Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities
Net loss	$ (49,762)	$ (34,495)	$ (41,975)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities
Depreciation and amortization	1,725	1,381	1,245
Net amortization (accretion) of premiums (discounts) on marketable securities	1,834	578	(473)
Stock-based compensation	8,237	3,609	2,168
Loss on sale of property and equipment	0	2	14
Realized gain on marketable securities	0	(18)	(8)
Changes in assets and liabilities
Accounts receivable	774	(1,877)	0
Prepaid expenses and other assets	(189)	(510)	(1,963)
Right-of-use assets	1,307	(148)	1,093
Accounts payable	1,166	225	(195)
Accrued and other liabilities	4,212	2,992	2,030
Contract liabilities	(23,541)	83,773	0
Lease liabilities	(1,542)	(49)	(1,249)
Net cash provided by (used in) operating activities	(55,779)	55,463	(39,313)
Cash flows from investing activities
Purchases of property and equipment, net	(2,644)	(493)	(1,353)
Purchases of marketable securities	(314,996)	(242,314)	(88,004)
Maturities of marketable securities	243,956	96,564	73,528
Sales of marketable securities	4,018	0	18,094
Net cash (used in) provided by investing activities	(69,666)	(146,243)	2,265
Cash flows from financing activities
Proceeds from issuance of common stock in public offering, net of issuance costs	85,990	100,664	50,321
Proceeds from issuance of common stock in private placement, net of issuance costs	0	19,988	0
Proceeds from issuance of common stock related to at-the-market offering program, net of issuance costs	57,263	6,582	0
Proceeds from exercise of common stock options, net of repurchases	1,504	1,190	289
Proceeds from ESPP purchases	697	326	0
Net cash provided by financing activities	145,454	128,750	50,610
Net increase in cash, cash equivalents and restricted cash	20,009	37,970	13,562
Cash, cash equivalents and restricted cash, at beginning of period	72,143	34,173	20,611
Cash, cash equivalents and restricted cash, at end of period	92,152	72,143	34,173
Reconciliation of cash, cash equivalents and restricted cash
Cash and cash equivalents	92,046	72,037	34,067
Restricted cash	106	106	106
Cash, cash equivalents and restricted cash, at end of period	92,152	72,143	34,173
Supplemental disclosure of cash flow information:
Cash paid for income taxes	4	1	1
Cash paid for interest	71	82	91
Supplemental non-cash investing and financing activities:
Right-of-use asset obtained in exchange for new operating lease liability	0	1,191	0
Vesting of early exercised options and restricted stock	24	56	114
Purchases of property and equipment in accounts payable and accrued liabilities	92	520	0
Conversion of redeemable convertible preferred stock into common stock	$ 0	$ 0	$ 138,391