Business Combinations and Asset Acquisitions (Purchase Price Allocations) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Jul. 01, 2021	Dec. 31, 2020
Total goodwill:
Goodwill	$ 44,710		$ 0
Acquisition of ECM Transport Group [Member]
Purchase price:
Cash consideration paid		$ 155,686
Cash and cash equivalents acquired		13,327
Working capital surplus (deficiency)		(1,068)
Total purchase price (fair value of consideration)		141,291
Assets acquired:
Accounts receivable, trade		16,170
Other receivables		43
Inventories and supplies		204
Prepaid taxes, licenses and permits		700
Other current assets		351
Property and equipment		68,772
Intangible assets		52,200
Other non-current assets		3,644
Total assets acquired		142,084
Liabilities assumed:
Accounts payable		510
Insurance and claims accruals		(890)
Accrued payroll		(2,130)
Accrued expenses		(3,006)
Other current liabilities		(1,185)
Other long-term liabilities		(2,460)
Total liabilities assumed		(10,181)
NCI:
Temporary equity - redeemable noncontrolling interest in ECM		35,322
Total goodwill:
Goodwill		$ 44,710