First Financial Bankshares (FFIN) 10-K14 Feb 202019 FY Annual reportFinancial data

Company Profile

Cover Page

Cover Page - USD ($) $ in Millions	12 Months Ended
Cover Page - USD ($) $ in Millions	Dec. 31, 2019	Feb. 14, 2020	Jun. 30, 2019
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Annual Report	true
Document Transition Report	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Document Period End Date	Dec. 31, 2019
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 Voluntary Filers	No
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		142,218,922
Entity Public Float			$ 3,970

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
ASSETS
CASH AND DUE FROM BANKS	$ 231,534	$ 207,835
FEDERAL FUNDS SOLD	3,150
INTEREST-BEARING DEPOSITS IN BANKS	47,920	40,812
Total cash and cash equivalents	282,604	248,647
INTEREST-BEARING TIME DEPOSITS IN BANKS	0	1,458
SECURITIES AVAILABLE-FOR-SALE, at fair value	3,413,317	3,158,777
LOANS:
Held-for-investment	4,194,969	3,953,636
Less – allowance for loan losses	(52,499)	(51,202)
Net loans held for investment	4,142,470	3,902,434
Held-for-sale ($23,076 and $19,185 at fair value option at December 31, 2019 and December 31, 2018)	28,228	21,672
Net loans	4,170,698	3,924,106
BANK PREMISES AND EQUIPMENT, net	131,022	133,421
INTANGIBLE ASSETS	173,667	174,683
OTHER ASSETS	90,919	90,762
Total assets	8,262,227	7,731,854
LIABILITIES AND SHAREHOLDERS' EQUITY
NONINTEREST-BEARING DEPOSITS	2,065,128	2,116,107
INTEREST-BEARING DEPOSITS	4,538,678	4,064,282
Total deposits	6,603,806	6,180,389
DIVIDENDS PAYABLE	16,306	14,227
BORROWINGS	381,356	468,706
OTHER LIABILITIES	33,562	15,237
Total liabilities	7,035,030	6,678,559
COMMITMENTS AND CONTINGENCIES
SHAREHOLDERS' EQUITY:
Common stock - $0.01 par value; authorized 200,000,000 shares; 135,891,755 and 67,753,133 shares issued at December 31, 2019 and 2018, respectively	1,359	678
Capital surplus	450,676	443,114
Retained earnings	707,656	606,658
Treasury stock (shares at cost: 927,408 and 467,811 at December 31, 2019 and 2018, respectively)	(8,222)	(7,507)
Deferred Compensation	8,222	7,507
Accumulated other comprehensive earnings	67,506	2,845
Total shareholders' equity	1,227,197	1,053,295
Total liabilities and shareholders' equity	$ 8,262,227	$ 7,731,854

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Loans held-for-sale, fair value	$ 23,076	$ 19,185
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	135,891,755	67,753,133
Treasury stock, shares	927,408	467,811

