DERIVATIVE FINANCIAL INSTRUMENTS - Effect on the consolidated statements of operations (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Derivatives, Fair Value [Line Items]
(Losses) gains on derivative instruments	$ (82,858,000)	$ (19,032,000)
Eurodollar Future [Member]
Derivatives, Fair Value [Line Items]
(Losses) gains on derivative instruments	(8,217,000)	(10,041,000)
Treasury Note Future [Member]
Derivatives, Fair Value [Line Items]
(Losses) gains on derivative instruments	(4,339,000)	(1,677,000)
Swap [Member]
Derivatives, Fair Value [Line Items]
(Losses) gains on derivative instruments	(60,623,000)	(2,295,000)
Payer Swaption [Member]
Derivatives, Fair Value [Line Items]
(Losses) gains on derivative instruments	(2,589,000)	(378,000)
TBA Contracts [Member]
Derivatives, Fair Value [Line Items]
(Losses) gains on derivative instruments	$ (7,090,000)	$ (4,641,000)