Allowance for Loan Losses and Credit Quality Information - Schedule of Consumer Credit Exposure (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	$ 3,004,672	$ 2,952,263
Total	100.00%	100.00%
Total Residential and Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	519,464	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	23,950	23,263
Total	5.00%	4.00%
Total Residential and Consumer Loan [Member] | Performing Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	495,514	500,491
Total	95.00%	96.00%
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	218,153	221,520
Residential [Member] | Nonperforming Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	18,413	17,852
Residential [Member] | Performing Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	199,740	203,668
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	301,311	302,234
Consumer [Member] | Nonperforming Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	5,537	5,411
Consumer [Member] | Performing Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	$ 295,774	$ 296,823