| Debt Securities, Available-for-Sale [Table Text Block] |
| | | | | | | Gross | | | Gross | | | | | |
| | | Amortized | | | Unrealized | | | Unrealized | | | Fair | |
| (Dollars in thousands) | | Cost | | | Gains | | | Losses | | | Value | |
| March 31, 2025 | | | | | | | | | | | | | | | | |
| U.S. Government agency debt obligations | | $ | 583,732 | | | $ | 1,380 | | | $ | (37,703 | ) | | $ | 547,409 | |
| Mortgage-backed securities | | | 30,848 | | | | 8 | | | | (5,674 | ) | | | 25,182 | |
| Municipal general obligation bonds | | | 192,160 | | | | 483 | | | | (7,853 | ) | | | 184,790 | |
| Municipal revenue bonds | | | 31,820 | | | | 119 | | | | (2,237 | ) | | | 29,702 | |
| Other investments | | | 500 | | | | 0 | | | | 0 | | | | 500 | |
| | | | | | | | | | | | | | | | | |
| | | $ | 839,060 | | | $ | 1,990 | | | $ | (53,467 | ) | | $ | 787,583 | |
| | | | | | | | | | | | | | | | | |
| December 31, 2024 | | | | | | | | | | | | | | | | |
| U.S. Government agency debt obligations | | $ | 542,676 | | | $ | 131 | | | $ | (47,226 | ) | | $ | 495,581 | |
| Mortgage-backed securities | | | 31,696 | | | | 4 | | | | (6,332 | ) | | | 25,368 | |
| Municipal general obligation bonds | | | 187,484 | | | | 513 | | | | (7,827 | ) | | | 180,170 | |
| Municipal revenue bonds | | | 31,066 | | | | 89 | | | | (2,422 | ) | | | 28,733 | |
| Other investments | | | 500 | | | | 0 | | | | 0 | | | | 500 | |
| | | | | | | | | | | | | | | | | |
| | | $ | 793,422 | | | $ | 737 | | | $ | (63,807 | ) | | $ | 730,352 | |
|
| Debt Securities, Available-for-Sale, Unrealized Loss Position, Fair Value [Table Text Block] |
| | | Less than 12 Months | | | 12 Months or More | | | Total | |
| | | Fair | | | Unrealized | | | Fair | | | Unrealized | | | Fair | | | Unrealized | |
| (Dollars in thousands) | | Value | | | Loss | | | Value | | | Loss | | | Value | | | Loss | |
| March 31, 2025 | | | | | | | | | | | | | | | | | | | | | | | | |
| U.S. Government agency debt obligations | | $ | 76,302 | | | $ | 685 | | | $ | 361,528 | | | $ | 37,018 | | | $ | 437,830 | | | $ | 37,703 | |
| Mortgage-backed securities | | | 12 | | | | 0 | | | | 24,625 | | | | 5,674 | | | | 24,637 | | | | 5,674 | |
| Municipal general obligation bonds | | | 52,177 | | | | 1,486 | | | | 101,963 | | | | 6,367 | | | | 154,140 | | | | 7,853 | |
| Municipal revenue bonds | | | 2,369 | | | | 21 | | | | 20,967 | | | | 2,216 | | | | 23,336 | | | | 2,237 | |
| Other investments | | | 0 | | | | 0 | | | | 0 | | | | 0 | | | | 0 | | | | 0 | |
| | | | | | | | | | | | | | | | | | | | | | | | | |
| | | $ | 130,860 | | | $ | 2,192 | | | $ | 509,083 | | | $ | 51,275 | | | $ | 639,943 | | | $ | 53,467 | |
| | | Less than 12 Months | | | 12 Months or More | | | Total | |
| | | Fair | | | Unrealized | | | Fair | | | Unrealized | | | Fair | | | Unrealized | |
| (Dollars in thousands) | | Value | | | Loss | | | Value | | | Loss | | | Value | | | Loss | |
| December 31, 2024 | | | | | | | | | | | | | | | | | | | | | | | | |
| U.S. Government agency debt obligations | | $ | 113,942 | | | $ | 2,379 | | | $ | 361,171 | | | $ | 44,847 | | | $ | 475,113 | | | $ | 47,226 | |
| Mortgage-backed securities | | | 194 | | | | 1 | | | | 24,865 | | | | 6,331 | | | | 25,059 | | | | 6,332 | |
| Municipal general obligation bonds | | | 63,387 | | | | 1,117 | | | | 92,153 | | | | 6,710 | | | | 155,540 | | | | 7,827 | |
| Municipal revenue bonds | | | 2,840 | | | | 28 | | | | 21,865 | | | | 2,394 | | | | 24,705 | | | | 2,422 | |
| Other investments | | | 0 | | | | 0 | | | | 0 | | | | 0 | | | | 0 | | | | 0 | |
| | | | | | | | | | | | | | | | | | | | | | | | | |
| | | $ | 180,363 | | | $ | 3,525 | | | $ | 500,054 | | | $ | 60,282 | | | $ | 680,417 | | | $ | 63,807 | |
|
| Investments Classified by Contractual Maturity Date [Table Text Block] |
| | | Amortized | | | Fair | |
| (Dollars in thousands) | | Cost | | | Value | |
| | | | | | | | | |
| Due in 2025 | | $ | 51,895 | | | $ | 51,218 | |
| Due in 2026 through 2030 | | | 456,080 | | | | 432,090 | |
| Due in 2031 through 2035 | | | 253,116 | | | | 232,846 | |
| Due in 2036 and beyond | | | 46,621 | | | | 45,747 | |
| Mortgage-backed securities | | | 30,848 | | | | 25,182 | |
| Other investments | | | 500 | | | | 500 | |
| | | | | | | | | |
| Total available for sale securities | | $ | 839,060 | | | $ | 787,583 | |
|