Condensed Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Net sales	$ 410,647	$ 390,713
Energy and related sales, net	1,428	1,129
Total revenues	412,075	391,842
Costs of products sold	363,169	336,213
Gross profit	48,906	55,629
Selling, general and administrative expenses	37,063	34,877
(Gains) losses on dispositions of plant, equipment and timberlands, net	(1,554)	32
Operating income	13,397	20,720
Non-operating income (expense)
Interest expense	(5,195)	(4,008)
Interest income	54	113
Other, net	229	812
Total non-operating expense	(4,912)	(3,083)
Income before income taxes	8,485	17,637
Income tax provision	2,769	6,034
Net income	$ 5,716	$ 11,603
Earnings per share
Basic	$ 0.13	$ 0.27
Diluted	0.13	0.26
Cash dividends declared per common share	$ 0.13	$ 0.13
Weighted average shares outstanding
Basic	43,700	43,583
Diluted	44,567	44,493