Derivative Financial Instruments - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2021 USD ($) Agreement	Dec. 31, 2020 USD ($)
Derivative Instruments, Gain (Loss) [Line Items]
Derivative assets and liabilities offset in balance sheet	$ 0
Total notional amount of the Company's swaps	$ 509,500,000	$ 503,800,000
Description of Conditions Relating to Clearing of Interest rate Swaps	As a result of the Bank exceeding $10 billion in assets, federal regulations required the Bank, beginning in January 2019, to clear most interest rate swaps through a clearing house (“centrally cleared”). These instruments contain language outlining collateral pledging requirements for each counterparty, in which collateral must be posted if market value exceeds certain agreed upon threshold limits. Cash or securities are pledged as collateral.
Interest-rate Swap Agreements with Customers [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Number of interest-rate swap agreements | Agreement	148
Total notional amount of the Company's swaps	$ 509,500,000