Loans Held for Investment and Allowance for Credit Losses on Loans - Activity in Allowance for Credit Losses on Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	$ 96,920	$ 86,935	$ 92,728	$ 83,936
Initial allowance on loans purchased with credit deterioration		(7)		71
Charge- offs	(1,730)	(451)	(3,012)	(1,688)
Recoveries	274	531	602	1,252
Net charge-offs	(1,456)	80	(2,410)	(436)
Provision for/(benefit from) credit losses	2,312	2,863	7,458	6,300
Balance at end of period	97,776	89,871	97,776	89,871
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	6,808	6,928	6,416	7,550
Charge- offs	(805)		(853)	(20)
Recoveries	3	426	55	504
Net charge-offs	(802)	426	(798)	484
Provision for/(benefit from) credit losses	809	(231)	1,197	(911)
Balance at end of period	6,815	7,123	6,815	7,123
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	33,432	16,315	30,190	16,807
Charge- offs			(3)
Net charge-offs			(3)
Provision for/(benefit from) credit losses	1,182	7,371	4,427	6,879
Balance at end of period	34,614	23,686	34,614	23,686
Real Estate [Member] | Construction and Development Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	3,440	3,680	3,778	3,454
Charge- offs			(4)
Recoveries	3	3	9	8
Net charge-offs	3	3	5	8
Provision for/(benefit from) credit losses	467	461	127	682
Balance at end of period	3,910	4,144	3,910	4,144
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	3,553	1,183	3,275	1,051
Provision for/(benefit from) credit losses	(9)	1,124	269	1,256
Balance at end of period	3,544	2,307	3,544	2,307
Real Estate [Member] | Residential Real Estate First Lien [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	4,755	3,355	4,092	3,048
Initial allowance on loans purchased with credit deterioration				2
Charge- offs	(100)	(11)	(144)	(60)
Recoveries		15	13	28
Net charge-offs	(100)	4	(131)	(32)
Provision for/(benefit from) credit losses	109	(18)	803	323
Balance at end of period	4,764	3,341	4,764	3,341
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	1,661	1,480	1,418	1,567
Charge- offs		(2)	(28)	(38)
Recoveries	1	1	4	403
Net charge-offs	1	(1)	(24)	365
Provision for/(benefit from) credit losses	3	84	271	(369)
Balance at end of period	1,665	1,563	1,665	1,563
Commercial Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	25,127	25,370	25,106	25,565
Initial allowance on loans purchased with credit deterioration		(4)		44
Charge- offs	(239)	(187)	(517)	(961)
Recoveries	243	26	392	162
Net charge-offs	4	(161)	(125)	(799)
Provision for/(benefit from) credit losses	(886)	(251)	(736)	144
Balance at end of period	24,245	24,954	24,245	24,954
Consumer Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	4,344	4,050	4,132	3,694
Initial allowance on loans purchased with credit deterioration		(3)		25
Charge- offs	(427)	(171)	(965)	(404)
Recoveries	24	59	116	139
Net charge-offs	(403)	(112)	(849)	(265)
Provision for/(benefit from) credit losses	448	270	1,106	751
Balance at end of period	4,389	4,205	4,389	4,205
Oil and Gas [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	7,374	16,618	8,104	12,808
Charge- offs			(2)
Net charge-offs			(2)
Provision for/(benefit from) credit losses	23	(6,576)	(705)	(2,766)
Balance at end of period	7,397	10,042	7,397	10,042
Agriculture [Member] | Real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	6,426	7,956	6,217	8,392
Charge- offs	(159)	(80)	(496)	(205)
Recoveries		1	13	8
Net charge-offs	(159)	(79)	(483)	(197)
Provision for/(benefit from) credit losses	166	629	699	311
Balance at end of period	$ 6,433	$ 8,506	$ 6,433	$ 8,506