CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Sales	$ 314,895	$ 359,238
Costs, expenses and other:
Costs of goods sold	266,880	321,320
Selling, general and administrative expenses	19,413	19,213
Other non-operating expense (income), net	1,604	3,546
Total costs, expenses and other	287,897	344,079
Income before taxes	26,998	15,159
Income tax expense	6,824	3,566
Net income	$ 20,174	$ 11,593
Earnings per common share
Basic (in dollars per share)	$ 0.70	$ 0.38
Diluted (in dollars per share)	$ 0.68	$ 0.37
Weighted average common shares outstanding
Basic (in shares)	28,820,603	30,488,601
Diluted (in shares)	29,786,957	31,285,365