ArcBest (ARCB) 10-K 26 Feb 21 2020 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2020	Feb. 19, 2021	Jun. 30, 2020
Document and Entity Information
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Document Transition Report	false
Entity File Number	0-19969
Entity Registrant Name	ARCBEST CORPORATION
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	71-0673405
Entity Address, Address Line One	8401 McClure Drive
Entity Address, City or Town	Fort Smith
Entity Address, State or Province	AR
Entity Address, Postal Zip Code	72916
City Area Code	479
Local Phone Number	785-6000
Title of 12(b) Security	Common Stock
Trading Symbol	ARCB
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 658,708,492
Entity Common Stock, Shares Outstanding		25,397,696
Entity Central Index Key	0000894405
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
CURRENT ASSETS
Cash and cash equivalents	$ 303,954	$ 201,909
Short-term investments	65,408	116,579
Accounts receivable, less allowances (2020 - $7,851; 2019 - $5,448)	320,870	282,579
Other accounts receivable, less allowances (2020 - $660; 2019 - $476)	14,343	18,774
Prepaid expenses	37,774	30,377
Prepaid and refundable income taxes	11,397	9,439
Other	4,422	4,745
TOTAL CURRENT ASSETS	758,168	664,402
PROPERTY, PLANT AND EQUIPMENT
Land and structures	342,178	342,122
Revenue equipment	916,760	896,020
Service, office, and other equipment	233,810	233,354
Software	163,193	151,068
Leasehold improvements	15,156	10,383
TOTAL PROPERTY, PLANT AND EQUIPMENT, Gross	1,671,097	1,632,947
Less allowances for depreciation and amortization	992,407	949,355
PROPERTY, PLANT AND EQUIPMENT, net	678,690	683,592
GOODWILL	88,320	88,320
INTANGIBLE ASSETS, net	54,981	58,832
OPERATING RIGHT-OF-USE ASSETS	115,195	68,470
DEFERRED INCOME TAXES	6,158	7,725
OTHER LONG-TERM ASSETS	77,496	79,866
TOTAL ASSETS	1,779,008	1,651,207
CURRENT LIABILITIES
Accounts payable	170,898	134,374
Income taxes payable	316	12
Accrued expenses	246,746	232,321
Current portion of long-term debt	67,105	57,305
Current portion of operating lease liabilities	21,482	20,265
TOTAL CURRENT LIABILITIES	506,547	444,277
LONG-TERM DEBT, less current portion	217,119	266,214
OPERATING LEASE LIABILITIES, less current portion	97,839	52,277
POSTRETIREMENT LIABILITIES, less current portion	18,555	20,294
OTHER LONG-TERM LIABILITIES	37,948	38,892
DEFERRED INCOME TAXES	72,407	66,210
STOCKHOLDERS' EQUITY
Common stock, $0.01 par value, authorized 70,000,000 shares; issued 2020: 29,045,309 shares, 2019: 28,810,902 shares	290	288
Additional paid-in capital	342,354	333,943
Retained earnings	595,932	533,187
Treasury stock, at cost, 2020: 3,656,938 shares; 2019: 3,404,639 shares	(111,173)	(104,578)
Accumulated other comprehensive income	1,190	203
TOTAL STOCKHOLDERS' EQUITY	828,593	763,043
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 1,779,008	$ 1,651,207

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
CONSOLIDATED BALANCE SHEETS
Accounts receivable, allowances (in dollars)	$ 7,851	$ 5,448
Other accounts receivable, allowances (in dollars)	$ 660	$ 476
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized shares	70,000,000	70,000,000
Common stock, issued shares	29,045,309	28,810,902
Treasury stock, at cost, shares	3,656,938	3,404,639

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
CONSOLIDATED STATEMENTS OF OPERATIONS
REVENUES	$ 816,414	$ 794,980	$ 627,370	$ 701,399	$ 717,418	$ 787,563	$ 771,490	$ 711,839	$ 2,940,163	$ 2,988,310	$ 3,093,788
OPERATING EXPENSES	786,162	755,198	606,945	693,580	728,647	756,355	736,290	703,248	2,841,885	2,924,540	2,984,690
OPERATING INCOME	30,252	39,782	20,425	7,819	(11,229)	31,208	35,200	8,591	98,278	63,770	109,098
OTHER INCOME (COSTS)
Interest and dividend income									3,616	6,453	3,914
Interest and other related financing costs									(11,697)	(11,467)	(9,468)
Other, net									2,299	(7,285)	(19,158)
TOTAL OTHER INCOME (COSTS)	(53)	(604)	309	(5,434)	(798)	(7,866)	(1,640)	(1,995)	(5,782)	(12,299)	(24,712)
INCOME BEFORE INCOME TAXES									92,496	51,471	84,386
INCOME TAX PROVISION	6,285	9,774	4,854	483	(6,478)	7,072	9,184	1,708	21,396	11,486	17,124
NET INCOME	$ 23,914	$ 29,404	$ 15,880	$ 1,902	$ (5,549)	$ 16,270	$ 24,376	$ 4,888	$ 71,100	$ 39,985	$ 67,262
EARNINGS PER COMMON SHARE
Basic (in dollars per share)	$ 0.94	$ 1.15	$ 0.62	$ 0.07	$ (0.22)	$ 0.64	$ 0.95	$ 0.19	$ 2.80	$ 1.56	$ 2.61
Diluted (in dollars per share)	$ 0.89	$ 1.11	$ 0.61	$ 0.07	$ (0.22)	$ 0.62	$ 0.92	$ 0.18	$ 2.69	$ 1.51	$ 2.51
AVERAGE COMMON SHARES OUTSTANDING
Basic (in shares)	25,427,449	25,470,094	25,463,559	25,390,377	25,490,393	25,527,982	25,554,286	25,570,415	25,410,232	25,535,529	25,679,736
Diluted (in shares)	26,734,287	26,592,457	26,217,957	26,246,800	25,490,393	26,416,595	26,431,592	26,512,349	26,422,523	26,450,055	26,698,831
CASH DIVIDENDS DECLARED PER COMMON SHARE (in dollars per share)	$ 0.08	$ 0.08	$ 0.08	$ 0.08	$ 0.08	$ 0.08	$ 0.08	$ 0.08	$ 0.32	$ 0.32	$ 0.32

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME
NET INCOME	$ 71,100	$ 39,985	$ 67,262
Pension and other postretirement benefit plans:
Net actuarial gain (loss), net of tax of: (2020 - $513; 2019 - $2,308, 2018 - $477)	1,480	6,657	(1,376)
Pension settlement expense, including termination expense, net of tax of: (2020 - $23; 2019 - $1,167, 2018 - $3,327)	66	7,338	9,598
Amortization of unrecognized net periodic benefit cost (credit), net of tax of: (2020 - $152; 2019 - $314, 2018 - $740)
Net actuarial (gain) loss	(437)	931	2,204
Prior service credit	(1)	(25)	(69)
Interest rate swap and foreign currency translation:
Change in unrealized (loss) on interest rate swap, net of tax of: (2020 - $277; 2019 - $357)	(782)	(1,007)
Change in unrealized gain on interest rate swap, net of tax of:(2018 - $84)			236
Change in foreign currency translation, net of tax of: (2020 - $232; 2019 - $194, 2018 - $241)	661	547	(681)
OTHER COMPREHENSIVE INCOME, net of tax	987	14,441	9,912
TOTAL COMPREHENSIVE INCOME	$ 72,087	$ 54,426	$ 77,174

CONSOLIDATED STATEMENTS OF CO_2

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME
Net actuarial loss, tax (benefit)	$ 513	$ 2,308	$ (477)
Pension settlement expense, tax	23	1,167	3,327
Amortization of unrecognized net periodic benefit costs (credit), tax	(152)	314	740
Change in unrealized (loss) on interest rate swap, tax (benefit)	(277)	(357)
Change in unrealized gain on interest rate swap, tax			84
Change in foreign currency translation, tax expense (benefit)	$ 232	$ 194	$ (241)

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Common StockCumulative Effect, Period of Adoption, Adjusted Balance	Common Stock	Additional Paid-In CapitalCumulative Effect, Period of Adoption, Adjusted Balance	Additional Paid-In Capital	Retained EarningsCumulative Effect, Period of Adoption, Adjustment	Retained EarningsCumulative Effect, Period of Adoption, Adjusted Balance	Retained Earnings	Treasury StockCumulative Effect, Period of Adoption, Adjusted Balance	Treasury Stock	Accumulated Other Comprehensive Income (Loss)Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income (Loss)Cumulative Effect, Period of Adoption, Adjusted Balance	Accumulated Other Comprehensive Income (Loss)	Cumulative Effect, Period of Adoption, Adjustment	Cumulative Effect, Period of Adoption, Adjusted Balance	Total
Balances at Dec. 31, 2017	$ 285	$ 285	$ 319,436	$ 319,436	$ 3,992	$ 442,371	$ 438,379	$ (86,064)	$ (86,064)	$ (3,576)	$ (24,150)	$ (20,574)	$ 416	$ 651,878	$ 651,462
Balances (in shares) at Dec. 31, 2017	28,496	28,496						2,852	2,852
Increase (Decrease) in Stockholders' Equity
Net income							67,262								67,262
Other comprehensive income (loss) net of tax												9,912			9,912
Issuance of common stock under share-based compensation plans		$ 2		(2)
Issuance of common stock under share-based compensation plans (in shares)		189
Tax effect of share-based compensation plans				(2,135)											(2,135)
Share-based compensation expense				8,413											8,413
Purchase of treasury stock									$ (9,404)						(9,404)
Purchase of treasury stock (in shares)									246
Dividends declared on common stock							(8,244)								(8,244)
Balances at Dec. 31, 2018		$ 287		325,712			501,389		$ (95,468)			(14,238)			717,682
Balances (in shares) at Dec. 31, 2018		28,685							3,098
Increase (Decrease) in Stockholders' Equity
Net income							39,985								39,985
Other comprehensive income (loss) net of tax												14,441			14,441
Issuance of common stock under share-based compensation plans		$ 1		(1)
Issuance of common stock under share-based compensation plans (in shares)		126
Tax effect of share-based compensation plans				(1,291)											(1,291)
Share-based compensation expense				9,523											9,523
Purchase of treasury stock									$ (9,110)						(9,110)
Purchase of treasury stock (in shares)									307
Dividends declared on common stock							(8,187)								(8,187)
Balances at Dec. 31, 2019	$ 288	$ 288	$ 333,943	333,943	$ (198)	$ 532,989	533,187	$ (104,578)	$ (104,578)		$ 203	203	$ (198)	$ 762,845	763,043
Balances (in shares) at Dec. 31, 2019	28,811	28,811						3,405	3,405
Increase (Decrease) in Stockholders' Equity
Net income							71,100								71,100
Other comprehensive income (loss) net of tax												987			987
Issuance of common stock under share-based compensation plans		$ 2		(2)
Issuance of common stock under share-based compensation plans (in shares)		234
Tax effect of share-based compensation plans				(2,065)											(2,065)
Share-based compensation expense				10,478											10,478
Purchase of treasury stock									$ (6,595)						(6,595)
Purchase of treasury stock (in shares)									252
Dividends declared on common stock							(8,157)								(8,157)
Balances at Dec. 31, 2020		$ 290		$ 342,354			$ 595,932		$ (111,173)			$ 1,190			$ 828,593
Balances (in shares) at Dec. 31, 2020		29,045							3,657

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
OPERATING ACTIVITIES
Net income	$ 71,100	$ 39,985	$ 67,262
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	114,379	108,099	104,114
Amortization of intangibles	4,012	4,367	4,521
Pension settlement expense, including termination expense	89	8,505	12,925
Share-based compensation expense	10,478	9,523	8,413
Provision for losses on accounts receivable	4,327	1,223	2,336
Change in deferred income taxes	7,715	5,411	1,872
Asset impairment		26,514
Gain on sale of property and equipment and lease termination	(2,376)	(5,247)	(59)
Gain on sale of subsidiaries			(1,945)
Changes in operating assets and liabilities:
Receivables	(38,129)	13,720	(23,554)
Prepaid expenses	(7,966)	(4,756)	(2,988)
Other assets	2,646	(1,365)	(4,341)
Income taxes	(1,712)	(8,720)	12,169
Operating right-of-use assets and lease liabilities, net	756	728
Multiemployer pension fund withdrawal liability	(611)	(584)	22,602
Accounts payable, accrued expenses, and other liabilities	41,281	(27,039)	52,020
NET CASH PROVIDED BY OPERATING ACTIVITIES	205,989	170,364	255,347
INVESTING ACTIVITIES
Purchases of property, plant and equipment, net of financings	(43,248)	(90,955)	(43,992)
Proceeds from sale of property and equipment	13,348	13,490	4,256
Proceeds from sale of subsidiaries			4,680
Purchases of short-term investments	(165,133)	(129,709)	(108,495)
Proceeds from sale of short-term investments	216,735	120,409	58,698
Capitalization of internally developed software	(14,241)	(11,476)	(10,097)
NET CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES	7,461	(98,241)	(94,950)
FINANCING ACTIVITIES
Borrowings under credit facilities	180,000
Borrowings under accounts receivable securitization program	45,000
Proceeds from notes payable		20,410
Payments on long-term debt	(326,098)	(58,938)	(71,260)
Net change in book overdrafts	6,510	(2,722)	262
Deferred financing costs		(562)	(202)
Payment of common stock dividends	(8,157)	(8,187)	(8,244)
Purchases of treasury stock	(6,595)	(9,110)	(9,404)
Payments for tax withheld on share-based compensation	(2,065)	(1,291)	(2,135)
NET CASH USED IN FINANCING ACTIVITIES	(111,405)	(60,400)	(90,983)
NET INCREASE IN CASH AND CASH EQUIVALENTS	102,045	11,723	69,414
Cash and cash equivalents at beginning of period	201,909	190,186	120,772
CASH AND CASH EQUIVALENTS CASH AT END OF PERIOD	303,954	201,909	190,186
NONCASH INVESTING ACTIVITIES
Equipment and other financings	61,803	70,372	94,016
Accruals for equipment received	1,667	234	$ 2,807
Lease liabilities arising from obtaining right-of-use assets	$ 67,819	$ 32,761

ORGANIZATION AND DESCRIPTION OF

ORGANIZATION AND DESCRIPTION OF THE BUSINESS AND FINANCIAL STATEMENT PRESENTATION	12 Months Ended
	Dec. 31, 2020
ORGANIZATION AND DESCRIPTION OF THE BUSINESS AND FINANCIAL STATEMENT PRESENTATION
ORGANIZATION AND DESCRIPTION OF THE BUSINESS AND FINANCIAL STATEMENT PRESENTATION	NOTE A – ORGANIZATION AND DESCRIPTION OF THE BUSINESS AND FINANCIAL STATEMENT PRESENTATIO N ​ Organization and Description of Business ​ ArcBest Corporation ™ ​ The Asset-Based segment represented approximately 68% of the Company’s 2020 total revenues before other revenues and intercompany eliminations. As of December 2020, approximately 82% of the Asset-Based segment’s employees were covered under a collective bargaining agreement, the ABF National Master Freight Agreement (the “2018 ABF NMFA”), with the International Brotherhood of Teamsters (the “IBT”) which will remain in effect through June 30, 2023. ​ Financial Statement Presentation ​ Consolidation: ​ Segment Information: ​ Use of Estimates: ​ Reclassifications: ​ Subsequent Events ​ In January 2021, the Asset-Based segment sold an unutilized property that will result in a gain on sale of property and equipment of approximately $8.5 million. ​ ​ ​

ACCOUNTING POLICIES

ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2020
ACCOUNTING POLICIES
ACCOUNTING POLICIES	NOTE B – ACCOUNTING POLICIES ​ Cash, Cash Equivalents, and Short-Term Investments: ​ Certificates of deposit are valued at cost plus accrued interest, which approximates fair value. Held-to-maturity U.S. Treasury securities are recorded at amortized cost with interest and amortization of premiums and discounts included in interest income. Quarterly, the Company evaluates held-to-maturity securities for any other-than-temporary impairments related to any intention to sell or requirement to sell before its amortized costs are recovered. If a security is considered to be other-than-temporarily impaired, the difference between amortized cost and the amount that is determined to be recoverable is recorded in earnings. ​ Concentration of Credit Risk: ​ The Company’s services are provided primarily to customers throughout the United States and, to a lesser extent, Canada, Mexico, and other international locations. On a consolidated basis, the Company had no single customer representing more than 4% of its revenues in 2020, 2019, or 2018 or more than 6% of its accounts receivable balance at December 31, 2020 and 2019. The Company performs ongoing credit evaluations of its customers and generally does not require collateral. Historically, credit losses have been within management’s expectations. ​ Allowances: Financial Instruments – Credit Losses ​ The Company maintains allowances for credit losses (formerly known as the allowance for doubtful accounts) and revenue adjustments on its trade receivables. The Company estimates the allowance for credit losses based on historical write-offs, factors surrounding the credit risk of specific customers, and forecasts of future economic conditions. In order to gather information regarding these trends and factors, the Company performs ongoing credit evaluations of customers, an analysis of accounts receivable aging by business segment, and an analysis of future economic conditions at period end. The allowance for revenue adjustments is an estimate based on historical revenue adjustments and current information regarding trends and business changes. Actual write-offs or adjustments could differ from the allowance estimates due to a number of factors, including future changes in the forecasted economic environment or new factors and risks surrounding a particular customer. Accounts receivable are written off when the accounts are turned over to a collection agency or when the accounts are determined to be uncollectible. Actual write-offs and adjustments are charged against the allowances for doubtful accounts and revenue adjustments. The allowance for credit losses on the Company’s trade accounts receivable totaled $3.6 million and $1.8 million at December 31, 2020 and 2019, respectively. During 2020, the allowance for credit losses increased $4.3 million and was reduced $2.5 million by write-offs, net of recoveries. ​ Property, Plant and Equipment, Including Repairs and Maintenance: Purchases of property, plant and equipment are recorded at cost. For financial reporting purposes, property, plant and equipment is depreciated principally by the straight-line method, using the following useful lives: structures – primarily 15 to 60 years ; revenue equipment – 3 to 16 years ; and other equipment – 2 to 15 years . The Company utilizes tractors and trailers in its operations. Tractors and trailers are commonly referred to as “revenue equipment” in the transportation business. The Company periodically reviews and adjusts, as appropriate, the residual values and useful lives of revenue equipment and other equipment. For tax reporting purposes, accelerated depreciation or cost recovery methods are used. Gains and losses on asset sales are reflected in the year of disposal. Exchanges of nonmonetary assets that have commercial substance are measured based on the fair value of the assets exchanged. Tires purchased with revenue equipment are capitalized as a part of the cost of such equipment, with replacement tires being expensed when placed in service. Repair and maintenance costs associated with property, plant and equipment are expensed as incurred if the costs do not extend the useful life of the asset. If such costs do extend the useful life of the asset, the costs are capitalized and depreciated over the appropriate remaining useful life. ​ Computer Software for Internal Use, Including Web Site Development and Cloud Computing Costs: The Company capitalizes the costs of software acquired from third parties and qualifying internal computer software costs incurred during the application development stage, or during the implementation stage for cloud computing or hosting arrangements. Costs incurred in the preliminary project stage and postimplementation-operation stage, which includes maintenance and training costs, are expensed as incurred. For financial reporting purposes, capitalized software costs are amortized by the straight-line method generally over 2 to 7 years . Capitalized costs related to cloud computing and hosting arrangements are presented within prepaid expenses in the accompanying consolidated balance sheets. The amount of costs capitalized within any period is dependent on the nature of software development activities and projects in each period. ​ Impairment Assessment of Long-Lived Assets: amount of the asset may not be recoverable . ​ Assets to be disposed of are reclassified as assets held for sale at the lower of their carrying amount or fair value less cost to sell. Assets held for sale primarily represent Asset-Based segment nonoperating properties, older revenue equipment, and other equipment. Adjustments to write down assets to fair value less the amount of costs to sell are reported in operating income. Assets held for sale are expected to be disposed of by selling the assets within the next 12 months. Gains and losses on property and equipment are reported in operating income. Assets held for sale of $1.1 million and $1.3 million are reported within other noncurrent assets as of December 31, 2020 and 2019, respectively. ​ Goodwill and Intangible Assets: ​ Indefinite-lived intangible assets are also not amortized but rather are evaluated for impairment annually or more frequently if indicators of impairment exist. If the carrying amount of the intangible asset exceeds its fair value, an impairment loss shall be recognized in an amount equal to that excess. Fair values are determined based on a discounted cash flow model, similar to the goodwill analysis. ​ The Company amortizes finite-lived intangible assets over their respective estimated useful lives. ​ Income Taxes: ​ Management applies considerable judgment in determining the consolidated income tax provision, including valuation allowances on deferred tax assets. The valuation allowance for deferred tax assets is determined by evaluating whether it is more likely than not that the benefits of deferred tax assets will be realized through future reversal of existing taxable temporary differences, taxable income in carryback years in jurisdictions in which they are allowable, projected future taxable income, or tax-planning strategies. Uncertain tax positions, which also require significant judgment, are measured to determine the amounts to be recognized in the financial statements. The income tax provision and valuation allowances are complicated by complex and frequently changing rules administered in multiple jurisdictions, including U.S. federal, state, and foreign governments. ​ The Company’s income taxes for the year ended December 31, 2018, were impacted by the recognition of the effects of the Tax Cuts and Jobs Act (the “Tax Reform Act”) that was signed into law on December 22, 2017 (see Note E). ​ Book Overdrafts: ​ Insurance Reserves ​ Liabilities for self-insured workers’ compensation and third-party casualty claims are based on the case reserve amounts plus an estimate of loss development and incurred but not reported (“IBNR”) claims, which is developed from an independent actuarial analysis. The process of determining reserve requirements utilizes historical trends and involves an evaluation of claim frequency and severity, claims management, and other factors. Case reserves are evaluated as loss experience develops and new information becomes available. Adjustments to previously estimated aggregate reserves are reflected in financial results in the periods in which they are made. Aggregate reserves represent an estimate of the costs of claims incurred, and it is possible that the ultimate liability may differ significantly from such estimates. ​ The Company develops an estimate of self-insured cargo loss and damage claims liabilities based on historical trends and certain event-specific information. Claims liabilities are recorded in accrued expenses and are not offset by insurance receivables which are reported in other accounts receivable. ​ Long-Term Debt: ​ Interest Rate Swap Derivative Instruments ​ Leases: Leases ​ The short-term lease exemption was elected under ASC Topic 842 for all classes of assets to include real property, revenue equipment, and service, office, and other equipment. The Company adopted the policy election as a lessee for all classes of assets to account for each lease component and its related non-lease component(s) as a single lease component. In determining the discount rate, the Company uses ArcBest Corporation’s incremental borrowing rate unless the rate implicit in the lease is readily determinable when entering into a lease as a lessee. The incremental borrowing rate is determined by the price of a fully collateralized loan with similar terms based on current market rates. ​ An assessment is made on or after the effective date of newly signed contracts as to whether the contract is, or contains, a lease at the inception of a contract. The assessment is based on: (1) whether the contract involves the use of a distinct identified asset; (2) whether the Company obtains the right to substantially all the economic benefit from the use of the asset throughout the period; and (3) whether the Company has the right to direct the use of the asset. For all operating leases that meet the scope of ASC Topic 842, a right-of-use asset and a lease liability are recognized. The right-of-use asset is measured as the initial amount of the lease liability, plus any initial direct costs incurred, less any prepayments prior to commencement or lease incentives received. The lease liability is initially measured at the present value of the lease payments, discounted using the Company’s secured incremental borrowing rate for the same term as the underlying lease unless the interest rate implicit in the lease is readily determined, then the implicit rate will be used. Lease payments included in the measurement of the lease liability are comprised of the following: (1) the fixed noncancelable lease payments, (2) payments for optional renewal periods where it is reasonably certain the renewal period will be exercised, and (3) payments for early termination options unless it is reasonably certain the lease will not be terminated early. Variable lease payments based on an index or rate are initially measured using the index or rate in effect at lease commencement and included in the measurement of the initial lease liability. Additional payments based on the change in an index or rate are recorded as a period expense when incurred. Lease modifications result in remeasurement of the lease liability. ​ Nonunion Defined Benefit Pension, Supplemental Benefit, and Postretirement Health Benefit Plans: ​ The Company recognizes the funded status of the supplemental benefit plan (the “SBP”) and postretirement health benefit plan in the consolidated balance sheet and recognizes changes in the funded status, net of tax, in the year in which they occur as a component of other comprehensive income or loss. The benefit obligations of the SBP and postretirement health benefit plan represent the funded status, as these plans do not have plan assets. Amounts recognized in other comprehensive income or loss are subsequently expensed as components of net periodic benefit cost by amortizing unrecognized net actuarial losses over the average remaining active service period of the plan participants and amortizing unrecognized prior service credits over the remaining years of service until full eligibility of the active participants at the time of the plan amendment which created the prior service credit. A corridor approach is not used for determining the amounts of net actuarial losses to be amortized. ​ The Company has not incurred service cost under the nonunion defined benefit pension plan or the SBP since the accrual of benefits under the plans was frozen on July 1, 2013 and December 31, 2009, respectively; however, the Company incurs service cost under the postretirement health benefit plan which is reported within operating expenses in the consolidated statements of operations. The other components of net periodic benefit cost (including pension settlement expense) of the nonunion defined benefit pension plan, the SBP, and the postretirement health benefit plan are reported within the other line item of other income (costs). ​ The expense and liability related to the SBP, postretirement health benefit plan, and, prior to termination, the nonunion defined benefit pension plan, are measured based upon a number of assumptions and using the services of a third-party actuary. The discount rates used to discount the plans’ obligations are determined by matching projected cash distributions with appropriate high-quality corporate bond yields in a yield curve analysis. Prior to plan termination, the Company established the expected rate of return on plan assets for the nonunion defined benefit pension plan by considering the historical and expected returns for the plan’s current investment mix. Assumptions are also made regarding expected retirement age, mortality, employee turnover, and, for the postretirement health benefit plan, future increases in health care costs. The assumptions used directly impact the net periodic benefit cost for a particular year. An actuarial gain or loss results when actual experience varies from the assumptions or when there are changes in actuarial assumptions. Actuarial gains and losses are not included in net periodic benefit cost in the period when they arise but are recognized as a component of other comprehensive income or loss and subsequently amortized as a component of net periodic benefit cost. ​ The Company uses December 31 as the measurement date for the SBP, postretirement health benefit plan, and, prior to termination, the nonunion defined benefit pension plan. Plan obligations are also remeasured upon curtailment and upon settlement. ​ The Company recorded quarterly pension settlement expense related to the nonunion defined benefit pension plan when qualifying distributions determined to be settlements were expected to exceed the estimated total annual interest cost of the plan. Benefit distributions under the SBP individually exceed the annual interest cost of the plan, and the Company records the related settlement expense when the amount of the benefit to be distributed is fixed, which is generally upon an employee’s termination of employment. Pension settlement expense for the nonunion defined benefit pension plan and SBP is presented in Note I. ​ In September 2018, the nonunion defined benefit pension plan received a favorable determination letter from the U.S. Internal Revenue Service (the “IRS”) regarding qualification of the plan termination as of December 31, 2017. Following receipt of the determination letter, the plan’s actuarial assumptions were updated to remeasure the benefit obligation on a plan termination basis as of September 30, 2018 in connection with recognition of the quarterly pension settlement charge. The Company made assumptions for participant benefit elections, rate of return, and discount rates, including the annuity contract interest rate. These assumptions were updated as of December 31, 2018 and upon each quarterly remeasurement for settlements during 2019 until the benefit obligation of the plan was settled as of September 30, 2019. For plan termination assumptions, the Company utilized a short-term discount rate which represented the Company’s current borrowing rate and an annuity contract interest rate based on current published rates. ​ Revenue Recognition: ​ Asset-Based Segment Asset-Based segment revenues consist primarily of less-than-truckload freight delivery. Performance obligations are satisfied upon final delivery of the freight to the specified destination. Revenue is recognized based on the relative transit time in each reporting period with expenses recognized as incurred. A bill-by-bill analysis is used to establish estimates of revenue in transit for recognition in the appropriate period. Because the bill-by-bill methodology utilizes the approximate location of the shipment in the delivery process to determine the revenue to recognize, management believes it to be a reliable method. ​ Certain contracts may provide for volume-based or other discounts which are accounted for as variable consideration. The Company estimates these amounts based on a historical expectation of discounts to be earned by customers, and revenue is recognized based on the estimates. Revenue adjustments may also occur due to rating or other billing adjustments. The Company estimates revenue adjustments based on historical information and revenue is recognized accordingly at the time of shipment. Management believes that actual amounts will not vary significantly from estimates of variable consideration. ​ Revenue, purchased transportation expense, and third-party service expenses are reported on a gross basis for certain shipments and services where the Company utilizes a third-party carrier for pickup, linehaul, delivery of freight, or performance of services but remains primarily responsible for fulfilling delivery to the customer and maintains discretion in setting the price for the services. ​ ArcBest Segment ArcBest segment revenues consist primarily of asset-light logistics services using third-party vendors to provide transportation services. ArcBest segment revenue is generally recognized based on the relative transit time in each reporting period using estimated standard delivery times for freight in transit at the end of the reporting period. Purchased transportation expense is recognized as incurred consistent with the recognition of revenue. ​ Revenue and purchased transportation expense are reported on a gross basis for shipments and services where the Company utilizes a third-party carrier for pickup and delivery but remains primarily responsible to the customer for delivery and maintains discretion in setting the price for the service. ​ FleetNet Segment FleetNet segment revenues consist of service fee revenue, roadside repair revenue and routine maintenance services revenue. Service fee revenue for the FleetNet segment is recognized upon response to the service event. Repair and routine maintenance service revenue for the FleetNet segment is recognized upon completion of the service by third-party vendors. Revenue and expense from repair and maintenance services performed by third-party vendors are reported on a gross basis as FleetNet controls the services prior to transfer to the customer and remains primarily responsible to the customer for completion of the services. ​ Other Recognition and Disclosure Payment terms with customers may vary depending on the service provided, location or specific agreement with the customer. The term between invoicing and when payment is due is not significant. For certain services, payment is required before the services are provided to the customer. ​ The Company expenses sales commissions when incurred because the amortization period is one year or less. ​ The Company has elected not to disclose the value of unsatisfied performance obligations for contracts with an original length of one year or less or contracts for which revenue is recognized at the amount to which the Company has the right to invoice for services performed. ​ Comprehensive Income or Loss: ​ Earnings Per Share: ​ Effective in 2020, the Company no longer has equity awards that are deemed participating securities. Basic earnings per share is calculated by dividing net income by the daily weighted number of shares of the Company’s common stock outstanding for the period. Diluted earnings per share is calculated using the treasury stock method. Under this method, the denominator used in calculating diluted earnings per share includes the impact of unvested restricted equity awards. ​ Share-Based Compensation: The fair value of restricted stock awards is determined based upon the closing market price of the Company’s common stock on the date of grant. The restricted stock units (“RSUs”) generally vest at the end of a five-year period following the date of grant for RSUs awarded prior to 2018 and at the end of a four-year period following the date of grant for subsequent grants. Awards granted to non-employee directors typically vest at the end of a one-year period, subject to accelerated vesting due to death, disability, retirement, or change-in-control provisions. When RSUs become vested, the Company issues new shares which are subsequently distributed. Effective in 2020, the Company no longer has equity awards which are paid dividends or dividend equivalents during the vesting period. The Company recognizes the income tax benefits of dividends on share-based payment awards as income tax expense or benefit in the consolidated statements of operations when awards vest or are settled. ​ Share-based awards are amortized to compensation expense on a straight-line basis over the vesting period of awards or over the period to which the recipient first becomes eligible for retirement, whichever is shorter, with vesting accelerated upon death or disability. The Company recognizes forfeitures as they occur and the income tax effects of awards are recognized in the statement of operations when awards vest or are settled. ​ Fair Value Measurements: ​ ● Level 1 – Quoted prices for identical assets and liabilities in active markets. ● Level 2 – Quoted prices for similar assets and liabilities in active markets, quoted prices for identical or similar assets and liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data. ● Level 3 – Unobservable inputs (Company’s market assumptions) that are significant to the valuation model. ​ Environmental Matters: ​ Exit or Disposal Activities: ​ Adopted Accounting Pronouncements ​ As previously discussed in the accounting policy for allowances within this Note, effective January 1, 2020, the Company adopted ASC Topic 326, which replaced the incurred loss methodology model with an expected loss methodology referred to as the CECL methodology for the Company’s trade receivables and other receivables. The Company adopted ASC Topic 326 with the modified retrospective approach. Under this approach, results for reporting periods after January 1, 2020 are presented under ASC Topic 326 while prior period amounts continue to be reported in accordance with previously applicable accounting guidance. The Company recorded a decrease to retained earnings of $0.2 million as of January 1, 2020 for the cumulative effect of adopting ASC Topic 326. ​ On January 1, 2020 the Company adopted ASC Subtopic 350-40, Intangibles – Goodwill and Other – Internal-Use Software: Customer’s Accounting for Fees Paid in a Cloud Computing Arrangement , (“ASC Subtopic 350-40”). The amendments to ASC Subtopic 350-40 clarify the accounting treatment for implementation costs incurred by the customer in a cloud computing software arrangement. The amendments allow implementation costs of cloud computing arrangements to be capitalized using the same method prescribed by ASC Subtopic 350-40, Internal-Use Software . The amendments to ASC Subtopic 350-40 were adopted on a prospective basis and did not have an impact on the Company’s consolidated financial statements. ​ On January 1, 2020 the Company adopted ASC Topic 820, Fair Value Measurement , which was amended to modify the disclosure requirements of fair value measurements, primarily impacting the disclosures for Level 3 fair value measurements. The amendment did not have an impact on the Company’s financial statement disclosures. ​ The amendments to ASC Topic 848, Reference Rate Reform ​ Accounting Pronouncements Not Yet Adopted ​ ASC Topic 740, Income Taxes ​

