SECURED BORROWINGS - Schedule of Average Borrowings Outstanding (Details) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Disclosure Of Repurchase Agreements [Abstract]
Average borrowings for the effects of related derivatives held as cash flow hedges	$ 11,957,518	$ 12,408,550
Effective borrowing rate considering cash flow hedges	1.82%	1.29%