Note 8 - Share-based Compensation - Stock Option Activity (Details)	3 Months Ended
Mar. 31, 2022 USD ($) $ / shares shares
Outstanding, number of options (in shares) \| shares	2,204,000
Outstanding, weighted average exercise price per share (in dollars per share)	$ 4.41
Outstanding, weighted average remaining contractual term (Year)	7 years 1 month 6 days
Granted (in dollars per share)
Expired, number of options (in shares) \| shares	(65,000)
Expired, weighted average exercise price per share (in dollars per share)	$ 1.10
Outstanding, number of options (in shares) \| shares	2,139,000
Outstanding, weighted average exercise price per share (in dollars per share)	$ 4.37
Balance, aggregate intrinsic value \| $
Options exercisable, number of options (in shares) \| shares	1,242,000
Options exercisable, weighted average exercise price per share (in dollars per share)	$ 3.98
Options exercisable, weighted average remaining contractual term (Year)	7 years 1 month 6 days

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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Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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

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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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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

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

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(ii)
-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

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-Publisher FASB
-Name Accounting Standards Codification
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-Paragraph 2
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-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

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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 grantees could have acquired the underlying shares with respect to stock options of the plan that expired.

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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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