Cara Therapeutics (CARA) 10-Q 9 May 22 2022 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2022	May 05, 2022
Document And Entity Information [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2022
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		53,591,225
Entity Central Index Key	0001346830
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q1
Amendment Flag	false

CONDENSED BALANCE SHEETS

CONDENSED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 21,362	$ 13,453
Marketable securities	119,749	153,582
Accounts receivable - related party	2,496	0
Inventory, net	1,907	2,584
Income tax receivable	697	697
Other receivables	438	455
Prepaid expenses	5,113	2,519
Total current assets	151,762	173,290
Operating lease right-of-use assets	2,629	2,973
Marketable securities, non-current	68,456	69,754
Property and equipment, net	611	631
Restricted cash	408	408
Total assets	223,866	247,056
Current liabilities:
Accounts payable and accrued expenses	16,501	15,861
Operating lease liabilities, current	1,795	1,755
Total current liabilities	18,296	17,616
Operating lease liabilities, non-current	1,455	1,918
Commitments and contingencies (Note 16)
Stockholders' equity:
Preferred stock; $0.001 par value; 5,000,000 shares authorized at March 31, 2022 and December 31, 2021, zero shares issued and outstanding at March 31, 2022 and December 31, 2021
Common stock; $0.001 par value; 100,000,000 shares authorized at March 31, 2022 and December 31, 2021, 53,591,225 shares and 53,480,812 shares issued and outstanding at March 31, 2022 and December 31, 2021, respectively	53	53
Additional paid-in capital	714,292	708,585
Accumulated deficit	(508,507)	(480,758)
Accumulated other comprehensive loss	(1,723)	(358)
Total stockholders' equity	204,115	227,522
Total liabilities and stockholders' equity	$ 223,866	$ 247,056

CONDENSED BALANCE SHEETS (Paren

CONDENSED BALANCE SHEETS (Parenthetical) - $ / shares	Mar. 31, 2022	Dec. 31, 2021
CONDENSED BALANCE SHEETS
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	53,591,225	53,480,812
Common stock, shares outstanding	53,591,225	53,480,812

CONDENSED STATEMENTS OF COMPREH

CONDENSED STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Revenue:
Total revenue	$ 4,790	$ 1,935
Operating expenses:
Cost of goods sold	2,081
Research and development	21,273	19,131
General and administrative	9,347	6,365
Total operating expenses	32,701	25,496
Operating loss	(27,911)	(23,561)
Other income, net	162	260
Net loss	$ (27,749)	$ (23,301)
Net loss per share:
Basic	$ (0.52)	$ (0.47)
Diluted	$ (0.52)	$ (0.47)
Weighted average shares:
Basic	53,507,060	49,917,990
Diluted	53,507,060	49,917,990
Other comprehensive loss, net of tax of $0:
Change in unrealized losses on available-for-sale marketable securities	$ (1,365)	$ (61)
Total comprehensive loss	(29,114)	(23,362)
Commercial Supply Revenue
Revenue:
Total revenue	$ 4,790
License and Milestone Fees
Revenue:
Total revenue		1,192
Collaborative Revenue
Revenue:
Total revenue		706
Clinical Compound Revenue
Revenue:
Total revenue		$ 37

CONDENSED STATEMENTS OF COMPR_2

CONDENSED STATEMENTS OF COMPREHENSIVE LOSS (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
CONDENSED STATEMENTS OF COMPREHENSIVE LOSS
Other comprehensive loss tax	$ 0	$ 0

CONDENSED STATEMENTS OF STOCKHO

CONDENSED STATEMENTS OF STOCKHOLDER'S EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive (Loss) Income	Total
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 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, 2021	$ 53	708,585	(480,758)	(358)	227,522
Balance, Shares at Dec. 31, 2021	53,480,812
Stock-based compensation expense		4,266			4,266
Shares issued upon exercise of stock options, value		3			3
Shares issued upon exercise of stock options, shares	470
Shares issued upon vesting of restricted stock units, value		1,438			1,438
Shares issued upon vesting of restricted stock units, shares	109,943
Net loss			(27,749)		(27,749)
Other comprehensive loss				(1,365)	(1,365)
Balance, Value at Mar. 31, 2022	$ 53	$ 714,292	$ (508,507)	$ (1,723)	$ 204,115
Balance, Shares at Mar. 31, 2022	53,591,225

CONDENSED STATEMENTS OF CASH FL

CONDENSED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Operating activities
Net loss	$ (27,749)	$ (23,301)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	5,704	4,132
Depreciation and amortization	63	63
Amortization expense component of lease expense	344	316
Amortization of available-for-sale marketable securities, net	292	194
Realized gain on sale of available-for-sale marketable securities		(39)
Realized gain on sale of property and equipment		(70)
Changes in operating assets and liabilities:
Accounts receivable - related party	(2,496)
Inventory, net	677
Other receivables	17	(1,687)
Prepaid expenses	(2,594)	(942)
Accounts payable and accrued expenses	640	(2,001)
Operating lease liabilities	(423)	(386)
Net cash used in operating activities	(25,525)	(23,721)
Investing activities
Proceeds from maturities of available-for-sale marketable securities	44,000	27,655
Proceeds from redemptions of available-for-sale marketable securities, at par		2,100
Proceeds from sale of available-for-sale marketable securities	0	8,029
Purchases of available-for-sale marketable securities	(10,526)	(23,985)
Purchases of property and equipment	(43)
Proceeds from sale of property and equipment		70
Net cash provided by investing activities	33,431	13,869
Financing activities
Proceeds from the exercise of stock options	3	688
Net cash provided by financing activities	3	688
Net increase (decrease) in cash, cash equivalents and restricted cash	7,909	(9,164)
Cash, cash equivalents and restricted cash at beginning of period	13,861	32,091
Cash, cash equivalents and restricted cash at end of period	$ 21,770	$ 22,927

Business

Business	3 Months Ended
	Mar. 31, 2022
Basis of Presentation
Business	1. Business Cara Therapeutics, Inc., or the Company, is an early commercial-stage biopharmaceutical corporation formed on July 2, 2004. The Company is leading a new treatment paradigm to improve the lives of patients suffering from pruritus. The Company’s primary activities to date have been organizing and staffing the Company, developing its lead product and product candidates, including conducting preclinical and clinical trials of difelikefalin-based product candidates, and raising capital. On August 23, 2021, the Company received U.S. Food and Drug Administration, or FDA, approval for KORSUVA TM Collaboration and Licensing Agreements) As of March 31, 2022, 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 $229,710 under its license and supply agreements for difelikefalin, primarily with 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. Additionally, in October 2020, the Company received net proceeds of $38,449 from the issuance and sale of 2,939,552 shares of the Company’s common stock to Vifor in connection with the Company’s license agreement with Vifor. Furthermore, in May 2018, the Company received net proceeds of $14,556 from the issuance and sale of 1,174,827 shares of the Company’s common stock to Vifor in connection with the Company’s license agreement with VFMCRP (see Note 11, Collaboration and Licensing Agreements As of March 31, 2022, the Company had unrestricted cash and cash equivalents and marketable securities of $209,567 and an accumulated deficit of $508,507. 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 $27,749 and $23,301 for the three months ended March 31, 2022 and 2021, respectively, and had net cash used in operating activities of $25,525 and $23,721 for the three months ended March 31, 2022 and 2021, 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 other product candidates, it will be unable to generate additional recurring product revenue or achieve profitability.

Basis of Presentation

Basis of Presentation	3 Months Ended
	Mar. 31, 2022
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, 2021 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, 2021. 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 amount and periods over which certain revenues will be recognized, including licensing and collaborative revenue recognized from non-refundable up-front and milestone payments, accounts receivable, inventory valuation and related reserves, 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, the incremental borrowing rate used in lease calculations and the likelihood of realization of deferred tax assets. The ongoing COVID-19 pandemic and geopolitical tensions, such as Russia’s recent incursion into Ukraine, have 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, 2021, except as disclosed below. ​ Accounts Receivable – Related Party Accounts receivable – related party consists of amounts due from sales of KORSUVA injection under the Company’s licensing agreement with Vifor. The Company does not obtain collateral for its accounts receivable. The Company makes judgments as to its ability to collect outstanding receivables and provides an allowance for credit losses when collection becomes doubtful. Provisions are made based upon a specific review of all significant outstanding invoices and the overall quality and age of those invoices not specifically reviewed. The Company believes that credit risk associated with its licensing partner Vifor is not significant. The Company reviews the need for an allowance for credit losses for any receivable based on various factors including payment history and historical bad debt experience. The Company had no allowance for credit losses as of March 31, 2022. ​

