Fair Value Measurements - Schedule of Quantitative Information of Assets Measured at Fair Value on Nonrecurring Basis (Detail) - Level III [Member] - Impaired Loans [Member] - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Discounted Cash Flow [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Estimate	$ 551	$ 3,033
Discounted Cash Flow [Member] \| Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Remaining term	4 months	6 months
Discount rate	4.40%	3.60%
Discounted Cash Flow [Member] \| Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Remaining term	24 years 6 months	25 years 6 months
Discount rate	7.50%	7.50%
Discounted Cash Flow [Member] \| Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Remaining term	20 months 9 days	16 months 21 days
Discount rate	5.30%	5.20%
Appraisal of Collateral [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Estimate	$ 1,522	$ 85
Liquidation expense	(10.00%)	(10.00%)
Appraisal of Collateral [Member] \| Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Appraisal adjustments	0.00%	0.00%
Appraisal of Collateral [Member] \| Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Appraisal adjustments	(25.00%)	0.00%
Appraisal of Collateral [Member] \| Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Appraisal adjustments	(6.80%)	(36.00%)

Fair value inputs liquidation expense.

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

+ Details

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- Definition

Period the instrument, asset or liability is expected to be outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Percentage of adjustment to the observed price for a similar asset or liability when an identical transaction does not exist, used as an input to measure fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

+ Details

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- Definition

Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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