestone payment in October 2021 from VFMCRP, which was recorded as license and milestone fees revenue for the three and nine months ended September 30, 2021, as the variable consideration was deemed probable upon the FDA approval in August 2021. In January 2021, the criteria for revenue recognition for a milestone event set forth in the Maruishi Agreement was achieved, and the Company recorded $1,192 as license and milestone fees revenue and $706 as collaboration revenue based on the relative standalone selling prices described above at contract inception for the nine months ended September 30, 2021. In May 2021, the Company received the $1,898 payment (after contractual foreign currency exchange adjustments) from Maruishi for the milestone event achieved. There were no milestone events related to the Maruishi Agreement that were probable of occurrence or achieved during the three months ended September 30, 2021, or during the three and nine months ended September 30, 2020. In May 2020, the criteria for revenue recognition for a milestone event set forth in the CKDP Agreement was achieved, and the Company recorded $626 (net of South Korean taxes) as license and milestone fees revenue in its Condensed Statements of Comprehensive Loss for the nine months ended September 30, 2020. No milestone events were probable of occurrence or achieved during the three and nine months ended September 30, 2021, or during the three months ended September 30, 2020. Sublicense payments Vifor’s, 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. Sales-based Royalty Payments The VFMCRP, Maruishi and CKDP agreements 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 to which some or all of the sales-based royalty has been allocated has been satisfied (or partially satisfied). 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, sales-based royalty payments are recognized as revenue when the customer’s sales occur. To date, no royalties have been earned or were otherwise due to the Company.

Net Income (Loss) Per Share

Net Income (Loss) Per Share	9 Months Ended
Net Income (Loss) Per Share	Sep. 30, 2021
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, 2021 and 2020, 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 Nine Months Ended September 30, September 30, 2021 2020 2021 2020 Basic: Weighted average common shares outstanding 50,114,710 46,885,424 50,031,615 46,803,659 Diluted: Weighted average common shares outstanding - Basic 50,114,710 46,885,424 50,031,615 46,803,659 Common stock equivalents* — — — — Denominator for diluted net loss per share 50,114,710 46,885,424 50,031,615 46,803,659 * 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 Nine Months Ended September 30, September 30, 2021 2020 2021 2020 Net loss - basic and diluted $ (1,013) $ (16,509) $ (55,059) $ (70,499) Weighted-average common shares outstanding: Basic and diluted 50,114,710 46,885,424 50,031,615 46,803,659 Net loss per share, Basic and Diluted: $ (0.02) $ (0.35) $ (1.10) $ (1.51) As of September 30, 2021, 5,974,549 stock options and 365,029 restricted stock units 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 as a result of the net loss for the period. In addition, the Company entered into the Vifor Agreement in October 2020. The Company issued 3,282,391 shares of its common stock in October 2021 upon U.S. regulatory approval of KORSUVA injection in August 2021. These shares were not included in the computation of basic or diluted net loss per share. As of September 30, 2020, 5,265,642 stock options and 272,000 restricted stock units 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 as a result of the net loss for the period.

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
Stock-Based Compensation	Sep. 30, 2021
Disclosure Of Compensation Related Costs Share Based Payments [Abstract]
Stock-Based Compensation	13. Stock-Based Compensation 2019 Inducement Plan In October 2019, the Company’s Board of Directors adopted the 2019 Inducement Plan, or the 2019 Plan, which is a non-stockholder approved stock plan adopted pursuant to the “inducement exception” provided under Nasdaq Listing Rule 5635(c)(4), or Rule 5635, for the purpose of awarding (i) non-statutory stock options, (ii) restricted stock awards, (iii) restricted stock unit awards, (iv) other stock awards (collectively, the Inducement Awards) to new employees of the Company, as inducement material to such new employees entering into employment with the Company. On November 20, 2019, the Company filed a Registration Statement on Form S-8 with the SEC covering the offering of up to 300,000 shares of its common stock, par value $0.001 , pursuant to the Company’s 2019 Plan. Initial grants of Inducement Awards made to employees 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. 2014 Equity Incentive Plan 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 quarterly 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 earlier of the first anniversary of the date of grant and the next Annual Meeting of Stockholders. 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, 2021, the aggregate number of shares of common stock that may be issued pursuant to Stock Awards under the 2014 Plan automatically increased from 7,488,513 to 8,984,679. 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 Pursuant to the Company’s non-employee director compensation policy, an aggregate of 43,200 restricted stock units were granted to non-employee directors on June 3, 2021, the date of the Company’s 2021 Annual Meeting of Stockholders, under the 2014 Plan with a grant date fair value of $13.06 per share. The restricted stock units will vest on the earlier of (i) June 3, 2022 and (ii) immediately prior to the Company’s next Annual Meeting of Stockholders following the grant date, subject to the recipient’s continued service through such date. As a result, the Company recognizes compensation expense associated with these restricted stock units ratably over the one-year vesting period following the grant date. For the three and nine months ended September 30, 2021, stock compensation expense of $142 and $184, respectively, was recognized in general and administrative, or G&A, expense. As of September 30, 2021, none of the 43,200 restricted stock units were vested or settled in shares of the Company’s common stock. On March 30, 2021, the Compensation Committee of the Company’s Board of Directors approved and granted a total of 176,000 restricted stock units to executive officers under the 2014 Plan with a grant date fair value of $20.59 per share. Vesting of the restricted stock units is contingent on the achievement of certain performance targets related to clinical and regulatory milestones, subject to the recipient’s continuous service through each performance target. Recognition of compensation expense associated with these awards begins when, and to the extent, the performance criteria is probable of achievement and the employee has met the service conditions. In August 2021, performance targets relating to 44,002 restricted stock units had been achieved and thus restricted stock units vested and the awards were settled in shares of common stock. For each of the three and nine months ended September 30, 2021, the Company recognized $906 of stock compensation expense, with $329 recorded in R&D expense and $577 recorded in G&A expense. As of September 30, 2021, 44,002 of the 176,000 restricted stock units vested and were settled in shares of the Company’s common stock. Additionally on March 30, 2021, the Compensation Committee of the Company’s Board of Directors also approved and granted a total of 100,000 time-based restricted stock units to certain executive officers under the 2014 Plan with a grant date fair value of $20.59 per share. The restricted stock units vest in three equal installments annually from the date of the grant. As a result, the Company recognizes compensation expense associated with these restricted stock units ratably over the three-year vesting period following the grant date. For the three months ended September 30, 2021, the Company recognized $173 of stock compensation expense, with $55 recorded in R&D expense and $118 in G&A expense. For the nine months ended September 30, 2021, the Company recognized $344 of stock compensation expense, with $110 recorded in R&D expense and $234 in G&A expense. As of September 30, 2021, none of the 100,000 restricted stock units were vested or settled in shares of the Company’s common stock. Pursuant to the Company’s non-employee director compensation policy, an aggregate of 36,000 restricted stock units were granted to non-employee directors on June 4, 2020, the date of the Company’s 2020 Annual Meeting of Stockholders, under the 2014 Plan with a grant date fair value of $15.62 per share. The restricted stock units fully vested on June 3, 2021. As a result, the Company has recognized compensation expense associated with these restricted stock units ratably over the one-year vesting period following the grant date. For the nine months ended September 30, 2021, stock compensation expense of $239 was recognized in G&A expense. No stock compensation expense relating to these restricted stock units were recognized during the three months ended September 30, 2021 as these restricted stock units fully vested and were settled in shares of the Company’s common stock in June 2021. For the three and nine months ended September 30, 2020, $142 and $182, respectively, of stock compensation expense relating to these restricted stock units was recognized in the Condensed Statements of Comprehensive Loss, all of which related to G&A expense. In February 2020, the Compensation Committee of the Company’s Board of Directors approved and granted a total of 138,000 restricted stock units to executive officers under the 2014 Plan with a grant date fair value of $16.36 per share. Vesting of the restricted stock units is contingent on the achievement of certain performance targets related to clinical and regulatory milestones, subject to the recipient’s continuous service through each performance target. Recognition of compensation expense associated with these awards begins when, and to the extent, the performance criteria is probable of achievement and the employee has met the service conditions. In February and March 2021, performance targets relating to 36,750 and 40,000 restricted stock units, respectively, had been achieved and thus restricted stock units vested and the awards were settled in shares of common stock. For the nine months ended September 30, 2021, the Company recognized $1,256 of stock compensation expense relating to the vesting of these restricted stock units, with $524 recorded in R&D expense and $732 in G&A expense. For the three months ended September 30, 2021, and the three and nine months ended September 30, 2020, no stock compensation expense relating to these restricted stock units were recognized. As of September 30, 2021, 113,500 of the 138,000 restricted stock units vested and were settled in shares of the Company’s common stock. Additionally in February 2020, the Compensation Committee of the Company’s Board of Directors also approved and granted a total of 98,000 time-based restricted stock units to executive officers under the 2014 Plan with a grant date fair value of $16.36 per share. The restricted stock units vest in three equal installments annually from the date of the grant. As a result, the Company recognizes compensation expense associated with these restricted stock units ratably over the three-year vesting period following the grant date. In February 2021, 32,669 of these restricted stock units vested and were settled in shares of the Company’s common stock in satisfaction of the first year of vesting. For the three months ended September 30, 2021, the Company recognized $135 of stock compensation expense, with $44 recorded in R&D expense and $91 in G&A expense. For the nine months ended September 30, 2021, the Company recognized $400 of stock compensation expense, with $130 recorded in R&D expense and $270 recorded in G&A expense. For the three months ended September 30, 2020, the Company recognized $134 of stock compensation expense, with $44 recorded in R&D expense and $90 in G&A expense. For the nine months ended September 30, 2020, the Company recognized $320 of stock compensation expense, with $105 recorded in R&D expense and $215 recorded in G&A expense. As of September 30, 2021, 32,669 of the 98,000 restricted stock units vested and were settled in shares of the Company’s common stock. Pursuant to the terms of the Company’s non-employee director compensation policy, an aggregate of 24,000 restricted stock units were granted to non-employee directors on June 4, 2019, the date of the Company’s 2019 Annual Meeting of Stockholders, under the 2014 Plan with a grant date fair value of $20.47 per share. The restricted stock units vested on the earlier of (i) June 4, 2020 and (ii) immediately prior to the Company’s next Annual Meeting of Stockholders following the grant date, subject to the recipient’s continued service through such date. As a result, the Company recognized compensation expense associated with these restricted stock units ratably over the one-year vesting period following the grant date. For the nine months ended September 30, 2020, the Company recognized $205 of stock compensation expense, all of which related to G&A expense. No stock compensation expense relating to these restricted stock units were recognized during the three months ended September 30, 2020 as these restricted stock units fully vested and were settled in shares of the Company’s common stock in June 2020. In March 2019, the Compensation Committee of the Company’s Board of Directors approved and granted a total of 215,000 restricted stock units to executive officers under the 2014 Plan with a grant date fair value of $16.10 per share. Vesting of the restricted stock units was contingent on the achievement of certain performance targets related to clinical milestones, subject to the recipient’s continuous service through the vesting events. Recognition of compensation expense associated with these awards begins when, and to the extent, the performance criteria is probable of achievement and the employee has met the service conditions. In April and June 2020, performance targets relating to 65,834 and 30,000 restricted stock units, respectively, had been achieved and thus such restricted stock units vested, and the awards were settled in shares of common stock. During the nine months ended September 30, 2020, the Company recognized $1,543 of stock compensation expense relating to the vesting of these restricted stock units, with $1,087 recorded in R&D expense and $456 recorded in G&A expense. No stock compensation expense relating to these restricted stock units were recognized during the three months ended September 30, 2020 as these restricted stock units either fully vested and were settled in shares of the Company’s common stock or were forfeited as of June 30, 2020. A summary of restricted stock unit activity related to employees and non-employee members of the Company’s Board of Directors as of and for the nine months ended September 30, 2021 is presented below: Weighted Number of Average Grant Units Date Fair Value Outstanding, December 31, 2020 235,250 $ 16.25 Awarded 319,200 19.57 Vested and released (189,421) 17.20 Outstanding, September 30, 2021 365,029 $ 18.66 Restricted stock units exercisable (vested and deferred), September 30, 2021 — Stock Options Under the 2014 Plan, the Company granted 30,000 and 345,000 stock options during the three months ended September 30, 2021 and 2020, respectively, and 819,250 and 1,165,350 stock options during the nine months ended September 30, 2021 and 2020, respectively. No Three Months Ended Nine Months Ended September 30, September 30, 2021 2020 2021 2020 Risk-free interest rate 0.92% - 1.01% 0.35% - 0.43% 0.66% - 1.23% 0.35% - 1.57% Expected volatility 83.0% - 83.4% 72.6% - 73.3% 71.6% - 83.5% 72.6% - 74.8% Expected dividend yield 0% 0% 0% 0% Expected life of employee and Board options (in years) 6.25 6.25 6.25 6.25 The weighted-average grant date fair value per share of options granted to employees and non-employee members of the Company’s Board of Directors for their Board service during the three months ended September 30, 2021 and 2020 was $9.24 and $11.11, respectively, and during the nine months ended September 30, 2021 and 2020 was $12.14 and $10.70, respectively. No options were granted to non-employee consultants during the three and nine months ended September 30, 2021 and 2020. During the three and nine months ended September 30, 2021 and 2020, the Company recognized compensation expense relating to stock options as follows: Three Months Ended Nine Months Ended September 30, September 30, 2021 2020 2021 2020 Research and development $ 1,833 $ 1,724 $ 5,228 $ 5,003 General and administrative 1,205 1,305 3,444 3,517 Total stock option expense $ 3,038 $ 3,029 $ 8,672 $ 8,520 The following were excluded from the table above as they are not related to stock options: compensation expense for (i) the vesting of executives’ restricted stock units for $429 in R&D expense and $785 in G&A expense for the three months ended September 30, 2021, and $1,094 in R&D expense and $1,812 in G&A expense for the nine months ended September 30, 2021; (ii) the vesting of executives’ restricted stock units for $44 in R&D expense and $90 in G&A expense for the three months ended September 30, 2020, and $1,192 in R&D expense and $671 in G&A expense for the nine months ended September 30, 2020; (iii) compensation expense relating to the Board of Directors’ restricted stock units for $142 and $423 in G&A expense for the three and nine months ended September 30, 2021, respectively; and (iv) compensation expense relating to the Board of Directors’ restricted stock units for $142 and $387 in G&A expense for the three and nine months ended September 30, 2020, respectively. 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, 2021 is presented below: Weighted Number of Average Exercise Shares Price Outstanding, December 31, 2020 5,469,393 $ 15.02 Granted 819,250 18.72 Exercised (114,354) 11.55 Forfeited (199,506) 17.20 Expired (234) 18.93 Outstanding, September 30, 2021 5,974,549 $ 15.52 Options exercisable, September 30, 2021 3,860,433 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 three and nine months ended September 30, 2021 and 2020.