Consolidated Statements of Earn

Consolidated Statements of Earnings - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
INTEREST INCOME:
Interest and fees on loans	$ 224,556	$ 200,347	$ 166,807
Interest on investment securities:
Taxable	55,670	50,052	32,825
Exempt from federal income tax	37,075	39,661	44,659
Interest on federal funds sold and interest-bearing deposits in banks	1,891	1,630	1,684
Total interest income	319,192	291,690	245,975
INTEREST EXPENSE:
Interest on deposits	27,122	16,946	8,213
Other	2,980	1,984	1,075
Total interest expense	30,102	18,930	9,288
Net interest income	289,090	272,760	236,687
PROVISION FOR LOAN LOSSES	2,965	5,665	6,530
Net interest income after provision for loan losses	286,125	267,095	230,157
NONINTEREST INCOME:
Trust fees	28,401	28,181	23,694
Service charges on deposit accounts	22,039	21,663	19,416
ATM, interchange and credit card fees	29,863	28,532	25,686
Real estate mortgage operations	18,144	15,157	15,109
Net gain on sale of available-for-sale securities (includes $733, $1,354 and $1,828 for the years ended December 31, 2019, 2018 and 2017, respectively, related to accumulated comprehensive earnings reclassifications)	733	1,354	1,828
Net gain (loss) on sale of foreclosed assets	274	116	(50)
Net gain (loss) on sale of assets	319	(147)	(396)
Interest on loan recoveries	2,092	938	1,128
Other	6,563	5,970	4,602
Total noninterest income	108,428	101,764	91,017
NONINTEREST EXPENSE:
Salaries and employee benefits	112,336	105,189	95,287
Cost related to termination of pension plan	2,673	1,546
Net occupancy expense	11,156	11,173	10,521
Equipment expense	9,052	10,118	10,120
FDIC insurance premiums	1,091	2,333	2,217
ATM, interchange and credit card expenses	9,856	9,282	7,452
Professional and service fees	7,853	8,894	8,063
Printing, stationery and supplies	1,812	1,997	1,989
Operational and other losses	1,879	2,188	3,192
Software amortization and expense	7,305	6,020	6,940
Amortization of intangible assets	1,016	1,272	613
Other	30,492	30,672	27,592
Total noninterest expense	196,521	190,684	173,986
EARNINGS BEFORE INCOME TAXES	198,032	178,175	147,188
INCOME TAX EXPENSE (includes $154, $284 and $640 for the years ended December 31, 2019, 2018 and 2017, related to income tax expense from reclassification items)	33,220	27,537	26,817
NET EARNINGS	$ 164,812	$ 150,638	$ 120,371
EARNINGS PER SHARE, BASIC	$ 1.22	$ 1.11	$ 0.91
EARNINGS PER SHARE, ASSUMING DILUTION	$ 1.21	$ 1.11	$ 0.91

Consolidated Statements of Ea_2

Consolidated Statements of Earnings (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Reclassifications adjustment for realized gains on investment securities included in net earnings (loss), before income tax	$ 733	$ 1,354	$ 1,828
Income tax expense from reclassification items	$ 154	$ 284	$ 640

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Earnings - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
NET EARNINGS	$ 164,812	$ 150,638	$ 120,371
OTHER ITEMS OF COMPREHENSIVE EARNINGS (LOSS):
Change in unrealized gain (loss) on investment securities available-for-sale, before income taxes	80,906	(38,185)	23,266
Reclassification adjustment for realized losses (gains) on investment securities included in net earnings, before income tax	(733)	(1,354)	(1,828)
Minimum liability pension adjustment, before income tax	1,676	1,970	257
Total other items of comprehensive earnings (losses)	81,849	(37,569)	21,695
Income tax benefit (expense) related to:
Investment securities	(16,836)	8,303	(13,774)
Minimum liability pension adjustment	(352)	(414)	420
Total income tax benefit (expense)	(17,188)	7,889	(13,354)
COMPREHENSIVE EARNINGS	$ 229,473	$ 120,958	$ 128,712

