v3.26.1
Fair Value Measurement of Assets and Liabilities - Carrying Amounts and Estimated Fair Values (Details) - USD ($)
$ in Thousands
 6 Months Ended 12 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Dec. 31, 2025
Financial assets      
Interest bearing deposits with banks $ 578,148   $ 1,268,399
Equity securities 88,541   82,774
Total held to maturity debt securities 3,368,350   3,129,603
Accrued interest receivable 250,703   243,897
Financial liabilities      
Deposits with stated maturities 12,902,637   11,424,123
Transfer of loans to loans held for sale, net 0 $ 10,200  
Non-performing loan held for sale      
Financial liabilities      
Transfer of loans to loans held for sale, net 8,800   18,000
U.S. government agency securities      
Financial assets      
Total held to maturity debt securities 248,786   253,062
Obligations of states and political subdivisions      
Financial assets      
Total held to maturity debt securities 357,745   333,834
Residential mortgage-backed securities      
Financial assets      
Total held to maturity debt securities 2,654,518   2,431,987
Trust preferred securities      
Financial assets      
Total held to maturity debt securities 31,720   30,689
Corporate and other debt securities      
Financial assets      
Total held to maturity debt securities 75,581   80,031
Carrying Amount      
Financial assets      
Total held to maturity debt securities 3,757,944   3,496,571
Carrying Amount | Level 1      
Financial assets      
Cash and due from banks 388,741   315,166
Interest bearing deposits with banks 578,148   1,268,399
Accrued interest receivable 250,703   243,897
Financial liabilities      
Deposits without stated maturities 41,215,970   40,758,970
Accrued interest payable 89,342   89,683
Carrying Amount | Level 2      
Financial assets      
FRB and FHLB stock 336,645   339,484
Financial liabilities      
Deposits with stated maturities 12,902,637   11,424,123
Short-term borrowings 433,484   91,475
Long-term borrowings 2,607,222   2,908,579
Junior subordinated debentures issued to capital trusts 57,977   57,803
Carrying Amount | Level 2 | U.S. government agency securities      
Financial assets      
Total held to maturity debt securities 290,828   292,269
Carrying Amount | Level 2 | Obligations of states and political subdivisions      
Financial assets      
Total held to maturity debt securities 380,713   353,875
Carrying Amount | Level 2 | Residential mortgage-backed securities      
Financial assets      
Total held to maturity debt securities 2,973,477   2,732,752
Carrying Amount | Level 2 | Trust preferred securities      
Financial assets      
Total held to maturity debt securities 36,115   36,103
Carrying Amount | Level 2 | Corporate and other debt securities      
Financial assets      
Total held to maturity debt securities 76,811   81,572
Carrying Amount | Level 3      
Financial assets      
Equity securities 56,116   49,371
Net loans (3) 51,885,401   49,571,352
Fair Value      
Financial assets      
Total held to maturity debt securities 3,368,350   3,129,603
Fair Value | Level 1      
Financial assets      
Cash and due from banks 388,741   315,166
Interest bearing deposits with banks 578,148   1,268,399
Accrued interest receivable 250,703   243,897
Financial liabilities      
Deposits without stated maturities 41,215,970   40,758,970
Accrued interest payable 89,342   89,683
Fair Value | Level 2      
Financial assets      
FRB and FHLB stock 336,645   339,484
Financial liabilities      
Deposits with stated maturities 12,896,051   11,465,247
Short-term borrowings 431,249   88,468
Long-term borrowings 2,547,300   2,916,674
Junior subordinated debentures issued to capital trusts 50,174   53,050
Fair Value | Level 2 | U.S. government agency securities      
Financial assets      
Total held to maturity debt securities 248,786   253,062
Fair Value | Level 2 | Obligations of states and political subdivisions      
Financial assets      
Total held to maturity debt securities 357,745   333,834
Fair Value | Level 2 | Residential mortgage-backed securities      
Financial assets      
Total held to maturity debt securities 2,654,518   2,431,987
Fair Value | Level 2 | Trust preferred securities      
Financial assets      
Total held to maturity debt securities 31,720   30,689
Fair Value | Level 2 | Corporate and other debt securities      
Financial assets      
Total held to maturity debt securities 75,581   80,031
Fair Value | Level 3      
Financial assets      
Equity securities 56,116   49,371
Net loans (3) $ 50,923,077   $ 47,868,967