Note 3 - Earnings Per Common Share - Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended		9 Months Ended
		Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Net income		$ (12.6)	$ (21.6)	$ 276.8	$ 248.6
Provision for preferred dividends		3.7	3.7	11.1	11.1
(Loss) income allocated to participating securities		0.0	(0.1)	0.4	0.4
(Loss) Income Available to Common Shareholders		$ (16.3)	$ (25.2)	$ 265.3	$ 237.1
Basic (in shares)		57.7	52.5	55.6	52.5
Basic (Loss) Earnings Per Common Share (in dollars per share)		$ (0.28)	$ (0.48)	$ 4.77	$ 4.52
Dilutive Effect of forward sales of common stock, restricted stock and restricted stock units (in millions)* (in shares)	[1]	0.0	0.0	0.1	0.1
Weighted Average Diluted Common Shares (in millions) (in shares)		57.7	52.5	55.7	52.6
Diluted (Loss) Earnings Per Common Share (in dollars per share)		$ (0.28)	$ (0.48)	$ 4.76	$ 4.51
* Calculation excludes certain outstanding or potential common shares (shown in millions by period at the right) attributable to (1) forward sales of common stock, (2) stock units subject to performance or market conditions and (3) restricted stock, which could have a dilutive effect in the future (in shares)		0.4	2.7	0.4	2.5

[1] Calculation excludes certain outstanding or potential common shares (shown in millions by period at the right) attributable to (1) forward sales of common stock, (2) stock units subject to performance or market conditions, and (3) restricted stock, which could have a dilutive effect in the future