Net Income per Share - Schedule of Components (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net income	$ 119,100	$ 137,890	$ 113,915	$ 107,130	$ 94,015	$ 107,583	$ 43,061	$ 53,714	$ 478,035	$ 298,373	$ 222,766
Denominator:
Shares used for basic net income per share (in shares)									162,706	167,312	171,559
Effect of dilutive securities:
Stock options (in shares)									68	132	260
RSUs and deferred stock units (in shares)									1,799	1,744	892
Convertible senior notes (in shares)									0	0	0
Warrants related to issuance of convertible senior notes (in shares)									0	0	0
Shares used for diluted net income per share (in shares)									164,573	169,188	172,711
Basic net income per share (in dollars per share)	$ 0.74	$ 0.85	$ 0.70	$ 0.66	$ 0.58	$ 0.65	$ 0.25	$ 0.32	$ 2.94	$ 1.78	$ 1.30
Diluted net income per share (in dollars per share)	$ 0.73	$ 0.84	$ 0.69	$ 0.65	$ 0.57	$ 0.64	$ 0.25	$ 0.31	$ 2.90	$ 1.76	$ 1.29