OFFSETTING ASSETS AND LIABILITIES - Offsetting of Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 17,160	$ 10,365
Gross Amount Of Assets Offset In The Balance Sheet	0	0
Net Amount Of Assets Presented In The Balance Sheet	17,160	10,365
Gross Amounts Of Financial Instruments Received Not Offset In Balance Sheet	0	0
Gross Amounts Of Cash Collateral Received Not Offset In Balance Sheet	(3,415)	(63)
Net Amount Of Assets	13,745	10,302
Swap [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	13,745	10,302
Gross Amount Of Assets Offset In The Balance Sheet	0	0
Net Amount Of Assets Presented In The Balance Sheet	13,745	10,302
Gross Amounts Of Financial Instruments Received Not Offset In Balance Sheet	0	0
Gross Amounts Of Cash Collateral Received Not Offset In Balance Sheet	0	0
Net Amount Of Assets	13,745	10,302
TBA securities [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	10	63
Gross Amount Of Assets Offset In The Balance Sheet	0	0
Net Amount Of Assets Presented In The Balance Sheet	10	63
Gross Amounts Of Financial Instruments Received Not Offset In Balance Sheet	0	0
Gross Amounts Of Cash Collateral Received Not Offset In Balance Sheet	(10)	(63)
Net Amount Of Assets	0	$ 0
Payer Swaption [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	3,405
Gross Amount Of Assets Offset In The Balance Sheet	0
Net Amount Of Assets Presented In The Balance Sheet	3,405
Gross Amounts Of Financial Instruments Received Not Offset In Balance Sheet	0
Gross Amounts Of Cash Collateral Received Not Offset In Balance Sheet	(3,405)
Net Amount Of Assets	$ 0