Net Income (Loss) per Share - Computation of Company's Basic and Diluted Net Loss Per Share of Common Stock (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net income (loss)	$ 22,869	$ (70,279)	$ (48,882)
Shares used in computing earnings per share
Basic	33,724	32,284	29,849
Diluted	34,238	32,284	29,849
Earnings per share:
Basic	$ 0.68	$ (2.18)	$ (1.64)
Diluted	$ 0.67	$ (2.18)	$ (1.64)