Net Income (Loss) Per Share - Computations of Basic and Diluted Net Income (Loss) Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Basic net income (loss) per share:
Net income (loss) applicable to common stockholders	$ 10,594	$ (14,473)	$ 114,833	$ (36,466)
Shares used in computation:
Weighted-average common shares outstanding	32,082	30,662	31,858	28,678
Basic net income (loss) per share	$ 0.33	$ (0.47)	$ 3.60	$ (1.27)
Diluted net income (loss) per share:
Net income (loss) applicable to common stockholders	$ 10,594	$ (14,473)	$ 114,833	$ (36,466)
Shares used in computation:
Weighted-average diluted common shares	35,272	30,662	34,884	28,678
Diluted	$ 0.30	$ (0.47)	$ 3.29	$ (1.27)
Common Shares [Member]
Shares used in computation:
Weighted-average diluted common shares	32,082	30,662	31,858	28,678
Stock Option [Member]
Shares used in computation:
Weighted-average diluted common shares	3,153		2,995
Restricted Stock Units [Member]
Shares used in computation:
Weighted-average diluted common shares	30		27
Employee Stock Purchase Plan [Member]
Shares used in computation:
Weighted-average diluted common shares	7		4