Note 5 - Shareholders' Equity (Details Textual) - USD ($) | Jan. 01, 2020 | Jan. 01, 2018 | Sep. 30, 2021 | Sep. 30, 2020 | Sep. 29, 2021 | Jun. 30, 2021 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number (in shares) | | | 1,685,462 | | | |
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year) | | | 2 years 9 months 18 days | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value | | | $ 2,100,000 | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value | | | $ 1,000,000 | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period (in shares) | | | 797,306 | 0 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value | | | $ 435,000 | | | |
Restricted Stock [Member] | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Ending Balance (in shares) | | | | | | 0 |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period (in shares) | | | | 149,824 | | |
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation (in shares) | | | | 17,928 | | |
Restricted Stock [Member] | Non-employee Directors [Member] | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Month) | | 1 year | | | | |
Restricted Stock Units (RSUs) [Member] | Non-employee Directors [Member] | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Month) | 1 year | | | | | |
Share-based Payment Arrangement, Expensed and Capitalized, Amount, Total | $ 25,000 | $ 15,000 | | | | |
Stock Options and Non-vested Stock [Member] | | | | | | |
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total | | | $ 138,000 | | | |
The 2011 Incentive Plan [Member] | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized (in shares) | | | 1,300,000 | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Additional Shares Authorized, Percentage of Outstanding Stock | | | 4.00% | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Outstanding Stock Maximum | | | 10.00% | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in shares) | | | 12,084,032 | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares) | | | 4,785,597 | | | |
Common Stock Capital Shares Reserved for Future Issuance Excluding Outstanding Awards (in shares) | | | 2,500,000 | | 4,785,597 | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number (in shares) | | | 3,194,573 | | | |
Common Stock, Capital Shares Reserved for Future Issuance (in shares) | | | 5,694,573 | | | |
The 2011 Incentive Plan [Member] | Share-based Payment Arrangement, Option [Member] | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year) | | | 10 years | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Month) | | | 48 months | | | |
The 2011 Incentive Plan [Member] | Share-based Payment Arrangement, Option [Member] | Cliff Vesting [Member] | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Month) | | | 1 year | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | | | 25.00% | | | |
The 2011 Incentive Plan [Member] | Share-based Payment Arrangement, Option [Member] | In Equal Monthly [Member] | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Month) | | | 36 months | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | | | 75.00% | | | |