Income Taxes - Summary of Net Deferred Tax Asset Reported in Other Assets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Provision for loan losses	$ 15,814	$ 13,662
Write-downs of other real estate owned	1,297	962
Deferred compensation	2,652	2,237
Stock-based compensation	3,190	2,934
Investments in partnership interests	1,966	1,170
Other	306us-gaap_DeferredTaxAssetsOther	1,479us-gaap_DeferredTaxAssetsOther
Gross deferred tax assets	25,225us-gaap_DeferredTaxAssetsGross	22,444us-gaap_DeferredTaxAssetsGross
Unrealized net gains on securities	(2,644)	(2,103)
Premium on securities of banks acquired	(715)	(800)
Intangibles	(2,917)	(2,561)
Basis difference related to tax credits	(1,977)	(1,620)
Depreciation	(5,504)	(5,975)
Leveraged lease	(1,964)	(2,282)
Other	(89)us-gaap_DeferredTaxLiabilitiesOther	(257)us-gaap_DeferredTaxLiabilitiesOther
Gross deferred tax liabilities	(15,810)us-gaap_DeferredIncomeTaxLiabilities	(15,598)us-gaap_DeferredIncomeTaxLiabilities
Net deferred tax asset	$ 9,415us-gaap_DeferredTaxAssetsLiabilitiesNet	$ 6,846us-gaap_DeferredTaxAssetsLiabilitiesNet

Deferred tax assets write downs of other real estate owned.

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Deferred tax liabilities basis difference related to tax credits.

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Deferred tax liabilities premium on securities of banks acquired.

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Deferred tax liabilities unrealized gains on securities.

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Amount 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 temporary differences and carryforwards.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from the entity's investment in its wholly-owned subsidiaries.

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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 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 employee compensation.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from share-based compensation.

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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 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 leasing arrangements.

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Amount of deferred tax liability attributable to taxable temporary differences not separately disclosed.

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Amount of deferred tax liability attributable to taxable temporary differences from property, plant, and equipment.

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