Note 6 - Stock-based Compensation (Details Textual) - USD ($) | 3 Months Ended | 6 Months Ended |
Mar. 31, 2022 | Dec. 31, 2021 | Mar. 31, 2021 | Mar. 31, 2022 | Mar. 31, 2021 |
Share-Based Payment Arrangement, Expense | $ 570,000 | | $ 334,000 | $ 1,010,000 | $ 623,000 |
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total | 4,694,000 | | | $ 4,694,000 | |
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year) | | | | 2 years 7 months 6 days | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares) | | | | 62,730 | 105,089 |
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year) | | | | 5 years | 5 years |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year) | | | | 3 years | 3 years |
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price (in dollars per share) | | | | $ 66.48 | $ 23.74 |
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term (Year) | | | | 2 years 1 month 13 days | |
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Intrinsic Value | $ 7,482,000 | | | $ 7,482,000 | |
Employee Stock Purchase Plan [Member] | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Market Price Percentage, Offering Date | | | | 85.00% | |
Stock Issued During Period, Shares, Employee Stock Purchase Plans (in shares) | | | | 7,678 | |
Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price (in dollars per share) | | | | $ 32.43 | |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares) | | 187,195 | | | |
Share-Based Payment Arrangement, Option [Member] | Minimum [Member] | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year) | | | | 3 years | |
Share-Based Payment Arrangement, Option [Member] | Maximum [Member] | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year) | | | | 5 years | |
Restricted Stock [Member] | | | | | |
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | | | | 29,512 | |
Restricted Stock [Member] | Stock Compensation Plan 2007 [Member] | Share-Based Payment Arrangement, Nonemployee [Member] | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year) | | | | 1 year | 1 year |
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | 2,758 | 318 | | 3,118 | 2,120 |
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period, Intrinsic Value, Amount Per Share (in dollars per share) | $ 63.35 | $ 62.77 | | $ 64.11 | $ 32.41 |
Restricted Stock [Member] | Stock Compensation Plan 2007 [Member] | Share-Based Payment Arrangement, Employee [Member] | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year) | | | | 3 years | 3 years |
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | | | | 23,318 | 37,687 |
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period, Intrinsic Value, Amount Per Share (in dollars per share) | | | | $ 66.48 | $ 23.74 |
Restricted Stock [Member] | Minimum [Member] | Stock Compensation Plan 2007 [Member] | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year) | | | | 1 year | |
Restricted Stock [Member] | Maximum [Member] | Stock Compensation Plan 2007 [Member] | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year) | | | | 10 years | |
Selling, General and Administrative Expenses [Member] | | | | | |
Share-Based Payment Arrangement, Expense | $ 538,000 | | 314,000 | $ 947,000 | $ 595,000 |
Cost of Sales [Member] | | | | | |
Share-Based Payment Arrangement, Expense | $ 32,000 | | $ 20,000 | $ 63,000 | $ 28,000 |