Cara Therapeutics (CARA) 10-K 6 Mar 23 2022 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2022	Mar. 02, 2023	Jun. 30, 2022
Document And Entity Information [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 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 Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 416,562,477
Entity Common Stock, Shares Outstanding		53,943,353
Auditor Name	Ernst & Young LLP
Auditor Firm ID	42
Auditor Location	Stamford, Connecticut
Entity Central Index Key	0001346830
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	FY
Amendment Flag	false

BALANCE SHEETS

BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 63,741	$ 13,453
Marketable securities	81,658	153,582
Accounts receivable, net - related party	3,260
Inventory, net	2,383	2,584
Income tax receivable	697	697
Other receivables	496	455
Prepaid expenses	16,267	2,519
Restricted cash	408
Total current assets	168,910	173,290
Operating lease right-of-use assets	1,551	2,973
Marketable securities, non-current	11,350	69,754
Property and equipment, net	426	631
Restricted cash, non-current		408
Total assets	182,237	247,056
Current liabilities:
Accounts payable and accrued expenses	21,540	15,861
Operating lease liabilities, current	1,918	1,755
Total current liabilities	23,458	17,616
Operating lease liabilities, non-current		1,918
Commitments and contingencies (Note 18)
Stockholders' equity:
Preferred stock; $0.001 par value; 5,000,000 shares authorized at December 31, 2022 and December 31, 2021, zero shares issued and outstanding at December 31, 2022 and December 31, 2021
Common stock; $0.001 par value; 100,000,000 shares authorized at December 31, 2022 and December 31, 2021, 53,797,341 shares and 53,480,812 shares issued and outstanding at December 31, 2022 and December 31, 2021, respectively	53	53
Additional paid-in capital	726,630	708,585
Accumulated deficit	(566,232)	(480,758)
Accumulated other comprehensive loss	(1,672)	(358)
Total stockholders' equity	158,779	227,522
Total liabilities and stockholders' equity	$ 182,237	$ 247,056

BALANCE SHEETS (Parenthetical)

BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2022	Dec. 31, 2021
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	53,797,341	53,480,812
Common stock, shares outstanding	53,797,341	53,480,812

STATEMENTS OF COMPREHENSIVE (LO

STATEMENTS OF COMPREHENSIVE (LOSS) INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Revenue:
Total revenue	$ 41,867	$ 23,028	$ 135,082
Operating expenses:
Cost of goods sold	7,266
Research and development	91,879	82,701	107,851
General and administrative	30,257	29,410	21,846
Total operating expenses	129,402	112,111	129,697
Operating (loss) income	(87,535)	(89,083)	5,385
Other income, net	2,061	642	2,334
(Loss) income before income tax benefit	(85,474)	(88,441)	7,719
Income tax benefit	0	0	691
Net (loss) income	$ (85,474)	$ (88,441)	$ 8,410
Net (loss) income per share:
Basic	$ (1.59)	$ (1.74)	$ 0.18
Diluted	$ (1.59)	$ (1.74)	$ 0.18
Weighted average shares:
Basic	53,653,564	50,718,765	47,413,250
Diluted	53,653,564	50,718,765	47,915,030
Other comprehensive loss, net of tax of $0:
Change in unrealized losses on available-for-sale marketable securities	$ (1,314)	$ (431)	$ (97)
Total comprehensive (loss) income	(86,788)	(88,872)	8,313
Collaborative Revenue
Revenue:
Total revenue	16,572	706
License and Milestone Fees
Revenue:
Total revenue	15,000	21,223	134,439
Commercial Supply Revenue
Revenue:
Total revenue	10,223	701
Clinical Compound Revenue
Revenue:
Total revenue		$ 398	$ 643
Royalty Revenue
Revenue:
Total revenue	$ 72

STATEMENTS OF COMPREHENSIVE (_2

STATEMENTS OF COMPREHENSIVE (LOSS) INCOME (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
STATEMENTS OF COMPREHENSIVE (LOSS) INCOME
Other comprehensive loss, net of tax	$ 0	$ 0	$ 0

STATEMENTS OF STOCKHOLDERS' EQU

STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive (Loss) Income.	Total
Balance, Value at Dec. 31, 2019	$ 47	$ 587,223	$ (400,727)	$ 170	$ 186,713
Balance, Shares at Dec. 31, 2019	46,720,225
Sale of common stock under license agreement with Vifor International, value	$ 3	38,446			38,449
Sale of common stock under license agreement with Vifor International, shares	2,939,552
Stock-based compensation expense		12,486			12,486
Shares issued upon exercise of stock options, value		691			691
Shares issued upon exercise of stock options, shares	55,852
Shares issued upon vesting of restricted stock units, value		2,349			2,349
Shares issued upon vesting of restricted stock units, shares	156,584
Net income (loss)			8,410		8,410
Other comprehensive loss				(97)	(97)
Balance, Value at Dec. 31, 2020	$ 50	641,195	(392,317)	73	249,001
Balance, Shares at Dec. 31, 2020	49,872,213
Sale of common stock under license agreement with Vifor International, value	$ 3	44,966			44,969
Sale of common stock under license agreement with Vifor International, shares	3,282,391
Stock-based compensation expense		17,850			17,850
Shares issued upon exercise of stock options, value		1,639			1,639
Shares issued upon exercise of stock options, shares	136,787
Shares issued upon vesting of restricted stock units, value		2,935			2,935
Shares issued upon vesting of restricted stock units, shares	189,421
Net income (loss)			(88,441)		(88,441)
Other comprehensive loss				(431)	(431)
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		14,345			14,345
Shares issued upon exercise of stock options, value		311			$ 311
Shares issued upon exercise of stock options, shares	48,307				48,307
Shares issued upon vesting of restricted stock units, value		3,389			$ 3,389
Shares issued upon vesting of restricted stock units, shares	268,222
Net income (loss)			(85,474)		(85,474)
Other comprehensive loss				(1,314)	(1,314)
Balance, Value at Dec. 31, 2022	$ 53	$ 726,630	$ (566,232)	$ (1,672)	$ 158,779
Balance, Shares at Dec. 31, 2022	53,797,341

STATEMENTS OF STOCKHOLDERS' E_2

STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) - $ / shares	Dec. 31, 2021	Dec. 31, 2020
License Agreements [Member] | Vifor International Ltd. [Member]
Price per share	$ 15.23	$ 17.0094

STATEMENTS OF CASH FLOWS

STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Operating activities
Net (loss) income	$ (85,474)	$ (88,441)	$ 8,410
Adjustments to reconcile net (loss) income to net cash used in operating activities:
Stock-based compensation expense	17,734	20,785	14,835
Depreciation and amortization	248	248	209
Amortization expense component of lease expense	1,422	1,306	806
Amortization of available-for-sale marketable securities, net	264	861	154
Realized gain on sale of available-for-sale marketable securities		(39)	(272)
Realized gain on sale of property and equipment	0	(70)	0
Deferred revenue			(22,262)
Changes in operating assets and liabilities:
Accounts receivable, net - related party	(3,260)
Inventory, net	201	(2,584)
Income tax receivable		810	(691)
Other receivables	(41)	102	414
Prepaid expenses	(13,748)	9,557	(3,213)
Accounts payable and accrued expenses	5,679	(1,020)	(2,784)
Operating lease liabilities	(1,755)	(1,602)	(1,093)
Net cash used in operating activities	(78,730)	(60,087)	(5,487)
Investing activities
Proceeds from maturities of available-for-sale marketable securities	220,435	173,484	144,320
Proceeds from redemptions of available-for-sale marketable securities, at par	4,000	20,500	27,035
Proceeds from sale of available-for-sale marketable securities	0	10,029	41,600
Purchases of available-for-sale marketable securities	(95,685)	(208,795)	(232,881)
Purchases of property and equipment	(43)	(39)	(349)
Proceeds from sale of property and equipment		70
Net cash provided by (used in) investing activities	128,707	(4,751)	(20,275)
Financing activities
Proceeds from the exercise of stock options	311	1,639	691
Proceeds from the sale of common stock under license agreement with Vifor International		44,969	38,449
Net cash provided by financing activities	311	46,608	39,140
Net increase (decrease) in cash, cash equivalents and restricted cash	50,288	(18,230)	13,378
Cash, cash equivalents and restricted cash at beginning of period	13,861	32,091	18,713
Cash, cash equivalents and restricted cash at end of period	$ 64,149	$ 13,861	$ 32,091

Business

Business	12 Months Ended
	Dec. 31, 2022
Business.
Business	1. Business Cara Therapeutics, Inc., or the Company, is a 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 studies and clinical trials of difelikefalin-based product candidates, and raising capital. In August 2021, the Company received U.S. Food and Drug Administration, or FDA, approval for KORSUVA ® ​ In April 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 approved Kapruvia for use in all member states of the European Union, or EU, as well as Iceland, Liechtenstein, and Norway. Kapruvia was also approved in the United Kingdom in April 2022. Commercial launches in Austria, Germany, Sweden, and Denmark have commenced, with the remaining EU countries to launch in 2023. In August 2022, as part of the Access Consortium, difelikefalin injection was approved in Switzerland under the brand name Kapruvia, as well as Singapore and Canada under the brand name KORSUVA. In November 2022, difelikefalin injection was approved in the last Access Consortium country, Australia, under the brand name KORSUVA. In 2018, the Company entered into a licensing and collaboration agreement with a joint venture between Vifor Pharma Group and Fresenius Medical Care Renal Pharmaceutical Ltd., or Vifor Fresenius Medical Care Renal Pharma Ltd., that provides full commercialization rights of Kapruvia, and where applicable KORSUVA, to Vifor Fresenius Medical Care Renal Pharma Ltd. worldwide (excluding the United States, Japan, and South Korea). In markets outside of the United States, the Company is eligible to receive tiered double-digit royalty payments based on annual net sales, as defined in the agreement with Vifor Fresenius Medical Care Renal Pharma Ltd., of difelikefalin injection in the licensed territories. In the U.S. market, the agreement with Vifor Fresenius Medical Care Renal Pharma Ltd. provides that Vifor Fresenius Medical Care Renal Pharma Ltd. will promote difelikefalin injection in the dialysis clinics of Fresenius Medical Care North America, or FMCNA, under a profit-sharing arrangement, whereby the Company is generally entitled to 50% of the annual net profits (as defined in the agreement with Vifor Fresenius Medical Care Renal Pharma Ltd.) based on net FMCNA clinic sales (as defined in the agreement with Vifor Fresenius Medical Care Renal Pharma Ltd.) and Vifor Fresenius Medical Care Renal Pharma Ltd. is entitled to 50% of such net profits, subject to potential adjustments in a calendar year based on certain conditions (see Note 12, Collaboration and Licensing Agreements ​ In 2020, the Company entered into a second licensing and collaboration agreement, along with stock purchase agreements, with Vifor (International) Ltd., or Vifor International, that provides full commercialization rights of KORSUVA injection to Vifor International in dialysis clinics in the United States under a profit-sharing arrangement, whereby total net sales of KORSUVA injection in the United States, as recorded by Vifor International, are reduced by Vifor International’s cost of goods sold, or COGS, as well as a marketing and distribution fee owed by the Company based on the level of annual net sales, and the resulting amount was to be shared according to a 60% (Company)/40% (Vifor International) profit split (excluding sales to Fresenius Medical Center dialysis clinics, compensation for which is governed by the agreement with Vifor Fresenius Medical Care Renal Pharma Ltd.), subject to potential temporary adjustment in future years based on certain conditions (see Note 12, Collaboration and Licensing Agreements ​ In May 2022, Vifor International assigned its rights and obligations under the license agreement and a supply agreement, as permitted under the agreements, to Vifor Fresenius Medical Care Renal Pharma Ltd. The Company’s rights and obligations under these agreements were unaffected by this assignment, and the assignment did not affect the Company’s economic rights under the agreements with Vifor International. ​ In August 2022, Vifor Pharma Group (which includes Vifor International) was acquired by CSL Limited and subsequently renamed CSL Vifor as part of the acquisition. The acquisition of Vifor Pharma Group did not affect any of the Company’s rights and obligations pursuant to these agreements. ​ The Company also has a license agreement with Maruishi Pharmaceutical Co. Ltd., or Maruishi, 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. In September 2022, Maruishi submitted a New Drug Application in Japan for approval of difelikefalin injection for the treatment of pruritus in hemodialysis patients (see Note 12, Collaboration and Licensing Agreements) As of December 31, 2022, the Company has 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. Including profit share revenue and royalties, the Company has also earned approximately $266,790 under its license and supply agreements for difelikefalin, primarily with CSL Vifor, 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 International 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 International in connection with the Company’s license agreement with Vifor International. 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 International in connection with the Company’s license agreement with CSL Vifor (see Notes 10, Shareholders’ Equity Collaboration and Licensing Agreements As of December 31, 2022, the Company had unrestricted cash and cash equivalents and marketable securities of $156,749 and an accumulated deficit of $566,232. 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 $85,474 and $88,441 for the years ended December 31, 2022 and 2021, respectively, and recognized net income of $8,410 for the year ended December 31, 2020. The Company had net cash used in operating activities of $78,730, $60,087, and $5,487 for the years ended December 31, 2022, 2021 and 2020, respectively. The Company is subject to risks common to other life science companies including, but not limited to, uncertainty of product development and commercialization, lack of marketing and sales history, development by its competitors of new technological innovations, dependence on key personnel, market acceptance of products, product liability, protection of proprietary technology, ability to raise additional financing, and compliance with FDA and other government regulations. If the Company does not successfully commercialize KORSUVA injection, Kapruvia or any of its other product candidates, it will be unable to generate additional recurring product revenue or achieve profitability.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2022
Business
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Use of Estimates The preparation of financial statements in conformity with generally-accepted accounting principles in the United States, or 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, related party accounts receivable reserve, as applicable, inventory valuation and related reserves, research and development, or R&D, clinical costs and accrued research projects included in prepaid expenses and accounts payable and accrued expenses, 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 COVID-19 pandemic and geopolitical tensions, such as Russia’s incursion into Ukraine, resulted in a global slowdown of economic activity, decades-high inflation, rising interest rates, and a potential recession in the United States. 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 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 financial statements as soon as they become known. Actual results could differ materially from the Company’s estimates and assumptions. Concentration of Credit Risk The Company’s financial instruments, which potentially subject the Company to significant concentrations of credit risk consist primarily of cash and cash equivalents, marketable securities, and related party accounts receivable. The Company invests its cash reserves in money market funds or high-quality marketable securities in accordance with its investment policy. The stated objectives of its investment policy are to preserve capital, provide liquidity consistent with forecasted cash flow requirements, maintain appropriate diversification and generate returns relative to these investment objectives and prevailing market conditions. The Company’s investment policy includes guidelines on acceptable investment securities, limits interest-bearing security investments to certain types of debt and money market instruments issued by the U.S. government and institutions with investment grade credit ratings and places restrictions on maturities and concentration by asset class and issuer. The Company’s cash and cash equivalents and marketable securities are held by three major financial institutions. In accordance with the Company’s policies, the Company monitors exposure with its counterparties. The Company also maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and management believes that the Company is not exposed to significant credit risk due to the financial position of the depository institutions in which those deposits are held. The percentages of revenue recognized from license agreement partners of the Company in the years ended December 31, 2022, 2021 and 2020 are included in the following table: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenue ​ ​ Year Ended December 31, ​ 2022 2021 2020 License Agreement Partner: ​ CSL Vifor* 100 % 92 % 100 % ______________ * Includes amounts earned from Vifor Fresenius Medical Care Renal Pharma Ltd. and Vifor International prior to Vifor International’s assignment of its rights and obligations to Vifor Fresenius Medical Care Renal Pharma Ltd. in May 2022. ​ For the years ended December 31, 2022, 2021 and 2020, no additional license agreement partners or customers accounted for more than 10% of the Company’s revenue. Concentration of Suppliers The Company relies on three suppliers to manufacture KORSUVA injection active pharmaceutical ingredient, or API, finished drug product, and finished goods. If any of the Company’s suppliers were to limit or terminate production or otherwise fail to meet the quality or delivery requirements to satisfy the supply commitments, the process of locating and qualifying alternate sources would require up to two years, during which time production could be delayed. Such delays could have a material adverse effect on the Company’s business, financial position, and results of operations. Cash and Cash Equivalents Cash and cash equivalents include cash on hand, demand deposits, deposits with banks and highly liquid money market funds with holdings of cash and other investments with original maturities of three months or less. Marketable Securities The Company deems certain of its investments to be marketable securities if the investment, or in the case of money market funds, the securities underlying the money market fund, meet the definition of a debt security. The Company’s investments in marketable securities, including U.S. Treasury securities, U.S. government agency obligations, corporate bonds, commercial paper, and municipal bonds are highly rated by Moody’s and S&P and have maturities primarily of less than one year but no longer than two years as of December 31, 2022. Accordingly, credit risk associated with the Company’s available-for-sale debt security portfolio is mitigated. The Company reviews each of its available-for-sale marketable securities for unrealized losses (declines in fair value below its amortized cost basis) at each balance sheet date presented in its financial statements and whenever events or changes in circumstances indicate that the amortized cost basis of an asset may not be recoverable. The Company determines whether any portion of the unrealized loss for any available-for-sale debt security is due to a credit loss, and if so, measures the amount of the credit loss. ​ The Company relies on both qualitative and quantitative factors to determine whether the unrealized loss for each available-for-sale debt security at any balance sheet date is due to a credit loss. Qualitative factors may include a credit downgrade, severity of the decline in fair value below amortized cost and other adverse conditions related specifically to the security, as well as the intent to sell the security, or whether the Company will “more likely than not” be required to sell the security before recovery of its amortized cost basis. The Company’s assessment of whether a security is impaired could change in the future due to new developments or changes in assumptions related to any particular security. If material qualitative factors indicate that a credit loss has occurred, the Company will determine the magnitude of that credit loss using a discounted cash flow model or other quantitative method. If the Company intends to sell the security or it is “more likely than not” that the Company will be forced to sell the security before recovery of the amortized cost of the security, the entire unrealized loss is deemed to be a credit loss, which is recognized in net (loss) income. Otherwise, the portion of the unrealized loss that is due to a credit loss will be recorded as an allowance for credit loss, which will offset the balance of marketable securities and as credit loss expense within other income, net. The portion of the unrealized loss that is not due to a credit loss as well as all unrealized gains will be recorded in Accumulated Other Comprehensive (Loss) Income (see Note 3, Available-for-Sale Marketable Securities Fair Value Measurements) ​ Accrued interest receivables are excluded from the Company’s amortized cost bases for its available-for-sale marketable securities and are included within other receivables. The Company’s policy is to not measure an allowance for credit losses on accrued interest receivable balances at each reporting period since it elects to write off uncollectible accrued interest receivable balances as credit loss expense in a timely manner, which is by maturity date for all categories of its debt securities. Fair Value of Financial Instruments The Company applies fair value accounting for all financial assets and liabilities that are recognized or disclosed at fair value in the financial statements on a recurring basis. The Company defines fair value as the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. When determining the fair value measurements for assets and liabilities which are required to be recorded at fair value, the Company considers the principal or most advantageous market in which it would transact and the market-based risk measurements or assumptions that market participants would use in pricing the asset or liability, such as risks inherent in valuation techniques, transfer restrictions and credit risks. The Company’s financial instruments consist of cash, cash equivalents, available-for-sale marketable securities, accounts receivable, net – related party, prepaid expenses, restricted cash, accounts payable and accrued liabilities. The fair values of cash, cash equivalents, accounts receivable, net – related party, prepaid expenses, restricted cash, accounts payable and accrued liabilities approximate their carrying values due to the short-term nature of these financial instruments. Available-for-sale marketable securities are reported at their fair values, based upon pricing of securities with the same or similar investment characteristics as provided by third-party pricing services, as described below. The valuation techniques used by the Company are based on observable and unobservable inputs. Observable inputs reflect readily obtainable data from independent sources, while unobservable inputs reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability and are developed based on the best information available in the circumstances. The Company classifies its investments in a fair value hierarchy that is intended to increase consistency and comparability in fair value measurements and related disclosures. The fair value hierarchy is divided into three levels based on the source of inputs as follows: ● Level 1 – Observable inputs – quoted prices in active markets for identical assets and liabilities. ● Level 2 – Observable inputs other than the quoted prices in active markets for identical assets and liabilities – such as quoted prices for similar instruments, quoted prices for identical or similar instruments in inactive markets, or other inputs that are observable or can be corroborated by observable market data. ● Level 3 – Unobservable inputs – includes amounts derived from valuation models where one or more significant inputs are unobservable and require the Company to develop relevant assumptions. The Company records transfers between levels in the hierarchy by assuming that the transfer occurred at the end of the quarter or year-to-date period. Valuation Techniques - Level 2 Inputs The Company estimates the fair values of its financial instruments categorized as level 2 in the fair value hierarchy, including U.S. Treasury securities, U.S. government agency obligations, corporate bonds, commercial paper and municipal bonds, by taking into consideration valuations obtained from third-party pricing services. The pricing services use industry standard valuation models, including both income- and market-based approaches, for which all significant inputs are observable, either directly or indirectly, to estimate fair value. These inputs include reported trades of and broker/dealer quotes on the same or similar securities, benchmark yields, issuer credit spreads, benchmark securities, and other observable inputs. The Company obtains a single price for each financial instrument and does not adjust the prices obtained from the pricing service. The Company validates the prices provided by its third-party pricing services by reviewing their pricing methods, obtaining market values from other pricing sources and comparing them to the share prices presented by the third-party pricing services. After completing its validation procedures, the Company did not adjust or override any fair value measurements provided by its pricing services as of December 31, 2022 or December 31, 2021. Accounts Receivable, Net – Related Party Accounts receivable, net – related party primarily consists of amounts due from sales of KORSUVA injection under the Company’s supply agreements with CSL Vifor, as well as revenues earned from its share of the profit generated from KORSUVA injection sales in the United States under the licensing agreements with CSL 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, CSL 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 an insignificant allowance for credit losses as of December 31, 2022. Inventory, net Inventories are stated at the lower of cost or net realizable value. The Company determines the cost of inventory using first-in, first-out, or FIFO, method. The Company capitalizes inventory costs associated with the Company’s products prior to regulatory approval, when, based on management’s judgment, future commercialization is considered probable and the future economic benefit is expected to be realized; otherwise, such costs are expensed. The determination to capitalize inventory costs is based on various factors, including status and expectations of the regulatory approval process, any known safety or efficacy concerns, potential labeling restrictions, and any other impediments to obtaining regulatory approval. As KORSUVA injection is the Company’s first commercial product and probability could not be established prior to regulatory approval on August 23, 2021, all inventory costs prior to regulatory approval were expensed as incurred. The Company periodically analyzes its inventory levels to identify inventory that may expire prior to expected sale or has a cost basis in excess of its estimated realizable value and writes down such inventories as appropriate. In addition, the Company’s products are subject to strict quality control and monitoring which the Company performs throughout the manufacturing process. If certain batches or units of product no longer meet quality specifications or become obsolete due to expiration, the Company records a charge to write down such unmarketable inventory to its estimated realizable value. Property and Equipment, net Property and equipment (consisting of computer and office equipment, furniture and fixtures and leasehold improvements) are stated at cost, net of accumulated depreciation and amortization of leasehold improvements. Depreciation and amortization are calculated using the straight-line method over the estimated useful lives of the respective assets. Leasehold improvements are amortized over the lesser of their useful lives or the life of the lease. ​ ​ ​ Asset Category Useful Lives Computer and office equipment 5 years Furniture and fixtures 7 years Leasehold improvements lesser of useful life of asset or life of lease (Stamford - 7 years) ​ The Company reviews the recorded values of property and equipment for impairment whenever events or changes in business circumstances indicate that the carrying amount of an asset or group of assets may not be fully recoverable. Leases The Company has two leases, a lease agreement for office space in Stamford, Connecticut, or the Stamford Lease, and an amendment to the Stamford Lease to add additional office space, or the Lease Amendment, which is included in operating lease right-of-use assets, or ROU assets, operating lease liabilities – current and operating lease liabilities – non-current as of December 31, 2022 and 2021 (see Note 18, Commitments and Contingencies: Leases In general, the Company determines if a contract, at its inception, is a lease or contains a lease based on whether the contract conveys the right to control the use of identified property, plant, or equipment (an identified asset) for a period of time in exchange for consideration. To determine whether a contract conveys the right to control the use of an identified asset for a period of time, the Company assesses whether, throughout the period of use, it has both the right to obtain substantially all of the economic benefits from use of the identified asset, and the right to direct the use of the identified asset. Both of these criteria are met by the Stamford Lease. The Company determines the amount of the operating lease liability based on the present value of the future minimum lease payments over the remaining lease term. The amount of the operating lease ROU asset is equal to the amount of the lease liability, less accrued rent and lease incentives received from the landlord. Initial direct costs were deemed to be immaterial. Since the Stamford Lease does not provide an implicit interest rate, the Company used an annual incremental borrowing rate of 7% based on the information available at the date of adoption for the purpose of determining the lease liability during the term of the lease. The Stamford Lease contains both a lease and non-lease component which are accounted for separately. The Company allocates the consideration to the lease and the non-lease component on a relative standalone price basis. Lease expense is recognized on a straight-line basis over the lease term. In June 2020, the Company entered into the Lease Amendment. The term of the Lease Amendment began when renovation of the additional space was completed and the Company took possession of the additional space in October 2020, or the Amendment Commencement Date, and ends on December 31, 2023. The Lease Amendment is also renewable for one five-year term, although this renewable period is not included as part of the lease term since it is not reasonably certain that the Company will exercise that option. The Lease Amendment contains both a lease and non-lease component which are accounted for separately. The Company allocates the consideration to the lease and non-lease component on a relative standalone price basis. The rent for the Lease Amendment is at market rate as of the signing of the Lease Amendment. The Lease Amendment requires monthly lease payments, including rent escalations, during the lease term. The Company began paying rent for the Lease Amendment on the Amendment Commencement Date. The Company accounted for the terms and conditions of the Lease Amendment as a lease modification because it grants an additional right-of-use to an underlying asset (the new additional space). A lease modification can result in either a new lease that is accounted for separately from the original lease or as a single modified lease. The Lease Amendment is accounted for separately from the original Stamford Lease because the Lease Amendment grants the right-of-use to additional space and the price of the additional right-of-use is commensurate with its standalone price as no discounts were provided to the Company. Furthermore, there were no material changes to the original Stamford Lease. As of the Amendment Commencement Date, the Company recorded the lease liability for the Lease Amendment as the sum of the present value of the future minimum lease payments over the term for the new lease. Since the Lease Amendment does not provide an implicit interest rate, the Company used an incremental borrowing rate of 7%, which is based on the rate that the Company could obtain in the market for a fully collateralized loan equal to the term of the Lease Amendment. The Company also recorded a ROU asset equal to the amount of the lease liability, as no lease incentives were identified in the Lease Amendment. During the term of the Lease Amendment, interest expense is calculated using the effective interest method and the ROU asset is amortized on a straight-line basis over the lease term, and both are recorded as lease expense. Revenue Recognition The Company recognizes revenue in an amount that reflects the consideration to which it expects to be entitled in exchange for the transfer of promised goods or services to customers. To determine revenue recognition for contracts with customers, the Company performs the following steps: (1) identifies the contract with the customer, (2) identifies the performance obligations in the contract, (3) determines the transaction price, (4) allocates the transaction price to the performance obligations in the contract, and (5) recognizes revenue when (or as) the entity satisfies a performance obligation. The Company has entered into agreements to license its intellectual property, or IP, related to difelikefalin to develop, manufacture and/or commercialize drug products. These agreements typically contain multiple performance obligations, including licenses of IP and R&D services. Payments to the Company under these agreements may include nonrefundable license fees, payments for research activities, payments based upon the achievement of certain milestones and royalties on any resulting net product sales. The Company receives its share of the net profits from the sale of KORSUVA injection in the United States through its license agreement with CSL Vifor. The Company has adopted a policy to recognize revenue net of tax withholdings, as applicable. The Company identifies agreements as contracts that create enforceable rights and obligations when the agreement is approved by the parties, identifies the rights of the parties and the payment terms, has commercial substance and it is probable that the Company will collect the consideration to which it will be entitled in exchange for the goods and services that will be transferred to the customer. The counterparty is considered to be a customer when it has contracted with the Company to obtain goods and services that are the output of the Company’s ordinary activities (i.e., development of pharmaceutical products) in exchange for consideration. A performance obligation is a promise to transfer distinct goods or services to a customer. Performance obligations that are both capable of being distinct and distinct within the context of the contract are considered to be separate performance obligations. Performance obligations are capable of being distinct if the counterparty is able to benefit from the good or service on its own or together with other resources that are readily available to it. Performance obligations are distinct within the context of the contract when each performance obligation is separately identifiable from each other; i.e., the Company is not using the goods or services as inputs to produce or deliver the combined output or outputs specified by the customer; one or more of the goods or services does not significantly modify or customize one of the other goods or services in the contract; and goods or services are not highly interdependent or not highly interrelated. Performance obligations that are not distinct are accounted for as a single performance obligation over the period that goods or services are transferred to the customer. The determination of whether performance obligations in a contract are distinct may require significant judgment. The transaction price is the amount of consideration that the Company expects to be entitled to in exchange for transferring promised goods or services to the customer based on the contract terms at inception of a contract. There is a constraint on inclusion of variable consideration related to licenses of IP, such as milestone payments or sales-based royalty payments, in the transaction price if there is uncertainty at inception of the contract as to whether such consideration will be recognized in the future because it is probable that there will be a significant reversal of revenue in the future when the uncertainty is resolved. The determination of whether or not it is probable that a significant reversal of revenue will occur in the future depends on the likelihood and magnitude of the reversal. Factors that could increase the likelihood or magnitude of a reversal of revenue include (a) the susceptibility of the amount of consideration to factors outside the entity’s influence, such as the outcome of clinical trials, the timing of initiation of clinical trials by the counterparty and the approval of drug product candidates by regulatory agencies, (b) situations in which the uncertainty is not expected to be resolved for a long period of time, and (c) level of the Company’s experience in the field. When it becomes probable that events will occur, for which variable consideration was constrained at inception of the contract, the Company allocates the related consideration to the separate performance obligations in the same manner as described below. At inception of a contract, the Company allocates the transaction price to the distinct performance obligations based upon their relative standalone selling prices. Standalone selling price is the price at which an entity would sell a promised good or service separately to a customer. The best evidence of standalone selling price is an observable price of a good or service when sold separately by an entity in similar circumstances to similar customers. Since the Company typically does not have such evidence, it estimates standalone selling price so that the amount that is allocated to each performance obligation equals the amount that the Company expects to receive for transferring goods or services. The methods that the Company uses to make such estimates include (1) the adjusted market assessment approach, under which the Company forecasts and analyzes difelikefalin in the appropriate market, the phase of clinical development as well as considering recent similar license arrangements within the same phase of clinical development, therapeutic area, type of agreement, etc. and (2) the expected cost of satisfying the performance obligations plus a margin, or the expected cost plus a margin approach. The Company recognizes revenue when, or as, it satisfies a performance obligation by transferring a promised good or service to a customer and the customer obtains control of the good or service. Revenue related to the grant of a license that is a distinct performance obligation and that is deemed to be functional IP is recognized at the point in time that the Company has the right to payment for the license, the customer has legal title to the license and can direct the use of the license (for example, to grant sublicenses), the customer has the significant risks and rewards of ownership of the license and the customer has accepted the asset (license) by signing the license agreement. Recognition of revenue related to R&D services that are a distinct performance obligation or that are combined with granting of a license as a single performance obligation is deferred at inception of a contract and is recognized as those services are performed based on the costs incurred as a percentage of the estimated total costs to be incurred to complete the performance obligation. The Company’s license agreements include the right to grant sub-licenses. The amount of any potential sub-license fees to be received by the Company, which is based on a formula if applicable to that respective agreement, 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. Milestone payments are considered to be variable consideration and are not included in the transaction price at inception of the contract if it is uncertain that the milestone will be achieved. Rather, when it becomes probable that the milestone will be achieved and, therefore, there will not be a significant reversal of revenue in future periods, the respective amount to be earned is included in the transaction price, allocated to the distinct performance obligations based on their relative standalone selling price and recognized as revenue, as described above. Sales milestones and sales-based royalty payments related to a license of IP are recognized as revenue when the respective sales occur. Collaborative Revenue Collaborative revenue includes the Company’s share of the profits generated by CSL Vifor’s sale of KORSUVA injection to third parties in the United States under its existing license agreements. The Company has adopted a policy to recognize revenue net of tax withholdings, as applicable. The Company determined that CSL Vifor is a customer in relation to its profit share arrangement with CSL Vifor. The Company sells commercial product to CSL Vifor, who ultimately sells the commercial product to third parties. The Company’s profit share arrangement revenues generated from sales of KORSUVA injection in the United States are considered akin to sales-based royalties. In accordance with the sales-based royalty exception, the Company recognizes its share of the pre-tax commercial net profit generated from the sales of KORSUVA injection in the United States in the period the product sales are earned, as reported by CSL Vifor. The related COGS for CSL Vifor associated with the net profit share arrangement as well as the marketing and distribution fee for the applicable period reduces the Company’s profit share revenue for the period. The net sales amounts are determined based on amounts provided by CSL Vifor and involve the use of estimates and judgments, such as product sales allowances and accruals related to prompt payment discounts, and chargebacks, which could be adjusted based on actual results in the future. The Company is dependent on CSL Vifor for timely and accurate information regarding the net revenues from sales of KORSUVA injection in the United States to accurately report its results of operations. If the Company does not receive timely and accurate information or incorrectly estimates activity levels associated with the profit share arrangement at a given point in time, the Company could be required to record adjustments in future periods. The Company records revenue transactions as net product revenue if it is deemed the principal in the transaction, which includes being the primary obligor, retaining inventory risk, and control over pricing. Given that the Company is not the primary obligor and does not have the inventory risks in the license agreement with CSL Vifor, it records its share of the net profits from the sales of KORSUVA injection in the United States on a net basis and presents the settlement payments from CSL Vifor as collaborative revenue. The Company and CSL Vifor settle the profit sharing quarterly (see Note 12, Collaboration and Licensing Agreements) Collaborative revenue also includes milestone payments associated with the Company’s license agreement with Maruishi. Upfront and milestone payments associated with the license agreement with Maruishi are allocated between license and milestone fees and collaborative revenue based on the relative standalone selling prices determined at contract inception that were allocated to the R&D services performance obligation (see Note 13, Revenue Recognition License and Mil

