Information by Credit Risk Rating Indicators for Those Remaining Segments of Loan Portfolio (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	$ 2,475,078	$ 2,239,692
Leases
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	5,618	6,954
Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	357,534	360,080
Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	472,426	448,662
Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	130,791	108,699
Performing Financing Receivable | Leases
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	4,650	6,099
Performing Financing Receivable | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	355,845	358,094
Nonperforming Financing Receivable | Leases | Loans 90 Days Or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	96	2
Nonperforming Financing Receivable | Leases | Non Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	872	853
Nonperforming Financing Receivable | Consumer | Loans 90 Days Or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	5	165
Nonperforming Financing Receivable | Consumer | Non Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	1,651	1,786
Nonperforming Financing Receivable | Consumer | Restructured Loans | Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	33	35
Homogeneous Loan Pools | Residential Real Estate Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	966,369	924,395
Homogeneous Loan Pools | Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	472,426	448,662
Homogeneous Loan Pools | Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	130,791	108,699
Homogeneous Loan Pools | Performing Financing Receivable | Residential Real Estate Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	952,444	905,430
Homogeneous Loan Pools | Performing Financing Receivable | Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	465,491	439,194
Homogeneous Loan Pools | Performing Financing Receivable | Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	126,458	102,043
Homogeneous Loan Pools | Nonperforming Financing Receivable | Residential Real Estate Portfolio Segment | Loans 90 Days Or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	192	577
Homogeneous Loan Pools | Nonperforming Financing Receivable | Residential Real Estate Portfolio Segment | Non Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	9,456	14,080
Homogeneous Loan Pools | Nonperforming Financing Receivable | Residential Real Estate Portfolio Segment | Restructured Loans | Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	4,277	4,308
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]
Loans and leases	91	167
Homogeneous Loan Pools | Nonperforming Financing Receivable | Residential Real Estate Portfolio Segment | Residential Mortgage | Non Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	2,600	5,722
Homogeneous Loan Pools | Nonperforming Financing Receivable | Residential Real Estate Portfolio Segment | Residential Mortgage | Restructured Loans | Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	4,244	3,579
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]
Loans and leases		243
Homogeneous Loan Pools | Nonperforming Financing Receivable | Residential Real Estate Portfolio Segment | Residential Construction | Non Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	4,333	5,719
Homogeneous Loan Pools | Nonperforming Financing Receivable | Residential Real Estate Portfolio Segment | Residential Construction | Restructured Loans | Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Loans and leases		$ 694