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Allowance for Loan Losses - Narrative (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) Contract	Sep. 30, 2017 USD ($) Contract	Sep. 30, 2018 USD ($) Contract	Sep. 30, 2017 USD ($) Contract	Dec. 31, 2017 USD ($)
Allowance For Loan Losses [Line Items]
TDRs performing under the restructured terms	$ 466,000		$ 466,000		$ 333,000
Loans modified under TDRs | Contract		0	1,000	0
Troubled debt restructuring loan subsequent default	0	$ 0	$ 0	$ 0
Troubled debt restructuring loan subsequent default period			90 days
Performing financing receivable
Allowance For Loan Losses [Line Items]
TDRs performing under the restructured terms	$ 269,000		$ 269,000		$ 282,000
Secured by 1-4 family residential | Real estate loans
Allowance For Loan Losses [Line Items]
Loans modified under TDRs | Contract	1
Financing Receivable, Allowance for Credit Losses, Period Increase (Decrease)			$ 19,000

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- Definition

Allowance For Loan Losses [Line Items]

+ References

No definition available.

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- Definition

Financing receivable modification as troubled debt restructuring that subsequently defaulted.

+ References

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- Definition

The increase (decrease) in the allowance for credit losses related to financing receivables.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953676-111524

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- Definition

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=82895541&loc=d3e18845-111554

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Amount of investment related to financing receivables modified by troubled debt restructurings within the previous 12 months, for which there was a payment default.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953682-111524

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