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		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Numerator [Abstract]
Net income (in dollars)	$ 67,200	$ 72,886	$ 144,946	$ 145,686
Denominator [Abstract]
Shares used for basic net income per share	178,682	178,081	178,614	178,393
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	180,738	180,841	180,782	181,439
Basic net income per share (in dollars per share)	$ 0.38	$ 0.41	$ 0.81	$ 0.82
Diluted net income per share (in dollars per share)	$ 0.37	$ 0.40	$ 0.80	$ 0.80
Stock options
Effect of dilutive securities:
Dilutive securities	912	1,242	954	1,312
RSUs and deferred stock units
Effect of dilutive securities:
Dilutive securities	1,144	1,518	1,214	1,734