Carrying Amounts and Estimated Fair Values of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Interest bearing deposits with banks	$ 192,364		$ 6,483
Accrued interest receivable	55,548		52,527
Trust preferred securities
Corporate and other debt securities	11,500
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1)
Cash and due from banks	412,895		372,566
Interest bearing deposits with banks	192,364		6,483
Accrued interest receivable	55,548		52,527
Federal Reserve Bank and Federal Home Loan Bank stock	145,328	[1]	129,669	[1]
Deposits without stated maturities	8,199,031		7,171,718
Short-term borrowings	288,865		212,849
Accrued interest payable	16,326	[2]	17,736	[2]
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Treasury Securities
Total investment securities held to maturity	99,906		100,018
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Significant Other Observable Inputs (Level 2)
Deposits with stated maturities	2,721,769		2,501,384
Long-term borrowings	2,698,403		2,726,099
Junior subordinated debentures issued to capital trusts	40,886		25,120
Total investment securities held to maturity	1,624,575		1,958,916
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Significant Other Observable Inputs (Level 2) | Obligations of states and political subdivisions
Corporate and other debt securities	492,617		433,284
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Significant Other Observable Inputs (Level 2) | Residential mortgage-backed securities
Corporate and other debt securities	852,375		1,180,104
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Significant Other Observable Inputs (Level 2) | Trust preferred securities
Corporate and other debt securities	127,510		193,312
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Significant Other Observable Inputs (Level 2) | Corporate and other debt securities
Corporate and other debt securities	52,167		52,198
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Significant Unobservable Inputs (Level 3)
Net loans	11,019,691		9,665,839
Estimate of Fair Value, Fair Value Disclosure | Quoted Prices in Active Markets for Identical Assets (Level 1)
Cash and due from banks	412,895		372,566
Interest bearing deposits with banks	192,364		6,483
Accrued interest receivable	55,548		52,527
Federal Reserve Bank and Federal Home Loan Bank stock	145,328	[1]	129,669	[1]
Deposits without stated maturities	8,199,031		7,171,718
Short-term borrowings	288,865		215,179
Accrued interest payable	16,326	[2]	17,736	[2]
Estimate of Fair Value, Fair Value Disclosure | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Treasury Securities
Total investment securities held to maturity	116,261		113,859
Estimate of Fair Value, Fair Value Disclosure | Significant Other Observable Inputs (Level 2)
Deposits with stated maturities	2,780,264		2,557,119
Long-term borrowings	3,128,748		3,154,150
Junior subordinated debentures issued to capital trusts	40,858		25,620
Total investment securities held to maturity	1,689,413		2,027,197
Estimate of Fair Value, Fair Value Disclosure | Significant Other Observable Inputs (Level 2) | Obligations of states and political subdivisions
Corporate and other debt securities	518,570		453,201
Estimate of Fair Value, Fair Value Disclosure | Significant Other Observable Inputs (Level 2) | Residential mortgage-backed securities
Corporate and other debt securities	886,156		1,230,993
Estimate of Fair Value, Fair Value Disclosure | Significant Other Observable Inputs (Level 2) | Trust preferred securities
Corporate and other debt securities	111,401		174,753
Estimate of Fair Value, Fair Value Disclosure | Significant Other Observable Inputs (Level 2) | Corporate and other debt securities
Corporate and other debt securities	57,025		54,391
Estimate of Fair Value, Fair Value Disclosure | Significant Unobservable Inputs (Level 3)
Net loans	$ 11,052,163		$ 9,645,517

[1] Included in other assets.

[2] Included in accrued expenses and other liabilities.