Loans and leases and the allowance for credit losses - Impaired Loans and Leases (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Recorded investment	$ 1,096,489	$ 1,072,026
Unpaid principal balance	1,373,861	1,354,133
Related allowance	134,839	132,682
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment	212,054	159,913
Unpaid principal balance	244,827	191,733
Related allowance	45,277	33,829
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment	192,507	199,922
Unpaid principal balance	240,843	244,183
Related allowance	19,859	23,641
Residential Builder and Developer [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment	174,195	189,613
Unpaid principal balance	296,075	321,656
Related allowance	19,956	25,661
Other Commercial Construction [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment	99,920	96,562
Unpaid principal balance	104,334	100,401
Related allowance	6,533	6,836
Residential [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment	190,336	189,793
Unpaid principal balance	219,985	218,267
Related allowance	5,464	3,521
Residential Alt-A [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment	153,864	160,245
Unpaid principal balance	192,836	200,708
Related allowance	17,000	17,000
Home Equity Lines and Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment	12,457	12,360
Unpaid principal balance	13,805	13,567
Related allowance	2,315	2,254
Automobile [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment	45,876	49,210
Unpaid principal balance	45,876	49,210
Related allowance	12,916	14,273
Other [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment	15,280	14,408
Unpaid principal balance	15,280	14,408
Related allowance	5,519	5,667
Impaired Financing Receivable With Related Allowance [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment	765,600	745,994
Unpaid principal balance	946,041	927,411
Related allowance	134,839	132,682
Impaired Financing Receivable With Related Allowance [Member] | Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment	165,867	127,282
Unpaid principal balance	186,405	149,534
Related allowance	45,277	33,829
Impaired Financing Receivable With Related Allowance [Member] | Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment	116,111	121,542
Unpaid principal balance	142,349	143,846
Related allowance	19,859	23,641
Impaired Financing Receivable With Related Allowance [Member] | Residential Builder and Developer [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment	106,510	115,306
Unpaid principal balance	202,139	216,218
Related allowance	19,956	25,661
Impaired Financing Receivable With Related Allowance [Member] | Other Commercial Construction [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment	73,622	73,544
Unpaid principal balance	77,164	76,869
Related allowance	6,533	6,836
Impaired Financing Receivable With Related Allowance [Member] | Residential [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment	104,096	103,451
Unpaid principal balance	123,244	121,819
Related allowance	5,464	3,521
Impaired Financing Receivable With Related Allowance [Member] | Residential Alt-A [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment	125,781	128,891
Unpaid principal balance	139,779	141,940
Related allowance	17,000	17,000
Impaired Financing Receivable With Related Allowance [Member] | Home Equity Lines and Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment	12,457	12,360
Unpaid principal balance	13,805	13,567
Related allowance	2,315	2,254
Impaired Financing Receivable With Related Allowance [Member] | Automobile [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment	45,876	49,210
Unpaid principal balance	45,876	49,210
Related allowance	12,916	14,273
Impaired Financing Receivable With Related Allowance [Member] | Other [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment	15,280	14,408
Unpaid principal balance	15,280	14,408
Related allowance	5,519	5,667
Impaired Financing Receivable With No Related Allowance [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment	330,889	326,032
Unpaid principal balance	427,820	426,722
Related allowance
Impaired Financing Receivable With No Related Allowance [Member] | Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment	46,187	32,631
Unpaid principal balance	58,422	42,199
Related allowance
Impaired Financing Receivable With No Related Allowance [Member] | Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment	76,396	78,380
Unpaid principal balance	98,494	100,337
Related allowance
Impaired Financing Receivable With No Related Allowance [Member] | Residential Builder and Developer [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment	67,685	74,307
Unpaid principal balance	93,936	105,438
Related allowance
Impaired Financing Receivable With No Related Allowance [Member] | Other Commercial Construction [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment	26,298	23,018
Unpaid principal balance	27,170	23,532
Related allowance
Impaired Financing Receivable With No Related Allowance [Member] | Residential [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment	86,240	86,342
Unpaid principal balance	96,741	96,448
Related allowance
Impaired Financing Receivable With No Related Allowance [Member] | Residential Alt-A [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment	28,083	31,354
Unpaid principal balance	53,057	58,768
Related allowance