Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Operating activities
Net income (loss)	$ (325,991)	$ (290,581)	$ 71,136
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation and amortization	10,383	8,593	8,531
Stock-based compensation expense	99,847	85,247	50,351
Net amortization of premiums and (discounts) on marketable securities	(1,637)	8,748	55
Non-cash adjustment to operating lease expense	(3,351)	(2,984)	(2,360)
Other non-cash items	63	0	38
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(2,760)	(12,865)	(10,569)
Accounts payable	2,274	3,705	(1,623)
Accruals and other current liabilities	10,918	4,732	22,106
Contract liabilities	(31,313)	(11,925)	(19,253)
Related party contract liability	(3,149)	(3,737)	297,418
Other non-current liabilities	0	(322)	322
Net cash provided by (used in) operating activities	(244,716)	(211,389)	416,152
Investing activities
Purchases of marketable securities	(1,115,040)	(1,422,938)	(1,285,468)
Purchases of property and equipment	(17,833)	(8,500)	(3,095)
Maturities and sales of marketable securities	991,486	1,409,812	665,357
Net cash used in investing activities	(141,387)	(21,626)	(623,206)
Financing activities
Proceeds from issuance of common stock in connection with Collaboration Agreements	0	0	420,146
Proceeds from public offering of common stock, net of issuance costs	296,215	0	193,948
Proceeds from exercise of awards under equity incentive plans	14,455	19,348	20,655
Net cash provided by financing activities	310,670	19,348	634,749
Net increase (decrease) in cash, cash equivalents and restricted cash	(75,433)	(213,667)	427,695
Cash, cash equivalents and restricted cash at beginning of year	294,977	508,644	80,949
Cash, cash equivalents and restricted cash at end of year	219,544	294,977	508,644
Supplemental disclosures of cash flow information
Cash paid during the year for income taxes	47	210	0
Issuance costs incurred but not yet paid	224	0	0
Property and equipment purchases accrued but not yet paid	$ 1,464	$ 593	$ 67