Allowance for Loan Losses and Credit Quality Information - Schedule of Consumer Credit Exposure (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	$ 3,041,477	$ 2,952,263
Total	100.00%	100.00%
Total Residential and Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	523,443	523,754
Total	100.00%	100.00%
Total Residential and Consumer Loan [Member] | Nonperforming Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	23,320	23,263
Total	4.00%	4.00%
Total Residential and Consumer Loan [Member] | Performing Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	500,123	500,491
Total	96.00%	96.00%
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	210,923	221,520
Residential [Member] | Nonperforming Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	17,743	17,852
Residential [Member] | Performing Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	193,180	203,668
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	312,520	302,234
Consumer [Member] | Nonperforming Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	5,577	5,411
Consumer [Member] | Performing Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	$ 306,943	$ 296,823