LOANS RECEIVABLE AND REVENUE - Revenue by Product (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue from External Customer [Line Items]
Revenue	$ 248,983	$ 216,944	$ 510,741	$ 441,524
Consumer Portfolio Segment | Unsecured Installment
Revenue from External Customer [Line Items]
Revenue	123,473	105,149	256,419	214,580
Consumer Portfolio Segment | Secured Installment
Revenue from External Customer [Line Items]
Revenue	25,777	23,173	52,633	46,842
Consumer Portfolio Segment | Open-End
Revenue from External Customer [Line Items]
Revenue	27,222	15,805	54,445	33,712
Consumer Portfolio Segment | Single-Pay
Revenue from External Customer [Line Items]
Revenue	61,602	63,241	125,307	127,031
Ancillary
Revenue from External Customer [Line Items]
Revenue	$ 10,909	$ 9,576	$ 21,937	$ 19,359