Summary Information on Allowance for Loan and Lease Loss Activity (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 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	1,585	1,151	2,249	2,666	1,428
Loan and lease charge-offs			(7,343)	(10,254)
Loan and lease recoveries			933	699	2,368
Net charge-offs			(6,410)	(9,555)	(14,137)
Balance at end of period	$ 45,265	$ 55,246	$ 45,265	$ 55,246	$ 49,426