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Borrowing Arrangements (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Mar. 31, 2021	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 12, 2018
Outstanding letter of credit accrued fees and expenses		$ 1.6
Cash and cash equivalents		228.2	$ 208.9	$ 111.3	$ 176.7
Future maturities of outstanding borrowings
Outstanding letters of credit		13.8
Domestic Line of Credit [Member]
Revolving credit facility amount		$ (175.0)
Line of Credit Facility, Interest Rate at Period End		200.00%
Excess availability reduced by outstanding borrowings, outstanding letters of credit and accrued fees and expenses		$ 154.4
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
Aggregate commitments availability		$ 17.5
Aggregate commitments availability, percentage		10.00%
Line of Credit Facility, Remaining Borrowing Capacity		$ 154.4
Unsecured Debt [Member]
Long-term Debt, Gross						$ 450.0
Future maturities of outstanding borrowings
Payments of debt issuance costs	$ 6.6
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		5.50%
Future maturities of outstanding borrowings
Financial Liabilities Fair Value Disclosure		$ 465.8
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%

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