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Fair Value Measurements - Quantitative Information about Level 3 Fair Value Measurements (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Other real estate owned, net of valuation allowance, 2018, $0; 2017, $0	$ 0	$ 326	[1]
Nonrecurring basis
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Other real estate owned, net of valuation allowance, 2018, $0; 2017, $0		326
Nonrecurring basis | Impaired loans, net
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	387
Nonrecurring basis | Significant Unobservable Inputs (Level 3)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Other real estate owned, net of valuation allowance, 2018, $0; 2017, $0		$ 326
Nonrecurring basis | Significant Unobservable Inputs (Level 3) | Impaired loans, net
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 387
Range (Weighted-Average)	10.00%
Nonrecurring basis | Significant Unobservable Inputs (Level 3) | Other real estate owned
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Range (Weighted-Average)		7.00%
[1] Derived from audited consolidated financial statements.

X

- 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

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+ References

No definition available.

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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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- Definition

Carrying amount as of the balance sheet date of other real estate and foreclosed assets. Other real estate may include real estate investments, real estate loans that qualify as investments in real estate, and premises that are no longer used in operations may also be included in real estate owned. Foreclosed assets include all assets obtained in full or partial satisfaction of a debt arrangement through foreclosure proceedings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.10(4))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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