Supplemental Guarantor Financial Information Condensed Consolidating Statement of Operations and Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Net sales		$ 437,204	$ 434,026
Cost and expenses:
Cost of sales		(368,647)	(389,832)
Selling, general and administrative expenses		(30,795)	(28,957)
Total operating costs and expenses		(399,442)	(418,789)
Income (loss) from operations		37,762	15,237
Interest expense, net		(7,643)	(7,782)
Earnings (loss) before income taxes		30,119	7,455
Income tax (provision) benefit		(11,673)	(1,698)
Equity in income (loss) of subsidiary		0	0
Net earnings (loss)		18,446	5,757
Other comprehensive income, net of tax	[1]	655	1,557
Comprehensive income		19,101	7,314
Issuer
Condensed Financial Statements, Captions [Line Items]
Net sales		419,046	395,387
Cost and expenses:
Cost of sales		(356,714)	(351,046)
Selling, general and administrative expenses		(26,837)	(24,788)
Total operating costs and expenses		(383,551)	(375,834)
Income (loss) from operations		35,495	19,553
Interest expense, net		(7,643)	(7,767)
Earnings (loss) before income taxes		27,852	11,786
Income tax (provision) benefit		(10,470)	(3,228)
Equity in income (loss) of subsidiary		1,064	(4,673)
Net earnings (loss)		18,446	3,885
Other comprehensive income, net of tax		655	1,557
Comprehensive income		19,101	5,442
Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net sales		77,625	73,328
Cost and expenses:
Cost of sales		(71,400)	(73,475)
Selling, general and administrative expenses		(3,958)	(4,169)
Total operating costs and expenses		(75,358)	(77,644)
Income (loss) from operations		2,267	(4,316)
Interest expense, net		0	(15)
Earnings (loss) before income taxes		2,267	(4,331)
Income tax (provision) benefit		(1,203)	(342)
Equity in income (loss) of subsidiary		0	0
Net earnings (loss)		1,064	(4,673)
Other comprehensive income, net of tax		0	0
Comprehensive income		1,064	(4,673)
Eliminations
Condensed Financial Statements, Captions [Line Items]
Net sales		(59,467)	(34,689)
Cost and expenses:
Cost of sales		59,467	34,689
Selling, general and administrative expenses		0	0
Total operating costs and expenses		59,467	34,689
Income (loss) from operations		0	0
Interest expense, net		0	0
Earnings (loss) before income taxes		0	0
Income tax (provision) benefit		0	1,872
Equity in income (loss) of subsidiary		(1,064)	4,673
Net earnings (loss)		(1,064)	6,545
Other comprehensive income, net of tax		0	0
Comprehensive income		$ (1,064)	$ 6,545

[1] For the three months ended March 31, 2016 and 2015, net periodic costs associated with our pension and other postretirement employee benefit, or OPEB, plans included in other comprehensive income and reclassified from accumulated other comprehensive loss included $1.5 million and $3.1 million, respectively, of actuarial loss amortization, as well as $0.4 million and $0.5 million, respectively, of prior service credit amortization, all net of tax totaling $0.4 million and $1.0 million, respectively. These accumulated other comprehensive loss components are included in the computation of net periodic pension and OPEB costs in Note 10, “Pension and Other Postretirement Employee Benefit Plans.”