Allowance for Loan and Lease Losses ("ALLL") and Credit Quality Indicators - Summary of Company's Allowance for Loan and Lease Losses (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	$ 54,147	$ 43,861	$ 52,918	$ 42,945	$ 42,945
Charge-offs	(1,904)	(2,732)	(7,298)	(3,856)	(8,338)
Recoveries	198	247	506	982	1,396
Provision	4,308	5,582	10,623	6,887	16,915
Ending balance	56,749	46,958	56,749	46,958	52,918
Real Estate [Member] | Residential 1-4 Family [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	5,657	4,622	5,482	4,701	4,701
Charge-offs	(92)	(142)	(621)	(341)	(577)
Recoveries	10	49	21	71	135
Provision	26	231	719	329	1,223
Ending balance	5,601	4,760	5,601	4,760	5,482
Real Estate [Member] | Non-Farm/Non-Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	17,766	14,013	17,190	13,633	13,633
Charge-offs	(119)	(1,181)	(324)	(1,254)	(1,357)
Recoveries	5	1	17	4	33
Provision	580	2,003	1,349	2,453	4,881
Ending balance	18,232	14,836	18,232	14,836	17,190
Real Estate [Member] | Construction/Land Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	17,580	12,828	15,960	12,306	12,306
Charge-offs	(469)	(14)	(771)	(14)	(638)
Recoveries	0	0	37	8	11
Provision	2,037	2,650	3,922	3,164	4,281
Ending balance	19,148	15,464	19,148	15,464	15,960
Real Estate [Member] | Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	2,526	3,018	2,558	3,000	3,000
Charge-offs	0	0	(13)	(15)	(214)
Recoveries	0	6	0	11	14
Provision	(66)	(116)	(85)	(88)	(242)
Ending balance	2,460	2,908	2,460	2,908	2,558
Real Estate [Member] | Multi Family Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	2,423	2,429	2,147	2,504	2,504
Charge-offs	(208)	0	(208)	0	0
Recoveries	0	0	0	0	0
Provision	671	(657)	947	(732)	(357)
Ending balance	2,886	1,772	2,886	1,772	2,147
Commercial And Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	3,301	2,738	4,873	2,855	2,855
Charge-offs	(93)	(48)	(2,540)	(422)	(720)
Recoveries	23	135	39	763	808
Provision	18	23	877	(348)	1,930
Ending balance	3,249	2,848	3,249	2,848	4,873
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	824	831	818	917	917
Charge-offs	(24)	(56)	(69)	(97)	(222)
Recoveries	21	18	42	36	80
Provision	4	133	34	70	43
Ending balance	825	926	825	926	818
Direct Financing Leases [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	3,258	2,438	2,989	2,266	2,266
Charge-offs	(155)	(121)	(341)	(267)	(602)
Recoveries	7	8	13	14	49
Provision	444	247	893	559	1,276
Ending balance	3,554	2,572	3,554	2,572	2,989
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	812	944	901	763	763
Charge-offs	(336)	(88)	(688)	(159)	(793)
Recoveries	132	30	337	75	266
Provision	186	(14)	244	193	665
Ending balance	794	872	794	872	901
Purchased Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	0	0	0	0	0
Charge-offs	(408)	(1,082)	(1,723)	(1,287)	(3,215)
Recoveries	0	0	0	0	0
Provision	408	1,082	1,723	1,287	3,215
Ending balance	$ 0	$ 0	$ 0	$ 0	$ 0