Condensed Consolidated Statements of Income (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Type of Revenue [Extensible List]	Product	Product	Product	Product
Net sales	$ 279,651	$ 233,473	$ 750,236	$ 681,216
Type of Cost, Good or Service [Extensible List]	Product	Product	Product	Product
Costs of products sold	$ 241,294	$ 195,222	$ 637,029	$ 574,100
Gross profit	38,357	38,251	113,207	107,116
Selling, general and administrative expenses	26,066	24,635	77,877	72,707
Gains on dispositions of plant, equipment and timberlands, net	(2,235)	(413)	(4,638)	(1,010)
Operating income	14,526	14,029	39,968	35,419
Non-operating income (expense)
Interest expense	(2,061)	(1,810)	(5,364)	(5,347)
Interest income	21	39	52	390
Pension settlement expenses, net	0	(389)	0	(6,792)
Other, net	(876)	(1,728)	(1,949)	(3,243)
Total non-operating expense	(2,916)	(3,888)	(7,261)	(14,992)
Income from continuing operations before income taxes	11,610	10,141	32,707	20,427
Income tax provision	3,551	3,614	14,762	8,775
Income from continuing operations	8,059	6,527	17,945	11,652
Discontinued operations:
Loss before income taxes	(532)	0	(614)	(135)
Income tax provision	0	0	0	0
Loss from discontinued operations	(532)	0	(614)	(135)
Net income	$ 7,527	$ 6,527	$ 17,331	$ 11,517
Basic earnings per share
Income (loss) from continuing operations (in dollars per share)	$ 0.18	$ 0.15	$ 0.40	$ 0.26
Loss from discontinued operations (in dollars per share)	(0.01)	0	(0.01)	0
Basic earnings per share (in dollars per share)	0.17	0.15	0.39	0.26
Diluted earnings per share
Income from continuing operations (in dollars per share)	0.18	0.15	0.40	0.26
Loss from discontinued operations (in dollars per share)	(0.01)	0	(0.01)	0
Diluted earnings per share (in dollars per share)	$ 0.17	$ 0.15	$ 0.39	$ 0.26
Weighted average shares outstanding
Basic (in shares)	44,593	44,368	44,536	44,329
Diluted (in shares)	44,939	44,636	44,889	44,549