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																12 Months Ended
	Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Numerator (basic and diluted):
Net income	$ 152,347		$ 186,489		$ 177,127		$ 154,329		$ 132,802		$ 159,332		$ 146,120		$ 147,492		$ 670,292		$ 585,746		$ 507,673
Denominator:
Denominator for basic earnings per share - weighted-average shares																	109,244		121,182		134,667
Effect of stock options																	1,857	[1]	2,132	[1]	2,316	[1]
Denominator for diluted earnings per share - weighted-average shares and assumed conversion																	111,101		123,314		136,983
Earnings per share - basic	$ 1.43	[2]	$ 1.72	[2]	$ 1.61	[2]	$ 1.38	[2]	$ 1.16	[2]	$ 1.34	[2]	$ 1.17	[2]	$ 1.16	[2]	$ 6.14		$ 4.83		$ 3.77
Earnings per share - assuming dilution	$ 1.40	[2]	$ 1.69	[2]	$ 1.58	[2]	$ 1.36	[2]	$ 1.14	[2]	$ 1.32	[2]	$ 1.15	[2]	$ 1.14	[2]	$ 6.03		$ 4.75		$ 3.71
Antidilutive stock options																	498	[1]	1,816	[1]	1,756	[1]
Weighted-average exercise price																	$ 103.80	[1]	$ 87.88	[1]	$ 62.79	[1]

[1] See Note 12 for further discussion on the terms of the Company's share-based compensation plans.

[2] Earnings per share amounts are computed independently for each quarter and annual period. The quarterly earnings per share amounts may not sum to equal the full-year earnings per share.