Condensed Consolidated Statements of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Income Statement [Abstract]
Net sales	$ 417,469	$ 455,721
Energy and related sales, net	2,068	5,262
Total revenues	419,537	460,983
Costs of products sold	367,429	405,943
Gross profit	52,108	55,040
Selling, general and administrative expenses	31,272	33,551
Gains on dispositions of plant, equipment and timberlands, net	(2,654)	(809)
Operating income	23,490	22,298
Non-operating income (expense)
Interest expense	(4,508)	(4,812)
Interest income	65	61
Other, net	(187)	211
Total non-operating expense	(4,630)	(4,540)
Income before income taxes	18,860	17,758
Income tax provision	4,935	3,110
Net income	$ 13,925	$ 14,648
Earnings per share
Basic	$ 0.32	$ 0.34
Diluted	$ 0.32	$ 0.33
Cash dividends declared per common share	$ 0.11	$ 0.11
Weighted average shares outstanding
Basic	43,252	43,366
Diluted	43,949	44,360