Note 10 - Stockholders' Equity - Summary of Stock Option Activity (Details) - $ / shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Balance, outstanding (in shares)		56,400	68,400
Balance, outstanding (in dollars per share)		$ 5.14	$ 5.17
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	0	0	0	0
Granted (in dollars per share)
Forfeited or cancelled (in shares)		(12,000)	(12,000)
Forfeited or cancelled (in dollars per share)		$ 5.14	$ 5.30
Exercised (in shares)		(44,400)
Exercised (in dollars per share)		$ 5.14
Balance, outstanding (in shares)			56,400	68,400
Balance, outstanding (in dollars per share)			$ 5.14	$ 5.17
Exercisable at end of year (in shares)			56,400
Exercisable at end of year (in dollars per share)			$ 5.14
Weighted-average fair value of options granted during year (in dollars per share)

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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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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

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