Investment Securities (Pledged Securities) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Securities [Line Items]
Pledged Financial Instruments, Not Separately Reported, Held-To-Maturity Securities for Federal Home Loan Bank and Federal Reserve Bank	$ 26.3
Carrying value of available-for-sale securities pledged to secure public and trust department deposits and repurchase agreements	314.5	260.9
Carrying value of held-to-maturity securities pledged to secure public and trust department deposits and repurchase agreements	21.4	45.3
Carrying value of available-for-sale securities pledged to secure additional borrowing capacity at Federal Home Loan Bank and Federal Reserve Bank	$ 17.4	$ 50.4