Loans and leases and the allowance for credit losses - Loan Modification Activities that were Considered Troubled Debt Restructurings (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013 Modification	Mar. 31, 2012 Modification
Financing Receivable, Modifications [Line Items]
Number of modifications	332	445
Pre-modification, Recorded investment	$ 79,681	$ 26,628
Post-modification, Recorded investment	79,660	26,661
Financial effects of modification, Recorded investment	(21)	33
Financial effects of modification, Interest	-884	-483
Principal deferral [Member] | Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	24	9
Pre-modification, Recorded investment	2,006	2,812
Post-modification, Recorded investment	1,982	2,954
Financial effects of modification, Recorded investment	(24)	142
Financial effects of modification, Interest		-
Principal deferral [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	8	2
Pre-modification, Recorded investment	18,478	2,425
Post-modification, Recorded investment	18,363	2,405
Financial effects of modification, Recorded investment	(115)	(20)
Financial effects of modification, Interest		-
Principal deferral [Member] | Residential Builder and Developer [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	8	5
Pre-modification, Recorded investment	1,357	6,822
Post-modification, Recorded investment	1,340	6,034
Financial effects of modification, Recorded investment	(17)	(788)
Financial effects of modification, Interest		-
Principal deferral [Member] | Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	7	15
Pre-modification, Recorded investment	566	1,505
Post-modification, Recorded investment	607	1,588
Financial effects of modification, Recorded investment	41	83
Financial effects of modification, Interest		-
Principal deferral [Member] | Residential Alt-A [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications		3
Pre-modification, Recorded investment		397
Post-modification, Recorded investment		407
Financial effects of modification, Recorded investment		10
Financial effects of modification, Interest		-
Principal deferral [Member] | Home Equity Lines and Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	2	1
Pre-modification, Recorded investment	79	117
Post-modification, Recorded investment	79	117
Financial effects of modification, Recorded investment
Financial effects of modification, Interest		-
Principal deferral [Member] | Automobile [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	121	153
Pre-modification, Recorded investment	1,586	1,885
Post-modification, Recorded investment	1,586	1,885
Financial effects of modification, Recorded investment
Financial effects of modification, Interest		-
Principal deferral [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	6	52
Pre-modification, Recorded investment	45	647
Post-modification, Recorded investment	45	647
Financial effects of modification, Recorded investment
Financial effects of modification, Interest		-
Other [Member] | Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	1	1
Pre-modification, Recorded investment	47,200	972
Post-modification, Recorded investment	47,200	1,098
Financial effects of modification, Recorded investment		126
Financial effects of modification, Interest		-
Other [Member] | Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	1
Pre-modification, Recorded investment	195
Post-modification, Recorded investment	195
Financial effects of modification, Recorded investment
Financial effects of modification, Interest
Other [Member] | Automobile [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	17	10
Pre-modification, Recorded investment	159	19
Post-modification, Recorded investment	159	19
Financial effects of modification, Recorded investment
Financial effects of modification, Interest		-
Other [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	1	9
Pre-modification, Recorded investment	12	49
Post-modification, Recorded investment	12	49
Financial effects of modification, Recorded investment
Financial effects of modification, Interest		-
Combination of concession types [Member] | Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	1	1
Pre-modification, Recorded investment	342	45
Post-modification, Recorded investment	342	44
Financial effects of modification, Recorded investment		(1)
Financial effects of modification, Interest		-33
Combination of concession types [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	2
Pre-modification, Recorded investment	582
Post-modification, Recorded investment	581
Financial effects of modification, Recorded investment	(1)
Financial effects of modification, Interest	-56
Combination of concession types [Member] | Residential Builder and Developer [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	1	2
Pre-modification, Recorded investment	1,701	2,350
Post-modification, Recorded investment	1,691	2,726
Financial effects of modification, Recorded investment	(10)	376
Financial effects of modification, Interest		-
Combination of concession types [Member] | Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	20	18
Pre-modification, Recorded investment	2,449	2,936
Post-modification, Recorded investment	2,536	3,007
Financial effects of modification, Recorded investment	87	71
Financial effects of modification, Interest	-371	-200
Combination of concession types [Member] | Residential Alt-A [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	5	8
Pre-modification, Recorded investment	907	1,360
Post-modification, Recorded investment	925	1,394
Financial effects of modification, Recorded investment	18	34
Financial effects of modification, Interest	-110	-5
Combination of concession types [Member] | Home Equity Lines and Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	2	2
Pre-modification, Recorded investment	211	235
Post-modification, Recorded investment	211	235
Financial effects of modification, Recorded investment
Financial effects of modification, Interest	-33	-24
Combination of concession types [Member] | Automobile [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	61	112
Pre-modification, Recorded investment	553	1,609
Post-modification, Recorded investment	553	1,609
Financial effects of modification, Recorded investment
Financial effects of modification, Interest	-42	-172
Combination of concession types [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	42	34
Pre-modification, Recorded investment	1,217	219
Post-modification, Recorded investment	1,217	219
Financial effects of modification, Recorded investment
Financial effects of modification, Interest	-267	-36
Interest rate reduction [Member] | Home Equity Lines and Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications		1
Pre-modification, Recorded investment		144
Post-modification, Recorded investment		144
Financial effects of modification, Interest		-6
Interest rate reduction [Member] | Automobile [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	2	4
Pre-modification, Recorded investment	36	57
Post-modification, Recorded investment	36	57
Financial effects of modification, Recorded investment
Financial effects of modification, Interest	-5	-4
Interest rate reduction [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications		3
Pre-modification, Recorded investment		23
Post-modification, Recorded investment		$ 23
Financial effects of modification, Interest		-3