v3.25.1
Investment Securities (Narrative) (Detail)
 3 Months Ended
Mar. 31, 2025
USD ($)
security
position
Mar. 31, 2024
USD ($)
Dec. 31, 2024
USD ($)
security
position
Schedule of Held-to-maturity Securities [Line Items]      
Available for sale debt securities, at fair value $ 2,878,785,000   $ 2,768,915,000
Held to maturity debt securities 314,005,000   327,623,000
Debt securities, available-for-sale, accrued interest, after allowance for credit loss 10,100,000   $ 9,700,000
Investments which pay principal on periodic basis, amortized cost 2,490,000,000    
Investments which pay principal on periodic basis, fair value 2,350,000,000    
Proceeds from sale of debt securities, available for sale, gross 1,700,000 $ 9,600,000  
Gain recognized on sale of securities 87,000 0  
Loss recognized on sale of securities 0 0  
Proceeds from sales of available for sale debt securities 1,670,000 0  
Proceeds from calls on securities $ 0    
Securities available for sale, number of securities in an unrealized loss position | position 502   646
Accrued interest on held to maturity $ 2,300,000   $ 2,900,000
Proceeds from sale of held-to-maturity securities 0 0  
Held to maturity securities, proceeds from calls 5,000,000 1,200,000  
Held to maturity securities, recognized gain on calls 0 0  
Held to maturity securities, recognized loss on calls 0 $ 1,200  
Held-to-maturity, debt securities, allowance $ 17,000   $ 14,000
Number of securities in an unrealized loss position | security 479   512
AAA      
Schedule of Held-to-maturity Securities [Line Items]      
Amount of total portfolio 18.00%    
AA      
Schedule of Held-to-maturity Securities [Line Items]      
Amount of total portfolio 72.00%    
A      
Schedule of Held-to-maturity Securities [Line Items]      
Amount of total portfolio 9.00%    
A rated or not rated      
Schedule of Held-to-maturity Securities [Line Items]      
Amount of total portfolio 1.00%