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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator (basic and diluted):
Net income		$ 353,073	$ 282,821	$ 657,979	$ 547,755
Denominator:
Weighted-average common shares outstanding - basic		81,733	90,030	82,624	91,012
Effect of stock options	[1]	803	1,269	806	1,335
Weighted-average common shares outstanding - assuming dilution		82,536	91,299	83,430	92,347
Earnings per share - basic		$ 4.32	$ 3.14	$ 7.96	$ 6.02
Earnings per share - assuming dilution		$ 4.28	$ 3.10	$ 7.89	$ 5.93
Antidilutive stock options	[1]	693	581	714	524
Weighted-average exercise price	[1]	$ 261.11	$ 262.25	$ 260.39	$ 265.02

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