MORTGAGE LOAN RECEIVABLES - Activity in Loan Portfolio (Details) - USD ($) $ in Thousands		3 Months Ended			9 Months Ended
		Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Provision for loan losses	[1]		$ (17,900)		$ (17,900)
Sale of loans, net		$ 11,247		$ 1,861	38,589	$ 12,893
Provision for loan losses	[1]	(18,500)			(18,500)
Loans held for sale transferred loan held for investment, book value			15,400	57,600		57,600
Combined book value			$ 15,500	55,400		$ 55,400
Remaining maturity			9 years 9 months 18 days			2 years 6 months
Loan loss provision		0		10,300	600	$ 13,600
Mortgage loans held by consolidated subsidiaries
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Mortgage loans receivable, beginning balance			$ 3,318,390		3,318,390	3,282,462
Origination of mortgage loan receivables					985,825	1,240,894
Purchases of mortgage loan receivables					0
Repayment of mortgage loan receivables					(1,105,506)	(787,167)
Non-cash disposition of loans via foreclosure					(17,611)
Transfer between held for investment and held for sale					35,940	55,403
Accretion/amortization of discount, premium and other fees					14,405	13,795
Mortgage loans receivable, ending balance		3,231,443		3,805,387	3,231,443	3,805,387
Mortgage loans transferred but not considered sold
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Mortgage loans receivable, beginning balance			0		0
Purchases of mortgage loan receivables					0
Proceeds from sales of mortgage loan receivables					(15,504)
Transfer between held for investment and held for sale					15,504
Mortgage loans receivable, ending balance		0			0
Total mortgage loan receivables held for investment, net, at amortized cost
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Provision for loan losses			(17,900)		(17,900)	(4,000)
Provision for loan losses					(600)	(13,600)
Provision for loan losses		(18,500)		(17,600)	(18,500)	(17,600)
Total mortgage loan receivables held for investment, net, at amortized cost | One Of Company Loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Loan loss provision				10,000		12,700
Reserve based on targeted percentage level in portfolio				300
Total mortgage loan receivables held for investment, net, at amortized cost | Two Of Company Loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Reserve based on targeted percentage level in portfolio						900
First mortgage loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Mortgage loans receivable, beginning balance			$ 182,439		182,439	230,180
Origination of mortgage loan receivables					554,115	1,115,218
Purchases of mortgage loan receivables					9,934
Repayment of mortgage loan receivables					(620)	(1,324)
Proceeds from sales of mortgage loan receivables					(558,799)	(926,402)
Non-cash disposition of loans via foreclosure					0
Sale of loans, net					38,589	12,893
Transfer between held for investment and held for sale					(51,444)	(55,403)
Mortgage loans receivable, ending balance		$ 174,214		375,162	$ 174,214	375,162
Realized losses				$ 500		$ 500

[1] Includes amounts relating to consolidated variable interest entities. See Note 10.