| In millions, except per share items | Dec-31-21 | Dec-31-20 | Dec-31-19 | Dec-31-18 | Dec-31-17 | Dec-31-16 | Dec-31-15 | Dec-31-14 |
| | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K |
| Interest Income | | | | | | | | |
| Interest and fees on loans | 136.7 | 150.5 | 170.0 | 142.1 | 125.8 | 118.1 | 115.1 | 116.7 |
| |
| Interest and dividends on investment securities: | | | | | | | | |
| Taxable | 23.1 | 23.4 | 23.4 | 17.3 | 14.4 | 12.4 | 10.8 | 11.8 |
| Tax-exempt | 5.0 | 3.9 | 3.0 | 2.8 | 2.7 | 1.6 | 1.1 | 1.1 |
| Interest on deposits in depository institutions | 0.7 | 0.5 | 1.3 | 1.7 | 0.1 | | | |
| Total Interest Income | 165.5 | 178.3 | 197.7 | 163.9 | 142.9 | 132.2 | 127.1 | 129.6 |
| |
| Interest Expense | | | | | | | | |
| Interest on deposits | 9.4 | 22.5 | 32.7 | 21.4 | 14.8 | 12.1 | 10.9 | 11.0 |
| Interest on customer repurchase agreements | 0.5 | 1.0 | 3.5 | 3.4 | 1.2 | 0.5 | 0.3 | 0.3 |
| Interest on FHLB long-term advances | | 0.1 | 0.2 | 0.9 | 0.8 | 0.7 | 0.6 | 0.6 |
| Total Interest Expense | 9.9 | 23.6 | 36.3 | 25.7 | 16.8 | 13.2 | 11.8 | 12.0 |
| Net Interest Income | 155.6 | 154.6 | 161.4 | 138.2 | 126.1 | 118.9 | 115.2 | 117.6 |
| |
| Provision for (recovery of) credit losses | | | | | | | | |
| Net Interest Income After Provision for (Recovery of) Credit Losses | 158.7 | 143.9 | 162.6 | 140.5 | 123.1 | 114.6 | 108.3 | 113.6 |
| |
| Non-Interest Income | | | | | | | | |
| |
| Revenue from contract with customer | | | | | | | | |
| Bank owned life insurance | 3.9 | 4.4 | 3.8 | 3.1 | 4.2 | 3.3 | 3.4 | 3.1 |
| Other income | 4.0 | 4.7 | 4.0 | 3.0 | 3.0 | 3.2 | 3.3 | 2.3 |
| Total Non-Interest Income | 69.6 | 82.7 | 68.5 | 60.6 | 63.6 | 58.8 | 67.2 | 58.7 |
| |
| Non-Interest Expense | | | | | | | | |
| Salaries and employee benefits | 61.9 | 62.1 | 62.1 | 54.4 | 51.1 | 50.9 | 47.8 | 51.7 |
| Occupancy related expense | 10.1 | 9.8 | 10.6 | 9.3 | 9.6 | 10.1 | 9.8 | 10.0 |
| Equipment and software related expense | 10.5 | 10.2 | 9.0 | 7.7 | 7.7 | 7.2 | 6.6 | |
| FDIC insurance expense | 1.6 | 0.9 | 0.6 | 1.3 | 1.3 | 1.6 | 1.8 | 1.6 |
| Advertising | 3.1 | 2.8 | 3.3 | 3.0 | | | | |
| Bankcard expenses | 6.5 | 5.9 | 5.6 | 4.5 | 3.9 | 4.5 | 4.1 | 3.8 |
| Postage, delivery, and statement mailings | 2.3 | 2.3 | 2.4 | 2.2 | 2.1 | 2.1 | 2.1 | 2.2 |
| Office supplies | 1.5 | 1.6 | 1.6 | 1.3 | 1.4 | 1.4 | 1.4 | 1.6 |
| Legal and professional fees | 2.3 | 2.2 | 2.4 | 1.8 | 2.0 | 1.9 | 1.5 | 1.9 |
| Telecommunications | 2.9 | 2.1 | 2.5 | 1.8 | 2.0 | 1.8 | 1.8 | 1.9 |
| |
| Repossessed asset losses (gains), net of expenses | | | | | | | | |
| Merger related expenses | | | 0.8 | 13.3 | | | 0.6 | |
| Other expenses | 14.7 | 15.3 | 16.1 | 11.7 | 11.2 | 11.2 | 11.7 | 10.4 |
| Total Non-Interest Expense | 117.2 | 115.3 | 117.6 | 113.1 | 96.0 | 96.2 | 93.0 | 95.0 |
| Income Before Income Taxes | 111.2 | 111.3 | 113.5 | 88.0 | 90.7 | 77.2 | 82.5 | 77.2 |
| Income tax expense | 23.1 | 21.7 | 24.1 | 18.0 | 36.4 | 25.1 | 28.4 | 24.3 |
| Net Income Available to Common Shareholders | 88.1 | 89.6 | 89.4 | 70.0 | 54.3 | 52.1 | 54.1 | 53.0 |
| |
| Weighted Average Number of Shares Outstanding Reconciliation [Abstract] | | | | | | | | |
| Average shares outstanding, basic (in shares) | 15.4 | 16.0 | 16.3 | 15.4 | 15.4 | 14.9 | 15.1 | 15.4 |
| Effect of dilutive securities (in shares) | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.1 |
| Average shares outstanding, diluted (in shares) | 15.4 | 16.0 | 16.3 | 15.4 | 15.4 | 14.9 | 15.2 | 15.5 |
| |
| Earnings Per Share [Abstract] | | | | | | | | |
| Basic earnings per common share (in dollars per share) | $5.67 | $5.55 | $5.43 | $4.50 | $3.49 | $3.46 | $3.54 | $3.40 |
| Diluted earnings per common share (in dollars per share) | $5.66 | $5.55 | $5.42 | $4.49 | $3.48 | $3.45 | $3.53 | $3.38 |