Investment Securities - Additional Information (Detail) - USD ($)	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Investment Holdings [Line Items]
Proceeds from sale of debt securities, available-for-sale	$ 0	$ 94,696,000
Debt securities, available-for-sale, realized gain		569,000
Debt securities, available-for-sale, realized loss		(227,000)
Securities, carrying value	617,400,000		$ 578,000,000.0
Equity securities, at fair value	14,590,000		$ 14,694,000
Proceeds from sales of equity securities	0	0
Loss on equity securities	$ 144,000	$ 653,000
Redemption of funds, notice period	60 days
Unfunded commitments	$ 0
Investment in government guaranteed loans, mortgage-backed securities, small business loans	11,100,000
Community reinvestment funds
Investment Holdings [Line Items]
Equity securities, at fair value	3,500,000
Other financial institutions
Investment Holdings [Line Items]
Unfunded commitments	$ 0

Investment in community development loans mortgage backed securities small business loans.

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Proceeds from Sale of Equity Securities, FV-NI

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Securities pledged to secure public deposit carrying value.

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Amount of realized gain on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of realized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Amount of realized gain (loss) from sale of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Notice period the entity is required to deliver before it can redeem an investment calculated using net asset value per share, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Includes, but is not limited to, investments calculated by per unit, per membership interest, other equity or ownership interest and alternative investments.

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The amount of unfunded commitments for which the entity is obligated, to those certain investments for which net asset value per share is calculated (including by unit, membership interest, or other equity (ownership interest) unit measure) (alternative investments).

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Amount of cash inflow from sale of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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