Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended						9 Months Ended
	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Jun. 30, 2024	Jun. 30, 2023
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 38.7	$ 45.0	$ 38.2	$ 46.8	$ 26.9	$ 20.8	$ 121.8	$ 94.5
Weighted average number of common shares	50,755,276			50,056,126			50,322,916	49,963,326
Dilutive effect of stock-based compensation	299,777			119,668			391,782	65,125
Adjusted weighted average number of common shares	51,055,053			50,175,794			50,714,698	50,028,451
Basic net income per common share	$ 0.76			$ 0.94			$ 2.42	$ 1.89
Diluted net income per common share	$ 0.76			$ 0.93			$ 2.40	$ 1.89
Retained Earnings
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 38.7	$ 45.0	$ 38.2	$ 46.8	$ 26.9	$ 20.8