Summary Information on Allowance for Loan and Lease Loss Activity (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year	$ 42,957	$ 49,426	$ 49,426
Provision for loan and lease losses	78	664	3,649
Loan and lease charge-offs	(3,108)	(5,298)
Loan and lease recoveries	1,319	269	(2,686)
Net charge-offs	(1,789)	(5,029)	(10,118)
Balance at period end	$ 41,246	$ 45,061	$ 42,957