OPERATING SEGMENT DATA - (Rev and Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
REVENUES
Revenues	$ 787,563	$ 826,158	$ 2,270,892	$ 2,319,509
OPERATING EXPENSES
Salaries, wages, and benefits	363,902	363,348	1,068,685	1,048,018
Fuel, supplies, and expenses	81,023	82,188	241,059	245,718
Depreciation and amortization	29,361	28,026	83,332	81,699
Multiemployer pension fund withdrawal liability charge				37,922
Gain on sale of property and equipment			(1,384)	(188)
Other	32,959	31,449	96,617	91,112
Restructuring costs		50		766
Gain on sale of subsidiaries				(1,945)
Total consolidated operating expenses	756,355	770,103	2,195,893	2,247,573
OPERATING INCOME
OPERATING INCOME	31,208	56,055	74,999	71,936
OTHER INCOME (COSTS)
Interest and dividend income	1,768	1,120	4,862	2,360
Interest and other related financing costs	(2,900)	(2,470)	(8,593)	(6,542)
Other, net	(6,734)	(714)	(7,770)	(4,038)
TOTAL OTHER INCOME (COSTS)	(7,866)	(2,064)	(11,501)	(8,220)
INCOME BEFORE INCOME TAXES	23,342	53,991	63,498	63,716
Operating Segments | Asset-Based
REVENUES
Revenues	565,621	585,290	1,631,348	1,626,644
OPERATING EXPENSES
Salaries, wages, and benefits	296,503	292,082	873,795	848,611
Fuel, supplies, and expenses	65,738	63,936	195,502	191,163
Operating taxes and licenses	12,865	12,261	37,477	35,927
Insurance	7,646	9,448	23,235	24,055
Communications and utilities	5,064	4,308	14,181	12,964
Depreciation and amortization	23,776	22,200	66,370	64,492
Rents and purchased transportation	61,102	70,946	167,234	180,332
Shared services	56,031	57,472	161,664	158,042
Multiemployer pension fund withdrawal liability charge				37,922
Gain on sale of property and equipment	(82)	(123)	(1,703)	(522)
Innovative technology costs	4,664	1,080	9,200	2,947
Other	592	1,530	2,878	3,778
Total consolidated operating expenses	533,899	535,140	1,549,833	1,559,711
OPERATING INCOME
OPERATING INCOME	31,722	50,150	81,515	66,933
Operating Segments | ArcBest
REVENUES
Revenues	199,758	205,449	554,135	587,369
OPERATING EXPENSES
Purchased transportation	164,521	164,322	452,178	475,614
Supplies and expenses	2,780	3,522	8,412	10,290
Depreciation and amortization	2,607	3,558	8,813	10,563
Shared services	25,032	23,453	71,204	68,857
Other	2,366	2,546	7,224	6,973
Restructuring costs				152
Gain on sale of subsidiaries		(1,945)		(1,945)
Total consolidated operating expenses	197,306	195,456	547,831	570,504
OPERATING INCOME
OPERATING INCOME	2,452	9,993	6,304	16,865
Operating Segments | FleetNet
REVENUES
Revenues	53,976	50,494	158,957	145,045
OPERATING EXPENSES
Total consolidated operating expenses	52,805	49,406	155,272	141,407
OPERATING INCOME
OPERATING INCOME	1,171	1,088	3,685	3,638
Other and eliminations
REVENUES
Revenues	(31,792)	(15,075)	(73,548)	(39,549)
OPERATING EXPENSES
Total consolidated operating expenses	(27,655)	(9,899)	(57,043)	(24,049)
OPERATING INCOME
OPERATING INCOME	$ (4,137)	$ (5,176)	$ (16,505)	$ (15,500)