| Segment Reporting [Table Text Block] |
| | | Trust | | | Bank | | | Consolidated | |
| (In Thousands of Dollars) | | Segment | | | Segment | | | Segment totals | |
| For Three Months Ended June 30, 2026 | | | | | | | | | | | | |
| Interest income - loans including fees | | $ | 0 | | | $ | 72,977 | | | $ | 72,977 | |
| Interest income - investments | | | 0 | | | | 11,516 | | | | 11,516 | |
| Trust fees | | | 3,089 | | | | 0 | | | | 3,089 | |
| Retirement plan consulting fees | | | 954 | | | | 0 | | | | 954 | |
| Total consolidated segment revenues | | | 4,043 | | | | 84,493 | | | | 88,536 | |
| Reconciliation of revenue | | | | | | | | | | | | |
| Other revenues | | | | | | | | | | | 11,971 | |
| Total consolidated revenues | | | | | | | | | | | 100,507 | |
| | | | | | | | | | | | | |
| Interest expense - deposits | | | 0 | | | | 25,985 | | | | 25,985 | |
| Interest expense - borrowings | | | 0 | | | | 4,077 | | | | 4,077 | |
| Credit for credit losses and unfunded loans | | | 0 | | | | 2,437 | | | | 2,437 | |
| Payroll expenses | | | 1,658 | | | | 19,626 | | | | 21,284 | |
| Total consolidated segment expenses | | | 1,658 | | | | 52,125 | | | | 53,783 | |
| | | | | | | | | | | | | |
| Segment profit | | | 2,385 | | | | 32,368 | | | | 34,753 | |
| Reconciliation of expenses | | | | | | | | | | | | |
| Other expenses * | | | | | | | | | | | 19,590 | |
| Total consolidated expenses | | | | | | | | | | | 73,373 | |
| | | | | | | | | | | | | |
| Total consolidated income before taxes | | | | | | | | | | $ | 27,134 | |
| Other segment disclosures | | | | | | | | | | | | |
| Occupancy and equipment | | | 133 | | | | 5,771 | | | | 5,904 | |
| Intangible amortization | | | 13 | | | | 1,182 | | | | 1,195 | |
| | | Trust | | | Bank | | | Consolidated | |
| (In Thousands of Dollars) | | Segment | | | Segment | | | Segment totals | |
| For Six Months Ended June 30, 2026 | | | | | | | | | | | | |
| Interest income - loans including fees | | $ | 0 | | | $ | 128,086 | | | $ | 128,086 | |
| Interest income - investments | | | 0 | | | | 22,060 | | | | 22,060 | |
| Trust fees | | | 6,119 | | | | 0 | | | | 6,119 | |
| Retirement plan consulting fees | | | 1,840 | | | | 0 | | | | 1,840 | |
| Total consolidated segment revenues | | | 7,959 | | | | 150,146 | | | | 158,105 | |
| Reconciliation of revenue | | | | | | | | | | | | |
| Other revenues | | | | | | | | | | | 23,204 | |
| Total consolidated revenues | | | | | | | | | | | 181,309 | |
| | | | | | | | | | | | | |
| Interest expense - deposits | | | 0 | | | | 46,424 | | | | 46,424 | |
| Interest expense - borrowings | | | 0 | | | | 8,186 | | | | 8,186 | |
| Provision for credit losses and unfunded loans | | | 0 | | | | 1,403 | | | | 1,403 | |
| Payroll expenses | | | 3,337 | | | | 36,436 | | | | 39,773 | |
| Total consolidated segment expenses | | | 3,337 | | | | 92,449 | | | | 95,786 | |
| | | | | | | | | | | | | |
| Segment profit | | | 4,622 | | | | 57,697 | | | | 62,319 | |
| Reconciliation of expenses | | | | | | | | | | | | |
| Other expenses * | | | | | | | | | | | 38,418 | |
| Total consolidated expenses | | | | | | | | | | | 134,204 | |
| | | | | | | | | | | | | |
| Total consolidated income before taxes | | | | | | | | | | $ | 47,105 | |
| Other segment disclosures | | | | | | | | | | | | |
| Occupancy and equipment | | | 266 | | | | 10,732 | | | | 10,998 | |
| Intangible amortization | | | 27 | | | | 2,033 | | | | 2,060 | |
