Net Loss Per Share - Computation of Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Numerator:
Net loss attributable to common stockholders	$ (2,768)	$ (15,214)	$ (13,223)	$ (44,166)
Deemed dividend to convertible preferred stockholders	(24,890)		(24,890)
Net income (loss) available to common stockholders	$ (27,658)	$ (15,214)	$ (38,113)	$ (44,166)
Denominator:
Weighted average shares used to compute net loss per share available to common stockholders, basic and diluted	67,732	23,943	39,612	22,282
Basic and diluted	$ (0.41)	$ (0.64)	$ (0.96)	$ (1.98)