Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Operating activities:
Net loss	$ (29,044)	$ (31,869)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	115	52
Stock-based compensation expense	3,148	3,130
Foreign currency remeasurement loss	395	0
Amortization of right-of-use asset	748	719
Loss on disposal of equipment	6	0
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	5,243	(505)
Other assets	21	175
Accounts payable	280	812
Accrued expenses and other liabilities	(4,805)	(1,204)
Operating lease liabilities	(1,239)	(841)
Cash used in operating activities	(25,132)	(29,531)
Investing activities:
Purchase of property and equipment	(26)	(364)
Proceeds from sale of marketable securities	0	4,385
Cash (used in) provided by investing activities	(26)	4,021
Financing activities:
Repayment of debt	(53)	(134)
Payment of financing costs	(197)	(245)
Proceeds from the issuance of common stock, net of issuance costs	5,650	0
Proceeds from option and BSPCE warrant exercises	78	471
Repayment of principal on finance lease	(28)	(9)
Cash provided by financing activities	5,450	83
Effect of foreign currency exchange rate changes on cash	(52)	5
Net decrease in cash, cash equivalents and restricted cash	(19,760)	(25,422)
Cash, cash equivalents and restricted cash at beginning of period	63,512	73,770
Cash, cash equivalents and restricted cash at end of period	43,752	48,348
Supplemental schedule of non-cash investing and financing activities:
Right-of-use assets acquired under operating leases	$ 0	$ 3,414