Condensed Consolidated Statements of Income - USD ($) shares in Thousands, $ 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	$ 413,325	$ 405,301	$ 1,191,380	$ 1,213,932
Energy and related sales, net	1,236	1,346	3,346	4,013
Total revenues	414,561	406,647	1,194,726	1,217,945
Costs of products sold	359,826	345,477	1,052,626	1,056,209
Gross profit	54,735	61,170	142,100	161,736
Selling, general and administrative expenses	33,399	35,747	100,484	104,796
(Gains) losses on dispositions of plant, equipment and timberlands, net	(24)	5	(50)	31
Operating income	21,360	25,418	41,666	56,909
Non-operating income (expense)
Interest expense	(4,547)	(3,895)	(13,031)	(11,964)
Interest income	51	52	209	204
Other, net	(478)	(573)	(906)	(956)
Total non-operating expense	(4,974)	(4,416)	(13,728)	(12,716)
Income before income taxes	16,386	21,002	27,938	44,193
Income tax provision	4,281	1,401	9,944	6,459
Net income	$ 12,105	$ 19,601	$ 17,994	$ 37,734
Earnings per share
Basic	$ 0.28	$ 0.45	$ 0.41	$ 0.87
Diluted	0.27	0.44	0.41	0.86
Cash dividends declared per common share	$ 0.13	$ 0.125	$ 0.39	$ 0.375
Weighted average shares outstanding
Basic	43,617	43,576	43,601	43,552
Diluted	44,182	44,133	44,410	44,059