PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Details) $ in Thousands	1 Months Ended	3 Months Ended			9 Months Ended		12 Months Ended
	Jan. 31, 2014 person	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Sep. 30, 2015 USD ($) plan	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)	Jun. 30, 2015	Mar. 31, 2015	Jan. 01, 2015
Components of net periodic benefit cost
Pension settlement expense		$ 800	$ 800		$ 2,478	$ 5,405
Pension settlement expense, net of tax		466	492		$ 1,514	3,303
Multiemployer pension plans | Freight Transportation (ABF Freight)
Multiemployer Plans
Number of multiemployer plans to which ABF Freight currently contributes | plan					25
Maximum projected time to insolvency for plans in "critical and declining" status					14 years
Maximum projected time to insolvency for plans in "critical and declining" status if additional criteria apply					19 years
Threshold ratio of inactive to active participants for greater insolvency period to determine "critical and declining" status					2
Threshold funded percentage for greater insolvency period to determine "critical and declining" status					80.00%
Multiemployer pension plans | Central States Pension Plan | Freight Transportation (ABF Freight)
Multiemployer Plans
Approximate proportion of multiemployer pension plan contributions (as a percent)					50.00%
Actuarially certified funded percentage of multiemployer pension plan										47.90%
Multiemployer pension plans | 707 Pension Fund | Freight Transportation (ABF Freight)
Multiemployer Plans
Approximate proportion of multiemployer pension plan contributions (as a percent)							1.00%
Nonunion Defined Benefit Pension Plan
Components of net periodic benefit cost
Interest cost		1,356	1,401		$ 3,899	4,643
Expected return on plan assets		(2,297)	(2,544)		(7,058)	(7,980)
Pension settlement expense		762	805		2,478	5,405
Amortization of net actuarial loss		640	595		2,276	1,729
Net periodic benefit cost		461	257		1,595	3,797
Number of plan participants for which vested pension benefits were settled | person	375
Pension settlement expense, net of tax		500	500		1,500	3,300
Premium paid to purchase nonparticipating annuity contract				$ 25,400
Lump-sum distributions		4,100	6,300		$ 16,600	28,800
Amortization period for unrecognized net actuarial loss					8 years
Change in projected benefit obligation
Projected benefit obligation at the beginning of the period					$ 174,410
Interest cost		1,356	1,401		3,899	4,643
Actuarial gain					(475)
Benefits paid					(16,756)
Projected benefit obligation at the end of the period		161,078			161,078		$ 174,410
Change in plan assets
Fair value of plan assets at beginning of period					158,265
Actual loss on plan assets					(3,616)
Employer contributions					50
Benefits paid					(16,756)
Fair value of plan assets at end of period		137,943			137,943		$ 158,265
Funded status		(23,135)			(23,135)
Accumulated benefit obligation		$ 161,078			$ 161,078
Discount rate (as a percent)		3.40%			3.40%		3.20%	3.50%	3.00%
Adjusted funding target attainment percentage										107.30%
Supplemental Benefit Plan
Components of net periodic benefit cost
Interest cost		$ 31	49		$ 92	147
Amortization of net actuarial loss		40	57		120	170
Net periodic benefit cost		71	106		212	317
Change in projected benefit obligation
Interest cost		31	49		92	147
Postretirement Health Benefit Plan
Components of net periodic benefit cost
Service cost		101	70		304	210
Interest cost		228	197		685	591
Amortization of prior service credit		(47)	(47)		(142)	(142)
Amortization of net actuarial loss		213	23		639	69
Net periodic benefit cost		495	243		1,486	728
Change in projected benefit obligation
Interest cost		$ 228	$ 197		$ 685	$ 591