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Financial Instruments - Amortized Cost and Fair Value of Securities Available-for-Sale (Details) - USD ($) $ in Thousands | Sep. 30, 2025 | Dec. 31, 2024
--- | --- | ---
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | $ 2,924,496 | $ 3,072,639
U.S. government-sponsored enterprises |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 247,315 | 284,790
U.S. government-sponsored mortgage-backed securities |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 1,241,056 | 1,324,684
Private mortgage-backed securities |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 147,901 | 171,394
Non-government-sponsored asset backed securities |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 171,033 | 225,648
State and political subdivisions |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 882,329 | 870,361
Other securities |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 234,862 | 195,762
Fair Value, Recurring |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 2,924,496 | 3,072,639
Fair Value, Recurring | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 0 | 0
Fair Value, Recurring | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 2,904,309 | 3,051,110
Fair Value, Recurring | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 20,187 | 21,529
Fair Value, Recurring | U.S. government-sponsored enterprises |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 247,315 | 284,790
Fair Value, Recurring | U.S. government-sponsored enterprises | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 0 | 0
Fair Value, Recurring | U.S. government-sponsored enterprises | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 247,315 | 284,790
Fair Value, Recurring | U.S. government-sponsored enterprises | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 0 | 0
Fair Value, Recurring | U.S. government-sponsored mortgage-backed securities |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 1,241,056 | 1,324,684
Fair Value, Recurring | U.S. government-sponsored mortgage-backed securities | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 0 | 0
Fair Value, Recurring | U.S. government-sponsored mortgage-backed securities | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 1,241,056 | 1,324,684
Fair Value, Recurring | U.S. government-sponsored mortgage-backed securities | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 0 | 0
Fair Value, Recurring | Private mortgage-backed securities |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 147,901 | 171,394
Fair Value, Recurring | Private mortgage-backed securities | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 0 | 0
Fair Value, Recurring | Private mortgage-backed securities | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 147,901 | 171,394
Fair Value, Recurring | Private mortgage-backed securities | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 0 | 0
Fair Value, Recurring | Non-government-sponsored asset backed securities |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 171,033 | 225,648
Fair Value, Recurring | Non-government-sponsored asset backed securities | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 0 | 0
Fair Value, Recurring | Non-government-sponsored asset backed securities | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 171,033 | 225,648
Fair Value, Recurring | Non-government-sponsored asset backed securities | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 0 | 0
Fair Value, Recurring | State and political subdivisions |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 882,329 | 870,361
Fair Value, Recurring | State and political subdivisions | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 0 | 0
Fair Value, Recurring | State and political subdivisions | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 867,014 | 853,699
Fair Value, Recurring | State and political subdivisions | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 15,315 | 16,662
Fair Value, Recurring | Other securities |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 234,862 | 195,762
Fair Value, Recurring | Other securities | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 0 | 0
Fair Value, Recurring | Other securities | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | 229,990 | 190,895
Fair Value, Recurring | Other securities | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Estimated Fair Value | $ 4,872 | $ 4,867

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