Earnings Per Share (Computation of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Numerator (basic and diluted):
Net income		$ 255,374	$ 212,864
Denominator:
Weighted-average common shares outstanding - basic		97,140	101,612
Effect of stock options	[1]	1,397	1,645
Weighted-average common shares outstanding - assuming dilution		98,537	103,257
Earnings per share - basic		$ 2.63	$ 2.09
Earnings per share - assuming dilution		$ 2.59	$ 2.06
Antidilutive stock options	[1]	268	278
Weighted-average exercise price	[1]	$ 256.19	$ 195.90

[1] See Note 6 for further information concerning the terms of the Company’s share-based compensation plans.