Income Taxes

Income Taxes	9 Months Ended
Income Taxes	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Income Taxes	14. Income Taxes For the three months ended September 30, 2021 and 2020, pre-tax losses were $1,013 and $16,641, respectively, and for the nine months ended September 30, 2021 and 2020, pre-tax losses were $55,059 and $70,935, respectively. The Company recognized a full tax valuation allowance against its deferred tax assets as of September 30, 2021 and December 31, 2020. 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 $132 and $436 for the three and nine months ended September 30, 2020, 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. Because the Company’s revenue in 2020 exceeded $70,000, it is not eligible to exchange its 2021 R&D tax credit for cash, therefore there was no benefit from income taxes for the three and nine months ended September 30, 2021. As of September 30, 2021 and December 31, 2020, the Company did not have any foreign subsidiaries and the international aspects of the Tax Cuts and Jobs Act are not applicable for the respective periods. On March 27, 2020, former President Trump signed into law the Coronavirus Aid, Relief, and Economic Security Act of 2020, or the CARES Act (H.R. 748), which was further expanded with the signing of the Consolidation Appropriations Act of 2021 (H.R. 133) on December 27, 2020. The CARES Act (and December expansion) includes a variety of economic and tax relief measures intended to stimulate the economy, including loans for small businesses, payroll tax credits/deferrals, and corporate income tax relief. Due to the Company’s history of tax loss carryforwards and full valuation allowance, the CARES Act did not have a significant effect to the income tax provision, as the corporate income tax relief was directed towards cash taxpayers.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
Commitments and Contingencies	Sep. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	15. Commitments and Contingencies License Agreement with Enteris Biopharma, Inc. In August 2019, the Company entered into a non-exclusive license agreement, or the Enteris License Agreement, with Enteris Biopharma, Inc., or Enteris, pursuant to which Enteris granted to the Company a non-exclusive, royalty-bearing license, including the right to grant sublicenses, under certain proprietary technology and patent rights related to or covering formulations for oral delivery of peptide active pharmaceutical ingredients with functional excipients to enhance permeability and/or solubility, known as Enteris’s Peptelligence ® technology, to develop, manufacture and commercialize products using such technology worldwide, excluding Japan and South Korea. As consideration for the licensed rights under the Enteris License Agreement, the Company paid an upfront fee equal to $8,000 , consisting of $4,000 in cash and $4,000 in shares of the Company’s common stock pursuant to the Purchase Agreement with Enteris. The Company is also obligated, pursuant to the Enteris License Agreement, to pay Enteris (1) milestone payments upon the achievement of certain development, regulatory and commercial milestones and (2) low-single digit royalty percentages on net sales of licensed products, subject to reductions in specified circumstances. Until the second anniversary of the entry into the Enteris License Agreement, the Company has the right, but not the obligation, to terminate its obligation to pay any royalties under the Enteris License Agreement in exchange for a lump sum payment in cash, or the Royalty Buyout. The Company did not exercise its Royalty Buyout right and such right expired in August 2021. In June 2021, the Company paid a $10,000 milestone payment to Enteris based on a successful End of Phase 2 Meeting with the FDA in April 2021, which was recorded in R&D expense for the nine months ended September 30, 2021. In October 2020, the Company paid $2,500 to Enteris for a milestone earned, which was recorded in R&D expense for the three and nine months ended September 30, 2020. Manufacturing Agreements In July 2021, the Company entered into an API Commercial Supply Agreement with Polypeptide Laboratories S.A., or PPL, that defines each party’s responsibilities with respect to PPL’s manufacture and supply of the active pharmaceutical ingredient CR845/difelikefalin, or API, for the CR845/difelikefalin injection product candidate. Under the API Commercial Supply Agreement, PPL shall manufacture API at its facility for sale and supply to the Company, in the amounts as set forth in purchase orders to be provided by the Company. The Company will be required to purchase its requirements of API for each year of the term of the agreement, based on internal forecasts. The API Commercial Supply Agreement will continue until the fifth anniversary of the approval by the FDA of the new drug application for KORSUVA injection, unless the API Commercial Supply Agreement is earlier terminated, and will automatically be extended for successive five-year periods unless either party gives notice to the other party of its intention to terminate. In July 2019, the Company entered into a Master Manufacturing Services Agreement, or MSA, with Patheon UK Limited, or Patheon. The MSA governs the general terms under which Patheon, or one of its affiliates, will provide non-exclusive manufacturing services to the Company for the drug products specified by the Company from time to time. Pursuant to the MSA, the Company has agreed to order from Patheon at least a certain percentage of its commercial requirements for a product under a related Product Agreement. Each Product Agreement that the Company may enter into from time to time will be governed by the terms of the MSA, unless expressly modified in such Product Agreement. In July 2019, the Company entered into two related Product Agreements under the MSA, one with each of Patheon and Patheon Manufacturing Services LLC, or Patheon Greenville, to govern the terms and conditions of the manufacture of commercial supplies of CR845/difelikefalin injection, the Company’s lead product candidate. Pursuant to the Product Agreements, Patheon and Patheon Greenville will manufacture commercial supplies of CR845/difelikefalin injection at the Monza, Italy and Greenville, North Carolina manufacturing sites, respectively, from active pharmaceutical ingredient supplied by the Company. Patheon and Patheon Greenville will be responsible for supplying the other required raw materials and packaging components, and will also provide supportive manufacturing services such as quality control testing for raw materials, packaging components and finished product. Leases In December 2015, the Company entered into a lease agreement, or the Stamford Lease, for office space in Stamford, Connecticut, or the Premises, for the purposes of relocating its headquarters. The initial term of the Stamford Lease commenced in May 2016, or the Commencement Date, and ends in December 2023 In connection with the signing of the Stamford Lease, the Company entered into a standby letter of credit agreement which serves as a security deposit for the Premises. The standby letter of credit is automatically renewed annually through November 2023 Restricted Cash On January 1, 2019, the Company adopted FASB ASC 842: Leases, or ASC 842. Under ASC 842, since the Company adopted the practical expedients not to re-evaluate whether a contract is or contains a lease and to maintain the lease classification under ASC 840, the Stamford Lease continues to be accounted for as an operating lease. Upon adoption of ASC 842, the Company was required to establish an operating lease right-of-use, or ROU, asset and operating lease liability for the Stamford Lease. In establishing the ROU asset, the operating lease liability of $5,198 was reduced by lease incentives relating to tenant improvements of $698 and deferred lease obligation of $864, which were outstanding upon adoption. In June 2020, the Company entered into an amendment to the Stamford Lease to add additional office space, or the Lease Amendment. The term of the Lease Amendment began when renovation of the additional space was completed and the Company took possession of the additional space in October 2020, or the Amendment Commencement Date, and ends on December 31, 2023. The Lease Amendment is also renewable for one five-year term. The rent for the Lease Amendment is at market rate as of the signing of the Lease Amendment. The Lease Amendment requires monthly lease payments, including rent escalations, during the lease term. The Company began paying rent for the Lease Amendment on the Amendment Commencement Date. In October 2020, the Company recorded an operating lease liability of $1,934 for the Lease Amendment as the sum of the present value of the future minimum lease payments