Subsequent Event - Additional Information (Detail) (Prosperity Bank [Member], USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		1 Months Ended
	Mar. 31, 2013 Location	Dec. 31, 2012	May 01, 2013 Subsequent Event [Member]	May 02, 2013 Subsequent Event [Member]
Subsequent Event [Line Items]
Number of banking locations	12
Assets acquired through merger		$ 742
Loans acquired through merger		464
Deposits acquired through merger		478
Share issued as consideration				3.125
Common stock value of Prosperity Bank				$ 41.5
Purchase consideration percentage				50.00%
Approximate transaction value			$ 15.7
Percentage of tangible book value			89.00%