Deposits - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Time Deposits [Line Items]
Certificates of deposit over $100 thousand	$ 1,200,000,000	$ 1,100,000,000
Interest expense on time deposits of $100 thousand or more	8,200,000	8,500,000	8,800,000
Deposits from certain directors, executive officers and their affiliates	$ 62,700,000	$ 54,500,000