over the term for the new lease. The Company also recorded a corresponding ROU asset of $1,934, as no lease incentives were identified in the Lease Amendment. Under ASC 842, lease expenses on the Stamford Lease and Lease Amendment are recognized on a straight-line basis over the lease term. As a result, $406 and $239 of operating lease cost, or lease expense, was recognized for the three months ended September 30, 2021 and 2020, respectively, consisting of $284 relating to R&D lease expense and $122 relating to G&A lease expense for the Stamford Lease and Lease Amendment in the 2021 period, and $167 relating to R&D lease expense and $72 relating to G&A lease expense for the Stamford Lease in the 2020 period. For the nine months ended September 30, 2021 and 2020, $1,218 and $709, respectively, of operating lease cost, or lease expense, was recognized, consisting of $853 relating to R&D lease expense and $365 relating to G&A lease expense for the Stamford Lease and Lease Amendment in the 2021 period, and $496 relating to R&D lease expense and $213 relating to G&A lease expense for the Stamford Lease in the 2020 period. Other information related to the Stamford Lease and Lease Amendment was as follows: Three Months Ended Nine Months Ended September 30, 2021 September 30, 2020 September 30, 2021 September 30, 2020 Cash paid for amounts included in the measurement of lease liabilities: Operating cash outflows relating to operating leases $ 482 $ 312 $ 1,436 $ 927 ROU assets obtained in exchange for new operating lease liabilities $ — $ — $ — $ — Remaining lease term - operating leases (years) 2.3 3.3 2.3 3.3 Discount rate - operating leases 7.0 % 7.0 % 7.0 % 7.0 % Future minimum lease payments under non-cancellable operating leases, as well as a reconciliation of these undiscounted cash flows to the operating lease liability as of September 30, 2021, were as follows: Year Ending December 31, 2021 (Excluding the nine months ended September 30, 2021) $ 485 2022 1,957 2023 1,992 Total future minimum lease payments, undiscounted 4,434 Less imputed interest (345) Total $ 4,089 Operating lease liabilities reported as of September 30, 2021: Operating lease liabilities - current $ 1,716 Operating lease liabilities - non-current 2,373 Total $ 4,089

Subsequent Events

Subsequent Events	9 Months Ended
Subsequent Events	Sep. 30, 2021
Subsequent Events [Abstract]
Subsequent Events	16. Subsequent Events In October 2021, the Company and its President and Chief Executive Officer, or CEO, agreed to the transition of the role from CEO to Senior Advisor beginning on November 9, 2021. In addition, the Company and the CEO entered into a Separation Agreement dated November 2, 2021, pursuant to which the CEO will provide transitional consulting services as a Senior Advisor to the Company from November 9, 2021 through June 30, 2022. The Company appointed a current non-employee director of the Company’s Board of Directors to the position of Senior Advisor, effective October 29, 2021 until November 8, 2021, and as President and CEO, effective as of November 9, 2021. In October 2021, after the expiration of the requisite waiting period under the HSR Act, the Company received the $50,000 milestone payment from Vifor and issued 3,282,391 shares of its common stock to Vifor at a price of $15.23 per share, in connection with U.S. regulatory approval of KORSUVA injection on August 23, 2021. In October 2021, the Company received the $15,000 milestone payment from VFMCRP.

Basis of Presentation (Policies

Basis of Presentation (Policies)	9 Months Ended
Basis of Presentation (Policies)	Sep. 30, 2021
Basis of Presentation
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. The more significant estimates include the fair value of marketable securities that are classified as level 2 of the fair value hierarchy, 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, the incremental borrowing rate used in lease calculations and the likelihood of realization of deferred tax assets. The ongoing COVID-19 pandemic has interrupted business operations across the globe. Estimates and assumptions about future events and their effects cannot be determined with certainty and therefore require the exercise of judgment. As of the date of issuance of these condensed financial statements, the Company is not aware of any specific event or circumstance that would require the Company to update its estimates, assumptions and judgments or revise the reported amounts of assets and liabilities or the disclosure of contingent assets and liabilities. These estimates, however, may change as new events occur and additional information is obtained, and are recognized in the condensed financial statements as soon as they become known. Actual results could differ materially from the Company’s estimates and assumptions.
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, 2020, except for the recent adoption of new accounting pronouncements as disclosed below.
Accounting Pronouncements Recently Adopted	Accounting Pronouncements Recently Adopted In December 2019, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, No. 2019-12, Income Taxes (Topic 740) of legal entities that are not subject to tax; and (iv) enacted changes in tax laws in interim periods. The amendments in ASU 2019-12 are effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020. The amendments in ASU 2019-12 related to separate financial statements of legal entities that are not subject to tax should be applied on a retrospective basis for all periods presented. The amendments related to changes in ownership of foreign equity method investments or foreign subsidiaries should be applied on a modified retrospective basis through a cumulative-effect adjustment to retained earnings as of the beginning of the fiscal year of adoption. The amendments related to franchise taxes that are partially based on income should be applied on either a retrospective basis for all periods presented or a modified retrospective basis through a cumulative-effect adjustment to retained earnings as of the beginning of the fiscal year of adoption. All other amendments should be applied on a prospective basis. The Company adopted ASU 2019-12 on January 1, 2021 and it did not have a material effect on its results of operations, financial position, and cash flows due to the full valuation allowance recorded.

Available-for-Sale Marketable_2

Available-for-Sale Marketable Securities (Tables)	9 Months Ended
Available-for-Sale Marketable Securities (Tables)	Sep. 30, 2021
Investments Debt And Equity Securities [Abstract]
Summary of Available-for-Sale Marketable Securities by Major Type of Security	As of September 30, 2021 Gross Unrealized Estimated Fair Type of Security Amortized Cost Gains Losses Value U.S. Treasury securities $ 10,067 $ 3 $ — $ 10,070 U.S. government agency obligations 17,046 3 (5) 17,044 Corporate bonds 46,920 17 (23) 46,914 Commercial paper 78,452 6 (4) 78,454 Municipal bonds 17,938 19 (15) 17,942 Total available-for-sale marketable securities $ 170,423 $ 48 $ (47) $ 170,424 As of December 31, 2020 Gross Unrealized Estimated Fair Type of Security Amortized Cost Gains Losses Value U.S. Treasury securities $ 20,710 $ 41 $ (1) $ 20,750 U.S. government agency obligations 22,125 4 (1) 22,128 Corporate bonds 49,080 61 (23) 49,118 Commercial paper 116,139 5 (17) 116,127 Municipal bonds 11,680 12 (8) 11,684 Total available-for-sale marketable securities $ 219,734 $ 123 $ (50) $ 219,807
Schedule of Fair Values and Continuous Unrealized Loss Positions of Available-for-Sale Marketable Securities	As of September 30, 2021 Less than 12 Months 12 Months or Greater Total Gross Gross Gross Fair Unrealized Fair Unrealized Fair Unrealized Value Losses Value Losses Value Losses U.S. government agency obligations $ 9,495 $ (5) $ — $ — $ 9,495 $ (5) Corporate bonds 24,488 (23) — — 24,488 (23) Commercial paper 25,976 (4) — — 25,976 (4) Municipal bonds 7,319 (15) — — 7,319 (15) Total $ 67,278 $ (47) $ — $ — $ 67,278 $ (47) As of December 31, 2020 Less than 12 Months 12 Months or Greater Total Gross Gross Gross Fair Unrealized Fair Unrealized Fair Unrealized Value Losses Value Losses Value Losses U.S. Treasury securities $ 12,682 $ (1) $ — $ — $ 12,682 $ (1) U.S. government agency obligations 2,500 (1) — — 2,500 (1) Corporate bonds 23,553 (23) — — 23,553 (23) Commercial paper 68,897 (17) — — 68,897 (17) Municipal bonds 6,259 (8) — — 6,259 (8) Total $ 113,891 $ (50) $ — $ — $ 113,891 $ (50)
Schedule of Amortized Cost and Fair Values of Marketable Debt Securities by Contractual Maturity	As of September 30, 2021 As of December 31, 2020 Contractual maturity Amortized Cost Fair Value Amortized Cost Fair Value Less than one year $ 121,189 $ 121,203 $ 149,164 $ 149,242 One year to three years 49,234 49,221 70,570 70,565 Total $ 170,423 $ 170,424 $ 219,734 $ 219,807

