Investment Securities - Amortized Cost and Fair Value of Securities Available for Sale (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 543,314	$ 692,824
Gross Unrealized Gains	464	1,316
Gross Unrealized Losses	(12,703)	(4,938)
Fair Value	531,075	689,202
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	100	200,077
Gross Unrealized Gains	0	11
Gross Unrealized Losses	0	0
Fair Value	100	200,088
Obligations of the U.S. government and agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	187,850	153,028
Gross Unrealized Gains	21	75
Gross Unrealized Losses	(4,615)	(2,059)
Fair Value	183,256	151,044
Obligations of state and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	17,483	21,352
Gross Unrealized Gains	11	11
Gross Unrealized Losses	(69)	(53)
Fair Value	17,425	21,310
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	298,704	275,958
Gross Unrealized Gains	416	887
Gross Unrealized Losses	(6,557)	(1,855)
Fair Value	292,563	274,990
Collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	38,077	37,596
Gross Unrealized Gains	16	14
Gross Unrealized Losses	(1,459)	(948)
Fair Value	36,634	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	(3)	(23)
Fair Value	$ 1,097	$ 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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