Available-for-Sale Marketable S

Available-for-Sale Marketable Securities	3 Months Ended
	Mar. 31, 2022
Investments Debt And Equity Securities [Abstract]
Available-for-Sale Marketable Securities	3. Available-for-Sale Marketable Securities As of March 31, 2022 and December 31, 2021, 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 March 31, 2022 and December 31, 2021: As of March 31, 2022 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross Unrealized ​ Estimated Fair Type of Security Amortized Cost Gains Losses Value U.S. Treasury securities ​ $ 15,577 ​ $ — ​ $ (27) ​ $ 15,550 U.S. government agency obligations ​ 12,000 ​ — ​ (370) ​ 11,630 Corporate bonds ​ 66,765 ​ — ​ (740) ​ 66,025 Commercial paper ​ ​ 72,952 ​ ​ — ​ ​ (163) ​ ​ 72,789 Municipal bonds ​ 22,634 ​ — ​ (423) ​ 22,211 Total available-for-sale marketable securities ​ $ 189,928 ​ $ — ​ $ (1,723) ​ $ 188,205 ​ As of December 31, 2021 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross Unrealized ​ Estimated Fair Type of Security Amortized Cost Gains Losses Value U.S. Treasury securities ​ $ 11,573 ​ $ — ​ $ (3) ​ $ 11,570 U.S. government agency obligations ​ 17,020 ​ — ​ (45) ​ 16,975 Corporate bonds ​ 66,495 ​ — ​ (171) ​ 66,324 Commercial paper ​ 106,914 ​ 5 ​ (31) ​ 106,888 Municipal bonds ​ ​ 21,692 ​ ​ — ​ ​ (113) ​ ​ 21,579 Total available-for-sale marketable securities ​ $ 223,694 ​ $ 5 ​ $ (363) ​ $ 223,336 ​ 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 March 31, 2022 and December 31, 2021: ​ As of March 31, 2022 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 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 ​ $ 15,550 ​ $ (27) ​ $ — ​ $ — ​ $ 15,550 ​ $ (27) U.S. government agency obligations ​ 9,687 ​ (313) ​ 1,943 ​ (57) ​ 11,630 ​ (370) Corporate bonds ​ ​ 61,610 ​ ​ (644) ​ ​ 4,415 ​ ​ (96) ​ ​ 66,025 ​ ​ (740) Commercial paper ​ ​ 72,789 ​ ​ (163) ​ ​ — ​ ​ — ​ ​ 72,789 ​ ​ (163) Municipal bonds ​ 21,213 ​ (396) ​ 998 ​ (27) ​ 22,211 ​ (423) Total ​ $ 180,849 ​ $ (1,543) ​ $ 7,356 ​ $ (180) ​ $ 188,205 ​ $ (1,723) ​ As of December 31, 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. Treasury securities ​ $ 11,570 ​ $ (3) ​ $ — ​ $ — ​ $ 11,570 ​ $ (3) U.S. government agency obligations ​ ​ 9,456 ​ ​ (45) ​ ​ — ​ ​ — ​ ​ 9,456 ​ ​ (45) Corporate bonds ​ 62,704 ​ (170) ​ 2,020 ​ (1) ​ 64,724 ​ (171) Commercial paper ​ 52,163 ​ (31) ​ — ​ — ​ 52,163 ​ (31) Municipal bonds ​ 20,562 ​ (105) ​ 1,017 ​ (8) ​ 21,579 ​ (113) Total ​ $ 156,455 ​ $ (354) ​ $ 3,037 ​ $ (9) ​ $ 159,492 ​ $ (363) ​ As of March 31, 2022 and December 31, 2021, 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 March 31, 2022 and December 31, 2021, the Company held a total of 73 out of 73 positions and 58 out of 76 positions, respectively, that were in an unrealized loss position, four of which had been in an unrealized loss position for 12 months or greater as of March 31, 2022. 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. Treasury and U.S. government agency obligations. positions for its U.S. government agency obligations, that were in unrealized loss positions as of March 31, 2022. Corporate bonds, commercial paper, and municipal bonds. factors. The credit ratings of these investments in the Company’s portfolio have not been downgraded below investment 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 25 out of 25 positions for its corporate bonds, 23 out of 23 positions for its commercial paper, and 15 out of 15 positions for its municipal bonds, that were in unrealized loss positions as of March 31, 2022. ​ The Company classifies its marketable debt securities based on their contractual maturity dates. As of March 31, 2022, the Company’s marketable debt securities mature at various dates through November 2024. The amortized cost and fair values of marketable debt securities by contractual maturity were as follows. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of March 31, 2022 ​ As of December 31, 2021 Contractual maturity Amortized Cost Fair Value Amortized Cost Fair Value Less than one year ​ $ 120,070 ​ $ 119,749 ​ $ 153,631 ​ $ 153,582 One year to three years ​ 69,858 ​ 68,456 ​ 70,063 ​ 69,754 Total ​ $ 189,928 ​ $ 188,205 ​ $ 223,694 ​ $ 223,336 ​ 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. There were no sales of available-for-sale marketable securities during the three months ended March 31, 2022. During the three months ended March 31, 2021, the Company sold certain shares of its available-for-sale debt securities with a total fair value of $8,029, which resulted in realized gains of $39 for the three months ended March 31, 2021. As of March 31, 2022 and December 31, 2021, accrued interest receivables on our available-for-sale debt securities were $438 and $455, respectively.

Accumulated Other Comprehensive

Accumulated Other Comprehensive (Loss) Income	3 Months Ended
	Mar. 31, 2022
Equity [Abstract]
Accumulated Other Comprehensive (Loss) Income	4. Accumulated Other Comprehensive (Loss) Income The following table summarizes the changes in accumulated other comprehensive (loss) income, net of tax, from unrealized gains (losses) on available-for-sale marketable securities, the Company’s only component of accumulated other comprehensive (loss) income, for the three months ended March 31, 2022 and 2021, respectively. ​ ​ ​ ​ ​ Total Accumulated ​ ​ Other Comprehensive ​ ​ (Loss) Income Balance, December 31, 2021 ​ $ (358) Other comprehensive loss before reclassifications ​ (1,365) Amount reclassified from accumulated other comprehensive loss ​ — Net current period other comprehensive loss ​ (1,365) Balance, March 31, 2022 ​ $ (1,723) ​ ​ ​ ​ Balance, December 31, 2020 ​ $ 73 Other comprehensive loss before reclassifications ​ (22) Amount reclassified from accumulated other comprehensive income ​ (39) Net current period other comprehensive loss ​ (61) Balance, March 31, 2021 ​ $ 12 ​ Amounts reclassified out of accumulated other comprehensive (loss) income into net loss are determined by specific identification. The reclassifications out of accumulated other comprehensive (loss) income and into net loss were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Affected Line Item in the Component of Accumulated Other ​ March 31, ​ Condensed Statements of Comprehensive (Loss) Income 2022 2021 Comprehensive Loss Unrealized gains (losses) on available-for-sale marketable securities: ​ ​ Realized gains on sales of securities ​ $ — ​ $ 39 ​ Other income, net Income tax effect ​ — ​ — ​ Benefit from income taxes Realized gains on sales of securities, net of tax ​ $ — ​ $ 39 ​ ​ ​

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2022
Fair Value Disclosures [Abstract]
Fair Value Measurements	5. Fair Value Measurements As of March 31, 2022 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 March 31, 2022 The following tables summarize the Company’s financial assets measured at fair value on a recurring basis as of March 31, 2022 Fair value measurement as of March 31, 2022 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 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 ​ $ 21,362 ​ $ 21,362 ​ $ — ​ $ — Available-for-sale marketable securities: ​ ​ ​ ​ ​ ​ ​ U.S. Treasury securities ​ 15,550 ​ — ​ 15,550 ​ — U.S. government agency obligations ​ 11,630 ​ — ​ 11,630 ​ — Corporate bonds ​ 66,025 ​ — ​ 66,025 ​ — Commercial paper ​ 72,789 ​ — ​ 72,789 ​ — Municipal bonds ​ 22,211 ​ — ​ 22,211 ​ — Restricted cash: ​ ​ ​ ​ ​ ​ ​ Commercial money market account ​ 408 ​ 408 ​ — ​ — Total financial assets ​ $ 209,975 ​ $ 21,770 ​ $ 188,205 ​ $ — ​ Fair value measurement as of December 31, 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 ​ $ 13,453 ​ $ 13,453 ​ $ — ​ $ — Available-for-sale marketable securities: ​ ​ ​ ​ U.S. Treasury securities ​ ​ 11,570 ​ ​ — ​ ​ 11,570 ​ ​ — U.S. government agency obligations ​ 16,975 ​ — ​ 16,975 ​ — Corporate bonds ​ 66,324 ​ — ​ 66,324 ​ — Commercial paper ​ 106,888 ​ — ​ 106,888 ​ — Municipal bonds ​ ​ 21,579 ​ ​ — ​ ​ 21,579 ​ ​ — Restricted cash: ​ ​ ​ ​ Commercial money market account ​ 408 ​ 408 ​ — ​ — Total financial assets ​ $ 237,197 ​ $ 13,861 ​ $ 223,336 ​ $ — ​ 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 months ended March 31, 2022 and 2021, respectively March 31, 2022 and 2021, respectively

Restricted Cash

Restricted Cash	3 Months Ended
	Mar. 31, 2022
Restricted Cash [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 16, Commitments and Contingencies: Leases balance to serve as collateral for the letter of credit issued to the landlord by the bank. As of March 31, 2022, the restricted cash balance for the Stamford Lease was invested in a commercial money market account. As of March 31, 2022 and December 31, 2021, 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. ​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, 2022 December 31, 2021 Cash and cash equivalents ​ $ 21,362 ​ $ 13,453 Restricted cash, long-term assets ​ 408 ​ 408 Total cash, cash equivalents, and restricted cash shown in the Condensed Statements of Cash Flows ​ $ 21,770 ​ $ 13,861 ​

Inventory, net

Inventory, net	3 Months Ended
	Mar. 31, 2022
Inventory Disclosure [Abstract]
Inventory, net	7. Inventory, net Inventories consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, 2022 December 31, 2021 Raw materials ​ $ 1,095 ​ $ 927 Work-in-process ​ 812 ​ 1,657 Total ​ $ 1,907 ​ $ 2,584 ​ As of March 31, 2022 and December 31, 2021, inventory balances include inventory costs subsequent to regulatory approval of KORSUVA injection on August 23, 2021. There were no write-downs of commercial supply inventory during the three months ended March 31, 2022.

Prepaid Expenses

Prepaid Expenses	3 Months Ended
	Mar. 31, 2022
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Prepaid Expenses	8. Prepaid expenses As of March 31, 2022, prepaid expenses were $5,113, consisting of $2,167 of prepaid R&D clinical costs, $2,134 of prepaid insurance and $812 of other prepaid costs. As of December 31, 2021, prepaid expenses were $2,519, consisting of $1,481 of prepaid R&D clinical costs, $369 of prepaid insurance, and $669 of other prepaid costs.

Accounts Payable and Accrued Ex

Accounts Payable and Accrued Expenses	3 Months Ended
	Mar. 31, 2022
Payables And Accruals [Abstract]
Accounts Payable and Accrued Expenses	9. Accounts Payable and Accrued Expenses Accounts payable and accrued expenses consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ March 31, 2022 December 31, 2021 Accounts payable ​ $ 5,594 ​ $ 5,625 Accrued research projects ​ 6,444 ​ 4,648 Accrued compensation and benefits ​ 2,412 ​ 4,959 Accrued professional fees and other ​ 2,051 ​ 629 Total ​ $ 16,501 ​ $ 15,861 ​

Stockholders' Equity

Stockholders' Equity	3 Months Ended
	Mar. 31, 2022
Equity [Abstract]
Stockholders' Equity	10. Stockholders’ Equity In March 2022, as a result of the achievement of certain performance targets, an aggregate of 37,999 performance-based restricted stock units of certain employees vested and were settled in shares of the Company’s common stock (see Note 14, Stock-Based Compensation ​ In March 2022, as a result of the completion of the first year of the three-year vesting period for restricted stock units granted in March 2021 and the full vesting of the Chief Executive Officer’s, or CEO’s, second tranche of restricted stock units granted in October 2021, an aggregate of 39,278 time-based restricted stock units vested and were settled in shares of the Company’s common stock (see Note 14, Stock-Based Compensation ​ In March 2022, the Company filed a universal shelf registration statement, or the Shelf Registration Statement, which provides for aggregate offerings of up to $300,000 of common stock, preferred stock, debt securities, warrants or any combination thereof. The Shelf Registration Statement has not yet been declared effective by the Securities and Exchange Commission. The securities registered under the Shelf Registration Statement include $154,525 of unsold securities that had been registered under the Company’s previous Registration Statement on Form S-3 (File No. 333-230333) that was declared effective on April 4, 2019. The Company may offer additional securities under its Shelf Registration Statement, when declared effective, from time to time in response to market conditions or other circumstances if it believes such a plan of financing is in the best interests of its stockholders. Also in March 2022, the Company entered into an open market sales agreement, or the Sales Agreement, with Jefferies LLC, as sales agent, pursuant to which it may, subject to the effectiveness of the Shelf Registration Statement, from time to time, issue and sell common stock with an aggregate value of up to $80,000 in an at-the-market offering. Jefferies is acting as sole sales agent for any sales made under the Sales Agreement for a 3% commission on gross proceeds. The common stock will be sold at prevailing market prices at the time of the sale, and, as a result, prices may vary. Unless otherwise terminated earlier, the Sales Agreement continues until all shares available under the Sales Agreement have been sold. In February 2022, as a result of the completion of the second year of the three-year vesting period for restricted stock units granted in February 2020, an aggregate of 32,666 time-based restricted stock units vested and were settled in shares of the Company’s common stock (see Note 14, 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 vested and were settled in shares of the Company’s common stock (see Note 14, Stock-Based Compensation ​ In February 2021, as a result of the completion of the first year of the three-year vesting period for restricted stock units granted in February 2020, an aggregate of 32,669 time-based restricted stock units vested and were settled in shares of the Company’s common stock (see Note 14, Stock-Based Compensation

