Summary Information on Allowance for Loan and Lease Loss Activity (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year			$ 49,426	$ 62,135	$ 62,135
Provision for loan and lease losses	232	(3,520)	2,481	(854)	1,428
Loan and lease charge-offs			(11,456)	(12,612)
Recoveries			2,167	1,051	2,368
Net charge-offs			(9,289)	(11,561)	(14,137)
Balance at end of period	$ 42,618	$ 49,720	$ 42,618	$ 49,720	$ 49,426