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Note 7 - Debt - Current and Long-term Debt (Details) (Parentheticals)
Mar. 31, 2018
Dec. 31, 2017
Revenue Equipment Installment Notes [Member]    
Debt Instrument, Interest Rate, Stated Percentage 3.40% 3.30%
Real Estate Note [Member]    
Debt Instrument, Interest Rate, Stated Percentage 3.40% 3.10%