First Financial Bankshares (FFIN) 10-Q 5 May 21 2021 Q1 Quarterly report Financial data

Cover Page

Cover Page - shares	3 Months Ended
	Mar. 31, 2021	Apr. 27, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Quarterly Report	true
Document Transition Report	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31
Document Period End Date	Mar. 31, 2021
Entity Registrant Name	FIRST FINANCIAL BANKSHARES INC
Entity Central Index Key	0000036029
Entity Filer Category	Large Accelerated Filer
Entity Interactive Data Current	Yes
Entity Current Reporting Status	Yes
Entity File Number	0-7674
Entity Incorporation, State or Country Code	TX
Entity Tax Identification Number	75-0944023
Entity Address, Address Line One	400 Pine Street
Entity Address, City or Town	Abilene
Entity Address, State or Province	TX
City Area Code	325
Local Phone Number	627-7155
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Title of 12(b) Security	Common Stock
Trading Symbol	FFIN
Security Exchange Name	NASDAQ
Entity Address, Postal Zip Code	79601
Entity Common Stock, Shares Outstanding		142,285,611

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
ASSETS
CASH AND DUE FROM BANKS	$ 190,350	$ 211,113	$ 191,486
INTEREST-BEARING DEMAND DEPOSITS IN BANKS	893,221	517,971	76,378
Total cash and cash equivalents	1,083,571	729,084	267,864
SECURITIES AVAILABLE-FOR-SALE, at fair value (amortized cost of these securities was $4,961,438, $3,950,510 and $4,177,179 as of March 31, 2021 and 2020 and December 31, 2020, respectively)	5,109,631	4,393,029	4,107,069
LOANS:
Held-for-investment	5,322,562	5,171,033	4,639,389
Less - allowance for credit losses	(62,974)	(66,534)	(60,440)
Net loans held for investment	5,259,588	5,104,499	4,578,949
Held-for-sale ($61,511, $39,659 and $79,585 at fair value at March 31, 2021 and 2020 and December 31, 2020, respectively)	65,405	83,969	42,034
BANK PREMISES AND EQUIPMENT, net	142,415	142,269	139,554
INTANGIBLE ASSETS, net	317,980	318,392	319,234
OTHER ASSETS	124,297	133,258	246,387
Total assets	12,102,887	10,904,500	9,701,091
LIABILITIES AND SHAREHOLDERS' EQUITY
NONINTEREST-BEARING DEPOSITS	3,350,145	2,982,697	2,288,597
INTEREST-BEARING DEPOSITS	6,063,302	5,693,120	4,921,869
Total deposits	9,413,447	8,675,817	7,210,466
DIVIDENDS PAYABLE	18,500	18,484	17,060
BORROWINGS	548,604	430,093	857,871
OTHER LIABILITIES	456,908	101,916	89,332
Total liabilities	10,437,459	9,226,310	8,174,729
COMMITMENTS AND CONTINGENCIES
SHAREHOLDERS' EQUITY:
Common stock - ($0.01 par value, authorized 200,000,000 shares; 142,285,611, 142,314,930 and 142,161,834 shares issued at March 31, 2021 and 2020 and December 31, 2020, respectively)	1,423	1,422	1,423
Capital surplus	671,849	669,644	673,535
Retained earnings	875,147	836,729	727,828
Treasury stock (shares at cost: 938,004, 928,417 and 938,591 at March 31, 2021 and 2020 and December 31, 2020, respectively)	(9,385)	(9,126)	(8,437)
Deferred Compensation	9,385	9,126	8,437
Accumulated other comprehensive earnings, net	117,009	170,395	123,576
Total shareholders' equity	1,665,428	1,678,190	1,526,362
Total liabilities and shareholders' equity	$ 12,102,887	$ 10,904,500	$ 9,701,091

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Statement of Financial Position [Abstract]
Securities, Available-for-sale, Amortized Cost	$ 4,961,438	$ 4,177,179	$ 3,950,510
Loans held-for-sale, fair value	$ 61,511	$ 79,585	$ 39,659
Common stock, par value	$ 0.01	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000	200,000,000
Common stock, shares issued	142,285,611	142,161,834	142,314,930
Treasury stock, shares	938,004	938,591	928,417

Consolidated Statements of Earn

Consolidated Statements of Earnings - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
INTEREST INCOME:
Interest and fees on loans	$ 66,435	$ 62,995
Interest on investment securities:
Taxable	10,264	14,655
Exempt from federal income tax	13,749	9,694
Interest on federal funds sold and interest-bearing demand deposits in banks	162	756
Total interest income	90,610	88,100
INTEREST EXPENSE:
Interest on deposits	1,695	6,681
Other	91	517
Total interest expense	1,786	7,198
Net interest income	88,824	80,902
PROVISION FOR CREDIT LOSSES	(1,997)	9,850
Net interest income after provisions for credit losses	90,821	71,052
NONINTEREST INCOME:
Trust fees	8,299	7,437
Service charges on deposit accounts	4,793	5,915
ATM, interchange and credit card fees	8,677	7,400
Gain on sale and fees on mortgage loans	9,894	3,852
Net gain on sale of available-for-sale securities	808	2,062
Net gain on sale of foreclosed assets	55	1
Net gain on sale of assets	145	116
Interest on loan recoveries	382	265
Other	1,821	1,684
Total noninterest income	34,874	28,732
NONINTEREST EXPENSE:
Salaries, commissions and employee benefits	34,931	29,642
Net occupancy expense	3,147	3,027
Equipment expense	2,164	2,075
FDIC insurance premiums	701	45
ATM, interchange and credit card expenses	2,772	2,985
Professional and service fees	2,139	2,594
Printing, stationery and supplies	325	566
Operational and other losses	287	576
Software amortization and expense	2,619	2,024
Amortization of intangible assets	412	509
Other	8,226	11,275
Total noninterest expense	57,723	55,318
EARNINGS BEFORE INCOME TAXES	67,972	44,466
INCOME TAX EXPENSE	11,054	7,234
NET EARNINGS	$ 56,918	$ 37,232
NET EARNINGS PER SHARE, BASIC	$ 0.40	$ 0.26
NET EARNINGS PER SHARE, DILUTED	0.40	0.26
DIVIDENDS PER SHARE	$ 0.13	$ 0.12

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Earnings - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement of Comprehensive Income [Abstract]
NET EARNINGS	$ 56,918	$ 37,232
OTHER ITEMS OF COMPREHENSIVE EARNINGS:
Change in unrealized gain on investment securities available-for-sale, before income taxes	(66,770)	73,037
Reclassification adjustment for realized gains on investment securities included in net earnings, before income taxes	(808)	(2,062)
Total other items of comprehensive earnings	(67,578)	70,975
Income tax benefit (expense) related to:
Change in unrealized gain on investment securities available-for-sale	14,022	(15,338)
Reclassification adjustment for realized gains on investment securities included in net earnings	170	433
Total income tax benefit (expense)	14,192	(14,905)
COMPREHENSIVE EARNINGS	$ 3,532	$ 93,302

Consolidated Statements of Shar

Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Capital Surplus [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Deferred Compensation [Member]	Accumulated Other Comprehensive Earnings (Losses) [Member]
Beginning Balance at Dec. 31, 2019	$ 1,227,197	$ 1,359	$ 450,676	$ 707,656	$ (8,222)	$ 8,222	$ 67,506
Beginning Balance, Shares at Dec. 31, 2019		135,891,755
Treasury Stock, Beginning Balance, Shares at Dec. 31, 2019					(927,408)
Stock issued in acquisition of TB&T Bancshares, Inc.	220,273	$ 63	220,210
Stock issued in acquisition of TB&T Bancshares, Inc., Shares		6,275,574
Net earnings (unaudited)	37,232			37,232
Stock option exercises (unaudited)	2,192	$ 1	2,191
Stock option exercises, Shares		144,188
Restricted stock grant/fortfeiture, net (unaudited)	118		118
Restricted stock grant/fortfeiture, net (unaudited), Shares		3,413
Cash dividends declared	(17,060)			(17,060)
Change in unrealized gain in investment securities available-for-sale, net of related income taxes (unaudited)	56,070						56,070
Shares purchased (redeemed) in connection with directors' deferred compensation plan, net (unaudited)					$ (215)	215
Shares purchased (redeemed) in connection with directors' deferred compensation plan, net, Shares					(1,009)
Stock option expense (unaudited)	340		340
Ending Balance at Mar. 31, 2020	$ 1,526,362	$ 1,423	673,535	727,828	$ (8,437)	8,437	123,576
Ending Balance, Shares at Mar. 31, 2020		142,314,930
Treasury Stock, Ending Balance, Shares at Mar. 31, 2020	(928,417)				(928,417)
Beginning Balance at Dec. 31, 2020	$ 1,678,190	$ 1,422	669,644	836,729	$ (9,126)	9,126	170,395
Beginning Balance, Shares at Dec. 31, 2020		142,161,834
Treasury Stock, Beginning Balance, Shares at Dec. 31, 2020	(938,591)				(938,591)
Net earnings (unaudited)	$ 56,918			56,918
Stock option exercises (unaudited)	1,904	$ 1	1,903
Stock option exercises, Shares		124,524
Restricted stock grant/fortfeiture, net (unaudited)	(17)		(17)
Restricted stock grant/fortfeiture, net (unaudited), Shares		(747)
Cash dividends declared	(18,500)			(18,500)
Change in unrealized gain in investment securities available-for-sale, net of related income taxes (unaudited)	(53,386)						(53,386)
Shares purchased (redeemed) in connection with directors' deferred compensation plan, net (unaudited)					$ (259)	259
Shares purchased (redeemed) in connection with directors' deferred compensation plan, net, Shares					587
Stock option expense (unaudited)	319		319
Ending Balance at Mar. 31, 2021	$ 1,665,428	$ 1,423	$ 671,849	$ 875,147	$ (9,385)	$ 9,385	$ 117,009
Ending Balance, Shares at Mar. 31, 2021		142,285,611
Treasury Stock, Ending Balance, Shares at Mar. 31, 2021	(938,004)				(938,004)

Consolidated Statements of Sh_2

Consolidated Statements of Shareholders' Equity (Parenthetical) - $ / shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash dividend per share	$ 0.13	$ 0.12
Retained Earnings [Member]
Cash dividend per share	$ 0.13	$ 0.12

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
CASH FLOWS FROM OPERATING ACTIVITIES:
Net earnings	$ 56,918	$ 37,232
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization	3,171	3,087
Provision for credit losses	(1,997)	9,850
Securities premium amortization, net	14,105	7,239
Discount accretion on purchased loans	(591)	(354)
Gain on sale of assets, net	(910)	(2,250)
Change in loans held-for-sale	16,365	(13,445)
Change in other assets	8,868	(15,046)
Change in other liabilities	840	4,919
Total adjustments	39,851	(6,000)
Net cash provided by operating activities	96,769	31,232
CASH FLOWS FROM INVESTING ACTIVITIES:
Cash received in acquisition of TB&T Bancshares, Inc.		61,028
Activity in available-for-sale securities:
Sales	10,631	95,437
Maturities	7,839,968	1,614,414
Purchases	(8,280,926)	(2,333,332)
Net (increase) decrease in loans held-for-investment	(148,615)	1,366
Purchases of bank premises and equipment	(3,322)	(5,734)
Proceeds from sale of bank premises and equipment and other assets	420	171
Net cash used in investing activities	(581,844)	(566,650)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net increase (decrease) in noninterest-bearing deposits	367,448	(14,356)
Net increase in interest-bearing deposits	370,182	72,633
Net increase in borrowings	118,511	476,515
Common stock transactions:
Proceeds from stock option exercises	1,904	2,192
Dividends paid	(18,483)	(16,306)
Net cash provided by financing activities	839,562	520,678
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	354,487	(14,740)
CASH AND CASH EQUIVALENTS, beginning of period	729,084	282,604
CASH AND CASH EQUIVALENTS, end of period	1,083,571	267,864
SUPPLEMENTAL INFORMATION AND NONCASH TRANSACTIONS:
Interest paid	1,843	7,042
Transfer of loans and bank premises to other real estate	255
Investment securities purchased but not settled	381,871	33,066
Investment securities sold but not yet settled		126,119
Restricted stock grant (forfeiture) to officers and directors	$ (17)	118
Stock issued in acquisition of TB&T Bancshares, Inc.		$ 220,273

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Note 1 – Summary of Significant Accounting Policies Nature of Operations First Financial Bankshares, Inc. (a Texas corporation) (“Bankshares”, “Company,” “we” or “us”) is a financial holding company which owns all of the capital stock of one bank with 78 locations located in Texas as of March 31, 2021. The Company’s subsidiary bank is First Financial Bank, N.A. The Company’s primary source of revenue is providing loans and banking services to consumers and commercial customers in the market area in which First Financial Bank, N.A. is located. In addition, the Company also owns First Financial Trust & Asset Management Company, N.A., First Financial Insurance Agency, Inc., First Technology Services, Inc. and First Financial Investments, Inc. Basis of Presentation A summary of significant accounting policies of the Company and its subsidiaries applied in the preparation of the accompanying consolidated financial statements follows. The accounting principles followed by the Company and the methods of applying them are in conformity with both United States generally accepted accounting principles (“GAAP”) and prevailing practices of the banking industry. The Company evaluated subsequent events for potential recognition through the date the consolidated financial statements were issued. Use of Estimates in Preparation of Financial Statements The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. The Company’s significant estimates include its allowance for credit losses and its valuation of financial instruments. Consolidation The accompanying consolidated financial statements include the accounts of the Company and its subsidiaries, all of which are wholly-owned. All significant intercompany accounts and transactions have been eliminated. Stock Repurchase On March 12, 2020, the Company’s Board of Directors authorized the repurchase of up to 4,000,000 common shares through September 30, 2021. Previously, the Board of Directors had authorized the repurchase of up to 2,000,000 common shares through September 30, 2020. The stock repurchase plan authorizes management to repurchase and retire the stock at such time as repurchases and retirements are considered beneficial to the Company and stockholders. Any repurchase of stock will be made through the open market, block trades or in privately negotiated transactions in accordance with applicable laws and regulations. Under the repurchase plan, there is no minimum number of shares that the Company is required to repurchase. Through March 31, 2021, 324,802 shares were repurchased and retired (all during the months of March and April 2020) totaling $8,008,000 under this repurchase plan. Acquisition On January 1, 2020, the Company acquired 100% of the outstanding capital stock of TB&T Bancshares, Inc. through the merger of a wholly-owned subsidiary with and into TB&T Bancshares, Inc. Following such merger, TB&T Bancshares, Inc. and its wholly-owned subsidiary, The Bank & Trust of Bryan/College Station, Texas were merged into the Company and First Financial Bank, N.A., respectively. The results of operations of TB&T Bancshares, Inc. subsequent to the acquisition date, are included in the consolidated earnings of the Company. See Note 10 for additional information. Adoption of New Accounting Standards On January 1, 2020, ASU 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments held-to-maturity off-balance-sheet available-for-sale available-for-sale On March 27, 2020, the Coronavirus Aid, Relief, and Economic Security Act (CARES Act) was signed by the President of the United States that included an option for entities to delay the implementation of ASC 326 until the earlier of the termination date of the national emergency declaration by the President or December 31, 2020. Under this option, the Company elected to delay its implementation of CECL and calculated and recorded the provision for credit losses through the nine-months ended September 2020 under the incurred loss model. At December 31, 2020, the Company elected to adopt ASC 326, effective as of January 1, 2020, through a transition charge to retained earnings of $589,000 ($466,000 net of applicable income taxes). This transition adjustment was comprised of a decrease of $619,000 in allowance for credit losses and an increase of $1,208,000 in the reserve for unfunded commitments. With the adoption of ASC 326, we revised certain accounting policies and implemented certain accounting policy elections which are described below. For the 2020 interim reporting periods, the allowance for credit losses were based on the incurred loss methodology in accordance with accounting policies disclosed in Note 1 of the Consolidated Financial Statements included in the Company’s 2019 Form 10-K. The Company adopted ASC 326 using the modified retrospective method for all financial assets measured at amortized cost, net investment in leases and OBS credit exposures. The Company adopted ASC 326 using the prospective transition approach for securities for which other-than-temporary impairment had been recognized prior to January 1, 2020. As a result, the amortized cost basis remains the same before and after the effective date of ASC 326. The effective interest rate on these debt securities was not changed. The Company adopted ASC 326 using the prospective transition approach for financial assets purchased with credit deterioration (“PCD”) that were previously classified as purchased credit impaired (“PCI”) and accounted for under ASC 310-30. Other Recently Issued and Effective Authoritative Accounting Guidance ASU 2017-04, 2017-04 2017-04 ASU 2018-13, 2018-13 2018-13 2018-13 ASU 2019-12, 2019-12, step-up 2019-12 2019-12 ASU 2020-04, 2020-04 2020-04 2020-04 2020-04 ASU 2021-01, 2021-01 2021-01 2021-01 2021-01 Investment Securities Management classifies debt securities as held-to-maturity, available-for-sale, held-to-maturity held-to-maturity available-for-sale Interest income includes amortization of purchase premiums and discounts over the period to maturity using a level-yield method, except for premiums on callable securities, which are amortized to their earliest call date. Realized gains and losses are recorded on the sale of securities in noninterest income. The Company has made a policy election to exclude accrued interest from the amortized cost basis of securities and report accrued interest separately in other assets on the consolidated balance sheets. A security is placed on nonaccrual status at the time any principal or interest payments become more than 90 days delinquent or if full collection of interest or principal becomes uncertain. Accrued interest for a security placed on nonaccrual is reversed against interest income. There was no accrued interest related to securities reversed against interest income for the three-months ended March 31, 2021 and 2020. The Company records its available-for-sale The Company’s investment portfolio currently consists of obligations of state and political subdivisions, mortgage pass-through securities, corporate bonds and general obligation or revenue based municipal bonds. Pricing for such securities is generally readily available and transparent in the market. The Company utilizes independent third-party pricing services to value its investment securities, which the Company reviews as well as the underlying pricing methodologies for reasonableness and to ensure such prices are aligned with pricing matrices. The Company validates prices supplied by the independent pricing services by comparison to prices obtained from other third-party sources on a quarterly basis. Allowance for Credit Losses – Available-for-Sale For available-for-sale charged-off available-for-sale Management has made the accounting policy election to exclude accrued interest receivable on available-for-sale Available-for-sale charged-off Prior to the adoption of ASC 326, declines in the fair value of securities below their cost that were deemed to be other-than-temporary were reflected in earnings as realized losses. In estimating other-than-temporary impairment losses prior to the adoption, management considered, among other things, the length of time and the extent to which the fair value had been less than cost, the financial condition and near-term prospects of the issuer and the intent and our ability to retain our investment in the issuer for a period of time sufficient to allow for any anticipated recovery in fair value.​​​​​​​ Allowance for Credit Losses – Held-to-Maturity The allowance for credit losses on held-to-maturity held-to-maturity Held-to-maturity charged-off held-to-maturity held-to-maturity At March 31, 2021, 2020 and December 31, 2020, the Company held no securities that were classified as held-to-maturity. Loans Held-for-Investment Loans that management has the intent and ability to hold for the foreseeable future or until maturity or payoff are reported at amortized cost, net of the allowance for credit losses. Amortized cost is the principal balance outstanding, net of purchase premiums and discounts, fair value hedge accounting adjustments, deferred loan fees and costs. The Company has made a policy election to exclude accrued interest from the amortized cost basis of loans and report accrued interest separately from the related loan balance in other assets on the condensed consolidated balance sheets. Interest on loans is calculated by using the simple interest method on daily balances of the principal amounts outstanding. The Company defers and amortizes net loan origination fees and costs as an adjustment to yield. Loans are considered past due if the required principal and interest payments have not been received as of the date such payments were due. Loans are placed on nonaccrual status when, in management’s opinion, the borrower may be unable to meet payment obligations as they become due, as well as when required by regulatory provisions. In determining whether or not a borrower may be unable to meet payment obligations for each class of loans, we consider the borrower’s debt service capacity through the analysis of current financial information, if available, and/or current information with regards to our collateral position. Regulatory provisions would typically require the placement of a loan on nonaccrual status if principal or interest has been in default for a period of 90 days or more unless the loan is both well secured and in the process of collection or full payment of principal and interest is not expected. Loans may be placed on nonaccrual status regardless of whether or not such loans are considered past due. When interest accrual is discontinued, all unpaid accrued interest is reversed. Interest income on nonaccrual loans is recognized only to the extent that cash payments are received in excess of principal due. A loan may be returned to accrual status when all the principal and interest amounts contractually due are brought current and future principal and interest amounts contractually due are reasonably assured. Prior to the adoption of ASC 326, loans were reported as impaired when, based on then current information and events, it was probable we would be unable to collect all amounts due in accordance with the original contractual terms of the loan agreement, including scheduled principal and interest payments. Impairment was evaluated in total for smaller-balance loans of a similar nature and on an individual loan basis for other loans. If a loan was impaired, a specific valuation allowance was allocated, if necessary, so that the loan was reported net, at the present value of estimated future cash flows using the loan’s existing rate or at the fair value of collateral if repayment was expected solely from the collateral. Interest payments on impaired loans were typically applied to principal unless collectability of the principal amount was reasonably assured, in which case interest was recognized on a cash basis. Impaired loans, or portions thereof, were charged off when deemed uncollectible. Further information regarding our accounting policies related to past due loans, nonaccrual loans and troubled-debt restructurings is presented in Note 3. Acquired Loans Loans acquired in connection with acquisitions are recorded at their acquisition-date fair value. The allowance for credit losses related to the acquired loan portfolio is not carried over. Acquired loans are classified into two categories based on the credit risk characteristics of the underlying borrowers as either purchased credit deteriorated (“PCD”) loans, or loans with no evidence of credit deterioration (“non-PCD”). PCD loans are defined as a loan or pool of loans that have experienced more-than-insignificant credit deterioration since the origination date. The Company uses a combination of individual and pooled review approaches to determine if acquired loans are PCD. At acquisition, the Company considers a number of factors to determine if an acquired loan or pool of loans has experienced more-than-insignificant credit deterioration. The initial allowance related to PCD loans that share similar risk characteristics is established using a pooled approach. The Company uses either a discounted cash flow or weighted average remaining life method to determine the required level of the allowance. PCD loans that were classified as nonaccrual as of the acquisition date and are collateral dependent are assessed for allowance on an individual basis. For PCD loans, an initial allowance is established on the acquisition date and combined with the fair value of the loan to arrive at acquisition date amortized cost. Subsequent to the acquisition date, the initial allowance for credit losses on PCD loans will increase or decrease based on future evaluations, with changes recognized in the provision for credit losses. Non-PCD Determining the fair value of the acquired loans involves estimating the principal and interest payment cash flows expected to be collected on the loans and discounting those cash flows at a market rate of interest. Management considers a number of factors in evaluating the acquisition-date fair value including the remaining life, interest rate profile, market interest rate environment, payment schedules, risk ratings, probability of default and loss given default, and estimated prepayment rates. For PCD loans, the non-credit non-credit non-PCD Prior to the adoption of ASC 326, loans acquired in a business combination that had evidence of credit impairment and for which it was probable, at acquisition, that the Company would be unable to collect all contractually required payments receivable were considered PCI. PCI loans were accounted for individually or aggregated into pools of loans based on common risk characteristics such as credit grade, loan type, and date of origination. Allowance for Credit Losses - Loans The allowance for credit losses (“allowance” or “ACL”) is a contra-asset valuation account, calculated in accordance with ASC 326, that is deducted from the amortized cost basis of loans. The ACL represents an amount which, in management’s judgement, is adequate to absorb the lifetime expected credit losses that may be experienced on outstanding loans at the balance sheet date based on the evaluation of the size and current risk characteristics of the loan portfolio, past events, current conditions, reasonable and supportable forecasts of future economic conditions and prepayment experience. The allowance for credit losses is measured and recorded upon the initial recognition of a financial asset. Determination of the adequacy of the allowance is inherently complex and requires the use of significant and highly subjective estimates. Loans are charged-off charged-off charged-off. The Company’s methodology for estimating the allowance includes: (1) a collective quantified reserve that reflects the Company’s historical default and loss experience adjusted for expected economic conditions throughout a reasonable and supportable forecast period, including the Company’s expected prepayment and curtailment rates; (2) collective qualitative factors that consider concentrations of the loan portfolio, expected changes to the economic forecasts, large relationships, early delinquencies, and factors related to credit administrations, including, among others, loan-to-value In calculating the allowance for credit losses, most loans are segmented into pools based upon similar characteristics and risk profiles. Common characteristics and risk profiles include the type/purpose of loan, underlying collateral, geographical similarity and historical/expected credit loss patterns. In developing these loan pools for the purposes of modeling expected credit losses, we also analyzed the degree of correlation in how loans within each portfolio respond when subjected to varying economic conditions and scenarios as well as other portfolio stress factors. For modeling purposes, our loan portfolio segments include Commercial and Industrial (“C&I”), Municipal, Agricultural, Construction and Development, Farm, Non-Owner Non-Auto. The Company applies two methodologies to estimate the allowance on its pooled portfolio segments; discounted cash flows method and weighted average remaining life method. Allowance estimates on the following portfolio segments are calculated using the discounted cash flows method: C&I, Municipal, Construction and Development, Farm, Non-Owner Non-Auto. one-year In some cases, management may determine that an individual loan exhibits unique risk characteristics which differentiate the loan from other loans within our loan pools. In such cases, the loans are evaluated for expected credit losses on an individual basis and excluded from the collective evaluation. Specific allocations of the allowance for credit losses are determined by analyzing the borrower’s ability to repay amounts owed, collateral deficiencies, the relative risk rating of the loan and economic conditions affecting the borrower’s industry, among other things. A loan is considered to be collateral dependent when, based upon management’s assessment, the borrower is experiencing financial difficulty and repayment is expected to be provided substantially through the sale of the collateral. In such cases, expected credit losses are based on the fair value of the collateral at the measurement date, adjusted for estimated selling costs if satisfaction of the loan depends on the sale of the collateral. We reevaluate the fair value of collateral supporting collateral dependent loans on an ongoing basis. Management qualitatively adjusts model results for risk factors that are not considered within our modeling processes but are nonetheless relevant in assessing the expected credit losses within our loan pools. These qualitative factor (“Q-Factor”) Q-Factor non-collateral Management believes it uses relevant information available to make determinations about the allowance and that it has established the existing allowance in accordance with GAAP. However, the determination of the allowance requires significant judgment, and estimates of expected lifetime losses in the loan portfolio can vary significantly from the amounts actually observed. While management uses available information to recognize expected losses, future additions to the allowance may be necessary based on changes in the loans comprising the portfolio, changes in the current and forecasted economic conditions, changes to the interest rate environment which may directly impact prepayment and curtailment rate assumptions, and changes in the financial condition of borrowers. The adoption of the CECL standard did not result in a significant change to any other credit risk management and monitoring processes, including identification of past due or delinquent borrowers, nonaccrual practices, assessment of troubled debt restructurings or charge-off Allowance for Credit Losses - Off-Balance-Sheet/Reserve The allowance for credit losses on off-balance-sheet Other Real Estate Other real estate owned is foreclosed property held pending disposition and is initially recorded at fair value, less estimated costs to sell. At foreclosure, if the fair value of the real estate, less estimated costs to sell, is less than the Company’s recorded investment in the related loan, a write-down is recognized through a charge to the allowance for credit losses. Any subsequent reduction in value is recognized by a charge to income. Operating and holding expenses of such properties, net of related income, and gains and losses on their disposition are included in net gain (loss) on sale of foreclosed assets as incurred. Bank Premises and Equipment Bank premises and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization are computed principally on a straight-line basis over the estimated useful lives of the related assets. Leasehold improvements are amortized over the life of the respective lease or the estimated useful lives of the improvements, whichever is shorter. Business Combinations, Goodwill and Other Intangible Assets The Company accounts for all business combinations under the purchase method of accounting. Tangible and intangible assets and liabilities of the acquired entity are recorded at fair value. Intangible assets with finite useful lives represent the future benefit associated with the acquisition of the core deposits and are amortized over seven years, utilizing a method that approximates the expected attrition of the deposits. Goodwill with an indefinite life is not amortized, but rather tested annually for impairment as of June 30 each year. There was no impairment recorded for the three-months ended March 31, 2021 or 2020, respectively. Securities Sold Under Agreements To Repurchase Securities sold under agreements to repurchase, which are classified as borrowings, generally mature within one to four days from the transaction date. Securities sold under agreements to repurchase are reflected at the amount of the cash received in connection with the transaction. The Company may be required to provide additional collateral based on the estimated fair value of the underlying securities. Segment Reporting The Company has determined that its banking regions meet the aggregation criteria of the current authoritative accounting guidance since each of its banking regions offer similar products and services, operate in a similar manner, have similar customers and report to the same regulatory authority, and therefore operate one line of business (community banking) located in a single geographic area (Texas). Statements of Cash Flows For purposes of reporting cash flows, cash and cash equivalents includes cash on hand, amounts due from banks, including interest-bearing demand deposits in banks with original maturity of 90 days or less, and federal funds sold. Accumulated Other Comprehensive Earnings (Loss) Unrealized net gains on the Company’s available-for-sale Income Taxes The Company’s provision for income taxes is based on income before income taxes adjusted for permanent differences between financial reporting and taxable income. Deferred tax assets and liabilities are determined using the liability (or balance sheet) method. Under this method, the net deferred tax asset or liability is determined based on the tax effects of the temporary differences between the book and tax bases of the various balance sheet assets and liabilities and gives current recognition to changes in tax rates and laws. Stock Based Compensation The Company grants stock options for a fixed number of shares to employees with an exercise price equal to the fair value of the shares at the grant date. The grant date fair value is amortized over the vesting period which generally is six years. The Company also grants restricted stock for a fixed number of shares. The grant date fair value is amortized over the vesting period which generally is one to three years. See Note 8 for further information. Advertising Costs Advertising costs are expensed as incurred. Per Share Data Net earnings per share (“EPS”) are computed by dividing net earnings by the weighted average number of common shares outstanding during the period. The Company calculates dilutive EPS assuming all outstanding stock options to purchase common shares and unvested restricted stock shares have been exercised and/or vested at the beginning of the year (or the time of issuance, if later.) The dilutive effect of the outstanding options and restricted stock is reflected by application of the treasury stock method, whereby the proceeds from the exercised options and unearned compensation for both restricted stock and stock options are assumed to be used to purchase common shares at the average market price during the respective period. There were no anti-dilutive shares for the three-months ended March 31, 2021 and 2020. The following table reconciles the computation of basic EPS to diluted EPS: Net Weighted Per Share For the three-months ended March 31, 2021: Net earnings per share, basic $ 56,918 142,146,275 $ 0.40 Effect of stock options and stock grants — 856,383 — Net earnings per share, diluted $ 56,918 143,002,658 $ 0.40 Net Weighted Per Share For the three-months ended March 31, 2020: Net earnings per share, basic $ 37,232 142,118,864 $ 0.26 Effect of stock options and stock grants — 616,344 — Net earnings per share, diluted $ 37,232 142,735,208 $ 0.26