Available-for-Sale Marketable S

Available-for-Sale Marketable Securities	12 Months Ended
	Dec. 31, 2022
Available-for-Sale Marketable Securities
Available-for-Sale Marketable Securities	3. Available-for-Sale Marketable Securities As of December 31, 2022 and 2021, the Company’s available-for-sale marketable securities consisted of debt securities issued by U.S. government-sponsored entities and investment grade institutions as well as municipal bonds. As of December 31, 2021, the Company’s available-for-sale marketable securities also consisted of debt securities issued by the U.S. Treasury. The following tables summarize the Company’s available-for-sale marketable securities by major type of security as of December 31, 2022 and 2021: As of December 31, 2022 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross Unrealized ​ Estimated Fair Type of Security Amortized Cost Gains Losses Value U.S. government agency obligations ​ $ 9,500 ​ $ — ​ $ (623) ​ $ 8,877 Corporate bonds ​ 35,828 ​ — ​ (643) ​ 35,185 Commercial paper ​ ​ 26,879 ​ ​ 2 ​ ​ (6) ​ ​ 26,875 Municipal bonds ​ 22,473 ​ — ​ (402) ​ 22,071 Total available-for-sale marketable securities ​ $ 94,680 ​ $ 2 ​ $ (1,674) ​ $ 93,008 ​ 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 December 31, 2022 and 2021: As of December 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. government agency obligations ​ $ — ​ $ — ​ $ 8,877 ​ $ (623) ​ $ 8,877 ​ $ (623) Corporate bonds ​ ​ 1,470 ​ ​ (26) ​ ​ 33,715 ​ ​ (617) ​ ​ 35,185 ​ ​ (643) Commercial paper ​ ​ 15,906 ​ ​ (6) ​ ​ — ​ ​ — ​ ​ 15,906 ​ ​ (6) Municipal bonds ​ 982 ​ (16) ​ 19,589 ​ (386) ​ 20,571 ​ (402) Total ​ $ 18,358 ​ $ (48) ​ $ 62,181 ​ $ (1,626) ​ $ 80,539 ​ $ (1,674) ​ 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 December 31, 2022 and 2021, respectively, 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 for the following categories of securities is as follows: ​ As of December 31, 2022 and 2021, the Company held a total of 35 out of 39 positions and 58 out of 76 positions, respectively, that were in an unrealized loss position, 28 of which had been in an unrealized loss position for 12 months or greater. Unrealized losses individually and in aggregate, including any in an unrealized loss position for 12 months or greater, were not considered to be material for each respective period. Based on the Company’s review of these securities, the Company believes that the cost basis of its available-for-sale marketable securities is recoverable. U.S. government agency obligations. Corporate bonds, commercial paper, and municipal bonds. The Company classifies its marketable debt securities based on their contractual maturity dates. As of December 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 December 31, 2022 ​ As of December 31, 2021 Contractual maturity Amortized Cost Fair Value Amortized Cost Fair Value Less than one year ​ $ 82,678 ​ $ 81,658 ​ $ 153,631 ​ $ 153,582 One year to three years ​ 12,002 ​ 11,350 ​ 70,063 ​ 69,754 Total ​ $ 94,680 ​ $ 93,008 ​ $ 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 year ended December 31, 2022. During the year ended December 31, 2021, the Company sold certain of its available-for-sale debt securities with a total fair value of $10,029, which resulted in realized gains of $39. During the year ended December 31, 2020, the Company sold certain of its available-for-sale debt securities with a total fair value of $41,600, which resulted in realized gains of $272. As of December 31, 2022 and 2021, accrued interest receivables on our available-for-sale debt securities were $489 and $455, respectively.

Accumulated Other Comprehensive

Accumulated Other Comprehensive (Loss) Income	12 Months Ended
	Dec. 31, 2022
Accumulated Other Comprehensive (Loss) Income
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 years ended December 31, 2022, 2021 and 2020. ​ ​ ​ ​ ​ Total Accumulated ​ ​ Other Comprehensive ​ ​ (Loss) Income Balance, December 31, 2019 ​ $ 170 Other comprehensive income before reclassifications ​ 175 Amount reclassified from accumulated other comprehensive income ​ (272) Net current period other comprehensive loss ​ (97) Balance, December 31, 2020 ​ 73 Other comprehensive loss before reclassifications ​ (392) Amount reclassified from accumulated other comprehensive income ​ (39) Net current period other comprehensive loss ​ (431) Balance, December 31, 2021 ​ $ (358) Other comprehensive loss before reclassifications ​ (1,314) Amount reclassified from accumulated other comprehensive loss ​ — Net current period other comprehensive loss ​ (1,314) Balance, December 31, 2022 ​ $ (1,672) ​ Amounts reclassified out of accumulated other comprehensive (loss) income into net (loss) income are determined by specific identification. The reclassifications out of accumulated other comprehensive (loss) income and into net (loss) income were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Affected Line Item in the Component of Accumulated Other ​ Year Ended December 31, ​ Statements of Comprehensive (Loss) Income 2022 2021 2020 Comprehensive (Loss) Income Unrealized gains on available-for-sale marketable securities: ​ ​ ​ Realized gains on sales of securities ​ $ — ​ $ 39 ​ $ 272 Other income, net Income tax effect ​ — ​ — ​ — Benefit from income taxes Realized gains on sales of securities, net of tax ​ $ — ​ $ 39 ​ $ 272 ​ ​ ​

Inventory, net

Inventory, net	12 Months Ended
	Dec. 31, 2022
Inventory, net
Inventory, net	5. Inventory, net Inventories consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2022 December 31, 2021 Raw materials ​ $ 1,918 ​ $ 927 Work-in-process ​ 499 ​ 1,657 ​ ​ ​ 2,417 ​ ​ 2,584 Less Inventory Reserve for Obsolescence ​ (34) ​ — Total ​ $ 2,383 ​ $ 2,584 ​ As of December 31, 2022 and December 31, 2021, inventory balances include inventory costs subsequent to regulatory approval of KORSUVA injection on August 23, 2021. During the year ended December 31, 2022, the Company wrote down $34 of commercial supply inventory due to obsolescence. There were no write-downs of commercial supply inventory during the year ended December 31, 2021.

Prepaid Expenses

Prepaid Expenses	12 Months Ended
	Dec. 31, 2022
Prepaid Expenses
Prepaid Expenses	6 As of December 31, 2022, the amount of prepaid expenses was $16,267, consisting of $15,188 of prepaid R&D clinical costs, $543 of prepaid insurance and $536 of other costs. As of December 31, 2021, the amount of prepaid expenses was $2,519, consisting of $1,481 of prepaid R&D clinical costs, $369 of prepaid insurance and $669 of other costs.

Property and Equipment, net

Property and Equipment, net	12 Months Ended
	Dec. 31, 2022
Property and Equipment, net
Property and Equipment, net	7. Property and Equipment, net Property and equipment, net consists of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2022 2021 Computer and office equipment ​ $ 239 ​ $ 239 Furniture and fixtures ​ 330 ​ 330 Leasehold improvements ​ 1,266 ​ 1,223 ​ ​ $ 1,835 ​ $ 1,792 Less accumulated depreciation and amortization ​ (1,409) ​ (1,161) Property and equipment, net ​ $ 426 ​ $ 631 ​ Depreciation and amortization expense included in R&D expense and G&A expense was $248, $248 and $209 for the years ended December 31, 2022, 2021 and 2020, respectively. During the year ended December 31, 2021, the Company sold laboratory equipment that was fully depreciated, which resulted in gains on sales of property and equipment of $70 . There were gains or losses on sales of property and equipment during the years ended December 31, 2022 and 2020.

Restricted Cash

Restricted Cash	12 Months Ended
	Dec. 31, 2022
Restricted Cash
Restricted Cash	8 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 18, Commitments and Contingencies: Leases As of December 31, 2022, the Company had $408 of restricted cash related to the Stamford lease in current assets. As of 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 Balance Sheets that sum to the total of the same such amounts shown in the Statements of Cash Flows. ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2022 December 31, 2021 Cash and cash equivalents ​ $ 63,741 ​ $ 13,453 Restricted cash, current assets ​ 408 ​ — Restricted cash, long-term assets ​ — ​ 408 Total cash, cash equivalents, and restricted cash shown in the Statements of Cash Flows ​ $ 64,149 ​ $ 13,861 ​

Accounts Payable and Accrued Ex

Accounts Payable and Accrued Expenses	12 Months Ended
	Dec. 31, 2022
Accounts Payable and Accrued Expenses
Accounts Payable and Accrued Expenses	9 Accounts payable and accrued expenses consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2022 December 31, 2021 Accounts payable ​ $ 9,604 ​ $ 5,625 Accrued research projects ​ 5,200 ​ 4,648 Accrued compensation and benefits ​ 5,219 ​ 4,959 Accrued professional fees and other ​ 1,517 ​ 629 Total ​ $ 21,540 ​ $ 15,861 ​

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2022
Stockholders' Equity
Stockholders' Equity	10. Stockholders’ Equity The Company’s Board of Directors has authorized 100,000,000 shares of the Company’s common stock, par value $0.001 per share, and 5,000,000 shares of undesignated preferred stock, par value $0.001 per share, that may be issued from time to time by the Board of Directors of the Company in one or more series. As of December 31, 2022, there were 53,797,341 shares of common issued outstanding Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are entitled to dividends when and if declared by the Board of Directors, subject to the preferential rights of the holders of preferred stock, if any. In December 2022, as a result of the achievement of certain performance targets, an aggregate of 26,204 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 October 2022, as a result of the completion of the first year of vesting associated with awards granted to the Company’s new Chief Executive Officer, or CEO, an aggregate of 35,500 restricted stock units vested and were settled in shares of the Company’s common stock (see Note 14, Stock-Based Compensation . In September 2022, as a result of the appointment of the Company’s new Chief Financial Officer, or CFO, 7,500 time-based restricted stock units held by the Company’s interim principal financial and accounting officer vested and were settled in shares of the Company’s common stock (see Note 14, Stock-Based Compensation In June 2022, as a result of the accelerated vesting of restricted stock units previously granted to the Company’s former CEO, an aggregate of 33,999 restricted stock units vested and were settled in shares of the Company’s common stock (see Note 14, Stock-Based Compensation ​ In June 2022, as a result of the completion of the one-year vesting period, an aggregate of 43,200 restricted stock units of members of the Board of Directors vested and were settled in shares of the Company’s common stock. Also in June 2022, the Company granted 11,876 fully vested restricted stock units, which were immediately settled in shares of common stock, to the Company’s chairman in consideration of his effort in connection with the Company’s CEO transition in 2021 (see Note 14, Stock-Based Compensation ​ 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 second tranche of restricted stock units granted to the new CEO 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 was declared effective on May 11, 2022. 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. 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, from time to time, issue and sell common stock with an aggregate value of up to $80,000 in an at-the-market offering pursuant to the Shelf Registration Statement. 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. No shares were sold under the Sales Agreement during the year ended December 31, 2022. The Company may offer additional securities under its Shelf Registration Statement 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. 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 October 2021, the Company issued 3,282,391 shares of its common stock to Vifor International in connection with the milestone earned for the U.S. regulatory approval of KORSUVA injection in August 2021 (see Note 12, Collaboration and Licensing Agreements ​ In August 2021, as a result of the achievement of certain performance targets, an aggregate of 44,002 performance-based restricted stock units of various executive officers vested and were settled in shares of the Company’s common stock (see Note 14, Stock-Based Compensation ​ In June 2021, as a result of the completion of the one-year vesting period, an aggregate of 36,000 restricted stock units of members of the Board of Directors vested and were settled in shares of the Company’s common stock (see Note 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 of various executive officers 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, an aggregate of 32,669 time-based restricted stock units of various executive officers vested and were settled in shares of the Company’s common stock (see Note 14, Stock-Based Compensation ​ In December 2020, as a result of the achievement of a performance target, an aggregate of 36,750 restricted stock units of various executive officers vested and were settled in shares of the Company’s common stock (see Note 14, Stock-Based Compensation ​ In October 2020, the Company issued 2,939,552 shares of its common stock to Vifor International in connection with the license agreement entered into with Vifor International (see Note 12, Collaboration and Licensing Agreements In June 2020, as a result of the completion of the one-year vesting period, an aggregate of 24,000 restricted stock units of members of the Board of Directors vested and were settled in shares of the Company’s common stock (see Note 14, Stock-Based Compensation ​ In April and June 2020, as a result of the achievement of certain performance targets, an aggregate of 95,834 restricted stock units of various executive officers vested and were settled in shares of the Company’s common stock (see Note 14, Stock-Based Compensation

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2022
Fair Value Measurements
Fair Value Measurements	11. Fair Value Measurements The following tables summarize the Company’s financial assets measured at fair value on a recurring basis as of December 31, 2022 and 2021, and by level within the fair value hierarchy: Fair value measurement as of December 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 ​ $ 63,741 ​ $ 63,741 ​ $ — ​ $ — Available-for-sale marketable securities: ​ ​ ​ ​ ​ ​ ​ U.S. government agency obligations ​ 8,877 ​ — ​ 8,877 ​ — Corporate bonds ​ 35,185 ​ — ​ 35,185 ​ — Commercial paper ​ 26,875 ​ — ​ 26,875 ​ — Municipal bonds ​ 22,071 ​ — ​ 22,071 ​ — Restricted cash: ​ ​ ​ ​ ​ ​ ​ Commercial money market account ​ 408 ​ 408 ​ — ​ — Total financial assets ​ $ 157,157 ​ $ 64,149 ​ $ 93,008 ​ $ — ​ 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 for the years ended December 31, 2022, 2021 and 2020. There were no transfers of financial assets between Levels 1, 2, or 3 classifications during the years ended December 31, 2022 and 2021.

