Income Taxes - Deferred Tax Assets and Deferred Tax Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Deferred tax assets:
Postretirement benefits	$ 3,830	$ 3,675
Deferred compensation	1,940	1,916
Deferred gain	0	271
Impairments	1,452	1,311
Alternative minimum tax and net operating loss carryforward	3,487	2,635
Total deferred tax assets	10,709	9,808
Deferred tax liabilities:
Depreciation	8,032	8,307
Inventory	1,146	1,695
Pension	4,240	5,742
Intangible assets and goodwill	24,224	16,486
Other, net	1,665	1,475
Total deferred tax liabilities	39,307	33,705
Net deferred tax liabilities	$ 28,598	$ 23,897