INVESTMENT SECURITIES - Additional Information (Detail) - USD ($)			12 Months Ended
	Sep. 01, 2020	Jan. 01, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Investments [Line Items]
Proceeds from sales of available-for-sale securities			$ 1,195,250,000	$ 0	$ 47,805,000
Available-for-sale realized gains			13,300,000
Available-for-sale gross realized losses			100,000
Available-for-sale net gain			13,200,000
Fair value			4,647,019,000	2,123,525,000
Gross unrealized loss			5,517,000	10,056,000
Available-for-sale, allowance for credit losses			1,310,000	0
Provision For Other Credit Losses Previous Expected Credit Losses			1,333,000
Charge-offs			331,000
Provision For Other Credit Losses No Previous Expected Credit Losses			308,000
Allowance for credit losses, Held-to-Maturity securities			8,845,000	0
Initial allowance on PCD debt securities	$ 1,269,000
Purchase price of debt securities at acquisition (initial fair value)	55,532,000
Debt Securities, Held-to-maturity, Past Due			$ 0
Debt Securities, Held-to-maturity, Threshold Period Past Due			30 years
ASC 326 [Member]
Schedule Of Investments [Line Items]
Allowance for credit losses, Held-to-Maturity securities		$ 8,134,000
ASC 326 [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member]
Schedule Of Investments [Line Items]
Allowance for credit losses, Held-to-Maturity securities		8,134,000
Municipal Bonds [Member] | Puerto Rico [Member]
Schedule Of Investments [Line Items]
Allowance for credit losses, Held-to-Maturity securities			$ 8,845,000	0
Initial allowance on PCD debt securities	$ 1,300,000	1,269,000
Municipal Bonds [Member] | Puerto Rico [Member] | ASC 326 [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member]
Schedule Of Investments [Line Items]
Impact of adopting ASC 326 on Held-to-maturity securities		$ 8,134,000
Puerto Rico government obligations [Member]
Schedule Of Investments [Line Items]
Available-for-sale, allowance for credit losses			308,000	0
Provision For Other Credit Losses Previous Expected Credit Losses			0
Charge-offs			0
Provision For Other Credit Losses No Previous Expected Credit Losses			308,000
Puerto Rico government obligations [Member] | Residential Mortgage Backed Securities [Member]
Schedule Of Investments [Line Items]
Fair value			2,900,000
Gross unrealized loss			1,100,000
Provision For Other Credit Losses No Previous Expected Credit Losses			300,000
MBS [Member]
Schedule Of Investments [Line Items]
Loss on Sale of Investments					59,000
Fair value			3,455,796,000	1,783,504,000
Gross unrealized loss			3,951,000	8,440,000
Available-for-sale, allowance for credit losses			1,002,000
MBS [Member] | Private label [Member]
Schedule Of Investments [Line Items]
Fair value			8,400,000
Gross unrealized loss			3,900,000
Available-for-sale, allowance for credit losses			1,002,000	$ 0
Provision For Other Credit Losses Previous Expected Credit Losses			1,333,000
Charge-offs			331,000
Provision For Other Credit Losses No Previous Expected Credit Losses			$ 0
US Government-sponsored Enterprises Debt Securities [Member] | Call Option [Member]
Schedule Of Investments [Line Items]
Gain on Sale of Investments					$ 22,000
Available-for-sale Securities [Member]
Schedule Of Investments [Line Items]
Percentage Of Debt Securities Government And Government Sponsored Agencies			99.00%
Available-for-sale Securities [Member] | MBS [Member] | Private label [Member] | FICO Score, Greater than 700 [Member] | LTV Less than 80 Percent [Member]
Schedule Of Investments [Line Items]
Financing Receivable, Credit Quality, Additional Information			The underlying collateral are fixed-rate, single-family residential mortgage loans in the United States with original FICO scores over 700 and moderate loan-to-value ratios (under 80%), as well as moderate delinquency levels.
Available-for-sale Securities [Member] | MBS [Member] | Private label [Member] | London Interbank Offered Rate (LIBOR) [Member]
Schedule Of Investments [Line Items]
Loans Receivable, Description of Variable Rate Basis			The interest rate on these private-label MBS is variable, tied to 3-month LIBOR and limited to the weighted-average coupon on the underlying collateral.
Held-to-maturity Securities [Member] | Municipal Bonds [Member] | Puerto Rico [Member]
Schedule Of Investments [Line Items]
Provision for credit loss expense			$ (558,000)