FAIR VALUE MEASUREMENTS - Summary of information about significant unobservable inputs (Level 3) used in the valuation of MSRs measured at fair value on a recurring basis (Level 3) (Details)	Sep. 30, 2020	Sep. 30, 2019
Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	9.25	9.25
Prepayment rate | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	2.99	4.42
Prepayment rate | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	86.98	72.79
Prepayment rate | Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	18.08	18.75