REAL ESTATE AND OTHER SECURITIES - Summary of Real Estate Securities in an Unrealized Loss Position (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2021 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Outstanding Face Amount	$ 30,726,412
Weighted Average Life (Years)	10 months 24 days
Less than 12 Months
Debt Securities, Available-for-sale [Line Items]
Outstanding Face Amount	$ 2,455
Before Credit Impairment - Amortized Cost Basis	651
Credit Impairment - Amortized Cost Basis	(195)
After Credit Impairment - Amortized Cost Basis	456
Gross Unrealized Losses - Less than 12 Months	(12)
Carrying Value - Less than 12 Months	$ 444
Number of Securities - Less than 12 Months | security	4
Weighted Average Rating	AAA
Weighted Average Coupon	0.80%
Weighted Average Yield	1.90%
Weighted Average Life (Years)	2 years 9 months 18 days
12 or More Months
Debt Securities, Available-for-sale [Line Items]
Outstanding Face Amount	$ 40,682
Before Credit Impairment - Amortized Cost Basis	33,009
Credit Impairment - Amortized Cost Basis	(5,827)
After Credit Impairment - Amortized Cost Basis	27,182
Gross Unrealized Losses - 12 or More Months	(1,038)
Carrying Value - 12 or More Months	$ 26,144
Number of Securities - 12 or More Months | security	18
Weighted Average Rating	AA+
Weighted Average Coupon	2.50%
Weighted Average Yield	1.00%
Weighted Average Life (Years)	2 years 8 months 12 days
Total/Weighted Average
Debt Securities, Available-for-sale [Line Items]
Outstanding Face Amount	$ 43,137
Before Credit Impairment - Amortized Cost Basis	33,660
Credit Impairment - Amortized Cost Basis	(6,022)
After Credit Impairment - Amortized Cost Basis	27,638
Gross Unrealized Losses - Total	(1,050)
Carrying Value - Total	$ 26,588
Number of Securities - Total | security	22
Weighted Average Rating	AAA
Weighted Average Coupon	2.40%
Weighted Average Yield	1.00%
Weighted Average Life (Years)	2 years 8 months 12 days