Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Insurance and claims accruals	$ 71,285	$ 74,651
Allowance for uncollectible accounts	6,138	8,260
Other	16,478	14,724
Gross deferred tax assets	93,901	97,635
Property and equipment	330,580	295,628
Prepaid expenses	7,229	6,913
Other	2,356	2,634
Gross deferred tax liabilities	340,165	305,175
Net deferred tax liability	$ 246,264	$ 207,540