Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Operating activities:
Net loss	$ (22,670)	$ (20,237)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	77	19
Stock-based compensation expense	2,060	1,934
Amortization of right-of-use asset	492	363
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	4,499	(2,908)
Other assets	10	(59)
Accounts payable	(88)	1,056
Accrued expenses and other liabilities	(1,593)	(892)
Operating lease liabilities	(817)	(450)
Cash used in operating activities	(18,030)	(21,174)
Investing activities:
Purchase of property and equipment	(26)	(277)
Proceeds from sale of marketable securities	0	4,385
Cash (used in) provided by investing activities	(26)	4,108
Financing activities:
Repayment of debt	0	(90)
Payment of financing costs	(197)	(162)
Proceeds from the issuance of common stock, net of issuance costs	5,650	0
Proceeds from option and warrant exercises	0	0
Proceeds from option and BSPCE warrant exercises	78	214
Repayment of principal on finance lease	(18)	0
Cash provided by (used in) financing activities	5,513	(38)
Effect of foreign currency exchange rate changes on cash	48	(35)
Net decrease in cash, cash equivalents and restricted cash	(12,495)	(17,139)
Cash, cash equivalents and restricted cash at beginning of period	63,512	73,770
Cash, cash equivalents and restricted cash at end of period	51,017	56,631
Supplemental schedule of non-cash investing and financing activities:
Right-of-use assets acquired under operating leases	0	1,840
Financing costs in accounts payable and accrued expenses	$ 0	$ 83