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, 2018	Mar. 31, 2017
Calculation of Basic and Diluted Net Income Per Share, Numerator [Abstract]
Net income	$ 144,538	$ 82,961
Less: undistributed earnings allocated to participating securities	(89)	(267)
Net income attributable to common stockholders, basic	144,449	82,694
Net income attributable to common stockholders, basic	144,449	82,694
Add: undistributed earnings allocated to participating securities	7	22
Net income attributable to common stockholders, diluted	$ 144,456	$ 82,716
Calculation of Basic and Diluted Net Income Per Share, Denominator [Abstract]
Weighted-average shares used in computing net income per share available to common stockholders, basic (in shares)	73,994	71,114
Add weighted-average effect of dilutive securities:
Stock options, RSUs and RSAs (in shares)	6,670	6,321
Employee stock purchase plan (in shares)	57	81
Weighted-average shares used in computing net income per share available to common stockholders, diluted (in shares)	80,721	77,516
Net income per share attributable to common stockholders:
Basic (in dollars per share)	$ 1.95	$ 1.16
Diluted (in dollars per share)	$ 1.79	$ 1.07