SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Gain (Loss) on Settlement of Investments, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Gain (loss) on sale of real estate securities, net	$ (29,936)	$ 20,642	$ (27,460)
Gain (loss) on sale of acquired residential mortgage loans, net	(7,677)	39,731	12,142
Gain (loss) on settlement of derivatives	54,867	(39,214)	(27,491)
Gain (loss) on liquidated residential mortgage loans	5,023	(10,201)	(1,810)
Gain (loss) on sale of REO	(12,424)	(9,215)	4,690
Gains reclassified from change in fair value of investments in excess MSRs and servicer advance investments	113,002	11,320	0
Other gains (losses)	(19,013)	(2,753)	(8,871)
Gain (loss) on settlement of investments, net	$ 103,842	$ 10,310	$ (48,800)