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, 2016	$ 837,885	$ 661	$ 372,245	$ 446,534	$ (6,671)	$ 6,671	$ 18,445
Beginning Balance, Shares at Dec. 31, 2016		66,094,695
Treasury Stock, Beginning Balance, Shares at Dec. 31, 2016					(507,409)
Net earnings (unaudited)	120,371			120,371
Stock option exercises (unaudited)	2,935	$ 2	2,933
Stock option exercises, Shares		140,250
Restricted stock grant (unaudited)	1,139		1,139
Restricted stock grant (unaudited), Shares		25,499
Cash dividends declared	(49,648)			(49,648)
Minimum liability pension adjustment, net of related income taxes	677						677
Change in unrealized gain (loss) in investment securities available-for-sale, net of related income taxes (unaudited)	7,664						7,664
Shares purchased (redeemed) in connection with directors' deferred compensation plan, net (unaudited)					$ (477)	477
Shares purchased (redeemed) in connection with directors' deferred compensation plan, net, Shares					11,445
Stock option expense (unaudited)	1,745		1,745
Ending Balance at Dec. 31, 2017	922,768	$ 663	378,062	517,257	$ (7,148)	7,148	26,786
Ending Balance, Shares at Dec. 31, 2017		66,260,444
Treasury Stock, Ending Balance, Shares at Dec. 31, 2017					(495,964)
Net earnings (unaudited)	150,638			150,638
Stock option exercises (unaudited)	3,863	$ 2	3,861
Stock option exercises, Shares		173,822
Restricted stock grant (unaudited)	1,609		1,609
Restricted stock grant (unaudited), Shares		29,496
Cash dividends declared	(55,499)			(55,499)
Stock issued in acquisition of Commercial Bancshares, Inc.	58,087	$ 13	58,074
Stock issued in acquisition of Commercial Bancshares, Inc, Shares		1,289,371
Minimum liability pension adjustment, net of related income taxes	1,556						1,556
Change in unrealized gain (loss) in investment securities available-for-sale, net of related income taxes (unaudited)	(31,235)						(31,235)
Shares purchased (redeemed) in connection with directors' deferred compensation plan, net (unaudited)					$ (359)	359
Shares purchased (redeemed) in connection with directors' deferred compensation plan, net, Shares					28,153
Stock option expense (unaudited)	1,508		1,508
Reclassification of certain income tax effects related to the change in the U.S. statutory federal income tax rate under the Tax Cuts and Jobs Act to retained earnings				(5,759)			5,759
Reclassification of unrealized gain in equity securities at December 31, 2017 from accumulated other comprehensive earnings to retained earnings (unaudited)				21			(21)
Ending Balance at Dec. 31, 2018	$ 1,053,295	$ 678	443,114	606,658	$ (7,507)	7,507	2,845
Ending Balance, Shares at Dec. 31, 2018		67,753,133
Treasury Stock, Ending Balance, Shares at Dec. 31, 2018	(467,811)				(467,811)
Net earnings (unaudited)	$ 164,812			164,812
Stock option exercises (unaudited)	4,293	$ 2	4,291
Stock option exercises, Shares		241,725
Restricted stock grant (unaudited)	1,782		1,782
Restricted stock grant (unaudited), Shares		56,687
Cash dividends declared	(63,135)			(63,135)
Minimum liability pension adjustment, net of related income taxes	1,324						1,324
