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Cash deposited in a special reserve account for the exclusive benefit of customers pursuant to SEC Regulations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 305
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6478312&loc=d3e61473-112792

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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Reserve requirements of vault cash and/or deposits, included in cash and equivalents		$ 12,700	$ 595
Forecast
Property, Plant and Equipment [Line Items]
Decrease to accumulated comprehensive income after adoption of ASU 2018-02	$ 1,000
Premises \| Minimum
Property, Plant and Equipment [Line Items]
Estimated useful live of premises and equipment		25 years
Premises \| Maximum
Property, Plant and Equipment [Line Items]
Estimated useful live of premises and equipment		40 years
Furniture and equipment \| Minimum
Property, Plant and Equipment [Line Items]
Estimated useful live of premises and equipment		3 years
Furniture and equipment \| Maximum
Property, Plant and Equipment [Line Items]
Estimated useful live of premises and equipment		7 years