OPERATING SEGMENT DATA - (Rev and Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
REVENUES
Revenues	$ 771,490	$ 793,350	$ 1,483,329	$ 1,493,351
OPERATING EXPENSES
Salaries, wages, and benefits	361,116	355,913	704,784	684,670
Fuel, supplies, and expenses	80,700	84,884	160,036	163,530
Depreciation and amortization	27,434	27,187	53,971	53,673
Multiemployer pension fund withdrawal liability charge		37,922		37,922
Gain on sale of property and equipment			(1,469)	(166)
Other	30,987	30,408	63,669	59,663
Restructuring costs		340		716
Total consolidated operating expenses	736,290	790,194	1,439,538	1,477,470
OPERATING INCOME
OPERATING INCOME	35,200	3,156	43,791	15,881
OTHER INCOME (COSTS)
Interest and dividend income	1,616	714	3,094	1,240
Interest and other related financing costs	(2,811)	(2,013)	(5,693)	(4,072)
Other, net	(445)	(1,123)	(1,036)	(3,324)
TOTAL OTHER INCOME (COSTS)	(1,640)	(2,422)	(3,635)	(6,156)
INCOME BEFORE INCOME TAXES	33,560	734	40,156	9,725
Operating Segments | Asset-Based
REVENUES
Revenues	559,648	559,239	1,065,727	1,041,354
OPERATING EXPENSES
Salaries, wages, and benefits	297,016	286,750	577,292	556,529
Fuel, supplies, and expenses	66,853	65,040	131,580	127,233
Operating taxes and licenses	12,214	11,910	24,612	23,666
Insurance	7,598	7,979	15,589	14,607
Communications and utilities	4,529	4,135	9,149	8,656
Depreciation and amortization	21,743	21,362	42,723	42,292
Rents and purchased transportation	57,687	63,253	107,599	109,386
Shared services	56,013	56,825	106,725	102,432
Multiemployer pension fund withdrawal liability charge		37,922		37,922
Gain on sale of property and equipment	(1,587)	(266)	(1,621)	(399)
Other	1,404	948	2,286	2,247
Total consolidated operating expenses	523,470	555,858	1,015,934	1,024,571
OPERATING INCOME
OPERATING INCOME	36,178	3,381	49,793	16,783
Operating Segments | ArcBest
REVENUES
Revenues	181,173	199,987	354,377	381,920
OPERATING EXPENSES
Purchased transportation	147,552	162,920	287,657	311,292
Supplies and expenses	2,858	3,538	5,632	6,768
Depreciation and amortization	3,055	3,597	6,206	7,005
Shared services	23,141	23,536	46,172	45,404
Other	2,445	2,546	4,858	4,427
Restructuring costs		143		152
Total consolidated operating expenses	179,051	196,280	350,525	375,048
OPERATING INCOME
OPERATING INCOME	2,122	3,707	3,852	6,872
Operating Segments | FleetNet
REVENUES
Revenues	51,722	46,792	104,981	94,551
OPERATING EXPENSES
Total consolidated operating expenses	50,696	45,763	102,467	92,001
OPERATING INCOME
OPERATING INCOME	1,026	1,029	2,514	2,550
Other and eliminations
REVENUES
Revenues	(21,053)	(12,668)	(41,756)	(24,474)
OPERATING EXPENSES
Total consolidated operating expenses	(16,927)	(7,707)	(29,388)	(14,150)
OPERATING INCOME
OPERATING INCOME	$ (4,126)	$ (4,961)	$ (12,368)	$ (10,324)