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Fair Value Measurements and Derivative Instruments - Additional Information (Details) | 9 Months Ended |
--- | --- | ---
Jun. 30, 2021 USD ($) Fuel gal | Sep. 30, 2020 USD ($)
Interest Rate Contracts |  |
Derivative [Line Items] |  |
Notional amount | $ 500,000,000.0 | $ 980,000,000.0
Interest Rate Swaps |  |
Derivative [Line Items] |  |
Net deferred losses on interest rate swap net of taxes expected to be recognized over the next 12 months | $ 2,200,000 |
Fuel Swap Contracts |  |
Derivative [Line Items] |  |
Number of outstanding fuel contracts | Fuel | 2 |
Notional volume | gal | 5.3 |
Net deferred gain on fuel swap net of taxes expected to be recognized over the next 12 months | $ 1,800,000 |
Maximum |  |
Derivative [Line Items] |  |
Percentage of participants compensation deferred | 70.00% |

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