OFFSETTING ASSETS AND LIABILITIES - Offsetting of Assets (Details) - USD ($)	Jun. 30, 2018	Dec. 31, 2017
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 34,207,000	$ 17,160,000
Gross Amount Of Assets Offset In The Balance Sheet	0	0
Net Amount Of Assets Presented In The Balance Sheet	34,207,000	17,160,000
Gross Amounts Of Financial Instruments Received Not Offset In Balance Sheet	0	0
Gross Amounts Of Cash Collateral Received Not Offset In Balance Sheet	(7,873,000)	(3,415,000)
Net Amount Of Assets	26,334,000	13,745,000
Swap [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	26,334,000	13,745,000
Gross Amount Of Assets Offset In The Balance Sheet	0	0
Net Amount Of Assets Presented In The Balance Sheet	26,334,000	13,745,000
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	26,334,000	13,745,000
TBA securities [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	10,000
Gross Amount Of Assets Offset In The Balance Sheet	0	0
Net Amount Of Assets Presented In The Balance Sheet	0	10,000
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	(10,000)
Net Amount Of Assets	0	0
Payer Swaption [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	7,873,000	3,405,000
Gross Amount Of Assets Offset In The Balance Sheet	0	0
Net Amount Of Assets Presented In The Balance Sheet	7,873,000	3,405,000
Gross Amounts Of Financial Instruments Received Not Offset In Balance Sheet	0	0
Gross Amounts Of Cash Collateral Received Not Offset In Balance Sheet	(7,873,000)	(3,405,000)
Net Amount Of Assets	$ 0	$ 0