Supplemental Guarantor Financial Information Condensed Consolidating Statement of Operations and Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2018	Jan. 21, 2013
Condensed Financial Statements, Captions [Line Items]
Net sales	$ 428,779		$ 436,952
Cost and expenses:
Income (loss) from operations	14,362		11,539
Interest expense, net	(8,486)		(8,020)
Non-operating pension and other postretirment benefit (costs) income	(1,314)		(1,279)
Earnings (loss) before income taxes	4,562		2,240
Income tax (provision) benefit	(725)		360
Equity in income (loss) of subsidiary	0		0
Net earnings (loss)	3,837		2,600
Other comprehensive income (loss), net of tax	1,239		1,419
Comprehensive income	5,076		4,019
Cost of sales	(384,246)		(392,433)
Selling, general and administrative expenses	(30,171)		(32,980)
Total operating costs and expenses	(414,417)		(425,413)
Issuer
Condensed Financial Statements, Captions [Line Items]
Net sales	412,395		455,177
Cost and expenses:
Income (loss) from operations	18,350		14,588
Interest expense, net	(8,385)		(7,929)
Non-operating pension and other postretirment benefit (costs) income	(1,314)		(1,279)
Earnings (loss) before income taxes	8,651		5,380
Income tax (provision) benefit	(1,806)		(382)
Equity in income (loss) of subsidiary	3,143		401
Net earnings (loss)	9,988		5,399
Other comprehensive income (loss), net of tax	1,239		1,419
Comprehensive income	11,227		6,818
Cost of sales	(367,800)		(412,957)
Selling, general and administrative expenses	(26,245)		(27,632)
Total operating costs and expenses	(394,045)		(440,589)
Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net sales	67,540		46,213
Cost and expenses:
Income (loss) from operations	4,096		505
Interest expense, net	(101)		(91)
Non-operating pension and other postretirment benefit (costs) income	0		0
Earnings (loss) before income taxes	3,995		414
Income tax (provision) benefit	(852)		(13)
Equity in income (loss) of subsidiary	0		0
Net earnings (loss)	3,143		401
Other comprehensive income (loss), net of tax	0		0
Comprehensive income	3,143		401
Cost of sales	(59,518)		(40,360)
Selling, general and administrative expenses	(3,926)		(5,348)
Total operating costs and expenses	(63,444)		(45,708)
Eliminations
Condensed Financial Statements, Captions [Line Items]
Net sales	(51,156)		(64,438)
Cost and expenses:
Income (loss) from operations	(8,084)		(3,554)
Interest expense, net	0		0
Non-operating pension and other postretirment benefit (costs) income	0		0
Earnings (loss) before income taxes	(8,084)		(3,554)
Income tax (provision) benefit	1,933		755
Equity in income (loss) of subsidiary	(3,143)		(401)
Net earnings (loss)	(9,294)		(3,200)
Other comprehensive income (loss), net of tax	0		0
Comprehensive income	(9,294)		(3,200)
Cost of sales	43,072		60,884
Selling, general and administrative expenses	0		0
Total operating costs and expenses	$ 43,072		$ 60,884
Senior Notes Due Twenty Twenty-Three [Member]
Condensed Financial Statements, Captions [Line Items]
Debt Instrument, Face Amount					$ 275,000
Cost and expenses:
Debt Instrument, Interest Rate, Stated Percentage					4.50%