DERIVATIVE FINANCIAL INSTRUMENTS - Schedule of Derivative Assets and Liabilties (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020
Derivative [Line Items]
Assets, at Fair Value	$ 47,383,000	$ 20,999,000
Liabilities, at Fair Value	10,288,000	33,227,000
Restricted cash	51,111,000	79,363,000
Other Liabilities	30,058,000	7,188,000
U.S. Treasury Notes	37,409,000	0
Not Designated as Hedging Instrument, Economic Hedge [Member]
Derivative [Line Items]
Assets, at Fair Value	47,383,000	20,999,000
Liabilities, at Fair Value	10,288,000	33,227,000
Restricted cash	19,736,000	14,451,000
Interest Rate Swap [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member]
Derivative [Line Items]
Assets, at Fair Value	16,972,000	7,000
Liabilities, at Fair Value	2,225,000	24,711,000
Restricted cash	0	19,761,000
U.S. Treasury Notes	29,927,000	0
TBA Contracts [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member]
Derivative [Line Items]
Assets, at Fair Value	0	3,559,000
Liabilities, at Fair Value	0	786,000
Restricted cash	0	284,000
Other Liabilities	0	2,520,000
Eurodollar Future Margin [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member]
Derivative [Line Items]
Restricted cash	2,475,000	489,000
Payer Swaption [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member]
Derivative [Line Items]
Restricted cash	1,099,000	0
Other Liabilities	13,765,000	3,563,000
Payer Swaption [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member] | Short [Member]
Derivative [Line Items]
Liabilities, at Fair Value	8,063,000	7,730,000
Payer Swaption [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member] | Long [Member]
Derivative [Line Items]
Assets, at Fair Value	28,051,000	17,433,000
Interest Rate Floor [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member]
Derivative [Line Items]
Assets, at Fair Value	$ 2,360,000	$ 0