MORTGAGE LOAN RECEIVABLES - Schedule of Mortgage Loans (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015	Jun. 30, 2016	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014
Mortgage Loans on Real Estate [Line Items]
Outstanding Face Amount	$ 2,437,995	$ 2,321,194
Provision for loan losses	(4,000)	(3,700)	$ (4,000)	$ (3,550)	$ (3,400)	$ (3,100)
Carrying Value	2,427,221	2,310,409
Mortgage loan receivables held for investment, at amortized cost
Mortgage Loans on Real Estate [Line Items]
Outstanding Face Amount	1,654,554	1,749,556
Carrying Value, gross	1,647,035	1,742,345
Provision for loan losses	(4,000)	(3,700)
Carrying Value	$ 1,643,035	$ 1,738,645
Weighted Average Yield (as a percent)	7.09%	7.56%
Remaining Maturity (years)	1 year 8 months 12 days	1 year 4 months 17 days
Mortgage loan receivables held for sale
Mortgage Loans on Real Estate [Line Items]
Outstanding Face Amount	$ 783,441	$ 571,638
Carrying Value	$ 784,186	$ 571,764
Weighted Average Yield (as a percent)	4.40%	4.56%
Remaining Maturity (years)	7 years 6 months 14 days	6 years 2 months 12 days