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Note 10 - Subsequent Event (Details Textual) |  | 3 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | --- | ---
Oct. 09, 2019 | Sep. 30, 2019 $ / shares shares | Sep. 30, 2018 $ / shares | Sep. 30, 2019 $ / shares shares | Sep. 30, 2018 $ / shares | Nov. 08, 2019 shares | Dec. 31, 2018 shares
Common Stock, Shares, Outstanding, Ending Balance |  | 3,211,565 |  | 3,211,565 |  |  | 3,244,332
Treasury Stock, Shares, Ending Balance |  | 435,581 |  | 435,581 |  |  | 386,165
Earnings Per Share, Basic, Total | $ / shares |  | $ 1.01 | $ 1.02 | $ 2.95 | $ 2.79 |  |
Earnings Per Share, Basic, If Two-for-one Stock Split Had Occurred | $ / shares |  |  |  | $ 1.48 |  |  |
Forecast [Member] |  |  |  |  |  |  |
Common Stock, Shares, Outstanding, Ending Balance |  |  |  |  |  | 6,400,000 |
Treasury Stock, Shares, Ending Balance |  |  |  |  |  | 871,000 |
Subsequent Event [Member] |  |  |  |  |  |  |
Stockholders' Equity Note, Stock Split, Conversion Ratio | 2 |  |  |  |  |  |

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