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
	Mar. 31, 2017	Mar. 31, 2016
Earnings Per Share [Abstract]
Net loss	$ (26,994)	$ (27,171)
Weighted-average shares used to compute basic and diluted net loss per share	97,475	90,519
Net loss per share:
Basic and diluted (usd per share)	$ (0.28)	$ (0.30)