Loans Held for Investment and Allowance for Loan Losses - Loans Held-for-Investment by Class of Financing Receivables (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	$ 5,304,602		$ 5,171,033	$ 5,253,067
Less: Allowance for credit losses	(62,138)	$ (62,974)	(66,534)	(68,947)	$ (60,440)	$ (52,499)
Net loans held for investment	5,242,464		5,104,499	5,184,120
C&I [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	983,103		1,131,382
Less: Allowance for credit losses	(10,186)	(12,323)	(13,609)
Municipal [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	179,356		181,325
Less: Allowance for credit losses	(588)	(2,191)	(1,552)
Construction & Development [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	550,928		553,959
Less: Allowance for credit losses	(15,632)	(13,246)	(13,512)
Farm [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	185,288		152,237
Less: Allowance for credit losses	(607)	(1,223)	(1,876)
Non-Owner Occupied CRE [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	673,608		617,686
Less: Allowance for credit losses	(10,432)	(9,492)	(8,391)
Owner Occupied CRE [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	820,055		746,974
Less: Allowance for credit losses	(10,399)	(9,878)	(12,347)
Residential [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	1,328,474		1,248,409
Less: Allowance for credit losses	(11,234)	(11,189)	(12,601)
Auto [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	383,764		353,595
Less: Allowance for credit losses	(1,266)	(1,068)	(1,020)
Non-Auto [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	104,814		90,602
Less: Allowance for credit losses	(482)	(379)	(371)
Commercial [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	1,162,459		1,312,707	1,509,454
Less: Allowance for credit losses				(18,572)	(11,773)	(12,122)
Commercial [Member] | C&I [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	983,103		1,131,382
Commercial [Member] | Municipal [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	179,356		181,325
Agriculture [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	95,212		94,864	97,448
Less: Allowance for credit losses	(1,312)	$ (1,985)	(1,255)	(2,544)	(2,154)	(1,206)
Real Estate [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	3,558,353		3,319,265	3,235,208
Less: Allowance for credit losses				(42,623)	(41,256)	(33,974)
Real Estate [Member] | Construction & Development [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	550,928		553,959
Real Estate [Member] | Farm [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	185,288		152,237
Real Estate [Member] | Non-Owner Occupied CRE [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	673,608		617,686
Real Estate [Member] | Owner Occupied CRE [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	820,055		746,974
Real Estate [Member] | Residential [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	1,328,474		1,248,409
Consumer [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	488,578		444,197	410,957
Less: Allowance for credit losses				$ (5,208)	$ (5,257)	$ (5,197)
Consumer [Member] | Auto [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	383,764		353,595
Consumer [Member] | Non-Auto [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	$ 104,814		$ 90,602