Fair Value Measurement of Assets and Liabilities - Carrying Amounts and Estimated Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Interest bearing deposits with banks	$ 178,423	$ 177,088
Investment securities held to maturity	2,358,720	2,034,943
Accrued interest receivable	105,637	95,296
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deposits with stated maturities	9,717,945	7,063,984
Carrying Amount
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity	2,336,095	2,068,246
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	256,264	251,541
Interest bearing deposits with banks	178,423	177,088
Accrued interest receivable	105,637	95,296
Federal Reserve Bank and Federal Home Loan Bank stock	214,421	232,080
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deposits without stated maturities	19,467,892	17,388,990
Short-term borrowings	1,093,280	2,118,914
Accrued interest payable	33,066	25,762
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	138,352	138,517
Carrying Amount \| Significant Other Observable Inputs (Level 2)
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deposits with stated maturities	9,717,945	7,063,984
Long-term borrowings	2,122,426	1,654,268
Junior subordinated debentures issued to capital trusts	55,718	55,370
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	7,345	8,721
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	500,705	585,656
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	1,620,119	1,266,770
Carrying Amount \| Significant Other Observable Inputs (Level 2) \| Trust preferred securities
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity	37,324	37,332
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	32,250	31,250
Carrying Amount \| Significant Unobservable Inputs (Level 3)
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Net loans	29,537,449	24,883,610
Fair Value
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity	2,358,720	2,034,943
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	256,264	251,541
Interest bearing deposits with banks	178,423	177,088
Accrued interest receivable	105,637	95,296
Federal Reserve Bank and Federal Home Loan Bank stock	214,421	232,080
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deposits without stated maturities	19,467,892	17,388,990
Short-term borrowings	1,081,879	2,091,892
Accrued interest payable	33,066	25,762
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	144,113	142,049
Fair Value \| Significant Other Observable Inputs (Level 2)
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deposits with stated maturities	9,747,867	7,005,573
Long-term borrowings	2,181,401	1,751,194
Junior subordinated debentures issued to capital trusts	53,889	55,692
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	7,362	8,641
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	513,607	586,033
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	1,629,572	1,235,605
Fair Value \| Significant Other Observable Inputs (Level 2) \| Trust preferred securities
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity	31,382	31,486
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	32,684	31,129
Fair Value \| Significant Unobservable Inputs (Level 3)
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Net loans	$ 28,964,396	$ 24,068,755

Interest, dividends, rents, ancillary and other revenues earned but not yet received by the entity on its investments.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value of subordinated debt obligations including, but not limited to, subordinated loan, subordinated bond, subordinated debenture or junior debt.

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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For banks and other depository institutions (including Federal Reserve Banks, if applicable): Interest-bearing deposits in other financial institutions for relatively short periods of time including, for example, certificates of deposits, which are presented separately from cash on the balance sheet.

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Fair value portion of investments in Federal Home Loan Bank (FHLBank) stock.

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Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

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Amount of time deposit liabilities, including certificates of deposit.

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Accrued interest payable fair value disclosure

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