Subordinated Deferrable Interest Debentures - Additional Information (Detail) (USD $)	12 Months Ended			12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 Scenario, Forecast [Member]	Dec. 31, 2013 First National Banc Statutory Trust I [Member]	Dec. 31, 2005 First National Banc Statutory Trust I [Member]	Dec. 31, 2013 Prosperity Banking Capital Trust I [Member]	Dec. 31, 2013 Prosperity Banking Capital Trust II [Member]	Dec. 31, 2013 Prosperity Bank Statutory Trust III [Member]	Dec. 31, 2013 Prosperity Bank Statutory Trust IV [Member]	Dec. 31, 2006 Ameris Statutory Trust I [Member]	Dec. 31, 2013 Ameris Statutory Trust I [Member]
Preferred Stock [Line Items]
Principal amount of trust preferred securities					$ 5,000,000	$ 5,000,000	$ 4,500,000	$ 10,000,000	$ 10,000,000
Variable rate of preferred securities					2.80%	2.57%	3.15%	1.60%	1.54%	1.63%
Trust preferred securities interest rate	3.05%					2.82%	3.40%	1.84%	1.78%
Maturity period of trust preferred securities				30 years		30 years	30 years	30 years	30 years
Principal amount outstanding			5,000,000			5,000,000	4,500,000	10,000,000	10,000,000
Aggregate principal amount			5,155,000			5,155,000	4,640,000	10,310,000	10,310,000	37,114,000
Principal amount issued	28,000,000	27,662,000								36,000,000
Rate per annum of principal amount											1.87%
Trust preferred securities maturity date											Dec. 31, 2036
Fair value of debenture						$ 3,210,000	$ 3,257,000	$ 5,034,000	$ 1,696,000