Investment Securities Pledged Securities (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Investments [Abstract]
Carrying value of available-for-sale securities pledged to secure public and trust department deposits and repurchase agreements	$ 495.5	$ 352.8
Carrying value of held-to-maturity securities pledged to secure public and trust department deposits and repurchase agreements	21.4	22.9
Carrying value of available-for-sale securities pledged to secure additional borrowing capacity at FHLB and FRB	11.1	13.5
Carrying value of held-to-maturity securities pledged to secure additional borrowing capacity at FHLB and FRB	$ 23.3	$ 24.5