Investment Securities - Summary of Unrealized Losses of Available-for-Sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Securities with losses under 12 months, fair value	$ 105,560	$ 93,037
Securities with losses under 12 months, gross unrealized loss	1,329	826
Securities with losses over 12 months, fair value	191,796	158,412
Securities with losses over 12 months, gross unrealized loss	9,834	4,528
Fair Value	297,356	251,449
Unrealized Loss	11,163	5,354
Obligations of state and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Securities with losses under 12 months, fair value	5,948	596
Securities with losses under 12 months, gross unrealized loss	44	5
Securities with losses over 12 months, fair value	12,714	12,716
Securities with losses over 12 months, gross unrealized loss	999	437
Fair Value	18,662	13,312
Unrealized Loss	1,043	442
Mutual funds
Debt Securities, Available-for-sale [Line Items]
Securities with losses under 12 months, fair value		2,061
Securities with losses under 12 months, gross unrealized loss		39
Securities with losses over 12 months, fair value		0
Securities with losses over 12 months, gross unrealized loss		0
Fair Value		2,061
Unrealized Loss		39
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Securities with losses under 12 months, fair value	2,908	2,990
Securities with losses under 12 months, gross unrealized loss	92	10
Securities with losses over 12 months, fair value	0	0
Securities with losses over 12 months, gross unrealized loss	0	0
Fair Value	2,908	2,990
Unrealized Loss	92	10
Collateralized Mortgage Backed Securities
Debt Securities, Available-for-sale [Line Items]
Securities with losses under 12 months, fair value	96,704	87,390
Securities with losses under 12 months, gross unrealized loss	1,193	772
Securities with losses over 12 months, fair value	179,082	145,696
Securities with losses over 12 months, gross unrealized loss	8,835	4,091
Fair Value	275,786	233,086
Unrealized Loss	$ 10,028	$ 4,863

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563

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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer.

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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), in unrealized loss position.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 6
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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-SubTopic 10
-Section 50
-Paragraph 6
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