FAIR VLUE - Assets and Liabilites Measured at Fair Value on Recurring Basis Using Unobservable Inputs (Level 3) (Detail) $ in Thousands	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale	$ 3,294,649	$ 2,123,525
Puerto Rico Government obligations [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale	6,900
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	8,839	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	$ 2,907	$ 2,974
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Minimum [Member] | Private label [Member] | Discount rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.124	0.137
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Minimum [Member] | Private label [Member] | Prepayment rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.026	0.068
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Minimum [Member] | Private label [Member] | Projected Cumulative Loss Rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.024	0.000
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Minimum [Member] | Puerto Rico Government obligations [Member] | Discount rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.085	0.069
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Minimum [Member] | Puerto Rico Government obligations [Member] | 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] | Projected Cumulative Loss Rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.134
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Maximum [Member] | Private label [Member] | Discount rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.124	0.137
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Maximum [Member] | Private label [Member] | Prepayment rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.137	0.103
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Maximum [Member] | Private label [Member] | Projected Cumulative Loss Rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.263	0.074
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Maximum [Member] | Puerto Rico Government obligations [Member] | Discount rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.085	0.069
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Maximum [Member] | Puerto Rico Government obligations [Member] | 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] | Projected Cumulative Loss Rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.134
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Weighted Average [Member] | Private label [Member] | Discount rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.124	0.137
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Weighted Average [Member] | Private label [Member] | Prepayment rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.109	0.079
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Weighted Average [Member] | Private label [Member] | Projected Cumulative Loss Rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.118	0.028
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Weighted Average [Member] | Puerto Rico Government obligations [Member] | Discount rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.085	0.069
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Weighted Average [Member] | Puerto Rico Government obligations [Member] | 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] | Projected Cumulative Loss Rate [Member]
Debt Securities, Available-for-sale, Sale [Abstract]
Debt Securities, Available-for-sale, Measurement Input	0.134