Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (62,879)	$ (40,813)
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	6,609	4,737
Depreciation and amortization	191	188
Asset impairment	106
Other	108	(101)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(586)	(416)
Accrued, other and operating lease liabilities	(1,624)	(2,345)
Accounts payable	531	22
Deferred revenue	200
Net cash used in operating activities	(39,619)	(38,728)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment	(12)	(33)
Net cash used in investing activities	(12)	(33)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock from At-The-Market equity offering, net of offering costs	1,140
Proceeds from exercise of common stock options		445
Net cash provided by financing activities	1,140	445
Effect of foreign exchange rate changes on cash, cash equivalents and restricted cash	(23)	(36)
NET DECREASE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	(38,514)	(38,352)
CASH, CASH EQUIVALENTS AND RESTRICTED CASH — Beginning of period	147,828	106,346
CASH, CASH EQUIVALENTS AND RESTRICTED CASH — End of period	109,314	67,994
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Cash paid for (refund of) income taxes, net	17	(95)
Cash paid for interest		246
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 deferred financing costs in accrued and other liabilities	$ 94