Fair Value Measurement of Assets and Liabilities - Carrying Amounts and Estimated Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Interest bearing deposits with banks	$ 171,710	$ 170,225
Investment securities held to maturity	1,924,597	1,621,039
Accrued interest receivable	66,816	63,554
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deposits with stated maturities	3,138,871	3,157,904
Carrying Amount
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity	1,925,572	1,596,385
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	220,791	243,575
Interest bearing deposits with banks	171,710	170,225
Accrued interest receivable	66,816	63,554
Federal Reserve Bank and Federal Home Loan Bank stock	147,127	145,068
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deposits without stated maturities	14,591,837	13,095,647
Short-term borrowings	1,080,960	1,076,991
Accrued interest payable	10,675	13,110
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	138,830	138,978
Carrying Amount | Significant Other Observable Inputs (Level 2)
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deposits with stated maturities	3,138,871	3,157,904
Long-term borrowings	1,433,906	1,810,728
Junior subordinated debentures issued to capital trusts	41,577	41,414
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	11,329	12,859
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	566,590	504,865
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	1,112,460	852,289
Carrying Amount | Significant Other Observable Inputs (Level 2) | Trust preferred securities
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity	59,804	59,785
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	36,559	27,609
Carrying Amount | Significant Unobservable Inputs (Level 3)
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Net loans	17,121,684	15,936,929
Fair Value
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity	1,924,597	1,621,039
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	220,791	243,575
Interest bearing deposits with banks	171,710	170,225
Accrued interest receivable	66,816	63,554
Federal Reserve Bank and Federal Home Loan Bank stock	147,127	145,068
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deposits without stated maturities	14,591,837	13,095,647
Short-term borrowings	1,081,751	1,076,991
Accrued interest payable	10,675	13,110
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	147,495	149,483
Fair Value | Significant Other Observable Inputs (Level 2)
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deposits with stated maturities	3,160,572	3,203,389
Long-term borrowings	1,523,386	1,945,741
Junior subordinated debentures issued to capital trusts	45,785	44,127
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	11,464	13,130
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	577,826	527,263
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	1,102,802	855,272
Fair Value | Significant Other Observable Inputs (Level 2) | Trust preferred securities
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity	47,290	46,437
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	37,720	29,454
Fair Value | Significant Unobservable Inputs (Level 3)
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Net loans	$ 16,756,655	$ 15,824,475