Note 7 - Share-based Compensation (Details Textual) - USD ($) | Mar. 25, 2020 | Apr. 01, 2019 | Feb. 25, 2019 | Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019 |
Share-based Payment Arrangement, Expense | | | | $ 1,560,000 | $ 829,000 | $ 3,818,000 | $ 2,179,000 |
Share-based Payment Arrangement, Option [Member] | | | | | | | |
Share-based Payment Arrangement, Expense | | | | 15,000 | 65,000 | 104,000 | 305,000 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value | | | | 28,600,000 | | 28,600,000 | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value | | | | 28,100,000 | | 28,100,000 | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value | | | | 2,200,000 | 1,700,000 | $ 6,800,000 | $ 5,200,000 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares) | | | | | | 0 | 0 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term (Year) | | | | | | 3 years 9 months 18 days | |
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total | | | | 43,000 | | $ 43,000 | |
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year) | | | | | | 1 year | |
Performance Shares [Member] | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares) | | | | | | 0 | |
Performance Shares [Member] | Management Performance Bonus Plan 2017 [Member] | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value | | | | 19,700,000 | | $ 19,700,000 | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value | | | | $ 0 | $ 2,300,000 | $ 239,000 | $ 2,300,000 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares) | | | | 0 | 0 | 0 | 0 |
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year) | | | | | | 1 year 2 months 12 days | |
Restricted Stock [Member] | | | | | | | |
Share-based Payment Arrangement, Expense | | | | $ 754,000 | $ 303,000 | $ 1,600,000 | $ 826,000 |
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total | | | | 10,000,000 | | $ 10,000,000 | |
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year) | | | | | | 3 years 3 months 18 days | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Fair Value | | | | 4,200,000 | 802,000,000,000 | $ 7,400,000 | 4,000,000 |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value | | | | 1,600,000 | 368,000 | $ 2,900,000 | 1,600,000 |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | | | | | | 448,267 | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share) | | | | | | $ 15.78 | |
Restricted Stock [Member] | Executive Officer [Member] | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | 34,154 | | | | | 34,154 | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share) | $ 9.18 | | | | | $ 9.18 | |
Performance-based Restricted Stock [Member] | | | | | | | |
Share-based Payment Arrangement, Expense | | | | 191,000 | | $ 569,000 | |
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total | | | | 191,000 | | $ 191,000 | |
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year) | | | | | | 3 months 18 days | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | 82,805 | | | | | 82,805 | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share) | $ 9.18 | | | | | $ 9.18 | |
Performance-based Restricted Stock [Member] | Minimum [Member] | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Awards | 0.00% | | | | | | |
Performance-based Restricted Stock [Member] | Maximum [Member] | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Awards | 125.00% | | | | | | |
Market-based Restricted Stock [Member] | | | | | | | |
Share-based Payment Arrangement, Expense | | | | 600,000 | $ 461,000 | $ 1,500,000 | $ 1,000,000 |
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total | | | | $ 1,300,000 | | $ 1,300,000 | |
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year) | | | | | | 10 months 24 days | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | 109,140 | 29,604 | 94,247 | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Ending Balance | 78.00% | 69.00% | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate | 0.00% | 0.00% | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant | 0.30% | 2.50% | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year) | 2 years | 2 years | | | | | |
Market-based Restricted Stock [Member] | Minimum [Member] | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Awards | 0.00% | 0.00% | | | | | |
Market-based Restricted Stock [Member] | Maximum [Member] | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Awards | 200.00% | 200.00% | | | | | |