LOANS - Narrative (Details) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2019 USD ($) modification	Sep. 30, 2019 USD ($) modification	Dec. 31, 2018 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying amount of acquired loans	$ 2,577,306	$ 2,577,306	$ 2,490,227
Borrower's sustained repayment performance period			6 months
Number of modifications which subsequently defaulted \| modification	0	0
Residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value of bank-owned residential real estate property	$ 2,500	$ 2,500	$ 2,500
Total residential loans included in held for sale loans	4,000	4,000	168
Residential mortgages \| Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Residential mortgage loans collateralized by real estate property in the process of foreclosure		931	1,500
Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying amount of acquired loans	749,170	749,170	859,330
Carrying value of purchased credit-impaired loans	8,400	8,400
Total note balances	11,500	11,500
Carrying amount of acquired loans considered not impaired at the acquisition date	740,800	740,800
Acquired Loans \| Residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying amount of acquired loans	$ 412,936	$ 412,936	$ 474,509

Represents the note balance amount of loans, considered impaired, at the time of acquisition.

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Represents the carrying amount of loans, not considered impaired, at the time of acquisition.

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Represents the reasonable period of a borrower's sustained repayment performance for consideration of returning the loan to performing status.

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The recorded balance, net of any applicable reductions (for example, unamortized accretable yield and allowance for loan losses). This relates to loans not accounted for debt securities with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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Number of financing receivable contracts modified as troubled debt restructuring within previous 12 months, with subsequent payment default.

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Carrying amount as of the balance sheet date of all assets obtained in full or partial satisfaction of a debt arrangement through foreclosure proceedings or defeasance; includes real and personal property; equity interests in corporations, partnerships, and joint ventures; and beneficial interests in trusts.

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Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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The face amount of loans that will be sold to other entities.

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The fair value of collateral received that was taken through foreclosure due to default by the original transferor in lieu of collection of the secured receivable.

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