OPERATING SEGMENT DATA - (Operating Expenses) (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
OPERATING EXPENSES
Salaries, wages, and benefits		$ 363,348	$ 349,294	$ 1,048,018	$ 1,023,803
Rents, purchased transportation, and other costs of services		265,042	235,346	742,338	651,131
Fuel, supplies, and expenses		82,188	75,716	245,718	226,666
Depreciation and amortization		28,026	25,497	81,699	76,821
Other		31,449	30,948	91,112	91,975
Multiemployer pension fund withdrawal liability charge				37,922
Restructuring costs		50	737	766	2,731
Total consolidated operating expenses		$ 770,103	$ 717,538	$ 2,247,573	$ 2,073,127
Asset-Based | Multiemployer pension plans | New England Pension Fund
OPERATING EXPENSES
Multiemployer pension fund withdrawal liability charge	$ 37,900