Investment Securities Investment Securities (Credit Ratings In State And Municipal Bond Portfolio) (Details)	Dec. 31, 2017 Rate
Schedule of Available-for-sale Securities [Line Items]
Percentage of State and Municipal Bond Portfolio, by credit rating	100.00%
Moody's, Aaa Rating [Member]
Schedule of Available-for-sale Securities [Line Items]
Percentage of State and Municipal Bond Portfolio, by credit rating	6.00%
Moody's Aa Rating [Member]
Schedule of Available-for-sale Securities [Line Items]
Percentage of State and Municipal Bond Portfolio, by credit rating	76.90%
Moody's A Rating [Member]
Schedule of Available-for-sale Securities [Line Items]
Percentage of State and Municipal Bond Portfolio, by credit rating	16.40%
Moody's Not Rated [Member]
Schedule of Available-for-sale Securities [Line Items]
Percentage of State and Municipal Bond Portfolio, by credit rating	0.70%