Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating activities
Net (loss) income	$ (88,441)	$ 8,410	$ (106,373)
Adjustments to reconcile net (loss) income to net cash used in operating activities:
Stock-based compensation expense	20,785	14,835	12,568
Depreciation and amortization	248	209	198
Amortization expense component of lease expense	1,306	806	601
Noncash expense related to oral formulation license agreement			4,000
Amortization (accretion) of available-for-sale marketable securities, net	861	154	(1,381)
Realized gain on sale of available-for-sale marketable securities	(39)	(272)
Realized gain on sale of property and equipment	(70)	0	0
Deferred revenue		(22,262)	(19,747)
Changes in operating assets and liabilities:
Income tax receivable	810	(691)	(152)
Other receivables	102	414	(45)
Inventory, net	(2,584)
Prepaid expenses	9,557	(3,213)	(4,058)
Accounts payable and accrued expenses	(1,020)	(2,784)	6,043
Operating lease liabilities	(1,602)	(1,093)	(879)
Net cash used in operating activities	(60,087)	(5,487)	(109,225)
Investing activities
Proceeds from maturities of available-for-sale marketable securities	173,484	144,320	253,584
Proceeds from redemptions of available-for-sale marketable securities, at par	20,500	27,035	2,000
Proceeds from sale of available-for-sale marketable securities	10,029	41,600	0
Purchases of available-for-sale marketable securities	(208,795)	(232,881)	(286,082)
Proceeds from sale of property and equipment	70
Purchases of property and equipment	(39)	(349)	(18)
Net cash used in investing activities	(4,751)	(20,275)	(30,516)
Financing activities
Proceeds from the sale of common stock under license agreement with Vifor	44,969	38,449
Proceeds from the sale of common stock in a follow-on public offering, net of issuance costs			136,498
Proceeds from the exercise of stock options	1,639	691	6,106
Net cash provided by financing activities	46,608	39,140	142,604
Net (decrease) increase in cash, cash equivalents and restricted cash	(18,230)	13,378	2,863
Cash, cash equivalents and restricted cash at beginning of period	32,091	18,713	15,850
Cash, cash equivalents and restricted cash at end of period	$ 13,861	$ 32,091	18,713
Noncash investing and financing activities
Shares of common stock issued in connection with oral formulation license agreement			4,000
Shares of common stock issued in exchange for consulting services			$ 197