Change in unrealized gain (loss) in investment securities available-for-sale, net of related income taxes (unaudited)	63,337						63,337
Shares purchased (redeemed) in connection with directors' deferred compensation plan, net (unaudited)					$ (715)	715
Shares purchased (redeemed) in connection with directors' deferred compensation plan, net, Shares					4,742
Stock option expense (unaudited)	1,489		1,489
Two-for-one stock spllit in the form of a 100% stock dividend (unaudited)		$ 679		679
Two-for-one stock spllit in the form of a 100% stock dividend (unaudited), shares		67,840,210			(464,339)
Ending Balance at Dec. 31, 2019	$ 1,227,197	$ 1,359	$ 450,676	$ 707,656	$ (8,222)	$ 8,222	$ 67,506
Ending Balance, Shares at Dec. 31, 2019		135,891,755			(927,408)
Treasury Stock, Ending Balance, Shares at Dec. 31, 2019	(927,408)

Consolidated Statements of Sh_2

Consolidated Statements of Shareholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Common Stock Dividend Percentage	100.00%
Retained Earnings [Member]
Cash dividend per share	$ 0.47	$ 0.41	$ 0.38

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net earnings	$ 164,812	$ 150,638	$ 120,371
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization	11,665	12,549	12,916
Provision for loan losses	2,965	5,665	6,530
Securities premium amortization (discount accretion), net	25,788	27,467	30,310
Gain on sale of assets, net	(1,477)	(1,216)	(1,167)
Deferred federal income tax benefit	(29)	(250)	(53)
Change in loans held-for-sale	(5,830)	(5,791)	11,769
Change in other assets	1,851	(1,697)	9,313
Change in other liabilities	4,374	1,621	285
Total adjustments	39,307	38,348	69,903
Net cash provided by operating activities	204,119	188,986	190,274
CASH FLOWS FROM INVESTING ACTIVITIES:
Cash received in acquisition of Commercial Bancshares, Inc., net		18,653
Net decrease in interest-bearing time deposits in banks	1,458		249
Activity in available-for-sale securities:
Sales	67,414	220,259	120,576
Maturities	4,460,703	3,439,028	4,392,131
Purchases	(4,727,430)	(3,731,821)	(4,768,420)
Activity in held-to-maturity securities – maturities			124
Net increase in loans	(245,190)	(205,238)	(134,627)
Purchases of bank premises and equipment and other assets	(8,671)	(17,646)	(14,162)
Proceeds from sale of bank premises and equipment and other assets	2,249	844	6,085
Net cash used in investing activities	(449,467)	(275,921)	(398,044)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net increase (decrease) in noninterest-bearing deposits	(50,979)	(87,583)	323,928
Net increase (decrease) in interest-bearing deposits	474,396	(36,891)	160,494
Net increase (decrease) in borrowings	(87,350)	137,706	(114,770)
Common stock transactions:
Proceeds from stock issuances	4,294	3,864	2,934
Dividends paid	(61,056)	(53,861)	(48,955)
Net cash provided by (used in) financing activities	279,305	(36,765)	323,631
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	33,957	(123,700)	115,861
CASH AND CASH EQUIVALENTS, beginning of year	248,647	372,347	256,486
CASH AND CASH EQUIVALENTS, end of year	$ 282,604	$ 248,647	$ 372,347

