OPERATING SEGMENT DATA - (Rev and 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
REVENUES
Revenues		$ 826,158	$ 744,280	$ 2,319,509	$ 2,115,736
OPERATING EXPENSES
Salaries, wages, and benefits		363,348	349,294	1,048,018	1,023,803
Fuel, supplies, and expenses		82,188	75,716	245,718	226,666
Depreciation and amortization		28,026	25,497	81,699	76,821
Multiemployer pension fund withdrawal liability charge				37,922
Gain on sale of property and equipment				(188)	(257)
Other		31,449	30,948	91,112	91,975
Restructuring costs		50	737	766	2,731
Gain on sale of subsidiaries				(1,945)	(152)
Total consolidated operating expenses		770,103	717,538	2,247,573	2,073,127
OPERATING INCOME
OPERATING INCOME		56,055	26,742	71,936	42,609
OTHER INCOME (COSTS)
Interest and dividend income		1,120	346	2,360	905
Interest and other related financing costs		(2,470)	(1,706)	(6,542)	(4,410)
Other, net		(714)	(1,314)	(4,038)	(3,548)
TOTAL OTHER INCOME (COSTS)		(2,064)	(2,674)	(8,220)	(7,053)
INCOME BEFORE INCOME TAXES		53,991	24,068	63,716	35,556
Asset-Based | Multiemployer pension plans | New England Pension Fund
OPERATING EXPENSES
Multiemployer pension fund withdrawal liability charge	$ 37,900
Operating Segments | Asset-Based
REVENUES
Revenues		585,290	517,417	1,626,644	1,496,310
OPERATING EXPENSES
Salaries, wages, and benefits		292,082	287,270	848,611	853,554
Fuel, supplies, and expenses		64,133	57,395	191,366	174,326
Operating taxes and licenses		12,261	11,712	35,927	35,726
Insurance		9,448	8,348	24,055	23,068
Communications and utilities		4,308	4,575	12,964	13,260
Depreciation and amortization		22,200	20,543	64,492	61,777
Rents and purchased transportation		70,946	55,381	180,332	154,996
Shared services		58,354	47,608	160,786	137,712
Multiemployer pension fund withdrawal liability charge				37,922
Gain on sale of property and equipment		(123)	(7)	(522)	(599)
Other		1,531	757	3,778	3,935
Restructuring costs			95		268
Total consolidated operating expenses		535,140	493,677	1,559,711	1,458,023
OPERATING INCOME
OPERATING INCOME		50,150	23,740	66,933	38,287
Operating Segments | ArcBest
REVENUES
Revenues		205,449	195,749	587,369	524,554
OPERATING EXPENSES
Purchased transportation		164,322	155,894	475,614	417,313
Supplies and expenses		3,522	3,853	10,290	11,265
Depreciation and amortization		3,558	3,015	10,563	9,511
Shared services		23,453	22,447	68,857	62,691
Other		2,546	2,854	6,973	8,192
Restructuring costs				152	875
Gain on sale of subsidiaries		(1,945)	(152)	(1,945)	(152)
Total consolidated operating expenses		195,456	187,911	570,504	509,695
OPERATING INCOME
OPERATING INCOME		9,993	7,838	16,865	14,859
Operating Segments | FleetNet
REVENUES
Revenues		50,494	39,568	145,045	116,307
OPERATING EXPENSES
Total consolidated operating expenses		49,406	38,646	141,407	113,617
OPERATING INCOME
OPERATING INCOME		1,088	922	3,638	2,690
Other and eliminations
REVENUES
Revenues		(15,075)	(8,454)	(39,549)	(21,435)
OPERATING EXPENSES
Total consolidated operating expenses		(9,899)	(2,696)	(24,049)	(8,208)
OPERATING INCOME
OPERATING INCOME		$ (5,176)	$ (5,758)	$ (15,500)	$ (13,227)