Note 8 - Income Taxes (Details Textual) - USD ($)	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Income Tax Expense (Benefit), Total	$ 2,735,000	$ (20,860,000)	$ 24,915,000	$ (15,580,000)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest, Total			$ 96,661,000	$ (57,696,000)
Effective Income Tax Rate Reconciliation before Realized and Unrealized Gains of Marketable Securities, Percent			19.28%
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			21.00%
Effective Income Tax Rate Reconciliation, Deduction, Dividends, Amount			$ 408,000
Effective Income Tax Rate Reconciliation, Unrealized Gains on Marketable Securities, Amount			19,680,000
Effective Income Tax Rate Reconciliation, Realized Gains on Marketable Securities, Amount			4,804,000
Effective Income Tax Rate Reconciliation, Tax Contingency, State and Local, Amount			$ 23,000
Effective Income Tax Rate Reconciliation, Percent, Total			25.80%	27.00%
Income Tax Expense (Benefit) from CARES Act				$ (187,000)
Income Tax Expense (Benefit) from Unrealized Losses on Investments				$ (15,425,000)
Domestic Tax Authority [Member]
Open Tax Year			2017 2018 2019 2020 2021
State and Local Jurisdiction [Member]
Open Tax Year			2016 2017 2018 2019 2020 2021