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
Summary of Significant Accounting Policies	Dec. 31, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	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 73 locations located in Texas as of December 31, 2019. The subsidiary bank is First Financial Bank, National Association, Abilene, Texas. The bank’s primary source of revenue is providing loans and banking services to consumers and commercial customers in the market area in which the subsidiary is located. In addition, the Company also owns First Financial Trust & Asset Management Company, National Association, First Financial Insurance Agency, Inc., and First Technology Services, Inc. A summary of significant accounting policies of Bankshares 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 U.S. 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 U.S. 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 loan losses and its valuation of financial instruments. Consolidation The accompanying consolidated financial statements include the accounts of Bankshares and its subsidiaries, all of which are wholly-owned. All significant intercompany accounts and transactions have been eliminated. Stock Split and Increase in Authorized Shares On April 23, 2019, the Company’s Board of Directors declared a two-for-one stock split of the Company’s outstanding common shares effective on June 3, 2019. In addition, the shareholders of the Company approved an amendment to the Amended and Restated Certificate of Formation to increase the number of authorized shares to 200,000,000. All per share amounts in the annual report on Form 10-K have been restated to reflect this stock split. An amount equal to the par value of the additional common shares to be issued pursuant to the stock split was reflected as a transfer from retained earnings to common stock in the consolidated financial statements as of and for the year ended December 31, 2019. Stock Repurchase On June 25, 2017, the Company’s Board of Directors authorized the repurchase of up to 2,000,000 common shares through September 30, 2020 shares were repurchased under this repurchase plan or the prior authorization that expired September 30, 2017. Acquisition On January 1, 2018, the Company acquired 100% of the outstanding capital stock of Commercial Bancshares, Inc. through the merger of a wholly-owned subsidiary with and into Commercial Bancshares, Inc. Following such merger, Commercial Bancshares, Inc. and its wholly-owned subsidiary, Commercial State Bank, Kingwood, Texas were merged into the Company and First Financial Bank, National Association, respectively. The results of operations of Commercial Bancshares, Inc. subsequent to the acquisition date, are include in the consolidated earnings of the Company. See Note 20 for additional information. Investment Securities Management classifies debt and equity securities as held-to-maturity, available-for-sale, held-to-maturity held-to-maturity available-for-sale Available-for-sale available-for-sale Effective January 1, 2018, in accordance with ASU 2016-01 decreases in available-for-sale The Company records its available-for-sale debt When the fair value of a debt security is below its amortized cost, and depending on the length of time the condition exists and the extent the fair value is below amortized cost, additional analysis is performed to determine whether an other-than-temporary impairment condition exists. Available-for-sale held-to-maturity The Company’s investment portfolio consists of U.S. Treasury securities, obligations of U.S. government sponsored enterprises and agencies, 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 - - Loans Held-for-Investment Loans held for investment are stated at the amount of unpaid principal, reduced by unearned income and an allowance for loan losses. 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. The allowance for loan losses is established through a provision for loan losses charged to expense. Loans are charged against the allowance for loan losses when management believes the collectability of the principal is unlikely. The allowance for loan losses is an amount which represents management’s best estimate of probable losses that are inherent in the Company’s loan portfolio as of the balance sheet date. The allowance for loan losses is comprised of three elements: (i) specific reserves determined based on probable losses on specific classified loans; (ii) a historical valuation reserve component that considers historical loss rates and estimated loss emergence periods; and (iii) qualitative reserves based upon general economic conditions and other qualitative risk factors both internal and external to the Company. The allowance for loan losses is increased by charges to income and decreased by charge-offs Although we believe we use the best information available to make loan loss allowance determinations, future adjustments could be necessary if circumstances or economic conditions differ substantially from the assumptions used in making our initial determinations. A decline in the economy could result in increased levels of non-performing Accrual of interest is discontinued on a loan and payments are applied to principal when management believes, after considering economic and business conditions and collection efforts, the borrower’s financial condition is such that collection of interest is doubtful. Except consumer loans, generally all loans past due greater than 90 days, based on contractual terms, are placed on non-accrual. charged-off charge-off Loans are considered impaired when, based on current information and events, management determines that it is probable we will be unable to collect all amounts due in accordance with the loan agreement, including scheduled principal and interest payments. If a loan is impaired, a specific valuation allowance is allocated, if necessary. Interest payments on impaired loans are typically applied to principal unless collectability of the principal amount is reasonably assured, in which case interest is recognized on a cash basis. Impaired loans, or portions thereof, are charged off when deemed uncollectable. The Company’s policy requires measurement of the allowance for an impaired, collateral dependent