Income Taxes Deferred tax assets and liabilties (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Income Taxes [Abstract]
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Allowance for Doubtful Accounts	$ 305	$ 288
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Accrued Liabilities	6,655	6,513
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost	579	46
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Self Insurance	27,549	27,677
Deferred Tax Assets, Unrealized Losses on Available-for-Sale Securities, Gross	449	1,078
Deferred Tax Assets, Tax Deferred Expense	5,658	5,767
Deferred Tax Assets, Other	1,011	1,230
Deferred Tax Assets, Gross	42,206	42,599
Deferred Tax Assets, Valuation Allowance	(449)	(1,078)
Deferred Tax Assets, Net	41,757	41,521
Deferred Tax Liabilities, Property, Plant and Equipment	(77,177)	(82,897)
Deferred Tax Liabilities, Goodwill and Intangible Assets	(1,351)	(1,195)
Deferred Tax Liabilities, Deferred Expense	(738)	(689)
Deferred Income Tax Liabilities	(79,266)	(84,781)
Deferred Tax Assets (Liabilities), Net	$ (37,509)	$ (43,260)