Loans and Leases (Credit Quality Indicators Credit Exposure) (Detail) (USD $)	Sep. 30, 2014		Dec. 31, 2013
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	$ 13,361,516,000		$ 13,503,392,000
Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	7,908,758,000		7,969,557,000
Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	5,516,963,000		5,606,529,000
Pass [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	7,198,728,000	[1]	7,155,065,000	[1]
Special Mention [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	326,399,000	[2]	363,772,000	[2]
Substandard [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	383,631,000	[3]	450,720,000	[3]
Performing [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	5,487,624,000		5,576,068,000
Nonperforming [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	29,339,000	[4]	30,461,000	[4]
Originated Loans And Leases [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	6,920,593,000		6,833,939,000
Originated Loans And Leases [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	5,072,576,000		5,097,007,000
Originated Loans And Leases [Member] | Pass [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	6,423,137,000	[1]	6,270,856,000	[1]
Originated Loans And Leases [Member] | Special Mention [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	231,740,000	[2]	277,533,000	[2]
Originated Loans And Leases [Member] | Substandard [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	265,716,000	[3]	285,550,000	[3]
Originated Loans And Leases [Member] | Performing [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	5,053,246,000		5,077,555,000
Originated Loans And Leases [Member] | Nonperforming [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	19,330,000	[4]	19,452,000	[4]
Purchased Loans And Leases [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	988,165,000		1,135,618,000
Purchased Loans And Leases [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	444,387,000		509,522,000
Purchased Loans And Leases [Member] | Pass [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	775,591,000	[1]	884,209,000	[1]
Purchased Loans And Leases [Member] | Special Mention [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	94,659,000	[2]	86,239,000	[2]
Purchased Loans And Leases [Member] | Substandard [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	117,915,000	[3]	165,170,000	[3]
Purchased Loans And Leases [Member] | Performing [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	434,378,000		498,513,000
Purchased Loans And Leases [Member] | Nonperforming [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	10,009,000	[4]	11,009,000	[4]
Commercial, Financial, And Agricultural [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	2,362,201,000		2,394,847,000
Commercial, Financial, And Agricultural [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	2,362,201,000		2,394,847,000
Commercial, Financial, And Agricultural [Member] | Pass [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	2,231,950,000	[1]	2,242,782,000	[1]
Commercial, Financial, And Agricultural [Member] | Special Mention [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	59,946,000	[2]	79,382,000	[2]
Commercial, Financial, And Agricultural [Member] | Substandard [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	70,305,000	[3]	72,683,000	[3]
Commercial, Financial, And Agricultural [Member] | Originated Loans And Leases [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	2,249,867,000		2,269,214,000
Commercial, Financial, And Agricultural [Member] | Originated Loans And Leases [Member] | Pass [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	2,136,043,000	[1]	2,133,884,000	[1]
Commercial, Financial, And Agricultural [Member] | Originated Loans And Leases [Member] | Special Mention [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	49,338,000	[2]	75,162,000	[2]
Commercial, Financial, And Agricultural [Member] | Originated Loans And Leases [Member] | Substandard [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	64,486,000	[3]	60,168,000	[3]
Commercial, Financial, And Agricultural [Member] | Purchased Loans And Leases [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	112,334,000		125,633,000
Commercial, Financial, And Agricultural [Member] | Purchased Loans And Leases [Member] | Pass [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	95,907,000	[1]	108,898,000	[1]
Commercial, Financial, And Agricultural [Member] | Purchased Loans And Leases [Member] | Special Mention [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	10,608,000	[2]	4,220,000	[2]
Commercial, Financial, And Agricultural [Member] | Purchased Loans And Leases [Member] | Substandard [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	5,819,000	[3]	12,515,000	[3]
Real Estate - Construction [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	817,492,000		735,877,000
Real Estate - Construction [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	698,917,000	[5]	609,715,000	[5]
Real Estate - Construction [Member] | Pass [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	611,572,000	[1],[5]	503,167,000	[1],[5]
Real Estate - Construction [Member] | Special Mention [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	47,454,000	[2],[5]	53,718,000	[2],[5]
Real Estate - Construction [Member] | Substandard [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	39,891,000	[3],[5]	52,830,000	[3],[5]
Real Estate - Construction [Member] | Originated Loans And Leases [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	646,430,000	[5]	542,587,000	[5]
Real Estate - Construction [Member] | Originated Loans And Leases [Member] | Pass [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	590,503,000	[1],[5]	478,097,000	[1],[5]
Real Estate - Construction [Member] | Originated Loans And Leases [Member] | Special Mention [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	27,060,000	[2],[5]	33,907,000	[2],[5]
Real Estate - Construction [Member] | Originated Loans And Leases [Member] | Substandard [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	28,867,000	[3],[5]	30,583,000	[3],[5]
Real Estate - Construction [Member] | Purchased Loans And Leases [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	52,487,000	[5]	67,128,000	[5]
Real Estate - Construction [Member] | Purchased Loans And Leases [Member] | Pass [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	21,069,000	[1],[5]	25,070,000	[1],[5]
Real Estate - Construction [Member] | Purchased Loans And Leases [Member] | Special Mention [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	20,394,000	[2],[5]	19,811,000	[2],[5]
Real Estate - Construction [Member] | Purchased Loans And Leases [Member] | Substandard [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	11,024,000	[3],[5]	22,247,000	[3],[5]
Real Estate Secured - Commercial [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	4,016,635,000		4,068,816,000
