INVESTMENTS IN CONSUMER LOANS - Carrying Value of Purchased Deteriorated Loans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Loans Receivable [Roll Forward]
Proceeds from repayments	$ (94,807)	$ (38,700)	$ (46,496)
Accretion and other amortization	1,031,384	747,932	525,298
Receivables Acquired with Deteriorated Credit Quality | Consumer Portfolio Segment
Loans Receivable [Roll Forward]
Beginning balance	316,532	0
SpringCastle Transaction		395,129
Provision for loan losses	3,013	(3,013)
Proceeds from repayments	(123,932)	(112,222)
Accretion and other amortization	40,836	36,638
Ending balance	$ 236,449	$ 316,532	$ 0