| Note 11 - Share-based Compensation - Summary of Activity Relating to Company's ESPP Program (Details) - USD ($) | 12 Months Ended | |
|---|---|---|
| Dec. 31, 2020 | Dec. 31, 2019 | |
| Compensation expense | $ 108,589 | $ 43,030 | 
| Shares of stock sold to employees (in shares) | 30,012 | 33,742 | 
| Weighted average fair value per ESPP award (in dollars per share) | $ 7.43 | $ 3.94 | 
| X | ||||||||||
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- Definition The weighted average purchase price of shares purchased under the employee stock purchase plan. No definition available. 
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| X | ||||||||||
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- Definition The amount of plan compensation cost recognized during the period. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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| X | ||||||||||
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- Definition Number of shares issued during the period as a result of an employee stock purchase plan. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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