Income Taxes (Schedule Of Deferred Tax Assets And Liabilities) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Abstract]
Insurance and claims accruals	$ 73,211	$ 72,613
Allowance for uncollectible accounts	7,813	6,913
Other	9,416	8,382
Gross deferred tax assets	90,440	87,908
Property and equipment	288,032	295,429
Prepaid expenses	6,774	6,710
Other	3,026	2,964
Gross deferred tax liabilities	297,832	305,103
Net deferred tax liability	$ 207,392	$ 217,195