FAIR VALUE - Assets and Liabilities Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Level 3) (Detail) $ in Thousands	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale	$ 4,647,019	$ 2,123,525
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Private label [Member] | Valuation Technique, Discounted Cash Flow [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale	8,428	11,116
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Puerto Rico government obligations [Member] | Valuation Technique, Discounted Cash Flow [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale	$ 2,899	$ 2,974
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Minimum [Member] | Private label [Member] | Measurement Input, Discount Rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.122	0.137
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Minimum [Member] | Private label [Member] | Measurement Input, Constant Prepayment Rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.012	0.068
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Minimum [Member] | Private label [Member] | Measurement Input, Loss Severity [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.026	0.000
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Minimum [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	0.079	0.069
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Minimum [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		0.030
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Minimum [Member] | Puerto Rico government obligations [Member] | Measurement Input, Loss Severity [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.124
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Maximum [Member] | Private label [Member] | Measurement Input, Discount Rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.122	0.137
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Maximum [Member] | Private label [Member] | Measurement Input, Constant Prepayment Rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.188	0.103
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Maximum [Member] | Private label [Member] | Measurement Input, Loss Severity [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.223	0.074
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Maximum [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	0.079	0.069
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Maximum [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		0.030
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Maximum [Member] | Puerto Rico government obligations [Member] | Measurement Input, Loss Severity [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.124
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Weighted Average [Member] | Private label [Member] | Measurement Input, Discount Rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.122	0.137
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Weighted Average [Member] | Private label [Member] | Measurement Input, Constant Prepayment Rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.121	0.079
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Weighted Average [Member] | Private label [Member] | Measurement Input, Loss Severity [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.102	0.028
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Weighted Average [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	0.079	0.069
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Weighted Average [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		0.030
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Weighted Average [Member] | Puerto Rico government obligations [Member] | Measurement Input, Loss Severity [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.124