Securities

Securities	3 Months Ended
	Mar. 31, 2021
Cash and Cash Equivalents [Abstract]
Interest-bearing Time Deposits in Banks and Securities	Note 2 - Securities Debt securities have been classified in the consolidated balance sheets according to management’s intent. The amortized cost, related gross unrealized gains and losses, allowance for credit losses and the fair value of available-for-sale March 31, 2021 Amortized Gross Gross Estimated Securities available-for-sale: Obligations of states and political subdivisions $ 2,418,227 $ 106,988 $ (8,198 ) $ 2,517,017 Residential mortgage-backed securities 2,073,647 43,575 (8,628 ) 2,108,594 Commercial mortgage-backed securities 431,137 15,916 — 447,053 Corporate bonds and other 38,427 79 (1,539 ) 36,967 Total securities available-for-sale $ 4,961,438 $ 166,558 $ (18,365 ) $ 5,109,631 March 31, 2020 Amortized Gross Gross Estimated Securities available-for-sale: U.S. Treasury securities $ 10,039 $ 74 $ — $ 10,113 Obligations of states and political subdivisions 1,731,392 78,996 (2,717 ) 1,807,671 Residential mortgage-backed securities 1,617,341 62,659 (20 ) 1,679,980 Commercial mortgage-backed securities 587,114 17,624 (184 ) 604,554 Corporate bonds and other 4,624 133 (6 ) 4,751 Total securities available-for-sale $ 3,950,510 $ 159,486 $ (2,927 ) $ 4,107,069 December 31, 2020 Amortized Gross Gross Estimated Securities available-for-sale: Obligations of states and political subdivisions $ 2,283,616 $ 143,339 $ (79 ) $ 2,426,876 Residential mortgage-backed securities 1,421,922 50,473 (115 ) 1,472,280 Commercial mortgage-backed securities 467,243 22,077 (4 ) 489,316 Corporate bonds and other 4,398 159 — 4,557 Total securities available-for-sale $ 4,177,179 $ 216,048 $ (198 ) $ 4,393,029 The Company did not hold any securities classified as held-to-maturity The Company invests in mortgage-backed securities that have expected maturities that differ from their contractual maturities. These differences arise because borrowers may have the right to call or prepay obligations with or without a prepayment penalty. These securities include collateralized mortgage obligations (CMOs) and other asset backed securities. The expected maturities of these securities at March 31, 2021 and 2020, and December 31, 2020, were computed by using scheduled amortization of balances and historical prepayment rates. The amortized cost and estimated fair value of available-for-sale Amortized Estimated Fair Due within one year $ 290,536 $ 295,145 Due after one year through five years 2,355,100 2,456,956 Due after five years through ten years 2,145,293 2,188,324 Due after ten years 170,509 169,206 Total $ 4,961,438 $ 5,109,631 The following tables disclose the Company’s investment securities that have been in a continuous unrealized-loss Less than 12 Months 12 Months or Longer Total March 31, 2021 Fair Value Unrealized Fair Value Unrealized Fair Value Unrealized Obligations of states and political subdivisions $ 533,213 $ 8,198 $ — $ — $ 533,213 $ 8,198 Residential mortgage-backed securities 589,353 8,618 999 10 590,352 8,628 Commercial mortgage-backed securities 471 — — — 471 — Corporate bonds and other 32,490 1,539 — — 32,490 1,539 Total $ 1,155,527 $ 18,355 $ 999 $ 10 $ 1,156,526 $ 18,365 Less than 12 Months 12 Months or Longer Total March 31, 2020 Fair Value Unrealized Fair Value Unrealized Fair Value Unrealized Obligations of states and political subdivisions $ 168,725 $ 2,717 $ — $ — $ 168,725 $ 2,717 Residential mortgage-backed securities 1 — 8,164 21 8,165 21 Commercial mortgage-backed securities 44,724 173 9,630 10 54,354 183 Corporate bonds and other 220 6 — — 220 6 Total $ 213,670 $ 2,896 $ 17,794 $ 31 $ 231,464 $ 2,927 Less than 12 Months 12 Months or Longer Total December 31, 2020 Fair Unrealized Fair Value Unrealized Fair Unrealized Obligations of state and political subdivisions $ $ 79 $ — $ — $ $ 79 Residential mortgage-backed securities 36,017 96 3,156 19 39,173 115 Commercial mortgage-backed securities 16,218 4 — — 16,218 4 Total $ 77,449 $ 179 $ 3,156 $ 19 $ 80,605 $ 198 The number of investments in an unrealized loss position totaled 149 at March 31, 2021. Any unrealized losses in the obligations of state and political subdivisions, residential and commercial mortgage-backed and asset-backed investment securities at March 31, 2021 and 2020, and December 31, 2020, are due to changes in interest rates and not credit-related events. As such, no allowance for credit losses is required at March 31, 2021 and 2020, and December 31, 2020. Unrealized losses on investment securities are expected to recover over time as these securities approach maturity. Our mortgage related securities are backed by GNMA, FNMA and FHLMC or are collateralized by securities backed by these agencies. At March 31, 2021, 77.27% of our available-for-sale At March 31, 2021, $3,103,077,000 of the Company’s securities were pledged as collateral for public or trust fund deposits, repurchase agreements, a borrowing line with the Federal Reserve Bank of Dallas and for other purposes required or permitted by law. During the three-months ended March 31, 2021 and 2020, sales of investment securities that were classified as available-for-sale The specific identification method was used to determine cost in order to compute the realized gains and losses.

