Amount of pre-tax expenses associated with multiemployer pension fund withdrawal liability.

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Represents the projected funded percentage of a specified multiemployer pension plan.

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No definition available.

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No definition available.

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Represents the minimum funded percentage of plans in the yellow zone.

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Represents the percentage of the entity's contributions to multiemployer pension plans that are made to the specified plan.

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No definition available.

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Represents the percentage of the entity's contributions to multiemployer pension plans that are made to plans in critical and declining status.

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The maximum period within which a plan in "critical and declining" status is expected to become insolvent, unless additional criteria relating to ratio of inactive to active participants or funded percentage are applicable.

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The maximum period within which a plan in "critical and declining" status is expected to become insolvent, if additional criteria relating to ratio of inactive to active participants or funded percentage are applicable.

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The period of time over which monthly payments have to be made for withdrawal liability settlement for multiemployer plan, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Represents the number of multiemployer plans to which the reporting entity currently contributes.

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Amount of cash outflow for initial lumpsum payment of withdrawal liability from multiemployer plan.

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The aggregate present value of the monthly payments for the multiemployer plan withdrawal liability.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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Increase (decrease) in employer's contractual contribution rate to multiemployer plan.

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Amount of cost for employer contribution to multiemployer plan. Multiemployer plan includes, but is not limited to, pension plan determined to be individually significant and insignificant and other postretirement benefit plan.

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EMPLOYEE BENEFIT PLANS - Multiemployer Plans (Details) $ in Thousands						1 Months Ended	3 Months Ended	12 Months Ended
	Aug. 01, 2020	Jan. 31, 2020	Aug. 01, 2019	Jan. 31, 2019	Aug. 01, 2018	Jun. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2020 USD ($) plan	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jan. 01, 2019	Jan. 01, 2018
Multiemployer Plans
Multiemployer pension fund withdrawal liability charge (pre-tax)										$ 37,922
Asset Based
Multiemployer Plans
Minimum funded percentage of plans in green zone								80.00%
Asset Based \| Nonunion Defined Benefit Pension Plan
Multiemployer Plans
Number of multiemployer plans to which ABF Freight currently contributes \| plan								25
Maximum funded percentage of plans in yellow zone								80.00%
Maximum funded percentage of plans in red zone								65.00%
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%
Percentage of contributions to the multiemployer pension plans that are in critical and declining status								56.00%
Percentage of contributions to the multiemployer pension plans that are in critical status								3.00%
Percentage of contributions to the multiemployer pension plans that are in endangered status								4.00%
Total multiemployer pension contributions paid								$ 142,194	$ 153,746	167,249
Asset Based \| Nonunion Defined Benefit Pension Plan \| Central States Pension Plan
Multiemployer Plans
Multiemployer pension contributions paid, individually significant								$ 68,704	$ 75,803	$ 74,177
Threshold percentage of the entity's contributions relative to total fund contributions, which was exceeded during the period									5.00%	5.00%
Maximum projected time to insolvency without legislative action								5 years
Percentage of contributions to multiemployer pension plan								50.00%	50.00%	50.00%
Actuarially certified projected funded percentage of multiemployer pension plan											24.80%	27.20%
Asset Based \| Nonunion Defined Benefit Pension Plan \| Western Conference Of Teamsters Pension Plan
Multiemployer Plans
Multiemployer pension contributions paid, individually significant								$ 23,633	$ 24,860	$ 25,268
Asset Based \| Nonunion Defined Benefit Pension Plan \| Central Pennsylvania Teamsters Pension Plan
Multiemployer Plans
Multiemployer pension contributions paid, individually significant								13,485	$ 13,907	$ 13,393
Threshold percentage of the entity's contributions relative to total fund contributions, which was exceeded during the period									5.00%	5.00%
Asset Based \| Nonunion Defined Benefit Pension Plan \| Local 710 Pension Fund
Multiemployer Plans
Multiemployer pension contributions paid, individually significant								9,885	$ 10,164	$ 9,929
Threshold percentage of the entity's contributions relative to total fund contributions, which was exceeded during the period		5.00%		5.00%
Asset Based \| Nonunion Defined Benefit Pension Plan \| New England Pension Fund
Multiemployer Plans
Multiemployer pension contributions paid, individually significant								4,464	4,802	20,090
Contributions to multiemployer plans related to pension fund withdrawal liability								$ 1,600	1,600	15,700
Contribution rate frozen period (in years)								10 years
Multiemployer pension fund withdrawal liability charge (pre-tax)						$ 37,900
Initial lump sum payment of withdrawal liability							$ 15,100
Withdrawal liability monthly payments period (in years)							23 years
Aggregate present value of monthly payments							$ 22,800
Outstanding withdrawal liability								$ 21,400
Asset Based \| Nonunion Defined Benefit Pension Plan \| New England Pension Fund \| Accrued expenses
Multiemployer Plans
Outstanding withdrawal liability								600
Asset Based \| Nonunion Defined Benefit Pension Plan \| New England Pension Fund \| Other long-term liabilities
Multiemployer Plans
Outstanding withdrawal liability								20,800
Asset Based \| Nonunion Defined Benefit Pension Plan \| Other Pension Plans
Multiemployer Plans
Multiemployer pension contributions paid, individually insignificant								$ 22,023	24,210	24,392
Asset Based \| Nonunion Defined Benefit Pension Plan \| Western Pennsylvania Teamsters And Employers Pension Fund
Multiemployer Plans
Percentage of contributions to individually insignificant multiemployer pension plan								1.00%
Asset Based \| Nonunion Defined Benefit Pension Plan \| New York State Teamsters Conference Pension and Retirement Fund
Multiemployer Plans
Percentage of contributions to individually insignificant multiemployer pension plan								1.00%
Asset Based \| Nonunion Defined Benefit Pension Plan \| North Jersey Welfare Fund
Multiemployer Plans
Percentage of contributions to individually insignificant multiemployer pension plan								2.00%
Asset Based \| Multiemployer health and welfare plans
Multiemployer Plans
Number of multiemployer plans to which ABF Freight currently contributes \| plan								38
Total multiemployer pension contributions paid								$ 163,800	$ 172,000	$ 162,100
Percentage increase in contribution rate for time worked related to benefit costs	4.00%		3.80%		4.10%
Asset Based \| Unionized employees concentration risk \| Number of employees
Multiemployer Plans
Percentage of Asset-Based segment employees covered under collective bargaining agreement with the IBT								82.00%