Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Insurance and claims accruals	$ 54,913	$ 48,537
Compensation - related accruals	16,054	8,067
Allowance for uncollectible accounts	4,070	3,690
Other	5,374	1,863
Gross deferred income tax assets	80,411	62,157
Property and equipment	308,145	305,575
Prepaid expenses	6,333	4,928
Other	3,803	1,323
Gross deferred income tax liabilities	318,281	311,826
Net deferred income tax liability	$ 237,870	$ 249,669