Income Taxes - Components of Deferred Income Taxes (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Deferred tax assets:
Allowance for loan losses	$ 7,405	$ 7,832
Deferred compensation	787	550
Deferred gain on interest rate swap	477us-gaap_DeferredTaxAssetsDeferredIncome	573us-gaap_DeferredTaxAssetsDeferredIncome
Unrealized loss on interest rate swap	460	130
Unrealized loss on securities available for sale		911
Nonaccrual interest	153	323
Purchase accounting adjustments	12,380	20,334
Other real estate owned	7,706	1,855
Net operating loss tax carryforward	12,146	6,074
Capitalized costs, accrued expenses and other	871us-gaap_DeferredTaxAssetsOther	1,976us-gaap_DeferredTaxAssetsOther
Deferred tax assets	42,385us-gaap_DeferredTaxAssetsNet	40,558us-gaap_DeferredTaxAssetsNet
Deferred tax liabilities:
Depreciation and amortization	4,821	4,355
Intangible assets	802
Purchase accounting adjustments	7,159	7,534
Deferred gain on FDIC-assisted transactions	8,809	12,218
Unrealized gain on securities available for sale	3,010
Deferred tax liabilities	24,601us-gaap_DeferredTaxLiabilities	24,107us-gaap_DeferredTaxLiabilities
Net deferred tax asset	$ 17,784us-gaap_DeferredTaxAssetsLiabilitiesNet	$ 16,451us-gaap_DeferredTaxAssetsLiabilitiesNet

Deferred tax assets nonaccrual interest.

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Deferred tax assets other real estate owned.

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Deferred tax assets purchase accounting adjustments.

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Deferred tax assets unrealized losses on trading securities and derivative instruments.

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Deferred tax liabilities deferred expense depreciation and amortization.

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Deferred tax liabilities deferred gains on FDIC assisted acquisitions.

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Deferred tax liabilities purchase accounting adjustment.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from deferred income.

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Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards, net of deferred tax liability attributable to taxable temporary differences.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences not separately disclosed.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from compensation and benefits costs.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from the provision for loan losses.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from unrealized losses on available-for-sale securities.

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Amount of deferred tax liability attributable to taxable temporary differences net of deferred tax asset attributable to deductible temporary differences and carryforwards after valuation allowances.

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Amount of deferred tax liability attributable to taxable temporary differences from intangible assets other than goodwill.

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Amount of deferred tax liability attributable to taxable temporary differences from unrealized gains on trading securities.

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