Unaudited Quarterly Data (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended			3 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Mar. 31, 2013 First Quarter [Member]	Mar. 31, 2012 First Quarter [Member]	Mar. 31, 2011 First Quarter [Member]	Jun. 30, 2013 Second Quarter [Member]	Jun. 30, 2012 Second Quarter [Member]	Jun. 30, 2011 Second Quarter [Member]	Sep. 30, 2013 Third Quarter [Member]	Sep. 30, 2012 Third Quarter [Member]	Sep. 30, 2011 Third Quarter [Member]	Dec. 31, 2013 Fourth Quarter [Member]	Dec. 31, 2012 Fourth Quarter [Member]	Dec. 31, 2011 Fourth Quarter [Member]
Unaudited Quarterly Data [Line Items]
Revenues	$ 3,104,183	$ 3,082,646	$ 2,882,184	$ 819,281	$ 835,254	$ 742,178	$ 760,511	$ 749,698	$ 698,253	$ 754,780	$ 739,314	$ 704,271	$ 769,611	$ 758,380	$ 737,482
Gross Profit	2,149,446	2,133,917	2,052,516	550,678	560,417	523,148	530,620	526,973	506,355	529,332	519,341	505,724	538,816	527,186	517,289
Operating profit	246,169	315,671	291,329	78,784	90,476	80,486	77,230	78,454	72,872	55,773	67,798	57,363	34,382	78,943	80,608
Net earnings	$ 128,238	$ 181,703	$ 163,464	$ 46,133	$ 50,968	$ 44,272	$ 41,876	$ 43,825	$ 39,713	$ 27,165	$ 39,701	$ 30,948	$ 13,064	$ 47,209	$ 48,531
Basic earnings per common share	$ 2.34	$ 3.08	$ 2.67	$ 0.80	$ 0.86	$ 0.70	$ 0.76	$ 0.74	$ 0.64	$ 0.51	$ 0.67	$ 0.52	$ 0.25	$ 0.81	$ 0.82
Diluted earnings per common share	$ 2.32	$ 3.06	$ 2.64	$ 0.79	$ 0.85	$ 0.69	$ 0.76	$ 0.74	$ 0.63	$ 0.50	$ 0.67	$ 0.51	$ 0.25	$ 0.80	$ 0.81
Cash dividends paid per common share	$ 0.84	$ 0.64	$ 0.44	$ 0.21	$ 0.16	$ 0.06	$ 0.21	$ 0.16	$ 0.06	$ 0.21	$ 0.16	$ 0.16	$ 0.21	$ 0.16	$ 0.16