Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Operating Activities
Net loss	$ (32,453)	$ (30,694)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation expense	6,650	5,075
Depreciation expense	177	108
Amortization of premium and accretion of discounts on marketable securities, net	1,100	850
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(2,630)	(2,860)
Other long-term assets	105	410
Accounts payable and accrued expenses	(5,251)	(1,452)
Other long-term liabilities	121	46
Net cash used in operating activities	(32,181)	(28,517)
Investing Activities
Purchases of marketable securities	(51,400)	(223,158)
Maturities of marketable securities	26,487	36,969
Purchases of property and equipment	(49)	(31)
Net cash used in investing activities	(24,962)	(186,220)
Financing Activities
Proceeds from issuance of stock under equity incentive plan	303	829
Repayment of long-term debt		(750)
Net cash (used in) provided by financing activities	303	79
Net decrease in cash, cash equivalents and restricted cash	(56,840)	(214,658)
Cash, cash equivalents and restricted cash at beginning of period	90,882	325,703
Cash, cash equivalents and restricted cash at end of period	$ 34,042	$ 111,045