Allowance for Loan Losses and Credit Quality Information - Schedule of Residential and Consumer Credit Exposure (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	$ 4,605,771	$ 4,469,216	$ 3,847,515
Total	100.00%	100.00%
Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	$ 252,602	$ 267,028	236,657
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	492,817	450,029	$ 374,634
Nonperforming | Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	14,023	13,547
Nonperforming | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	8,396	7,863
Performing | Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	237,727	252,621
Performing | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	$ 484,175	$ 441,797
Acquired impaired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1.00%	1.00%
Acquired impaired | Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	$ 852	$ 860
Acquired impaired | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	246	369
Total Residential and Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	$ 745,419	$ 717,057
Total	100.00%	100.00%
Total Residential and Consumer | Nonperforming
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	$ 22,419	$ 21,410
Total	3.00%	3.00%
Total Residential and Consumer | Performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	$ 721,902	$ 694,418
Total	97.00%	97.00%
Total Residential and Consumer | Acquired impaired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	$ 1,098	$ 1,229
Total	0.00%	0.00%