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Note 2 - Summary of Significant Accounting Policies - Investment in Financial Instruments (Details) - USD ($)
12 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Marketable securities, fair value $ 347,573,000 $ 179,368,000
Marketable securities, gross unrealized gains 244,093,000 137,593,000
Common Stock [Member]    
Marketable securities, fair value 347,573,000 179,368,000
Marketable securities, amortized cost 103,480,000 41,775,000
Marketable securities, gross unrealized gains $ 244,093,000 $ 137,593,000