CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Operating activities:
Net loss	$ (302,110)	$ (169,514)
Non-cash adjustments reconciling net loss to operating cash flows:
Change in fair value of long-term investment	6,682	0
Depreciation of property and equipment	705	253
Amortization of premium and accretion of discounts on investments	2,225	(863)
Share-based compensation expense	52,691	42,354
Changes in operating assets and liabilities:
Other current assets	(68,047)	1,029
Other long-term assets	(8,550)	(282)
Right-of-use asset	1,185	(127)
Lease liability	2,578	56
Accounts payable, accrued liabilities, deferred revenue and other liabilities	108,858	8,747
Cash flows used in operating activities	(203,783)	(118,347)
Investing activities:
Purchases of short-term investments	(765,888)	(384,127)
Sales and maturities of short-term investments	352,258	240,878
Purchases of property and equipment	(5,137)	(1,425)
Cash flows used in investing activities	(418,767)	(144,674)
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	16,494	23,932
Proceeds from stock issuances under employee stock purchase plan	1,214	524
Cash flows provided by financing activities	17,708	348,474
(Decrease) increase in cash, cash equivalents and restricted cash	(604,842)	85,453
Cash, cash equivalents and restricted cash, beginning of period	886,182	46,856
Cash, cash equivalents and restricted cash, end of period	281,340	132,309
Reconciliation of cash, cash equivalents and restricted cash, end of period:
Cash and cash equivalents	280,720	131,689
Restricted cash included in other long-term assets	620	620
Total cash, cash equivalents and restricted cash	281,340	132,309
Supplemental disclosures of non-cash investing activities:
Purchases of property and equipment included within accounts payable and accrued liabilities	$ 0	$ 239