Fair Value Measurement - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
ASSETS
Total securities available-for-sale	$ 683,479	$ 660,963
US Treasury Securities
ASSETS
Total securities available-for-sale	15,103	14,941
Obligations of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	262,265	263,303
Collateralized Mortgage Obligations of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	143,262	128,835
Residential Mortgage-Backed Securities of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	38,014	40,125
Commercial Mortgage-Backed Securities of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	81,668	69,204
Obligations of States and Political Subdivisions
ASSETS
Total securities available-for-sale	134,250	134,886
Marketable Equity Securities
ASSETS
Total securities available-for-sale	8,917	9,669
Fair Value Measurements, Recurring
ASSETS
Total securities available-for-sale	683,479	660,963
Trading securities held in a Rabbi Trust	4,196	4,021
Total securities	687,675	664,984
Total Assets	705,244	676,540
LIABILITIES
Total Liabilities	16,990	11,281
Fair Value Measurements, Recurring \| Interest Rate Swaps
ASSETS
Derivative financial assets	16,926	11,295
LIABILITIES
Derivative financial liabilities	16,786	11,276
Fair Value Measurements, Recurring \| Interest Rate Lock Commitments
ASSETS
Derivative financial assets	643	261
Fair Value Measurements, Recurring \| Forward Sale Contracts
LIABILITIES
Derivative financial liabilities	204	5
Fair Value Measurements, Recurring \| US Treasury Securities
ASSETS
Total securities available-for-sale	15,103	14,941
Fair Value Measurements, Recurring \| Obligations of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	262,265	263,303
Fair Value Measurements, Recurring \| Collateralized Mortgage Obligations of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	143,262	128,835
Fair Value Measurements, Recurring \| Residential Mortgage-Backed Securities of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	38,014	40,125
Fair Value Measurements, Recurring \| Commercial Mortgage-Backed Securities of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	81,668	69,204
Fair Value Measurements, Recurring \| Obligations of States and Political Subdivisions
ASSETS
Total securities available-for-sale	134,250	134,886
Fair Value Measurements, Recurring \| Marketable Equity Securities
ASSETS
Total securities available-for-sale	8,917	9,669
Fair Value Measurements, Recurring \| Level 1
ASSETS
Total securities available-for-sale	0	0
Trading securities held in a Rabbi Trust	4,196	4,021
Total securities	4,196	4,021
Total Assets	4,196	4,021
LIABILITIES
Total Liabilities	0	0
Fair Value Measurements, Recurring \| Level 1 \| Interest Rate Swaps
ASSETS
Derivative financial assets	0	0
LIABILITIES
Derivative financial liabilities	0	0
Fair Value Measurements, Recurring \| Level 1 \| Interest Rate Lock Commitments
ASSETS
Derivative financial assets	0	0
Fair Value Measurements, Recurring \| Level 1 \| Forward Sale Contracts
LIABILITIES
Derivative financial liabilities	0	0
Fair Value Measurements, Recurring \| Level 1 \| US Treasury Securities
ASSETS
Total securities available-for-sale	0	0
Fair Value Measurements, Recurring \| Level 1 \| Obligations of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	0	0
Fair Value Measurements, Recurring \| Level 1 \| Collateralized Mortgage Obligations of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	0	0
Fair Value Measurements, Recurring \| Level 1 \| Residential Mortgage-Backed Securities of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	0	0
Fair Value Measurements, Recurring \| Level 1 \| Commercial Mortgage-Backed Securities of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	0	0
Fair Value Measurements, Recurring \| Level 1 \| Obligations of States and Political Subdivisions
ASSETS
Total securities available-for-sale	0	0
Fair Value Measurements, Recurring \| Level 1 \| Marketable Equity Securities
ASSETS
Total securities available-for-sale	0	0
Fair Value Measurements, Recurring \| Level 2
ASSETS
Total securities available-for-sale	683,479	660,963
Trading securities held in a Rabbi Trust	0	0
Total securities	683,479	660,963
Total Assets	701,048	672,519
LIABILITIES
Total Liabilities	16,990	11,281
Fair Value Measurements, Recurring \| Level 2 \| Interest Rate Swaps
ASSETS
Derivative financial assets	16,926	11,295
LIABILITIES
Derivative financial liabilities	16,786	11,276
Fair Value Measurements, Recurring \| Level 2 \| Interest Rate Lock Commitments
ASSETS
Derivative financial assets	643	261
Fair Value Measurements, Recurring \| Level 2 \| Forward Sale Contracts
LIABILITIES
Derivative financial liabilities	204	5
Fair Value Measurements, Recurring \| Level 2 \| US Treasury Securities
ASSETS
Total securities available-for-sale	15,103	14,941
Fair Value Measurements, Recurring \| Level 2 \| Obligations of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	262,265	263,303
Fair Value Measurements, Recurring \| Level 2 \| Collateralized Mortgage Obligations of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	143,262	128,835
Fair Value Measurements, Recurring \| Level 2 \| Residential Mortgage-Backed Securities of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	38,014	40,125
Fair Value Measurements, Recurring \| Level 2 \| Commercial Mortgage-Backed Securities of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	81,668	69,204
Fair Value Measurements, Recurring \| Level 2 \| Obligations of States and Political Subdivisions
ASSETS
Total securities available-for-sale	134,250	134,886
Fair Value Measurements, Recurring \| Level 2 \| Marketable Equity Securities
ASSETS
Total securities available-for-sale	8,917	9,669
Fair Value Measurements, Recurring \| Level 3
ASSETS
Total securities available-for-sale	0	0
Trading securities held in a Rabbi Trust	0	0
Total securities	0	0
Total Assets	0	0
LIABILITIES
Total Liabilities	0	0
Fair Value Measurements, Recurring \| Level 3 \| Interest Rate Swaps
ASSETS
Derivative financial assets	0	0
LIABILITIES
Derivative financial liabilities	0	0
Fair Value Measurements, Recurring \| Level 3 \| Interest Rate Lock Commitments
ASSETS
Derivative financial assets	0	0
Fair Value Measurements, Recurring \| Level 3 \| Forward Sale Contracts
LIABILITIES
Derivative financial liabilities	0	0
Fair Value Measurements, Recurring \| Level 3 \| US Treasury Securities
ASSETS
Total securities available-for-sale	0	0
Fair Value Measurements, Recurring \| Level 3 \| Obligations of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	0	0
Fair Value Measurements, Recurring \| Level 3 \| Collateralized Mortgage Obligations of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	0	0
Fair Value Measurements, Recurring \| Level 3 \| Residential Mortgage-Backed Securities of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	0	0
Fair Value Measurements, Recurring \| Level 3 \| Commercial Mortgage-Backed Securities of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	0	0
Fair Value Measurements, Recurring \| Level 3 \| Obligations of States and Political Subdivisions
ASSETS
Total securities available-for-sale	0	0
Fair Value Measurements, Recurring \| Level 3 \| Marketable Equity Securities
ASSETS
Total securities available-for-sale	$ 0	$ 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 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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