Earnings per Share - EPS Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Numerator:
Net income	$ 76.6	$ 41.7
Less: Allocation to participating securities	(2.4)	(1.2)
Net income allocated to common stockholders	$ 74.2	$ 40.5
Denominator:
Common shares outstanding (in shares)	19,771,816	19,383,303
Dilutive potential common shares outstanding:
Share-based awards (in shares)	728,036	475,409
Diluted weighted - average common shares (in shares)	20,499,852	19,858,712