Loans and leases and the allowance for credit losses - Interest Income Recognized on Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Loans And Leases Receivable [Line Items]
Average Recorded Investment	$ 1,017,603	$ 1,148,537	$ 1,072,657	$ 1,144,988
Interest Income Recognized, Total	6,784	6,727	23,779	19,271
Interest Income Recognized, Cash Basis	4,060	3,567	15,512	9,510
Commercial, financial, leasing, etc [Member]
Loans And Leases Receivable [Line Items]
Average Recorded Investment	141,166	152,368	155,627	163,005
Interest Income Recognized, Total	1,507	1,172	2,659	2,844
Interest Income Recognized, Cash Basis	1,507	1,166	2,659	2,820
Commercial real estate loans [Member]
Loans And Leases Receivable [Line Items]
Average Recorded Investment	180,009	195,832	179,524	191,818
Interest Income Recognized, Total	531	810	2,087	1,705
Interest Income Recognized, Cash Basis	531	808	2,087	1,630
Residential builder and developer [Member]
Loans And Leases Receivable [Line Items]
Average Recorded Investment	237,847	338,897	260,858	321,386
Interest Income Recognized, Total	476	422	1,202	1,261
Interest Income Recognized, Cash Basis	370	98	801	338
Other commercial construction [Member]
Loans And Leases Receivable [Line Items]
Average Recorded Investment	84,604	96,482	100,242	102,978
Interest Income Recognized, Total	9	62	5,019	759
Interest Income Recognized, Cash Basis	9	51	5,019	522
Residential [Member]
Loans And Leases Receivable [Line Items]
Average Recorded Investment	131,114	98,885	128,646	92,918
Interest Income Recognized, Total	1,269	1,183	3,926	3,209
Interest Income Recognized, Cash Basis	765	630	2,453	1,770
Residential Alt-A [Member]
Loans And Leases Receivable [Line Items]
Average Recorded Investment	167,780	192,609	174,390	199,066
Interest Income Recognized, Total	1,836	1,872	5,432	5,858
Interest Income Recognized, Cash Basis	593	494	1,666	1,455
Home equity lines and loans [Member]
Loans And Leases Receivable [Line Items]
Average Recorded Investment	11,949	11,814	11,024	11,989
Interest Income Recognized, Total	172	174	502	523
Interest Income Recognized, Cash Basis	48	26	136	74
Automobile [Member]
Loans And Leases Receivable [Line Items]
Average Recorded Investment	51,138	56,071	52,249	57,704
Interest Income Recognized, Total	863	957	2,632	2,925
Interest Income Recognized, Cash Basis	185	262	553	850
Other [Member]
Loans And Leases Receivable [Line Items]
Average Recorded Investment	11,996	5,579	10,097	4,124
Interest Income Recognized, Total	121	75	320	187
Interest Income Recognized, Cash Basis	$ 52	$ 32	$ 138	$ 51