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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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