CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019		Dec. 31, 2018
Operating activities:
Net loss	$ (357,937)	$ (213,256)		$ (98,418)
Non-cash adjustments reconciling net loss to operating cash flows
Non-cash consideration earned from license agreement	(11,424)	0		0
Change in fair value on long-term investment	(4,205)	0		0
Depreciation of property and equipment	641	249		175
Accretion of discount on investments	(674)	(3,421)		(1,320)
Share-based compensation expense	85,847	55,537		15,854
Changes in operating assets and liabilities:
Other current assets	(4,180)	(5,487)		1,052
Other long-term assets	(2,842)	(4,375)		(359)
Accounts payable, accrued liabilities, deferred revenue and other liabilities	23,243	23,027		12,920
Cash flows used in operating activities	(271,531)	(147,726)		(70,096)
Investing activities:
Purchases of short-term investments	(662,824)	(530,228)		(255,795)
Sales and maturities of short-term investments	527,334	355,640		110,152
Purchases of property and equipment	(4,367)	(1,552)		(122)
Cash flows used in investing activities	(139,857)	(176,140)		(145,765)
Financing activities:
Proceeds from issuance of common stock and warrants, net of issuance costs	1,203,576	327,830	[1]	130,663
Proceeds from issuance of common stock under equity incentive plans	45,891	8,473		9,747
Proceeds from disgorgement of shareholders' short-swing profits	41	1,050		0
Proceeds from issuances under employee stock purchase plan	1,206	675		442
Cash flows provided by financing activities	1,250,714	338,028		140,852
Increase (decrease) in cash, cash equivalents and restricted cash	839,326	14,162		(75,009)
Cash, cash equivalents and restricted cash, beginning of year	46,856	32,694		107,703
Cash, cash equivalents and restricted cash, end of year	886,182	46,856		32,694
Reconciliation of cash, cash equivalents and restricted cash, end of period:
Total cash, cash equivalents and restricted cash	886,182	32,694		32,694
Supplemental disclosures of non-cash investing activities:
Accrued Capital Expenditures	292	0		0
Allowance utilized for tenant improvements	2,015	0		0
Initial recognition of operating right-of-use asset	39,890	0		0
Initial recognition of operating lease liability	$ 41,905	$ 0		$ 0

[1] Proceeds in 2018 include pre-funded warrants to purchase up to 421,650 shares of the Company's common stock at a public offering price of $38.849 per warrant, net of issuance costs.