Net Income per Share - Schedule of Components Used in Diluted and Basic Income Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Numerator [Abstract]
Net income (in dollars)	$ 88,040	$ 91,155	$ 232,986	$ 236,841
Denominator [Abstract]
Shares used for basic net income per share	178,547	178,186	178,591	178,324
Effect of dilutive securities:
Convertible senior notes	0	0	0	0
Warrants related to issuance of convertible senior notes	0	0	0	0
Shares used for diluted net income per share	180,364	180,955	180,642	181,278
Basic net income per share (in dollars per share)	$ 0.49	$ 0.51	$ 1.30	$ 1.33
Diluted net income per share (in dollars per share)	$ 0.49	$ 0.50	$ 1.29	$ 1.31
Stock options
Effect of dilutive securities:
Dilutive securities	667	1,146	858	1,257
RSUs and deferred stock units
Effect of dilutive securities:
Dilutive securities	1,150	1,623	1,193	1,697