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Tables)	9 Months Ended
Accumulated Other Comprehensive Income (Loss) (Tables)	Sep. 30, 2021
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), net of tax, from unrealized gains (losses) on available-for-sale marketable securities, the Company’s only component of accumulated other comprehensive income (loss), for the nine months ended September 30, 2021 and September 30, 2020. Total Accumulated Other Comprehensive Income (Loss) Balance, December 31, 2020 $ 73 Other comprehensive loss before reclassifications (33) Amount reclassified from accumulated other comprehensive income (39) Net current period other comprehensive loss (72) Balance, September 30, 2021 $ 1 Balance, December 31, 2019 $ 170 Other comprehensive income before reclassifications 319 Amount reclassified from accumulated other comprehensive income (126) Net current period other comprehensive income 193 Balance, September 30, 2020 $ 363
Schedule of Reclassification Out of Accumulated Other Comprehensive Income (Loss)	Three Months Ended Nine Months Ended Affected Line Item in the Component of Accumulated Other September 30, September 30, Condensed Statements of Comprehensive Income (Loss) 2021 2020 2021 2020 Comprehensive Income (Loss) Unrealized gains (losses) on available-for-sale marketable securities: Realized gains on sales of securities $ — $ 66 $ 39 $ 126 Other income, net Income tax effect — — — — Benefit from income taxes Realized gains on sales of securities, net of tax $ — $ 66 $ 39 $ 126

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
Fair Value Measurements (Tables)	Sep. 30, 2021
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, 2021 Fair value measurement as of September 30, 2021 Quoted prices in Significant other Significant Financial assets 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 funds and checking accounts $ 22,991 $ 22,991 $ — $ — Available-for-sale marketable securities: U.S. Treasury securities 10,070 — 10,070 — U.S. government agency obligations 17,044 — 17,044 — Corporate bonds 46,914 — 46,914 — Commercial paper 78,454 — 78,454 — Municipal bonds 17,942 — 17,942 — Restricted cash: Commercial money market account 408 408 — — Total financial assets $ 193,823 $ 23,399 $ 170,424 $ — Fair value measurement as of December 31, 2020: Quoted prices in Significant other Significant Financial assets 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 funds and checking accounts $ 31,683 $ 31,683 $ — $ — Available-for-sale marketable securities: U.S. Treasury securities 20,750 — 20,750 — U.S. government agency obligations 22,128 — 22,128 — Corporate bonds 49,118 — 49,118 — Commercial paper 116,127 — 116,127 — Municipal bonds 11,684 — 11,684 — Restricted cash: Commercial money market account 408 408 — — Total financial assets $ 251,898 $ 32,091 $ 219,807 $ —

Restricted Cash (Tables)

Restricted Cash (Tables)	9 Months Ended
Restricted Cash (Tables)	Sep. 30, 2021
Receivables [Abstract]
Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash	September 30, 2021 December 31, 2020 Cash and cash equivalents $ 22,991 $ 31,683 Restricted cash, long-term assets 408 408 Total cash, cash equivalents, and restricted cash shown in the Condensed Statements of Cash Flows $ 23,399 $ 32,091

Accounts Payable and Accrued _2

Accounts Payable and Accrued Expenses (Tables)	9 Months Ended
Accounts Payable and Accrued Expenses (Tables)	Sep. 30, 2021
Payables And Accruals [Abstract]
Schedule of Accounts Payable and Accrued Expenses	Accounts payable and accrued expenses consist of the following: September 30, 2021 December 31, 2020 Accounts payable $ 5,369 $ 4,893 Accrued research projects 3,496 6,194 Accrued compensation and benefits 4,125 4,955 Accrued professional fees and other 822 839 Total $ 13,812 $ 16,881

Net Income (Loss) Per Share (Ta

Net Income (Loss) Per Share (Tables)	9 Months Ended
Net Income (Loss) Per Share (Tables)	Sep. 30, 2021
Earnings Per Share [Abstract]
Computation of Denominators Used in Net Income (Loss) per Share	The denominators used in the net loss per share computations are as follows: Three Months Ended Nine Months Ended September 30, September 30, 2021 2020 2021 2020 Basic: Weighted average common shares outstanding 50,114,710 46,885,424 50,031,615 46,803,659 Diluted: Weighted average common shares outstanding - Basic 50,114,710 46,885,424 50,031,615 46,803,659 Common stock equivalents* — — — — Denominator for diluted net loss per share 50,114,710 46,885,424 50,031,615 46,803,659 * No amounts were considered as their effects would be anti-dilutive.
Computation of Basic and Diluted Net Income (Loss) per Share	Basic and diluted net loss per share are computed as follows: Three Months Ended Nine Months Ended September 30, September 30, 2021 2020 2021 2020 Net loss - basic and diluted $ (1,013) $ (16,509) $ (55,059) $ (70,499) Weighted-average common shares outstanding: Basic and diluted 50,114,710 46,885,424 50,031,615 46,803,659 Net loss per share, Basic and Diluted: $ (0.02) $ (0.35) $ (1.10) $ (1.51)

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
Stock-Based Compensation (Tables)	Sep. 30, 2021
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, 2021 and 2020 were estimated as of the dates of grant using the Black-Scholes option pricing model with the following assumptions: Three Months Ended Nine Months Ended September 30, September 30, 2021 2020 2021 2020 Risk-free interest rate 0.92% - 1.01% 0.35% - 0.43% 0.66% - 1.23% 0.35% - 1.57% Expected volatility 83.0% - 83.4% 72.6% - 73.3% 71.6% - 83.5% 72.6% - 74.8% Expected dividend yield 0% 0% 0% 0% Expected life of employee and Board options (in years) 6.25 6.25 6.25 6.25
Summary of Compensation Expense Relating to Stock Options	During the three and nine months ended September 30, 2021 and 2020, the Company recognized compensation expense relating to stock options as follows: Three Months Ended Nine Months Ended September 30, September 30, 2021 2020 2021 2020 Research and development $ 1,833 $ 1,724 $ 5,228 $ 5,003 General and administrative 1,205 1,305 3,444 3,517 Total stock option expense $ 3,038 $ 3,029 $ 8,672 $ 8,520
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, 2021 is presented below: Weighted Number of Average Exercise Shares Price Outstanding, December 31, 2020 5,469,393 $ 15.02 Granted 819,250 18.72 Exercised (114,354) 11.55 Forfeited (199,506) 17.20 Expired (234) 18.93 Outstanding, September 30, 2021 5,974,549 $ 15.52 Options exercisable, September 30, 2021 3,860,433
Employees And Non-Employee Members Of Board Of Directors [Member]
Summary of Restricted Stock Unit Activity	A summary of restricted stock unit activity related to employees and non-employee members of the Company’s Board of Directors as of and for the nine months ended September 30, 2021 is presented below: Weighted Number of Average Grant Units Date Fair Value Outstanding, December 31, 2020 235,250 $ 16.25 Awarded 319,200 19.57 Vested and released (189,421) 17.20 Outstanding, September 30, 2021 365,029 $ 18.66 Restricted stock units exercisable (vested and deferred), September 30, 2021 —

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
Commitments and Contingencies (Tables)	Sep. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Schedule of Other Information related to Stamford Lease and lease amendment	Other information related to the Stamford Lease and Lease Amendment was as follows: Three Months Ended Nine Months Ended September 30, 2021 September 30, 2020 September 30, 2021 September 30, 2020 Cash paid for amounts included in the measurement of lease liabilities: Operating cash outflows relating to operating leases $ 482 $ 312 $ 1,436 $ 927 ROU assets obtained in exchange for new operating lease liabilities $ — $ — $ — $ — Remaining lease term - operating leases (years) 2.3 3.3 2.3 3.3 Discount rate - operating leases 7.0 % 7.0 % 7.0 % 7.0 %
Schedule of Future Minimum Lease Payments under Non-cancellable Operating Leases, Reconciliation of Undiscounted Cash Flows to the Operating Lease Liability	Future minimum lease payments under non-cancellable operating leases, as well as a reconciliation of these undiscounted cash flows to the operating lease liability as of September 30, 2021, were as follows: Year Ending December 31, 2021 (Excluding the nine months ended September 30, 2021) $ 485 2022 1,957 2023 1,992 Total future minimum lease payments, undiscounted 4,434 Less imputed interest (345) Total $ 4,089 Operating lease liabilities reported as of September 30, 2021: Operating lease liabilities - current $ 1,716 Operating lease liabilities - non-current 2,373 Total $ 4,089

