MORTGAGE LOAN RECEIVABLES - Provision for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan losses at beginning of period	$ 18,200	$ 7,000	$ 17,900	$ 4,000
Provision for loan losses	300	300	600	3,300
Provision for loan losses at end of period	18,500	$ 7,300	18,500	$ 7,300
Principal balance of loans on non-accrual status	$ 36,946		$ 36,946		$ 36,850