CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Operating activities:
Net loss	$ (382,164)	$ (256,850)
Non-cash adjustments reconciling net loss to operating cash flows:
Non-cash consideration earned from license agreement	0	(11,424)
Change in fair value of long-term investment	4,376	24
Depreciation of property and equipment	1,219	435
Amortization of premium and accretion of discounts on investments	3,503	(877)
Share-based compensation expense	79,624	64,104
Changes in operating assets and liabilities:
Other current assets	(3,939)	(6,985)
Other long-term assets	(9,218)	(871)
Right-of-use asset	1,718	28
Lease liability	3,927	(98)
Accounts payable, accrued liabilities, deferred revenue and other liabilities	50,139	17,404
Cash flows used in operating activities	(250,815)	(195,110)
Investing activities:
Purchases of short-term investments	(1,059,140)	(456,608)
Sales and maturities of short-term investments	648,223	378,952
Purchases of property and equipment	(7,146)	(2,861)
Cash flows used in investing activities	(418,063)	(80,517)
Financing activities:
Proceeds from issuance of common stock, net of issuance costs	0	324,018
Proceeds from issuance of common stock under equity incentive plans	24,726	36,283
Proceeds from stock issuances under employee stock purchase plan	1,214	524
Cash flows provided by financing activities	25,940	360,825
(Decrease) increase in cash, cash equivalents and restricted cash	(642,938)	85,198
Cash, cash equivalents and restricted cash, beginning of period	886,182	46,856
Cash, cash equivalents and restricted cash, end of period	243,244	132,054
Reconciliation of cash, cash equivalents and restricted cash, end of period:
Cash and cash equivalents	242,624	131,434
Restricted cash included in other long-term assets	620	620
Total cash, cash equivalents and restricted cash	243,244	132,054
Supplemental disclosures of non-cash investing activities:
Purchases of property and equipment included within accounts payable and accrued liabilities	$ 279	$ 1,662