Loans - Schedule of Aging of Recorded Investment in Past Due Loans by Class of Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	$ 17,594	$ 9,018
Aging of Recorded Investment, Loans Not Past Due	2,798,870	2,665,925
Total	2,816,464	2,674,943
Construction and Land Development
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	538	2,828
Aging of Recorded Investment, Loans Not Past Due	591,003	581,612
Total	591,541	584,440
Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	993,912	805,260
Residential Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	643,601	682,882
Commercial and Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	8,554	701
Aging of Recorded Investment, Loans Not Past Due	574,087	596,092
Total	582,641	596,793
Consumer and Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	0	0
Aging of Recorded Investment, Loans Not Past Due	4,769	5,568
Total	4,769	5,568
Nonfarm, nonresidential | Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	3,981	515
Aging of Recorded Investment, Loans Not Past Due	940,040	753,728
Total	944,021	754,243
Commercial real estate, other | Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	0	0
Aging of Recorded Investment, Loans Not Past Due	49,891	51,017
Total	49,891	51,017
Closed-end 1-4 family | Residential Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	2,920	3,022
Aging of Recorded Investment, Loans Not Past Due	453,000	490,043
Total	455,920	493,065
Residential real estate, other | Residential Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	1,601	1,952
Aging of Recorded Investment, Loans Not Past Due	186,080	187,865
Total	187,681	189,817
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	7,925	3,582
30-59 Days Past Due | Construction and Land Development
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	508	294
30-59 Days Past Due | Commercial and Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	663	241
30-59 Days Past Due | Consumer and Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	0	0
30-59 Days Past Due | Nonfarm, nonresidential | Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	3,981	515
30-59 Days Past Due | Commercial real estate, other | Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	0	0
30-59 Days Past Due | Closed-end 1-4 family | Residential Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	2,688	2,390
30-59 Days Past Due | Residential real estate, other | Residential Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	85	142
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	8,341	2,642
60-89 Days Past Due | Construction and Land Development
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	0	1,986
60-89 Days Past Due | Commercial and Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	7,156	252
60-89 Days Past Due | Consumer and Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	0	0
60-89 Days Past Due | Nonfarm, nonresidential | Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	0	0
60-89 Days Past Due | Commercial real estate, other | Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	0	0
60-89 Days Past Due | Closed-end 1-4 family | Residential Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	224	404
60-89 Days Past Due | Residential real estate, other | Residential Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	961	0
Greater Than 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	1,328	2,794
Greater Than 89 Days Past Due | Construction and Land Development
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	30	548
Greater Than 89 Days Past Due | Commercial and Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	735	208
Greater Than 89 Days Past Due | Consumer and Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	0	0
Greater Than 89 Days Past Due | Nonfarm, nonresidential | Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	0	0
Greater Than 89 Days Past Due | Commercial real estate, other | Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	0	0
Greater Than 89 Days Past Due | Closed-end 1-4 family | Residential Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	8	228
Greater Than 89 Days Past Due | Residential real estate, other | Residential Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aging of Recorded Investment, Total Past Due	$ 555	$ 1,810