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DEBT SECURITIES - Additional Information (Detail) - USD ($)
 3 Months Ended 12 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Dec. 31, 2023
Dec. 31, 2022
Schedule Of Investments [Line Items]        
Fair value $ 5,047,179,000   $ 5,229,984,000  
Gross Unrealized Losses 648,137,000   633,049,000  
Available-for-sale, allowance for credit losses 442,000 $ 449,000 511,000 $ 458,000
Provision For Other Credit Losses Previous Expected Credit Losses 69,000 9,000    
Allowance for credit losses, Held-to-Maturity securities 1,235,000   2,197,000  
Provision for credit loss expense (1,031,000) (649,000)    
Debt Securities, Held-to-maturity 349,330,000   354,178,000  
Accrued interest receivable 73,154,000   77,716,000  
Held to maturity securities classified as cash and cash equivalents 0   0  
Past Due [Member]        
Schedule Of Investments [Line Items]        
Debt Securities, Held-to-maturity $ 0   0  
FICO Score, Greater than 700 [Member] | LTV Less than 80 Percent [Member] | Private label [Member]        
Schedule Of Investments [Line Items]        
Loan To Value Coverage Percentage 80.00%      
Puerto Rico government obligations [Member]        
Schedule Of Investments [Line Items]        
Available-for-sale, allowance for credit losses $ 326,000 366,000 395,000 375,000
Provision For Other Credit Losses Previous Expected Credit Losses 69,000 9,000    
Residential MBS [Member]        
Schedule Of Investments [Line Items]        
Fair value 2,527,054,000   2,633,161,000  
Gross Unrealized Losses 456,073,000   436,055,000  
Available-for-sale, allowance for credit losses 116,000   116,000  
Allowance for credit losses, Held-to-Maturity securities 0   0  
Debt Securities, Held-to-maturity 142,677,000   146,468,000  
Residential MBS [Member] | Private label [Member]        
Schedule Of Investments [Line Items]        
Available-for-sale, allowance for credit losses $ 100,000   $ 100,000  
Residential MBS [Member] | SOFR [Member] | Private label [Member]        
Schedule Of Investments [Line Items]        
Spread on variable rate 0.26161%   0.26161%  
Debt Instrument Description Of Variable Rate Basis 3-month CME Term SOFR      
Residential MBS [Member] | Private label [Member]        
Schedule Of Investments [Line Items]        
Available-for-sale, allowance for credit losses $ 116,000 83,000 $ 116,000 $ 83,000
Provision For Other Credit Losses Previous Expected Credit Losses 0 $ 0    
Available-for-sale Securities [Member]        
Schedule Of Investments [Line Items]        
Accrued interest receivable 10,200,000   10,600,000  
Held-to-maturity Securities [Member]        
Schedule Of Investments [Line Items]        
Accrued interest receivable $ 2,800,000   $ 4,800,000