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Basis of Presentation - Additional Information (Detail)	3 Months Ended
Basis of Presentation - Additional Information (Detail)	Mar. 31, 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