Consolidated 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	$ (36,329)	$ (190,228)	$ (105,385)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	6,329	5,870	3,775
Stock-based compensation	40,785	30,522	16,281
Amortization of premiums and accretion of discounts on marketable securities	2,099	584	(4,701)
Amortization of right-of-use assets	1,986	1,395	1,799
Impairment loss on right-of-use assets	0	238	1,158
Loss from disposal of property and equipment, net	0	107	(39)
Changes in operating assets and liabilities:
Receivable from collaboration partner	(7,391)	0	0
Prepaid expenses and other current assets	1,132	(3,839)	(1,596)
Other assets	(2,957)	(2,498)	(42)
Accounts payable	1,917	2,409	152
Accrued liabilities and accrued clinical supply costs	2,391	12,232	9,210
Deferred revenue	292,915	(21,098)	(21,219)
Lease liabilities	(4,012)	(2,407)	868
Other long-term liabilities	(314)	(21)	353
Net cash provided by (used in) operating activities	298,551	(166,734)	(99,308)
Cash flows from investing activities:
Purchase of property and equipment	(3,247)	(5,032)	(15,265)
Purchase of marketable securities	(343,402)	(506,809)	(529,609)
Sale of marketable securities	10,696	0	0
Maturities of marketable securities	286,290	406,790	496,000
Net cash used in investing activities	(49,663)	(105,051)	(48,874)
Cash flows from financing activities:
Proceeds from issuance of common stock upon initial public offering, net of issuance costs	0	224,603	170,036
Proceeds from the exercise of options to purchase common stock	28,530	6,331	1,519
Proceeds from issuance of stock from employee stock purchase plan	1,765	1,179	798
Net cash provided by financing activities	30,295	232,113	172,353
Net increase (decrease) in cash, cash equivalents, and restricted cash	279,183	(39,672)	24,171
Cash, cash equivalents, and restricted cash at beginning of period	51,441	91,113	66,942
Cash, cash equivalents, and restricted cash at end of period	330,624	51,441	91,113
Non-cash investing and financing activities:
Property and equipment purchases included in accounts payable and accrued liabilities	705	428	3,471
Deferred offering costs in accrued liabilities	0	0	465
Tenant improvements paid by landlord	$ 0	$ 0	$ 8,286