Quarterly Financial Information (Unaudited) (Details) - USD ($)	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 Information Disclosure [Abstract]
Net Sales	$ 453,409,000	$ 460,253,000	$ 454,981,000	$ 465,420,000	$ 459,570,000	$ 438,628,000	$ 443,139,000	$ 453,535,000	$ 1,834,063,697	$ 1,794,872,578	$ 1,678,924,756
Gross Profit	172,044,000	172,990,000	172,804,000	172,628,000	180,290,000	171,230,000	167,208,000	175,801,000	690,466,692	694,528,266	668,452,244
Operating Income	125,499,000	127,428,000	126,683,000	128,515,000	133,994,000	129,073,000	125,865,000	134,427,000	508,125,547	523,358,352	511,742,935
Net income	$ 106,275,000	$ 111,336,000	$ 109,024,000	$ 111,249,000	$ 130,469,000	$ 90,230,000	$ 88,536,000	$ 97,557,000	$ 437,883,097	$ 406,791,922	$ 347,591,276
Earnings Per Share (Basic) (in dollars per share)	$ 0.41	$ 0.42	$ 0.40	$ 0.40	$ 0.46	$ 0.32	$ 0.31	$ 0.34	$ 1.64	$ 1.42	$ 1.21
Earnings Per Share (Diluted) (in dollars per share)	$ 0.41	$ 0.42	$ 0.40	$ 0.40	$ 0.46	$ 0.31	$ 0.31	$ 0.33	$ 1.62	$ 1.41	$ 1.19