Investment Securities - Amortized Cost and Fair Value of Securities Available for Sale (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 745,328	$ 692,824
Gross Unrealized Gains	805	1,316
Gross Unrealized Losses	(8,691)	(4,938)
Fair Value	737,442	689,202
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	200,026	200,077
Gross Unrealized Gains	0	11
Gross Unrealized Losses	(13)	0
Fair Value	200,013	200,088
Obligations of the U.S. government and agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	198,604	153,028
Gross Unrealized Gains	107	75
Gross Unrealized Losses	(2,856)	(2,059)
Fair Value	195,855	151,044
Obligations of state and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	11,372	21,352
Gross Unrealized Gains	3	11
Gross Unrealized Losses	(43)	(53)
Fair Value	11,332	21,310
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	294,076	275,958
Gross Unrealized Gains	554	887
Gross Unrealized Losses	(4,740)	(1,855)
Fair Value	289,890	274,990
Collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	40,150	37,596
Gross Unrealized Gains	141	14
Gross Unrealized Losses	(1,039)	(948)
Fair Value	39,252	36,662
Other investment securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,100	4,813
Gross Unrealized Gains	0	318
Gross Unrealized Losses	0	(23)
Fair Value	$ 1,100	$ 5,108

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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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
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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 security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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-Publisher FASB
-Name Accounting Standards Codification
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