Note 3 - Cash, Cash Equivalents and Investments (Tables)  | 
6 Months Ended | ||||||||||||||||||||||||||||||||||||
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Mar. 31, 2020  | |||||||||||||||||||||||||||||||||||||
| Notes Tables | |||||||||||||||||||||||||||||||||||||
| Investments Classified by Contractual Maturity Date [Table Text Block] | 
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| X | ||||||||||
- Definition Tabular disclosure of maturities of an entity's investments as well as any other information pertinent to the investments. No definition available. 
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| X | ||||||||||
- References No definition available. 
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