Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ 46.3	$ (41.6)	$ 44.4
Net derivative (losses) gains arising during the period, net of tax of $(0.8), $3.6, and $2.4, respectively	2.1	(9.4)	(6.4)
Reclassification of losses into net (loss) income, net of tax of $(1.2), $5.1, and $2.0, respectively	3.3	14.2	5.1
Other comprehensive income (loss)	5.4	4.8	(1.3)
Comprehensive income (loss)	$ 51.7	$ (36.8)	$ 43.1