Collaboration and Licensing Agr

Collaboration and Licensing Agreements	3 Months Ended
	Mar. 31, 2022
Basis of Presentation
Collaboration and Licensing Agreements	Vifor (International) Ltd. (Vifor) 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 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, 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 is generally entitled to 60% of the net profits (as defined in the Vifor Agreement) from sales of 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 difelikefalin injection in the United States, the Company pays a marketing and distribution fee to Vifor based on the level of annual net sales. This fee is 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 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, or COGS, as calculated under GAAP, plus an agreed upon margin. The Vifor Supply Agreement will co-terminate with the Vifor Agreement. The Vifor 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 Vifor Supply Agreement is the Company’s COGS plus an agreed upon margin, which is commensurate with the “COGS 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. Vifor Fresenius Medical Care Renal Pharma Ltd. (VFMCRP) 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 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 difelikefalin injection in the licensed territories. The Company retained full commercialization rights for difelikefalin injection for the treatment of chronic kidney disease associated pruritus, or 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 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. Subsequently, the remaining commercialization rights in the U.S. were granted to Vifor as part of the Vifor Agreement in 2020, as discussed above. 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 COGS, 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 COGS plus an agreed upon margin, which is commensurate with the “COGS 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 compound 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. Maruishi Pharmaceutical Co., Ltd. (Maruishi) 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 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 difelikefalin in the United States and Japan, respectively. In addition, the Company provided Maruishi specific clinical development services for 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. Chong Kun Dang Pharmaceutical Corporation (CKDP) 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 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 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 difelikefalin in South Korea, if any, and share in any sub-license fees.

Revenue Recognition

Revenue Recognition	3 Months Ended
	Mar. 31, 2022
Revenue Recognition [Abstract]
Revenue Recognition	12. Revenue Recognition The Company currently recognizes revenue for the Vifor, VFMCRP, Maruishi and CKDP agreements (see Note 11 , Collaboration and Licensing Agreements Contract balances As of March 31, 2022, the Company recorded accounts receivable – related party of $2,496 which related to sales of KORSUVA injection to Vifor during the three months ended March 2022. There were no material balances of receivables as of December 31, 2021, and no other contract assets or contract liabilities related to the Vifor, VFMCRP, Maruishi and CKDP agreements as of March 31, 2022 and December 31, 2021. The Company routinely assesses the creditworthiness of its license and collaboration partners. The Company has not experienced any losses related to receivables from its license and collaboration partners as of March 31, 2022 and December 31, 2021. Performance obligations Under the Vifor Agreement, the Company’s only performance obligation is granting a license to allow Vifor to commercialize difelikefalin in the United States, which occurred at inception of the contract in October 2020 (see Note 11, Collaboration and Licensing Agreements Under the Vifor Supply Agreement, the Company’s only performance obligation is the delivery of KORSUVA injection to Vifor in accordance with the receipt of purchase orders. Revenue from the sale of the Licensed Product to Vifor is recognized as delivery of the Licensed Product occurs. The Company had commercial supply revenue of $4,790 for the three months ended March 31, 2022, of which $2,295 was recognized in January 2022 with no associated COGS since these inventory costs were incurred prior to regulatory approval on August 23, 2021, and $2,495 was recognized in March 2022 with associated COGS of $2,081 since these inventory costs were capitalized as inventory subsequent to regulatory approval. Under the VFMCRP Agreement, the Company’s performance obligations of granting a license to allow VFMCRP to commercialize 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 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 11, Collaboration and Licensing Agreements The Company’s only performance obligation under the VFMCRP Supply Agreement is to deliver difelikefalin injection to VFMCRP in accordance with the receipt of purchase orders. Revenue from the sale of the Licensed Product to VFMCRP is recognized as delivery of the Licensed Product occurs. There were no sales of clinical or commercial compound to VFMCRP during the three months ended March 31, 2022 and 2021. 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 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 difelikefalin and to conduct Phase 1 and proof-of-concept Phase 2 clinical trials of an intravenous formulation of 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 11, 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. There were no sales of clinical compound to Maruishi during the three months ended March 31, 2022. The Company had clinical compound revenue of $37 during the three months ended March 31, 2021, for the sale of clinical compound to Maruishi. Under the CKDP Agreement, the Company’s only performance obligation is to transfer the license to the Company’s IP related to difelikefalin, which occurred at inception of the contract in 2012 (see Note 11, 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. Variable Consideration 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). There were no license and milestone fees revenue or collaborative revenue recognized under the Maruishi Agreement during the three months ended March 31, 2022. During the three months ended March 31, 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. There were no revenues recognized under the CKDP Agreement during the three months ended March 31, 2022 and 2021. 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 Loss Per Share

