Net Loss per Share - Computation of Basic and Diluted Net Loss per Share of Common Stock (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Net loss	$ (29,306)	$ (26,254)	$ (56,300)	$ (53,425)
Weighted-average shares used to compute basic and diluted net loss per share	99,506	92,174	98,545	91,351
Net loss per share, basic and diluted (usd per share)	$ (0.29)	$ (0.28)	$ (0.57)	$ (0.58)