Purchased Receivables - Summary of Components of Net Purchased Receivables (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Purchased Receivables [Abstract]
Purchased receivables	$ 19,621	$ 22,431
Reserve for purchased receivable losses	(209)	(200)	$ (183)	$ (171)
Total	$ 19,412	$ 22,231