Investments in Unconsolidated Entities - Outstanding Borrowings of Unconsolidated Entities and Equity in Income (Loss) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Schedule of Equity Method Investments [Line Items]
Total equity of unconsolidated entities	$ 606,062	$ 593,171	$ 539,280	$ 538,754
Total outstanding borrowings of unconsolidated entities	1,131,725	1,130,801
Equity Method Investment, Nonconsolidated Investee or Group of Investees
Schedule of Equity Method Investments [Line Items]
Investment in unconsolidated entities	3,928	4,003
Total equity of unconsolidated entities	7,310	7,079
Total outstanding borrowings of unconsolidated entities	$ 10,843	$ 8,807