Fair Value Measurement of Assets and Liabilities - Carrying Amounts and Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Interest bearing deposits with banks	$ 1,071,360	$ 178,423
Equity securities	29,378	41,410
Investment securities held to maturity	2,227,612	2,358,720
Accrued interest receivable	106,230	105,637
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deposits with stated maturities	6,714,678	9,717,945
Carrying Amount
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity	2,173,011	2,336,095
Carrying Amount | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and due from banks	257,845	256,264
Interest bearing deposits with banks	1,071,360	178,423
Accrued interest receivable	106,230	105,637
Federal Reserve Bank and Federal Home Loan Bank stock	250,116	214,421
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deposits without stated maturities	25,220,924	19,467,892
Short-term borrowings	1,147,958	1,093,280
Accrued interest payable	18,839	33,066
Carrying Amount | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Treasury securities
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity	68,126	138,352
Carrying Amount | Significant Other Observable  Inputs (Level 2)
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deposits with stated maturities	6,714,678	9,717,945
Long-term borrowings	2,295,665	2,122,426
Junior subordinated debentures issued to capital trusts	56,065	55,718
Carrying Amount | Significant Other Observable  Inputs (Level 2) | U.S. government agency securities
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity	6,222	7,345
Carrying Amount | Significant Other Observable  Inputs (Level 2) | Obligations of states and political subdivisions
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity	470,259	500,705
Carrying Amount | Significant Other Observable  Inputs (Level 2) | Residential mortgage-backed securities
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity	1,550,306	1,620,119
Carrying Amount | Significant Other Observable  Inputs (Level 2) | Trust preferred securities
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity	37,348	37,324
Carrying Amount | Significant Other Observable  Inputs (Level 2) | Corporate and other debt securities
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity	40,750	32,250
Carrying Amount | Significant Unobservable Inputs (Level 3)
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Equity securities	2,999	0
Net loans	31,876,869	29,537,449
Fair Value
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity	2,227,612	2,358,720
Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and due from banks	257,845	256,264
Interest bearing deposits with banks	1,071,360	178,423
Accrued interest receivable	106,230	105,637
Federal Reserve Bank and Federal Home Loan Bank stock	250,116	214,421
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deposits without stated maturities	25,220,924	19,467,892
Short-term borrowings	1,151,478	1,081,879
Accrued interest payable	18,839	33,066
Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Treasury securities
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity	75,484	144,113
Fair Value | Significant Other Observable  Inputs (Level 2)
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deposits with stated maturities	6,639,022	9,747,867
Long-term borrowings	2,405,345	2,181,401
Junior subordinated debentures issued to capital trusts	57,779	53,889
Fair Value | Significant Other Observable  Inputs (Level 2) | U.S. government agency securities
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity	6,513	7,362
Fair Value | Significant Other Observable  Inputs (Level 2) | Obligations of states and political subdivisions
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity	484,506	513,607
Fair Value | Significant Other Observable  Inputs (Level 2) | Residential mortgage-backed securities
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity	1,589,655	1,629,572
Fair Value | Significant Other Observable  Inputs (Level 2) | Trust preferred securities
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity	30,033	31,382
Fair Value | Significant Other Observable  Inputs (Level 2) | Corporate and other debt securities
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity	41,421	32,684
Fair Value | Significant Unobservable Inputs (Level 3)
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Equity securities	2,999	0
Net loans	$ 31,635,060	$ 28,964,396