Credit Quality Assessment (Information by Credit Risk Rating Indicators for Those Remaining Segments of Loan Portfolio) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	$ 3,127,392,000	$ 2,784,266,000
Leases
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	54,000	703,000
Consumer
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	425,552,000	373,657,000
Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	717,886,000	618,381,000
Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	136,741,000	129,177,000
Performing Financing Receivable | Leases
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	54,000	703,000
Performing Financing Receivable | Consumer
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	423,884,000	371,368,000
Performing Financing Receivable | Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	712,210,000	607,449,000
Performing Financing Receivable | Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	135,636,000	126,862,000
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	0
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	1,000
Nonperforming Financing Receivable | Consumer | Non Accrual Loans
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	1,668,000	2,259,000
Nonperforming Financing Receivable | Consumer | Restructured Loans | Accrual Loans
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	0	29,000
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
Nonperforming Financing Receivable | Residential Real Estate Portfolio Segment | Residential Mortgage | Non Accrual Loans
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	3,012,000	5,735,000
Nonperforming Financing Receivable | Residential Real Estate Portfolio Segment | Residential Mortgage | Restructured Loans | Accrual Loans
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	2,664,000	5,197,000
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
Nonperforming Financing Receivable | Residential Real Estate Portfolio Segment | Residential Construction | Non Accrual Loans
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	1,105,000	2,315,000
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
Homogeneous Loan Pools
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	1,280,233,000	1,121,918,000
Homogeneous Loan Pools | Performing Financing Receivable
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	1,271,784,000	1,106,382,000
Homogeneous Loan Pools | Nonperforming Financing Receivable | Loans 90 Days Or More Past Due
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	0	1,000
Homogeneous Loan Pools | Nonperforming Financing Receivable | Non Accrual Loans
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	5,785,000	10,309,000
Homogeneous Loan Pools | Nonperforming Financing Receivable | Restructured Loans | Accrual Loans
Financing Receivable Recorded Investment [Line Items]
Total loans and leases	$ 2,664,000	$ 5,226,000