LONG-TERM DEBT AND FINANCING ARRANGEMENTS (Assets Sec) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Arrangements
Total assets securing notes payable or held under finance leases	$ 293,799	$ 273,615
Less accumulated depreciation and amortization	71,405	79,961
Net assets securing notes payable or held under finance leases	$ 222,394	193,654
Weighted-average interest rate (as a percent)	3.10%
Interest paid, net of capitalized interest	$ 10,900	8,700	$ 5,800
Capitalized interest	200	200	$ 900
Revenue equipment
Financing Arrangements
Total assets securing notes payable or held under finance leases	265,315	264,396
Land and structures (service centers)
Financing Arrangements
Total assets securing notes payable or held under finance leases		1,794
Software
Financing Arrangements
Total assets securing notes payable or held under finance leases	2,140	1,484
Service, office, and other equipment
Financing Arrangements
Total assets securing notes payable or held under finance leases	$ 26,344	$ 5,941