Loans and leases - Loan Modification Activities that were Considered Troubled Debt Restructurings (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 Modification	Dec. 31, 2011 Modification
Financing Receivable, Modifications [Line Items]
Number of modifications	1,608	1,780
Pre-modification Recorded Investment	$ 256,681	$ 332,160
Post-modification Recorded Investment	251,018	313,827
Financial effects of modification recorded investment	(5,663)	(18,333)
Financial effects of modification interest	-2853	-6338
Principal deferral [Member] | Commercial, Financial, Leasing, etc [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	61	53
Pre-modification Recorded Investment	23,888	10,703
Post-modification Recorded Investment	22,456	10,778
Financial effects of modification recorded investment	(1,432)	75
Financial effects of modification interest		-
Principal deferral [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	24	29
Pre-modification Recorded Investment	22,855	16,804
Post-modification Recorded Investment	23,059	16,704
Financial effects of modification recorded investment	204	(100)
Financial effects of modification interest		-
Principal deferral [Member] | Residential Builder and Developer [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	23	9
Pre-modification Recorded Investment	36,868	33,208
Post-modification Recorded Investment	34,740	26,811
Financial effects of modification recorded investment	(2,128)	(6,397)
Financial effects of modification interest		-
Principal deferral [Member] | Other Commercial Construction [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	6	3
Pre-modification Recorded Investment	81,062	8,436
Post-modification Recorded Investment	79,312	8,553
Financial effects of modification recorded investment	(1,750)	117
Financial effects of modification interest		-
Principal deferral [Member] | Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	36	37
Pre-modification Recorded Investment	4,643	8,175
Post-modification Recorded Investment	4,808	8,235
Financial effects of modification recorded investment	165	60
Financial effects of modification interest		-
Principal deferral [Member] | Residential Alt-A [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	7	3
Pre-modification Recorded Investment	968	800
Post-modification Recorded Investment	989	835
Financial effects of modification recorded investment	21	35
Financial effects of modification interest		-
Principal deferral [Member] | Home equity lines and loans [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	15	3
Pre-modification Recorded Investment	1,285	259
Post-modification Recorded Investment	1,285	259
Financial effects of modification recorded investment
Financial effects of modification interest		-
Principal deferral [Member] | Automobile [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	618	746
Pre-modification Recorded Investment	8,347	10,053
Post-modification Recorded Investment	8,347	10,053
Financial effects of modification recorded investment
Financial effects of modification interest		-
Principal deferral [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	80	23
Pre-modification Recorded Investment	1,201	400
Post-modification Recorded Investment	1,201	400
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	5	3
Pre-modification Recorded Investment	628	2,049
Post-modification Recorded Investment	740	2,046
Financial effects of modification recorded investment	112	(3)
Financial effects of modification interest	-102	-654
Combination of concession types [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	7	3
Pre-modification Recorded Investment	1,637	15,778
Post-modification Recorded Investment	1,656	15,777
Financial effects of modification recorded investment	19	(1)
Financial effects of modification interest	-351	-1463
Combination of concession types [Member] | Residential Builder and Developer [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	7	5
Pre-modification Recorded Investment	37,602	2,540
Post-modification Recorded Investment	36,148	2,561
Financial effects of modification recorded investment	(1,454)	21
Financial effects of modification interest		-
Combination of concession types [Member] | Other Commercial Construction [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications		3
Pre-modification Recorded Investment		65,813
Post-modification Recorded Investment		60,973
Financial effects of modification recorded investment		(4,840)
Financial effects of modification interest		-
Combination of concession types [Member] | Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	62	111
Pre-modification Recorded Investment	12,886	19,508
Post-modification Recorded Investment	13,146	19,934
Financial effects of modification recorded investment	260	426
Financial effects of modification interest	-657	-1559
Combination of concession types [Member] | Residential Alt-A [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	38	34
Pre-modification Recorded Investment	8,525	6,813
Post-modification Recorded Investment	8,717	6,978
Financial effects of modification recorded investment	192	165
Financial effects of modification interest	-159	-889
Combination of concession types [Member] | Home equity lines and loans [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	29	26
Pre-modification Recorded Investment	2,332	2,156
Post-modification Recorded Investment	2,332	2,158
Financial effects of modification recorded investment		2
Financial effects of modification interest	-368	-444
Combination of concession types [Member] | Automobile [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	375	431
Pre-modification Recorded Investment	5,857	6,703
Post-modification Recorded Investment	5,857	6,703
Financial effects of modification recorded investment
Financial effects of modification interest	-684	-808
Combination of concession types [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	84	102
Pre-modification Recorded Investment	1,015	803
Post-modification Recorded Investment	1,015	803
Financial effects of modification recorded investment
Financial effects of modification interest	-268	-189
Other [Member] | Commercial, Financial, Leasing, etc [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	3
Pre-modification Recorded Investment	2,967
Post-modification Recorded Investment	3,052
Financial effects of modification recorded investment	85
Financial effects of modification interest
Other [Member] | Residential Builder and Developer [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications		6
Pre-modification Recorded Investment		118,114
Post-modification Recorded Investment		110,156
Financial effects of modification recorded investment		(7,958)
Financial effects of modification interest		-
Other [Member] | Home equity lines and loans [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications		3
Pre-modification Recorded Investment		86
Post-modification Recorded Investment		86
Financial effects of modification interest		-
Other [Member] | Automobile [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	67	111
Pre-modification Recorded Investment	300	739
Post-modification Recorded Investment	300	739
Financial effects of modification recorded investment
Financial effects of modification interest		-
Other [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	13	4
Pre-modification Recorded Investment	54	103
Post-modification Recorded Investment	54	103
Financial effects of modification recorded investment
Financial effects of modification interest		-
Interest rate reduction [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	2
Pre-modification Recorded Investment	665
Post-modification Recorded Investment	708
Financial effects of modification recorded investment	43
Financial effects of modification interest	-129
Interest rate reduction [Member] | Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	1	14
Pre-modification Recorded Investment	109	1,926
Post-modification Recorded Investment	109	1,991
Financial effects of modification recorded investment		65
Financial effects of modification interest	-20	-318
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 recorded investment
Financial effects of modification interest	-6
Interest rate reduction [Member] | Automobile [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	22	17
Pre-modification Recorded Investment	328	183
Post-modification Recorded Investment	328	183
Financial effects of modification recorded investment
Financial effects of modification interest	-24	-13
Interest rate reduction [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications	22	1
Pre-modification Recorded Investment	515	8
Post-modification Recorded Investment	515	8
Financial effects of modification recorded investment
Financial effects of modification interest	-85	-1