Information by Credit Risk Rating Indicators for Those Remaining Segments of Loan Portfolio (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	$ 2,531,128	$ 2,239,692
Leases
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	3,421	6,954
Consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	356,990	360,080
Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	523,364	448,662
Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	120,314	108,699
Performing Financing Receivable | Leases
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	3,421	6,099
Performing Financing Receivable | Consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	354,535	360,080
Nonperforming Financing Receivable | Leases | Loans 90 Days Or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	0	577
Nonperforming Financing Receivable | Leases | Non Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	865	2
Nonperforming Financing Receivable | Consumer | Loans 90 Days Or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	14	165
Nonperforming Financing Receivable | Consumer | Non Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	2,410	1,786
Nonperforming Financing Receivable | Consumer | Restructured Loans | Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	356,990	35
Homogeneous Loan Pools | Residential Real Estate Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1,004,089	924,395
Homogeneous Loan Pools | Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	523,364	448,662
Homogeneous Loan Pools | Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	120,314	108,699
Homogeneous Loan Pools | Performing Financing Receivable | Residential Real Estate Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	988,760	905,430
Homogeneous Loan Pools | Performing Financing Receivable | Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	523,364	439,194
Homogeneous Loan Pools | Performing Financing Receivable | Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	117,189	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]
Total loans and leases	14	0
Homogeneous Loan Pools | Nonperforming Financing Receivable | Residential Real Estate Portfolio Segment | Non Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	11,081	14,080
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	31	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]
Total loans and leases	0	167
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	4,203	3,579
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	3,125	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]
Total loans and leases	$ 0	$ 694