Quarterly Results (unaudited) (Unaudited Operating Data) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015		Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Data [Abstract]
Sales	$ 1,949,052		$ 2,080,201		$ 2,035,518		$ 1,901,903		$ 1,764,178		$ 1,876,872		$ 1,847,088		$ 1,727,943		$ 7,966,674	$ 7,216,081	$ 6,649,237
Gross profit	1,027,639		1,089,254		1,058,791		986,959		912,107		968,201		950,877		877,716		4,162,643	3,708,901	3,369,001
Operating income	362,620		415,260		385,768		350,373		303,012		343,768		336,474		287,120		1,514,021	1,270,374	1,103,485
Net income	$ 218,576		$ 266,268		$ 233,508		$ 212,864		$ 181,678		$ 216,997		$ 205,647		$ 173,860		$ 931,216	$ 778,182	$ 670,292
Earnings per share - basic	$ 2.22	[1]	$ 2.68	[1]	$ 2.32	[1]	$ 2.09	[1]	$ 1.79	[1]	$ 2.10	[1]	$ 1.94	[1]	$ 1.64	[1]	$ 9.32	$ 7.46	$ 6.14
Earnings per share - assuming dilution	$ 2.19	[1]	$ 2.64	[1]	$ 2.29	[1]	$ 2.06	[1]	$ 1.76	[1]	$ 2.06	[1]	$ 1.91	[1]	$ 1.61	[1]	$ 9.17	$ 7.34	$ 6.03

[1] 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 amount.