Fair Value Measurement of Assets and Liabilities - Carrying Amounts and Estimated Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands		Dec. 31, 2015	Dec. 31, 2014
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Interest bearing deposits with banks		$ 170,225	$ 367,838
Investment securities held to maturity		1,621,039	1,815,976
Accrued interest receivable		63,554	57,333
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deposits with stated maturities		3,157,904	2,742,468
Carrying Amount [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity		1,596,385	1,778,316
Carrying Amount [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and due from banks		243,575	462,569
Interest bearing deposits with banks		170,225	367,838
Accrued interest receivable		63,554	57,333
Federal Reserve Bank and Federal Home Loan Bank stock	[1]	145,068	133,117
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deposits without stated maturities		13,095,647	11,291,646
Short-term borrowings		1,076,991	146,781
Accrued interest payable	[2]	13,110	15,526
Carrying Amount [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Treasury securities [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity		138,978	139,121
Carrying Amount [Member] | Significant Other Observable Inputs (Level 2) [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deposits with stated maturities		3,157,904	2,742,468
Long-term borrowings		1,810,728	2,526,408
Junior subordinated debentures issued to capital trusts		41,414	41,252
Carrying Amount [Member] | Significant Other Observable Inputs (Level 2) [Member] | U.S. government agency securities [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity		12,859	14,081
Carrying Amount [Member] | Significant Other Observable Inputs (Level 2) [Member] | Obligations of states and political subdivisions [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity		504,865	500,018
Carrying Amount [Member] | Significant Other Observable Inputs (Level 2) [Member] | Residential mortgage-backed securities [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity		852,289	986,992
Carrying Amount [Member] | Significant Other Observable Inputs (Level 2) [Member] | Trust preferred securities [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity		59,785	98,456
Carrying Amount [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate and other debt securities [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity		27,609	39,648
Carrying Amount [Member] | Significant Unobservable Inputs (Level 3) [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Net loans		15,936,929	13,371,560
Fair Value [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity		1,621,039	1,815,976
Fair Value [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and due from banks		243,575	462,569
Interest bearing deposits with banks		170,225	367,838
Accrued interest receivable		63,554	57,333
Federal Reserve Bank and Federal Home Loan Bank stock	[1]	145,068	133,117
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deposits without stated maturities		13,095,647	11,291,648
Short-term borrowings		1,076,991	146,781
Accrued interest payable	[2]	13,110	15,526
Fair Value [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Treasury securities [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity		149,483	151,300
Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deposits with stated maturities		3,203,389	2,807,522
Long-term borrowings		1,945,741	2,738,122
Junior subordinated debentures issued to capital trusts		44,127	44,584
Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | U.S. government agency securities [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity		13,130	14,385
Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | Obligations of states and political subdivisions [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity		527,263	519,693
Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | Residential mortgage-backed securities [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity		855,272	998,981
Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | Trust preferred securities [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity		46,437	86,243
Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate and other debt securities [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity		29,454	45,374
Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Net loans		$ 15,824,475	$ 13,085,830

[1] Included in other assets.

[2] Included in accrued expenses and other liabilities.