MORTGAGE LOAN RECEIVABLES - Schedule of Mortgage Loans (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Mortgage Loans on Real Estate [Line Items]
Outstanding Face Amount	$ 1,935,631	$ 2,321,194
Provision for loan losses	(3,850)	(3,700)	$ (3,250)	$ (3,100)
Carrying Value	1,926,164	2,310,409
Mortgage loan receivables held for investment, at amortized cost
Mortgage Loans on Real Estate [Line Items]
Outstanding Face Amount	1,582,358	1,749,556
Carrying Value, gross	1,576,683	1,742,345
Provision for loan losses	(3,850)	(3,700)
Carrying Value	$ 1,572,833	$ 1,738,645
Weighted Average Yield (as a percent)	7.61%	7.56%
Remaining Maturity (years)	1 year 5 months 19 days	1 year 4 months 17 days
Mortgage loan receivables held for sale
Mortgage Loans on Real Estate [Line Items]
Outstanding Face Amount	$ 353,273	$ 571,638
Carrying Value	$ 353,331	$ 571,764
Weighted Average Yield (as a percent)	4.33%	4.56%
Remaining Maturity (years)	5 years 8 months 15 days	6 years 2 months 12 days