Investment Securities (Amortized Cost of held to Maturity Debt Securities by Year of Originations and Credit Rating) (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	$ 354,688	$ 363,111
U.S. Treasury obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	5,767	5,146
Agency-guaranteed obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	11,058	11,058
State and municipal obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	331,292	339,816
Corporate obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	6,571	7,091
AAA
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	63,056	60,457
AAA | U.S. Treasury obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	5,767	5,146
AAA | Agency-guaranteed obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	11,058	11,058
AAA | State and municipal obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	45,728	43,749
AAA | Corporate obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	503	504
AA
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	255,302	158,948
AA | U.S. Treasury obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	0	0
AA | Agency-guaranteed 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	252,805	156,438
AA | Corporate obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	2,497	2,510
A
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	33,757	141,283
A | U.S. Treasury obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	0	0
A | Agency-guaranteed 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	30,211	137,231
A | Corporate obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	3,546	4,052
BBB
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	0	0
BBB | U.S. Treasury obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	0	0
BBB | Agency-guaranteed 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	2,573	2,423
Not Rated | U.S. Treasury obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	0	0
Not Rated | Agency-guaranteed 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	2,548	2,398
Not Rated | Corporate obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	$ 25	$ 25