Allowance for Loan Losses and Credit Quality Information - Schedule of Loans Identified as Troubled Debt Restructurings During Periods Indicated (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Modifications [Line Items]
Pre Modification	$ 14,412	$ 6,145
Post Modification	14,412	6,145
Commercial
Financing Receivable, Modifications [Line Items]
Pre Modification	954	1,407
Post Modification	954	1,407
Construction
Financing Receivable, Modifications [Line Items]
Pre Modification	6,054	0
Post Modification	6,054	0
Residential
Financing Receivable, Modifications [Line Items]
Pre Modification	1,652	2,754
Post Modification	1,652	2,754
Consumer loan commitments
Financing Receivable, Modifications [Line Items]
Pre Modification	2,498	873
Post Modification	2,498	873
Owner-occupied commercial
Financing Receivable, Modifications [Line Items]
Pre Modification	3,071	0
Post Modification	3,071	0
Commercial mortgages
Financing Receivable, Modifications [Line Items]
Pre Modification	183	1,111
Post Modification	$ 183	$ 1,111

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No definition available.

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- Definition

Post-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953676-111524

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- Definition

Pre-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

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