Loans and leases and the allowance for credit losses - Interest Income Recognized on Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Loans And Leases Receivable [Line Items]
Average recorded investment	$ 1,064,446	$ 1,111,622
Interest income recognized, Total	7,816	5,580
Interest income recognized, Cash basis	5,189	2,759
Commercial, Financial, Leasing, etc. [Member]
Loans And Leases Receivable [Line Items]
Average recorded investment	167,793	167,724
Interest income recognized, Total	2,434	409
Interest income recognized, Cash basis	2,434	409
Commercial Real Estate [Member]
Loans And Leases Receivable [Line Items]
Average recorded investment	194,446	178,315
Interest income recognized, Total	303	318
Interest income recognized, Cash basis	303	318
Residential Builder and Developer [Member]
Loans And Leases Receivable [Line Items]
Average recorded investment	183,853	282,495
Interest income recognized, Total	140	341
Interest income recognized, Cash basis	65	179
Other Commercial Construction [Member]
Loans And Leases Receivable [Line Items]
Average recorded investment	98,318	104,105
Interest income recognized, Total	635	170
Interest income recognized, Cash basis	635	170
Residential [Member]
Loans And Leases Receivable [Line Items]
Average recorded investment	188,075	126,376
Interest income recognized, Total	1,470	1,342
Interest income recognized, Cash basis	922	878
Residential Alt-A [Member]
Loans And Leases Receivable [Line Items]
Average recorded investment	156,971	181,018
Interest income recognized, Total	1,740	1,843
Interest income recognized, Cash basis	591	546
Home Equity Lines and Loans [Member]
Loans And Leases Receivable [Line Items]
Average recorded investment	12,454	9,998
Interest income recognized, Total	167	166
Interest income recognized, Cash basis	39	42
Automobile [Member]
Loans And Leases Receivable [Line Items]
Average recorded investment	47,606	53,289
Interest income recognized, Total	776	898
Interest income recognized, Cash basis	146	178
Other [Member]
Loans And Leases Receivable [Line Items]
Average recorded investment	14,930	8,302
Interest income recognized, Total	151	93
Interest income recognized, Cash basis	$ 54	$ 39