Loans Held for Investment and Allowance for Loan Losses - Changes in Allowance for Loan Losses (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 63,465,000	$ 66,534,000
Provision for loan losses	(3,747,000)	(3,429,000)
Recoveries	360,000	443,000
Charge-offs	(659,000)	(574,000)
Ending balance	66,913,000	62,974,000
C&I [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	12,280,000	13,609,000
Provision for loan losses	(3,455,000)	1,239,000
Recoveries	156,000	223,000
Charge-offs	(154,000)	(270,000)
Ending balance	15,737,000	12,323,000
Municipal [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	348,000	1,552,000
Provision for loan losses	(1,070,000)	(639,000)
Ending balance	1,418,000	2,191,000
Construction & Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	17,627,000	13,512,000
Provision for loan losses	(360,000)	268,000
Recoveries		2,000
Charge-offs	(100,000)
Ending balance	17,887,000	13,246,000
Farm [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	663,000	1,876,000
Provision for loan losses	(210,000)	662,000
Recoveries		9,000
Ending balance	873,000	1,223,000
Non-Owner Occupied CRE [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	10,722,000	8,391,000
Provision for loan losses	2,278,000	(1,052,000)
Recoveries	55,000	55,000
Charge-offs		(6,000)
Ending balance	8,499,000	9,492,000
Owner Occupied CRE [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	10,828,000	12,347,000
Provision for loan losses	(789,000)	2,467,000
Recoveries	7,000	6,000
Charge-offs	(88,000)	(8,000)
Ending balance	11,536,000	9,878,000
Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	8,133,000	12,601,000
Provision for loan losses	163,000	1,384,000
Recoveries	5,000	19,000
Charge-offs	(146,000)	(47,000)
Ending balance	7,829,000	11,189,000
Auto [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	896,000	1,020,000
Provision for loan losses	20,000	(141,000)
Recoveries	66,000	73,000
Charge-offs	(73,000)	(166,000)
Ending balance	869,000	1,068,000
Non-Auto [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	371,000	371,000
Provision for loan losses	(35,000)	(38,000)
Recoveries	46,000	47,000
Charge-offs	(98,000)	(77,000)
Ending balance	354,000	379,000
Agriculture [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,597,000	1,255,000
Provision for loan losses	(289,000)	(721,000)
Recoveries	25,000	9,000
Ending balance	$ 1,911,000	$ 1,985,000