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Note 2 - Summary of Significant Accounting Policies (Details Textual) - USD ($)
12 Months Ended 36 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2018
Jan. 01, 2019
Dec. 31, 2015
Cash and Cash Equivalents, at Carrying Value, Ending Balance $ 7,600,000 $ 14,612,000 $ 6,377,000 $ 7,600,000   $ 5,566,000
Equity Securities, FV-NI $ 0 0   0    
Number of Operating Segments 4          
Self Insurance, Per Claim Amount, Personal Injury and Property Damage Claims       500,000    
Self Insurance, Per Claim Deductible, Workers' Compensation Claims       100,000    
Self Insurance Reserve $ 260,000,000 238,000,000   260,000,000    
Prepaid Insurance, Current and Noncurrent 261,000,000 256,000,000   261,000,000    
Assets, Current, Total 1,502,981,000 1,338,728,000   1,502,981,000    
Subsequent Event [Member]            
Operating Lease, Right-of-Use Asset         $ 102,400,000  
Operating Lease, Liability, Total         $ 102,400,000  
Accounts and Other Receivables, Net, Current [Member]            
Assets, Current, Total $ 158,000,000 $ 193,000,000   $ 158,000,000    
Customer Concentration Risk [Member] | Sales Revenue, Net [Member] | Top 10 Customers [Member]            
Concentration Risk, Percentage 30.00% 29.00% 29.00%      
Customer Concentration Risk [Member] | Accounts Receivable [Member] | Top 10 Customers [Member]            
Concentration Risk, Percentage 32.00% 31.00%        
Minimum [Member]            
Property, Plant and Equipment, Salvage Value, Percentage 10.00%     10.00%    
Finite-Lived Intangible Asset, Useful Life 5 years          
Maximum [Member]            
Property, Plant and Equipment, Salvage Value, Percentage 30.00%     30.00%    
Finite-Lived Intangible Asset, Useful Life 10 years          
Tractors [Member] | Minimum [Member]            
Property, Plant and Equipment, Useful Life 4 years          
Tractors [Member] | Maximum [Member]            
Property, Plant and Equipment, Useful Life 10 years          
Trailing Equipment [Member] | Minimum [Member]            
Property, Plant and Equipment, Useful Life 7 years          
Trailing Equipment [Member] | Maximum [Member]            
Property, Plant and Equipment, Useful Life 20 years          
Land, Buildings and Improvements [Member] | Minimum [Member]            
Property, Plant and Equipment, Useful Life 10 years          
Land, Buildings and Improvements [Member] | Maximum [Member]            
Property, Plant and Equipment, Useful Life 40 years          
Furniture and Fixtures [Member] | Minimum [Member]            
Property, Plant and Equipment, Useful Life 3 years          
Furniture and Fixtures [Member] | Maximum [Member]            
Property, Plant and Equipment, Useful Life 10 years          
Trade Accounts Receivable [Member]            
Allowance for Doubtful Accounts Receivable, Ending Balance $ 23,600,000 $ 15,400,000   $ 23,600,000    
Other Receivables [Member]            
Cash and Cash Equivalents, at Carrying Value, Ending Balance $ 12,200,000 $ 8,600,000   $ 12,200,000