Fair Value Measurement - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)	Sep. 30, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers between Level 1 to Level 2	$ 0
ASSETS
Total securities available-for-sale	671,128,000	$ 660,963,000
US Treasury Securities
ASSETS
Total securities available-for-sale	15,056,000	14,941,000
Obligations of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	250,924,000	263,303,000
Collateralized Mortgage Obligations of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	137,460,000	128,835,000
Residential Mortgage-Backed Securities of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	36,285,000	40,125,000
Commercial Mortgage-Backed Securities of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	88,499,000	69,204,000
Obligations of States and Political Subdivisions
ASSETS
Total securities available-for-sale	132,536,000	134,886,000
Marketable Equity Securities
ASSETS
Total securities available-for-sale	10,368,000	9,669,000
Fair Value Measurements, Recurring
ASSETS
Total securities available-for-sale	671,128,000	660,963,000
Trading securities held in a Rabbi Trust	4,312,000	4,021,000
Total securities	675,440,000	664,984,000
Total Assets	691,434,000	676,540,000
LIABILITIES
Total Liabilities	15,300,000	11,281,000
Fair Value Measurements, Recurring \| Interest Rate Swaps
ASSETS
Derivative financial assets	15,255,000	11,295,000
LIABILITIES
Derivative financial liabilities	15,202,000	11,276,000
Fair Value Measurements, Recurring \| Interest Rate Lock Commitments
ASSETS
Derivative financial assets	739,000	261,000
Fair Value Measurements, Recurring \| Forward Sale Contracts
LIABILITIES
Derivative financial liabilities	98,000	5,000
Fair Value Measurements, Recurring \| US Treasury Securities
ASSETS
Total securities available-for-sale	15,056,000	14,941,000
Fair Value Measurements, Recurring \| Obligations of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	250,924,000	263,303,000
Fair Value Measurements, Recurring \| Collateralized Mortgage Obligations of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	137,460,000	128,835,000
Fair Value Measurements, Recurring \| Residential Mortgage-Backed Securities of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	36,285,000	40,125,000
Fair Value Measurements, Recurring \| Commercial Mortgage-Backed Securities of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	88,499,000	69,204,000
Fair Value Measurements, Recurring \| Obligations of States and Political Subdivisions
ASSETS
Total securities available-for-sale	132,536,000	134,886,000
Fair Value Measurements, Recurring \| Marketable Equity Securities
ASSETS
Total securities available-for-sale	10,368,000	9,669,000
Fair Value Measurements, Recurring \| Level 1
ASSETS
Total securities available-for-sale	0	0
Trading securities held in a Rabbi Trust	4,312,000	4,021,000
Total securities	4,312,000	4,021,000
Total Assets	4,312,000	4,021,000
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	671,128,000	660,963,000
Trading securities held in a Rabbi Trust	0	0
Total securities	671,128,000	660,963,000
Total Assets	687,122,000	672,519,000
LIABILITIES
Total Liabilities	15,300,000	11,281,000
Fair Value Measurements, Recurring \| Level 2 \| Interest Rate Swaps
ASSETS
Derivative financial assets	15,255,000	11,295,000
LIABILITIES
Derivative financial liabilities	15,202,000	11,276,000
Fair Value Measurements, Recurring \| Level 2 \| Interest Rate Lock Commitments
ASSETS
Derivative financial assets	739,000	261,000
Fair Value Measurements, Recurring \| Level 2 \| Forward Sale Contracts
LIABILITIES
Derivative financial liabilities	98,000	5,000
Fair Value Measurements, Recurring \| Level 2 \| US Treasury Securities
ASSETS
Total securities available-for-sale	15,056,000	14,941,000
Fair Value Measurements, Recurring \| Level 2 \| Obligations of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	250,924,000	263,303,000
Fair Value Measurements, Recurring \| Level 2 \| Collateralized Mortgage Obligations of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	137,460,000	128,835,000
Fair Value Measurements, Recurring \| Level 2 \| Residential Mortgage-Backed Securities of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	36,285,000	40,125,000
Fair Value Measurements, Recurring \| Level 2 \| Commercial Mortgage-Backed Securities of U.S. Government Corporations and Agencies
ASSETS
Total securities available-for-sale	88,499,000	69,204,000
Fair Value Measurements, Recurring \| Level 2 \| Obligations of States and Political Subdivisions
ASSETS
Total securities available-for-sale	132,536,000	134,886,000
Fair Value Measurements, Recurring \| Level 2 \| Marketable Equity Securities
ASSETS
Total securities available-for-sale	10,368,000	9,669,000
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, 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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Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

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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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