Note 7 - Long-Term Debt and Revolving Line of Credit - Interest Margin and Commitment Fee Payable (Details)	9 Months Ended
	Sep. 30, 2017
Debt Instrument Leverage Ratio Less than 1.00 [Member]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.15%
Debt Instrument Leverage Ratio Greater Than Or Equal To 1 But Less Than 2 [Member]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.20%
Debt Instrument Leverage Ratio Greater Than Or Equal To 2 But Less Than 3 [Member]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.25%
Debt Instrument Leverage Ratio Greater Than Or Equal To 3 But Less Than 3.50 [Member]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.30%
Debt Instrument Leverage Ratio Greater Than Or Equal To 3.50 But Less Than 4 [Member]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.35%
Debt Instrument Leverage Ratio Greater Than Or Equal To 4 But Less Than 4.50 [Member]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.40%
Debt Instrument Leverage Ratio Greater Than Or Equal To 4.50 But Less Than 5 [Member]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.45%
Debt Instrument Leverage Ratio Greater Than Or Equal To 5 But Less Than 6 [Member]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.50%
Debt Instrument Leverage Ratio Greater Than Or Equal To 6 [Member]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.55%
London Interbank Offered Rate (LIBOR) [Member] | Debt Instrument Leverage Ratio Less than 1.00 [Member]
Debt Instrument, Basis Spread on Variable Rate	1.25%
London Interbank Offered Rate (LIBOR) [Member] | Debt Instrument Leverage Ratio Greater Than Or Equal To 1 But Less Than 2 [Member]
Debt Instrument, Basis Spread on Variable Rate	1.50%
London Interbank Offered Rate (LIBOR) [Member] | Debt Instrument Leverage Ratio Greater Than Or Equal To 2 But Less Than 3 [Member]
Debt Instrument, Basis Spread on Variable Rate	1.75%
London Interbank Offered Rate (LIBOR) [Member] | Debt Instrument Leverage Ratio Greater Than Or Equal To 3 But Less Than 3.50 [Member]
Debt Instrument, Basis Spread on Variable Rate	2.25%
London Interbank Offered Rate (LIBOR) [Member] | Debt Instrument Leverage Ratio Greater Than Or Equal To 3.50 But Less Than 4 [Member]
Debt Instrument, Basis Spread on Variable Rate	2.50%
London Interbank Offered Rate (LIBOR) [Member] | Debt Instrument Leverage Ratio Greater Than Or Equal To 4 But Less Than 4.50 [Member]
Debt Instrument, Basis Spread on Variable Rate	3.00%
London Interbank Offered Rate (LIBOR) [Member] | Debt Instrument Leverage Ratio Greater Than Or Equal To 4.50 But Less Than 5 [Member]
Debt Instrument, Basis Spread on Variable Rate	3.50%
London Interbank Offered Rate (LIBOR) [Member] | Debt Instrument Leverage Ratio Greater Than Or Equal To 5 But Less Than 6 [Member]
Debt Instrument, Basis Spread on Variable Rate	4.00%
London Interbank Offered Rate (LIBOR) [Member] | Debt Instrument Leverage Ratio Greater Than Or Equal To 6 [Member]
Debt Instrument, Basis Spread on Variable Rate	6.00%
Base Rate [Member] | Debt Instrument Leverage Ratio Less than 1.00 [Member]
Debt Instrument, Basis Spread on Variable Rate	0.00%
Base Rate [Member] | Debt Instrument Leverage Ratio Greater Than Or Equal To 1 But Less Than 2 [Member]
Debt Instrument, Basis Spread on Variable Rate	0.00%
Base Rate [Member] | Debt Instrument Leverage Ratio Greater Than Or Equal To 2 But Less Than 3 [Member]
Debt Instrument, Basis Spread on Variable Rate	0.00%
Base Rate [Member] | Debt Instrument Leverage Ratio Greater Than Or Equal To 3 But Less Than 3.50 [Member]
Debt Instrument, Basis Spread on Variable Rate	0.00%
Base Rate [Member] | Debt Instrument Leverage Ratio Greater Than Or Equal To 3.50 But Less Than 4 [Member]
Debt Instrument, Basis Spread on Variable Rate	0.25%
Base Rate [Member] | Debt Instrument Leverage Ratio Greater Than Or Equal To 4 But Less Than 4.50 [Member]
Debt Instrument, Basis Spread on Variable Rate	0.75%
Base Rate [Member] | Debt Instrument Leverage Ratio Greater Than Or Equal To 4.50 But Less Than 5 [Member]
Debt Instrument, Basis Spread on Variable Rate	1.25%
Base Rate [Member] | Debt Instrument Leverage Ratio Greater Than Or Equal To 5 But Less Than 6 [Member]
Debt Instrument, Basis Spread on Variable Rate	1.75%
Base Rate [Member] | Debt Instrument Leverage Ratio Greater Than Or Equal To 6 [Member]
Debt Instrument, Basis Spread on Variable Rate	3.75%