Net Loss Per Share	3 Months Ended
	Mar. 31, 2022
Net Loss Per Share
Net Loss Per Share	13. Net Loss Per Share The Company computes basic net loss per share by dividing net 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 months ended March 31, 2022 and 2021, 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 ​ ​ ​ March 31, ​ ​ 2022 2021 Basic: Weighted average common shares outstanding 53,507,060 49,917,990 Diluted: Weighted average common shares outstanding - Basic 53,507,060 49,917,990 Common stock equivalents* — — Denominator for diluted net loss per share 53,507,060 49,917,990 * 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 ​ ​ ​ March 31, ​ ​ 2022 2021 Net loss - basic and diluted ​ $ (27,749) ​ $ (23,301) ​ Weighted-average common shares outstanding: ​ ​ ​ ​ Basic and diluted ​ 53,507,060 ​ 49,917,990 ​ Net loss per share, Basic and Diluted: ​ $ (0.52) ​ $ (0.47) ​ ​ As of March 31, 2022, 7,430,629 stock options and 736,272 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. ​ As of March 31, 2021, 5,918,808 stock options and 401,831 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	3 Months Ended
	Mar. 31, 2022
Disclosure Of Compensation Related Costs Share Based Payments [Abstract]
Stock-Based Compensation	14. 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 generally 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, 2022, the aggregate number of shares of common stock that may be issued pursuant to Stock Awards under the 2014 Plan automatically increased from 8,984,679 to 10,589,103. 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 On February 25, 2022, the Compensation Committee of the Company’s Board of Directors, or the Compensation Committee, approved and granted a total of 243,000 restricted stock units to certain employees under the 2014 Plan with a grant date fair value of $10.46 per share. Vesting of the restricted stock units is contingent on the achievement of certain performance targets related to commercial 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 are probable of achievement and the employee has met the service conditions. For the three months ended March 31, 2022, no stock compensation expense relating to these restricted stock units was recognized. As of March 31, 2022, none of the restricted stock units were vested or settled in shares of the Company’s common stock. Additionally on February 25, 2022, the Compensation Committee also approved and granted a total of 145,170 time-based restricted stock units to certain employees under the 2014 Plan with a grant date fair value of $10.46 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 March 31, 2022, the Company recognized $50 of stock compensation expense associated with these awards, with $18 recorded in R&D expense and $32 in general and administrative, or G&A, expense. As of March 31, 2022, none of the restricted stock units were vested or settled in shares of the Company’s common stock. On December 17, 2021, the Compensation Committee approved and granted a total of 63,573 time-based restricted stock units to certain employees under the 2014 Plan with a grant date fair value of $12.45 per share. The restricted stock units vest in two equal installments on December 15, 2022 and June 15, 2023. As a result, the Company recognizes compensation expense associated with these restricted stock units ratably over the 18-month vesting period following the grant date. For the three months ended March 31, 2022, the Company recognized $131 of stock compensation expense associated with these awards, with $52 recorded in R&D expense and $79 in G&A expense. As of March 31, 2022, none of the restricted stock units were vested or settled in shares of the Company’s common stock. On October 29, 2021, the Compensation Committee also approved and granted 147,942 time-based restricted stock units in connection with the appointment of the Company’s new CEO under the 2014 Plan with a grant date fair value of $16.83 per share. The first tranche of 142,000 restricted stock units vests 25% on the first anniversary of the date of grant and the balance quarterly over the next 36 months. The second tranche of 5,942 restricted stock units fully vested on March 31, 2022. As a result, the Company recognizes compensation expense associated with these two restricted stock unit tranches ratably over their respective vesting periods following the grant date. For the three months ended March 31, 2022, stock compensation expense associated with these awards of $206 was recognized in G&A expense. As of March 31, 2022, 5,942 of the 147,942 restricted stock units were vested and settled in shares of the Company’s common stock. 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 2022 Annual Meeting of Stockholders, 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 months ended March 31, 2022, stock compensation expense associated with these awards of $139 was recognized in G&A expense. As of March 31, 2022, none of the restricted stock units were vested or settled in shares of the Company’s common stock. On March 30, 2021, the Compensation Committee approved and granted a total of 176,000 restricted stock units to certain employees under the 2014 Plan with a grant date fair value of $20.59 per share. Vesting of the restricted stock units was 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 2022, performance targets relating to 37,999 restricted stock units had been achieved and thus restricted stock units vested and the awards were settled in shares of common stock. For the three months ended March 31, 2022, the Company recognized $729 of stock compensation expense associated with these awards in G&A expense. G&A amounts recorded for the three months ended March 31, 2022 included $303 of stock compensation expense relating to the modification of certain of these restricted stock units on November 1, 2021 (see Stock Award Modifications Additionally on March 30, 2021, the Compensation Committee also approved and granted a total of 100,000 time-based restricted stock units to certain employees 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. In March 2022, 33,336 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 March 31, 2022, the Company recognized $284 of stock compensation expense associated with these awards, with $54 recorded in R&D expense and $230 in G&A expense. For the three months ended March 31, 2021, the Company recognized an immaterial amount of stock compensation expense for the one day of outstanding time-based restricted stock units. G&A amounts recorded for the three months ended March 31, 2022 included $203 of stock compensation expense relating to the modification of certain of these restricted stock units on November 1, 2021 (see Stock Award Modifications 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 three months ended March 31, 2021, stock compensation expense of $139 was recognized in G&A expense. All of the restricted stock units were vested and settled in shares of the Company’s common stock as of June 2021. In February 2020, the Compensation Committee approved and granted a total of 138,000 restricted stock units to certain employees under the 2014 Plan with a grant date fair value of $16.36 per share. Vesting of the restricted stock units was 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, were achieved and thus restricted stock units vested and the awards were settled in shares of common stock. For the three months ended March 31, 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. As of March 31, 2022, 113,500 of the 138,000 restricted stock units vested and were settled in shares of the Company’s common stock, while the remaining 24,500 restricted stock units were forfeited as a result of not achieving certain defined performance targets of the awards. Additionally in February 2020, the Compensation Committee also approved and granted a total of 98,000 time-based restricted stock units to certain employees 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 2022, 32,666 of these restricted stock units vested and were settled in shares of the Company’s common stock in satisfaction of the second year of vesting. 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 March 31, 2022, the Company recognized $219 of stock compensation expense associated with these awards, with $43 recorded in R&D expense and $176 in G&A expense. G&A amounts recorded for the three months ended March 31, 2022 included $155 of stock compensation expense relating to the modification of certain of these restricted stock units on November 1, 2021 (see Stock Award Modifications restricted stock units vested and were settled in shares of the Company’s common stock. 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 three months ended March 31, 2022 is presented below: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ Number of ​ Average Grant ​ Units Date Fair Value Outstanding, December 31, 2021 576,544 ​ $ 17.50 Awarded 388,170 ​ 10.46 Vested and released (109,943) ​ 19.13 Forfeited (118,499) ​ 19.72 Outstanding, March 31, 2022 736,272 ​ $ 13.19 Restricted stock units exercisable (vested and deferred), March 31, 2022 — ​ ​ ​ ​ Stock Options Under the 2014 Plan, the Company granted 977,438 and 673,200 stock options during the three months ended March 31, 2022 and 2021, respectively. No ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ ​ March 31, ​ ​ 2022 2021 Risk-free interest rate 1.70% - 2.35% ​ 0.66% - 1.21% Expected volatility 81.4% - 81.9% ​ 71.6% - 71.8% Expected dividend yield 0% ​ 0% Expected life of employee and Board options (in years) 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 March 31, 2022 and 2021 was $7.55 and $12.49, respectively. No options were granted to non-employee members of the Company’s Board of Directors for their Board service or to non-employee consultants during the three months ended March 31, 2022 and 2021. During the three months ended March 31, 2022 and 2021, the Company recognized compensation expense relating to stock options as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ ​ March 31, ​ ​ 2022 2021 Research and development ​ $ 1,917 ​ $ 1,590 ​ General and administrative ​ 2,030 ​ 1,014 ​ Total stock option expense ​ $ 3,947 ​ $ 2,604 ​ ​ The following were excluded from the table above as they are not related to stock options: compensation expense for (i) the vesting of certain employees’ restricted stock units for $167 in R&D expense and $1,452 in G&A expense for the three months ended March 31, 2022; (ii) the vesting of certain employees’ restricted stock units for $568 in R&D expense and $822 in G&A expense for the three months ended March 31, 2021; and (iii) compensation expense relating to the Board of Directors’ restricted stock units for $139 in G&A expense for each of the three months ended March 31, 2022 and 2021. 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 three months ended March 31, 2022 is presented below: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ Number of ​ Average Exercise ​ ​ Shares Price Outstanding, December 31, 2021 6,512,280 ​ $ 15.58 Granted 977,438 ​ 10.63 Exercised (470) ​ 6.50 Forfeited (37,241) ​ 15.22 Expired (21,378) ​ 25.16 Outstanding, March 31, 2022 7,430,629 ​ $ 14.91 ​ Options exercisable, March 31, 2022 4,357,399 ​ ​ ​ ​ ​ 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 months ended March 31, 2022 and 2021. ​ Stock Award Modifications In November 2021, the Company and the former President and CEO mutually agreed to a transition from CEO to a consulting role through June 30, 2022, if not terminated earlier per the terms of the consulting agreement. As a result, the Company modified the terms of its former CEO’s outstanding Stock Awards to (1) automatically vest any unvested stock options or time-based restricted stock units that would have vested in the twelve month period following the end of the consulting period if continuous service is achieved with the Company during such twelve-month period; (2) extend the period during which the vested stock options may be exercised through the earlier of (i) eighteen months following the separation date (November 8, 2021); or (ii) the original expiration date applicable to each of the stock options, unless terminated earlier in accordance with the 2014 Plan, if continuous service is achieved with the Company; and (3) extend the period in which performance-based vesting milestones for restricted stock units may be achieved through March 31, 2022, if continuous service is achieved with the Company. ​ The Company determined that vested Stock Awards which had modifications due to the extension of the exercise period were Type 1 modifications pursuant to Financial Accounting Standards Board Accounting Standards Codification 718, or ASC 718, because those Stock Awards would have vested before and after the modification. Acceleration of vesting for the Stock Awards that would have vested in the twelve-month period following the consulting term was determined to be a Type 3 modification requiring stock compensation expense pursuant to ASC 718 because absent the modification terms, those Stock Awards would have been forfeited as of the last day that the former CEO provided continuous service as a consultant. In addition, Type 4 performance-based restricted stock units were not considered probable of achieving performance targets on the modification date, but 17,333 performance-based restricted stock units were achieved in February 2022, which resulted in additional stock compensation expense being recorded during the three months ended March 31, 2022. ​ During the three months ended March 31, 2022, total incremental stock compensation expense relating to modifications of stock options, time-based and performance-based restricted stock units of the former CEO was $1,564, which is included in G&A expense for the three months ended March 31, 2022. Of this total amount, $903 is included in G&A expense in the stock option compensation expense table above.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2022
Income Tax Disclosure [Abstract]
Income Taxes	15. Income Taxes The Company has recognized a full tax valuation allowance against its deferred tax assets as of March 31, 2022 and December 31, 2021. 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. As such, the Company’s effective tax rate is zero for both periods. Historically, the Company’s benefit from income taxes 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 was not eligible to exchange its 2021 R&D tax credit for cash, therefore there was no benefit from income taxes for the three months ended March 31, 2021. As of March 31, 2022, the Company does not qualify to receive a refund of the 2022 credit, therefore no receivable or benefit from income taxes have been recorded for the 2022 credit.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2022
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	16. 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. During the three months ended March 31, 2022 and 2021, no milestone payments or royalties were paid to Enteris by the Company in relation to the Enteris License Agreement. 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 difelikefalin, or API, for the 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 difelikefalin injection, the Company’s lead product candidate. Pursuant to the Product Agreements, Patheon and Patheon Greenville will manufacture commercial supplies of 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 Lease expense is recognized on a straight-line basis over the lease term of the Company’s lease agreements for its original headquarters, and additional office space, in Stamford, Connecticut. As a result, $406 of operating lease cost, or lease expense, was recognized for each of the three months ended March 31, 2022 and 2021, consisting of $284 relating to R&D lease expense and $122 relating to G&A lease expense in each of the periods. Other information related to the leases was as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ ​ March 31, ​ ​ 2022 2021 ​ Cash paid for amounts included in the measurement of lease liabilities: ​ ​ ​ ​ Operating cash outflows relating to operating leases ​ $ 485 ​ $ 476 ​ ROU assets obtained in exchange for new operating lease liabilities ​ $ — ​ $ — ​ Remaining lease term - operating leases (years) ​ 1.8 ​ 2.8 ​ Discount rate - operating leases ​ ​ 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 liabilities as of March 31, 2022, were as follows: ​ ​ ​ ​ Year Ending December 31, ​ ​ 2022 (Excluding the three months ended March 31, 2022) $ 1,473 2023 ​ 1,991 Total future minimum lease payments, undiscounted ​ 3,464 Less imputed interest ​ (214) Total ​ $ 3,250 ​ ​ ​ ​ Operating lease liabilities reported as of March 31, 2022: ​ Operating lease liabilities - current ​ $ 1,795 Operating lease liabilities - non-current ​ 1,455 Total ​ $ 3,250 ​

Related Party Transactions

Related Party Transactions	3 Months Ended
	Mar. 31, 2022
Related Party Transactions [Abstract]
Related Party Transactions	17. Related Party Transactions As of March 31, 2022, Vifor owned 7,396,770 , or 13.8% , of the Company’s common stock. Both Vifor and VFMCRP are considered related parties as of March 31, 2022 and December 31, 2021 (see Note 11, Collaboration and Licensing Agreements ). Sales of KORSUVA injection to Vifor of $4,790 were included within Commercial supply revenue on the Company’s Condensed Statement of Comprehensive Loss for the three months ended March 31, 2022. Amounts due from Vifor of $2,496 relating to sales of KORSUVA injection to Vifor during the three months ended March 31, 2022 were included within Accounts receivable – related party on the Company’s Condensed Balance Sheet as of March 31, 2022.

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2022
Subsequent Events [Abstract]
Subsequent Events	18. Subsequent Events On April 27, 2022, the European Commission granted marketing authorization to difelikefalin injection under the brand name Kapruvia® (difelikefalin), or Kapruvia, for the treatment of moderate-to-severe pruritus associated with chronic kidney disease in adult hemodialysis patients. The marketing authorization approves Kapruvia for use in all member states of the European Union, as well as Iceland, Liechtenstein and Norway. The Company expects commercial launch of Kapruvia in these markets in the second half of 2022. As a result of the European Commission’s regulatory approval of Kapruvia in April 2022, the Company achieved a $15,000 regulatory milestone payment from VFMCRP under the VFMCRP Agreement, which will be recorded as license and milestone fees revenue in the second quarter of 2022. ​

Basis of Presentation (Policies

Basis of Presentation (Policies)	3 Months Ended
	Mar. 31, 2022
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 amount and periods over which certain revenues will be recognized, including licensing and collaborative revenue recognized from non-refundable up-front and milestone payments, accounts receivable, inventory valuation and related reserves, 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, the incremental borrowing rate used in lease calculations and the likelihood of realization of deferred tax assets. The ongoing COVID-19 pandemic and geopolitical tensions, such as Russia’s recent incursion into Ukraine, have 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, 2021, except as disclosed below.
Accounts Receivable - Related Party	Accounts Receivable – Related Party Accounts receivable – related party consists of amounts due from sales of KORSUVA injection under the Company’s licensing agreement with Vifor. The Company does not obtain collateral for its accounts receivable. The Company makes judgments as to its ability to collect outstanding receivables and provides an allowance for credit losses when collection becomes doubtful. Provisions are made based upon a specific review of all significant outstanding invoices and the overall quality and age of those invoices not specifically reviewed. The Company believes that credit risk associated with its licensing partner Vifor is not significant. The Company reviews the need for an allowance for credit losses for any receivable based on various factors including payment history and historical bad debt experience. The Company had no allowance for credit losses as of March 31, 2022.

