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Note 9 - Stock-based Compensation - Shares Authorized Under Stock Option Plan (Details) | 12 Months Ended
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Dec. 31, 2020 $ / shares shares
Number of shares outstanding (in shares) | shares | 844,455
Weighted average remaining contractual life (Year) | 3 years 7 months 28 days
Weighted average exercise price (in dollars per share) | $ 2.00
Price Range 1 [Member] |
Exercise price, lower range (in dollars per share) | 0.49
Exercise price, upper range (in dollars per share) | $ 1.00
Number of shares outstanding (in shares) | shares | 3,571
Weighted average remaining contractual life (Year) | 10 months 28 days
Weighted average exercise price (in dollars per share) | $ 0.49
Price Range 2 [Member] |
Exercise price, lower range (in dollars per share) | 1.01
Exercise price, upper range (in dollars per share) | $ 1.50
Number of shares outstanding (in shares) | shares | 110,449
Weighted average remaining contractual life (Year) | 9 months 10 days
Weighted average exercise price (in dollars per share) | $ 1.19
Price Range 3 [Member] |
Exercise price, lower range (in dollars per share) | 1.51
Exercise price, upper range (in dollars per share) | $ 2.50
Number of shares outstanding (in shares) | shares | 676,367
Weighted average remaining contractual life (Year) | 4 years 25 days
Weighted average exercise price (in dollars per share) | $ 1.95
Price Range 4 [Member] |
Exercise price, lower range (in dollars per share) | 2.51
Exercise price, upper range (in dollars per share) | $ 8.60
Number of shares outstanding (in shares) | shares | 54,068
Weighted average remaining contractual life (Year) | 4 years 7 months 20 days
Weighted average exercise price (in dollars per share) | $ 4.49

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- Definition Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(i) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition The number of shares reserved for issuance pertaining to the outstanding stock options as of the balance sheet date for all option plans in the customized range of exercise prices. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition The ceiling of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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