SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Accretion and Other Amortization (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accretion of discount and other amortization:
Accretion of servicer advances receivable discount and servicer advance investments	$ 214,876	$ 542,983	$ 364,350
Accretion of excess mortgage servicing rights income	44,440	103,053	150,141
Accretion of net discount on securities and loans	452,500	398,213	253,243
Amortization of deferred financing costs	(7,795)	(12,076)	(18,326)
Amortization of discount on notes and bonds payable	(2,054)	(789)	(1,476)
Accretion and other amortization	$ 701,967	$ 1,031,384	$ 747,932