Available-for-Sale Marketable_2

Available-for-Sale Marketable Securities (Tables)	3 Months Ended
	Mar. 31, 2022
Investments Debt And Equity Securities [Abstract]
Summary of Available-for-Sale Marketable Securities by Major Type of Security	As of March 31, 2022 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross Unrealized ​ Estimated Fair Type of Security Amortized Cost Gains Losses Value U.S. Treasury securities ​ $ 15,577 ​ $ — ​ $ (27) ​ $ 15,550 U.S. government agency obligations ​ 12,000 ​ — ​ (370) ​ 11,630 Corporate bonds ​ 66,765 ​ — ​ (740) ​ 66,025 Commercial paper ​ ​ 72,952 ​ ​ — ​ ​ (163) ​ ​ 72,789 Municipal bonds ​ 22,634 ​ — ​ (423) ​ 22,211 Total available-for-sale marketable securities ​ $ 189,928 ​ $ — ​ $ (1,723) ​ $ 188,205 ​ As of December 31, 2021 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross Unrealized ​ Estimated Fair Type of Security Amortized Cost Gains Losses Value U.S. Treasury securities ​ $ 11,573 ​ $ — ​ $ (3) ​ $ 11,570 U.S. government agency obligations ​ 17,020 ​ — ​ (45) ​ 16,975 Corporate bonds ​ 66,495 ​ — ​ (171) ​ 66,324 Commercial paper ​ 106,914 ​ 5 ​ (31) ​ 106,888 Municipal bonds ​ ​ 21,692 ​ ​ — ​ ​ (113) ​ ​ 21,579 Total available-for-sale marketable securities ​ $ 223,694 ​ $ 5 ​ $ (363) ​ $ 223,336
Schedule of Fair Values and Continuous Unrealized Loss Positions of Available-for-Sale Marketable Securities	As of March 31, 2022 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 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 ​ $ 15,550 ​ $ (27) ​ $ — ​ $ — ​ $ 15,550 ​ $ (27) U.S. government agency obligations ​ 9,687 ​ (313) ​ 1,943 ​ (57) ​ 11,630 ​ (370) Corporate bonds ​ ​ 61,610 ​ ​ (644) ​ ​ 4,415 ​ ​ (96) ​ ​ 66,025 ​ ​ (740) Commercial paper ​ ​ 72,789 ​ ​ (163) ​ ​ — ​ ​ — ​ ​ 72,789 ​ ​ (163) Municipal bonds ​ 21,213 ​ (396) ​ 998 ​ (27) ​ 22,211 ​ (423) Total ​ $ 180,849 ​ $ (1,543) ​ $ 7,356 ​ $ (180) ​ $ 188,205 ​ $ (1,723) ​ As of December 31, 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. Treasury securities ​ $ 11,570 ​ $ (3) ​ $ — ​ $ — ​ $ 11,570 ​ $ (3) U.S. government agency obligations ​ ​ 9,456 ​ ​ (45) ​ ​ — ​ ​ — ​ ​ 9,456 ​ ​ (45) Corporate bonds ​ 62,704 ​ (170) ​ 2,020 ​ (1) ​ 64,724 ​ (171) Commercial paper ​ 52,163 ​ (31) ​ — ​ — ​ 52,163 ​ (31) Municipal bonds ​ 20,562 ​ (105) ​ 1,017 ​ (8) ​ 21,579 ​ (113) Total ​ $ 156,455 ​ $ (354) ​ $ 3,037 ​ $ (9) ​ $ 159,492 ​ $ (363)
Schedule of Amortized Cost and Fair Values of Marketable Debt Securities by Contractual Maturity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of March 31, 2022 ​ As of December 31, 2021 Contractual maturity Amortized Cost Fair Value Amortized Cost Fair Value Less than one year ​ $ 120,070 ​ $ 119,749 ​ $ 153,631 ​ $ 153,582 One year to three years ​ 69,858 ​ 68,456 ​ 70,063 ​ 69,754 Total ​ $ 189,928 ​ $ 188,205 ​ $ 223,694 ​ $ 223,336

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive (Loss) Income (Tables)	3 Months Ended
	Mar. 31, 2022
Equity [Abstract]
Summary of Changes in Accumulated Other Comprehensive (Loss) Income, Net of Tax, from Unrealized Gains (Losses) on Available-for-Sale Marketable Securities	The following table summarizes the changes in accumulated other comprehensive (loss) income, net of tax, from unrealized gains (losses) on available-for-sale marketable securities, the Company’s only component of accumulated other comprehensive (loss) income, for the three months ended March 31, 2022 and 2021, respectively. ​ ​ ​ ​ ​ Total Accumulated ​ ​ Other Comprehensive ​ ​ (Loss) Income Balance, December 31, 2021 ​ $ (358) Other comprehensive loss before reclassifications ​ (1,365) Amount reclassified from accumulated other comprehensive loss ​ — Net current period other comprehensive loss ​ (1,365) Balance, March 31, 2022 ​ $ (1,723) ​ ​ ​ ​ Balance, December 31, 2020 ​ $ 73 Other comprehensive loss before reclassifications ​ (22) Amount reclassified from accumulated other comprehensive income ​ (39) Net current period other comprehensive loss ​ (61) Balance, March 31, 2021 ​ $ 12
Schedule of Reclassification Out of Accumulated Other Comprehensive (Loss) Income	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Affected Line Item in the Component of Accumulated Other ​ March 31, ​ Condensed Statements of Comprehensive (Loss) Income 2022 2021 Comprehensive Loss Unrealized gains (losses) on available-for-sale marketable securities: ​ ​ Realized gains on sales of securities ​ $ — ​ $ 39 ​ Other income, net Income tax effect ​ — ​ — ​ Benefit from income taxes Realized gains on sales of securities, net of tax ​ $ — ​ $ 39 ​ ​

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2022
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 March 31, 2022 Fair value measurement as of March 31, 2022 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 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 ​ $ 21,362 ​ $ 21,362 ​ $ — ​ $ — Available-for-sale marketable securities: ​ ​ ​ ​ ​ ​ ​ U.S. Treasury securities ​ 15,550 ​ — ​ 15,550 ​ — U.S. government agency obligations ​ 11,630 ​ — ​ 11,630 ​ — Corporate bonds ​ 66,025 ​ — ​ 66,025 ​ — Commercial paper ​ 72,789 ​ — ​ 72,789 ​ — Municipal bonds ​ 22,211 ​ — ​ 22,211 ​ — Restricted cash: ​ ​ ​ ​ ​ ​ ​ Commercial money market account ​ 408 ​ 408 ​ — ​ — Total financial assets ​ $ 209,975 ​ $ 21,770 ​ $ 188,205 ​ $ — ​ Fair value measurement as of December 31, 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 ​ $ 13,453 ​ $ 13,453 ​ $ — ​ $ — Available-for-sale marketable securities: ​ ​ ​ ​ U.S. Treasury securities ​ ​ 11,570 ​ ​ — ​ ​ 11,570 ​ ​ — U.S. government agency obligations ​ 16,975 ​ — ​ 16,975 ​ — Corporate bonds ​ 66,324 ​ — ​ 66,324 ​ — Commercial paper ​ 106,888 ​ — ​ 106,888 ​ — Municipal bonds ​ ​ 21,579 ​ ​ — ​ ​ 21,579 ​ ​ — Restricted cash: ​ ​ ​ ​ Commercial money market account ​ 408 ​ 408 ​ — ​ — Total financial assets ​ $ 237,197 ​ $ 13,861 ​ $ 223,336 ​ $ —

Restricted Cash (Tables)

Restricted Cash (Tables)	3 Months Ended
	Mar. 31, 2022
Restricted Cash [Abstract]
Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash	​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, 2022 December 31, 2021 Cash and cash equivalents ​ $ 21,362 ​ $ 13,453 Restricted cash, long-term assets ​ 408 ​ 408 Total cash, cash equivalents, and restricted cash shown in the Condensed Statements of Cash Flows ​ $ 21,770 ​ $ 13,861

Inventory, net (Tables)

Inventory, net (Tables)	3 Months Ended
	Mar. 31, 2022
Inventory Disclosure [Abstract]
Schedule of Inventories	​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, 2022 December 31, 2021 Raw materials ​ $ 1,095 ​ $ 927 Work-in-process ​ 812 ​ 1,657 Total ​ $ 1,907 ​ $ 2,584

Accounts Payable and Accrued _2

Accounts Payable and Accrued Expenses (Tables)	3 Months Ended
	Mar. 31, 2022
Payables And Accruals [Abstract]
Schedule of Accounts Payable and Accrued Expenses	Accounts payable and accrued expenses consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ March 31, 2022 December 31, 2021 Accounts payable ​ $ 5,594 ​ $ 5,625 Accrued research projects ​ 6,444 ​ 4,648 Accrued compensation and benefits ​ 2,412 ​ 4,959 Accrued professional fees and other ​ 2,051 ​ 629 Total ​ $ 16,501 ​ $ 15,861

Net (Loss) Income Per Share (Ta

Net (Loss) Income Per Share (Tables)	3 Months Ended
	Mar. 31, 2022
Net Loss Per Share
Computation of Denominators Used in Net (Loss) Income per Share	The denominators used in the net loss per share computations are as follows: ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ ​ March 31, ​ ​ 2022 2021 Basic: Weighted average common shares outstanding 53,507,060 49,917,990 Diluted: Weighted average common shares outstanding - Basic 53,507,060 49,917,990 Common stock equivalents* — — Denominator for diluted net loss per share 53,507,060 49,917,990 * No amounts were considered as their effects would be anti-dilutive.
Computation of Basic and Diluted Net (Loss) Income per Share	Basic and diluted net loss per share are computed as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ ​ March 31, ​ ​ 2022 2021 Net loss - basic and diluted ​ $ (27,749) ​ $ (23,301) ​ Weighted-average common shares outstanding: ​ ​ ​ ​ Basic and diluted ​ 53,507,060 ​ 49,917,990 ​ Net loss per share, Basic and Diluted: ​ $ (0.52) ​ $ (0.47) ​

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2022
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 three months ended March 31, 2022 is presented below: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ Number of ​ Average Exercise ​ ​ Shares Price Outstanding, December 31, 2021 6,512,280 ​ $ 15.58 Granted 977,438 ​ 10.63 Exercised (470) ​ 6.50 Forfeited (37,241) ​ 15.22 Expired (21,378) ​ 25.16 Outstanding, March 31, 2022 7,430,629 ​ $ 14.91 ​ Options exercisable, March 31, 2022 4,357,399 ​ ​ ​ ​
Summary of Assumptions Used in Black-Scholes Option Pricing Model	The fair values of stock options granted during the three months ended March 31, 2022 and 2021 were estimated as of the dates of grant using the Black-Scholes option pricing model with the following assumptions: ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ ​ March 31, ​ ​ 2022 2021 Risk-free interest rate 1.70% - 2.35% ​ 0.66% - 1.21% Expected volatility 81.4% - 81.9% ​ 71.6% - 71.8% Expected dividend yield 0% ​ 0% Expected life of employee and Board options (in years) 6.25 ​ 6.25
Summary of Compensation Expense Relating to Stock Options	During the three months ended March 31, 2022 and 2021, the Company recognized compensation expense relating to stock options as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ ​ March 31, ​ ​ 2022 2021 Research and development ​ $ 1,917 ​ $ 1,590 ​ General and administrative ​ 2,030 ​ 1,014 ​ Total stock option expense ​ $ 3,947 ​ $ 2,604 ​
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 three months ended March 31, 2022 is presented below: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ Number of ​ Average Grant ​ Units Date Fair Value Outstanding, December 31, 2021 576,544 ​ $ 17.50 Awarded 388,170 ​ 10.46 Vested and released (109,943) ​ 19.13 Forfeited (118,499) ​ 19.72 Outstanding, March 31, 2022 736,272 ​ $ 13.19 Restricted stock units exercisable (vested and deferred), March 31, 2022 — ​ ​ ​

