Note 3 - Earnings Per Common Share - Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended
		Dec. 31, 2022	Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021
Net Income		$ 91.0	$ 91.0	$ 55.7	$ 55.7
Provision for preferred dividends		3.7	3.7	3.7	3.7
Income allocated to participating securities		0.1	0.1	0.1	0.1
Income Available to Common Shareholders		$ 87.2	$ 87.2	$ 51.9	$ 51.9
Basic (in shares)		52.4	52.4	51.6	51.6
Basic Earnings Per Common Share (in dollars per share)		$ 1.66	$ 1.66	$ 1.01	$ 1.01
Dilutive Effect of Restricted Stock and Restricted Stock Units (in millions)* (in shares)	[1]	0.2		0.1
Weighted Average Diluted Common Shares (in millions) (in shares)		52.6	52.6	51.7	51.7
Diluted Earnings Per Common Share (in dollars per share)		$ 1,660,000	$ 1.66	$ 1,010,000.00	$ 1.01
* Calculation excludes certain outstanding common shares (shown in millions by period at the right) attributable to stock units subject to performance or market conditions and restricted stock, which could have a dilutive effect in the future (in shares)		0.2		0.2

[1] Calculation excludes certain outstanding common shares (shown in millions by period at the right) attributable to stock units subject to performance or market conditions and restricted stock, which could have a dilutive effect in the future