Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (26,179)	$ (15,934)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	86	19
Stock-based compensation	2,211	864
Foreign currency transactions	25	51
Changes in assets and liabilities:
Other current assets	759	902
Other assets	(11)	(56)
Accounts payable	1,740	(134)
Accrued liabilities and other	(387)	805
NET CASH USED IN OPERATING ACTIVITIES	(21,756)	(13,483)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchase of property and equipment	(26)	(126)
NET CASH USED IN INVESTING ACTIVITIES	(26)	(126)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from exercised stock options	370
NET CASH PROVIDED BY FINANCING ACTIVITIES	370
Effect of exchange rates on cash, cash equivalents and restricted cash	50	13
NET DECREASE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	(21,362)	(13,596)
Cash, cash equivalents and restricted cash at the beginning of period	207,136	147,871
Cash, cash equivalents and restricted cash at the end of period	$ 185,774	134,275
SUPPLEMENTAL DISCLOSURE OF NON-CASH ACTIVITIES
Property and equipment purchases in accounts payable		88
Right-of-use assets obtained in exchange for lease obligations		$ 2,320