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		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	$ 94,760	$ 87,239	$ 92,728	$ 83,936
Initial allowance on loans purchased with credit deterioration				78
Charge- offs	(850)	(915)	(1,282)	(1,237)
Recoveries	186	110	328	721
Net charge-offs	(664)	(805)	(954)	(516)
Provision for/(benefit from) credit losses	2,824	501	5,146	3,437
Balance at end of period	96,920	86,935	96,920	86,935
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	6,547	8,262	6,416	7,550
Charge- offs		(4)	(48)	(20)
Recoveries	3	30	52	78
Net charge-offs	3	26	4	58
Provision for/(benefit from) credit losses	258	(1,360)	388	(680)
Balance at end of period	6,808	6,928	6,808	6,928
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	32,120	16,348	30,190	16,807
Charge- offs			(3)
Net charge-offs			(3)
Provision for/(benefit from) credit losses	1,312	(33)	3,245	(492)
Balance at end of period	33,432	16,315	33,432	16,315
Real Estate [Member] | Construction and Development Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	3,608	3,272	3,778	3,454
Charge- offs	(2)		(4)
Recoveries	3	2	6	5
Net charge-offs	1	2	2	5
Provision for/(benefit from) credit losses	(169)	406	(340)	221
Balance at end of period	3,440	3,680	3,440	3,680
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	3,226	1,103	3,275	1,051
Provision for/(benefit from) credit losses	327	80	278	132
Balance at end of period	3,553	1,183	3,553	1,183
Real Estate [Member] | Residential Real Estate First Lien [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	4,454	3,394	4,092	3,048
Initial allowance on loans purchased with credit deterioration				2
Charge- offs	(42)	(5)	(44)	(49)
Recoveries	10	6	13	13
Net charge-offs	(32)	1	(31)	(36)
Provision for/(benefit from) credit losses	333	(40)	694	341
Balance at end of period	4,755	3,355	4,755	3,355
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	1,444	1,560	1,418	1,567
Charge- offs	(2)	(36)	(28)	(36)
Recoveries	1		3	402
Net charge-offs	(1)	(36)	(25)	366
Provision for/(benefit from) credit losses	218	(44)	268	(453)
Balance at end of period	1,661	1,480	1,661	1,480
Commercial Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	25,079	25,163	25,106	25,565
Initial allowance on loans purchased with credit deterioration				48
Charge- offs	(102)	(717)	(278)	(774)
Recoveries	127	26	149	136
Net charge-offs	25	(691)	(129)	(638)
Provision for/(benefit from) credit losses	23	898	150	395
Balance at end of period	25,127	25,370	25,127	25,370
Consumer Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	4,232	3,730	4,132	3,694
Initial allowance on loans purchased with credit deterioration				28
Charge- offs	(398)	(153)	(538)	(233)
Recoveries	35	42	92	80
Net charge-offs	(363)	(111)	(446)	(153)
Provision for/(benefit from) credit losses	475	431	658	481
Balance at end of period	4,344	4,050	4,344	4,050
Oil and Gas [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	7,782	16,389	8,104	12,808
Charge- offs	(2)		(2)
Net charge-offs	(2)		(2)
Provision for/(benefit from) credit losses	(406)	229	(728)	3,810
Balance at end of period	7,374	16,618	7,374	16,618
Agriculture [Member] | Real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	6,268	8,018	6,217	8,392
Charge- offs	(302)		(337)	(125)
Recoveries	7	4	13	7
Net charge-offs	(295)	4	(324)	(118)
Provision for/(benefit from) credit losses	453	(66)	533	(318)
Balance at end of period	$ 6,426	$ 7,956	$ 6,426	$ 7,956