Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (11,092)	$ (10,538)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	1,527	1,363
Depreciation	53	52
Other	35	13
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	568	(85)
Accrued liabilities	(1,003)	(1,451)
Accounts payable	(1,452)	1,415
Net cash used in operating activities	(11,364)	(9,231)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment	(78)	(179)
Change in restricted cash	13	25
Net cash used in investing activities	(65)	(154)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock upon follow-on offering, net of offering costs	27,422
Proceeds from exercise of common stock options	23	96
Payment of deferred offering costs		(15)
Net cash provided by financing activities	27,445	81
Effect of exchange rate changes on cash and cash equivalents	2	(5)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	16,018	(9,309)
CASH AND CASH EQUIVALENTS - Beginning of period	109,007	150,180
CASH AND CASH EQUIVALENTS - End of period	125,025	140,871
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Cash paid for income taxes	90
SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING INFORMATION:
Property and equipment purchases included in accounts payable and accrued liabilities	$ 7	$ 20