Information by Credit Risk Rating Indicators for Those Remaining Segments of Loan Portfolio (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	$ 2,605,458	$ 2,531,128
Leases
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1,415	3,421
Consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	363,114	356,990
Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	565,282	523,364
Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	116,736	120,314
Performing Financing Receivable | Leases
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1,415	2,556
Performing Financing Receivable | Consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	360,779	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	0	14
Nonperforming Financing Receivable | Consumer | Non Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	2,305	2,410
Nonperforming Financing Receivable | Consumer | Restructured Loans | Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	30	31
Homogeneous Loan Pools | Residential Real Estate Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1,046,547	1,004,089
Homogeneous Loan Pools | Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	565,282	523,364
Homogeneous Loan Pools | Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	116,736	120,314
Homogeneous Loan Pools | Performing Financing Receivable | Residential Real Estate Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1,032,578	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	556,206	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	114,178	117,189
Homogeneous Loan Pools | Nonperforming Financing Receivable | Residential Mortgage | Non Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	5,581	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	0	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	10,444	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	3,525	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	3,495	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	2,558	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