Investment Securities (Amortized Cost of held to Maturity Debt Securities by Year of Originations and Credit Rating) (Detail) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	$ 378,919	$ 387,950
Agency obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	12,096	9,997
State and municipal obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	357,003	366,164
Corporate obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	9,820	11,789
AAA
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	59,726	58,957
AAA | Agency obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	12,096	9,997
AAA | State and municipal obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	47,125	48,453
AAA | Corporate obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	505	507
AA
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	168,669	175,526
AA | 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	166,596	171,934
AA | Corporate obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	2,073	3,592
A
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	148,976	151,244
A | 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	142,830	143,829
A | Corporate obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	6,146	7,415
BBB
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	0	770
BBB | 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	770
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	1,548	1,453
Not Rated | 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	452	1,178
Not Rated | Corporate obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	$ 1,096	$ 275