Note 7 - Stock-based Compensation - Stock Option Activities (Details) - USD ($)	3 Months Ended	12 Months Ended
Mar. 31, 2020	Dec. 31, 2019
Outstanding (in shares)	146,300
Outstanding, weighted average exercise price (in dollars per share)	$ 14.92
Outstanding, average remaining contractual term (Year)	4 years 328 days	5 years
Outstanding, aggregate intrinsic value		$ 53,166
Granted (in shares)
Granted, weighted average exercise price (in dollars per share)
Exercised (in shares)
Exercised, weighted average exercise price (in dollars per share)
Forfeited or expired (in shares)	(900)
Forfeited or expired, weighted average exercise price (in dollars per share)	$ 14.90
Outstanding (in shares)	145,400	146,300
Outstanding, weighted average exercise price (in dollars per share)	$ 14.91	$ 14.92
Exercisable (in shares)	57,260
Exercisable, weighted average exercise price (in dollars per share)	$ 14.92
Exercisable, average remaining contractual term (Year)	4 years 328 days
Exercisable, aggregate intrinsic value

The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

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Weighted average price of options that were either forfeited or expired.

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Gross number of share options (or share units) granted during the period.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Number of share options (or share units) exercised during the current period.

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