Income Taxes - Reconciliation of IncomeTax Attributable to Pre-Ttax Income at Federal Statutory Tax Rates to Income Tax Expense (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Tax at statutory rate, value	$ 11,336	$ 8,057	$ 8,241
Tax exempt income, net value	(1,684)	(1,664)	(1,553)
Bank owned life insurance, value	(364)	(543)	(341)
Merger costs, value	0	233	0
Other, value	26	257	64
Income tax expense	$ 9,314us-gaap_IncomeTaxExpenseBenefit	$ 6,340us-gaap_IncomeTaxExpenseBenefit	$ 6,411us-gaap_IncomeTaxExpenseBenefit
Tax at statutory rate, percent	35.00%	35.00%	35.00%
Tax exempt income, net percent	(5.20%)	(7.20%)	(6.60%)
Bank owned life insurance, percent	(1.10%)	(2.40%)	(1.40%)
Merger costs, percent	0.00%	1.00%	0.00%
Other, percent	0.10%	1.10%	0.20%
Income tax expense, percent	28.80%	27.50%	27.20%

Income tax reconciliation nondeductible expense merger costs.

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Income tax reconciliation nondeductible expense merger costs percentage.

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to life insurance expense.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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The amount of income tax expense or benefit for the period computed by applying the domestic federal statutory tax rates to pretax income from continuing operations.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to nondeductible life insurance expense.

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