REAL ESTATE SECURITIES - Securities by Remaining Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Within 1 year	$ 305,980	$ 232,681
1-5 years	369,876	801,978
5-10 years	10,486	23,659
After 10 years	16,958	0
Total	703,280	1,058,298
Allowance for current expected credit losses	(20)	(20)
CMBS
Debt Securities, Available-for-sale [Line Items]
Within 1 year	304,357	230,977
1-5 years	354,670	748,953
5-10 years	10,307	23,371
After 10 years	16,958	0
Total	686,292	1,003,301
CMBS interest-only
Debt Securities, Available-for-sale [Line Items]
Within 1 year	1,018	1,572
1-5 years	14,868	20,641
5-10 years	0	0
After 10 years	0	0
Total	15,886	22,213
GNMA interest-only
Debt Securities, Available-for-sale [Line Items]
Within 1 year	102	65
1-5 years	278	647
5-10 years	179	288
After 10 years	0	0
Total	559	1,000
Agency securities
Debt Securities, Available-for-sale [Line Items]
Within 1 year	503	0
1-5 years	60	605
5-10 years	0	0
After 10 years	0	0
Total	$ 563	605
GNMA permanent securities
Debt Securities, Available-for-sale [Line Items]
Within 1 year		67
1-5 years		31,132
5-10 years		0
After 10 years		0
Total		$ 31,199