FINANCIAL INSTRUMENTS AND FAIR

FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS	12 Months Ended
	Dec. 31, 2020
FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS
FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS	NOTE C – FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS ​ Financial Instruments ​ The following table presents the components of cash and cash equivalents and short-term investments: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31 December 31 ​ ​ 2020 ​ 2019 ​ ​ ​ (in thousands) ​ Cash and cash equivalents ​ ​ ​ ​ ​ ​ ​ Cash deposits (1) ​ $ 240,687 ​ $ 166,619 ​ Variable rate demand notes (1)(2) ​ 29,066 ​ 14,750 ​ Money market funds (3) ​ 34,201 ​ 20,540 ​ Total cash and cash equivalents ​ $ 303,954 ​ $ 201,909 ​ ​ ​ ​ ​ ​ ​ ​ ​ Short-term investments ​ ​ ​ ​ ​ ​ ​ Certificates of deposit (1) ​ $ 53,297 ​ $ 69,314 ​ U.S. Treasury securities (4) ​ ​ 12,111 ​ ​ 47,265 ​ Total short-term investments ​ $ 65,408 ​ $ 116,579 ​ (1) Recorded at cost plus accrued interest, which approximates fair value. (2) Amounts may be redeemed on a daily basis with the original issuer. (3) Recorded at fair value as determined by quoted market prices (see amounts presented in the table of financial assets and liabilities measured at fair value within this Note). (4) Recorded at amortized cost plus accrued interest, which approximates fair value. U.S. Treasury securities included in short-term investments are held-to-maturity investments with maturity dates of less than one year. ​ Concentrations of Credit Risk of Financial Instruments The Company is potentially subject to concentrations of credit risk related to its cash, cash equivalents, and short-term investments. The Company reduces credit risk by maintaining its cash deposits primarily in FDIC-insured accounts and placing its short-term investments primarily in FDIC-insured certificates of deposit. However, certain cash deposits and certificates of deposit may exceed federally insured limits. At December 31, 2020 and 2019, cash, cash equivalents, and short-term investments totaling $156.4 million and $66.2 million, respectively, were neither FDIC insured nor direct obligations of the U.S. government. ​ ​ Fair value and carrying value disclosures of financial instruments as of December 31 are presented in the following table: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 2019 ​ ​ (in thousands) ​ ​ ​ ​ Carrying ​ Fair ​ Carrying ​ Fair ​ ​ ​ ​ Value ​ Value ​ Value ​ Value ​ Credit Facility (1) ​ $ 70,000 ​ $ 70,000 ​ $ 70,000 ​ $ 70,000 ​ Accounts receivable securitization borrowings (2) ​ ​ — ​ ​ — ​ ​ 40,000 ​ ​ 40,000 ​ Notes payable (3) ​ 214,216 ​ 217,226 ​ 213,504 ​ 216,432 ​ New England Pension Fund withdrawal liability (4) ​ ​ 21,407 ​ ​ 25,523 ​ ​ 22,018 ​ ​ 24,462 ​ ​ ​ $ 305,623 ​ $ 312,749 ​ $ 345,522 ​ $ 350,894 ​ (1) The Credit Facility carries a variable interest rate based on LIBOR, plus a margin, that is considered to be priced at market for debt instruments having similar terms and collateral requirements (Level 2 of the fair value hierarchy). (2) Borrowings under the Company’s accounts receivable securitization program carry a variable interest rate based on LIBOR, plus a margin, that is considered to be priced at market for debt instruments having similar terms and collateral requirements (Level 2 of the fair value hierarchy). (3) Fair value of the notes payable was determined using a present value income approach based on quoted interest rates from lending institutions with which the Company would enter into similar transactions (Level 2 of the fair value hierarchy). (4) ABF Freight’s multiemployer pension plan obligation with the New England Teamsters and Trucking Industry Pension Fund (the “New England Pension Fund”) was restructured under a transition agreement effective on August 1, 2018, which resulted in a related withdrawal liability (see Note I). The fair value of the outstanding withdrawal liability is equal to the present value of the future withdrawal liability payments, discounted at an interest rate of 2.6% and 3.4% at December 31, 2020 and 2019, respectively, determined using the 20-year U.S. Treasury rate plus a spread (Level 2 of the fair value hierarchy). Included in other long-term liabilities with the current portion included in accrued expenses. ​ Assets and Liabilities Measured at Fair Value on a Recurring Basis ​ The following table presents the assets and liabilities that are measured at fair value on a recurring basis: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ ​ ​ ​ ​ ​ Fair Value Measurements Using ​ ​ ​ ​ ​ ​ Quoted Prices Significant Significant ​ ​ ​ ​ ​ In Active ​ Observable ​ Unobservable ​ ​ ​ ​ ​ ​ Markets ​ Inputs ​ Inputs ​ ​ ​ Total (Level 1) (Level 2) (Level 3) ​ ​ (in thousands) ​ Assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds (1) ​ $ 34,201 ​ $ 34,201 ​ $ — ​ $ — ​ Equity, bond, and money market mutual funds held in trust related to the Voluntary Savings Plan (2) ​ 2,955 ​ 2,955 ​ — ​ — ​ ​ ​ $ 37,156 ​ $ 37,156 ​ $ — ​ $ — ​ Liabilities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Interest rate swaps (3) ​ $ 1,622 ​ $ — ​ $ 1,622 ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ ​ ​ ​ ​ ​ Fair Value Measurements Using ​ ​ ​ ​ ​ ​ Quoted Prices Significant Significant ​ ​ ​ ​ ​ In Active ​ Observable ​ Unobservable ​ ​ ​ ​ ​ ​ Markets ​ Inputs ​ Inputs ​ ​ ​ Total (Level 1) (Level 2) (Level 3) ​ ​ ​ (in thousands) ​ Assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds (1) ​ $ 20,540 ​ $ 20,540 ​ $ — ​ $ — ​ Equity, bond, and money market mutual funds held in trust related to the Voluntary Savings Plan (2) ​ 2,427 ​ 2,427 ​ — ​ — ​ ​ ​ $ 22,967 ​ $ 22,967 ​ $ — ​ $ — ​ Liabilities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Interest rate swaps (3) ​ $ 563 ​ $ — ​ $ 563 ​ $ — ​ ​ ​ (1) Included in cash and cash equivalents. (2) Nonqualified deferred compensation plan investments consist of U.S. and international equity mutual funds, government and corporate bond mutual funds, and money market funds which are held in a trust with a third-party brokerage firm. Included in other long-term assets, with a corresponding liability reported within other long-term liabilities. (3) Included in other long-term liabilities. The fair values of the interest rate swaps were determined by discounting future cash flows and receipts based on expected interest rates observed in market interest rate curves adjusted for estimated credit valuation considerations reflecting nonperformance risk of the Company and the counterparty, which are considered to be in Level 3 of the fair value hierarchy. The Company assessed Level 3 inputs as insignificant to the valuation at December 31, 2020 and December 31, 2019 and considers the interest rate swap valuations in Level 2 of the fair value hierarchy. ​ ​ Assets Measured at Fair Value on a Nonrecurring Basis ​ There were no assets remeasured on a nonrecurring basis at December 31, 2020. The following table presents the fair value of assets remeasured on a nonrecurring basis as of December 31, 2019. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ ​ ​ ​ Nonrecurring Fair Value Remeasurements ​ ​ ​ Significant ​ ​ ​ ​ ​ ​ Unobservable Inputs ​ Total ​ ​ ​ ​ (Level 3) Losses ​ ​ ​ (in thousands) ​ Assets: ​ ​ ​ ​ ​ ​ ​ ​ Goodwill (1) ​ $ 83,842 ​ $ (20,000) ​ ​ Long-lived assets (2) ​ 6,805 ​ (6,514) ​ ​ ​ ​ $ 90,647 ​ $ (26,514) ​ ​ (1) A portion of the goodwill within the ArcBest segment was reduced to its implied fair value as of October 1, 2019 (see Note D). (2) Represents fair value of the dedicated asset group within the ArcBest segment. Losses include write-downs of $6.0 million related to customer relationship intangibles (see Note D) and $0.5 million related to revenue equipment within the dedicated asset group included in the ArcBest segment reducing the carrying amounts to implied fair value as of October 1, 2019.

GOODWILL AND INTANGIBLE ASSETS

GOODWILL AND INTANGIBLE ASSETS	12 Months Ended
	Dec. 31, 2020
GOODWILL AND INTANGIBLE ASSETS
GOODWILL AND INTANGIBLE ASSETS	NOTE D – GOODWILL AND INTANGIBLE ASSETS ​ Goodwill by reportable operating segment consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total ArcBest FleetNet ​ ​ (in thousands) Balances at December 31, 2018 ​ $ 108,320 ​ $ 107,690 ​ $ 630 ​ Goodwill impairment (1) ​ ​ (20,000) ​ ​ (20,000) ​ ​ — ​ Balances at December 31, 2019 and 2020 (2) ​ $ 88,320 ​ $ 87,690 ​ $ 630 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Accumulated impairment at December 31, 2019 and 2020 ​ $ (20,000) ​ $ (20,000) ​ $ — ​ (1) Goodwill impairment charge related to the ArcBest segment further described within this Note. (2) Goodwill was not adjusted during the year ended December 31, 2020. ​ The annual impairment evaluation of the goodwill balance of the domestic freight reporting unit, which includes the Company’s expedite, truckload, and dedicated operations, was performed as of October 1, 2020 and it was determined that there was no impairment of the recorded balance. In making this analysis, management considered current and forecasted business levels and estimated future cash flows over several years. Management’s assumptions include a continuing economic recovery into 2021. The goodwill balance for each of the other reporting units was assessed qualitatively and it was determined that it was more likely than not that there was no impairment of goodwill as of the assessment date. Furthermore, as of December 31, 2020, no indicators of impairment were identified. ​ As of the October 1, 2019 annual impairment testing, it was determined that the recorded balances of the domestic freight reporting unit within the ArcBest segment exceeded the estimated fair value of the reporting unit. As a result, the Company recorded a noncash goodwill impairment charge of $20.0 million, which was recognized in “Asset impairment” within the ArcBest segment operating expenses for the year ended December 31, 2019. It was also determined that potential impairment indicators existed and an impairment test of the asset groups, including the Company’s finite-lived intangible assets was performed as of October 1, 2019. The Company recorded a noncash impairment charge of $6.5 million, which was recognized in “Asset impairment” within the ArcBest segment operating expenses for the year ended December 31, 2019 to record the asset group at fair value. Approximately $6.0 million of the impairment was related to customer relationships and an additional $0.5 million was related to revenue equipment. The impairment resulted primarily from underperformance of the truckload and dedicated businesses within the domestic freight reporting unit of the ArcBest segment during 2019. Economic conditions during 2019, including lack of growth in the industrial and manufacturing sectors, tariff impacts of international trade, and higher customer inventory levels, contributed to uncertainty on projected shipment levels for purposes of these accounting assessments. ​ Intangible assets consisted of the following as of December 31: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ 2019 ​ ​ Weighted-Average ​ ​ ​ ​ Accumulated ​ Net ​ ​ ​ ​ Accumulated ​ Net ​ Amortization Period Cost Amortization Value ​ Cost Amortization Value ​ ​ (in years) ​ (in thousands) ​ (in thousands) Finite-lived intangible assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Customer relationships 14 ​ $ 52,721 ​ $ 30,477 ​ $ 22,244 ​ $ 52,721 ​ $ 26,667 ​ $ 26,054 ​ Other ​ 13 ​ ​ 980 ​ ​ 543 ​ ​ 437 ​ ​ 1,294 ​ ​ 816 ​ ​ 478 ​ ​ 14 ​ 53,701 ​ 31,020 ​ 22,681 ​ ​ 54,015 ​ 27,483 ​ 26,532 ​ Indefinite-lived intangible assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Trade name N/A ​ 32,300 ​ N/A ​ 32,300 ​ ​ 32,300 ​ N/A ​ 32,300 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total intangible assets N/A ​ $ 86,001 ​ $ 31,020 ​ $ 54,981 ​ $ 86,315 ​ $ 27,483 ​ $ 58,832 ​ ​ ​ The annual impairment evaluation of indefinite-lived intangible assets was performed as of October 1, 2020 and it was determined that there was no impairment of the recorded balances. ​ The future amortization for intangible assets acquired through business acquisitions as of December 31, 2020 were as follows: ​ ​ ​ ​ ​ ​ ​ Amortization of ​ ​ Intangible Assets ​ ​ ​ (in thousands) ​ 2021 ​ $ 3,838 ​ 2022 ​ 3,815 ​ 2023 ​ 3,722 ​ 2024 ​ 3,689 ​ 2025 ​ ​ 3,674 ​ Thereafter ​ ​ 3,943 ​ Total amortization ​ $ 22,681 ​ ​

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2020
INCOME TAXES
INCOME TAXES	NOTE E – INCOME TAXES ​ On December 22, 2017, H.R. 1/Public Law 115-97 which includes tax legislation titled Tax Cuts and Jobs Act ​ In addition to the effect on net deferred tax liabilities, the Company recorded a reduction in current income tax expense of $0.1 million at December 31, 2018, as a result of the Tax Reform Act, to reflect the Company’s application of a blended rate due to the use of a fiscal year rather than a calendar year for U.S. income tax filing. Because the Company’s fiscal tax year included the effective date of the rate change under the Tax Reform Act, taxes are required to be calculated by applying a blended rate to the taxable income for the tax year ending February 28, 2018. The blended rate is calculated based on the ratio of days in the fiscal tax year prior to and after the effective date of the rate change. In computing total tax expense for the twelve months ended December 31, 2018, a federal blended rate of 32.74% was applied to the two months ended February 28, 2018, and a 21.0% federal statutory rate was applied to the ten months ended December 31, 2018. ​ The Tax Reform Act made many other changes in the tax law applicable to corporations, including the one-time transition tax on earnings of foreign subsidiaries, the tax on global intangible low-taxed income, and the tax on base erosion payments. At December 31, 2020, the Company has determined these provisions of the Tax Reform Act will not have a significant impact on the Company’s consolidated financial statements. ​ Additional tax law changes occurred in December 2019 which had an impact on the 2019 tax provision. The nature and effect of these 2019 changes are described in the reconciliation of the effective tax rate and the statutory tax rate below. ​ Significant components of the provision or benefit for income taxes for the years ended December 31 were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 2019 2018 (1) ​ ​ (in thousands) Current provision: ​ ​ ​ ​ Federal ​ $ 10,001 ​ $ 2,202 ​ $ 9,750 ​ State ​ 3,267 ​ 1,813 ​ 3,264 ​ Foreign ​ 413 ​ 2,060 ​ 2,238 ​ ​ ​ 13,681 ​ 6,075 ​ 15,252 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Deferred provision (benefit): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Federal ​ 5,948 ​ 4,196 ​ 1,157 ​ State ​ 1,789 ​ 1,221 ​ 737 ​ Foreign ​ (22) ​ (6) ​ (22) ​ ​ ​ 7,715 ​ 5,411 ​ 1,872 ​ Total provision for income taxes ​ $ 21,396 ​ $ 11,486 ​ $ 17,124 ​ (1) For 2018, the income tax provision reflects the impact of the Tax Reform Act, as previously disclosed in this Note. ​ Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Components of the deferred tax provision or benefit for the years ended December 31, were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 (1) ​ 2019 (1) ​ 2018 (1)(2) ​ ​ (in thousands) Amortization, depreciation, and basis differences for property, plant and equipment and other long-lived assets $ 4,975 $ 16,255 $ 23,153 ​ Amortization of intangibles and impairment ​ 183 ​ (6,933) ​ (763) ​ Changes in reserves for workers’ compensation, third-party casualty, and cargo claims ​ (182) ​ (1,880) ​ 469 ​ Revenue recognition ​ (1,481) ​ (1,437) ​ (2,524) ​ Allowance for doubtful accounts ​ (652) ​ 541 ​ (115) ​ Nonunion pension and other retirement plans ​ 957 ​ 564 ​ (2,810) ​ Multiemployer pension fund withdrawal (3) ​ ​ 157 ​ ​ 150 ​ ​ (5,818) ​ Federal and state net operating loss carryforwards utilized (generated) ​ (259) ​ 59 ​ 746 ​ State depreciation adjustments ​ 343 ​ (1,302) ​ (1,761) ​ Share-based compensation ​ (195) ​ (709) ​ (529) ​ Valuation allowance increase (decrease) ​ 617 ​ 383 ​ (744) ​ Other accrued expenses ​ 1,663 ​ (699) ​ (4,881) ​ Impact of the Tax Reform Act (2) ​ ​ — ​ ​ — ​ ​ (3,772) ​ Prepaid expenses ​ ​ 1,207 ​ ​ 1,782 ​ ​ 1,313 ​ Operating lease right-of-use assets/liabilities – net (4) ​ ​ (13) ​ ​ (1,049) ​ ​ — ​ Other ​ 395 ​ (314) ​ (92) ​ Deferred tax provision ​ $ 7,715 ​ $ 5,411 ​ $ 1,872 ​ (1) The components of the deferred tax provision reflect the statutory U.S. income tax rate in effect for the applicable year, which is a blended rate for 2018 (as previously discussed within this Note), and 21% for 2019 and 2020. (2) For 2018, the effect of the change in the U.S. corporate tax rate from 35% to 21% in accordance with the Tax Reform Act is reflected as a separate component of the deferred tax provision. (3) ABF Freight recorded a multiemployer pension fund withdrawal liability in 2018 resulting from the transition agreement it entered into with the New England Pension Fund (see Note I). (4) Net change in operating lease right-of-use deferred tax assets and liabilities recorded due to the adoption of ASC Topic 842 in 2019. ​ Significant components of the deferred tax assets and liabilities at December 31 were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ 2019 ​ ​ (in thousands) Deferred tax assets: ​ ​ ​ Accrued expenses ​ $ 40,502 ​ $ 41,757 ​ Operating lease liabilities (1) ​ ​ 33,933 ​ ​ 19,726 ​ Supplemental pension liabilities ​ ​ 103 ​ ​ 1,091 ​ Multiemployer pension fund withdrawal (2) ​ ​ 5,409 ​ ​ 5,546 ​ Postretirement liabilities other than pensions ​ 4,871 ​ 5,359 ​ Share-based compensation ​ 5,827 ​ 5,605 ​ Federal and state net operating loss carryovers ​ 1,353 ​ 1,093 ​ Revenue recognition ​ ​ 1,426 ​ ​ — ​ Other ​ 1,297 ​ 1,538 ​ Total deferred tax assets ​ 94,721 ​ 81,715 ​ Valuation allowance ​ (1,284) ​ (668) ​ Total deferred tax assets, net of valuation allowance ​ 93,437 ​ 81,047 ​ ​ ​ ​ ​ ​ ​ ​ ​ Deferred tax liabilities: ​ ​ ​ ​ ​ ​ ​ Amortization, depreciation, and basis differences for property, plant and equipment, and other long-lived assets ​ 113,092 ​ 107,835 ​ Operating lease right-of-use assets (1) ​ ​ 32,923 ​ ​ 18,703 ​ Intangibles ​ 7,520 ​ 7,373 ​ Revenue recognition ​ — ​ 669 ​ Prepaid expenses ​ 6,151 ​ 4,952 ​ Total deferred tax liabilities ​ 159,686 ​ 139,532 ​ Net deferred tax liabilities ​ $ (66,249) ​ $ (58,485) ​ (1) Operating lease right-of-use assets and liabilities were recorded in 2019 due to the adoption of ASC Topic 842. (2) ABF Freight recorded a multiemployer pension fund withdrawal liability in 2018 resulting from the transition agreement it entered into with the New England Pension Fund (see Note I). ​ Reconciliation between the effective income tax rate, as computed on income before income taxes, and the statutory federal income tax rate for the years ended December 31 is presented in the following table: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 (1) ​ 2019 (1) ​ 2018 (1) ​ ​ (in thousands, except percentages) Income tax provision at the statutory federal rate $ 19,424 $ 10,809 $ 17,721 ​ Federal income tax effects of: ​ ​ ​ ​ ​ ​ ​ ​ ​ State income taxes ​ (1,062) ​ (637) ​ (840) ​ Nondeductible expenses ​ 1,395 ​ 1,344 ​ 1,682 ​ Life insurance proceeds and changes in cash surrender value ​ (488) ​ (775) ​ 7 ​ Alternative fuel credit ​ (1,261) ​ (2,340) ​ (1,203) ​ Net increase (decrease) in valuation allowances ​ 617 ​ 382 ​ (891) ​ Net increase (decrease) in uncertain tax positions ​ ​ (933) ​ ​ (20) ​ ​ 933 ​ Settlement of share-based compensation ​ ​ 420 ​ ​ 388 ​ ​ (649) ​ Impact of the Tax Reform Act on current tax (1) ​ ​ — ​ ​ — ​ ​ (52) ​ Impact of the Tax Reform Act on deferred tax (1) ​ ​ — ​ ​ — ​ ​ (3,772) ​ Nonunion pension termination expense ​ ​ — ​ ​ 1,040 ​ ​ — ​ Foreign tax credits generated ​ ​ (391) ​ ​ (2,054) ​ ​ (2,216) ​ Federal research and development tax credits ​ ​ (2,078) ​ ​ (1,354) ​ ​ — ​ Other ​ 306 ​ (385) ​ 187 ​ Federal income tax provision ​ 15,949 ​ 6,398 ​ 10,907 ​ State income tax provision ​ 5,056 ​ 3,034 ​ 4,001 ​ Foreign income tax provision ​ 391 ​ 2,054 ​ 2,216 ​ Total provision for income taxes ​ $ 21,396 ​ $ 11,486 ​ $ 17,124 ​ Effective tax rate ​ 23.1 % 22.3 % 20.3 % (1) Amounts in this reconciliation reflect the statutory U.S. income tax rate in effect for the applicable year after the enactment of the Tax Reform Act, which is 21% . The effect of applying a blended rate of 32.74% for the two months ended February 28, 2018, in accordance with the Tax Reform Act, is reflected in separate components of the reconciliation. ​ Income taxes paid, excluding income tax refunds, totaled $28.6 million, $28.1 million, and $21.8 million in 2020, 2019, and 2018, respectively. Income tax refunds totaled $13.3 million, $13.1 million, and $18.5 million in 2020, 2019, and 2018, respectively. ​ Under ASC Topic 718, Compensation – Stock Compensation ​ At December 31, 2020, the Company had gross federal net operating loss carryforwards of $1.3 million. The use of these net operating loss carryforwards is limited by Section 382 of the Internal Revenue Code (“IRC”). Of the total amount, $1.0 million will expire if not used within five years ; however, it is not expected that the Section 382 limitation will result in the expiration of these net operating loss carryforwards prior to their availability under Section 382. The remaining $0.3 million will expire in 10 years if not used. Due to taxable losses for three prior tax years for the business to which this amount relates, a valuation allowance of $0.1 million for these federal net operating losses was established at December 31, 2020. ​ At December 31, 2020, the Company had total gross state net operating losses of $18.4 million. Gross state net operating losses of $5.3 million are from the acquisition of Panther and relate to periods ending on or prior to June 15, 2012. State carryforward periods for the remaining Panther net operating losses vary from 10 to 20 years . Gross state net operating losses of $11.6 million are for subsidiaries that have had taxable losses for three prior tax years or have other nexus issues that reduce the likelihood of the utilization of the losses. A valuation allowance of $0.6 million was established for these state net operating losses at December 31, 2020. Also due to three -year taxable losses and nexus issues, state tax credit carryforwards of $0.2 million were fully reserved by a valuation allowance of $0.2 million at December 31, 2020. The unused state tax credits have a carryforward period of 20 years . ​ As the Canadian tax rate is now higher than the U.S. tax rate, it is unlikely that foreign tax credit carryforwards will be useable, as U.S. taxes paid will be at a lower rate than the tax rates in Canada. Thus, the foreign tax credit carryover is fully reserved, resulting in valuation allowances of $0.4 million and $0.7 million at December 31, 2020 and 2019, respectively. ​ Consolidated federal income tax returns filed for tax years through 2016 are closed by the applicable statute of limitations. The Company is under examination by one state taxing authority at December 31, 2020. The Company is not under examination by foreign taxing authorities at December 31, 2020. ​ At December 31, 2019 and 2018, the Company had reserves for uncertain tax positions of $0.9 million and $1.0 million, respectively. These reserves related to credits taken on federal returns and were fully removed upon the expiration of the statute of limitations in the first quarter of 2020 and the fourth quarter of 2019, respectively. No reserve for uncertain tax positions remained at December 31, 2020. ​ For 2020, 2019, and 2018, interest paid or accrued related to foreign and state income taxes was immaterial.

LEASES

LEASES	12 Months Ended
	Dec. 31, 2020
Leases
LEASES	​ NOTE F – LEASES ​ The Company leases, under finance and operating lease arrangements, certain facilities used primarily in the Asset-Based segment service center operations, certain revenue equipment used in the ArcBest segment operations, and certain other office equipment. Current operating leases have remaining terms of less than 12.1 years, some of which include one or more options to renew, with renewal option terms up to five years . There are no available termination options as of December 31, 2020. The right-of-use assets and lease liabilities as of December 31, 2020 and 2019 do not assume the option to early terminate any of the Company’s leases, and all renewal options that have been exercised or are reasonably certain to be exercised as of December 31, 2020 and 2019 are included in the right-of-use assets and lease liabilities. Variable lease cost for operating leases consists of subsequent changes in CPI index, rent payments that are based on usage, and other lease related payments which are subject to change and not considered fixed payments. All fixed lease and non-lease component payments are combined in determining the right-of-use asset and lease liability. ​ The components of operating lease expense were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31 ​ 2020 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) Operating lease expense ​ $ 24,559 ​ $ 22,291 ​ Variable lease expense ​ ​ 3,152 ​ ​ 3,366 ​ Sublease income ​ ​ (398) ​ ​ (324) ​ ​ ​ ​ ​ ​ ​ ​ ​ Total operating lease expense (1) ​ $ 27,313 ​ $ 25,333 ​ (1) Operating lease expense excludes short-term leases with a term of 12 months or less. ​ Rental expense for operating leases, excluding expenses related to leases with initial terms of less than one year, totaled $20.5 million, net of sublease income, for 2018. ​ The operating cash flows from operating lease activity were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31 ​ ​ ​ 2020 ​ 2019 ​ ​ ​ (in thousands) ​ Noncash change in operating right-of-use assets ​ $ 21,184 ​ $ 20,439 ​ Change in operating lease liabilities ​ ​ (20,428) ​ ​ (19,711) ​ Operating right-of-use-assets and lease liabilities, net ​ $ 756 ​ $ 728 ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash paid for amounts included in the measurement of operating lease liabilities ​ $ (23,810) ​ $ (21,714) ​ ​ Supplemental balance sheet information related to operating leases was as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ ​ (in thousands, except lease term and discount rate) ​ ​ ​ ​ ​ Land and ​ Equipment ​ ​ ​ Total ​ Structures ​ and Others Operating right-of-use assets (long-term) ​ $ 115,195 ​ $ 114,908 ​ $ 287 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Operating lease liabilities (current) ​ $ 21,482 ​ $ 21,207 ​ $ 275 Operating lease liabilities (long-term) ​ 97,839 ​ ​ 97,828 ​ ​ 11 Total operating lease liabilities ​ $ 119,321 ​ $ 119,035 ​ $ 286 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average remaining lease term (in years) ​ ​ 6.7 ​ ​ ​ ​ ​ ​ Weighted-average discount rate ​ ​ 3.18% ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ ​ ​ (in thousands, except lease term and discount rate) ​ ​ ​ ​ ​ ​ Land and ​ Equipment ​ ​ ​ ​ Total ​ Structures ​ and Others ​ Operating right-of-use assets (long-term) ​ $ 68,470 ​ $ 67,227 ​ $ 1,243 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Operating lease liabilities (current) ​ $ 20,265 ​ $ 19,293 ​ $ 972 ​ Operating lease liabilities (long-term) ​ 52,277 ​ ​ 52,008 ​ ​ 269 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total operating lease liabilities ​ $ 72,542 ​ $ 71,301 ​ $ 1,241 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average remaining lease term (in years) ​ ​ 5.3 ​ ​ ​ ​ ​ ​ ​ Weighted-average discount rate ​ ​ 3.77% ​ ​ ​ ​ ​ ​ ​ ​ Maturities of operating lease liabilities at December 31, 2020 were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Equipment ​ ​ ​ ​ ​ ​ Land and ​ and ​ ​ Total Structures Other ​ (in thousands) ​ 2021 ​ $ 24,629 ​ $ 24,352 ​ $ 277 ​ 2022 ​ 21,073 ​ 21,062 ​ 11 ​ 2023 ​ 16,755 ​ 16,755 ​ — ​ 2024 ​ 14,668 ​ 14,668 ​ — ​ 2025 ​ 12,153 ​ 12,153 ​ — ​ Thereafter ​ 43,035 ​ 43,035 ​ — ​ Total lease payments ​ ​ 132,313 ​ ​ 132,025 ​ ​ 288 ​ Less imputed interest ​ ​ (12,992) ​ ​ (12,990) ​ ​ (2) ​ Total ​ $ 119,321 ​ $ 119,035 ​ $ 286 ​ ​

LONG-TERM DEBT AND FINANCING AR

LONG-TERM DEBT AND FINANCING ARRANGEMENTS	12 Months Ended
	Dec. 31, 2020
LONG-TERM DEBT AND FINANCING ARRANGEMENTS
LONG-TERM DEBT AND FINANCING ARRANGEMENTS	​ ​ NOTE G – LONG-TERM DEBT AND FINANCING ARRANGEMENTS ​ Long-Term Debt Obligations ​ Long-term debt consisted of borrowings outstanding under the Company’s revolving credit facility and accounts receivable securitization program, both of which are further described in Financing Arrangements within this Note, and notes payable and finance lease obligations related to the financing of revenue equipment (tractors and trailers used primarily in Asset-Based segment operations), certain other equipment, and software as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31 ​ December 31 ​ ​ 2020 2019 ​ ​ (in thousands) ​ Credit Facility (interest rate of 1.3% (1) ​ $ 70,000 ​ $ 70,000 ​ Accounts receivable securitization borrowings ​ — ​ 40,000 ​ Notes payable (weighted-average interest rate of 3.0% at December 31, 2020) ​ 214,216 ​ 213,504 ​ Finance lease obligations (weighted-average interest rate of 3.3% at December 31, 2020) ​ 8 ​ 15 ​ ​ ​ 284,224 ​ 323,519 ​ Less current portion ​ 67,105 ​ 57,305 ​ Long-term debt, less current portion ​ $ 217,119 ​ $ 266,214 ​ (1) The interest rate swap mitigates interest rate risk by effectively converting $50.0 million of borrowings under the Credit Facility from variable-rate interest to fixed-rate interest with a per annum rate of 3.12% and 2.98% based on the margin of the Credit Facility as of December 31, 2020 and 2019, respectively. ​ Scheduled maturities of long term debt obligations as of December 31, 2020 were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Credit Notes Finance Lease ​ ​ ​ Total ​ Facility (1) ​ Payable ​ Obligations ​ ​ ​ (in thousands) ​ 2021 ​ $ 73,386 ​ $ 886 ​ $ 72,493 ​ $ 7 ​ 2022 ​ 64,750 ​ 914 ​ ​ 63,835 ​ 1 ​ 2023 ​ 48,892 ​ 971 ​ ​ 47,921 ​ — ​ 2024 ​ 102,393 ​ 70,823 ​ ​ 31,570 ​ — ​ 2025 ​ 9,576 ​ ​ — ​ ​ 9,576 ​ ​ — ​ Thereafter ​ — ​ ​ — ​ ​ — ​ ​ — ​ Total payments ​ 298,997 ​ 73,594 ​ ​ 225,395 ​ 8 ​ Less amounts representing interest ​ 14,773 ​ 3,594 ​ 11,179 ​ — ​ Long-term debt ​ $ 284,224 ​ $ 70,000 ​ $ 214,216 ​ $ 8 ​ (1) The future interest payments included in the scheduled maturities due are calculated using variable interest rates based on the LIBOR swap curve, plus the anticipated applicable margin. ​ ​ Assets securing notes payable or held under finance leases at December 31 were included in property, plant and equipment as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 2019 ​ ​ (in thousands) Revenue equipment $ 326,823 $ 265,315 ​ Software ​ ​ — ​ ​ 2,140 ​ Service, office, and other equipment ​ ​ 26,270 ​ ​ 26,344 ​ Total assets securing notes payable or held under finance leases ​ 353,093 ​ 293,799 ​ Less accumulated depreciation and amortization (1) ​ 115,424 ​ 71,405 ​ Net assets securing notes payable or held under finance leases ​ $ 237,669 ​ $ 222,394 ​ (1) Amortization of assets held under finance leases and depreciation of assets securing notes payable are included in depreciation expense. ​ The Company’s long-term debt obligations have a weighted-average interest rate of 2.9% at December 31, 2020. The Company paid interest of $11.3 million, $10.9 million, and $8.7 million in 2020, 2019, and 2018, respectively, net of capitalized interest which totaled $0.3 million for 2020 and $0.2 million for 2019 and 2018. ​ Financing Arrangements ​ Credit Facility The Company has a revolving credit facility (the “Credit Facility”) under its Third Amended and Restated Credit Agreement (the “Credit Agreement”) with an initial maximum credit amount of $250.0 million, including a swing line facility in an aggregate amount of up to $25.0 million and a letter of credit sub-facility providing for the issuance of letters of credit up to an aggregate amount of $20.0 million. The Company may request additional revolving commitments or incremental term loans thereunder up to an aggregate amount of up to $125.0 million, subject to certain additional conditions as provided in the Credit Agreement. The Company borrowed an additional $180.0 million under the Credit Facility in March 2020 as a precautionary measure to preserve financial flexibility during the COVID-19 pandemic, and repaid the borrowing during the third quarter of 2020. As of December 31, 2020, the Company had available borrowing capacity of $180.0 million under the initial maximum credit amount of the Credit Facility. ​ Principal payments under the Credit Facility are due upon maturity of the facility on October 1, 2024; however, borrowings may be repaid, at the Company’s discretion, in whole or in part at any time, without penalty, subject to required notice periods and compliance with minimum prepayment amounts. Borrowings under the Credit Agreement can either be, at the Company’s election: (i) at an Alternate Base Rate (as defined in the Credit Agreement) plus a spread; or (ii) at a Eurodollar Rate (as defined in the Credit Agreement) plus a spread. The applicable spread is dependent upon the Company’s Adjusted Leverage Ratio (as defined in the Credit Agreement). The Credit Agreement contains conditions, representations and warranties, events of default, and indemnification provisions that are customary for financings of this type, including, but not limited to, a minimum interest coverage ratio, a maximum adjusted leverage ratio, and limitations on incurrence of debt, investments, liens on assets, certain sale and leaseback transactions, transactions with affiliates, mergers, consolidations, purchases and sales of assets, and certain restricted payments. The Company was in compliance with the covenants under the Credit Agreement at December 31, 2020. ​ Interest Rate Swaps The Company has an interest rate swap agreement with a $50.0 million notional amount which started on January 2, 2020 and will mature on June 30, 2022. The Company receives floating - rate interest amounts based on one-month LIBOR in exchange for fixed-rate interest payments of 1.99% over the life of the agreement. The interest rate swap mitigates interest rate risk by effectively converting $50.0 million of borrowings under the Credit Facility from variable - rate interest to fixed - rate interest with a per annum rate of 3.12% based on the margin of the Credit Facility as of December 31, 2020. The fair value of the interest rate swap of $1.4 million and $0.6 million was recorded in other long-term liabilities in the consolidated balance sheet at December 31, 2020 and 2019, respectively. The Company had a five-year interest rate swap agreement with a $50.0 million notional amount that matured on January 2, 2020 for which less than $0.1 million was recorded in other long-term liabilities in the consolidated balance sheet at December 31, 2019. ​ On May 4, 2020, the Company extended the term of its $50.0 million notional amount interest rate swap agreement from June 30, 2022 to October 1, 2024. The Company will receive floating-rate interest amounts based on one-month LIBOR in exchange for fixed-rate interest payments of 0.43% beginning on June 30, 2022 throughout the remaining term of the agreement. From June 30, 2022 to October 1, 2024, the extended interest rate swap agreement will effectively convert $50.0 million of borrowings under the Credit Facility from variable-rate interest to fixed-rate interest with a per annum rate of 1.56% based on the margin of the Credit Facility as of December 31, 2020. The fair value of the interest rate swap of $0.2 million was recorded in other long-term liabilities in the consolidated balance sheet at December 31, 2020. ​ The unrealized loss on the interest rate swap instruments was reported as a component of accumulated other comprehensive income, net of tax, in stockholders’ equity at December 31, 2020 and 2019, and the change in the unrealized loss on the interest rate swaps for the years ended December 31, 2020 and 2019 was reported in other comprehensive income, net of tax, in the consolidated statements of comprehensive income. The interest rate swaps are subject to certain customary provisions that could allow the counterparty to request immediate settlement of the fair value liability or asset upon violation of any or all of the provisions. The Company was in compliance with all provisions of the interest rate swap agreements at December 31, 2020. ​ Accounts Receivable Securitization Program The Company’s accounts receivable securitization program, which matures on October 1, 2021, allows for cash proceeds of $125.0 million to be provided under the program and has an accordion feature allowing the Company to request additional borrowings up to $25.0 million, subject to certain conditions. As of December 31, 2019, $40.0 million was borrowed under the program. The Company borrowed an additional $45.0 million under the program in March 2020 as a precautionary measure to preserve financial flexibility during the COVID-19 pandemic, and repaid the outstanding balance of $85.0 million during the third quarter of 2020. ​ Under this program, certain subsidiaries of the Company continuously sell a designated pool of trade accounts receivables to a wholly owned subsidiary which, in turn, may borrow funds on a revolving basis. This wholly owned consolidated subsidiary is a separate bankruptcy-remote entity, and its assets would be available only to satisfy the claims related to the lender’s interest in the trade accounts receivables. Borrowings under the accounts receivable securitization program bear interest based upon LIBOR, plus a margin, and an annual facility fee. The securitization agreement contains representations and warranties, affirmative and negative covenants, and events of default that are customary for financings of this type, including a maximum adjusted leverage ratio covenant. The Company was in compliance with the covenants under the accounts receivable securitization program at December 31, 2020. ​ The accounts receivable securitization program includes a provision under which the Company may request and the letter of credit issuer may issue standby letters of credit, primarily in support of workers’ compensation and third-party casualty claims liabilities in various states in which the Company is self-insured. The outstanding standby letters of credit reduce the availability of borrowings under the program. As of December 31, 2020, standby letters of credit of $11.7 million have been issued under the program, which reduced the available borrowing capacity to $113.3 million. ​ Letter of Credit Agreements and Surety Bond Programs As of December 31, 2020 and 2019, the Company had letters of credit outstanding of $12.3 million and $12.8 million, respectively, (including $11.7 million and $12.2 million, respectively, issued under the accounts receivable securitization program). The Company has programs in place with multiple surety companies for the issuance of surety bonds in support of its self-insurance program. As of December 31, 2020 and 2019, surety bonds outstanding related to the self-insurance program totaled $61.7 million and $62.3 million, respectively. ​ Notes Payable The Company has financed the purchase of certain revenue equipment, other equipment, and software through promissory note arrangements, including $61.8 million and $90.8 million for revenue equipment and other equipment during the year ended December 31, 2020 and 2019, respectively.

