Deposits - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Deposit Liabilities [Line Items]
Time deposit accounts individually equal to or greater than $100,000	$ 126.0	$ 343.5
Interest expense paid on time deposit accounts individually equal to or greater than $100,000	0.9	1.5	2.1
Time deposit accounts individually equal to or greater than $100,000 scheduled to mature within one year	$ 125.6