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Loans and Allowance for Credit Losses - Age Analysis of Past Due Loans Segregated by Class of Loans (Details) - USD ($) $ in Thousands | Mar. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
--- | --- | --- | ---
Financing Receivable, Past Due [Line Items] |  |  |
Total | $ 7,656,034 | $ 7,653,341 |
Nonaccrual | 33,209 | 22,947 | $ 19,052
Current |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 7,599,427 | 7,615,273 |
Total Past Due Loans |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 56,607 | 38,068 |
30-59 Days Past Due |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 14,019 | 7,247 |
60-89 Days Past Due |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 9,379 | 7,874 |
Commercial Loans | Commercial real estate |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 2,699,782 | 2,659,135 |
Nonaccrual | 17,153 | 6,320 | 7,100
Commercial Loans | Commercial and industrial |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 1,410,517 | 1,436,183 |
Nonaccrual | 612 | 878 | 283
Commercial Loans | Commercial construction |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 347,375 | 350,583 |
Nonaccrual | 4,960 | 4,960 | 384
Commercial Loans | Business banking |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 1,307,155 | 1,360,765 |
Nonaccrual | 3,907 | 4,147 | 4,490
Commercial Loans | Current | Commercial real estate |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 2,682,629 | 2,649,412 |
Commercial Loans | Current | Commercial and industrial |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 1,399,799 | 1,435,301 |
Commercial Loans | Current | Commercial construction |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 342,415 | 345,623 |
Commercial Loans | Current | Business banking |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 1,297,451 | 1,351,048 |
Commercial Loans | Total Past Due Loans | Commercial real estate |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 17,153 | 9,723 |
Commercial Loans | Total Past Due Loans | Commercial and industrial |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 10,718 | 882 |
Commercial Loans | Total Past Due Loans | Commercial construction |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 4,960 | 4,960 |
Commercial Loans | Total Past Due Loans | Business banking |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 9,704 | 9,717 |
Commercial Loans | 30-59 Days Past Due | Commercial real estate |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 0 | 0 |
Commercial Loans | 30-59 Days Past Due | Commercial and industrial |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 2,109 | 4 |
Commercial Loans | 30-59 Days Past Due | Commercial construction |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 0 | 0 |
Commercial Loans | 30-59 Days Past Due | Business banking |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 5,487 | 3,525 |
Commercial Loans | 60-89 Days Past Due | Commercial real estate |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 0 | 3,403 |
Commercial Loans | 60-89 Days Past Due | Commercial and industrial |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 7,997 | 0 |
Commercial Loans | 60-89 Days Past Due | Commercial construction |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 0 | 0 |
Commercial Loans | 60-89 Days Past Due | Business banking |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 310 | 2,045 |
Consumer Loans | Consumer real estate |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 1,782,973 | 1,731,778 |
Nonaccrual | 6,371 | 6,312 | 6,526
Consumer Loans | Other consumer |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 108,232 | 114,897 |
Nonaccrual | 206 | 330 | $ 269
Consumer Loans | Current | Consumer real estate |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 1,769,518 | 1,719,751 |
Consumer Loans | Current | Other consumer |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 107,615 | 114,138 |
Consumer Loans | Total Past Due Loans | Consumer real estate |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 13,455 | 12,027 |
Consumer Loans | Total Past Due Loans | Other consumer |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 617 | 759 |
Consumer Loans | 30-59 Days Past Due | Consumer real estate |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 6,204 | 3,352 |
Consumer Loans | 30-59 Days Past Due | Other consumer |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 219 | 366 |
Consumer Loans | 60-89 Days Past Due | Consumer real estate |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | 880 | 2,363 |
Consumer Loans | 60-89 Days Past Due | Other consumer |  |  |
Financing Receivable, Past Due [Line Items] |  |  |
Total | $ 192 | $ 63 |

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