Business - Additional Informati

Business - Additional Information (Detail) $ in Thousands	1 Months Ended			3 Months Ended						9 Months Ended
Business - Additional Information (Detail) $ in Thousands	Oct. 31, 2021USD ($)shares	Oct. 31, 2020USD ($)shares	May 31, 2018USD ($)shares	Sep. 30, 2021USD ($)	Jun. 30, 2021USD ($)	Mar. 31, 2021USD ($)	Sep. 30, 2020USD ($)	Jun. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Sep. 30, 2021USD ($)item	Sep. 30, 2020USD ($)	Dec. 31, 2020USD ($)
Nature Of Business [Line Items]
Date of formation										Jul. 2, 2004
Proceeds from equity and debt financing				$ 519,600						$ 519,600
Number of follow-on public offerings \| item										4
Upfront and milestone payments received in connection with license agreements				224,100						$ 224,100
Unrestricted cash and cash equivalents and marketable securities				193,415						193,415
Accumulated deficit				447,376						447,376		$ 392,317
Net Loss				$ (1,013)	$ (30,745)	$ (23,301)	$ (16,509)	$ (25,068)	$ (28,922)	(55,059)	$ (70,499)
Net cash used in operating activities										$ (58,842)	$ (87,575)
Vifor International Ltd. [Member]
Nature Of Business [Line Items]
Proceeds from sale of common stock in connection with license agreement		$ 38,449	$ 14,556
Vifor International Ltd. [Member] \| Subsequent Event [Member]
Nature Of Business [Line Items]
Proceeds from sale of common stock in connection with regulatory milestone	$ 44,969
Vifor International Ltd. [Member] \| Common Stock [Member]
Nature Of Business [Line Items]
Common stock, shares issued \| shares		2,939,552	1,174,827
Vifor International Ltd. [Member] \| Common Stock [Member] \| Subsequent Event [Member]
Nature Of Business [Line Items]
Common stock, shares issued \| shares	3,282,391

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, 2021	Dec. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 170,423	$ 219,734
Gross Unrealized Gains	48	123
Gross Unrealized Losses	(47)	(50)
Estimated Fair Value	170,424	219,807
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,067	20,710
Gross Unrealized Gains	3	41
Gross Unrealized Losses		(1)
Estimated Fair Value	10,070	20,750
U.S. Government Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	17,046	22,125
Gross Unrealized Gains	3	4
Gross Unrealized Losses	(5)	(1)
Estimated Fair Value	17,044	22,128
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	46,920	49,080
Gross Unrealized Gains	17	61
Gross Unrealized Losses	(23)	(23)
Estimated Fair Value	46,914	49,118
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	78,452	116,139
Gross Unrealized Gains	6	5
Gross Unrealized Losses	(4)	(17)
Estimated Fair Value	78,454	116,127
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	17,938	11,680
Gross Unrealized Gains	19	12
Gross Unrealized Losses	(15)	(8)
Estimated Fair Value	$ 17,942	$ 11,684

Available-for-Sale Marketable_4

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, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Fair Value	$ 67,278	$ 113,891
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Gross Unrealized Losses	(47)	(50)
Available-for-sale marketable securities, continuous unrealized loss position, 12 Months or Greater, Gross Unrealized Losses	0	0
Available-for-sale marketable securities, continuous unrealized loss position, Fair Value	67,278	113,891
Available-for-sale marketable securities, continuous unrealized loss position, Gross Unrealized Losses	(47)	(50)
U.S. Treasury Securities [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Fair Value		12,682
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Gross Unrealized Losses		(1)
Available-for-sale marketable securities, continuous unrealized loss position, Fair Value		12,682
Available-for-sale marketable securities, continuous unrealized loss position, Gross Unrealized Losses		(1)
U.S. Government Agency Obligations [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Fair Value	9,495	2,500
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Gross Unrealized Losses	(5)	(1)
Available-for-sale marketable securities, continuous unrealized loss position, Fair Value	9,495	2,500
Available-for-sale marketable securities, continuous unrealized loss position, Gross Unrealized Losses	(5)	(1)
Corporate Bonds [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Fair Value	24,488	23,553
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Gross Unrealized Losses	(23)	(23)
Available-for-sale marketable securities, continuous unrealized loss position, Fair Value	24,488	23,553
Available-for-sale marketable securities, continuous unrealized loss position, Gross Unrealized Losses	(23)	(23)
Commercial Paper [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Fair Value	25,976	68,897
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Gross Unrealized Losses	(4)	(17)
Available-for-sale marketable securities, continuous unrealized loss position, Fair Value	25,976	68,897
Available-for-sale marketable securities, continuous unrealized loss position, Gross Unrealized Losses	(4)	(17)
Municipal Bonds [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Fair Value	7,319	6,259
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Gross Unrealized Losses	(15)	(8)
Available-for-sale marketable securities, continuous unrealized loss position, Fair Value	7,319	6,259
Available-for-sale marketable securities, continuous unrealized loss position, Gross Unrealized Losses	$ (15)	$ (8)

Available-for-Sale Marketable_5

Available-for-Sale Marketable Securities - Additional Information (Detail) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021USD ($)position	Dec. 31, 2020USD ($)position
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale allowance for credit loss \| $	$ 0	$ 0
Available-for-sale unrealized credit losses \| $	$ 0	$ 0
Number of available-for-sale marketable securities in unrealized loss positions	26	30
Total number of positions	59	59
Available-for-sale marketable securities, continuous unrealized loss position, 12 Months or Greater, Gross Unrealized Losses \| $	$ 0	$ 0
U.S. Government Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of available-for-sale marketable securities in unrealized loss positions	3
Total number of positions	5
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of available-for-sale marketable securities in unrealized loss positions	10
Total number of positions	20
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of available-for-sale marketable securities in unrealized loss positions	7
Total number of positions	19
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of available-for-sale marketable securities in unrealized loss positions	6
Total number of positions	12

Available-for-Sale Marketable_6

Available-for-Sale Marketable Securities - Schedule of Amortized Cost and Fair Values of Marketable Debt Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Investments Debt And Equity Securities [Abstract]
Amortized Cost of marketable debt securities, contractual maturity, less than one year	$ 121,189		$ 121,189		$ 149,164
Amortized Cost of marketable debt securities, contractual maturity, One year to three years	49,234		49,234		70,570
Amortized Cost	170,423		170,423		219,734
Fair value of marketable debt securities, contractual maturities, less than one year	121,203		121,203		149,242
Fair value of marketable debt securities, contractual maturity, One year to three years	49,221		49,221		70,565
Total fair Value of marketable debt securities, contractual maturity	170,424		170,424		219,807
Proceeds from sale of available-for-sale marketable securities	1,000	$ 12,471	10,029	$ 23,148
Realized gain (loss)	0	$ 66	39	$ 126
Interest receivable	$ 318		$ 318		$ 311

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, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Accumulated Other Comprehensive Income Loss [Line Items]
Balance, Value	$ 203,466	$ 230,459	$ 249,001	$ 140,928	$ 160,474	$ 186,713	$ 249,001	$ 186,713
Amount reclassified from accumulated other comprehensive income				(66)			(39)	(126)
Net current period other comprehensive income (loss)	6	(17)	(61)	(272)	703	(238)
Balance, Value	207,191	203,466	230,459	127,847	140,928	160,474	207,191	127,847
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance, Value	(5)	12	73	635	(68)	170	73	170
Other comprehensive income (loss) before reclassifications							(33)	319
Amount reclassified from accumulated other comprehensive income							(39)	(126)
Net current period other comprehensive income (loss)	6	(17)	(61)	(272)	703	(238)	(72)	193
Balance, Value	$ 1	$ (5)	$ 12	$ 363	$ 635	$ (68)	$ 1	$ 363

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Income (Loss) - Schedule of Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Other income, net	$ 111	$ 379	$ 502	$ 1,970
Benefit from income taxes	$ 0	(132)	0	(436)
Net of tax		66	39	126
Accumulated Net Unrealized Investment Gain Attributable to Parent [Member] \| Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Other income, net		$ 66	$ 39	$ 126

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financial assets
Available-for-sale marketable securities	$ 170,424	$ 219,807
Recurring [Member]
Financial assets
Total financial assets	193,823	251,898
U.S. Government Agency Obligations [Member]
Financial assets
Available-for-sale marketable securities	17,044	22,128
U.S. Government Agency Obligations [Member] \| Recurring [Member]
Financial assets
Available-for-sale marketable securities	17,044	22,128
Corporate Bonds [Member]
Financial assets
Available-for-sale marketable securities	46,914	49,118
Corporate Bonds [Member] \| Recurring [Member]
Financial assets
Available-for-sale marketable securities	46,914	49,118
Municipal Bonds [Member]
Financial assets
Available-for-sale marketable securities	17,942	11,684
Municipal Bonds [Member] \| Recurring [Member]
Financial assets
Available-for-sale marketable securities	17,942	11,684
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Recurring [Member]
Financial assets
Total financial assets	23,399	32,091
Significant Other Observable Inputs (Level 2) [Member] \| Recurring [Member]
Financial assets
Total financial assets	170,424	219,807
Significant Other Observable Inputs (Level 2) [Member] \| U.S. Government Agency Obligations [Member] \| Recurring [Member]
Financial assets
Available-for-sale marketable securities	17,044	22,128
Significant Other Observable Inputs (Level 2) [Member] \| Corporate Bonds [Member] \| Recurring [Member]
Financial assets
Available-for-sale marketable securities	46,914	49,118
Significant Other Observable Inputs (Level 2) [Member] \| Municipal Bonds [Member] \| Recurring [Member]
Financial assets
Available-for-sale marketable securities	17,942	11,684
Money Market Funds [Member] \| Recurring [Member]
Financial assets
Cash and cash equivalents	22,991	31,683
Restricted cash	408	408
Money Market Funds [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Recurring [Member]
Financial assets
Cash and cash equivalents	22,991	31,683
Restricted cash	408	408
U.S. Treasury Securities [Member] \| Recurring [Member]
Financial assets
Available-for-sale marketable securities	10,070	20,750
U.S. Treasury Securities [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Recurring [Member]
Financial assets
Available-for-sale marketable securities	10,070	20,750
Commercial Paper [Member] \| Recurring [Member]
Financial assets
Available-for-sale marketable securities	78,454	116,127
Commercial Paper [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Recurring [Member]
Financial assets
Available-for-sale marketable securities	$ 78,454	$ 116,127

