Purchased Receivables - Summary of Components of Net Purchased Receivables (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Purchased Receivables [Abstract]
Purchased receivables	$ 20,524	$ 22,431
Reserve for purchased receivable losses	(201)	(200)
Total	$ 20,323	$ 22,231