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Note 2 - Summary of Significant Accounting Policies (Details Textual) - USD ($)
12 Months Ended 36 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2016
Allowance for Doubtful Accounts Receivable $ 13,400,000 $ 9,900,000   $ 13,400,000
Self Insurance Reserve 98,000,000 95,000,000   98,000,000
Prepaid Insurance, Current and Noncurrent 93,000,000 87,000,000   93,000,000
Available-for-sale Securities 0 $ 0   0
Reduction of Current Assets as Result of ASU 2015-03 [Member]        
Prior Period Reclassification Adjustment 1,400,000      
Reduction of Other Assets as Result of ASU 2015-03 [Member]        
Prior Period Reclassification Adjustment 5,600,000      
Reduction of Long-term Debt as Result of ASU 2015-03 [Member]        
Prior Period Reclassification Adjustment $ 7,000,000      
Personal Injury and Property Damage [Member]        
Per Claim Self Insured Portion       500,000
Workers Compensation [Member]        
Self Insurance Per Claim Deductible       $ 100,000
Customer Concentration Risk [Member] | Sales Revenue, Net [Member] | Top 10 Customers [Member]        
Concentration Risk, Percentage 29.00% 29.00% 28.00%  
Customer Concentration Risk [Member] | Accounts Receivable [Member] | Top 10 Customers [Member]        
Concentration Risk, Percentage 28.00% 27.00%    
Minimum [Member]        
Property, Plant and Equipment, Salvage Value, Percentage 10.00%     10.00%
Maximum [Member]        
Property, Plant and Equipment, Salvage Value, Percentage 30.00%     30.00%
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