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Purchases of financial assets	$ 0	$ 0	$ 0	$ 0
Sales of financial assets	0	0	0	0
Maturities of financial assets	0	0	0	0
Transfer of financial asset into level 3 of fair value	0	0	0	0
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Unrealized gains	0	0	0	0
Unrealized losses	$ 0	$ 0	$ 0	$ 0

Restricted Cash - Additional In

Restricted Cash - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash balance	$ 408	$ 408
Stamford Lease [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash balance	$ 408	$ 408

Restricted Cash - Schedule of R

Restricted Cash - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Cash And Cash Equivalents [Abstract]
Cash and cash equivalents	$ 22,991	$ 31,683
Restricted cash balance	408	408
Total cash, cash equivalents, and restricted cash shown in the Statements of Cash Flows	$ 23,399	$ 32,091	$ 75,689	$ 18,713

Prepaid Expenses - Additional I

Prepaid Expenses - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Prepaid expenses	$ 6,258	$ 12,076
Prepaid R&D clinical costs	4,098	11,286
Prepaid insurance	855	223
Other prepaid costs	$ 1,305	$ 567

Accounts Payable and Accrued _3

Accounts Payable and Accrued Expenses - Schedule of Accounts Payable and Accrued Expenses (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Payables And Accruals [Abstract]
Accounts payable	$ 5,369	$ 4,893
Accrued research projects	3,496	6,194
Accrued compensation and benefits	4,125	4,955
Accrued professional fees and other	822	839
Total	$ 13,812	$ 16,881

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended						3 Months Ended			9 Months Ended
	Oct. 31, 2021	Aug. 31, 2021	Jun. 30, 2021	Feb. 28, 2021	Oct. 31, 2020	Jun. 30, 2020	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2021
Sale Of Stock [Line Items]
Stock subscription receivable										$ 44,969
Share Price										$ 15.23
Regulatory Milestones [Member]
Sale Of Stock [Line Items]
Proceeds from the sale of stock	$ 50,000
Regulatory Milestones [Member] \| Vifor International Ltd. [Member]
Sale Of Stock [Line Items]
Proceeds from the sale of stock		$ 50,000
Stock subscription receivable										$ 44,969
Stock Issued During Period Shares New Issues	3,282,391
Share Price		$ 15.23								$ 15.23
Regulatory Milestones [Member] \| License and Milestone Fees \| Vifor International Ltd. [Member]
Sale Of Stock [Line Items]
Premium from sale of stock										$ 5,031
Vifor Agreement [Member] \| Vifor International Ltd. [Member]
Sale Of Stock [Line Items]
Stock Issued During Period Shares New Issues					2,939,552
Common Stock [Member]
Sale Of Stock [Line Items]
Restricted stock units vested shares									119,834
Restricted Stock Units [Member] \| Common Stock [Member] \| Director [Member]
Sale Of Stock [Line Items]
Restricted stock units vested shares			36,000			24,000
Vesting period of awards granted			1 year			1 year
Performance Restricted Stock Units [Member] \| Common Stock [Member] \| Executive Officers [Member]
Sale Of Stock [Line Items]
Restricted stock units vested shares		44,002					76,750	95,834
Time-based Restricted Stock Units [Member] \| Common Stock [Member] \| Executive Officers [Member]
Sale Of Stock [Line Items]
Restricted stock units vested shares				32,669
Vesting period of awards granted				3 years

Collaboration and Licensing A_2

Collaboration and Licensing Agreements - Additional Information (Detail) $ / shares in Units, $ in Thousands	Oct. 15, 2020USD ($)	May 17, 2018USD ($)item$ / sharesshares	Oct. 31, 2021USD ($)$ / sharesshares	Oct. 31, 2020USD ($)$ / sharesshares	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue from contract with customer					$ 20,272	$ 9,266	$ 22,207	$ 22,993
Collaborative Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue from contract with customer							706
Clinical Compound Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue from contract with customer					241	9	278	616
Vifor Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of net profit sharing				60.00%
Regulatory Milestones [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Proceeds from the sale of stock			$ 50,000
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Non-refundable, non-creditable upfront payment		$ 50,000
Common stock, shares issued \| shares		1,174,827
Purchase of common stock value		$ 20,000
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
Number of combined performance obligations for revenue recognized \| item		1
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member] \| Clinical Compound Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue from contract with customer					241	0	241	88
Cost of clinical compound related to R&D expense					228		228	79
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member] \| Regulatory Milestones [Member] \| Subsequent Event [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Proceeds from milestone payments			$ 15,000
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member] \| Maximum [Member] \| Regulatory and Commercial Milestones [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments		$ 455,000
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member] \| Maximum [Member] \| Regulatory Milestones [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments					15,000		15,000
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member] \| Maximum [Member] \| Tiered Commercial Milestones [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments					440,000		440,000
Maruishi Pharmaceutical Co., Ltd. [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Cost of clinical compound related to R&D expense							33	476
Maruishi Pharmaceutical Co., Ltd. [Member] \| Clinical Compound Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue from contract with customer					0	$ 0	37	$ 528
Vifor International Ltd. [Member] \| License [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue from contract with customer							0
Vifor International Ltd. [Member] \| Vifor Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of net profit sharing				40.00%
Common stock, shares issued \| shares				2,939,552
Purchase common stock per share amount \| $ / shares				$ 17.0094
Vifor International Ltd. [Member] \| Vifor Agreement [Member] \| License [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Non-refundable, non-creditable upfront payment				$ 100,000
Vifor International Ltd. [Member] \| Regulatory Milestones [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Common stock, shares issued \| shares			3,282,391
Proceeds from the sale of stock	$ 50,000		$ 50,000
Purchase common stock per share amount \| $ / shares			$ 15.23
Premium from sale of stock					$ 5,031		$ 5,031
Potential milestone payments	$ 50,000
Percentage of premium on common stock investment	20.00%		20.00%
Stock issuance price measurement period	30 days		30 days
Vifor International Ltd. [Member] \| Regulatory Milestones [Member] \| Subsequent Event [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Common stock, shares issued \| shares			3,282,391
Proceeds from the sale of stock			$ 50,000
Purchase common stock per share amount \| $ / shares			$ 15.23
Vifor International Ltd. [Member] \| Maximum [Member] \| Sales-based Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments	$ 240,000

Revenue Recognition - Additiona

Revenue Recognition - Additional Information (Detail) Milestone in Thousands, $ in Thousands	Oct. 31, 2021USD ($)$ / shares	Oct. 15, 2020USD ($)item	May 17, 2018USD ($)item$ / sharesshares	Oct. 31, 2021USD ($)$ / sharesshares	May 31, 2021USD ($)	Apr. 30, 2013USD ($)item	Sep. 30, 2021USD ($)Milestone	Dec. 31, 2020USD ($)item	Sep. 30, 2020USD ($)Milestone	Sep. 30, 2021USD ($)item	Sep. 30, 2020USD ($)Milestone	Dec. 31, 2020USD ($)item
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Stock subscription receivable							$ 44,969			$ 44,969
Total revenue							20,272		$ 9,266	22,207	$ 22,993
Regulatory Milestones [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Proceeds from the sale of stock				$ 50,000
License and Milestone Fees
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Total revenue							20,031		$ 9,257	21,223	$ 22,377
Royalty [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue from contract with customer										0
Collaborative Revenue
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Total revenue										$ 706
Vifor Agreement [Member] \| License and Milestone Fees
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Total revenue								$ 111,551
Number of remaining performance obligations										0
Number of performance obligations for revenue recognized \| item		1						1
upfront payment												$ 100,000
Premium from sale of stock												11,551
Revenue from contract with customer												$ 111,551
Vifor Agreement [Member] \| License and Milestone Fees \| Regulatory Milestones [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Premium from sale of stock										$ 5,031
VFMCRP Agreement [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Deferred revenue			$ 55,444
Number of combined performance obligations for revenue recognized \| item			1
Number of remaining performance obligations										0
Number of performance obligations for revenue recognized \| item			2
upfront payment			$ 50,000
Premium from sale of stock			$ 5,444
VFMCRP Agreement [Member] \| Regulatory Milestones [Member] \| Subsequent Event [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Proceeds from milestone payments	$ 15,000
VFMCRP Agreement [Member] \| License and Milestone Fees
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Number of remaining performance obligations \| item										0
VFMCRP Agreement [Member] \| License and Milestone Fees \| Regulatory Milestones [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Receivables							15,000			$ 15,000
Vifor, VFMCRP, and CKDP Agreements [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Number of performance obligations for revenue recognized \| item												1
Vifor And VFMCRP Agreements [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Deferred revenue, current							0	$ 0		0		$ 0
Other assets							0	0		0		0
Vifor And VFMCRP Agreements [Member] \| License and Milestone Fees \| Regulatory Milestones [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Receivables							20,031			$ 20,031
Vifor, Maruishi and CKDP Agreements [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
License agreements with IP as separate performance obligation \| item										3
Maruishi and CKDP Agreements [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Deferred revenue, non current							0	0		$ 0		0
Receivables							0	0		0		0
Other assets							$ 0	$ 0		$ 0		$ 0
Number of remaining performance obligations \| item										0
Maruishi Agreement [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Number of performance obligations for revenue recognized \| item						2
Upfront non-refundable, non-creditable license fee and premium from sale of stock						$ 15,337
Number of milestone event probable of occurrence or achieved \| Milestone							0		0		0
Maruishi Agreement [Member] \| License and Milestone Fees
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Total revenue										$ 1,192
Proceeds from milestone payments					$ 1,898
Maruishi Agreement [Member] \| License [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Estimated selling price						10,200
Upfront payments on obligations						9,637
Maruishi Agreement [Member] \| R&D Services [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Estimated selling price						6,200
Upfront payments on obligations						$ 5,700
Maruishi Agreement [Member] \| Collaborative Revenue
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Total revenue										$ 706
CKDP Agreement [Member] \| License and Milestone Fees
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Total revenue											$ 626
Number of milestone event probable of occurrence or achieved							0		0	0
Vifor International Ltd. [Member] \| Regulatory Milestones [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Premium on Common Stock Investment, Percentage	20.00%	20.00%		20.00%
Proceeds from the sale of stock		$ 50,000		$ 50,000
Stock Issued During Period Shares New Issues \| shares				3,282,391
Stock Issuance Price Measurement Period		30 days		30 days
Shares Issued Price Per Share \| $ / shares	$ 15.23			$ 15.23
Stock subscription receivable							$ 44,969			$ 44,969
Premium from sale of stock							5,031			5,031
Potential milestone payments		$ 50,000
Vifor International Ltd. [Member] \| Regulatory Milestones [Member] \| Subsequent Event [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Proceeds from the sale of stock				$ 50,000
Stock Issued During Period Shares New Issues \| shares				3,282,391
Shares Issued Price Per Share \| $ / shares	$ 15.23			$ 15.23
Vifor International Ltd. [Member] \| License and Milestone Fees \| Regulatory Milestones [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Premium from sale of stock							5,031			5,031
Vifor International Ltd. [Member] \| License [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Total revenue										0
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Stock Issued During Period Shares New Issues \| shares			1,174,827
Shares Issued Price Per Share \| $ / shares			$ 17.024
Number of combined performance obligations for revenue recognized \| item			1
upfront payment			$ 50,000
Premium from sale of stock			$ 5,444
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member] \| Regulatory Milestones [Member] \| Subsequent Event [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Proceeds from milestone payments				$ 15,000
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member] \| Regulatory Milestones [Member] \| Maximum [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Potential milestone payments							$ 15,000			$ 15,000

