INVESTMENTS IN REAL ESTATE AND OTHER SECURITIES - Summary of the Geographic Distribution of the Collateral Securing Non-Agency RMBS (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Non-Agency
Debt Securities, Available-for-sale [Line Items]
Outstanding Face Amount	$ 22,993,294	$ 24,747,959
Percentage of Total Outstanding	100.00%	100.00%
Non-Agency | Western U.S.
Debt Securities, Available-for-sale [Line Items]
Outstanding Face Amount	$ 8,023,586	$ 9,048,847
Percentage of Total Outstanding	34.90%	36.60%
Non-Agency | Southeastern U.S.
Debt Securities, Available-for-sale [Line Items]
Outstanding Face Amount	$ 6,001,777	$ 5,983,966
Percentage of Total Outstanding	26.10%	24.20%
Non-Agency | Northeastern U.S.
Debt Securities, Available-for-sale [Line Items]
Outstanding Face Amount	$ 5,204,930	$ 5,416,137
Percentage of Total Outstanding	22.60%	21.90%
Non-Agency | Midwestern U.S.
Debt Securities, Available-for-sale [Line Items]
Outstanding Face Amount	$ 2,527,550	$ 2,562,269
Percentage of Total Outstanding	11.00%	10.40%
Non-Agency | Southwestern U.S.
Debt Securities, Available-for-sale [Line Items]
Outstanding Face Amount	$ 1,222,822	$ 1,440,467
Percentage of Total Outstanding	5.30%	5.80%
Non-Agency | Other U.S.
Debt Securities, Available-for-sale [Line Items]
Outstanding Face Amount	$ 12,629	$ 296,273
Percentage of Total Outstanding	0.10%	1.10%
Consumer Loan | Bonds
Debt Securities, Available-for-sale [Line Items]
Face amount of investment	$ 16,400	$ 25,000
Corporate Loan | Bonds
Debt Securities, Available-for-sale [Line Items]
Face amount of investment	$ 10,300	$ 85,000