loan based on the fair value of the collateral less cost to sell. Other loan impairments for non-collateral From time to time, the Company modifies its loan agreement with a borrower. A modified loan is considered a troubled debt restructuring when two conditions are met: (i) the borrower is experiencing financial difficulty and (ii) concessions are made by the Company that would not otherwise be considered for a borrower with similar credit risk characteristics. Modifications to loan terms may include a lower interest rate, a reduction of principal, or a longer term to maturity. For all impaired loans, including the Company’s troubled debt restructurings, the Company performs a periodic, well-documented credit evaluation of the borrower’s financial condition and prospects for repayment to assess the likelihood that all principal and interest payments required under the terms of the agreement will be collected in full. When doubt exists about the ultimate collectability of principal and interest, the troubled debt restructuring remains on non-accrual non-accrual The Company originates certain mortgage loans for sale in the secondary market. Accordingly, these loans are classified as held-for-sale Loans acquired, including loans acquired in a business combination, are initially recorded at fair value with no valuation allowance. Acquired loans are segregated between those considered to be credit impaired and those deemed performing. To make this determination, management considers such factors as past due status, non-accrual Purchased credit impaired loans are those loans that showed evidence of deterioration of credit quality since origination and for which it is probable, at acquisition, that the Company will be unable to collect all amounts contractually owed. Their acquisition fair value, which includes a credit component at the acquisition date, was based on the estimate of cash flows, both principal and interest, expected to be collected or estimated collateral values if cash flows are not estimable, discounted at prevailing market rates of interest. The difference between the discounted cash flows expected at acquisition and the investment in the loan is recognized as interest income on a level-yield method over the life of the loan, unless management was unable to reasonably forecast cash flows in which case the loans were placed on nonaccrual. Subsequent to the acquisition date, increases in expected cash flows will generally result in a recovery of any previously recorded allowance for loan loss, to the extent applicable, and/or a reclassification from the non-accretable 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 loan 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 and totaled $ 171,565,000 The carrying amount of goodwill arising from acquisitions that qualify as an asset purchase for federal income tax purposes was $18,680,000 and $22,526,000 at December 31, 2019 and 2018, respectively, and is deductible for federal income tax purposes. For the year ended December 31, 2017, the Company sold its mortgage servicing rights totaling $1,795,000 to an unrelated third party resulting in a loss on sale of approximately $215,000. 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 deposits in banks with original maturity of 90 days or less, and federal funds sold. Accumulated Other Comprehensive Income (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 Company recorded stock option expense totaling $1,489,000, $1,508,000 and $1,745,000 for the years ended December 31, 2019, 2018 and 2017, respectively. The Company also grants restricted stock for a fixed number of shares. The Company recorded expenses associated with its director and officer restricted stock grants totaling $620,000, $560,000 and $483,000 and $995,000, $ See Note 17 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 stock shares outstanding during the period. The Company calculates dilutive EPS assuming all outstanding stock options to purchase common stock have been exercised 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 restricted stock are assumed to be used to purchase common stock at the average market price during the respective year. Anti-dilutive shares are excluded from the computation of EPS . Net Earnings Weighted Per For the year ended December 31, 2019: Net earnings per share, basic $ 164,812 135,647,354 $ 1.22 Effect of stock options and stock grants — 698,665 (0.01 ) Net earnings per share, assuming dilution $ 164,812 136,346,019 $ 1.21 For the year ended December 31, 2018: Net earnings per share, basic $ 150,638 135,218,734 $ 1.11 Effect of stock options and stock grants — 747,294 — Net earnings per share, assuming dilution $ 150,638 135,966,028 $ 1.11 For the year ended December 31, 2017: Net earnings per share, basic $ 120,371 132,253,726 $ 0.91 Effect of stock options and stock grants — 394,934 — Net earnings per share, assuming dilution $ 120,371 132,648,660 $ 0.91 Recently Issued and Effective Authoritative Accounting Guidance Accounting Standards Update (“ASU”) 2014-09, “Revenue from Contracts with Customers 2014-09 2015-04 2014-09 2014-09, non-interest ASU 2016-01, ASU 2016-01 “Financial Instruments – Overall: Recognition and Measurement of Financial Assets and Financial Liabilities 2016-01, available-for-sale 2016-1 ASU 2016-02, “Leases 2016-02 right-of-use 2016-02 ASU 2016-09, “Compensation – Stock Compensation: Improvements to Employee Share-Based Payment Accounting 2016-09 income statement during the period in which they occur. Previously, such amounts were recorded in capital surplus. Additionally, excess tax benefits are classified along with other income tax cash flows as an operating activity rather than a financing activity, as was previously the case. ASU 2016-09 2016-09 ASU 2016-15, “Statement of Cash Flows (Topic 230) – Classification of Certain Cash Receipts and Cash Payments.” 2016-15 2016-15 ASU 2017-08, “Receivables – Nonrefundable Fees and Other Costs: Premium Amortization on Purchased Callable Debt Securities.” 2017-08 2017-08 2017-08 ASU 2017-09, Compensation – Stock Compensation (Topic 718) – Scope of Modification Accounting 2017-09 2017-09, 2017-09 ASU 2018-02, “Income Statement – Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income.” 2018-02 2018-02 2018-02