ACCRUED EXPENSES

ACCRUED EXPENSES	12 Months Ended
	Dec. 31, 2020
ACCRUED EXPENSES
ACCRUED EXPENSES	NOTE H – ACCRUED EXPENSES ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31 ​ ​ 2020 2019 ​ ​ ​ (in thousands) ​ Workers’ compensation, third-party casualty, and loss and damage claims reserves ​ $ 103,898 ​ $ 107,149 ​ Accrued vacation pay ​ 51,728 ​ 47,730 ​ Accrued compensation, including retirement benefits (1) ​ ​ 67,690 ​ ​ 52,720 ​ Taxes other than income ​ 10,468 ​ 8,722 ​ Other ​ 12,962 ​ 16,000 ​ Total accrued expenses ​ $ 246,746 ​ $ 232,321 ​ (1) Certain reclassifications have been made to the prior period accrued expenses in this table to conform to the current year presentation. There was no impact on total current liabilities as a result of the reclassifications. Current portion of pension and postretirement liabilities previously presented in a separate line in the consolidated balance sheets have been reclassed to “Accrued compensation, including retirement benefits” to conform to the current year presentation of accrued expenses. ​ ​

EMPLOYEE BENEFIT PLANS 10K

EMPLOYEE BENEFIT PLANS 10K	12 Months Ended
	Dec. 31, 2020
EMPLOYEE BENEFIT PLANS
EMPLOYEE BENEFIT PLANS	NOTE I – EMPLOYEE BENEFIT PLANS ​ Nonunion Defined Benefit Pension, Supplemental Benefit, and Postretirement Health Benefit Plans ​ The Company had a noncontributory defined benefit pension plan covering substantially all noncontractual employees hired before January 1, 2006. In June 2013, the Company amended the nonunion defined benefit pension plan to freeze the participants’ final average compensation and years of credited service as of July 1, 2013. The amendment resulted in a plan curtailment and eliminated the service cost of the plan. The plan amendment did not impact the vested benefits of retirees or former employees whose benefits had not yet been paid from the plan. ​ In November 2017, an amendment was executed to terminate the nonunion defined benefit pension plan with a termination date of December 31, 2017. In September 2018, the plan received a favorable determination letter from the IRS regarding qualification of the plan termination. The plan began distributing immediate lump sum benefit payments related to the plan termination in fourth quarter 2018 and continued making these distributions during 2019. The plan purchased a nonparticipating annuity contract from an insurance company during 2019 to settle the pension obligation related to the vested benefits of plan participants and beneficiaries who were either receiving monthly benefit payments at the time of the contract purchase or who did not elect to receive a lump sum benefit upon plan termination. The remaining benefit obligation for the vested benefits of plan participants who could not be located for payment was transferred to the Pension Benefit Guaranty Corporation (the “PBGC”). The Company made $7.7 million of tax-deductible cash contributions to the plan in 2019 to fund the plan benefit and expense distributions in excess of plan assets. Termination of the nonunion defined benefit plan was completed in 2019 and the plan was liquidated as of December 31, 2019. ​ The Company recognized ​ The Company also has an unfunded supplemental benefit plan (“SBP”) for the purpose of supplementing benefits under the Company’s nonunion defined benefit pension plan for executive officers designated as participants in the SBP by the Company’s board of directors (the “Board of Directors”). The Compensation Committee of the Board of Directors (“Compensation Committee”) elected to close the SBP to new entrants and to place a cap on the maximum payment per participant to existing participants in the SBP effective January 1, 2006. In place of the SBP, eligible officers of the Company appointed after 2005 participate in a long-term cash incentive plan (see Cash Long-Term Incentive Compensation Plan section within this Note). Effective December 31, 2009, the Compensation Committee elected to freeze the accrual of benefits for remaining participants under the SBP. With the exception of early retirement penalties that may apply in certain cases, the valuation inputs for calculating the frozen SBP benefits to be paid to participants, including final average salary and the interest rate, were frozen at December 31, 2009. As presented in the tables within this Note, pension settlement expense and a corresponding reduction in the net actuarial loss was recorded in 2020 and 2019 related to lump-sum SBP benefit distributions. The SBP did not incur pension settlement expense in 2018. ​ The Company sponsors an insured postretirement health benefit plan that provides supplemental medical benefits and dental and vision benefits primarily to certain officers of the Company and certain subsidiaries. Effective January 1, 2011, retirees began paying a portion of the premiums under the plan according to age and coverage levels. The amendment to the plan to implement retiree premiums resulted in an unrecognized prior service credit which was recorded in accumulated other comprehensive loss and is being amortized over approximately nine years . ​ The following table discloses the changes in benefit obligations and plan assets of the Company’s nonunion defined benefit plans for years ended December 31, the measurement date of the plans: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nonunion Defined ​ Supplemental ​ Postretirement ​ ​ Benefit Pension Plan ​ Benefit Plan ​ Health Benefit Plan ​ 2020 2019 2020 2019 2020 2019 ​ ​ (in thousands) Change in benefit obligations ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Benefit obligations, beginning of year ​ $ — ​ $ 33,373 ​ $ 3,236 ​ $ 3,948 ​ $ 20,630 ​ $ 29,488 ​ Service cost ​ — ​ — ​ — ​ — ​ 187 ​ 320 ​ Interest cost ​ — ​ 624 ​ 9 ​ 39 ​ 576 ​ 1,212 ​ Actuarial (gain) loss (1) ​ — ​ 300 ​ 34 ​ 186 ​ (2,027) ​ (9,542) ​ Benefits paid ​ — ​ (34,297) ​ (2,887) ​ (937) ​ (615) ​ (848) ​ Benefit obligations, end of year ​ — ​ — ​ 392 ​ 3,236 ​ 18,751 ​ 20,630 ​ Change in plan assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value of plan asset, beginning of year ​ — ​ 26,646 ​ — ​ — ​ — ​ — ​ Actual return on plan assets ​ — ​ (59) ​ — ​ — ​ — ​ — ​ Employer contributions ​ — ​ 7,710 ​ 2,887 ​ 937 ​ 615 ​ 848 ​ Benefits paid ​ — ​ (34,297) ​ (2,887) ​ (937) ​ (615) ​ (848) ​ Fair value of plan assets, end of year ​ — ​ — ​ — ​ — ​ — ​ — ​ Funded status at period end ​ $ — ​ $ — ​ $ (392) ​ $ (3,236) ​ $ (18,751) ​ $ (20,630) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Accumulated benefit obligation ​ $ — ​ $ — ​ $ 392 ​ $ 3,236 ​ $ 18,751 ​ $ 20,630 ​ (1) The actuarial gain on the postretirement health benefit plan for 2020 is primarily related to the impact of actuarial assumptions on the valuation of plan costs, including lower health care cost trend rates, partially offset by a decrease in the discount rate used to remeasure the plan obligation at December 31, 2020 versus December 31, 2019. The actuarial gain on the postretirement health benefit plan for 2019 was primarily related to the impact of a lower cost prescription drug plan effective January 1, 2020. ​ Amounts recognized in the consolidated balance sheets at December 31 consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Supplemental ​ Postretirement ​ ​ Benefit Plan ​ Health Benefit Plan ​ 2020 2019 2020 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Current portion of pension and postretirement liabilities ​ $ — ​ $ (2,886) ​ $ (588) ​ $ (686) ​ Pension and postretirement liabilities, less current portion ​ (392) ​ (350) ​ (18,163) ​ (19,944) ​ Liabilities recognized ​ $ (392) ​ $ (3,236) ​ $ (18,751) ​ $ (20,630) ​ ​ The following is a summary of the components of net periodic benefit cost for the Company’s nonunion benefit plans for the years ended December 31: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nonunion Defined ​ Supplemental ​ Postretirement ​ ​ ​ Benefit Pension Plan ​ Benefit Plan ​ Health Benefit Plan ​ ​ 2020 2019 2018 2020 2019 2018 2020 2019 2018 ​ ​ (in thousands) ​ ​ ​ Service cost ​ $ — ​ $ — ​ $ — ​ $ — ​ $ — ​ $ — ​ $ 187 ​ $ 320 ​ $ 366 ​ Interest cost ​ — ​ 624 ​ 4,269 ​ 9 ​ 39 ​ 108 ​ 576 ​ 1,212 ​ 837 ​ Expected return on plan assets ​ — ​ (31) ​ (1,582) ​ — ​ — ​ — ​ — ​ — ​ — ​ Amortization of prior service credit ​ — ​ — ​ — ​ — ​ — ​ — ​ (1) ​ (33) ​ (93) ​ Pension settlement expense (1) ​ — ​ 4,164 ​ 12,925 ​ 89 ​ 370 ​ — ​ — ​ — ​ — ​ Amortization of net actuarial (gain) loss (2) ​ — ​ 260 ​ 2,583 ​ 8 ​ 95 ​ 81 ​ (597) ​ 898 ​ 304 ​ Net periodic benefit cost ​ $ — ​ $ 5,017 ​ $ 18,195 ​ $ 106 ​ $ 504 ​ $ 189 ​ $ 165 ​ $ 2,397 ​ $ 1,414 ​ (1) For 2019, the presentation of pension settlement expense excludes a $4.0 million noncash pension termination expense which is further described within this Note. (2) The Company amortizes actuarial losses over the average remaining active service period of the plan participants and does not use a corridor approach. ​ The following is a summary of the pension settlement distributions and pension settlement expense for the years ended December 31: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nonunion Defined ​ Supplemental ​ ​ Benefit Pension Plan ​ Benefit Plan ​ 2020 2019 (1) 2018 (2) 2020 (3) 2019 (4) 2018 ​ ​ (in thousands, except per share data) Pension settlement distributions ​ $ — ​ $ 33,938 ​ $ 105,279 ​ $ 2,887 ​ $ 937 ​ $ — ​ Pension settlement expense, pre-tax (5) ​ $ — ​ $ 4,164 ​ $ 12,925 ​ $ 89 ​ $ 370 ​ $ — ​ Pension settlement expense per diluted share, net of taxes ​ $ — ​ $ 0.12 ​ $ 0.36 ​ $ — ​ $ 0.01 ​ $ — ​ (1) Pension settlement distributions for 2019 represent $18.4 million of lump-sum benefit distributions, including participant-elected distributions associated with the plan’s termination, a $14.0 million nonparticipating annuity contract purchase, and a $1.5 million transfer of benefit obligations to the PBGC. (2) Pension settlement distributions for 2018 represent lump-sum benefit distributions, including participant-elected distributions associated with the plan’s termination. (3) The 2020 SBP distributions include the portion of a benefit related to an officer retirement that occurred in 2019 which was delayed for six months after retirement in accordance with IRC Section 409A. (4) The 2019 SBP distribution excludes the portion of the benefit related to an officer retirement which was delayed for six months after retirement in accordance with IRC Section 409A. The pension settlement expense related to the delayed distribution was recognized in 2019. (5) For 2019, the presentation of pension settlement expense excludes a $4.0 million noncash pension termination expense which is further described within this Note. ​ Included in accumulated other comprehensive loss at December 31 were the following pre-tax amounts that have not yet been recognized in net periodic benefit cost: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Supplemental ​ Postretirement ​ ​ Benefit Plan ​ Health Benefit Plan ​ 2020 2019 2020 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Unrecognized net actuarial (gain) loss ​ $ 64 ​ $ 127 ​ $ (4,454) ​ $ (3,024) ​ Unrecognized prior service credit ​ — ​ — ​ — ​ (1) ​ Total ​ $ 64 ​ $ 127 ​ $ (4,454) ​ $ (3,025) ​ ​ ​ The discount rate is determined by matching projected cash distributions with appropriate high-quality corporate bond yields in a yield curve analysis. Weighted-average assumptions used to determine nonunion benefit obligations at December 31 were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Supplemental ​ Postretirement ​ ​ Benefit Plan ​ Health Benefit Plan ​ 2020 2019 2020 2019 Discount rate ​ 1.1 % 2.4 % 2.3 % 3.1 % ​ Weighted-average assumptions used to determine net periodic benefit cost for the Company’s nonunion benefit plans for the years ended December 31 were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nonunion Defined ​ Supplemental ​ Postretirement ​ ​ Benefit Pension Plan ​ Benefit Plan ​ Health Benefit Plan ​ 2020 2019 (1) 2018 (2) 2020 2019 2018 2020 2019 2018 Discount rate ​ N/A ​ 3.9 % 3.1 % 2.4 % 3.6 % 2.8 % 3.1 % 4.2 % 3.5 % Expected return on plan assets ​ N/A ​ 1.4 % 1.4 % N/A N/A N/A N/A N/A N/A ​ (1) The discount rate presented was used to determine the first quarter 2019 expense, and the short-term discount rate established upon quarterly settlements in 2019 of 3.8% and 3.7% , was used to calculate the expense for the second and third quarter of 2019, respectively. The expected return on plan assets presented was used to determine nonunion pension expense for first quarter 2019, and a 0.0% expected return on plan assets was used to determine nonunion pension expense for the second and third quarters of 2019. (2) The discount rate presented was used to determine the first quarter 2018 credit, and the interim discount rate established upon each quarterly settlement in 2018 of 3.6% , 3.8% , and 3.6% was used to calculate the expense for the second, third, and fourth quarter of 2018, respectively. ​ The assumed health care cost trend rates for the Company’s postretirement health benefit plan at December 31 were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 2019 Health care cost trend rate assumed for next year (1) ​ 7.0 % 7.5 % Rate to which the cost trend rate is assumed to decline ​ 4.5 % 5.0 % Year that the rate reaches the cost trend assumed rate 2032 2026 (1) At each December 31 measurement date, health care cost rates for the following year are based on known premiums for the fully-insured postretirement health benefit plan. Therefore, the first year of assumed health care cost trend rates presented as of December 31, 2020 and 2019 are for 2022 and 2021, respectively. ​ Estimated future benefit payments from the Company’s SBP and postretirement health benefit plans, which reflect expected future service as appropriate, as of December 31, 2020 are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Supplemental Postretirement ​ ​ Benefit ​ Health ​ ​ Plan ​ Benefit Plan ​ ​ ​ ​ ​ ​ ​ 2021 ​ $ — ​ $ 588 ​ 2022 ​ $ — ​ $ 618 ​ 2023 ​ $ — ​ $ 667 ​ 2024 ​ $ — ​ $ 667 ​ 2025 ​ $ — ​ $ 691 ​ 2026-2030 ​ $ 424 ​ $ 3,781 ​ ​ Deferred Compensation Plans ​ The Company has deferred salary agreements with certain executives for which liabilities of $1.8 million and $2.1 million were recorded as of December 31, 2020 and 2019, respectively. The deferred salary agreements include a provision that immediately vests all benefits and provides for a lump-sum payment upon a change in control of the Company that is followed by a termination of the executive. The Compensation Committee elected to close the deferred salary agreement program to new entrants effective January 1, 2006. In place of the deferred salary agreement program, officers appointed after 2005 participate in the Cash Long-Term Incentive Plan (see Cash Long-Term Incentive Compensation Plan section within this Note). ​ The Company maintains a Voluntary Savings Plan (“VSP”), a nonqualified deferred compensation program for the benefit of certain executives of the Company and certain subsidiaries. Eligible employees may defer receipt of a portion of their salary and incentive compensation into the VSP by making an election prior to the beginning of the year in which the salary compensation is payable and, for incentive compensation, by making an election at least six months prior to the end of the performance period to which the incentive relates. The Company credits participants’ accounts with applicable rates of return based on a portfolio selected by the participants from the investments available in the plan. The Company match related to the VSP was suspended beginning January 1, 2010. All deferrals, Company match, and investment earnings are considered part of the general assets of the Company until paid. Accordingly, the consolidated balance sheets reflect the fair value of the aggregate participant balances, based on quoted prices of the mutual fund investments, as both an asset and a liability of the Company. As of December 31, 2020 and 2019, VSP balances of $3.0 million and $2.4 million, respectively, were included in other long-term assets with a corresponding amount recorded in other long-term liabilities. ​ Defined Contribution Plans ​ The Company and its subsidiaries have various defined contribution 401(k) plans that cover substantially all employees. The plans permit participants to defer a portion of their salary up to a maximum of 69% as determined under Section 401(k) of the IRC. For certain participating subsidiaries, the Company matches 50% of nonunion participant contributions up to the first 6% of annual compensation. The Company’s matching expense for the 401(k) plans totaled $4.6 million, $6.8 million, and $6.1 million for 2020, 2019, and 2018, respectively. The plans also allow for discretionary 401(k) Company contributions determined annually. The Company recognized expense of $12.6 million, $10.9 million, and $11.6 million in 2020, 2019, and 2018, respectively, related to its discretionary contributions to the defined contribution plan. Participants are fully vested in their benefits under the defined contribution plan after three years of service. ​ Cash Long-Term Incentive Compensation Plan ​ The Company maintains a performance-based Cash Long-Term Incentive Compensation Plan (“LTIP”) for certain officers of the Company or its subsidiaries. The LTIP incentive, which is earned over three years , is based, in part, upon a proportionate weighting of return on capital employed and shareholder returns compared to a peer group, as specifically defined in the plan document. As of December 31, 2020, 2019, and 2018, $14.2 million, $13.7 million, $18.3 million, respectively, were accrued for future payments under the plans. ​ Other Plans ​ Other long-term assets include $55.7 million and $53.2 million at December 31, 2020 and 2019, respectively, in the cash surrender value of life insurance policies. These policies are intended to provide funding for long-term nonunion benefit arrangements such as the Company’s SBP and deferred compensation plans. A portion of the Company’s cash surrender value of variable life insurance policies have investments, through separate accounts, in equity and fixed income securities and, therefore, are subject to market volatility. The Company recognized a gain of $2.3 million and $3.7 million for 2020 and 2019, respectively, and a loss of less than $0.1 million for 2018, associated with changes in the cash surrender value and proceeds from life insurance policies. ​ Multiemployer Plans ​ ABF Freight System, Inc. and certain other subsidiaries reported in the Company’s Asset-Based operating segment (“ABF Freight”) contribute to multiemployer pension and health and welfare plans, which have been established pursuant to the Taft-Hartley Act, to provide benefits for its contractual employees. ABF Freight’s contributions generally are based on the time worked by its contractual employees, in accordance with the 2018 ABF NMFA and other related supplemental agreements. ABF Freight recognizes as expense the contractually required contributions for each period and recognizes as a liability any contributions due and unpaid. ​ The multiemployer plans to which ABF Freight segment primarily contributes are jointly trusteed (half of the trustees of each plan are selected by the participating employers, the other half by the IBT) and cover collectively-bargained employees of multiple unrelated employers. Due to the inherent nature of multiemployer plans, there are risks associated with participation in these plans that differ from single employer plans. Assets received by the plans are not segregated by employer, and contributions made by one employer can be and are used to provide benefits to current and former employees of other employers. If a participating employer in a multiemployer pension plan no longer contributes to the plan, the unfunded obligations of the plan may be borne by the remaining participating employers. If a participating employer in a multiemployer pension plan completely withdraws from the plan, it owes to the plan its proportionate share of the plan’s unfunded vested benefits, referred to as a withdrawal liability. A complete withdrawal generally occurs when the employer permanently ceases to have an obligation to contribute to the plan. Withdrawal liability is also owed in the event the employer withdraws from a plan in connection with a mass withdrawal, which generally occurs when all or substantially all employers withdraw from the plan pursuant to an agreement in a relatively short period of time. Were ABF Freight to completely withdraw from certain multiemployer pension plans, whether in connection with a mass withdrawal or otherwise, under current law, ABF Freight would have material liabilities for its share of the unfunded vested liabilities of each such plan. ​ Pension Plans The 25 multiemployer pension plans to which ABF Freight contributes vary greatly in size and in funded status. Contribution obligations to these plans are generally specified in the 2018 ABF NMFA, which will remain in effect through June 30, 2023. The funding obligations to the pension plans are intended to satisfy the requirements imposed by the Pension Protection Act of 2006 (the “PPA”), which was permanently extended by the Multiemployer Pension Reform Act (the “Reform Act”) included in the Consolidated and Further Continuing Appropriations Act of 2015. Through the term of its current collective bargaining agreement, ABF Freight’s contribution obligations generally will be satisfied by making the specified contributions when due. However, the Company cannot determine with any certainty the contributions that will be required under future collective bargaining agreements for ABF Freight’s contractual employees. ​ The PPA requires that “endangered” (generally less than 80% funded and commonly called “yellow zone”) plans adopt “funding improvement plans” and that “critical” (generally less than 65% funded and commonly called “red zone”) plans adopt “rehabilitation plans” that are intended to improve the plan’s funded status over time. The Reform Act includes provisions to address the funding of multiemployer pension plans in “critical and declining” status, including certain of those in which ABF Freight participates. Critical and declining status is applicable to critical status plans that are projected to become insolvent anytime within the next 14 plan years, or if the plan is projected to become insolvent within the next 19 plan years and either the plan’s ratio of inactive participants to active participants exceeds two to one or the plan’s funded percentage is less than 80% . Provisions of the Reform Act include, among others, providing qualifying plans the ability to self - correct funding issues, subject to various requirements and restrictions, including applying to the U.S. Department of Treasury (the “Treasury Department”) for the reduction of certain accrued benefits. ​ Based on the most recent annual funding notices the Company has received, most of which are for plan year ended December 31, 2019, approximately 56% of ABF Freight’s multiemployer pension plan contributions for the year ended December 31, 2020 were made to plans that are in “critical and declining status,” including the Central States, Southeast and Southwest Areas Pension Plan (the “Central States Pension Plan”) discussed below, approximately 3% were made to plans that are in “critical status” but not “critical and declining status,” and approximately 4% were made to plans that are in “endangered status,” each as defined by the PPA. ABF Freight’s participation in multiemployer pension plans is summarized in the table below. The multiemployer pension plans listed separately in the table represent plans that are individually significant to the Asset-Based segment based on the amount of plan contributions. The severity of a plan’s underfunded status was also considered in the analysis of individually significant funds to be separately disclosed. ​ Significant multiemployer pension funds and key participation information were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Pension ​ FIP/RP ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Protection Act ​ Status ​ Contributions (d) ​ ​ ​ ​ EIN/Pension ​ Zone Status (b) ​ Pending/ ​ (in thousands) ​ Surcharge Legal Name of Plan Plan Number (a) 2020 2019 Implemented (c) 2020 2019 2018 Imposed (e) Central States, Southeast and Southwest Areas Pension Plan (1)(2) 36-6044243 Critical and Declining Critical and Declining Implemented (3) ​ $ 68,704 ​ $ 75,803 ​ $ 74,177 No ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Western Conference of Teamsters Pension Plan (2) 91-6145047 Green Green No ​ 23,633 ​ 24,860 ​ 25,268 No ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Central Pennsylvania Teamsters Defined Benefit Plan (1)(2) 23-6262789 Green Green No ​ 13,485 ​ 13,907 ​ 13,393 No ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ I. B. of T. Union Local No. 710 Pension Fund (5)(6) 36-2377656 Green (4) Green (4) No ​ 9,885 ​ 10,164 ​ 9,929 No ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ New England Teamsters Pension Fund (7)(8) 04-6372430 Critical and Declining (9) Critical and Declining (9) Implemented (10) ​ 4,464 ​ 4,802 ​ 20,090 ​ No ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ All other plans in the aggregate ​ ​ ​ ​ ​ ​ ​ ​ ​ 22,023 ​ 24,210 ​ 24,392 ​ ​ Total multiemployer pension contributions paid (11) ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 142,194 ​ $ 153,746 ​ $ 167,249 ​ ​ Table Heading Definitions ​ (a) The “EIN/Pension Plan Number” column provides the Federal Employer Identification Number (EIN) and the three-digit plan number, if applicable. (b) Unless otherwise noted, the most recent PPA zone status available in 2020 and 2019 is for the plan’s year-end status at December 31, 2019 and 2018, respectively. The zone status is based on information received from the plan and was certified by the plan’s actuary. Green zone funds are those that are in neither endangered, critical, or critical and declining status and generally have a funded percentage of at least 80% . (c) The “FIP/RP Status Pending/Implemented” column indicates if a funding improvement plan (FIP) or a rehabilitation plan (RP), if applicable, is pending or has been implemented. (d) Amounts reflect contributions made in the respective year and differ from amounts expensed during the year. (e) The surcharge column indicates if a surcharge was paid by ABF Freight to the plan. ​ (1) ABF Freight System, Inc. was listed by the plan as providing more than 5% of the total contributions to the plan for the plan years ended December 31, 2019 and 2018. (2) Information for this fund was obtained from the annual funding notice, other notices received from the plan, and the Form 5500 filed for the plan years ended December 31, 2019 and 2018. (3) Adopted a rehabilitation plan effective March 25, 2008 as updated. Utilized amortization extension granted by the IRS effective December 31, 2003. (4) PPA zone status relates to plan years February 1, 2019 – January 31, 2020 and February 1, 2018 – January 31, 2019. (5) The Company was listed by the plan as providing more than 5% of the total contributions to the plan for the plan years ended January 31, 2020 and 2019. (6) Information for this fund was obtained from the annual funding notice, other notices received from the plan, and the Form 5500 filed for the plan years ended January 31, 2020 and 2019. (7) Contributions include $1.6 million for 2020 and 2019, respectively, and $15.7 million for 2018, related to the multiemployer pension fund withdrawal liability which is further discussed in this Note. (8) Information for this fund was obtained from the annual funding notice, other notices received from the plan, and the Form 5500 filed for the plan years ended September 30, 2019 and 2018. (9) PPA zone status relates to plan years October 1, 2019 – September 30, 2020 and October 1, 2018 – September 30, 2019. (10) Adopted a rehabilitation plan effective January 1, 2009. (11) Contribution levels can be impacted by several factors such as changes in business levels and the related time worked by contractual employees, contractual rate increases for pension benefits, and the specific funding structure, which differs among funds. The 2018 ABF NMFA and the related supplemental agreements provided for contributions to multiemployer pension plans to be frozen at the current rates for each fund. The year-over-year changes in multiemployer pension plan contributions presented above were influenced by the previously mentioned payments related to the New England Pension Fund and changes in Asset-Based business levels. Due to the negative impact of the COVID-19 pandemic on tonnage levels, the Company made operational changes in the Asset-Based network in the second and third quarters of 2020, including workforce reductions to better align resources with business levels. The reduction in hours worked by a portion of ABF Freight’s contractual employees contributed to lower contributions to multiemployer pension plans for 2020, compared to 2019. ​ For 2020, 2019, and 2018, approximately one half of ABF Freight’s multiemployer pension contributions were made to the Central States Pension Plan. The funded percentages of the Central States Pension Plan, as set forth in information provided by the Central States Pension Plan, were 24.8% , and 27.2% as of January 1, 2019 and 2018, respectively. ABF Freight received a Notice of Critical and Declining Status for the Central States Pension Plan dated March 30, 2020, in which the plan’s actuary certified that, as of January 1, 2020, the plan is in critical and declining status, as defined by the Reform Act. Although the future of the Central States Pension Plan is impacted by a number of factors, without legislative action, the plan is currently projected to become insolvent within 5 years . ​ On July 9, 2018, ABF Freight reached a tentative agreement with the IBT bargaining representatives for the Northern and Southern New England Supplemental Agreements on terms for new supplemental agreements to the 2018 ABF NMFA for 2018 to 2023 (the “New England Supplemental Agreements”). The New England Supplemental Agreements were ratified by the local unions in the region covered by the supplements on July 25, 2018. In accordance with the New England Supplemental Agreements, ABF Freight’s multiemployer pension plan obligation with the New England Teamsters and Trucking Industry Pension Fund (the “New England Pension Fund”) was restructured under a transition agreement effective on August 1, 2018. The New England Pension Fund was previously restructured to utilize a “two pool approach,” which effectively subdivides the plan assets and liabilities between two groups of beneficiaries. In accordance with ABF Freight’s transition agreement with the New England Pension Fund, ABF Freight agreed to withdraw from the original pool to which it has historically been a participant (the “Existing Employer Pool”) and transition to a new liability pool (the “New Employer Pool”), which does not have an associated unfunded liability. The terms of the transition are pursuant to the Second Chance Policy on Retroactive Withdrawal Liability, as adopted by the New England Pension Fund. ​ ABF Freight’s transition agreement with the New England Pension Fund triggered a withdrawal liability settlement which satisfies ABF Freight’s existing potential withdrawal liability obligations to the Existing Employer Pool and minimizes the potential for future increases in withdrawal liability under the New Employer Pool. ABF Freight transitioned to the New Employer Pool at a lower pension contribution rate than its previous contribution rate under the Existing Employer Pool, and the new contribution rate will be frozen for a period of 10 years . ​ ABF Freight recognized a one-time charge of $37.9 million (pre-tax) to record the withdrawal liability as of June 30, 2018 when the transition agreement was determined to be probable. The withdrawal liability was partially settled through the initial lump sum cash payment of $15.1 million made in third quarter 2018, and the remainder will be settled with monthly payments to the New England Pension Fund over a period of 23 years with an initial aggregate present value of $22.8 million. In accordance with current tax law, these payments are deductible for income taxes when paid. As of December 31, 2020, the outstanding withdrawal liability totaled $21.4 million, of which $0.6 million and $20.8 million was recorded in accrued expenses and other long-term liabilities, respectively. ​ Prior to 2020, the Company received notices that a reduction of benefits was authorized by the Treasury Department for the Western Pennsylvania Teamsters and Employers Pension Fund and the New York State Teamsters Conference Pension and Retirement Fund. The Company also previously received notice that the PBGC will provide financial assistance to the Road Carriers Local 707 Pension Fund, which was declared insolvent, by paying retiree benefits not to exceed the PBGC guarantee limits. Approximately 1% of ABF Freight’s total multiemployer pension contributions for the year ended December 31, 2020 were made to each of these funds. The Company received a notice of insolvency dated September 30, 2020 for the Trucking Employees of North Jersey Welfare Fund, Inc. – Pension Fund (the “North Jersey Welfare Fund”) which is expected to become insolvent in April 2021. While the board of trustees of the 560 Pension Fund will continue to administer the fund, the PBGC will provide financial assistance to the fund by paying retiree benefits not to exceed the PBGC guarantee limits for insolvent multiemployer plans. Approximately 2% of ABF Freight’s total multiemployer pension contributio

STOCKHOLDERS' EQUITY

STOCKHOLDERS' EQUITY	12 Months Ended
	Dec. 31, 2020
STOCKHOLDERS' EQUITY
STOCKHOLDERS' EQUITY	NOTE J – STOCKHOLDERS’ EQUITY ​ Accumulated Other Comprehensive Income (Loss) ​ Components of accumulated other comprehensive income (loss) were as follows at December 31: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 2019 2018 ​ ​ (in thousands) Pre-tax amounts: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Unrecognized net periodic benefit credit (costs) ​ $ 4,390 ​ $ 2,898 ​ $ (11,821) ​ Interest rate swap ​ ​ (1,622) ​ ​ (563) ​ ​ 801 ​ Foreign currency translation ​ (1,182) ​ (2,075) ​ (2,816) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total ​ $ 1,586 ​ $ 260 ​ $ (13,836) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ After-tax amounts: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Unrecognized net periodic benefit credit (costs) (1) ​ $ 3,260 ​ $ 2,152 ​ $ (12,749) ​ Interest rate swap ​ ​ (1,198) ​ ​ (416) ​ ​ 591 ​ Foreign currency translation ​ (872) ​ (1,533) ​ (2,080) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total ​ $ 1,190 ​ $ 203 ​ $ (14,238) ​ (1) The year ended December 31, 2018 includes $4.0 million related to a previous valuation allowance on deferred tax assets for nonunion defined benefit pension liabilities which was recognized as pension termination expense during 2019 upon extinguishment of the nonunion defined benefit pension plan (see Note I). The reclassification of stranded income tax effects related to this item was not permitted by the amendment to ASC Topic 220, Comprehensive Income , which the Company adopted as of January 1, 2018. ​ ​ ​ The following is a summary of the changes in accumulated other comprehensive income (loss), net of tax, by component: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Unrecognized Net ​ ​ Interest Foreign ​ ​ ​ ​ ​ ​ Periodic Benefit ​ ​ Rate ​ Currency ​ ​ ​ Total Credit (Costs) ​ Swap Translation ​ ​ ​ (in thousands) ​ Balances at December 31, 2018 ​ $ (14,238) ​ $ (12,749) ​ $ 591 ​ $ (2,080) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Other comprehensive income (loss) before reclassifications ​ 6,197 ​ 6,657 ​ ​ (1,007) ​ 547 ​ Amounts reclassified from accumulated other comprehensive loss ​ 8,244 ​ 8,244 ​ ​ — ​ — ​ Net current-period other comprehensive income (loss) ​ 14,441 ​ 14,901 ​ ​ (1,007) ​ 547 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balances at December 31, 2019 ​ $ 203 ​ $ 2,152 ​ $ (416) ​ $ (1,533) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Other comprehensive income (loss) before reclassifications ​ ​ 1,359 ​ ​ 1,480 ​ ​ (782) ​ ​ 661 ​ Amounts reclassified from accumulated other comprehensive income ​ ​ (372) ​ ​ (372) ​ ​ — ​ ​ — ​ Net current-period other comprehensive income (loss) ​ ​ 987 ​ ​ 1,108 ​ ​ (782) ​ ​ 661 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balances at December 31, 2020 ​ $ 1,190 ​ $ 3,260 ​ $ (1,198) ​ $ (872) ​ ​ ​ The following is a summary of the significant reclassifications out of accumulated other comprehensive income (loss) by component for the years ended December 31: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Unrecognized Net Periodic ​ ​ ​ Benefit Credit (Costs) (1)(2) ​ 2020 2019 ​ ​ (in thousands) Amortization of net actuarial gain (loss) ​ $ 589 ​ $ (1,253) ​ Amortization of prior service credit ​ ​ 1 ​ 33 ​ Pension settlement expense, including termination expense (3)(4) ​ ​ (89) ​ (8,505) ​ Total, pre-tax ​ ​ 501 ​ (9,725) ​ Tax benefit (expense) ​ ​ (129) ​ 1,481 ​ Total, net of tax ​ $ 372 ​ $ (8,244) ​ (1) Amounts in parentheses indicate increases in expense or loss. (2) These components of accumulated other comprehensive income (loss) are included in the computation of net periodic benefit cost (see Note I). (3) For the year ended December 31, 2019, amounts included in accumulated other comprehensive income related to the nonunion defined benefit pension plan were reclassed to net income in their entirety upon settlement of the pension benefit obligation. These amounts include amortization of net actuarial loss of $0.3 million (pre-tax) and pension settlement expense, including termination expense, of $8.1 million (pre-tax) which were recognized in the “Other, net” line of other income (costs). These reclassifications impacted net income by $7.3 million for the year ended December 31, 2019. (4) The year ended December 31, 2019 includes a $4.0 million noncash pension termination expense (with no tax benefit) related to an amount which was stranded in accumulated other comprehensive income until the pension benefit obligation was settled upon plan termination (see Note I). ​ Dividends on Common Stock ​ The following table is a summary of dividends declared during the applicable quarter: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ 2019 ​ ​ Per Share Amount Per Share Amount ​ ​ (in thousands, except per share data) First quarter ​ $ 0.08 ​ $ 2,033 ​ $ 0.08 ​ $ 2,052 ​ Second quarter ​ $ 0.08 ​ $ 2,049 ​ $ 0.08 ​ $ 2,050 ​ Third quarter ​ $ 0.08 ​ $ 2,040 ​ $ 0.08 ​ $ 2,043 ​ Fourth quarter ​ $ 0.08 ​ $ 2,035 ​ $ 0.08 ​ $ 2,042 ​ ​ On January 28, 2021, the Company’s Board of Directors declared a dividend of $0.08 per share payable to stockholders of record as of February 11, 2021. ​ Treasury Stock ​ The Company has a program to repurchase its common stock in the open market or in privately negotiated transactions. The program has no expiration date but may be terminated at any time at the Board of Directors’ discretion. Repurchases may be made using the Company’s cash reserves or other available sources. In October 2015, the Board of Directors extended the share repurchase program, making a total of $50.0 million available for purchases of the Company’s common stock. During 2020, the Company purchased 252,299 shares for an aggregate cost of $6.6 million, leaving $6.6 million available for repurchase under the program as of December 31, 2020. Treasury shares totaled 3,656,938 and 3,404,639 as of December 31, 2020 and 2019, respectively. ​ As previously announced in the Company’s Current Report on Form 8-K filed with the U.S. Securities and Exchange Commission on January 28, 2021, the Board of Directors extended the share repurchase program by authorizing a total of $50.0 million to be available for purchases of the Company’s common stock.

