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
	Mar. 31, 2014		Mar. 31, 2013
Numerator (basic and diluted):
Net income	$ 173,860		$ 154,329
Denominator:
Denominator for basic earnings per share - weighted-average shares	106,191		111,557
Effect of stock options	1,879	[1]	1,839	[1]
Denominator for diluted earnings per share - weighted-average shares	108,070		113,396
Earnings per share - basic	$ 1.64		$ 1.38
Earnings per share - assuming dilution	$ 1.61		$ 1.36
Antidilutive stock options	288	[1]	1,555	[1]
Weighted-average exercise price	$ 135.22	[1]	$ 91.08	[1]

[1] See Note 6 for further discussion on the terms of the Company's share-based compensation plans.