Note 9 - Stock-based Compensation (Details Textual) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total	$ 2,055
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition	3 years 73 days
Share-based Payment Arrangement, Amount Capitalized	$ 0	$ 0
Restricted Stock [Member]
Share-based Payment Arrangement, Expense	183	121
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value	$ 239	$ 169
Restricted Stock [Member] \| Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	4 years
Restricted Stock [Member] \| Independent Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	1 year
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	36,000	32,000
Share-based Payment Arrangement, Expense	$ 257	$ 270
Restricted Stock [Member] \| Independent Directors [Member] \| Share-based Payment Arrangement, 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 Payment Arrangement, 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 Payment Arrangement, 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%
Share-based Payment Arrangement, 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	$ 3.13	$ 3.61

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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