Note 8 - Stock-based Compensation Expense - Stock Option Plan (Details) - $ / shares	3 Months Ended	6 Months Ended
Mar. 31, 2022	Jun. 30, 2022
Granted during period (in shares)		12,500
Exercised during period (in shares)	0	0
Ending balance, number outstanding (in shares)		599,500
Number of shares exercisable (in shares)		297,500
The 2007 Share Incentive Plan [Member]
Beginning balance, number outstanding (in shares)	220,000	220,000
Granted during period (in shares)		0
Exercised during period (in shares)		0
Canceled during period (in shares)		(25,000)
Ending balance, number outstanding (in shares)		195,000
Number of shares exercisable (in shares)		195,000
Beginning balance, weighted average exercise price (in dollars per share)	$ 12.56	$ 12.56
Granted during period, weighted average exercise price (in dollars per share)		0
Exercised during period, weighted average exercise price (in dollars per share)		0
Canceled during period, weighted average exercise price (in dollars per share)		15.00
Ending balance, weighted average exercise price (in dollars per share)		12.24
Number of options exercisable, weighted average exercise price (in dollars per share)		$ 12.24
The 2016 Share Incentive Plan [Member]
Beginning balance, number outstanding (in shares)	398,500	398,500
Granted during period (in shares)		12,500
Exercised during period (in shares)		0
Canceled during period (in shares)		(6,500)
Ending balance, number outstanding (in shares)		404,500
Number of shares exercisable (in shares)		102,500
Beginning balance, weighted average exercise price (in dollars per share)	$ 4.43	$ 4.43
Granted during period, weighted average exercise price (in dollars per share)		4.60
Exercised during period, weighted average exercise price (in dollars per share)		0
Canceled during period, weighted average exercise price (in dollars per share)		4.01
Ending balance, weighted average exercise price (in dollars per share)		4.44
Number of options exercisable, weighted average exercise price (in dollars per share)		$ 5.33

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

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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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