Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Statement [Abstract]
Revenue	$ 0
Operating expenses:
Research and development	9,047	$ 7,829	$ 29,933	$ 23,724
General and administrative	8,388	3,197	18,295	8,860
Total operating expenses	17,435	11,026	48,228	32,584
Loss from operations	(17,435)	(11,026)	(48,228)	(32,584)
Other income (expense):
Interest income	421	274	1,052	882
Interest expense	(561)	(202)	(1,039)	(406)
Other income (expense), net	(207)	(182)	(567)	(639)
Total other income (expense)	(347)	(110)	(554)	(163)
Net loss	$ (17,782)	$ (11,136)	$ (48,782)	$ (32,747)
Net loss per share basic and diluted	$ (0.65)	$ (0.52)	$ (2.04)	$ (1.52)
Weighted average common shares outstanding, basic and diluted	27,524	21,507	23,938	21,478
Other comprehensive (loss) income:
Unrealized gains from available-for-sale securities, net of tax of $0	$ 38	$ 9	$ (70)	$ 8
Total other comprehensive (loss) income	38	9	(70)	8
Comprehensive loss	$ (17,744)	$ (11,127)	$ (48,852)	$ (32,739)