Earnings Per Share (Computation of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Numerator (basic and diluted):
Net income		$ 282,821	$ 257,794	$ 547,755	$ 513,168
Denominator:
Weighted-average common shares outstanding - basic		90,030	95,967	91,012	96,554
Effect of stock options	[1]	1,269	1,315	1,335	1,357
Weighted-average common shares outstanding - assuming dilution		91,299	97,282	92,347	97,911
Earnings per share - basic		$ 3.14	$ 2.69	$ 6.02	$ 5.31
Earnings per share - assuming dilution		$ 3.10	$ 2.65	$ 5.93	$ 5.24
Antidilutive stock options	[1]	581	285	524	312
Weighted-average exercise price	[1]	$ 262.25	$ 262.49	$ 265.02	$ 259.46

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