LONG-TERM DEBT AND FINANCING ARRANGEMENTS (Assets Sec) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financing Arrangements
Total assets securing notes payable or held under finance leases	$ 264,617	$ 273,615
Less accumulated depreciation and amortization	82,843	79,961
Net assets securing notes payable or held under finance leases	181,774	193,654
Revenue equipment
Financing Arrangements
Total assets securing notes payable or held under finance leases	255,398	264,396
Land and structures (service centers)
Financing Arrangements
Total assets securing notes payable or held under finance leases	1,794	1,794
Software
Financing Arrangements
Total assets securing notes payable or held under finance leases	1,484	1,484
Service, office, and other equipment
Financing Arrangements
Total assets securing notes payable or held under finance leases	$ 5,941	$ 5,941