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INVESTMENT SECURITIES - Significant Assumptions in Valuation of Private Label MBS (Detail) - Private label MBS [Member]
Jun. 30, 2019
Dec. 31, 2018
Discount rate [Member] | Weighted Average [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Debt Securities, Available-for-sale, Measurement Input 0.138 0.145
Discount rate [Member] | Minimum [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Debt Securities, Available-for-sale, Measurement Input 0.138 0.145
Discount rate [Member] | Maximum [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Debt Securities, Available-for-sale, Measurement Input 0.138 0.145
Prepayment rate [Member] | Weighted Average [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Debt Securities, Available-for-sale, Measurement Input 0.091 0.114
Prepayment rate [Member] | Minimum [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Debt Securities, Available-for-sale, Measurement Input 0.033 0.033
Prepayment rate [Member] | Maximum [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Debt Securities, Available-for-sale, Measurement Input 0.170 0.209
Projected Cumulative Loss Rate [Member] | Weighted Average [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Debt Securities, Available-for-sale, Measurement Input 0.031 0.03
Projected Cumulative Loss Rate [Member] | Minimum [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Debt Securities, Available-for-sale, Measurement Input 0.000 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 0.066 0.068