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, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year			$ 42,957	$ 49,426	$ 49,426
Provision (credit) for loan and lease losses	(2,876)	1,585	(2,798)	2,249
Loan and lease charge-offs			(4,448)	(7,343)
Recoveries			3,304	933	2,686
Net charge-offs			(1,144)	(6,410)	(10,118)
Balance at period end	$ 39,015	$ 45,265	$ 39,015	$ 45,265	$ 42,957