| Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Table Text Block] |
| | | | | | | | | | | | | | Investment securities (available for sale and trading): | | | | | | | | | | | | | | | | | | | | $ | 200.1 | | | $ | 200.1 | | | $ | — | | | $ | — | | Obligations of U.S. government & agencies | | | 82.2 | | | | — | | | | 82.2 | | | | — | | Obligations of state & political subdivisions | | | 33.5 | | | | — | | | | 33.5 | | | | — | | Mortgage-backed securities | | | 188.8 | | | | — | | | | 188.8 | | | | — | | Collateralized mortgage obligations | | | 48.7 | | | | — | | | | 48.7 | | | | — | | | | | | | | | | | | — | | | | — | | | | | | 1.3 | | | | — | | | | 1.3 | | | | — | | Total assets measured on a recurring basis at fair value | | $ | 573.7 | | | $ | 219.2 | | | $ | 354.5 | | | $ | — | | | | | | | | | | | | | | | | Mortgage servicing rights | | $ | 6.2 | | | $ | — | | | $ | — | | | $ | 6.2 | | Impaired loans and leases | | | 14.3 | | | | — | | | | — | | | | 14.3 | | | | | | 1.0 | | | | — | | | | — | | | | 1.0 | | | | | | | | | | | | | | | | | | | | Total assets measured at fair value on a non-recurring basis | | $ | 21.5 | | | $ | — | | | $ | — | | | $ | 21.5 | | | | | | | | | | | | | | | | Investment securities (available for sale and trading): | | | | | | | | | | | | | | | | | | | | $ | 0.1 | | | $ | 0.1 | | | $ | — | | | $ | — | | Obligations of U.S. government & agencies | | | 101.5 | | | | — | | | | 101.5 | | | | — | | Obligations of state & political subdivisions | | | 42.0 | | | | — | | | | 42.0 | | | | — | | Mortgage-backed securities | | | 158.7 | | | | — | | | | 158.7 | | | | — | | Collateralized mortgage obligations | | | 29.8 | | | | — | | | | 29.8 | | | | — | | | | | | | | | | | | — | | | | — | | | | | | 1.6 | | | | — | | | | 1.6 | | | | — | | Total assets measured on a recurring basis at fair value | | $ | 352.9 | | | $ | 19.3 | | | $ | 333.6 | | | $ | — | | | | | | | | | | | | | | | | Mortgage servicing rights | | $ | 5.7 | | | $ | — | | | $ | — | | | $ | 5.7 | | Impaired loans and leases | | | 13.8 | | | | — | | | | — | | | | 13.8 | | | | | | 2.6 | | | | — | | | | — | | | | 2.6 | | | | | | | | | | | | | | | | | | | | Total assets measured at fair value on a non-recurring basis | | $ | 22.1 | | | $ | — | | | $ | — | | | $ | 22.1 | | |