FAIR VALUE MEASUREMENTS - Summary of Aggregate Fair Value and the Aggregate Remaining Principal Balance for Residential Mortgage Loans Held for Sale (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Residential mortgage loans held for sale Aggregate Fair Value	$ 208,493	$ 80,457
Residential mortgage loans held for sale Aggregate Principal Balance	198,138	77,787
Residential mortgage loans held for sale Difference	10,355	2,670
Mortgage Banking [Member]
Residential mortgage loans held for sale Difference	$ 7,504	$ 2,492	$ 257