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Borrowing Arrangements (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Jun. 30, 2022	Jun. 30, 2021	Jun. 12, 2018
Outstanding letter of credit accrued fees and expenses		$ 0.2
Cash and cash equivalents	$ 208.9		$ 228.6
Future maturities of outstanding borrowings
Outstanding letters of credit		14.1
Domestic Line of Credit [Member]
Revolving credit facility amount		$ (175.0)
Line of Credit Facility, Interest Rate at Period End		200.00%
Future maturities of outstanding borrowings
Line of Credit Facility, Maximum Borrowing Capacity		$ 175.0
Potential increase size of the credit facility by an additional amount		150.0
Unsecured Debt [Member]
Long-term Debt, Gross				$ 450.0
Future maturities of outstanding borrowings
Payments of debt issuance costs	$ 5.5
Swing Line Loans [Member]
Revolving credit facility amount		(25.0)
Future maturities of outstanding borrowings
Line of Credit Facility, Maximum Borrowing Capacity		25.0
Letters Of Credit Outstanding [Member]
Revolving credit facility amount		(60.0)
Future maturities of outstanding borrowings
Line of Credit Facility, Maximum Borrowing Capacity		$ 60.0
5.5% Senior Notes
Debt Instrument, Interest Rate, Effective Percentage		4.00%
Future maturities of outstanding borrowings
Financial Liabilities Fair Value Disclosure		$ 392.8
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] \| Domestic Line of Credit [Member]
Debt Instrument, Basis Spread on Variable Rate		225.00%
Base Rate [Member] \| Maximum [Member] \| Domestic Line of Credit [Member]
Debt Instrument, Basis Spread on Variable Rate		125.00%