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, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	$ 86,935	$ 83,963	$ 83,936	$ 91,366
Initial allowance on loans purchased with credit deterioration	(7)	1,027	71	8,299
Charge- offs	(451)	(300)	(1,688)	(5,414)
Recoveries	531	290	1,252	678
Net charge-offs	80	(10)	(436)	(4,736)
Provision for (benefit from) credit losses	2,863	1,483	6,300	(8,466)
Balance at end of period	89,871	86,463	89,871	86,463
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	6,945	8,298	7,568	8,470
Initial allowance on loans purchased with credit deterioration		93		1,080
Charge- offs		(3)	(20)	(3)
Recoveries	426	72	504	73
Net charge-offs	426	69	484	70
Provision for (benefit from) credit losses	(291)	91	(972)	(1,069)
Balance at end of period	7,080	8,551	7,080	8,551
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	22,937	15,038	16,987	12,318
Initial allowance on loans purchased with credit deterioration		191		824
Charge- offs		(7)		(803)
Recoveries		67		67
Net charge-offs		60		(736)
Provision for (benefit from) credit losses	988	46	6,938	2,929
Balance at end of period	23,925	15,335	23,925	15,335
Real Estate [Member] | Construction and Development Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	3,728	3,095	3,490	2,723
Initial allowance on loans purchased with credit deterioration				173
Recoveries	3	4	8	9
Net charge-offs	3	4	8	9
Provision for (benefit from) credit losses	449	(417)	682	611
Balance at end of period	4,180	3,516	4,180	3,516
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	2,292	998	1,092	726
Provision for (benefit from) credit losses	115	(25)	1,315	247
Balance at end of period	2,407	973	2,407	973
Real Estate [Member] | Residential Real Estate First Lien [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	3,383	2,921	3,076	2,822
Initial allowance on loans purchased with credit deterioration		9	2	126
Charge- offs	(11)	(4)	(60)	(56)
Recoveries	15	9	28	36
Net charge-offs	4	5	(32)	(20)
Provision for (benefit from) credit losses	(8)	(199)	333	206
Balance at end of period	3,379	3,134	3,379	3,134
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	2,051	1,963	2,104	2,236
Charge- offs	(2)		(38)	(46)
Recoveries	1	46	403	50
Net charge-offs	(1)	46	365	4
Provision for (benefit from) credit losses	59	206	(360)	(25)
Balance at end of period	2,109	2,215	2,109	2,215
Commercial and Agricultural Non-Real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	27,833	34,310	28,085	34,643
Initial allowance on loans purchased with credit deterioration	(4)	952	44	5,663
Charge- offs	(267)	(219)	(1,166)	(3,817)
Recoveries	27	43	170	195
Net charge-offs	(240)	(176)	(996)	(3,622)
Provision for (benefit from) credit losses	545	(489)	1,001	(2,087)
Balance at end of period	28,134	34,597	28,134	34,597
Consumer Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	4,094	3,481	3,734	3,542
Initial allowance on loans purchased with credit deterioration	(3)	30	25	38
Charge- offs	(171)	(67)	(404)	(689)
Recoveries	59	49	139	247
Net charge-offs	(112)	(18)	(265)	(442)
Provision for (benefit from) credit losses	268	66	753	421
Balance at end of period	4,247	3,559	4,247	3,559
Oil and Gas [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	9,307	10,132	12,978	20,733
Provision for (benefit from) credit losses	839	(3)	(2,832)	(10,598)
Balance at end of period	10,146	10,135	10,146	10,135
Farmland [Member] | Real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	4,365	3,727	4,822	3,153
Initial allowance on loans purchased with credit deterioration		(248)		395
Recoveries				1
Net charge-offs				1
Provision for (benefit from) credit losses	(101)	969	(558)	(899)
Balance at end of period	$ 4,264	$ 4,448	$ 4,264	$ 4,448