Loans - Summary of Loans Troubled Debt Restructurings (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012 Contract	Dec. 31, 2011 Contract
Financing Receivable, Recorded Investment [Line Items]
Number of loans	4	19
Recorded investment	$ 2,415	$ 7,345
Nonfarm nonresidential [Member]
Financing Receivable, Recorded Investment [Line Items]
Number of loans	2	5
Recorded investment	2,122	5,760
Single-family real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Number of loans	2	8
Recorded investment	293	966
Commercial and industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Number of loans		6
Recorded investment		619
Other Loans Held for Sale [Member]
Financing Receivable, Recorded Investment [Line Items]
Number of loans		(1)
Recorded investment		(2,979)
Loans, Gross [Member]
Financing Receivable, Recorded Investment [Line Items]
Number of loans	4	18
Recorded investment	$ 2,415	$ 4,366