Earnings per Share - EPS Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Numerator:
Net income	$ 41.7	$ 19.5
Less: Allocation to participating securities	(1.2)	(0.5)
Net income allocated to common stockholders	$ 40.5	$ 19.0
Denominator:
Common shares outstanding (in shares)	19,383,303	18,940,876
Dilutive potential common shares outstanding:
Share-based awards (in shares)	475,409	529,977
Diluted weighted - average common shares (in shares)	19,858,712	19,470,853