Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (31,912)	$ (13,032)
Adjustments to reconcile net loss to net cash used in operating activities:
Changes in fair value of warrant liabilities	16,240
Securities issuance obligation	1,485
Stock-based compensation	918	1,699
Depreciation and amortization	55	62
Other	2	(26)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	429	(1,003)
Accrued, other and operating lease liabilities	(1,522)	(2,599)
Accounts payable	357	(667)
Net cash used in operating activities	(13,948)	(15,566)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment		(14)
Net cash used in investing activities		(14)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from exercise of common stock options		445
Net cash provided by financing activities		445
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(46)	(3)
NET (DECREASE) IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	(13,994)	(15,138)
CASH, CASH EQUIVALENTS AND RESTRICTED CASH — Beginning of period	147,828	106,346
CASH, CASH EQUIVALENTS AND RESTRICTED CASH — End of period	133,834	91,208
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Cash paid for (refund of) income taxes, net	14	(29)
Cash paid for interest		81
SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING INFORMATION:
Issuance of common stock and common stock warrant in connection with an amendment to the asset purchase agreement	11,970
Reclassification of warrant liabilities to equity	62,175
Right-of-use asset obtained in exchange for operating lease obligation		$ 771
Unpaid property and equipment in accrued and other liabilities	12
Unpaid deferred financing costs in accrued and other liabilities	$ 45