Loans Receivable - Aging of the Loans Receivable Balance (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due loans receivable	14.90%	14.80%
Current loans receivable	85.10%	85.20%
Balance of Credit Card Loans on Nonaccrual Status	$ 2,016	$ 2,016
30-59 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due loans receivable	7.00%	7.10%
60-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due loans receivable	3.40%	3.60%
90 or more days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due loans receivable	4.50%	4.10%
Balance of Loans Receivable 90 or More Days Past Due and Still Accruing Interest and Fees	$ 0	$ 0