Quarterly Results (unaudited) (Unaudited Operating Data) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Data [Abstract]
Sales	$ 2,314,957		$ 2,482,717		$ 2,456,073		$ 2,282,681		$ 2,190,808		$ 2,339,830		$ 2,290,829		$ 2,156,259		$ 9,536,428	$ 8,977,726	$ 8,593,096
Gross profit	1,234,315		1,315,755		1,288,638		1,201,258		1,159,180		1,230,294		1,200,062		1,131,147		5,039,966	4,720,683	4,509,011
Operating income	428,040		485,148		479,150		422,846		402,835		461,963		457,445		403,157		1,815,184	1,725,400	1,699,206
Net income	$ 300,357		$ 366,151		$ 353,073		$ 304,906		$ 302,315		$ 283,734		$ 282,821		$ 264,934		$ 1,324,487	$ 1,133,804	$ 1,037,691
Earnings per share - basic	$ 3.76	[1]	$ 4.54	[1]	$ 4.32	[1]	$ 3.65	[1]	$ 3.56	[1]	$ 3.26	[1]	$ 3.14	[1]	$ 2.88	[1]	$ 16.27	$ 12.82	$ 10.87
Earnings per share - assuming dilution	$ 3.72	[1]	$ 4.50	[1]	$ 4.28	[1]	$ 3.61	[1]	$ 3.52	[1]	$ 3.22	[1]	$ 3.10	[1]	$ 2.83	[1]	$ 16.10	$ 12.67	$ 10.73

[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.