Commitments and Contingencies (

Commitments and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2022
Commitments And Contingencies Disclosure [Abstract]
Schedule of Other Information related to Stamford Lease and lease amendment	Other information related to the leases was as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ ​ March 31, ​ ​ 2022 2021 ​ Cash paid for amounts included in the measurement of lease liabilities: ​ ​ ​ ​ Operating cash outflows relating to operating leases ​ $ 485 ​ $ 476 ​ ROU assets obtained in exchange for new operating lease liabilities ​ $ — ​ $ — ​ Remaining lease term - operating leases (years) ​ 1.8 ​ 2.8 ​ Discount rate - operating leases ​ ​ 7.0 % ​ 7.0 %
Schedule of Future Minimum Lease Payments under Non-cancellable Operating Leases, Reconciliation of Undiscounted Cash Flows to the Operating Lease Liabilities	Future minimum lease payments under non-cancellable operating leases, as well as a reconciliation of these undiscounted cash flows to the operating lease liabilities as of March 31, 2022, were as follows: ​ ​ ​ ​ Year Ending December 31, ​ ​ 2022 (Excluding the three months ended March 31, 2022) $ 1,473 2023 ​ 1,991 Total future minimum lease payments, undiscounted ​ 3,464 Less imputed interest ​ (214) Total ​ $ 3,250 ​ ​ ​ ​ Operating lease liabilities reported as of March 31, 2022: ​ Operating lease liabilities - current ​ $ 1,795 Operating lease liabilities - non-current ​ 1,455 Total ​ $ 3,250

Business - Additional Informati

Business - Additional Information (Detail) $ in Thousands	Aug. 23, 2021	Oct. 31, 2021USD ($)shares	Oct. 31, 2020USD ($)shares	May 31, 2018USD ($)shares	Mar. 31, 2022USD ($)item	Mar. 31, 2021USD ($)	Dec. 31, 2021USD ($)
Nature Of Business [Line Items]
Date of formation					Jul. 2, 2004
Proceeds from equity and debt financing					$ 519,600
Number of follow-on public offerings | item					4
Payments received in connection with license agreements					$ 229,710
Unrestricted cash and cash equivalents and marketable securities					209,567
Accumulated deficit					508,507		$ 480,758
Net loss					(27,749)	$ (23,301)
Net cash used in operating activities					$ (25,525)	$ (23,721)
Vifor Agreement [Member]
Nature Of Business [Line Items]
Percentage of net profit sharing	60.00%		60.00%
Vifor International Ltd. [Member]
Nature Of Business [Line Items]
Proceeds from sale of common stock in connection with license agreement			$ 38,449	$ 14,556
Proceeds from sale of common stock in connection with regulatory milestone		$ 44,969
Vifor International Ltd. [Member] | Vifor Agreement [Member]
Nature Of Business [Line Items]
Percentage of net profit sharing	40.00%		40.00%
Common stock, shares issued | shares			2,939,552
Vifor International Ltd. [Member] | Regulatory Milestones [Member]
Nature Of Business [Line Items]
Common stock, shares issued | shares		3,282,391
Vifor International Ltd. [Member] | Common Stock [Member]
Nature Of Business [Line Items]
Common stock, shares issued | shares		3,282,391	2,939,552	1,174,827

Basis of Presentation (Detail)

Basis of Presentation (Detail) $ in Thousands	Mar. 31, 2022USD ($)
Basis of Presentation
Allowance for credit losses	$ 0

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	Mar. 31, 2022	Dec. 31, 2021
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 189,928	$ 223,694
Gross Unrealized Gains		5
Gross Unrealized Losses	(1,723)	(363)
Estimated Fair Value	188,205	223,336
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	15,577	11,573
Gross Unrealized Losses	(27)	(3)
Estimated Fair Value	15,550	11,570
U.S. Government Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	12,000	17,020
Gross Unrealized Losses	(370)	(45)
Estimated Fair Value	11,630	16,975
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	66,765	66,495
Gross Unrealized Losses	(740)	(171)
Estimated Fair Value	66,025	66,324
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	72,952	106,914
Gross Unrealized Gains		5
Gross Unrealized Losses	(163)	(31)
Estimated Fair Value	72,789	106,888
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	22,634	21,692
Gross Unrealized Losses	(423)	(113)
Estimated Fair Value	$ 22,211	$ 21,579

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	Mar. 31, 2022	Dec. 31, 2021
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	$ 180,849	$ 156,455
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Gross Unrealized Losses	(1,543)	(354)
Available-for-sale marketable securities, continuous unrealized loss position, 12 Months or Greater, Fair Value	7,356	3,037
Available-for-sale marketable securities, continuous unrealized loss position, 12 Months or Greater, Gross Unrealized Losses	(180)	(9)
Available-for-sale marketable securities, continuous unrealized loss position, Fair Value	188,205	159,492
Available-for-sale marketable securities, continuous unrealized loss position, Gross Unrealized Losses	(1,723)	(363)
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	15,550	11,570
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Gross Unrealized Losses	(27)	(3)
Available-for-sale marketable securities, continuous unrealized loss position, Fair Value	15,550	11,570
Available-for-sale marketable securities, continuous unrealized loss position, Gross Unrealized Losses	(27)	(3)
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	9,687	9,456
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Gross Unrealized Losses	(313)	(45)
Available-for-sale marketable securities, continuous unrealized loss position, 12 Months or Greater, Fair Value	1,943
Available-for-sale marketable securities, continuous unrealized loss position, 12 Months or Greater, Gross Unrealized Losses	(57)
Available-for-sale marketable securities, continuous unrealized loss position, Fair Value	11,630	9,456
Available-for-sale marketable securities, continuous unrealized loss position, Gross Unrealized Losses	(370)	(45)
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	61,610	62,704
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Gross Unrealized Losses	(644)	(170)
Available-for-sale marketable securities, continuous unrealized loss position, 12 Months or Greater, Fair Value	4,415	2,020
Available-for-sale marketable securities, continuous unrealized loss position, 12 Months or Greater, Gross Unrealized Losses	(96)	(1)
Available-for-sale marketable securities, continuous unrealized loss position, Fair Value	66,025	64,724
Available-for-sale marketable securities, continuous unrealized loss position, Gross Unrealized Losses	(740)	(171)
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	72,789	52,163
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Gross Unrealized Losses	(163)	(31)
Available-for-sale marketable securities, continuous unrealized loss position, Fair Value	72,789	52,163
Available-for-sale marketable securities, continuous unrealized loss position, Gross Unrealized Losses	(163)	(31)
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	21,213	20,562
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Gross Unrealized Losses	(396)	(105)
Available-for-sale marketable securities, continuous unrealized loss position, 12 Months or Greater, Fair Value	998	1,017
Available-for-sale marketable securities, continuous unrealized loss position, 12 Months or Greater, Gross Unrealized Losses	(27)	(8)
Available-for-sale marketable securities, continuous unrealized loss position, Fair Value	22,211	21,579
Available-for-sale marketable securities, continuous unrealized loss position, Gross Unrealized Losses	$ (423)	$ (113)

Available-for-Sale Marketable_5

Available-for-Sale Marketable Securities - Additional Information (Detail) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2022USD ($)position	Dec. 31, 2021USD ($)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	73	58
Total number of positions	73	76
Number of positions of available-for-sale in unrealized loss position for 12 months or greater	4
Available-for-sale marketable securities, continuous unrealized loss position, 12 Months or Greater, Gross Unrealized Losses | $	$ 180	$ 9
U.S. Treasury Securities [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	6
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	4
Total number of positions	4
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of available-for-sale marketable securities in unrealized loss positions	25
Total number of positions	25
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of available-for-sale marketable securities in unrealized loss positions	23
Total number of positions	23
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of available-for-sale marketable securities in unrealized loss positions	15
Total number of positions	15

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
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Debt Securities [Abstract]
Amortized Cost of marketable debt securities, contractual maturity, less than one year	$ 120,070		$ 153,631
Amortized Cost of marketable debt securities, contractual maturity, One year to three years	69,858		70,063
Amortized Cost	189,928		223,694
Fair value of marketable debt securities, contractual maturities, less than one year	119,749		153,582
Fair value of marketable debt securities, contractual maturity, One year to three years	68,456		69,754
Total fair Value of marketable debt securities, contractual maturity	188,205		223,336
Proceeds from sale of available-for-sale marketable securities	0	$ 8,029
Realized gain		$ 39
Interest receivable	$ 438		$ 455

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive (Loss) Income - Summary of Changes in Accumulated Other Comprehensive (Loss) Income, Net of Tax, from Unrealized Gains (Losses) on Available-for-Sale Marketable Securities (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Accumulated Other Comprehensive Income Loss [Line Items]
Balance, Value	$ 227,522	$ 249,001
Amount reclassified from accumulated other comprehensive income		(39)
Net current period other comprehensive loss	(1,365)	(61)
Balance, Value	204,115	230,459
Accumulated Other Comprehensive (Loss) Income
Accumulated Other Comprehensive Income Loss [Line Items]
Balance, Value	(358)	73
Other comprehensive loss before reclassifications	(1,365)	(22)
Amount reclassified from accumulated other comprehensive income		(39)
Net current period other comprehensive loss	(1,365)	(61)
Balance, Value	$ (1,723)	$ 12

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive (Loss) Income - Schedule of Reclassifications Out of Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Other income, net	$ 162	$ 260
Benefit from income taxes	$ 0	0
Net of tax		39
Accumulated Net Unrealized Investment Gain (Loss) Attributable to Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Other income, net		$ 39

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Financial assets
Available-for-sale marketable securities	$ 188,205	$ 223,336
Recurring [Member]
Financial assets
Total financial assets	209,975	237,197
U.S. Government Agency Obligations [Member]
Financial assets
Available-for-sale marketable securities	11,630	16,975
U.S. Government Agency Obligations [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities	11,630	16,975
Corporate Bonds [Member]
Financial assets
Available-for-sale marketable securities	66,025	66,324
Corporate Bonds [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities	66,025	66,324
Municipal Bonds [Member]
Financial assets
Available-for-sale marketable securities	22,211	21,579
Municipal Bonds [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities	22,211	21,579
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring [Member]
Financial assets
Total financial assets	21,770	13,861
Significant Other Observable Inputs (Level 2) [Member] | Recurring [Member]
Financial assets
Total financial assets	188,205	223,336
Significant Other Observable Inputs (Level 2) [Member] | U.S. Government Agency Obligations [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities	11,630	16,975
Significant Other Observable Inputs (Level 2) [Member] | Corporate Bonds [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities	66,025	66,324
Significant Other Observable Inputs (Level 2) [Member] | Municipal Bonds [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities	22,211	21,579
Money Market Funds [Member] | Recurring [Member]
Financial assets
Cash and cash equivalents	21,362	13,453
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	21,362	13,453
Restricted cash	408	408
U.S. Treasury Securities [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities	15,550	11,570
U.S. Treasury Securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities	15,550	11,570
Commercial Paper [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities	72,789	106,888
Commercial Paper [Member] | Significant Other Observable Inputs (Level 2) [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities	$ 72,789	$ 106,888

