INVESTMENT SECURITIES - Significant Assumptions in Valuation of Private Label MBS (Detail) - MBS [Member] - Private label [Member]	Dec. 31, 2020	Dec. 31, 2019
Discount rate [Member] | Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input	0.122	0.137
Discount rate [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input	0.122	0.137
Discount rate [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input	0.122	0.137
Prepayment rate [Member] | Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input	0.121	0.079
Prepayment rate [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input	0.012	0.068
Prepayment rate [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input	0.188	0.103
Projected Cumulative Loss Rate [Member] | Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input	0.102	0.028
Projected Cumulative Loss Rate [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input	0.026	0.000
Projected Cumulative Loss Rate [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Measurement Input	0.223	0.074