INVESTMENTS IN RESIDENTIAL MORTGAGE LOANS - Required Payments Receivable, Cash Flows Expected to be Collected, and Fair Value at Acquisition Date for Loans Acquired during the Period (Details) - PCD Loans $ in Thousands	Dec. 31, 2017 USD ($)
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Line Items]
Contractually Required Payments Receivable	$ 94,951
Cash Flows Expected to be Collected	80,744
Fair Value	$ 58,884