Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021
Cash flows from operating activities
Net loss	$ (248,315)	$ (203,009)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	33,189	49,639
Premium on marketable securities	(1,454)	(16,873)
Amortization of premium on marketable securities	6,114	4,688
Depreciation expense	554	3,475
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,614)	(6,025)
Collaboration receivable - related party	(5,216)	(48,438)
Other long-term assets	(656)	(258)
Right-of-use operating asset	2,730	2,602
Operating lease liabilities, current	95	97
Operating lease liabilities, non-current	(3,164)	(2,945)
Accounts payable	(5,225)	(774)
Accrued expenses and other liabilities	8,723	5,966
Net cash used in operating activities	(214,239)	(211,855)
Cash flows from investing activities
Proceeds from sales and maturities of marketable securities	556,100	360,939
Purchases of marketable securities	(431,105)	(1,308,143)
Purchases of property and equipment	(291)
Net cash provided by (used in) investing activities	124,704	(947,204)
Cash flows from financing activities
Proceeds from stock option exercises and employee stock purchase plan issuances	1,836	12,484
Payment of employee tax obligations related to vesting of restricted stock units	(24)	(796)
Net cash provided by financing activities	1,812	11,688
Net decrease in cash, cash equivalents and restricted cash	(87,723)	(1,147,371)
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	207,779	515,427
Supplemental disclosure of non-cash operating and investing activities
Purchases of property and equipment included in accounts payable	$ 256
Lease asset de-recognized upon lease cancellation		$ 3,733