Note 4 - Earnings Per Share - Shares Used in Calculation of Earnings Per Share (Details) - shares	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Weighted-average common shares issued (in shares)	7,305,653	7,294,014	7,301,091	7,283,808
Average treasury stock shares (in shares)	(929,362)	(835,756)	(913,510)	(797,606)
Weighted-average common shares and common stock equivalents used to calculate basic earnings per share (in shares)	6,376,291	6,458,258	6,387,581	6,486,202
Additional common stock equivalents (stock options and restricted stock) used to calculate diluted earnings per share (in shares)	9,474	20,808	10,093	20,636
Weighted-average common shares and common stock equivalents used to calculate diluted earnings per share (in shares)	6,385,765	6,479,066	6,397,674	6,506,838

Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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Number of shares of treasury stock determined by relating the portion of time within a reporting period that treasury shares have been outstanding to the total time in that period. Treasury stock is stock that the Entity has issued but subsequently reacquired.

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