Other Real Estate Owned - Additional Information (Detail) - USD ($)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Real Estate [Line Items]
Residential real estate carrying amount included in OREO	$ 326,000	$ 250,000	$ 2,903,000
Net expenses applicable to other real estate owned	5,000	46,000
Residential Real Estate Properties
Other Real Estate [Line Items]
Residential real estate carrying amount included in OREO	0	$ 0
Mortgage loans foreclosed	$ 0

The amount of mortgage loans on real estate which were foreclosed on during the reporting period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29.6)
-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 10
-Section S99
-Paragraph 6
-Subparagraph (SX 210.5-04.(c) Schedule IV)
-URI http://asc.fasb.org/extlink&oid=27047687&loc=d3e5864-122674

Name:	us-gaap_MortgageLoansOnRealEstateForeclosures
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration