Quarterly Financial Data (Schedule Of Quarterly Financial Information) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	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, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Data [Abstract]
Sales	$ 679,856	$ 603,550	$ 616,904	$ 566,501	$ 607,507	$ 574,341	$ 579,342	$ 549,225	$ 625,719	$ 630,191	$ 664,038	$ 620,925	$ 2,466,811	$ 2,310,415	$ 2,540,873
Gross profit	61,895	58,155	58,587	49,060	57,470	52,822	52,854	50,317	56,909	54,563	55,997	51,785	227,697	213,463	219,254
Net income (loss)	$ (76,340)	$ 17,512	$ 17,176	$ 9,687	$ 18,568	$ 21,742	$ 12,685	$ 11,052	$ 39,421	$ 20,565	$ 21,210	$ 14,205	$ (31,965)	$ 64,047	$ 95,401
Earnings per common share, Basic	$ (1.54)	$ 0.35	$ 0.35	$ 0.2	$ 0.38	$ 0.44	$ 0.26	$ 0.22	$ 0.78	$ 0.4	$ 0.41	$ 0.27	$ (0.64)	$ 1.3	$ 1.85
Earnings per common share, Diluted	$ (1.54)	$ 0.35	$ 0.34	$ 0.19	$ 0.37	$ 0.44	$ 0.26	$ 0.22	$ 0.77	$ 0.4	$ 0.4	$ 0.27	$ (0.64)	$ 1.29	$ 1.83