Other Income (Expense) - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Other Income (Expense) [Line Items]
Other-than-temporary impairment loss	$ 63	$ 366
Effective interest rate	4.90%
Litigation settlement, amount received		$ 3,500
Minimum
Other Income (Expense) [Line Items]
Retained interest, effective interest rate	3.70%
Maximum
Other Income (Expense) [Line Items]
Retained interest, effective interest rate	12.10%