| Note 3 - Cash, Cash Equivalents and Investments (Details Textual) | 3 Months Ended | 
|---|---|
| Dec. 31, 2018 | |
| Maximum [Member] | |
| Held-to-maturity Securities, Investment Term | 5 years | 
| X | ||||||||||
| 
- Definition Represents information about the Company's investment term in money market accounts and bank certificates of deposit. No definition available. 
 | 
| X | ||||||||||
| 
- Details 
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