CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating activities
Net loss	$ (118,513)	$ (85,474)	$ (88,441)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	13,730	17,734	20,785
Non-cash interest expense on liability related to sales of future royalties and milestones, net of issuance costs accretion	604
Depreciation and amortization	259	248	248
Noncash lease expense	2,075	1,422	1,306
(Accretion)/amortization of available-for-sale marketable securities, net	(400)	264	861
Realized gain on sale of available-for-sale marketable securities			(39)
Realized gain on sale of property and equipment	0	0	(70)
Changes in operating assets and liabilities:
Accounts receivable, net - related party	495	(3,260)
Inventory, net	(438)	201	(2,584)
Income tax receivable			810
Other receivables	(59)	(41)	102
Prepaid expenses	8,113	(13,748)	9,557
Accounts payable and accrued expenses	3,275	5,679	(1,020)
Operating lease liabilities	(1,918)	(1,755)	(1,602)
Reimbursement of lease incentive	807
Other	(108)
Net cash used in operating activities	(92,078)	(78,730)	(60,087)
Investing activities
Proceeds from maturities of available-for-sale marketable securities	155,441	220,435	173,484
Proceeds from redemptions of available-for-sale marketable securities, at par	4,000	4,000	20,500
Proceeds from sale of available-for-sale marketable securities	0	0	10,029
Purchases of available-for-sale marketable securities	(113,605)	(95,685)	(208,795)
Purchases of property and equipment	(2,375)	(43)	(39)
Proceeds from sale of property and equipment			70
Net cash provided by (used in) investing activities	43,461	128,707	(4,751)
Financing activities
Proceeds from royalty purchase and sale agreement, net of $1.0 million of issuance costs	36,474
Net proceeds from sales of common stock under open market sales agreement	1,117
Proceeds from the exercise of stock options	560	311	1,639
Proceeds from the sale of common stock under license agreement with Vifor International			44,969
Net cash provided by financing activities	38,151	311	46,608
Net (decrease) increase in cash, cash equivalents and restricted cash	(10,466)	50,288	(18,230)
Cash, cash equivalents and restricted cash at beginning of period	64,149	13,861	32,091
Cash, cash equivalents and restricted cash at end of period	53,683	$ 64,149	$ 13,861
Noncash investing and financing activities
Accrual for leasehold improvements	$ 778