Fair Value Measurement of Assets and Liabilities - Carrying Amounts and Estimated Fair Values (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Financial assets
Interest bearing deposits with banks	$ 531,067	$ 607,135
Equity securities	69,105	64,464
Total held to maturity debt securities	3,139,948	3,302,312
Net loans	8,800
Accrued interest receivable	251,167	245,498
Financial liabilities
Deposits with stated maturities	14,283,348	13,176,724
U.S. Treasury securities
Financial assets
Total held to maturity debt securities	25,579	25,978
U.S. government agency securities
Financial assets
Total held to maturity debt securities	257,457	261,555
Obligations of states and political subdivisions
Financial assets
Total held to maturity debt securities	366,611	387,527
Residential mortgage-backed securities
Financial assets
Total held to maturity debt securities	2,379,255	2,521,926
Trust preferred securities
Financial assets
Total held to maturity debt securities	29,848	30,650
Corporate and other debt securities
Financial assets
Total held to maturity debt securities	81,198	74,676
Carrying Amount
Financial assets
Total held to maturity debt securities	3,651,454	3,740,413
Carrying Amount | Level 1
Financial assets
Cash and due from banks	478,006	284,090
Interest bearing deposits with banks	531,067	607,135
Accrued interest receivable	251,167	245,498
Financial liabilities
Deposits without stated maturities	35,828,829	36,066,105
Accrued interest payable	135,049	159,496
Carrying Amount | Level 1 | U.S. Treasury securities
Financial assets
Total held to maturity debt securities	25,861	26,232
Carrying Amount | Level 2
Financial assets
FRB and FHLB stock	327,561	320,727
Financial liabilities
Deposits with stated maturities	14,283,348	13,176,724
Short-term borrowings	63,770	917,834
Long-term borrowings	3,264,530	2,328,375
Junior subordinated debentures issued to capital trusts	57,282	57,108
Carrying Amount | Level 2 | U.S. government agency securities
Financial assets
Total held to maturity debt securities	304,308	305,996
Carrying Amount | Level 2 | Obligations of states and political subdivisions
Financial assets
Total held to maturity debt securities	393,163	405,470
Carrying Amount | Level 2 | Residential mortgage-backed securities
Financial assets
Total held to maturity debt securities	2,804,769	2,885,303
Carrying Amount | Level 2 | Trust preferred securities
Financial assets
Total held to maturity debt securities	37,071	37,062
Carrying Amount | Level 2 | Corporate and other debt securities
Financial assets
Total held to maturity debt securities	86,282	80,350
Carrying Amount | Level 3
Financial assets
Equity securities	33,852	29,031
Net loans	49,792,392	49,764,215
Fair Value
Financial assets
Total held to maturity debt securities	3,139,948	3,302,312
Fair Value | Level 1
Financial assets
Cash and due from banks	478,006	284,090
Interest bearing deposits with banks	531,067	607,135
Accrued interest receivable	251,167	245,498
Financial liabilities
Deposits without stated maturities	35,828,829	36,066,105
Accrued interest payable	135,049	159,496
Fair Value | Level 1 | U.S. Treasury securities
Financial assets
Total held to maturity debt securities	25,579	25,978
Fair Value | Level 2
Financial assets
FRB and FHLB stock	327,561	320,727
Financial liabilities
Deposits with stated maturities	14,251,483	13,103,381
Short-term borrowings	47,379	901,617
Long-term borrowings	3,209,974	2,256,997
Junior subordinated debentures issued to capital trusts	48,130	47,374
Fair Value | Level 2 | U.S. government agency securities
Financial assets
Total held to maturity debt securities	257,457	261,555
Fair Value | Level 2 | Obligations of states and political subdivisions
Financial assets
Total held to maturity debt securities	366,611	387,527
Fair Value | Level 2 | Residential mortgage-backed securities
Financial assets
Total held to maturity debt securities	2,379,255	2,521,926
Fair Value | Level 2 | Trust preferred securities
Financial assets
Total held to maturity debt securities	29,848	30,650
Fair Value | Level 2 | Corporate and other debt securities
Financial assets
Total held to maturity debt securities	81,198	74,676
Fair Value | Level 3
Financial assets
Equity securities	33,852	29,031
Net loans	$ 48,010,633	$ 47,981,499