Fair Value Measurement of Assets and Liabilities - Carrying Amounts and Estimated Fair Values (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Financial assets
Interest bearing deposits with banks	$ 745,547	$ 1,478,713
Equity securities	77,408	71,513
Total held to maturity debt securities	3,088,401	3,028,284
Net loans	8,800	8,800
Accrued interest receivable	238,278	239,941
Financial liabilities
Deposits with stated maturities	12,886,881	12,342,544
U.S. Treasury securities
Financial assets
Total held to maturity debt securities	25,079	25,461
U.S. government agency securities
Financial assets
Total held to maturity debt securities	253,739	252,302
Obligations of states and political subdivisions
Financial assets
Total held to maturity debt securities	328,494	346,361
Residential mortgage-backed securities
Financial assets
Total held to maturity debt securities	2,370,561	2,292,148
Trust preferred securities
Financial assets
Total held to maturity debt securities	29,728	29,145
Corporate and other debt securities
Financial assets
Total held to maturity debt securities	80,800	82,867
Carrying Amount
Financial assets
Total held to maturity debt securities	3,531,561	3,532,220
Carrying Amount | Level 1
Financial assets
Cash and due from banks	440,870	411,412
Interest bearing deposits with banks	745,547	1,478,713
Accrued interest receivable	238,278	239,941
Financial liabilities
Deposits without stated maturities	37,838,403	37,733,313
Accrued interest payable	118,608	150,564
Carrying Amount | Level 1 | U.S. Treasury securities
Financial assets
Total held to maturity debt securities	25,095	25,480
Carrying Amount | Level 2
Financial assets
FRB and FHLB stock	344,052	328,497
Financial liabilities
Deposits with stated maturities	12,886,881	12,342,544
Short-term borrowings	162,244	72,718
Long-term borrowings	2,903,091	3,174,155
Junior subordinated debentures issued to capital trusts	57,629	57,455
Carrying Amount | Level 2 | U.S. government agency securities
Financial assets
Total held to maturity debt securities	297,057	301,315
Carrying Amount | Level 2 | Obligations of states and political subdivisions
Financial assets
Total held to maturity debt securities	358,377	372,489
Carrying Amount | Level 2 | Residential mortgage-backed securities
Financial assets
Total held to maturity debt securities	2,731,797	2,710,642
Carrying Amount | Level 2 | Trust preferred securities
Financial assets
Total held to maturity debt securities	36,092	36,081
Carrying Amount | Level 2 | Corporate and other debt securities
Financial assets
Total held to maturity debt securities	83,143	86,213
Carrying Amount | Level 3
Financial assets
Equity securities	43,640	36,871
Net loans	48,811,920	48,240,861
Fair Value
Financial assets
Total held to maturity debt securities	3,088,401	3,028,284
Fair Value | Level 1
Financial assets
Cash and due from banks	440,870	411,412
Interest bearing deposits with banks	745,547	1,478,713
Accrued interest receivable	238,278	239,941
Financial liabilities
Deposits without stated maturities	37,838,403	37,733,313
Accrued interest payable	118,608	150,564
Fair Value | Level 1 | U.S. Treasury securities
Financial assets
Total held to maturity debt securities	25,079	25,461
Fair Value | Level 2
Financial assets
FRB and FHLB stock	344,052	328,497
Financial liabilities
Deposits with stated maturities	12,929,115	12,363,365
Short-term borrowings	159,081	68,032
Long-term borrowings	2,874,547	3,109,622
Junior subordinated debentures issued to capital trusts	53,054	54,957
Fair Value | Level 2 | U.S. government agency securities
Financial assets
Total held to maturity debt securities	253,739	252,302
Fair Value | Level 2 | Obligations of states and political subdivisions
Financial assets
Total held to maturity debt securities	328,494	346,361
Fair Value | Level 2 | Residential mortgage-backed securities
Financial assets
Total held to maturity debt securities	2,370,561	2,292,148
Fair Value | Level 2 | Trust preferred securities
Financial assets
Total held to maturity debt securities	29,728	29,145
Fair Value | Level 2 | Corporate and other debt securities
Financial assets
Total held to maturity debt securities	80,800	82,867
Fair Value | Level 3
Financial assets
Equity securities	43,640	36,871
Net loans	$ 47,085,699	$ 46,634,654