DERIVATIVE FINANCIAL INSTRUMENTS - TBA positions (Details) - USD ($)	Jun. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Assets, at Fair Value	$ 34,207,000	$ 17,160,000
Liabilities, at Fair Value	2,240,000	2,038,000
30 Year [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	(400,000,000)	(300,444,000)
Cost Basis	(390,384,000)	(292,403,000)
Market Value Of TBA Contract	(392,624,000)	(294,216,000)
Liabilities, at Fair Value	(392,624,000)	(1,813,000)
30 Year [Member] | 3% [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	(200,000,000)	(300,000,000)
Cost Basis	(192,404,000)	(299,371,000)
Market Value Of TBA Contract	(193,624,000)	(300,153,000)
Liabilities, at Fair Value	(1,220,000)	(782,000)
30 Year [Member] | 3.5% [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	(200,000,000)
Cost Basis	(197,980,000)
Market Value Of TBA Contract	(199,000,000)
Liabilities, at Fair Value	$ (1,020,000)
30 Year [Member] | 4.0% [Member]
Derivatives, Fair Value [Line Items]
Notional Amount		(357,000,000)
Cost Basis		(373,403,000)
Market Value Of TBA Contract		(373,477,000)
Liabilities, at Fair Value		(74,000)
30 Year [Member] | 4.5% [Member] | Long [Member]
Derivatives, Fair Value [Line Items]
Notional Amount		356,556,000
Cost Basis		380,371,000
Market Value Of TBA Contract		379,414,000
Liabilities, at Fair Value		$ (957,000)