Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Insurance and claims accruals	$ 74,015	$ 71,285
Compensation - related liabilities	10,056	10,187
Allowance for uncollectible accounts	6,135	6,138
Other	4,168	6,291
Gross deferred tax assets	94,374	93,901
Property and equipment	377,093	330,580
Prepaid expenses	7,737	7,229
Other	2,313	2,356
Gross deferred tax liabilities	387,143	340,165
Net deferred tax liability	$ 292,769	$ 246,264