Note 2 - Summary of Significant Accounting Policies - Investment in Financial Instruments (Details) - USD ($)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Marketable securities, fair value	$ 179,368,000	$ 194,581,000
Marketable securities, gross unrealized gains	137,593,000	140,692,000
Common Stock [Member]
Marketable securities, fair value	179,368,000	194,581,000
Marketable securities, amortized cost	41,775,000	53,889,000
Marketable securities, gross unrealized gains	$ 137,593,000	$ 140,692,000