Borrowings - Schedule of Unsecured Notes (Details) - USD ($) $ in Thousands	Jun. 30, 2026	Sep. 30, 2025	Jun. 30, 2025
Debt Instrument [Line Items]
Unamortized Financing Costs	$ (9,141)	$ (11,306)
Carrying Value	2,624,800		$ 2,409,400
Unsecured Notes
Debt Instrument [Line Items]
Outstanding Principal	1,150,000	1,150,000
Unamortized Financing Costs	(9,100)	(11,300)
Unaccreted Discount	(2,400)	(3,000)
Swap Fair Value Adjustment	(4,000)	19,500
Carrying Value	1,134,500	1,155,200
Fair Value	1,168,700	1,204,100
2028 Notes | Unsecured Notes
Debt Instrument [Line Items]
Outstanding Principal	350,000	350,000
Unamortized Financing Costs	(2,100)	(2,800)
Unaccreted Discount	(800)	(1,100)
Swap Fair Value Adjustment	1,900	9,000
Carrying Value	349,000	355,100
Fair Value	366,100	380,100
2029 Notes | Unsecured Notes
Debt Instrument [Line Items]
Outstanding Principal	400,000	400,000
Unamortized Financing Costs	(3,100)	(3,800)
Unaccreted Discount	(1,500)	(1,800)
Swap Fair Value Adjustment	(1,500)	6,500
Carrying Value	393,900	400,900
Fair Value	403,200	415,100
2030 Notes | Unsecured Notes
Debt Instrument [Line Items]
Outstanding Principal	400,000	400,000
Unamortized Financing Costs	(3,900)	(4,700)
Unaccreted Discount	(100)	(100)
Swap Fair Value Adjustment	(4,400)	4,000
Carrying Value	391,600	399,200
Fair Value	$ 399,400	$ 408,900