Information by Credit Risk Rating Indicators for Those Remaining Segments of Loan Portfolio (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	$ 2,468,985	$ 2,239,692
Leases
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	4,233	6,954
Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	353,999	360,080
Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	499,806	448,662
Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	128,606	108,699
Performing Financing Receivable | Leases
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	3,272	6,099
Performing Financing Receivable | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	352,342	358,094
Nonperforming Financing Receivable | Leases | Loans 90 Days Or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	127	2
Nonperforming Financing Receivable | Leases | Non Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	834	853
Nonperforming Financing Receivable | Consumer | Loans 90 Days Or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	18	165
Nonperforming Financing Receivable | Consumer | Non Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	1,607	1,786
Nonperforming Financing Receivable | Consumer | Restructured Loans | Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	32	35
Homogeneous Loan Pools | Residential Real Estate Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	986,644	924,395
Homogeneous Loan Pools | Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	499,806	448,662
Homogeneous Loan Pools | Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	128,606	108,699
Homogeneous Loan Pools | Performing Financing Receivable | Residential Real Estate Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	972,801	905,430
Homogeneous Loan Pools | Performing Financing Receivable | Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	491,817	439,194
Homogeneous Loan Pools | Performing Financing Receivable | Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	125,370	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	261	577
Homogeneous Loan Pools | Nonperforming Financing Receivable | Residential Real Estate Portfolio Segment | Non Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Loans and leases	9,321	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	4,261	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	116	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	3,644	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	4,229	3,579
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	3,236	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