Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (23,485)	$ (21,421)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	3,281	3,038
Depreciation	59	156
Other	(170)	17
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(1,043)	696
Accrued liabilities	693	(133)
Accounts payable	(212)	(2,035)
Net cash used in operating activities	(20,877)	(19,682)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment	(30)	(87)
Net cash used in investing activities	(30)	(87)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock upon follow-on offering, net of offering costs	45,996	27,422
Proceeds from exercise of common stock options	133	23
Net cash provided by financing activities	46,129	27,445
Effect of foreign exchange rate changes on cash, cash equivalents and restricted cash	(33)	3
NET INCREASE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	25,189	7,679
CASH, CASH EQUIVALENTS AND RESTRICTED CASH-Beginning of period	100,536	109,207
CASH, CASH EQUIVALENTS AND RESTRICTED CASH-End of period	125,725	116,886
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Cash paid for income taxes	104	187
SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING INFORMATION:
Property and equipment purchases included in accrued liabilities		$ 10
Offering costs included in accounts payable and accrued liabilities	$ 43