LOANS - Investment Loan Activity (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($)
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Beginning balance	$ 4,585,975	[1],[2]
Purchases	2,920,426
Sales and transfers	(3,105,533)
Principal payments	(456,300)
Gains / (losses)	(2,276)
(Amortization) / accretion	4,322
Ending balance	3,946,614	[2]
Residential
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Beginning balance	1,359,806
Purchases	1,894,303
Sales and transfers	(1,878,218)
Principal payments	(156,579)
Gains / (losses)	1,671
(Amortization) / accretion	(1,581)
Ending balance	1,219,402
Commercial
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Beginning balance	1,338,987
Purchases	395,058
Sales and transfers	(958,912)
Principal payments	(156,437)
Gains / (losses)	(9,207)
(Amortization) / accretion	1,940
Ending balance	611,429
Corporate
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Beginning balance	1,887,182
Purchases	631,065
Sales and transfers	(268,403)
Principal payments	(143,284)
Gains / (losses)	5,260
(Amortization) / accretion	3,963
Ending balance	$ 2,115,783

[1] ⁽¹⁾  Derived from the audited consolidated financial statements at December 31, 2018.

[2] ⁽⁴⁾  Includes $76.3 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 September 30, 2019 and December 31, 2018, respectively.