Investment Securities - Additional Information (Detail) - USD ($)	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Investment Holdings [Line Items]
Securities, carrying value	$ 640,300,000		$ 581,100,000
Equity securities, at fair value	16,902,000		$ 16,473,000
Purchase of equity securities	1,082,000	$ 95,000
Proceeds from sales of equity securities	0	1,138,000
Loss on equity securities	653,000	$ (353,000)
Investment in community development loans	$ 3,500,000
Redemption of funds	60 days
Unfunded commitments	$ 0
Investment in government guaranteed loans, mortgage-backed securities, small business loans	12,500,000
Other financial institutions
Investment Holdings [Line Items]
Equity securities, at fair value	915,000
Unfunded commitments	0
Community reinvestment funds
Investment Holdings [Line Items]
Equity securities, at fair value	$ 16,000,000.0

Investment in community development loans.

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

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Payments to Acquire Equity Securities, FV-NI

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
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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).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=116654751&loc=SL75117546-209714

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Period when redemption restriction has been in effect for investments for which net asset value per share is calculated (including by unit, membership interest, or other equity (ownership interest) unit measure), in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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