Supplemental Guarantor Financial Information Condensed Consolidating Balance Sheet (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Current assets:
Cash	$ 8,519	$ 23,001	$ 9,395	$ 5,610
Restricted cash	0	0
Short-term investments	0	0
Receivables, net	130,805	147,074
Taxes receivable	5,479	9,709
Inventories	243,313	258,029
Other Assets, Current	7,866	8,682
Total current assets	395,982	446,495
Property, plant and equipment, net	991,061	945,328
Goodwill	244,283	244,283
Intangible assets, net	36,513	40,485
Investment in subsidiary	0	0
Other assets, net	10,750	7,751
TOTAL ASSETS	1,678,589	1,684,342
Line of Credit, Current	108,000	135,000
Current liabilities:
Accounts payable and accrued liabilities	224,177	223,699
Current liability for pensions and other postretirement employee benefits	7,821	7,821
Total current liabilities	339,998	366,520
Long-term debt	570,139	569,755
Liability for pensions and other postretirement employee benefits	79,442	81,812
Other long-term obligations	40,776	41,776
Accrued taxes	2,567	2,434
Deferred Tax Liabilities, Gross, Noncurrent	162,081	152,172
Liabilities	1,195,003	1,214,469
Accumulated other comprehensive loss, net of tax	(51,226)	(51,753)
Stockholders' equity excluding accumulated other comprehensive loss	534,812	521,626
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	1,678,589	1,684,342
Issuer
Current assets:
Cash	8,519	19,586	9,395	5,610
Receivables, net	108,087	130,098
Taxes receivable	5,433	15,143
Inventories	204,231	208,472
Other Assets, Current	7,119	8,161
Total current assets	333,389	381,460
Property, plant and equipment, net	868,143	802,064
Goodwill	244,283	244,283
Intangible assets, net	2,612	3,135
Intercompany receivable (payable)	2,730	30,034
Investment in subsidiary	145,332	145,089
Other assets, net	11,085	8,433
TOTAL ASSETS	1,607,574	1,614,498
Line of Credit, Current	108,000	135,000
Current liabilities:
Accounts payable and accrued liabilities	202,026	202,187
Current liability for pensions and other postretirement employee benefits	7,821	7,821
Total current liabilities	317,847	345,008
Long-term debt	570,139	569,755
Liability for pensions and other postretirement employee benefits	79,442	81,812
Other long-term obligations	40,642	41,424
Accrued taxes	1,736	1,614
Deferred Tax Liabilities, Gross, Noncurrent	114,182	105,012
Liabilities	1,123,988	1,144,625
Accumulated other comprehensive loss, net of tax	(51,226)	(51,753)
Stockholders' equity excluding accumulated other comprehensive loss	534,812	521,626
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	1,607,574	1,614,498
Guarantor Subsidiaries
Current assets:
Cash	0	3,415	0	0
Receivables, net	22,718	27,252
Taxes receivable	28	35
Inventories	42,002	51,432
Other Assets, Current	747	521
Total current assets	65,495	82,655
Property, plant and equipment, net	122,918	143,264
Goodwill	0	0
Intangible assets, net	33,901	37,350
Intercompany receivable (payable)	(5,650)	(31,909)
Investment in subsidiary	0	0
Other assets, net	3,682	2,853
TOTAL ASSETS	220,346	234,213
Line of Credit, Current	0	0
Current liabilities:
Accounts payable and accrued liabilities	22,133	37,257
Current liability for pensions and other postretirement employee benefits	0	0
Total current liabilities	22,133	37,257
Long-term debt	0	0
Liability for pensions and other postretirement employee benefits	0	0
Other long-term obligations	134	352
Accrued taxes	831	820
Deferred Tax Liabilities, Gross, Noncurrent	51,916	50,695
Liabilities	75,014	89,124
Accumulated other comprehensive loss, net of tax	0	0
Stockholders' equity excluding accumulated other comprehensive loss	145,332	145,089
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	220,346	234,213
Eliminations
Current assets:
Cash	0	0	$ 0	$ 0
Receivables, net	0	(10,276)
Taxes receivable	18	(5,469)
Inventories	(2,920)	(1,875)
Other Assets, Current	0	0
Total current assets	(2,902)	(17,620)
Property, plant and equipment, net	0	0
Goodwill	0	0
Intangible assets, net	0	0
Intercompany receivable (payable)	2,920	1,875
Investment in subsidiary	(145,332)	(145,089)
Other assets, net	(4,017)	(3,535)
TOTAL ASSETS	(149,331)	(164,369)
Line of Credit, Current	0	0
Current liabilities:
Accounts payable and accrued liabilities	18	(15,745)
Current liability for pensions and other postretirement employee benefits	0	0
Total current liabilities	18	(15,745)
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	(4,017)	(3,535)
Liabilities	(3,999)	(19,280)
Accumulated other comprehensive loss, net of tax	0	0
Stockholders' equity excluding accumulated other comprehensive loss	(145,332)	(145,089)
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ (149,331)	$ (164,369)