Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Numerator:
Net income	$ 76,730	$ 78,245	$ 200,879	$ 238,518
Denominator:
Denominator for basic earnings per share - weighted-average shares outstanding	187,459	186,864	187,120	186,326
Effect of dilutive employee stock awards	1,521	2,807	1,710	2,956
Denominator for diluted earnings per share - weighted-average shares outstanding	188,980	189,671	188,830	189,282
Basic earnings per share (in dollars per share)	$ 0.41	$ 0.42	$ 1.07	$ 1.28
Diluted earnings per share (in dollars per share)	$ 0.41	$ 0.41	$ 1.06	$ 1.26
Anti-dilutive weighted-average shares	3,286	3,355	3,851	3,336