FAIR VALUE - Fair Value Inputs and Valuation Techniques (Details)	Sep. 30, 2021 $ / loan	Dec. 31, 2020 $ / loan
Derivative | IRLCs | Minimum | Pull-through rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative, measurement input	0.030	0.028
Derivative | IRLCs | Maximum | Pull-through rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative, measurement input	0.999	0.999
Derivative | IRLCs | Weighted Average | Pull-through rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative, measurement input	0.761	0.705
Servicing rights | Minimum | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing right, measurement input	0.047	0.050
Servicing rights | Minimum | Prepayment rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing right, measurement input	0.086	0.134
Servicing rights | Minimum | Cost to service (per loan)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing right, measurement input	70	71
Servicing rights | Maximum | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing right, measurement input	0.091	0.100
Servicing rights | Maximum | Prepayment rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing right, measurement input	0.190	0.348
Servicing rights | Maximum | Cost to service (per loan)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing right, measurement input	126	139
Servicing rights | Weighted Average | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing right, measurement input	0.060	0.062
Servicing rights | Weighted Average | Prepayment rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing right, measurement input	0.101	0.140
Servicing rights | Weighted Average | Cost to service (per loan)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing right, measurement input	84	89