Consolidated Statements of Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net (loss)	$ (12.0)	$ (12.6)
Net derivative gains arising during the period, net of tax benefit of $— and $(0.1), respectively		0.2
Reclassification of losses into net (loss), net of tax expense of $1.4 and $0.7, respectively	3.6	1.9
Other comprehensive income	3.6	2.1
Comprehensive (loss)	$ (8.4)	$ (10.5)