Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (19,915)	$ (31,912)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	2,931	918
Depreciation and amortization	47	55
Changes in fair value of warrant liabilities		16,240
Securities issuance obligation		1,485
Other	(11)	2
Changes in operating assets and liabilities:
Prepaid expenses and other assets	406	429
Accrued, other and operating lease liabilities	(736)	(1,522)
Accounts payable	317	357
Net cash used in operating activities	(16,961)	(13,948)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock from At-The-Market equity offering, net of offering costs	19,632
Proceeds from exercise of common stock warrants	660
Proceeds from exercise of common stock options	288
Net cash provided by financing activities	20,580
Effect of foreign exchange rate changes on cash, cash equivalents and restricted cash	(16)	(46)
NET INCREASE (DECREASE) IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	3,603	(13,994)
CASH, CASH EQUIVALENTS AND RESTRICTED CASH — Beginning of period	104,355	147,828
CASH, CASH EQUIVALENTS AND RESTRICTED CASH — End of period	107,958	133,834
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Cash paid for income taxes, net	13	14
SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING INFORMATION:
Unpaid deferred financing costs in accounts payable and accrued and other liabilities	$ 110	45
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
Unpaid property and equipment in accrued and other liabilities		$ 12