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