Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($)	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Operating activities
Net loss	$ (21,564,000)	$ (15,035,000)
Reconciliation of net loss to net cash used in operating activities:
Depreciation	87,000	33,000
Amortization of premium/discount on available-for-sale securities	108,000	580,000
Unrealized (gain) loss on forward foreign currency contracts included in net income	(127,000)	426,000
Foreign currency remeasurement (gain) loss	(6,000)	29,000
Stock-based compensation	2,499,000	1,494,000
Changes in:
Prepaid expenses and other assets	(20,000)	(181,000)
Interest receivable	46,000	(214,000)
Accounts payable, accrued expenses and other current liabilities	869,000	488,000
Net cash used in operating activities	(18,108,000)	(12,380,000)
Investing activities
Purchases of available-for-sale investments	(39,756,000)	(66,136,000)
Proceeds from maturities of available-for-sale investments	44,603,000	43,752,000
Proceeds from sale of available-for-sale investments		2,006,000
Purchase of property and equipment	(259,000)	(171,000)
Net cash provided by (used in) investing activities	4,588,000	(20,549,000)
Financing activities
Exercise of stock options	156,000	49,000
Proceeds from issuance of common stock under ESPP	5,000	52,000
Net cash provided by financing activities	161,000	101,000
Effect of exchange rate changes on cash	6,000	(29,000)
Decrease in cash and cash equivalents	(13,353,000)	(32,857,000)
Cash and cash equivalents, beginning of period	40,031,000	68,840,000
Cash and cash equivalents, end of period	$ 26,678,000	$ 35,983,000