Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash flows from operating activities:
Net loss	$ (133,310)	$ (36,329)	$ (190,228)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	5,714	6,329	5,870
Stock-based compensation	46,146	40,785	30,522
Amortization of premiums and accretion of discounts on marketable securities	(1,163)	2,099	584
Amortization of right-of-use assets	2,758	1,986	1,395
Impairment loss on right-of-use assets	0	0	238
Loss from disposal of property and equipment, net	0	0	107
Changes in operating assets and liabilities:
Receivable from collaboration partner	4,804	(7,391)	0
Prepaid expenses and other current assets	(3,926)	1,132	(3,839)
Other assets	(835)	(2,957)	(2,498)
Accounts payable	(572)	1,917	2,409
Accrued liabilities and accrued clinical supply costs	(2,655)	2,391	12,232
Deferred revenue	66,383	292,915	(21,098)
Lease liabilities	(4,274)	(4,012)	(2,407)
Other long-term liabilities	601	(314)	(21)
Net cash provided by (used in) operating activities	(20,329)	298,551	(166,734)
Cash flows from investing activities:
Purchase of property and equipment	(4,117)	(3,247)	(5,032)
Purchase of marketable securities	(556,898)	(343,402)	(506,809)
Sale of marketable securities	0	10,696	0
Maturities of marketable securities	402,001	286,290	406,790
Net cash used in investing activities	(159,014)	(49,663)	(105,051)
Cash flows from financing activities:
Proceeds from issuance of common stock upon public offerings, net of issuance costs	0	0	224,603
Proceeds from the exercise of options to purchase common stock	3,059	28,530	6,331
Proceeds from issuance of stock from employee stock purchase plan	1,455	1,765	1,179
Net cash provided by financing activities	4,514	30,295	232,113
Net increase (decrease) in cash, cash equivalents, and restricted cash	(174,829)	279,183	(39,672)
Cash, cash equivalents, and restricted cash at beginning of period	330,624	51,441	91,113
Cash, cash equivalents, and restricted cash at end of period	155,795	330,624	51,441
Non-cash investing and financing activities:
Property and equipment purchases included in accounts payable and accrued liabilities	$ 493	$ 705	$ 428