Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Operating activities
Net loss	$ (14,992)	$ (20,729)
Reconciliation of net loss to net cash used in operating activities:
Depreciation	279	115
Amortization of premium/discount on available-for-sale securities	(4)	(51)
Foreign currency remeasurement (loss)		(25)
Stock-based compensation	943	3,429
Changes in:
Prepaid expenses and other assets	608	141
Operating lease right-of-use asset	200
Interest receivable	17	49
Accounts payable and accrued expenses	(2,497)	(6,162)
Operating lease liability	(200)
Net cash used in operating activities	(15,646)	(23,233)
Investing activities
Purchases of available-for-sale investments		(15,443)
Proceeds from maturities of available-for-sale investments	2,500	31,990
Proceeds from sale of available-for-sale investments		1,999
Purchase of property and equipment	(16)	(119)
Net cash provided by (used in) investing activities	2,484	18,427
Financing activities
Proceeds from issuance of common stock, net of issuance costs		2,853
Proceeds from issuance of common stock under ESPP		132
Net cash provided by financing activities		2,985
Effect of exchange rate changes on cash		22
Decrease in cash, cash equivalents and restricted cash	(13,162)	(1,799)
Cash, cash equivalents and restricted cash, beginning of period	19,393	21,192
Cash, cash equivalents and restricted cash, end of period	$ 6,231	$ 19,393