Net Loss per Share (Details 2) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Numerator
Net loss attributable to holders of common stock									$ (26,733)	$ (29,088)	$ (28,300)
Denominator:
Weighted-average shares of common stock outstanding, basic and diluted	45,651,475	41,645,894	41,362,476	40,978,741	40,577,087	40,269,937	39,304,884	7,698,709	42,420,356	32,075,107	7,432,055
Net loss per share attributable to holders of common stock, basic and diluted (in dollars per share)	$ (0.07)	$ (0.20)	$ (0.23)	$ (0.13)	$ (0.10)	$ (0.18)	$ (0.27)	$ (0.92)	$ (0.63)	$ (0.91)	$ (3.81)