Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Operating activities
Net loss	$ (12,106)	$ (14,457)
Reconciliation of net loss to net cash used in operating activities:
Depreciation	77	52
Amortization of premium/discount on available-for-sale securities	1	71
Unrealized gain on forward foreign currency contracts included in net income		(125)
Foreign currency remeasurement gain	279	21
Stock-based compensation	1,712	1,812
Changes in:
Prepaid expenses and other assets	263	460
Interest receivable	(12)	(26)
Accounts payable, accrued expenses and other current liabilities	(942)	730
Net cash used in operating activities	(10,728)	(11,462)
Investing activities
Purchases of available-for-sale investments	(13,360)	(26,718)
Proceeds from maturities of available-for-sale investments	4,920	32,414
Purchase of property and equipment	(14)	(202)
Net cash (used in) provided by investing activities	(8,454)	5,494
Financing activities
Exercise of stock options	109	139
Proceeds from issuance of common stock under ESPP	58	5
Proceeds from issuance of common stock, net of issuance costs	1,287
Net cash provided by financing activities	1,454	144
Effect of exchange rate changes on cash	(279)	(21)
Decrease in cash and cash equivalents	(18,007)	(5,845)
Cash and cash equivalents, beginning of period	36,392	40,031
Cash and cash equivalents, end of period	$ 18,385	$ 34,186