Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Net sales	$ 426,504	$ 435,320	$ 1,293,692	$ 1,309,195
Costs and expenses:
Cost of sales	(386,581)	(396,605)	(1,154,344)	(1,127,103)
Selling, general and administrative expenses	(34,472)	(29,435)	(93,674)	(94,885)
Total operating costs and expenses	(421,053)	(426,040)	(1,248,018)	(1,221,988)
Income from operations	5,451	9,280	45,674	87,207
Interest expense, net	(7,683)	(7,520)	(23,399)	(22,559)
Earnings (loss) before income taxes	(2,232)	1,760	22,275	64,648
Income tax provision	3,095	(859)	(5,860)	(24,437)
Net earnings (loss)	$ 863	$ 901	$ 16,415	$ 40,211
Net earnings per common share:
Basic (in dollars per share)	$ 0.05	$ 0.05	$ 1.00	$ 2.35
Diluted (in dollars per share)	$ 0.05	$ 0.05	$ 0.99	$ 2.33