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Note 10 - Stock-based Compensation (Details Textual) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Total	$ 1,511		$ 1,511
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition			3 years 109 days
Restricted Stock [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs, Capitalized Amount			$ 0	$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period			4 years
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period			79,200
Allocated Share-based Compensation Expense, Total			$ 121	88
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value			$ 169	$ 105
Restricted Stock [Member] \| Independent Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	32,000	22,500
Allocated Share-based Compensation Expense, Total	$ 270	$ 143
Restricted Stock [Member] \| Independent Directors [Member] \| Share-based Compensation Award, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage			25.00%
Restricted Stock [Member] \| Independent Directors [Member] \| Share-based Compensation Award, Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage			25.00%
Restricted Stock [Member] \| Independent Directors [Member] \| Share-based Compensation Award, Tranche Three [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage			25.00%
Restricted Stock [Member] \| Independent Directors [Member] \| Share-based Compensation Award, Tranche Four [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage			25.00%
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period			4 years
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period			10 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value			$ 3.61	$ 2.64