Collaboration and Licensing Agr

Collaboration and Licensing Agreements	12 Months Ended
	Dec. 31, 2022
Collaboration and Licensing Agreements.
Collaboration and Licensing Agreements	12. Collaboration and Licensing Agreements Vifor (International) Ltd. (Vifor International) In October 2020, the Company entered into a license agreement with Vifor International, or Vifor Agreement No. 1, under which the Company granted Vifor International 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 Vifor Agreement No. 1, 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 Joint Commercialization Committee, or JCC, have the responsibility for overall coordination and oversight of Vifor International (and any affiliates or sublicensees). The Company’s membership on the JCC is at its sole discretion and is not its obligation. ​ After the assignment of rights of Vifor Agreement No. 1 from Vifor International to Vifor Fresenius Medical Care Renal Pharma Ltd. in May 2022, Vifor Agreement No. 1 provides full commercialization rights in dialysis clinics to CSL 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 Vifor Agreement No. 1) from sales of difelikefalin injection in the United States and CSL Vifor is entitled to 40% of such net profits (excluding sales to Fresenius Medical Center dialysis clinics, compensation for which is governed by Vifor Agreement No. 2, as defined below), subject to potential temporary adjustment in future years based on certain conditions. Under Vifor Agreement No. 1, in consideration of CSL 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 CSL Vifor based on the level of annual net sales. This fee as well as CSL Vifor’s COGS are deducted from net sales in calculating the net profits that are subject to the profit-sharing arrangement under Vifor Agreement No. 1. ​ Under the terms of Vifor Agreement No. 1, the Company received from Vifor International 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 represented 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. The excess of the stock purchase price over the cost of the purchased shares at the closing price of the Company’s common stock on the purchase date of $11,551 was added to the upfront payment for accounting purposes (see Note 13, Revenue Recognition – License and Milestone Fees ​ 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 represented a 20% premium to the 30-day Revenue Recognition – License and Milestone Fees In addition, pursuant to Vifor Agreement No. 1, the Company is eligible to receive payments of up to $240,000 from CSL Vifor upon the achievement of certain sales-based milestones. ​ The license also requires CSL Vifor to promote and take orders for difelikefalin injection, or Licensed Product, throughout the United States, including coordinating with CSL Vifor promotional activities to FMC U.S. Dialysis Clinics which are subject to the Company’s rights under Vifor Agreement No. 2. The license also allows CSL Vifor to grant sub-licenses, which, in certain cases, requires the Company’s prior written consent. The Company retains the rights to import, distribute, promote, sell and otherwise commercialize the Licensed Product on an exclusive basis outside of the Field either in or outside of the United States. The Company retains the rights to make and have made the Licensed Product, on a non-exclusive basis, in the United States for commercial sale of the Licensed Product for use for 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 CSL Vifor under the terms of a supply agreement, or the Vifor International Supply Agreement, which was executed in September 2021. The supply price is the Company’s COGS, as calculated under GAAP, plus an agreed upon margin. The Vifor International Supply Agreement will co-terminate with Vifor Agreement No. 1. The Vifor International 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 International 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 CSL Vifor is not a performance obligation under Vifor Agreement No. 1 but rather the Vifor International Supply Agreement is a separate agreement from Vifor Agreement No. 1. The only performance obligation under the Vifor International Supply Agreement is the delivery of the Licensed Product to CSL Vifor for commercialization. ​ Vifor Agreement No. 1 will continue in effect until its expiration upon the cessation of commercial sale of difelikefalin injection in the United States by CSL Vifor and its affiliates and sublicensees, or until the earlier termination of Vifor Agreement No. 1. Vifor Agreement No. 1 may be terminated earlier by either party for material breach that is not cured within 60 days, bankruptcy by either party and by both parties upon mutual written consent. The Company may terminate Vifor Agreement No. 1 if CSL Vifor challenges the validity of any licensed patent rights, except if such patent challenge results from the Company’s action against CSL Vifor for infringement of any licensed patent in the United States. In addition, upon the earlier of (1) the acceptance for filing of an NDA covering Licensed Product filed with the FDA (after completion of the Phase 3 program) or (2) the third anniversary of the Effective Date, Vifor Agreement No. 1 may be terminated by CSL Vifor in its entirety upon written notice to the Company. Such termination will be effective twelve months following the date of such notice. ​ Vifor Fresenius Medical Care Renal Pharma Ltd. In May 2018, the Company entered into a license agreement with Vifor Fresenius Medical Care Renal Pharma Ltd., or Vifor Agreement No. 2, under which the Company granted Vifor Fresenius Medical Care Renal Pharma Ltd. an exclusive, royalty-bearing license, or the Vifor License, to seek regulatory approval to commercialize, import, export, use, distribute, offer for sale, promote, sell and otherwise commercialize the Licensed Product in the Field worldwide (excluding the United States, Japan and South Korea), or the Territory. Vifor Fresenius Medical Care Renal Pharma Ltd. cannot perform development activities on their own unless specifically allocated to Vifor Fresenius Medical Care Renal Pharma Ltd. by the Joint Development Committee, or JDC, and Joint Steering Committee, or JSC. The Company’s membership on the JSC or JDC is at its sole discretion and is not its obligation. The Company is responsible, at its own cost, to undertake clinical and non-clinical development, or the R&D services. The Company is also responsible to provide all content and subject matter expertise required for registration with the European Medicines Agency, or EMA, in the EU that will be needed by Vifor Fresenius Medical Care Renal Pharma Ltd. for such registration, including participation in regulatory meetings, as needed. CSL Vifor will contribute, at its own cost, its clinical development expertise as reasonably useful for such development activities, such as preparing the clinical results that the Company presents to it in a format acceptable to the EMA to obtain marketing approval in the EU. Upon entry into Vifor Agreement No. 2, Vifor Fresenius Medical Care Renal Pharma Ltd. made a non-refundable, non-creditable $50,000 upfront payment to the Company and Vifor International purchased 1,174,827 shares of the Company’s common stock, for $20,000 at a price of $17.024 per share, which represented a premium over a pre-determined average closing price of the Company’s common stock. The purchase of the Company’s common stock was governed by a separate stock purchase agreement. The excess of the stock purchase price over the cost of the Vifor International shares at the closing price of the Company’s common stock on the purchase date of $5,444 was added to the upfront payment for accounting purposes (see Note 13, Revenue Recognition – License and Milestone Fees As a result of the European Commission’s regulatory approval of Kapruvia in April 2022, the Company received a $15,000 regulatory milestone payment from Vifor Fresenius Medical Care Renal Pharma Ltd. under Vifor Agreement No. 2 during the year ended December 31, 2022. In addition, after U.S. regulatory approval of KORSUVA injection in August 2021, the Company earned a $15,000 regulatory milestone payment from Vifor Fresenius Medical Care Renal Pharma Ltd. under Vifor Agreement No. 2 during the year ended December 31, 2021. The Company is eligible to receive from Vifor Fresenius Medical Care Renal Pharma Ltd. additional commercial milestone payments in the aggregate of up to $440,000, 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 Vifor Agreement No. 2, of difelikefalin injection in the licensed territories. The Company retains full commercialization rights for difelikefalin injection for the treatment of CKD-aP in the United States except in the dialysis clinics of FMCNA, where Vifor Fresenius Medical Care Renal Pharma Ltd. will promote difelikefalin injection under a profit-sharing arrangement (as defined in Vifor Agreement No. 2) based on net FMCNA clinic sales (as defined in Vifor Agreement No. 2) and Vifor Fresenius Medical Care Renal Pharma Ltd. is entitled to 50% of such net profits, subject to potential adjustments in a calendar year based on certain conditions. The license also requires Vifor Fresenius Medical Care Renal Pharma Ltd. to promote and take orders in the United States for sale by the Company to FMC U.S. Dialysis Clinics and allows Vifor Fresenius Medical Care Renal Pharma Ltd. to grant sub-licenses, which, in certain cases, requires the Company’s prior written consent. The Company retains the rights to import, distribute, promote, sell and otherwise commercialize the Licensed Product outside of the Field and outside of the Territory. The Company retains the rights to make and have made the Licensed Product in the Territory for commercial sale by Vifor Fresenius Medical Care Renal Pharma Ltd. in the Field in or outside the Territory and for supply of Licensed Product to Vifor Fresenius Medical Care Renal Pharma Ltd. under the terms of a supply agreement, or the Vifor Supply Agreement, which was executed in May 2020. The supply price is the Company’s COGS, as calculated under U.S. GAAP, plus an agreed upon margin. The Vifor Supply Agreement will co-terminate with the Vifor Agreement No. 2. 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 clinical compound to Vifor Fresenius Medical Care Renal Pharma Ltd. is not a performance obligation under Vifor Agreement No. 2 but rather the Vifor Supply Agreement is a separate agreement from Vifor Agreement No. 2. The only performance obligation under the Vifor Supply Agreement is the delivery of the Licensed Product to Vifor Fresenius Medical Care Renal Pharma Ltd. for commercialization. Vifor Agreement No. 2 terminates upon the expiration of all royalty terms with respect to the Licensed Products, which expire on a Product-by-Product and country-by-country basis, at the latest of (a) the expiration of all patent rights licensed to Vifor Fresenius Medical Care Renal Pharma Ltd. covering such Licensed Product; (b) the expiration of all regulatory and data exclusivity applicable to such Licensed Product in such country and (c) the tenth anniversary of the first commercial sale of such Product in such country. Vifor Agreement No. 2 may be terminated earlier by either party for material breach that is not cured within 60 days, bankruptcy by either party and by both parties upon mutual written consent. The Company may terminate Vifor Agreement No. 2 if Vifor Fresenius Medical Care Renal Pharma Ltd. challenges the validity of any licensed patent rights, except if such patent challenge results from the Company’s action against Vifor Fresenius Medical Care Renal Pharma Ltd. for infringement of any licensed patent in the Territory. In addition, upon the earlier of (1) the acceptance for filing of an NDA covering Licensed Product filed with the FDA (after completion of the Phase 3 program) or (2) the third anniversary of the Effective Date, Vifor Agreement No. 2 may be terminated by Vifor Fresenius Medical Care Renal Pharma Ltd. in its entirety or with respect to any countries within the Territory upon written notice to the Company. Such termination will be effective twelve months following the date of such notice. If Vifor Agreement No. 2 terminates early for any reason stated above, Vifor Fresenius Medical Care Renal Pharma Ltd.’s licenses will terminate, Vifor Fresenius Medical Care Renal Pharma Ltd.’s rights to use the Company’s confidential information and the Company’s know-how will revert to the Company and Vifor Fresenius Medical Care Renal Pharma Ltd. will assign and transfer to the Company all right, title and interest in all regulatory applications (IND’s and NDA’s), regulatory approval applications and regulatory approvals in the Territory covering Licensed Product. Maruishi Pharmaceutical Co., Ltd. (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. In September 2022, Maruishi submitted a New Drug Application in Japan for approval of difelikefalin injection for the treatment of pruritus in hemodialysis patients. Chong Kun Dang Pharmaceutical Corporation (CKDP) In April 2012, the Company entered into a license agreement with CKDP, or the CKDP Agreement, 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. 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	12 Months Ended
	Dec. 31, 2022
Revenue Recognition
Revenue Recognition	13. Revenue Recognition The Company has primarily recognized revenue under its license and collaboration agreements from (1) its share of the profit generated by KORSUVA injection sales; (2) upfront license fees and milestone payments, including development and regulatory milestones; (3) commercial supply revenue from CSL Vifor; (4) royalty revenue from net sales of Kapruvia; and (5) clinical compound sales from certain license agreements. As of December 31, 2022, the Company has not earned any sales-based milestones under its collaboration agreements. As of December 31, 2022, the Company had license and collaboration agreements with CSL Vifor, Maruishi and CKDP. The following table provides amounts included in the Company’s Statements of Comprehensive (Loss) Income as revenue for the years ended December 31, 2022, 2021 and 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ 2022 2021 2020 Collaborative revenue ​ ​ ​ ​ ​ ​ ​ ​ ​ CSL Vifor (KORSUVA injection profit sharing) ​ $ 16,572 ​ $ — ​ $ — Maruishi ​ ​ — ​ ​ 706 ​ ​ — Total collaborative revenue ​ $ 16,572 ​ $ 706 ​ $ — License and milestone fees ​ ​ ​ ​ ​ ​ ​ ​ ​ CSL Vifor* ​ ​ 15,000 ​ ​ 20,031 ​ ​ 133,813 Maruishi ​ ​ — ​ ​ 1,192 ​ ​ — CKDP ​ ​ — ​ ​ — ​ ​ 626 Total license and milestone fees ​ $ 15,000 ​ $ 21,223 ​ $ 134,439 Commercial supply revenue ​ ​ ​ ​ ​ ​ ​ ​ ​ CSL Vifor* (KORSUVA injection) ​ $ 10,223 ​ $ 701 ​ $ — Total commercial supply revenue ​ $ 10,223 ​ $ 701 ​ $ — Royalty revenue ​ ​ ​ ​ ​ ​ ​ ​ ​ CSL Vifor (Kapruvia ex U.S.) ​ $ 72 ​ $ — ​ $ — Total royalty revenue ​ $ 72 ​ $ — ​ $ — Clinical compound revenue ​ ​ ​ ​ ​ ​ ​ ​ ​ CSL Vifor* (difelikefalin injection) ​ $ — ​ $ 361 ​ $ 115 Maruishi ​ ​ — ​ ​ 37 ​ ​ 528 Total clinical compound revenue ​ $ — ​ $ 398 ​ $ 643 _____________________________ * Includes amounts earned from Vifor Fresenius Medical Care Renal Pharma Ltd. and Vifor International prior to Vifor International’s assignment of its rights and obligations to Vifor Fresenius Medical Care Renal Pharma Ltd. in May 2022. ​ Collaborative revenue Beginning in April 2022, the Company began recording its share of the profit generated by KORSUVA injection sales by CSL Vifor to third parties in the United States. Under the license agreements with CSL Vifor, KORSUVA injection net sales are calculated by CSL Vifor which are net of discounts, rebates, and allowances. These amounts include the use of estimates and judgments, which could be adjusted based on actual results in the future. The Company records its share of the net profits from the sales of KORSUVA injection in the United States and presents the revenue earned each period as collaborative revenue. During the year ended December 31, 2022, the Company recorded $16,572 as collaborative revenue for its profit-share from the sales of KORSUVA injection in the United States. There was no profit share revenue recorded during the years ended December 31, 2021 or 2020. The Company’s distinct performance obligations under the Maruishi Agreement included 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 (considered license and milestone fees revenue), and performance of R&D services, which occurred from 2013 to 2015 (considered collaborative revenue), 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 and were included as collaborative revenue. In addition, the Company’s promise in the Maruishi Agreement to transfer the license is separately identifiable from the promise to provide defined R&D services (i.e., distinct within the context of the contract) because the Company was not using the goods or services as inputs to produce or deliver the combined output or outputs specified by the customer. The combined output specified by Maruishi is its right to conduct development activities related to difelikefalin in Japan, which could result in regulatory approval in Japan. That right is derived from the Company’s grant of the license. Maruishi is conducting clinical trials on its own and does not require the R&D services provided by the Company. Furthermore, the R&D services do not significantly modify or customize the license and vice versa. Finally, the license and R&D services were not highly interdependent or highly interrelated because the Company was able to fulfill its promise to transfer the initial license independently from its promise to subsequently provide the R&D services, which Maruishi can obtain on its own. There were no remaining performance obligations under the Maruishi Agreement as of December 31, 2022. There was no collaborative revenue recognized under the Maruishi Agreement during the years ended December 31, 2022 and 2020. During the year ended December 31 2021, the criteria for revenue recognition for a milestone event set forth in the Maruishi Agreement was achieved, and the Company recorded $706 as collaborative revenue based on the relative standalone selling prices described above at contract inception (see Note 2, Summary of Significant Accounting Policies – Revenue Recognition) License and milestone fees revenue Under Vifor Agreement No. 1, the Company identified one performance obligation at contract inception: granting of the license to Vifor International. The one performance obligation was satisfied when the license was granted to Vifor International in October 2020, and as a result, $111,551 (including the upfront payment of $100,000 and the premium on the common stock purchased by Vifor International of $11,551) was recognized as license and milestone fees revenue during the year ended December 31, 2020. There were no remaining performance obligations under Vifor Agreement No. 1 as of December 31, 2022. The remaining potential consideration was considered to be variable consideration and was constrained at inception of the contract, which included regulatory and sales milestones (see Note 12, Collaboration and Licensing Agreements Under Vifor Agreement No. 2, the Company identified two performance obligations at contract inception in 2018: (1) granting of the license to CSL Vifor, and (2) the R&D services. The Company determined that these two performance obligations were not capable of being distinct (i.e., did not have standalone value for CSL Vifor) because CSL Vifor could not benefit (derive potential cash flows) from either one on its own or together with other resources that are readily available to it since CSL Vifor was relying on the Company’s expertise in investigating chronic kidney disease-associated pruritus, or CKD-aP, and its know-how obtained from multiple years of pre-clinical and clinical development, and years of interactions with the FDA which other companies or CROs would not have. The license to CSL Vifor did not provide benefit to CSL Vifor until and unless the Company conducted the pivotal clinical trials and other supportive trials in CKD-aP to gather sufficient clinical data for CSL Vifor to obtain marketing approval in the Territory. Furthermore, CSL Vifor did not have the right to perform development activities on its own unless specifically allocated by the JDC or JSC. The two identified performance obligations were also not distinct within the context of the contract, (i.e., were not separately identifiable from each other) because of the nature of the promise within the context of the contract. The nature of the promise was to transfer a combined deliverable to CSL Vifor based on the agreement (to support the ability of CSL Vifor to commercialize the Licensed Product) and the Company determined that the license granted to CSL Vifor and the R&D services are inputs rather than a transfer of each of these goods and services individually. In addition, the two identified performance obligations were highly interrelated and interdependent because satisfaction of both performance obligations was required for CSL Vifor to derive benefit from Vifor Agreement No. 2 for commercialization of the Licensed Product in the Territory. Therefore, the two performance obligations were not distinct from each other and were accounted for as a single performance obligation. Under Vifor Agreement No. 2, the single combined performance obligation was satisfied as the R&D services were rendered and the transaction price (including the upfront payment of $50,000 and the premium on the common stock purchased by Vifor International of $5,444) was recognized as revenue as the R&D services were performed based on the costs incurred as a percentage of the estimated total costs to be incurred to complete the performance obligation. There were no remaining performance obligations under Vifor Agreement No. 2 as of December 31, 2022. The remaining potential consideration was considered to be variable consideration and was constrained at inception of the contract, which included regulatory approvals and sales milestones and sales royalties. As a result, $22,262 was recorded as license and milestone fee revenue for the year ended December 31, 2020 under Vifor Agreement No. 2 based on the percentage of R&D services that had been completed during 2020 (see Note 2, Summary of Significant Accounting Policies – Revenue Recognition After U.S. regulatory approval of KORSUVA injection in August 2021, the Company achieved a $15,000 regulatory milestone payment and was recorded as license and milestone fees revenue for the year ended December 31, 2021, since this regulatory milestone payment was considered variable consideration at contract inception, was not included in the transaction price at the inception of the agreement and was allocated to the one performance obligation identified at contract inception (see Note 2, Summary of Significant Accounting Policies – Revenue Recognition In addition, 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 represented a 20% premium to the 30-day trailing average price of the Company’s common stock as of the date of the achievement of the milestone. The excess of the stock purchase price over the cost of the purchased shares at the closing price of the Company’s common stock on the date of the achievement of the milestone of $5,031 was allocated to the one performance obligation identified at contract inception and included as license and milestone fees revenue for the year ended December 31, 2021 (see Note 2, Summary of Significant Accounting Policies – Revenue Recognition As a result of the European Commission’s regulatory approval of Kapruvia in April 2022, the Company received a $15,000 regulatory milestone payment from CSL Vifor under Vifor Agreement No. 2, which was recorded as license and milestone fees revenue for the year ended December 31, 2022, since this regulatory milestone payment was considered variable consideration at contract inception, was not included in the transaction price at the inception of the agreement and was allocated to the one combined performance obligation identified at contract inception (see Note 2, Summary of Significant Accounting Policies – Revenue Recognition There were no license and milestone fees revenue recognized under the Maruishi Agreement during the years ended December 31, 2022 or 2020. During the year ended December 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 based on the relative standalone selling prices described above at contract inception (see Note 2, Summary of Significant Accounting Policies – Revenue Recognition Under the CKDP Agreement, the Company’s only performance obligation was to transfer the license to the Company’s IP related to difelikefalin. As of December 31, 2022, there was no remaining performance obligation under the CKDP Agreement. As such, future milestones and sales-based payments were not included in the transaction price at inception of the CKDP Agreement and are allocated to the one performance obligation in accordance with Note 2, Significant Accounting Polices: Revenue Recognition. Commercial supply revenue Under the Vifor International Supply Agreement, the Company’s only performance obligation is the delivery of KORSUVA injection to CSL Vifor in accordance with the receipt of purchase orders. Revenue from the sale of commercial supply product to CSL Vifor is recognized as delivery of the Licensed Product occurs. The Company had commercial supply revenue of $10,223 for the year ended December 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 $7,928 was recognized throughout the remainder of 2022 with associated COGS of $7,266 since these inventory costs were capitalized as inventory subsequent to regulatory approval. The Company had $701 of commercial supply revenue for the year ended December 31, 2021 with no associated COGS since these inventory costs were incurred prior to regulatory approval on August 23, 2021. Clinical compound revenue The Company’s only performance obligation under the Vifor Supply Agreement is to deliver compound to CSL Vifor in accordance with the receipt of purchase orders. There were no sales of clinical compound under the Vifor Supply Agreement during the year ended December 31, 2022. During the years ended December 31, 2021 and 2020, the Company recognized clinical compound revenue of $361 and $115, respectively, from the sale of clinical compound to CSL Vifor and as a result, the Company incurred R&D expense of $343 and $108 during these respective periods. 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 year ended December 31, 2022. During the years ended December 31, 2021 and 2020, the Company recognized clinical compound revenue of $37 and $528, respectively, from the sale of clinical compound to Maruishi and as a result, the Company incurred R&D expense of $33 and $476 during these respective periods. Contract balances As of December 31, 2022, the Company recorded accounts receivable, net – related party of $3,260 which primarily related to its profit-sharing revenue from sales of KORSUVA injection in the United States by CSL Vifor and its commercial supply of KORSUVA injection to CSL Vifor. There were no material balances of receivables as of December 31, 2021, and no other contract assets or contract liabilities related to the CSL Vifor, Maruishi and CKDP agreements as of December 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 December 31, 2022 and December 31, 2021.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2022
Stock-Based Compensation
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. In November 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. No stock options were granted under the 2019 Plan during the years ended December 31, 2022, 2021 and 2020. 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. As of December 31, 2022, 300,000 shares remained available for grant pursuant to the Plan. 2014 Equity Incentive Plan The Company’s 2014 Equity Incentive Plan, or the 2014 Plan, is administered by the Company’s Board of Directors or a duly authorized committee thereof, referred to as the Plan administrator. The 2014 Plan provides for the grant of incentive stock options, non-statutory stock options, restricted stock awards, restricted stock unit awards, stock appreciation rights, performance stock awards and other forms of equity compensation, collectively referred to as Stock Awards. Additionally, the 2014 Plan provides for the grant of performance cash awards. Incentive stock options may be granted only to employees. All other awards may be granted to employees, including officers, non-employee directors, and consultants. No incentive stock options may be granted under the 2014 Plan after the tenth anniversary of the effective date of the 2014 Plan. Stock Awards granted under the 2014 Plan vest at the rate specified by the Plan administrator. Initial grants of Stock Awards made to employees and non-employee consultants generally vest as to 25% on the first anniversary of the date of grant and the balance ratably over the next 36 months and subsequent grants vest monthly over a period of four years from the grant date. Stock options initially granted to members of the Company’s Board of Directors vest over a period of three years in equal quarterly installments from the date of the grant, subject to the option holder’s continued service as a Director through such date. Subsequent grants to Directors that are made automatically at Annual Meetings of Stockholders vest fully on the earlier of the first anniversary of the date of grant and the next Annual Meeting of Stockholders. The Plan administrator determines the term of Stock Awards granted under the 2014 Plan up to a maximum of ten years. The aggregate number of shares of the Company’s common stock reserved for issuance under the 2014 Plan has automatically increased on January 1 of each year, beginning on January 1, 2015 and will continue to increase on January 1 of each year through and including January 1, 2024, by 3% of the total number of shares of the Company’s capital stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares determined by the Company’s Board of Directors. On January 1, 2023, the aggregate number of shares of common stock that may be issued pursuant to Stock Awards under the 2014 Plan automatically increased from 10,589,103 to 12,203,023. 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 October 12, 2022, the Compensation Committee of the Company’s Board of Directors, or the Compensation Committee, approved and granted a total of 7,267 time-based restricted stock units under the 2014 Plan, with a grant date fair value of $9.42 per share, to an executive officer of the Company. The restricted stock unit grant fully vests on August 31, 2023, subject to the recipient’s continued service through such date. For the year ended December 31, 2022, the Company recognized $17 of stock compensation expense associated with these awards, all of which was recorded within G&A expense. As of December 31, 2022, none of the 7,267 restricted stock units were vested and settled in shares of the Company’s common stock. On June 15, 2022, the Compensation Committee approved and granted a total of 7,500 time-based restricted stock units under the 2014 Plan, with a grant date fair value of $7.94 per share, to the Company’s interim principal financial and accounting officer, in connection with his assuming the responsibilities of the Company’s former Chief Financial Officer, or CFO, on an interim basis. The Company accelerated the recognition of compensation expense and the restricted stock units vested fully on September 12, 2022, when the appointment of the Company’s new CFO occurred. For the year ended December 31, 2022, the Company recognized $60 of stock compensation expense associated with these awards, all of which was recorded within G&A expense. As of December 31, 2022, all Pursuant to the Company’s non-employee director compensation policy, an aggregate of 59,380 restricted stock units were granted to non-employee directors on June 2, 2022, the date of the Company’s 2022 Annual Meeting of Stockholders, under the 2014 Plan with a grant date fair value of $8.42 per share. The restricted stock units will vest on the earlier of (i) June 2, 2023 and (ii) immediately prior to the Company’s next Annual Meeting of Stockholders following the grant date, subject to the recipient’s continued service through such date. As a result, the Company recognizes compensation expense associated with these restricted stock units ratably over the one-year vesting period following the grant date. For the year ended December 31, 2022, stock compensation expense of $290 was recognized in G&A expense. As of December 31, 2022, none of the 59,380 restricted stock units were vested or settled in shares of the Company’s common stock. Also in June 2022, the Company granted 11,876 fully vested restricted stock units, which were immediately settled in shares of common stock, to the Company’s chairman in consideration of his effort in connection with the Company’s CEO transition in 2021. For the year ended December 31, 2022, stock compensation expense of $100 was recognized in G&A expense associated with this award. On February 25, 2022, the Compensation Committee also 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 year ended December 31, 2022, no stock compensation expense relating to these restricted stock units was recognized. In June 2022, 29,000 of these restricted stock units were forfeited as a result of the resignation of the Company’s former CFO. In December 2022, 214,000 of these restricted stock units were cancelled as the performance targets associated with them were not achieved. As a result, there were no outstanding restricted stock units as of December 31, 2022 under these grants. 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 year ended December 31, 2022, the Company recognized $390 of stock compensation expense associated with these awards, with $161 recorded in R&D expense and $229 in G&A expense. In June 2022, 20,000 of these restricted stock units were forfeited as a result of the resignation of the Company’s former CFO. As of December 31, 2022, none of the remaining 125,170 outstanding 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 executive officers 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. In December 2022, an aggregate of 26,204 of these restricted stock units vested and were settled in shares of the Company’s common stock. The Company recognizes compensation expense associated with these restricted stock units ratably over the 18-month vesting period following the grant date. For the year ended December 31, 2022, the Company recognized $433 of stock compensation expense, with $210 recorded in R&D expense and $223 in G&A expense. For the year ended December 31, 2021, the Company recognized $20 of stock compensation expense, with $8 recorded in R&D expense and $12 in G&A expense. In June 2022, 11,170 of these restricted stock units were forfeited as a result of the resignation of the Company’s former CFO. As of December 31, 2022, 26,204 of the remaining 52,403 restricted stock units were vested and 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 Chief Executive Officer, or 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 vested 25% on the first anniversary of the date of grant and the balance quarterly over the next 36 months. In October 2022, 35,500 of these restricted stock units vested and were settled in the Company’s common stock. The second tranche of 5,942 restricted stock units fully vested on March 31, 2022. 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 years ended December 31, 2022 and 2021, stock compensation expense of $657 and $144 respectively, was recognized in G&A expense. As of December 31, 2022, 41,442 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 vested on June 3, 2022. As a result, the Company recognized compensation expense associated with these restricted stock units ratably over the one-year vesting period following the grant date. For the years ended December 31, 2022 and 2021, stock compensation expense of $238 and $326 respectively, was recognized in G&A expense. As of December 31, 2022, all 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 is contingent on the achievement of certain performance targets related to clinical and regulatory milestones, subject to the recipient’s continuous service through each performance target. Recognition of compensation expense associated with these awards begins when, and to the extent, the performance criteria is probable of achievement and the employee has met the service conditions. In February 2022 and August 2021, performance targets relating to 37,999 and 44,002 restricted stock units, respectively, had been achieved and thus restricted stock units vested and the awards were settled in shares of common stock. For the year ended December 31, 2022, the Company recognized $729 of stock compensation expense associated with these awards in G&A expense. G&A amounts recorded for the year ended December 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 executive officers under the 2014 Plan with a grant date fair value of $20.59 per share. The restricted stock units vest in three equal installments annually from the date of the grant. As a result, the Company recognizes compensation expense associated with these restricted stock units ratably over the three-year vesting period following the grant date. On June 30, 2022, 17,333 of these restricted stock units vested and were settled in shares of the Company’s common stock, while 17,333 restricted stock units were forfeited on June 30, 2022 as a result of the completion of the consulting agreement in relation to the modification of certain of these restricted stock units on November 1, 2021 (see Stock Award Modifications 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 recognized compensation expense associated with these restricted stock units ratably over the one-year vesting period following the grant date. For the years ended December 31, 2021 and 2020, $239 and $323, respectively, of stock compensation expense relating to these restricted stock units was recognized in G&A expense. All 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, had been achieved and thus restricted stock units vested and the awards were settled in shares of common stock. For the year ended December 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 a result of the achievement of a performance target relating to its NDA filing in December 2020, the Company recognized $601 of stock compensation expense, with $196 recorded in R&D expense and $405 in G&A expense for the year ended December 31, 2020. As of December 31, 2022, 113,500 of the 138,000 restricted stock units had vested and were settled in shares of the Company’s common stock, while the remaining 24,500 restricted stock units had been forfeited as a result of not achieving certain defined performance targets of the awards. As a result, there were no outstanding restricted stock units as of December 31, 2022 under these grants. Additionally in February 2020, the Compensation Committee of the Company’s Board of Directors also approved and granted a total of 98,000 time-based restricted stock units to executive officers under the 2014 Plan with a grant date fair value of $16.36 per share. The restricted stock units vest in three equal installments annually from the date of the grant. As a result, the Company recognizes compensation expense associated with these restricted stock units ratably over the three-year vesting period following the grant date. In June 2022, 16,666 of these restricted stock units vested and were settled in shares of the Company’s common stock in accordance with the acceleration of vesting provisions relating to the modification of certain of these restricted stock units on November 1, 2021 (see Stock Award Modifications Stock Award Modifications Stock Award Modifications Pursuant to the terms of the Company’s non-employee director compensation policy, an aggregate of 24,000 restricted stock units were granted to non-employee directors on June 4, 2019, the date of the Company’s 2019 Annual Meeting of Stockholders, under the 2014 Plan with a grant date fair value of $20.47 per share. As a result, the Company recognized compensation expense associated with these restricted stock units ratably over the one-year vesting period following the grant date and were fully vested in June 2020. For the year ended December 31, 2020, the Company recognized $205 of stock compensation expense relating to these restricted stock units in G&A expense. As of June 30, 2020, all of the 24,000 restricted stock units had vested and were settled in shares of the Company’s common stock. In March 2019, the Compensation Committee approved and granted a total of 215,000 restricted stock units to certain employees under the 2014 Plan with a grant date fair value of $16.10 per share. Vesting of the restricted stock units was contingent on the achievement of certain performance targets related to clinical milestones, subject to the recipient’s continuous service through the vesting events. Recognition of compensation expense associated with these awards begins when, and to the extent, the performance criteria is probable of achievement and the employee has met the service conditions. In April and June 2020, performance targets relating to 65,834 and 30,000 restricted stock units, respectively, had been achieved and thus such restricted stock units vested, and the awards were settled in shares common 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 year ended December 31, 2022 is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ Number of ​ Average Grant ​ Units Date Fair Value Outstanding, December 31, 2021 576,544 ​ $ 17.50 Awarded 474,193 ​ 10.10 Vested and released (268,222) ​ 16.33 Forfeited (410,002) ​ 13.62 Outstanding, December 31, 2022 372,513 ​ $ 13.20 Restricted stock units exercisable (vested and deferred), December 31, 2022 — ​ ​ ​ ​ Stock Options A summary of the Company’s stock option activity related to employees, non-employee members of the Board of Directors and non-employee consultants for the 2019 Plan and the 2014 Plan as of and for the year ended December 31, 2022 is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ Aggregate ​ ​ Number of ​ Average Exercise ​ Intrinsic ​ Shares Price Value Outstanding, December 31, 2021 6,512,280 ​ $ 15.58 ​ Granted 1,899,919 ​ 10.25 ​ Exercised (48,307) ​ 6.43 ​ Forfeited (356,819) ​ 14.50 ​ Expired (317,624) ​ 16.09 ​ Outstanding, December 31, 2022 7,689,449 ​ $ 14.35 ​ $ 3,028 Weighted average remaining contractual life as of December 31, 2022 (in years) 5.95 ​ ​ Options exercisable, December 31, 2022 4,972,944 ​ $ 15.06 ​ $ 1,940 Weighted average remaining contractual life as of December 31, 2022 (in years) 4.40 ​ ​ Options vested and expected to vest as of December 31, 2022 7,689,449 ​ $ 14.35 ​ $ 3,028 Weighted average remaining contractual life as of December 31, 2022 (in years) 5.95 ​ ​ ​ The total fair value of options vested during the years ended December 31, 2022, 2021 and 2020 was $14,156, $12,844, and $12,819, respectively. The intrinsic value of options exercised during the years ended December 31, 2022, 2021 and 2020 was $118, $965, and $152, respectively. During the years ended December 31, 2022, 2021 and 2020, the Company granted 1,899,919, 1,422,750 and 1,377,850 stock options, respectively, to employees and non-employee members of the Board of Directors. There were no options granted to nonemployee consultants during the years ended December 31, 2022, 2021 and 2020. The fair values of the stock options granted to those groups were estimated using the Black-Scholes option valuation model with the following ranges of assumptions (see Note 2, Summary of Significant Accounting Policies – Stock-Based Compensation ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ ​ 2022 2021 2020 Risk-free interest rate 1.70% - 4.21 % 0.66% - 1.41 % 0.35% - 1.57 % Expected volatility 77.7% - 81.9 % 71.6% - 83.5 % 71.8% - 74.8 % Expected dividend yield 0 % 0 % 0 % Expected life of employee and Board options (in years) 6.25 6.25 6.25 ​ ​ The weighted average grant date fair value of options granted to employees and non-employee members of the Board of Directors for their Board service during the years ended December 31, 2022, 2021 and 2020 was $7.25, $12.00, and $10.33, respectively. During the years ended December 31, 2022, 2021 and 2020, the Company recognized compensation expense relating to stock options as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ 2022 2021 2020 Research and development ​ $ 7,222 ​ $ 7,126 ​ $ 6,765 General and administrative ​ 6,426 ​ 9,569 ​ 4,943 Total stock option expense ​ $ 13,648 ​ $ 16,695 ​ $ 11,708 ​ 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 $765, $1,201 and $1,432 in R&D expense for the years ended December 31, 2022, 2021 and 2020, respectively, and $2,693, $2,324 and $1,167 in G&A expense for the years ended December 31, 2022, 2021 and 2020, respectively; ii) compensation expense relating to the Board of Directors’ restricted stock units for $628, $565 and $528 in G&A expense for the years ended December 31, 2022, 2021 and 2020, respectively. As of December 31, 2022, the total compensation expense relating to unvested options granted to employees and non-employee members of the Board of Directors that had not yet been recognized was $22,186, which is expected to be realized over a weighted average period of 2.72 years. The Company will issue shares upon exercise of options from common stock reserved. 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 or cash flows from financing activities for the years ended December 31, 2022, 2021 and 2020. 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 consulting agreement ended on June 30, 2022. ​ The Company determined that vested Stock Awards which had modifications due to the extension of the exercise period were Type 1 modifications pursuant to 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 the vesting targets were achieved with respect to 17,333 performance-based restricted stock units in February 2022, which resulted in additional stock compensation expense being recorded through June 30, 2022. ​ During the year ended December 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 $2,563, which is included in G&A expense. Of this total amount, $1,679 is included in G&A expense in the stock option expense table above for the year ended December 31, 2022. During the year ended December 31, 2021, total incremental stock compensation expense relating to modifications of stock options and time-based restricted stock units of the former CEO was $5,056, which is included in G&A expense. Of that total amount, $4,908 is included in G&A expense in the stock option compensation expense table above for the year ended December 31, 2021.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2022
Income Taxes
Income Taxes	15. Income Taxes The Company’s benefit from income taxes is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2022 2021 2020 Current: ​ ​ ​ Federal ​ $ — ​ $ — ​ $ — State ​ — ​ — ​ (691) ​ ​ — ​ — ​ (691) Deferred: ​ ​ ​ Federal ​ — ​ — ​ — State ​ — ​ — ​ — ​ ​ — ​ — ​ — Benefit from income taxes ​ $ — ​ $ — ​ $ (691) ​ Historically, the Company’s benefit from income taxes related to state R&D tax credits exchanged for cash. The State of Connecticut provides companies with the opportunity to exchange certain R&D credit carryforwards for cash in exchange for foregoing the carryforward of the R&D credit. The program provides for such exchange of the R&D credits at a rate of 65% of the annual R&D credit, as defined. During the year ended December 31, 2020, the Company recorded a benefit from income taxes of $691. 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 year ended December 31, 2021. As of December 31, 2022, the Company does not expect to receive a refund of its 2022 credit. A reconciliation of income taxes computed using the U.S. federal statutory rate to that reflected in operations is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2022 2021 2020 Income taxes using U.S. federal statutory rate 21.00 % 21.00 % 21.00 % State income taxes, net of federal benefit (1.00) % 7.84 % (58.68) % Tax Cuts and Jobs Act 0.00 % 0.00 % 0.00 % Impact of R&D tax credit on effective tax rate 4.91 % 2.87 % (52.06) % Stock option shortfalls and cancellations (3.33) % (4.74) % 0.35 % Permanent items and other (1.86) % (1.29) % (5.08) % Change in valuation allowance (19.88) % (25.69) % 84.61 % Provision to return 0.16 % 0.01 % 0.92 % Non-taxable revenue 0.00 % 0.00 % 0.00 % ​ 0.00 % 0.00 % (8.94) % ​ Significant components of the Company’s deferred tax assets and liabilities are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2022 2021 Valuation allowance $ (160,814) $ (143,388) ​ ​ ​ ​ ​ ​ ​ Net operating loss carryforwards ​ ​ 113,058 ​ ​ 113,636 Federal and state tax credits ​ 26,358 ​ 24,428 Stock-based compensation expense ​ 3,434 ​ 5,023 Intangible asset amortization ​ ​ 17,265 ​ ​ — Other ​ 1,167 ​ 1,268 Deferred tax assets ​ 161,282 ​ 144,355 ​ ​ ​ ​ ​ ​ ​ Other ​ (468) ​ (967) Deferred tax liabilities: ​ (468) ​ (967) ​ ​ ​ ​ ​ Net deferred tax asset: ​ $ — ​ $ — ​ A 100% valuation allowance has been recorded on the deferred tax asset as of December 31, 2022 and 2021 because management believes it is more likely than not that the asset will not be realized. The change in the valuation allowance during 2022 and 2021 was an increase of $17,426 and $22,722, respectively. The financial statements reflect expected future tax consequences of such positions presuming the taxing authorities possess full knowledge of the position and all relevant facts. As of December 31, 2022 and 2021, the Company had no unrecognized tax benefits or related interest and penalties accrued. In the event the Company determines that accrual of interest or penalties are necessary in the future, the amount will be presented as a component of income tax expense. At December 31, 2022, the Company had federal and state net operating loss, or NOL, carryforwards of $440,195 and $347,975, respectively. The federal and state tax loss carryforwards will begin to expire in 2026 and 2027, respectively, unless previously utilized. The federal NOLs arising in 2018 and forward have an unlimited carryforward period and losses from 2018-2020 may be carried back five years due to the Coronavirus Aid, Relief, and Economic Security Act of 2020, or the CARES Act. The Company conducted a 382 analysis in the first quarter of 2021. This analysis showed a limited change of ownership had occurred, and thus the full amount of the Company’s NOL carryforwards and R&D tax credits could be utilized annually in the future to offset taxable income or tax, respectively. The Company also had federal and state R&D tax credit carryforwards of $23,892 and $2,861, respectively. The federal credits will begin expiring in 2025 unless previously utilized. The Connecticut credit carryforwards have no expiration period. Because of the NOL and research credit carryforwards, tax years 2006 through 2022 remain open to U.S. federal and state tax examinations. Further, beginning in the Company’s tax year ending December 31, 2022, as a result of the Tax Cuts and Jobs Act of 2017, current R&D expenditures incurred in the United States must be capitalized for tax purposes, and amortized over a period of five years (fifteen years in the case of R&D performed outside the United States). In March 2020, former President Trump signed into law the CARES Act (H.R. 748), which was further expanded with the signing of the Consolidation Appropriations Act of 2021 (H.R. 133) on December 27, 2020. The CARES Act (and December expansion) includes a variety of economic and tax relief measures intended to stimulate the economy, including loans for small businesses, payroll tax credits/deferrals, and corporate income tax relief. Due to the Company’s history of tax loss carryforwards and full valuation allowance, the CARES Act did not have a significant effect to the income tax provision, as the corporate income tax relief was directed towards cash taxpayers.

