Consolidated Statements of Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net (loss)	$ (20.5)	$ (3.6)	$ (33.1)	$ (12.4)
Net derivative (losses) arising during the period, net of tax benefit of $3.7, $0.3, $3.7, and $1.4, respectively	(9.9)	(0.8)	(9.7)	(3.8)
Reclassification of losses into net (loss), net of tax expense of $1.0, $0.7, $1.8, and $1.0, respectively	2.9	1.9	4.8	2.4
Other comprehensive (loss) income	(7.0)	1.1	(4.9)	(1.4)
Comprehensive (loss)	$ (27.5)	$ (2.5)	$ (38.0)	$ (13.8)