LOANS - Investment Loan Activity (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2022 USD ($)
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Beginning balance January 1, 2022	$ 4,242,043	[1],[2]
Ending balance March 31, 2022	3,617,818	[2]
Transfer of residential loans to securitization vehicles, carrying value, noncash	2,500,000
Total
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Beginning balance January 1, 2022	4,241,063
Purchases / originations	2,197,627
Sales and transfers	(2,550,155)
Principal payments	(208,522)
Gains / (losses)	(61,262)
(Amortization) / accretion	(933)
Ending balance March 31, 2022	3,617,818
Residential
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Beginning balance January 1, 2022	2,272,072
Purchases / originations	2,025,930
Sales and transfers	(2,550,155)
Principal payments	(34,284)
Gains / (losses)	(60,654)
(Amortization) / accretion	(2,758)
Ending balance March 31, 2022	1,650,151
Corporate Debt
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Beginning balance January 1, 2022	1,968,991
Purchases / originations	171,697
Sales and transfers	0
Principal payments	(174,238)
Gains / (losses)	(608)
(Amortization) / accretion	1,825
Ending balance March 31, 2022	$ 1,967,667

[1] (1)Derived from the audited consolidated financial statements at December 31, 2021.

[2] (4)Includes $1.9 million and $2.3 million of residential mortgage loans held for sale at March 31, 2022 and December 31, 2021, respectively.