| | | Trust | | | Bank | | | Consolidated | |
| (In Thousands of Dollars) | | Segment | | | Segment | | | Segment totals | |
| For Three Months Ended June 30, 2025 | | | | | | | | | | | | |
| Interest income - loans including fees | | $ | 0 | | | $ | 47,050 | | | $ | 47,050 | |
| Interest income - investments | | | 0 | | | | 9,729 | | | | 9,729 | |
| Trust fees | | | 2,596 | | | | 0 | | | | 2,596 | |
| Retirement plan consulting fees | | | 783 | | | | 0 | | | | 783 | |
| Total consolidated segment revenues | | | 3,379 | | | | 56,779 | | | | 60,158 | |
| Reconciliation of revenue | | | | | | | | | | | | |
| Other revenues | | | | | | | | | | | 9,666 | |
| Total consolidated revenues | | | | | | | | | | | 69,824 | |
| | | | | | | | | | | | | |
| Interest expense - deposits | | | 0 | | | | 20,240 | | | | 20,240 | |
| Interest expense - borrowings | | | 0 | | | | 2,541 | | | | 2,541 | |
| Provision for credit losses and unfunded loans | | | 0 | | | | 3,548 | | | | 3,548 | |
| Payroll expenses | | | 1,441 | | | | 13,258 | | | | 14,699 | |
| Total consolidated segment expenses | | | 1,441 | | | | 39,587 | | | | 41,028 | |
| | | | | | | | | | | | | |
| Segment profit | | | 1,938 | | | | 17,192 | | | | 19,130 | |
| Reconciliation of expenses | | | | | | | | | | | | |
| Other expenses * | | | | | | | | | | | 12,476 | |
| Total consolidated expenses | | | | | | | | | | | 53,504 | |
| | | | | | | | | | | | | |
| Total consolidated income before taxes | | | | | | | | | | $ | 16,320 | |
| Other segment disclosures | | | | | | | | | | | | |
| Occupancy and equipment | | | 140 | | | | 3,964 | | | | 4,104 | |
| Intangible amortization | | | 23 | | | | 712 | | | | 735 | |
| | | Trust | | | Bank | | | Consolidated | |
| (In Thousands of Dollars) | | Segment | | | Segment | | | Segment totals | |
| For Six Months Ended June 30, 2025 | | | | | | | | | | | | |
| Interest income - loans including fees | | $ | 0 | | | $ | 93,758 | | | $ | 93,758 | |
| Interest income - investments | | | 0 | | | | 19,243 | | | | 19,243 | |
| Trust fees | | | 5,237 | | | | 0 | | | | 5,237 | |
| Retirement plan consulting fees | | | 1,581 | | | | 0 | | | | 1,581 | |
| Total consolidated segment revenues | | | 6,818 | | | | 113,001 | | | | 119,819 | |
| Reconciliation of revenue | | | | | | | | | | | | |
| Other revenues | | | | | | | | | | | 17,792 | |
| Total consolidated revenues | | | | | | | | | | | 137,611 | |
| | | | | | | | | | | | | |
| Interest expense - deposits | | | 0 | | | | 39,957 | | | | 39,957 | |
| Interest expense - borrowings | | | 0 | | | | 5,934 | | | | 5,934 | |
| Provision for credit losses and unfunded loans | | | 0 | | | | 3,344 | | | | 3,344 | |
| Payroll expenses | | | 2,915 | | | | 27,939 | | | | 30,854 | |
| Total consolidated segment expenses | | | 2,915 | | | | 77,174 | | | | 80,089 | |
| | | | | | | | | | | | | |
| Segment profit | | | 3,903 | | | | 35,827 | | | | 39,730 | |
| Reconciliation of expenses | | | | | | | | | | | | |
| Other expenses * | | | | | | | | | | | 24,847 | |
| Total consolidated expenses | | | | | | | | | | | 104,936 | |
| | | | | | | | | | | | | |
| Total consolidated income before taxes | | | | | | | | | | $ | 32,675 | |
| Other segment disclosures | | | | | | | | | | | | |
| Occupancy and equipment | | | 283 | | | | 7,948 | | | | 8,231 | |
| Intangible amortization | | | 46 | | | | 1,424 | | | | 1,470 | |
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