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Note 1 - Summary of Significant Accounting Policies (Details Textual) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Letters of Credit Outstanding, Amount   $ 12,900,000    
Income Tax Expense (Benefit)   $ (33,811,000) $ 23,602,000 $ 24,946,000
Number of Operating Segments   5    
Number of Reportable Segments   4    
Accounting Standards Update 2016-09 [Member]        
Income Tax Expense (Benefit)   $ (176,000)    
Accounting Standards Update 2014-09 [Member] | Scenario, Forecast [Member]        
Cumulative Effect on Retained Earnings, before Tax $ 485,000      
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | Walmart [Member]        
Concentration Risk, Percentage   19.00% 17.00% 13.00%
Sales Revenue, Net [Member] | Geographic Concentration Risk [Member] | UNITED STATES        
Concentration Risk, Percentage   99.00% 99.00% 99.00%
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Walmart [Member]        
Concentration Risk, Percentage   15.00% 17.00%  
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   12,900,000    
Supplies and Maintenance Costs [Member]        
Amortization   $ 7,100,000 $ 6,900,000 $ 6,300,000
Tractor [Member]        
Replacement Of Equipment Period After Purchase   3 years 292 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 255 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