INVESTMENTS IN RESIDENTIAL MORTGAGE LOANS - Schedule of Gain on Sale of Originated Mortgage Loans, Net (Details) - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Receivables [Abstract]
Gain on loans originated and sold					$ 38,415
Gain (loss) on settlement of mortgage loan origination derivative instruments					1,234
MSRs retained on transfer of loans					35,311
Other					14,057
Gain on sale of originated mortgage loans, net	$ 43,285	$ 45,732	$ 0	$ 0	$ 89,017	$ 0	$ 0