v3.25.1
Investment Securities (Schedule of Amortized Cost of held to Maturity Debt Securities by Year of Originations and Credit Rating) (Detail) - USD ($)
$ in Thousands
Mar. 31, 2025
Dec. 31, 2024
Schedule of Held-to-maturity Securities [Line Items]    
Amortized cost $ 314,022 $ 327,637
Government-agency obligations    
Schedule of Held-to-maturity Securities [Line Items]    
Amortized cost 9,999 9,999
State and municipal obligations    
Schedule of Held-to-maturity Securities [Line Items]    
Amortized cost 297,966 311,118
Corporate obligations    
Schedule of Held-to-maturity Securities [Line Items]    
Amortized cost 6,057 6,520
AAA    
Schedule of Held-to-maturity Securities [Line Items]    
Amortized cost 55,284 55,321
AAA | Government-agency obligations    
Schedule of Held-to-maturity Securities [Line Items]    
Amortized cost 9,999 9,999
AAA | State and municipal obligations    
Schedule of Held-to-maturity Securities [Line Items]    
Amortized cost 44,785 44,821
AAA | Corporate obligations    
Schedule of Held-to-maturity Securities [Line Items]    
Amortized cost 500 501
AA    
Schedule of Held-to-maturity Securities [Line Items]    
Amortized cost 225,353 236,225
AA | Government-agency obligations    
Schedule of Held-to-maturity Securities [Line Items]    
Amortized cost 0 0
AA | State and municipal obligations    
Schedule of Held-to-maturity Securities [Line Items]    
Amortized cost 223,348 234,212
AA | Corporate obligations    
Schedule of Held-to-maturity Securities [Line Items]    
Amortized cost 2,005 2,013
A    
Schedule of Held-to-maturity Securities [Line Items]    
Amortized cost 28,465 32,716
A | Government-agency obligations    
Schedule of Held-to-maturity Securities [Line Items]    
Amortized cost 0 0
A | State and municipal obligations    
Schedule of Held-to-maturity Securities [Line Items]    
Amortized cost 24,938 28,735
A | Corporate obligations    
Schedule of Held-to-maturity Securities [Line Items]    
Amortized cost 3,527 3,981
BBB    
Schedule of Held-to-maturity Securities [Line Items]    
Amortized cost 0 0
BBB | Government-agency obligations    
Schedule of Held-to-maturity Securities [Line Items]    
Amortized cost 0 0
BBB | State and municipal obligations    
Schedule of Held-to-maturity Securities [Line Items]    
Amortized cost 0 0
BBB | Corporate obligations    
Schedule of Held-to-maturity Securities [Line Items]    
Amortized cost 0 0
Not Rated    
Schedule of Held-to-maturity Securities [Line Items]    
Amortized cost 4,920 3,375
Not Rated | Government-agency obligations    
Schedule of Held-to-maturity Securities [Line Items]    
Amortized cost 0 0
Not Rated | State and municipal obligations    
Schedule of Held-to-maturity Securities [Line Items]    
Amortized cost 4,895 3,350
Not Rated | Corporate obligations    
Schedule of Held-to-maturity Securities [Line Items]    
Amortized cost $ 25 $ 25