CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Operating activities:
Net loss	$ (169,514)	$ (86,607)
Non-cash adjustments reconciling net loss to operating cash flows:
Depreciation of property and equipment	253	99
Accretion of discount on investments	(863)	(1,964)
Share-based compensation expense	42,354	23,720
Changes in operating assets and liabilities:
Other current assets	1,029	(6,313)
Other long-term assets	(409)	(3,982)
Accounts payable, accrued liabilities, deferred revenue and other liabilities	8,803	2,097
Cash flows used in operating activities	(118,347)	(72,950)
Investing activities:
Purchases of short-term investments	(384,127)	(212,666)
Sales and maturities of short-term investments	240,878	171,600
Purchases of property, plant, and equipment	(1,425)	(69)
Cash flows used in investing activities	(144,674)	(41,135)
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	23,932	4,300
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	348,474	333,483
Increase in cash, cash equivalents and restricted cash	85,453	219,398
Cash, cash equivalents and restricted cash, beginning of period	46,856	32,694
Cash, cash equivalents and restricted cash, end of period	132,309	252,092
Reconciliation of cash, cash equivalents and restricted cash, end of period:
Total cash, cash equivalents and restricted cash	132,309	252,092
Supplemental disclosures of non-cash investing activities:
Purchases of property, plant, and equipment included within accounts payable and accrued liabilities	$ 239	$ 0