RESIDENTIAL MORTGAGE LOANS - Schedule of Aggregate Unpaid Principal Balance and Aggregate Carrying Value (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Principal Balance	$ 303,655	$ 52,389
90 to 119 | Residential Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Principal Balance	82,036	71,567
Notes receivable	76,074	59,679
Fair Value Over (Under) Unpaid Principal Balance	(5,962)	(11,888)
120 or greater | Residential Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Principal Balance	620,386	950,564
Notes receivable	579,643	790,788
Fair Value Over (Under) Unpaid Principal Balance	(40,742)	(159,776)
Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Principal Balance	306,000	51,575
Notes receivable	303,655	52,389
Past Due | Residential Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Principal Balance	702,422	1,022,131
Notes receivable	655,717	850,467
Fair Value Over (Under) Unpaid Principal Balance	$ (46,704)	$ (171,664)