Note 7 - Investments in Marketable Securities (Details Textual) - USD ($)		1 Months Ended	3 Months Ended
	Dec. 31, 2021	Dec. 31, 2021	Dec. 31, 2021	Dec. 31, 2020	Sep. 30, 2021
Marketable Securities, Accumulated Unrealized Gain (Loss)	$ 208,005,000	$ 208,005,000	$ 208,005,000		$ 244,093,000
Marketable Securities, Unrealized Gain (Loss), Total			36,088,000	$ (81,212,000)
Marketable Securities, Unrealized Gain (Loss), Total			(36,088,000)	81,212,000
Proceeds from Sale and Maturity of Debt Securities, Available-for-sale, Total		50,020,000	50,020,000
Marketable Securities, Realized Gain (Loss), Total		46,694,000	46,694,000	0
Borrowed Funds from Margin Loan Account		37,014,000
Payments to Acquire Marketable Securities, Total		$ 87,125,000	$ 87,125,000
Newly Purchased Marketable Securities [Member]
Marketable Securities, Unrealized Gain (Loss), Total	29,921,000
Marketable Securities, Unrealized Gain (Loss), Total	$ (29,921,000)