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Note 2 - Summary of Significant Accounting Policies - Investment in Financial Instruments (Details) - USD ($)
12 Months Ended
Sep. 30, 2023
Sep. 30, 2022
Marketable securities, fair value $ 303,128,000 $ 275,529,000
Marketable securities, gross unrealized gains 137,716,000 120,692,000
Common Stock [Member]    
Marketable securities, fair value 303,128,000 275,529,000
Marketable securities, amortized cost 165,412,000 154,837,000
Marketable securities, gross unrealized gains $ 137,716,000 $ 120,692,000