Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Net sales	$ 399,917	$ 413,325	$ 387,342	$ 390,713	$ 390,865	$ 405,301	$ 406,413	$ 402,218	$ 1,591,297	$ 1,604,797	$ 1,661,084
Energy and related sales, net									5,126	6,141	5,664
Total revenues									1,596,423	1,610,938	1,666,748
Costs of products sold									1,403,913	1,392,335	1,463,783
Gross profit	$ 50,410	$ 54,735	$ 30,436	$ 56,929	$ 56,867	$ 61,170	$ 42,723	$ 57,843	192,510	218,603	202,965
Selling, general and administrative expenses									134,394	190,694	127,706
Losses (gains) on dispositions of plant, equipment and timberlands, net									26	216	(21,113)
Operating income									58,090	27,693	96,372
Non-operating income (expense)
Interest expense									(17,772)	(15,822)	(17,464)
Interest income									237	206	283
Other, net									(1,220)	(1,271)	(615)
Total non-operating expense									(18,755)	(16,887)	(17,796)
Income before income taxes									39,335	10,806	78,576
Income tax provision (benefit)									31,421	(10,748)	14,001
Net income									$ 7,914	$ 21,554	$ 64,575
Earnings per share
Basic									$ 0.18	$ 0.49	$ 1.49
Diluted									0.18	0.49	1.47
Cash dividends declared per common share									$ 0.52	$ 0.50	$ 0.48
Weighted average shares outstanding
Basic									43,609	43,558	43,397
Diluted									44,439	44,129	43,942