Net Income (Loss) per Share - C

Net Income (Loss) per Share - Computation of Denominators Used in Net Loss per Share (Detail) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Basic:
Weighted average common shares outstanding - Basic	50,114,710	46,885,424	50,031,615	46,803,659
Diluted:
Weighted average common shares outstanding - Basic	50,114,710	46,885,424	50,031,615	46,803,659
Common stock equivalents	0	0	0	0
Denominator for diluted net loss per share	50,114,710	46,885,424	50,031,615	46,803,659

Net Income (Loss) per Share -_2

Net Income (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, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Net loss - basic and diluted	$ (1,013)	$ (30,745)	$ (23,301)	$ (16,509)	$ (25,068)	$ (28,922)	$ (55,059)	$ (70,499)
Weighted-average common shares outstanding:
Weighted average number of shares outstanding basic and diluted	50,114,710			46,885,424			50,031,615	46,803,659
Net loss per share, Basic and Diluted	$ (0.02)			$ (0.35)			$ (1.10)	$ (1.51)

Net Income (Loss) per Share - A

Net Income (Loss) per Share - Additional Information (Detail) - USD ($) $ in Thousands	Oct. 15, 2020	Oct. 31, 2021	Sep. 30, 2021	Sep. 30, 2020
Number of options outstanding			5,974,549	5,265,642
Number of restricted stock units outstanding			365,029	272,000
Vifor International Ltd. [Member] \| Regulatory Milestones [Member]
Stock Issued During Period Shares New Issues		3,282,391
Potential milestone payment	$ 50,000
Percentage of premium on common stock investment	20.00%	20.00%
Stock issuance price measurement period	30 days	30 days

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) $ / shares in Units, $ in Thousands

Jun. 03, 2021$ / sharesshares

Mar. 30, 2021installment$ / sharesshares

Jun. 04, 2020$ / shares

Jun. 04, 2019$ / sharesshares

Aug. 31, 2021shares

Mar. 31, 2021shares

Feb. 28, 2021shares

Jun. 30, 2020shares

Apr. 30, 2020shares

Feb. 29, 2020installment$ / sharesshares

Mar. 31, 2019$ / sharesshares

Sep. 30, 2021USD ($)$ / sharesshares

Mar. 31, 2021shares

Sep. 30, 2020USD ($)$ / sharesshares

Sep. 30, 2021USD ($)$ / sharesshares

Sep. 30, 2020USD ($)$ / sharesshares

Dec. 31, 2015shares

Jan. 01, 2021shares

Dec. 31, 2020$ / sharesshares

Nov. 20, 2019$ / sharesshares

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Common stock, par value | $ / shares

$ 0.001

Common stock, shares outstanding

50,175,988

49,872,213

Common stock, shares issued

50,175,988

49,872,213

Number of options outstanding

5,974,549

5,265,642

5,974,549

5,265,642

Restricted Stock Units [Member] | Research and Development [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Compensation expense | $

$ 429

$ 44

$ 1,094

$ 1,192

Restricted Stock Units [Member] | General and Administrative [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Compensation expense | $

$ 785

$ 90

$ 1,812

$ 671

Share-based Payment Arrangement, Employee [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Fair value of options granted | $ / shares

$ 9.24

$ 11.11

$ 12.14

$ 10.70

Director [Member] | Restricted Stock Units [Member] | General and Administrative [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Compensation expense | $

$ 142

$ 423

$ 387

Non-employee Consultants [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Options granted

2019 Inducement Plan [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Common stock, par value | $ / shares

$ 0.001

Awarded

2019 Inducement Plan [Member] | Maximum [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

300,000

2019 Inducement Plan [Member] | Share-based Payment Arrangement, Employee [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%

2019 Inducement Plan [Member] | Share-based Payment Arrangement, Employee [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

2019 Inducement Plan [Member] | Share-based Payment Arrangement, Employee [Member] | Share Based Compensation Subsequent Awards [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vesting period of awards granted

4 years

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

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

8,984,679

7,488,513

Number of options outstanding

5,974,549

5,469,393

Options granted

30,000

345,000

819,250

1,165,350

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] | Director [Member] | Incentive Stock Options [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vesting period of awards granted

3 years

2014 Equity Incentive Plan [Member] | Director [Member] | Share-based Payment Arrangement, Nonemployee [Member] | General and Administrative [Member] | June 2019 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Compensation expense | $

$ 0

2014 Equity Incentive Plan [Member] | Director [Member] | Share-based Payment Arrangement, Nonemployee [Member] | Restricted Stock Units [Member] | June 2020 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vesting period of awards granted

1 year

Awarded

36,000

Restricted stock units, grant date fair value | $ / shares

$ 15.62

Restricted stock units vesting date

Jun. 3,
2021

2014 Equity Incentive Plan [Member] | Director [Member] | Share-based Payment Arrangement, Nonemployee [Member] | Restricted Stock Units [Member] | June 2019 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vesting period of awards granted

1 year

Awarded

24,000

Restricted stock units, grant date fair value | $ / shares

$ 20.47

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Compensation expense | $

$ 182

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Compensation expense | $

$ 0

142

$ 239

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Compensation expense | $

205

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Restricted stock units vesting date

Jun. 4,
2020

2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Restricted Stock Units [Member] | Research and Development [Member] | March 2019 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Compensation expense | $

2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Performance Restricted Stock Units [Member] | March 2021 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Awarded

176,000

Restricted stock units, grant date fair value | $ / shares

$ 20.59

Compensation expense | $

906

$ 906

Restricted stock units, vested

44,002

2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Performance Restricted Stock Units [Member] | February 2020 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Awarded

138,000

Restricted stock units, grant date fair value | $ / shares

$ 16.36

Compensation expense | $

$ 1,256

Restricted stock units, vested

40,000

36,750

113,500

2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Performance Restricted Stock Units [Member] | March 2019 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Awarded

215,000

Restricted stock units, grant date fair value | $ / shares

$ 16.10

Compensation expense | $

1,543

Restricted stock units, vested

30,000

65,834

2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Performance Restricted Stock Units [Member] | Research and Development [Member] | March 2021 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Compensation expense | $

329

$ 329

2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Performance Restricted Stock Units [Member] | Research and Development [Member] | February 2020 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Compensation expense | $

524

2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Performance Restricted Stock Units [Member] | Research and Development [Member] | March 2019 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Compensation expense | $

1,087

2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Performance Restricted Stock Units [Member] | General and Administrative [Member] | March 2021 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Compensation expense | $

577

2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Performance Restricted Stock Units [Member] | General and Administrative [Member] | February 2020 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Compensation expense | $

732

2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Performance Restricted Stock Units [Member] | General and Administrative [Member] | March 2019 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Compensation expense | $

456

2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Time-based Restricted Stock Units [Member] | March 2021 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vesting period of awards granted

3 years

Awarded

100,000

Restricted stock units, grant date fair value | $ / shares

$ 20.59

Number of equal installment | installment

Compensation expense | $

173

$ 344

Restricted stock units, vested

2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Time-based Restricted Stock Units [Member] | February 2020 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vesting period of awards granted

3 years

Awarded

98,000

Restricted stock units, grant date fair value | $ / shares

$ 16.36

Number of equal installment | installment

Compensation expense | $

135

134

$ 400

320

Restricted stock units, vested

32,669

2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Time-based Restricted Stock Units [Member] | Research and Development [Member] | March 2021 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Compensation expense | $

$ 110

2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Time-based Restricted Stock Units [Member] | Research and Development [Member] | February 2020 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Compensation expense | $

130

105

2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Time-based Restricted Stock Units [Member] | General and Administrative [Member] | March 2021 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Compensation expense | $

