Earnings Per Share (Computation of Basic and Diluted 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 (basic and diluted):
Net income	$ 186,489		$ 159,332		$ 517,945		$ 452,944
Denominator:
Denominator for basic earnings per share - weighted-average shares	108,307		118,546		110,034		123,448
Effect of stock options	1,886	[1]	1,993	[1]	1,851	[1]	2,222	[1]
Denominator for diluted earnings per share - weighted-average shares	110,193		120,539		111,885		125,670
Earnings per share - basic	$ 1.72		$ 1.34		$ 4.71		$ 3.67
Earnings per share - assuming dilution	$ 1.69		$ 1.32		$ 4.63		$ 3.60

[1] See Note 8 for further discussion on the terms of the Company's share-based compensation plans.