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Derivative Financial Instruments and Fair Value Measurements - Cash Flow Hedges (Details) - USD ($) $ in Millions | Sep. 30, 2021 | Sep. 30, 2020
--- | --- | ---
Derivative financial instruments |  |
Fixed Rate (as a percent) | 1.349% |
Interest rate swap agreements |  |
Derivative financial instruments |  |
Notional Amount | $ 400.0 |
Designated as Hedging Instrument | Cash Flow Hedging | Interest rate swap agreements | USD | March 2018 |  |
Derivative financial instruments |  |
Notional Amount | $ 200.0 | $ 200.0
Fixed Rate (as a percent) | 2.60% | 2.60%
Designated as Hedging Instrument | Cash Flow Hedging | Interest rate swap agreements | USD | February 2023 |  |
Derivative financial instruments |  |
Notional Amount | $ 400.0 |
Fixed Rate (as a percent) | 1.349% |

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