Net Income Per Share Available to Common Stock - Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Numerator:
Net income	$ 82,961	$ 35,245
Less: undistributed earnings allocated to participating securities	(267)	(324)
Net income attributable to common stockholders, basic	82,694	34,921
Add: undistributed earnings allocated to participating securities	22	20
Net income attributable to common stockholders, diluted	$ 82,716	$ 34,941
Denominator:
Weighted-average shares used in computing net income per share available to common stockholders, basic (in shares)	71,114	67,737
Add weighted-average effect of dilutive securities:
Stock options and RSUs (in shares)	6,321	4,443
Employee stock purchase plan (in shares)	81	34
Weighted-average shares used in computing net income per share available to common stockholders, diluted (in shares)	77,516	72,214
Net income per share attributable to common stockholders:
Basic (in usd per share)	$ 1.16	$ 0.52
Diluted (in usd per share)	$ 1.07	$ 0.48