Investment Securities (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) security item	Dec. 31, 2016 USD ($)
Securities [Line Items]
Available-for-sale securities pledged as collateral | $	$ 105.9	$ 116.7
Percent of principal outstanding collected of held-to-maturity securities	85.00%
Collateralized Mortgage Obligations GSE [Member]
Securities [Line Items]
Securities in unrealized loss positions qualitative disclosure number of positions | security	19
Number of securities, impaired for more than 12 months	16
Government Sponsored Entities (GSE) Mortgage-Backed Securities [Member]
Securities [Line Items]
Securities in unrealized loss positions qualitative disclosure number of positions | security	19
Number of securities, impaired for more than 12 months	14
US Government Agency Obligations [Member]
Securities [Line Items]
Securities in unrealized loss positions qualitative disclosure number of positions | security	11
Number of securities, impaired for more than 12 months	3
State and Municipal Tax-Exempt [Member]
Securities [Line Items]
Securities in unrealized loss positions qualitative disclosure number of positions | security	37
Number of securities, impaired for more than 12 months	20
Number Of Impaired Municipal Securities, School Districts, Additional Private Insurance	11
Number Of Impaired Municipal Securities, Remaining	15
Number Of Impaired Municipal Securities School Districts State Qualified School Aid	22
Number of impaired municipal securities, insured school districts	1
Number of impaired municipal securities, unisured school districts	2
Number Of Impaired Municipal Securities, Townships	7
Corporate Bonds [Member]
Securities [Line Items]
Securities in unrealized loss positions qualitative disclosure number of positions | security	8
Number of securities, impaired for more than 12 months	4
Maximum [Member] | Collateralized Mortgage Obligations GSE [Member]
Securities [Line Items]
Unrealized loss of security from book value	5.52%
Maximum [Member] | Government Sponsored Entities (GSE) Mortgage-Backed Securities [Member]
Securities [Line Items]
Unrealized loss of security from book value	3.12%
Maximum [Member] | US Government Agency Obligations [Member]
Securities [Line Items]
Unrealized loss of security from book value	1.56%
Maximum [Member] | State and Municipal Tax-Exempt [Member]
Securities [Line Items]
Unrealized loss of security from book value	4.08%
Maximum [Member] | Corporate Bonds [Member]
Securities [Line Items]
Unrealized loss of security from book value	3.64%