Note 7 - Investments in Marketable Securities (Details Textual) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended
	Jan. 31, 2021	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Sep. 30, 2019
Marketable Securities, Accumulated Unrealized Gain (Loss)		$ 269,347,000		$ 269,347,000		$ 137,593,000
Marketable Securities, Unrealized Gain (Loss), Total		$ 55,686,000	$ 16,489,000	131,754,000	$ (41,191,000)
Proceeds from Sale and Maturity of Debt Securities, Available-for-sale, Total	$ 20,002,000			20,002,000	0
Marketable Securities, Realized Gain (Loss), Total	18,478,000			18,478,000	0
Payments to Acquire Marketable Securities, Total	$ 39,995,000			39,995,000	$ (0)
Newly Purchased Marketable Securities [Member]
Marketable Securities, Unrealized Gain (Loss), Total				$ (2,504,000)