Loans Held for Investment and Allowance for Loan Losses - Loans Held-for-Investment by Class of Financing Receivables (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	$ 5,322,562	$ 5,171,033	$ 4,639,389
Less: Allowance for credit losses	(62,974)	(66,534)	(60,440)	$ (52,499)
Net loans held for investment	5,259,588	5,104,499	4,578,949
C&I [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	1,178,126	1,131,382
Less: Allowance for credit losses	(12,323)	(13,609)
Municipal [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	176,949	181,325
Less: Allowance for credit losses	(2,191)	(1,552)
Construction & Development [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	587,928	553,959
Less: Allowance for credit losses	(13,246)	(13,512)
Farm [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	162,046	152,237
Less: Allowance for credit losses	(1,223)	(1,876)
Non-Owner Occupied CRE [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	650,144	617,686
Less: Allowance for credit losses	(9,492)	(8,391)
Owner Occupied CRE [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	759,906	746,974
Less: Allowance for credit losses	(9,878)	(12,347)
Residential [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	1,254,727	1,248,409
Less: Allowance for credit losses	(11,189)	(12,601)
Auto [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	370,027	353,595
Less: Allowance for credit losses	(1,068)	(1,020)
Non-Auto [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	92,343	90,602
Less: Allowance for credit losses	(379)	(371)
Commercial [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	1,355,075	1,312,707	869,450
Less: Allowance for credit losses			(11,773)	(12,122)
Commercial [Member] | C&I [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	1,178,126	1,131,382
Commercial [Member] | Municipal [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	176,949	181,325
Agriculture [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	90,366	94,864	99,582
Less: Allowance for credit losses	(1,985)	(1,255)	(2,154)	(1,206)
Real Estate [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	3,414,751	3,319,265	3,249,249
Less: Allowance for credit losses			(41,256)	(33,974)
Real Estate [Member] | Construction & Development [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	587,928	553,959
Real Estate [Member] | Farm [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	162,046	152,237
Real Estate [Member] | Non-Owner Occupied CRE [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	650,144	617,686
Real Estate [Member] | Owner Occupied CRE [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	759,906	746,974
Real Estate [Member] | Residential [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	1,254,727	1,248,409
Consumer [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	462,370	444,197	421,108
Less: Allowance for credit losses			$ (5,257)	$ (5,197)
Consumer [Member] | Auto [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	370,027	353,595
Consumer [Member] | Non-Auto [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	$ 92,343	$ 90,602