SECURITIES - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Other than Temporary Impairment Losses, Investments [Abstract]
Guaranteed portion of student loan backed bonds			student loan backed bonds which are guaranteed by the U.S. Department of Education for 97% to 100% of principal.
Credit support for student loan backed bonds description			the bonds have credit support of 3% to 5%
Proceeds from sales of securities available for sale	$ 0		$ 230,372	$ 26,685
Securities gross losses realized		$ 260	(7,921)	260
Proceeds from calls of securities		$ 0	900	$ 0
Fair value of securities pledged to secure public deposits and FHLB and FRB overnight borrowings	317,100		317,100		$ 513,500
Amount owned in FHLB, ACBB and FRB stock	$ 25,162		$ 25,162		$ 35,349

Represents description of credit support for student loan backed bonds.

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Represents description of guaranteed portion of student loan backed bonds.

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Amount of unrealized and realized gain (loss) on investment in debt and equity securities.

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Cash received from maturities, prepayments and calls of trading securities and other securities, classified as operating.

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Amount of cash inflow from sale of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Investments which are not defined as or included in marketable (debt, equity, or other) securities whose use is restricted in whole or in part, generally by contractual agreements or regulatory requirements. For use in an unclassified balance sheet.

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Fair value of financial instrument held by the entity for its own account (proprietary securities) for trading or investment purposes that are carried at fair value and pledged to counterparties as collateral for financing transactions.

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