Loans Receivable - Aging of the Loans Receivable Balance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due loans receivable (percentage)	14.80%	14.30%
Current loans receivable (percentage)	85.20%	85.70%
Balance of Loans Receivable on Nonaccrual Status	$ 2,016	$ 1,072
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due loans receivable (percentage)	7.10%	6.80%
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due loans receivable (percentage)	3.60%	3.20%
90 or more Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due loans receivable (percentage)	4.10%	4.30%
Balance of Loans Receivable 90 or More Days Past Due and Still Accruing Interest and Fees	$ 0	$ 0