Investments in Unconsolidated Entities - Equity and Outstanding Borrowings of Unconsolidated Entities and Equity in Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Schedule of Equity Method Investments [Line Items]
Total equity of unconsolidated entities	$ 802,357	$ 633,767	$ 802,357	$ 633,767	$ 755,259	$ 724,884	$ 606,062	$ 593,171
Total outstanding borrowings of unconsolidated entities	1,049,895		1,049,895			1,054,030
Equity in income of unconsolidated entities	163	$ 186	451	$ 111
Equity Method Investment, Nonconsolidated Investee or Group of Investees
Schedule of Equity Method Investments [Line Items]
Investment in unconsolidated entities	4,667		4,667			4,464
Total equity of unconsolidated entities	7,491		7,491			7,316
Total outstanding borrowings of unconsolidated entities	$ 15,549		$ 15,549			$ 12,708