Investment Securities (Pledged Securities) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Carrying value of available-for-sale securities pledged to secure public and trust department deposits and repurchase agreements	$ 495.3	$ 495.5
Carrying value of held-to-maturity securities pledged to secure public and trust department deposits and repurchase agreements	20.5	21.4
Carrying value of available-for-sale securities pledged to secure additional borrowing capacity at Federal Home Loan Bank and Federal Reserve Bank	10.0	11.1
Pledged Financial Instruments, Not Separately Reported, Held-To-Maturity Securities for Federal Home Loan Bank and Federal Reserve Bank	$ 22.8	$ 23.3