Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement [Abstract]
Net sales	$ 412,852	$ 419,960	$ 410,803	$ 417,469	$ 436,261	$ 465,092	$ 445,341	$ 455,721	$ 1,661,084	$ 1,802,415	$ 1,722,615
Energy and related sales, net									5,664	7,927	3,153
Total revenues									1,666,748	1,810,342	1,725,768
Costs of products sold									1,463,783	1,575,188	1,507,108
Gross profit	$ 58,116	$ 59,908	$ 32,833	$ 52,108	$ 58,164	$ 80,513	$ 41,437	$ 55,040	202,965	235,154	218,660
Selling, general and administrative expenses									127,706	133,235	133,867
Gains on dispositions of plant, equipment and timberlands, net									(21,113)	(4,861)	(1,726)
Operating income									96,372	106,780	86,519
Non-operating income (expense)
Interest expense									(17,464)	(18,921)	(17,965)
Interest income									283	159	310
Other, net									(615)	(635)	337
Total other expense									(17,796)	(19,397)	(17,318)
Income before income taxes									78,576	87,383	69,201
Income tax provision									14,001	18,137	2,043
Net income									$ 64,575	$ 69,246	$ 67,158
Earnings per share
Basic									$ 1.49	$ 1.60	$ 1.56
Diluted	$ 0.78	$ 0.31	$ 0.06	$ 0.32	$ 0.45	$ 0.69	$ 0.11	$ 0.33	1.47	1.57	1.52
Cash dividends declared per common share									$ 0.48	$ 0.44	$ 0.40
Weighted average shares outstanding
Basic									43,397	43,201	43,158
Diluted									43,942	44,066	44,299