Information by Credit Risk Rating Indicators for Those Remaining Segments of Loan Portfolio (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	$ 2,565,069	$ 2,531,128
Leases
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1,974	3,421
Consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	353,341	356,990
Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	538,346	523,364
Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	122,698	120,314
Performing Financing Receivable | Leases
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1,974	2,556
Performing Financing Receivable | Consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	350,868	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	54	14
Nonperforming Financing Receivable | Consumer | Non Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	2,388	2,410
Nonperforming Financing Receivable | Consumer | Restructured Loans | Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	31	31
Homogeneous Loan Pools | Residential Real Estate Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1,016,359	1,004,089
Homogeneous Loan Pools | Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	538,346	523,364
Homogeneous Loan Pools | Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	122,698	120,314
Homogeneous Loan Pools | Performing Financing Receivable | Residential Real Estate Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1,001,051	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	528,769	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	119,440	117,189
Homogeneous Loan Pools | Nonperforming Financing Receivable | Residential Mortgage | Non Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	5,393	4,681
Homogeneous Loan Pools | Nonperforming Financing Receivable | Residential Real Estate Portfolio Segment | Loans 90 Days Or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	54	14
Homogeneous Loan Pools | Nonperforming Financing Receivable | Residential Real Estate Portfolio Segment | Non Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	11,039	11,081
Homogeneous Loan Pools | Nonperforming Financing Receivable | Residential Real Estate Portfolio Segment | Restructured Loans | Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	4,215	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 | Restructured Loans | Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	4,184	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	3,258	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