RESIDENTIAL MORTGAGE LOANS - Schedule of Aggregate Unpaid Principal Balance and Aggregate Carrying Value (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans of unfunded and available revolving credit privileges	$ 289,065	$ 51,575
Fair Value	290,180	52,389
Fair Value Over (Under) Unpaid Principal Balance	1,115	814
Residential Mortgage Loans | Less than 120
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans of unfunded and available revolving credit privileges	11,101,345	5,131,755
Fair Value	11,323,443	5,099,094
Fair Value Over (Under) Unpaid Principal Balance	222,098	(32,661)
Residential Mortgage Loans | 120+
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans of unfunded and available revolving credit privileges	623,093	950,564
Fair Value	594,335	790,788
Fair Value Over (Under) Unpaid Principal Balance	(28,758)	(159,776)
Residential Mortgage Loans | Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans of unfunded and available revolving credit privileges	11,724,438	6,082,319
Fair Value	11,917,778	5,889,882
Fair Value Over (Under) Unpaid Principal Balance	$ 193,340	$ (192,437)