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, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net income	$ 113,370	$ 158,623	$ 161,915	$ 123,146	$ 119,100	$ 137,890	$ 113,915	$ 107,130	$ 557,054	$ 478,035	$ 298,373
Denominator:
Shares used for basic net income per share (in shares)									162,490	162,706	167,312
Effect of dilutive securities:
Stock options (in shares)									31	68	132
RSUs and deferred stock units (in shares)									1,819	1,799	1,744
Convertible senior notes (in shares)									873	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)									165,213	164,573	169,188
Basic net income per share (in dollars per share)	$ 0.70	$ 0.97	$ 1.00	$ 0.76	$ 0.74	$ 0.85	$ 0.70	$ 0.66	$ 3.43	$ 2.94	$ 1.78
Diluted net income per share (in dollars per share)	$ 0.68	$ 0.95	$ 0.98	$ 0.75	$ 0.73	$ 0.84	$ 0.69	$ 0.65	$ 3.37	$ 2.90	$ 1.76