Investment Securities (Held to Maturity) (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	$ 354,688	$ 363,111
Gross unrealized gains	93	245
Gross unrealized losses	(13,322)	(10,755)
Held-to-maturity, debt securities	341,459	352,601
Accrued interest on held to maturity	2,400	3,100
U.S. Treasury obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	5,767	5,146
Gross unrealized gains	0	1
Gross unrealized losses	0	0
Held-to-maturity, debt securities	5,767	5,147
Agency-guaranteed obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	11,058	11,058
Gross unrealized gains	0	0
Gross unrealized losses	(633)	(652)
Held-to-maturity, debt securities	10,425	10,406
State and municipal obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	331,292	339,816
Gross unrealized gains	93	244
Gross unrealized losses	(12,315)	(9,700)
Held-to-maturity, debt securities	319,070	330,360
Corporate obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	6,571	7,091
Gross unrealized gains	0	0
Gross unrealized losses	(374)	(403)
Held-to-maturity, debt securities	$ 6,197	$ 6,688