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								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Calculation of Basic and Diluted Net Income Per Share, Numerator [Abstract]
Net income	$ 103,833	$ 133,722	$ 102,685	$ 82,961	$ 58,783	$ 51,257	$ 38,904	$ 35,245	$ 423,201	$ 184,189	$ 121,102
Less: undistributed earnings allocated to participating securities									(801)	(1,224)	(1,987)
Net income attributable to common stockholders, basic									422,400	182,965	119,115
Add: undistributed earnings allocated to participating securities									68	74	149
Net income attributable to common stockholders, diluted									$ 422,468	$ 183,039	$ 119,264
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)									72,258	68,771	65,964
Add weighted-average effect of dilutive securities:
Stock options, RSUs and RSAs (in shares)									6,599	4,408	5,363
Employee stock purchase plan (in shares)									120	43	84
Weighted-average shares used in computing net income per share available to common stockholders, diluted (in shares)									78,977	73,222	71,411
Net income per share attributable to common stockholders:
Basic (in dollars per share)	$ 1.42	$ 1.84	$ 1.42	$ 1.16	$ 0.84	$ 0.74	$ 0.57	$ 0.52	$ 5.85	$ 2.66	$ 1.81
Diluted (in dollars per share)	$ 1.29	$ 1.68	$ 1.30	$ 1.07	$ 0.79	$ 0.69	$ 0.53	$ 0.48	$ 5.35	$ 2.50	$ 1.67