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Note 6 - Share-based Payments - Amounts of Compensation Expense Recognized Under Stock-based Payment Programs (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019
Stock compensation expense | $ 1,275 | $ 1,301 | $ 5,282 | $ 5,245
Stock Performance Awards [Member] | Executive Officer [Member] |  |  |  |
Stock compensation expense | 758 | 743 | 3,170 | 3,274
Restricted Stock Units (RSUs) [Member] | Executive Officers and Key Employees [Member] |  |  |  |
Stock compensation expense | 106 | 189 | 891 | 999
Restricted Stock Units (RSUs) [Member] | Nonemployee Directors [Member] |  |  |  |
Stock compensation expense | 237 | 203 | 677 | 572
Restricted Stock Units (RSUs) [Member] | Non-executive Employees [Member] |  |  |  |
Stock compensation expense | 133 | 112 | 408 | 346
Employee Stock Purchase Plan [Member] |  |  |  |
Stock compensation expense | $ 41 | $ 54 | $ 136 | $ 54

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