Fair Value Measurement of Assets and Liabilities - Carrying Amounts and Estimated Fair Values of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Deposits with stated maturities	$ 2,508,766		$ 2,501,384
Interest bearing deposits with banks	463,022		6,483
Accrued interest receivable	52,375		52,527
Trust preferred securities [Member]
Corporate and other debt securities	11,400
Carrying Amount [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Cash and due from banks	390,078		372,566
Interest bearing deposits with banks	463,022		6,483
Accrued interest receivable	52,375		52,527
Federal Reserve Bank and Federal Home Loan Bank stock	138,533	[1]	129,669	[1]
Deposits without stated maturities	8,755,252		7,171,718
Short-term borrowings	154,323		212,849
Accrued interest payable	15,917	[2]	17,736	[2]
Carrying Amount [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Treasury securities [Member]
Total investment securities held to maturity	99,869		100,018
Carrying Amount [Member] | Significant Other Observable Inputs (Level 2) [Member]
Deposits with stated maturities	2,508,766		2,501,384
Long-term borrowings	2,697,299		2,726,099
Junior subordinated debentures issued to capital trusts	40,927		25,120
Total investment securities held to maturity	1,599,707		1,958,916
Carrying Amount [Member] | Significant Other Observable Inputs (Level 2) [Member] | Obligations of states and political subdivisions [Member]
Corporate and other debt securities	506,473		433,284
Carrying Amount [Member] | Significant Other Observable Inputs (Level 2) [Member] | Residential mortgage-backed securities [Member]
Corporate and other debt securities	813,647		1,180,104
Carrying Amount [Member] | Significant Other Observable Inputs (Level 2) [Member] | Trust preferred securities [Member]
Corporate and other debt securities	127,505		193,312
Carrying Amount [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate and other debt securities [Member]
Corporate and other debt securities	52,213		52,198
Carrying Amount [Member] | Significant Unobservable Inputs (Level 3) [Member]
Net loans	10,892,599		9,665,839
Fair Value [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Cash and due from banks	390,078		372,566
Interest bearing deposits with banks	463,022		6,483
Accrued interest receivable	52,375		52,527
Federal Reserve Bank and Federal Home Loan Bank stock	138,533	[1]	129,669	[1]
Deposits without stated maturities	8,755,252		7,171,718
Short-term borrowings	154,323		215,179
Accrued interest payable	15,917	[2]	17,736	[2]
Fair Value [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Treasury securities [Member]
Total investment securities held to maturity	115,329		113,859
Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member]
Deposits with stated maturities	2,563,726		2,557,119
Long-term borrowings	3,100,173		3,154,150
Junior subordinated debentures issued to capital trusts	40,776		25,620
Total investment securities held to maturity	1,657,950		2,027,197
Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | Obligations of states and political subdivisions [Member]
Corporate and other debt securities	531,966		453,201
Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | Residential mortgage-backed securities [Member]
Corporate and other debt securities	838,116		1,230,993
Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | Trust preferred securities [Member]
Corporate and other debt securities	113,657		174,753
Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate and other debt securities [Member]
Corporate and other debt securities	58,882		54,391
Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member]
Net loans	$ 10,908,742		$ 9,645,517

[1] Included in other assets.

[2] Included in accrued expenses and other liabilities.