Fair Value of Financial Instruments Summary of Estimated Fair Values of Financial Instruments not Carried at Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	$ 5,080		$ 166,110
Time Deposits	213,860		155,188
Federal Funds Purchased
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	0		160,000
Other short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	5,080	[1]	6,110	[1]
5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes	348,209		347,995
6.05% Subordinated Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Subordinated Notes	51,987	[2]	54,571	[2]
7.0% Junior Subordinated Debentures
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Junior Subordinated Debentures	55,020		55,196
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	1,538,779		1,008,983
Non-marketable securities (cost and equity method accounting)	378,309		391,253
Net commercial loans	9,796,878		8,013,563
Net consumer loans	966,622		822,719
FHLB and FRB stock	40,632		39,806
Accrued interest receivable	67,772		64,167
Deposits	22,259,119	[3]	19,021,264	[3]
Time Deposits	213,860		155,188
Accrued interest payable	6,858		6,494
Commitments to extend credit	0		0
Carrying Amount | Federal Funds Purchased
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	0		160,000
Carrying Amount | Other short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	5,080		6,110
Carrying Amount | 5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes	348,209		347,995
Carrying Amount | 6.05% Subordinated Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Subordinated Notes	51,987	[4]	54,571	[4]
Carrying Amount | 7.0% Junior Subordinated Debentures
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Junior Subordinated Debentures	55,020		55,196
Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	1,538,779		1,008,983
Non-marketable securities (cost and equity method accounting)	0		0
Net commercial loans	0		0
Net consumer loans	0		0
FHLB and FRB stock	0		0
Accrued interest receivable	0		0
Deposits	22,259,119	[3]	19,021,264	[3]
Time Deposits	0		0
Accrued interest payable	0		0
Commitments to extend credit	0		0
Estimated Fair Value | 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	0		160,000
Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	5,080		6,110
Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1) | 5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes	0		0
Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1) | 6.05% Subordinated Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Subordinated Notes	0	[4]	0	[4]
Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1) | 7.0% Junior Subordinated Debentures
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Junior Subordinated Debentures	0		0
Estimated Fair Value | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0		0
Non-marketable securities (cost and equity method accounting)	0		0
Net commercial loans	0		0
Net consumer loans	0		0
FHLB and FRB stock	0		0
Accrued interest receivable	67,772		64,167
Deposits	0	[3]	0	[3]
Time Deposits	213,874		155,027
Accrued interest payable	6,858		6,494
Commitments to extend credit	0		0
Estimated Fair Value | Significant Other Observable Inputs (Level 2) | Federal Funds Purchased
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	0		0
Estimated Fair Value | Significant Other Observable Inputs (Level 2) | Other short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	0		0
Estimated Fair Value | Significant Other Observable Inputs (Level 2) | 5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes	383,782		393,701
Estimated Fair Value | Significant Other Observable Inputs (Level 2) | 6.05% Subordinated Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Subordinated Notes	56,297	[4]	61,639	[4]
Estimated Fair Value | Significant Other Observable Inputs (Level 2) | 7.0% Junior Subordinated Debentures
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Junior Subordinated Debentures	51,915		51,959
Estimated Fair Value | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0		0
Non-marketable securities (cost and equity method accounting)	447,783		425,741
Net commercial loans	9,935,917		8,180,597
Net consumer loans	1,005,080		860,772
FHLB and FRB stock	40,632		39,806
Accrued interest receivable	0		0
Deposits	0	[3]	0	[3]
Time Deposits	0		0
Accrued interest payable	0		0
Commitments to extend credit	24,285		20,562
Estimated Fair Value | Significant Unobservable Inputs (Level 3) | Federal Funds Purchased
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	0		0
Estimated Fair Value | Significant Unobservable Inputs (Level 3) | Other short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	0		0
Estimated Fair Value | Significant Unobservable Inputs (Level 3) | 5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes	0		0
Estimated Fair Value | Significant Unobservable Inputs (Level 3) | 6.05% Subordinated Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Subordinated Notes	0	[4]	0	[4]
Estimated Fair Value | Significant Unobservable Inputs (Level 3) | 7.0% Junior Subordinated Debentures
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Junior Subordinated Debentures	$ 0		$ 0

[1] Represents cash collateral received from our counterparty for our interest rate swap agreement related to our 6.05% Subordinated Notes.

[2] At December 31, 2013 and 2012, included in the carrying value of our 6.05% Subordinated Notes were $6 million and $9 million, respectively, related to hedge accounting associated with the notes.

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

[4] At December 31, 2013 and 2012, included in the carrying value and estimated fair value of our 6.05% Subordinated Notes was $6.5 million and $9.0 million, respectively, related to hedge accounting associated with the notes.