Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Income Statement [Abstract]
Revenue	$ 0
Operating expenses:
Research and development	8,905	$ 9,640	$ 20,886	$ 15,895
General and administrative	5,215	2,904	9,907	5,664
Total operating expenses	14,120	12,544	30,793	21,559
Loss from operations	(14,120)	(12,544)	(30,793)	(21,559)
Other income (expense):
Interest income	295	440	631	608
Interest expense	(202)		(478)	(204)
Other income (expense), net	(158)	(332)	(360)	(455)
Total other income (expense)	(65)	108	(207)	(51)
Net loss	$ (14,185)	$ (12,436)	$ (31,000)	$ (21,610)
Net loss per share basic and diluted	$ (0.63)	$ (0.58)	$ (1.40)	$ (1.01)
Weighted average common shares outstanding, basic and diluted	22,666	21,475	22,115	21,463
Other comprehensive (loss) income:
Unrealized gains from available-for-sale securities, net of tax of $0	$ (18)	$ (22)	$ (108)	$ (1)
Total other comprehensive (loss) income	(18)	(22)	(108)	(1)
Comprehensive loss	$ (14,203)	$ (12,458)	$ (31,108)	$ (21,611)