Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022
Cash flows from operating activities
Net loss	$ (307,153)	$ (248,315)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	31,731	33,189
Premium on marketable securities	(71)	(1,454)
Amortization of premium (discount) on marketable securities	(7,570)	6,114
Depreciation expense	654	554
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	4,505	(1,614)
Collaboration receivable - related party	(1,430)	(5,216)
Other long-term assets	(2,119)	(656)
Right-of-use operating asset	2,972	2,730
Operating lease liabilities, current	82	95
Operating lease liabilities, non-current	(3,488)	(3,164)
Accounts payable	(9,566)	(5,225)
Accrued expenses and other liabilities	6,253	8,723
Net cash used in operating activities	(285,200)	(214,239)
Cash flows from investing activities
Proceeds from sales and maturities of marketable securities	630,452	556,100
Purchases of marketable securities	(389,655)	(431,105)
Purchases of property and equipment	(337)	(291)
Net cash provided by investing activities	240,460	124,704
Cash flows from financing activities
Proceeds from stock option exercises and employee stock purchase plan issuances	4,156	1,836
Payment of employee tax obligations related to vesting of restricted stock units	(637)	(24)
Net cash provided by financing activities	3,519	1,812
Net decrease in cash, cash equivalents and restricted cash	(41,221)	(87,723)
Cash, cash equivalents and restricted cash at beginning of period	163,969	295,502
Cash, cash equivalents and restricted cash at end of period	122,748	207,779
Supplemental disclosure of non-cash operating activities
Purchases of property and equipment included in accounts payable	$ 36	$ 256