Loans Held for Investment and A

Loans Held for Investment and Allowance for Loan Losses	3 Months Ended
	Mar. 31, 2021
Receivables [Abstract]
Loans Held for Investment and Allowance for Credit Losses	Note 3 – Loans Held-for-Investment In conjunction with the adoption of ASC 326, the Company expanded its four loan portfolios into ten portfolio segments. For the periods ended March 31, 2021 and December 31, 2020, the following tables outline the Company’s loan portfolio by the ten portfolio segments where applicable. For disclosures related to the period ended March 31, 2020, management has elected to maintain its previously disclosed loan segments. Loans held-for-investment March 31, December 31, 2021 2020 2020 Commercial: C&I $ 1,178,126 $ N/A $ 1,131,382 Municipal 176,949 N/A 181,325 Total Commercial 1,355,075 869,450 1,312,707 Agricultural 90,366 99,582 94,864 Real Estate: Construction & Development 587,928 N/A 553,959 Farm 162,046 N/A 152,237 Non-Owner 650,144 N/A 617,686 Owner Occupied CRE 759,906 N/A 746,974 Residential 1,254,727 N/A 1,248,409 Total Real Estate 3,414,751 3,249,249 3,319,265 Consumer: Auto 370,027 N/A 353,595 Non-Auto 92,343 N/A 90,602 Total Consumer 462,370 421,108 444,197 Total Loans 5,322,562 4,639,389 5,171,033 Less: Allowance for credit losses (62,974 ) (60,440 ) (66,534 ) Loans, net $ 5,259,588 $ 4,578,949 $ 5,104,499 Outstanding loan balances at March 31, 2021 and 2020, and December 31, 2020, are net of unearned income, including net deferred loan fees. Our subsidiary bank has established a line of credit with the Federal Home Loan Bank of Dallas (“FHLB”) to provide liquidity and meet pledging requirements for those customers eligible to have securities pledged to secure certain uninsured deposits. At March 31, 2021, $3,252,192,000 in loans held by our bank subsidiary were subject to blanket liens as security for this line of credit. At March 31, 2021, there was no balance outstanding under this line of credit. The Company’s nonaccrual loans, loans still accruing and past due 90 days or more and restructured loans are as follows (in thousands): March 31, December 31, 2021 2020 2020 Non-accrual $ 39,333 $ 39,226 $ 42,619 Loans still accruing and past due 90 days or more 2 209 113 Troubled debt restructured loans still accruing* 23 26 24 Total $ 39,358 $ 39,461 $ 42,756 * Troubled debt restructured loans of $ 6,619,000 4,733,000 7,407,000 The Company had $39,658,000, $40,444,000 and $42,898,000 in non-accrual, Non-accrual March 31, December 31, 2021 2020 2020 Commercial: C&I $ 4,709 $ N/A $ 5,015 Municipal — N/A — Total Commercial 4,709 5,620 5,015 Agricultural 1,068 1,128 1,076 Real Estate: Construction & Development 1,296 N/A 3,838 Farm 6,859 N/A 7,299 Non-Owner 7,088 N/A 5,243 Owner Occupied CRE 9,557 N/A 10,797 Residential 8,364 N/A 8,851 Total Real Estate 33,164 32,156 36,028 Consumer: Auto 317 N/A 407 Non-Auto 75 N/A 93 Total Consumer 392 322 500 Total $ 39,333 $ 39,226 $ 42,619 No Summary information on the allowance for credit losses for the three-months ended March 31, 2021 and 2020, are outlined by portfolio segment in the following tables (in thousands): March 31, 2021 C&I Municipal Agricultural Construction & Farm Beginning balance $ 13,609 $ 1,552 $ 1,255 $ 13,512 $ 1,876 Provision for loan losses (1,239 ) 639 721 (268 ) (662 ) Recoveries 223 — 9 2 9 Charge-offs (270 ) — — — — Ending balance $ 12,323 $ 2,191 $ 1,985 $ 13,246 $ 1,223 March 31, 2021 (continued) Non-Owner Owner Residential Auto Non-Auto Total Beginning balance $ 8,391 $ 12,347 $ 12,601 $ 1,020 $ 371 $ 66,534 Provision for loan losses 1,052 (2,467 ) (1,384 ) 141 38 (3,429 ) Recoveries 55 6 19 73 47 443 Charge-offs (6 ) (8 ) (47 ) (166 ) (77 ) (574 ) Ending balance $ 9,492 $ 9,878 $ 11,189 $ 1,068 $ 379 $ 62,974 March 31, 2020 Commercial Agricultural Real Estate Consumer Total Beginning balance $ 12,122 $ 1,206 $ 33,974 $ 5,197 $ 52,499 Provision for loan losses 794 949 7,921 186 9,850 Recoveries 149 1 76 92 318 Charge-offs (1,292 ) (2 ) (715 ) (218 ) (2,227 ) Ending balance $ 11,773 $ 2,154 $ 41,256 $ 5,257 $ 60,440 Additionally, the Company records a reserve for unfunded commitments in other liabilities which totaled $6,918,000, $809,000 and $5,486,000 at March 31, 2021 and 2020, and December 31, 2020, respectively. The reversal of provision for credit losses of $ 1,997,000 3,429,000 1,432,000 The Company’s loans that are individually evaluated for credit losses (both collateral and non-collateral March 31, 2021 Collateral Collateral Non-Collateral Total Loans Related Related Non-Collateral Total Commercial: C&I $ 1,806 $ 2,903 $ 14,580 $ 19,289 $ 777 $ 3,104 $ 3,881 Municipal — — 9,777 9,777 — 1,536 1,536 Total Commercial 1,806 2,903 24,357 29,066 777 4,640 5,417 Agricultural 457 612 5,790 6,859 170 1,620 1,790 Real Estate: Construction & Development 1,124 171 11,202 12,497 12 868 880 Farm 2,241 4,618 3,436 10,295 590 81 671 Non-Owner 6,045 1,043 32,299 39,387 226 3,109 3,335 Owner Occupied CRE 6,081 3,476 45,893 55,450 599 3,000 3,599 Residential 4,210 4,154 26,331 34,695 577 2,297 2,874 Total Real Estate 19,701 13,462 119,161 152,324 2,004 9,355 11,359 Consumer: Auto — 317 1,399 1,716 1 4 5 Non-Auto — 75 376 451 — 2 2 Total Consumer — 392 1,775 2,167 1 6 7 Total $ 21,964 $ 17,369 $ 151,083 $ 190,416 $ 2,952 $ 15,621 $ 18,573 December 31, 2020 Collateral Collateral Non-Collateral Total Loans Related Related Non-Collateral Total Commercial: C&I $ 1,544 $ 3,471 $ 25,629 $ 30,644 $ 799 $ 4,592 $ 5,391 Municipal — — 9,439 9,439 — 1,435 1,435 Total Commercial 1,544 3,471 35,068 40,083 799 6,027 6,826 Agricultural 470 606 5,572 6,648 96 886 982 Real Estate: Construction & Development 1,176 2,661 11,368 15,205 35 617 652 Farm 2,614 4,685 3,349 10,648 654 658 1,312 Non-Owner 4,009 1,234 17,383 22,626 500 1,421 1,921 Owner Occupied CRE 7,279 3,518 51,933 62,730 657 5,172 5,829 Residential 4,347 4,504 28,196 37,047 676 2,431 3,107 Total Real Estate 19,425 16,602 112,229 148,256 2,522 10,299 12,821 Consumer: Auto — 407 1,523 1,930 1 5 6 Non-Auto — 94 440 534 1 1 2 Total Consumer — 501 1,963 2,464 2 6 8 Total $ 21,439 $ 21,180 $ 154,832 $ 197,451 $ 3,419 $ 17,218 $ 20,637 The following table presents the recorded investment with respect to impaired loans, the associated allowance by the applicable portfolio segment and the unpaid contractual principal balance of the impaired loans at March 31, 2020, in accordance with the legacy “incurred loss” methodology disclosure requirements (in thousands): March 31, 2020 Unpaid Recorded Recorded Total Related Three-Month Commercial $ 7,300 $ 992 $ 4,628 $ 5,620 $ 1,271 $ 6,409 Agricultural 1,340 632 496 1,128 98 1,200 Real Estate 44,208 9,496 22,660 32,156 2,016 36,683 Consumer 436 — 322 322 1 342 Total $ 53,284 $ 11,120 $ 28,106 $ 39,226 $ 3,386 $ 44,634 The Company’s allowance for loans that are individually evaluated for credit losses and collectively evaluated for credit losses as of March 31, 2021 and December 31, 2020, are summarized in the following table by loan segment (in thousands).​​​​​​​ Allocation of a portion of the allowance to one category of loans does not preclude its availability to absorb losses in other categories. March 31, 2021 C&I Municipal Agricultural Construction Farm Loans individually evaluated for credit losses $ 3,881 $ 1,536 $ 1,790 $ 880 $ 671 Loans collectively evaluated for credit losses 8,442 655 195 12,366 552 Total $ 12,323 $ 2,191 $ 1,985 $ 13,246 $ 1,223 March 31, 2021 (continued) Non-Owner Owner Residential Auto Non-Auto Total Loans individually evaluated for credit losses $ 3,335 $ 3,599 $ 2,874 $ 5 $ 2 $ 18,573 Loans collectively evaluated for credit losses 6,157 6,279 8,315 1,063 377 44,401 Total $ 9,492 $ 9,878 $ 11,189 $ 1,068 $ 379 $ 62,974 December 31, 2020 C&I Municipal Agricultural Construction & Farm Loans individually evaluated for credit losses $ 5,391 $ 1,435 $ 982 $ 652 $ 1,312 Loans collectively evaluated for credit losses 8,218 117 273 12,860 564 Total $ 13,609 $ 1,552 $ 1,255 $ 13,512 $ 1,876 December 31, 2020 (continued) Non-Owner Owner Residential Auto Non-Auto Total Loans individually evaluated for credit losses $ 1,921 $ 5,829 $ 3,107 $ 6 $ 2 $ 20,637 Loans collectively evaluated for credit losses 6,470 6,518 9,494 1,014 369 45,897 Total $ 8,391 $ 12,347 $ 12,601 $ 1,020 $ 371 $ 66,534 The Company’s allowance for loans that are individually evaluated for credit losses and collectively evaluated for credit losses as of March 31, 2020, are summarized in the following table by loan segment in accordance with the legacy “incurred loss” methodology disclosure requirements (in thousands): March 31, 2020 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 1,271 $ 98 $ 2,016 $ 1 $ 3,386 Loan collectively evaluated for impairment 10,502 2,056 39,240 5,256 57,054 Total $ 11,773 $ 2,154 $ 41,256 $ 5,257 $ 60,440 The Company’s recorded investment in loans as of March 31, 2021 and December 31, 2020, related to the balance in the allowance for credit losses on the basis of the Company’s adopted ASC 326 evaluation methodology follows below (in thousands): March 31, 2021 C&I Municipal Agricultural Construction & Farm Loans individually evaluated for credit losses $ 19,289 $ 9,777 $ 6,859 $ 12,497 $ 10,295 Loans collectively evaluated for credit losses 1,158,837 167,172 83,507 575,431 151,751 Total $ 1,178,126 $ 176,949 $ 90,366 $ 587,928 $ 162,046 March 31, 2021 (continued) Non-Owner Owner Residential Auto Non-Auto Total Loans individually evaluated for credit losses $ 39,387 $ 55,450 $ 34,695 $ 1,716 $ 451 $ 190,416 Loans collectively evaluated for credit losses 610,757 704,456 1,220,032 368,311 91,892 5,132,146 Total $ 650,144 $ 759,906 $ 1,254,727 $ 370,027 $ 92,343 $ 5,322,562 December 31, 2020 C&I Municipal Agricultural Construction & Farm Loans individually evaluated for credit losses $ 30,644 $ 9,439 $ 6,648 $ 15,205 $ 10,648 Loans collectively evaluated for credit losses 1,100,738 171,886 88,216 538,754 141,589 Total $ 1,131,382 $ 181,325 $ 94,864 $ 553,959 $ 152,237 December 31, 2020 (continued) Non-Owner Owner Residential Auto Non-Auto Total Loans individually evaluated for credit losses $ 22,626 $ 62,730 $ 37,047 $ 1,930 $ 534 $ 197,451 Loans collectively evaluated for credit losses 595,060 684,244 1,211,362 351,665 90,068 4,973,582 Total $ 617,686 $ 746,974 $ 1,248,409 $ 353,595 $ 90,602 $ 5,171,033 The Company’s recorded investment in loans as of March 31, 2020, related to the balance in the allowance for loan losses on the basis of the Company’s legacy “incurred loss” impairment methodology follows below (in thousands): March 31, 2020 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 5,620 $ 1,128 $ 32,156 $ 322 $ 39,226 Loan collectively evaluated for impairment 863,830 98,454 3,217,093 420,786 4,600,163 Total $ 869,450 $ 99,582 $ 3,249,249 $ 421,108 $ 4,639,389 From a credit risk standpoint, the Company rates its loans in one of five categories: (i) pass, (ii) special mention, (iii) substandard, (iv) doubtful or (v) loss (which are charged-off). The ratings of loans reflect a judgment about the risks of default and loss associated with the loan. The Company reviews the ratings on our credits as part of our on-going Credits rated special mention show clear signs of financial weaknesses or deterioration in credit worthiness, however, such concerns are not so pronounced that the Company generally expects to experience significant loss within the short-term. Such credits typically maintain the ability to perform within standard credit terms and credit exposure is not as prominent as credits rated more harshly. Credits rated substandard are those in which the normal repayment of principal and interest may be, or has been, jeopardized by reason of adverse trends or developments of a financial, managerial, economic or political nature, or important weaknesses exist in collateral. A protracted workout on these credits is a distinct possibility. Prompt corrective action is therefore required to strengthen the Company’s position, and/or to reduce exposure and to assure that adequate remedial measures are taken by the borrower. Credit exposure becomes more likely in such credits and a serious evaluation of the secondary support to the credit is performed. Credits rated doubtful are those in which full collection of principal appears highly questionable, and which some degree of loss is anticipated, even though the ultimate amount of loss may not yet be certain and/or other factors exist which could affect collection of debt. Based upon available information, positive action by the Company is required to avert or minimize loss. Credits rated doubtful are generally also placed on nonaccrual. The following summarizes the Company’s internal ratings of its loans held-for-investment, March 31, 2021 2020 2019 2018 2017 Prior Revolving Total C&I Risk rating: Pass $ 303 $ 647 $ 84 $ 61 $ 24 $ 41 $ — $ 1,160 Special mention 2 3 1 — 1 — — 7 Substandard 1 6 1 3 1 — — 12 Doubtful — — — — — — — — Total $ 306 $ 656 $ 86 $ 64 $ 26 $ 41 $ — $ 1,179 March 31, 2021 2020 2019 2018 2017 Prior Revolving Total Municipal Risk rating: Pass $ 2 $ 21 $ 16 $ 23 $ 13 $ 92 $ — $ 167 Special mention — — — — — — — — Substandard — 2 — — 6 2 — 10 Doubtful — — — — — — — — Total $ 2 $ 23 $ 16 $ 23 $ 19 $ 94 $ — $ 177 March 31, 2021 2020 2019 2018 2017 Prior Revolving Total Agricultural Risk rating: Pass $ 15 $ 42 $ 16 $ 7 $ 2 $ 1 $ — $ 83 Special mention 1 — — — — — — 1 Substandard — 5 — — 1 — — 6 Doubtful — — — — — — — — Total $ 16 $ 47 $ 16 $ 7 $ 3 $ 1 $ — $ 90 March 31, 2021 2020 2019 2018 2017 Prior Revolving Total Construction & Development Risk rating: Pass $ 101 $ 347 $ 62 $ 35 $ 17 $ 13 $ — $ 575 Special mention — 2 4 — — 1 — 7 Substandard 1 3 1 — — 1 — 6 Doubtful — — — — — — — — Total $ 102 $ 352 $ 67 $ 35 $ 17 $ 15 $ — $ 588 March 31, 2021 2020 2019 2018 2017 Prior Revolving Total Farm Risk rating: Pass $ 20 $ 54 $ 21 $ 17 $ 10 $ 30 $ — $ 152 Special mention — — — — — — — — Substandard — 7 1 1 — 1 — 10 Doubtful — — — — — — — — Total $ 20 $ 61 $ 22 $ 18 $ 10 $ 31 $ — $ 162 March 31, 2021 2020 2019 2018 2017 Prior Revolving Total Non-Owner Risk rating: Pass $ 45 $ 198 $ 105 $ 86 $ 41 $ 136 $ — $ 611 Special mention — 1 13 1 8 4 — 27 Substandard — — 2 — 2 8 — 12 Doubtful — — — — — — — — Total $ 45 $ 199 $ 120 $ 87 $ 51 $ 148 $ — $ 650 March 31, 2021 2020 2019 2018 2017 Prior Revolving Total Owner Occupied CRE Risk rating: Pass $ 74 $ 168 $ 126 $ 96 $ 72 $ 169 $ — $ 705 Special mention — 3 4 — 4 — — 11 Substandard 1 5 4 18 4 12 — 44 Doubtful — — — — — — — — Total $ 75 $ 176 $ 134 $ 114 $ 80 $ 181 $ — $ 760 March 31, 2021 2020 2019 2018 2017 Prior Revolving Total Residential Risk rating: Pass $ 109 $ 346 $ 157 $ 119 $ 93 $ 302 $ 94 $ 1,220 Special mention — 3 1 1 1 3 — 9 Substandard 1 5 2 4 2 11 1 26 Doubtful — — — — — — — — Total $ 110 $ 354 $ 160 $ 124 $ 96 $ 316 $ 95 $ 1,255 March 31, 2021 2020 2019 2018 2017 Prior Revolving Total Auto Risk rating: Pass $ 61 $ 161 $ 90 $ 32 $ 16 $ 8 $ — $ 368 Special mention — — — — — — — — Substandard — 1 1 — — — — 2 Doubtful — — — — — — — — Total $ 61 $ 162 $ 91 $ 32 $ 16 $ 8 $ — $ 370 March 31, 2021 2020 2019 2018 2017 Prior Revolving Total Non-Auto Risk rating: Pass $ 17 $ 40 $ 17 $ 6 $ 3 $ 2 $ 7 $ 92 Special mention — — — — — — — — Substandard — — — — — — — — Doubtful — — — — — — — — Total $ 17 $ 40 $ 17 $ 6 $ 3 $ 2 $ 7 $ 92 March 31, 2021 2020 2019 2018 2017 Prior Revolving Total Total Loans Risk rating: Pass $ 747 $ 2,024 $ 694 $ 482 $ 291 $ 794 $ 101 $ 5,133 Special mention 3 12 23 2 14 8 — 62 Substandard 4 34 12 26 16 35 1 128 Doubtful — — — — — — — — Total $ 754 $ 2,070 $ 729 $ 510 $ 321 $ 837 $ 102 $ 5,323 The following summarizes the Company’s internal ratings of its loans held-for-investment, December 31, 2020 2019 2018 2017 2016 Prior Revolving Total C&I Risk rating: Pass $ 874 $ 101 $ 70 $ 28 $ 10 $ 16 $ — $ 1,099 Special mention 9 2 — 1 — — — 12 Substandard 12 4 4 — — — — 20 Doubtful — — — — — — — — Total $ 895 $ 107 $ 74 $ 29 $ 10 $ 16 $ — $ 1,131 December 31, 2020 2019 2018 2017 2016 Prior Revolving Total Municipal Risk rating: Pass $ 26 $ 19 $ 29 $ 14 $ 13 $ 71 $ — $ 172 Special mention — — — — — — — — Substandard 2 — — 5 1 1 — 9 Doubtful — — — — — — — — Total $ 28 $ 19 $ 29 $ 19 $ 14 $ 72 $ — $ 181 December 31, 2020 2019 2018 2017 2016 Prior Revolving Total Agricultural Risk rating: Pass $ 57 $ 19 $ 9 $ 3 $ 1 $ — $ — $ 89 Special mention — — — — — — — — Substandard 6 — — — — — — 6 Doubtful — — — — — — — — Total $ 63 $ 19 $ 9 $ 3 $ 1 $ — $ — $ 95 December 31, 2020 2019 2018 2017 2016 Prior Revolving Total Construction & Development Risk rating: Pass $ $ 97 $ 36 $ 19 $ 7 $ 9 $ — $ 539 Special mention 2 4 — — — — — 6 Substandard 4 1 — 3 — 1 — 9 Doubtful — — — — — — — — Total $ 377 $ 102 $ 36 $ 22 $ 7 $ 10 $ — $ 554 December 31, 2020 2019 2018 2017 2016 Prior Revolving Total Farm Risk rating: Pass $ 57 $ 22 $ 18 $ 11 $ 11 $ 23 $ — $ 142 Special mention — — — — — — — — Substandard 7 1 — 1 — 1 — 10 Doubtful — — — — — — — — Total $ 64 $ 23 $ 18 $ 12 $ 11 $ 24 $ — $ 152 December 31, 2020 2019 2018 2017 2016 Prior Revolving Total Non-Owner Risk rating: Pass $ 197 $ 117 $ 93 $ 44 $ 55 $ 88 $ — $ 594 Special mention 1 — 1 8 1 — — 11 Substandard — 2 — — — 11 — 13 Doubtful — — — — — — — — Total $ 198 $ 119 $ 94 $ 52 $ 56 $ 99 $ — $ 618 December 31, 2020 2019 2018 2017 2016 Prior Revolving Total Owner Occupied CRE Risk rating: Pass $ 176 $ 132 $ 105 $ 75 $ 65 $ 132 $ — $ 685 Special mention 5 5 2 4 1 1 — 18 Substandard 5 4 20 4 1 10 — 44 Doubtful — — — — — — — — Total $ 186 $ 141 $ 127 $ 83 $ 67 $ 143 $ — $ 747 December 31, 2020 2019 2018 2017 2016 Prior Revolving Total Residential Risk rating: Pass $ 373 $ 172 $ 134 $ 101 $ 101 $ 237 $ 93 $ 1,211 Special mention 3 1 1 1 1 3 — 10 Substandard 5 3 3 3 1 10 2 27 Doubtful — — — — — — — — Total $ 381 $ 176 $ 138 $ 105 $ 103 $ 250 $ 95 $ 1,248 December 31, 2020 2019 2018 2017 2016 Prior Revolving Total Auto Risk rating: Pass $ 177 $ 104 $ 39 $ 21 $ 9 $ 2 $ — $ 352 Special mention — — — — — — — — Substandard 1 1 — — — — — 2 Doubtful — — — — — — — — Total $ 178 $ 105 $ 39 $ 21 $ 9 $ 2 $ — $ 354 December 31, 2020 2019 2018 2017 2016 Prior Revolving Total Non-Auto Risk rating: Pass $ 48 $ 21 $ 7 $ 4 $ 1 $ 2 $ 7 $ 90 Special mention — — — — — — — — Substandard — — — — — 1 — 1 Doubtful — — — — — — — — Total $ 48 $ 21 $ 7 $ 4 $ 1 $ 3 $ 7 $ 91 December 31, 2020 2019 2018 2017 2016 Prior Revolving Total Total Loans Risk rating: Pass $ 2,356 $ 804 $ 540 $ 320 $ 273 $ 580 $ 100 $ 4,973 Special mention 20 12 4 14 3 4 — 57 Substandard 42 16 27 16 3 35 2 141 Doubtful — — — — — — — — Total $ 2,418 $ 832 $ 571 $ 350 $ 279 $ 619 $ 102 $ 5,171 The following tables summarize the Company’s internal ratings of its loans held-for-investment, March 31, 2020 Pass Special Substandard Doubtful Total Commercial $ 832 $ 25 $ 12 $ — $ 869 Agricultural 92 6 2 — 100 Real Estate 3,106 56 87 — 3,249 Consumer 419 — 2 — 421 Total $ 4,449 $ 87 $ 103 $ — $ 4,639 The Company’s past due loans are as follows (in thousands): March 31, 2021 15-59 60-89 Greater Total Past Current Total Loans 90 Days Commercial: C&I $ 3,469 $ 283 $ 303 $ 4,055 $ 1,174,071 $ 1,178,126 $ 1 Municipal 19 — — 19 176,930 176,949 — Total Commercial 3,488 283 303 4,074 1,351,001 1,355,075 1 Agricultural 2,535 — — 2,535 87,831 90,366 — Real Estate: Construction & Development 1,810 41 66 1,917 586,011 587,928 — Farm 71 — — 71 161,975 162,046 — Non-Owner 695 — — 695 649,449 650,144 — Owner Occupied CRE 1,847 — — 1,847 758,059 759,906 1 Residential 6,920 67 — 6,987 1,247,740 1,254,727 — Total Real Estate 11,343 108 66 11,517 3,403,234 3,414,751 1 Consumer: Auto 470 31 10 511 369,516 370,027 — Non-Auto 129 11 — 140 92,203 92,343 — Total Consumer 599 42 10 651 461,719 462,370 — Total $ 17,965 $ 433 $ 379 $ 18,777 $ 5,303,785 $ 5,322,562 $ 2 December 31, 2020 15-59 60-89 Greater Total Past Current Total Loans 90 Days Commercial: C&I $ 3,647 $ 406 $ 576 $ 4,629 $ 1,126,753 $ 1,131,382 $ 21 Municipal — — — — 181,325 181,325 — Total Commercial 3,647 406 576 4,629 1,308,078 1,312,707 21 Agricultural 193 95 — 288 94,576 94,864 — Real Estate: Construction & Development 4,775 44 — 4,819 549,140 553,959 — Farm 708 — — 708 151,529 152,237 — Non-Owner 613 — — 613 617,073 617,686 — Owner Occupied CRE 1,393 322 133 1,848 745,126 746,974 — Residential 8,072 18 275 8,365 1,240,044 1,248,409 33 Total Real Estate 15,561 384 408 16,353 3,302,912 3,319,265 33 Consumer: Auto 551 158 75 784 352,811 353,595 59 Non-Auto 214 24 — 238 90,364 90,602 — Total Consumer 765 182 75 1,022 443,175 444,197 59 Total $ 20,166 $ 1,067 $ 1,059 $ 22,292 $ 5,148,741 $ 5,171,033 $ 113 March 31, 2020 15-59 60-89 Greater Total Current Total Loans 90 Days Commercial $ 4,807 $ 388 $ 382 $ 5,577 $ 863,873 $ 869,450 $ 116 Agricultural 621 — 62 683 98,899 99,582 — Real Estate 25,788 742 413 26,943 3,222,306 3,249,249 — Consumer 862 116 102 1,080 420,028 421,108 93 Total $ 32,078 $ 1,246 $ 959 $ 34,283 $ 4,605,106 $ 4,639,389 $ 209 * The Company monitors commercial, agricultural and real estate loans after such loans are 15 days past due. Consumer loans are monitored after such loans are 30 days past due. The restructuring of a loan is considered a “troubled debt restructuring” if both the borrower is experiencing financial difficulties and the creditor has granted a concession. Concessions may include interest rate reductions or below market interest rates, principal forgiveness, restructuring amortization schedules, reductions in collateral and other actions intended to minimize potential losses. The Company’s loans that were modified and considered troubled debt restructurings are as follows (in thousands): Three-Months Ended March 31, 2021 Pre-Modification Post- Recorded Recorded Number Investment Investment Commercial: C&I 2 $ 149 $ 149 Municipal — — — Total Commercial 2 149 149 Agricultural — — — Real Estate: Construction & Development — — — Farm — — — Non-Owner — — — Owner Occupied CRE 1 500 500 Residential 2 197 197 Total Real Estate 3 697 697 Consumer: Auto — — — Non-Auto — — — Total Consumer — — — Total 5 $ 846 $ 846 Three-Months Ended March 31, 2020 Pre-Modification Post- Recorded Recorded Number Investment Investment Commercial 5 $ 288 $ 288 Agricultural 1 134 134 Real Estate — — — Consumer 1 14 14 Total 7 $ 436 $ 436 The balances below provide information as to how the loans were modified as troubled debt restructured loans (in thousands): Three-Months Ended March 31, 2021 Adjusted Combined Interest Extended Rate and Rate Maturity Maturity Commercial: C&I $ — $ — $ 149 Municipal — — — Total Commercial — — 149 Agricultural — — — Real Estate: Construction & Development — — — Farm — — — Non-Owner — — — Owner Occupied CRE — — 500 Residential — — 197 Total Real Estate — — 697 Consumer: Auto — — — Non-Auto — — — Total Consumer — — — Total $ — $ — $ 846 Three-Months Ended March 31, 2020 Adjusted Extended Combined Commercial $ — $ 260 $ 28 Agricultural — 134 — Real Estate — — — Consumer — 14 — Total $ — $ 408 $ 28 During the three-months ended March 31, 2021 and 2020, no loans were modified as a troubled debt restructured loan within the previous 12 months and for which there was a payment default. A default for purposes of this disclosure is a troubled debt restructured loan in which the borrower is 90 days past due or more or results in the foreclosure and repossession of the applicable collateral. As of March 31, 2021, the Company has no

Loans Held for Sale

Loans Held for Sale	3 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Loans Held for Sale	Note 4 - Loans Held-for-Sale Loans held-for-sale These loans, which are sold on a servicing released basis, are valued using a market approach by utilizing either: (i) the fair value of the securities backed by similar mortgage loans, adjusted for certain factors to approximate the fair value of a whole mortgage loan, including the value attributable to mortgage servicing and credit risk, (ii) current commitments to purchase loans or (iii) recent observable market trades for similar loans, adjusted for credit risk and other individual loan characteristics. As these prices are derived from market observable inputs, the Company classifies these valuations as Level 2 in the fair value disclosures (see Note 9). Interest income on mortgage loans held-for-sale The Company originates certain mortgage loans for sale in the secondary market. The mortgage loan sales contracts contain indemnification clauses should the loans default, generally in the first three to six months, or if documentation is determined not to be in compliance with regulations. The Company’s historic losses as a result of these indemnities have been insignificant.

Derivative Financial Instrument

Derivative Financial Instruments	3 Months Ended
	Mar. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments	Note 5 - Derivative Financial Instruments The Company enters into interest rate lock commitments (“IRLCs”) with customers to originate residential mortgage loans at a specific interest rate that are ultimately sold in the secondary market. These commitments, which contain fixed expiration dates, offer the borrower an interest rate guarantee provided the loan meets underwriting guidelines and closes within the timeframe established by the Company. The Company purchases forward mortgage-backed securities contracts to manage the changes in fair value associated with changes in interest rates related to a portion of the IRLCs. These instruments are typically entered into at the time the IRLC is made in the aggregate. These financial instruments are not designated as hedging instruments for accounting purposes. All derivatives are carried at fair value in either other assets or other liabilities, through earnings in the statement of earnings. The fair values of IRLCs are based on current secondary market prices for underlying loans and estimated servicing value with similar coupons, maturity and credit quality, subject to the anticipated loan funding probability (pull-through rate) net of estimated costs to originate the loan. The fair value of IRLCs is subject to change primarily due to changes in interest rates and the estimated pull-through rate. These commitments are classified as Level 2 in the fair value disclosures (see Note 9), as the valuations are based on observable market inputs. Forward mortgage-backed securities contracts are exchange-traded or traded within highly active dealer markets. In order to determine the fair value of these instruments, the Company utilizes the exchange price or dealer market price for the particular derivative contract and these instruments are therefore classified as Level 2 in the fair value disclosures (see Note 9). The estimated fair values are subject to change primarily due to changes in interest rates. The impact of these forward contracts is included in gain on sale and fees on mortgage loans in the statement of earnings. The following table provides the outstanding notional balances and fair values of outstanding derivative positions (in thousands): March 31, 2021: Outstanding Asset Liability IRLCs $ 180,596 $ 1,645 $ — Forward mortgage-backed securities trades 317,500 2,806 — March 31, 2020: Outstanding Asset Liability IRLCs $ 187,747 $ 296 $ — Forward mortgage-backed securities trades 198,000 — 3,200 December 31, 2020: Outstanding Asset Liability IRLCs $ 202,906 $ 4,618 $ — Forward mortgage-backed securities trades 198,000 — 1,560

Borrowings

Borrowings	3 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Borrowings	Note 6 - Borrowings Borrowings consisted of the following (dollars in thousands): March 31, December 31, 2021 2020 2020 Securities sold under agreements with customers to repurchase $ 523,254 $ 410,146 $ 412,743 Federal funds purchased 25,350 1,725 17,350 Advances from Federal Home Loan Bank of Dallas — 446,000 — Total $ 548,604 $ 857,871 $ 430,093 Securities sold under repurchase agreements are generally with significant customers of the Company that require short-term liquidity for their funds for which the Company pledges certain securities that have a fair value equal to at least the amount of the borrowings. The agreements mature daily and therefore the risk arising from a decline in the fair value of the collateral pledged is minimal. The securities pledged are mortgage-backed securities. These agreements do not include “right of set-off”

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	Note 7 – Income Taxes Income tax expense was $11,054,000 for the first quarter of 2021 as compared to $7,234,000 for the same period in 2020. The Company’s effective tax rates on pretax income were 16.26% and 16.27% for the first quarters of 2021 and 2020, respectively. The effective tax rates differ from the statutory federal tax rate of 21% primarily due to tax exempt interest income earned on certain investment securities and loans, the deductibility of dividends paid to our employee stock ownership plan and excess tax benefits related to our directors’ deferred compensation plan.

Stock Option Plan and Restricte

Stock Option Plan and Restricted Stock Plan	3 Months Ended
	Mar. 31, 2021
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock Option Plan and Restricted Stock Plan	Note 8 - Stock Option Plan and Restricted Stock Plan Stock Option Plans The Company has two incentive stock plans previously approved by the Company’s shareholders to provide for the granting of options to employees of the Company at prices not less than market value at the date of grant. At March 31, 2021, the Company had reserved 3,559,402 shares of stock for issuance under the plan. The option plan provides that options granted vest and are exercisable after two years from the date of grant and vest at a rate of 20% each year and have a 10-year Shares Weighted- Outstanding, December 31, 2020 1,833,057 $ 20.85 Granted — — Exercised (124,524 ) 16.35 Cancelled (14,100 ) 24.60 Outstanding, March 31, 2021 1,694,433 21.15 Exercisable, March 31, 2021 764,953 $ 17.36 The options outstanding at March 31, 2021 had exercise prices ranging between $7.87 and $34.55. Stock options have been adjusted retroactively for the effects of stock dividends and splits. The Company grants incentive stock options for a fixed number of shares with an exercise price equal to the fair value of the shares at the date of grant to employees. On January 28, 2020, the Company granted 11,250 incentive stock options with an exercise price of $34.55 per share. The Company recorded stock option expense totaling $319,000 and $340,000 for the three-month periods ended March 31, 2021 and 2020, respectively. As of March 31, 2021, there was $3,753,000 of total unrecognized compensation cost related to unvested share-based compensation arrangements related to stock options granted under the Company’s stock option plans. That cost is expected to be recognized over a weighted-average period of 1.77 years. The total fair value of shares vested during the three-months ended March 31, 2021 and 2020 was $31,000 and $119,000, respectively. Restricted Stock Plan On April 28, 2015, shareholders of the Company approved a restricted stock plan for selected employees, officers, non-employee The following table summarized information about vested and unvested restricted stock outstanding at March 31, 2021 and 2020, respectively. For the three-months ended March 31, 2021 2020 Restricted Weighted Restricted Weighted Balance at beginning of period 95,888 $ 29.89 105,309 $ 29.93 Grants — — 3,413 34.55 Vesting (993 ) 34.55 — — Forfeited/expired (479 ) 34.55 — — Balance at end of period 94,416 $ 29.82 108,722 $ 30.08 The total fair value of restricted stock vested was $39,000 for the three-months ended March 31, 2021. No The Company recorded restricted stock expense for employees of $290,000 and $275,000, respectively, for the three-months ended March 31, 2021 and 2020, respectively. The Company recorded director expense related to these restricted stock grants of $150,000 and $175,000 for the three-months ended March 31, 2021 and 2020, respectively. As of March 31, 2021, and 2020, there were $1,701,000 and $2,118,000, respectively, of total unrecognized compensation cost related to unvested restricted stock which is expected to be recognized over a weighted-average period of 1.44 years and 1.43 years, respectively. At March 31, 2021 and 2020, and December 31, 2020, there was $61,000, $41,000 and $49,000, respectively, accrued in other liabilities related to dividends declared to be paid upon vesting. On April 28, 2021, the Company approved a new 2021 Omnibus Stock and Incentive Plan and registered and reserved 2,500,000 shares of the Company’s common stock for issuance under this plan. This plan supersedes all prior stock option and restricted stock plans with previously reserved shares cancelled.

