Fair Value Measurement - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
ASSETS
Total securities available-for-sale	$ 660,046	$ 640,273
US Treasury Securities [Member]
ASSETS
Total securities available-for-sale	15,062	14,880
Obligations of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	271,332	269,285
Collateralized Mortgage Obligations of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	135,216	118,006
Residential Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	42,065	46,668
Commercial Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	50,223	39,673
Obligations of States and Political Subdivisions [Member]
ASSETS
Total securities available-for-sale	137,335	142,702
Marketable Equity Securities [Member]
ASSETS
Total securities available-for-sale	8,813	9,059
Fair Value Measurements, Recurring [Member]
ASSETS
Total securities available-for-sale	660,046	640,273
Trading securities held in a Rabbi Trust	3,690	3,456
Total securities	663,736	643,729
Total Assets	678,542	656,945
LIABILITIES
Total Liabilities	14,310	13,010
Fair Value Measurements, Recurring [Member] \| Interest Rate Swaps [Member]
ASSETS
Derivative financial assets	14,232	12,981
LIABILITIES
Derivative financial liabilities	14,184	12,953
Fair Value Measurements, Recurring [Member] \| Interest Rate Lock Commitments [Member]
ASSETS
Derivative financial assets	574	235
Fair Value Measurements, Recurring [Member] \| Forward Sale Contracts [Member]
LIABILITIES
Derivative financial liabilities	126	57
Fair Value Measurements, Recurring [Member] \| US Treasury Securities [Member]
ASSETS
Total securities available-for-sale	15,062	14,880
Fair Value Measurements, Recurring [Member] \| Obligations of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	271,332	269,285
Fair Value Measurements, Recurring [Member] \| Collateralized Mortgage Obligations of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	135,216	118,006
Fair Value Measurements, Recurring [Member] \| Residential Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	42,065	46,668
Fair Value Measurements, Recurring [Member] \| Commercial Mortgage-Backed Securities of U.S. Government Corporations and Agencies [Member]
ASSETS
Total securities available-for-sale	50,223	39,673
Fair Value Measurements, Recurring [Member] \| Obligations of States and Political Subdivisions [Member]
ASSETS
Total securities available-for-sale	137,335	142,702
Fair Value Measurements, Recurring [Member] \| Marketable Equity Securities [Member]
ASSETS
Total securities available-for-sale	8,813	9,059
Level 1 [Member] \| Fair Value Measurements, Recurring [Member]
ASSETS
Total securities available-for-sale	0	178
Trading securities held in a Rabbi Trust	3,690	3,456
Total securities	3,690	3,634
Total Assets	3,690	3,634
LIABILITIES
Total Liabilities	0	0
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] \| Marketable Equity Securities [Member]
ASSETS
Total securities available-for-sale	0	178
Level 2 [Member] \| Fair Value Measurements, Recurring [Member]
ASSETS
Total securities available-for-sale	660,046	640,095
Total securities	660,046	640,095
Total Assets	674,852	653,311
LIABILITIES
Total Liabilities	14,310	13,010
Level 2 [Member] \| Fair Value Measurements, Recurring [Member] \| Interest Rate Swaps [Member]
ASSETS
Derivative financial assets	14,232	12,981
LIABILITIES
Derivative financial liabilities	14,184	12,953
Level 2 [Member] \| Fair Value Measurements, Recurring [Member] \| Interest Rate Lock Commitments [Member]
ASSETS
Derivative financial assets	574	235
Level 2 [Member] \| Fair Value Measurements, Recurring [Member] \| Forward Sale Contracts [Member]
LIABILITIES
Derivative financial liabilities	126	57
Level 2 [Member] \| Fair Value Measurements, Recurring [Member] \| US Treasury Securities [Member]
ASSETS
Total securities available-for-sale	15,062	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	271,332	269,285
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	135,216	118,006
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	42,065	46,668
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	50,223	39,673
Level 2 [Member] \| Fair Value Measurements, Recurring [Member] \| Obligations of States and Political Subdivisions [Member]
ASSETS
Total securities available-for-sale	137,335	142,702
Level 2 [Member] \| Fair Value Measurements, Recurring [Member] \| Marketable Equity Securities [Member]
ASSETS
Total securities available-for-sale	8,813	8,881
Level 3 [Member] \| Fair Value Measurements, Recurring [Member]
LIABILITIES
Total Liabilities	$ 0
Level 3 [Member] \| Fair Value Measurements, Recurring [Member] \| US Treasury Securities [Member]
ASSETS
Total securities available-for-sale		$ 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 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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