Investment Securities (Pledged Securities) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Carrying value of available-for-sale securities pledged to secure public and trust department deposits and repurchase agreements	$ 488.8	$ 352.8
Carrying value of held-to-maturity securities pledged to secure public and trust department deposits and repurchase agreements	21.8	22.9
Carrying value of available-for-sale securities pledged to secure additional borrowing capacity at Federal Home Loan Bank and Federal Reserve Bank	11.7	13.5
Pledged Financial Instruments, Not Separately Reported, Held-To-Maturity Securities for Federal Home Loan Bank and Federal Reserve Bank	$ 23.6	$ 24.5