SERVICER ADVANCE INVESTMENTS - Summary of Investments in Servicer Advances - Additional Information (Details) - USD ($) $ in Thousands		Sep. 30, 2020	Dec. 31, 2019
Investments in and Advances to Affiliates [Line Items]
Servicer advance investments, at fair value	[1]	$ 535,760	$ 581,777
Face Amount of Secured Notes and Bonds Payable		22,429,761
Servicer advance investments | Servicer Advances
Investments in and Advances to Affiliates [Line Items]
UPB of Underlying Mortgages		27,484,426	31,442,267
Servicer advance investments, at fair value		$ 434,998	$ 462,843
Servicer Advances to UPB of Underlying Residential Mortgage Loans		1.60%	1.50%
Face Amount of Secured Notes and Bonds Payable		$ 412,538	$ 443,248
Gross Loan-to-Value		88.00%	88.30%
Net Loan-to-Value		87.00%	87.20%
Gross Cost of Funds		2.30%	3.40%
Net Cost of Funds		1.50%	2.80%

[1] See Note 13 regarding consolidated VIEs.