Fair Value Disclosures

Fair Value Disclosures	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Disclosures	Note 9 - Fair Value Disclosures The authoritative accounting guidance for fair value measurements defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. A fair value measurement assumes that the transaction to sell the asset or transfer the liability occurs in the principal market for the asset or liability or, in the absence of a principal market, the most advantageous market for the asset or liability. The price in the principal (or most advantageous) market used to measure the fair value of the asset or liability shall not be adjusted for transaction costs. An orderly transaction is a transaction that assumes exposure to the market for a period prior to the measurement date to allow for marketing activities that are usual and customary for transactions involving such assets and liabilities; it is not a forced transaction. Market participants are buyers and sellers in the principal market that are (i) independent, (ii) knowledgeable, (iii) able to transact, and (iv) willing to transact. The authoritative accounting guidance requires the use of valuation techniques that are consistent with the market approach, the income approach and/or the cost approach. The market approach uses prices and other relevant information generated by market transactions involving identical or comparable assets and liabilities. The income approach uses valuation techniques to convert future amounts, such as cash flows or earnings, to a single present amount on a discounted basis. The cost approach is based on the amount that currently would be required to replace the service capacity of an asset (replacement costs). Valuation techniques should be consistently applied. Inputs to valuation techniques refer to the assumptions that market participants would use in pricing the asset or liability. Inputs may be observable, meaning those that reflect the assumptions market participants would use in pricing the asset or liability developed based on market data obtained from independent sources, or unobservable, meaning those that reflect the reporting entity’s own assumptions about the assumptions market participants would use in pricing the asset or liability developed based on the best information available in the circumstances. In that regard, the authoritative guidance establishes a fair value hierarchy for valuation inputs that gives the highest priority to quoted prices in active markets for identical assets or liabilities and the lowest priority to unobservable inputs. The fair value hierarchy is as follows: • Level 1 Inputs – Unadjusted quoted prices in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. • Level 2 Inputs – Inputs other than quoted prices included in Level 1 that are observable for the asset or liability, either directly or indirectly. These include quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability (for example, interest rates, volatilities, prepayment speeds, loss severities, credit risks and default rates) or inputs that are derived principally from or corroborated by observable market data by correlation or other means. • Level 3 Inputs – Significant unobservable inputs that reflect an entity’s own assumptions that market participants would use in pricing the assets or liabilities. A description of the valuation methodologies used for assets and liabilities measured at fair value, as well as the general classification of such instruments pursuant to the valuation hierarchy, is set forth below. In general, fair value is based upon quoted market prices, where available. If such quoted market prices are not available, fair value is based upon internally developed models that primarily use, as inputs, observable market-based parameters. Valuation adjustments may be made to ensure that financial instruments are recorded at fair value. While management believes the Company’s valuation methodologies are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different estimate of fair value at the reporting date. Securities classified as available-for-sale See Notes 4 and 5 related to the determination of fair value for loans held-for-sale, There were no transfers between Level 2 and Level 3 during the three-months ended March 31, 2021 and 2020, and the year ended December 31, 2020. The following table summarizes the Company’s available-for-sale held-for-sale, March 31, 2021 Level 1 Level 2 Level 3 Total Fair Available-for-sale Obligations of states and political subdivisions $ — $ 2,517,017 $ — $ 2,517,017 Corporate bonds — 32,490 — 32,490 Residential mortgage-backed securities — 2,108,594 — 2,108,594 Commercial mortgage-backed securities — 447,053 — 447,053 Other securities 4,477 — — 4,477 Total $ 4,477 $ 5,105,154 $ — $ 5,109,631 Loans held-for-sale $ — $ 61,511 $ — $ 61,511 IRLCs $ — $ 1,645 $ — $ 1,645 Forward mortgage-backed securities trades asset $ — $ 2,806 $ — $ 2,806 March 31, 2020 Level 1 Level 2 Level 3 Total Fair Available-for-sale U.S. Treasury securities $ 10,113 $ — $ — $ 10,113 Obligations of states and political subdivisions — 1,807,671 — 1,807,671 Corporate bonds — 220 — 220 Residential mortgage-backed securities — 1,679,980 — 1,679,980 Commercial mortgage-backed securities — 604,554 — 604,554 Other securities 4,531 — — 4,531 Total $ 14,644 $ 4,092,425 $ — $ 4,107,069 Loans held-for-sale $ — $ 39,659 $ — $ 39,659 IRLCs $ — $ 296 $ — $ 296 Forward mortgage-backed securities trades liability $ — $ (3,200 ) $ — $ (3,200 ) December 31, 2020 Level 1 Level 2 Level 3 Total Fair Available-for-sale Obligations of state and political subdivisions $ — $ 2,426,876 $ — $ 2,426,876 Residential mortgage-backed securities — 1,472,280 — 1,472,280 Commercial mortgage-backed securities — 489,316 — 489,316 Other securities 4,557 — — 4,557 Total $ 4,557 $ 4,388,472 $ — $ 4,393,029 Loans held-for-sale $ — $ 79,585 $ — $ 79,585 IRLCs $ — $ 4,618 $ — $ 4,618 Forward mortgage-backed securities trades liability $ — $ (1,560 ) $ — $ (1,560 ) The following table summarizes the Company’s loans held-for-sale March 31, December 31, 2021 2020 2020 Unpaid principal balance on loans held-for-sale $ 60,727 $ 38,563 $ 76,602 Net unrealized gains on loans held-for-sale 784 1,096 2,983 Loans held-for-sale $ 61,511 $ 39,659 $ 79,585 The following table summarizes the Company’s gains on sale and fees of mortgage loans for the three-months ended March 31, 2021 and 2020 (in thousand): Three-Months ended 2021 2020 Realized gain on sale and fees on mortgage loans* $ 10,728 $ 4,545 Change in fair value on loans held-for-sale (5,200 ) 2,355 Change in forward mortgage-backed securities trades 4,366 (3,048 ) Total gain on sale of mortgage loans $ 9,894 $ 3,852 * This includes gains on loans held-for-sale No residential mortgage loans held-for-sale held-for-sale Certain non-financial non-financial non-financial Non-financial non-recurring re-measured Re-evaluation re-measured At March 31, 2021 and 2020, and December 31, 2020, other real estate owned totaled $255,000, $982,000 and $119,000, respectively. The Company is required under current authoritative accounting guidance to disclose the estimated fair value of their financial instrument assets and liabilities including those subject to the requirements discussed above. For the Company, as for most financial institutions, substantially all of its assets and liabilities are considered financial instruments. Many of the Company’s financial instruments, however, lack an available trading market as characterized by a willing buyer and willing seller engaging in an exchange transaction. The estimated fair value amounts of financial instruments have been determined by the Company using available market information and appropriate valuation methodologies. However, considerable judgment is required to interpret data to develop the estimates of fair value. Accordingly, the estimates presented herein are not necessarily indicative of the amounts the Company could realize in a current market exchange. The use of different market assumptions and/or estimation methodologies may have a material effect on the estimated fair value amounts. In addition, reasonable comparability between financial institutions may not be likely due to the wide range of permitted valuation techniques and numerous estimates that must be made given the absence of active secondary markets for many of the financial instruments. This lack of uniform valuation methodologies also introduces a greater degree of subjectivity to these estimated fair values. Cash and due from banks, federal funds sold, interest-bearing deposits and time deposits in banks and accrued interest receivable and payable are liquid in nature and considered Levels 1 or 2 of the fair value hierarchy. Financial instruments with stated maturities have been valued using a present value discounted cash flow with a discount rate approximating current market for similar assets and liabilities and are considered Levels 2 and 3 of the fair value hierarchy. Financial instrument liabilities with no stated maturities have an estimated fair value equal to both the amount payable on demand and the carrying value and are considered Level 1 of the fair value hierarchy. The carrying value and the estimated fair value of the Company’s contractual off-balance-sheet The estimated fair values and carrying values of all financial instruments under current authoritative guidance were as follows (in thousands). March 31, December 31, 2021 2020 2020 Carrying Estimated Carrying Estimated Carrying Estimated Fair Value Value Fair Value Value Fair Value Value Fair Value Hierarchy Cash and due from banks $ 190,350 $ 190,350 $ 191,486 $ 191,486 $ 211,113 $ 211,113 Level 1 Interest-bearing demand deposits in banks 893,221 893,221 76,378 76,378 517,971 517,971 Level 1 Available-for-sale 5,109,631 5,109,631 4,107,069 4,107,069 4,393,029 4,393,029 Levels 1 and 2 Loans held-for-investment, 5,259,588 5,273,235 4,578,949 4,558,577 5,104,499 5,109,885 Level 3 Loans held-for-sale 65,405 65,273 42,034 41,593 83,969 84,233 Level 2 Accrued interest receivable 42,322 42,322 34,329 34,329 53,433 53,433 Level 2 Deposits with stated maturities 483,685 485,193 465,808 467,804 475,542 477,218 Level 2 Deposits with no stated maturities 8,929,762 8,929,762 6,744,658 6,744,658 8,200,275 8,200,275 Level 1 Borrowings 548,604 548,604 857,871 857,871 430,093 430,093 Level 2 Accrued interest payable 320 320 783 783 377 377 Level 2 IRLCs 1,645 1,645 296 296 4,618 4,618 Level 2 Forward mortgage-backed securi-ties trades asset (liability) 2,806 2,806 (3,200 ) (3,200 ) (1,560 ) (1,560 ) Level 2

Acquisition

Acquisition	3 Months Ended
	Mar. 31, 2021
Business Combinations [Abstract]
Acquisition	Note 10 – Acquisition On September 19, 2019, we entered into an agreement and plan of reorganization to acquire TB&T Bancshares, Inc. and its wholly-owned bank subsidiary, The Bank & Trust of Bryan/College Station, Texas. On January 1, 2020, the transaction was completed. Pursuant to the agreement, we issued 6,275,574 shares of the Company’s common stock in exchange for all of the outstanding shares of TB&T Bancshares, Inc. In addition, TBT Bancshares, Inc. made a $1,920,000 special dividend to its shareholders prior to closing of the transaction. At closing, a wholly-owned subsidiary of the Company merged into TB&T Bancshares, Inc. and immediately thereafter TB&T Bancshares, Inc. was merged into the Company and The Bank & Trust of Bryan/College Station, Texas, was merged into First Financial Bank, N.A., a wholly-owned subsidiary of the Company. The primary purpose of the acquisition was to expand the Company’s market share near the Houston market. Factors that contributed to a purchase price resulting in goodwill include its record of earnings, strong management and board of directors, strong local economic environment and opportunity for growth. The results of operations from this acquisition are included in the consolidated earnings of the Company commencing January 1, 2020. The following table presents the final amounts recorded on the consolidated balance sheet on the acquisition date (dollars in thousands): Fair value of consideration paid: Common stock issued (6,275,574 shares) $ 220,273 Fair value of identifiable assets acquired: Cash and cash equivalents $ 61,028 Securities available-for-sale 93,967 Loans 447,702 Identifiable intangible assets 4,798 Other assets 25,377 Total identifiable assets acquired $ 632,872 Fair value of liabilities assumed: Deposits $ 549,125 Other liabilities 5,397 Total liabilities assumed $ 554,522 Fair value of net identifiable assets acquired 78,350 Goodwill resulting from acquisition $ 141,923 Goodwill recorded in the acquisition was accounted for in accordance with the authoritative business combination guidance. Accordingly, goodwill will not be amortized but will be tested for impairment annually. The goodwill recorded is not deductible for federal income tax purposes. The fair value of total loans acquired was $447,702,000 at acquisition compared to contractual amounts of $455,181,000.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Nature of Operations	Nature of Operations First Financial Bankshares, Inc. (a Texas corporation) (“Bankshares”, “Company,” “we” or “us”) is a financial holding company which owns all of the capital stock of one bank with 78 locations located in Texas as of March 31, 2021. The Company’s subsidiary bank is First Financial Bank, N.A. The Company’s primary source of revenue is providing loans and banking services to consumers and commercial customers in the market area in which First Financial Bank, N.A. is located. In addition, the Company also owns First Financial Trust & Asset Management Company, N.A., First Financial Insurance Agency, Inc., First Technology Services, Inc. and First Financial Investments, Inc.
Basis of Presentation	Basis of Presentation A summary of significant accounting policies of the Company and its subsidiaries applied in the preparation of the accompanying consolidated financial statements follows. The accounting principles followed by the Company and the methods of applying them are in conformity with both United States generally accepted accounting principles (“GAAP”) and prevailing practices of the banking industry. The Company evaluated subsequent events for potential recognition through the date the consolidated financial statements were issued.
Use of Estimates in Preparation of Financial Statements	Use of Estimates in Preparation of Financial Statements The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. The Company’s significant estimates include its allowance for credit losses and its valuation of financial instruments.
Consolidation	Consolidation The accompanying consolidated financial statements include the accounts of the Company and its subsidiaries, all of which are wholly-owned. All significant intercompany accounts and transactions have been eliminated.
Stock Repurchase	Stock Repurchase On March 12, 2020, the Company’s Board of Directors authorized the repurchase of up to 4,000,000 common shares through September 30, 2021. Previously, the Board of Directors had authorized the repurchase of up to 2,000,000 common shares through September 30, 2020. The stock repurchase plan authorizes management to repurchase and retire the stock at such time as repurchases and retirements are considered beneficial to the Company and stockholders. Any repurchase of stock will be made through the open market, block trades or in privately negotiated transactions in accordance with applicable laws and regulations. Under the repurchase plan, there is no minimum number of shares that the Company is required to repurchase. Through March 31, 2021, 324,802 shares were repurchased and retired (all during the months of March and April 2020) totaling $8,008,000 under this repurchase plan.
Acquisition	Acquisition On January 1, 2020, the Company acquired 100% of the outstanding capital stock of TB&T Bancshares, Inc. through the merger of a wholly-owned subsidiary with and into TB&T Bancshares, Inc. Following such merger, TB&T Bancshares, Inc. and its wholly-owned subsidiary, The Bank & Trust of Bryan/College Station, Texas were merged into the Company and First Financial Bank, N.A., respectively. The results of operations of TB&T Bancshares, Inc. subsequent to the acquisition date, are included in the consolidated earnings of the Company. See Note 10 for additional information.
Adoption of New Accounting Standards	Adoption of New Accounting Standards On January 1, 2020, ASU 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments held-to-maturity off-balance-sheet available-for-sale available-for-sale On March 27, 2020, the Coronavirus Aid, Relief, and Economic Security Act (CARES Act) was signed by the President of the United States that included an option for entities to delay the implementation of ASC 326 until the earlier of the termination date of the national emergency declaration by the President or December 31, 2020. Under this option, the Company elected to delay its implementation of CECL and calculated and recorded the provision for credit losses through the nine-months ended September 2020 under the incurred loss model. At December 31, 2020, the Company elected to adopt ASC 326, effective as of January 1, 2020, through a transition charge to retained earnings of $589,000 ($466,000 net of applicable income taxes). This transition adjustment was comprised of a decrease of $619,000 in allowance for credit losses and an increase of $1,208,000 in the reserve for unfunded commitments. With the adoption of ASC 326, we revised certain accounting policies and implemented certain accounting policy elections which are described below. For the 2020 interim reporting periods, the allowance for credit losses were based on the incurred loss methodology in accordance with accounting policies disclosed in Note 1 of the Consolidated Financial Statements included in the Company’s 2019 Form 10-K. The Company adopted ASC 326 using the modified retrospective method for all financial assets measured at amortized cost, net investment in leases and OBS credit exposures. The Company adopted ASC 326 using the prospective transition approach for securities for which other-than-temporary impairment had been recognized prior to January 1, 2020. As a result, the amortized cost basis remains the same before and after the effective date of ASC 326. The effective interest rate on these debt securities was not changed. The Company adopted ASC 326 using the prospective transition approach for financial assets purchased with credit deterioration (“PCD”) that were previously classified as purchased credit impaired (“PCI”) and accounted for under ASC 310-30.
Other Recently Issued and Effective Authoritative Accounting Guidance	Other Recently Issued and Effective Authoritative Accounting Guidance ASU 2017-04, 2017-04 2017-04 ASU 2018-13, 2018-13 2018-13 2018-13 ASU 2019-12, 2019-12, step-up 2019-12 2019-12 ASU 2020-04, 2020-04 2020-04 2020-04 2020-04 ASU 2021-01, 2021-01 2021-01 2021-01 2021-01
Investment Securities	Investment Securities Management classifies debt securities as held-to-maturity, available-for-sale, held-to-maturity held-to-maturity available-for-sale Interest income includes amortization of purchase premiums and discounts over the period to maturity using a level-yield method, except for premiums on callable securities, which are amortized to their earliest call date. Realized gains and losses are recorded on the sale of securities in noninterest income. The Company has made a policy election to exclude accrued interest from the amortized cost basis of securities and report accrued interest separately in other assets on the consolidated balance sheets. A security is placed on nonaccrual status at the time any principal or interest payments become more than 90 days delinquent or if full collection of interest or principal becomes uncertain. Accrued interest for a security placed on nonaccrual is reversed against interest income. There was no accrued interest related to securities reversed against interest income for the three-months ended March 31, 2021 and 2020. The Company records its available-for-sale The Company’s investment portfolio currently consists of obligations of state and political subdivisions, mortgage pass-through securities, corporate bonds and general obligation or revenue based municipal bonds. Pricing for such securities is generally readily available and transparent in the market. The Company utilizes independent third-party pricing services to value its investment securities, which the Company reviews as well as the underlying pricing methodologies for reasonableness and to ensure such prices are aligned with pricing matrices. The Company validates prices supplied by the independent pricing services by comparison to prices obtained from other third-party sources on a quarterly basis.
Allowance for Credit Losses – Available-for-Sale Securities	Allowance for Credit Losses – Available-for-Sale For available-for-sale charged-off available-for-sale Management has made the accounting policy election to exclude accrued interest receivable on available-for-sale Available-for-sale charged-off
Allowance for Credit Losses – Held-to-Maturity Securities	Allowance for Credit Losses – Held-to-Maturity The allowance for credit losses on held-to-maturity held-to-maturity Held-to-maturity charged-off held-to-maturity held-to-maturity At March 31, 2021, 2020 and December 31, 2020, the Company held no securities that were classified as held-to-maturity.
Loans Held-for-Investment	Loans Held-for-Investment Loans that management has the intent and ability to hold for the foreseeable future or until maturity or payoff are reported at amortized cost, net of the allowance for credit losses. Amortized cost is the principal balance outstanding, net of purchase premiums and discounts, fair value hedge accounting adjustments, deferred loan fees and costs. The Company has made a policy election to exclude accrued interest from the amortized cost basis of loans and report accrued interest separately from the related loan balance in other assets on the condensed consolidated balance sheets. Interest on loans is calculated by using the simple interest method on daily balances of the principal amounts outstanding. The Company defers and amortizes net loan origination fees and costs as an adjustment to yield. Loans are considered past due if the required principal and interest payments have not been received as of the date such payments were due. Loans are placed on nonaccrual status when, in management’s opinion, the borrower may be unable to meet payment obligations as they become due, as well as when required by regulatory provisions. In determining whether or not a borrower may be unable to meet payment obligations for each class of loans, we consider the borrower’s debt service capacity through the analysis of current financial information, if available, and/or current information with regards to our collateral position. Regulatory provisions would typically require the placement of a loan on nonaccrual status if principal or interest has been in default for a period of 90 days or more unless the loan is both well secured and in the process of collection or full payment of principal and interest is not expected. Loans may be placed on nonaccrual status regardless of whether or not such loans are considered past due. When interest accrual is discontinued, all unpaid accrued interest is reversed. Interest income on nonaccrual loans is recognized only to the extent that cash payments are received in excess of principal due. A loan may be returned to accrual status when all the principal and interest amounts contractually due are brought current and future principal and interest amounts contractually due are reasonably assured. Prior to the adoption of ASC 326, loans were reported as impaired when, based on then current information and events, it was probable we would be unable to collect all amounts due in accordance with the original contractual terms of the loan agreement, including scheduled principal and interest payments. Impairment was evaluated in total for smaller-balance loans of a similar nature and on an individual loan basis for other loans. If a loan was impaired, a specific valuation allowance was allocated, if necessary, so that the loan was reported net, at the present value of estimated future cash flows using the loan’s existing rate or at the fair value of collateral if repayment was expected solely from the collateral. Interest payments on impaired loans were typically applied to principal unless collectability of the principal amount was reasonably assured, in which case interest was recognized on a cash basis. Impaired loans, or portions thereof, were charged off when deemed uncollectible. Further information regarding our accounting policies related to past due loans, nonaccrual loans and troubled-debt restructurings is presented in Note 3.
Acquired Loans	Acquired Loans Loans acquired in connection with acquisitions are recorded at their acquisition-date fair value. The allowance for credit losses related to the acquired loan portfolio is not carried over. Acquired loans are classified into two categories based on the credit risk characteristics of the underlying borrowers as either purchased credit deteriorated (“PCD”) loans, or loans with no evidence of credit deterioration (“non-PCD”). PCD loans are defined as a loan or pool of loans that have experienced more-than-insignificant credit deterioration since the origination date. The Company uses a combination of individual and pooled review approaches to determine if acquired loans are PCD. At acquisition, the Company considers a number of factors to determine if an acquired loan or pool of loans has experienced more-than-insignificant credit deterioration. The initial allowance related to PCD loans that share similar risk characteristics is established using a pooled approach. The Company uses either a discounted cash flow or weighted average remaining life method to determine the required level of the allowance. PCD loans that were classified as nonaccrual as of the acquisition date and are collateral dependent are assessed for allowance on an individual basis. For PCD loans, an initial allowance is established on the acquisition date and combined with the fair value of the loan to arrive at acquisition date amortized cost. Subsequent to the acquisition date, the initial allowance for credit losses on PCD loans will increase or decrease based on future evaluations, with changes recognized in the provision for credit losses. Non-PCD Determining the fair value of the acquired loans involves estimating the principal and interest payment cash flows expected to be collected on the loans and discounting those cash flows at a market rate of interest. Management considers a number of factors in evaluating the acquisition-date fair value including the remaining life, interest rate profile, market interest rate environment, payment schedules, risk ratings, probability of default and loss given default, and estimated prepayment rates. For PCD loans, the non-credit non-credit non-PCD Prior to the adoption of ASC 326, loans acquired in a business combination that had evidence of credit impairment and for which it was probable, at acquisition, that the Company would be unable to collect all contractually required payments receivable were considered PCI. PCI loans were accounted for individually or aggregated into pools of loans based on common risk characteristics such as credit grade, loan type, and date of origination.
Allowance for Credit Losses - Loans	Allowance for Credit Losses - Loans The allowance for credit losses (“allowance” or “ACL”) is a contra-asset valuation account, calculated in accordance with ASC 326, that is deducted from the amortized cost basis of loans. The ACL represents an amount which, in management’s judgement, is adequate to absorb the lifetime expected credit losses that may be experienced on outstanding loans at the balance sheet date based on the evaluation of the size and current risk characteristics of the loan portfolio, past events, current conditions, reasonable and supportable forecasts of future economic conditions and prepayment experience. The allowance for credit losses is measured and recorded upon the initial recognition of a financial asset. Determination of the adequacy of the allowance is inherently complex and requires the use of significant and highly subjective estimates. Loans are charged-off charged-off charged-off. The Company’s methodology for estimating the allowance includes: (1) a collective quantified reserve that reflects the Company’s historical default and loss experience adjusted for expected economic conditions throughout a reasonable and supportable forecast period, including the Company’s expected prepayment and curtailment rates; (2) collective qualitative factors that consider concentrations of the loan portfolio, expected changes to the economic forecasts, large relationships, early delinquencies, and factors related to credit administrations, including, among others, loan-to-value In calculating the allowance for credit losses, most loans are segmented into pools based upon similar characteristics and risk profiles. Common characteristics and risk profiles include the type/purpose of loan, underlying collateral, geographical similarity and historical/expected credit loss patterns. In developing these loan pools for the purposes of modeling expected credit losses, we also analyzed the degree of correlation in how loans within each portfolio respond when subjected to varying economic conditions and scenarios as well as other portfolio stress factors. For modeling purposes, our loan portfolio segments include Commercial and Industrial (“C&I”), Municipal, Agricultural, Construction and Development, Farm, Non-Owner Non-Auto. The Company applies two methodologies to estimate the allowance on its pooled portfolio segments; discounted cash flows method and weighted average remaining life method. Allowance estimates on the following portfolio segments are calculated using the discounted cash flows method: C&I, Municipal, Construction and Development, Farm, Non-Owner Non-Auto. one-year In some cases, management may determine that an individual loan exhibits unique risk characteristics which differentiate the loan from other loans within our loan pools. In such cases, the loans are evaluated for expected credit losses on an individual basis and excluded from the collective evaluation. Specific allocations of the allowance for credit losses are determined by analyzing the borrower’s ability to repay amounts owed, collateral deficiencies, the relative risk rating of the loan and economic conditions affecting the borrower’s industry, among other things. A loan is considered to be collateral dependent when, based upon management’s assessment, the borrower is experiencing financial difficulty and repayment is expected to be provided substantially through the sale of the collateral. In such cases, expected credit losses are based on the fair value of the collateral at the measurement date, adjusted for estimated selling costs if satisfaction of the loan depends on the sale of the collateral. We reevaluate the fair value of collateral supporting collateral dependent loans on an ongoing basis. Management qualitatively adjusts model results for risk factors that are not considered within our modeling processes but are nonetheless relevant in assessing the expected credit losses within our loan pools. These qualitative factor (“Q-Factor”) Q-Factor non-collateral Management believes it uses relevant information available to make determinations about the allowance and that it has established the existing allowance in accordance with GAAP. However, the determination of the allowance requires significant judgment, and estimates of expected lifetime losses in the loan portfolio can vary significantly from the amounts actually observed. While management uses available information to recognize expected losses, future additions to the allowance may be necessary based on changes in the loans comprising the portfolio, changes in the current and forecasted economic conditions, changes to the interest rate environment which may directly impact prepayment and curtailment rate assumptions, and changes in the financial condition of borrowers. The adoption of the CECL standard did not result in a significant change to any other credit risk management and monitoring processes, including identification of past due or delinquent borrowers, nonaccrual practices, assessment of troubled debt restructurings or charge-off
Allowance for Credit Losses - Off-Balance-Sheet/Reserve for Unfunded Commitments	Allowance for Credit Losses - Off-Balance-Sheet/Reserve The allowance for credit losses on off-balance-sheet
Other Real Estate	Other Real Estate Other real estate owned is foreclosed property held pending disposition and is initially recorded at fair value, less estimated costs to sell. At foreclosure, if the fair value of the real estate, less estimated costs to sell, is less than the Company’s recorded investment in the related loan, a write-down is recognized through a charge to the allowance for credit losses. Any subsequent reduction in value is recognized by a charge to income. Operating and holding expenses of such properties, net of related income, and gains and losses on their disposition are included in net gain (loss) on sale of foreclosed assets as incurred.
Bank Premises and Equipment	Bank Premises and Equipment Bank premises and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization are computed principally on a straight-line basis over the estimated useful lives of the related assets. Leasehold improvements are amortized over the life of the respective lease or the estimated useful lives of the improvements, whichever is shorter.
Business Combinations, Goodwill and Other Intangible Assets	Business Combinations, Goodwill and Other Intangible Assets The Company accounts for all business combinations under the purchase method of accounting. Tangible and intangible assets and liabilities of the acquired entity are recorded at fair value. Intangible assets with finite useful lives represent the future benefit associated with the acquisition of the core deposits and are amortized over seven years, utilizing a method that approximates the expected attrition of the deposits. Goodwill with an indefinite life is not amortized, but rather tested annually for impairment as of June 30 each year. There was no impairment recorded for the three-months ended March 31, 2021 or 2020, respectively.
Securities Sold Under Agreements To Repurchase	Securities Sold Under Agreements To Repurchase Securities sold under agreements to repurchase, which are classified as borrowings, generally mature within one to four days from the transaction date. Securities sold under agreements to repurchase are reflected at the amount of the cash received in connection with the transaction. The Company may be required to provide additional collateral based on the estimated fair value of the underlying securities.
Segment Reporting	Segment Reporting The Company has determined that its banking regions meet the aggregation criteria of the current authoritative accounting guidance since each of its banking regions offer similar products and services, operate in a similar manner, have similar customers and report to the same regulatory authority, and therefore operate one line of business (community banking) located in a single geographic area (Texas).
Statements of Cash Flows	Statements of Cash Flows For purposes of reporting cash flows, cash and cash equivalents includes cash on hand, amounts due from banks, including interest-bearing demand deposits in banks with original maturity of 90 days or less, and federal funds sold.
Accumulated Other Comprehensive Earnings (Loss)	Accumulated Other Comprehensive Earnings (Loss) Unrealized net gains on the Company’s available-for-sale
Income Taxes	Income Taxes The Company’s provision for income taxes is based on income before income taxes adjusted for permanent differences between financial reporting and taxable income. Deferred tax assets and liabilities are determined using the liability (or balance sheet) method. Under this method, the net deferred tax asset or liability is determined based on the tax effects of the temporary differences between the book and tax bases of the various balance sheet assets and liabilities and gives current recognition to changes in tax rates and laws.
Stock Based Compensation	Stock Based Compensation The Company grants stock options for a fixed number of shares to employees with an exercise price equal to the fair value of the shares at the grant date. The grant date fair value is amortized over the vesting period which generally is six years. The Company also grants restricted stock for a fixed number of shares. The grant date fair value is amortized over the vesting period which generally is one to three years. See Note 8 for further information.
Advertising Costs	Advertising Costs Advertising costs are expensed as incurred.
Per Share Data	Per Share Data Net earnings per share (“EPS”) are computed by dividing net earnings by the weighted average number of common shares outstanding during the period. The Company calculates dilutive EPS assuming all outstanding stock options to purchase common shares and unvested restricted stock shares have been exercised and/or vested at the beginning of the year (or the time of issuance, if later.) The dilutive effect of the outstanding options and restricted stock is reflected by application of the treasury stock method, whereby the proceeds from the exercised options and unearned compensation for both restricted stock and stock options are assumed to be used to purchase common shares at the average market price during the respective period. There were no anti-dilutive shares for the three-months ended March 31, 2021 and 2020. The following table reconciles the computation of basic EPS to diluted EPS: Net Weighted Per Share For the three-months ended March 31, 2021: Net earnings per share, basic $ 56,918 142,146,275 $ 0.40 Effect of stock options and stock grants — 856,383 — Net earnings per share, diluted $ 56,918 143,002,658 $ 0.40 Net Weighted Per Share For the three-months ended March 31, 2020: Net earnings per share, basic $ 37,232 142,118,864 $ 0.26 Effect of stock options and stock grants — 616,344 — Net earnings per share, diluted $ 37,232 142,735,208 $ 0.26

