v3.26.1
Financial Instruments - Amortized Cost and Fair Value of Securities Available-for-Sale (Details) - USD ($)
$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Estimated Fair Value $ 2,803,847 $ 2,871,931
U.S. government-sponsored enterprises    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Estimated Fair Value 218,971 240,782
U.S. government-sponsored mortgage-backed securities    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Estimated Fair Value 1,177,874 1,212,948
Private mortgage-backed securities    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Estimated Fair Value 142,527 145,720
Non-government-sponsored asset backed securities    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Estimated Fair Value 154,826 157,844
State and political subdivisions    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Estimated Fair Value 878,978 887,838
Other securities    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Estimated Fair Value 230,671 226,799
Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Estimated Fair Value 2,803,847 2,871,931
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 2,774,309 2,841,820
Fair Value, Recurring | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Estimated Fair Value 29,538 30,111
Fair Value, Recurring | U.S. government-sponsored enterprises    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Estimated Fair Value 218,971 240,782
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 218,971 240,782
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 1,177,874 1,212,948
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 1,177,874 1,212,948
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 142,527 145,720
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 142,527 145,720
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 154,826 157,844
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 154,826 157,844
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 878,978 887,838
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 863,661 872,522
Fair Value, Recurring | State and political subdivisions | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Estimated Fair Value 15,317 15,316
Fair Value, Recurring | Other securities    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Estimated Fair Value 230,671 226,799
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 216,450 212,004
Fair Value, Recurring | Other securities | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Estimated Fair Value $ 14,221 $ 14,795