Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net (loss) income	$ (41.6)	$ 44.4	$ (15.1)
Net derivative (losses) gains arising during the period, net of tax of $3.6, $2.4, and $(3.1), respectively	(9.4)	(6.4)	6.8
Reclassification of losses into net (loss) income, net of tax of $5.1, $2.0, and $3.0, respectively	14.2	5.1	6.8
Other comprehensive income (loss)	4.8	(1.3)	13.6
Comprehensive (loss) income	$ (36.8)	$ 43.1	$ (1.5)