LOANS - Investment Loan Activity (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($)
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Beginning balance	$ 4,462,350	[1],[2]
Impact of adopting CECL	(33,253)
Purchases / originations	1,203,394
Sales and transfers	(1,294,348)
Principal payments	(134,622)
Gains / (losses) (2)	(136,583)
(Amortization) / accretion	1,251
Ending balance	4,068,189	[2]
Residential
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Beginning balance	1,647,787
Impact of adopting CECL	0
Purchases / originations	642,795
Sales and transfers	(922,773)
Principal payments	(41,732)
Gains / (losses) (2)	(56,082)
(Amortization) / accretion	(1,912)
Ending balance	1,268,083
Commercial
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Beginning balance	669,713
Impact of adopting CECL	(3,600)
Purchases / originations	173,517
Sales and transfers	(95,730)
Principal payments	(38,425)
Gains / (losses) (2)	(56,475)
(Amortization) / accretion	843
Ending balance	649,843
Corporate Debt
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Beginning balance	2,144,850
Impact of adopting CECL	(29,653)
Purchases / originations	387,082
Sales and transfers	(275,845)
Principal payments	(54,465)
Gains / (losses) (2)	(24,026)
(Amortization) / accretion	2,320
Ending balance	$ 2,150,263

[1] Derived from the audited consolidated financial statements at December 31, 2019.

[2] Includes $57.8 million and $66.7 million of residential mortgage loans held for sale at March 31, 2020 and December 31, 2019, respectively.