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Computation of Basic EPS to Dilutive EPS	The following table reconciles the computation of basic EPS to diluted EPS: Net Weighted Per Share For the three-months ended March 31, 2021: Net earnings per share, basic $ 56,918 142,146,275 $ 0.40 Effect of stock options and stock grants — 856,383 — Net earnings per share, diluted $ 56,918 143,002,658 $ 0.40 Net Weighted Per Share For the three-months ended March 31, 2020: Net earnings per share, basic $ 37,232 142,118,864 $ 0.26 Effect of stock options and stock grants — 616,344 — Net earnings per share, diluted $ 37,232 142,735,208 $ 0.26

Securities (Tables)

Securities (Tables)	3 Months Ended
	Mar. 31, 2021
Cash and Cash Equivalents [Abstract]
Summary of Available-for-Sale Securities	The amortized cost, related gross unrealized gains and losses, allowance for credit losses and the fair value of available-for-sale March 31, 2021 Amortized Gross Gross Estimated Securities available-for-sale: Obligations of states and political subdivisions $ 2,418,227 $ 106,988 $ (8,198 ) $ 2,517,017 Residential mortgage-backed securities 2,073,647 43,575 (8,628 ) 2,108,594 Commercial mortgage-backed securities 431,137 15,916 — 447,053 Corporate bonds and other 38,427 79 (1,539 ) 36,967 Total securities available-for-sale $ 4,961,438 $ 166,558 $ (18,365 ) $ 5,109,631 March 31, 2020 Amortized Gross Gross Estimated Securities available-for-sale: U.S. Treasury securities $ 10,039 $ 74 $ — $ 10,113 Obligations of states and political subdivisions 1,731,392 78,996 (2,717 ) 1,807,671 Residential mortgage-backed securities 1,617,341 62,659 (20 ) 1,679,980 Commercial mortgage-backed securities 587,114 17,624 (184 ) 604,554 Corporate bonds and other 4,624 133 (6 ) 4,751 Total securities available-for-sale $ 3,950,510 $ 159,486 $ (2,927 ) $ 4,107,069 December 31, 2020 Amortized Gross Gross Estimated Securities available-for-sale: Obligations of states and political subdivisions $ 2,283,616 $ 143,339 $ (79 ) $ 2,426,876 Residential mortgage-backed securities 1,421,922 50,473 (115 ) 1,472,280 Commercial mortgage-backed securities 467,243 22,077 (4 ) 489,316 Corporate bonds and other 4,398 159 — 4,557 Total securities available-for-sale $ 4,177,179 $ 216,048 $ (198 ) $ 4,393,029
Amortized Cost and Estimated Fair Value of Available-for-Sale Securities	The amortized cost and estimated fair value of available-for-sale Amortized Estimated Fair Due within one year $ 290,536 $ 295,145 Due after one year through five years 2,355,100 2,456,956 Due after five years through ten years 2,145,293 2,188,324 Due after ten years 170,509 169,206 Total $ 4,961,438 $ 5,109,631
Continuous Unrealized-Loss Position of Available-for-Sale Securities	The following tables disclose the Company’s investment securities that have been in a continuous unrealized-loss Less than 12 Months 12 Months or Longer Total March 31, 2021 Fair Value Unrealized Fair Value Unrealized Fair Value Unrealized Obligations of states and political subdivisions $ 533,213 $ 8,198 $ — $ — $ 533,213 $ 8,198 Residential mortgage-backed securities 589,353 8,618 999 10 590,352 8,628 Commercial mortgage-backed securities 471 — — — 471 — Corporate bonds and other 32,490 1,539 — — 32,490 1,539 Total $ 1,155,527 $ 18,355 $ 999 $ 10 $ 1,156,526 $ 18,365 Less than 12 Months 12 Months or Longer Total March 31, 2020 Fair Value Unrealized Fair Value Unrealized Fair Value Unrealized Obligations of states and political subdivisions $ 168,725 $ 2,717 $ — $ — $ 168,725 $ 2,717 Residential mortgage-backed securities 1 — 8,164 21 8,165 21 Commercial mortgage-backed securities 44,724 173 9,630 10 54,354 183 Corporate bonds and other 220 6 — — 220 6 Total $ 213,670 $ 2,896 $ 17,794 $ 31 $ 231,464 $ 2,927 Less than 12 Months 12 Months or Longer Total December 31, 2020 Fair Unrealized Fair Value Unrealized Fair Unrealized Obligations of state and political subdivisions $ $ 79 $ — $ — $ $ 79 Residential mortgage-backed securities 36,017 96 3,156 19 39,173 115 Commercial mortgage-backed securities 16,218 4 — — 16,218 4 Total $ 77,449 $ 179 $ 3,156 $ 19 $ 80,605 $ 198

Loans Held for Investment and_2

Loans Held for Investment and Allowance for Loan Losses (Tables)	3 Months Ended
	Mar. 31, 2021
Receivables [Abstract]
Loans Held-for-Investment by Portfolio Segment	Loans held-for-investment March 31, December 31, 2021 2020 2020 Commercial: C&I $ 1,178,126 $ N/A $ 1,131,382 Municipal 176,949 N/A 181,325 Total Commercial 1,355,075 869,450 1,312,707 Agricultural 90,366 99,582 94,864 Real Estate: Construction & Development 587,928 N/A 553,959 Farm 162,046 N/A 152,237 Non-Owner 650,144 N/A 617,686 Owner Occupied CRE 759,906 N/A 746,974 Residential 1,254,727 N/A 1,248,409 Total Real Estate 3,414,751 3,249,249 3,319,265 Consumer: Auto 370,027 N/A 353,595 Non-Auto 92,343 N/A 90,602 Total Consumer 462,370 421,108 444,197 Total Loans 5,322,562 4,639,389 5,171,033 Less: Allowance for credit losses (62,974 ) (60,440 ) (66,534 ) Loans, net $ 5,259,588 $ 4,578,949 $ 5,104,499
Non-Accrual Loans, Loans Still Accruing and Past Due 90 Days or More and Restructured Loans	The Company’s nonaccrual loans, loans still accruing and past due 90 days or more and restructured loans are as follows (in thousands): March 31, December 31, 2021 2020 2020 Non-accrual $ 39,333 $ 39,226 $ 42,619 Loans still accruing and past due 90 days or more 2 209 113 Troubled debt restructured loans still accruing* 23 26 24 Total $ 39,358 $ 39,461 $ 42,756 * Troubled debt restructured loans of $ 6,619,000 4,733,000 7,407,000
Schedule of Non-Accrual Loans	Non-accrual March 31, December 31, 2021 2020 2020 Commercial: C&I $ 4,709 $ N/A $ 5,015 Municipal — N/A — Total Commercial 4,709 5,620 5,015 Agricultural 1,068 1,128 1,076 Real Estate: Construction & Development 1,296 N/A 3,838 Farm 6,859 N/A 7,299 Non-Owner 7,088 N/A 5,243 Owner Occupied CRE 9,557 N/A 10,797 Residential 8,364 N/A 8,851 Total Real Estate 33,164 32,156 36,028 Consumer: Auto 317 N/A 407 Non-Auto 75 N/A 93 Total Consumer 392 322 500 Total $ 39,333 $ 39,226 $ 42,619
Changes in Allowance for Loan Losses	Summary information on the allowance for credit losses for the three-months ended March 31, 2021 and 2020, are outlined by portfolio segment in the following tables (in thousands): March 31, 2021 C&I Municipal Agricultural Construction & Farm Beginning balance $ 13,609 $ 1,552 $ 1,255 $ 13,512 $ 1,876 Provision for loan losses (1,239 ) 639 721 (268 ) (662 ) Recoveries 223 — 9 2 9 Charge-offs (270 ) — — — — Ending balance $ 12,323 $ 2,191 $ 1,985 $ 13,246 $ 1,223 March 31, 2021 (continued) Non-Owner Owner Residential Auto Non-Auto Total Beginning balance $ 8,391 $ 12,347 $ 12,601 $ 1,020 $ 371 $ 66,534 Provision for loan losses 1,052 (2,467 ) (1,384 ) 141 38 (3,429 ) Recoveries 55 6 19 73 47 443 Charge-offs (6 ) (8 ) (47 ) (166 ) (77 ) (574 ) Ending balance $ 9,492 $ 9,878 $ 11,189 $ 1,068 $ 379 $ 62,974 March 31, 2020 Commercial Agricultural Real Estate Consumer Total Beginning balance $ 12,122 $ 1,206 $ 33,974 $ 5,197 $ 52,499 Provision for loan losses 794 949 7,921 186 9,850 Recoveries 149 1 76 92 318 Charge-offs (1,292 ) (2 ) (715 ) (218 ) (2,227 ) Ending balance $ 11,773 $ 2,154 $ 41,256 $ 5,257 $ 60,440
Schedule of loans that are individually evaluated for credit losses	The Company’s loans that are individually evaluated for credit losses (both collateral and non-collateral March 31, 2021 Collateral Collateral Non-Collateral Total Loans Related Related Non-Collateral Total Commercial: C&I $ 1,806 $ 2,903 $ 14,580 $ 19,289 $ 777 $ 3,104 $ 3,881 Municipal — — 9,777 9,777 — 1,536 1,536 Total Commercial 1,806 2,903 24,357 29,066 777 4,640 5,417 Agricultural 457 612 5,790 6,859 170 1,620 1,790 Real Estate: Construction & Development 1,124 171 11,202 12,497 12 868 880 Farm 2,241 4,618 3,436 10,295 590 81 671 Non-Owner 6,045 1,043 32,299 39,387 226 3,109 3,335 Owner Occupied CRE 6,081 3,476 45,893 55,450 599 3,000 3,599 Residential 4,210 4,154 26,331 34,695 577 2,297 2,874 Total Real Estate 19,701 13,462 119,161 152,324 2,004 9,355 11,359 Consumer: Auto — 317 1,399 1,716 1 4 5 Non-Auto — 75 376 451 — 2 2 Total Consumer — 392 1,775 2,167 1 6 7 Total $ 21,964 $ 17,369 $ 151,083 $ 190,416 $ 2,952 $ 15,621 $ 18,573 December 31, 2020 Collateral Collateral Non-Collateral Total Loans Related Related Non-Collateral Total Commercial: C&I $ 1,544 $ 3,471 $ 25,629 $ 30,644 $ 799 $ 4,592 $ 5,391 Municipal — — 9,439 9,439 — 1,435 1,435 Total Commercial 1,544 3,471 35,068 40,083 799 6,027 6,826 Agricultural 470 606 5,572 6,648 96 886 982 Real Estate: Construction & Development 1,176 2,661 11,368 15,205 35 617 652 Farm 2,614 4,685 3,349 10,648 654 658 1,312 Non-Owner 4,009 1,234 17,383 22,626 500 1,421 1,921 Owner Occupied CRE 7,279 3,518 51,933 62,730 657 5,172 5,829 Residential 4,347 4,504 28,196 37,047 676 2,431 3,107 Total Real Estate 19,425 16,602 112,229 148,256 2,522 10,299 12,821 Consumer: Auto — 407 1,523 1,930 1 5 6 Non-Auto — 94 440 534 1 1 2 Total Consumer — 501 1,963 2,464 2 6 8 Total $ 21,439 $ 21,180 $ 154,832 $ 197,451 $ 3,419 $ 17,218 $ 20,637 The following table presents the recorded investment with respect to impaired loans, the associated allowance by the applicable portfolio segment and the unpaid contractual principal balance of the impaired loans at March 31, 2020, in accordance with the legacy “incurred loss” methodology disclosure requirements (in thousands): March 31, 2020 Unpaid Recorded Recorded Total Related Three-Month Commercial $ 7,300 $ 992 $ 4,628 $ 5,620 $ 1,271 $ 6,409 Agricultural 1,340 632 496 1,128 98 1,200 Real Estate 44,208 9,496 22,660 32,156 2,016 36,683 Consumer 436 — 322 322 1 342 Total $ 53,284 $ 11,120 $ 28,106 $ 39,226 $ 3,386 $ 44,634
Schedule of Allowance for Loan Losses by Portfolio Segment	The Company’s allowance for loans that are individually evaluated for credit losses and collectively evaluated for credit losses as of March 31, 2021 and December 31, 2020, are summarized in the following table by loan segment (in thousands).​​​​​​​ Allocation of a portion of the allowance to one category of loans does not preclude its availability to absorb losses in other categories. March 31, 2021 C&I Municipal Agricultural Construction Farm Loans individually evaluated for credit losses $ 3,881 $ 1,536 $ 1,790 $ 880 $ 671 Loans collectively evaluated for credit losses 8,442 655 195 12,366 552 Total $ 12,323 $ 2,191 $ 1,985 $ 13,246 $ 1,223 March 31, 2021 (continued) Non-Owner Owner Residential Auto Non-Auto Total Loans individually evaluated for credit losses $ 3,335 $ 3,599 $ 2,874 $ 5 $ 2 $ 18,573 Loans collectively evaluated for credit losses 6,157 6,279 8,315 1,063 377 44,401 Total $ 9,492 $ 9,878 $ 11,189 $ 1,068 $ 379 $ 62,974 December 31, 2020 C&I Municipal Agricultural Construction & Farm Loans individually evaluated for credit losses $ 5,391 $ 1,435 $ 982 $ 652 $ 1,312 Loans collectively evaluated for credit losses 8,218 117 273 12,860 564 Total $ 13,609 $ 1,552 $ 1,255 $ 13,512 $ 1,876 December 31, 2020 (continued) Non-Owner Owner Residential Auto Non-Auto Total Loans individually evaluated for credit losses $ 1,921 $ 5,829 $ 3,107 $ 6 $ 2 $ 20,637 Loans collectively evaluated for credit losses 6,470 6,518 9,494 1,014 369 45,897 Total $ 8,391 $ 12,347 $ 12,601 $ 1,020 $ 371 $ 66,534 The Company’s allowance for loans that are individually evaluated for credit losses and collectively evaluated for credit losses as of March 31, 2020, are summarized in the following table by loan segment in accordance with the legacy “incurred loss” methodology disclosure requirements (in thousands): March 31, 2020 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 1,271 $ 98 $ 2,016 $ 1 $ 3,386 Loan collectively evaluated for impairment 10,502 2,056 39,240 5,256 57,054 Total $ 11,773 $ 2,154 $ 41,256 $ 5,257 $ 60,440
Schedule of Investment in Loans Related to Balance in Allowance for Loan Losses on Basis of Company's Impairment Methodology	The Company’s recorded investment in loans as of March 31, 2021 and December 31, 2020, related to the balance in the allowance for credit losses on the basis of the Company’s adopted ASC 326 evaluation methodology follows below (in thousands): March 31, 2021 C&I Municipal Agricultural Construction & Farm Loans individually evaluated for credit losses $ 19,289 $ 9,777 $ 6,859 $ 12,497 $ 10,295 Loans collectively evaluated for credit losses 1,158,837 167,172 83,507 575,431 151,751 Total $ 1,178,126 $ 176,949 $ 90,366 $ 587,928 $ 162,046 March 31, 2021 (continued) Non-Owner Owner Residential Auto Non-Auto Total Loans individually evaluated for credit losses $ 39,387 $ 55,450 $ 34,695 $ 1,716 $ 451 $ 190,416 Loans collectively evaluated for credit losses 610,757 704,456 1,220,032 368,311 91,892 5,132,146 Total $ 650,144 $ 759,906 $ 1,254,727 $ 370,027 $ 92,343 $ 5,322,562 December 31, 2020 C&I Municipal Agricultural Construction & Farm Loans individually evaluated for credit losses $ 30,644 $ 9,439 $ 6,648 $ 15,205 $ 10,648 Loans collectively evaluated for credit losses 1,100,738 171,886 88,216 538,754 141,589 Total $ 1,131,382 $ 181,325 $ 94,864 $ 553,959 $ 152,237 December 31, 2020 (continued) Non-Owner Owner Residential Auto Non-Auto Total Loans individually evaluated for credit losses $ 22,626 $ 62,730 $ 37,047 $ 1,930 $ 534 $ 197,451 Loans collectively evaluated for credit losses 595,060 684,244 1,211,362 351,665 90,068 4,973,582 Total $ 617,686 $ 746,974 $ 1,248,409 $ 353,595 $ 90,602 $ 5,171,033 The Company’s recorded investment in loans as of March 31, 2020, related to the balance in the allowance for loan losses on the basis of the Company’s legacy “incurred loss” impairment methodology follows below (in thousands): March 31, 2020 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 5,620 $ 1,128 $ 32,156 $ 322 $ 39,226 Loan collectively evaluated for impairment 863,830 98,454 3,217,093 420,786 4,600,163 Total $ 869,450 $ 99,582 $ 3,249,249 $ 421,108 $ 4,639,389
Schedule of Company's Internal Ratings of its Loans Held-for-Investment, Including The Year of Origination, by Portfolio Segments	The following summarizes the Company’s internal ratings of its loans held-for-investment, March 31, 2021 2020 2019 2018 2017 Prior Revolving Total C&I Risk rating: Pass $ 303 $ 647 $ 84 $ 61 $ 24 $ 41 $ — $ 1,160 Special mention 2 3 1 — 1 — — 7 Substandard 1 6 1 3 1 — — 12 Doubtful — — — — — — — — Total $ 306 $ 656 $ 86 $ 64 $ 26 $ 41 $ — $ 1,179 March 31, 2021 2020 2019 2018 2017 Prior Revolving Total Municipal Risk rating: Pass $ 2 $ 21 $ 16 $ 23 $ 13 $ 92 $ — $ 167 Special mention — — — — — — — — Substandard — 2 — — 6 2 — 10 Doubtful — — — — — — — — Total $ 2 $ 23 $ 16 $ 23 $ 19 $ 94 $ — $ 177 March 31, 2021 2020 2019 2018 2017 Prior Revolving Total Agricultural Risk rating: Pass $ 15 $ 42 $ 16 $ 7 $ 2 $ 1 $ — $ 83 Special mention 1 — — — — — — 1 Substandard — 5 — — 1 — — 6 Doubtful — — — — — — — — Total $ 16 $ 47 $ 16 $ 7 $ 3 $ 1 $ — $ 90 March 31, 2021 2020 2019 2018 2017 Prior Revolving Total Construction & Development Risk rating: Pass $ 101 $ 347 $ 62 $ 35 $ 17 $ 13 $ — $ 575 Special mention — 2 4 — — 1 — 7 Substandard 1 3 1 — — 1 — 6 Doubtful — — — — — — — — Total $ 102 $ 352 $ 67 $ 35 $ 17 $ 15 $ — $ 588 March 31, 2021 2020 2019 2018 2017 Prior Revolving Total Farm Risk rating: Pass $ 20 $ 54 $ 21 $ 17 $ 10 $ 30 $ — $ 152 Special mention — — — — — — — — Substandard — 7 1 1 — 1 — 10 Doubtful — — — — — — — — Total $ 20 $ 61 $ 22 $ 18 $ 10 $ 31 $ — $ 162 March 31, 2021 2020 2019 2018 2017 Prior Revolving Total Non-Owner Risk rating: Pass $ 45 $ 198 $ 105 $ 86 $ 41 $ 136 $ — $ 611 Special mention — 1 13 1 8 4 — 27 Substandard — — 2 — 2 8 — 12 Doubtful — — — — — — — — Total $ 45 $ 199 $ 120 $ 87 $ 51 $ 148 $ — $ 650 March 31, 2021 2020 2019 2018 2017 Prior Revolving Total Owner Occupied CRE Risk rating: Pass $ 74 $ 168 $ 126 $ 96 $ 72 $ 169 $ — $ 705 Special mention — 3 4 — 4 — — 11 Substandard 1 5 4 18 4 12 — 44 Doubtful — — — — — — — — Total $ 75 $ 176 $ 134 $ 114 $ 80 $ 181 $ — $ 760 March 31, 2021 2020 2019 2018 2017 Prior Revolving Total Residential Risk rating: Pass $ 109 $ 346 $ 157 $ 119 $ 93 $ 302 $ 94 $ 1,220 Special mention — 3 1 1 1 3 — 9 Substandard 1 5 2 4 2 11 1 26 Doubtful — — — — — — — — Total $ 110 $ 354 $ 160 $ 124 $ 96 $ 316 $ 95 $ 1,255 March 31, 2021 2020 2019 2018 2017 Prior Revolving Total Auto Risk rating: Pass $ 61 $ 161 $ 90 $ 32 $ 16 $ 8 $ — $ 368 Special mention — — — — — — — — Substandard — 1 1 — — — — 2 Doubtful — — — — — — — — Total $ 61 $ 162 $ 91 $ 32 $ 16 $ 8 $ — $ 370 March 31, 2021 2020 2019 2018 2017 Prior Revolving Total Non-Auto Risk rating: Pass $ 17 $ 40 $ 17 $ 6 $ 3 $ 2 $ 7 $ 92 Special mention — — — — — — — — Substandard — — — — — — — — Doubtful — — — — — — — — Total $ 17 $ 40 $ 17 $ 6 $ 3 $ 2 $ 7 $ 92 March 31, 2021 2020 2019 2018 2017 Prior Revolving Total Total Loans Risk rating: Pass $ 747 $ 2,024 $ 694 $ 482 $ 291 $ 794 $ 101 $ 5,133 Special mention 3 12 23 2 14 8 — 62 Substandard 4 34 12 26 16 35 1 128 Doubtful — — — — — — — — Total $ 754 $ 2,070 $ 729 $ 510 $ 321 $ 837 $ 102 $ 5,323 The following summarizes the Company’s internal ratings of its loans held-for-investment, December 31, 2020 2019 2018 2017 2016 Prior Revolving Total C&I Risk rating: Pass $ 874 $ 101 $ 70 $ 28 $ 10 $ 16 $ — $ 1,099 Special mention 9 2 — 1 — — — 12 Substandard 12 4 4 — — — — 20 Doubtful — — — — — — — — Total $ 895 $ 107 $ 74 $ 29 $ 10 $ 16 $ — $ 1,131 December 31, 2020 2019 2018 2017 2016 Prior Revolving Total Municipal Risk rating: Pass $ 26 $ 19 $ 29 $ 14 $ 13 $ 71 $ — $ 172 Special mention — — — — — — — — Substandard 2 — — 5 1 1 — 9 Doubtful — — — — — — — — Total $ 28 $ 19 $ 29 $ 19 $ 14 $ 72 $ — $ 181 December 31, 2020 2019 2018 2017 2016 Prior Revolving Total Agricultural Risk rating: Pass $ 57 $ 19 $ 9 $ 3 $ 1 $ — $ — $ 89 Special mention — — — — — — — — Substandard 6 — — — — — — 6 Doubtful — — — — — — — — Total $ 63 $ 19 $ 9 $ 3 $ 1 $ — $ — $ 95 December 31, 2020 2019 2018 2017 2016 Prior Revolving Total Construction & Development Risk rating: Pass $ $ 97 $ 36 $ 19 $ 7 $ 9 $ — $ 539 Special mention 2 4 — — — — — 6 Substandard 4 1 — 3 — 1 — 9 Doubtful — — — — — — — — Total $ 377 $ 102 $ 36 $ 22 $ 7 $ 10 $ — $ 554 December 31, 2020 2019 2018 2017 2016 Prior Revolving Total Farm Risk rating: Pass $ 57 $ 22 $ 18 $ 11 $ 11 $ 23 $ — $ 142 Special mention — — — — — — — — Substandard 7 1 — 1 — 1 — 10 Doubtful — — — — — — — — Total $ 64 $ 23 $ 18 $ 12 $ 11 $ 24 $ — $ 152 December 31, 2020 2019 2018 2017 2016 Prior Revolving Total Non-Owner Risk rating: Pass $ 197 $ 117 $ 93 $ 44 $ 55 $ 88 $ — $ 594 Special mention 1 — 1 8 1 — — 11 Substandard — 2 — — — 11 — 13 Doubtful — — — — — — — — Total $ 198 $ 119 $ 94 $ 52 $ 56 $ 99 $ — $ 618 December 31, 2020 2019 2018 2017 2016 Prior Revolving Total Owner Occupied CRE Risk rating: Pass $ 176 $ 132 $ 105 $ 75 $ 65 $ 132 $ — $ 685 Special mention 5 5 2 4 1 1 — 18 Substandard 5 4 20 4 1 10 — 44 Doubtful — — — — — — — — Total $ 186 $ 141 $ 127 $ 83 $ 67 $ 143 $ — $ 747 December 31, 2020 2019 2018 2017 2016 Prior Revolving Total Residential Risk rating: Pass $ 373 $ 172 $ 134 $ 101 $ 101 $ 237 $ 93 $ 1,211 Special mention 3 1 1 1 1 3 — 10 Substandard 5 3 3 3 1 10 2 27 Doubtful — — — — — — — — Total $ 381 $ 176 $ 138 $ 105 $ 103 $ 250 $ 95 $ 1,248 December 31, 2020 2019 2018 2017 2016 Prior Revolving Total Auto Risk rating: Pass $ 177 $ 104 $ 39 $ 21 $ 9 $ 2 $ — $ 352 Special mention — — — — — — — — Substandard 1 1 — — — — — 2 Doubtful — — — — — — — — Total $ 178 $ 105 $ 39 $ 21 $ 9 $ 2 $ — $ 354 December 31, 2020 2019 2018 2017 2016 Prior Revolving Total Non-Auto Risk rating: Pass $ 48 $ 21 $ 7 $ 4 $ 1 $ 2 $ 7 $ 90 Special mention — — — — — — — — Substandard — — — — — 1 — 1 Doubtful — — — — — — — — Total $ 48 $ 21 $ 7 $ 4 $ 1 $ 3 $ 7 $ 91 December 31, 2020 2019 2018 2017 2016 Prior Revolving Total Total Loans Risk rating: Pass $ 2,356 $ 804 $ 540 $ 320 $ 273 $ 580 $ 100 $ 4,973 Special mention 20 12 4 14 3 4 — 57 Substandard 42 16 27 16 3 35 2 141 Doubtful — — — — — — — — Total $ 2,418 $ 832 $ 571 $ 350 $ 279 $ 619 $ 102 $ 5,171
Schedule of Internal Ratings of Loans	The following tables summarize the Company’s internal ratings of its loans held-for-investment, March 31, 2020 Pass Special Substandard Doubtful Total Commercial $ 832 $ 25 $ 12 $ — $ 869 Agricultural 92 6 2 — 100 Real Estate 3,106 56 87 — 3,249 Consumer 419 — 2 — 421 Total $ 4,449 $ 87 $ 103 $ — $ 4,639
Schedule of Past Due Loans	The Company’s past due loans are as follows (in thousands): March 31, 2021 15-59 60-89 Greater Total Past Current Total Loans 90 Days Commercial: C&I $ 3,469 $ 283 $ 303 $ 4,055 $ 1,174,071 $ 1,178,126 $ 1 Municipal 19 — — 19 176,930 176,949 — Total Commercial 3,488 283 303 4,074 1,351,001 1,355,075 1 Agricultural 2,535 — — 2,535 87,831 90,366 — Real Estate: Construction & Development 1,810 41 66 1,917 586,011 587,928 — Farm 71 — — 71 161,975 162,046 — Non-Owner 695 — — 695 649,449 650,144 — Owner Occupied CRE 1,847 — — 1,847 758,059 759,906 1 Residential 6,920 67 — 6,987 1,247,740 1,254,727 — Total Real Estate 11,343 108 66 11,517 3,403,234 3,414,751 1 Consumer: Auto 470 31 10 511 369,516 370,027 — Non-Auto 129 11 — 140 92,203 92,343 — Total Consumer 599 42 10 651 461,719 462,370 — Total $ 17,965 $ 433 $ 379 $ 18,777 $ 5,303,785 $ 5,322,562 $ 2 December 31, 2020 15-59 60-89 Greater Total Past Current Total Loans 90 Days Commercial: C&I $ 3,647 $ 406 $ 576 $ 4,629 $ 1,126,753 $ 1,131,382 $ 21 Municipal — — — — 181,325 181,325 — Total Commercial 3,647 406 576 4,629 1,308,078 1,312,707 21 Agricultural 193 95 — 288 94,576 94,864 — Real Estate: Construction & Development 4,775 44 — 4,819 549,140 553,959 — Farm 708 — — 708 151,529 152,237 — Non-Owner 613 — — 613 617,073 617,686 — Owner Occupied CRE 1,393 322 133 1,848 745,126 746,974 — Residential 8,072 18 275 8,365 1,240,044 1,248,409 33 Total Real Estate 15,561 384 408 16,353 3,302,912 3,319,265 33 Consumer: Auto 551 158 75 784 352,811 353,595 59 Non-Auto 214 24 — 238 90,364 90,602 — Total Consumer 765 182 75 1,022 443,175 444,197 59 Total $ 20,166 $ 1,067 $ 1,059 $ 22,292 $ 5,148,741 $ 5,171,033 $ 113 March 31, 2020 15-59 60-89 Greater Total Current Total Loans 90 Days Commercial $ 4,807 $ 388 $ 382 $ 5,577 $ 863,873 $ 869,450 $ 116 Agricultural 621 — 62 683 98,899 99,582 — Real Estate 25,788 742 413 26,943 3,222,306 3,249,249 — Consumer 862 116 102 1,080 420,028 421,108 93 Total $ 32,078 $ 1,246 $ 959 $ 34,283 $ 4,605,106 $ 4,639,389 $ 209 * The Company monitors commercial, agricultural and real estate loans after such loans are 15 days past due. Consumer loans are monitored after such loans are 30 days past due.
Schedule of Loans Modified and Considered Troubled Debt Restructurings	The Company’s loans that were modified and considered troubled debt restructurings are as follows (in thousands): Three-Months Ended March 31, 2021 Pre-Modification Post- Recorded Recorded Number Investment Investment Commercial: C&I 2 $ 149 $ 149 Municipal — — — Total Commercial 2 149 149 Agricultural — — — Real Estate: Construction & Development — — — Farm — — — Non-Owner — — — Owner Occupied CRE 1 500 500 Residential 2 197 197 Total Real Estate 3 697 697 Consumer: Auto — — — Non-Auto — — — Total Consumer — — — Total 5 $ 846 $ 846 Three-Months Ended March 31, 2020 Pre-Modification Post- Recorded Recorded Number Investment Investment Commercial 5 $ 288 $ 288 Agricultural 1 134 134 Real Estate — — — Consumer 1 14 14 Total 7 $ 436 $ 436
Schedule of How Loans Were Modified as Troubled Debt Restructured Loans	The balances below provide information as to how the loans were modified as troubled debt restructured loans (in thousands): Three-Months Ended March 31, 2021 Adjusted Combined Interest Extended Rate and Rate Maturity Maturity Commercial: C&I $ — $ — $ 149 Municipal — — — Total Commercial — — 149 Agricultural — — — Real Estate: Construction & Development — — — Farm — — — Non-Owner — — — Owner Occupied CRE — — 500 Residential — — 197 Total Real Estate — — 697 Consumer: Auto — — — Non-Auto — — — Total Consumer — — — Total $ — $ — $ 846 Three-Months Ended March 31, 2020 Adjusted Extended Combined Commercial $ — $ 260 $ 28 Agricultural — 134 — Real Estate — — — Consumer — 14 — Total $ — $ 408 $ 28

