Annual report pursuant to Section 13 and 15(d)

Accounting Policies (Details)

v3.20.4
Accounting Policies (Details)
 12 Months Ended
Dec. 31, 2020
USD ($)
numberOfSegments
Dec. 31, 2019
USD ($)
numberOfSegments
Dec. 31, 2018
USD ($)
Accounting Policies [Line Items]      
Number of principal reporting segments | numberOfSegments 2 3  
Cash $ 25,246,000 $ 64,749,000  
Cash equivalents 15,008,000    
Average monthly revenue adjustments 396,000    
Average monthly revenue $ 105,798,000    
Average monthly revenue adjustments as a percentage of monthly revenue 0.40%    
Capitalized software development costs $ 23,480,000 21,536,000  
Accounting Policies, Use of Estimates [Abstract]      
Liability insurance coverage 100,000    
Self-insurance retention workers' compensation 500,000    
Self Insurance Reserve 72,650,000 66,176,000  
Self Insurance Reserve, Noncurrent 52,308,000 49,810,000  
Insurance Settlements Receivable $ 36,743,000 34,091,000  
Accounting Policies, Cash and Cash Equivalents [Abstract]      
Maximum term for liquid investments to be considered cash equivalents, in months 3 months    
Accounting Policies, Software Development [Abstract]      
Capitalized computer software, accumulated amortization $ 16,025,000 14,133,000  
Capitalized Computer Software, Amortization 2,053,000 1,714,000 $ 1,779,000
Capitalized software future estimated amortization expense      
2021 1,988,000    
2022 1,749,000    
2023 1,472,000    
2024 1,124,000    
2025 507,000    
Undistributed Earnings (Loss) Allocated to Participating Securities, Basic 385,000 945,000 $ 881,000
Accounting Policies, Share-based Payments [Abstract]      
Self Insurance Reserve, Current 20,342,000 $ 16,366,000  
Other operating expenses $ 1,560,000    
Software and Software Development Costs [Member]      
Accounting Policies, Property and Equipment [Abstract]      
Property and equipment, useful life 5 years    
Stock Option [Member]      
Accounting Policies, Share-based Payments [Abstract]      
Share-based awards, vesting period 3 years    
Minimum [Member] | Building [Member]      
Accounting Policies, Property and Equipment [Abstract]      
Property and equipment, useful life 30 years    
Minimum [Member] | Equipment [Member]      
Accounting Policies, Property and Equipment [Abstract]      
Property and equipment, useful life 3 years    
Maximum [Member] | Building [Member]      
Accounting Policies, Property and Equipment [Abstract]      
Property and equipment, useful life 40 years    
Maximum [Member] | Equipment [Member]      
Accounting Policies, Property and Equipment [Abstract]      
Property and equipment, useful life 10 years    
Aggregate deductible for claims between $3,000 and $5,000 [Member]      
Accounting Policies, Share-based Payments [Abstract]      
Self insurance retention liability additional deductible $ 6,000,000    
Aggregate deductible for claims between $3,000 and $5,000 [Member] | Minimum [Member]      
Accounting Policies, Use of Estimates [Abstract]      
Self insurance retention liability additonal deductible applicable range 3,000,000    
Aggregate deductible for claims between $3,000 and $5,000 [Member] | Maximum [Member]      
Accounting Policies, Use of Estimates [Abstract]      
Self insurance retention liability additonal deductible applicable range 5,000,000    
Aggregate deductible for claims between $5,000 and $10,000 [Member]      
Accounting Policies, Share-based Payments [Abstract]      
Self insurance retention liability additional deductible 5,000,000    
Aggregate deductible for claims between $5,000 and $10,000 [Member] | Minimum [Member]      
Accounting Policies, Use of Estimates [Abstract]      
Self insurance retention liability additonal deductible applicable range 5,000,000    
Aggregate deductible for claims between $5,000 and $10,000 [Member] | Maximum [Member]      
Accounting Policies, Use of Estimates [Abstract]      
Self insurance retention liability additonal deductible applicable range 10,000,000    
Expedited LTL [Member] | Aggregate deductible for claims between $0 and $3,000      
Accounting Policies, Share-based Payments [Abstract]      
Self insurance retention liability additional deductible 3,000,000    
Expedited LTL [Member] | Aggregate deductible for claims between $0 and $3,000 | Minimum [Member]      
Accounting Policies, Use of Estimates [Abstract]      
Self insurance retention liability additonal deductible applicable range 0    
Expedited LTL [Member] | Aggregate deductible for claims between $0 and $3,000 | Maximum [Member]      
Accounting Policies, Use of Estimates [Abstract]      
Self insurance retention liability additonal deductible applicable range 3,000,000    
Truckload [Member] | Aggregate deductible for claims between $0 and $2,000 [Member]      
Accounting Policies, Share-based Payments [Abstract]      
Self insurance retention liability additional deductible 2,000,000    
Truckload [Member] | Aggregate deductible for claims between $0 and $2,000 [Member] | Minimum [Member]      
Accounting Policies, Use of Estimates [Abstract]      
Self insurance retention liability additonal deductible applicable range 0    
Truckload [Member] | Aggregate deductible for claims between $0 and $2,000 [Member] | Maximum [Member]      
Accounting Policies, Use of Estimates [Abstract]      
Self insurance retention liability additonal deductible applicable range 2,000,000    
Intermodal [Member] | Aggregate deductible for claims between $0 and $3,000 | Minimum [Member]      
Accounting Policies, Use of Estimates [Abstract]      
Self insurance retention liability additonal deductible applicable range 0    
Intermodal [Member] | Aggregate deductible for claims between $0 and $3,000 | Maximum [Member]      
Accounting Policies, Use of Estimates [Abstract]      
Self insurance retention liability additonal deductible applicable range 250,000    
Intermodal [Member] | Aggregate deductible for claims between $0 and $250      
Accounting Policies, Share-based Payments [Abstract]      
Self insurance retention liability additional deductible $ 250,000