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Borrowing Arrangements (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Sep. 30, 2020	Sep. 30, 2019
Outstanding letter of credit accrued fees and expenses	$ 1.7		$ 1.7
Cash and cash equivalents	228.6	$ 170.7	228.6	$ 170.7	$ 208.9	$ 176.7
Future maturities of outstanding borrowings
Outstanding letters of credit	15.0		15.0
Gain (Loss) on Extinguishment of Debt	16.7	$ 0.0	16.7	$ 0.0
Payment for Debt Extinguishment or Debt Prepayment Cost	12.4
Write off of Deferred Debt Issuance Cost	4.3
Domestic Line of Credit [Member]
Revolving credit facility amount	$ (175.0)		$ (175.0)
Line of Credit Facility, Interest Rate at Period End	200.00%		200.00%
Excess availability reduced by outstanding borrowings, outstanding letters of credit and accrued fees and expenses	$ 145.1		$ 145.1
Future maturities of outstanding borrowings
Line of Credit Facility, Maximum Borrowing Capacity	175.0		175.0
Potential increase size of the credit facility by an additional amount			150.0
Aggregate commitments availability			$ 17.5
Aggregate commitments availability, percentage			10.00%
Line of Credit Facility, Remaining Borrowing Capacity	145.1		$ 145.1
Swing Line Loans [Member]
Revolving credit facility amount	(25.0)		(25.0)
Future maturities of outstanding borrowings
Line of Credit Facility, Maximum Borrowing Capacity	25.0		25.0
Letters Of Credit Outstanding [Member]
Revolving credit facility amount	(60.0)		(60.0)
Future maturities of outstanding borrowings
Line of Credit Facility, Maximum Borrowing Capacity	$ 60.0		$ 60.0
4.0% Senior Notes [Member]
Debt Instrument, Interest Rate, Effective Percentage	4.00%		4.00%
Future maturities of outstanding borrowings
Payments of debt issuance costs	$ 5.5
Financial Liabilities Fair Value Disclosure	$ 461.3		$ 461.3
5.5% Notes
Debt Instrument, Interest Rate, Effective Percentage	5.50%		5.50%
Minimum [Member] | Domestic Line of Credit [Member]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage			37.50%
London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member] | Long-term Debt [Member]
Debt Instrument, Basis Spread on Variable Rate			100.00%
London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member] | Domestic Line of Credit [Member]
Debt Instrument, Basis Spread on Variable Rate			200.00%
London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member] | Long-term Debt [Member]
Debt Instrument, Basis Spread on Variable Rate			125.00%
London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member] | Domestic Line of Credit [Member]
Debt Instrument, Basis Spread on Variable Rate			225.00%

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