Loans - Summary of Information Regarding Impaired Loans (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Impaired [Line Items]
Recorded Investment	$ 97	$ 378
Recorded Investment	2,260	4,417
Unpaid Principal	97	392
Unpaid Principal	2,537	4,706
Reserve	12	230
Average Investment	272	394
Average Investment	2,319	4,865
Interest Recognized	6	15
Interest Recognized	52	255
Recorded Investment	2,163	4,039
Unpaid Principal	2,440	4,314
Reserve	0	0
Average Investment	2,247	4,471
Interest Recognized	52	240
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	635	2,024
Unpaid Principal	635	2,024
Reserve	0	0
Average Investment	665	2,192
Interest Recognized	33	148
Commercial Land [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	303	303
Unpaid Principal	303	303
Reserve	0	0
Average Investment	303	303
Commercial Other [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment		202
Unpaid Principal		202
Reserve	0	0
Average Investment	25	138
Interest Recognized		3
Residential Real Estate First Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	97	378
Unpaid Principal	97	392
Reserve	12	230
Average Investment	72	394
Interest Recognized		15
Recorded Investment	1,225	1,510
Unpaid Principal	1,502	1,785
Reserve	0	0
Average Investment	1,254	1,838
Interest Recognized	19	89
Residential Real Estate Construction [Member]
Financing Receivable, Impaired [Line Items]
Reserve	0	0
Consumer Home Equity and Lines of Credit [Member]
Financing Receivable, Impaired [Line Items]
Average Investment	11
Reserve	0	0
Consumer Other [Member]
Financing Receivable, Impaired [Line Items]
Average Investment	190
Interest Recognized	6
Reserve	$ 0	$ 0

Impaired financing receivable with no related allowance.

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- Definition

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+ References

No definition available.

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- Definition

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
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- Definition

Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

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Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

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Amount of allowance for credit losses related to recorded investment.

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- Definition

Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

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Amount of average investment of impaired financing receivables for which there is no related allowance for credit losses.

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