Quarterly Results (unaudited) (Unaudited Operating Data) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Results (Unaudited)
Sales	$ 2,482,975	$ 2,666,528	$ 2,589,874	$ 2,410,608	$ 2,314,957	$ 2,482,717	$ 2,456,073	$ 2,282,681	$ 10,149,985	$ 9,536,428	$ 8,977,726
Gross profit	1,324,584	1,422,530	1,368,287	1,279,290	1,234,315	1,315,755	1,288,638	1,201,258	5,394,691	5,039,966	4,720,683
Operating income	441,503	536,363	498,074	444,786	428,040	485,148	479,150	422,846	1,920,726	1,815,184	1,725,400
Net income	$ 324,916	$ 391,293	$ 353,681	$ 321,152	$ 300,357	$ 366,151	$ 353,073	$ 304,906	$ 1,391,042	$ 1,324,487	$ 1,133,804
Earnings per share - basic	$ 4.29	$ 5.14	$ 4.56	$ 4.09	$ 3.76	$ 4.54	$ 4.32	$ 3.65	$ 18.07	$ 16.27	$ 12.82
Earnings per share - assuming dilution	$ 4.25	$ 5.08	$ 4.51	$ 4.05	$ 3.72	$ 4.50	$ 4.28	$ 3.61	$ 17.88	$ 16.10	$ 12.67