Quarterly Financial Information (Unaudited) (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
Net Sales	$ 350,411,000	$ 350,914,000	$ 338,437,000	$ 335,739,000	$ 326,770,000	$ 288,622,000	$ 286,974,000	$ 269,499,000	$ 1,375,501,159	$ 1,171,864,171	$ 1,099,559,521
Gross Profit	134,673,000	138,626,000	134,292,000	131,299,000	128,694,000	105,962,000	102,613,000	93,464,000	538,889,695	430,732,902	372,818,559
Operating Income	98,615,000	103,206,000	99,835,000	97,178,000	95,636,000	73,656,000	71,596,000	63,854,000	398,834,174	304,741,813	234,455,232
Net Income	$ 70,975,000	$ 72,337,000	$ 76,727,000	$ 68,566,000	$ 69,881,000	$ 55,521,000	$ 52,097,000	$ 45,431,000	$ 288,604,579	$ 222,929,949	$ 168,586,840
Earnings Per Share (Diluted) (in dollars per share)	$ 0.24	$ 0.25	$ 0.26	$ 0.24	$ 0.24	$ 0.19	$ 0.18	$ 0.16	$ 0.98	$ 0.77	$ 0.59
Earnings Per Share (Basic) (in dollars per share)	$ 0.24	$ 0.25	$ 0.27	$ 0.24	$ 0.24	$ 0.20	$ 0.18	$ 0.16	$ 0.99	$ 0.78	$ 0.59