Loans and the Allowance for Loan Losses - Summary of Credit Quality Indicators, Disaggregated by Class of Loan (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	$ 745,341	$ 558,386
Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	105,387	61,062
Farmland [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	9,963	16,097
1-4 Family Residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	96,267	41,552
Multi-family Residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	18,597	11,369
Nonfarm Nonresidential [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	295,268	215,797
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	193,226	185,291
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	26,633	27,218
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	674,323	501,916
Pass [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	97,573	56,740
Pass [Member] | Farmland [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	9,963	16,097
Pass [Member] | 1-4 Family Residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	88,189	39,702
Pass [Member] | Multi-family Residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	17,278	10,463
Pass [Member] | Nonfarm Nonresidential [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	263,292	190,356
Pass [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	171,808	161,904
Pass [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	26,220	26,654
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	26,560	32,901
Special Mention [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	3,445	2,069
Special Mention [Member] | 1-4 Family Residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	1,890	912
Special Mention [Member] | Multi-family Residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	945	906
Special Mention [Member] | Nonfarm Nonresidential [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	12,437	16,410
Special Mention [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	7,462	12,087
Special Mention [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	381	517
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	35,700	20,541
Substandard [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	1,508	642
Substandard [Member] | 1-4 Family Residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	3,489	786
Substandard [Member] | Multi-family Residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	374
Substandard [Member] | Nonfarm Nonresidential [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	18,008	7,812
Substandard [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	12,289	11,254
Substandard [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	32	47
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	8,758	3,028
Doubtful [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	2,861	1,611
Doubtful [Member] | 1-4 Family Residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	2,699	152
Doubtful [Member] | Nonfarm Nonresidential [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	1,531	1,219
Doubtful [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit quality indicators	$ 1,667	$ 46