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Summary of Outstanding Notional Balances and Fair Values of Outstanding Derivative Positions	The following table provides the outstanding notional balances and fair values of outstanding derivative positions (in thousands): March 31, 2021: Outstanding Asset Liability IRLCs $ 180,596 $ 1,645 $ — Forward mortgage-backed securities trades 317,500 2,806 — March 31, 2020: Outstanding Asset Liability IRLCs $ 187,747 $ 296 $ — Forward mortgage-backed securities trades 198,000 — 3,200 December 31, 2020: Outstanding Asset Liability IRLCs $ 202,906 $ 4,618 $ — Forward mortgage-backed securities trades 198,000 — 1,560

Borrowings (Tables)

Borrowings (Tables)	3 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Schedule of Borrowings	Borrowings consisted of the following (dollars in thousands): March 31, December 31, 2021 2020 2020 Securities sold under agreements with customers to repurchase $ 523,254 $ 410,146 $ 412,743 Federal funds purchased 25,350 1,725 17,350 Advances from Federal Home Loan Bank of Dallas — 446,000 — Total $ 548,604 $ 857,871 $ 430,093

Stock Option Plan and Restric_2

Stock Option Plan and Restricted Stock Plan (Tables)	3 Months Ended
	Mar. 31, 2021
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Analysis of Stock Option Activity	An analysis of stock option activity for the quarter-ended March 31, 2021 is presented in the table and narrative below: Shares Weighted- Outstanding, December 31, 2020 1,833,057 $ 20.85 Granted — — Exercised (124,524 ) 16.35 Cancelled (14,100 ) 24.60 Outstanding, March 31, 2021 1,694,433 21.15 Exercisable, March 31, 2021 764,953 $ 17.36
Summary of Vested and Unvested Restricted Stock Outstanding	The following table summarized information about vested and unvested restricted stock outstanding at March 31, 2021 and 2020, respectively. For the three-months ended March 31, 2021 2020 Restricted Weighted Restricted Weighted Balance at beginning of period 95,888 $ 29.89 105,309 $ 29.93 Grants — — 3,413 34.55 Vesting (993 ) 34.55 — — Forfeited/expired (479 ) 34.55 — — Balance at end of period 94,416 $ 29.82 108,722 $ 30.08

Fair Value Disclosures (Tables)

Fair Value Disclosures (Tables)	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Financial Assets and Financial Liabilities Measured at Fair Value on Recurring Basis	The following table summarizes the Company’s available-for-sale held-for-sale, March 31, 2021 Level 1 Level 2 Level 3 Total Fair Available-for-sale Obligations of states and political subdivisions $ — $ 2,517,017 $ — $ 2,517,017 Corporate bonds — 32,490 — 32,490 Residential mortgage-backed securities — 2,108,594 — 2,108,594 Commercial mortgage-backed securities — 447,053 — 447,053 Other securities 4,477 — — 4,477 Total $ 4,477 $ 5,105,154 $ — $ 5,109,631 Loans held-for-sale $ — $ 61,511 $ — $ 61,511 IRLCs $ — $ 1,645 $ — $ 1,645 Forward mortgage-backed securities trades asset $ — $ 2,806 $ — $ 2,806 March 31, 2020 Level 1 Level 2 Level 3 Total Fair Available-for-sale U.S. Treasury securities $ 10,113 $ — $ — $ 10,113 Obligations of states and political subdivisions — 1,807,671 — 1,807,671 Corporate bonds — 220 — 220 Residential mortgage-backed securities — 1,679,980 — 1,679,980 Commercial mortgage-backed securities — 604,554 — 604,554 Other securities 4,531 — — 4,531 Total $ 14,644 $ 4,092,425 $ — $ 4,107,069 Loans held-for-sale $ — $ 39,659 $ — $ 39,659 IRLCs $ — $ 296 $ — $ 296 Forward mortgage-backed securities trades liability $ — $ (3,200 ) $ — $ (3,200 ) December 31, 2020 Level 1 Level 2 Level 3 Total Fair Available-for-sale Obligations of state and political subdivisions $ — $ 2,426,876 $ — $ 2,426,876 Residential mortgage-backed securities — 1,472,280 — 1,472,280 Commercial mortgage-backed securities — 489,316 — 489,316 Other securities 4,557 — — 4,557 Total $ 4,557 $ 4,388,472 $ — $ 4,393,029 Loans held-for-sale $ — $ 79,585 $ — $ 79,585 IRLCs $ — $ 4,618 $ — $ 4,618 Forward mortgage-backed securities trades liability $ — $ (1,560 ) $ — $ (1,560 )
Summary of Loans Held-for-Sale at Fair Value	The following table summarizes the Company’s loans held-for-sale March 31, December 31, 2021 2020 2020 Unpaid principal balance on loans held-for-sale $ 60,727 $ 38,563 $ 76,602 Net unrealized gains on loans held-for-sale 784 1,096 2,983 Loans held-for-sale $ 61,511 $ 39,659 $ 79,585
Summary of Gain Loss on Sale of Mortgage Loans	The following table summarizes the Company’s gains on sale and fees of mortgage loans for the three-months ended March 31, 2021 and 2020 (in thousand): Three-Months ended 2021 2020 Realized gain on sale and fees on mortgage loans* $ 10,728 $ 4,545 Change in fair value on loans held-for-sale (5,200 ) 2,355 Change in forward mortgage-backed securities trades 4,366 (3,048 ) Total gain on sale of mortgage loans $ 9,894 $ 3,852 * This includes gains on loans held-for-sale
Schedule of Estimated Fair Values and Carrying Values of All Financial Instruments	The estimated fair values and carrying values of all financial instruments under current authoritative guidance were as follows (in thousands). March 31, December 31, 2021 2020 2020 Carrying Estimated Carrying Estimated Carrying Estimated Fair Value Value Fair Value Value Fair Value Value Fair Value Hierarchy Cash and due from banks $ 190,350 $ 190,350 $ 191,486 $ 191,486 $ 211,113 $ 211,113 Level 1 Interest-bearing demand deposits in banks 893,221 893,221 76,378 76,378 517,971 517,971 Level 1 Available-for-sale 5,109,631 5,109,631 4,107,069 4,107,069 4,393,029 4,393,029 Levels 1 and 2 Loans held-for-investment, 5,259,588 5,273,235 4,578,949 4,558,577 5,104,499 5,109,885 Level 3 Loans held-for-sale 65,405 65,273 42,034 41,593 83,969 84,233 Level 2 Accrued interest receivable 42,322 42,322 34,329 34,329 53,433 53,433 Level 2 Deposits with stated maturities 483,685 485,193 465,808 467,804 475,542 477,218 Level 2 Deposits with no stated maturities 8,929,762 8,929,762 6,744,658 6,744,658 8,200,275 8,200,275 Level 1 Borrowings 548,604 548,604 857,871 857,871 430,093 430,093 Level 2 Accrued interest payable 320 320 783 783 377 377 Level 2 IRLCs 1,645 1,645 296 296 4,618 4,618 Level 2 Forward mortgage-backed securi-ties trades asset (liability) 2,806 2,806 (3,200 ) (3,200 ) (1,560 ) (1,560 ) Level 2

Acquisition (Tables)

Acquisition (Tables)	3 Months Ended
	Mar. 31, 2021
Schedule of Preliminary Estimated Fair Value Amounts Assigned to Major Asset and Liability Categories at Acquisition Date	The following table presents the final amounts recorded on the consolidated balance sheet on the acquisition date (dollars in thousands): Fair value of consideration paid: Common stock issued (6,275,574 shares) $ 220,273 Fair value of identifiable assets acquired: Cash and cash equivalents $ 61,028 Securities available-for-sale 93,967 Loans 447,702 Identifiable intangible assets 4,798 Other assets 25,377 Total identifiable assets acquired $ 632,872 Fair value of liabilities assumed: Deposits $ 549,125 Other liabilities 5,397 Total liabilities assumed $ 554,522 Fair value of net identifiable assets acquired 78,350 Goodwill resulting from acquisition $ 141,923

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail)	May 05, 2021USD ($)	Mar. 31, 2021USD ($)Locationshares	Mar. 31, 2020USD ($)shares	Dec. 31, 2020USD ($)	Sep. 30, 2020shares	Mar. 27, 2020USD ($)	Mar. 12, 2020shares	Jan. 01, 2020
Equity, Class of Treasury Stock [Line Items]
Number of locations | Location		78
Minimum number of shares that company is required to repurchase | shares		0
Minimum number of days to consider the loans as non-accrual		90 days
Impairment recorded		$ 0	$ 0
Other identifiable intangible assets, amortized period (years)		7 years
Securities sold under agreements to repurchase maturity range (in days)		one to four days
Interest-bearing time deposits, maturity period (in days)		90 days or less
Unrealized net gains in available-for-sale securities, included in accumulated other comprehensive income		$ 117,009,000	123,576,000	$ 170,395,000
Retained earnings net of tax after transitional charges		$ 875,147,000	$ 727,828,000	836,729,000		$ 466,000
First financial antidilutive securities excluded from eps computation | shares		0	0
Allowance for Credit Losses [Member]
Equity, Class of Treasury Stock [Line Items]
Increase (decrease) in valuation and qualifying accounts and reserves from adjustment				619,000
Reserve for Unfunded Commitments [Member]
Equity, Class of Treasury Stock [Line Items]
Increase (decrease) in valuation and qualifying accounts and reserves from adjustment				1,208,000
Common Stock [Member]
Equity, Class of Treasury Stock [Line Items]
Shares repurchased under stock repurchase authorization, shares | shares		324,802
Cumulative Effect, Period of Adoption, Adjustment [Member]
Equity, Class of Treasury Stock [Line Items]
Retained earnings net of tax after transitional charges						$ 589,000
Subsequent Event [Member]
Equity, Class of Treasury Stock [Line Items]
Treasury Stock, Value, Acquired	$ 8,008,000
Commitments to Extend Credit [Member]
Equity, Class of Treasury Stock [Line Items]
Reserve for unfunded commitments		$ 6,918,000	$ 809,000	5,486,000
Held-to-maturity Securities [Member]
Equity, Class of Treasury Stock [Line Items]
Securities held to maturity		$ 0	$ 0	$ 0
Commercial Bancshares Inc and Commercial State Bank [Member]
Equity, Class of Treasury Stock [Line Items]
Percentage of common stock acquired								100.00%
Maximum [Member]
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, number of shares authorized to be repurchased | shares					2,000,000		4,000,000

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Computation of Basic EPS to Dilutive EPS (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share [Abstract]
Net earnings per share, basic, Net Earnings	$ 56,918	$ 37,232
Effect of stock options and stock grants, Net Earnings	0	0
Net earnings per share, diluted, Net Earnings	$ 56,918	$ 37,232
Net earnings per share, basic, Weighted Average Shares	142,146,275	142,118,864
Effect of stock options and stock grants, Weighted Average Shares	856,383	616,344
Net earnings per share, diluted, Weighted Average Shares	143,002,658	142,735,208
Net earnings per share, basic, Per Share Amount	$ 0.40	$ 0.26
Effect of stock options and stock grants, Per Share Amount	0	0
Net earnings per share, diluted, Per Share Amount	$ 0.40	$ 0.26

Securities - Additional Informa

Securities - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2021USD ($)Investment	Mar. 31, 2020USD ($)
Interest Bearing Time Deposits In Banks And Securities [Line Items]
Interest-bearing time deposits, maturity period, years	12 months
Number of investment positions | Investment	149
Securities pledged as collateral	$ 3,103,077,000
Sales of investment securities available-for-sale	10,631,000	$ 95,437,000
Gross realized gains from security sales	808,000	2,062,000
Gross realized losses from security sales or calls	$ 0	$ 0
Obligations of State and Political Subdivisions [Member] | Texas [Member]
Interest Bearing Time Deposits In Banks And Securities [Line Items]
Percentage of securities guaranteed by Texas Permanent School Fund	52.70%
Obligations of State and Political Subdivisions [Member] | Texas [Member] | Available-for-Sale Securities [Member] | Geographic Concentration Risk [Member]
Interest Bearing Time Deposits In Banks And Securities [Line Items]
Concentration risk, percentage	77.27%

Securities - Summary of Availab

Securities - Summary of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	$ 4,961,438	$ 4,177,179	$ 3,950,510
Securities available-for-sale, Gross Unrealized Holding Gains	166,558	216,048	159,486
Securities available-for-sale, Gross Unrealized Holding Losses	(18,365)	(198)	(2,927)
Securities available-for-sale, Estimated Fair Value	5,109,631	4,393,029	4,107,069
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total			10,039
Securities available-for-sale, Gross Unrealized Holding Gains			74
Securities available-for-sale, Estimated Fair Value			10,113
Obligations of State and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	2,418,227	2,283,616	1,731,392
Securities available-for-sale, Gross Unrealized Holding Gains	106,988	143,339	78,996
Securities available-for-sale, Gross Unrealized Holding Losses	(8,198)	(79)	(2,717)
Securities available-for-sale, Estimated Fair Value	2,517,017	2,426,876	1,807,671
Corporate Bonds and Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	38,427	4,398	4,624
Securities available-for-sale, Gross Unrealized Holding Gains	79	159	133
Securities available-for-sale, Gross Unrealized Holding Losses	(1,539)		(6)
Securities available-for-sale, Estimated Fair Value	36,967	4,557	4,751
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	2,073,647	1,421,922	1,617,341
Securities available-for-sale, Gross Unrealized Holding Gains	43,575	50,473	62,659
Securities available-for-sale, Gross Unrealized Holding Losses	(8,628)	(115)	(20)
Securities available-for-sale, Estimated Fair Value	2,108,594	1,472,280	1,679,980
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	431,137	467,243	587,114
Securities available-for-sale, Gross Unrealized Holding Gains	15,916	22,077	17,624
Securities available-for-sale, Gross Unrealized Holding Losses		(4)	(184)
Securities available-for-sale, Estimated Fair Value	$ 447,053	$ 489,316	$ 604,554

Securities - Amortized Cost and

Securities - Amortized Cost and Estimated Fair Value of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Available-for-Sale, Amortized Cost Basis, Due within one year	$ 290,536
Available-for-Sale, Amortized Cost Basis, Due after one year through five years	2,355,100
Available-for-Sale, Amortized Cost Basis, Due after five years through ten years	2,145,293
Available-for-Sale, Amortized Cost Basis, Due after ten years	170,509
Available-for-Sale, Amortized Cost Basis, Total	4,961,438	$ 4,177,179	$ 3,950,510
Available-for-Sale, Estimated Fair Value, Due within one year	295,145
Available-for-Sale, Estimated Fair Value, Due after one year through five years	2,456,956
Available-for-Sale, Estimated Fair Value, Due after five years through ten years	2,188,324
Available-for-Sale, Estimated Fair Value, Due after ten years	169,206
Securities available-for-sale, Estimated Fair Value, Total	$ 5,109,631	$ 4,393,029	$ 4,107,069

