Fair Value Measurement of Assets and Liabilities - Carrying Amounts and Estimated Fair Values (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Financial assets
Interest bearing deposits with banks	$ 527,960	$ 607,135
Equity securities	73,071	64,464
Total held to maturity debt securities	3,204,496	3,302,312
Net loans	8,800
Accrued interest receivable	250,131	245,498
Financial liabilities
Deposits with stated maturities	14,172,807	13,176,724
U.S. Treasury securities
Financial assets
Total held to maturity debt securities	25,682	25,978
U.S. government agency securities
Financial assets
Total held to maturity debt securities	269,208	261,555
Obligations of states and political subdivisions
Financial assets
Total held to maturity debt securities	364,290	387,527
Residential mortgage-backed securities
Financial assets
Total held to maturity debt securities	2,432,867	2,521,926
Trust preferred securities
Financial assets
Total held to maturity debt securities	29,774	30,650
Corporate and other debt securities
Financial assets
Total held to maturity debt securities	82,675	74,676
Carrying Amount
Financial assets
Total held to maturity debt securities	3,575,036	3,740,413
Carrying Amount | Level 1
Financial assets
Cash and due from banks	511,945	284,090
Interest bearing deposits with banks	527,960	607,135
Accrued interest receivable	250,131	245,498
Financial liabilities
Deposits without stated maturities	36,223,159	36,066,105
Accrued interest payable	127,685	159,496
Carrying Amount | Level 1 | U.S. Treasury securities
Financial assets
Total held to maturity debt securities	25,671	26,232
Carrying Amount | Level 2
Financial assets
FRB and FHLB stock	327,645	320,727
Financial liabilities
Deposits with stated maturities	14,172,807	13,176,724
Short-term borrowings	58,268	917,834
Long-term borrowings	3,274,340	2,328,375
Junior subordinated debentures issued to capital trusts	57,368	57,108
Carrying Amount | Level 2 | U.S. government agency securities
Financial assets
Total held to maturity debt securities	303,200	305,996
Carrying Amount | Level 2 | Obligations of states and political subdivisions
Financial assets
Total held to maturity debt securities	380,653	405,470
Carrying Amount | Level 2 | Residential mortgage-backed securities
Financial assets
Total held to maturity debt securities	2,742,188	2,885,303
Carrying Amount | Level 2 | Trust preferred securities
Financial assets
Total held to maturity debt securities	37,076	37,062
Carrying Amount | Level 2 | Corporate and other debt securities
Financial assets
Total held to maturity debt securities	86,248	80,350
Carrying Amount | Level 3
Financial assets
Equity securities	37,579	29,031
Net loans	48,806,992	49,764,215
Fair Value
Financial assets
Total held to maturity debt securities	3,204,496	3,302,312
Fair Value | Level 1
Financial assets
Cash and due from banks	511,945	284,090
Interest bearing deposits with banks	527,960	607,135
Accrued interest receivable	250,131	245,498
Financial liabilities
Deposits without stated maturities	36,223,159	36,066,105
Accrued interest payable	127,685	159,496
Fair Value | Level 1 | U.S. Treasury securities
Financial assets
Total held to maturity debt securities	25,682	25,978
Fair Value | Level 2
Financial assets
FRB and FHLB stock	327,645	320,727
Financial liabilities
Deposits with stated maturities	14,227,913	13,103,381
Short-term borrowings	45,079	901,617
Long-term borrowings	3,291,136	2,256,997
Junior subordinated debentures issued to capital trusts	47,879	47,374
Fair Value | Level 2 | U.S. government agency securities
Financial assets
Total held to maturity debt securities	269,208	261,555
Fair Value | Level 2 | Obligations of states and political subdivisions
Financial assets
Total held to maturity debt securities	364,290	387,527
Fair Value | Level 2 | Residential mortgage-backed securities
Financial assets
Total held to maturity debt securities	2,432,867	2,521,926
Fair Value | Level 2 | Trust preferred securities
Financial assets
Total held to maturity debt securities	29,774	30,650
Fair Value | Level 2 | Corporate and other debt securities
Financial assets
Total held to maturity debt securities	82,675	74,676
Fair Value | Level 3
Financial assets
Equity securities	37,579	29,031
Net loans	$ 47,796,832	$ 47,981,499