SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Allowance for Risk Sharing Obligations (Details)	12 Months Ended
	Dec. 31, 2021
Debt
Reasonable and supportable forecast period used for determining CECL reserves	1 year
Period of time rate reverts to historical rate	1 year
Fannie Mae DUS program | Maximum
Debt
Term of targeted debt	15 years
Maximum delinquency period of loans at which initial loss recognition occurs	60 days
Amount of loss absorbed at time of loan default as a percent of the origination unpaid principal balance	20.00%