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Purchases of financial assets	$ 0	$ 0
Sales of financial assets	0	0
Maturities of financial assets	0	0
Transfer of financial asset into level 3 of fair value	0	0
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Unrealized gains	0	0
Unrealized losses	$ 0	$ 0

Restricted Cash - Additional In

Restricted Cash - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash, long-term assets	$ 408	$ 408
Stamford Lease [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash, long-term assets	$ 408	$ 408

Restricted Cash - Schedule of R

Restricted Cash - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Restricted Cash [Abstract]
Cash and cash equivalents	$ 21,362	$ 13,453
Restricted cash, long-term assets	408	408
Total cash, cash equivalents, and restricted cash shown in the Condensed Statements of Cash Flows	$ 21,770	$ 13,861	$ 22,927	$ 32,091

Inventory, net - Schedule of In

Inventory, net - Schedule of Inventories (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Inventory Disclosure [Abstract]
Raw materials	$ 1,095	$ 927
Work-in-process	812	1,657
Total	$ 1,907	$ 2,584

Inventory, net - Additional Inf

Inventory, net - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2022USD ($)
Inventory Disclosure [Abstract]
Inventory write-down	$ 0

Prepaid Expenses - Additional I

Prepaid Expenses - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Prepaid expenses	$ 5,113	$ 2,519
Prepaid R&D clinical costs	2,167	1,481
Prepaid insurance	2,134	369
Other prepaid costs	$ 812	$ 669

Accounts Payable and Accrued _3

Accounts Payable and Accrued Expenses - Schedule of Accounts Payable and Accrued Expenses (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Payables And Accruals [Abstract]
Accounts payable	$ 5,594	$ 5,625
Accrued research projects	6,444	4,648
Accrued compensation and benefits	2,412	4,959
Accrued professional fees and other	2,051	629
Total	$ 16,501	$ 15,861

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Aug. 20, 2019	Mar. 31, 2022	Feb. 28, 2022	Feb. 28, 2021	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Sale Of Stock [Line Items]
Common stock, shares authorized		100,000,000			100,000,000		100,000,000
Common stock, par value		$ 0.001			$ 0.001		$ 0.001
Preferred stock, shares authorized		5,000,000			5,000,000		5,000,000
Preferred stock, par value		$ 0.001			$ 0.001		$ 0.001
Common stock, shares outstanding		53,591,225			53,591,225		53,480,812
Common stock, shares issued		53,591,225			53,591,225		53,480,812
Preferred stock, shares issued		0			0		0
Preferred Stock Shares Outstanding		0			0		0
Non-Exclusive License Agreement | Enteris Biopharma, Inc. [Member]
Sale Of Stock [Line Items]
Upfront fee payment, cash	$ 4,000
Upfront fee payment, stock	$ 4,000
Maximum [Member]
Sale Of Stock [Line Items]
Aggregate offering price of securities		$ 300,000			$ 300,000
Unsold Securities Under Shelf Registration Statement dated April 4, 2019 [Member]
Sale Of Stock [Line Items]
Aggregate offering price of securities		154,525			154,525
Open Market Sales Agreement [Member] | Jeffries LLC [Member]
Sale Of Stock [Line Items]
Aggregate offering price of securities		$ 80,000			$ 80,000
Stock Sale Commission Percentage		3.00%
Common Stock
Sale Of Stock [Line Items]
Restricted stock units vested shares					109,943	109,419
Restricted Stock Units [Member] | General and Administrative [Member]
Sale Of Stock [Line Items]
Compensation expense					$ 1,452	$ 822
Restricted Stock Units [Member] | General and Administrative [Member] | Director [Member]
Sale Of Stock [Line Items]
Compensation expense					$ 139	$ 139
Performance Restricted Stock Units [Member] | Common Stock | Executive Officers [Member] | March 2022 [Member]
Sale Of Stock [Line Items]
Vesting period of awards granted		3 years
Restricted stock units, vested		37,999
Performance Restricted Stock Units [Member] | Common Stock | Executive Officers [Member] | February and March 2021 [Member]
Sale Of Stock [Line Items]
Restricted stock units vested shares					76,750
Time-based Restricted Stock Units [Member] | Common Stock | Executive Officers [Member] | March 2022 [Member]
Sale Of Stock [Line Items]
Restricted stock units vested shares		39,278
Time-based Restricted Stock Units [Member] | Common Stock | Executive Officers [Member] | February 2022 [Member]
Sale Of Stock [Line Items]
Vesting period of awards granted			3 years
Restricted stock units vested shares			32,666
Time-based Restricted Stock Units [Member] | Common Stock | Executive Officers [Member] | February 2021 [Member]
Sale Of Stock [Line Items]
Vesting period of awards granted				3 years
Restricted stock units vested shares				32,669

Collaboration and Licensing A_2

Collaboration and Licensing Agreements - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Aug. 23, 2021	Oct. 15, 2020	May 17, 2018	Oct. 31, 2021	Oct. 31, 2020	Mar. 31, 2022	Mar. 31, 2021
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue from contract with customer						$ 4,790	$ 1,935
Collaborative Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue from contract with customer							706
Commercial Supply Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue from contract with customer						4,790
Clinical Compound Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue from contract with customer							37
Vifor Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of net profit sharing	60.00%				60.00%
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			1,174,827
Purchase of common stock value			$ 20,000
Purchase common stock per share amount			$ 17.024
Closing prices of company common stock description			over a pre-determined average closing price of the Company’s common stock
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
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
Maruishi Pharmaceutical Co., Ltd. [Member] | Clinical Compound Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue from contract with customer						$ 0	$ 37
Vifor International Ltd. [Member] | Vifor Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of net profit sharing	40.00%				40.00%
Common stock, shares issued					2,939,552
Purchase common stock per share amount					$ 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				3,282,391
Proceeds from the sale of common stock		$ 50,000		$ 50,000
Purchase common stock per share amount				$ 15.23
Percentage of premium on common stock investment				20.00%
Stock issuance price measurement period				30 days
Vifor International Ltd. [Member] | Maximum [Member] | Sales-based Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential sales-based milestone payments				$ 240,000

Revenue Recognition - Additiona

Revenue Recognition - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Oct. 15, 2020	May 17, 2018	Apr. 30, 2022	Mar. 31, 2022	Jan. 31, 2022	Oct. 31, 2021	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Accounts receivable - related party				$ 2,496			$ 2,496		$ 0
Total revenue							4,790	$ 1,935
Commercial Supply Revenue
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Total revenue							4,790
Commercial Supply Revenue With No Associated Costs Of Goods Sold [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue					$ 2,295
Cost of goods sold					$ 0
Commercial Supply Revenue With Associated Costs Of Goods Sold [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue				2,495
Cost of goods sold				2,081
License and Milestone Fees
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Total revenue								1,192
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
Clinical Compound Revenue
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Total revenue								37
VFMCRP Agreement [Member] | License and Milestone Fees | Subsequent Event [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Total revenue			$ 15,000
Vifor, VFMCRP, Maruishi and CKDP Agreements [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Other contract Assets				0			0		0
Other contract liabilities				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
Maruishi Agreement [Member] | Collaborative Revenue
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Total revenue								706
Maruishi Agreement [Member] | License and milestone or Collaborative revenue
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Total revenue							0
CKDP Agreement [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Total revenue							0	0
Maruishi Pharmaceutical Co., Ltd. [Member] | Clinical Compound Revenue
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Total revenue							0	37
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%
Proceeds from the sale of common stock	$ 50,000					$ 50,000
Stock Issued During Period Shares New Issues						3,282,391
Stock Issuance Price Measurement Period						30 days
Shares Issued Price Per Share						$ 15.23
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		1,174,827
Shares Issued Price Per Share		$ 17.024
upfront payment		$ 50,000
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
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member] | Clinical or Commercial Compound
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Total revenue							$ 0	$ 0

Net (Loss) Income per Share - C

Net (Loss) Income per Share - Computation of Denominators Used in Net Loss per Share (Detail) - shares	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Basic:
Weighted average common shares outstanding - Basic	53,507,060	49,917,990
Diluted:
Weighted average common shares outstanding - Basic	53,507,060	49,917,990
Common stock equivalents	0	0
Denominator for diluted net loss per share	53,507,060	49,917,990

Net (Loss) Income per Share -_2

Net (Loss) Income per Share - Computation of Basic and Diluted Net Loss per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Net Loss Per Share
Net loss - basic and diluted	$ (27,749)	$ (23,301)
Weighted-average common shares outstanding:
Basic	53,507,060	49,917,990
Diluted	53,507,060	49,917,990
Net loss per share:
Basic	$ (0.52)	$ (0.47)
Diluted	$ (0.52)	$ (0.47)

Net (Loss) Income per Share - A

Net (Loss) Income per Share - Additional Information (Detail) - shares	Mar. 31, 2022	Mar. 31, 2021
Net Loss Per Share
Number of options outstanding	7,430,629	5,918,808
Number of restricted stock units outstanding	736,272	401,831

Stock-Based Compensation - Addi

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

Feb. 25, 2022installment$ / sharesshares

Dec. 17, 2021installment$ / sharesshares

Oct. 29, 2021tranche$ / sharesshares

Jun. 03, 2021$ / sharesshares

Mar. 30, 2021installment$ / sharesshares

Jun. 04, 2020$ / shares

Mar. 31, 2022$ / sharesshares

Feb. 28, 2022shares

Mar. 31, 2021shares

Feb. 28, 2021shares

Jun. 30, 2020shares

Feb. 29, 2020installment$ / sharesshares

Mar. 31, 2022USD ($)$ / sharesshares

Mar. 31, 2021USD ($)$ / sharesshares

Dec. 31, 2015shares

Jan. 01, 2022shares

Dec. 31, 2021$ / sharesshares

Nov. 20, 2019$ / sharesshares

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

Common stock, par value | $ / shares

$ 0.001

$ 0.001

$ 0.001

Common stock, shares outstanding

53,591,225

53,591,225

53,480,812

Common stock, shares issued

53,591,225

53,591,225

53,480,812

Number of options outstanding

7,430,629

5,918,808

7,430,629

5,918,808

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

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

Compensation expense | $

$ 167

$ 568

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

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

Compensation expense | $

$ 1,452

$ 822

Share-based Payment Arrangement, Employee [Member]

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

Fair value of options granted | $ / shares

$ 7.55

$ 12.49

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

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

Compensation expense | $

$ 139

$ 139

Non-employee Consultants [Member]

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

Options granted

0

0

2019 Inducement Plan [Member]

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

Common stock, par value | $ / shares

$ 0.001

Awarded

0

0

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

0

Annual increases in number of shares reserved for issuance as a percentage of shares of capital stock outstanding through January 1, 2024

3.00%

Share-based compensation arrangement by share-based payment award, number of shares authorized

10,589,103

8,984,679

Number of options outstanding

7,430,629

7,430,629

6,512,280

Options granted

977,438

673,200

2014 Equity Incentive Plan [Member] | Maximum [Member]

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

Term of awards granted

10 years

2014 Equity Incentive Plan [Member] | Maximum [Member] | Incentive Stock Options [Member]

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

Share-based compensation arrangement by share-based payment award, number of shares authorized

