OPERATING SEGMENT DATA - (Operating Expenses) (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
OPERATING EXPENSES
Salaries, wages, and benefits		$ 355,913	$ 349,200	$ 684,670	$ 681,790
Rents, purchased transportation, and other costs of services		253,540	216,237	477,296	416,108
Fuel, supplies, and expenses		84,884	68,451	163,530	141,113
Depreciation and amortization		27,187	25,209	53,673	50,603
Other		30,408	35,141	59,663	63,981
Multiemployer pension fund withdrawal liability charge		37,922		37,922
Restructuring costs		340	363	716	1,994
Total consolidated operating expenses		$ 790,194	$ 694,601	$ 1,477,470	$ 1,355,589
Asset-Based | Multiemployer pension plans | New England Pension Fund
OPERATING EXPENSES
Multiemployer pension fund withdrawal liability charge	$ 37,900