Securities - Additional Information (Detail)	3 Months Ended	6 Months Ended
Jun. 30, 2018 USD ($) Securities	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) Securities	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Investments, Debt and Equity Securities [Abstract]
Fair value of pledged securities	$ 96,000,000		$ 96,000,000		$ 94,000,000
Restricted stock investment in FHLB stock	4,100,000		4,100,000		4,100,000
Federal Reserve Bank stock	471,000		471,000		$ 471,000
Proceeds from sale of available-for-sale securities	$ 0	$ 0	$ 0	$ 0
Number of securities in an unrealized loss position, Total \| Securities	119		119
Number of securities in continuous unrealized loss position, 12 months or more \| Securities	36

Number Of Securities In Unrealized Loss Position

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- Definition

Number Of Securities In Unrealized Loss Position For Period Of One Year Or Greater

+ References

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- Definition

Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 325
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=75031641&loc=d3e63345-112809

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- Definition

Federal Reserve Bank stock represents an equity interest in the Federal Reserve Bank. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

+ References

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- References

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- Definition

The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26853-111562

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (a),(b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3179-108585

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- Definition

Fair value of the securities pledged as collateral against securities loaned.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226013-175313

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