Summary of Significant Accounting Policies - Additional Information (Detail)			12 Months Ended
	Mar. 27, 2020	Jan. 01, 2020 USD ($)	Dec. 31, 2020 USD ($) Branch Property Portfolio	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of branches | Branch			233
Number of ATM | Property			226
Wholly-owned trust subsidiaries | Property			11
Held for sale securities, percentage of purchase price as condition for sale			15.00%
Allowance for credit losses, held-to-maturity debt securities			$ 326,000
Non-accrual status period			90 days
Loans returned to accrual status, performance period			6 months
Consumer loan TDR extended maturity period			6 months
Number of categories of loan portfolio | Portfolio			3
Minimum loan balance individually tested for impairment			$ 1,000,000	$ 1,000,000
Indefinite - lived intangible assets			$ 0
Period of interest rate lock commitments			60 days
Recognition on retained earnings			$ 101,960,000	11,065,000	$ 7,597,000
Recognition after tax for retained earnings			831,688,000	824,694,000
ASU 2016-13 [Member]
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, held-to-maturity debt securities		$ 200,000	$ 326,000	229,000
Regulatory capital transition adoption, delay period			2 years
Regulatory capital transition adoption, transition period			3 years
Regulatory capital transition period, start date			Jan. 01, 2022
Regulatory capital transition period, end date			Dec. 31, 2024
Percentage of change in allowance for credit loss upon adjustment of regulatory capital transition			25.00%
Adjustment for loan credit losses		6,700,000	$ 6,700,000
Adjustment for loan commitments			$ 3,000,000.0
Regulatory capital impact period			1 year
ASU 2016-13 [Member] | Revision of Prior Period, Accounting Standards Update, Adjustment [Member]
Summary Of Significant Accounting Policies [Line Items]
Recognition on retained earnings		$ 41,400,000	$ 41,442,000
ASU 2016-13 [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member]
Summary Of Significant Accounting Policies [Line Items]
Recognition after tax for retained earnings			$ 26,600,000
Land Improvements [Member]
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, Useful life			15 years
Commercial [Member] | Hospitality Sector [Member]
Summary Of Significant Accounting Policies [Line Items]
Description of extension period for loan principal and interest payments under the plan			If a loan were to meet the criteria, they would be eligible to have twelve months of interest payments deferred or three months of principal and interest payments plus nine months of interest-only payments. There are predetermined contractual re-evaluation triggers reviewed throughout the deferred period to determine if a borrower should return to a normal amortization schedule prior to the completion of the twelve month period.
CARES Act, Paycheck Protection Program [Member]
Summary Of Significant Accounting Policies [Line Items]
Loans receivable, Interest rate	1.00%
Mortgage-Backed Securities and Collateralized Mortgage Obligations of Government Sponsored Entities and Agencies [Member]
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, held-to-maturity debt securities			$ 0
Consumer Loan [Member]
Summary Of Significant Accounting Policies [Line Items]
Period of closed end loans loans charged down to net realizable value			120 days
Home Equity [Member]
Summary Of Significant Accounting Policies [Line Items]
Period of closed end loans loans charged down to net realizable value			180 days
Recognition on retained earnings			$ 1,234,000	$ 851,000	$ 138,000
Home Equity [Member] | ASU 2016-13 [Member] | Revision of Prior Period, Accounting Standards Update, Adjustment [Member]
Summary Of Significant Accounting Policies [Line Items]
Recognition on retained earnings			$ (3,936,000)
Residential Real Estate Loans [Member]
Summary Of Significant Accounting Policies [Line Items]
Period of closed end loans loans charged down to net realizable value			180 days
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of voting interest			50.00%
Forecast period to measure expected credit losses on loan portfolio			1 year
Model reversion period to measure expected credit losses on loan portfolio			1 year
Weighted-average estimated useful lives			10 years
Non-compete agreements, amortization period			1 year
Minimum [Member] | Furniture and Equipment [Member]
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, Useful life			3 years
Minimum [Member] | Building and Building Improvements [Member]
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, Useful life			15 years
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Forecast period to measure expected credit losses on loan portfolio			2 years
Model reversion period to measure expected credit losses on loan portfolio			3 years
Weighted-average estimated useful lives			16 years
Non-compete agreements, amortization period			4 years
Maximum [Member] | Furniture and Equipment [Member]
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, Useful life			10 years
Maximum [Member] | Building and Building Improvements [Member]
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, Useful life			39 years
Maximum [Member] | CARES Act, Paycheck Protection Program [Member]
Summary Of Significant Accounting Policies [Line Items]
Extension period for loan principal and interest payments			180 days
Loans receivable, threshold period past due			30 days