Income Taxes - Provision (Benefit) for Income Taxes Results in Effective Tax Rates (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Tax Expense Benefit [Line Items]
Expected federal income tax provision	$ 6,584	$ 2,471	$ 2,736
State income tax, net of federal income tax effect	775	298	325
Municipal securities tax benefit	(631)	(422)	(93)
Equity-based compensation	25	68	98
Benefit of purchased tax credits	(181)	(289)	(231)
Low-income housing tax credits	(142)	(142)	(123)
Deferred tax rate adjustments and other	(271)	(266)	12
Income tax provision	$ 6,159	$ 1,718	$ 2,724
Percentage of expected federal income tax provision	35.00%	35.00%	35.00%
Percentage of state income tax, net of federal income tax effect	4.12%	4.22%	4.17%
Percentage of municipal securities tax benefit	(3.35%)	(5.98%)	(1.19%)
Percentage of equity-based compensation	0.13%	0.96%	1.25%
Percentage of benefit of purchased tax credits	(0.96%)	(4.09%)	(2.96%)
Percentage of low-income housing tax credits	(0.75%)	(2.01%)	(1.57%)
Percentage of deferred tax rate adjustments and other	(1.45%)	(3.77%)	0.15%
Percentage of income tax provision	32.74%	24.33%	34.85%