Summary of Estimated Fair Values of Financial Instruments not Carried at Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 1,411,725		$ 1,114,948
Non-marketable securities (cost and equity method accounting)	372,605		267,508
Net commercial loans	6,968,693		6,192,578
Net consumer loans	722,893		687,557
FHLB and FRB stock	39,301		39,189
Accrued interest receivable	62,359		58,108
Short-term borrowings	5,880
Deposits	18,068,812		16,709,536
Accrued interest payable	6,496		6,689
Other long-term debt			1,439	[1]
Federal Funds Purchased
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	5,880
No Stated Maturity
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	17,900,604	[2]	16,553,787	[2]
Bank Time Deposits
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	168,208		155,749
5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes	347,893		347,793
5.70% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes			143,969	[3],[4]
6.05% Subordinated Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Subordinated Notes	55,054	[5],[6]	55,075	[5],[6]
7.0% Junior Subordinated Debentures
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Junior Subordinated Debentures	55,285		55,372
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	1,411,725		1,114,948
Quoted Prices in Active Markets for Identical Assets (Level 1) | Federal Funds Purchased
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	5,880
Quoted Prices in Active Markets for Identical Assets (Level 1) | No Stated Maturity
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	17,900,604	[2]	16,553,787	[2]
Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Accrued interest receivable	62,359		58,108
Accrued interest payable	6,496		6,689
Significant Other Observable Inputs (Level 2) | Bank Time Deposits
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	167,917		155,346
Significant Other Observable Inputs (Level 2) | 5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes	380,961		362,786
Significant Other Observable Inputs (Level 2) | 5.70% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes			145,184	[4]
Significant Other Observable Inputs (Level 2) | 6.05% Subordinated Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Subordinated Notes	60,411	[6]	57,746	[6]
Significant Other Observable Inputs (Level 2) | 7.0% Junior Subordinated Debentures
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Junior Subordinated Debentures	51,897		51,526
Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Non-marketable securities (cost and equity method accounting)	407,262		290,393
Net commercial loans	7,145,552		6,336,705
Net consumer loans	743,208		627,733
FHLB and FRB stock	39,301		39,189
Commitments to extend credit	22,343		21,232
Other long-term debt			$ 1,439

[1] Represents long-term notes payable related to one of our debt fund investments. The last payment related to the notes was made in April 2012.

[2] Includes noninterest-bearing demand deposits, interest-bearing checking accounts, money market accounts and interest-bearing sweep deposits.

[3] At December 31, 2011, included in the carrying value of our 5.70% Senior Notes was $2.6 million related to the fair value of the interest rate swap associated with the notes.

[4] At December 31, 2011, included in the carrying value and estimated fair value of our 5.70% Senior Notes was $2.6 million related to the fair value of the interest rate swap associated with the notes.

[5] At June 30, 2012 and December 31, 2011, included in the carrying value of our 6.05% Subordinated Notes were $9.3 million and $8.8 million, respectively, related to the fair value of the interest rate swap associated with the notes.

[6] At June 30, 2012 and December 31, 2011, included in the carrying value and estimated fair value of our 6.05% Subordinated Notes was $9.3 million and $8.8 million, respectively, related to the fair value of the interest rate swap associated with the notes.