Investment Securities (Amortized Cost of held to Maturity Debt Securities by Year of Originations and Credit Rating) (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	$ 421,992	$ 436,189
U.S. Treasury obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	1,430
Agency obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	9,997	9,996
Mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	13	21
State and municipal obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	400,629	415,724
Corporate obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	9,923	10,448
AAA
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	65,140	65,110
AAA | U.S. Treasury obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	1,430
AAA | Agency obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	9,997	9,996
AAA | Mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	13	21
AAA | State and municipal obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	53,191	54,583
AAA | Corporate obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	509	510
AA
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	307,985	317,030
AA | U.S. Treasury obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	0
AA | Agency obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	0	0
AA | Mortgage-backed securities
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	305,861	314,396
AA | Corporate obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	2,124	2,634
A
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	46,929	51,671
A | U.S. Treasury obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	0
A | Agency obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	0	0
A | Mortgage-backed securities
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	39,664	44,392
A | Corporate obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	7,265	7,279
BBB
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	945	945
BBB | U.S. Treasury obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	0
BBB | Agency obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	0	0
BBB | Mortgage-backed securities
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	945	945
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	993	1,433
Not Rated | U.S. Treasury obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	0
Not Rated | Agency obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	0	0
Not Rated | Mortgage-backed securities
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	968	1,408
Not Rated | Corporate obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	$ 25	$ 25