CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating activities:
Net loss	$ (86,655)	$ (40,912)
Non-cash adjustments reconciling net loss to operating cash flows:
Depreciation of property and equipment	126	44
Accretion of discount on investments	(520)	(917)
Share-based compensation expense	21,567	11,131
Changes in operating assets and liabilities:
Other current assets	(100)	(1,528)
Other long-term assets	(331)	(1,229)
Accounts payable, accrued liabilities, deferred revenue and other liabilities	6,909	(1,071)
Cash flows used in operating activities	(59,004)	(34,482)
Investing activities:
Purchases of short-term investments	(230,384)	(127,458)
Sales and maturities of short-term investments	108,381	92,250
Purchases of property, plant, and equipment	(224)	0
Cash flows used in investing activities	(122,227)	(35,208)
Financing activities:
Proceeds from issuance of common stock, net of issuance costs	323,977	107,883
Proceeds from stock options exercised	15,183	2,668
Proceeds from disgorgement of shareholders' short-swing profits	41	1,050
Cash flows provided by financing activities	339,201	111,601
Increase in cash, cash equivalents and restricted cash	157,970	41,911
Cash, cash equivalents and restricted cash, beginning of period	46,856	32,694
Cash, cash equivalents and restricted cash, end of period	204,826	74,605
Reconciliation of cash, cash equivalents and restricted cash, end of period:
Total cash, cash equivalents and restricted cash	204,826	74,605
Supplemental disclosures of non-cash investing activities:
Purchases of property, plant, and equipment included within accounts payable and accrued liabilities	$ 408	$ 0