| Schedule of Segment Reporting Information, by Segment [Table Text Block] |
| | As of or for the Twelve Months Ended December 31, | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | $ | 106,233 | | | $ | 3 | | | $ | 106,236 | | | $ | 100,124 | | | $ | 3 | | | $ | 100,127 | | | $ | 76,825 | | | $ | 3 | | | $ | 76,828 | | Less: loan loss provision | | | 4,326 | | | | — | | | | 4,326 | | | | 4,396 | | | | — | | | | 4,396 | | | | 884 | | | | — | | | | 884 | | Net interest income after loan loss provision | | | 101,907 | | | | 3 | | | | 101,910 | | | | 95,728 | | | | 3 | | | | 95,731 | | | | 75,941 | | | | 3 | | | | 75,944 | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Fees for wealth management services | | | — | | | | 36,690 | | | | 36,690 | | | | — | | | | 36,894 | | | | 36,894 | | | | — | | | | 36,774 | | | | 36,774 | | Service charges on deposit accounts | | | 2,791 | | | | — | | | | 2,791 | | | | 2,927 | | | | — | | | | 2,927 | | | | 2,578 | | | | — | | | | 2,578 | | Loan servicing and other fees | | | 1,939 | | | | — | | | | 1,939 | | | | 2,087 | | | | — | | | | 2,087 | | | | 1,755 | | | | — | | | | 1,755 | | Net gain on sale of loans | | | 3,119 | | | | — | | | | 3,119 | | | | 3,022 | | | | — | | | | 3,022 | | | | 1,772 | | | | — | | | | 1,772 | | Net gain (loss) on sale of available for sale securities | | | (77 | | | | — | | | | (77 | | | | 931 | | | | — | | | | 931 | | | | 471 | | | | — | | | | 471 | | Net gain (loss) on sale of other real estate owned | | | (76 | | | | — | | | | (76 | | | | 123 | | | | — | | | | 123 | | | | 175 | | | | — | | | | 175 | | | | | | — | | | | 3,722 | | | | 3,722 | | | | — | | | | 3,745 | | | | 3,745 | | | | — | | | | 1,210 | | | | 1,210 | | | | | | 5,773 | | | | 158 | | | | 5,931 | | | | 6,082 | | | | 149 | | | | 6,231 | | | | 3,419 | | | | 168 | | | | 3,587 | | | | | | 13,469 | | | | 40,570 | | | | 54,039 | | | | 15,172 | | | | 40,788 | | | | 55,960 | | | | 10,170 | | | | 38,152 | | | | 48,322 | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 32,321 | | | | 15,090 | | | | 47,411 | | | | 30,391 | | | | 14,184 | | | | 44,575 | | | | 24,612 | | | | 12,501 | | | | 37,113 | | | | | | 6,257 | | | | 3,291 | | | | 9,548 | | | | 7,298 | | | | 2,907 | | | | 10,205 | | | | 4,306 | | | | 3,034 | | | | 7,340 | | Loss on pension plan settlement | | | — | | | | — | | | | — | | | | 17,377 | | | | — | | | | 17,377 | | | | — | | | | — | | | | — | | Occupancy and bank premises | | | 8,005 | | | | 1,606 | | | | 9,611 | | | | 8,662 | | | | 1,643 | | | | 10,305 | | | | 5,753 | | | | 1,552 | | | | 7,305 | | Amortization of other intangible assets | | | 872 | | | | 2,626 | | | | 3,498 | | | | 1,172 | | | | 2,655 | | | | 3,827 | | | | 276 | | | | 2,383 | | | | 2,659 | | | | | | 3,516 | | | | 143 | | | | 3,659 | | | | 3,227 | | | | 126 | | | | 3,353 | | | | 2,923 | | | | 94 | | | | 3,017 | | | | | | 24,183 | | | | 3,835 | | | | 28,018 | | | | 32,150 | | | | 3,973 | | | | 36,123 | | | | 20,457 | | | | 3,527 | | | | 23,984 | | | | | | 75,154 | | | | 26,591 | | | | 101,745 | | | | 100,277 | | | | 25,488 | | | | 125,765 | | | | 58,327 | | | | 23,091 | | | | 81,418 | | | | | | 40,222 | | | | 13,982 | | | | 54,204 | | | | 10,623 | | | | 15,303 | | | | 25,926 | | | | 27,784 | | | | 15,064 | | | | 42,848 | | Intersegment (revenues) expenses* | | | (396 | | | | 396 | | | | — | | | | (422 | | | | 422 | | | | — | | | | (372 | | | | 372 | | | | — | | Pre-tax segment profit after eliminations | | $ | 39,826 | | | $ | 14,378 | | | $ | 54,204 | | | $ | 10,201 | | | $ | 15,725 | | | $ | 25,926 | | | $ | 27,412 | | | $ | 15,436 | | | $ | 42,848 | | % of segment pre-tax profit after eliminations | | | 73.5 | % | | | 26.5 | % | | | 100.0 | % | | | 39.3 | % | | | 60.7 | % | | | 100.0 | % | | | 64.0 | % | | | 36.0 | % | | | 100.0 | % | Segment assets (dollars in millions) | | $ | 3,377.1 | | | $ | 44.4 | | | $ | 3,421.5 | | | $ | 2,983.2 | | | $ | 47.8 | | | $ | 3,031.0 | | | $ | 2,197.8 | | | $ | 48.7 | | | $ | 2,246.5 | |
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