Qualified Affordable Housing Project Investments - Additional Information (Detail) - USD ($)	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Investments In Affordable Housing Projects [Abstract]
Investment for qualified affordable housing projects included in other assets	$ 5,624,000		$ 5,624,000		$ 5,154,000
Unfunded commitments related to the investments in qualified affordable housing projects	6,459,000		6,459,000		$ 5,417,000
Recognized amortization expense	156,000	$ 133,000	489,000	$ 399,000
Recognized tax credits and other benefits from its investment in affordable housing tax credits	304,000	275,000	888,000	827,000
Impairment losses related to its investment in qualified affordable housing projects	$ 0	$ 0	$ 0	$ 0

Amount of write-down from impairment of an investment in a qualified affordable housing project.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 740
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Amount of affordable housing tax credits and other tax benefits recognized.

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Amount of investment in qualified affordable housing projects.

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Amount of amortization expense of investment in qualified affordable housing projects.

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Amount of commitment or contingent commitments to qualified affordable housing project investments.

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