SHARE-BASED COMPENSATION

SHARE-BASED COMPENSATION	12 Months Ended
	Dec. 31, 2020
SHARE-BASED COMPENSATION
SHARE-BASED COMPENSATION	NOTE K – SHARE-BASED COMPENSATION ​ Stock Awards ​ The Company had outstanding RSUs granted under the ArcBest Corporation Ownership Incentive Plan (the “Ownership Incentive Plan”) as of December 31, 2020 and 2019. The Ownership Incentive Plan provides for the granting of 4.3 million shares, which may be awarded as incentive and nonqualified stock options, stock appreciation rights, restricted stock, RSUs, or performance award units. ​ Restricted Stock Units ​ A summary of the Company’s RSU award program is presented below: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ ​ ​ ​ Grant Date ​ ​ ​ Units ​ Fair Value ​ Outstanding – January 1, 2020 ​ 1,617,120 ​ $ 24.82 ​ Granted ​ 579,660 ​ $ 19.22 ​ Vested ​ (320,788) ​ $ 30.29 ​ Forfeited (1) ​ (34,842) ​ $ 25.48 ​ Outstanding – December 31, 2020 ​ 1,841,150 ​ $ 22.09 ​ (1) Forfeitures are recognized as they occur. ​ The Compensation Committee of the Company’s Board of Directors granted RSUs during the years ended December 31, 2020, 2019, and 2018 as follows: ​ k ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ ​ ​ ​ Grant Date ​ Units Fair Value 2020 579,660 ​ $ 19.22 ​ 2019 386,840 ​ $ 27.75 ​ 2018 231,510 ​ $ 44.50 ​ ​ Beginning with 2018 grants, the vesting date for RSUs granted to employees was reduced from the end of a five-year period to the end of a four-year period following the date of grant. The fair value of restricted stock awards that vested in 2020, 2019, and 2018 was $7.8 million, $4.9 million, and $9.6 million, respectively. Unrecognized compensation cost related to restricted stock awards outstanding as of December 31, 2020 was $18.0 million, which is expected to be recognized over a weighted-average period of approximately 2 years.

EARNINGS PER SHARE

EARNINGS PER SHARE	12 Months Ended
	Dec. 31, 2020
EARNINGS PER SHARE
EARNINGS PER SHARE	NOTE L – EARNINGS PER SHARE ​ The following table sets forth the computation of basic and diluted earnings per share for the years ended December 31: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 2019 2018 ​ ​ (in thousands, except share and per share data) Basic ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Numerator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income ​ $ 71,100 ​ $ 39,985 ​ $ 67,262 ​ Effect of unvested restricted stock awards ​ — ​ (22) ​ (150) ​ Adjusted net income ​ $ 71,100 ​ $ 39,963 ​ $ 67,112 ​ Denominator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average shares ​ 25,410,232 ​ 25,535,529 ​ 25,679,736 ​ Earnings per common share ​ $ 2.80 ​ $ 1.56 ​ $ 2.61 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Diluted ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Numerator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income ​ $ 71,100 ​ $ 39,985 ​ $ 67,262 ​ Effect of unvested restricted stock awards ​ — ​ (21) ​ (145) ​ Adjusted net income ​ $ 71,100 ​ $ 39,964 ​ $ 67,117 ​ Denominator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average shares ​ 25,410,232 ​ 25,535,529 ​ 25,679,736 ​ Effect of dilutive securities ​ 1,012,291 ​ 914,526 ​ 1,019,095 ​ Adjusted weighted-average shares and assumed conversions ​ 26,422,523 ​ 26,450,055 ​ 26,698,831 ​ Earnings per common share ​ $ 2.69 ​ $ 1.51 ​ $ 2.51 ​ ​ Under the two-class method of calculating earnings per share, dividends paid and a portion of undistributed net income, but not losses, are allocated to unvested RSUs that receive dividends, which are considered participating securities. Beginning with 2015 grants, the RSU agreements were modified to remove dividend rights and, therefore, the RSUs granted in 2020, 2019, and 2018 are not participating securities. ​ During 2019, the remaining unvested RSUs receiving dividends became vested; therefore, in 2020 the Company began using the treasury stock method for calculating earnings per share. ​ For the year ended December 31, 2019 and 2018 outstanding stock awards of 0.2 million and 0.1 million, respectively, were not included in the diluted earnings per share calculations because their inclusion would have the effect of increasing the earnings per share.

OPERATING SEGMENT DATA

OPERATING SEGMENT DATA	12 Months Ended
	Dec. 31, 2020
OPERATING SEGMENT DATA
OPERATING SEGMENT DATA	NOTE M – OPERATING SEGMENT DATA ​ The Company uses the “management approach” to determine its reportable operating segments, as well as to determine the basis of reporting the operating segment information. The management approach focuses on financial information that the Company’s management uses to make operating decisions. Management uses revenues, operating expense categories, operating ratios, operating income, and key operating statistics to evaluate performance and allocate resources to the Company’s operations. ​ Shared services represent costs incurred to support all segments, including sales, pricing, customer service, marketing, capacity sourcing functions, human resources, financial services, information technology, and other company-wide services. Certain overhead costs are not attributable to any segment and remain unallocated in “Other and eliminations.” Included in unallocated costs are expenses related to investor relations, legal, the ArcBest Board of Directors, and certain technology investments. Shared services costs attributable to the operating segments are predominantly allocated based upon estimated and planned resource utilization-related metrics such as estimated shipment levels, number of pricing proposals, or number of personnel supported. The bases for such charges are modified and adjusted by management when necessary or appropriate to reflect fairly and equitably the actual incidence of cost incurred by the operating segments. Management believes the methods used to allocate expenses are reasonable. ​ The Company’s reportable operating segments are as follows: ​ ● The Asset-Based segment includes the results of operations of ABF Freight System, Inc. and certain other subsidiaries (“ABF Freight”). The segment operations include national, inter-regional, and regional transportation of general commodities through standard, expedited, and guaranteed LTL services. The Asset-Based segment provides services to the ArcBest segment, including freight transportation related to certain consumer household goods self-move services. ​ ● The ArcBest segment includes the results of operations of the Company’s service offerings in ground expedite, truckload, dedicated, intermodal, household goods moving, managed transportation, warehousing and distribution, and international freight transportation for air, ocean, and ground. The ArcBest segment provides services to the Asset-Based segment. ​ ● FleetNet includes the results of operations of FleetNet America, Inc. and certain other subsidiaries that provide roadside assistance and maintenance management services for commercial vehicles through a network of third-party service providers. FleetNet also provides services to the Asset-Based and ArcBest segments. ​ The Company’s other business activities and operating segments that are not reportable include ArcBest Corporation and certain other subsidiaries. Certain costs incurred by the parent holding company and the Company’s shared services subsidiary are allocated to the reporting segments. The Company eliminates intercompany transactions in consolidation. However, the information used by the Company’s management with respect to its reportable segments is before intersegment eliminations of revenues and expenses. ​ Further classifications of operations or revenues by geographic location are impracticable and, therefore, are not provided. The Company’s foreign operations are not significant. ​ ​ ​ ​ The following table reflects reportable operating segment information for the years ended December 31: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 2019 2018 ​ ​ (in thousands) REVENUES ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Asset-Based ​ $ 2,092,031 ​ $ 2,144,679 ​ $ 2,175,585 ​ ArcBest ​ 779,115 ​ 738,392 ​ 781,123 ​ FleetNet ​ 205,049 ​ 211,738 ​ 195,126 ​ Other and eliminations ​ (136,032) ​ (106,499) ​ (58,046) ​ Total consolidated revenues ​ $ 2,940,163 ​ $ 2,988,310 ​ $ 3,093,788 ​ OPERATING EXPENSES ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Asset-Based ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Salaries, wages, and benefits ​ $ 1,095,694 ​ $ 1,148,761 ​ $ 1,128,030 ​ Fuel, supplies, and expenses ​ 209,095 ​ 257,133 ​ 255,655 ​ Operating taxes and licenses ​ 49,300 ​ 50,209 ​ 48,792 ​ Insurance ​ 33,568 ​ 32,516 ​ 32,887 ​ Communications and utilities ​ 17,916 ​ 18,614 ​ 16,983 ​ Depreciation and amortization ​ 94,326 ​ 89,798 ​ 85,951 ​ Rents and purchased transportation ​ 250,159 ​ 221,479 ​ 242,247 ​ Shared services ​ ​ 217,258 ​ ​ 212,773 ​ ​ 215,302 ​ Multiemployer pension fund withdrawal liability charge (1) ​ ​ — ​ ​ — ​ ​ 37,922 ​ Gain on sale of property and equipment ​ (3,309) ​ (5,892) ​ (410) ​ Innovative technology costs (2) ​ ​ 22,458 ​ ​ 13,739 ​ ​ 3,810 ​ Other ​ 6,701 ​ 3,488 ​ 4,554 ​ Total Asset-Based ​ 1,993,166 ​ 2,042,618 ​ 2,071,723 ​ ArcBest ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Purchased transportation ​ 649,933 ​ 606,113 ​ 631,501 ​ Supplies and expenses ​ 9,627 ​ 10,789 ​ 13,329 ​ Depreciation and amortization ​ 9,714 ​ 11,344 ​ 13,750 ​ Shared services ​ ​ 90,983 ​ ​ 93,961 ​ ​ 91,266 ​ Other ​ ​ 9,203 ​ 9,860 ​ 9,143 ​ Asset impairment (3) ​ ​ — ​ ​ 26,514 ​ ​ — ​ Restructuring costs (4) ​ ​ — ​ — ​ 491 ​ Gain on sale of subsidiaries (5) ​ ​ — ​ ​ — ​ ​ (1,945) ​ Total ArcBest ​ 769,460 ​ 758,581 ​ 757,535 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ FleetNet ​ 201,682 ​ 206,932 ​ 190,741 ​ Other and eliminations ​ (122,423) ​ (83,591) ​ (35,309) ​ Total consolidated operating expenses ​ $ 2,841,885 ​ $ 2,924,540 ​ $ 2,984,690 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (1) ABF Freight recorded a one-time charge in 2018 for the multiemployer pension fund withdrawal liability resulting from the transition agreement it entered into with the New England Pension Fund (see Note I). (2) Represents costs associated with the freight handling pilot test program at ABF Freight. (3) The ArcBest segment recognized a noncash impairment charge in 2019 related to a portion of the goodwill, customer relationship intangible assets, and revenue equipment associated with the acquisition of truckload and dedicated businesses within the segment (see Note D). (4) Restructuring costs relate to the realignment of the Company’s corporate structure (see Note N). (5) Gain recognized in 2018 relates to the sale of the ArcBest segment’s military moving business in December 2017. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Year Ended December 31 ​ ​ 2020 2019 2018 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) OPERATING INCOME (LOSS) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Asset-Based ​ $ 98,865 ​ $ 102,061 ​ $ 103,862 ​ ArcBest ​ 9,655 ​ (20,189) ​ 23,588 ​ FleetNet ​ 3,367 ​ 4,806 ​ 4,385 ​ Other and eliminations ​ (13,609) ​ (22,908) ​ (22,737) ​ Total consolidated operating income ​ $ 98,278 ​ $ 63,770 ​ $ 109,098 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ OTHER INCOME (COSTS) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Interest and dividend income ​ $ 3,616 ​ $ 6,453 ​ $ 3,914 ​ Interest and other related financing costs ​ (11,697) ​ (11,467) ​ (9,468) ​ Other, net (1) ​ 2,299 ​ (7,285) ​ (19,158) ​ Total other costs ​ (5,782) ​ (12,299) ​ (24,712) ​ INCOME BEFORE INCOME TAXES ​ $ 92,496 ​ $ 51,471 ​ $ 84,386 ​ (1) Includes the components of net periodic benefit cost other than service cost, including pension settlement and termination expense (see Note I), and proceeds and changes in cash surrender value of life insurance policies. ​ The following table reflects information about revenues from customers and intersegment revenues: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 2019 2018 ​ ​ (in thousands) Revenues from customers ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Asset-Based ​ $ 1,998,549 ​ $ 2,077,287 ​ $ 2,131,571 ​ ArcBest ​ 770,560 ​ 731,366 ​ 773,968 ​ FleetNet ​ 166,654 ​ 175,055 ​ 182,861 ​ Other ​ 4,400 ​ 4,602 ​ 5,388 ​ Total consolidated revenues ​ $ 2,940,163 ​ $ 2,988,310 ​ $ 3,093,788 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Intersegment revenues ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Asset-Based ​ $ 93,482 ​ $ 67,392 ​ $ 44,014 ​ ArcBest ​ ​ 8,555 ​ ​ 7,026 ​ ​ 7,155 ​ FleetNet ​ ​ 38,395 ​ ​ 36,683 ​ ​ 12,265 ​ Other and eliminations ​ ​ (140,432) ​ ​ (111,101) ​ ​ (63,434) ​ Total intersegment revenues ​ $ — ​ $ — ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total segment revenues ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Asset-Based ​ $ 2,092,031 ​ ​ 2,144,679 ​ ​ 2,175,585 ​ ArcBest ​ ​ 779,115 ​ ​ 738,392 ​ ​ 781,123 ​ FleetNet ​ ​ 205,049 ​ ​ 211,738 ​ ​ 195,126 ​ Other and eliminations ​ ​ (136,032) ​ ​ (106,499) ​ ​ (58,046) ​ Total consolidated revenues ​ $ 2,940,163 ​ $ 2,988,310 ​ $ 3,093,788 ​ ​ ​ The following table provides capital expenditure and depreciation and amortization information by reportable operating segment: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the year ended December 31 ​ ​ 2020 2019 2018 ​ ​ ​ (in thousands) ​ CAPITAL EXPENDITURES, GROSS ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Asset-Based (1) ​ $ 85,135 ​ $ 122,437 ​ $ 116,505 ​ ArcBest ​ ​ 1,258 ​ ​ 3,909 ​ ​ 5,174 ​ FleetNet ​ 675 ​ 590 ​ 1,365 ​ Other and eliminations (2)(3) ​ 17,983 ​ 33,748 ​ 14,631 ​ ​ ​ $ 105,051 ​ $ 160,684 ​ $ 137,675 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the year ended December 31 ​ ​ ​ 2020 2019 2018 ​ ​ ​ (in thousands) ​ DEPRECIATION AND AMORTIZATION EXPENSE (2) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Asset-Based ​ $ 94,326 ​ $ 89,798 ​ $ 85,951 ​ ArcBest (4) ​ ​ 9,714 ​ ​ 11,344 ​ ​ 13,750 ​ FleetNet (5) ​ 1,622 ​ 1,341 ​ 1,140 ​ Other and eliminations (2) ​ 12,729 ​ 9,983 ​ 7,794 ​ ​ ​ $ 118,391 ​ $ 112,466 ​ $ 108,635 ​ (1) Includes assets acquired through notes payable of $61.8 million, $67.6 million, and $86.8 million in 2020, 2019, and 2018, respectively. (2) Other and eliminations includes certain assets held for the benefit of multiple segments, including information systems equipment. Depreciation and amortization associated with these assets is allocated to the reporting segments. Depreciation and amortization expense includes amortization of internally developed capitalized software which has not been included in gross capital expenditures presented in the table. (3) Includes assets acquired through notes payable of $23.2 million and $6.9 million in 2019 and 2018, respectively. (4) Includes amortization of intangibles of $3.7 million, $4.2 million, and $4.3 million in 2020, 2019, and 2018, respectively. (5) Includes amortization of intangibles which totaled $0.2 million in 2020, 2019, and 2018. ​ A table of assets by reportable operating segment has not been presented as segment assets are not included in reports regularly provided to management nor does management consider segment assets for assessing segment operating performance or allocating resources. ​ The following table presents operating expenses by category on a consolidated basis: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the year ended December 31 ​ 2020 2019 2018 ​ ​ (in thousands) ​ OPERATING EXPENSES ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Salaries, wages, and benefits ​ $ 1,368,588 ​ $ 1,408,409 ​ $ 1,398,348 ​ Rents, purchased transportation, and other costs of services ​ 974,835 ​ 934,958 ​ 989,006 ​ Fuel, supplies, and expenses ​ 250,221 ​ 316,047 ​ 325,126 ​ Depreciation and amortization (1) ​ 118,391 ​ 112,466 ​ 108,635 ​ Other ​ 129,850 ​ 126,146 ​ 123,998 ​ Asset impairment (2) ​ ​ — ​ ​ 26,514 ​ ​ — ​ Multiemployer pension fund withdrawal liability charge (3) ​ ​ — ​ ​ — ​ ​ 37,922 ​ Restructuring costs (4) ​ — ​ — ​ 1,655 ​ ​ ​ $ 2,841,885 ​ $ 2,924,540 ​ $ 2,984,690 ​ (1) Includes amortization of intangible assets. (2) The ArcBest segment recognized a noncash impairment charge in 2019 related to a portion of the goodwill, customer relationship intangible assets, and revenue equipment associated with the acquisition of truckload and dedicated businesses within the segment (see Note D). (3) ABF Freight recorded a one-time charge in 2018 for the multiemployer pension fund withdrawal liability resulting from the transition agreement it entered into with the New England Pension Fund (see Note I). (4) Restructuring costs relate to the realignment of the Company’s corporate structure (see Note N).

RESTRUCTURING CHARGES

RESTRUCTURING CHARGES	12 Months Ended
	Dec. 31, 2020
RESTRUCTURING CHARGES
RESTRUCTURING CHARGES	NOTE N – RESTRUCTURING CHARGES ​ On November 3, 2016, the Company announced its plan to implement an enhanced market approach to better serve its customers. The enhanced market approach unified the Company’s sales, pricing, customer service, marketing, and capacity sourcing functions effective January 1, 2017, and allows the Company to operate as one logistics provider under the ArcBest brand. The Company recorded $1.7 million of charges in operating expenses related to the restructuring during 2018, the majority of which were noncash. These restructuring charges included $0.4 million associated with the termination of noncancelable lease and consulting agreements and $1.3 million primarily related to severance payments resulting from headcount reductions and other employee-related costs.

LEGAL PROCEEDINGS, ENVIRONMENTA

LEGAL PROCEEDINGS, ENVIRONMENTAL MATTERS, AND OTHER EVENTS	12 Months Ended
	Dec. 31, 2020
LEGAL PROCEEDINGS, ENVIRONMENTAL MATTERS, AND OTHER EVENTS
LEGAL PROCEEDINGS, ENVIRONMENTAL MATTERS, AND OTHER EVENTS	NOTE O – LEGAL PROCEEDINGS, ENVIRONMENTAL MATTERS, AND OTHER EVENTS ​ The Company is involved in various legal actions arising in the ordinary course of business. The Company maintains liability insurance against certain risks arising out of the normal course of its business, subject to certain self-insured retention limits. The Company routinely establishes and reviews the adequacy of reserves for estimated legal, environmental, and self-insurance exposures. While management believes that amounts accrued in the consolidated financial statements are adequate, estimates of these liabilities may change as circumstances develop. Considering amounts recorded, routine legal matters are not expected to have a material adverse effect on the Company’s financial condition, results of operations, or cash flows. ​ Environmental Matters ​ The Company’s subsidiaries store fuel for use in tractors and trucks in underground tanks at certain facilities. Maintenance of such tanks is regulated at the federal and, in most cases, state levels. The Company believes it is in substantial compliance with all such regulations. The Company’s underground storage tanks are required to have leak detection systems. The Company is not aware of any leaks from such tanks that could reasonably be expected to have a material adverse effect on the Company. ​ The Company has received notices from the Environmental Protection Agency (the “EPA”) and others that it has been identified as a potentially responsible party under the Comprehensive Environmental Response Compensation and Liability Act, or other federal or state environmental statutes, at several hazardous waste sites. After investigating the Company’s involvement in waste disposal or waste generation at such sites, the Company has either agreed to de minimis settlements or determined that its obligations, other than those specifically accrued with respect to such sites, would involve immaterial monetary liability, although there can be no assurances in this regard. The Company maintains an accrual, which is included in accrued expenses in the consolidated balance sheets, for estimated environmental cleanup costs of properties currently or previously operated by the Company. Amounts accrued reflect management’s best estimate of the future undiscounted exposure related to identified properties based on current environmental regulations, management’s experience with similar environmental matters, and testing performed at certain sites. ​ Certain Asset-Based service center facilities operate with no exposure certifications or stormwater permits under the federal Clean Water Act (“the CWA”). The no exposure certification and stormwater permits may require periodic facility inspections and monitoring and reporting of stormwater sampling results. The Company determined that certain procedures regarding sampling, documentation, and reporting were not appropriately being performed in accordance with the CWA. As such, the Company self-reported the matter to the EPA. An estimated settlement expense for this matter is accrued within accrued expenses in the consolidated balance sheet as of December 31, 2020. Resolution of this matter is not expected to have a material adverse effect on the Company’s financial condition, results of operations, or cash flows. ​ Other Events ​ In February 2021, the Company received a Notice of Assessment from a state pertaining to uncollected sales and use tax, including interest and penalties, for the period September 1, 2016 to November 30, 2018. The Company does not agree with the basis of the assessment and plans to appeal the assessment and defend its position. The Company has previously accrued an amount related to this assessment consistent with applicable accounting guidance, but if the state prevails in its position, the Company may owe additional tax. Management does not believe the amount involved will have a material adverse effect on the Company’s financial condition, results of operations, or cash flows. ​

QUARTERLY RESULTS OF OPERATIONS

QUARTERLY RESULTS OF OPERATIONS (UNAUDITED)	12 Months Ended
	Dec. 31, 2020
QUARTERLY RESULTS OF OPERATIONS (UNAUDITED)
QUARTERLY RESULTS OF OPERATIONS (UNAUDITED)	NOTE P – QUARTERLY RESULTS OF OPERATIONS (UNAUDITED) ​ The tables below present unaudited quarterly financial information for 2020 and 2019. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ ​ First Second Third Fourth ​ Quarter Quarter (1) Quarter Quarter ​ ​ (in thousands, except share and per share data) Revenues ​ $ 701,399 ​ $ 627,370 ​ $ 794,980 ​ $ 816,414 ​ Operating expenses ​ 693,580 ​ 606,945 ​ 755,198 ​ 786,162 ​ Operating income ​ 7,819 ​ 20,425 ​ 39,782 ​ 30,252 ​ Other income (costs) ​ (5,434) ​ 309 ​ (604) ​ (53) ​ Income tax provision ​ 483 ​ 4,854 ​ 9,774 ​ 6,285 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income ​ $ 1,902 ​ $ 15,880 ​ $ 29,404 ​ $ 23,914 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings per common share ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basic ​ $ 0.07 ​ $ 0.62 ​ $ 1.15 ​ $ 0.94 ​ Diluted ​ $ 0.07 ​ $ 0.61 ​ $ 1.11 ​ $ 0.89 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Average common shares outstanding ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basic ​ 25,390,377 ​ 25,463,559 ​ 25,470,094 ​ 25,427,449 ​ Diluted ​ 26,246,800 ​ 26,217,957 ​ 26,592,457 ​ 26,734,287 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 ​ ​ First Second Third Fourth ​ Quarter Quarter Quarter Quarter ​ ​ (in thousands, except share and per share data) Revenues ​ $ 711,839 ​ $ 771,490 ​ $ 787,563 ​ $ 717,418 ​ Operating expenses (2) ​ 703,248 ​ 736,290 ​ 756,355 ​ 728,647 ​ Operating income (2) ​ 8,591 ​ 35,200 ​ 31,208 ​ (11,229) ​ Other costs (3) ​ (1,995) ​ (1,640) ​ (7,866) ​ (798) ​ Income tax provision (benefit) ​ 1,708 ​ 9,184 ​ 7,072 ​ (6,478) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income (loss) (2)(3) ​ $ 4,888 ​ $ 24,376 ​ $ 16,270 ​ $ (5,549) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings (loss) per common share (4) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basic (2)(3) ​ $ 0.19 ​ $ 0.95 ​ $ 0.64 ​ $ (0.22) ​ Diluted (2)(3) ​ $ 0.18 ​ $ 0.92 ​ $ 0.62 ​ $ (0.22) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Average common shares outstanding ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basic ​ 25,570,415 ​ 25,554,286 ​ 25,527,982 ​ 25,490,393 ​ Diluted ​ 26,512,349 ​ 26,431,592 ​ 26,416,595 ​ 25,490,393 ​ (1) Quarterly results for the second quarter of 2020 do not reflect typical seasonal trends in business levels due to the negative impact of the COVID-19 pandemic on demand for the Company’s services which resulted in lower revenues and operating results for second quarter 2020. (2) Fourth quarter 2019 includes a noncash impairment charge of $26.5 million (pre-tax), or $19.8 million (after-tax) and $0.78 per diluted share, related to a portion of the goodwill, customer relationship intangible assets, and revenue equipment associated with the acquisition of truckload and dedicated businesses within the ArcBest segment. See Note D. (3) Includes nonunion pension expense, including settlement, for the first three quarters of 2019. In third quarter 2019, when the benefit obligation of the plan was settled, nonunion defined benefit pension expense, including settlement and termination expense, totaled $6.7 million (pre-tax), or $6.0 million (after-tax) and $0.23 diluted share. See Note I for annual amounts of nonunion pension expense, including settlement and termination expense. (4) The Company used the two-class method for calculating earnings per share. See Note L.

SCHEDULE II - VALUATION AND QUA

SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES	12 Months Ended
	Dec. 31, 2020
SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES
SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES	SCHEDULE II VALUATION AND QUALIFYING ACCOUNTS AND RESERVES ARCBEST CORPORATION ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balances at ​ Additions ​ ​ ​ ​ Balances at ​ ​ ​ Beginning of ​ Charged to Costs ​ Charged to ​ ​ ​ ​ End of ​ Description Period and Expenses Other Accounts Deductions Period ​ ​ (in thousands) Year Ended December 31, 2020 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Deducted from asset accounts: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Allowance for doubtful accounts receivable and revenue adjustments ​ $ 5,448 ​ $ 4,327 ​ $ 1,887 (a) $ 3,811 (b) $ 7,851 ​ Allowance for other accounts receivable ​ $ 476 ​ $ (14) (c) $ 198 (d) $ — ​ $ 660 ​ Allowance for deferred tax assets ​ $ 668 ​ $ — ​ $ — ​ $ (616) (e) $ 1,284 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Deducted from asset accounts: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Allowance for doubtful accounts receivable and revenue adjustments ​ $ 7,380 ​ $ 1,223 ​ $ (245) (a) $ 2,910 (b) $ 5,448 ​ Allowance for other accounts receivable ​ $ 806 ​ $ (330) (c) $ — ​ $ — ​ $ 476 ​ Allowance for deferred tax assets ​ $ 53 ​ $ — ​ $ — ​ $ (615) (e) $ 668 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, 2018 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Deducted from asset accounts: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Allowance for doubtful accounts receivable and revenue adjustments ​ $ 7,657 ​ $ 2,336 ​ $ 863 (a) $ 3,476 (b) $ 7,380 ​ Allowance for other accounts receivable ​ $ 921 ​ $ (115) (c) $ — ​ $ — ​ $ 806 ​ Allowance for deferred tax assets ​ $ 844 ​ $ — ​ $ — ​ $ 791 (e) $ 53 ​ ​ Note a – Change in allowance due to recoveries of amounts previously written off and adjustment of revenue. Note b – Uncollectible accounts written off. Note c – Charged / (credited) to workers’ compensation expense. Note d – Charged to retained earnings as of January 1, 2020 due to the adoption of ASC Topic 326, Financial Instruments - Credit Losses. Note e – Decrease (increase) in allowance due to changes in expectations of realization of certain federal and state net operating losses and federal and state deferred tax assets.

