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Securities - Additional Information (Details) $ in Thousands		Mar. 31, 2018 USD ($) security	Jan. 01, 2018 USD ($)	Dec. 31, 2017 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Number of debt securities in unrealized loss position | security		71		51
Securities pledged for regulatory and legal requirements		$ 221,000		$ 249,000
Accounting Standards Update 2016-01 | AOCI
Schedule of Available-for-sale Securities [Line Items]
Net unrealized gains and losses, net of tax, reclassified from AOCI to retained earnings on marketable equity securities	[1]		$ (862)
Accounting Standards Update 2016-01 | Retained Earnings
Schedule of Available-for-sale Securities [Line Items]
Net unrealized gains and losses, net of tax, reclassified from AOCI to retained earnings on marketable equity securities	[1]		$ 862
[1] Reclassification due to the adoption of ASU No. 2016-01

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(i)
-URI http://asc.fasb.org/extlink&oid=64858031&loc=SL6224234-111729

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