Loans - Summary of Loans Modified (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
Number of contracts	4	4	14	32
Pre- modification outstanding recorded investment	$ 900	$ 961	$ 7,291	$ 23,679
Post- modification outstanding recorded investment	900	961	7,286	22,631
Construction, land development, and other land loans [Member]
Number of contracts				3
Pre- modification outstanding recorded investment			4,089
Post- modification outstanding recorded investment			4,089
Nonfarm nonresidential [Member]
Number of contracts		2		14
Pre- modification outstanding recorded investment	255		2,066
Post- modification outstanding recorded investment	255		2,066
Total commercial real estate [Member]
Number of contracts		2		17
Pre- modification outstanding recorded investment	255		6,155
Post- modification outstanding recorded investment	255		6,155
Single family residential closed end, first lien [Member]
Number of contracts		1		9
Pre- modification outstanding recorded investment	645		715
Post- modification outstanding recorded investment	645		715
Commercial and Industrial [Member]
Number of contracts				5
Pre- modification outstanding recorded investment			421
Post- modification outstanding recorded investment			416
Loans Gross [Member]
Number of contracts	4	4	14	29
Pre- modification outstanding recorded investment	900	961	7,291	12,429
Post- modification outstanding recorded investment	900	961	7,286	11,762
Total consumer [Member]
Number of contracts		1		1
Other Loans Held for Sale [Member]
Number of contracts				3
Troubled Debt Restructuring [Member]
Number of contracts	4		14
Troubled Debt Restructuring [Member] | Construction, land development, and other land loans [Member]
Number of contracts			1
Troubled Debt Restructuring [Member] | Nonfarm nonresidential [Member]
Number of contracts	1		7
Troubled Debt Restructuring [Member] | Total commercial real estate [Member]
Number of contracts	1		8
Troubled Debt Restructuring [Member] | Single family residential closed end, first lien [Member]
Number of contracts	3		4
Troubled Debt Restructuring [Member] | Commercial and Industrial [Member]
Number of contracts			2
Troubled Debt Restructuring [Member] | Loans Gross [Member]
Number of contracts	4		14
Other Loans Held for Sale [Member]
Number of contracts				3
Pre- modification outstanding recorded investment				11,250
Post- modification outstanding recorded investment				10,869
Construction, land development, and other land loans [Member]
Number of contracts			1
Pre- modification outstanding recorded investment				5,964
Post- modification outstanding recorded investment				5,964
Nonfarm nonresidential [Member]
Number of contracts	1	2	6	4
Pre- modification outstanding recorded investment		840		15,729
Post- modification outstanding recorded investment		840		15,108
Total commercial real estate [Member]
Number of contracts	1	2	7	4
Pre- modification outstanding recorded investment		840		21,693
Post- modification outstanding recorded investment		840		21,072
Single family residential closed end, first lien [Member]
Pre- modification outstanding recorded investment		111		991
Post- modification outstanding recorded investment		111		991
Commercial and Industrial [Member]
Number of contracts				4
Pre- modification outstanding recorded investment				985
Post- modification outstanding recorded investment				558
Total consumer [Member]
Pre- modification outstanding recorded investment		10		10
Post- modification outstanding recorded investment		10		10
Loans Gross [Member]
Number of contracts	1	4	8	11
Pre- modification outstanding recorded investment		961		12,429
Post- modification outstanding recorded investment		961		11,762
Term concession [Member]
Number of contracts	2	1	6	19
Pre- modification outstanding recorded investment	439	10	5,047	10,969
Post- modification outstanding recorded investment	439	10	5,047	10,543
Rate and term Concessions [Member]
Number of contracts	2	3	8	8
Pre- modification outstanding recorded investment	461	951	2,244	6,080
Post- modification outstanding recorded investment	461	951	2,239	5,840
Rate Concessions [Member]
Number of contracts				3
Pre- modification outstanding recorded investment				1,982
Post- modification outstanding recorded investment				1,982
Required Principal Paydowns Concession [Member]
Number of contracts				1
Pre- modification outstanding recorded investment				1,736
Post- modification outstanding recorded investment				1,355
Other [Member]
Number of contracts				1
Pre- modification outstanding recorded investment				2,912
Post- modification outstanding recorded investment				$ 2,911