ACCOUNTING POLICIES (Policies)

ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2020
ACCOUNTING POLICIES
Consolidation, Policy [Policy Text Block]	Consolidation:
Segment Reporting, Policy [Policy Text Block]	Segment Information:
Use of Estimates, Policy [Policy Text Block]	Use of Estimates: ​ Reclassifications: ​ Subsequent Events ​ In January 2021, the Asset-Based segment sold an unutilized property that will result in a gain on sale of property and equipment of approximately $8.5 million. ​
Cash, Cash Equivalents, and Short-Term Investments	​ Cash, Cash Equivalents, and Short-Term Investments: ​ Certificates of deposit are valued at cost plus accrued interest, which approximates fair value. Held-to-maturity U.S. Treasury securities are recorded at amortized cost with interest and amortization of premiums and discounts included in interest income. Quarterly, the Company evaluates held-to-maturity securities for any other-than-temporary impairments related to any intention to sell or requirement to sell before its amortized costs are recovered. If a security is considered to be other-than-temporarily impaired, the difference between amortized cost and the amount that is determined to be recoverable is recorded in earnings.
Concentration of Credit Risk	Concentration of Credit Risk: ​ The Company’s services are provided primarily to customers throughout the United States and, to a lesser extent, Canada, Mexico, and other international locations. On a consolidated basis, the Company had no single customer representing more than 4% of its revenues in 2020, 2019, or 2018 or more than 6% of its accounts receivable balance at December 31, 2020 and 2019. The Company performs ongoing credit evaluations of its customers and generally does not require collateral. Historically, credit losses have been within management’s expectations.
Allowances	Allowances: Financial Instruments – Credit Losses ​ The Company maintains allowances for credit losses (formerly known as the allowance for doubtful accounts) and revenue adjustments on its trade receivables. The Company estimates the allowance for credit losses based on historical write-offs, factors surrounding the credit risk of specific customers, and forecasts of future economic conditions. In order to gather information regarding these trends and factors, the Company performs ongoing credit evaluations of customers, an analysis of accounts receivable aging by business segment, and an analysis of future economic conditions at period end. The allowance for revenue adjustments is an estimate based on historical revenue adjustments and current information regarding trends and business changes. Actual write-offs or adjustments could differ from the allowance estimates due to a number of factors, including future changes in the forecasted economic environment or new factors and risks surrounding a particular customer. Accounts receivable are written off when the accounts are turned over to a collection agency or when the accounts are determined to be uncollectible. Actual write-offs and adjustments are charged against the allowances for doubtful accounts and revenue adjustments. The allowance for credit losses on the Company’s trade accounts receivable totaled $3.6 million and $1.8 million at December 31, 2020 and 2019, respectively. During 2020, the allowance for credit losses increased $4.3 million and was reduced $2.5 million by write-offs, net of recoveries. ​
Property, Plant and Equipment, Including Repairs and Maintenance	Property, Plant and Equipment, Including Repairs and Maintenance: Purchases of property, plant and equipment are recorded at cost. For financial reporting purposes, property, plant and equipment is depreciated principally by the straight-line method, using the following useful lives: structures – primarily 15 to 60 years ; revenue equipment – 3 to 16 years ; and other equipment – 2 to 15 years . The Company utilizes tractors and trailers in its operations. Tractors and trailers are commonly referred to as “revenue equipment” in the transportation business. The Company periodically reviews and adjusts, as appropriate, the residual values and useful lives of revenue equipment and other equipment. For tax reporting purposes, accelerated depreciation or cost recovery methods are used. Gains and losses on asset sales are reflected in the year of disposal. Exchanges of nonmonetary assets that have commercial substance are measured based on the fair value of the assets exchanged. Tires purchased with revenue equipment are capitalized as a part of the cost of such equipment, with replacement tires being expensed when placed in service. Repair and maintenance costs associated with property, plant and equipment are expensed as incurred if the costs do not extend the useful life of the asset. If such costs do extend the useful life of the asset, the costs are capitalized and depreciated over the appropriate remaining useful life.
Computer Software for Internal Use, Including Web Site Development and Cloud Computing Costs	Computer Software for Internal Use, Including Web Site Development and Cloud Computing Costs: The Company capitalizes the costs of software acquired from third parties and qualifying internal computer software costs incurred during the application development stage, or during the implementation stage for cloud computing or hosting arrangements. Costs incurred in the preliminary project stage and postimplementation-operation stage, which includes maintenance and training costs, are expensed as incurred. For financial reporting purposes, capitalized software costs are amortized by the straight-line method generally over 2 to 7 years . Capitalized costs related to cloud computing and hosting arrangements are presented within prepaid expenses in the accompanying consolidated balance sheets. The amount of costs capitalized within any period is dependent on the nature of software development activities and projects in each period.
Impairment Assessment of Long-Lived Assets	Impairment Assessment of Long-Lived Assets: amount of the asset may not be recoverable . ​ Assets to be disposed of are reclassified as assets held for sale at the lower of their carrying amount or fair value less cost to sell. Assets held for sale primarily represent Asset-Based segment nonoperating properties, older revenue equipment, and other equipment. Adjustments to write down assets to fair value less the amount of costs to sell are reported in operating income. Assets held for sale are expected to be disposed of by selling the assets within the next 12 months. Gains and losses on property and equipment are reported in operating income. Assets held for sale of $1.1 million and $1.3 million are reported within other noncurrent assets as of December 31, 2020 and 2019, respectively.
Goodwill and Intangible Assets	Goodwill and Intangible Assets: ​ Indefinite-lived intangible assets are also not amortized but rather are evaluated for impairment annually or more frequently if indicators of impairment exist. If the carrying amount of the intangible asset exceeds its fair value, an impairment loss shall be recognized in an amount equal to that excess. Fair values are determined based on a discounted cash flow model, similar to the goodwill analysis. ​ The Company amortizes finite-lived intangible assets over their respective estimated useful lives. ​
Income Taxes	Income Taxes: ​ Management applies considerable judgment in determining the consolidated income tax provision, including valuation allowances on deferred tax assets. The valuation allowance for deferred tax assets is determined by evaluating whether it is more likely than not that the benefits of deferred tax assets will be realized through future reversal of existing taxable temporary differences, taxable income in carryback years in jurisdictions in which they are allowable, projected future taxable income, or tax-planning strategies. Uncertain tax positions, which also require significant judgment, are measured to determine the amounts to be recognized in the financial statements. The income tax provision and valuation allowances are complicated by complex and frequently changing rules administered in multiple jurisdictions, including U.S. federal, state, and foreign governments. ​ The Company’s income taxes for the year ended December 31, 2018, were impacted by the recognition of the effects of the Tax Cuts and Jobs Act (the “Tax Reform Act”) that was signed into law on December 22, 2017 (see Note E). ​
Book Overdrafts	Book Overdrafts: ​
Insurance Reserves	Insurance Reserves ​ Liabilities for self-insured workers’ compensation and third-party casualty claims are based on the case reserve amounts plus an estimate of loss development and incurred but not reported (“IBNR”) claims, which is developed from an independent actuarial analysis. The process of determining reserve requirements utilizes historical trends and involves an evaluation of claim frequency and severity, claims management, and other factors. Case reserves are evaluated as loss experience develops and new information becomes available. Adjustments to previously estimated aggregate reserves are reflected in financial results in the periods in which they are made. Aggregate reserves represent an estimate of the costs of claims incurred, and it is possible that the ultimate liability may differ significantly from such estimates. ​ The Company develops an estimate of self-insured cargo loss and damage claims liabilities based on historical trends and certain event-specific information. Claims liabilities are recorded in accrued expenses and are not offset by insurance receivables which are reported in other accounts receivable.
Long-Term Debt	Long-Term Debt:
Interest Rate Swap Derivative Instruments	Interest Rate Swap Derivative Instruments
Leases	Leases: Leases ​ The short-term lease exemption was elected under ASC Topic 842 for all classes of assets to include real property, revenue equipment, and service, office, and other equipment. The Company adopted the policy election as a lessee for all classes of assets to account for each lease component and its related non-lease component(s) as a single lease component. In determining the discount rate, the Company uses ArcBest Corporation’s incremental borrowing rate unless the rate implicit in the lease is readily determinable when entering into a lease as a lessee. The incremental borrowing rate is determined by the price of a fully collateralized loan with similar terms based on current market rates. ​ An assessment is made on or after the effective date of newly signed contracts as to whether the contract is, or contains, a lease at the inception of a contract. The assessment is based on: (1) whether the contract involves the use of a distinct identified asset; (2) whether the Company obtains the right to substantially all the economic benefit from the use of the asset throughout the period; and (3) whether the Company has the right to direct the use of the asset. For all operating leases that meet the scope of ASC Topic 842, a right-of-use asset and a lease liability are recognized. The right-of-use asset is measured as the initial amount of the lease liability, plus any initial direct costs incurred, less any prepayments prior to commencement or lease incentives received. The lease liability is initially measured at the present value of the lease payments, discounted using the Company’s secured incremental borrowing rate for the same term as the underlying lease unless the interest rate implicit in the lease is readily determined, then the implicit rate will be used. Lease payments included in the measurement of the lease liability are comprised of the following: (1) the fixed noncancelable lease payments, (2) payments for optional renewal periods where it is reasonably certain the renewal period will be exercised, and (3) payments for early termination options unless it is reasonably certain the lease will not be terminated early. Variable lease payments based on an index or rate are initially measured using the index or rate in effect at lease commencement and included in the measurement of the initial lease liability. Additional payments based on the change in an index or rate are recorded as a period expense when incurred. Lease modifications result in remeasurement of the lease liability. ​
Nonunion Defined Benefit Pension, Supplemental Benefit, and Postretirement Health Benefit Plans	Nonunion Defined Benefit Pension, Supplemental Benefit, and Postretirement Health Benefit Plans: ​ The Company recognizes the funded status of the supplemental benefit plan (the “SBP”) and postretirement health benefit plan in the consolidated balance sheet and recognizes changes in the funded status, net of tax, in the year in which they occur as a component of other comprehensive income or loss. The benefit obligations of the SBP and postretirement health benefit plan represent the funded status, as these plans do not have plan assets. Amounts recognized in other comprehensive income or loss are subsequently expensed as components of net periodic benefit cost by amortizing unrecognized net actuarial losses over the average remaining active service period of the plan participants and amortizing unrecognized prior service credits over the remaining years of service until full eligibility of the active participants at the time of the plan amendment which created the prior service credit. A corridor approach is not used for determining the amounts of net actuarial losses to be amortized. ​ The Company has not incurred service cost under the nonunion defined benefit pension plan or the SBP since the accrual of benefits under the plans was frozen on July 1, 2013 and December 31, 2009, respectively; however, the Company incurs service cost under the postretirement health benefit plan which is reported within operating expenses in the consolidated statements of operations. The other components of net periodic benefit cost (including pension settlement expense) of the nonunion defined benefit pension plan, the SBP, and the postretirement health benefit plan are reported within the other line item of other income (costs). ​ The expense and liability related to the SBP, postretirement health benefit plan, and, prior to termination, the nonunion defined benefit pension plan, are measured based upon a number of assumptions and using the services of a third-party actuary. The discount rates used to discount the plans’ obligations are determined by matching projected cash distributions with appropriate high-quality corporate bond yields in a yield curve analysis. Prior to plan termination, the Company established the expected rate of return on plan assets for the nonunion defined benefit pension plan by considering the historical and expected returns for the plan’s current investment mix. Assumptions are also made regarding expected retirement age, mortality, employee turnover, and, for the postretirement health benefit plan, future increases in health care costs. The assumptions used directly impact the net periodic benefit cost for a particular year. An actuarial gain or loss results when actual experience varies from the assumptions or when there are changes in actuarial assumptions. Actuarial gains and losses are not included in net periodic benefit cost in the period when they arise but are recognized as a component of other comprehensive income or loss and subsequently amortized as a component of net periodic benefit cost. ​ The Company uses December 31 as the measurement date for the SBP, postretirement health benefit plan, and, prior to termination, the nonunion defined benefit pension plan. Plan obligations are also remeasured upon curtailment and upon settlement. ​ The Company recorded quarterly pension settlement expense related to the nonunion defined benefit pension plan when qualifying distributions determined to be settlements were expected to exceed the estimated total annual interest cost of the plan. Benefit distributions under the SBP individually exceed the annual interest cost of the plan, and the Company records the related settlement expense when the amount of the benefit to be distributed is fixed, which is generally upon an employee’s termination of employment. Pension settlement expense for the nonunion defined benefit pension plan and SBP is presented in Note I. ​ In September 2018, the nonunion defined benefit pension plan received a favorable determination letter from the U.S. Internal Revenue Service (the “IRS”) regarding qualification of the plan termination as of December 31, 2017. Following receipt of the determination letter, the plan’s actuarial assumptions were updated to remeasure the benefit obligation on a plan termination basis as of September 30, 2018 in connection with recognition of the quarterly pension settlement charge. The Company made assumptions for participant benefit elections, rate of return, and discount rates, including the annuity contract interest rate. These assumptions were updated as of December 31, 2018 and upon each quarterly remeasurement for settlements during 2019 until the benefit obligation of the plan was settled as of September 30, 2019. For plan termination assumptions, the Company utilized a short-term discount rate which represented the Company’s current borrowing rate and an annuity contract interest rate based on current published rates.
Revenue Recognition	Revenue Recognition: ​ Asset-Based Segment Asset-Based segment revenues consist primarily of less-than-truckload freight delivery. Performance obligations are satisfied upon final delivery of the freight to the specified destination. Revenue is recognized based on the relative transit time in each reporting period with expenses recognized as incurred. A bill-by-bill analysis is used to establish estimates of revenue in transit for recognition in the appropriate period. Because the bill-by-bill methodology utilizes the approximate location of the shipment in the delivery process to determine the revenue to recognize, management believes it to be a reliable method. ​ Certain contracts may provide for volume-based or other discounts which are accounted for as variable consideration. The Company estimates these amounts based on a historical expectation of discounts to be earned by customers, and revenue is recognized based on the estimates. Revenue adjustments may also occur due to rating or other billing adjustments. The Company estimates revenue adjustments based on historical information and revenue is recognized accordingly at the time of shipment. Management believes that actual amounts will not vary significantly from estimates of variable consideration. ​ Revenue, purchased transportation expense, and third-party service expenses are reported on a gross basis for certain shipments and services where the Company utilizes a third-party carrier for pickup, linehaul, delivery of freight, or performance of services but remains primarily responsible for fulfilling delivery to the customer and maintains discretion in setting the price for the services. ​ ArcBest Segment ArcBest segment revenues consist primarily of asset-light logistics services using third-party vendors to provide transportation services. ArcBest segment revenue is generally recognized based on the relative transit time in each reporting period using estimated standard delivery times for freight in transit at the end of the reporting period. Purchased transportation expense is recognized as incurred consistent with the recognition of revenue. ​ Revenue and purchased transportation expense are reported on a gross basis for shipments and services where the Company utilizes a third-party carrier for pickup and delivery but remains primarily responsible to the customer for delivery and maintains discretion in setting the price for the service. ​ FleetNet Segment FleetNet segment revenues consist of service fee revenue, roadside repair revenue and routine maintenance services revenue. Service fee revenue for the FleetNet segment is recognized upon response to the service event. Repair and routine maintenance service revenue for the FleetNet segment is recognized upon completion of the service by third-party vendors. Revenue and expense from repair and maintenance services performed by third-party vendors are reported on a gross basis as FleetNet controls the services prior to transfer to the customer and remains primarily responsible to the customer for completion of the services. ​ Other Recognition and Disclosure Payment terms with customers may vary depending on the service provided, location or specific agreement with the customer. The term between invoicing and when payment is due is not significant. For certain services, payment is required before the services are provided to the customer. ​ The Company expenses sales commissions when incurred because the amortization period is one year or less. ​ The Company has elected not to disclose the value of unsatisfied performance obligations for contracts with an original length of one year or less or contracts for which revenue is recognized at the amount to which the Company has the right to invoice for services performed. ​
Comprehensive Income or Loss	Comprehensive Income or Loss:
Earnings Per Share	Earnings Per Share: ​ Effective in 2020, the Company no longer has equity awards that are deemed participating securities. Basic earnings per share is calculated by dividing net income by the daily weighted number of shares of the Company’s common stock outstanding for the period. Diluted earnings per share is calculated using the treasury stock method. Under this method, the denominator used in calculating diluted earnings per share includes the impact of unvested restricted equity awards. ​
Share-Based Compensation	Share-Based Compensation: The fair value of restricted stock awards is determined based upon the closing market price of the Company’s common stock on the date of grant. The restricted stock units (“RSUs”) generally vest at the end of a five-year period following the date of grant for RSUs awarded prior to 2018 and at the end of a four-year period following the date of grant for subsequent grants. Awards granted to non-employee directors typically vest at the end of a one-year period, subject to accelerated vesting due to death, disability, retirement, or change-in-control provisions. When RSUs become vested, the Company issues new shares which are subsequently distributed. Effective in 2020, the Company no longer has equity awards which are paid dividends or dividend equivalents during the vesting period. The Company recognizes the income tax benefits of dividends on share-based payment awards as income tax expense or benefit in the consolidated statements of operations when awards vest or are settled. ​ Share-based awards are amortized to compensation expense on a straight-line basis over the vesting period of awards or over the period to which the recipient first becomes eligible for retirement, whichever is shorter, with vesting accelerated upon death or disability. The Company recognizes forfeitures as they occur and the income tax effects of awards are recognized in the statement of operations when awards vest or are settled.
Fair Value Measurements	Fair Value Measurements: ​ ● Level 1 – Quoted prices for identical assets and liabilities in active markets. ● Level 2 – Quoted prices for similar assets and liabilities in active markets, quoted prices for identical or similar assets and liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data. ● Level 3 – Unobservable inputs (Company’s market assumptions) that are significant to the valuation model. ​
Environmental Matters	Environmental Matters:
Exit or Disposal Activities	Exit or Disposal Activities:
Adopted Accounting Pronouncements and Accounting Pronouncements Not Yet Adopted	Adopted Accounting Pronouncements ​ As previously discussed in the accounting policy for allowances within this Note, effective January 1, 2020, the Company adopted ASC Topic 326, which replaced the incurred loss methodology model with an expected loss methodology referred to as the CECL methodology for the Company’s trade receivables and other receivables. The Company adopted ASC Topic 326 with the modified retrospective approach. Under this approach, results for reporting periods after January 1, 2020 are presented under ASC Topic 326 while prior period amounts continue to be reported in accordance with previously applicable accounting guidance. The Company recorded a decrease to retained earnings of $0.2 million as of January 1, 2020 for the cumulative effect of adopting ASC Topic 326. ​ On January 1, 2020 the Company adopted ASC Subtopic 350-40, Intangibles – Goodwill and Other – Internal-Use Software: Customer’s Accounting for Fees Paid in a Cloud Computing Arrangement , (“ASC Subtopic 350-40”). The amendments to ASC Subtopic 350-40 clarify the accounting treatment for implementation costs incurred by the customer in a cloud computing software arrangement. The amendments allow implementation costs of cloud computing arrangements to be capitalized using the same method prescribed by ASC Subtopic 350-40, Internal-Use Software . The amendments to ASC Subtopic 350-40 were adopted on a prospective basis and did not have an impact on the Company’s consolidated financial statements. ​ On January 1, 2020 the Company adopted ASC Topic 820, Fair Value Measurement , which was amended to modify the disclosure requirements of fair value measurements, primarily impacting the disclosures for Level 3 fair value measurements. The amendment did not have an impact on the Company’s financial statement disclosures. ​ The amendments to ASC Topic 848, Reference Rate Reform ​ Accounting Pronouncements Not Yet Adopted ​ ASC Topic 740, Income Taxes

FINANCIAL INSTRUMENTS AND FAI_2

FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS (Tables)	12 Months Ended
	Dec. 31, 2020
FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS
Schedule components of cash and cash equivalents, short term investments, and restricted funds	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31 December 31 ​ ​ 2020 ​ 2019 ​ ​ ​ (in thousands) ​ Cash and cash equivalents ​ ​ ​ ​ ​ ​ ​ Cash deposits (1) ​ $ 240,687 ​ $ 166,619 ​ Variable rate demand notes (1)(2) ​ 29,066 ​ 14,750 ​ Money market funds (3) ​ 34,201 ​ 20,540 ​ Total cash and cash equivalents ​ $ 303,954 ​ $ 201,909 ​ ​ ​ ​ ​ ​ ​ ​ ​ Short-term investments ​ ​ ​ ​ ​ ​ ​ Certificates of deposit (1) ​ $ 53,297 ​ $ 69,314 ​ U.S. Treasury securities (4) ​ ​ 12,111 ​ ​ 47,265 ​ Total short-term investments ​ $ 65,408 ​ $ 116,579 ​ (1) Recorded at cost plus accrued interest, which approximates fair value. (2) Amounts may be redeemed on a daily basis with the original issuer. (3) Recorded at fair value as determined by quoted market prices (see amounts presented in the table of financial assets and liabilities measured at fair value within this Note). (4) Recorded at amortized cost plus accrued interest, which approximates fair value. U.S. Treasury securities included in short-term investments are held-to-maturity investments with maturity dates of less than one year.
Schedule of fair value and carrying value disclosures of financial instruments	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 2019 ​ ​ (in thousands) ​ ​ ​ ​ Carrying ​ Fair ​ Carrying ​ Fair ​ ​ ​ ​ Value ​ Value ​ Value ​ Value ​ Credit Facility (1) ​ $ 70,000 ​ $ 70,000 ​ $ 70,000 ​ $ 70,000 ​ Accounts receivable securitization borrowings (2) ​ ​ — ​ ​ — ​ ​ 40,000 ​ ​ 40,000 ​ Notes payable (3) ​ 214,216 ​ 217,226 ​ 213,504 ​ 216,432 ​ New England Pension Fund withdrawal liability (4) ​ ​ 21,407 ​ ​ 25,523 ​ ​ 22,018 ​ ​ 24,462 ​ ​ ​ $ 305,623 ​ $ 312,749 ​ $ 345,522 ​ $ 350,894 ​ (1) The Credit Facility carries a variable interest rate based on LIBOR, plus a margin, that is considered to be priced at market for debt instruments having similar terms and collateral requirements (Level 2 of the fair value hierarchy). (2) Borrowings under the Company’s accounts receivable securitization program carry a variable interest rate based on LIBOR, plus a margin, that is considered to be priced at market for debt instruments having similar terms and collateral requirements (Level 2 of the fair value hierarchy). (3) Fair value of the notes payable was determined using a present value income approach based on quoted interest rates from lending institutions with which the Company would enter into similar transactions (Level 2 of the fair value hierarchy). (4) ABF Freight’s multiemployer pension plan obligation with the New England Teamsters and Trucking Industry Pension Fund (the “New England Pension Fund”) was restructured under a transition agreement effective on August 1, 2018, which resulted in a related withdrawal liability (see Note I). The fair value of the outstanding withdrawal liability is equal to the present value of the future withdrawal liability payments, discounted at an interest rate of 2.6% and 3.4% at December 31, 2020 and 2019, respectively, determined using the 20-year U.S. Treasury rate plus a spread (Level 2 of the fair value hierarchy). Included in other long-term liabilities with the current portion included in accrued expenses.
Schedule of financial assets and liabilities measured at fair value on a recurring basis	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ ​ ​ ​ ​ ​ Fair Value Measurements Using ​ ​ ​ ​ ​ ​ Quoted Prices Significant Significant ​ ​ ​ ​ ​ In Active ​ Observable ​ Unobservable ​ ​ ​ ​ ​ ​ Markets ​ Inputs ​ Inputs ​ ​ ​ Total (Level 1) (Level 2) (Level 3) ​ ​ (in thousands) ​ Assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds (1) ​ $ 34,201 ​ $ 34,201 ​ $ — ​ $ — ​ Equity, bond, and money market mutual funds held in trust related to the Voluntary Savings Plan (2) ​ 2,955 ​ 2,955 ​ — ​ — ​ ​ ​ $ 37,156 ​ $ 37,156 ​ $ — ​ $ — ​ Liabilities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Interest rate swaps (3) ​ $ 1,622 ​ $ — ​ $ 1,622 ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ ​ ​ ​ ​ ​ Fair Value Measurements Using ​ ​ ​ ​ ​ ​ Quoted Prices Significant Significant ​ ​ ​ ​ ​ In Active ​ Observable ​ Unobservable ​ ​ ​ ​ ​ ​ Markets ​ Inputs ​ Inputs ​ ​ ​ Total (Level 1) (Level 2) (Level 3) ​ ​ ​ (in thousands) ​ Assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds (1) ​ $ 20,540 ​ $ 20,540 ​ $ — ​ $ — ​ Equity, bond, and money market mutual funds held in trust related to the Voluntary Savings Plan (2) ​ 2,427 ​ 2,427 ​ — ​ — ​ ​ ​ $ 22,967 ​ $ 22,967 ​ $ — ​ $ — ​ Liabilities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Interest rate swaps (3) ​ $ 563 ​ $ — ​ $ 563 ​ $ — ​ ​ ​ (1) Included in cash and cash equivalents. (2) Nonqualified deferred compensation plan investments consist of U.S. and international equity mutual funds, government and corporate bond mutual funds, and money market funds which are held in a trust with a third-party brokerage firm. Included in other long-term assets, with a corresponding liability reported within other long-term liabilities. (3) Included in other long-term liabilities. The fair values of the interest rate swaps were determined by discounting future cash flows and receipts based on expected interest rates observed in market interest rate curves adjusted for estimated credit valuation considerations reflecting nonperformance risk of the Company and the counterparty, which are considered to be in Level 3 of the fair value hierarchy. The Company assessed Level 3 inputs as insignificant to the valuation at December 31, 2020 and December 31, 2019 and considers the interest rate swap valuations in Level 2 of the fair value hierarchy. ​
Schedule of fair value of assets measured on non recurring basis	There were no assets remeasured on a nonrecurring basis at December 31, 2020. The following table presents the fair value of assets remeasured on a nonrecurring basis as of December 31, 2019. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ ​ ​ ​ Nonrecurring Fair Value Remeasurements ​ ​ ​ Significant ​ ​ ​ ​ ​ ​ Unobservable Inputs ​ Total ​ ​ ​ ​ (Level 3) Losses ​ ​ ​ (in thousands) ​ Assets: ​ ​ ​ ​ ​ ​ ​ ​ Goodwill (1) ​ $ 83,842 ​ $ (20,000) ​ ​ Long-lived assets (2) ​ 6,805 ​ (6,514) ​ ​ ​ ​ $ 90,647 ​ $ (26,514) ​ ​ (1) A portion of the goodwill within the ArcBest segment was reduced to its implied fair value as of October 1, 2019 (see Note D). (2) Represents fair value of the dedicated asset group within the ArcBest segment. Losses include write-downs of $6.0 million related to customer relationship intangibles (see Note D) and $0.5 million related to revenue equipment within the dedicated asset group included in the ArcBest segment reducing the carrying amounts to implied fair value as of October 1, 2019.

GOODWILL AND INTANGIBLE ASSETS

GOODWILL AND INTANGIBLE ASSETS (Tables)	12 Months Ended
	Dec. 31, 2020
GOODWILL AND INTANGIBLE ASSETS
Schedule of goodwill by reportable operating segment	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total ArcBest FleetNet ​ ​ (in thousands) Balances at December 31, 2018 ​ $ 108,320 ​ $ 107,690 ​ $ 630 ​ Goodwill impairment (1) ​ ​ (20,000) ​ ​ (20,000) ​ ​ — ​ Balances at December 31, 2019 and 2020 (2) ​ $ 88,320 ​ $ 87,690 ​ $ 630 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Accumulated impairment at December 31, 2019 and 2020 ​ $ (20,000) ​ $ (20,000) ​ $ — ​ (1) Goodwill impairment charge related to the ArcBest segment further described within this Note. (2) Goodwill was not adjusted during the year ended December 31, 2020.
Schedule of intangible assets	Intangible assets consisted of the following as of December 31: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ 2019 ​ ​ Weighted-Average ​ ​ ​ ​ Accumulated ​ Net ​ ​ ​ ​ Accumulated ​ Net ​ Amortization Period Cost Amortization Value ​ Cost Amortization Value ​ ​ (in years) ​ (in thousands) ​ (in thousands) Finite-lived intangible assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Customer relationships 14 ​ $ 52,721 ​ $ 30,477 ​ $ 22,244 ​ $ 52,721 ​ $ 26,667 ​ $ 26,054 ​ Other ​ 13 ​ ​ 980 ​ ​ 543 ​ ​ 437 ​ ​ 1,294 ​ ​ 816 ​ ​ 478 ​ ​ 14 ​ 53,701 ​ 31,020 ​ 22,681 ​ ​ 54,015 ​ 27,483 ​ 26,532 ​ Indefinite-lived intangible assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Trade name N/A ​ 32,300 ​ N/A ​ 32,300 ​ ​ 32,300 ​ N/A ​ 32,300 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total intangible assets N/A ​ $ 86,001 ​ $ 31,020 ​ $ 54,981 ​ $ 86,315 ​ $ 27,483 ​ $ 58,832 ​
Schedule of future amortization for intangible assets	​ ​ ​ ​ ​ ​ ​ Amortization of ​ ​ Intangible Assets ​ ​ ​ (in thousands) ​ 2021 ​ $ 3,838 ​ 2022 ​ 3,815 ​ 2023 ​ 3,722 ​ 2024 ​ 3,689 ​ 2025 ​ ​ 3,674 ​ Thereafter ​ ​ 3,943 ​ Total amortization ​ $ 22,681 ​

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2020
INCOME TAXES
Schedule of significant components of the provision or benefit for income taxes	Significant components of the provision or benefit for income taxes for the years ended December 31 were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 2019 2018 (1) ​ ​ (in thousands) Current provision: ​ ​ ​ ​ Federal ​ $ 10,001 ​ $ 2,202 ​ $ 9,750 ​ State ​ 3,267 ​ 1,813 ​ 3,264 ​ Foreign ​ 413 ​ 2,060 ​ 2,238 ​ ​ ​ 13,681 ​ 6,075 ​ 15,252 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Deferred provision (benefit): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Federal ​ 5,948 ​ 4,196 ​ 1,157 ​ State ​ 1,789 ​ 1,221 ​ 737 ​ Foreign ​ (22) ​ (6) ​ (22) ​ ​ ​ 7,715 ​ 5,411 ​ 1,872 ​ Total provision for income taxes ​ $ 21,396 ​ $ 11,486 ​ $ 17,124 ​ (1) For 2018, the income tax provision reflects the impact of the Tax Reform Act, as previously disclosed in this Note.
Schedule of components of the deferred tax provision or benefit	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 (1) ​ 2019 (1) ​ 2018 (1)(2) ​ ​ (in thousands) Amortization, depreciation, and basis differences for property, plant and equipment and other long-lived assets $ 4,975 $ 16,255 $ 23,153 ​ Amortization of intangibles and impairment ​ 183 ​ (6,933) ​ (763) ​ Changes in reserves for workers’ compensation, third-party casualty, and cargo claims ​ (182) ​ (1,880) ​ 469 ​ Revenue recognition ​ (1,481) ​ (1,437) ​ (2,524) ​ Allowance for doubtful accounts ​ (652) ​ 541 ​ (115) ​ Nonunion pension and other retirement plans ​ 957 ​ 564 ​ (2,810) ​ Multiemployer pension fund withdrawal (3) ​ ​ 157 ​ ​ 150 ​ ​ (5,818) ​ Federal and state net operating loss carryforwards utilized (generated) ​ (259) ​ 59 ​ 746 ​ State depreciation adjustments ​ 343 ​ (1,302) ​ (1,761) ​ Share-based compensation ​ (195) ​ (709) ​ (529) ​ Valuation allowance increase (decrease) ​ 617 ​ 383 ​ (744) ​ Other accrued expenses ​ 1,663 ​ (699) ​ (4,881) ​ Impact of the Tax Reform Act (2) ​ ​ — ​ ​ — ​ ​ (3,772) ​ Prepaid expenses ​ ​ 1,207 ​ ​ 1,782 ​ ​ 1,313 ​ Operating lease right-of-use assets/liabilities – net (4) ​ ​ (13) ​ ​ (1,049) ​ ​ — ​ Other ​ 395 ​ (314) ​ (92) ​ Deferred tax provision ​ $ 7,715 ​ $ 5,411 ​ $ 1,872 ​ (1) The components of the deferred tax provision reflect the statutory U.S. income tax rate in effect for the applicable year, which is a blended rate for 2018 (as previously discussed within this Note), and 21% for 2019 and 2020. (2) For 2018, the effect of the change in the U.S. corporate tax rate from 35% to 21% in accordance with the Tax Reform Act is reflected as a separate component of the deferred tax provision. (3) ABF Freight recorded a multiemployer pension fund withdrawal liability in 2018 resulting from the transition agreement it entered into with the New England Pension Fund (see Note I). (4) Net change in operating lease right-of-use deferred tax assets and liabilities recorded due to the adoption of ASC Topic 842 in 2019.
Schedule of significant components of deferred tax assets and liabilities	Significant components of the deferred tax assets and liabilities at December 31 were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ 2019 ​ ​ (in thousands) Deferred tax assets: ​ ​ ​ Accrued expenses ​ $ 40,502 ​ $ 41,757 ​ Operating lease liabilities (1) ​ ​ 33,933 ​ ​ 19,726 ​ Supplemental pension liabilities ​ ​ 103 ​ ​ 1,091 ​ Multiemployer pension fund withdrawal (2) ​ ​ 5,409 ​ ​ 5,546 ​ Postretirement liabilities other than pensions ​ 4,871 ​ 5,359 ​ Share-based compensation ​ 5,827 ​ 5,605 ​ Federal and state net operating loss carryovers ​ 1,353 ​ 1,093 ​ Revenue recognition ​ ​ 1,426 ​ ​ — ​ Other ​ 1,297 ​ 1,538 ​ Total deferred tax assets ​ 94,721 ​ 81,715 ​ Valuation allowance ​ (1,284) ​ (668) ​ Total deferred tax assets, net of valuation allowance ​ 93,437 ​ 81,047 ​ ​ ​ ​ ​ ​ ​ ​ ​ Deferred tax liabilities: ​ ​ ​ ​ ​ ​ ​ Amortization, depreciation, and basis differences for property, plant and equipment, and other long-lived assets ​ 113,092 ​ 107,835 ​ Operating lease right-of-use assets (1) ​ ​ 32,923 ​ ​ 18,703 ​ Intangibles ​ 7,520 ​ 7,373 ​ Revenue recognition ​ — ​ 669 ​ Prepaid expenses ​ 6,151 ​ 4,952 ​ Total deferred tax liabilities ​ 159,686 ​ 139,532 ​ Net deferred tax liabilities ​ $ (66,249) ​ $ (58,485) ​ (1) Operating lease right-of-use assets and liabilities were recorded in 2019 due to the adoption of ASC Topic 842. (2) ABF Freight recorded a multiemployer pension fund withdrawal liability in 2018 resulting from the transition agreement it entered into with the New England Pension Fund (see Note I). ​
Reconciliation between the effective income tax rate, as computed on income or loss before income taxes, and the statutory federal income tax rate	Reconciliation between the effective income tax rate, as computed on income before income taxes, and the statutory federal income tax rate for the years ended December 31 is presented in the following table: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 (1) ​ 2019 (1) ​ 2018 (1) ​ ​ (in thousands, except percentages) Income tax provision at the statutory federal rate $ 19,424 $ 10,809 $ 17,721 ​ Federal income tax effects of: ​ ​ ​ ​ ​ ​ ​ ​ ​ State income taxes ​ (1,062) ​ (637) ​ (840) ​ Nondeductible expenses ​ 1,395 ​ 1,344 ​ 1,682 ​ Life insurance proceeds and changes in cash surrender value ​ (488) ​ (775) ​ 7 ​ Alternative fuel credit ​ (1,261) ​ (2,340) ​ (1,203) ​ Net increase (decrease) in valuation allowances ​ 617 ​ 382 ​ (891) ​ Net increase (decrease) in uncertain tax positions ​ ​ (933) ​ ​ (20) ​ ​ 933 ​ Settlement of share-based compensation ​ ​ 420 ​ ​ 388 ​ ​ (649) ​ Impact of the Tax Reform Act on current tax (1) ​ ​ — ​ ​ — ​ ​ (52) ​ Impact of the Tax Reform Act on deferred tax (1) ​ ​ — ​ ​ — ​ ​ (3,772) ​ Nonunion pension termination expense ​ ​ — ​ ​ 1,040 ​ ​ — ​ Foreign tax credits generated ​ ​ (391) ​ ​ (2,054) ​ ​ (2,216) ​ Federal research and development tax credits ​ ​ (2,078) ​ ​ (1,354) ​ ​ — ​ Other ​ 306 ​ (385) ​ 187 ​ Federal income tax provision ​ 15,949 ​ 6,398 ​ 10,907 ​ State income tax provision ​ 5,056 ​ 3,034 ​ 4,001 ​ Foreign income tax provision ​ 391 ​ 2,054 ​ 2,216 ​ Total provision for income taxes ​ $ 21,396 ​ $ 11,486 ​ $ 17,124 ​ Effective tax rate ​ 23.1 % 22.3 % 20.3 % (1) Amounts in this reconciliation reflect the statutory U.S. income tax rate in effect for the applicable year after the enactment of the Tax Reform Act, which is 21% . The effect of applying a blended rate of 32.74% for the two months ended February 28, 2018, in accordance with the Tax Reform Act, is reflected in separate components of the reconciliation. ​

