Derivatives - Summary of Net Gains (Losses) Relating to Free-Standing Derivative Instruments Used for Risk Management (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Interest rate contracts for customers
Derivative [Line Items]
Derivative instruments	$ 19	$ 31	$ (54)
Forward contracts related to mortgage loans held for sale and interest rate contracts
Derivative [Line Items]
Derivative instruments	$ 56	$ 94	$ 32

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5618551-113959

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