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Note 7 - Indebtedness (Details Textual) - Revolving Credit Facility [Member] - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 02, 2013
Line of Credit Facility, Maximum Borrowing Capacity   $ 40,000
Long-term Line of Credit $ 0  
Letters of Credit Outstanding, Amount $ 600  
London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member]    
Debt Instrument, Basis Spread on Variable Rate 1.00%  
London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member]    
Debt Instrument, Basis Spread on Variable Rate 1.50%  
Prime Rate [Member] | Minimum [Member]    
Debt Instrument, Basis Spread on Variable Rate 0.00%  
Prime Rate [Member] | Maximum [Member]    
Debt Instrument, Basis Spread on Variable Rate 0.25%