Real Estate Secured - Commercial [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	4,847,640,000	[6]	4,964,995,000	[6]
Real Estate Secured - Commercial [Member] | Pass [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	4,355,206,000	[1],[6]	4,409,116,000	[1],[6]
Real Estate Secured - Commercial [Member] | Special Mention [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	218,999,000	[2],[6]	230,672,000	[2],[6]
Real Estate Secured - Commercial [Member] | Substandard [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	273,435,000	[3],[6]	325,207,000	[3],[6]
Real Estate Secured - Commercial [Member] | Originated Loans And Leases [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	4,024,296,000	[6]	4,022,138,000	[6]
Real Estate Secured - Commercial [Member] | Originated Loans And Leases [Member] | Pass [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	3,696,591,000	[1],[6]	3,658,875,000	[1],[6]
Real Estate Secured - Commercial [Member] | Originated Loans And Leases [Member] | Special Mention [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	155,342,000	[2],[6]	168,464,000	[2],[6]
Real Estate Secured - Commercial [Member] | Originated Loans And Leases [Member] | Substandard [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	172,363,000	[3],[6]	194,799,000	[3],[6]
Real Estate Secured - Commercial [Member] | Purchased Loans And Leases [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	823,344,000	[6]	942,857,000	[6]
Real Estate Secured - Commercial [Member] | Purchased Loans And Leases [Member] | Pass [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	658,615,000	[1],[6]	750,241,000	[1],[6]
Real Estate Secured - Commercial [Member] | Purchased Loans And Leases [Member] | Special Mention [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	63,657,000	[2],[6]	62,208,000	[2],[6]
Real Estate Secured - Commercial [Member] | Purchased Loans And Leases [Member] | Substandard [Member] | Commercial Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	101,072,000	[3],[6]	130,408,000	[3],[6]
Real Estate Secured - Residential [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	4,172,943,000		4,204,430,000
Real Estate Secured - Residential [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	3,460,513,000		3,434,413,000
Real Estate Secured - Residential [Member] | Performing [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	3,432,443,000		3,406,469,000
Real Estate Secured - Residential [Member] | Nonperforming [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	28,070,000	[4]	27,944,000	[4]
Real Estate Secured - Residential [Member] | Originated Loans And Leases [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	3,021,325,000		2,931,484,000
Real Estate Secured - Residential [Member] | Originated Loans And Leases [Member] | Performing [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	3,003,259,000		2,914,547,000
Real Estate Secured - Residential [Member] | Originated Loans And Leases [Member] | Nonperforming [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	18,066,000	[4]	16,937,000	[4]
Real Estate Secured - Residential [Member] | Purchased Loans And Leases [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	439,188,000		502,929,000
Real Estate Secured - Residential [Member] | Purchased Loans And Leases [Member] | Performing [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	429,184,000		491,922,000
Real Estate Secured - Residential [Member] | Purchased Loans And Leases [Member] | Nonperforming [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	10,004,000	[4]	11,007,000	[4]
Consumer [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	730,687,000		953,000,000
Consumer [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	730,687,000		953,000,000
Consumer [Member] | Performing [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	730,448,000		951,970,000
Consumer [Member] | Nonperforming [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	239,000	[4]	1,030,000	[4]
Consumer [Member] | Originated Loans And Leases [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	725,488,000		946,407,000
Consumer [Member] | Originated Loans And Leases [Member] | Performing [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	725,254,000		945,379,000
Consumer [Member] | Originated Loans And Leases [Member] | Nonperforming [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	234,000	[4]	1,028,000	[4]
Consumer [Member] | Purchased Loans And Leases [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	5,199,000		6,593,000
Consumer [Member] | Purchased Loans And Leases [Member] | Performing [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	5,194,000		6,591,000
Consumer [Member] | Purchased Loans And Leases [Member] | Nonperforming [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	5,000	[4]	2,000	[4]
Leases [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	1,325,763,000		1,219,116,000
Leases [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	1,325,763,000		1,219,116,000
Leases [Member] | Performing [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	1,324,733,000		1,217,629,000
Leases [Member] | Nonperforming [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	1,030,000	[4]	1,487,000	[4]
Leases [Member] | Originated Loans And Leases [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	1,325,763,000		1,219,116,000
Leases [Member] | Originated Loans And Leases [Member] | Performing [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	1,324,733,000		1,217,629,000
Leases [Member] | Originated Loans And Leases [Member] | Nonperforming [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	1,030,000	[4]	1,487,000	[4]
Leases [Member] | Purchased Loans And Leases [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	0		0
Leases [Member] | Purchased Loans And Leases [Member] | Performing [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	0		0
Leases [Member] | Purchased Loans And Leases [Member] | Nonperforming [Member] | Other Credit Exposure [Member]
Financing Receivable Recorded Investment [Line Items]
Credit Exposure	$ 0	[4]	$ 0	[4]

[1] Includes loans identified as having acceptable risk, which are loans for which the possibility of loss is considered unlikely.

[2] Includes loans considered potentially weak; however, no loss of principal or interest is anticipated.

[3] Includes loans that are inadequately protected by the current net-worth and paying capacity of the borrower or by the collateral pledged, if any. Loss of principal or interest is considered reasonably possible or likely.

[4] Includes loans that are on nonaccrual status or past due ninety days or more.

[5] Includes only construction loans granted to commercial customers. Construction loans for individuals are included in Real Estate – Secured – Residential, below.

[6] Includes loans obtained for commercial purposes that are also secured by residential real estate.