LOANS - Investment Loan Activity (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Beginning balance	$ 4,585,975	[1]
Purchases	4,384,684
Sales and transfers	(3,768,246)
Principal payments	(726,064)
Gains / (losses)	(20,835)
(Amortization) / accretion	(6,836)
Ending balance, carrying value	669,713
Ending balance	4,462,350	[1]
Residential
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Beginning balance	1,359,806
Purchases	2,905,112
Sales and transfers	(2,417,798)
Principal payments	(190,336)
Gains / (losses)	(6,130)
(Amortization) / accretion	2,867
Ending balance	1,647,787
Commercial
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Beginning balance	1,338,987
Purchases	589,530
Sales and transfers	(1,085,230)
Principal payments	(166,801)
Gains / (losses)	(9,207)
(Amortization) / accretion	(2,434)
Ending balance	669,713
Corporate
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Beginning balance	1,887,182
Purchases	890,042
Sales and transfers	(265,218)
Principal payments	(368,927)
Gains / (losses)	(5,498)
(Amortization) / accretion	(7,269)
Ending balance	$ 2,144,850

[1] Includes $66.7 million and $97.5 million of residential mortgage loans held for sale and $0 and $42.2 million of commercial mortgage loans held for sale at December 31, 2019 and 2018, respectively.