SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of General and Administrative Expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Compensation and benefits expense	$ 109,870	$ 0	$ 663
Legal and professional expense	45,234	40,182	23,983
Loan origination expense	16,050	0	0
Occupancy expense	8,868	0	0
Other	51,557	26,977	13,924
General and Administrative Expense	$ 231,579	$ 67,159	$ 38,570