Supplemental Consolidating Financial Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Net sales	$ 825,847	$ 812,171	$ 1,587,837	$ 1,586,423
Cost of sales	716,307	693,346	1,401,559	1,372,497
Selling, general and administrative	57,708	62,484	117,558	116,261
Depreciation	13,089	13,455	26,588	27,082
Amortization	2,342	2,341	4,683	4,683
Equity in earnings of investees	(332)	(72)	(332)	(72)
Restructuring and relocation costs	0	41	460	258
Operating income	36,733	40,576	37,321	65,714
Interest income	641	775	1,305	1,507
Interest expense	(15,299)	(14,778)	(30,767)	(29,342)
Loss on debt extinguishment	0	0	(521)	(6,275)
Other income (expense), net	(242)	1,568	(4,136)	2,123
Income before income taxes	21,833	28,141	3,202	33,727
Income tax benefit (expense)	(3,997)	2,959	(9,969)	(250)
Net income (loss)	17,836	31,100	(6,767)	33,477
Reportable Legal Entities [Member] | Parent Company [Member]
Net sales	0	0	0	0
Cost of sales	0	(96)	0	0
Selling, general and administrative	10,333	11,453	23,700	19,405
Depreciation	0	0	0	0
Amortization	0	0	0	0
Equity in earnings of investees	(37,463)	(44,500)	(37,368)	(64,312)
Restructuring and relocation costs	0	0	460	0
Operating income	27,130	33,143	13,208	44,907
Interest income	0	0	0	0
Interest expense	(5,295)	(5,002)	(10,587)	(11,374)
Loss on debt extinguishment	0	0	0	(843)
Other income (expense), net	(2)	0	581	1,037
Income before income taxes	21,833	28,141	3,202	33,727
Income tax benefit (expense)	(3,997)	2,959	(9,969)	(250)
Net income (loss)	17,836	31,100	(6,767)	33,477
Reportable Legal Entities [Member] | Subsidiary Issuer [Member]
Net sales	225,172	201,929	434,216	386,971
Cost of sales	217,303	186,841	419,303	366,654
Selling, general and administrative	4,724	5,034	8,511	8,741
Depreciation	1,094	1,011	2,370	2,459
Amortization	0	0	0	0
Equity in earnings of investees	(44,600)	(45,195)	(52,165)	(78,914)
Restructuring and relocation costs	0	82	0	153
Operating income	46,651	54,156	56,197	87,878
Interest income	0	6	2	11
Interest expense	(9,175)	(9,663)	(18,406)	(17,820)
Loss on debt extinguishment	0	0	(521)	(5,432)
Other income (expense), net	(13)	1	96	(325)
Income before income taxes	37,463	44,500	37,368	64,312
Income tax benefit (expense)	(6,069)	(317)	(6,412)	606
Net income (loss)	31,394	44,183	30,956	64,918
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Net sales	318,525	329,311	611,798	637,037
Cost of sales	276,824	292,378	539,696	563,149
Selling, general and administrative	21,644	23,750	43,816	43,428
Depreciation	6,819	6,957	13,018	13,656
Amortization	2,336	2,335	4,671	4,671
Equity in earnings of investees	778	5	4,251	(27)
Restructuring and relocation costs	0	(41)	0	108
Operating income	10,124	3,927	6,346	12,052
Interest income	1	48	34	102
Interest expense	(683)	(110)	(1,567)	(125)
Loss on debt extinguishment	0	0	0	0
Other income (expense), net	84	64	(367)	165
Income before income taxes	9,526	3,929	4,446	12,194
Income tax benefit (expense)	(3,728)	(1,562)	(1,760)	(4,836)
Net income (loss)	5,798	2,367	2,686	7,358
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Net sales	538,098	511,546	1,040,357	1,023,539
Cost of sales	478,105	444,836	940,684	903,799
Selling, general and administrative	21,007	22,247	41,531	44,687
Depreciation	5,176	5,487	11,200	10,967
Amortization	6	6	12	12
Equity in earnings of investees	(332)	(72)	(332)	(72)
Restructuring and relocation costs	0	0	0	(3)
Operating income	34,136	39,042	47,262	64,149
Interest income	640	721	1,269	1,394
Interest expense	(146)	(3)	(207)	(23)
Loss on debt extinguishment	0	0	0	0
Other income (expense), net	(334)	1,502	(4,856)	1,227
Income before income taxes	34,296	41,262	43,468	66,747
Income tax benefit (expense)	(2,491)	1,309	(3,405)	658
Net income (loss)	31,805	42,571	40,063	67,405
Consolidation, Eliminations [Member]
Net sales	(255,948)	(230,615)	(498,534)	(461,124)
Cost of sales	(255,925)	(230,613)	(498,124)	(461,105)
Selling, general and administrative	0	0	0	0
Depreciation	0	0	0	0
Amortization	0	0	0	0
Equity in earnings of investees	81,285	89,690	85,282	143,253
Restructuring and relocation costs	0	0	0	0
Operating income	(81,308)	(89,692)	(85,692)	(143,272)
Interest income	0	0	0	0
Interest expense	0	0	0	0
Loss on debt extinguishment	0	0	0	0
Other income (expense), net	23	1	410	19
Income before income taxes	(81,285)	(89,691)	(85,282)	(143,253)
Income tax benefit (expense)	12,288	570	11,577	3,572
Net income (loss)	$ (68,997)	$ (89,121)	$ (73,705)	$ (139,681)