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Note 1 - Summary of Significant Accounting Policies (Details Textual) - USD ($)
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Sales Revenue, Net [Member] | Geographic Concentration Risk [Member] | UNITED STATES      
Concentration Risk, Percentage 99.00% 99.00% 99.00%
Sales Revenue, Net [Member] | Customer Concentration Risk [Member]      
Concentration Risk, Percentage 13.00% 9.00% 8.00%
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Walmart [Member]      
Concentration Risk, Percentage 12.00%    
Tractor [Member]      
Replacement Of Equipment Period After Purchase 4 years 36 days    
Property, Plant and Equipment, Useful Life 5 years    
Property, Plant and Equipment, Salvage Value, Percentage 25.00%    
Trailer [Member]      
Replacement Of Equipment Period After Purchase 5 years 36 days    
Property, Plant and Equipment, Useful Life 7 years    
Property, Plant and Equipment, Salvage Value, Percentage 35.00%    
Tires In Service [Member]      
Property, Plant and Equipment, Useful Life 2 years    
Supplies and Maintenance Costs [Member]      
Amortization $ 6,300,000 $ 5,700,000 $ 5,800,000
Uninsured Risk [Member] | Auto Liability Claim [Member]      
Loss Contingency Range Possible Loss Per Claim 1,000,000    
Uninsured Risk [Member] | Workers Compensation Liability Claim [Member]      
Loss Contingency Range Possible Loss Per Claim 750,000    
Insurance Claims [Member]      
Letters of Credit Outstanding, Amount $ 10,400,000    
Subsidiary or Equity Method Investee, Cumulative Percentage Ownership after All Transactions 45.00%    
Letters of Credit Outstanding, Amount $ 10,400,000    
Number of Operating Segments 6    
Number of Reportable Segments 4 4 2