Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
ASSETS
Total securities available-for-sale	$ 640,273us-gaap_AvailableForSaleSecurities	$ 509,425us-gaap_AvailableForSaleSecurities
US Treasury Securities [Member]
ASSETS
Total securities available-for-sale	14,880	0
Obligations of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	269,285	234,751
Collateralized Mortgage Obligations of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	118,006	63,774
Residential Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	46,668	48,669
Commercial Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	39,673	39,052
Obligations of States and Political Subdivisions [Member]
ASSETS
Total securities available-for-sale	142,702	114,264
Marketable Equity Securities [Member]
ASSETS
Total securities available-for-sale	9,059	8,915
Fair Value Measurements, Recurring [Member]
ASSETS
Total securities available-for-sale	640,273	509,425
Trading securities held in a Rabbi Trust	3,456	2,864
Total securities	643,729	512,289
Total Assets	656,945	526,106
LIABILITIES
Total Liabilities	13,010	13,647
Fair Value Measurements, Recurring [Member] \| US Treasury Securities [Member]
ASSETS
Total securities available-for-sale	14,880
Fair Value Measurements, Recurring [Member] \| Obligations of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	269,285	234,751
Fair Value Measurements, Recurring [Member] \| Collateralized Mortgage Obligations of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	118,006	63,774
Fair Value Measurements, Recurring [Member] \| Residential Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	46,668	48,669
Fair Value Measurements, Recurring [Member] \| Commercial Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	39,673	39,052
Fair Value Measurements, Recurring [Member] \| Obligations of States and Political Subdivisions [Member]
ASSETS
Total securities available-for-sale	142,702	114,264
Fair Value Measurements, Recurring [Member] \| Marketable Equity Securities [Member]
ASSETS
Total securities available-for-sale	9,059	8,915
Fair Value Measurements, Recurring [Member] \| Interest Rate Swap [Member]
ASSETS
Derivative financial assets	12,981	13,698
LIABILITIES
Derivative financial liabilities	12,953	13,647
Fair Value Measurements, Recurring [Member] \| Interest Rate Lock Commitments [Member]
ASSETS
Derivative financial assets	235	85
Fair Value Measurements, Recurring [Member] \| Forward Sale Contracts [Member]
ASSETS
Derivative financial assets		34
LIABILITIES
Derivative financial liabilities	57
Level 1 [Member] \| Fair Value Measurements, Recurring [Member]
ASSETS
Total securities available-for-sale	178	202
Trading securities held in a Rabbi Trust	3,456	2,864
Total securities	3,634	3,066
Total Assets	3,634	3,066
Level 1 [Member] \| Fair Value Measurements, Recurring [Member] \| US Treasury Securities [Member]
ASSETS
Total securities available-for-sale	0
Level 1 [Member] \| Fair Value Measurements, Recurring [Member] \| Obligations of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	0	0
Level 1 [Member] \| Fair Value Measurements, Recurring [Member] \| Collateralized Mortgage Obligations of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	0	0
Level 1 [Member] \| Fair Value Measurements, Recurring [Member] \| Residential Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	0	0
Level 1 [Member] \| Fair Value Measurements, Recurring [Member] \| Commercial Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	0	0
Level 1 [Member] \| Fair Value Measurements, Recurring [Member] \| Obligations of States and Political Subdivisions [Member]
ASSETS
Total securities available-for-sale	0	0
Level 1 [Member] \| Fair Value Measurements, Recurring [Member] \| Marketable Equity Securities [Member]
ASSETS
Total securities available-for-sale	178	202
Level 1 [Member] \| Fair Value Measurements, Recurring [Member] \| Interest Rate Swap [Member]
ASSETS
Derivative financial assets	0	0
LIABILITIES
Derivative financial liabilities	0	0
Level 1 [Member] \| Fair Value Measurements, Recurring [Member] \| Interest Rate Lock Commitments [Member]
