FAIR VALUE - Assets and Liabilities Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Level 3) (Detail) $ in Thousands	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale	$ 1,942,568	$ 1,891,016
Minimum [Member] | Private label MBS [Member] | Measurement Input, Discount Rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.1449	0.14
Minimum [Member] | Private label MBS [Member] | Measurement Input, Loss Severity [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0	0
Maximum [Member] | Private label MBS [Member] | Measurement Input, Discount Rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.1449	0.14
Maximum [Member] | Private label MBS [Member] | Measurement Input, Loss Severity [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.068	0.068
Weighted Average [Member] | Private label MBS [Member] | Measurement Input, Discount Rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.145	0.14
Weighted Average [Member] | Private label MBS [Member] | Measurement Input, Loss Severity [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.03	0.03
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Private label MBS [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale	$ 13,914	$ 17,060
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Private label MBS [Member] | Measurement Input, Discount Rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.145	0.14
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Puerto Rico-government obligations [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale	$ 2,824	$ 2,695
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Puerto Rico-government obligations [Member] | Measurement Input, Discount Rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.0628	0.0661
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Puerto Rico-government obligations [Member] | Measurement Input, Constant Prepayment Rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.03	0.03
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Minimum [Member] | Private label MBS [Member] | Measurement Input, Constant Prepayment Rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.033	0.12
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Minimum [Member] | Private label MBS [Member] | Measurement Input, Loss Severity [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Maximum [Member] | Private label MBS [Member] | Measurement Input, Constant Prepayment Rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.209	0.29
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Maximum [Member] | Private label MBS [Member] | Measurement Input, Loss Severity [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.068	0.068
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Weighted Average [Member] | Private label MBS [Member] | Measurement Input, Constant Prepayment Rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.114	0.164
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Weighted Average [Member] | Private label MBS [Member] | Measurement Input, Loss Severity [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.03	0.03