Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Operating activities
Net loss	$ (9,652)	$ (5,394)
Reconciliation of net loss to net cash used in operating activities:
Depreciation	17	13
Amortization of premium/discount on available-for-sale securities	$ 415	6
Accretion of discount and debt issuance cost of convertible notes payable		$ 742
Unrealized loss on currency forward contracts included in net income	$ 112
Foreign currency remeasurement loss	6
Stock-based compensation	$ 883	$ 49
Change in fair value of investor rights/obligation		18
Change in fair value of derivative liability		81
Changes in:
Prepaid expenses and other assets	$ (419)	(1,480)
Interest receivable	(198)	(1)
Accounts payable and accrued expenses	$ 366	1,617
Accrued interest payable		115
Net cash used in operating activities	$ (8,470)	(4,234)
Investing activities
Purchases of available-for-sale investments	(58,890)	(16,795)
Proceeds from maturities of available-for-sale investments	15,320	2,355
Purchase of property and equipment	(36)	(36)
Net cash used in investing activities	(43,606)	$ (14,476)
Financing activities
Exercise of stock options	$ 7
Proceeds from issuance of Series D preferred stock		$ 25,000
Issuance costs for preferred stock		$ (437)
Proceeds from issuance of common stock under ESPP	$ 52
Net cash provided by financing activities	59	$ 24,563
Effect of exchange rate changes on cash	(6)
(Decrease) increase in cash and cash equivalents	(52,023)	$ 5,853
Cash and cash equivalents, beginning of period	68,840	2,793
Cash and cash equivalents, end of period	$ 16,817	8,646
Supplemental disclosure of non-cash investing and financing activities
Accretion of redeemable convertible preferred stock to redemption value		$ 3,409