Financial Instruments with Off-Balance-Sheet Risk - Schedule of Financial Instruments with Off-Balance-sheet Risk (Detail) $ in Thousands	12 Months Ended
Dec. 31, 2018 USD ($)
Concentration Risk [Line Items]
Financial instruments whose contract amounts represent credit risk	$ 960,924
Unfunded Lines of Credit [Member]
Concentration Risk [Line Items]
Financial instruments whose contract amounts represent credit risk	632,667
Unfunded Commitments to Extend Credit [Member]
Concentration Risk [Line Items]
Financial instruments whose contract amounts represent credit risk	301,616
Standby Letters of Credit [Member]
Concentration Risk [Line Items]
Financial instruments whose contract amounts represent credit risk	$ 26,641

Maximum amount of loss due to credit risk that, based on the gross fair value of the financial instrument, the entity would incur if parties to the financial instruments that make up the concentration failed completely to perform according to the terms of the contracts and the collateral or other security, if any, for the amount due proved to be of no value to the entity.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13537-108611

Name:	us-gaap_ConcentrationRiskCreditRiskFinancialInstrumentMaximumExposure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration