Earnings per Share - EPS Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Numerator:
Net income	$ 19.5	$ 16.3
Less: Allocation to participating securities	(0.5)	(0.3)
Net income allocated to common stockholders	$ 19.0	$ 16.0
Denominator:
Common shares outstanding (in shares)	18,940,876	18,750,270
Dilutive potential common shares outstanding:
Share-based awards (in shares)	529,977	324,292
Diluted weighted - average common shares (in shares)	19,470,853	19,074,562