Quarterly Financial Data (Schedule Of Quarterly Financial Information) (Details) - USD ($) $ / shares in Units, $ in Thousands	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, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Data [Abstract]
Sales	$ 607,507	$ 574,341	$ 579,342	$ 549,225	$ 625,719	$ 630,191	$ 664,038	$ 620,925	$ 709,547	$ 731,302	$ 716,868	$ 639,344	$ 2,310,415	$ 2,540,873	$ 2,797,061
Gross profit	57,470	52,822	52,854	50,317	56,909	54,563	55,997	51,785	56,107	55,299	57,757	51,153	213,463	219,254	220,316
Net income	$ 18,568	$ 21,742	$ 12,685	$ 11,052	$ 39,421	$ 20,565	$ 21,210	$ 14,205	$ 23,338	$ 16,906	$ 21,558	$ 19,439	$ 64,047	$ 95,401	$ 81,241
Earnings per common share, Basic	$ 0.38	$ 0.44	$ 0.26	$ 0.22	$ 0.78	$ 0.4	$ 0.41	$ 0.27	$ 0.44	$ 0.32	$ 0.4	$ 0.36	$ 1.3	$ 1.85	$ 1.52
Earnings per common share, Diluted	$ 0.37	$ 0.44	$ 0.26	$ 0.22	$ 0.77	$ 0.4	$ 0.4	$ 0.27	$ 0.44	$ 0.31	$ 0.4	$ 0.36	$ 1.29	$ 1.83	$ 1.5