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Debt - 2024 Senior Notes (Details) - USD ($) |  | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | ---
Jun. 25, 2021 | Sep. 30, 2021 | Jun. 30, 2021 | Mar. 31, 2021 | Dec. 31, 2020 | Sep. 30, 2020 | Jun. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2019 | Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2019 | Apr. 13, 2021 | Oct. 06, 2014
Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest expense |  | $ (25,900,000) | $ (149,000,000.0) | $ (32,800,000) | $ (30,700,000) | $ (47,500,000) | $ (35,000,000.0) | $ (37,100,000) | $ (40,400,000) | $ (238,352,000) | $ (159,914,000) | $ (161,482,000) |  |
2014 Senior Notes | The 2024 Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest expense | $ 217,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |
2024 Senior Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash tender |  |  |  |  |  |  |  |  |  |  |  |  | $ 700,000,000 |
Interest rate (as a percent) | 5.875% |  |  |  |  |  |  |  |  |  |  |  | 5.875% |
2024 Senior Notes | The 2024 Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 800,000,000
Interest rate (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  | 5.875%
Fair value of debt instrument |  |  | $ 117,500,000 |  |  |  |  |  |  |  |  |  |  |
Redemption price (in percent) | 115.108% |  |  |  |  |  |  |  |  |  |  |  |  |

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