Quarterly Financial Information (Unaudited) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Net Sales	$ 419,913,000	$ 429,643,000	$ 423,801,000	$ 405,568,000	$ 405,593,000	$ 389,829,000	$ 379,258,000	$ 368,937,000	$ 1,678,924,756	$ 1,543,617,706	$ 1,375,501,159
Gross Profit	169,167,000	173,822,000	166,773,000	158,691,000	163,244,000	151,897,000	145,543,000	143,092,000	668,452,244	603,776,052	538,889,695
Operating Income	127,936,000	134,212,000	128,746,000	120,849,000	126,662,000	116,263,000	108,133,000	107,709,000	511,742,935	458,766,439	398,834,174
Net Income	$ 88,761,000	$ 92,065,000	$ 86,485,000	$ 80,280,000	$ 88,396,000	$ 78,332,000	$ 74,558,000	$ 77,183,000	$ 347,591,276	$ 318,469,859	$ 288,604,579
Earnings Per Share (Diluted) (in dollars per share)	$ 0.31	$ 0.32	$ 0.30	$ 0.28	$ 0.30	$ 0.27	$ 0.25	$ 0.26	$ 1.19	$ 1.08	$ 0.98
Earnings Per Share (Basic) (in dollars per share)	$ 0.31	$ 0.32	$ 0.30	$ 0.28	$ 0.30	$ 0.27	$ 0.25	$ 0.26	$ 1.21	$ 1.09	$ 0.99