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
	Mar. 31, 2023	Mar. 31, 2022
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	$ 92,728	$ 83,936
Initial allowance on loans purchased with credit deterioration		78
Charge- offs	(432)	(322)
Recoveries	142	611
Net charge-offs	(290)	289
Provision for/(benefit from) credit losses	2,322	2,936
Balance at end of period	94,760	87,239
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	6,416	7,550
Charge- offs	(48)	(16)
Recoveries	49	48
Net charge-offs	1	32
Provision for/(benefit from) credit losses	130	680
Balance at end of period	6,547	8,262
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	30,190	16,807
Charge- offs	(3)
Net charge-offs	(3)
Provision for/(benefit from) credit losses	1,933	459
Balance at end of period	32,120	16,348
Real Estate [Member] | Construction and Development Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	3,778	3,454
Charge- offs	(2)
Recoveries	3	3
Net charge-offs	1	3
Provision for/(benefit from) credit losses	(171)	(185)
Balance at end of period	3,608	3,272
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	3,275	1,051
Provision for/(benefit from) credit losses	(49)	52
Balance at end of period	3,226	1,103
Real Estate [Member] | Residential Real Estate First Lien [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	4,092	3,048
Initial allowance on loans purchased with credit deterioration		2
Charge- offs	(2)	(44)
Recoveries	3	7
Net charge-offs	1	(37)
Provision for/(benefit from) credit losses	361	381
Balance at end of period	4,454	3,394
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	1,418	1,567
Charge- offs	(26)
Recoveries	2	402
Net charge-offs	(24)	402
Provision for/(benefit from) credit losses	50	(409)
Balance at end of period	1,444	1,560
Commercial Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	25,106	25,565
Initial allowance on loans purchased with credit deterioration		48
Charge- offs	(176)	(57)
Recoveries	22	110
Net charge-offs	(154)	53
Provision for/(benefit from) credit losses	127	(503)
Balance at end of period	25,079	25,163
Consumer Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	4,132	3,694
Initial allowance on loans purchased with credit deterioration		28
Charge- offs	(140)	(80)
Recoveries	57	38
Net charge-offs	(83)	(42)
Provision for/(benefit from) credit losses	183	50
Balance at end of period	4,232	3,730
Oil and Gas [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	8,104	12,808
Provision for/(benefit from) credit losses	(322)	(3,581)
Balance at end of period	7,782	16,389
Agriculture [Member] | Real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	6,217	8,392
Charge- offs	(35)	(125)
Recoveries	6	3
Net charge-offs	(29)	(122)
Provision for/(benefit from) credit losses	80	(252)
Balance at end of period	$ 6,268	$ 8,018