Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($)	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers between Level 1 to Level 2	$ 0	$ 0
ASSETS
Debt securities available-for-sale	675,922,000	680,056,000
Marketable equity securities	4,498,000	4,816,000
U.S. Treasury securities
ASSETS
Debt securities available-for-sale	9,837,000	9,736,000
Obligations of U.S. government corporations and agencies
ASSETS
Debt securities available-for-sale	129,369,000	128,261,000
Collateralized mortgage obligations of U.S. government corporations and agencies
ASSETS
Debt securities available-for-sale	154,159,000	148,659,000
Residential mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Debt securities available-for-sale	22,514,000	24,350,000
Commercial mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Debt securities available-for-sale	237,554,000	246,784,000
Obligations of states and political subdivisions
ASSETS
Debt securities available-for-sale	122,489,000	122,266,000
Fair Value Measurements, Recurring
ASSETS
Debt securities available-for-sale	675,922,000	680,056,000
Marketable equity securities	4,498,000	4,816,000
Total securities	680,420,000	684,872,000
Securities held in a deferred compensation plan	5,343,000	4,725,000
Total Assets	696,835,000	695,407,000
LIABILITIES
Total Liabilities	10,602,000	5,340,000
Fair Value Measurements, Recurring \| U.S. Treasury securities
ASSETS
Debt securities available-for-sale	9,837,000	9,736,000
Fair Value Measurements, Recurring \| Obligations of U.S. government corporations and agencies
ASSETS
Debt securities available-for-sale	129,369,000	128,261,000
Fair Value Measurements, Recurring \| Collateralized mortgage obligations of U.S. government corporations and agencies
ASSETS
Debt securities available-for-sale	154,159,000	148,659,000
Fair Value Measurements, Recurring \| Residential mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Debt securities available-for-sale	22,514,000	24,350,000
Fair Value Measurements, Recurring \| Commercial mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Debt securities available-for-sale	237,554,000	246,784,000
Fair Value Measurements, Recurring \| Obligations of states and political subdivisions
ASSETS
Debt securities available-for-sale	122,489,000	122,266,000
Fair Value Measurements, Recurring \| Interest rate swaps
ASSETS
Derivative financial assets	10,645,000	5,504,000
LIABILITIES
Interest rate swaps	10,602,000	5,340,000
Fair Value Measurements, Recurring \| Interest rate lock commitments
ASSETS
Derivative financial assets	339,000	251,000
Fair Value Measurements, Recurring \| Forward sale contracts—mortgage loans
ASSETS
Derivative financial assets	88,000	55,000
Fair Value Measurements, Recurring \| Level 1
ASSETS
Debt securities available-for-sale	0	0
Marketable equity securities	0	0
Total securities	0	0
Securities held in a deferred compensation plan	5,343,000	4,725,000
Total Assets	5,343,000	4,725,000
LIABILITIES
Total Liabilities	0	0
Fair Value Measurements, Recurring \| Level 1 \| U.S. Treasury securities
ASSETS
Debt securities available-for-sale	0	0
Fair Value Measurements, Recurring \| Level 1 \| Obligations of U.S. government corporations and agencies
ASSETS
Debt securities available-for-sale	0	0
Fair Value Measurements, Recurring \| Level 1 \| Collateralized mortgage obligations of U.S. government corporations and agencies
ASSETS
Debt securities available-for-sale	0	0
Fair Value Measurements, Recurring \| Level 1 \| Residential mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Debt securities available-for-sale	0	0
Fair Value Measurements, Recurring \| Level 1 \| Commercial mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Debt securities available-for-sale	0	0
Fair Value Measurements, Recurring \| Level 1 \| Obligations of states and political subdivisions
ASSETS
Debt securities available-for-sale	0	0
Fair Value Measurements, Recurring \| Level 1 \| Interest rate swaps
ASSETS
Derivative financial assets	0	0
LIABILITIES
Interest rate swaps	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—mortgage loans
ASSETS
Derivative financial assets	0	0
Fair Value Measurements, Recurring \| Level 2
ASSETS
Debt securities available-for-sale	675,922,000	680,056,000
Marketable equity securities	4,498,000	4,816,000
Total securities	680,420,000	684,872,000
Securities held in a deferred compensation plan	0	0
Total Assets	691,492,000	690,682,000
LIABILITIES
Total Liabilities	10,602,000	5,340,000
Fair Value Measurements, Recurring \| Level 2 \| U.S. Treasury securities
ASSETS
Debt securities available-for-sale	9,837,000	9,736,000
Fair Value Measurements, Recurring \| Level 2 \| Obligations of U.S. government corporations and agencies
ASSETS
Debt securities available-for-sale	129,369,000	128,261,000
Fair Value Measurements, Recurring \| Level 2 \| Collateralized mortgage obligations of U.S. government corporations and agencies
ASSETS
Debt securities available-for-sale	154,159,000	148,659,000
Fair Value Measurements, Recurring \| Level 2 \| Residential mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Debt securities available-for-sale	22,514,000	24,350,000
Fair Value Measurements, Recurring \| Level 2 \| Commercial mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Debt securities available-for-sale	237,554,000	246,784,000
Fair Value Measurements, Recurring \| Level 2 \| Obligations of states and political subdivisions
ASSETS
Debt securities available-for-sale	122,489,000	122,266,000
Fair Value Measurements, Recurring \| Level 2 \| Interest rate swaps
ASSETS
Derivative financial assets	10,645,000	5,504,000
LIABILITIES
Interest rate swaps	10,602,000	5,340,000
Fair Value Measurements, Recurring \| Level 2 \| Interest rate lock commitments
ASSETS
Derivative financial assets		251,000
Fair Value Measurements, Recurring \| Level 2 \| Forward sale contracts—mortgage loans
ASSETS
Derivative financial assets		55,000
Fair Value Measurements, Recurring \| Level 3
ASSETS
Debt securities available-for-sale	0	0
Marketable equity securities	0	0
Total securities	0	0
Securities held in a deferred compensation plan	0	0
Total Assets	0	0
LIABILITIES
Total Liabilities	0	0
Fair Value Measurements, Recurring \| Level 3 \| U.S. Treasury securities
ASSETS
Debt securities available-for-sale	0	0
Fair Value Measurements, Recurring \| Level 3 \| Obligations of U.S. government corporations and agencies
ASSETS
Debt securities available-for-sale	0	0
Fair Value Measurements, Recurring \| Level 3 \| Collateralized mortgage obligations of U.S. government corporations and agencies
ASSETS
Debt securities available-for-sale	0	0
Fair Value Measurements, Recurring \| Level 3 \| Residential mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Debt securities available-for-sale	0	0
Fair Value Measurements, Recurring \| Level 3 \| Commercial mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Debt securities available-for-sale	0	0
Fair Value Measurements, Recurring \| Level 3 \| Obligations of states and political subdivisions
ASSETS
Debt securities available-for-sale	0	0
Fair Value Measurements, Recurring \| Level 3 \| Interest rate swaps
ASSETS
Derivative financial assets	0	0
LIABILITIES
Interest rate swaps	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—mortgage loans
ASSETS
Derivative financial assets	$ 0	$ 0

Assets Held-in-Trust, Fair Value Disclosure

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- Definition

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 security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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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 investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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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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