Securities (Additional Information) (Details) $ in Thousands	12 Months Ended
Dec. 31, 2009 USD ($)	Mar. 31, 2018 USD ($) investment	Dec. 31, 2017 USD ($) investment
Schedule of Available-for-sale Securities [Line Items]
Carrying value of securities pledged to secure repurchase agreements, public and trust deposits and other by law		$ 226,893	$ 165,404
Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Number of non-controlling investments in a single banking organization \| investment		1	1
Original amount in non-controlling investment security in a single banking organization	$ 1,350
Other than temporary impairment loss recognized in earnings, non-controlling investment in single banking organization	$ 997

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- Definition

Amount of equity securities categorized neither as held-to-maturity nor as trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
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-Name Accounting Standards Codification
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-Section 45
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-Publisher FASB
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-Section 50
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-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=75019621&loc=d3e62557-112803

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- Definition

Carrying value of securities sold under agreements to repurchase and deposits received for securities loaned.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.13(1))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
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- Definition

The amount of other than temporary impairment losses on investments in debt and equity securities categorized as Available-for-sale which have been recognized in earnings during the period. Such impairment losses consist of other than temporary impairments (OTTI) on equity securities, credit losses on investments in debt securities, and when the entity intends to sell an impaired debt security or it is more likely than not that the entity will be required to sell the impaired debt security before recovery of its amortized cost basis.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Topic 320
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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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