Disclosures about Fair Value of Assets and Liabilities - Additional Information (Detail) - USD ($)	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016
Fair Value Disclosures [Abstract]
Reduced in carrying amount of mortgage servicing rights	$ 75,000	$ 193,000

The increase (decrease) in the fair value of servicing assets that are subsequently measured at fair value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122625-111746

Name:	us-gaap_ServicingAssetAtFairValuePeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration