Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Income Statement [Abstract]
Revenue	$ 0	$ 0
Operating expenses:
Research and development	11,981	6,255
General and administrative	4,692	2,760
Total operating expenses	16,673	9,015
Loss from operations	(16,673)	(9,015)
Other income (expense):
Interest income	336	168
Interest expense	(276)	(204)
Other income (expense), net	(202)	(123)
Total other income (expense)	(142)	(159)
Net loss	$ (16,815)	$ (9,174)
Net loss per share basic and diluted	$ (0.78)	$ (0.43)
Weighted average common shares outstanding, basic and diluted	21,570	21,451
Other comprehensive (loss) income:
Unrealized gains from available-for-sale securities, net of tax of $0	$ (89)	$ 21
Total other comprehensive (loss) income	(89)	21
Comprehensive loss	$ (16,904)	$ (9,153)