Supplemental Guarantor Financial Information Condensed Consolidating Balance Sheet (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Current assets:
Cash	$ 8,478	$ 23,001	$ 331	$ 5,610
Restricted cash	0	0
Short-term investments	0	0
Receivables, net	135,946	147,074
Taxes receivable	14,578	9,709
Inventories	257,833	258,029
Other Assets, Current	6,450	8,682
Total current assets	423,285	446,495
Property, plant and equipment, net	1,014,835	945,328
Goodwill	244,283	244,283
Intangible assets, net	34,528	40,485
Investment in subsidiary	0	0
Other assets, net	12,080	7,751
TOTAL ASSETS	1,729,011	1,684,342
Line of Credit, Current	110,000	135,000
Current liabilities:
Accounts payable and accrued liabilities	263,148	223,699
Current liability for pensions and other postretirement employee benefits	7,821	7,821
Total current liabilities	380,969	366,520
Long-term debt	570,331	569,755
Liability for pensions and other postretirement employee benefits	78,440	81,812
Other long-term obligations	40,942	41,776
Accrued taxes	2,557	2,434
Deferred Tax Liabilities, Gross, Noncurrent	169,410	152,172
Liabilities	1,242,649	1,214,469
Accumulated other comprehensive loss, net of tax	(50,969)	(51,753)
Stockholders' equity excluding accumulated other comprehensive loss	537,331	521,626
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	1,729,011	1,684,342
Issuer
Current assets:
Cash	8,478	19,586	331	5,610
Receivables, net	116,392	130,098
Taxes receivable	14,543	15,143
Inventories	221,233	208,472
Other Assets, Current	5,846	8,161
Total current assets	366,492	381,460
Property, plant and equipment, net	898,859	802,064
Goodwill	244,283	244,283
Intangible assets, net	2,351	3,135
Intercompany receivable (payable)	(4,041)	30,034
Investment in subsidiary	144,691	145,089
Other assets, net	11,787	8,433
TOTAL ASSETS	1,664,422	1,614,498
Line of Credit, Current	110,000	135,000
Current liabilities:
Accounts payable and accrued liabilities	241,938	202,187
Current liability for pensions and other postretirement employee benefits	7,821	7,821
Total current liabilities	359,759	345,008
Long-term debt	570,331	569,755
Liability for pensions and other postretirement employee benefits	78,440	81,812
Other long-term obligations	40,800	41,424
Accrued taxes	1,721	1,614
Deferred Tax Liabilities, Gross, Noncurrent	127,009	105,012
Liabilities	1,178,060	1,144,625
Accumulated other comprehensive loss, net of tax	(50,969)	(51,753)
Stockholders' equity excluding accumulated other comprehensive loss	537,331	521,626
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	1,664,422	1,614,498
Guarantor Subsidiaries
Current assets:
Cash	0	3,415	0	0
Receivables, net	19,554	27,252
Taxes receivable	35	35
Inventories	40,455	51,432
Other Assets, Current	604	521
Total current assets	60,648	82,655
Property, plant and equipment, net	115,976	143,264
Goodwill	0	0
Intangible assets, net	32,177	37,350
Intercompany receivable (payable)	186	(31,909)
Investment in subsidiary	0	0
Other assets, net	3,466	2,853
TOTAL ASSETS	212,453	234,213
Line of Credit, Current	0	0
Current liabilities:
Accounts payable and accrued liabilities	21,210	37,257
Current liability for pensions and other postretirement employee benefits	0	0
Total current liabilities	21,210	37,257
Long-term debt	0	0
Liability for pensions and other postretirement employee benefits	0	0
Other long-term obligations	142	352
Accrued taxes	836	820
Deferred Tax Liabilities, Gross, Noncurrent	45,574	50,695
Liabilities	67,762	89,124
Accumulated other comprehensive loss, net of tax	0	0
Stockholders' equity excluding accumulated other comprehensive loss	144,691	145,089
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	212,453	234,213
Eliminations
Current assets:
Cash	0	0	$ 0	$ 0
Receivables, net	0	(10,276)
Taxes receivable	0	(5,469)
Inventories	(3,855)	(1,875)
Other Assets, Current	0	0
Total current assets	(3,855)	(17,620)
Property, plant and equipment, net	0	0
Goodwill	0	0
Intangible assets, net	0	0
Intercompany receivable (payable)	3,855	1,875
Investment in subsidiary	(144,691)	(145,089)
Other assets, net	(3,173)	(3,535)
TOTAL ASSETS	(147,864)	(164,369)
Line of Credit, Current	0	0
Current liabilities:
Accounts payable and accrued liabilities	0	(15,745)
Current liability for pensions and other postretirement employee benefits	0	0
Total current liabilities	0	(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	(3,173)	(3,535)
Liabilities	(3,173)	(19,280)
Accumulated other comprehensive loss, net of tax	0	0
Stockholders' equity excluding accumulated other comprehensive loss	(144,691)	(145,089)
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ (147,864)	$ (164,369)