Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Operating activities
Net loss	$ (14,457)	$ (9,652)
Reconciliation of net loss to net cash used in operating activities:
Depreciation	52	17
Amortization of premium/discount on available-for-sale securities	71	415
Unrealized (gain) loss on forward foreign currency contracts included in net income	(125)	112
Foreign currency remeasurement loss	21	6
Stock-based compensation	1,812	883
Changes in:
Prepaid expenses and other assets	460	(419)
Interest receivable	(26)	(198)
Accounts payable, accrued expenses and other current liabilities	730	366
Net cash used in operating activities	(11,462)	(8,470)
Investing activities
Purchases of available-for-sale investments	(26,718)	(58,890)
Proceeds from maturities of available-for-sale investments	32,414	15,320
Purchase of property and equipment	(202)	(36)
Net cash provided by (used in) investing activities	5,494	(43,606)
Financing activities
Exercise of stock options	139	7
Proceeds from issuance of common stock under ESPP	5	52
Net cash provided by financing activities	144	59
Effect of exchange rate changes on cash	(21)	(6)
Decrease in cash and cash equivalents	(5,845)	(52,023)
Cash and cash equivalents, beginning of period	40,031	68,840
Cash and cash equivalents, end of period	$ 34,186	$ 16,817