OFF-BALANCE-SHEET ARRANGEMENTS, COMMITMENTS AND CONTINGENCIES - Narrative (Details) ft² in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) ft²	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jan. 01, 2019 USD ($)
Long-term Purchase Commitment [Line Items]
Number of square feet in building acquired | ft²	202
Number of square feet occupied | ft²	41
Lease revenue	$ 3,000,000	$ 3,100,000	$ 3,100,000
Securities
Unsettled trades to purchase securities	6,378,000	0	160,000
Unsettled trades to sell securities	0	0
Deposits [Abstract]
Unsettled issuances of brokered certificates of deposit	15,236,000	0	0
Land, Buildings and Improvements
Long-term Purchase Commitment [Line Items]
Rent expense	1,800,000	1,700,000	3,900,000
Office Equipment
Long-term Purchase Commitment [Line Items]
Rent expense	$ 160,000	$ 178,000	$ 261,000
Subsequent Event | Accounting Standards Update 2016-02
Long-term Purchase Commitment [Line Items]
Increase in Operating Liabilities				$ 10,100,000
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability				$ 9,800,000