MORTGAGE LOAN RECEIVABLES - Schedule of Mortgage Loans (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Mortgage Loans on Real Estate [Line Items]
Outstanding Face Amount	$ 2,837,900	$ 2,371,827
Provision for loan losses	(4,000)	(4,000)	$ (3,850)	$ (3,700)
Carrying Value	$ 2,816,675	$ 2,353,977
Weighted Average Yield (as a percent)	6.59%	6.73%
Remaining Maturity (years)	2 years 9 months 21 days	2 years 1 month 6 days
Mortgage loan receivables held for investment, at amortized cost
Mortgage Loans on Real Estate [Line Items]
Outstanding Face Amount	$ 2,317,221	$ 2,011,309
Carrying Value, gross	2,304,093	2,000,095
Provision for loan losses	(4,000)	(4,000)
Carrying Value	$ 2,300,093	$ 1,996,095
Weighted Average Yield (as a percent)	6.93%	7.17%
Remaining Maturity (years)	1 year 8 months 12 days	1 year 7 months 28 days
Mortgage loan receivables held for sale
Mortgage Loans on Real Estate [Line Items]
Outstanding Face Amount	$ 520,679	$ 360,518
Carrying Value	$ 516,582	$ 357,882
Weighted Average Yield (as a percent)	5.06%	4.20%
Remaining Maturity (years)	7 years 8 months 15 days	4 years 6 months 18 days