Securities - Continuous Unreali

Securities - Continuous Unrealized-Loss Position of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Fair Value	$ 1,155,527	$ 77,449	$ 213,670
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	18,355	179	2,896
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	999	3,156	17,794
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	10	19	31
Available-for-sale securities, continuous unrealized loss position, Fair Value	1,156,526	80,605	231,464
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	18,365	198	2,927
Obligations of State and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Fair Value	533,213	25,214	168,725
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	8,198	79	2,717
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	0	0	0
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	0	0	0
Available-for-sale securities, continuous unrealized loss position, Fair Value	533,213		168,725
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	8,198	79	2,717
Corporate Bonds and Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Fair Value	32,490		220
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	1,539		6
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	0		0
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	0		0
Available-for-sale securities, continuous unrealized loss position, Fair Value	32,490		220
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	1,539		6
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Fair Value	589,353	36,017	1
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	8,618	96	0
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	999	3,156	8,164
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	10	19	21
Available-for-sale securities, continuous unrealized loss position, Fair Value	590,352	39,173	8,165
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	8,628	115	21
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Fair Value	471	16,218	44,724
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	0	4	173
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	0	0	9,630
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	0	0	10
Available-for-sale securities, continuous unrealized loss position, Fair Value	471	16,218	54,354
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	$ 0	$ 4	$ 183

Loans Held for Investment and_3

Loans Held for Investment and Allowance for Loan Losses - Loans Held-for-Investment by Class of Financing Receivables (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	$ 5,322,562	$ 5,171,033	$ 4,639,389
Less: Allowance for credit losses	(62,974)	(66,534)	(60,440)	$ (52,499)
Net loans held for investment	5,259,588	5,104,499	4,578,949
C&I [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	1,178,126	1,131,382
Less: Allowance for credit losses	(12,323)	(13,609)
Municipal [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	176,949	181,325
Less: Allowance for credit losses	(2,191)	(1,552)
Construction & Development [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	587,928	553,959
Less: Allowance for credit losses	(13,246)	(13,512)
Farm [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	162,046	152,237
Less: Allowance for credit losses	(1,223)	(1,876)
Non-Owner Occupied CRE [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	650,144	617,686
Less: Allowance for credit losses	(9,492)	(8,391)
Owner Occupied CRE [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	759,906	746,974
Less: Allowance for credit losses	(9,878)	(12,347)
Residential [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	1,254,727	1,248,409
Less: Allowance for credit losses	(11,189)	(12,601)
Auto [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	370,027	353,595
Less: Allowance for credit losses	(1,068)	(1,020)
Non-Auto [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	92,343	90,602
Less: Allowance for credit losses	(379)	(371)
Commercial [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	1,355,075	1,312,707	869,450
Less: Allowance for credit losses			(11,773)	(12,122)
Commercial [Member] | C&I [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	1,178,126	1,131,382
Commercial [Member] | Municipal [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	176,949	181,325
Agriculture [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	90,366	94,864	99,582
Less: Allowance for credit losses	(1,985)	(1,255)	(2,154)	(1,206)
Real Estate [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	3,414,751	3,319,265	3,249,249
Less: Allowance for credit losses			(41,256)	(33,974)
Real Estate [Member] | Construction & Development [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	587,928	553,959
Real Estate [Member] | Farm [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	162,046	152,237
Real Estate [Member] | Non-Owner Occupied CRE [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	650,144	617,686
Real Estate [Member] | Owner Occupied CRE [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	759,906	746,974
Real Estate [Member] | Residential [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	1,254,727	1,248,409
Consumer [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	462,370	444,197	421,108
Less: Allowance for credit losses			$ (5,257)	$ (5,197)
Consumer [Member] | Auto [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	370,027	353,595
Consumer [Member] | Non-Auto [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	$ 92,343	$ 90,602

Loans Held for Investment and_4

Loans Held for Investment and Allowance for Loan Losses - Non-Accrual Loans, Loans Still Accruing and Past Due 90 Days or More and Restructured Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Receivables [Abstract]
Non-accrual loans	$ 39,333	$ 42,619	$ 39,226
Loans still accruing and past due 90 days or more	2	113	209
Troubled debt restructured loans still accruing	23	24	26
Total	$ 39,358	$ 42,756	$ 39,461

Loans Held for Investment and_5

Loans Held for Investment and Allowance for Loan Losses - Non-Accrual Loans, Loans Still Accruing and Past Due 90 Days or More and Restructured Loans (Parenthetical) (Detail) - USD ($)	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Loans and Leases Receivable Disclosure [Line Items]
Troubled debt restructured loans still accruing	$ 23,000	$ 24,000	$ 26,000
Doubtful [Member]
Loans and Leases Receivable Disclosure [Line Items]
Troubled debt restructured loans still accruing	$ 6,619,000	$ 7,407,000	$ 4,733,000

Loans Held for Investment and_6

Loans Held for Investment and Allowance for Loan Losses - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual, past due 90 days or more and still accruing, restructured loans and foreclosed assets	$ 39,658,000	$ 40,444,000	$ 42,898,000
Additional funds advanced in connection with impaired loans	$ 0
Default for purposes of this disclosure is a troubled debt restructured loan	90 days
Commitments to lend additional funds to borrowers with loan that have been modified as TDRs	$ 0
Loans held by subsidiaries subject to blanket liens	3,252,192,000
Unfunded loan commitments	6,918,000	809,000	$ 5,486,000
Provision for loan losses	(3,429,000)	$ 9,850,000
Unfunded Loan Commitment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for loan losses	$ 1,432,000

Loans Held for Investment and_7

Loans Held for Investment and Allowance for Loan Losses - Schedule of Non-Accrual Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	$ 39,333	$ 42,619	$ 39,226
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	4,709	5,015	5,620
Commercial [Member] | C&I [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	4,709	5,015
Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	1,068	1,076	1,128
Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	33,164	36,028	32,156
Real Estate [Member] | Construction & Development [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	1,296	3,838
Real Estate [Member] | Farm [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	6,859	7,299
Real Estate [Member] | Non-Owner Occupied CRE [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	7,088	5,243
Real Estate [Member] | Owner Occupied CRE [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	9,557	10,797
Real Estate [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	8,364	8,851
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	392	500	$ 322
Consumer [Member] | Auto [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	317	407
Consumer [Member] | Non-Auto [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	$ 75	$ 93

Loans Held for Investment and_8

Loans Held for Investment and Allowance for Loan Losses - Changes in Allowance for Loan Losses (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 66,534,000	$ 52,499,000
Provision for loan losses	(3,429,000)	9,850,000
Recoveries	443,000	318,000
Charge-offs	(574,000)	(2,227,000)
Ending balance	62,974,000	60,440,000
C&I [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	13,609,000
Provision for loan losses	(1,239,000)
Recoveries	223,000
Charge-offs	(270,000)
Ending balance	12,323,000
Municipal [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,552,000
Provision for loan losses	639,000
Recoveries	0
Charge-offs	0
Ending balance	2,191,000
Construction & Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	13,512,000
Provision for loan losses	(268,000)
Recoveries	2,000
Charge-offs	0
Ending balance	13,246,000
Farm [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,876,000
Provision for loan losses	(662,000)
Recoveries	9,000
Charge-offs	0
Ending balance	1,223,000
Non-Owner Occupied CRE [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	8,391,000
Provision for loan losses	1,052,000
Recoveries	55,000
Charge-offs	(6,000)
Ending balance	9,492,000
Owner Occupied CRE [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	12,347,000
Provision for loan losses	(2,467,000)
Recoveries	6,000
Charge-offs	(8,000)
Ending balance	9,878,000
Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	12,601,000
Provision for loan losses	(1,384,000)
Recoveries	19,000
Charge-offs	(47,000)
Ending balance	11,189,000
Auto [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,020,000
Provision for loan losses	141,000
Recoveries	73,000
Charge-offs	(166,000)
Ending balance	1,068,000
Non-Auto [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	371,000
Provision for loan losses	38,000
Recoveries	47,000
Charge-offs	(77,000)
Ending balance	379,000
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance		12,122,000
Provision for loan losses		794,000
Recoveries		149,000
Charge-offs		(1,292,000)
Ending balance		11,773,000
Agriculture [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,255,000	1,206,000
Provision for loan losses	721,000	949,000
Recoveries	9,000	1,000
Charge-offs	0	(2,000)
Ending balance	$ 1,985,000	2,154,000
Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance		33,974,000
Provision for loan losses		7,921,000
Recoveries		76,000
Charge-offs		(715,000)
Ending balance		41,256,000
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance		5,197,000
Provision for loan losses		186,000
Recoveries		92,000
Charge-offs		(218,000)
Ending balance		$ 5,257,000

Loans Held for Investment and_9

Loans Held for Investment and Allowance for Loan Losses - Schedule of loans that are individually evaluated for credit losses (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	$ 53,284
Recorded Investment With No Allowance	11,120
Recorded Investment With Allowance	28,106
Total Recorded Investment	39,226	$ 190,416	$ 197,451
Related Allowance	3,386	18,573	20,637
Average Recorded Investment	44,634
Collateral Pledged [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Allowance		21,964	21,439
Recorded Investment With Allowance		17,369	21,180
Related Allowance		2,952	3,419
Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		151,083	154,832
Related Allowance		15,621	17,218
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	7,300
Recorded Investment With No Allowance	992
Recorded Investment With Allowance	4,628
Total Recorded Investment	5,620	29,066	40,083
Related Allowance	1,271	5,417	6,826
Average Recorded Investment	6,409
Commercial [Member] | Collateral Pledged [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Allowance		1,806	1,544
Recorded Investment With Allowance		2,903	3,471
Related Allowance		777	799
Commercial [Member] | Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		24,357	35,068
Related Allowance		4,640	6,027
Commercial [Member] | C&I [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		19,289	30,644
Related Allowance		3,881	5,391
Commercial [Member] | C&I [Member] | Collateral Pledged [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Allowance		1,806	1,544
Recorded Investment With Allowance		2,903	3,471
Related Allowance		777	799
Commercial [Member] | C&I [Member] | Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		14,580	25,629
Related Allowance		3,104	4,592
Commercial [Member] | Municipal [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		9,777	9,439
Related Allowance		1,536	1,435
Commercial [Member] | Municipal [Member] | Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		9,777	9,439
Related Allowance		1,536	1,435
Agriculture [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	1,340
Recorded Investment With No Allowance	632
Recorded Investment With Allowance	496
Total Recorded Investment	1,128	6,859	6,648
Related Allowance	98	1,790	982
Average Recorded Investment	1,200
Agriculture [Member] | Collateral Pledged [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Allowance		457	470
Recorded Investment With Allowance		612	606
Related Allowance		170	96
Agriculture [Member] | Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		5,790	5,572
Related Allowance		1,620	886
Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	44,208
Recorded Investment With No Allowance	9,496
Recorded Investment With Allowance	22,660
Total Recorded Investment	32,156	152,324	148,256
Related Allowance	2,016	11,359	12,821
Average Recorded Investment	36,683
Real Estate [Member] | Collateral Pledged [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Allowance		19,701	19,425
Recorded Investment With Allowance		13,462	16,602
Related Allowance		2,004	2,522
Real Estate [Member] | Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		119,161	112,229
Related Allowance		9,355	10,299
Real Estate [Member] | Construction & Development [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		12,497	15,205
Related Allowance		880	652
Real Estate [Member] | Construction & Development [Member] | Collateral Pledged [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Allowance		1,124	1,176
Recorded Investment With Allowance		171	2,661
Related Allowance		12	35
Real Estate [Member] | Construction & Development [Member] | Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		11,202	11,368
Related Allowance		868	617
Real Estate [Member] | Farm [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		10,295	10,648
Related Allowance		671	1,312
Real Estate [Member] | Farm [Member] | Collateral Pledged [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Allowance		2,241	2,614
Recorded Investment With Allowance		4,618	4,685
Related Allowance		590	654
Real Estate [Member] | Farm [Member] | Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		3,436	3,349
Related Allowance		81	658
Real Estate [Member] | Non-Owner Occupied CRE [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		39,387	22,626
Related Allowance		3,335	1,921
Real Estate [Member] | Non-Owner Occupied CRE [Member] | Collateral Pledged [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Allowance		6,045	4,009
Recorded Investment With Allowance		1,043	1,234
Related Allowance		226	500
Real Estate [Member] | Non-Owner Occupied CRE [Member] | Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		32,299	17,383
Related Allowance		3,109	1,421
Real Estate [Member] | Owner Occupied CRE [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		55,450	62,730
Related Allowance		3,599	5,829
Real Estate [Member] | Owner Occupied CRE [Member] | Collateral Pledged [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Allowance		6,081	7,279
Recorded Investment With Allowance		3,476	3,518
Related Allowance		599	657
Real Estate [Member] | Owner Occupied CRE [Member] | Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		45,893	51,933
Related Allowance		3,000	5,172
Real Estate [Member] | Residential [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		34,695	37,047
Related Allowance		2,874	3,107
Real Estate [Member] | Residential [Member] | Collateral Pledged [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Allowance		4,210	4,347
Recorded Investment With Allowance		4,154	4,504
Related Allowance		577	676
Real Estate [Member] | Residential [Member] | Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		26,331	28,196
Related Allowance		2,297	2,431
Consumer [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	436
Recorded Investment With Allowance	322
Total Recorded Investment	322	2,167	2,464
Related Allowance	1	7	8
Average Recorded Investment	$ 342
Consumer [Member] | Collateral Pledged [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With Allowance		392	501
Related Allowance		1	2
Consumer [Member] | Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		1,775	1,963
Related Allowance		6	6
Consumer [Member] | Auto [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		1,716	1,930
Related Allowance		5	6
Consumer [Member] | Auto [Member] | Collateral Pledged [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With Allowance		317	407
Related Allowance		1	1
Consumer [Member] | Auto [Member] | Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		1,399	1,523
Related Allowance		4	5
Consumer [Member] | Non-Auto [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		451	534
Related Allowance		2	2
Consumer [Member] | Non-Auto [Member] | Collateral Pledged [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With Allowance		75	94
Related Allowance			1
Consumer [Member] | Non-Auto [Member] | Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		376	440
Related Allowance		$ 2	$ 1

Loans Held for Investment an_10

Loans Held for Investment and Allowance for Loan Losses - Schedule of Allowance for Loan Losses by Portfolio Segment (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for credit losses	$ 18,573	$ 20,637	$ 3,386
Loans collectively evaluated for credit losses	44,401	45,897	57,054
Total allowance for loan losses	62,974	66,534	60,440	$ 52,499
C&I [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for credit losses	3,881	5,391
Loans collectively evaluated for credit losses	8,442	8,218
Total allowance for loan losses	12,323	13,609
Municipal [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for credit losses	1,536	1,435
Loans collectively evaluated for credit losses	655	117
Total allowance for loan losses	2,191	1,552
Agriculture [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for credit losses	1,790	982
Loans collectively evaluated for credit losses	195	273
Total allowance for loan losses	1,985	1,255
Construction & Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for credit losses	880	652
Loans collectively evaluated for credit losses	12,366	12,860
Total allowance for loan losses	13,246	13,512
Farm [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for credit losses	671	1,312
Loans collectively evaluated for credit losses	552	564
Total allowance for loan losses	1,223	1,876
Non-Owner Occupied CRE [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for credit losses	3,335	1,921
Loans collectively evaluated for credit losses	6,157	6,470
Total allowance for loan losses	9,492	8,391
Owner Occupied CRE [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for credit losses	3,599	5,829
Loans collectively evaluated for credit losses	6,279	6,518
Total allowance for loan losses	9,878	12,347
Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for credit losses	2,874	3,107
Loans collectively evaluated for credit losses	8,315	9,494
Total allowance for loan losses	11,189	12,601
Auto [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for credit losses	5	6
Loans collectively evaluated for credit losses	1,063	1,014
Total allowance for loan losses	1,068	1,020
Non-Auto [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for credit losses	2	2
Loans collectively evaluated for credit losses	377	369
Total allowance for loan losses	379	371
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for credit losses			1,271
Loans collectively evaluated for credit losses			10,502
Total allowance for loan losses			11,773	12,122
Agriculture [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for credit losses			98
Loans collectively evaluated for credit losses			2,056
Total allowance for loan losses	$ 1,985	$ 1,255	2,154	1,206
Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for credit losses			2,016
Loans collectively evaluated for credit losses			39,240
Total allowance for loan losses			41,256	33,974
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for credit losses			1
Loans collectively evaluated for credit losses			5,256
Total allowance for loan losses			$ 5,257	$ 5,197

Loans Held for Investment an_11

Loans Held for Investment and Allowance for Loan Losses - Schedule of Investment in Loans Related to Balance in Allowance for Loan Losses on Basis of Company's Impairment Methodology (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	$ 190,416	$ 197,451	$ 39,226
Loan collectively evaluated for impairment	5,132,146	4,973,582	4,600,163
Total	5,322,562	5,171,033	4,639,389
C&I [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	19,289	30,644
Loan collectively evaluated for impairment	1,158,837	1,100,738
Total	1,178,126	1,131,382
Municipal [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	9,777	9,439
Loan collectively evaluated for impairment	167,172	171,886
Total	176,949	181,325
Agriculture [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	6,859	6,648
Loan collectively evaluated for impairment	83,507	88,216
Total	90,366	94,864
Construction & Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	12,497	15,205
Loan collectively evaluated for impairment	575,431	538,754
Total	587,928	553,959
Farm [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	10,295	10,648
Loan collectively evaluated for impairment	151,751	141,589
Total	162,046	152,237
Non-Owner Occupied CRE [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	39,387	22,626
Loan collectively evaluated for impairment	610,757	595,060
Total	650,144	617,686
Owner Occupied CRE [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	55,450	62,730
Loan collectively evaluated for impairment	704,456	684,244
Total	759,906	746,974
Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	34,695	37,047
Loan collectively evaluated for impairment	1,220,032	1,211,362
Total	1,254,727	1,248,409
Auto [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	1,716	1,930
Loan collectively evaluated for impairment	368,311	351,665
Total	370,027	353,595
Non-Auto [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	451	534
Loan collectively evaluated for impairment	91,892	90,068
Total	92,343	90,602
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment			5,620
Loan collectively evaluated for impairment			863,830
Total	1,355,075	1,312,707	869,450
Commercial [Member] | C&I [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	1,178,126	1,131,382
Commercial [Member] | Municipal [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	176,949	181,325
Agriculture [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment			1,128
Loan collectively evaluated for impairment			98,454
Total	90,366	94,864	99,582
Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment			32,156
Loan collectively evaluated for impairment			3,217,093
Total	3,414,751	3,319,265	3,249,249
Real Estate [Member] | Construction & Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	587,928	553,959
Real Estate [Member] | Farm [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	162,046	152,237
Real Estate [Member] | Non-Owner Occupied CRE [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	650,144	617,686
Real Estate [Member] | Owner Occupied CRE [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	759,906	746,974
Real Estate [Member] | Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	1,254,727	1,248,409
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment			322
Loan collectively evaluated for impairment			420,786
Total	462,370	444,197	$ 421,108
Consumer [Member] | Auto [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	370,027	353,595
Consumer [Member] | Non-Auto [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	$ 92,343	$ 90,602

Loans Held-for-Investment and A

Loans Held-for-Investment and Allowance for Loan Losses - Schedule of Company's Internal Ratings of its Loans Held-for-Investment, Including The Year of Origination, by Portfolio Segments (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
2021	$ 754,000	$ 2,418,000
2020	2,070,000	832,000
2019	729,000	571,000
2018	510,000	350,000
2017	321,000	279,000
Prior	837,000	619,000
Revolving Loans Amort Cost Basis	102,000	102,000
Total	5,323,000	5,171,000
C&I [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	306,000	895,000
2020	656,000	107,000
2019	86,000	74,000
2018	64,000	29,000
2017	26,000	10,000
Prior	41,000	16,000
Total	1,179,000	1,131,000
Municipal [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	2,000	28,000
2020	23,000	19,000
2019	16,000	29,000
2018	23,000	19,000
2017	19,000	14,000
Prior	94,000	72,000
Total	177,000	181,000
Agriculture [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	16,000	63,000
2020	47,000	19,000
2019	16,000	9,000
2018	7,000	3,000
2017	3,000	1,000
Prior	1,000
Total	90,000	95,000
Construction & Development [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	102,000	377,000
2020	352,000	102,000
2019	67,000	36,000
2018	35,000	22,000
2017	17,000	7,000
Prior	15,000	10,000
Total	588,000	554,000
Farm [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	20,000	64,000
2020	61,000	23,000
2019	22,000	18,000
2018	18,000	12,000
2017	10,000	11,000
Prior	31,000	24,000
Total	162,000	152,000
Non-Owner Occupied CRE [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	45,000	198,000
2020	199,000	119,000
2019	120,000	94,000
2018	87,000	52,000
2017	51,000	56,000
Prior	148,000	99,000
Total	650,000	618,000
Owner Occupied CRE [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	75,000	186,000
2020	176,000	141,000
2019	134,000	127,000
2018	114,000	83,000
2017	80,000	67,000
Prior	181,000	143,000
Total	760,000	747,000
Residential [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	110,000	381,000
2020	354,000	176,000
2019	160,000	138,000
2018	124,000	105,000
2017	96,000	103,000
Prior	316,000	250,000
Revolving Loans Amort Cost Basis	95,000	95,000
Total	1,255,000	1,248,000
Auto [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	61,000	178,000
2020	162,000	105,000
2019	91,000	39,000
2018	32,000	21,000
2017	16,000	9,000
Prior	8,000	2,000
Total	370,000	354,000
Non-Auto [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	17,000	48,000
2020	40,000	21,000
2019	17,000	7,000
2018	6,000	4,000
2017	3,000	1,000
Prior	2,000	3,000
Revolving Loans Amort Cost Basis	7,000	7,000
Total	92,000	91,000
Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	747,000	2,356,000
2020	2,024,000	804,000
2019	694,000	540,000
2018	482,000	320,000
2017	291,000	273,000
Prior	794,000	580,000
Revolving Loans Amort Cost Basis	101,000	100,000
Total	5,133,000	4,973,000
Pass [Member] | C&I [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	303,000	874,000
2020	647,000	101,000
2019	84,000	70,000
2018	61,000	28,000
2017	24,000	10,000
Prior	41,000	16,000
Total	1,160,000	1,099,000
Pass [Member] | Municipal [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	2,000	26,000
2020	21,000	19,000
2019	16,000	29,000
2018	23,000	14,000
2017	13,000	13,000
Prior	92,000	71,000
Total	167,000	172,000
Pass [Member] | Agriculture [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	15,000	57,000
2020	42,000	19,000
2019	16,000	9,000
2018	7,000	3,000
2017	2,000	1,000
Prior	1,000
Total	83,000	89,000
Pass [Member] | Construction & Development [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	101,000	371
2020	347,000	97,000
2019	62,000	36,000
2018	35,000	19,000
2017	17,000	7,000
Prior	13,000	9,000
Total	575,000	539,000
Pass [Member] | Farm [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	20,000	57,000
2020	54,000	22,000
2019	21,000	18,000
2018	17,000	11,000
2017	10,000	11,000
Prior	30,000	23,000
Total	152,000	142,000
Pass [Member] | Non-Owner Occupied CRE [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	45,000	197,000
2020	198,000	117,000
2019	105,000	93,000
2018	86,000	44,000
2017	41,000	55,000
Prior	136,000	88,000
Total	611,000	594,000
Pass [Member] | Owner Occupied CRE [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	74,000	176,000
2020	168,000	132,000
2019	126,000	105,000
2018	96,000	75,000
2017	72,000	65,000
Prior	169,000	132,000
Total	705,000	685,000
Pass [Member] | Residential [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	109,000	373,000
2020	346,000	172,000
2019	157,000	134,000
2018	119,000	101,000
2017	93,000	101,000
Prior	302,000	237,000
Revolving Loans Amort Cost Basis	94,000	93,000
Total	1,220,000	1,211,000
Pass [Member] | Auto [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	61,000	177,000
2020	161,000	104,000
2019	90,000	39,000
2018	32,000	21,000
2017	16,000	9,000
Prior	8,000	2,000
Total	368,000	352,000
Pass [Member] | Non-Auto [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	17,000	48,000
2020	40,000	21,000
2019	17,000	7,000
2018	6,000	4,000
2017	3,000	1,000
Prior	2,000	2,000
Revolving Loans Amort Cost Basis	7,000	7,000
Total	92,000	90,000
Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	3,000	20,000
2020	12,000	12,000
2019	23,000	4,000
2018	2,000	14,000
2017	14,000	3,000
Prior	8,000	4,000
Total	62,000	57,000
Special Mention [Member] | C&I [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	2,000	9,000
2020	3,000	2,000
2019	1,000
2018		1,000
2017	1,000
Total	7,000	12,000
Special Mention [Member] | Agriculture [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	1,000
Total	1,000
Special Mention [Member] | Construction & Development [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021		2,000
2020	2,000	4,000
2019	4,000
Prior	1,000
Total	7,000	6,000
Special Mention [Member] | Non-Owner Occupied CRE [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021		1,000
2020	1,000
2019	13,000	1,000
2018	1,000	8,000
2017	8,000	1,000
Prior	4,000
Total	27,000	11,000
Special Mention [Member] | Owner Occupied CRE [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021		5,000
2020	3,000	5,000
2019	4,000	2,000
2018		4,000
2017	4,000	1,000
Prior		1,000
Total	11,000	18,000
Special Mention [Member] | Residential [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021		3,000
2020	3,000	1,000
2019	1,000	1,000
2018	1,000	1,000
2017	1,000	1,000
Prior	3,000	3,000
Total	9,000	10,000
Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	4,000	42,000
2020	34,000	16,000
2019	12,000	27,000
2018	26,000	16,000
2017	16,000	3,000
Prior	35,000	35,000
Revolving Loans Amort Cost Basis		2,000
Total	128,000	141,000
Substandard [Member] | C&I [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	1,000	12,000
2020	6,000	4,000
2019	1,000	4,000
2018	3,000
2017	1,000
Total	12,000	20,000
Substandard [Member] | Municipal [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021		2,000
2020	2,000
2018		5,000
2017	6,000	1,000
Prior	2,000	1,000
Total	10,000	9,000
Substandard [Member] | Agriculture [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021		6,000
2020	5,000
2017	1,000
Total	6,000	6,000
Substandard [Member] | Construction & Development [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	1,000	4,000
2020	3,000	1,000
2019	1,000
2018		3,000
Prior	1,000	1,000
Total	6,000	9,000
Substandard [Member] | Farm [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021		7,000
2020	7,000	1,000
2019	1,000
2018	1,000	1,000
Prior	1,000	1,000
Total	10,000	10,000
Substandard [Member] | Non-Owner Occupied CRE [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020		2,000
2019	2,000
2017	2,000
Prior	8,000	11,000
Total	12,000	13,000
Substandard [Member] | Owner Occupied CRE [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	1,000	5,000
2020	5,000	4,000
2019	4,000	20,000
2018	18,000	4,000
2017	4,000	1,000
Prior	12,000	10,000
Total	44,000	44,000
Substandard [Member] | Residential [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	1,000	5,000
2020	5,000	3,000
2019	2,000	3,000
2018	4,000	3,000
2017	2,000	1,000
Prior	11,000	10,000
Revolving Loans Amort Cost Basis		2,000
Total	26,000	27,000
Substandard [Member] | Auto [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021		1,000
2020	1,000	1,000
2019	1,000
Total	$ 2,000	2,000
Substandard [Member] | Non-Auto [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Prior		1,000
Total		$ 1,000

