CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Operating activities:
Net loss	$ (256,850)	$ (140,880)
Non-cash adjustments reconciling net loss to operating cash flows:
Non-cash consideration earned from license agreement	(11,424)	0
Change in fair value of long-term investment	24	0
Depreciation of property and equipment	435	156
Accretion of discount on investments	(877)	(2,818)
Share-based compensation expense	64,104	38,826
Changes in operating assets and liabilities:
Other current assets	(6,985)	(6,566)
Other long-term assets	(843)	(3,873)
Accounts payable, accrued liabilities, deferred revenue and other liabilities	17,306	9,331
Cash flows used in operating activities	(195,110)	(105,824)
Investing activities:
Purchases of short-term investments	(456,608)	(458,115)
Sales and maturities of short-term investments	378,952	289,134
Purchases of property, plant, and equipment	(2,861)	(220)
Cash flows used in investing activities	(80,517)	(169,201)
Financing activities:
Proceeds from issuance of common stock, net of issuance costs	323,977	327,810
Proceeds from issuance of common stock under equity incentive plans	36,283	5,372
Proceeds from disgorgement of shareholders' short-swing profits	41	1,050
Proceeds from stock issuances under employee stock purchase plan	524	323
Cash flows provided by financing activities	360,825	334,555
Increase in cash, cash equivalents and restricted cash	85,198	59,530
Cash, cash equivalents and restricted cash, beginning of period	46,856	32,694
Cash, cash equivalents and restricted cash, end of period	132,054	92,224
Reconciliation of cash, cash equivalents and restricted cash, end of period:
Total cash, cash equivalents and restricted cash	132,054	92,224
Supplemental disclosures of non-cash investing activities:
Allowance utilized for tenant improvements	1,662	0
Fair value of long-term investment earned from license agreement	$ 11,400	$ 0