Income Taxes (Deferred Taxes) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Deferred tax assets:
Net operating loss carryforward and federal credits	$ 34,401	$ 35,814
Capital and operating leases	1,742	763
Post-retirement employee benefits	62,823	65,695
Employee benefits other than post-retirement	18,010	17,324
Inventory reserve	3,181	3,172
Deferred revenue	10,770	9,624
Other	458	221
Deferred tax assets	131,385	132,613
Deferred tax liabilities:
Accelerated depreciation	(147,282)	(130,180)
Partnership items	(9,418)	(12,384)
State taxes	(1,724)	(802)
Valuation allowance against deferred tax assets	(229)	(229)
Deferred tax liabilities	158,653	143,595
Net deferred tax (liability)	$ (27,268)	$ (10,982)