Loans Held for Investment and Allowance for Credit Losses on Loans - Activity in Allowance for Credit Losses on Loans (Detail) - USD ($) $ in Thousands		12 Months Ended
	Jan. 01, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	$ 54,238	$ 91,366	$ 54,238
Decrease in allowance for credit losses upon adoption of ASC 326	(3,200)		(3,195)
Initial allowance on loans purchased with credit deterioration		8,299	502
Charge- offs		(7,845)	(23,832)
Recoveries		806	1,005
Net charge-offs		(7,039)	(22,827)
Provision for credit losses on loans		(8,690)	62,648	$ 8,287
Balance at end of period		83,936	91,366	54,238
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	5,600	6,911	5,600
Decrease in allowance for credit losses upon adoption of ASC 326			(2,704)
Initial allowance on loans purchased with credit deterioration		1,080	432
Charge- offs		(38)	(773)
Recoveries		74	10
Net charge-offs		36	(763)
Provision for credit losses on loans		(1,617)	4,346
Balance at end of period		6,410	6,911	5,600
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	8,459	12,318	8,459
Decrease in allowance for credit losses upon adoption of ASC 326			(5,265)
Initial allowance on loans purchased with credit deterioration		824
Charge- offs		(803)	(3,609)
Recoveries		67
Net charge-offs		(736)	(3,609)
Provision for credit losses on loans		4,581	12,733
Balance at end of period		16,987	12,318	8,459
Real Estate [Member] | Construction and Development Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	2,276	2,723	2,276
Decrease in allowance for credit losses upon adoption of ASC 326			(916)
Initial allowance on loans purchased with credit deterioration		173
Charge- offs			(59)
Recoveries		12	123
Net charge-offs		12	64
Provision for credit losses on loans		582	1,299
Balance at end of period		3,490	2,723	2,276
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	1,960	726	1,960
Decrease in allowance for credit losses upon adoption of ASC 326			(690)
Charge- offs			(29)
Net charge-offs			(29)
Provision for credit losses on loans		366	(515)
Balance at end of period		1,092	726	1,960
Real Estate [Member] | Residential Real Estate First Lien [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	8,781	2,822	8,781
Decrease in allowance for credit losses upon adoption of ASC 326			(3,052)
Initial allowance on loans purchased with credit deterioration		126	7
Charge- offs		(87)	(465)
Recoveries		55	44
Net charge-offs		(32)	(421)
Provision for credit losses on loans		160	(2,493)
Balance at end of period		3,076	2,822	8,781
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	2,763	2,236	2,763
Decrease in allowance for credit losses upon adoption of ASC 326			(1,383)
Charge- offs		(521)	(126)
Recoveries		52	54
Net charge-offs		(469)	(72)
Provision for credit losses on loans		337	928
Balance at end of period		2,104	2,236	2,763
Commercial and Agricultural Non-Real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	12,310	33,020	12,310
Decrease in allowance for credit losses upon adoption of ASC 326			13,949
Initial allowance on loans purchased with credit deterioration		5,663	62
Charge- offs		(4,509)	(4,161)
Recoveries		218	540
Net charge-offs		(4,291)	(3,621)
Provision for credit losses on loans		(8,319)	10,320
Balance at end of period		26,073	33,020	12,310
Consumer Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	3,284	3,542	3,284
Decrease in allowance for credit losses upon adoption of ASC 326			(548)
Initial allowance on loans purchased with credit deterioration		38
Charge- offs		(864)	(1,142)
Recoveries		326	224
Net charge-offs		(538)	(918)
Provision for credit losses on loans		692	1,724
Balance at end of period		3,734	3,542	3,284
Oil and Gas [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	3,355	20,733	3,355
Decrease in allowance for credit losses upon adoption of ASC 326			(1,068)
Charge- offs			(11,245)
Net charge-offs			(11,245)
Provision for credit losses on loans		(7,755)	29,691
Balance at end of period		12,978	20,733	3,355
Other Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	2,632	3,182	2,632
Decrease in allowance for credit losses upon adoption of ASC 326			(116)
Charge- offs		(134)	(168)
Recoveries		1	10
Net charge-offs		(133)	(158)
Provision for credit losses on loans		121	824
Balance at end of period		3,170	3,182	2,632
Farmland [Member] | Real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	$ 2,818	3,153	2,818
Decrease in allowance for credit losses upon adoption of ASC 326			(1,402)
Initial allowance on loans purchased with credit deterioration		395	1
Charge- offs		(889)	(2,055)
Recoveries		1
Net charge-offs		(888)	(2,055)
Provision for credit losses on loans		2,162	3,791
Balance at end of period		$ 4,822	$ 3,153	$ 2,818