Information by Credit Risk Rating Indicators for Those Remaining Segments of Loan Portfolio (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	$ 2,662,010	$ 2,531,128
Leases
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	962	3,421
Consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	368,764	356,990
Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	595,180	523,364
Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	118,316	120,314
Performing Financing Receivable | Leases
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	962	2,556
Performing Financing Receivable | Consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	366,721	354,535
Nonperforming Financing Receivable | Leases | Loans 90 Days Or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	0	0
Nonperforming Financing Receivable | Leases | Non Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	0	865
Nonperforming Financing Receivable | Leases | Restructured Loans | Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	0	0
Nonperforming Financing Receivable | Consumer | Loans 90 Days Or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	10	14
Nonperforming Financing Receivable | Consumer | Non Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	2,004	2,410
Nonperforming Financing Receivable | Consumer | Restructured Loans | Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	29	31
Homogeneous Loan Pools
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1,083,222	1,004,089
Homogeneous Loan Pools | Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	595,180	523,364
Homogeneous Loan Pools | Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	118,316	120,314
Homogeneous Loan Pools | Performing Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1,069,731	988,760
Homogeneous Loan Pools | Performing Financing Receivable | Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	586,059	514,480
Homogeneous Loan Pools | Performing Financing Receivable | Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	115,989	117,189
Homogeneous Loan Pools | Nonperforming Financing Receivable | Loans 90 Days Or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	10	14
Homogeneous Loan Pools | Nonperforming Financing Receivable | Non Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	9,974	11,081
Homogeneous Loan Pools | Nonperforming Financing Receivable | Restructured Loans | Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	3,507	4,234
Homogeneous Loan Pools | Nonperforming Financing Receivable | Residential Real Estate Portfolio Segment | Residential Mortgage | Loans 90 Days Or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	0	0
Homogeneous Loan Pools | Nonperforming Financing Receivable | Residential Real Estate Portfolio Segment | Residential Mortgage | Non Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	5,643	4,681
Homogeneous Loan Pools | Nonperforming Financing Receivable | Residential Real Estate Portfolio Segment | Residential Mortgage | Restructured Loans | Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	3,478	4,203
Homogeneous Loan Pools | Nonperforming Financing Receivable | Residential Real Estate Portfolio Segment | Residential Construction | Loans 90 Days Or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	0	0
Homogeneous Loan Pools | Nonperforming Financing Receivable | Residential Real Estate Portfolio Segment | Residential Construction | Non Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	2,327	3,125
Homogeneous Loan Pools | Nonperforming Financing Receivable | Residential Real Estate Portfolio Segment | Residential Construction | Restructured Loans | Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	$ 0	$ 0