OFFSETTING ASSETS AND LIABILITIES - Offsetting of Assets (Details) - USD ($)	Mar. 31, 2019	Dec. 31, 2018
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 13,199,000	$ 16,885,000
Gross Amount Of Assets Offset In The Balance Sheet	0	0
Net Amount Of Assets Presented In The Balance Sheet	13,199,000	16,885,000
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	(14,431,000)
Net Amount Of Assets	13,199,000	2,454,000
Swap [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	13,146,000	16,762,000
Gross Amount Of Assets Offset In The Balance Sheet	0	0
Net Amount Of Assets Presented In The Balance Sheet	13,146,000	16,762,000
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	(14,308,000)
Net Amount Of Assets	13,146,000	2,454,000
TBA securities [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	0
Gross Amount Of Assets Offset In The Balance Sheet	0	0
Net Amount Of Assets Presented In The Balance Sheet	0	0
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	0	0
Payer Swaption [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	53,000	123,000
Gross Amount Of Assets Offset In The Balance Sheet	0	0
Net Amount Of Assets Presented In The Balance Sheet	53,000	123,000
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	(123,000)
Net Amount Of Assets	$ 53,000	$ 0