Supplemental Cash Flow Information - Supplemental Disclosure of Non-cash Activity (Details) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Sep. 30, 2023	Sep. 30, 2022
Supplemental disclosure of non-cash activity:
Increase in operating lease right-of-use assets	$ 0	$ 7,034
Increase in operating lease liabilities	0	7,482
Supplemental disclosure of cash activity:
Interest payments	34,555	33,406
Income tax payments	7,010	378
Tax refunds received	0	9,667
Reconciliation of cash, cash equivalents, and restricted cash:
Cash and cash equivalents	132,867	240,829	$ 345,590
Restricted cash	32,527	38,321	40,699
Total cash, cash equivalents, and restricted cash shown in the statement of cash flows	$ 165,394	$ 279,150	$ 386,289	$ 251,828