Loans Held for Investment and Allowance for Loan Losses - Changes in Allowance for Loan Losses (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 66,913,000	$ 62,974,000	$ 63,465,000	$ 66,534,000
Provision for loan losses	4,103,000	(1,039,000)	7,850,000	(4,468,000)
Recoveries	1,191,000	595,000	1,551,000	1,038,000
Charge-offs	(275,000)	(392,000)	(934,000)	(966,000)
Ending balance	71,932,000	62,138,000	71,932,000	62,138,000
C&I [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	15,737,000	12,323,000	12,280,000	13,609,000
Provision for loan losses	2,521,000	(2,327,000)	5,976,000	(3,566,000)
Recoveries	402,000	308,000	558,000	531,000
Charge-offs	(71,000)	(118,000)	(225,000)	(388,000)
Ending balance	18,589,000	10,186,000	18,589,000	10,186,000
Municipal [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,418,000	2,191,000	348,000	1,552,000
Provision for loan losses	(66,000)	(1,603,000)	1,004,000	(964,000)
Recoveries	0
Charge-offs	0
Ending balance	1,352,000	588,000	1,352,000	588,000
Construction & Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	17,887,000	13,246,000	17,627,000	13,512,000
Provision for loan losses	3,198,000	2,386,000	3,558,000	2,118,000
Recoveries	0	0		2,000
Charge-offs	0		(100,000)
Ending balance	21,085,000	15,632,000	21,085,000	15,632,000
Farm [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	873,000	1,223,000	663,000	1,876,000
Provision for loan losses	133,000	(617,000)	343,000	(1,279,000)
Recoveries	0	1,000		10,000
Charge-offs	0
Ending balance	1,006,000	607,000	1,006,000	607,000
Non-Owner Occupied CRE [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	8,499,000	9,492,000	10,722,000	8,391,000
Provision for loan losses	(576,000)	901,000	(2,854,000)	1,953,000
Recoveries	487,000	39,000	542,000	94,000
Charge-offs		0		(6,000)
Ending balance	8,410,000	10,432,000	8,410,000	10,432,000
Owner Occupied CRE [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	11,536,000	9,878,000	10,828,000	12,347,000
Provision for loan losses	(809,000)	517,000	(20,000)	(1,950,000)
Recoveries	13,000	4,000	20,000	10,000
Charge-offs		0	(88,000)	(8,000)
Ending balance	10,740,000	10,399,000	10,740,000	10,399,000
Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	7,829,000	11,189,000	8,133,000	12,601,000
Provision for loan losses	466,000	26,000	303,000	(1,358,000)
Recoveries	12,000	64,000	17,000	83,000
Charge-offs	(3,000)	(45,000)	(149,000)	(92,000)
Ending balance	8,304,000	11,234,000	8,304,000	11,234,000
Auto [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	869,000	1,068,000	896,000	1,020,000
Provision for loan losses	64,000	257,000	44,000	398,000
Recoveries	102,000	103,000	168,000	176,000
Charge-offs	(123,000)	(162,000)	(196,000)	(328,000)
Ending balance	912,000	1,266,000	912,000	1,266,000
Non-Auto [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	354,000	379,000	371,000	371,000
Provision for loan losses	4,000	88,000	39,000	126,000
Recoveries	83,000	61,000	129,000	108,000
Charge-offs	(69,000)	(46,000)	(167,000)	(123,000)
Ending balance	372,000	482,000	372,000	482,000
Agriculture [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,911,000	1,985,000	1,597,000	1,255,000
Provision for loan losses	(832,000)	(667,000)	(543,000)	54,000
Recoveries	92,000	15,000	117,000	24,000
Charge-offs	(9,000)	(21,000)	(9,000)	(21,000)
Ending balance	$ 1,162,000	$ 1,312,000	$ 1,162,000	$ 1,312,000