Income Taxes (Schedule of Components of Deferred Income Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Pensions	$ 19,439	$ 37,423
Other postretirement employee benefits	7,891	13,002
Net operating loss carryforwards	54	983
Inventories	353	443
Tax credits	2,443	2,207
Nondeductible accruals	2,566	2,067
Incentive compensation	1,131	1,643
Employee benefits	1,037	1,444
Other	88	120
Total deferred tax assets	35,002	59,332
Valuation allowance	(790)	(650)	$ (500)
Deferred tax assets, net of valuation allowance	34,212	58,682
Timber and timberlands, net	(1,432)	(2,165)
Property, plant and equipment, net	(12,683)	(14,018)
Other	(301)	(448)
Total deferred tax liabilities	(14,416)	(16,631)
Deferred tax assets, net	$ 19,796	$ 42,051