Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Numerator:
Net loss	$ (84,482)	$ (61,889)	$ (32,497)
Denominator:
Weighted-average shares outstanding	78,867,000	48,332,000	13,009,000
Less: weighted average shares subject to repurchase	(112,000)	(815,000)	(3,056,000)
Weighted-average shares used to compute basic and diluted net loss per share	78,755,000	47,517,000	9,953,000
Basic and diluted net loss per share	$ (1.07)	$ (1.30)	$ (3.27)