Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating activities
Net loss	$ (6,081)	$ (6,498)
Reconciliation of net loss to net cash used in operating activities:
Depreciation	32	40
Amortization of premium/discount on available-for-sale securities	3	4
Foreign currency remeasurement gain	(136)	(59)
Stock-based compensation	821	845
Changes in:
Prepaid expenses and other assets	125	278
Accounts payable and accrued expenses	(220)	(2,056)
Net cash used in operating activities	(5,456)	(7,446)
Investing activities
Proceeds from maturities of available-for-sale investments	7,515	4,920
Proceeds from sale of available-for-sale investments	1,999
Purchase of property and equipment	(9)	(6)
Net cash provided by investing activities	9,505	4,914
Financing activities
Proceeds from issuance of common stock, net of issuance costs		105
Exercise of stock options		108
Net cash provided by financing activities		213
Effect of exchange rate changes on cash	137	59
Increase (decrease) in cash, cash equivalents and restricted cash	4,186	(2,260)
Cash, cash equivalents and restricted cash, beginning of period	21,192	36,406
Cash, cash equivalents and restricted cash, end of period	$ 25,378	$ 34,146