Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Income Statement [Abstract]
Net sales	$ 437,204	$ 434,026
Costs 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 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	(11,673)	(1,698)
Net earnings (loss)	$ 18,446	$ 5,757
Net earnings per common share:
Basic (in dollars per share)	$ 1.05	$ 0.30
Diluted (in dollars per share)	$ 1.05	$ 0.30