Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ 68.0	$ (220.5)
Other comprehensive income (loss):
Foreign currency translation adjustment	0.4	3.9
Unrealized gain (loss) due to change in fair value of derivatives, net of tax	3.6	1.6
Total other comprehensive income (loss)	4.0	5.5
Comprehensive income (loss)	$ 72.0	$ (215.0)