Fair Value Measurements (Narrative) (Details) - Recurring [Member] - USD ($)	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Transfers of assets and liabilities between level 1, 2, 3	$ 0	$ 0
Investment Securities [Member] | Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Targeted duration	2 years
Investment Securities [Member] | Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Targeted duration	5 years