Fair Value Measurements (Narrative) (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Credit Risk Valuation Adjustment, Derivative Assets	$ 0	$ 0	$ 0
Derivative Credit Risk Valuation Adjustment, Derivative Liabilities	$ 0	$ 0	$ 0
Maximum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Collateral discount	30.00%	30.00%	30.00%
Minimum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Collateral discount	20.00%	20.00%	20.00%