Loans Held for Investment an_12

Loans Held for Investment and Allowance for Loan Losses - Schedule of Internal Ratings of Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Internal ratings of loan	$ 5,322,562	$ 5,171,033	$ 4,639,389
Commercial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Internal ratings of loan	1,355,075	1,312,707	869,450
Agriculture [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Internal ratings of loan	90,366	94,864	99,582
Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Internal ratings of loan	3,414,751	3,319,265	3,249,249
Consumer [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Internal ratings of loan	$ 462,370	$ 444,197	421,108
Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Internal ratings of loan			4,449,000
Pass [Member] | Commercial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Internal ratings of loan			832,000
Pass [Member] | Agriculture [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Internal ratings of loan			92,000
Pass [Member] | Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Internal ratings of loan			3,106,000
Pass [Member] | Consumer [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Internal ratings of loan			419,000
Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Internal ratings of loan			87,000
Special Mention [Member] | Commercial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Internal ratings of loan			25,000
Special Mention [Member] | Agriculture [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Internal ratings of loan			6,000
Special Mention [Member] | Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Internal ratings of loan			56,000
Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Internal ratings of loan			103,000
Substandard [Member] | Commercial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Internal ratings of loan			12,000
Substandard [Member] | Agriculture [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Internal ratings of loan			2,000
Substandard [Member] | Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Internal ratings of loan			87,000
Substandard [Member] | Consumer [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Internal ratings of loan			$ 2,000

Loans Held for Investment an_13

Loans Held for Investment and Allowance for Loan Losses - Schedule of Past Due Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 18,777	$ 22,292	$ 34,283
Total Current	5,303,785	5,148,741	4,605,106
Total Loans	5,322,562	5,171,033	4,639,389
Total 90 Days Past Due Still Accruing	2	113	209
C&I [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	1,178,126	1,131,382
Municipal [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	176,949	181,325
Construction & Development [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	587,928	553,959
Farm [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	162,046	152,237
Non-Owner Occupied CRE [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	650,144	617,686
Owner Occupied CRE [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	759,906	746,974
Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	1,254,727	1,248,409
Auto [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	370,027	353,595
Non-Auto [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	92,343	90,602
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,074	4,629	5,577
Total Current	1,351,001	1,308,078	863,873
Total Loans	1,355,075	1,312,707	869,450
Total 90 Days Past Due Still Accruing	1	21	116
Commercial [Member] | C&I [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,055	4,629
Total Current	1,174,071	1,126,753
Total Loans	1,178,126	1,131,382
Total 90 Days Past Due Still Accruing	1	21
Commercial [Member] | Municipal [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	19
Total Current	176,930	181,325
Total Loans	176,949	181,325
Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,535	288	683
Total Current	87,831	94,576	98,899
Total Loans	90,366	94,864	99,582
Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	11,517	16,353	26,943
Total Current	3,403,234	3,302,912	3,222,306
Total Loans	3,414,751	3,319,265	3,249,249
Total 90 Days Past Due Still Accruing	1	33
Real Estate [Member] | Construction & Development [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,917	4,819
Total Current	586,011	549,140
Total Loans	587,928	553,959
Real Estate [Member] | Farm [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	71	708
Total Current	161,975	151,529
Total Loans	162,046	152,237
Real Estate [Member] | Non-Owner Occupied CRE [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	695	613
Total Current	649,449	617,073
Total Loans	650,144	617,686
Total 90 Days Past Due Still Accruing	0
Real Estate [Member] | Owner Occupied CRE [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,847	1,848
Total Current	758,059	745,126
Total Loans	759,906	746,974
Real Estate [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	6,987	8,365
Total Current	1,247,740	1,240,044
Total Loans	1,254,727	1,248,409
Total 90 Days Past Due Still Accruing		33
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	651	1,022	1,080
Total Current	461,719	443,175	420,028
Total Loans	462,370	444,197	421,108
Total 90 Days Past Due Still Accruing		59	93
Consumer [Member] | Auto [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	511	784
Total Current	369,516	352,811
Total Loans	370,027	353,595
Total 90 Days Past Due Still Accruing		59
Consumer [Member] | Non-Auto [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	140	238
Total Current	92,203	90,364
Total Loans	92,343	90,602
15-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	17,965	20,166	32,078
15-59 Days Past Due [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,488	3,647	4,807
15-59 Days Past Due [Member] | Commercial [Member] | C&I [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,469	3,647
15-59 Days Past Due [Member] | Commercial [Member] | Municipal [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	19
15-59 Days Past Due [Member] | Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,535	193	621
15-59 Days Past Due [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	11,343	15,561	25,788
15-59 Days Past Due [Member] | Real Estate [Member] | Construction & Development [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,810	4,775
15-59 Days Past Due [Member] | Real Estate [Member] | Farm [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	71	708
15-59 Days Past Due [Member] | Real Estate [Member] | Non-Owner Occupied CRE [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	695	613
15-59 Days Past Due [Member] | Real Estate [Member] | Owner Occupied CRE [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,847	1,393
15-59 Days Past Due [Member] | Real Estate [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	6,920	8,072
15-59 Days Past Due [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	599	765	862
15-59 Days Past Due [Member] | Consumer [Member] | Auto [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	470	551
15-59 Days Past Due [Member] | Consumer [Member] | Non-Auto [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	129	214
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	433	1,067	1,246
60-89 Days Past Due [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	283	406	388
60-89 Days Past Due [Member] | Commercial [Member] | C&I [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	283	406
60-89 Days Past Due [Member] | Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		95
60-89 Days Past Due [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	108	384	742
60-89 Days Past Due [Member] | Real Estate [Member] | Construction & Development [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	41	44
60-89 Days Past Due [Member] | Real Estate [Member] | Owner Occupied CRE [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		322
60-89 Days Past Due [Member] | Real Estate [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	67	18
60-89 Days Past Due [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	42	182	116
60-89 Days Past Due [Member] | Consumer [Member] | Auto [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	31	158
60-89 Days Past Due [Member] | Consumer [Member] | Non-Auto [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	11	24
Greater than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	379	1,059	959
Greater than 90 Days [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	303	576	382
Greater than 90 Days [Member] | Commercial [Member] | C&I [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	303	576
Greater than 90 Days [Member] | Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due			62
Greater than 90 Days [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	66	408	413
Greater than 90 Days [Member] | Real Estate [Member] | Construction & Development [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	66
Greater than 90 Days [Member] | Real Estate [Member] | Owner Occupied CRE [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		133
Greater than 90 Days [Member] | Real Estate [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		275
Greater than 90 Days [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	10	75	$ 102
Greater than 90 Days [Member] | Consumer [Member] | Auto [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 10	$ 75

Loans Held for Investment an_14

Loans Held for Investment and Allowance for Loan Losses - Schedule of Loans Modified and Considered Troubled Debt Restructurings (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)SecurityLoan	Mar. 31, 2020USD ($)SecurityLoan
Financing Receivable, Modifications [Line Items]
Number | SecurityLoan	5,000	7,000
Pre-Modification Recorded Investment	$ 846	$ 436
Post-Modification Recorded Investment	$ 846	$ 436
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number | SecurityLoan	2,000	5,000
Pre-Modification Recorded Investment	$ 149	$ 288
Post-Modification Recorded Investment	$ 149	$ 288
Commercial [Member] | Commercial – C&I [Member]
Financing Receivable, Modifications [Line Items]
Number | SecurityLoan	2,000
Pre-Modification Recorded Investment	$ 149
Post-Modification Recorded Investment	$ 149
Agriculture [Member]
Financing Receivable, Modifications [Line Items]
Number | SecurityLoan		1,000
Pre-Modification Recorded Investment		$ 134
Post-Modification Recorded Investment		$ 134
Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number | SecurityLoan	3,000
Pre-Modification Recorded Investment	$ 697
Post-Modification Recorded Investment	$ 697
Real Estate [Member] | Owner Occupied CRE [Member]
Financing Receivable, Modifications [Line Items]
Number | SecurityLoan	1,000
Pre-Modification Recorded Investment	$ 500
Post-Modification Recorded Investment	$ 500
Real Estate [Member] | Residential [Member]
Financing Receivable, Modifications [Line Items]
Number | SecurityLoan	2,000
Pre-Modification Recorded Investment	$ 197
Post-Modification Recorded Investment	$ 197
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Number | SecurityLoan		1,000
Pre-Modification Recorded Investment		$ 14
Post-Modification Recorded Investment		$ 14

Loans Held for Investment an_15

Loans Held for Investment and Allowance for Loan Losses - Schedule of How Loans Were Modified as Troubled Debt Restructured Loans (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	$ 846	$ 436
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	149	288
Commercial [Member] | C&I [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	149
Agriculture [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		134
Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	697
Real Estate [Member] | Owner Occupied CRE [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	500
Real Estate [Member] | Residential [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	197
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		14
Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		408
Extended Maturity [Member] | Commercial [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		260
Extended Maturity [Member] | Agriculture [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		134
Extended Maturity [Member] | Consumer [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		14
Combined Rate and Maturity [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		28
Combined Rate and Maturity [Member] | Commercial [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	149	$ 28
Combined Rate and Maturity [Member] | Commercial [Member] | C&I [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	149
Combined Rate and Maturity [Member] | Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	697
Combined Rate and Maturity [Member] | Real Estate [Member] | Owner Occupied CRE [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	500
Combined Rate and Maturity [Member] | Real Estate [Member] | Residential [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	197
Combined Rate and Maturity [Member] | Consumer [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	$ 846

Loans Held for Sale - Additiona

Loans Held for Sale - Additional Information (Detail) - USD ($)	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Loans Receivables Held For Sale Net [Abstract]
Loans held for sale	$ 65,405,000	$ 83,969,000	$ 42,034,000
Loans held-for-sale at the lower of cost or fair value	$ 3,894,000	$ 4,384,000	$ 2,375,000

Derivative Financial Instrume_3

Derivative Financial Instruments - Summary of Outstanding Notional Balances and Fair Values of Outstanding Derivative Positions (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
IRLCs [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Outstanding Notional Balance	$ 180,596	$ 202,906	$ 187,747
Asset Derivative Fair Value	1,645	4,618	296
Liability Derivative Fair Value	0	0	0
Forward Mortgage-Backed Securities Trades [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Outstanding Notional Balance	317,500	198,000	198,000
Asset Derivative Fair Value	$ 2,806	$ 0	0
Liability Derivative Fair Value			$ 0	$ 1,560	$ 3,200

Borrowings - Schedule of Borrow

Borrowings - Schedule of Borrowings (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Debt Disclosure [Abstract]
Securities sold under agreements with customers to repurchase	$ 523,254	$ 412,743	$ 410,146
Federal funds purchased	25,350	17,350	1,725
Advances from Federal Home Loan Bank of Dallas	0		446,000
Total	$ 548,604	$ 430,093	$ 857,871

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Taxes [Line Items]
Federal statutory tax rate	21.00%
Income tax expense	$ 11,054	$ 7,234
Effective tax rates on pre-tax income	16.26%	16.27%

Stock Option Plan and Restric_3

Stock Option Plan and Restricted Stock Plan - Additional Information (Detail) - USD ($)	Jan. 28, 2020	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Apr. 28, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of stock for issuance under the plan		3,559,402
Percentage of options granted		20.00%
Duration of options granted, years		10 years
Stock options outstanding, exercise price range, lower		$ 7.87
Stock options outstanding, exercise price range, upper		$ 34.55
Total unrecognized compensation cost related to nonvested share-based compensation arrangements granted under the Plan		$ 3,753,000
Weighted-average period of unrecognized compensation cost recognition, years		1 year 9 months 7 days
Total fair value of shares vested		$ 31,000	$ 119,000
Stock compensation expense		319,000	340,000
Granted, Shares	11,250
Granted the period exercise price	$ 34.55
Dividends Payable		18,500,000	17,060,000	$ 18,484,000
Two Thousand Twenty One Omnibus Stock and Incentive Plan [Member] | Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of stock for issuance under the plan					2,500,000
Other Liabilities [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividends Payable		$ 61,000	41,000	49,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of stock for issuance under the plan		633,003
Total unrecognized compensation cost related to nonvested share-based compensation arrangements granted under the Plan		$ 1,701,000	$ 2,118,000
Weighted-average period of unrecognized compensation cost recognition, years		1 year 5 months 8 days	1 year 5 months 4 days
Total fair value of shares vested		$ 39,000	$ 0
Restricted Stock [Member] | Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense		150,000	$ 175,000
Restricted Stock [Member] | Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense		$ 290,000		$ 275,000
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares vesting period		2 years

Stock Option Plan and Restric_4

Stock Option Plan and Restricted Stock Plan - Schedule of Analysis of Stock Option Activity (Detail)	3 Months Ended
	Mar. 31, 2021$ / sharesshares
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Outstanding, beginning of year, Shares | shares	1,833,057
Exercised, Shares | shares	(124,524)
Cancelled, Shares | shares	(14,100)
Outstanding, end of year, Shares | shares	1,694,433
Exercisable at end of year, Shares | shares	764,953
Outstanding, beginning of year, Weighted-Average Ex. Price | $ / shares	$ 20.85
Exercised, Weighted-Average Ex. Price | $ / shares	16.35
Cancelled, Weighted-Average Ex. Price | $ / shares	24.60
Outstanding, end of year, Weighted-Average Ex. Price | $ / shares	21.15
Exercisable at end of year, Weighted-Average Ex. Price | $ / shares	$ 17.36

Stock Option Plan and Restric_5

Stock Option Plan and Restricted Stock Plan - Summary of Vested and Unvested Restricted Stock Outstanding (Detail) - $ / shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Balance at beginning of period	95,888	105,309
Grants		3,413
Vesting	(993)
Forfeited/expired	(479)
Balance at end of period	94,416	108,722
Balance at beginning of period	$ 29.89	$ 29.93
Grants		34.55
Vesting	34.55
Forfeited/expired	34.55
Balance at end of period	$ 29.82	$ 30.08

Fair Value Disclosures - Additi

Fair Value Disclosures - Additional Information (Detail)	3 Months Ended		12 Months Ended
	Mar. 31, 2021USD ($)Loans	Mar. 31, 2020USD ($)Loans	Dec. 31, 2020USD ($)Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets transfer between Level 2 and Level 3	$ 0	$ 0	$ 0
Other real estate owned, total	$ 255,000	$ 982,000	$ 119,000
Residential Mortgage [Member] | Greater than 90 Days [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of loans held-for-sale | Loans	0	0	0
Recognized credit losses	$ 0	$ 0
Minimum [Member] | Measurement Input, Discount Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt discounts, percentage	5
Maximum [Member] | Measurement Input, Discount Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt discounts, percentage	25

Fair Value Disclosures - Financ

Fair Value Disclosures - Financial Assets and Financial Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	$ 5,109,631	$ 4,393,029	$ 4,107,069
Loans held-for-sale	65,405	83,969	42,034
U.S. Treasury Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value			10,113
Obligations of State and Political Subdivisions [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	2,517,017	2,426,876	1,807,671
Residential Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	2,108,594	1,472,280	1,679,980
Commercial Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	447,053	489,316	604,554
IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	1,645	4,618	296
Forward mortgage-backed securities trades	0	0	0
Forward Mortgage-Backed Securities Trades [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	2,806	0	0
Forward mortgage-backed securities trades			0	$ 1,560	$ 3,200
Fair Value, Measurements, Recurring [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	5,109,631	4,393,029	4,107,069
Loans held-for-sale	61,511	79,585	39,659
Fair Value, Measurements, Recurring [Member] | U.S. Treasury Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value			10,113
Fair Value, Measurements, Recurring [Member] | Obligations of State and Political Subdivisions [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	2,517,017	2,426,876	1,807,671
Fair Value, Measurements, Recurring [Member] | Residential Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	2,108,594	1,472,280	1,679,980
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	447,053	489,316	604,554
Fair Value, Measurements, Recurring [Member] | IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	1,645	4,618	296
Fair Value, Measurements, Recurring [Member] | Forward Mortgage-Backed Securities Trades [Member]
Available-for-sale investment securities:
Forward mortgage-backed securities trades	2,806	(1,560)	(3,200)
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	32,490		220
Fair Value, Measurements, Recurring [Member] | Other Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	4,477	4,557	4,531
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	4,477	4,557	14,644
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member] | U.S. Treasury Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value			10,113
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member] | Other Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	4,477	4,557	4,531
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	5,105,154	4,388,472	4,092,425
Loans held-for-sale	61,511	79,585	39,659
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Obligations of State and Political Subdivisions [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	2,517,017	2,426,876	1,807,671
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Residential Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	2,108,594	1,472,280	1,679,980
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Commercial Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	447,053	489,316	604,554
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	1,645	4,618	296
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Forward Mortgage-Backed Securities Trades [Member]
Available-for-sale investment securities:
Forward mortgage-backed securities trades	2,806	$ (1,560)	(3,200)
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Corporate Bonds [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	$ 32,490		$ 220

Fair Value Disclosures - Summar

Fair Value Disclosures - Summary of Loans Held-for-Sale at Fair Value (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Fair Value Measurements Loans Held For Sale [Abstract]
Unpaid principal balance on loans held-for-sale	$ 60,727	$ 76,602	$ 38,563
Net unrealized gains on loans held-for-sale	784	2,983	1,096
Loans held-for-sale at fair value	$ 61,511	$ 79,585	$ 39,659

Fair Value Disclosures - Schedu

Fair Value Disclosures - Schedule of Gain Loss on Sale of Mortgage Loans (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Schedule Of Gain Loss On Sale Of Mortgage Loans [Abstract]
Realized gain on sale and fees on mortgage loans	$ 10,728	$ 4,545
Change in fair value on loans held-for-sale and IRLCs	(5,200)	2,355
Change in forward mortgage-backed securities trades	4,366	(3,048)
Total gain on sale of mortgage loans	$ 9,894	$ 3,852

Fair Value Disclosures - Sche_2

Fair Value Disclosures - Schedule of Estimated Fair Values and Carrying Values of All Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	$ 190,350	$ 211,113	$ 191,486
Interest-bearing demand deposits in banks	893,221	517,971	76,378
Available-for-sale securities	5,109,631	4,393,029	4,107,069
Loans held-for-investment, net of allowance for credit losses	5,259,588	5,104,499	4,578,949
Loans held for sale	65,405	83,969	42,034
Borrowings	548,604	430,093	857,871
IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset Derivative Fair Value	1,645	4,618	296
Forward mortgage-backed securi-ties trades asset (liability)	0	0	0
Forward Mortgage-Backed Securities Trades [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset Derivative Fair Value	2,806	0	0
Forward mortgage-backed securi-ties trades asset (liability)			0	$ 1,560	$ 3,200
Carrying Value [Member] | Level 1 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	190,350	211,113	191,486
Interest-bearing demand deposits in banks	893,221	517,971	76,378
Deposits with no stated maturities	8,929,762	8,200,275	6,744,658
Carrying Value [Member] | Level 1 Inputs [Member] | Forward Mortgage-Backed Securities Trades [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Forward mortgage-backed securi-ties trades asset (liability)	2,806	(1,560)	(3,200)
Carrying Value [Member] | Level 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for sale	65,405	83,969	42,034
Accrued interest receivable	42,322	53,433	34,329
Deposits with stated maturities	483,685	475,542	465,808
Borrowings	548,604	430,093	857,871
Accrued interest payable	320	377	783
Carrying Value [Member] | Level 2 Inputs [Member] | IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset Derivative Fair Value	1,645	4,618	296
Carrying Value [Member] | Levels 1 and 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale securities	5,109,631	4,393,029	4,107,069
Carrying Value [Member] | Level 3 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held-for-investment, net of allowance for credit losses	5,259,588	5,104,499	4,578,949
Estimated Fair Value [Member] | Level 1 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	190,350	211,113	191,486
Interest-bearing demand deposits in banks	893,221	517,971	76,378
Deposits with no stated maturities	8,929,762	8,200,275	6,744,658
Estimated Fair Value [Member] | Level 1 Inputs [Member] | Forward Mortgage-Backed Securities Trades [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Forward mortgage-backed securi-ties trades asset (liability)	2,806	(1,560)	(3,200)
Estimated Fair Value [Member] | Level 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for sale	65,273	84,233	41,593
Accrued interest receivable	42,322	53,433	34,329
Deposits with stated maturities	485,193	477,218	467,804
Borrowings	548,604	430,093	857,871
Accrued interest payable	320	377	783
Estimated Fair Value [Member] | Level 2 Inputs [Member] | IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset Derivative Fair Value	1,645	4,618	296
Estimated Fair Value [Member] | Levels 1 and 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale securities	5,109,631	4,393,029	4,107,069
Estimated Fair Value [Member] | Level 3 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held-for-investment, net of allowance for credit losses	$ 5,273,235	$ 5,109,885	$ 4,558,577

Acquisition - Additional Inform

Acquisition - Additional Information (Detail) - USD ($)	Jan. 02, 2020	Sep. 19, 2019	Mar. 31, 2021	Mar. 31, 2020
FBC Bancshares, Inc. and First Bank, N.A. [Member]
Business Acquisition [Line Items]
Payment for all outstanding shares of acquired entity by shares		6,275,574
Fair value of total loans			$ 447,702,000	$ 447,702,000
Total loans of contractual amounts			$ 455,181,000
Commercial Bancshares, Inc [Member]
Business Acquisition [Line Items]
Business acquisition, agreement date			Sep. 19, 2019
Payment for all outstanding shares of acquired entity by shares	6,275,574
Business acquisition, special dividend	$ 1,920,000

Acquisition - Schedule of Amoun

Acquisition - Schedule of Amounts Recorded on Consolidated Balance Sheet on Acquisition Date (Detail) $ in Thousands	Sep. 19, 2019USD ($)
FBC Bancshares, Inc. and First Bank, N.A. [Member]
Business Acquisition [Line Items]
Common stock issued (6,275,574 shares)	$ 220,273

Acquisition - Schedule of Amo_2

Acquisition - Schedule of Amounts Recorded on Consolidated Balance Sheet on Acquisition Date (Parenthetical) (Detail)	Sep. 19, 2019shares
FBC Bancshares, Inc. and First Bank, N.A. [Member]
Business Acquisition [Line Items]
Common stock issued	6,275,574

Acquisition - Schedule of Preli

Acquisition - Schedule of Preliminary Estimated Fair Value Amounts Assigned to Major Asset and Liability Categories at Acquisition Date (Detail) - FBC Bancshares, Inc. and First Bank, N.A. [Member] - USD ($) $ in Thousands	Mar. 31, 2021	Mar. 31, 2020
Business Acquisition [Line Items]
Cash and cash equivalents		$ 61,028
Securities available-for-sale		93,967
Loans	$ 447,702	447,702
Identifiable intangible assets		4,798
Other assets		25,377
Total identifiable assets acquired		632,872
Deposits		549,125
Other liabilities		5,397
Total liabilities assumed		554,522
Fair value of net identifiable assets acquired		78,350
Goodwill resulting from acquisition		$ 141,923