Senior Notes - Principal Amounts Carrying Amounts and Fair Values (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Sep. 30, 2021
Debt Instrument [Line Items]
Carrying amounts	$ 1,300,000	$ 750,000
Fair value	1,148,750	810,000
Debt issuance costs	14,300	9,000
May 2018 Senior Notes
Debt Instrument [Line Items]
Carrying amounts	400,000	400,000
Fair value	381,500	453,000
December 2019 Senior Notes
Debt Instrument [Line Items]
Carrying amounts	900,000	350,000
Fair value	$ 767,250	$ 357,000

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

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