SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Accretion and Other Amortization (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Accretion of net discount on securities and loans	$ 32,670	$ 96,148	$ 323,652
Accretion of servicer advances receivable discount and investments	1,822	55,664	28,094
Accretion of Excess MSRs income	30,855	28,352	32,647
Amortization of deferred financing costs	(14,174)	(22,733)	(4,019)
Total accretion and other amortization	49,382	151,540	379,129
Secured Notes And Bonds Payable
Debt Instrument [Line Items]
Amortization of discount	(13)	(388)	(1,245)
Term Loan
Debt Instrument [Line Items]
Amortization of discount	$ (1,778)	$ (5,503)	$ 0