Investment Securities - Amortized Cost and Estimated Fair Value of Available for Sale Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Debt Securities, Available-for-sale [Line Items]
Other equity securities	$ 2,978	$ 3,414	$ 3,327
Securities available for sale, Amortized Cost	314,219
Securities available for sale, Unrealized Gains	144
Securities available for sale, Unrealized Losses	(9,315)
Securities available for sale	305,048
Amortized Cost		303,845	309,046
Unrealized Gains		859	1,932
Unrealized Losses		(4,532)	(2,832)
Fair Value (Estimated)		300,172	308,146
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	306,286
Unrealized Gains	144
Unrealized Losses	(9,052)
Fair Value (Estimated)	297,378
Amortized Cost		293,689	290,379
Unrealized Gains		722	1,381
Unrealized Losses		(4,422)	(2,769)
Fair Value (Estimated)		289,989	288,991
State and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,955
Unrealized Gains	0
Unrealized Losses	(263)
Fair Value (Estimated)	$ 4,692
Amortized Cost		6,860	15,401
Unrealized Gains		16	486
Unrealized Losses		(107)	(59)
Fair Value (Estimated)		6,769	15,828
Other equity securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		3,296	3,266
Unrealized Gains		121	65
Unrealized Losses		(3)	(4)
Fair Value (Estimated)		$ 3,414	$ 3,327

Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax and Equity Securities

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Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax and Equity Securities

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Debt Securities, Available-for-sale, Amortized Cost and Equity Securities

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Debt Securities, Available-for-sale and Equity Securities

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on 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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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on 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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Amortized cost 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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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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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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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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