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, 2018	Mar. 31, 2017
Numerator (basic and diluted):
Net income		$ 304,906	$ 264,934
Denominator:
Weighted-average common shares outstanding - basic		83,530	92,001
Effect of stock options	[1]	993	1,494
Weighted-average common shares outstanding - assuming dilution		84,523	93,495
Earnings per share - basic		$ 3.65	$ 2.88
Earnings per share - assuming dilution		$ 3.61	$ 2.83
Antidilutive stock options	[1]	761	478
Weighted-average exercise price	[1]	$ 259.28	$ 266.71

[1] See Note 7 for further information concerning the terms of the Company’s share-based compensation plans.