Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (11,525)	$ (11,092)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	1,499	1,527
Depreciation	29	53
Other	41	35
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(795)	568
Accrued liabilities	(1,261)	(1,003)
Accounts payable	(597)	(1,452)
Net cash used in operating activities	(12,609)	(11,364)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment		(78)
Net cash used in investing activities		(78)
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	101	23
Net cash provided by financing activities	46,097	27,445
Effect of foreign exchange rate changes on cash, cash equivalents and restricted cash	(20)	2
NET INCREASE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	33,468	16,005
CASH, CASH EQUIVALENTS AND RESTRICTED CASH - Beginning of period	100,536	109,207
CASH, CASH EQUIVALENTS AND RESTRICTED CASH - End of period	134,004	125,212
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Cash paid for income taxes	73	90
SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING INFORMATION:
Property and equipment purchases included in accrued liabilities	21	$ 7
Offering costs included in accrued liabilities	$ 209