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Borrowing Arrangements (Narrative) (Details) - USD ($) | 3 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2021 | Mar. 31, 2020 | Dec. 31, 2020 | Sep. 30, 2020 | Jun. 12, 2018
Outstanding letter of credit accrued fees and expenses | $ 1,400,000 |  |  |  |
Excess availability reduced by outstanding borrowings, outstanding letters of credit and accrued fees and expenses | 133.8 |  |  |  |
Cash and cash equivalents |  |  | $ 223,000,000.0 | $ 208,900,000 |
Future maturities of outstanding borrowings |  |  |  |  |
Line of Credit Facility, Remaining Borrowing Capacity | 133.8 |  |  |  |
Outstanding letters of credit | 15,000,000.0 |  |  |  |
Domestic Line of Credit [Member] |  |  |  |  |
Revolving credit facility amount | $ (175,000,000.0) |  |  |  |
Line of Credit Facility, Interest Rate at Period End | 200.00% |  |  |  |
Future maturities of outstanding borrowings |  |  |  |  |
Line of Credit Facility, Maximum Borrowing Capacity | $ 175,000,000.0 |  |  |  |
Potential increase size of the credit facility by an additional amount | 150,000,000.0 |  |  |  |
Unsecured Debt [Member] |  |  |  |  |
Long-term Debt, Gross |  |  |  |  | $ 450,000,000
Future maturities of outstanding borrowings |  |  |  |  |
Payments of debt issuance costs |  | $ 5,500,000 |  |  |
Swing Line Loans [Member] |  |  |  |  |
Revolving credit facility amount | (25,000,000.0) |  |  |  |
Future maturities of outstanding borrowings |  |  |  |  |
Line of Credit Facility, Maximum Borrowing Capacity | 25,000,000.0 |  |  |  |
Letters Of Credit Outstanding [Member] |  |  |  |  |
Revolving credit facility amount | (60,000,000.0) |  |  |  |
Future maturities of outstanding borrowings |  |  |  |  |
Line of Credit Facility, Maximum Borrowing Capacity | $ 60,000,000.0 |  |  |  |
5.5% Senior Notes |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 4.00% |  |  |  |
Future maturities of outstanding borrowings |  |  |  |  |
Financial Liabilities Fair Value Disclosure | $ 456,900,000 |  |  |  |
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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