Loans and the Allowance for Credit Losses - Additional Information (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Financing Receivable, Recorded Investment [Line Items]
Net deferred loan fee income (costs)	$ (11,800,000)		$ (11,500,000)
Un-accreted discount on purchased loans from acquisitions	12,700,000			$ 13,500,000
Reserve on accrued interest related to CARES Act	$ 100,000
Percentage of national unemployment projection	4.30%
Expected average percentage of national unemployment in future	4.70%
Accrued interest receivable for loans	$ 63,200,000		62,200,000
Accrued interest receivable for loans related to CARES Act	15,100,000		15,600,000
Aggregate amount of residential real estate, home equity and consumer loans classified as substandard	21,300,000		20,000,000
Internally assigned loan grades to residential real estate, home equity and consumer loans	4,900,000		4,600,000
Unfunded commercial loan commitments	62,800,000		21,200,000
Other real estate owned	1,210,000		1,207,000
Net charge-offs	5,935,000	$ 1,919,000
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Other real estate owned	0		0
Foreclosure proceedings in process on residential real estate loans	4,200,000		4,000,000
Net charge-offs	101,000	(88,000)
90 Days or More Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Modification loans	0	0
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Net charge-offs	4,409,000	$ 186,000
Commercial and Industrial [Member] | Maximum [Member]
Financing Receivable, Recorded Investment [Line Items]
Annual sales of borrowers	100,000,000
Unfunded Loan Commitment [Member]
Financing Receivable, Recorded Investment [Line Items]
Modification loans	$ 700,000		$ 1,800,000