118

234

2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Time-based Restricted Stock Units [Member] | General and Administrative [Member] | February 2020 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Compensation expense | $

$ 90

$ 270

$ 215

2014 Equity Incentive Plan [Member] | Employee And Nonemployee Consultants [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] | Employee And Nonemployee Consultants [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] | Employee And Nonemployee Consultants [Member] | Share Based Compensation Subsequent Awards [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vesting period of awards granted

4 years

2014 Equity Incentive Plan [Member] | Non-employee Directors [Member] | Restricted Stock Units [Member] | June 2021 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vesting period of awards granted

1 year

Awarded

43,200

Restricted stock units, grant date fair value | $ / shares

$ 13.06

Restricted stock units, vested

2014 Equity Incentive Plan [Member] | Non-employee Directors [Member] | Restricted Stock Units [Member] | General and Administrative [Member] | June 2021 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Compensation expense | $

$ 142

$ 184

2014 Equity Incentive Plan [Member] | Employees And Non-Employee Members Of Board Of Directors [Member] | Restricted Stock Units [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Awarded

319,200

Restricted stock units, grant date fair value | $ / shares

$ 19.57

Restricted stock units, vested

189,421

Stock-Based Compensation - Rest

Stock-Based Compensation - Restricted Stock Unit Activity (Details) - $ / shares	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2021
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding, Ending Balance	272,000	365,029
2014 Equity Incentive Plan [Member] \| Employees And Non-Employee Members Of Board Of Directors [Member] \| Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding, Beginning Balance		235,250
Awarded		319,200
Vested and released		(189,421)
Outstanding, Ending Balance		365,029
Weighted Average Grant Date Fair Value
Weighted-average grant date fair value, outstanding, Beginning Balance		$ 16.25
Weighted-average grant date fair value, awarded		19.57
Weighted-average grant date fair value, vested and released		17.20
Weighted-average grant date fair value, outstanding, Ending Balance		$ 18.66

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, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate, minimum	0.92%	0.35%	0.66%	0.35%
Risk-free interest rate, maximum	1.01%	0.43%	1.23%	1.57%
Expected volatility, minimum	83.00%	72.60%	71.60%	72.60%
Expected volatility, maximum	83.40%	73.30%	83.50%	74.80%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Employee and Board of Directors 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

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Compensation Expense Relating to Stock Options (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Excess tax benefits from stock option activity or stock-based compensation expense recognized in cash flows from operations	$ 0	$ 0	$ 0	$ 0
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Compensation expense	3,038	3,029	8,672	8,520
Stock Options [Member] \| Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Compensation expense	1,833	1,724	5,228	5,003
Stock Options [Member] \| General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Compensation expense	1,205	1,305	3,444	3,517
Restricted Stock Units [Member] \| Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Compensation expense	429	44	1,094	1,192
Restricted Stock Units [Member] \| General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Compensation expense	785	90	1,812	671
Restricted Stock Units [Member] \| Director [Member] \| General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Compensation expense	$ 142	$ 142	$ 423	$ 387

Stock-Based Compensation - Su_3

Stock-Based Compensation - Summary of Stock Option Activity (Detail) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Options, Outstanding, Ending Balance	5,974,549	5,265,642	5,974,549	5,265,642
2014 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Options, Outstanding, Beginning Balance			5,469,393
Number of Options, Granted	30,000	345,000	819,250	1,165,350
Number of Options, Exercised			(114,354)
Number of Options, Expired			(234)
Number of Options, Forfeited			(199,506)
Number of Options, Outstanding, Ending Balance	5,974,549		5,974,549
Number of Options, Options exercisable	3,860,433		3,860,433
Weighted-Average Exercise Price, Outstanding, Beginning Balance			$ 15.02
Weighted-Average Exercise Price, Granted			18.72
Weighted-Average Exercise Price, Exercised			11.55
Weighted-Average Exercise Price, Expired			18.93
Weighted-Average Exercise Price, Forfeited			17.20
Weighted-Average Exercise Price, Outstanding, Ending Balance	$ 15.52		$ 15.52

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)subsidiary	Sep. 30, 2020USD ($)	Dec. 31, 2020subsidiary
Income Tax Disclosure [Abstract]
Pre-tax losses	$ 1,013	$ 16,641	$ 55,059	$ 70,935
Benefit from income taxes	$ 0	$ 132	$ 0	$ 436
Percentage of annual research and development credit for cash		65.00%		65.00%
Number of foreign subsidiaries \| subsidiary			0		0

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) $ in Thousands	Aug. 20, 2019USD ($)	Oct. 31, 2020USD ($)	Jun. 30, 2020lease	Jul. 31, 2019agreement	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)lease	Sep. 30, 2020USD ($)	Dec. 31, 2020USD ($)	Jan. 01, 2019USD ($)
Other Commitments [Line Items]
Research and development expense					$ 15,514	$ 21,067	$ 59,870	$ 80,711
Operating lease liabilities					4,089		4,089
Operating lease right-of-use assets					$ 3,310		$ 3,310		$ 4,279
New Stamford Lease [Member]
Other Commitments [Line Items]
Number of renewable terms \| lease			1
Operating Lease, renewable term			5 years
Operating lease, expiration date			Dec. 31, 2023
Operating lease liabilities		$ 1,934
Operating lease right-of-use assets		1,934
Lease incentives		0
Stamford Operating Lease [Member]
Other Commitments [Line Items]
Number of renewable terms \| lease							1
Operating Lease, renewable term					5 years		5 years
Operating lease, expiration date							Dec. 31, 2023
Deferred lease obligation										$ 864
Operating lease cost						239		709
Stamford Operating Lease [Member] \| Research and Development [Member]
Other Commitments [Line Items]
Operating lease cost						167		496
Stamford Operating Lease [Member] \| General and Administrative [Member]
Other Commitments [Line Items]
Operating lease cost						$ 72		$ 213
Stamford Operating Lease [Member] \| ASC 842 [Member]
Other Commitments [Line Items]
Operating lease liabilities										5,198
Stamford Operating Lease [Member] \| Standby Letter of Credit [Member]
Other Commitments [Line Items]
Letter of credit, renewal term							automatically renewed annually through November 2023.
Letter of credit, expiration date							Nov. 30, 2023
Stamford Operating Lease [Member] \| Leasehold Improvements [Member]
Other Commitments [Line Items]
Tenant improvement expenses										$ 698
Stamford Operating Lease and New Stamford Lease [Member]
Other Commitments [Line Items]
Operating lease cost					$ 406		$ 1,218
Stamford Operating Lease and New Stamford Lease [Member] \| Research and Development [Member]
Other Commitments [Line Items]
Operating lease cost					284		853
Stamford Operating Lease and New Stamford Lease [Member] \| General and Administrative [Member]
Other Commitments [Line Items]
Operating lease cost					122		365
Non-Exclusive License Agreement
Other Commitments [Line Items]
Payment of milestone payment		$ 2,500
Non-Exclusive License Agreement \| Enteris Biopharma, Inc. [Member]
Other Commitments [Line Items]
Upfront fee	$ 8,000
Upfront fee payment, cash	4,000
Upfront fee payment, stock	$ 4,000
Payment of milestone payment					$ 10,000		$ 10,000
MSA \| Patheon and Patheon Manufacturing Services LLC [Member]
Other Commitments [Line Items]
Number of related product agreements \| agreement				2

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Other Information related to Stamford Lease (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Stamford Operating Lease [Member]
Other Commitments [Line Items]
Operating cash outflows relating to operating leases		$ 312		$ 927
Remaining lease term - operating leases (years)		3 years 3 months 18 days		3 years 3 months 18 days
Discount rate - operating leases		7.00%		7.00%
Stamford Operating Lease and New Stamford Lease [Member]
Other Commitments [Line Items]
Operating cash outflows relating to operating leases	$ 482		$ 1,436
Remaining lease term - operating leases (years)	2 years 3 months 18 days		2 years 3 months 18 days
Discount rate - operating leases	7.00%		7.00%

Commitments and Contingencies_3

Commitments and Contingencies - Schedule of Future Minimum Lease Payments under Non-cancellable Operating Leases, Reconciliation of Undiscounted Cash Flows to the Operating Lease Liability (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Operating Lease Liabilities, Payments Due [Abstract]
2021 (Excluding the nine months ended September 30, 2021)	$ 485
2022	1,957
2023	1,992
Total future minimum lease payments, undiscounted	4,434
Less imputed interest	(345)
Operating lease liabilities	4,089
Operating lease liabilities reported as of September 30, 2021:
Operating lease liabilities - current	1,716	$ 1,602
Operating lease liabilities - non-current	2,373	$ 3,673
Total	$ 4,089

Subsequent Events (Details)

Subsequent Events (Details) - USD ($) $ / shares in Units, $ in Thousands	Oct. 15, 2020	May 17, 2018	Oct. 31, 2021
Regulatory Milestones [Member]
Subsequent Event [Line Items]
Proceeds from the sale of stock			$ 50,000
Vifor International Ltd. [Member] \| Regulatory Milestones [Member]
Subsequent Event [Line Items]
Proceeds from the sale of stock	$ 50,000		$ 50,000
Common stock, shares issued			3,282,391
Shares Issued Price Per Share			$ 15.23
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member]
Subsequent Event [Line Items]
Common stock, shares issued		1,174,827
Shares Issued Price Per Share		$ 17.024
Subsequent Event [Member] \| Vifor International Ltd. [Member] \| Regulatory Milestones [Member]
Subsequent Event [Line Items]
Proceeds from the sale of stock			$ 50,000
Common stock, shares issued			3,282,391
Shares Issued Price Per Share			$ 15.23
Subsequent Event [Member] \| Vifor Fresenius Medical Care Renal Pharma Ltd. [Member] \| Regulatory Milestones [Member]
Subsequent Event [Line Items]
Proceeds from milestone payments			$ 15,000