LEASES (Tables)

LEASES (Tables)	12 Months Ended
	Dec. 31, 2020
Leases
Schedule of components of lease expense	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31 ​ 2020 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) Operating lease expense ​ $ 24,559 ​ $ 22,291 ​ Variable lease expense ​ ​ 3,152 ​ ​ 3,366 ​ Sublease income ​ ​ (398) ​ ​ (324) ​ ​ ​ ​ ​ ​ ​ ​ ​ Total operating lease expense (1) ​ $ 27,313 ​ $ 25,333 ​ (1) Operating lease expense excludes short-term leases with a term of 12 months or less.
Schedule of operating cash flows from operating lease activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31 ​ ​ ​ 2020 ​ 2019 ​ ​ ​ (in thousands) ​ Noncash change in operating right-of-use assets ​ $ 21,184 ​ $ 20,439 ​ Change in operating lease liabilities ​ ​ (20,428) ​ ​ (19,711) ​ Operating right-of-use-assets and lease liabilities, net ​ $ 756 ​ $ 728 ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash paid for amounts included in the measurement of operating lease liabilities ​ $ (23,810) ​ $ (21,714) ​
Schedule of supplemental balance sheet information related to lease liabilities	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ ​ (in thousands, except lease term and discount rate) ​ ​ ​ ​ ​ Land and ​ Equipment ​ ​ ​ Total ​ Structures ​ and Others Operating right-of-use assets (long-term) ​ $ 115,195 ​ $ 114,908 ​ $ 287 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Operating lease liabilities (current) ​ $ 21,482 ​ $ 21,207 ​ $ 275 Operating lease liabilities (long-term) ​ 97,839 ​ ​ 97,828 ​ ​ 11 Total operating lease liabilities ​ $ 119,321 ​ $ 119,035 ​ $ 286 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average remaining lease term (in years) ​ ​ 6.7 ​ ​ ​ ​ ​ ​ Weighted-average discount rate ​ ​ 3.18% ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ ​ ​ (in thousands, except lease term and discount rate) ​ ​ ​ ​ ​ ​ Land and ​ Equipment ​ ​ ​ ​ Total ​ Structures ​ and Others ​ Operating right-of-use assets (long-term) ​ $ 68,470 ​ $ 67,227 ​ $ 1,243 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Operating lease liabilities (current) ​ $ 20,265 ​ $ 19,293 ​ $ 972 ​ Operating lease liabilities (long-term) ​ 52,277 ​ ​ 52,008 ​ ​ 269 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total operating lease liabilities ​ $ 72,542 ​ $ 71,301 ​ $ 1,241 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average remaining lease term (in years) ​ ​ 5.3 ​ ​ ​ ​ ​ ​ ​ Weighted-average discount rate ​ ​ 3.77% ​ ​ ​ ​ ​ ​ ​
Schedule of maturities of operating lease liabilities	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Equipment ​ ​ ​ ​ ​ ​ Land and ​ and ​ ​ Total Structures Other ​ (in thousands) ​ 2021 ​ $ 24,629 ​ $ 24,352 ​ $ 277 ​ 2022 ​ 21,073 ​ 21,062 ​ 11 ​ 2023 ​ 16,755 ​ 16,755 ​ — ​ 2024 ​ 14,668 ​ 14,668 ​ — ​ 2025 ​ 12,153 ​ 12,153 ​ — ​ Thereafter ​ 43,035 ​ 43,035 ​ — ​ Total lease payments ​ ​ 132,313 ​ ​ 132,025 ​ ​ 288 ​ Less imputed interest ​ ​ (12,992) ​ ​ (12,990) ​ ​ (2) ​ Total ​ $ 119,321 ​ $ 119,035 ​ $ 286 ​

LONG-TERM DEBT AND FINANCING _2

LONG-TERM DEBT AND FINANCING ARRANGEMENTS (Tables)	12 Months Ended
	Dec. 31, 2020
LONG-TERM DEBT AND FINANCING ARRANGEMENTS
Schedule of long-term debt	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31 ​ December 31 ​ ​ 2020 2019 ​ ​ (in thousands) ​ Credit Facility (interest rate of 1.3% (1) ​ $ 70,000 ​ $ 70,000 ​ Accounts receivable securitization borrowings ​ — ​ 40,000 ​ Notes payable (weighted-average interest rate of 3.0% at December 31, 2020) ​ 214,216 ​ 213,504 ​ Finance lease obligations (weighted-average interest rate of 3.3% at December 31, 2020) ​ 8 ​ 15 ​ ​ ​ 284,224 ​ 323,519 ​ Less current portion ​ 67,105 ​ 57,305 ​ Long-term debt, less current portion ​ $ 217,119 ​ $ 266,214 ​ (1) The interest rate swap mitigates interest rate risk by effectively converting $50.0 million of borrowings under the Credit Facility from variable-rate interest to fixed-rate interest with a per annum rate of 3.12% and 2.98% based on the margin of the Credit Facility as of December 31, 2020 and 2019, respectively.
Scheduled maturities of long-term debt obligations	Scheduled maturities of long term debt obligations as of December 31, 2020 were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Credit Notes Finance Lease ​ ​ ​ Total ​ Facility (1) ​ Payable ​ Obligations ​ ​ ​ (in thousands) ​ 2021 ​ $ 73,386 ​ $ 886 ​ $ 72,493 ​ $ 7 ​ 2022 ​ 64,750 ​ 914 ​ ​ 63,835 ​ 1 ​ 2023 ​ 48,892 ​ 971 ​ ​ 47,921 ​ — ​ 2024 ​ 102,393 ​ 70,823 ​ ​ 31,570 ​ — ​ 2025 ​ 9,576 ​ ​ — ​ ​ 9,576 ​ ​ — ​ Thereafter ​ — ​ ​ — ​ ​ — ​ ​ — ​ Total payments ​ 298,997 ​ 73,594 ​ ​ 225,395 ​ 8 ​ Less amounts representing interest ​ 14,773 ​ 3,594 ​ 11,179 ​ — ​ Long-term debt ​ $ 284,224 ​ $ 70,000 ​ $ 214,216 ​ $ 8 ​ (1) The future interest payments included in the scheduled maturities due are calculated using variable interest rates based on the LIBOR swap curve, plus the anticipated applicable margin. ​ ​ Assets securing notes payable or held under finance leases at December 31 were included in property, plant and equipment as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 2019 ​ ​ (in thousands) Revenue equipment $ 326,823 $ 265,315 ​ Software ​ ​ — ​ ​ 2,140 ​ Service, office, and other equipment ​ ​ 26,270 ​ ​ 26,344 ​ Total assets securing notes payable or held under finance leases ​ 353,093 ​ 293,799 ​ Less accumulated depreciation and amortization (1) ​ 115,424 ​ 71,405 ​ Net assets securing notes payable or held under finance leases ​ $ 237,669 ​ $ 222,394 ​ (1) Amortization of assets held under finance leases and depreciation of assets securing notes payable are included in depreciation expense. ​
Schedule of assets securing notes payable or held under capital leases	​

ACCRUED EXPENSES (Tables)

ACCRUED EXPENSES (Tables)	12 Months Ended
	Dec. 31, 2020
ACCRUED EXPENSES
Schedule of accrued expenses	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31 ​ ​ 2020 2019 ​ ​ ​ (in thousands) ​ Workers’ compensation, third-party casualty, and loss and damage claims reserves ​ $ 103,898 ​ $ 107,149 ​ Accrued vacation pay ​ 51,728 ​ 47,730 ​ Accrued compensation, including retirement benefits (1) ​ ​ 67,690 ​ ​ 52,720 ​ Taxes other than income ​ 10,468 ​ 8,722 ​ Other ​ 12,962 ​ 16,000 ​ Total accrued expenses ​ $ 246,746 ​ $ 232,321 ​

EMPLOYEE BENEFIT PLANS (Tables)

EMPLOYEE BENEFIT PLANS (Tables)	12 Months Ended
	Dec. 31, 2020
EMPLOYEE BENEFIT PLANS
Schedule of changes in benefit obligations and plan assets and disclosure of funded status and accumulated benefit obligation of nonunion defined benefit plans	The following table discloses the changes in benefit obligations and plan assets of the Company’s nonunion defined benefit plans for years ended December 31, the measurement date of the plans: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nonunion Defined ​ Supplemental ​ Postretirement ​ ​ Benefit Pension Plan ​ Benefit Plan ​ Health Benefit Plan ​ 2020 2019 2020 2019 2020 2019 ​ ​ (in thousands) Change in benefit obligations ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Benefit obligations, beginning of year ​ $ — ​ $ 33,373 ​ $ 3,236 ​ $ 3,948 ​ $ 20,630 ​ $ 29,488 ​ Service cost ​ — ​ — ​ — ​ — ​ 187 ​ 320 ​ Interest cost ​ — ​ 624 ​ 9 ​ 39 ​ 576 ​ 1,212 ​ Actuarial (gain) loss (1) ​ — ​ 300 ​ 34 ​ 186 ​ (2,027) ​ (9,542) ​ Benefits paid ​ — ​ (34,297) ​ (2,887) ​ (937) ​ (615) ​ (848) ​ Benefit obligations, end of year ​ — ​ — ​ 392 ​ 3,236 ​ 18,751 ​ 20,630 ​ Change in plan assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value of plan asset, beginning of year ​ — ​ 26,646 ​ — ​ — ​ — ​ — ​ Actual return on plan assets ​ — ​ (59) ​ — ​ — ​ — ​ — ​ Employer contributions ​ — ​ 7,710 ​ 2,887 ​ 937 ​ 615 ​ 848 ​ Benefits paid ​ — ​ (34,297) ​ (2,887) ​ (937) ​ (615) ​ (848) ​ Fair value of plan assets, end of year ​ — ​ — ​ — ​ — ​ — ​ — ​ Funded status at period end ​ $ — ​ $ — ​ $ (392) ​ $ (3,236) ​ $ (18,751) ​ $ (20,630) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Accumulated benefit obligation ​ $ — ​ $ — ​ $ 392 ​ $ 3,236 ​ $ 18,751 ​ $ 20,630 ​ (1) The actuarial gain on the postretirement health benefit plan for 2020 is primarily related to the impact of actuarial assumptions on the valuation of plan costs, including lower health care cost trend rates, partially offset by a decrease in the discount rate used to remeasure the plan obligation at December 31, 2020 versus December 31, 2019. The actuarial gain on the postretirement health benefit plan for 2019 was primarily related to the impact of a lower cost prescription drug plan effective January 1, 2020.
Schedule of amounts recognized in the consolidated balance sheets related to nonunion defined benefit plans	Amounts recognized in the consolidated balance sheets at December 31 consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Supplemental ​ Postretirement ​ ​ Benefit Plan ​ Health Benefit Plan ​ 2020 2019 2020 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Current portion of pension and postretirement liabilities ​ $ — ​ $ (2,886) ​ $ (588) ​ $ (686) ​ Pension and postretirement liabilities, less current portion ​ (392) ​ (350) ​ (18,163) ​ (19,944) ​ Liabilities recognized ​ $ (392) ​ $ (3,236) ​ $ (18,751) ​ $ (20,630) ​ ​
Summary of the components of net periodic benefit cost	The following is a summary of the components of net periodic benefit cost for the Company’s nonunion benefit plans for the years ended December 31: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nonunion Defined ​ Supplemental ​ Postretirement ​ ​ ​ Benefit Pension Plan ​ Benefit Plan ​ Health Benefit Plan ​ ​ 2020 2019 2018 2020 2019 2018 2020 2019 2018 ​ ​ (in thousands) ​ ​ ​ Service cost ​ $ — ​ $ — ​ $ — ​ $ — ​ $ — ​ $ — ​ $ 187 ​ $ 320 ​ $ 366 ​ Interest cost ​ — ​ 624 ​ 4,269 ​ 9 ​ 39 ​ 108 ​ 576 ​ 1,212 ​ 837 ​ Expected return on plan assets ​ — ​ (31) ​ (1,582) ​ — ​ — ​ — ​ — ​ — ​ — ​ Amortization of prior service credit ​ — ​ — ​ — ​ — ​ — ​ — ​ (1) ​ (33) ​ (93) ​ Pension settlement expense (1) ​ — ​ 4,164 ​ 12,925 ​ 89 ​ 370 ​ — ​ — ​ — ​ — ​ Amortization of net actuarial (gain) loss (2) ​ — ​ 260 ​ 2,583 ​ 8 ​ 95 ​ 81 ​ (597) ​ 898 ​ 304 ​ Net periodic benefit cost ​ $ — ​ $ 5,017 ​ $ 18,195 ​ $ 106 ​ $ 504 ​ $ 189 ​ $ 165 ​ $ 2,397 ​ $ 1,414 ​ (1) For 2019, the presentation of pension settlement expense excludes a $4.0 million noncash pension termination expense which is further described within this Note. (2) The Company amortizes actuarial losses over the average remaining active service period of the plan participants and does not use a corridor approach. ​
Summary of pension settlement distributions and settlement expense	The following is a summary of the pension settlement distributions and pension settlement expense for the years ended December 31: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nonunion Defined ​ Supplemental ​ ​ Benefit Pension Plan ​ Benefit Plan ​ 2020 2019 (1) 2018 (2) 2020 (3) 2019 (4) 2018 ​ ​ (in thousands, except per share data) Pension settlement distributions ​ $ — ​ $ 33,938 ​ $ 105,279 ​ $ 2,887 ​ $ 937 ​ $ — ​ Pension settlement expense, pre-tax (5) ​ $ — ​ $ 4,164 ​ $ 12,925 ​ $ 89 ​ $ 370 ​ $ — ​ Pension settlement expense per diluted share, net of taxes ​ $ — ​ $ 0.12 ​ $ 0.36 ​ $ — ​ $ 0.01 ​ $ — ​ (1) Pension settlement distributions for 2019 represent $18.4 million of lump-sum benefit distributions, including participant-elected distributions associated with the plan’s termination, a $14.0 million nonparticipating annuity contract purchase, and a $1.5 million transfer of benefit obligations to the PBGC. (2) Pension settlement distributions for 2018 represent lump-sum benefit distributions, including participant-elected distributions associated with the plan’s termination. (3) The 2020 SBP distributions include the portion of a benefit related to an officer retirement that occurred in 2019 which was delayed for six months after retirement in accordance with IRC Section 409A. (4) The 2019 SBP distribution excludes the portion of the benefit related to an officer retirement which was delayed for six months after retirement in accordance with IRC Section 409A. The pension settlement expense related to the delayed distribution was recognized in 2019. (5) For 2019, the presentation of pension settlement expense excludes a $4.0 million noncash pension termination expense which is further described within this Note. ​
Pre-tax amounts included in accumulated other comprehensive loss that have not yet been recognized in net periodic benefit cost	​
Weighted-average assumptions used to determine benefit obligations and net periodic benefit cost for nonunion defined benefit plans	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Supplemental ​ Postretirement ​ ​ Benefit Plan ​ Health Benefit Plan ​ 2020 2019 2020 2019 Discount rate ​ 1.1 % 2.4 % 2.3 % 3.1 % ​ Weighted-average assumptions used to determine net periodic benefit cost for the Company’s nonunion benefit plans for the years ended December 31 were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nonunion Defined ​ Supplemental ​ Postretirement ​ ​ Benefit Pension Plan ​ Benefit Plan ​ Health Benefit Plan ​ 2020 2019 (1) 2018 (2) 2020 2019 2018 2020 2019 2018 Discount rate ​ N/A ​ 3.9 % 3.1 % 2.4 % 3.6 % 2.8 % 3.1 % 4.2 % 3.5 % Expected return on plan assets ​ N/A ​ 1.4 % 1.4 % N/A N/A N/A N/A N/A N/A ​ (1) The discount rate presented was used to determine the first quarter 2019 expense, and the short-term discount rate established upon quarterly settlements in 2019 of 3.8% and 3.7% , was used to calculate the expense for the second and third quarter of 2019, respectively. The expected return on plan assets presented was used to determine nonunion pension expense for first quarter 2019, and a 0.0% expected return on plan assets was used to determine nonunion pension expense for the second and third quarters of 2019. (2) The discount rate presented was used to determine the first quarter 2018 credit, and the interim discount rate established upon each quarterly settlement in 2018 of 3.6% , 3.8% , and 3.6% was used to calculate the expense for the second, third, and fourth quarter of 2018, respectively.
Schedule of the assumed health care cost trend rates for the postretirement health benefit plan	The assumed health care cost trend rates for the Company’s postretirement health benefit plan at December 31 were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 2019 Health care cost trend rate assumed for next year (1) ​ 7.0 % 7.5 % Rate to which the cost trend rate is assumed to decline ​ 4.5 % 5.0 % Year that the rate reaches the cost trend assumed rate 2032 2026 (1) At each December 31 measurement date, health care cost rates for the following year are based on known premiums for the fully-insured postretirement health benefit plan. Therefore, the first year of assumed health care cost trend rates presented as of December 31, 2020 and 2019 are for 2022 and 2021, respectively.
Schedule of estimated future benefit payments for nonunion defined benefit plans	Estimated future benefit payments from the Company’s SBP and postretirement health benefit plans, which reflect expected future service as appropriate, as of December 31, 2020 are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Supplemental Postretirement ​ ​ Benefit ​ Health ​ ​ Plan ​ Benefit Plan ​ ​ ​ ​ ​ ​ ​ 2021 ​ $ — ​ $ 588 ​ 2022 ​ $ — ​ $ 618 ​ 2023 ​ $ — ​ $ 667 ​ 2024 ​ $ — ​ $ 667 ​ 2025 ​ $ — ​ $ 691 ​ 2026-2030 ​ $ 424 ​ $ 3,781 ​
Schedule of multiemployer pension funds and key participation information	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Pension ​ FIP/RP ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Protection Act ​ Status ​ Contributions (d) ​ ​ ​ ​ EIN/Pension ​ Zone Status (b) ​ Pending/ ​ (in thousands) ​ Surcharge Legal Name of Plan Plan Number (a) 2020 2019 Implemented (c) 2020 2019 2018 Imposed (e) Central States, Southeast and Southwest Areas Pension Plan (1)(2) 36-6044243 Critical and Declining Critical and Declining Implemented (3) ​ $ 68,704 ​ $ 75,803 ​ $ 74,177 No ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Western Conference of Teamsters Pension Plan (2) 91-6145047 Green Green No ​ 23,633 ​ 24,860 ​ 25,268 No ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Central Pennsylvania Teamsters Defined Benefit Plan (1)(2) 23-6262789 Green Green No ​ 13,485 ​ 13,907 ​ 13,393 No ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ I. B. of T. Union Local No. 710 Pension Fund (5)(6) 36-2377656 Green (4) Green (4) No ​ 9,885 ​ 10,164 ​ 9,929 No ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ New England Teamsters Pension Fund (7)(8) 04-6372430 Critical and Declining (9) Critical and Declining (9) Implemented (10) ​ 4,464 ​ 4,802 ​ 20,090 ​ No ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ All other plans in the aggregate ​ ​ ​ ​ ​ ​ ​ ​ ​ 22,023 ​ 24,210 ​ 24,392 ​ ​ Total multiemployer pension contributions paid (11) ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 142,194 ​ $ 153,746 ​ $ 167,249 ​ ​ Table Heading Definitions ​ (a) The “EIN/Pension Plan Number” column provides the Federal Employer Identification Number (EIN) and the three-digit plan number, if applicable. (b) Unless otherwise noted, the most recent PPA zone status available in 2020 and 2019 is for the plan’s year-end status at December 31, 2019 and 2018, respectively. The zone status is based on information received from the plan and was certified by the plan’s actuary. Green zone funds are those that are in neither endangered, critical, or critical and declining status and generally have a funded percentage of at least 80% . (c) The “FIP/RP Status Pending/Implemented” column indicates if a funding improvement plan (FIP) or a rehabilitation plan (RP), if applicable, is pending or has been implemented. (d) Amounts reflect contributions made in the respective year and differ from amounts expensed during the year. (e) The surcharge column indicates if a surcharge was paid by ABF Freight to the plan. ​ (1) ABF Freight System, Inc. was listed by the plan as providing more than 5% of the total contributions to the plan for the plan years ended December 31, 2019 and 2018. (2) Information for this fund was obtained from the annual funding notice, other notices received from the plan, and the Form 5500 filed for the plan years ended December 31, 2019 and 2018. (3) Adopted a rehabilitation plan effective March 25, 2008 as updated. Utilized amortization extension granted by the IRS effective December 31, 2003. (4) PPA zone status relates to plan years February 1, 2019 – January 31, 2020 and February 1, 2018 – January 31, 2019. (5) The Company was listed by the plan as providing more than 5% of the total contributions to the plan for the plan years ended January 31, 2020 and 2019. (6) Information for this fund was obtained from the annual funding notice, other notices received from the plan, and the Form 5500 filed for the plan years ended January 31, 2020 and 2019. (7) Contributions include $1.6 million for 2020 and 2019, respectively, and $15.7 million for 2018, related to the multiemployer pension fund withdrawal liability which is further discussed in this Note. (8) Information for this fund was obtained from the annual funding notice, other notices received from the plan, and the Form 5500 filed for the plan years ended September 30, 2019 and 2018. (9) PPA zone status relates to plan years October 1, 2019 – September 30, 2020 and October 1, 2018 – September 30, 2019. (10) Adopted a rehabilitation plan effective January 1, 2009. (11) Contribution levels can be impacted by several factors such as changes in business levels and the related time worked by contractual employees, contractual rate increases for pension benefits, and the specific funding structure, which differs among funds. The 2018 ABF NMFA and the related supplemental agreements provided for contributions to multiemployer pension plans to be frozen at the current rates for each fund. The year-over-year changes in multiemployer pension plan contributions presented above were influenced by the previously mentioned payments related to the New England Pension Fund and changes in Asset-Based business levels. Due to the negative impact of the COVID-19 pandemic on tonnage levels, the Company made operational changes in the Asset-Based network in the second and third quarters of 2020, including workforce reductions to better align resources with business levels. The reduction in hours worked by a portion of ABF Freight’s contractual employees contributed to lower contributions to multiemployer pension plans for 2020, compared to 2019.

STOCKHOLDERS' EQUITY (Tables)

STOCKHOLDERS' EQUITY (Tables)	12 Months Ended
	Dec. 31, 2020
STOCKHOLDERS' EQUITY
Components of accumulated other comprehensive income (loss)	​ Components of accumulated other comprehensive income (loss) were as follows at December 31: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 2019 2018 ​ ​ (in thousands) Pre-tax amounts: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Unrecognized net periodic benefit credit (costs) ​ $ 4,390 ​ $ 2,898 ​ $ (11,821) ​ Interest rate swap ​ ​ (1,622) ​ ​ (563) ​ ​ 801 ​ Foreign currency translation ​ (1,182) ​ (2,075) ​ (2,816) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total ​ $ 1,586 ​ $ 260 ​ $ (13,836) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ After-tax amounts: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Unrecognized net periodic benefit credit (costs) (1) ​ $ 3,260 ​ $ 2,152 ​ $ (12,749) ​ Interest rate swap ​ ​ (1,198) ​ ​ (416) ​ ​ 591 ​ Foreign currency translation ​ (872) ​ (1,533) ​ (2,080) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total ​ $ 1,190 ​ $ 203 ​ $ (14,238) ​ (1) The year ended December 31, 2018 includes $4.0 million related to a previous valuation allowance on deferred tax assets for nonunion defined benefit pension liabilities which was recognized as pension termination expense during 2019 upon extinguishment of the nonunion defined benefit pension plan (see Note I). The reclassification of stranded income tax effects related to this item was not permitted by the amendment to ASC Topic 220, Comprehensive Income , which the Company adopted as of January 1, 2018. ​ ​ ​
Summary of changes in accumulated other comprehensive income (loss), net of tax, by component	The following is a summary of the changes in accumulated other comprehensive income (loss), net of tax, by component: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Unrecognized Net ​ ​ Interest Foreign ​ ​ ​ ​ ​ ​ Periodic Benefit ​ ​ Rate ​ Currency ​ ​ ​ Total Credit (Costs) ​ Swap Translation ​ ​ ​ (in thousands) ​ Balances at December 31, 2018 ​ $ (14,238) ​ $ (12,749) ​ $ 591 ​ $ (2,080) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Other comprehensive income (loss) before reclassifications ​ 6,197 ​ 6,657 ​ ​ (1,007) ​ 547 ​ Amounts reclassified from accumulated other comprehensive loss ​ 8,244 ​ 8,244 ​ ​ — ​ — ​ Net current-period other comprehensive income (loss) ​ 14,441 ​ 14,901 ​ ​ (1,007) ​ 547 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balances at December 31, 2019 ​ $ 203 ​ $ 2,152 ​ $ (416) ​ $ (1,533) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Other comprehensive income (loss) before reclassifications ​ ​ 1,359 ​ ​ 1,480 ​ ​ (782) ​ ​ 661 ​ Amounts reclassified from accumulated other comprehensive income ​ ​ (372) ​ ​ (372) ​ ​ — ​ ​ — ​ Net current-period other comprehensive income (loss) ​ ​ 987 ​ ​ 1,108 ​ ​ (782) ​ ​ 661 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balances at December 31, 2020 ​ $ 1,190 ​ $ 3,260 ​ $ (1,198) ​ $ (872) ​
Summary of the significant reclassifications out of accumulated other comprehensive income (loss) by component	The following is a summary of the significant reclassifications out of accumulated other comprehensive income (loss) by component for the years ended December 31: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Unrecognized Net Periodic ​ ​ ​ Benefit Credit (Costs) (1)(2) ​ 2020 2019 ​ ​ (in thousands) Amortization of net actuarial gain (loss) ​ $ 589 ​ $ (1,253) ​ Amortization of prior service credit ​ ​ 1 ​ 33 ​ Pension settlement expense, including termination expense (3)(4) ​ ​ (89) ​ (8,505) ​ Total, pre-tax ​ ​ 501 ​ (9,725) ​ Tax benefit (expense) ​ ​ (129) ​ 1,481 ​ Total, net of tax ​ $ 372 ​ $ (8,244) ​ (1) Amounts in parentheses indicate increases in expense or loss. (2) These components of accumulated other comprehensive income (loss) are included in the computation of net periodic benefit cost (see Note I). (3) For the year ended December 31, 2019, amounts included in accumulated other comprehensive income related to the nonunion defined benefit pension plan were reclassed to net income in their entirety upon settlement of the pension benefit obligation. These amounts include amortization of net actuarial loss of $0.3 million (pre-tax) and pension settlement expense, including termination expense, of $8.1 million (pre-tax) which were recognized in the “Other, net” line of other income (costs). These reclassifications impacted net income by $7.3 million for the year ended December 31, 2019. (4) The year ended December 31, 2019 includes a $4.0 million noncash pension termination expense (with no tax benefit) related to an amount which was stranded in accumulated other comprehensive income until the pension benefit obligation was settled upon plan termination (see Note I). ​
Summary of dividends declared	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ 2019 ​ ​ Per Share Amount Per Share Amount ​ ​ (in thousands, except per share data) First quarter ​ $ 0.08 ​ $ 2,033 ​ $ 0.08 ​ $ 2,052 ​ Second quarter ​ $ 0.08 ​ $ 2,049 ​ $ 0.08 ​ $ 2,050 ​ Third quarter ​ $ 0.08 ​ $ 2,040 ​ $ 0.08 ​ $ 2,043 ​ Fourth quarter ​ $ 0.08 ​ $ 2,035 ​ $ 0.08 ​ $ 2,042 ​

SHARE-BASED COMPENSATION (Table

SHARE-BASED COMPENSATION (Tables)	12 Months Ended
	Dec. 31, 2020
SHARE-BASED COMPENSATION
Summary of the Company's restricted stock unit award program	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ ​ ​ ​ Grant Date ​ ​ ​ Units ​ Fair Value ​ Outstanding – January 1, 2020 ​ 1,617,120 ​ $ 24.82 ​ Granted ​ 579,660 ​ $ 19.22 ​ Vested ​ (320,788) ​ $ 30.29 ​ Forfeited (1) ​ (34,842) ​ $ 25.48 ​ Outstanding – December 31, 2020 ​ 1,841,150 ​ $ 22.09 ​ (1) Forfeitures are recognized as they occur.
Schedule of restricted stock units granted during the year	The Compensation Committee of the Company’s Board of Directors granted RSUs during the years ended December 31, 2020, 2019, and 2018 as follows: ​ k ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ ​ ​ ​ Grant Date ​ Units Fair Value 2020 579,660 ​ $ 19.22 ​ 2019 386,840 ​ $ 27.75 ​ 2018 231,510 ​ $ 44.50 ​

EARNINGS PER SHARE (Tables)

EARNINGS PER SHARE (Tables)	12 Months Ended
	Dec. 31, 2020
EARNINGS PER SHARE
Schedule of computation of basic and diluted earnings (loss) per share	The following table sets forth the computation of basic and diluted earnings per share for the years ended December 31: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 2019 2018 ​ ​ (in thousands, except share and per share data) Basic ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Numerator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income ​ $ 71,100 ​ $ 39,985 ​ $ 67,262 ​ Effect of unvested restricted stock awards ​ — ​ (22) ​ (150) ​ Adjusted net income ​ $ 71,100 ​ $ 39,963 ​ $ 67,112 ​ Denominator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average shares ​ 25,410,232 ​ 25,535,529 ​ 25,679,736 ​ Earnings per common share ​ $ 2.80 ​ $ 1.56 ​ $ 2.61 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Diluted ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Numerator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income ​ $ 71,100 ​ $ 39,985 ​ $ 67,262 ​ Effect of unvested restricted stock awards ​ — ​ (21) ​ (145) ​ Adjusted net income ​ $ 71,100 ​ $ 39,964 ​ $ 67,117 ​ Denominator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average shares ​ 25,410,232 ​ 25,535,529 ​ 25,679,736 ​ Effect of dilutive securities ​ 1,012,291 ​ 914,526 ​ 1,019,095 ​ Adjusted weighted-average shares and assumed conversions ​ 26,422,523 ​ 26,450,055 ​ 26,698,831 ​ Earnings per common share ​ $ 2.69 ​ $ 1.51 ​ $ 2.51 ​ ​

OPERATING SEGMENT DATA (Tables)

