Loans - Summary of Loans Modified (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 Contract	Dec. 31, 2011 Contract
Troubled Debt Restructured Loan Modifications by Class [Line Items]
Number of loans	16	57
Pre- modification outstanding recorded investment	$ 7,615	$ 29,468
Post- modification outstanding recorded investment	7,610	28,420
Other Loans Held for Sale [Member]
Troubled Debt Restructured Loan Modifications by Class [Line Items]
Number of loans		(3)
Pre- modification outstanding recorded investment		(11,250)
Post- modification outstanding recorded investment		(10,869)
Rate Concessions [Member]
Troubled Debt Restructured Loan Modifications by Class [Line Items]
Number of loans		5
Pre- modification outstanding recorded investment		2,390
Post- modification outstanding recorded investment		2,390
Term concession [Member]
Troubled Debt Restructured Loan Modifications by Class [Line Items]
Number of loans	6	28
Pre- modification outstanding recorded investment	5,047	11,589
Post- modification outstanding recorded investment	5,047	11,162
Rate and term Concessions [Member]
Troubled Debt Restructured Loan Modifications by Class [Line Items]
Number of loans	10	17
Pre- modification outstanding recorded investment	2,568	10,012
Post- modification outstanding recorded investment	2,563	9,772
Rate Term And Required Principal Paydown Concessions [Member]
Troubled Debt Restructured Loan Modifications by Class [Line Items]
Number of loans		1
Pre- modification outstanding recorded investment		504
Post- modification outstanding recorded investment		504
Required Principal Paydown Concession [Member]
Troubled Debt Restructured Loan Modifications by Class [Line Items]
Number of loans		1
Pre- modification outstanding recorded investment		1,736
Post- modification outstanding recorded investment		1,355
Other Commercial Loans [Member]
Troubled Debt Restructured Loan Modifications by Class [Line Items]
Number of loans		5
Pre- modification outstanding recorded investment		3,237
Post- modification outstanding recorded investment		3,237
Construction, land development, and other land loans [Member]
Troubled Debt Restructured Loan Modifications by Class [Line Items]
Number of loans	1	6
Pre- modification outstanding recorded investment	4,089	6,657
Post- modification outstanding recorded investment	4,089	6,657
Nonfarm nonresidential [Member]
Troubled Debt Restructured Loan Modifications by Class [Line Items]
Number of loans	8	19
Pre- modification outstanding recorded investment	2,305	19,466
Post- modification outstanding recorded investment	2,305	18,845
Total commercial real estate [Member]
Troubled Debt Restructured Loan Modifications by Class [Line Items]
Number of loans	9	25
Pre- modification outstanding recorded investment	6,394	26,123
Post- modification outstanding recorded investment	6,394	25,502
Single-family real estate [Member]
Troubled Debt Restructured Loan Modifications by Class [Line Items]
Number of loans	4	21
Pre- modification outstanding recorded investment	715	1,964
Post- modification outstanding recorded investment	715	1,964
Commercial and Industrial [Member]
Troubled Debt Restructured Loan Modifications by Class [Line Items]
Number of loans	3	8
Pre- modification outstanding recorded investment	506	1,337
Post- modification outstanding recorded investment	501	910
Consumer [Member]
Troubled Debt Restructured Loan Modifications by Class [Line Items]
Number of loans		3
Pre- modification outstanding recorded investment		44
Post- modification outstanding recorded investment		44
Loans, Gross [Member]
Troubled Debt Restructured Loan Modifications by Class [Line Items]
Number of loans	16	54
Pre- modification outstanding recorded investment	7,615	18,218
Post- modification outstanding recorded investment	$ 7,610	$ 17,551