Net (Loss) Income per Share

Net (Loss) Income per Share	12 Months Ended
	Dec. 31, 2022
Net (Loss) Income per Share
Net (Loss) Income per Share	16. Net (Loss) Income per Share The denominators used in the net (loss) income per share computations are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ 2022 2021 2020 Basic: Weighted average common shares outstanding 53,653,564 50,718,765 47,413,250 Diluted: Weighted average common shares outstanding - Basic 53,653,564 50,718,765 47,413,250 Common stock equivalents* — — 501,780 Denominator for diluted net (loss) income per share 53,653,564 50,718,765 47,915,030 * For the year end December 31, 2020, common stock equivalents include dilutive stock options and restricted stock units. For the years ended December 31, 2022 and 2021, no amounts were considered as their effects would have been anti-dilutive due to net losses for those periods. Basic and diluted net (loss) income per share is computed as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ 2022 2021 2020 Net (loss) income - basic and diluted ​ $ (85,474) ​ $ (88,441) ​ $ 8,410 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average common shares outstanding - basic ​ 53,653,564 ​ 50,718,765 ​ 47,413,250 Effect of dilutive securities: ​ ​ ​ ​ ​ ​ Stock options ​ ​ — ​ ​ — ​ ​ 481,254 Restricted stock units ​ ​ — ​ ​ — ​ ​ 20,526 Weighted-average common shares outstanding - diluted ​ ​ 53,653,564 ​ ​ 50,718,765 ​ ​ 47,915,030 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net (loss) income per share: ​ ​ ​ Basic ​ $ (1.59) ​ $ (1.74) ​ $ 0.18 Diluted ​ $ (1.59) ​ $ (1.74) ​ $ 0.18 ​ As of December 31, 2022, 7,689,449 stock options and 372,513 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 December 31, 2021, 6,512,280 stock options and 576,544 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 December 31, 2020, 5,469,393 stock options and 235,250 restricted stock units were outstanding, which could potentially dilute basic earnings per share in the future. 481,254 of these outstanding stock options and 20,526 of these restricted stock units were considered dilutive and included in the computation of diluted net income per share for the year ended December 31, 2020.

Employee Benefit Plan

Employee Benefit Plan	12 Months Ended
	Dec. 31, 2022
Employee Benefit Plan
Employee Benefit Plan	17. Employee Benefit Plan The Company’s defined contribution retirement plan complies with Section 401(k) of the Internal Revenue Code. All employees over the age of 21 are eligible to participate in the plan on the first day of the month after completing three consecutive months of service . Employees are able to defer a portion of their pay into the plan on the first day of the month on or after the day all age and service requirements have been met. All eligible employees receive an employer contribution equal to 3% of their salary up to the annual IRS limit. During the years ended December 31, 2022, 2021 and 2020, employer contributions to the plan were $505 , $460 , and $349 , respectively.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2022
Commitments and Contingencies
Commitments and Contingencies	18. 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 had 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 years ended December 31, 2022, 2021 and 2020, the Company paid $5,000 , $15,000 and $5,000 , respectively, to Enteris for milestones earned in relation to the Enteris License Agreement and as a result, the Company recognized $5,000 , $15,000 and $5,000 of R&D expense related to the Enteris License Agreement during these respective years. The Enteris License Agreement will expire on a country-by-country, licensed product-by-licensed product basis upon the later of (1) the expiration (or invalidation) of all valid claims in licensed patent rights that cover such product in such country, (2) the end of the calendar quarter in which generic competition (as defined in the Enteris License Agreement) occurs for such product in such country and (3) ten years from the first commercial sale of such product. Either party may terminate the Enteris License Agreement upon written notice if the other party has failed to remedy a material breach within 60 days (or 30 days in the case of a material breach of a payment obligation). Enteris may terminate the Enteris License Agreement upon 30 days ’ written notice to the Company if the Company or any of its affiliates formally challenge the validity of any licensed patent rights or assists a third party in doing so. The Company may terminate the Enteris License Agreement for any reason or no reason (a) prior to receipt of first regulatory approval for a licensed product in the United States for any indication upon 30 days ’ prior written notice to Enteris or (b) on or after receipt of first regulatory approval for a licensed product in the United States for any indication upon 60 days ’ prior written notice to Enteris. 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 API difelikefalin, 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. The MSA has an initial term ending December 31, 2024, and will automatically renew after the initial term for successive terms of two years each if there is a Product Agreement in effect, unless either party gives notice of its intention to terminate the MSA at least 18 months prior to the end of the then current term. Either party may terminate the MSA or a Product Agreement upon written notice if the other party (1) has failed to remedy a material breach within a specified time or (2) is declared insolvent or bankrupt, voluntarily files a petition of bankruptcy or assigns such agreement for the benefit of creditors. The Company may terminate a Product Agreement (a) upon 90 days’ prior written notice if any governmental agency takes any action that prevents the Company from selling the relevant product in the relevant territory, (b) upon six months’ prior written notice if it does not intend to order manufacturing services due to a product’s discontinuance in the market, or (c) upon 90 days’ prior written notice if it determines that the manufacture or supply of a product likely infringes third-party rights. Patheon may terminate the MSA or a Product Agreement (i) upon six months’ prior written notice if the Company assigns such agreement to an assignee that is unacceptable to Patheon for certain reasons, or (ii) upon 30 days’ prior written notice if, after the first year of commercial sales, the Company forecasts zero volume for 12 months. The MSA contains, among other provisions, customary representations and warranties by the parties, a grant to Patheon of certain limited license rights to the Company’s intellectual property in connection with Patheon’s performance of the services under the MSA, certain indemnification rights in favor of both parties, limitations of liability and customary confidentiality provisions. Also 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 API 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 The Company’s Stamford Lease has an initial 7-year December 2023 In connection with the signing of the Stamford Lease, the Company entered into a standby letter of credit agreement which serves as a security deposit for the Premises. The standby letter of credit is automatically renewed annually through November 2023. This standby letter of credit is secured with restricted cash in a money market account and is included within current assets as of December 31, 2022 (refer to Note 8, Restricted Cash In June 2020, the Company entered into an amendment to the Stamford Lease to add additional office space, or the Lease Amendment. The term of the Lease Amendment began when renovation of the additional space was completed and the Company took possession of the additional space in October 2020, or the Amendment Commencement Date, and ends on December 31, 2023. The Lease Amendment is also renewable for one five-year term (see Note 2 - Summary of Significant Accounting Policies – Leases The rent for the Lease Amendment is at market rate as of the signing of the Lease Amendment. The Lease Amendment requires monthly lease payments, including rent escalations, during the lease term. The Company began paying rent for the Lease Amendment on the Amendment Commencement Date. In October 2020, the Company recorded an operating lease liability of $1,934 for the Lease Amendment as the sum of the present value of the future minimum lease payments over the term for the new lease. The Company also recorded a corresponding ROU asset of $1,934, as no lease incentives were identified in the Lease Amendment. Lease expenses on the Stamford lease and Lease Amendment are recognized on a straight-line basis over the lease term. As a result, $1,624, $1,624 and $1,116 of operating lease cost, or lease expense, was recognized for the years ended December 31, 2022, 2021 and 2020, respectively, consisting of $1,137 relating to R&D lease expense and $487 relating to G&A lease expense for the Stamford Lease and Lease Amendment in the 2022 period, $1,137 relating to R&D lease expense and $487 relating to G&A lease expense for the Stamford Lease and Lease Amendment in the 2021 period, and $781 relating to R&D lease expense and $335 relating to G&A lease expense for the Stamford Lease and Lease Amendment in the 2020 period. Other information related to the Stamford Lease and Lease Amendment was as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ ​ 2022 2021 ​ Cash paid for amounts included in the measurement of lease liabilities: ​ ​ ​ ​ Operating cash outflows relating to operating leases ​ $ 1,957 ​ $ 1,921 ​ ROU assets obtained in exchange for new operating lease liabilities ​ $ — ​ $ — ​ Remaining lease term - operating leases (years) ​ 1.0 ​ 2.0 ​ Discount rate - operating leases ​ ​ 7.0 % ​ 7.0 % ​ Future minimum lease payments under the non-cancellable operating leases for the Stamford lease and the Lease Amendment, as well as a reconciliation of these undiscounted cash flows to the operating lease liabilities as of December 31, 2022, were as follows: ​ ​ ​ ​ Year Ending December 31, ​ ​ 2023 $ 1,992 Total future minimum lease payments, undiscounted ​ 1,992 Less imputed interest ​ (74) Total ​ $ 1,918 ​ ​ ​ ​ Operating lease liabilities reported as of December 31, 2022: ​ Operating lease liabilities - current ​ $ 1,918 Operating lease liabilities - non-current ​ — Total ​ $ 1,918 ​

