Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flow from operating activities
Net income (loss)	$ 52,830	$ (122,858)	$ (84,710)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	54,528	21,825	8,981
Depreciation and amortization	3,843	3,149	3,578
Noncash lease expense	3,214	1,042
Share of loss from equity method investee, net		613	1,202
Amortization of premiums on investments	4,772	(46)	(2,638)
Effective interest on liability for sale of future royalties	260
Changes in operating assets and liabilities:
Receivable from collaboration partners (($17,092), ($943) and $0 from a related party)	(17,046)	(917)	(132)
Amounts owed by PACT Pharma			83
Prepaid expenses and other current assets	(5,944)	(838)	(1,982)
Other long-term assets	3,322	(5,374)	(588)
Accounts payable	(4,773)	9,272	1,726
Accrued research and development	8,355	13,735	1,756
Other accrued liabilities	10,138	4,593	1,743
Other current liabilities			57
Deferred revenue (($360,884), $195,082 and $0 to a related party)	(367,884)	188,082	(2,000)
Operating lease liabilities	(1,288)	(993)
Deferred rent			(538)
Other long-term liabilities	(498)	498
Net cash provided by (used in) operating activities	(256,171)	111,170	(73,462)
Cash flow from investing activities
Purchases of short-term and long-term investments	(718,865)	(739,658)	(247,755)
Proceeds from maturities of short-term and long-term investments	690,074	307,343	308,892
Sales of short-term and long-term investments	51,001	1,003
Purchases of property and equipment	(26,078)	(3,055)	(1,925)
Net cash provided by (used in) investing activities	(3,868)	(434,367)	59,212
Cash flow from financing activities
Proceeds from issuance of common stock and rights to purchase additional shares ($220,235, $164,207 and $0 from a related party)	220,235	433,776
Proceeds from sale of future royalties	5,000
Proceeds from issuance of common stock pursuant to equity award plans	12,111	4,953	1,217
Repurchase of unvested shares of stock	(6)	(54)	(94)
Net cash provided by financing activities	237,340	438,675	1,123
Net increase (decrease) in cash, cash equivalents and restricted cash	(22,699)	115,478	(13,127)
Cash, cash equivalents and restricted cash at beginning of period	173,618	58,140	71,267
Cash, cash equivalents and restricted cash at end of period	150,919	173,618	58,140
Non-cash investing and financing activities:
Unpaid portion of property and equipment purchases included in accounts payable and accrued liabilities	996	1,583	12
Unpaid portion of other assets included in accrued research and development	1,425
Vesting of early exercised stock options and restricted stock	$ 686	848	$ 1,029
Unpaid Portion of Financing Costs Included in Accounts Payable		$ 61