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Note 2 - Summary of Significant Accounting Policies (Tables) | 12 Months Ended
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Sep. 30, 2020
Notes Tables |
Schedule of Available-for-sale Securities Reconciliation [Table Text Block] |
|  | September 30, 2020 |  |  | September 30, 2019 |
|  | Aggregate fair value |  |  | Amortized/ Adjusted cost basis |  |  | Pretax unrealized gains |  |  | Aggregate fair value |  |  | Amortized/ Adjusted cost basis |  |  | Pretax unrealized gains |
Marketable securities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stocks |  | $ | 179,368,000 |  |  | $ | 41,775,000 |  |  | $ | 137,593,000 |  |  | $ | 194,581,000 |  |  | $ | 53,889,000 |  |  | $ | 140,692,000 |
Valuation and Qualifying Accounts [Table Text Block] |
Description |  | Balance at Beginning of Year |  |  | Additions Charged to Costs and Expenses |  |  | Accounts Charged off less Recoveries |  |  | Balance at End of Year |
Fiscal 2020 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Allowance for doubtful accounts |  | $ | 200,000 |  |  | $ | 116,000 |  |  | $ | (66,000 | ) |  | $ | 250,000 |
Fiscal 2019 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Allowance for doubtful accounts |  | $ | 200,000 |  |  | $ | 8,000 |  |  | $ | (8,000 | ) |  | $ | 200,000 |

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