Legal Matters

Legal Matters	12 Months Ended
	Dec. 31, 2022
Commitments and Contingencies
Legal Matters	19. Legal Matters From time to time, the Company may become subject to arbitration, litigation or claims arising in the ordinary course of its business. The Company is not currently a party to any arbitration or legal proceeding that, if determined adversely to the Company, would have a material adverse effect on its business, operating results or financial condition. The results of any future claims or proceedings cannot be predicted with certainty, and regardless of the outcome, litigation can have an adverse impact on the Company because of defense and settlement costs, diversion of management resources and other factors.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2022
Related Party Transactions
Related Party Transactions	20. Related Party Transactions As of December 31, 2022, Vifor International owned 7,396,770 , or 13.7% , of the Company’s common stock. CSL Vifor and its affiliates are considered related parties as of December 31, 2022 and 2021 (see Note 12, Collaboration and Licensing Agreements ). As of December 31, 2022, amounts due from CSL Vifor of $3,260 primarily relating to the Company’s share of the profit generated by sales of KORSUVA injection in the United States by CSL Vifor and its commercial supply of KORSUVA injection to CSL Vifor were included within accounts receivable, net – related party. The Company’s collaborative revenue of $16,572 from its share of the profit generated by sales of KORSUVA injection in the United States by CSL Vifor was included within collaborative revenue for the year ended December 31, 2022. The Company’s $15,000 milestone payment received from CSL Vifor for the approval of Kapruvia in April 2022 was included within license and milestone fees revenue for the year ended December 31, 2022. The Company’s $15,000 milestone payment received from CSL Vifor for the approval of KORSUVA injection in August 2021, and the $5,031 of premium from Vifor International’s purchase of the Company’s common stock were included within license and milestone fees revenue for the year ended December 31, 2021. Sales of KORSUVA injection to CSL Vifor of $10,223 and $701 were included within commercial supply revenue for the years ended December 31, 2022 and 2021, respectively. The associated COGS for the Company’s commercial supply revenue from CSL Vifor was $7,266 for the year ended December 31, 2022. Royalty revenue from the net sales of Kapruvia in Europe of $72 were included within royalty revenue for the year ended December 31, 2022. Sales of clinical compound to CSL Vifor for $361 were included within clinical compound revenue for the year ended December 31, 2021.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2022
Business
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with generally-accepted accounting principles in the United States, or 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, related party accounts receivable reserve, as applicable, inventory valuation and related reserves, research and development, or R&D, clinical costs and accrued research projects included in prepaid expenses and accounts payable and accrued expenses, 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 COVID-19 pandemic and geopolitical tensions, such as Russia’s incursion into Ukraine, resulted in a global slowdown of economic activity, decades-high inflation, rising interest rates, and a potential recession in the United States. 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 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 financial statements as soon as they become known. Actual results could differ materially from the Company’s estimates and assumptions.
Concentration of Credit Risk and Suppliers	Concentration of Credit Risk The Company’s financial instruments, which potentially subject the Company to significant concentrations of credit risk consist primarily of cash and cash equivalents, marketable securities, and related party accounts receivable. The Company invests its cash reserves in money market funds or high-quality marketable securities in accordance with its investment policy. The stated objectives of its investment policy are to preserve capital, provide liquidity consistent with forecasted cash flow requirements, maintain appropriate diversification and generate returns relative to these investment objectives and prevailing market conditions. The Company’s investment policy includes guidelines on acceptable investment securities, limits interest-bearing security investments to certain types of debt and money market instruments issued by the U.S. government and institutions with investment grade credit ratings and places restrictions on maturities and concentration by asset class and issuer. The Company’s cash and cash equivalents and marketable securities are held by three major financial institutions. In accordance with the Company’s policies, the Company monitors exposure with its counterparties. The Company also maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and management believes that the Company is not exposed to significant credit risk due to the financial position of the depository institutions in which those deposits are held. The percentages of revenue recognized from license agreement partners of the Company in the years ended December 31, 2022, 2021 and 2020 are included in the following table: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenue ​ ​ Year Ended December 31, ​ 2022 2021 2020 License Agreement Partner: ​ CSL Vifor* 100 % 92 % 100 % ______________ * Includes amounts earned from Vifor Fresenius Medical Care Renal Pharma Ltd. and Vifor International prior to Vifor International’s assignment of its rights and obligations to Vifor Fresenius Medical Care Renal Pharma Ltd. in May 2022. ​ For the years ended December 31, 2022, 2021 and 2020, no additional license agreement partners or customers accounted for more than 10% of the Company’s revenue. Concentration of Suppliers The Company relies on three suppliers to manufacture KORSUVA injection active pharmaceutical ingredient, or API, finished drug product, and finished goods. If any of the Company’s suppliers were to limit or terminate production or otherwise fail to meet the quality or delivery requirements to satisfy the supply commitments, the process of locating and qualifying alternate sources would require up to two years, during which time production could be delayed. Such delays could have a material adverse effect on the Company’s business, financial position, and results of operations.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents include cash on hand, demand deposits, deposits with banks and highly liquid money market funds with holdings of cash and other investments with original maturities of three months or less.
Marketable Securities	Marketable Securities The Company deems certain of its investments to be marketable securities if the investment, or in the case of money market funds, the securities underlying the money market fund, meet the definition of a debt security. The Company’s investments in marketable securities, including U.S. Treasury securities, U.S. government agency obligations, corporate bonds, commercial paper, and municipal bonds are highly rated by Moody’s and S&P and have maturities primarily of less than one year but no longer than two years as of December 31, 2022. Accordingly, credit risk associated with the Company’s available-for-sale debt security portfolio is mitigated. The Company reviews each of its available-for-sale marketable securities for unrealized losses (declines in fair value below its amortized cost basis) at each balance sheet date presented in its financial statements and whenever events or changes in circumstances indicate that the amortized cost basis of an asset may not be recoverable. The Company determines whether any portion of the unrealized loss for any available-for-sale debt security is due to a credit loss, and if so, measures the amount of the credit loss. ​ The Company relies on both qualitative and quantitative factors to determine whether the unrealized loss for each available-for-sale debt security at any balance sheet date is due to a credit loss. Qualitative factors may include a credit downgrade, severity of the decline in fair value below amortized cost and other adverse conditions related specifically to the security, as well as the intent to sell the security, or whether the Company will “more likely than not” be required to sell the security before recovery of its amortized cost basis. The Company’s assessment of whether a security is impaired could change in the future due to new developments or changes in assumptions related to any particular security. If material qualitative factors indicate that a credit loss has occurred, the Company will determine the magnitude of that credit loss using a discounted cash flow model or other quantitative method. If the Company intends to sell the security or it is “more likely than not” that the Company will be forced to sell the security before recovery of the amortized cost of the security, the entire unrealized loss is deemed to be a credit loss, which is recognized in net (loss) income. Otherwise, the portion of the unrealized loss that is due to a credit loss will be recorded as an allowance for credit loss, which will offset the balance of marketable securities and as credit loss expense within other income, net. The portion of the unrealized loss that is not due to a credit loss as well as all unrealized gains will be recorded in Accumulated Other Comprehensive (Loss) Income (see Note 3, Available-for-Sale Marketable Securities Fair Value Measurements) ​ Accrued interest receivables are excluded from the Company’s amortized cost bases for its available-for-sale marketable securities and are included within other receivables. The Company’s policy is to not measure an allowance for credit losses on accrued interest receivable balances at each reporting period since it elects to write off uncollectible accrued interest receivable balances as credit loss expense in a timely manner, which is by maturity date for all categories of its debt securities.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company applies fair value accounting for all financial assets and liabilities that are recognized or disclosed at fair value in the financial statements on a recurring basis. The Company defines fair value as the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. When determining the fair value measurements for assets and liabilities which are required to be recorded at fair value, the Company considers the principal or most advantageous market in which it would transact and the market-based risk measurements or assumptions that market participants would use in pricing the asset or liability, such as risks inherent in valuation techniques, transfer restrictions and credit risks. The Company’s financial instruments consist of cash, cash equivalents, available-for-sale marketable securities, accounts receivable, net – related party, prepaid expenses, restricted cash, accounts payable and accrued liabilities. The fair values of cash, cash equivalents, accounts receivable, net – related party, prepaid expenses, restricted cash, accounts payable and accrued liabilities approximate their carrying values due to the short-term nature of these financial instruments. Available-for-sale marketable securities are reported at their fair values, based upon pricing of securities with the same or similar investment characteristics as provided by third-party pricing services, as described below. The valuation techniques used by the Company are based on observable and unobservable inputs. Observable inputs reflect readily obtainable data from independent sources, while unobservable inputs reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability and are developed based on the best information available in the circumstances. The Company classifies its investments in a fair value hierarchy that is intended to increase consistency and comparability in fair value measurements and related disclosures. The fair value hierarchy is divided into three levels based on the source of inputs as follows: ● Level 1 – Observable inputs – quoted prices in active markets for identical assets and liabilities. ● Level 2 – Observable inputs other than the quoted prices in active markets for identical assets and liabilities – such as quoted prices for similar instruments, quoted prices for identical or similar instruments in inactive markets, or other inputs that are observable or can be corroborated by observable market data. ● Level 3 – Unobservable inputs – includes amounts derived from valuation models where one or more significant inputs are unobservable and require the Company to develop relevant assumptions. The Company records transfers between levels in the hierarchy by assuming that the transfer occurred at the end of the quarter or year-to-date period. Valuation Techniques - Level 2 Inputs The Company estimates the fair values of its financial instruments categorized as level 2 in the fair value hierarchy, including U.S. Treasury securities, U.S. government agency obligations, corporate bonds, commercial paper and municipal bonds, by taking into consideration valuations obtained from third-party pricing services. The pricing services use industry standard valuation models, including both income- and market-based approaches, for which all significant inputs are observable, either directly or indirectly, to estimate fair value. These inputs include reported trades of and broker/dealer quotes on the same or similar securities, benchmark yields, issuer credit spreads, benchmark securities, and other observable inputs. The Company obtains a single price for each financial instrument and does not adjust the prices obtained from the pricing service. The Company validates the prices provided by its third-party pricing services by reviewing their pricing methods, obtaining market values from other pricing sources and comparing them to the share prices presented by the third-party pricing services. After completing its validation procedures, the Company did not adjust or override any fair value measurements provided by its pricing services as of December 31, 2022 or December 31, 2021.
Accounts Receivable, net - Related Party	Accounts Receivable, Net – Related Party Accounts receivable, net – related party primarily consists of amounts due from sales of KORSUVA injection under the Company’s supply agreements with CSL Vifor, as well as revenues earned from its share of the profit generated from KORSUVA injection sales in the United States under the licensing agreements with CSL 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, CSL 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 an insignificant allowance for credit losses as of December 31, 2022.
Inventory, net	Inventory, net Inventories are stated at the lower of cost or net realizable value. The Company determines the cost of inventory using first-in, first-out, or FIFO, method. The Company capitalizes inventory costs associated with the Company’s products prior to regulatory approval, when, based on management’s judgment, future commercialization is considered probable and the future economic benefit is expected to be realized; otherwise, such costs are expensed. The determination to capitalize inventory costs is based on various factors, including status and expectations of the regulatory approval process, any known safety or efficacy concerns, potential labeling restrictions, and any other impediments to obtaining regulatory approval. As KORSUVA injection is the Company’s first commercial product and probability could not be established prior to regulatory approval on August 23, 2021, all inventory costs prior to regulatory approval were expensed as incurred. The Company periodically analyzes its inventory levels to identify inventory that may expire prior to expected sale or has a cost basis in excess of its estimated realizable value and writes down such inventories as appropriate. In addition, the Company’s products are subject to strict quality control and monitoring which the Company performs throughout the manufacturing process. If certain batches or units of product no longer meet quality specifications or become obsolete due to expiration, the Company records a charge to write down such unmarketable inventory to its estimated realizable value.
Property and Equipment, net	Property and Equipment, net Property and equipment (consisting of computer and office equipment, furniture and fixtures and leasehold improvements) are stated at cost, net of accumulated depreciation and amortization of leasehold improvements. Depreciation and amortization are calculated using the straight-line method over the estimated useful lives of the respective assets. Leasehold improvements are amortized over the lesser of their useful lives or the life of the lease. ​ ​ ​ Asset Category Useful Lives Computer and office equipment 5 years Furniture and fixtures 7 years Leasehold improvements lesser of useful life of asset or life of lease (Stamford - 7 years) ​ The Company reviews the recorded values of property and equipment for impairment whenever events or changes in business circumstances indicate that the carrying amount of an asset or group of assets may not be fully recoverable.
Leases	Leases The Company has two leases, a lease agreement for office space in Stamford, Connecticut, or the Stamford Lease, and an amendment to the Stamford Lease to add additional office space, or the Lease Amendment, which is included in operating lease right-of-use assets, or ROU assets, operating lease liabilities – current and operating lease liabilities – non-current as of December 31, 2022 and 2021 (see Note 18, Commitments and Contingencies: Leases In general, the Company determines if a contract, at its inception, is a lease or contains a lease based on whether the contract conveys the right to control the use of identified property, plant, or equipment (an identified asset) for a period of time in exchange for consideration. To determine whether a contract conveys the right to control the use of an identified asset for a period of time, the Company assesses whether, throughout the period of use, it has both the right to obtain substantially all of the economic benefits from use of the identified asset, and the right to direct the use of the identified asset. Both of these criteria are met by the Stamford Lease. The Company determines the amount of the operating lease liability based on the present value of the future minimum lease payments over the remaining lease term. The amount of the operating lease ROU asset is equal to the amount of the lease liability, less accrued rent and lease incentives received from the landlord. Initial direct costs were deemed to be immaterial. Since the Stamford Lease does not provide an implicit interest rate, the Company used an annual incremental borrowing rate of 7% based on the information available at the date of adoption for the purpose of determining the lease liability during the term of the lease. The Stamford Lease contains both a lease and non-lease component which are accounted for separately. The Company allocates the consideration to the lease and the non-lease component on a relative standalone price basis. Lease expense is recognized on a straight-line basis over the lease term. In June 2020, the Company entered into the Lease Amendment. The term of the Lease Amendment began when renovation of the additional space was completed and the Company took possession of the additional space in October 2020, or the Amendment Commencement Date, and ends on December 31, 2023. The Lease Amendment is also renewable for one five-year term, although this renewable period is not included as part of the lease term since it is not reasonably certain that the Company will exercise that option. The Lease Amendment contains both a lease and non-lease component which are accounted for separately. The Company allocates the consideration to the lease and non-lease component on a relative standalone price basis. The rent for the Lease Amendment is at market rate as of the signing of the Lease Amendment. The Lease Amendment requires monthly lease payments, including rent escalations, during the lease term. The Company began paying rent for the Lease Amendment on the Amendment Commencement Date. The Company accounted for the terms and conditions of the Lease Amendment as a lease modification because it grants an additional right-of-use to an underlying asset (the new additional space). A lease modification can result in either a new lease that is accounted for separately from the original lease or as a single modified lease. The Lease Amendment is accounted for separately from the original Stamford Lease because the Lease Amendment grants the right-of-use to additional space and the price of the additional right-of-use is commensurate with its standalone price as no discounts were provided to the Company. Furthermore, there were no material changes to the original Stamford Lease. As of the Amendment Commencement Date, the Company recorded the lease liability for the Lease Amendment as the sum of the present value of the future minimum lease payments over the term for the new lease. Since the Lease Amendment does not provide an implicit interest rate, the Company used an incremental borrowing rate of 7%, which is based on the rate that the Company could obtain in the market for a fully collateralized loan equal to the term of the Lease Amendment. The Company also recorded a ROU asset equal to the amount of the lease liability, as no lease incentives were identified in the Lease Amendment. During the term of the Lease Amendment, interest expense is calculated using the effective interest method and the ROU asset is amortized on a straight-line basis over the lease term, and both are recorded as lease expense.
Revenue Recognition	Revenue Recognition The Company recognizes revenue in an amount that reflects the consideration to which it expects to be entitled in exchange for the transfer of promised goods or services to customers. To determine revenue recognition for contracts with customers, the Company performs the following steps: (1) identifies the contract with the customer, (2) identifies the performance obligations in the contract, (3) determines the transaction price, (4) allocates the transaction price to the performance obligations in the contract, and (5) recognizes revenue when (or as) the entity satisfies a performance obligation. The Company has entered into agreements to license its intellectual property, or IP, related to difelikefalin to develop, manufacture and/or commercialize drug products. These agreements typically contain multiple performance obligations, including licenses of IP and R&D services. Payments to the Company under these agreements may include nonrefundable license fees, payments for research activities, payments based upon the achievement of certain milestones and royalties on any resulting net product sales. The Company receives its share of the net profits from the sale of KORSUVA injection in the United States through its license agreement with CSL Vifor. The Company has adopted a policy to recognize revenue net of tax withholdings, as applicable. The Company identifies agreements as contracts that create enforceable rights and obligations when the agreement is approved by the parties, identifies the rights of the parties and the payment terms, has commercial substance and it is probable that the Company will collect the consideration to which it will be entitled in exchange for the goods and services that will be transferred to the customer. The counterparty is considered to be a customer when it has contracted with the Company to obtain goods and services that are the output of the Company’s ordinary activities (i.e., development of pharmaceutical products) in exchange for consideration. A performance obligation is a promise to transfer distinct goods or services to a customer. Performance obligations that are both capable of being distinct and distinct within the context of the contract are considered to be separate performance obligations. Performance obligations are capable of being distinct if the counterparty is able to benefit from the good or service on its own or together with other resources that are readily available to it. Performance obligations are distinct within the context of the contract when each performance obligation is separately identifiable from each other; i.e., the Company is not using the goods or services as inputs to produce or deliver the combined output or outputs specified by the customer; one or more of the goods or services does not significantly modify or customize one of the other goods or services in the contract; and goods or services are not highly interdependent or not highly interrelated. Performance obligations that are not distinct are accounted for as a single performance obligation over the period that goods or services are transferred to the customer. The determination of whether performance obligations in a contract are distinct may require significant judgment. The transaction price is the amount of consideration that the Company expects to be entitled to in exchange for transferring promised goods or services to the customer based on the contract terms at inception of a contract. There is a constraint on inclusion of variable consideration related to licenses of IP, such as milestone payments or sales-based royalty payments, in the transaction price if there is uncertainty at inception of the contract as to whether such consideration will be recognized in the future because it is probable that there will be a significant reversal of revenue in the future when the uncertainty is resolved. The determination of whether or not it is probable that a significant reversal of revenue will occur in the future depends on the likelihood and magnitude of the reversal. Factors that could increase the likelihood or magnitude of a reversal of revenue include (a) the susceptibility of the amount of consideration to factors outside the entity’s influence, such as the outcome of clinical trials, the timing of initiation of clinical trials by the counterparty and the approval of drug product candidates by regulatory agencies, (b) situations in which the uncertainty is not expected to be resolved for a long period of time, and (c) level of the Company’s experience in the field. When it becomes probable that events will occur, for which variable consideration was constrained at inception of the contract, the Company allocates the related consideration to the separate performance obligations in the same manner as described below. At inception of a contract, the Company allocates the transaction price to the distinct performance obligations based upon their relative standalone selling prices. Standalone selling price is the price at which an entity would sell a promised good or service separately to a customer. The best evidence of standalone selling price is an observable price of a good or service when sold separately by an entity in similar circumstances to similar customers. Since the Company typically does not have such evidence, it estimates standalone selling price so that the amount that is allocated to each performance obligation equals the amount that the Company expects to receive for transferring goods or services. The methods that the Company uses to make such estimates include (1) the adjusted market assessment approach, under which the Company forecasts and analyzes difelikefalin in the appropriate market, the phase of clinical development as well as considering recent similar license arrangements within the same phase of clinical development, therapeutic area, type of agreement, etc. and (2) the expected cost of satisfying the performance obligations plus a margin, or the expected cost plus a margin approach. The Company recognizes revenue when, or as, it satisfies a performance obligation by transferring a promised good or service to a customer and the customer obtains control of the good or service. Revenue related to the grant of a license that is a distinct performance obligation and that is deemed to be functional IP is recognized at the point in time that the Company has the right to payment for the license, the customer has legal title to the license and can direct the use of the license (for example, to grant sublicenses), the customer has the significant risks and rewards of ownership of the license and the customer has accepted the asset (license) by signing the license agreement. Recognition of revenue related to R&D services that are a distinct performance obligation or that are combined with granting of a license as a single performance obligation is deferred at inception of a contract and is recognized as those services are performed based on the costs incurred as a percentage of the estimated total costs to be incurred to complete the performance obligation. The Company’s license agreements include the right to grant sub-licenses. The amount of any potential sub-license fees to be received by the Company, which is based on a formula if applicable to that respective agreement, 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. Milestone payments are considered to be variable consideration and are not included in the transaction price at inception of the contract if it is uncertain that the milestone will be achieved. Rather, when it becomes probable that the milestone will be achieved and, therefore, there will not be a significant reversal of revenue in future periods, the respective amount to be earned is included in the transaction price, allocated to the distinct performance obligations based on their relative standalone selling price and recognized as revenue, as described above. Sales milestones and sales-based royalty payments related to a license of IP are recognized as revenue when the respective sales occur. Collaborative Revenue Collaborative revenue includes the Company’s share of the profits generated by CSL Vifor’s sale of KORSUVA injection to third parties in the United States under its existing license agreements. The Company has adopted a policy to recognize revenue net of tax withholdings, as applicable. The Company determined that CSL Vifor is a customer in relation to its profit share arrangement with CSL Vifor. The Company sells commercial product to CSL Vifor, who ultimately sells the commercial product to third parties. The Company’s profit share arrangement revenues generated from sales of KORSUVA injection in the United States are considered akin to sales-based royalties. In accordance with the sales-based royalty exception, the Company recognizes its share of the pre-tax commercial net profit generated from the sales of KORSUVA injection in the United States in the period the product sales are earned, as reported by CSL Vifor. The related COGS for CSL Vifor associated with the net profit share arrangement as well as the marketing and distribution fee for the applicable period reduces the Company’s profit share revenue for the period. The net sales amounts are determined based on amounts provided by CSL Vifor and involve the use of estimates and judgments, such as product sales allowances and accruals related to prompt payment discounts, and chargebacks, which could be adjusted based on actual results in the future. The Company is dependent on CSL Vifor for timely and accurate information regarding the net revenues from sales of KORSUVA injection in the United States to accurately report its results of operations. If the Company does not receive timely and accurate information or incorrectly estimates activity levels associated with the profit share arrangement at a given point in time, the Company could be required to record adjustments in future periods. The Company records revenue transactions as net product revenue if it is deemed the principal in the transaction, which includes being the primary obligor, retaining inventory risk, and control over pricing. Given that the Company is not the primary obligor and does not have the inventory risks in the license agreement with CSL Vifor, it records its share of the net profits from the sales of KORSUVA injection in the United States on a net basis and presents the settlement payments from CSL Vifor as collaborative revenue. The Company and CSL Vifor settle the profit sharing quarterly (see Note 12, Collaboration and Licensing Agreements) Collaborative revenue also includes milestone payments associated with the Company’s license agreement with Maruishi. Upfront and milestone payments associated with the license agreement with Maruishi are allocated between license and milestone fees and collaborative revenue based on the relative standalone selling prices determined at contract inception that were allocated to the R&D services performance obligation (see Note 13, Revenue Recognition License and Milestone Fees License and milestone fees include upfront and milestone payments associated with the Company’s license agreements with CSL Vifor, Maruishi and CKDP. All upfront and milestone payments associated with the license agreements with CSL Vifor and CKDP are recognized as license and milestone fees since they contain only one performance obligation. Upfront and milestone payments associated with the license agreement with Maruishi are allocated between license and milestone fees and collaborative revenue based on the relative standalone selling prices determined at contract inception (see Note 13, Revenue Recognition Commercial Supply Revenue Commercial supply revenue includes sales of KORSUVA injection commercial product to CSL Vifor, which ultimately acts as the principal in the net profit-sharing arrangement between the two parties since commercial launch in April 2022, which then sells to third parties in the United States. Commercial supply revenue is recognized when CSL Vifor obtains control of the Company’s commercial product, which occurs at a point in time, typically upon receipt of KORSUVA injection by CSL Vifor, and generally occurs after the commercial product has passed all quality testing required for acceptance by CSL Vifor. The Company calculates its commercial supply revenue based on its COGS plus an agreed upon margin. Royalty Revenue Royalty revenue includes amounts related to the Company’s royalties earned from CSL Vifor on the net sales of Kapruvia in Europe, based on the amount of net sales in a licensed territory during a calendar year. Sales-based royalty payments related to a license of IP are recognized as revenue when the respective sales occur, and the net sales tier is achieved. Clinical Compound Revenue Clinical compound revenue includes sales of clinical compound to CSL Vifor (prior to FDA approval), and Maruishi. The Company recognizes revenue on clinical compound sales when control has transferred to CSL Vifor and Maruishi, which occurs at a point in time, typically upon receipt of the clinical compound, and generally occurs after the clinical compound has passed all quality testing required for acceptance. The sales of clinical compound are reimbursed at COGS plus an agreed upon margin.
Cost of Goods Sold (COGS)	Cost of Goods Sold (COGS) COGS includes costs related to sales of the Company’s commercial product, KORSUVA injection, to CSL Vifor. Costs related to the sales of KORSUVA injection are generally recognized upon receipt of shipment by CSL Vifor. The Company’s COGS for KORSUVA injection includes the cost of producing commercial product that correspond with commercial supply revenue, such as third-party supply and overhead costs, as well as certain period costs related to freight, packaging, stability, and quality testing. No COGS was recognized prior to January 1, 2022, as regulatory approval of KORSUVA injection occurred in August 2021 and all inventory costs prior to regulatory approval were expensed as incurred.
Research and Development (R&D) Expenses	Research and Development (R&D) Expenses R&D costs are charged to expense as incurred. Costs incurred under agreements with third parties are charged to expense as incurred in accordance with the specific contractual performance terms of such agreements. R&D expenses include, among other costs, compensation and other personnel-related costs, including consultant costs, and costs to conduct clinical trials using clinical research organizations, or CROs, which include upfront, milestone and monthly expenses as well as reimbursement for pass through costs. The amount of clinical trial expense recognized in any period varies depending on the duration and progress of each clinical trial, including the required level of patient enrollment, the rate at which patients actually enroll in and drop-out of the clinical trial, and the number of sites involved in the trial as well as the activities to be performed by the sites each period. R&D costs also include costs to manufacture product candidates and clinical supplies, laboratory supplies costs, facility-related costs and stock-based compensation for R&D personnel. Non-refundable R&D advance payments are deferred and capitalized as prepaid R&D expense. The capitalized amounts are expensed as the related goods are delivered or services are performed. As of December 31, 2022 and 2021, the Company recorded $15,188 and $1,481 as prepaid R&D expense, respectively.
General and Administrative (G&A) Expenses	General and Administrative (G&A) Expenses G&A costs are charged to expense as incurred. G&A expenses consist primarily of salaries and other related costs, including stock-based compensation, for personnel in executive, finance, accounting, legal, business development, information technology, human resources, project management, alliance management, and procurement functions. Other costs include facility costs not otherwise included in R&D expenses, legal fees, insurance costs, investor relations costs, patent costs and fees for accounting and consulting services. As noted in Note 12, Collaboration and Licensing Agreements ​
Stock-Based Compensation	Stock-Based Compensation The Company grants stock options to employees, non-employee members of the Company’s Board of Directors and non-employee consultants as compensation for services performed. All share-based payments, including grants of stock options, are recognized based on their grant date fair values. The grant date fair value of stock options is estimated using the Black-Scholes option valuation model. Using this model, fair value is calculated based on assumptions with respect to (i) the fair value or market price of the Company’s common stock on the grant date; (ii) expected volatility of the Company’s common stock price, (iii) the periods of time over which employees and members of the Company’s Board of Directors or non-employee consultants are expected to hold their options prior to exercise (expected term), (iv) expected dividend yield on the Company’s common stock, and (v) risk-free interest rates. The Company’s common stock has been traded on a public exchange only since January 31, 2014. Since that time, exercises of stock options have been limited due to various factors, including fluctuations in the Company’s stock price to below the exercise prices of awards and blackout periods during which exercises are not allowed, among others. Therefore, the Company believes that as of December 31, 2022, it does not have sufficient company-specific information available to determine the expected term based on its historical data. As a result, the expected term of stock options granted is determined using the average of the vesting period and term (6.25 years), an accepted method for the Company’s option grants under the SEC’s Staff Accounting Bulletin No. 110, Share-Based Payment. The Company calculates the expected volatility using company-specific trading activity of its common stock over the option’s expected term. The expected dividend yield is zero as the Company has never paid dividends and does not currently anticipate paying any in the foreseeable future. Risk-free interest rates are based on quoted U.S. Treasury rates for securities with maturities approximating the option’s expected term. The Company’s policy is to account for forfeitures of share-based payments as they occur. Compensation cost for all share-based payments granted with service-based graded vesting schedules is recognized using the straight-line method over the requisite service period.
Other Income, Net	Other Income, Net Other income, net consists of interest and dividend income earned on the Company’s cash, cash equivalents, and marketable securities, realized gains and losses on the sale of marketable securities and property and equipment, as well as accretion of discounts/amortization of premiums on purchases of marketable securities. In the event the Company records a credit loss expense on its available-for-sale debt securities, those expenses would be offset against other income.
Income Taxes	Income Taxes The Company accounts for income taxes using the asset and liability method. Under this method, deferred tax assets and liabilities are determined based on differences between the financial reporting and tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. Deferred income tax assets are reduced, as necessary, by a valuation allowance when management determines it is more likely than not that some or all of the tax benefits will not be realized. There were no material uncertain tax positions taken as of December 31, 2022 and 2021. The Company does not have any interest or penalties accrued related to tax positions as it does not have any unrecognized tax benefits. In the event the Company determines that accrual of interest or penalties are necessary in the future, the amount will be presented as a component of interest expense.
(Loss) Income Per Share	(Loss) Income Per Share The Company computes basic net (loss) income per share by dividing net (loss) income by the weighted average number of shares of common stock outstanding. Diluted net (loss) income per share includes the potential dilutive effect of common stock equivalents as if such securities were converted or exercised during the period, when the effect is dilutive. Common stock equivalents may include outstanding stock options and restricted stock units, which are included under the treasury stock method when dilutive. For each of the years ended December 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 have been anti-dilutive due to the Company’s net losses for those periods. For the year ended December 31, 2020, the Company included the effects of dilutive shares that were outstanding in the denominator as their inclusion was dilutive due to the Company’s net income for the period.
Segment Reporting	Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business as one operating segment, which includes all activities related to the discovery, development, and commercialization of novel therapeutics to treat serious medical conditions, including pruritus.
Litigation Reserves	Litigation Reserves From time to time, the Company may become subject to arbitration, litigation or claims arising in the ordinary course of its business. Accruals are recorded when it is probable that a liability has been incurred and the amount of the liability can be reasonably estimated. The Company reviews these reserves at least quarterly and adjusts these reserves to reflect current law, progress of each case, opinions and views of legal counsel and other advisers, the Company’s experience in similar matters and intended response to the litigation. The Company expenses amounts for administering or litigating claims as incurred. Accruals for legal proceedings, if any, are included in accounts payable and accrued expenses.
Accounting Pronouncements Recently Adopted and Recent Accounting Pronouncements Not Yet Adopted	Accounting Pronouncements Recently Adopted In December 2022, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, 2022-06, Reference Rate Reform (Topic 848): Deferral of the Sunset Date of Topic 848 Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting,

