Supplemental Guarantor Financial Information Condensed Consolidating Balance Sheet (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Current assets:
Cash	$ 2,228	$ 5,610	$ 29,796	$ 27,331
Restricted cash	2,270	2,270
Short-term investments	0	250
Receivables, net	134,875	139,052
Taxes receivable	679	14,851
Inventories	243,419	255,573
Other Assets, Current	9,376	9,331
Total current assets	392,847	426,937
Property, plant and equipment, net	873,112	866,538
Goodwill	209,087	209,087
Intangible assets, net	18,753	19,990
Investment in subsidiary	0	0
Defined Benefit Plan, Assets for Plan Benefits, Noncurrent	1,086	596
Other assets, net	4,329	4,221
TOTAL ASSETS	1,499,214	1,527,369
Line of Credit, Current	6,005	0
Current liabilities:
Accounts payable and accrued liabilities	192,820	220,368
Current liability for pensions and other postretirement employee benefits	7,559	7,559
Total current liabilities	206,384	227,927
Long-term debt	569,179	568,987
Liability for pensions and other postretirement employee benefits	87,609	89,057
Other long-term obligations	43,779	46,738
Accrued taxes	1,525	1,676
Deferred Tax Liabilities, Gross, Noncurrent	123,032	118,118
Accumulated other comprehensive loss, net of tax	(54,893)	(55,548)	(69,306)	(70,863)
Stockholders' equity excluding accumulated other comprehensive loss	522,599	530,414
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	1,499,214	1,527,369
Issuer
Current assets:
Cash	2,228	5,610	29,796	27,331
Restricted cash	2,270	2,270
Short-term investments		250
Receivables, net	119,319	123,131
Taxes receivable	646	16,221
Inventories	209,823	219,130
Other Assets, Current	8,880	8,838
Total current assets	343,166	375,450
Property, plant and equipment, net	729,072	719,436
Goodwill	209,087	209,087
Intangible assets, net	3,918	4,180
Intercompany receivable (payable)	10,088	14,013
Investment in subsidiary	140,822	139,758
Defined Benefit Plan, Assets for Plan Benefits, Noncurrent	1,086	596
Other assets, net	4,680	4,142
TOTAL ASSETS	1,441,919	1,466,662
Line of Credit, Current	6,005
Current liabilities:
Accounts payable and accrued liabilities	173,306	196,891
Current liability for pensions and other postretirement employee benefits	7,559	7,559
Total current liabilities	186,870	204,450
Long-term debt	569,179	568,987
Liability for pensions and other postretirement employee benefits	87,609	89,057
Other long-term obligations	43,293	46,182
Accrued taxes	718	874
Deferred Tax Liabilities, Gross, Noncurrent	86,544	82,246
Accumulated other comprehensive loss, net of tax	(54,893)	(55,548)
Stockholders' equity excluding accumulated other comprehensive loss	522,599	530,414
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	1,441,919	1,466,662
Guarantor Subsidiaries
Current assets:
Cash	0	0	0	0
Restricted cash	0	0
Short-term investments		0
Receivables, net	15,556	15,921
Taxes receivable	33	(1,370)
Inventories	33,596	36,443
Other Assets, Current	496	493
Total current assets	49,681	51,487
Property, plant and equipment, net	144,040	147,102
Goodwill	0	0
Intangible assets, net	14,835	15,810
Intercompany receivable (payable)	(10,088)	(15,151)
Investment in subsidiary	0	0
Defined Benefit Plan, Assets for Plan Benefits, Noncurrent	0	0
Other assets, net	977	79
TOTAL ASSETS	199,445	199,327
Line of Credit, Current	0
Current liabilities:
Accounts payable and accrued liabilities	19,514	23,477
Current liability for pensions and other postretirement employee benefits	0	0
Total current liabilities	19,514	23,477
Long-term debt	0	0
Liability for pensions and other postretirement employee benefits	0	0
Other long-term obligations	486	556
Accrued taxes	807	802
Deferred Tax Liabilities, Gross, Noncurrent	37,816	34,734
Accumulated other comprehensive loss, net of tax	0	0
Stockholders' equity excluding accumulated other comprehensive loss	140,822	139,758
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	199,445	199,327
Eliminations
Current assets:
Cash	0	0	$ 0	$ 0
Restricted cash	0	0
Short-term investments		0
Receivables, net	0	0
Taxes receivable	0	0
Inventories	0	0
Other Assets, Current	0	0
Total current assets	0	0
Property, plant and equipment, net	0	0
Goodwill	0	0
Intangible assets, net	0	0
Intercompany receivable (payable)		1,138
Investment in subsidiary	(140,822)	(139,758)
Defined Benefit Plan, Assets for Plan Benefits, Noncurrent	0	0
Other assets, net	(1,328)	0
TOTAL ASSETS	(142,150)	(138,620)
Line of Credit, Current	0
Current liabilities:
Accounts payable and accrued liabilities	0	0
Current liability for pensions and other postretirement employee benefits	0	0
Total current liabilities	0	0
Long-term debt	0	0
Liability for pensions and other postretirement employee benefits	0	0
Other long-term obligations	0	0
Accrued taxes	0	0
Deferred Tax Liabilities, Gross, Noncurrent	(1,328)	1,138
Accumulated other comprehensive loss, net of tax	0	0
Stockholders' equity excluding accumulated other comprehensive loss	(140,822)	(139,758)
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ (142,150)	$ (138,620)