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, 2015		Mar. 31, 2014
Numerator (basic and diluted):
Net income	$ 212,864		$ 173,860
Denominator:
Denominator for basic earnings per share - weighted-average shares	101,612		106,191
Effect of stock options	1,645	[1]	1,879	[1]
Denominator for diluted earnings per share - weighted-average shares	103,257		108,070
Earnings per share - basic	$ 2.09		$ 1.64
Earnings per share - assuming dilution	$ 2.06		$ 1.61
Antidilutive stock options	278	[1]	288	[1]
Weighted-average exercise price	$ 195.90	[1]	$ 135.22	[1]

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