Note 7 - Investments in Marketable Securities (Details Textual) - USD ($)	1 Months Ended		3 Months Ended		6 Months Ended
	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021	Sep. 30, 2021
Marketable Securities, Accumulated Unrealized Gain (Loss)	$ 199,684,000		$ 199,684,000		$ 199,684,000		$ 244,093,000
Marketable Securities, Unrealized Gain (Loss)			(8,321,000)	$ (5,144,000)	(44,409,000)	$ 76,068,000
Proceeds from Sale and Maturity of Debt Securities, Available-for-Sale, Total	80,570,000	$ 80,570,000			80,570,000	20,002,000
Marketable Securities, Realized Gain (Loss)	14,249,000	14,249,000	$ (32,445,000)	$ 18,478,000	14,249,000	18,478,000
Borrowed Funds from Margin Loan Account	43,000,000	43,000,000
Payments to Acquire Marketable Securities	$ 117,678,000	$ 117,678,000			$ 117,678,000	$ 39,995,000