Summary of Activity in Allowance for Loan Losses (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]
Beginning balance	$ 23,010	$ 22,887	$ 23,011	$ 22,293	$ 22,293
Loan charge-offs	(861)	(1,170)	(1,950)	(2,017)	(5,025)
Recoveries on loans previously charged off	287	306	384	630	1,002
Net charge-offs	(574)	(864)	(1,566)	(1,387)
Provision for loan losses	826	966	1,817	2,083	4,741
Ending balance	$ 23,262	$ 22,989	$ 23,262	$ 22,989	$ 23,011