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Note 2 - Summary of Significant Accounting Policies (Details Textual) - USD ($)
3 Months Ended 12 Months Ended 48 Months Ended
Sep. 30, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2017
Available-for-sale Securities   $ 0 $ 0   $ 0
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   238,000,000 220,000,000   238,000,000
Prepaid Insurance, Current and Noncurrent   256,000,000 254,000,000   $ 256,000,000
Income Tax Expense (Benefit)   $ (91,024,000) $ 263,707,000 $ 262,968,000  
Accounting Standards Update 2016-09 [Member]          
Income Tax Expense (Benefit) $ (4,900,000)        
Customer Concentration Risk [Member] | Sales Revenue, Net [Member] | Top 10 Customers [Member]          
Concentration Risk, Percentage   29.00% 29.00% 29.00%  
Customer Concentration Risk [Member] | Accounts Receivable [Member] | Top 10 Customers [Member]          
Concentration Risk, Percentage   31.00% 28.00%    
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   $ 15,400,000 $ 13,400,000   $ 15,400,000
Other Receivables [Member]          
Allowance for Doubtful Accounts Receivable   8,600,000     $ 8,600,000
Reclassification of Insurance Receivables from Claims Accruals to Other Receivables [Member] | Year Ended December 31, 2016 [Member]          
Prior Period Reclassification Adjustment   $ 121,700,000