Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Operating activities
Net loss	$ (10,960)	$ (12,106)
Reconciliation of net loss to net cash used in operating activities:
Depreciation	61	77
Amortization of premium/discount on available-for-sale securities	(14)	1
Foreign currency remeasurement (loss)/gain	(25)	279
Stock-based compensation	1,743	1,712
Changes in:
Prepaid expenses and other assets	396	263
Interest receivable	4	(12)
Accounts payable and accrued expenses	(7,009)	(942)
Net cash used in operating activities	(15,804)	(10,728)
Investing activities
Purchases of available-for-sale investments	(10,957)	(13,360)
Proceeds from maturities of available-for-sale investments	15,990	4,920
Proceeds from sale of available-for-sale investments	1,999
Purchase of property and equipment	(21)	(14)
Net cash provided by (used in) investing activities	7,011	(8,454)
Financing activities
Proceeds from issuance of common stock, net of issuance costs		1,287
Proceeds from issuance of common stock under ESPP	84	58
Exercise of stock options		109
Net cash provided by financing activities	84	1,454
Effect of exchange rate changes on cash	24	(279)
Decrease in cash, cash equivalents and restricted cash	(8,685)	(18,007)
Cash, cash equivalents and restricted cash, beginning of period	21,192	36,406
Cash, cash equivalents and restricted cash, end of period	$ 12,507	$ 18,399