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Other Real Estate Owned (OREO) - Narrative (Detail) - USD ($)	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Other Real Estate [Line Items]
Residential real estate carrying amount included in OREO	$ 0		$ 326,000	$ 250,000
Net expenses applicable to other real estate owned	2,000	$ 6,000	5,000
Residential real estate properties
Other Real Estate [Line Items]
Residential real estate carrying amount included in OREO	$ 0		$ 0

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- Definition

Other Real Estate [Line Items]

+ References

No definition available.

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- Definition

Other real estate owned expenses.

+ References

No definition available.

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- Definition

Carrying amount of other real estate not separately disclosed, including, but not limited to, 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. This does not include real estate assets taken in settlement of troubled loans through surrender or foreclosure.

+ 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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