Qualified Affordable Housing Project Investments - Additional Information (Detail) - USD ($)	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Schedule Of Equity Method Investments [Line Items]
Investment in qualified affordable housing projects	$ 8,200,000		$ 8,400,000
Unfunded commitments of investments in qualified affordable housing projects	5,900,000		$ 6,500,000
Recognized amortization expense included in income tax expense	172,000	$ 122,000
Recognized tax credits and other benefits from investment in affordable housing tax credits	197,000	138,000
Impairment losses related to investment in qualified affordable housing projects	$ 0	$ 0
Minimum [Member]
Schedule Of Equity Method Investments [Line Items]
Expected period for fulfillment of investment commitments	8 years
Maximum [Member]
Schedule Of Equity Method Investments [Line Items]
Expected period for fulfillment of investment commitments	10 years

Qualified affordable housing project investments commitment expected period for fulfillment.

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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 740
-Section 50
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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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount of amortization expense of investment in qualified affordable housing projects.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-SubTopic 740
-Section 50
-Paragraph 2
-Subparagraph (c)
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Amount of commitment or contingent commitments to qualified affordable housing project investments.

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-Name Accounting Standards Codification
-Topic 323
-SubTopic 740
-Section 50
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