Loans Held for Investment and Allowance for Loan Losses - Schedule of Allowance for Loan Losses by Portfolio Segment (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for credit losses	$ 19,077	$ 17,573		$ 16,845
Loans collectively evaluated for credit losses	70,485	71,161		63,973
Total allowance for loan losses	89,562	88,734	$ 89,562	80,818	$ 75,834
C&I [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for credit losses	5,711	5,858		7,523
Loans collectively evaluated for credit losses	10,395	9,840		8,560
Total allowance for loan losses	16,106	15,698		16,083	16,129
Municipal [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for credit losses	0	0		0
Loans collectively evaluated for credit losses	195	195		1,067
Total allowance for loan losses	195	195		1,067	1,026
Construction & Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for credit losses	2,243	2,401		2,397
Loans collectively evaluated for credit losses	22,568	26,152		26,230
Total allowance for loan losses	24,811	28,553		28,627	26,443
Farm [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for credit losses	758	994		0
Loans collectively evaluated for credit losses	1,759	1,920		1,937
Total allowance for loan losses	2,517	2,914		1,937	1,957
Non-Owner Occupied CRE [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for credit losses	3,007	3,684		2,081
Loans collectively evaluated for credit losses	11,961	9,741		6,970
Total allowance for loan losses	14,968	13,425	14,968	9,051	9,075
Owner Occupied CRE [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for credit losses	2,238	1,663		2,605
Loans collectively evaluated for credit losses	10,518	12,150		9,343
Total allowance for loan losses	12,756	13,813	12,756	11,948	9,928
Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for credit losses	2,256	2,159		1,663
Loans collectively evaluated for credit losses	11,309	9,495		8,039
Total allowance for loan losses	13,565	11,654	13,565	9,702	9,075
Auto [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for credit losses	5	4		3
Loans collectively evaluated for credit losses	902	806		854
Total allowance for loan losses	907	810	907	857	845
Non-Auto [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for credit losses	129	60		2
Loans collectively evaluated for credit losses	365	331		330
Total allowance for loan losses	494	391	$ 494	332	315
Agriculture [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for credit losses	2,730	750		571
Loans collectively evaluated for credit losses	513	531		643
Total allowance for loan losses	$ 3,243	$ 1,281		$ 1,214	$ 1,041