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2022
Business
Schedule of percentages of revenue recognized from license agreement partners	The percentages of revenue recognized from license agreement partners of the Company in the years ended December 31, 2022, 2021 and 2020 are included in the following table: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenue ​ ​ Year Ended December 31, ​ 2022 2021 2020 License Agreement Partner: ​ CSL Vifor* 100 % 92 % 100 % ______________ * Includes amounts earned from Vifor Fresenius Medical Care Renal Pharma Ltd. and Vifor International prior to Vifor International’s assignment of its rights and obligations to Vifor Fresenius Medical Care Renal Pharma Ltd. in May 2022.
Summary of Useful Lives of Property and Equipment	Property and equipment (consisting of computer and office equipment, furniture and fixtures and leasehold improvements) are stated at cost, net of accumulated depreciation and amortization of leasehold improvements. Depreciation and amortization are calculated using the straight-line method over the estimated useful lives of the respective assets. Leasehold improvements are amortized over the lesser of their useful lives or the life of the lease. ​ ​ ​ Asset Category Useful Lives Computer and office equipment 5 years Furniture and fixtures 7 years Leasehold improvements lesser of useful life of asset or life of lease (Stamford - 7 years) ​

Available-for-Sale Marketable_2

Available-for-Sale Marketable Securities (Tables)	12 Months Ended
	Dec. 31, 2022
Available-for-Sale Marketable Securities
Summary of Available-for-Sale Marketable Securities by Major Type of Security	The following tables summarize the Company’s available-for-sale marketable securities by major type of security as of December 31, 2022 and 2021: As of December 31, 2022 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross Unrealized ​ Estimated Fair Type of Security Amortized Cost Gains Losses Value U.S. government agency obligations ​ $ 9,500 ​ $ — ​ $ (623) ​ $ 8,877 Corporate bonds ​ 35,828 ​ — ​ (643) ​ 35,185 Commercial paper ​ ​ 26,879 ​ ​ 2 ​ ​ (6) ​ ​ 26,875 Municipal bonds ​ 22,473 ​ — ​ (402) ​ 22,071 Total available-for-sale marketable securities ​ $ 94,680 ​ $ 2 ​ $ (1,674) ​ $ 93,008 ​ 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	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 December 31, 2022 and 2021: As of December 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. government agency obligations ​ $ — ​ $ — ​ $ 8,877 ​ $ (623) ​ $ 8,877 ​ $ (623) Corporate bonds ​ ​ 1,470 ​ ​ (26) ​ ​ 33,715 ​ ​ (617) ​ ​ 35,185 ​ ​ (643) Commercial paper ​ ​ 15,906 ​ ​ (6) ​ ​ — ​ ​ — ​ ​ 15,906 ​ ​ (6) Municipal bonds ​ 982 ​ (16) ​ 19,589 ​ (386) ​ 20,571 ​ (402) Total ​ $ 18,358 ​ $ (48) ​ $ 62,181 ​ $ (1,626) ​ $ 80,539 ​ $ (1,674) ​ 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	The Company classifies its marketable debt securities based on their contractual maturity dates. As of December 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 December 31, 2022 ​ As of December 31, 2021 Contractual maturity Amortized Cost Fair Value Amortized Cost Fair Value Less than one year ​ $ 82,678 ​ $ 81,658 ​ $ 153,631 ​ $ 153,582 One year to three years ​ 12,002 ​ 11,350 ​ 70,063 ​ 69,754 Total ​ $ 94,680 ​ $ 93,008 ​ $ 223,694 ​ $ 223,336 ​

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive (Loss) Income (Tables)	12 Months Ended
	Dec. 31, 2022
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	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 years ended December 31, 2022, 2021 and 2020. ​ ​ ​ ​ ​ Total Accumulated ​ ​ Other Comprehensive ​ ​ (Loss) Income Balance, December 31, 2019 ​ $ 170 Other comprehensive income before reclassifications ​ 175 Amount reclassified from accumulated other comprehensive income ​ (272) Net current period other comprehensive loss ​ (97) Balance, December 31, 2020 ​ 73 Other comprehensive loss before reclassifications ​ (392) Amount reclassified from accumulated other comprehensive income ​ (39) Net current period other comprehensive loss ​ (431) Balance, December 31, 2021 ​ $ (358) Other comprehensive loss before reclassifications ​ (1,314) Amount reclassified from accumulated other comprehensive loss ​ — Net current period other comprehensive loss ​ (1,314) Balance, December 31, 2022 ​ $ (1,672) ​
Schedule of Reclassification Out of Accumulated Other Comprehensive (Loss) Income	Amounts reclassified out of accumulated other comprehensive (loss) income into net (loss) income are determined by specific identification. The reclassifications out of accumulated other comprehensive (loss) income and into net (loss) income were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Affected Line Item in the Component of Accumulated Other ​ Year Ended December 31, ​ Statements of Comprehensive (Loss) Income 2022 2021 2020 Comprehensive (Loss) Income Unrealized gains on available-for-sale marketable securities: ​ ​ ​ Realized gains on sales of securities ​ $ — ​ $ 39 ​ $ 272 Other income, net Income tax effect ​ — ​ — ​ — Benefit from income taxes Realized gains on sales of securities, net of tax ​ $ — ​ $ 39 ​ $ 272 ​ ​

Inventory, net (Tables)

Inventory, net (Tables)	12 Months Ended
	Dec. 31, 2022
Inventory, net
Schedule of Inventory, net	Inventories consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2022 December 31, 2021 Raw materials ​ $ 1,918 ​ $ 927 Work-in-process ​ 499 ​ 1,657 ​ ​ ​ 2,417 ​ ​ 2,584 Less Inventory Reserve for Obsolescence ​ (34) ​ — Total ​ $ 2,383 ​ $ 2,584 ​

Property and Equipment, net (Ta

Property and Equipment, net (Tables)	12 Months Ended
	Dec. 31, 2022
Property and Equipment, net
Property and Equipment, net	Property and equipment, net consists of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2022 2021 Computer and office equipment ​ $ 239 ​ $ 239 Furniture and fixtures ​ 330 ​ 330 Leasehold improvements ​ 1,266 ​ 1,223 ​ ​ $ 1,835 ​ $ 1,792 Less accumulated depreciation and amortization ​ (1,409) ​ (1,161) Property and equipment, net ​ $ 426 ​ $ 631 ​

Restricted Cash (Tables)

Restricted Cash (Tables)	12 Months Ended
	Dec. 31, 2022
Restricted Cash
Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the Balance Sheets that sum to the total of the same such amounts shown in the Statements of Cash Flows. ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2022 December 31, 2021 Cash and cash equivalents ​ $ 63,741 ​ $ 13,453 Restricted cash, current assets ​ 408 ​ — Restricted cash, long-term assets ​ — ​ 408 Total cash, cash equivalents, and restricted cash shown in the Statements of Cash Flows ​ $ 64,149 ​ $ 13,861

Accounts Payable and Accrued _2

Accounts Payable and Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2022
Accounts Payable and Accrued Expenses
Schedule of Accounts Payable and Accrued Expenses	Accounts payable and accrued expenses consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2022 December 31, 2021 Accounts payable ​ $ 9,604 ​ $ 5,625 Accrued research projects ​ 5,200 ​ 4,648 Accrued compensation and benefits ​ 5,219 ​ 4,959 Accrued professional fees and other ​ 1,517 ​ 629 Total ​ $ 21,540 ​ $ 15,861

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2022
Fair Value Measurements
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 December 31, 2022 and 2021, and by level within the fair value hierarchy: Fair value measurement as of December 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 ​ $ 63,741 ​ $ 63,741 ​ $ — ​ $ — Available-for-sale marketable securities: ​ ​ ​ ​ ​ ​ ​ U.S. government agency obligations ​ 8,877 ​ — ​ 8,877 ​ — Corporate bonds ​ 35,185 ​ — ​ 35,185 ​ — Commercial paper ​ 26,875 ​ — ​ 26,875 ​ — Municipal bonds ​ 22,071 ​ — ​ 22,071 ​ — Restricted cash: ​ ​ ​ ​ ​ ​ ​ Commercial money market account ​ 408 ​ 408 ​ — ​ — Total financial assets ​ $ 157,157 ​ $ 64,149 ​ $ 93,008 ​ $ — ​ 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 ​ $ — ​

Revenue Recognition (Tables)

Revenue Recognition (Tables)	12 Months Ended
	Dec. 31, 2022
Revenue Recognition
Schedule of disaggregation of revenue	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ 2022 2021 2020 Collaborative revenue ​ ​ ​ ​ ​ ​ ​ ​ ​ CSL Vifor (KORSUVA injection profit sharing) ​ $ 16,572 ​ $ — ​ $ — Maruishi ​ ​ — ​ ​ 706 ​ ​ — Total collaborative revenue ​ $ 16,572 ​ $ 706 ​ $ — License and milestone fees ​ ​ ​ ​ ​ ​ ​ ​ ​ CSL Vifor* ​ ​ 15,000 ​ ​ 20,031 ​ ​ 133,813 Maruishi ​ ​ — ​ ​ 1,192 ​ ​ — CKDP ​ ​ — ​ ​ — ​ ​ 626 Total license and milestone fees ​ $ 15,000 ​ $ 21,223 ​ $ 134,439 Commercial supply revenue ​ ​ ​ ​ ​ ​ ​ ​ ​ CSL Vifor* (KORSUVA injection) ​ $ 10,223 ​ $ 701 ​ $ — Total commercial supply revenue ​ $ 10,223 ​ $ 701 ​ $ — Royalty revenue ​ ​ ​ ​ ​ ​ ​ ​ ​ CSL Vifor (Kapruvia ex U.S.) ​ $ 72 ​ $ — ​ $ — Total royalty revenue ​ $ 72 ​ $ — ​ $ — Clinical compound revenue ​ ​ ​ ​ ​ ​ ​ ​ ​ CSL Vifor* (difelikefalin injection) ​ $ — ​ $ 361 ​ $ 115 Maruishi ​ ​ — ​ ​ 37 ​ ​ 528 Total clinical compound revenue ​ $ — ​ $ 398 ​ $ 643 _____________________________ * Includes amounts earned from Vifor Fresenius Medical Care Renal Pharma Ltd. and Vifor International prior to Vifor International’s assignment of its rights and obligations to Vifor Fresenius Medical Care Renal Pharma Ltd. in May 2022.

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2022
Summary of Assumptions Used in Black-Scholes Option Pricing Model	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ ​ 2022 2021 2020 Risk-free interest rate 1.70% - 4.21 % 0.66% - 1.41 % 0.35% - 1.57 % Expected volatility 77.7% - 81.9 % 71.6% - 83.5 % 71.8% - 74.8 % Expected dividend yield 0 % 0 % 0 % Expected life of employee and Board options (in years) 6.25 6.25 6.25 ​ ​
Summary of Compensation Expense Relating to Stock Options	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ 2022 2021 2020 Research and development ​ $ 7,222 ​ $ 7,126 ​ $ 6,765 General and administrative ​ 6,426 ​ 9,569 ​ 4,943 Total stock option expense ​ $ 13,648 ​ $ 16,695 ​ $ 11,708
Summary of Stock Option Activity	A summary of the Company’s stock option activity related to employees, non-employee members of the Board of Directors and non-employee consultants for the 2019 Plan and the 2014 Plan as of and for the year ended December 31, 2022 is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ Aggregate ​ ​ Number of ​ Average Exercise ​ Intrinsic ​ Shares Price Value Outstanding, December 31, 2021 6,512,280 ​ $ 15.58 ​ Granted 1,899,919 ​ 10.25 ​ Exercised (48,307) ​ 6.43 ​ Forfeited (356,819) ​ 14.50 ​ Expired (317,624) ​ 16.09 ​ Outstanding, December 31, 2022 7,689,449 ​ $ 14.35 ​ $ 3,028 Weighted average remaining contractual life as of December 31, 2022 (in years) 5.95 ​ ​ Options exercisable, December 31, 2022 4,972,944 ​ $ 15.06 ​ $ 1,940 Weighted average remaining contractual life as of December 31, 2022 (in years) 4.40 ​ ​ Options vested and expected to vest as of December 31, 2022 7,689,449 ​ $ 14.35 ​ $ 3,028 Weighted average remaining contractual life as of December 31, 2022 (in years) 5.95 ​ ​ ​
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 year ended December 31, 2022 is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ Number of ​ Average Grant ​ Units Date Fair Value Outstanding, December 31, 2021 576,544 ​ $ 17.50 Awarded 474,193 ​ 10.10 Vested and released (268,222) ​ 16.33 Forfeited (410,002) ​ 13.62 Outstanding, December 31, 2022 372,513 ​ $ 13.20 Restricted stock units exercisable (vested and deferred), December 31, 2022 — ​ ​ ​ ​

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2022
Income Taxes
Components of Income Taxes (Benefit)	The Company’s benefit from income taxes is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2022 2021 2020 Current: ​ ​ ​ Federal ​ $ — ​ $ — ​ $ — State ​ — ​ — ​ (691) ​ ​ — ​ — ​ (691) Deferred: ​ ​ ​ Federal ​ — ​ — ​ — State ​ — ​ — ​ — ​ ​ — ​ — ​ — Benefit from income taxes ​ $ — ​ $ — ​ $ (691) ​
Schedule of Reconciliation of Income Taxes Computed Using U.S. Federal Statutory Rate to that Reflected in Operations	A reconciliation of income taxes computed using the U.S. federal statutory rate to that reflected in operations is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2022 2021 2020 Income taxes using U.S. federal statutory rate 21.00 % 21.00 % 21.00 % State income taxes, net of federal benefit (1.00) % 7.84 % (58.68) % Tax Cuts and Jobs Act 0.00 % 0.00 % 0.00 % Impact of R&D tax credit on effective tax rate 4.91 % 2.87 % (52.06) % Stock option shortfalls and cancellations (3.33) % (4.74) % 0.35 % Permanent items and other (1.86) % (1.29) % (5.08) % Change in valuation allowance (19.88) % (25.69) % 84.61 % Provision to return 0.16 % 0.01 % 0.92 % Non-taxable revenue 0.00 % 0.00 % 0.00 % ​ 0.00 % 0.00 % (8.94) % ​
Schedule of Significant Components of Company's Deferred Tax Assets and Liabilities	Significant components of the Company’s deferred tax assets and liabilities are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2022 2021 Valuation allowance $ (160,814) $ (143,388) ​ ​ ​ ​ ​ ​ ​ Net operating loss carryforwards ​ ​ 113,058 ​ ​ 113,636 Federal and state tax credits ​ 26,358 ​ 24,428 Stock-based compensation expense ​ 3,434 ​ 5,023 Intangible asset amortization ​ ​ 17,265 ​ ​ — Other ​ 1,167 ​ 1,268 Deferred tax assets ​ 161,282 ​ 144,355 ​ ​ ​ ​ ​ ​ ​ Other ​ (468) ​ (967) Deferred tax liabilities: ​ (468) ​ (967) ​ ​ ​ ​ ​ Net deferred tax asset: ​ $ — ​ $ — ​

Net (Loss) Income per Share (Ta

Net (Loss) Income per Share (Tables)	12 Months Ended
	Dec. 31, 2022
Net (Loss) Income per Share
Computation of Denominators Used in Net (Loss) Income per Share	The denominators used in the net (loss) income per share computations are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ 2022 2021 2020 Basic: Weighted average common shares outstanding 53,653,564 50,718,765 47,413,250 Diluted: Weighted average common shares outstanding - Basic 53,653,564 50,718,765 47,413,250 Common stock equivalents* — — 501,780 Denominator for diluted net (loss) income per share 53,653,564 50,718,765 47,915,030 * For the year end December 31, 2020, common stock equivalents include dilutive stock options and restricted stock units. For the years ended December 31, 2022 and 2021, no amounts were considered as their effects would have been anti-dilutive due to net losses for those periods.
Computation of Basic and Diluted Net (Loss) Income per Share	Basic and diluted net (loss) income per share is computed as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ 2022 2021 2020 Net (loss) income - basic and diluted ​ $ (85,474) ​ $ (88,441) ​ $ 8,410 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average common shares outstanding - basic ​ 53,653,564 ​ 50,718,765 ​ 47,413,250 Effect of dilutive securities: ​ ​ ​ ​ ​ ​ Stock options ​ ​ — ​ ​ — ​ ​ 481,254 Restricted stock units ​ ​ — ​ ​ — ​ ​ 20,526 Weighted-average common shares outstanding - diluted ​ ​ 53,653,564 ​ ​ 50,718,765 ​ ​ 47,915,030 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net (loss) income per share: ​ ​ ​ Basic ​ $ (1.59) ​ $ (1.74) ​ $ 0.18 Diluted ​ $ (1.59) ​ $ (1.74) ​ $ 0.18 ​

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2022
Commitments and Contingencies
Schedule of Other Information related to Stamford Lease and lease amendment	Other information related to the Stamford Lease and Lease Amendment was as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ ​ 2022 2021 ​ Cash paid for amounts included in the measurement of lease liabilities: ​ ​ ​ ​ Operating cash outflows relating to operating leases ​ $ 1,957 ​ $ 1,921 ​ ROU assets obtained in exchange for new operating lease liabilities ​ $ — ​ $ — ​ Remaining lease term - operating leases (years) ​ 1.0 ​ 2.0 ​ 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 the non-cancellable operating leases for the Stamford lease and the Lease Amendment, as well as a reconciliation of these undiscounted cash flows to the operating lease liabilities as of December 31, 2022, were as follows: ​ ​ ​ ​ Year Ending December 31, ​ ​ 2023 $ 1,992 Total future minimum lease payments, undiscounted ​ 1,992 Less imputed interest ​ (74) Total ​ $ 1,918 ​ ​ ​ ​ Operating lease liabilities reported as of December 31, 2022: ​ Operating lease liabilities - current ​ $ 1,918 Operating lease liabilities - non-current ​ — Total ​ $ 1,918

Business - Additional Informati

Business - Additional Information (Detail) $ in Thousands		1 Months Ended			12 Months Ended
	May 17, 2018 shares	Oct. 31, 2021 USD ($) shares	Oct. 31, 2020 USD ($) shares	May 31, 2018 USD ($) shares	Dec. 31, 2022 USD ($) item	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Nature Of Business [Line Items]
Date of formation					Jul. 02, 2004
Proceeds from equity and debt financing					$ 519,600
Number of follow-on public offerings | item					4
Payments received in connection with license and supply agreements					$ 266,790
Proceeds from the sale of common stock under license agreement with Vifor International						$ 44,969	$ 38,449
Unrestricted cash and cash equivalents and marketable securities					156,749
Accumulated deficit					566,232	480,758
Net (loss) income					(85,474)	(88,441)	8,410
Net cash used in operating activities					$ (78,730)	$ (60,087)	$ (5,487)
Vifor Fresenius Medical Care Renal Pharma Ltd Agreement No 1 [Member]
Nature Of Business [Line Items]
Percentage of net profit sharing			60%				60%
Vifor Fresenius Medical Care Renal Pharma Ltd Agreement No 2 [Member]
Nature Of Business [Line Items]
Percentage of net profit sharing				50%
Vifor International Ltd. [Member]
Nature Of Business [Line Items]
Proceeds from the sale of common stock under license agreement with Vifor International			$ 38,449	$ 14,556
Proceeds from sale of common stock in connection with regulatory milestone		$ 44,969
Vifor International Ltd. [Member] | Vifor Fresenius Medical Care Renal Pharma Ltd Agreement No 1 [Member]
Nature Of Business [Line Items]
Percentage of net profit sharing			40%				40%
Common stock, shares issued | shares		3,282,391	2,939,552
Vifor International Ltd. [Member] | Vifor Fresenius Medical Care Renal Pharma Ltd Agreement No 2 [Member]
Nature Of Business [Line Items]
Common stock, shares issued | shares	1,174,827
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
Vifor Fresenius Medical Care Renal Pharma, Ltd [Member] | Vifor Fresenius Medical Care Renal Pharma Ltd Agreement No 2 [Member]
Nature Of Business [Line Items]
Percentage of net profit sharing				50%

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($) item segment	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Prepaid R&D expense | $	$ 15,188	$ 1,481
Expected dividend yield	0%	0%	0%
Number of operating segments | segment	1
Commercial Supply Revenue
Summary Of Significant Accounting Policies [Line Items]
Number of parties in net profit sharing arrangement | item	2
CSL Vifor and CKDP Agreements [Member] | License and Milestone Fees
Summary Of Significant Accounting Policies [Line Items]
Number of performance obligations for revenue recognized | item	1
Prior to Regulatory Approval [Member]
Summary Of Significant Accounting Policies [Line Items]
Cost of goods sold | $		$ 0	$ 0
Options [Member]
Summary Of Significant Accounting Policies [Line Items]
Expected life of options (in years)	6 years 3 months	6 years 3 months	6 years 3 months
Expected dividend yield	0%	0%	0%

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Concentration of Credit Risk (Detail)	12 Months Ended
	Dec. 31, 2022 Institution item	Dec. 31, 2021	Dec. 31, 2020
Concentration Risk [Line Items]
Number of suppliers | item	3
Maximum [Member]
Concentration Risk [Line Items]
Period that would require for locating and qualifying alternate sources if the suppliers fail to meet supply commitments	2 years
Revenue from Contract with Customer Benchmark [Member] | Customer Concentration Risk [Member] | CSL Vifor [Member]
Concentration Risk [Line Items]
Concentration of revenue percentage	100%	92%	100%
Cash And Cash Equivalents And Marketable Securities [Member]
Concentration Risk [Line Items]
Number Of Financial Institutions | Institution	3

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Summary of Useful Lives of Property and Equipment, net (Detail)	12 Months Ended
	Dec. 31, 2022
Computer and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives, years	5 years
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives, years	7 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives, description	lesser of useful life of asset or life of lease (Stamford - 7 years)
Stamford Operating Lease [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives, years	7 years

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Leases (Details)	1 Months Ended	12 Months Ended
	Jun. 30, 2020 item	Dec. 31, 2022 item lease	Dec. 31, 2021 lease
Stamford Operating Lease [Member]
Lessee, Lease, Description [Line Items]
Number of renewable terms		1
Operating Lease, renewable term		5 years
New Stamford Lease [Member]
Lessee, Lease, Description [Line Items]
Number of renewable terms	1	1
Operating Lease, renewable term	5 years	5 years
Lessee Operating Lease Discount Rate		7%
Stamford Operating Lease and New Stamford Lease [Member]
Lessee, Lease, Description [Line Items]
Lessee Operating Lease Discount Rate		7%	7%
ASC 842 [Member] | New Stamford Lease [Member]
Lessee, Lease, Description [Line Items]
Number of renewable terms		1
Operating Lease, renewable term		5 years
ASC 842 [Member] | Stamford Operating Lease and New Stamford Lease [Member]
Lessee, Lease, Description [Line Items]
Number Of Operating Lease | lease		2	2
Lessee Operating Lease Discount Rate		7%

