Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
Cash flows from operating activities
Net loss	$ (385,638)	$ (333,180)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	46,358	83,981
Premium on marketable securities	(1,464)	(19,792)
Amortization of premium on marketable securities	7,182	8,722
Depreciation expense	832	3,849
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(13,176)	(11,522)
Collaboration receivable - related party	58	(24,185)
Other long-term assets	(658)	(534)
Right-of-use operating asset	4,139	3,898
Operating lease liabilities, current	135	152
Operating lease liabilities, non-current	(4,800)	(4,427)
Accounts payable	(3,357)	1,042
Accrued expenses and other liabilities	17,285	11,315
Net cash used in operating activities	(333,104)	(280,681)
Cash flows from investing activities
Proceeds from sales and maturities of marketable securities	918,816	699,212
Purchases of marketable securities	(682,505)	(1,671,399)
Purchases of property and equipment	(655)
Net cash provided by (used in) investing activities	235,656	(972,187)
Cash flows from financing activities
Proceeds from stock option exercises and employee stock purchase plan issuances	3,080	14,300
Payment of employee tax obligations related to vesting of restricted stock units	(39)	(796)
Net cash provided by financing activities	3,041	13,504
Net decrease in cash, cash equivalents and restricted cash	(94,407)	(1,239,364)
Cash, cash equivalents and restricted cash at beginning of period	295,502	1,662,798
Cash, cash equivalents and restricted cash at end of period	201,095	423,434
Supplemental disclosure of non-cash operating and investing activities
Purchases of property and equipment included in accounts payable	$ 54
Lease asset de-recognized upon lease cancellation		$ 3,733