INVESTMENT SECURITIES - ROLLFORWARD OF CREDIT LOSSES (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Bank's private label mortgage backed security credit losses recognized in earnings
Available-for-sale Securities, Debt Securities	$ 417,983	$ 524,303
Number of securities held	182	185
Private label mortgage backed security
Bank's private label mortgage backed security credit losses recognized in earnings
Available-for-sale Securities, Debt Securities	$ 4,120	$ 4,449
Number of securities held	1

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

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)
-URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 320
-Section 50
-Paragraph 2
-Subparagraph (b)-(g)
-URI http://asc.fasb.org/extlink&oid=75019621&loc=d3e62557-112803

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Balance Type:	debit
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