MORTGAGE LOAN RECEIVABLES - Provision for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan losses at beginning of period	$ 18,500	$ 7,300	$ 17,900	$ 4,000
Provision for loan losses	0	10,300	600	13,600
Provision for loan losses at end of period	18,500	$ 17,600	18,500	$ 17,600
Principal balance of loans on non-accrual status	$ 37,161		$ 37,161		$ 36,850