Income Taxes Deferred tax assets and liabilties (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Income Taxes [Abstract]
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Allowance for Doubtful Accounts	$ 291	$ 305
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Accrued Liabilities	6,980	6,655
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost	648	579
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Self Insurance	26,000	27,549
Deferred Tax Assets, Unrealized Losses on Available-for-Sale Securities, Gross	0	449
Deferred Tax Assets, Tax Deferred Expense	4,846	5,658
Deferred Tax Assets, Other	1,889	1,011
Deferred Tax Assets, Gross	40,654	42,206
Deferred Tax Assets, Valuation Allowance	0	(449)
Deferred Tax Assets, Net	40,654	41,757
Deferred Tax Liabilities, Property, Plant and Equipment	(85,849)	(77,177)
Deferred Tax Liabilities, Goodwill and Intangible Assets	(1,835)	(1,351)
Deferred Tax Liabilities, Deferred Expense	(741)	(738)
Deferred Income Tax Liabilities	(88,425)	(79,266)
Deferred Tax Assets (Liabilities), Net	$ (47,771)	$ (37,509)