MORTGAGE LOAN RECEIVABLES - Schedule of Mortgage Loans (Details) - USD ($) $ in Thousands		6 Months Ended	12 Months Ended
		Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Outstanding Face Amount		$ 3,248,433	$ 3,522,286
Provision for loan losses	[1]	(18,500)	(17,900)
Carrying Value		$ 3,213,334	$ 3,482,929
Weighted Average Yield		7.96%	7.76%
Remaining Maturity		1 year 5 months 23 days	1 year 9 months 7 days
Mortgage loans held by consolidated subsidiaries
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Outstanding Face Amount		$ 3,136,334	$ 3,340,381
Carrying Value gross, consumer and commercial real estate		$ 3,119,857	$ 3,318,390
Weighted Average Yield		8.01%	7.84%
Remaining Maturity		1 year 2 months 8 days	1 year 3 months 25 days
Mortgage loan receivables held for investment, net, at amortized cost
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Outstanding Face Amount		$ 3,136,334	$ 3,340,381
Provision for loan losses		(18,500)	(17,900)	$ (7,300)	$ (4,000)
Carrying Value		3,101,357	3,300,490
Mortgage loan receivables held for sale
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Outstanding Face Amount		112,099	181,905
Carrying Value		$ 111,977	$ 182,439
Weighted Average Yield		5.05%	5.46%
Remaining Maturity		9 years 4 months 28 days	9 years 9 months

[1] Includes amounts relating to consolidated variable interest entities. See Note 3.