Basis of Presentation - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2018 RetailBankingOffice LoanProductionCenter ManagementOffice
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of retail banking offices | RetailBankingOffice	35
Number of loan production centers | LoanProductionCenter	13
Number of wealth management offices | ManagementOffice	3
HSB Insurance, Inc. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Operations commenced date	Jun. 01, 2017