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	Dec. 31, 2022	Dec. 31, 2021
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 94,680	$ 223,694
Gross Unrealized Gains	2	5
Gross Unrealized Losses	(1,674)	(363)
Estimated fair value	93,008	223,336
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost		11,573
Gross Unrealized Losses		(3)
Estimated fair value		11,570
U.S. Government Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	9,500	17,020
Gross Unrealized Losses	(623)	(45)
Estimated fair value	8,877	16,975
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	35,828	66,495
Gross Unrealized Losses	(643)	(171)
Estimated fair value	35,185	66,324
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	26,879	106,914
Gross Unrealized Gains	2	5
Gross Unrealized Losses	(6)	(31)
Estimated fair value	26,875	106,888
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	22,473	21,692
Gross Unrealized Losses	(402)	(113)
Estimated fair value	$ 22,071	$ 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	Dec. 31, 2022	Dec. 31, 2021
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Fair Value	$ 18,358	$ 156,455
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Gross Unrealized Losses	(48)	(354)
Available-for-sale marketable securities, continuous unrealized loss position, 12 Months or Greater, Fair Value	62,181	3,037
Available-for-sale marketable securities, continuous unrealized loss position, 12 Months or Greater, Gross Unrealized Losses	(1,626)	(9)
Available-for-sale marketable securities, continuous unrealized loss position, Fair Value	80,539	159,492
Available-for-sale marketable securities, continuous unrealized loss position, Gross Unrealized Losses	(1,674)	(363)
U.S. Treasury Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Fair Value		11,570
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Gross Unrealized Losses		(3)
Available-for-sale marketable securities, continuous unrealized loss position, Fair Value		11,570
Available-for-sale marketable securities, continuous unrealized loss position, Gross Unrealized Losses		(3)
U.S. Government Agency Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Fair Value		9,456
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Gross Unrealized Losses		(45)
Available-for-sale marketable securities, continuous unrealized loss position, 12 Months or Greater, Fair Value	8,877
Available-for-sale marketable securities, continuous unrealized loss position, 12 Months or Greater, Gross Unrealized Losses	(623)
Available-for-sale marketable securities, continuous unrealized loss position, Fair Value	8,877	9,456
Available-for-sale marketable securities, continuous unrealized loss position, Gross Unrealized Losses	(623)	(45)
Corporate Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Fair Value	1,470	62,704
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Gross Unrealized Losses	(26)	(170)
Available-for-sale marketable securities, continuous unrealized loss position, 12 Months or Greater, Fair Value	33,715	2,020
Available-for-sale marketable securities, continuous unrealized loss position, 12 Months or Greater, Gross Unrealized Losses	(617)	(1)
Available-for-sale marketable securities, continuous unrealized loss position, Fair Value	35,185	64,724
Available-for-sale marketable securities, continuous unrealized loss position, Gross Unrealized Losses	(643)	(171)
Commercial Paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Fair Value	15,906	52,163
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Gross Unrealized Losses	(6)	(31)
Available-for-sale marketable securities, continuous unrealized loss position, Fair Value	15,906	52,163
Available-for-sale marketable securities, continuous unrealized loss position, Gross Unrealized Losses	(6)	(31)
Municipal Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Fair Value	982	20,562
Available-for-sale marketable securities, continuous unrealized loss position, Less than 12 Months, Gross Unrealized Losses	(16)	(105)
Available-for-sale marketable securities, continuous unrealized loss position, 12 Months or Greater, Fair Value	19,589	1,017
Available-for-sale marketable securities, continuous unrealized loss position, 12 Months or Greater, Gross Unrealized Losses	(386)	(8)
Available-for-sale marketable securities, continuous unrealized loss position, Fair Value	20,571	21,579
Available-for-sale marketable securities, continuous unrealized loss position, Gross Unrealized Losses	$ (402)	$ (113)

Available-for-Sale Marketable_5

Available-for-Sale Marketable Securities - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($) position	Dec. 31, 2021 USD ($) 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	35	58
Total number of positions	39	76
Number of positions of available-for-sale in unrealized loss position for 12 months or greater	28
U.S. Government Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of available-for-sale marketable securities in unrealized loss positions	3
Total number of positions	3
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of available-for-sale marketable securities in unrealized loss positions	13
Total number of positions	13
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of available-for-sale marketable securities in unrealized loss positions	5
Total number of positions	8
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of available-for-sale marketable securities in unrealized loss positions	14
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	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Debt Securities [Abstract]
Amortized Cost of marketable debt securities, contractual maturity, less than one year	$ 82,678	$ 153,631
Amortized Cost of marketable debt securities, contractual maturity, One year to three years	12,002	70,063
Amortized cost	94,680	223,694
Fair value of marketable debt securities, contractual maturities, less than one year	81,658	153,582
Fair value of marketable debt securities, contractual maturity, One year to three years	11,350	69,754
Total fair Value of marketable debt securities, contractual maturity	93,008	223,336
Proceeds from sale of available-for-sale marketable securities	0	10,029	$ 41,600
Realized gain		39	$ 272
Interest receivable	$ 489	$ 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	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Accumulated Other Comprehensive Income Loss [Line Items]
Balance, Value	$ 227,522	$ 249,001	$ 186,713
Amount reclassified from accumulated other comprehensive income (loss)		(39)	(272)
Net current period other comprehensive loss	(1,314)	(431)	(97)
Balance, Value	158,779	227,522	249,001
Accumulated Other Comprehensive (Loss) Income.
Accumulated Other Comprehensive Income Loss [Line Items]
Balance, Value	(358)	73	170
Other comprehensive loss before reclassifications	(1,314)	(392)	175
Amount reclassified from accumulated other comprehensive income (loss)		(39)	(272)
Net current period other comprehensive loss	(1,314)	(431)	(97)
Balance, Value	$ (1,672)	$ (358)	$ 73

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive (Loss) Income - Schedule of Reclassifications Out of Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Other income, net	$ 2,061	$ 642	$ 2,334
Benefit from income taxes	0	0	(691)
Net of tax		39	272
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	272
Benefit from income taxes	$ 0	$ 0	$ 0

Inventory, net - Schedule of In

Inventory, net - Schedule of Inventories (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Inventory, net
Raw materials	$ 1,918	$ 927
Work-in-process	499	1,657
Inventory gross	2,417	2,584
Less Inventory Reserve for Obsolescence	(34)
Total	$ 2,383	$ 2,584

Inventory, net - Additional Inf

Inventory, net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Inventory, net
Inventory write-down	$ 34	$ 0

Prepaid Expenses - Additional I

Prepaid Expenses - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Prepaid Expenses
Prepaid expenses	$ 16,267	$ 2,519
Prepaid R&D clinical costs	15,188	1,481
Prepaid insurance	543	369
Other prepaid costs	$ 536	$ 669

Property and Equipment, net - P

Property and Equipment, net - Property and Equipment, net (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,835	$ 1,792
Less accumulated depreciation and amortization	(1,409)	(1,161)
Property, Plant and Equipment, net, Total	426	631
Computer and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	239	239
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	330	330
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,266	$ 1,223

Property and Equipment, net - A

Property and Equipment, net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Depreciation and amortization expense	$ 248	$ 248	$ 209
Realized gain on sale of property and equipment	$ 0	70	$ 0
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Realized gain on sale of property and equipment		$ 70

Restricted Cash - Additional In

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

Restricted Cash - Schedule of R

Restricted Cash - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Restricted Cash
Cash and cash equivalents	$ 63,741	$ 13,453
Restricted cash in current assets	408
Restricted cash, long-term assets		408
Total cash, cash equivalents, and restricted cash shown in the Condensed Statements of Cash Flows	$ 64,149	$ 13,861	$ 32,091	$ 18,713

Accounts Payable and Accrued _3

Accounts Payable and Accrued Expenses - Schedule of Accounts Payable and Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Accounts Payable and Accrued Expenses
Accounts payable	$ 9,604	$ 5,625
Accrued research projects	5,200	4,648
Accrued compensation and benefits	5,219	4,959
Accrued professional fees and other	1,517	629
Total	$ 21,540	$ 15,861

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) $ / shares in Units, $ in Thousands

1 Months Ended

2 Months Ended

3 Months Ended

12 Months Ended

Jun. 04, 2020

Dec. 31, 2022 $ / shares shares

Oct. 31, 2022 shares

Sep. 30, 2022 shares

Jun. 30, 2022 shares

Mar. 31, 2022 USD ($) shares

Feb. 28, 2022 shares

Oct. 31, 2021 shares

Aug. 31, 2021 shares

Jun. 30, 2021 shares

Feb. 28, 2021 shares

Dec. 31, 2020 shares

Oct. 31, 2020 shares

Jun. 30, 2020 shares

Feb. 29, 2020

Mar. 31, 2021 shares

Jun. 30, 2020 shares

Dec. 31, 2022 item $ / shares shares

Dec. 31, 2021 $ / shares shares

Dec. 31, 2020 shares

Aug. 31, 2019 USD ($)

Sale Of Stock [Line Items]

Common stock, shares authorized

100,000,000

100,000,000

100,000,000

Common stock, shares issued

53,797,341

53,797,341

53,480,812

Common stock, shares outstanding

53,797,341

53,797,341

53,480,812

Common stock, par value | $ / shares

$ 0.001

$ 0.001

$ 0.001

Preferred stock, shares authorized

5,000,000

5,000,000

5,000,000

Preferred stock, par value | $ / shares

$ 0.001

$ 0.001

$ 0.001

Preferred stock, shares issued

0

0

0

Preferred stock, shares outstanding

0

0

0

Number of votes for each share of common stock | item

1

Regulatory Milestones [Member] | Vifor International Ltd. [Member]

Sale Of Stock [Line Items]

Common stock, shares issued

3,282,391

Non-Exclusive License Agreement | Enteris Biopharma, Inc. [Member]

Sale Of Stock [Line Items]

Upfront fee | $

$ 8,000

Exclusive License Agreement [Member] | Vifor International Ltd. [Member]

Sale Of Stock [Line Items]

Common stock, shares issued

2,939,552

Unsold Securities Under Shelf Registration Statement dated April 4, 2019 [Member]

Sale Of Stock [Line Items]

Aggregate offering price of securities | $

$ 154,525

Open Market Sales Agreement [Member] | Jeffries LLC [Member]

Sale Of Stock [Line Items]

Common stock, shares issued

0

Stock Sale Commission Percentage

3%

Open Market Sales Agreement [Member] | Maximum [Member] | Jeffries LLC [Member]

Sale Of Stock [Line Items]

Aggregate offering price of securities | $

$ 80,000

2022 Shelf Registration Statement [Member] | Maximum [Member]

Sale Of Stock [Line Items]

Aggregate offering price of securities | $

$ 300,000

Common Stock

Sale Of Stock [Line Items]

Restricted stock units vested shares

268,222

189,421

156,584

Restricted Stock Units [Member] | 2014 Equity Incentive Plan [Member] | Director [Member] | June 2020 [Member]

Sale Of Stock [Line Items]

Vesting period of awards granted

1 year

Restricted stock units, vested

36,000

Restricted Stock Units [Member] | Chief Executive Officer | 2014 Equity Incentive Plan [Member] | Director [Member] | June 2020 [Member]

Sale Of Stock [Line Items]

Restricted stock units, vested

36,000

Restricted Stock Units [Member] | Common Stock | Board of Directors Chairman [Member] | June 2022 [Member]

Sale Of Stock [Line Items]

Restricted stock units vested shares

11,876

Restricted Stock Units [Member] | Common Stock | Director [Member] | June 2022 [Member]

Sale Of Stock [Line Items]

Vesting period of awards granted

1 year

Restricted stock units, vested

43,200

Restricted Stock Units [Member] | Common Stock | Director [Member] | June 2021 [Member]

Sale Of Stock [Line Items]

Vesting period of awards granted

1 year

Restricted stock units vested shares

36,000

Restricted Stock Units [Member] | Common Stock | Director [Member] | June 2020 [Member]

Sale Of Stock [Line Items]

Vesting period of awards granted

1 year

Restricted stock units, vested

24,000

Restricted Stock Units [Member] | Common Stock | Former Chief Executive Officer [Member] | June 2022 [Member]

Sale Of Stock [Line Items]

Restricted stock units vested shares

33,999

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

Sale Of Stock [Line Items]

Restricted stock units, vested

36,750

Performance Restricted Stock Units [Member] | Common Stock | Executive Officers [Member] | December 2022

Sale Of Stock [Line Items]

Restricted stock units, vested

26,204

Performance Restricted Stock Units [Member] | Common Stock | Executive Officers [Member] | March 2022 [Member]

Sale Of Stock [Line Items]

Restricted stock units, vested

37,999

Performance Restricted Stock Units [Member] | Common Stock | Executive Officers [Member] | August 2021 [Member]

Sale Of Stock [Line Items]

Restricted stock units, vested

44,002

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

Performance Restricted Stock Units [Member] | Common Stock | Executive Officers [Member] | April And June 2020 [Member]

Sale Of Stock [Line Items]

Restricted stock units, vested

95,834

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

Sale Of Stock [Line Items]

Vesting period of awards granted

3 years

Restricted stock units, vested

16,666

32,666

32,669

82,001

Time-based Restricted Stock Units [Member] | 2014 Equity Incentive Plan [Member] | Executive Officers [Member] | October 2022 [Member]

Sale Of Stock [Line Items]

Restricted stock units, vested

0

Time-based Restricted Stock Units [Member] | 2014 Equity Incentive Plan [Member] | Interim Principal Financial and Accounting Officer [Member] | June 2022 [Member]

Sale Of Stock [Line Items]

Restricted stock units, vested

7,500

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

Sale Of Stock [Line Items]

Restricted stock units, vested

35,500

41,442

Time-based Restricted Stock Units [Member] | 2014 Equity Incentive Plan [Member] | Chief Executive Officer [Member] | October 2022 [Member]

Sale Of Stock [Line Items]

Restricted stock units, vested

35,500

Time-based 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 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

Time-based Restricted Stock Units [Member] | Common Stock | Interim Principal Financial and Accounting Officer [Member] | September 2022 [Member]

Sale Of Stock [Line Items]

Restricted stock units, vested

7,500

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Financial assets
Available-for-sale marketable securities	$ 93,008	$ 223,336
Restricted cash	408
Restricted cash, non-current		408
Recurring [Member]
Financial assets
Total financial assets	157,157	237,197
U.S. Government Agency Obligations [Member]
Financial assets
Available-for-sale marketable securities	8,877	16,975
U.S. Government Agency Obligations [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities	8,877	16,975
Corporate Bonds [Member]
Financial assets
Available-for-sale marketable securities	35,185	66,324
Corporate Bonds [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities	35,185	66,324
Commercial Paper [Member]
Financial assets
Available-for-sale marketable securities	26,875	106,888
Municipal Bonds [Member]
Financial assets
Available-for-sale marketable securities	22,071	21,579
Municipal Bonds [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities	22,071	21,579
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring [Member]
Financial assets
Total financial assets	64,149	13,861
Significant Other Observable Inputs (Level 2) [Member] | Recurring [Member]
Financial assets
Total financial assets	93,008	223,336
Significant Other Observable Inputs (Level 2) [Member] | U.S. Government Agency Obligations [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities	8,877	16,975
Significant Other Observable Inputs (Level 2) [Member] | Corporate Bonds [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities	35,185	66,324
Significant Other Observable Inputs (Level 2) [Member] | Municipal Bonds [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities	22,071	21,579
Money Market Funds [Member] | Recurring [Member]
Financial assets
Cash and cash equivalents	63,741	13,453
Restricted cash	408
Restricted cash, non-current		408
Money Market Funds [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring [Member]
Financial assets
Cash and cash equivalents	63,741	13,453
Restricted cash	408
Restricted cash, non-current		408
U.S. Treasury Securities [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities		11,570
U.S. Treasury Securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities		11,570
Commercial Paper [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities	26,875	106,888
Commercial Paper [Member] | Significant Other Observable Inputs (Level 2) [Member] | Recurring [Member]
Financial assets
Available-for-sale marketable securities	$ 26,875	$ 106,888

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfer of financial assets into or out of level 3 of fair value	$ 0	$ 0
Fair value assets level 2 to level 1 transfer	0	0
Fair value assets level 1 to level 2 transfers	0	0
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Purchases of financial assets	0	0	$ 0
Sales of financial assets	0	0	0
Maturities of financial assets	0	0	0
Unrealized gains	0	0	0
Unrealized losses	$ 0	$ 0	$ 0

Collaboration and Licensing A_2

Collaboration and Licensing Agreements - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands					1 Months Ended				12 Months Ended
	Oct. 15, 2022	Oct. 15, 2021	Oct. 15, 2020	May 17, 2018	Apr. 30, 2022	Oct. 31, 2021	Oct. 31, 2020	May 31, 2018	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues									$ 41,867	$ 23,028	$ 135,082
License and Milestone Fees
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues									15,000	21,223	134,439
Collaborative Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues									16,572	706
Commercial Supply Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues									$ 10,223	701
Clinical Compound Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues										398	$ 643
Vifor Fresenius Medical Care Renal Pharma Ltd Agreement No 1 [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of net profit sharing							60%				60%
Number of days to terminate agreement									60 days
Vifor Fresenius Medical Care Renal Pharma Ltd Agreement No 2 [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of net profit sharing								50%
CSL Vifor Maximum [Member] | Vifor Fresenius Medical Care Renal Pharma Ltd Agreement No 1 [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential sales-based milestone payments			$ 240,000
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Non-refundable, non-creditable upfront payment				$ 50,000
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member] | Vifor Fresenius Medical Care Renal Pharma Ltd Agreement No 2 [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of days to terminate agreement				60 days
Termination notice effective period				12 months
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member] | Vifor Fresenius Medical Care Renal Pharma Ltd Agreement No 2 [Member] | License and Milestone Fees
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues					$ 15,000					15,000
Maruishi Pharmaceutical Co., Ltd. [Member] | License and Milestone Fees
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues										1,192
Maruishi Pharmaceutical Co., Ltd. [Member] | Clinical Compound Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues										37	$ 528
Vifor International Ltd. [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Closing prices of company common stock description				over a pre-determined average closing price of the Company’s common stock.
Vifor International Ltd. [Member] | Vifor Fresenius Medical Care Renal Pharma Ltd Agreement No 1 [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of net profit sharing							40%				40%
Common stock, shares issued						3,282,391	2,939,552
Proceeds from the sale of common stock		$ 50,000	$ 50,000
Purchase common stock per share amount						$ 15.23	$ 17.0094
Premium from sale of stock										5,031
Percentage of premium on common stock investment	20%
Stock issuance price measurement period	30 days
Vifor International Ltd. [Member] | Vifor Fresenius Medical Care Renal Pharma Ltd Agreement No 1 [Member] | License [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Non-refundable, non-creditable upfront payment							$ 100,000
Vifor International Ltd. [Member] | Vifor Fresenius Medical Care Renal Pharma Ltd Agreement No 1 [Member] | License and Milestone Fees
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Premium from sale of stock						$ 11,551
Vifor International Ltd. [Member] | Vifor Fresenius Medical Care Renal Pharma Ltd Agreement No 2 [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Common stock, shares issued				1,174,827
Purchase of common stock value				$ 20,000
Purchase common stock per share amount				$ 17.024
Premium from sale of stock				$ 5,444
CSL Vifor [Member] | License and Milestone Fees
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues									$ 15,000	20,031	$ 133,813
CSL Vifor [Member] | Collaborative Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues									16,572	0	0
CSL Vifor [Member] | Commercial Supply Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues									$ 10,223	701
CSL Vifor [Member] | Clinical Compound Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues										$ 361	$ 115
CSL Vifor [Member] | Vifor Fresenius Medical Care Renal Pharma Ltd Agreement No 1 [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of net profit sharing							40%
Vifor Fresenius Medical Care Renal Pharma Ltd Agreement No 2 [Member] | Maximum [Member] | Regulatory and Commercial Milestones [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments				$ 440,000

Revenue Recognition - Disaggreg

Revenue Recognition - Disaggregation of Revenue (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Total revenue	$ 41,867	$ 23,028	$ 135,082
License and Milestone Fees
Disaggregation of Revenue [Line Items]
Total revenue	15,000	21,223	134,439
License and Milestone Fees | Maruishi Agreement [Member]
Disaggregation of Revenue [Line Items]
Total revenue	0	1,192	0
License and Milestone Fees | CKDP Agreement [Member]
Disaggregation of Revenue [Line Items]
Total revenue	0	0	626
License and Milestone Fees | CSL Vifor [Member]
Disaggregation of Revenue [Line Items]
Total revenue	15,000	20,031	133,813
License and Milestone Fees | Maruishi Pharmaceutical Co., Ltd. [Member]
Disaggregation of Revenue [Line Items]
Total revenue		1,192
License and Milestone Fees | Chong Kun Dang Pharmaceutical Corp. [Member]
Disaggregation of Revenue [Line Items]
Total revenue			626
Collaborative Revenue
Disaggregation of Revenue [Line Items]
Total revenue	16,572	706
Collaborative Revenue | CSL Vifor Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Total revenue	16,572
Collaborative Revenue | Maruishi Agreement [Member]
Disaggregation of Revenue [Line Items]
Total revenue	0	706	0
Collaborative Revenue | CSL Vifor [Member]
Disaggregation of Revenue [Line Items]
Total revenue	16,572	0	0
Commercial Supply Revenue
Disaggregation of Revenue [Line Items]
Total revenue	10,223	701
Commercial Supply Revenue | CSL Vifor [Member]
Disaggregation of Revenue [Line Items]
Total revenue	10,223	701
Clinical Compound Revenue
Disaggregation of Revenue [Line Items]
Total revenue		398	643
Clinical Compound Revenue | CSL Vifor [Member]
Disaggregation of Revenue [Line Items]
Total revenue		361	115
Clinical Compound Revenue | Maruishi Pharmaceutical Co., Ltd. [Member]
Disaggregation of Revenue [Line Items]
Total revenue		$ 37	$ 528
Royalty Revenue
Disaggregation of Revenue [Line Items]
Total revenue	72
Royalty Revenue | CSL Vifor [Member]
Disaggregation of Revenue [Line Items]
Total revenue	$ 72

Revenue Recognition - Additiona

Revenue Recognition - Additional Information (Detail) $ / shares in Units, $ in Thousands		1 Months Ended			11 Months Ended	12 Months Ended
	May 17, 2018 item	Apr. 30, 2022 USD ($) item	Jan. 31, 2022 USD ($)	Oct. 31, 2021 USD ($) item $ / shares shares	Dec. 31, 2022 USD ($)	Dec. 31, 2022 USD ($) item	Dec. 31, 2021 USD ($) item	Dec. 31, 2020 USD ($)	Dec. 31, 2018 USD ($) item
Collaboration Arrangement [Line Items]
Accounts receivable, net - related party					$ 3,260	$ 3,260
Total revenue						41,867	$ 23,028	$ 135,082
Research and development expense						91,879	82,701	107,851
Commercial Supply Revenue
Collaboration Arrangement [Line Items]
Total revenue						10,223	701
License and Milestone Fees
Collaboration Arrangement [Line Items]
Total revenue						15,000	21,223	134,439
Royalty Revenue
Collaboration Arrangement [Line Items]
Total revenue						72
Collaborative Revenue
Collaboration Arrangement [Line Items]
Total revenue						16,572	706
Clinical Compound Revenue
Collaboration Arrangement [Line Items]
Total revenue							398	643
Vifor Fresenius Medical Care Renal Pharma Ltd Agreement No 2 [Member]
Collaboration Arrangement [Line Items]
Number of performance obligations for revenue recognized | item									2
Vifor Fresenius Medical Care Renal Pharma Ltd Agreement No 2 [Member] | License and Milestone Fees
Collaboration Arrangement [Line Items]
Total revenue								22,262
Vifor Fresenius Medical Care Renal Pharma Ltd Agreement No 2 [Member] | License and Milestone Fees | Regulatory Milestones [Member]
Collaboration Arrangement [Line Items]
Number Of Combined Performance Obligation At Contract Inception | item		1
Vifor Fresenius Medical Care Renal Pharma Ltd Agreement No 1 [Member] | License and Milestone Fees
Collaboration Arrangement [Line Items]
Number of performance obligations for revenue recognized | item	1
Vifor Fresenius Medical Care Renal Pharma Ltd Agreement No 1 [Member] | License and Milestone Fees | Regulatory Milestones [Member]
Collaboration Arrangement [Line Items]
Proceeds from milestone payments							$ 15,000
Number of performance obligations for revenue recognized | item							1
CSL Vifor, Maruishi and CKDP Agreements [Member]
Collaboration Arrangement [Line Items]
Accounts receivable, net - related party							$ 0
Other contract Assets					0	$ 0	0
CSL Vifor and CKDP Agreements [Member] | License and Milestone Fees
Collaboration Arrangement [Line Items]
Number of performance obligations for revenue recognized | item						1
Maruishi Agreement [Member]
Collaboration Arrangement [Line Items]
Remaining performance obligations					0	$ 0
Maruishi Agreement [Member] | License and Milestone Fees
Collaboration Arrangement [Line Items]
Total revenue						0	1,192	0
Maruishi Agreement [Member] | Collaborative Revenue
Collaboration Arrangement [Line Items]
Total revenue						0	706	0
CKDP Agreement [Member] | License and Milestone Fees
Collaboration Arrangement [Line Items]
Total revenue						0	0	626
Remaining performance obligations					0	0
Maruishi Pharmaceutical Co., Ltd. [Member] | License and Milestone Fees
Collaboration Arrangement [Line Items]
Total revenue							1,192
Maruishi Pharmaceutical Co., Ltd. [Member] | Clinical Compound Revenue
Collaboration Arrangement [Line Items]
Total revenue							37	528
Research and development expense							33	476
Vifor International Ltd. [Member] | Vifor Fresenius Medical Care Renal Pharma Ltd Agreement No 2 [Member]
Collaboration Arrangement [Line Items]
Premium from sale of stock									$ 5,444
Upfront payments on obligations									$ 50,000
Remaining performance obligations					0	0
Vifor International Ltd. [Member] | Vifor Fresenius Medical Care Renal Pharma Ltd Agreement No 1 [Member]
Collaboration Arrangement [Line Items]
Proceeds from the sale of common stock				$ 50,000
Common stock, shares issued | shares				3,282,391
Price per share | $ / shares				$ 15.23
Percentage of premium on common stock investment				20%
Stock Issuance Price Measurement Period				30 days
Number of performance obligations for revenue recognized | item				1
Premium from sale of stock							5,031
Vifor International Ltd. [Member] | Vifor Fresenius Medical Care Renal Pharma Ltd Agreement No 1 [Member] | License and Milestone Fees
Collaboration Arrangement [Line Items]
Total revenue								111,551
Premium from sale of stock								11,551
Upfront payments on obligations								100,000
Remaining performance obligations					0	0
CSL Vifor [Member]
Collaboration Arrangement [Line Items]
Accounts receivable, net - related party					3,260	3,260
CSL Vifor [Member] | Commercial Supply Revenue
Collaboration Arrangement [Line Items]
Total revenue						10,223	701
CSL Vifor [Member] | Commercial Supply Revenue With No Associated Costs Of Goods Sold [Member]
Collaboration Arrangement [Line Items]
Total revenue			$ 2,295				701
CSL Vifor [Member] | Commercial Supply Revenue With Associated Costs Of Goods Sold [Member]
Collaboration Arrangement [Line Items]
Total revenue					7,928
Cost of goods sold					$ 7,266
CSL Vifor [Member] | License and Milestone Fees
Collaboration Arrangement [Line Items]
Total revenue						15,000	20,031	133,813
CSL Vifor [Member] | Royalty Revenue
Collaboration Arrangement [Line Items]
Total revenue						72
CSL Vifor [Member] | Collaborative Revenue
Collaboration Arrangement [Line Items]
Total revenue						16,572	0	0
CSL Vifor [Member] | Clinical Compound Revenue
Collaboration Arrangement [Line Items]
Total revenue							361	115
CSL Vifor [Member] | Vifor Fresenius Medical Care Renal Pharma Ltd Agreement No 2 [Member] | License and Milestone Fees | Regulatory Milestones [Member]
Collaboration Arrangement [Line Items]
Proceeds from milestone payments		$ 15,000
CSL Vifor [Member] | Vifor Fresenius Medical Care Renal Pharma Ltd Agreement No 2 [Member] | Clinical Compound Revenue
Collaboration Arrangement [Line Items]
Total revenue						$ 0	361	115
Research and development expense							$ 343	$ 108

