Fair Value of Assets and Liabilities - Carrying amounts and estimated fair values of assets and liabilities measured at fair value on a recurring or nonrecurring basis (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Liabilities:
Finance charge reversal liability	$ 107,047	$ 94,148
Carrying Value | Measured at fair value on a nonrecurring basis | Level 2
Assets:
Loan receivables held for sale, net	43,489	73,606
Carrying Value | Measured at fair value on a recurring basis | Level 2
Liabilities:
Term loan	387,979	338,263
Carrying Value | Measured at fair value on a recurring basis | Level 3
Liabilities:
Finance charge reversal liability	107,047	94,148
Servicing liability	2,272	2,071
Fair Value | Measured at fair value on a nonrecurring basis | Level 2
Assets:
Loan receivables held for sale, net	44,294	74,190
Fair Value | Measured at fair value on a recurring basis | Level 2
Liabilities:
Term loan	398,037	345,820
Fair Value | Measured at fair value on a recurring basis | Level 3
Liabilities:
Finance charge reversal liability	107,047	94,148
Servicing liability	$ 2,272	$ 2,071