OPERATING SEGMENT DATA (Tables)	12 Months Ended
	Dec. 31, 2020
OPERATING SEGMENT DATA
Schedule of revenues from contracts with customers and intersegment revenues	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 2019 2018 ​ ​ (in thousands) Revenues from customers ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Asset-Based ​ $ 1,998,549 ​ $ 2,077,287 ​ $ 2,131,571 ​ ArcBest ​ 770,560 ​ 731,366 ​ 773,968 ​ FleetNet ​ 166,654 ​ 175,055 ​ 182,861 ​ Other ​ 4,400 ​ 4,602 ​ 5,388 ​ Total consolidated revenues ​ $ 2,940,163 ​ $ 2,988,310 ​ $ 3,093,788 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Intersegment revenues ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Asset-Based ​ $ 93,482 ​ $ 67,392 ​ $ 44,014 ​ ArcBest ​ ​ 8,555 ​ ​ 7,026 ​ ​ 7,155 ​ FleetNet ​ ​ 38,395 ​ ​ 36,683 ​ ​ 12,265 ​ Other and eliminations ​ ​ (140,432) ​ ​ (111,101) ​ ​ (63,434) ​ Total intersegment revenues ​ $ — ​ $ — ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total segment revenues ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Asset-Based ​ $ 2,092,031 ​ ​ 2,144,679 ​ ​ 2,175,585 ​ ArcBest ​ ​ 779,115 ​ ​ 738,392 ​ ​ 781,123 ​ FleetNet ​ ​ 205,049 ​ ​ 211,738 ​ ​ 195,126 ​ Other and eliminations ​ ​ (136,032) ​ ​ (106,499) ​ ​ (58,046) ​ Total consolidated revenues ​ $ 2,940,163 ​ $ 2,988,310 ​ $ 3,093,788 ​
Schedule of reportable operating segment information	The following table reflects reportable operating segment information for the years ended December 31: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 2019 2018 ​ ​ (in thousands) REVENUES ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Asset-Based ​ $ 2,092,031 ​ $ 2,144,679 ​ $ 2,175,585 ​ ArcBest ​ 779,115 ​ 738,392 ​ 781,123 ​ FleetNet ​ 205,049 ​ 211,738 ​ 195,126 ​ Other and eliminations ​ (136,032) ​ (106,499) ​ (58,046) ​ Total consolidated revenues ​ $ 2,940,163 ​ $ 2,988,310 ​ $ 3,093,788 ​ OPERATING EXPENSES ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Asset-Based ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Salaries, wages, and benefits ​ $ 1,095,694 ​ $ 1,148,761 ​ $ 1,128,030 ​ Fuel, supplies, and expenses ​ 209,095 ​ 257,133 ​ 255,655 ​ Operating taxes and licenses ​ 49,300 ​ 50,209 ​ 48,792 ​ Insurance ​ 33,568 ​ 32,516 ​ 32,887 ​ Communications and utilities ​ 17,916 ​ 18,614 ​ 16,983 ​ Depreciation and amortization ​ 94,326 ​ 89,798 ​ 85,951 ​ Rents and purchased transportation ​ 250,159 ​ 221,479 ​ 242,247 ​ Shared services ​ ​ 217,258 ​ ​ 212,773 ​ ​ 215,302 ​ Multiemployer pension fund withdrawal liability charge (1) ​ ​ — ​ ​ — ​ ​ 37,922 ​ Gain on sale of property and equipment ​ (3,309) ​ (5,892) ​ (410) ​ Innovative technology costs (2) ​ ​ 22,458 ​ ​ 13,739 ​ ​ 3,810 ​ Other ​ 6,701 ​ 3,488 ​ 4,554 ​ Total Asset-Based ​ 1,993,166 ​ 2,042,618 ​ 2,071,723 ​ ArcBest ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Purchased transportation ​ 649,933 ​ 606,113 ​ 631,501 ​ Supplies and expenses ​ 9,627 ​ 10,789 ​ 13,329 ​ Depreciation and amortization ​ 9,714 ​ 11,344 ​ 13,750 ​ Shared services ​ ​ 90,983 ​ ​ 93,961 ​ ​ 91,266 ​ Other ​ ​ 9,203 ​ 9,860 ​ 9,143 ​ Asset impairment (3) ​ ​ — ​ ​ 26,514 ​ ​ — ​ Restructuring costs (4) ​ ​ — ​ — ​ 491 ​ Gain on sale of subsidiaries (5) ​ ​ — ​ ​ — ​ ​ (1,945) ​ Total ArcBest ​ 769,460 ​ 758,581 ​ 757,535 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ FleetNet ​ 201,682 ​ 206,932 ​ 190,741 ​ Other and eliminations ​ (122,423) ​ (83,591) ​ (35,309) ​ Total consolidated operating expenses ​ $ 2,841,885 ​ $ 2,924,540 ​ $ 2,984,690 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (1) ABF Freight recorded a one-time charge in 2018 for the multiemployer pension fund withdrawal liability resulting from the transition agreement it entered into with the New England Pension Fund (see Note I). (2) Represents costs associated with the freight handling pilot test program at ABF Freight. (3) The ArcBest segment recognized a noncash impairment charge in 2019 related to a portion of the goodwill, customer relationship intangible assets, and revenue equipment associated with the acquisition of truckload and dedicated businesses within the segment (see Note D). (4) Restructuring costs relate to the realignment of the Company’s corporate structure (see Note N). (5) Gain recognized in 2018 relates to the sale of the ArcBest segment’s military moving business in December 2017. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Year Ended December 31 ​ ​ 2020 2019 2018 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) OPERATING INCOME (LOSS) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Asset-Based ​ $ 98,865 ​ $ 102,061 ​ $ 103,862 ​ ArcBest ​ 9,655 ​ (20,189) ​ 23,588 ​ FleetNet ​ 3,367 ​ 4,806 ​ 4,385 ​ Other and eliminations ​ (13,609) ​ (22,908) ​ (22,737) ​ Total consolidated operating income ​ $ 98,278 ​ $ 63,770 ​ $ 109,098 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ OTHER INCOME (COSTS) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Interest and dividend income ​ $ 3,616 ​ $ 6,453 ​ $ 3,914 ​ Interest and other related financing costs ​ (11,697) ​ (11,467) ​ (9,468) ​ Other, net (1) ​ 2,299 ​ (7,285) ​ (19,158) ​ Total other costs ​ (5,782) ​ (12,299) ​ (24,712) ​ INCOME BEFORE INCOME TAXES ​ $ 92,496 ​ $ 51,471 ​ $ 84,386 ​ (1) Includes the components of net periodic benefit cost other than service cost, including pension settlement and termination expense (see Note I), and proceeds and changes in cash surrender value of life insurance policies. ​ The following table reflects information about revenues from customers and intersegment revenues: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 2019 2018 ​ ​ (in thousands) Revenues from customers ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Asset-Based ​ $ 1,998,549 ​ $ 2,077,287 ​ $ 2,131,571 ​ ArcBest ​ 770,560 ​ 731,366 ​ 773,968 ​ FleetNet ​ 166,654 ​ 175,055 ​ 182,861 ​ Other ​ 4,400 ​ 4,602 ​ 5,388 ​ Total consolidated revenues ​ $ 2,940,163 ​ $ 2,988,310 ​ $ 3,093,788 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Intersegment revenues ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Asset-Based ​ $ 93,482 ​ $ 67,392 ​ $ 44,014 ​ ArcBest ​ ​ 8,555 ​ ​ 7,026 ​ ​ 7,155 ​ FleetNet ​ ​ 38,395 ​ ​ 36,683 ​ ​ 12,265 ​ Other and eliminations ​ ​ (140,432) ​ ​ (111,101) ​ ​ (63,434) ​ Total intersegment revenues ​ $ — ​ $ — ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total segment revenues ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Asset-Based ​ $ 2,092,031 ​ ​ 2,144,679 ​ ​ 2,175,585 ​ ArcBest ​ ​ 779,115 ​ ​ 738,392 ​ ​ 781,123 ​ FleetNet ​ ​ 205,049 ​ ​ 211,738 ​ ​ 195,126 ​ Other and eliminations ​ ​ (136,032) ​ ​ (106,499) ​ ​ (58,046) ​ Total consolidated revenues ​ $ 2,940,163 ​ $ 2,988,310 ​ $ 3,093,788 ​ ​ ​ The following table provides capital expenditure and depreciation and amortization information by reportable operating segment: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the year ended December 31 ​ ​ 2020 2019 2018 ​ ​ ​ (in thousands) ​ CAPITAL EXPENDITURES, GROSS ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Asset-Based (1) ​ $ 85,135 ​ $ 122,437 ​ $ 116,505 ​ ArcBest ​ ​ 1,258 ​ ​ 3,909 ​ ​ 5,174 ​ FleetNet ​ 675 ​ 590 ​ 1,365 ​ Other and eliminations (2)(3) ​ 17,983 ​ 33,748 ​ 14,631 ​ ​ ​ $ 105,051 ​ $ 160,684 ​ $ 137,675 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the year ended December 31 ​ ​ ​ 2020 2019 2018 ​ ​ ​ (in thousands) ​ DEPRECIATION AND AMORTIZATION EXPENSE (2) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Asset-Based ​ $ 94,326 ​ $ 89,798 ​ $ 85,951 ​ ArcBest (4) ​ ​ 9,714 ​ ​ 11,344 ​ ​ 13,750 ​ FleetNet (5) ​ 1,622 ​ 1,341 ​ 1,140 ​ Other and eliminations (2) ​ 12,729 ​ 9,983 ​ 7,794 ​ ​ ​ $ 118,391 ​ $ 112,466 ​ $ 108,635 ​ (1) Includes assets acquired through notes payable of $61.8 million, $67.6 million, and $86.8 million in 2020, 2019, and 2018, respectively. (2) Other and eliminations includes certain assets held for the benefit of multiple segments, including information systems equipment. Depreciation and amortization associated with these assets is allocated to the reporting segments. Depreciation and amortization expense includes amortization of internally developed capitalized software which has not been included in gross capital expenditures presented in the table. (3) Includes assets acquired through notes payable of $23.2 million and $6.9 million in 2019 and 2018, respectively. (4) Includes amortization of intangibles of $3.7 million, $4.2 million, and $4.3 million in 2020, 2019, and 2018, respectively. (5) Includes amortization of intangibles which totaled $0.2 million in 2020, 2019, and 2018. ​ A table of assets by reportable operating segment has not been presented as segment assets are not included in reports regularly provided to management nor does management consider segment assets for assessing segment operating performance or allocating resources. ​ The following table presents operating expenses by category on a consolidated basis: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the year ended December 31 ​ 2020 2019 2018 ​ ​ (in thousands) ​ OPERATING EXPENSES ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Salaries, wages, and benefits ​ $ 1,368,588 ​ $ 1,408,409 ​ $ 1,398,348 ​ Rents, purchased transportation, and other costs of services ​ 974,835 ​ 934,958 ​ 989,006 ​ Fuel, supplies, and expenses ​ 250,221 ​ 316,047 ​ 325,126 ​ Depreciation and amortization (1) ​ 118,391 ​ 112,466 ​ 108,635 ​ Other ​ 129,850 ​ 126,146 ​ 123,998 ​ Asset impairment (2) ​ ​ — ​ ​ 26,514 ​ ​ — ​ Multiemployer pension fund withdrawal liability charge (3) ​ ​ — ​ ​ — ​ ​ 37,922 ​ Restructuring costs (4) ​ — ​ — ​ 1,655 ​ ​ ​ $ 2,841,885 ​ $ 2,924,540 ​ $ 2,984,690 ​ (1) Includes amortization of intangible assets. (2) The ArcBest segment recognized a noncash impairment charge in 2019 related to a portion of the goodwill, customer relationship intangible assets, and revenue equipment associated with the acquisition of truckload and dedicated businesses within the segment (see Note D). (3) ABF Freight recorded a one-time charge in 2018 for the multiemployer pension fund withdrawal liability resulting from the transition agreement it entered into with the New England Pension Fund (see Note I). (4) Restructuring costs relate to the realignment of the Company’s corporate structure (see Note N).

QUARTERLY RESULTS OF OPERATIO_2

QUARTERLY RESULTS OF OPERATIONS (UNAUDITED) (Tables)	12 Months Ended
	Dec. 31, 2020
QUARTERLY RESULTS OF OPERATIONS (UNAUDITED)
Schedule of unaudited quarterly financial information	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ ​ First Second Third Fourth ​ Quarter Quarter (1) Quarter Quarter ​ ​ (in thousands, except share and per share data) Revenues ​ $ 701,399 ​ $ 627,370 ​ $ 794,980 ​ $ 816,414 ​ Operating expenses ​ 693,580 ​ 606,945 ​ 755,198 ​ 786,162 ​ Operating income ​ 7,819 ​ 20,425 ​ 39,782 ​ 30,252 ​ Other income (costs) ​ (5,434) ​ 309 ​ (604) ​ (53) ​ Income tax provision ​ 483 ​ 4,854 ​ 9,774 ​ 6,285 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income ​ $ 1,902 ​ $ 15,880 ​ $ 29,404 ​ $ 23,914 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings per common share ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basic ​ $ 0.07 ​ $ 0.62 ​ $ 1.15 ​ $ 0.94 ​ Diluted ​ $ 0.07 ​ $ 0.61 ​ $ 1.11 ​ $ 0.89 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Average common shares outstanding ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basic ​ 25,390,377 ​ 25,463,559 ​ 25,470,094 ​ 25,427,449 ​ Diluted ​ 26,246,800 ​ 26,217,957 ​ 26,592,457 ​ 26,734,287 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 ​ ​ First Second Third Fourth ​ Quarter Quarter Quarter Quarter ​ ​ (in thousands, except share and per share data) Revenues ​ $ 711,839 ​ $ 771,490 ​ $ 787,563 ​ $ 717,418 ​ Operating expenses (2) ​ 703,248 ​ 736,290 ​ 756,355 ​ 728,647 ​ Operating income (2) ​ 8,591 ​ 35,200 ​ 31,208 ​ (11,229) ​ Other costs (3) ​ (1,995) ​ (1,640) ​ (7,866) ​ (798) ​ Income tax provision (benefit) ​ 1,708 ​ 9,184 ​ 7,072 ​ (6,478) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income (loss) (2)(3) ​ $ 4,888 ​ $ 24,376 ​ $ 16,270 ​ $ (5,549) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings (loss) per common share (4) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basic (2)(3) ​ $ 0.19 ​ $ 0.95 ​ $ 0.64 ​ $ (0.22) ​ Diluted (2)(3) ​ $ 0.18 ​ $ 0.92 ​ $ 0.62 ​ $ (0.22) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Average common shares outstanding ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basic ​ 25,570,415 ​ 25,554,286 ​ 25,527,982 ​ 25,490,393 ​ Diluted ​ 26,512,349 ​ 26,431,592 ​ 26,416,595 ​ 25,490,393 ​ (1) Quarterly results for the second quarter of 2020 do not reflect typical seasonal trends in business levels due to the negative impact of the COVID-19 pandemic on demand for the Company’s services which resulted in lower revenues and operating results for second quarter 2020. (2) Fourth quarter 2019 includes a noncash impairment charge of $26.5 million (pre-tax), or $19.8 million (after-tax) and $0.78 per diluted share, related to a portion of the goodwill, customer relationship intangible assets, and revenue equipment associated with the acquisition of truckload and dedicated businesses within the ArcBest segment. See Note D. (3) Includes nonunion pension expense, including settlement, for the first three quarters of 2019. In third quarter 2019, when the benefit obligation of the plan was settled, nonunion defined benefit pension expense, including settlement and termination expense, totaled $6.7 million (pre-tax), or $6.0 million (after-tax) and $0.23 diluted share. See Note I for annual amounts of nonunion pension expense, including settlement and termination expense. (4) The Company used the two-class method for calculating earnings per share. See Note L.

ORGANIZATION AND DESCRIPTION _2

ORGANIZATION AND DESCRIPTION OF THE BUSINESS AND FINANCIAL STATEMENT PRESENTATION - Organization (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2021USD ($)	Dec. 31, 2020USD ($)segment	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Organization and description of business
Number of reportable operating segments | segment		3
Gain on sale of property and equipment		$ 2,376	$ 5,247	$ 59
Asset Based
Organization and description of business
Percentage of the Company's revenues, before other revenues and intercompany eliminations, represented by the Asset-Based segment		68.00%
Asset Based | Subsequent Event
Organization and description of business
Gain on sale of property and equipment	$ 8,500
Asset Based | Unionized employees concentration risk | Number of employees
Organization and description of business
Percentage of Asset-Based segment employees covered under collective bargaining agreement with the IBT		82.00%

ACCOUNTING POLICIES - Concentra

ACCOUNTING POLICIES - Concentration (Details) - Minimum	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues | Customer concentration risk
Concentrations
Percentage for concentration of credit risk disclosure	4.00%	4.00%	4.00%
Accounts receivable | Credit concentration risk
Concentrations
Percentage for concentration of credit risk disclosure	6.00%	6.00%

ACCOUNTING POLICIES - Allowance

ACCOUNTING POLICIES - Allowances (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowances
Allowance for credit losses on trade accounts receivable	$ 3,600	$ 1,800
Provision for losses on accounts receivable	4,327	$ 1,223	$ 2,336
Write-offs, net of recoveries	$ 2,500

ACCOUNTING POLICIES - Property

ACCOUNTING POLICIES - Property (Details) - USD ($) $ in Thousands	Oct. 01, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020
Property, Plant and Equipment
Long-lived assets impairment				$ 6,500
Goodwill impairment	$ 0			20,000	$ 20,000
Asset Impairment Charges		$ 26,500		26,514
ArcBest
Property, Plant and Equipment
Long-lived assets impairment				6,500
Goodwill impairment				20,000	20,000
Held-for-sale | Other long-term assets
Property, Plant and Equipment
Assets held for sale which are reported within other noncurrent assets		$ 1,300	$ 1,100	$ 1,300	$ 1,100
Structures | Minimum
Property, Plant and Equipment
Depreciation/amortization period			15 years
Structures | Maximum
Property, Plant and Equipment
Depreciation/amortization period			60 years
Revenue equipment | Minimum
Property, Plant and Equipment
Depreciation/amortization period			3 years
Revenue equipment | Maximum
Property, Plant and Equipment
Depreciation/amortization period			16 years
Service, office, and other equipment | Minimum
Property, Plant and Equipment
Depreciation/amortization period			2 years
Service, office, and other equipment | Maximum
Property, Plant and Equipment
Depreciation/amortization period			15 years
Software | Minimum
Property, Plant and Equipment
Depreciation/amortization period			2 years
Software | Maximum
Property, Plant and Equipment
Depreciation/amortization period			7 years

ACCOUNTING POLICIES - Book Over

ACCOUNTING POLICIES - Book Overdrafts (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Accounts Payable
Book Overdrafts
Amount of book overdrafts	$ 21.3	$ 14.7

ACCOUNTING POLICIES - Other Rec

ACCOUNTING POLICIES - Other Recognition and Disclosure (Details)	12 Months Ended
	Dec. 31, 2020
Other Recognition and Disclosure
Revenue, Practical Expedient, Incremental Cost of Obtaining Contract	true
Revenue, Practical Expedient, Remaining Performance Obligation	true

ACCOUNTING POLICIES - Share-Bas

ACCOUNTING POLICIES - Share-Based Compensation (Details) - Restricted Stock Units	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Employee
Share-Based Compensation
Vesting period	4 years	4 years	4 years	5 years
Nonemployee Director
Share-Based Compensation
Vesting period	1 year	1 year	1 year	1 year	1 year

ACCOUNTING POLICIES - Adopted P

ACCOUNTING POLICIES - Adopted Pronouncements (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Accounting Pronouncements
Retained earnings	$ 595,932		$ 533,187
ASC Topic 326, Financial Instruments-Credit Losses
Assets and liabilities
Change in Accounting Principle, Accounting Standards Update, Adopted		true
ASC Topic 326, Financial Instruments-Credit Losses | Cumulative Effect, Period of Adoption, Adjustment
Accounting Pronouncements
Retained earnings			$ (200)
ASC Topic 350-40, Goodwill and Other-Internal-Use Software
Assets and liabilities
Change in Accounting Principle, Accounting Standards Update, Adopted		true
ASC Topic 820, Fair Value Measurement
Assets and liabilities
Change in Accounting Principle, Accounting Standards Update, Adopted		true

FINANCIAL INSTRUMENTS AND FAI_3

FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS - Cash and Cash Equivalents and Short-term Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair value disclosure
Cash and cash equivalents	$ 303,954	$ 201,909
Short-term investments	65,408	116,579
Concentrations of Credit Risk of Financial Instruments
Cash, cash equivalents and short-term investments not FDIC-insured	156,400	66,200
Cash deposits
Fair value disclosure
Cash and cash equivalents	240,687	166,619
Variable rate demand notes
Fair value disclosure
Cash and cash equivalents	29,066	14,750
Money market funds
Fair value disclosure
Cash and cash equivalents	34,201	20,540
Certificates of deposit
Fair value disclosure
Short-term investments	53,297	69,314
U.S. Treasury securities
Fair value disclosure
Short-term investments	$ 12,111	$ 47,265

FINANCIAL INSTRUMENTS AND FAI_4

FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS - Debt (Details) $ in Thousands	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Carrying Value
Fair value disclosure
Financial instruments	$ 305,623	$ 345,522
Fair Value
Fair value disclosure
Financial instruments	312,749	350,894
Credit Facility | Carrying Value | Level 2
Fair value disclosure
Financial instruments	70,000	70,000
Credit Facility | Fair Value | Level 2
Fair value disclosure
Financial instruments	70,000	70,000
Accounts receivable securitization borrowings | Carrying Value | Level 2
Fair value disclosure
Financial instruments		40,000
Accounts receivable securitization borrowings | Fair Value | Level 2
Fair value disclosure
Financial instruments		40,000
Notes payable | Carrying Value | Level 2
Fair value disclosure
Financial instruments	214,216	213,504
Notes payable | Fair Value | Level 2
Fair value disclosure
Financial instruments	$ 217,226	$ 216,432
New England Pension Fund withdrawal liability | Discount Rate
Fair value disclosure
Measurement input	0.026	0.034
New England Pension Fund withdrawal liability | Carrying Value | Level 2
Fair value disclosure
Financial instruments	$ 21,407	$ 22,018
New England Pension Fund withdrawal liability | Fair Value | Level 2
Fair value disclosure
Financial instruments	$ 25,523	$ 24,462

FINANCIAL INSTRUMENTS AND FAI_5

FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS - Assets and Liabilities (Details) - Recurring basis - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets:
Assets	$ 37,156	$ 22,967
Cash and cash equivalents
Assets:
Money market funds	34,201	20,540
Other long-term assets
Assets:
Equity, bond, and money market mutual funds held in trust related to the Voluntary Savings Plan	2,955	2,427
Other long-term liabilities
Liabilities:
Interest rate swap	1,622	563
Level 1
Assets:
Assets	37,156	22,967
Level 1 | Cash and cash equivalents
Assets:
Money market funds	34,201	20,540
Level 1 | Other long-term assets
Assets:
Equity, bond, and money market mutual funds held in trust related to the Voluntary Savings Plan	2,955	2,427
Level 2 | Other long-term liabilities
Liabilities:
Interest rate swap	$ 1,622	$ 563

FINANCIAL INSTRUMENTS AND FAI_6

FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS - Nonrecurring (Details) - USD ($) $ in Thousands	Oct. 01, 2020	Oct. 01, 2019	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill impairment	$ 0			$ (20,000)	$ (20,000)
Long-lived assets impairment				(6,500)
Total Losses/Impairment			$ (26,500)	(26,514)
Level 3 | Nonrecurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill			83,842	83,842
Long-lived assets			6,805	6,805
Assets			$ 90,647	90,647	0
Goodwill impairment				(20,000)
Long-lived assets impairment				(6,514)
Total Losses/Impairment				(26,514)
ArcBest
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill impairment				(20,000)	$ (20,000)
Long-lived assets impairment				(6,500)
ArcBest | Customer relationships
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of customer relationship intangibles				(6,000)
ArcBest | Revenue Equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of revenue equipment				$ (500)
ArcBest | Level 3 | Customer relationships | Nonrecurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of customer relationship intangibles		$ (6,000)
ArcBest | Level 3 | Revenue Equipment | Nonrecurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of revenue equipment		$ (500)

GOODWILL AND INTANGIBLE ASSET_2

GOODWILL AND INTANGIBLE ASSETS - Goodwill (Details) - USD ($) $ in Thousands	Oct. 01, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2018
Goodwill by reportable operating segment
Goodwill impairment	$ 0	$ (20,000)	$ (20,000)
Goodwill		88,320	88,320	$ 108,320
Accumulated impairment			(20,000)
ArcBest
Goodwill by reportable operating segment
Goodwill impairment		$ (20,000)	(20,000)
Goodwill			87,690	107,690
Accumulated impairment			(20,000)
FleetNet
Goodwill by reportable operating segment
Goodwill			$ 630	$ 630

GOODWILL AND INTANGIBLE ASSET_3

GOODWILL AND INTANGIBLE ASSETS - Intangible (Details) - USD ($) $ in Thousands	Oct. 01, 2020	Dec. 31, 2020	Dec. 31, 2019
Finite-lived intangible assets
Weighted Average Amortization Period		14 years
Cost		$ 53,701	$ 54,015
Accumulated Amortization		31,020	27,483
Net Value		22,681	26,532
Total intangible assets
Cost		86,001	86,315
Net Value		54,981	58,832
Impairment Assessment of Intangible Assets
Long-lived assets impairment			6,500
Impairment of indefinite-lived intangible assets	$ 0
ArcBest
Impairment Assessment of Intangible Assets
Long-lived assets impairment			6,500
Trade name
Indefinite-lived intangible assets
Net Value		$ 32,300	32,300
Customer relationships
Finite-lived intangible assets
Weighted Average Amortization Period		14 years
Cost		$ 52,721	52,721
Accumulated Amortization		30,477	26,667
Net Value		$ 22,244	26,054
Customer relationships | ArcBest
Impairment Assessment of Intangible Assets
Impairment of finite-lived intangible assets			6,000
Other intangible assets
Finite-lived intangible assets
Weighted Average Amortization Period		13 years
Cost		$ 980	1,294
Accumulated Amortization		543	816
Net Value		$ 437	478
Revenue Equipment | ArcBest
Impairment Assessment of Intangible Assets
Impairment of revenue equipment			$ 500

GOODWILL AND INTANGIBLE ASSET_4

GOODWILL AND INTANGIBLE ASSETS - Amortization (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Future amortization for intangible assets
2021	$ 3,838
2022	3,815
2023	3,722
2024	3,689
2025	3,674
Thereafter	3,943
Net Value	$ 22,681	$ 26,532

INCOME TAXES - Tax Reform Act (

INCOME TAXES - Tax Reform Act (Details) - USD ($) $ in Thousands	2 Months Ended	10 Months Ended	12 Months Ended
	Feb. 28, 2018	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Impact of Tax Reform Act
Statutory federal rate (as a percent)	32.74%	21.00%	21.00%	21.00%	21.00%	35.00%
Reduction of deferred tax liabilities due to Tax Reform Act					$ 3,772
Reduction in current income tax expense due to Tax Reform Act reflecting use of fiscal year rather than calendar year federal income tax filing					$ (100)

INCOME TAXES - Provision (Detai

INCOME TAXES - Provision (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current provision:
Federal									$ 10,001	$ 2,202	$ 9,750
State									3,267	1,813	3,264
Foreign									413	2,060	2,238
Current tax provision									13,681	6,075	15,252
Deferred provision (benefit):
Federal									5,948	4,196	1,157
State									1,789	1,221	737
Foreign									(22)	(6)	(22)
Deferred tax provision									7,715	5,411	1,872
Total provision (benefit) for income taxes	$ 6,285	$ 9,774	$ 4,854	$ 483	$ (6,478)	$ 7,072	$ 9,184	$ 1,708	$ 21,396	$ 11,486	$ 17,124

INCOME TAXES - Deferred income

INCOME TAXES - Deferred income taxes (Details) - USD ($) $ in Thousands	2 Months Ended	10 Months Ended	12 Months Ended
	Feb. 28, 2018	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Components of the deferred tax provision or benefit
Amortization, depreciation, and basis differences for property, plant and equipment and other long-lived assets			$ 4,975	$ 16,255	$ 23,153
Amortization of intangibles and impairment			183	(6,933)	(763)
Changes in reserves for workers' compensation, third-party casualty, and cargo claims			(182)	(1,880)	469
Revenue recognition			(1,481)	(1,437)	(2,524)
Allowance for doubtful accounts			(652)	541	(115)
Nonunion pension and other retirement plans			957	564	(2,810)
Multiemployer pension fund withdrawal			157	150	(5,818)
Federal and state net operating loss carryforwards utilized (generated)			(259)	59	746
State depreciation adjustments			343	(1,302)	(1,761)
Share-based compensation			(195)	(709)	(529)
Valuation allowance increase (decrease)			617	383	(744)
Other accrued expenses			1,663	(699)	(4,881)
Impact of the Tax Reform Act					(3,772)
Prepaid expenses			1,207	1,782	1,313
Operating lease right-of-use assets/liabilities - net			(13)	(1,049)
Other			395	(314)	(92)
Deferred tax provision			$ 7,715	$ 5,411	$ 1,872
Statutory federal rate (as a percent)	32.74%	21.00%	21.00%	21.00%	21.00%	35.00%

INCOME TAXES - Deferred (Detail

INCOME TAXES - Deferred (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Accrued expenses	$ 40,502	$ 41,757
Operating lease liabilities	33,933	19,726
Supplemental pension liabilities	103	1,091
Multiemployer pension fund withdrawal	5,409	5,546
Postretirement liabilities other than pensions	4,871	5,359
Share-based compensation	5,827	5,605
Federal and state net operating loss carryforwards	1,353	1,093
Revenue recognition	1,426
Other	1,297	1,538
Total deferred tax assets	94,721	81,715
Valuation allowance	(1,284)	(668)
Total deferred tax assets, net of valuation allowance	93,437	81,047
Deferred tax liabilities:
Amortization, depreciation, and basis differences for property, plant and equipment, and other long-lived assets	113,092	107,835
Operating lease right-of-use assets	32,923	18,703
Intangibles	7,520	7,373
Revenue recognition		669
Prepaid expenses	6,151	4,952
Total deferred tax liabilities	159,686	139,532
Net deferred tax liabilities	$ (66,249)	$ (58,485)

INCOME TAXES - Rate Reconciliat

INCOME TAXES - Rate Reconciliation (Details) - USD ($) $ in Thousands	2 Months Ended	3 Months Ended								10 Months Ended	12 Months Ended
	Feb. 28, 2018	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation between the effective income tax rate, as computed on income (loss) before income taxes, and the statutory federal income tax rate
Income tax provision at the statutory federal rate											$ 19,424	$ 10,809	$ 17,721
Federal income tax effects of:
State income taxes											(1,062)	(637)	(840)
Nondeductible expenses											1,395	1,344	1,682
Life insurance proceeds and changes in cash surrender value											(488)	(775)	7
Alternative fuel tax credit											(1,261)	(2,340)	(1,203)
Net increase (decrease) in valuation allowances											617	382	(891)
Net increase (decrease) in uncertain tax positions											(933)	(20)	933
Settlement of share-based compensation											420	388	(649)
Impact of the Tax Reform Act on current tax													(52)
Impact of the Tax Reform Act on deferred tax													(3,772)
Nonunion pension termination expense												1,040
Foreign tax credits generated											(391)	(2,054)	(2,216)
Federal research and development tax credits											(2,078)	(1,354)
Other											306	(385)	187
Federal income tax provision											15,949	6,398	10,907
State income tax provision											5,056	3,034	4,001
Foreign income tax provision											391	2,054	2,216
Total provision (benefit) for income taxes		$ 6,285	$ 9,774	$ 4,854	$ 483	$ (6,478)	$ 7,072	$ 9,184	$ 1,708		$ 21,396	$ 11,486	$ 17,124
Effective tax (benefit) rate (as a percent)											23.10%	22.30%	20.30%
Statutory federal rate (as a percent)	32.74%									21.00%	21.00%	21.00%	21.00%	35.00%
Income taxes paid, excluding income tax refunds											$ 28,600	$ 28,100	$ 21,800
Income tax refunds											$ 13,300	$ 13,100	$ 18,500

INCOME TAXES - ASC Topic 718 (D

INCOME TAXES - ASC Topic 718 (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounting Pronouncements
Effective tax (benefit) rate (as a percent)	23.10%	22.30%	20.30%
Maximum
Accounting Pronouncements
Tax benefit realized from dividends on share-based payment awards	$ 0.1	$ 0.1	$ 0.1
ASC Topic 718, Compensation - Stock Compensation
Accounting Pronouncements
Effective tax (benefit) rate (as a percent)	0.50%	0.90%	(0.80%)

INCOME TAXES - NOL (Details)

INCOME TAXES - NOL (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)Yitem	Dec. 31, 2019USD ($)
Operating loss and contribution carryforwards
Valuation allowance	$ 1,284	$ 668
Number of state taxing authorities for which the entity is under examination | item	1
State
Operating loss and contribution carryforwards
Operating loss carryforwards	$ 18,400
Net operating loss and contribution carryforwards expiration period	20 years
Number of prior years with taxable losses | Y	3
Valuation allowance related to net operating loss carryforwards	$ 600
Amount of tax credit carryforward reserved	200
Valuation allowance, tax credit carryforwards	200
State tax department of Panther
Operating loss and contribution carryforwards
Operating loss carryforwards	5,300
State tax department of other subsidiaries
Operating loss and contribution carryforwards
Operating loss carryforwards	11,600
Foreign
Operating loss and contribution carryforwards
Valuation allowance	400	$ 700
Federal
Operating loss and contribution carryforwards
Operating loss carryforwards	1,300
Operating loss carryforwards, expire within five years	1,000
Operating loss carryforwards, expire in ten years	$ 300
Net operating loss and contribution carryforwards expiration period	10 years
Number of prior years with taxable losses | Y	3
Valuation allowance related to net operating loss carryforwards	$ 100
Minimum | State tax department of Panther
Operating loss and contribution carryforwards
Net operating loss and contribution carryforwards expiration period	10 years
Maximum | State tax department of Panther
Operating loss and contribution carryforwards
Net operating loss and contribution carryforwards expiration period	20 years
Maximum | Federal
Operating loss and contribution carryforwards
Net operating loss and contribution carryforwards expiration period	5 years

INCOME TAXES - Uncertain Tax Po

INCOME TAXES - Uncertain Tax Positions (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
INCOME TAXES
Reserve for uncertain tax positions	$ 0	$ 900,000	$ 1,000,000

LEASES - Lease terms (Details)

LEASES - Lease terms (Details)	12 Months Ended
	Dec. 31, 2020
Operating leases
Lessor, Operating Lease, Existence of Option to Terminate [true false]	false
Maximum
Operating leases
Remaining lease term	12 years 1 month 6 days
Operating lease, renewal term	5 years

LEASES - Components of Lease Ex

LEASES - Components of Lease Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Leases
Operating lease expense	$ 24,559	$ 22,291
Variable lease expense	3,152	3,366
Sublease income	(398)	(324)
Total operating lease expense	$ 27,313	$ 25,333
Rental expense for operating leases			$ 20,500

LEASES - Cash flows (Details)

LEASES - Cash flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Operating leases
Noncash change in operating right-of-use assets	$ 21,184	$ 20,439
Change in operating lease liabilities	(20,428)	(19,711)
Operating right-of-use assets and lease liabilities, net	756	728
Cash paid for amounts included in the measurement of operating lease liabilities	$ (23,810)	$ (21,714)

LEASES Supplemental Balance She

LEASES Supplemental Balance Sheet Information (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Operating leases
Operating right-of-use assets (long-term)	$ 115,195	$ 68,470
Operating lease liabilities (current)	21,482	20,265
Operating lease liabilities (long-term)	97,839	52,277
Total operating lease liabilities	$ 119,321	$ 72,542
Weighted average remaining lease term (in years)	6 years 8 months 12 days	5 years 3 months 18 days
Weighted average discount rate	3.18%	3.77%
Land and Structures
Operating leases
Operating right-of-use assets (long-term)	$ 114,908	$ 67,227
Operating lease liabilities (current)	21,207	19,293
Operating lease liabilities (long-term)	97,828	52,008
Total operating lease liabilities	119,035	71,301
Equipment and Others
Operating leases
Operating right-of-use assets (long-term)	287	1,243
Operating lease liabilities (current)	275	972
Operating lease liabilities (long-term)	11	269
Total operating lease liabilities	$ 286	$ 1,241

LEASES - Maturities of Operatin

LEASES - Maturities of Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Maturities of operating lease liabilities
2021	$ 24,629
2022	21,073
2023	16,755
2024	14,668
2025	12,153
Thereafter	43,035
Total lease payments	132,313
Less imputed interest	(12,992)
Total operating lease liabilities	119,321	$ 72,542
Land and Structures
Maturities of operating lease liabilities
2021	24,352
2022	21,062
2023	16,755
2024	14,668
2025	12,153
Thereafter	43,035
Total lease payments	132,025
Less imputed interest	(12,990)
Total operating lease liabilities	119,035	71,301
Equipment and Others
Maturities of operating lease liabilities
2021	277
2022	11
Total lease payments	288
Less imputed interest	(2)
Total operating lease liabilities	$ 286	$ 1,241

LONG-TERM DEBT AND FINANCING _3

LONG-TERM DEBT AND FINANCING ARRANGEMENTS - Summary (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Long-term debt obligations
Long-term debt	$ 284,224	$ 323,519
Less current portion	67,105	57,305
Long-term debt, less current portion	$ 217,119	266,214
Weighted-average interest rate (as a percent)	2.90%
Payments under long-term debt obligations
2021	$ 73,386
2022	64,750
2023	48,892
2024	102,393
2025	9,576
Total payments	298,997
Less amounts representing interest	14,773
Long-term debt	284,224	323,519
Credit Facility
Long-term debt obligations
Long-term debt	$ 70,000	70,000
Interest rate (as a percent)	1.30%
Payments under long-term debt obligations
2021	$ 886
2022	914
2023	971
2024	70,823
Total payments	73,594
Less amounts representing interest	3,594
Long-term debt	70,000	70,000
Accounts receivable securitization borrowings
Long-term debt obligations
Long-term debt		40,000
Payments under long-term debt obligations
Long-term debt		40,000
Notes payable
Long-term debt obligations
Long-term debt	$ 214,216	213,504
Weighted-average interest rate (as a percent)	3.00%
Payments under long-term debt obligations
2021	$ 72,493
2022	63,835
2023	47,921
2024	31,570
2025	9,576
Total payments	225,395
Less amounts representing interest	11,179
Long-term debt	214,216	213,504
Finance lease obligations
Long-term debt obligations
Long-term debt	$ 8	15
Weighted-average interest rate (as a percent)	3.30%
Payments under long-term debt obligations
2021	$ 7
2022	1
Total payments	8
Long-term debt	$ 8	$ 15

LONG-TERM DEBT AND FINANCING _4

LONG-TERM DEBT AND FINANCING ARRANGEMENTS - Assets securing notes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Financing Arrangements
Total assets securing notes payable or held under finance leases	$ 353,093	$ 293,799
Less accumulated depreciation and amortization	115,424	71,405
Net assets securing notes payable or held under finance leases	$ 237,669	222,394
Weighted-average interest rate (as a percent)	2.90%
Interest paid, net of capitalized interest	$ 11,300	10,900	$ 8,700
Capitalized interest	300	200
Revenue equipment
Financing Arrangements
Total assets securing notes payable or held under finance leases	326,823	265,315
Software
Financing Arrangements
Total assets securing notes payable or held under finance leases		2,140
Service, office, and other equipment
Financing Arrangements
Total assets securing notes payable or held under finance leases	$ 26,270	$ 26,344