Stock-Based Compensation - Addi

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

1 Months Ended

12 Months Ended

Oct. 12, 2022 $ / shares shares

Jun. 15, 2022 $ / shares shares

Jun. 02, 2022 $ / shares shares

Feb. 25, 2022 installment $ / shares shares

Dec. 17, 2021 installment $ / shares shares

Nov. 01, 2021 USD ($)

Oct. 29, 2021 tranche $ / shares shares

Jun. 03, 2021 $ / shares shares

Mar. 30, 2021 installment $ / shares shares

Jun. 04, 2020 $ / shares shares

Jun. 04, 2019 $ / shares shares

Oct. 31, 2022 shares

Jun. 30, 2022 shares

Mar. 31, 2022 shares

Feb. 28, 2022 shares

Aug. 31, 2021 shares

Jun. 30, 2021 shares

Mar. 31, 2021 shares

Feb. 28, 2021 shares

Jun. 30, 2020 shares

Apr. 30, 2020 shares

Feb. 29, 2020 installment $ / shares shares

Mar. 31, 2019 $ / shares shares

Dec. 31, 2022 USD ($) $ / shares shares

Dec. 31, 2021 USD ($) $ / shares shares

Dec. 31, 2020 USD ($) $ / shares shares

Dec. 31, 2015 shares

Jan. 01, 2023 shares

Nov. 20, 2019 $ / shares shares

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

Common stock, par value | $ / shares

$ 0.001

$ 0.001

Common stock, shares outstanding

53,797,341

53,480,812

Common stock, shares issued

53,797,341

53,480,812

Number of restricted stock units outstanding

372,513

576,544

235,250

Number of options outstanding

7,689,449

6,512,280

5,469,393

Options granted

1,899,919

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

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

Compensation expense | $

$ 765

$ 1,201

$ 1,432

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

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

Compensation expense | $

$ 628

$ 565

528

Director [Member] | Restricted Stock Units [Member] | General and Administrative [Member] | June 2019 [Member]

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

Compensation expense | $

$ 205

Consultants [Member] | Chief Executive Officer

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

Options granted

0

0

0

Employees And Non-Employee Members Of Board Of Directors [Member]

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

Fair value of options granted | $ / shares

$ 7.25

$ 12

$ 10.33

Options granted

1,899,919

1,422,750

1,377,850

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

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

Compensation expense | $

$ 2,693

$ 2,324

$ 1,167

2019 Inducement Plan [Member]

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

Common stock, par value | $ / shares

$ 0.001

2019 Inducement Plan [Member] | Incentive Stock Options [Member]

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

Options granted

0

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 Arrangement by Share-based Payment Award [Line Items]

Number of shares available for future issuance

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%

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%

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

10,589,103

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

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

Awarded

147,942

2014 Equity Incentive Plan [Member] | Subsequent Event [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

12,203,023

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] | Board of Directors Chairman [Member] | Restricted Stock Units [Member] | General and Administrative [Member] | June 2022 [Member]

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

Compensation expense | $

$ 100

2014 Equity Incentive Plan [Member] | Board of Directors Chairman [Member] | Chief Executive Officer | Restricted Stock Units [Member] | June 2022 [Member]

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

Awarded

11,876

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

Compensation expense | $

$ 0

Restricted stock units, Forfeited

214,000

Number of restricted stock units outstanding

0

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

176,000

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

$ 20.59

Compensation expense | $

$ 906

Restricted stock units, vested

37,999

44,002

82,001

Restricted stock units, Forfeited

93,999

Number of restricted stock units outstanding

0

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

138,000

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

$ 16.36

Compensation expense | $

1,256

$ 601

Restricted stock units, vested

40,000

36,750

113,500

Restricted stock units, Forfeited

24,500

Number of restricted stock units outstanding

0

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

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

Awarded

215,000

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

$ 16.10

Compensation expense | $

$ 1,543

Restricted stock units, vested

30,000

65,834

215,000

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

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

Compensation expense | $

329

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

$ 196

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

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

Compensation expense | $

1,087

2014 Equity Incentive Plan [Member] | Employees [Member] | Performance Restricted Stock Units [Member] | General and Administrative [Member] | Modified November 2021 Awards [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] | March 2021 [Member]

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

Compensation expense | $

729

577

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

405

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

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

Compensation expense | $

456

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

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

Restricted stock units, Forfeited

17,333

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 | $

$ 390

Restricted stock units, vested

0

Number of options outstanding

125,170

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 | $

$ 646

592

Restricted stock units, vested

17,333

33,336

0

Number of restricted stock units outstanding

31,998

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 | $

$ 161

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 | $

219

166

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

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

Compensation expense | $

75

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

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

Compensation expense | $

317

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 | $

229

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 | $

$ 427

426

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] | 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. 03, 2021

Restricted stock units, vested

36,000

2014 Equity Incentive Plan [Member] | Director [Member] | Restricted Stock Units [Member] | June 2019 [Member]

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

Vesting period of awards granted

1 year

Awarded

24,000

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

$ 20.47

Restricted stock units, vested

24,000

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

$ 239

323

2014 Equity Incentive Plan [Member] | Director [Member] | Chief Executive Officer | Restricted Stock Units [Member] | June 2020 [Member]

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

Restricted stock units, vested

36,000

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

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

Common stock, shares issued

30,000

65,834

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

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

Compensation expense | $

73

2014 Equity Incentive Plan [Member] | Executive Officers [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

52,403

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

$ 12.45

Number of equal installment | installment

2

Compensation expense | $

$ 433

20

Restricted stock units, vested

26,204

2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Time-based Restricted Stock Units [Member] | October 2022 [Member]

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

Awarded

7,267

7,267

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

$ 9.42

Restricted stock units, vested

0

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

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

Vesting period of awards granted

3 years

Awarded

98,000

98,000

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

$ 16.36

Number of equal installment | installment

3

Compensation expense | $

$ 526

607

455

Restricted stock units, vested

16,666

32,666

32,669

82,001

2014 Equity Incentive Plan [Member] | Executive Officers [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 | $

$ 210

8

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

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

Compensation expense | $

175

174

149

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

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

Compensation expense | $

$ 264

2014 Equity Incentive Plan [Member] | Executive Officers [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 | $

223

12

2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Time-based Restricted Stock Units [Member] | General and Administrative [Member] | October 2022 [Member]

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

Compensation expense | $

17

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

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

Compensation expense | $

$ 351

433

$ 306

2014 Equity Incentive Plan [Member] | Former Chief Financial Officer [Member] | Performance Restricted Stock Units [Member] | February 2022 [Member]

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

Restricted stock units, Forfeited

29,000

2014 Equity Incentive Plan [Member] | Former Chief Financial Officer [Member] | Time-based Restricted Stock Units [Member] | February 2022 [Member]

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

Restricted stock units, Forfeited

20,000

2014 Equity Incentive Plan [Member] | Former Chief Financial Officer [Member] | Time-based Restricted Stock Units [Member] | December 2021 [Member]

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

Restricted stock units, Forfeited

11,170

2014 Equity Incentive Plan [Member] | Interim Principal Financial and Accounting Officer [Member] | Time-based Restricted Stock Units [Member] | June 2022 [Member]

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

Awarded

7,500

7,500

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

$ 7.94

Restricted stock units, vested

7,500

2014 Equity Incentive Plan [Member] | Interim Principal Financial and Accounting Officer [Member] | Time-based Restricted Stock Units [Member] | General and Administrative [Member] | June 2022 [Member]

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

Compensation expense | $

$ 60

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

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

$ 16.83

Number of restricted stock unit tranches | tranche

2

Restricted stock units, vested

35,500

41,442

2014 Equity Incentive Plan [Member] | Chief Executive Officer [Member] | Time-based Restricted Stock Units [Member] | October 2022 [Member]

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

Restricted stock units, vested

35,500

2014 Equity Incentive Plan [Member] | Chief Executive Officer [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 | $

$ 657

144

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%

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%

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 2022 [Member]

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

Vesting period of awards granted

1 year

Awarded

59,380

59,380

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

$ 8.42

Restricted stock units, vested

0

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

43,200

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

$ 13.06

Restricted stock units, vested

43,200

2014 Equity Incentive Plan [Member] | Non-employee Directors [Member] | Restricted Stock Units [Member] | General and Administrative [Member] | June 2022 [Member]

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

Compensation expense | $

$ 290

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 | $

$ 238

$ 326

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

474,193

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

$ 10.10

Restricted stock units, vested

268,222

Restricted stock units, Forfeited

410,002

Number of restricted stock units outstanding

372,513

576,544

Stock-Based Compensation - Rest

Stock-Based Compensation - Restricted Stock Unit Activity (Details) - $ / shares	1 Months Ended	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2022
Number of Units
Outstanding, Beginning Balance		576,544
Outstanding, Ending Balance	235,250	372,513
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		474,193
Vested and released		(268,222)
Forfeited		(410,002)
Outstanding, Ending Balance		372,513
Weighted Average Grant Date Fair Value
Weighted-average grant date fair value, outstanding, Beginning Balance		$ 17.50
Weighted-average grant date fair value, awarded		10.10
Weighted-average grant date fair value, vested and released		16.33
Weighted-average grant date fair value, forfeited		13.62
Weighted-average grant date fair value, outstanding, Ending Balance		$ 13.20

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Assumptions Used in Black-Scholes Option Pricing Model (Detail)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate, minimum	1.70%	0.66%	0.35%
Risk-free interest rate, maximum	4.21%	1.41%	1.57%
Expected volatility, minimum	77.70%	71.60%	71.80%
Expected volatility, maximum	81.90%	83.50%	74.80%
Expected dividend yield	0%	0%	0%
Employee and Board of Directors Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life of options (in years)	6 years 3 months	6 years 3 months	6 years 3 months

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Compensation Expense Relating to Stock Options (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Excess tax benefits from stock option activity or stock-based compensation expense recognized in cash flows from operations	$ 0	$ 0	$ 0
Excess tax benefits from stock option activity or stock-based compensation expense recognized in cash flows from financing activities	0	0	0
Employees And Non-Employee Members Of Board Of Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Compensation expense not yet recognized	$ 22,186
Weighted average period of compensation expense not yet recognized	2 years 8 months 19 days
Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Compensation expense	$ 13,648	16,695	11,708
Options [Member] | Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Compensation expense	7,222	7,126	6,765
Options [Member] | General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Compensation expense	6,426	9,569	4,943
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	$ 628	$ 565	$ 528

Stock-Based Compensation - Su_3

Stock-Based Compensation - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Options, Outstanding, Beginning Balance	6,512,280	5,469,393
Number of Options, Granted	1,899,919
Number of Options, Exercised	(48,307)
Number of Options, Forfeited	(356,819)
Number of Options, Expired	(317,624)
Number of Options, Outstanding, Ending Balance	7,689,449	6,512,280	5,469,393
Number of Options, Outstanding, Weighted average remaining contractual life as of December 31, 2022	5 years 11 months 12 days
Number of Options, Options exercisable	4,972,944
Number of Options, Exercisable, Weighted average remaining contractual life as of December 31, 2022	4 years 4 months 24 days
Number of Options, Options vested and expected to vest at December 31, 2022	7,689,449
Number of Options, Vested and expected to vest, Weighted average remaining contractual life as of December 31, 2022	5 years 11 months 12 days
Weighted-Average Exercise Price, Outstanding, Beginning Balance	$ 15.58
Weighted-Average Exercise Price, Granted	10.25
Weighted-Average Exercise Price, Exercised	6.43
Weighted-Average Exercise Price, Forfeited	14.50
Weighted-Average Exercise Price, Expired	16.09
Weighted-Average Exercise Price, Outstanding, Ending Balance	14.35	$ 15.58
Weighted-Average Exercise Price, Options exercisable, December 31, 2022	15.06
Weighted-Average Exercise Price, Options vested and expected to vest at December 31, 2022	$ 14.35
Aggregate Intrinsic Value, Outstanding at December 31, 2022	$ 3,028
Aggregate Intrinsic Value, Options exercisable at December 31, 2022	1,940
Aggregate Intrinsic Value, Options vested and expected to vest at December 31, 2022	3,028
Fair value of options vested	14,156	$ 12,844	$ 12,819
Intrinsic value of options exercised	$ 118	$ 965	$ 152

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock Award Modifications (Details) - Modified Awards [Member] - Former President and C E O [Member] - USD ($) $ in Thousands	1 Months Ended		12 Months Ended
	Feb. 28, 2022	Nov. 30, 2021	Dec. 31, 2022	Dec. 31, 2021
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 modified exercise period of awards		18 months
Performance Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock units, vested	17,333
Performance Restricted Stock Units [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			$ 2,563	$ 5,056
Incremental stock compensation expense relating to modification of stock options			$ 1,679	$ 4,908

Income Taxes - Components of In

Income Taxes - Components of Income Taxes (Benefit) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Current:
State			$ (691)
Total Current			(691)
Deferred:
Benefit from income taxes	$ 0	$ 0	$ (691)

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Income Taxes Computed Using U.S. Federal Statutory Rate to that Reflected in Operations (Detail)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Taxes
Income taxes using U.S. federal statutory rate	21%	21%	21%
State income taxes, net of federal benefit	(1.00%)	7.84%	(58.68%)
Tax Cuts and Jobs Act	0%	0%	0%
Impact of R&D tax credit on effective tax rate	4.91%	2.87%	(52.06%)
Stock option shortfalls and cancellations	(3.33%)	(4.74%)	0.35%
Permanent items and other	(1.86%)	(1.29%)	(5.08%)
Change in valuation allowance	(19.88%)	(25.69%)	84.61%
Provision to return	0.16%	0.01%	0.92%
Non-taxable revenue	0%	0%	0%
Total	0%	0%	(8.94%)

Income Taxes - Schedule of Sign

Income Taxes - Schedule of Significant Components of Company's Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Income Taxes
Valuation allowance	$ (160,814)	$ (143,388)
Deferred tax assets:
Net operating loss carryforwards	113,058	113,636
Federal and state tax credits	26,358	24,428
Stock-based compensation expense	3,434	5,023
Intangible asset amortization	17,265
Other	1,167	1,268
Deferred tax assets	161,282	144,355
Deferred tax liabilities:
Other	(468)	(967)
Deferred tax liabilities	$ (468)	$ (967)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Operating Loss Carryforwards [Line Items]
Threshold revenue for exchanging research and development tax credits for cash			$ 70,000
Benefit from income taxes	$ 0	$ 0	$ (691)
Valuation allowance on the deferred tax asset	100%	100%
Change in valuation allowance	$ 17,426	$ 22,722
Unrecognized tax benefits, related interest and penalties	$ 0	$ 0
Tax examinations, description	tax years 2006 through 2022 remain open to U.S. federal and state tax examinations.
Income taxes using U.S. federal statutory rate	21%	21%	21%
Federal [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 440,195
Federal [Member] | Earliest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Tax loss carryforwards expiration year	2026
Federal [Member] | R&D Tax Credit Carryforwards [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	$ 23,892
Federal [Member] | R&D Tax Credit Carryforwards [Member] | Earliest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Tax credit expiration year	2025
State and Local [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 347,975
State and Local [Member] | Earliest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Tax loss carryforwards expiration year	2027
State and Local [Member] | R&D Tax Credit Carryforwards [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	$ 2,861

Net (Loss) Income per Share - C

Net (Loss) Income per Share - Computation of Denominators Used in Net Loss per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Basic:
Weighted average common shares outstanding - Basic	53,653,564	50,718,765	47,413,250
Diluted:
Weighted average common shares outstanding - Basic	53,653,564	50,718,765	47,413,250
Common stock equivalents	0	0	501,780
Denominator for diluted net loss per share	53,653,564	50,718,765	47,915,030

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	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Net (Loss) Income per Share
Net loss - basic and diluted	$ (85,474)	$ (88,441)	$ 8,410
Weighted-average common shares outstanding:
Basic	53,653,564	50,718,765	47,413,250
Diluted	53,653,564	50,718,765	47,915,030
Stock options			481,254
Restricted stock units			20,526
Net (loss) income per share:
Basic	$ (1.59)	$ (1.74)	$ 0.18
Diluted	$ (1.59)	$ (1.74)	$ 0.18

Net Loss Per Share - Additional

Net Loss Per Share - Additional Information (Detail) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2022	Dec. 31, 2021
Net (Loss) Income per Share
Number of options outstanding	5,469,393	7,689,449	6,512,280
Number of restricted stock units outstanding	235,250	372,513	576,544
Dilutive stock options	481,254
Dilutive restricted stock units	20,526

Employee Benefit Plan - Additio

Employee Benefit Plan - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Defined Contribution Plan Disclosure [Line Items]
Defined contribution retirement plan, description	All employees over the age of 21 are eligible to participate in the plan on the first day of the month after completing three consecutive months of service
Employer contributions to the plan	$ 505	$ 460	$ 349
Defined contribution retirement plan, employer contribution percentage	3%
Minimum [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined contribution retirement plan, employee eligible age to participate	21 years
Defined contribution retirement plan, employee eligible service period	3 months

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) $ in Thousands				1 Months Ended		12 Months Ended
	Oct. 31, 2020 USD ($)	Aug. 31, 2019 USD ($)	Jul. 31, 2019	Jun. 30, 2020 item	Jul. 31, 2019 agreement	Dec. 31, 2022 USD ($) item	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	May 31, 2016 USD ($)
Other Commitments [Line Items]
Research and development expense						$ 91,879	$ 82,701	$ 107,851
Operating lease liabilities						1,918
Operating lease right-of-use assets						$ 1,551	2,973
New Stamford Lease [Member]
Other Commitments [Line Items]
Operating lease liabilities	$ 1,934
Operating lease right-of-use assets	1,934
Lease incentives	$ 0
Stamford Operating Lease [Member]
Other Commitments [Line Items]
Number of renewable terms | item						1
Operating Lease, renewable term						5 years
Operating lease, expiration date						Dec. 31, 2023
Tenant improvement expenses									$ 1,094
Operating lease cost								1,116
Stamford Operating Lease [Member] | Standby Letter of Credit [Member]
Other Commitments [Line Items]
Letter of credit, renewal term						automatically renewed annually through November 2023.
New Stamford Lease [Member]
Other Commitments [Line Items]
Number of renewable terms | item				1		1
Operating Lease, renewable term				5 years		5 years
Operating lease, expiration date				Dec. 31, 2023
New Stamford Lease [Member] | ASC 842 [Member]
Other Commitments [Line Items]
Number of renewable terms | item						1
Operating Lease, renewable term						5 years
Stamford Operating Lease and New Stamford Lease [Member]
Other Commitments [Line Items]
Operating lease cost						$ 1,624	1,624
Stamford Operating Lease and New Stamford Lease [Member] | Research and Development [Member]
Other Commitments [Line Items]
Operating lease cost						1,137	1,137	781
Stamford Operating Lease and New Stamford Lease [Member] | General and Administrative [Member]
Other Commitments [Line Items]
Operating lease cost						487	487	335
Non-Exclusive License Agreement
Other Commitments [Line Items]
Research and development expense						5,000	15,000	5,000
Non-Exclusive License Agreement | Enteris Biopharma, Inc. [Member]
Other Commitments [Line Items]
Upfront fee		$ 8,000
Upfront fee payment, cash		4,000
Upfront fee payment, stock		$ 4,000
Payment of milestone payment						$ 5,000	$ 15,000	$ 5,000
License agreement expiration period, first commercial sale		10 years
Agreement termination period for material breach		60 days
Agreement termination period for material breach of a payment obligation		30 days
Agreement termination period for challenged patent rights		30 days
Agreement termination period prior to first regulatory approval		30 days
Agreement termination period after first regulatory approval		60 days
Patheon MSA [Member]
Other Commitments [Line Items]
Agreement initial term, expiration date			Dec. 31, 2024
Agreement renewal term			2 years
Patheon MSA [Member] | Minimum [Member]
Other Commitments [Line Items]
Termination notice effective period			18 months
Patheon MSA [Member] | Patheon and Patheon Manufacturing Services LLC [Member]
Other Commitments [Line Items]
Number of related product agreements | agreement					2
Patheon MSA or Product Agreement [Member]
Other Commitments [Line Items]
Agreement Termination Notice Description			Either party may terminate the MSA or a Product Agreement upon written notice if the other party (1) has failed to remedy a material breach within a specified time or (2) is declared insolvent or bankrupt, voluntarily files a petition of bankruptcy or assigns such agreement for the benefit of creditors. The Company may terminate a Product Agreement (a) upon 90 days’ prior written notice if any governmental agency takes any action that prevents the Company from selling the relevant product in the relevant territory, (b) upon six months’ prior written notice if it does not intend to order manufacturing services due to a product’s discontinuance in the market, or (c) upon 90 days’ prior written notice if it determines that the manufacture or supply of a product likely infringes third-party rights. Patheon may terminate the MSA or a Product Agreement (i) upon six months’ prior written notice if the Company assigns such agreement to an assignee that is unacceptable to Patheon for certain reasons, or (ii) upon 30 days’ prior written notice if, after the first year of commercial sales, the Company forecasts zero volume for 12 months.
Termination notice effective period upon government agency restrictions			90 days
Termination notice effective period upon discontinuance in the market			6 months
Termination notice period if likely infringes on third-party rights			90 days
Termination notice period if assignee is unacceptable			6 months
Termination notice period if zero volume is forecasted after first year of commercial sales			30 days

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Other Information related to Stamford Lease and New Stamford Lease (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2016
Stamford Operating Lease [Member]
Other Commitments [Line Items]
Remaining lease term - operating leases (years)			7 years
Stamford Operating Lease and New Stamford Lease [Member]
Other Commitments [Line Items]
Operating cash outflows relating to operating leases	$ 1,957	$ 1,921
Remaining lease term - operating leases (years)	1 year	2 years
Discount rate - operating leases	7%	7%

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	Dec. 31, 2022	Dec. 31, 2021
Operating Lease Liabilities, Payments Due [Abstract]
2023	$ 1,992
Total future minimum lease payments, undiscounted	1,992
Less imputed interest	(74)
Operating lease liabilities	1,918
Operating lease liabilities reported as of December 31, 2022
Operating lease liabilities - current	1,918	$ 1,755
Operating lease liabilities - non-current		$ 1,918
Total	$ 1,918

Related Party Transactions (Det

Related Party Transactions (Detail) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Aug. 31, 2021	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Related Party Transaction [Line Items]
Accounts due from related parties		$ 3,260
Revenue From Contract With Customer Excluding Assessed Tax		41,867	$ 23,028	$ 135,082
Commercial Supply Revenue
Related Party Transaction [Line Items]
Revenue From Contract With Customer Excluding Assessed Tax		10,223	701
Collaborative Revenue
Related Party Transaction [Line Items]
Revenue From Contract With Customer Excluding Assessed Tax		16,572	706
Clinical Compound Revenue
Related Party Transaction [Line Items]
Revenue From Contract With Customer Excluding Assessed Tax			398	643
License and Milestone Fees
Related Party Transaction [Line Items]
Revenue From Contract With Customer Excluding Assessed Tax		15,000	21,223	$ 134,439
Royalty Revenue
Related Party Transaction [Line Items]
Revenue From Contract With Customer Excluding Assessed Tax		72
CSL Vifor Profit Sharing [Member] | Collaborative Revenue
Related Party Transaction [Line Items]
Revenue From Contract With Customer Excluding Assessed Tax		$ 16,572
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		13.70%
CSL Vifor [Member]
Related Party Transaction [Line Items]
Accounts due from related parties		$ 3,260
CSL Vifor [Member] | Commercial Supply Revenue
Related Party Transaction [Line Items]
Revenue from related parties		10,223	701
Related party cost of goods sold		7,266
CSL Vifor [Member] | Clinical Compound Revenue
Related Party Transaction [Line Items]
Revenue from related parties			$ 361
CSL Vifor [Member] | License and Milestone Fees
Related Party Transaction [Line Items]
Revenue from related parties	$ 15,000	15,000
CSL Vifor [Member] | Royalty Revenue
Related Party Transaction [Line Items]
Revenue from related parties		72
CSL Vifor [Member] | CSL Vifor Profit Sharing [Member] | Collaborative Revenue
Related Party Transaction [Line Items]
Revenue From Contract With Customer Excluding Assessed Tax		$ 16,572
CSL Vifor [Member] | Vifor International Ltd. [Member] | License and Milestone Fees
Related Party Transaction [Line Items]
Stock Sale Premium	$ 5,031