Summary of Significant Accounting Policies (Details 3) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Net Loss per Share
Common stock shares subject to repurchase, excluded from net loss per share calculations			82		583
Loss allocated to participating securities, basic			$ 0	$ 0
Loss allocated to participating securities, diluted			0	0
Net loss	$ (13,250)	$ (8,780)	(33,888)	(23,829)
Adjustment to net loss resulting from convertible preferred stock modification			(2,384)
Net loss attributable to common stockholders	$ (13,250)	$ (8,780)	$ (36,272)	$ (23,829)
Weighted average common stock outstanding (in shares)	12,280	241	10,935	241
Net loss per share, basic and diluted (in dollars per share)	$ (1.08)	$ (36.43)	$ (3.32)	$ (98.88)
Anti-dilutive shares excluded from computation of earnings per share			5,269,602	5,627,702
Convertible preferred stock outstanding
Net Loss per Share
Anti-dilutive shares excluded from computation of earnings per share				4,259,998
Common stock options
Net Loss per Share
Anti-dilutive shares excluded from computation of earnings per share			3,056,207	316,733
Common stock warrants
Net Loss per Share
Anti-dilutive shares excluded from computation of earnings per share			2,213,395	1,050,971