Derivative Financial Instruments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Derivatives, Fair Value
Derivative, notional amount	$ 350.0		$ 350.0
Accumulated other comprehensive income (loss), cumulative changes in net gain (loss) from cash flow hedges, before tax	(10.0)		(10.0)
Accumulated other comprehensive income (loss), cumulative changes in net gain (loss) from cash flow hedges, net of tax	(9.3)		(9.3)
Unrealized net gain (loss) on derivatives to be reclassified during next 12 months, net	(2.3)		(2.3)
Derivative asset, fair value, gross liability	11.2		11.2
Net gain (loss) on derivatives, before tax	0.0	$ 0.0	(10.4)	$ 0.0
Gain (loss), net on derivatives	(2.1)		(1.9)
Fair Value Adjustment
Derivatives, Fair Value
Gain (loss), net on derivatives	(0.6)		(0.6)
Net Cash Settlements
Derivatives, Fair Value
Gain (loss), net on derivatives	(0.9)		(0.7)
Reclassified from AOCI
Derivatives, Fair Value
Gain (loss), net on derivatives	(0.6)		(0.6)
Other current liabilities
Derivatives, Fair Value
Derivative asset, fair value, gross liability	4.4		4.4
Other noncurrent liabilities
Derivatives, Fair Value
Derivative asset, fair value, gross liability	6.8		6.8
Other liabilities
Derivatives, Fair Value
Derivative asset, fair value, gross liability	$ 11.2		$ 11.2