ASSETS
Derivative financial assets	0	0
Level 1 [Member] \| Fair Value Measurements, Recurring [Member] \| Forward Sale Contracts [Member]
ASSETS
Derivative financial assets		0
LIABILITIES
Derivative financial liabilities	0
Level 2 [Member] \| Fair Value Measurements, Recurring [Member]
ASSETS
Total securities available-for-sale	640,095	509,223
Trading securities held in a Rabbi Trust	0	0
Total securities	640,095	509,223
Total Assets	653,311	523,040
LIABILITIES
Total Liabilities	13,010	13,647
Level 2 [Member] \| Fair Value Measurements, Recurring [Member] \| US Treasury Securities [Member]
ASSETS
Total securities available-for-sale	14,880
Level 2 [Member] \| Fair Value Measurements, Recurring [Member] \| Obligations of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	269,285	234,751
Level 2 [Member] \| Fair Value Measurements, Recurring [Member] \| Collateralized Mortgage Obligations of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	118,006	63,774
Level 2 [Member] \| Fair Value Measurements, Recurring [Member] \| Residential Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	46,668	48,669
Level 2 [Member] \| Fair Value Measurements, Recurring [Member] \| Commercial Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	39,673	39,052
Level 2 [Member] \| Fair Value Measurements, Recurring [Member] \| Obligations of States and Political Subdivisions [Member]
ASSETS
Total securities available-for-sale	142,702	114,264
Level 2 [Member] \| Fair Value Measurements, Recurring [Member] \| Marketable Equity Securities [Member]
ASSETS
Total securities available-for-sale	8,881	8,713
Level 2 [Member] \| Fair Value Measurements, Recurring [Member] \| Interest Rate Swap [Member]
ASSETS
Derivative financial assets	12,981	13,698
LIABILITIES
Derivative financial liabilities	12,953	13,647
Level 2 [Member] \| Fair Value Measurements, Recurring [Member] \| Interest Rate Lock Commitments [Member]
ASSETS
Derivative financial assets	235	85
Level 2 [Member] \| Fair Value Measurements, Recurring [Member] \| Forward Sale Contracts [Member]
ASSETS
Derivative financial assets		34
LIABILITIES
Derivative financial liabilities	57
Level 3 [Member] \| Fair Value Measurements, Recurring [Member]
ASSETS
Trading securities held in a Rabbi Trust	0	0
Level 3 [Member] \| Fair Value Measurements, Recurring [Member] \| US Treasury Securities [Member]
ASSETS
Total securities available-for-sale	0
Level 3 [Member] \| Fair Value Measurements, Recurring [Member] \| Obligations of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	0	0
Level 3 [Member] \| Fair Value Measurements, Recurring [Member] \| Collateralized Mortgage Obligations of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	0	0
Level 3 [Member] \| Fair Value Measurements, Recurring [Member] \| Residential Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	0	0
Level 3 [Member] \| Fair Value Measurements, Recurring [Member] \| Commercial Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	0	0
Level 3 [Member] \| Fair Value Measurements, Recurring [Member] \| Obligations of States and Political Subdivisions [Member]
ASSETS
Total securities available-for-sale	0	0
Level 3 [Member] \| Fair Value Measurements, Recurring [Member] \| Marketable Equity Securities [Member]
ASSETS
Total securities available-for-sale	0	0
Level 3 [Member] \| Fair Value Measurements, Recurring [Member] \| Interest Rate Swap [Member]
ASSETS
Derivative financial assets	0	0
LIABILITIES
Derivative financial liabilities	0	0
Level 3 [Member] \| Fair Value Measurements, Recurring [Member] \| Interest Rate Lock Commitments [Member]
ASSETS
Derivative financial assets	0	0
Level 3 [Member] \| Fair Value Measurements, Recurring [Member] \| Forward Sale Contracts [Member]
ASSETS
Derivative financial assets		$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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Fair value of financial and nonfinancial obligations.

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Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.

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