Condensed Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Operating activities
Net loss	$ (55,059)	$ (70,499)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	12,001	10,770
Depreciation and amortization	186	147
Amortization expense component of lease expense	969	496
Amortization of available-for-sale marketable securities, net	590	28
Realized gain on sale of available-for-sale marketable securities	(39)	(126)
Realized gain on sale of property and equipment	(70)
Deferred revenue		(21,751)
Changes in operating assets and liabilities:
Income tax receivable	810	(436)
Other receivables	(19,793)	509
Prepaid expenses	5,818	(1,391)
Accounts payable and accrued expenses	(3,069)	(4,608)
Operating lease liabilities	(1,186)	(714)
Net cash used in operating activities	(58,842)	(87,575)
Investing activities
Proceeds from maturities of available-for-sale marketable securities	134,220	119,895
Proceeds from redemptions of available-for-sale marketable securities, at par	13,500	22,035
Proceeds from sale of available-for-sale marketable securities	10,029	23,148
Purchases of available-for-sale marketable securities	(108,989)	(21,016)
Proceeds from sale of property and equipment	70
Purchases of property and equipment		(182)
Net cash provided by investing activities	48,830	143,880
Financing activities
Proceeds from the exercise of stock options	1,320	671
Net cash provided by financing activities	1,320	671
Net (decrease) increase in cash, cash equivalents and restricted cash	(8,692)	56,976
Cash, cash equivalents and restricted cash at beginning of period	32,091	18,713
Cash, cash equivalents and restricted cash at end of period	23,399	$ 75,689
Noncash investing and financing activities
Stock subscription receivable from Vifor	$ 44,969