SEGMENTS - Product Concentration (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Product concentration
Servicing portfolio loans unpaid principal balance	$ 115,700,564	$ 107,211,972	$ 93,225,169
Fannie Mae DUS Program
Product concentration
Servicing portfolio loans unpaid principal balance	53,401,457	48,818,185	40,049,095
Freddie Mac
Product concentration
Servicing portfolio loans unpaid principal balance	37,138,836	37,072,587	32,583,842
Ginnie Mae-HUD
Product concentration
Servicing portfolio loans unpaid principal balance	9,889,289	9,606,506	9,972,989
Life insurance companies and other
Product concentration
Servicing portfolio loans unpaid principal balance	$ 15,270,982	$ 11,714,694	$ 10,619,243