Loans - Summary of Loans Troubled Debt Restructurings (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012 Contract	Sep. 30, 2011 Contract	Sep. 30, 2012 Contract	Sep. 30, 2011 Contract
Financing Receivable, Recorded Investment [Line Items]
Recorded investment	$ 256	$ 2,415	$ 2,335	$ 3,703
Number of contracts	4	4	14	32
Construction, land development, and other land loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Recorded investment			488
Number of contracts			1
Nonfarm nonresidential [Member]
Financing Receivable, Recorded Investment [Line Items]
Recorded investment	256	2,122	1,801	2,780
Number of contracts	1	2	6	4
Total commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Recorded investment	256	2,122	2,289	2,780
Number of contracts	1	2	7	4
Single-family real estate, closed end, [Member]
Financing Receivable, Recorded Investment [Line Items]
Recorded investment		293	46	462
Number of contracts		2	1	3
Loans Gross [Member]
Financing Receivable, Recorded Investment [Line Items]
Recorded investment	256	2,415	2,335	3,703
Number of contracts	1	4	8	11
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Recorded investment				$ 461
Number of contracts				4