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, 2020	Mar. 31, 2019
Numerator:
Net income	$ 138,431	$ 201,029
Less: undistributed earnings allocated to participating securities	0	(118)
Net income attributable to common stockholders, basic	138,431	200,911
Net income attributable to common stockholders, basic	138,431	200,911
Add: undistributed earnings allocated to participating securities	0	7
Net income attributable to common stockholders, diluted	$ 138,431	$ 200,918
Denominator:
Weighted-average shares used in computing net income per share available to common stockholders, basic (in shares)	76,264	75,920
Add weighted-average effect of dilutive securities:
Stock options and RSUs (in shares)	3,675	5,279
Employee stock purchase plan (in shares)	0	2
Weighted-average shares used in computing net income per share available to common stockholders, diluted (in shares)	79,939	81,201
Net income per share attributable to common stockholders:
Basic (in dollars per share)	$ 1.82	$ 2.65
Diluted (in dollars per share)	$ 1.73	$ 2.47