LOANS HELD FOR INVESTMENT - Narrative (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) Loan	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Receivables [Abstract]
Number of loans originated or co-originated | Loan	44
Number of loans repaid or sold | Loan	76
Total Commitment	$ 1,700,000,000
Loans held for investment, Carrying Amount	1,524,873,000	$ 1,726,283,000	$ 1,313,937,000
Amount funded	544,200,000
Amount of repayments, excluding non-controlling interests held by third parties	$ 746,800,000
Percentage of Loans Held for Investment Having LIBOR Floors	89.80%
Weighted average floor (as a percent)	1.38%
Unleveraged effective yield dispositions, early prepayments or defaults	$ 0
Mortgage loans on real estate impairment charges recognized	$ 0	$ 0	$ 0