Loans Held for Investment and Allowance for Loan Losses - Changes in Allowance for Loan Losses (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 71,932,000	$ 62,138,000	$ 63,465,000	$ 66,534,000
Provision for loan losses	1,060,000		8,910,000	(4,468,000)
Recoveries	1,409,000	2,707,000	2,960,000	3,745,000
Charge-offs	293,000	(1,475,000)	1,227,000	(2,441,000)
Ending balance	74,108,000	63,370,000	74,108,000	63,370,000
C&I [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	18,589,000	10,186,000	12,280,000	13,609,000
Provision for loan losses	(2,378,000)	(31,000)	3,598,000	(3,597,000)
Recoveries	266,000	1,140,000	824,000	1,671,000
Charge-offs	(38,000)	(902,000)	(263,000)	(1,290,000)
Ending balance	16,439,000	10,393,000	16,439,000	10,393,000
Municipal [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,352,000	588,000	348,000	1,552,000
Provision for loan losses	(33,000)	(273,000)	971,000	(1,237,000)
Recoveries	0		0
Charge-offs	0		0
Ending balance	1,319,000	315,000	1,319,000	315,000
Construction & Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	21,085,000	15,632,000	17,627,000	13,512,000
Provision for loan losses	4,614,000	1,230,000	8,172,000	3,348,000
Recoveries	0	0	0	2,000
Charge-offs	0		(100,000)
Ending balance	25,699,000	16,862,000	25,699,000	16,862,000
Farm [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,006,000	607,000	663,000	1,876,000
Provision for loan losses	149,000	(21,000)	492,000	(1,300,000)
Recoveries	0	0	0	10,000
Charge-offs	0		0
Ending balance	1,155,000	586,000	1,155,000	586,000
Non-Owner Occupied CRE [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	8,410,000	10,432,000	10,722,000	8,391,000
Provision for loan losses	(498,000)	(344,000)	(3,352,000)	1,609,000
Recoveries	283,000	556,000	825,000	650,000
Charge-offs	0	0	0	(6,000)
Ending balance	8,195,000	10,644,000	8,195,000	10,644,000
Owner Occupied CRE [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	10,740,000	10,399,000	10,828,000	12,347,000
Provision for loan losses	(1,303,000)	(94,000)	(1,323,000)	(2,044,000)
Recoveries	649,000	806,000	669,000	816,000
Charge-offs	0	(222,000)	(88,000)	(230,000)
Ending balance	10,086,000	10,889,000	10,086,000	10,889,000
Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	8,304,000	11,234,000	8,133,000	12,601,000
Provision for loan losses	557,000	(1,184,000)	860,000	(2,542,000)
Recoveries	93,000	7,000	110,000	90,000
Charge-offs	0	0	(149,000)	(92,000)
Ending balance	8,954,000	10,057,000	8,954,000	10,057,000
Auto [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	912,000	1,266,000	896,000	1,020,000
Provision for loan losses	72,000	(259,000)	116,000	139,000
Recoveries	47,000	129,000	215,000	305,000
Charge-offs	(119,000)	(176,000)	(315,000)	(504,000)
Ending balance	912,000	960,000	912,000	960,000
Non-Auto [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	372,000	482,000	371,000	371,000
Provision for loan losses	67,000	(46,000)	106,000	80,000
Recoveries	53,000	64,000	182,000	172,000
Charge-offs	(136,000)	(125,000)	(303,000)	(248,000)
Ending balance	356,000	375,000	356,000	375,000
Agriculture [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,162,000	1,312,000	1,597,000	1,255,000
Provision for loan losses	(187,000)	1,022,000	(730,000)	1,076,000
Recoveries	18,000	5,000	135,000	29,000
Charge-offs	0	(50,000)	(9,000)	(71,000)
Ending balance	$ 993,000	$ 2,289,000	$ 993,000	$ 2,289,000