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Note 2 - Summary of Significant Accounting Policies (Details Textual)
12 Months Ended
Dec. 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Accounts Receivable, Allowance for Credit Loss, Recovery $ 5,600,000    
Accounts Receivable, Allowance for Credit Loss, Writeoff 500,000    
Equity Securities, FV-NI $ 0 $ 0  
Number of Operating Segments 5    
Self Insurance, Per Claim Amount, Personal Injury and Property Damage Claims $ 500,000 500,000 $ 500,000
Self Insurance, Per Claim Deductible, Workers' Compensation Claims     $ 100,000
Self Insurance Reserve 257,000,000 263,000,000  
Prepaid Insurance, Current and Noncurrent 304,000,000 281,000,000  
Assets, Current, Total 1,842,117,000 1,481,299,000  
Accounts and Other Receivables, Net, Current [Member]      
Assets, Current, Total $ 167,000,000 $ 157,000,000  
Customer Concentration Risk [Member] | Revenue Benchmark [Member]      
Number of Major Customers 10 10 10
Customer Concentration Risk [Member] | Revenue Benchmark [Member] | Top 10 Customers [Member]      
Concentration Risk, Percentage 37.00% 32.00% 30.00%
Customer Concentration Risk [Member] | Revenue Benchmark [Member] | One Customer [Member]      
Concentration Risk, Percentage 10.00% 8.00% 6.00%
Customer Concentration Risk [Member] | Accounts Receivable [Member] | Top 10 Customers [Member]      
Number of Major Customers 10 10  
Concentration Risk, Percentage 37.00% 34.00%  
Minimum [Member]      
Property, Plant and Equipment, Salvage Value, Percentage 10.00%    
Finite-Lived Intangible Asset, Useful Life (Year) 2 years    
Maximum [Member]      
Property, Plant and Equipment, Salvage Value, Percentage 30.00%    
Finite-Lived Intangible Asset, Useful Life (Year) 15 years    
Tractors [Member] | Minimum [Member]      
Property, Plant and Equipment, Useful Life (Year) 4 years    
Tractors [Member] | Maximum [Member]      
Property, Plant and Equipment, Useful Life (Year) 10 years    
Trailing Equipment [Member] | Minimum [Member]      
Property, Plant and Equipment, Useful Life (Year) 7 years    
Trailing Equipment [Member] | Maximum [Member]      
Property, Plant and Equipment, Useful Life (Year) 20 years    
Land, Buildings and Improvements [Member] | Minimum [Member]      
Property, Plant and Equipment, Useful Life (Year) 10 years    
Land, Buildings and Improvements [Member] | Maximum [Member]      
Property, Plant and Equipment, Useful Life (Year) 40 years    
Computer Hardware and Software [Member] | Minimum [Member]      
Property, Plant and Equipment, Useful Life (Year) 3 years    
Computer Hardware and Software [Member] | Maximum [Member]      
Property, Plant and Equipment, Useful Life (Year) 7 years    
Furniture and Fixtures [Member] | Minimum [Member]      
Property, Plant and Equipment, Useful Life (Year) 3 years    
Furniture and Fixtures [Member] | Maximum [Member]      
Property, Plant and Equipment, Useful Life (Year) 10 years    
Trade Accounts Receivable [Member]      
Accounts Receivable, Allowance for Credit Loss, Ending Balance $ 18,400,000 $ 13,300,000