Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Insurance and claims accruals	$ 47,031	$ 41,986
Compensation - related accruals	7,413	6,797
Allowance for uncollectible accounts	3,628	3,599
Other	1,896	1,979
Gross deferred income tax assets	59,968	54,361
Property and equipment	287,061	243,482
Prepaid expenses	4,772	4,699
Other	1,585	1,367
Gross deferred income tax liabilities	293,418	249,548
Net deferred income tax liability	$ 233,450	$ 195,187