MORTGAGE LOANS - Schedule of Amortized Cost Basis of Mortgage Loans Receivable by Origination Year (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
2020	$ 307,054
2019	2,493,801
2018	1,579,679
2017	1,351,404
2016	942,827
Prior	2,658,102
Total	9,332,867	$ 9,379,401
Performing
Financing Receivable, Credit Quality Indicator [Line Items]
2020	307,054
2019	2,493,801
2018	1,579,679
2017	1,351,404
2016	942,827
Prior	2,658,102
Total	9,332,867
Non-performing
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Total	$ 0