INVESTMENTS IN EXCESS MORTGAGE SERVICING RIGHTS ASSETS - Schedule of Activity Related to the Carrying Value of Investments in Excess MSRs (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2020 USD ($)
Carrying Value of Investments in Excess MSRs
Beginning balance	$ 5,686,233
Ending balance	4,781,624
Excess MSRs
Carrying Value of Investments in Excess MSRs
Beginning balance	379,747
Interest income	25,176
Other income	(12,175)
Proceeds from repayments	(52,291)
Proceeds from sales	(61)
Change in fair value	(11,773)
Ending balance	328,623
Excess MSRs | Mr. Cooper
Carrying Value of Investments in Excess MSRs
Beginning balance	377,692
Interest income	25,167
Other income	(12,175)
Proceeds from repayments	(51,980)
Proceeds from sales	(61)
Change in fair value	(11,939)
Ending balance	326,704
Excess MSRs | SLS
Carrying Value of Investments in Excess MSRs
Beginning balance	2,055
Interest income	9
Other income	0
Proceeds from repayments	(311)
Proceeds from sales	0
Change in fair value	166
Ending balance	$ 1,919