LONG-TERM DEBT AND FINANCING _5

LONG-TERM DEBT AND FINANCING ARRANGEMENTS - Credit Facility (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Financing Arrangements
Borrowings under credit facilities			$ 180,000
Repayment of debt			326,098	$ 58,938	$ 71,260
Credit Facility
Financing Arrangements
Maximum borrowing capacity			250,000
Additional borrowing capacity that may be requested			125,000
Borrowings under credit facilities	$ 180,000
Repayment of debt		$ 180,000
Remaining borrowing capacity			180,000
Swing Line Facility
Financing Arrangements
Maximum borrowing capacity			25,000
Letters of Credit, Sub-Facility
Financing Arrangements
Maximum borrowing capacity			$ 20,000

LONG-TERM DEBT AND FINANCING _6

LONG-TERM DEBT AND FINANCING ARRANGEMENTS - Interest rate swaps (Details) - USD ($) $ in Millions	Nov. 30, 2014	Jun. 30, 2022	Dec. 31, 2020	May 04, 2020	Jan. 02, 2020	Dec. 31, 2019
Interest rate swap agreement | Credit Facility
Financing Arrangements
Amount of borrowings covered by the interest rate swap			$ 50			$ 50
Effective fixed interest rate on hedged borrowings (as a percent)			3.12%			2.98%
Interest rate swap agreement, maturing on June 30, 2022
Financing Arrangements
Notional amount					$ 50
Fixed interest rate payments (as a percent)					1.99%
Interest rate swap agreement, maturing on June 30, 2022 | Other long-term liabilities
Financing Arrangements
Fair value of interest rate swap, liability			$ 1.4			$ 0.6
Interest rate swap agreement, maturing on June 30, 2022 | Credit Facility
Financing Arrangements
Amount of borrowings covered by the interest rate swap			$ 50
Effective fixed interest rate on hedged borrowings (as a percent)			3.12%
Interest rate swap, maturing on January 2, 2020
Financing Arrangements
Term of swap agreement	5 years
Notional amount	$ 50
Interest rate swap, maturing on January 2, 2020 | Other long-term liabilities | Maximum
Financing Arrangements
Fair value of interest rate swap, liability						$ 0.1
Amended interest rate swap agreement, maturing on October 1, 2024
Financing Arrangements
Notional amount				$ 50
Fixed interest rate payments (as a percent)				0.43%
Amended interest rate swap agreement, maturing on October 1, 2024 | Other long-term liabilities
Financing Arrangements
Fair value of interest rate swap, liability			$ 0.2
Amended interest rate swap agreement, maturing on October 1, 2024 | Credit Facility | Forecast
Financing Arrangements
Amount of borrowings covered by the interest rate swap		$ 50
Effective fixed interest rate on hedged borrowings (as a percent)		1.56%

LONG-TERM DEBT AND FINANCING _7

LONG-TERM DEBT AND FINANCING ARRANGEMENTS - Securitization program (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Financing Arrangements
Long-term debt			$ 284,224	$ 323,519
Additional borrowings under accounts receivable securitization program			45,000
Outstanding letters of credit			12,300	12,800
Accounts receivable securitization borrowings
Financing Arrangements
Maximum borrowing capacity			125,000
Additional borrowing capacity that may be requested			25,000
Long-term debt				40,000
Additional borrowings under accounts receivable securitization program		$ 45,000
Repayment of accounts receivable securitization	$ 85,000
Outstanding letters of credit			11,700	$ 12,200
Remaining borrowing capacity			$ 113,300

LONG-TERM DEBT AND FINANCING _8

LONG-TERM DEBT AND FINANCING ARRANGEMENTS - Letters of credit & Surety bonds (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Financing Arrangements
Outstanding letters of credit	$ 12.3	$ 12.8
Accounts receivable securitization borrowings
Financing Arrangements
Outstanding letters of credit	11.7	12.2
Surety bonds
Financing Arrangements
Outstanding surety bonds under uncollateralized bond programs	$ 61.7	$ 62.3

LONG-TERM DEBT AND FINANCING _9

LONG-TERM DEBT AND FINANCING ARRANGEMENTS - Notes Payable (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Notes payable | Revenue equipment and software
Financing Arrangements
Assets financed during the period under promissory note arrangements	$ 61.8	$ 90.8

ACCRUED EXPENSES (Details)

ACCRUED EXPENSES (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
ACCRUED EXPENSES
Workers' compensation, third-party casualty, and loss and damage claims reserves	$ 103,898	$ 107,149
Accrued vacation pay	51,728	47,730
Accrued compensation, including retirement benefits	67,690	52,720
Taxes other than income	10,468	8,722
Other	12,962	16,000
Total accrued expenses	$ 246,746	$ 232,321

EMPLOYEE BENEFIT PLANS - Plan s

EMPLOYEE BENEFIT PLANS - Plan summary (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Nonunion Defined Benefit Pension Plan
Pension and other postretirement benefit plans
Employer contributions		$ 7,710
Noncash charge to pension settlement expense		4,000
Noncash charge to pension settlement expense, tax benefit		0
Postretirement Health Benefit Plan
Pension and other postretirement benefit plans
Employer contributions	$ 615	$ 848
Unrecognized prior service credit, amortization period	9 years

EMPLOYEE BENEFIT PLANS - Funded

EMPLOYEE BENEFIT PLANS - Funded status (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Nonunion Defined Benefit Pension Plan
Change in benefit obligations
Benefit obligations at beginning of period		$ 33,373
Interest cost		624	$ 4,269
Actuarial (gain) loss		300
Benefits paid		(34,297)
Benefit obligations at end of period			33,373
Change in plan assets
Fair value of plan assets at beginning of period		26,646
Actual return on plan assets		(59)
Employer contributions		7,710
Benefits paid		(34,297)
Fair value of plan assets at end of period			26,646
Supplemental Benefit Plan
Change in benefit obligations
Benefit obligations at beginning of period	$ 3,236	3,948
Interest cost	9	39	108
Actuarial (gain) loss	34	186
Benefits paid	(2,887)	(937)
Benefit obligations at end of period	392	3,236	3,948
Change in plan assets
Employer contributions	2,887	937
Benefits paid	(2,887)	(937)
Funded status at period end	(392)	(3,236)
Accumulated benefit obligation	392	3,236
Postretirement Health Benefit Plan
Change in benefit obligations
Benefit obligations at beginning of period	20,630	29,488
Service cost	187	320	366
Interest cost	576	1,212	837
Actuarial (gain) loss	(2,027)	(9,542)
Benefits paid	(615)	(848)
Benefit obligations at end of period	18,751	20,630	$ 29,488
Change in plan assets
Employer contributions	615	848
Benefits paid	(615)	(848)
Funded status at period end	(18,751)	(20,630)
Accumulated benefit obligation	$ 18,751	$ 20,630

EMPLOYEE BENEFIT PLANS - Recogn

EMPLOYEE BENEFIT PLANS - Recognized in Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Amounts recognized in the consolidated balance sheets
Pension and postretirement liabilities, less current portion	$ (18,555)	$ (20,294)
Supplemental Benefit Plan
Amounts recognized in the consolidated balance sheets
Current portion of pension and postretirement liabilities		(2,886)
Pension and postretirement liabilities, less current portion	(392)	(350)
Liabilities recognized	(392)	(3,236)
Postretirement Health Benefit Plan
Amounts recognized in the consolidated balance sheets
Current portion of pension and postretirement liabilities	(588)	(686)
Pension and postretirement liabilities, less current portion	(18,163)	(19,944)
Liabilities recognized	$ (18,751)	$ (20,630)

EMPLOYEE BENEFIT PLANS - Compon

EMPLOYEE BENEFIT PLANS - Components of cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Components of net periodic benefit cost
Pension settlement expense, including termination expense	$ 89	$ 8,505	$ 12,925
Nonunion Defined Benefit Pension Plan
Components of net periodic benefit cost
Interest cost		624	4,269
Expected return on plan assets		(31)	(1,582)
Pension settlement expense, including termination expense		4,164	12,925
Amortization of net actuarial (gain) loss		260	2,583
Net periodic benefit cost		5,017	18,195
Noncash charge to pension settlement expense		4,000
Supplemental Benefit Plan
Components of net periodic benefit cost
Interest cost	9	39	108
Pension settlement expense, including termination expense	89	370
Amortization of net actuarial (gain) loss	8	95	81
Net periodic benefit cost	106	504	189
Postretirement Health Benefit Plan
Components of net periodic benefit cost
Service cost	187	320	366
Interest cost	576	1,212	837
Amortization of prior service credit	(1)	(33)	(93)
Amortization of net actuarial (gain) loss	(597)	898	304
Net periodic benefit cost	$ 165	$ 2,397	$ 1,414

EMPLOYEE BENEFIT PLANS - Settle

EMPLOYEE BENEFIT PLANS - Settlement distributions and expense (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Distributions and pension settlement expense
Pension settlement expense, pre-tax	$ 89	$ 8,505	$ 12,925
Nonunion Defined Benefit Pension Plan
Distributions and pension settlement expense
Pension settlement distributions		33,938	105,279
Pension settlement expense, pre-tax		$ 4,164	$ 12,925
Pension settlement expense per diluted share, net of taxes		$ 0.12	$ 0.36
Lump-sum distributions		$ 18,400
Nonparticipating annuity contract purchase price		14,000
Transfer of remaining obligation to PGBC		1,500
Noncash charge to pension settlement expense		4,000
Supplemental Benefit Plan
Distributions and pension settlement expense
Pension settlement distributions	2,887	937
Pension settlement expense, pre-tax	$ 89	$ 370
Pension settlement expense per diluted share, net of taxes		$ 0.01
Period of delay for pension settlement distribution to key employees	6 months	6 months

EMPLOYEE BENEFIT PLANS - Includ

EMPLOYEE BENEFIT PLANS - Included in AOCI (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Supplemental Benefit Plan
Pre-tax amounts included in accumulated other comprehensive loss that have not yet been recognized in net periodic benefit cost
Unrecognized net actuarial (gain) loss	$ 64	$ 127
Total	64	127
Postretirement Health Benefit Plan
Pre-tax amounts included in accumulated other comprehensive loss that have not yet been recognized in net periodic benefit cost
Unrecognized net actuarial (gain) loss	(4,454)	(3,024)
Unrecognized prior service credit		(1)
Total	$ (4,454)	$ (3,025)

EMPLOYEE BENEFIT PLANS - Discou

EMPLOYEE BENEFIT PLANS - Discount rate and assumptions (Details)	3 Months Ended					12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Nonunion Defined Benefit Pension Plan
Weighted-average assumptions used to determine net periodic benefit cost
Discount rate (as a percent)	3.70%	3.80%	3.60%	3.80%	3.60%		3.90%	3.10%
Expected return on plan assets, net of estimated expenses (as a percent)	0.00%	0.00%					1.40%	1.40%
Supplemental Benefit Plan
Weighted-average assumptions used to determine nonunion benefit obligations
Discount rate (as a percent)						1.10%	2.40%
Weighted-average assumptions used to determine net periodic benefit cost
Discount rate (as a percent)						2.40%	3.60%	2.80%
Postretirement Health Benefit Plan
Weighted-average assumptions used to determine nonunion benefit obligations
Discount rate (as a percent)						2.30%	3.10%
Weighted-average assumptions used to determine net periodic benefit cost
Discount rate (as a percent)						3.10%	4.20%	3.50%

EMPLOYEE BENEFIT PLANS - Health

EMPLOYEE BENEFIT PLANS - Health care trend rates (Details) - Postretirement Health Benefit Plan	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Assumed health care cost trend rates
Health care cost trend rate assumed for next year (as a percent)	7.00%	7.50%
Rate to which the cost trend rate is assumed to decline (as a percent)	4.50%	5.00%
Year that the rate reaches the cost trend assumed rate	2032	2026

EMPLOYEE BENEFIT PLANS - Future

EMPLOYEE BENEFIT PLANS - Future benefit payments (Details) $ in Thousands	Dec. 31, 2020USD ($)
Supplemental Benefit Plan
Estimated future benefit payments
2026-2030	$ 424
Postretirement Health Benefit Plan
Estimated future benefit payments
2021	588
2022	618
2023	667
2024	667
2025	691
2026-2030	$ 3,781

EMPLOYEE BENEFIT PLANS - Deferr

EMPLOYEE BENEFIT PLANS - Deferred Comp Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Deferred salary agreements
Deferred Compensation Plans
Recorded liabilities	$ 1.8	$ 2.1
Voluntary Savings Plan - mutual funds held in trust
Deferred Compensation Plans
Minimum period for election to defer receipt of a portion of salary and incentive compensation	6 months
Voluntary Savings Plan - mutual funds held in trust | Other long-term assets
Deferred Compensation Plans
VSP assets	$ 3	2.4
Voluntary Savings Plan - mutual funds held in trust | Other long-term liabilities
Deferred Compensation Plans
VSP liabilities	$ 3	$ 2.4

EMPLOYEE BENEFIT PLANS - Define

EMPLOYEE BENEFIT PLANS - Defined Contribution Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash Long-Term Incentive Compensation Plan
Earning period of Long-term cash incentive plan	3 years
Incentive payments accrued for Long-Term Cash Incentive Plan	$ 14.2	$ 13.7	$ 18.3
Other Plans
Cash surrender value of life insurance policies	55.7	53.2
Recognized gains associated with changes in the cash surrender value and proceeds from life insurance policies	$ 2.3	3.7
Maximum
Other Plans
Recognized gains associated with changes in the cash surrender value and proceeds from life insurance policies			(0.1)
401(k) Plan
Defined Contribution Plans
Maximum percentage of salary permitted to be deferred by plan participants	69.00%
Rate of employer match on participant contributions	50.00%
Maximum percentage of participants compensation that is eligible for 50% matching contribution	6.00%
Expense for employer contribution to defined contribution plan	$ 4.6	6.8	6.1
DC Retirement Plan
Defined Contribution Plans
Period of service for participants' full vesting in the employer's contributions	3 years
Expense for employer contribution to defined contribution plan	$ 12.6	$ 10.9	$ 11.6

EMPLOYEE BENEFIT PLANS - Multie

EMPLOYEE BENEFIT PLANS - Multiemployer Plans (Details) $ in Thousands	Aug. 01, 2020	Jan. 31, 2020	Aug. 01, 2019	Jan. 31, 2019	Aug. 01, 2018	Jun. 30, 2018USD ($)	Sep. 30, 2018USD ($)	Dec. 31, 2020USD ($)plan	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	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%

STOCKHOLDERS' EQUITY - AOCI (De

STOCKHOLDERS' EQUITY - AOCI (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss)
Total after-tax amount	$ 828,593	$ 763,043	$ 717,682	$ 651,462
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss)
Total pre-tax amount	1,586	260	(13,836)
Total after-tax amount	1,190	203	(14,238)	$ (20,574)
Unrecognized Net Periodic Benefit Credit (costs)
Accumulated Other Comprehensive Income (Loss)
Total pre-tax amount	4,390	2,898	(11,821)
Total after-tax amount	3,260	2,152	(12,749)
Amount remaining in unrecognized net periodic benefit costs portion of accumulated other comprehensive income for previous valuation allowance on deferred tax assets			4,000
Interest Rate Swap
Accumulated Other Comprehensive Income (Loss)
Total pre-tax amount	(1,622)	(563)
Total after-tax amount	(1,198)	(416)	591
Interest Rate Swap, 2018
Accumulated Other Comprehensive Income (Loss)
Total pre-tax amount			801
Total after-tax amount			591
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss)
Total pre-tax amount	(1,182)	(2,075)	(2,816)
Total after-tax amount	$ (872)	$ (1,533)	$ (2,080)

STOCKHOLDERS' EQUITY - AOCI com

STOCKHOLDERS' EQUITY - AOCI components (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Changes in accumulated other comprehensive income (loss), net of tax, by component
Balances	$ 763,043	$ 717,682	$ 651,462
OTHER COMPREHENSIVE INCOME, net of tax	987	14,441	9,912
Balances	828,593	763,043	717,682
Accumulated Other Comprehensive Income (Loss)
Changes in accumulated other comprehensive income (loss), net of tax, by component
Balances	203	(14,238)	(20,574)
Other comprehensive income (loss) before reclassifications	1,359	6,197
Amounts reclassified from accumulated other comprehensive income (loss)	(372)	8,244
OTHER COMPREHENSIVE INCOME, net of tax	987	14,441	9,912
Balances	1,190	203	(14,238)
Unrecognized Net Periodic Benefit Credit (costs)
Changes in accumulated other comprehensive income (loss), net of tax, by component
Balances	2,152	(12,749)
Other comprehensive income (loss) before reclassifications	1,480	6,657
Amounts reclassified from accumulated other comprehensive income (loss)	(372)	8,244
OTHER COMPREHENSIVE INCOME, net of tax	1,108	14,901
Balances	3,260	2,152	(12,749)
Interest Rate Swap
Changes in accumulated other comprehensive income (loss), net of tax, by component
Balances	(416)	591
Other comprehensive income (loss) before reclassifications	(782)	(1,007)
OTHER COMPREHENSIVE INCOME, net of tax	(782)	(1,007)
Balances	(1,198)	(416)	591
Interest Rate Swap, 2018
Changes in accumulated other comprehensive income (loss), net of tax, by component
Balances		591
Balances			591
Foreign Currency Translation
Changes in accumulated other comprehensive income (loss), net of tax, by component
Balances	(1,533)	(2,080)
Other comprehensive income (loss) before reclassifications	661	547
OTHER COMPREHENSIVE INCOME, net of tax	661	547
Balances	$ (872)	$ (1,533)	$ (2,080)

STOCKHOLDERS' EQUITY - Reclass

STOCKHOLDERS' EQUITY - Reclass (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Unrecognized Net Periodic Benefit Credit (costs)
Significant reclassifications out of accumulated other comprehensive loss by component
Total, pre-tax	$ 501	$ (9,725)
Tax benefit (expense)	(129)	1,481
Total, net of tax	372	(8,244)
Unrecognized Net Periodic Benefit Credit (costs) | Nonunion Defined Benefit Pension Plan
Significant reclassifications out of accumulated other comprehensive loss by component
Total, net of tax		(7,300)
Amortization of net actuarial gain (loss)
Significant reclassifications out of accumulated other comprehensive loss by component
Total, pre-tax	589	(1,253)
Amortization of net actuarial gain (loss) | Nonunion Defined Benefit Pension Plan
Significant reclassifications out of accumulated other comprehensive loss by component
Total, pre-tax		(300)
Amortization of prior service credit
Significant reclassifications out of accumulated other comprehensive loss by component
Total, pre-tax	1	33
Pension settlement expense, including termination expense
Significant reclassifications out of accumulated other comprehensive loss by component
Total, pre-tax	$ (89)	(8,505)
Pension settlement expense, including termination expense | Nonunion Defined Benefit Pension Plan
Significant reclassifications out of accumulated other comprehensive loss by component
Total, pre-tax		(8,100)
Pension termination expense | Nonunion Defined Benefit Pension Plan
Significant reclassifications out of accumulated other comprehensive loss by component
Total, pre-tax		(4,000)
Tax benefit (expense)		$ 0

STOCKHOLDERS' EQUITY - Dividend

STOCKHOLDERS' EQUITY - Dividends (Details) - USD ($) $ / shares in Units, $ in Thousands	Jan. 28, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Dividends on Common Stock
Dividends declared (in dollars per share)		$ 0.08	$ 0.08	$ 0.08	$ 0.08	$ 0.08	$ 0.08	$ 0.08	$ 0.08	$ 0.32	$ 0.32	$ 0.32
Dividend Amount		$ 2,035	$ 2,040	$ 2,049	$ 2,033	$ 2,042	$ 2,043	$ 2,050	$ 2,052	$ 8,157	$ 8,187	$ 8,244
Subsequent Event
Dividends on Common Stock
Dividends declared (in dollars per share)	$ 0.08

STOCKHOLDERS' EQUITY - Treasury

STOCKHOLDERS' EQUITY - Treasury Stock (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jan. 28, 2021	Oct. 31, 2015
Treasury Stock
Aggregate cost of shares repurchased during the period	$ 6,595	$ 9,110	$ 9,404
Treasury stock (in shares)	3,656,938	3,404,639
Stock Repurchase Program
Treasury Stock
Amount of stock repurchases authorized					$ 50,000
Number of shares repurchased during the period	252,299
Aggregate cost of shares repurchased during the period	$ 6,600
Amount available for repurchase	$ 6,600
Stock Repurchase Program | Subsequent Event
Treasury Stock
Amount of stock repurchases authorized				$ 50,000

SHARE-BASED COMPENSATION (Detai

SHARE-BASED COMPENSATION (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based compensation
Number of shares authorized	4,300,000
Restricted Stock Units
Award activity
Outstanding at the beginning of the period (in shares)	1,617,120
Granted (in shares)	579,660	386,840	231,510
Vested (in shares)	(320,788)
Forfeited (in shares)	(34,842)
Outstanding at the end of the period (in shares)	1,841,150	1,617,120
Weighted-Average Grant Date Fair Value
Outstanding at the beginning of the period (in dollars per share)	$ 24.82
Granted (in dollars per share)	19.22	$ 27.75	$ 44.50
Vested (in dollars per share)	30.29
Forfeited (in dollars per share)	25.48
Outstanding at the end of the period (in dollars per share)	$ 22.09	$ 24.82
Other disclosure
Fair value of restricted stock awards vested	$ 7.8	$ 4.9	$ 9.6
Unrecognized compensation cost	$ 18
Weighted-average period of recognition of unrecognized compensation cost	2 years
Restricted Stock Units | Employee
Other disclosure
Vesting period	4 years	4 years	4 years	5 years

EARNINGS PER SHARE - Basic and

EARNINGS PER SHARE - Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Basic, numerator:
Net income	$ 23,914	$ 29,404	$ 15,880	$ 1,902	$ (5,549)	$ 16,270	$ 24,376	$ 4,888	$ 71,100	$ 39,985	$ 67,262
Effect of unvested restricted stock unit awards										(22)	(150)
Adjusted net income									$ 71,100	$ 39,963	$ 67,112
Basic, denominator:
Weighted-average shares	25,427,449	25,470,094	25,463,559	25,390,377	25,490,393	25,527,982	25,554,286	25,570,415	25,410,232	25,535,529	25,679,736
Earnings per common share (in dollars per share)	$ 0.94	$ 1.15	$ 0.62	$ 0.07	$ (0.22)	$ 0.64	$ 0.95	$ 0.19	$ 2.80	$ 1.56	$ 2.61
Diluted, numerator:
Net income	$ 23,914	$ 29,404	$ 15,880	$ 1,902	$ (5,549)	$ 16,270	$ 24,376	$ 4,888	$ 71,100	$ 39,985	$ 67,262
Effect of unvested restricted stock unit awards										(21)	(145)
Adjusted net income									$ 71,100	$ 39,964	$ 67,117
Diluted, denominator:
Weighted-average shares	25,427,449	25,470,094	25,463,559	25,390,377	25,490,393	25,527,982	25,554,286	25,570,415	25,410,232	25,535,529	25,679,736
Effect of dilutive securities									1,012,291	914,526	1,019,095
Adjusted weighted-average shares and assumed conversions	26,734,287	26,592,457	26,217,957	26,246,800	25,490,393	26,416,595	26,431,592	26,512,349	26,422,523	26,450,055	26,698,831
Earnings per common share (in dollars per share)	$ 0.89	$ 1.11	$ 0.61	$ 0.07	$ (0.22)	$ 0.62	$ 0.92	$ 0.18	$ 2.69	$ 1.51	$ 2.51

EARNINGS PER SHARE - Antidiluti

EARNINGS PER SHARE - Antidilutive securities (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Stock awards
Antidilutive securities
Antidilutive securities	0.2	0.1

OPERATING SEGMENT DATA - Revenu

OPERATING SEGMENT DATA - Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues
Revenues	$ 816,414	$ 794,980	$ 627,370	$ 701,399	$ 717,418	$ 787,563	$ 771,490	$ 711,839	$ 2,940,163	$ 2,988,310	$ 3,093,788
Asset Based
Revenues
Revenues									1,998,549	2,077,287	2,131,571
ArcBest
Revenues
Revenues									770,560	731,366	773,968
FleetNet
Revenues
Revenues									166,654	175,055	182,861
Other
Revenues
Revenues									4,400	4,602	5,388
Operating Segments | Asset Based
Revenues
Revenues									2,092,031	2,144,679	2,175,585
Operating Segments | ArcBest
Revenues
Revenues									779,115	738,392	781,123
Operating Segments | FleetNet
Revenues
Revenues									205,049	211,738	195,126
Other and eliminations
Revenues
Revenues									(136,032)	(106,499)	(58,046)
Intersegment revenues
Revenues
Revenues									(140,432)	(111,101)	(63,434)
Intersegment revenues | Asset Based
Revenues
Revenues									93,482	67,392	44,014
Intersegment revenues | ArcBest
Revenues
Revenues									8,555	7,026	7,155
Intersegment revenues | FleetNet
Revenues
Revenues									$ 38,395	$ 36,683	$ 12,265

OPERATING SEGMENT DATA - Operat

OPERATING SEGMENT DATA - Operating expenses (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
OPERATING EXPENSES
Salaries, wages, and benefits									$ 1,368,588	$ 1,408,409	$ 1,398,348
Fuel, supplies, and expenses									250,221	316,047	325,126
Depreciation and amortization									118,391	112,466	108,635
Multiemployer pension fund withdrawal liability charge											37,922
Gain on sale of property and equipment									(2,376)	(5,247)	(59)
Other									129,850	126,146	123,998
Asset impairment					$ 26,500					26,514
Restructuring costs											1,655
Gain on sale of subsidiaries											(1,945)
Total consolidated operating expenses	$ 786,162	$ 755,198	$ 606,945	$ 693,580	$ 728,647	$ 756,355	$ 736,290	$ 703,248	2,841,885	2,924,540	2,984,690
Operating Segments | Asset Based
OPERATING EXPENSES
Salaries, wages, and benefits									1,095,694	1,148,761	1,128,030
Fuel, supplies, and expenses									209,095	257,133	255,655
Operating taxes and licenses									49,300	50,209	48,792
Insurance									33,568	32,516	32,887
Communications and utilities									17,916	18,614	16,983
Depreciation and amortization									94,326	89,798	85,951
Rents and purchased transportation									250,159	221,479	242,247
Shared services									217,258	212,773	215,302
Multiemployer pension fund withdrawal liability charge											37,922
Gain on sale of property and equipment									(3,309)	(5,892)	(410)
Innovative technology costs									22,458	13,739	3,810
Other									6,701	3,488	4,554
Total consolidated operating expenses									1,993,166	2,042,618	2,071,723
Operating Segments | ArcBest
OPERATING EXPENSES
Purchased transportation									649,933	606,113	631,501
Supplies and expenses									9,627	10,789	13,329
Depreciation and amortization									9,714	11,344	13,750
Shared services									90,983	93,961	91,266
Other									9,203	9,860	9,143
Asset impairment										26,514
Restructuring costs											491
Gain on sale of subsidiaries											(1,945)
Total consolidated operating expenses									769,460	758,581	757,535
Operating Segments | FleetNet
OPERATING EXPENSES
Depreciation and amortization									1,622	1,341	1,140
Total consolidated operating expenses									201,682	206,932	190,741
Other and eliminations
OPERATING EXPENSES
Depreciation and amortization									12,729	9,983	7,794
Total consolidated operating expenses									$ (122,423)	$ (83,591)	$ (35,309)

OPERATING SEGMENT DATA - Income

OPERATING SEGMENT DATA - Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
OPERATING INCOME (LOSS)
Operating income (loss)	$ 30,252	$ 39,782	$ 20,425	$ 7,819	$ (11,229)	$ 31,208	$ 35,200	$ 8,591	$ 98,278	$ 63,770	$ 109,098
OTHER INCOME (COSTS)
Interest and dividend income									3,616	6,453	3,914
Interest and other related financing costs									(11,697)	(11,467)	(9,468)
Other, net									2,299	(7,285)	(19,158)
TOTAL OTHER INCOME (COSTS)	$ (53)	$ (604)	$ 309	$ (5,434)	$ (798)	$ (7,866)	$ (1,640)	$ (1,995)	(5,782)	(12,299)	(24,712)
INCOME BEFORE INCOME TAXES									92,496	51,471	84,386
Operating Segments | Asset Based
OPERATING INCOME (LOSS)
Operating income (loss)									98,865	102,061	103,862
Operating Segments | ArcBest
OPERATING INCOME (LOSS)
Operating income (loss)									9,655	(20,189)	23,588
Operating Segments | FleetNet
OPERATING INCOME (LOSS)
Operating income (loss)									3,367	4,806	4,385
Other and eliminations
OPERATING INCOME (LOSS)
Operating income (loss)									$ (13,609)	$ (22,908)	$ (22,737)

OPERATING SEGMENT DATA - Capita

OPERATING SEGMENT DATA - Capital expenditures, depreciation and amortization (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
OPERATING SEGMENT DATA
CAPITAL EXPENDITURES, GROSS	$ 105,051	$ 160,684	$ 137,675
DEPRECIATION AND AMORTIZATION EXPENSE	118,391	112,466	108,635
Amortization of intangibles	4,012	4,367	4,521
Operating Segments | Asset Based
OPERATING SEGMENT DATA
CAPITAL EXPENDITURES, GROSS	85,135	122,437	116,505
DEPRECIATION AND AMORTIZATION EXPENSE	94,326	89,798	85,951
Assets acquired through notes payable	61,800	67,600	86,800
Operating Segments | ArcBest
OPERATING SEGMENT DATA
CAPITAL EXPENDITURES, GROSS	1,258	3,909	5,174
DEPRECIATION AND AMORTIZATION EXPENSE	9,714	11,344	13,750
Amortization of intangibles	3,700	4,200	4,300
Operating Segments | FleetNet
OPERATING SEGMENT DATA
CAPITAL EXPENDITURES, GROSS	675	590	1,365
DEPRECIATION AND AMORTIZATION EXPENSE	1,622	1,341	1,140
Amortization of intangibles	200	200	200
Other and eliminations
OPERATING SEGMENT DATA
CAPITAL EXPENDITURES, GROSS	17,983	33,748	14,631
DEPRECIATION AND AMORTIZATION EXPENSE	$ 12,729	9,983	7,794
Assets acquired through notes payable		$ 23,200	$ 6,900

OPERATING SEGMENT DATA - Oper_2

OPERATING SEGMENT DATA - Operating Expenses by Category (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
OPERATING EXPENSES
Salaries, wages, and benefits									$ 1,368,588	$ 1,408,409	$ 1,398,348
Rents, purchased transportation, and other costs of services									974,835	934,958	989,006
Fuel, supplies, and expenses									250,221	316,047	325,126
Depreciation and amortization									118,391	112,466	108,635
Other									129,850	126,146	123,998
Asset impairment					$ 26,500					26,514
Multiemployer pension fund withdrawal liability charge											37,922
Restructuring costs											1,655
Total consolidated operating expenses	$ 786,162	$ 755,198	$ 606,945	$ 693,580	$ 728,647	$ 756,355	$ 736,290	$ 703,248	$ 2,841,885	$ 2,924,540	$ 2,984,690

RESTRUCTURING CHARGES - (Detail

RESTRUCTURING CHARGES - (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)
Restructuring Charges
Restructuring charges	$ 1,655
Contract terminations
Restructuring Charges
Restructuring charges	400
Severance and other
Restructuring Charges
Restructuring charges	$ 1,300

QUARTERLY RESULTS OF OPERATIO_3

QUARTERLY RESULTS OF OPERATIONS (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues	$ 816,414	$ 794,980	$ 627,370	$ 701,399	$ 717,418	$ 787,563	$ 771,490	$ 711,839	$ 2,940,163	$ 2,988,310	$ 3,093,788
Operating expenses	786,162	755,198	606,945	693,580	728,647	756,355	736,290	703,248	2,841,885	2,924,540	2,984,690
OPERATING INCOME	30,252	39,782	20,425	7,819	(11,229)	31,208	35,200	8,591	98,278	63,770	109,098
Other income (costs)	(53)	(604)	309	(5,434)	(798)	(7,866)	(1,640)	(1,995)	(5,782)	(12,299)	(24,712)
Income tax provision (benefit)	6,285	9,774	4,854	483	(6,478)	7,072	9,184	1,708	21,396	11,486	17,124
NET INCOME	$ 23,914	$ 29,404	$ 15,880	$ 1,902	$ (5,549)	$ 16,270	$ 24,376	$ 4,888	$ 71,100	$ 39,985	$ 67,262
Earnings (loss) per common share
Basic (in dollars per share)	$ 0.94	$ 1.15	$ 0.62	$ 0.07	$ (0.22)	$ 0.64	$ 0.95	$ 0.19	$ 2.80	$ 1.56	$ 2.61
Diluted (in dollars per share)	$ 0.89	$ 1.11	$ 0.61	$ 0.07	$ (0.22)	$ 0.62	$ 0.92	$ 0.18	$ 2.69	$ 1.51	$ 2.51
AVERAGE COMMON SHARES OUTSTANDING
Basic (in shares)	25,427,449	25,470,094	25,463,559	25,390,377	25,490,393	25,527,982	25,554,286	25,570,415	25,410,232	25,535,529	25,679,736
Diluted (in shares)	26,734,287	26,592,457	26,217,957	26,246,800	25,490,393	26,416,595	26,431,592	26,512,349	26,422,523	26,450,055	26,698,831
Goodwill and Intangible Asset Impairment [Abstract]
Noncash impairment charge (pre-tax)					$ 26,500					$ 26,514
Noncash impairment charge (after-tax)					$ 19,800
Noncash impairment charge diluted (in dollars per share)					$ 0.78
Nonunion Defined Benefit Pension Plan
Nonunion pension expense
Nonunion pension expense, including settlement and termination expense (pre-tax)						$ 6,700
Nonunion pension expense, including settlement and termination expense (after-tax)						$ 6,000
Nonunion pension expense per diluted share, including settlement and termination expense (in dollars per share)						$ 0.23

SCHEDULE II - VALUATION AND Q_2

SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for doubtful accounts receivable and revenue adjustments
Changes in valuation and qualifying accounts and reserves
Balance at Beginning of Period	$ 5,448	$ 7,380	$ 7,657
Additions, Charged to Costs and Expenses	4,327	1,223	2,336
Additions, Charged to Other Accounts	1,887	(245)	863
Deductions	3,811	2,910	3,476
Balance at End of Period	7,851	5,448	7,380
Allowance for other accounts receivable
Changes in valuation and qualifying accounts and reserves
Balance at Beginning of Period	476	806	921
Additions, Charged to Costs and Expenses	(14)	(330)	(115)
Additions, Charged to Other Accounts	198
Balance at End of Period	660	476	806
Allowance for deferred tax assets
Changes in valuation and qualifying accounts and reserves
Balance at Beginning of Period	668	53	844
Deductions	(616)	(615)	791
Balance at End of Period	$ 1,284	$ 668	$ 53