Qualified Affordable Housing Project Investments - Additional Information (Detail) - USD ($)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Investments In Affordable Housing Projects [Abstract]
Investments in qualified affordable housing projects included in other assets	$ 4,276,000	$ 3,204,000
Unfunded commitments related to the investments in qualified affordable housing projects	4,922,000	4,510,000
Recognized amortization expense included in pre-tax income	473,000	354,000	$ 304,000
Recognized tax credits and other benefits from its investments in affordable housing tax credits	903,000	686,000	538,000
Impairment losses related to its investment in qualified affordable housing projects	$ 0	$ 0	$ 0

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 740
-Section 50
-Paragraph 2
-Subparagraph (f)
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Amount of affordable housing tax credits and other tax benefits recognized.

+ References

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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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