Net Income per Share - Schedule of Components Used in Diluted and Basic Income Per Common Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Numerator [Abstract]
Net income (in dollars)	$ 91,155	$ 79,756	$ 236,841	$ 213,138
Denominator [Abstract]
Shares used for basic net income per share	178,186	178,235	178,324	178,008
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	180,955	181,922	181,278	181,623
Basic net income per share (in dollars per share)	$ 0.51	$ 0.45	$ 1.33	$ 1.20
Diluted net income per share (in dollars per share)	$ 0.50	$ 0.44	$ 1.31	$ 1.17
Stock options
Effect of dilutive securities:
Dilutive securities	1,146	1,580	1,257	1,693
RSUs and deferred stock units
Effect of dilutive securities:
Dilutive securities	1,623	2,107	1,697	1,922