30,000,000

2014 Equity Incentive Plan [Member] | Employees [Member] | Restricted Stock Units [Member] | February 2022 [Member]

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

Compensation expense | $

$ 0

Restricted stock units, vested

0

2014 Equity Incentive Plan [Member] | Employees [Member] | Performance Restricted Stock Units [Member] | February 2022 [Member]

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

Awarded

243,000

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

$ 10.46

2014 Equity Incentive Plan [Member] | Employees [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 | $

$ 729

Restricted stock units, vested

37,999

82,001

Restricted stock units, Forfeited

93,999

2014 Equity Incentive Plan [Member] | Employees [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

Restricted stock units, Forfeited

24,500

2014 Equity Incentive Plan [Member] | Employees [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] | Employees [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 | $

$ 303

2014 Equity Incentive Plan [Member] | Employees [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] | Employees [Member] | Time-based Restricted Stock Units [Member] | February 2022 [Member]

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

Vesting period of awards granted

3 years

Awarded

145,170

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

$ 10.46

Number of equal installment | installment

3

Compensation expense | $

$ 50

Restricted stock units, vested

0

2014 Equity Incentive Plan [Member] | Employees [Member] | Time-based Restricted Stock Units [Member] | December 2021 [Member]

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

Vesting period of awards granted

18 months

Awarded

63,573

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

$ 12.45

Number of equal installment | installment

2

Compensation expense | $

$ 131

Restricted stock units, vested

0

2014 Equity Incentive Plan [Member] | Employees [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

3

Compensation expense | $

$ 284

Restricted stock units, vested

33,336

33,336

2014 Equity Incentive Plan [Member] | Employees [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

3

Compensation expense | $

$ 219

132

Restricted stock units, vested

32,666

32,669

65,335

2014 Equity Incentive Plan [Member] | Employees [Member] | Time-based Restricted Stock Units [Member] | Research and Development [Member] | February 2022 [Member]

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

Compensation expense | $

$ 18

2014 Equity Incentive Plan [Member] | Employees [Member] | Time-based Restricted Stock Units [Member] | Research and Development [Member] | December 2021 [Member]

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

Compensation expense | $

52

2014 Equity Incentive Plan [Member] | Employees [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 | $

54

2014 Equity Incentive Plan [Member] | Employees [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 | $

43

43

2014 Equity Incentive Plan [Member] | Employees [Member] | Time-based Restricted Stock Units [Member] | General and Administrative [Member] | Modified February 2020 Awards [Member]

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

Compensation expense | $

155

2014 Equity Incentive Plan [Member] | Employees [Member] | Time-based Restricted Stock Units [Member] | General and Administrative [Member] | February 2022 [Member]

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

Compensation expense | $

32

2014 Equity Incentive Plan [Member] | Employees [Member] | Time-based Restricted Stock Units [Member] | General and Administrative [Member] | December 2021 [Member]

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

Compensation expense | $

79

2014 Equity Incentive Plan [Member] | Employees [Member] | Time-based Restricted Stock Units [Member] | General and Administrative [Member] | October 2021 [Member]

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

Compensation expense | $

203

2014 Equity Incentive Plan [Member] | Employees [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 | $

230

2014 Equity Incentive Plan [Member] | Employees [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 | $

$ 176

89

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] | 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] | General and Administrative [Member] | June 2020 [Member]

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

Compensation expense | $

$ 139

2014 Equity Incentive Plan [Member] | Chief Executive Officer [Member] | Time-based Restricted Stock Units [Member] | October 2021 [Member]

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

Awarded

147,942

147,942

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

$ 16.83

Number of restricted stock unit tranches | tranche

2

Compensation expense | $

$ 206

Restricted stock units, vested

5,942

2014 Equity Incentive Plan [Member] | Chief Executive Officer [Member] | Share-Based Compensation Award, Tranche One [Member] | Time-based Restricted Stock Units [Member] | October 2021 [Member]

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

Percentage of vested shares on first anniversary of grant date

25.00%

Awarded

142,000

2014 Equity Incentive Plan [Member] | Chief Executive Officer [Member] | Share-based Compensation Award, Tranche Two [Member] | Time-based Restricted Stock Units [Member] | October 2021 [Member]

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

Vesting period of awards granted

36 months

Awarded

5,942

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

0

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 | $

$ 139

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

388,170

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

$ 10.46

Restricted stock units, vested

109,943

Restricted stock units, Forfeited

118,499

Stock-Based Compensation - Rest

Stock-Based Compensation - Restricted Stock Unit Activity (Details) - $ / shares	1 Months Ended	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2022
Number of Units
Outstanding, Ending Balance	401,831	736,272
2014 Equity Incentive Plan [Member] | Employees And Non-Employee Members Of Board Of Directors [Member] | Restricted Stock Units [Member]
Number of Units
Outstanding, Beginning Balance		576,544
Awarded		388,170
Vested and released		(109,943)
Forfeited		(118,499)
Outstanding, Ending Balance		736,272
Weighted Average Grant Date Fair Value
Weighted-average grant date fair value, outstanding, Beginning Balance		$ 17.50
Weighted-average grant date fair value, awarded		10.46
Weighted-average grant date fair value, vested and released		19.13
Weighted-average grant date fair value, forfeited		19.72
Weighted-average grant date fair value, outstanding, Ending Balance		$ 13.19

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Assumptions Used in Black-Scholes Option Pricing Model (Detail)	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate, minimum	1.70%	0.66%
Risk-free interest rate, maximum	2.35%	1.21%
Expected volatility, minimum	81.40%	71.60%
Expected volatility, maximum	81.90%	71.80%
Expected dividend yield	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

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Compensation Expense Relating to Stock Options (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
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
Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Compensation expense	3,947	2,604
Options [Member] | Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Compensation expense	1,917	1,590
Options [Member] | General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Compensation expense	2,030	1,014
Restricted Stock Units [Member] | Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Compensation expense	167	568
Restricted Stock Units [Member] | General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Compensation expense	1,452	822
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	$ 139	$ 139

Stock-Based Compensation - Su_3

Stock-Based Compensation - Summary of Stock Option Activity (Detail) - $ / shares	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Options, Outstanding, Ending Balance	7,430,629	5,918,808
2014 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Options, Outstanding, Beginning Balance	6,512,280
Number of Options, Granted	977,438	673,200
Number of Options, Exercised	(470)
Number of Options, Forfeited	(37,241)
Number of Options, Expired	(21,378)
Number of Options, Outstanding, Ending Balance	7,430,629
Number of Options, Options exercisable	4,357,399
Weighted-Average Exercise Price, Outstanding, Beginning Balance	$ 15.58
Weighted-Average Exercise Price, Granted	10.63
Weighted-Average Exercise Price, Exercised	6.50
Weighted-Average Exercise Price, Forfeited	15.22
Weighted-Average Exercise Price, Expired	25.16
Weighted-Average Exercise Price, Outstanding, Ending Balance	$ 14.91

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock Award Modifications (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended
	Feb. 28, 2022	Nov. 30, 2021	Mar. 31, 2022	Mar. 31, 2021
Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Compensation expense			$ 3,947	$ 2,604
Options [Member] | General and Administrative [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Compensation expense			2,030	$ 1,014
Modified Awards [Member] | Former President and C E O [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period of awards granted		12 months
Share-based Compensation Arrangement Period During Which Continuous Service Must Be Performed For Awards To Be Modified		12 months
Awards that would have vested during the period following the consulting period are deemed to be type 3 modifications		12 months
Term of awards granted		18 months
Modified Awards [Member] | Former President and C E O [Member] | General and Administrative [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total incremental stock compensation expense relating to modifications of Stock Awards			1,564
Incremental stock compensation expense relating to modification of stock options			$ 903
Modified Awards [Member] | Former President and C E O [Member] | Performance Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock units, vested	17,333

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Income Tax Disclosure [Abstract]
Company's effective tax rate	0.00%	0.00%
Income tax benefit	$ 0	$ 0
Percentage of annual research and development credit for cash	65.00%	65.00%

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) $ in Thousands	Aug. 20, 2019USD ($)	Jul. 31, 2019agreement	Mar. 31, 2022USD ($)	Mar. 31, 2021USD ($)	Dec. 31, 2021USD ($)
Other Commitments [Line Items]
Research and development expense			$ 21,273	$ 19,131
Lease term			1 year 9 months 18 days	2 years 9 months 18 days
Operating lease liabilities			$ 3,250
Operating lease right-of-use assets			2,629		$ 2,973
Enteris Biopharma, Inc. [Member]
Other Commitments [Line Items]
Payment of milestone payment			0	$ 0
Payments for Royalties			0	0
Stamford Operating Lease and New Stamford Lease [Member]
Other Commitments [Line Items]
Operating lease cost			406	406
Stamford Operating Lease and New Stamford Lease [Member] | Research and Development [Member]
Other Commitments [Line Items]
Operating lease cost			284	284
Stamford Operating Lease and New Stamford Lease [Member] | General and Administrative [Member]
Other Commitments [Line Items]
Operating lease cost			$ 122	$ 122
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
MSA [Member] | Patheon and Patheon Manufacturing Services LLC [Member]
Other Commitments [Line Items]
Number of related product agreements | agreement		2
API Commercial Supply Agreement - PPL [Member]
Other Commitments [Line Items]
Agreement renewal term			5 years

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Other Information related to Stamford Lease (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Commitments And Contingencies Disclosure [Abstract]
Operating cash outflows relating to operating leases	$ 485	$ 476
Remaining lease term - operating leases (years)	1 year 9 months 18 days	2 years 9 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	Mar. 31, 2022	Dec. 31, 2021
Operating Lease Liabilities, Payments Due [Abstract]
2022 (Excluding the three months ended March 31, 2022)	$ 1,473
2023	1,991
Total future minimum lease payments, undiscounted	3,464
Less imputed interest	(214)
Operating lease liabilities	3,250
Operating lease liabilities reported as of March 31, 2022:
Operating lease liabilities - current	1,795	$ 1,755
Operating lease liabilities - non-current	1,455	$ 1,918
Total	$ 3,250

Related Party Transactions (Det

Related Party Transactions (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Related Party Transaction [Line Items]
Accounts due from related parties	$ 2,496	$ 0
Vifor International Ltd. [Member]
Related Party Transaction [Line Items]
Shares owned as a result of upfront and milestone payments	7,396,770
Related party ownership percentage	13.80%
Accounts due from related parties	$ 2,496
Vifor International Ltd. [Member] | Commercial Supply Revenue
Related Party Transaction [Line Items]
Revenue from related parties	$ 4,790

Subsequent Events (Details)

Subsequent Events (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Apr. 30, 2022	Mar. 31, 2022	Mar. 31, 2021
Subsequent Event [Line Items]
Revenue from contract with customer		$ 4,790	$ 1,935
License and Milestone Fees
Subsequent Event [Line Items]
Revenue from contract with customer			$ 1,192
Subsequent Event [Member] | License and Milestone Fees | VFMCRP Agreement [Member]
Subsequent Event [Line Items]
Revenue from contract with customer	$ 15,000