Income Taxes Deferred tax assets and liabilties (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Income Taxes [Abstract]
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Allowance for Doubtful Accounts	$ 288	$ 282
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Accrued Liabilities	6,513	6,456
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Self Insurance	27,677	27,514
Deferred Tax Assets, Unrealized Losses on Available-for-Sale Securities, Gross	1,078	1,078
Deferred Tax Assets, Tax Deferred Expense	5,767	6,413
Deferred Tax Assets, Other	1,276	561
Deferred Tax Assets, Gross	42,599	42,304
Deferred Tax Assets, Valuation Allowance	(1,078)	(1,078)
Deferred Tax Assets, Net	41,521	41,226
Deferred Tax Liabilities, Property, Plant and Equipment	(82,897)	(68,109)
Deferred Tax Liabilities, Goodwill and Intangible Assets	(1,195)	(984)
Deferred Tax Liabilities, Deferred Expense	(689)	(650)
Deferred Income Tax Liabilities	(84,781)	(69,743)
Deferred Tax Assets (Liabilities), Net	$ (43,260)	$ (28,517)