Fair Value of Financial Instruments - Carrying Value and Fair Value, Finance Receivables (Details) - Level 2 - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Carrying value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of finance receivables, net	$ 88,151	$ 45,564
Fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of finance receivables, net	$ 91,400	$ 47,514