Fair Value Measurement of Assets and Liabilities - Carrying Amounts and Estimated Fair Values (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Financial assets
Interest bearing deposits with banks	$ 542,006	$ 607,135
Equity securities	66,951	64,464
Total held to maturity debt securities	3,217,402	3,302,312
Accrued interest receivable	253,893	245,498
Financial liabilities
Deposits with stated maturities	12,743,734	13,176,724
U.S. Treasury securities
Financial assets
Total held to maturity debt securities	25,742	25,978
U.S. government agency securities
Financial assets
Total held to maturity debt securities	260,175	261,555
Obligations of states and political subdivisions
Financial assets
Total held to maturity debt securities	378,032	387,527
Residential mortgage-backed securities
Financial assets
Total held to maturity debt securities	2,441,934	2,521,926
Trust preferred securities
Financial assets
Total held to maturity debt securities	30,482	30,650
Corporate and other debt securities
Financial assets
Total held to maturity debt securities	81,037	74,676
Carrying Amount
Financial assets
Total held to maturity debt securities	3,711,818	3,740,413
Carrying Amount | Level 1
Financial assets
Cash and due from banks	398,827	284,090
Interest bearing deposits with banks	542,006	607,135
Accrued interest receivable	253,893	245,498
Financial liabilities
Deposits without stated maturities	36,334,212	36,066,105
Accrued interest payable	109,477	159,496
Carrying Amount | Level 1 | U.S. Treasury securities
Financial assets
Total held to maturity debt securities	26,048	26,232
Carrying Amount | Level 2
Financial assets
FRB and FHLB stock	323,981	320,727
Financial liabilities
Deposits with stated maturities	12,743,734	13,176,724
Short-term borrowings	75,224	917,834
Long-term borrowings	3,262,341	2,328,375
Junior subordinated debentures issued to capital trusts	57,195	57,108
Carrying Amount | Level 2 | U.S. government agency securities
Financial assets
Total held to maturity debt securities	305,543	305,996
Carrying Amount | Level 2 | Obligations of states and political subdivisions
Financial assets
Total held to maturity debt securities	400,523	405,470
Carrying Amount | Level 2 | Residential mortgage-backed securities
Financial assets
Total held to maturity debt securities	2,856,322	2,885,303
Carrying Amount | Level 2 | Trust preferred securities
Financial assets
Total held to maturity debt securities	37,066	37,062
Carrying Amount | Level 2 | Corporate and other debt securities
Financial assets
Total held to maturity debt securities	86,316	80,350
Carrying Amount | Level 3
Financial assets
Equity securities	31,525	29,031
Net loans	49,486,937	49,764,215
Carrying Amount | Level 3 | Construction
Financial assets
Net loans	34,100
Fair Value
Financial assets
Total held to maturity debt securities	3,217,402	3,302,312
Fair Value | Level 1
Financial assets
Cash and due from banks	398,827	284,090
Interest bearing deposits with banks	542,006	607,135
Accrued interest receivable	253,893	245,498
Financial liabilities
Deposits without stated maturities	36,334,212	36,066,105
Accrued interest payable	109,477	159,496
Fair Value | Level 1 | U.S. Treasury securities
Financial assets
Total held to maturity debt securities	25,742	25,978
Fair Value | Level 2
Financial assets
FRB and FHLB stock	323,981	320,727
Financial liabilities
Deposits with stated maturities	12,685,362	13,103,381
Short-term borrowings	57,603	901,617
Long-term borrowings	3,176,646	2,256,997
Junior subordinated debentures issued to capital trusts	47,597	47,374
Fair Value | Level 2 | U.S. government agency securities
Financial assets
Total held to maturity debt securities	260,175	261,555
Fair Value | Level 2 | Obligations of states and political subdivisions
Financial assets
Total held to maturity debt securities	378,032	387,527
Fair Value | Level 2 | Residential mortgage-backed securities
Financial assets
Total held to maturity debt securities	2,441,934	2,521,926
Fair Value | Level 2 | Trust preferred securities
Financial assets
Total held to maturity debt securities	30,482	30,650
Fair Value | Level 2 | Corporate and other debt securities
Financial assets
Total held to maturity debt securities	81,037	74,676
Fair Value | Level 3
Financial assets
Equity securities	31,525	29,031
Net loans	$ 47,672,062	$ 47,981,499