Loans and Allowance for Loan Losses - Components of Loan Portfolio Disaggregated by Class of Loan and Percentage Change in Total Loans (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 1,075,487,000	$ 1,041,189,000	$ 1,035,288,000
Loan portfolio classes and segments as a percentage of aggregate loans	100.00%	100.00%
Loans and leases receivable net of deferred income increase decrease percentage	3.30%
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	286,887,000	285,322,000
Loan portfolio classes and segments as a percentage of aggregate loans	26.70%	27.40%
Loans and leases receivable net of deferred income increase decrease percentage	0.50%
Commercial Vacant Land, Land Development, and Residential Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	40,741,000	48,099,000
Loan portfolio classes and segments as a percentage of aggregate loans	3.80%	4.60%
Loans and leases receivable net of deferred income increase decrease percentage	(15.30%)
Commercial Real Estate - Owner Occupied [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	258,656,000	259,277,000
Loan portfolio classes and segments as a percentage of aggregate loans	24.10%	24.90%
Loans and leases receivable net of deferred income increase decrease percentage	(0.20%)
Commercial Real Estate - Non-Owner Occupied [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	368,301,000	324,886,000
Loan portfolio classes and segments as a percentage of aggregate loans	34.20%	31.20%
Loans and leases receivable net of deferred income increase decrease percentage	13.40%
Commercial Real Estate - Multi-Family and Residential Rental [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	53,178,000	50,922,000
Loan portfolio classes and segments as a percentage of aggregate loans	4.90%	4.90%
Loans and leases receivable net of deferred income increase decrease percentage	4.40%
Commercial Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,007,763,000	968,506,000	957,411,000
Loan portfolio classes and segments as a percentage of aggregate loans	93.70%	93.00%
Loans and leases receivable net of deferred income increase decrease percentage	4.10%
Retail Home Equity and Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	36,575,000	38,917,000
Loan portfolio classes and segments as a percentage of aggregate loans	3.40%	3.70%
Loans and leases receivable net of deferred income increase decrease percentage	(6.00%)
Retail 1-4 Family Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	31,149,000	33,766,000
Loan portfolio classes and segments as a percentage of aggregate loans	2.90%	3.30%
Loans and leases receivable net of deferred income increase decrease percentage	(7.80%)
Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 67,724,000	$ 72,683,000	$ 77,877,000
Loan portfolio classes and segments as a percentage of aggregate loans	6.30%	7.00%
Loans and leases receivable net of deferred income increase decrease percentage	(6.80%)