Borrowings - DB Credit Facility (Details) - USD ($) $ in Thousands	9 Months Ended
	Jun. 30, 2024	Sep. 30, 2023
Debt Instrument [Line Items]
Debt	$ 4,337,697	$ 3,133,332
DB Credit Facility
Debt Instrument [Line Items]
Debt	565,778
Revolving Credit Facility | DB Credit Facility | Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 625,000
Line of credit facility, commitment fee percentage	0.06944%
Line of credit facility, non-usage fee, percentage	0.25%
Line of credit facility, prepayment fee, first year after effective date, percentage	0.50%
Line of credit facility, prepayment fee, second year after effective date, percentage	0.25%
Debt	$ 565,778
Revolving Credit Facility | DB Credit Facility | Line of Credit | Base Rate
Debt Instrument [Line Items]
Line of credit facility, interest rate during period	2.30%
Line of credit facility, interest rate at period end	2.80%
Revolving Credit Facility | DB Credit Facility | Line of Credit | Canadian Overnight Repo Rate Average
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	0.32138%