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Note 13 - Share-based Compensation (Details Textual) | 12 Months Ended
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Dec. 31, 2018 USD ($) $ / shares shares | Dec. 31, 2017 USD ($) $ / shares shares | Dec. 31, 2016 USD ($) $ / shares shares
Number Of Active Stock Incentive Plans |  | 1 |  |
Number Of Inactive Stock Option Plans |  | 1 |  |
Common Stock, Capital Shares Reserved for Future Issuance |  | 537,978 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures, Total |  | 0 | 0 | 0
Restricted Stock Units and Performance Share Award Target Level, Percentage |  | 100.00% |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period |  | 0 | 0 | 0
Director [Member] |  |  |  |
Share-based Goods and Nonemployee Services Transaction, Quantity of Securities Issued |  | 11,172 | 14,944 | 27,640
Share-based Compensation Arrangement by Stock-based Payment Award, Grant Date Fair Value | $ / shares |  | $ 21.48 | $ 14.72 | $ 9.95
Minimum [Member] |  |  |  |
Performance Awards Issued Multiplier |  | 0.00% |  |
Maximum [Member] |  |  |  |
Performance Awards Issued Multiplier |  | 200.00% |  |
Employee Stock Option [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period |  | 5 years |  |
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period |  | 10 years |  |
Restricted Stock Units (RSUs) [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period |  | 3 years |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ / shares |  |  |  | $ 9.50
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period |  | 0 | 0 |
Performance Shares [Member] |  |  |  |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options | $ |  | $ 0 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ / shares |  | $ 19.97 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period |  |  | 0 | 0
Restricted Stock Units and Performance Stock Awards [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ / shares |  | $ 19.97 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | [1] | 43,077 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value | $ |  | $ 1,600,000 | $ 100,000 | $ 100,000
[1] | The number of shares disclosed in this table are at the target level of 100%.

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