Securities - Schedule of Amortized Cost and Fair Value of HTM Securities Portfolio (Detail) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 0	$ 121,617,000
Gross Unrecognized Gains		500,000
Gross Unrecognized Losses		(3,162,000)
Fair Value	$ 0	118,955,000
Mortgage-backed securities: residential
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost		75,944,000
Gross Unrecognized Gains		34,000
Gross Unrecognized Losses		(3,072,000)
Fair Value		72,906,000
State and political subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost		45,673,000
Gross Unrecognized Gains		466,000
Gross Unrecognized Losses		(90,000)
Fair Value		$ 46,049,000

Amount of investment in debt security measured at amortized cost (held-to-maturity).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26610-111562

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-Publisher FASB
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Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
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-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27232-111563

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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-Name Accounting Standards Codification
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