Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Numerator:
Net income	$ 55,939	$ 59,688
Denominator:
Denominator for basic earnings per share - weighted-average shares outstanding	183,997	186,658
Effect of dilutive employee stock awards	1,684	2,353
Denominator for diluted earnings per share - weighted-average shares outstanding	185,681	189,011
Basic earnings per share (in dollars per share)	$ 0.30	$ 0.32
Diluted earnings per share (in dollars per share)	$ 0.30	$ 0.32
Anti-dilutive weighted-average shares	4,564	3,928