Interest-bearing Time Deposits

Interest-bearing Time Deposits in Banks and Securities	12 Months Ended
Interest-bearing Time Deposits in Banks and Securities	Dec. 31, 2019
Cash and Cash Equivalents [Abstract]
Interest-bearing Time Deposits in Banks and Securities	2. INTEREST-BEARING TIME DEPOSITS IN BANKS AND SECURITIES: Interest-bearing time deposits in banks totaled $1,458,000 at December 31, 2018. There were no A summary of the Company’s available-for-sale December 31, 2019 Amortized Gross Gross Estimated Securities available-for-sale: U.S. Treasury securities $ 9,997 $ 22 $ — $ 10,019 Obligations of state and political subdivisions 1,231,619 57,764 (400 ) 1,288,983 Corporate bonds and other 4,643 65 — 4,708 Residential mortgage-backed 1,586,872 23,139 (1,148 ) 1,608,863 Commercial mortgage-backed securities 494,674 6,356 (286 ) 500,744 Total securities available-for-sale $ 3,327,805 $ 87,346 $ (1,834 ) $ 3,413,317 December 31, 201 8 Gross Gross Unrealized Estimated Securities available-for-sale: U.S. Treasury securities $ 9,970 $ — $ (8 ) $ 9,962 Obligations of U.S. government sponsored enterprises and agencies 301 — — 301 Obligations of state and political subdivisions 1,229,828 30,013 (1,970 ) 1,257,871 Corporate bonds and other 4,875 — (77 ) 4,798 Residential mortgage-backed securities 1,472,228 3,928 (21,611 ) 1,454,545 Commercial mortgage-backed securities 436,366 670 (5,736 ) 431,300 Total securities available-for-sale $ 3,153,568 $ 34,611 $ (29,402 ) $ 3,158,777 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 December 31, 2019, were computed by using scheduled amortization of balances and historical prepayment rates. At December 31, 2019 and 2018, the Company did not hold any CMOs that entail higher risks than standard mortgage-backed securities. The amortized cost and estimated fair value of available-for-sale Amortized Estimated Due within one year $ 150,912 $ 152,445 Due after one year through five years 485,838 510,783 Due after five years through ten years 607,770 638,239 Due after ten years 1,739 2,243 Mortgage-backed securities 2,081,546 2,109,607 Total $ 3,327,805 $ 3,413,317 The following tables disclose, as of December 31, 2019 and 2018, the Company’s investment securities that have been in a continuous unrealized-loss Less than 12 Months 12 Months or Longer Total December 31, 2019 Fair Unrealized Fair Value Unrealized Fair Value Unrealized Obligations of state and political subdivisions $ 65,787 $ 400 $ 326 $ — $ 66,113 $ 400 Residential mortgage-backed securities 100,004 306 103,983 842 203,987 1,148 Commercial mortgage-backed securities 74,560 178 35,178 108 109,738 286 Total $ 240,351 $ 884 $ 139,487 $ 950 $ 379,838 $ 1,834 Less than 12 Months 12 Months or Longer Total December 31, 2018 Fair Unrealized Fair Value Unrealized Fair Value Unrealized U.S. Treasury securities $ 9,962 $ 8 $ — $ — $ 9,962 $ 8 Obligations of U.S. government sponsored enterprises and agencies — — 301 — 301 — Obligations of state and political subdivisions 27,489 107 114,461 1,863 141,950 1,970 Corporate bonds and other 4,348 68 450 9 4,798 77 Residential mortgage-backed securities 119,584 483 922,289 21,128 1,041,873 21,611 Commercial mortgage-backed securities 1,994 5 343,015 5,731 345,009 5,736 Total $ 163,377 $ 671 $ 1,380,516 $ 28,731 $ 1,543,893 $ 29,402 The number of investments in an unrealized loss position totaled 93 at December 31, 2019. We do not believe these unrealized losses are “other-than-temporary”. In estimating other-than-temporary impairment losses, management considers, among other things, the length of time and the extent to which the fair value has been less than cost and the financial condition and near-term prospects of the issuer. Additionally management does not (i) have the intent to sell our securities prior to recovery and/or maturity and, (ii) it is more likely than not that we will not have to sell our securities prior to recovery and/or maturity and (iii) that the length of time and extent that fair value has been less than cost is not indicative of recoverability. The unrealized losses noted are interest rate related due to the level of interest rates at December 31, 2019 compared to the time of purchase. We have reviewed the ratings of the issuers and have not identified any issues related to the ultimate repayment of principal as a result of credit concerns on these securities. Our mortgage related securities are backed by GNMA, FNMA and FHLMC or are collateralized by securities backed by these agencies. At December 31, 2019 and 2018 and 84.70% , respectively , available-for-sale and 32.65%, resp ectively, were Securities, carried at approximately $2,329,784,000 and $1,988,579,000 December 31, 2019 and 2018, respectively, were pledged as collateral for public or trust fund deposits, repurchase agreements and for other purposes required or permitted by law. During 2019, 2018 and 2017, sales of investment securities that were classified as available-for-sale

Loans Held for Investment and A

Loans Held for Investment and Allowance for Loan Losses	12 Months Ended
Loans Held for Investment and Allowance for Loan Losses	Dec. 31, 2019
Receivables [Abstract]
Loans Held for Investment and Allowance for Loan Losses	3. LOANS HELD FOR INVESTMENT AND ALLOWANCE FOR LOAN LOSSES: Loans held-for-investment December 31, 2019 2018 Commercial $ 856,326 $ 844,953 Agricultural 103,640 96,677 Real estate 2,823,372 2,639,346 Consumer 411,631 372,660 Total loans held-for-investment $ 4,194,969 $ 3,953,636 The Company’s non-accrual December 31, 2019 2018 Non-accrual $ 24,582 $ 27,534 Loans still accruing and past due 90 days or more 153 1,008 Troubled debt restructured loans** 26 513 Total $ 24,761 $ 29,055 * Includes $251,000 and $827,000, respectively, of purchased credit impaired loans as of December 31, 2019 and 2018. ** Our troubled debt restructured loans of $4,791,000 and $3,840,000, whose interest collection, after considering economic and business conditions and collection efforts, is doubtful are included in non-accrual The Company’s recorded investment in impaired loans and the related valuation allowance are as follows (dollars in thousands): December 31, 2019 December 31, 2018 Recorded Investment Valuation Allowance Recorded Investment Valuation Allowance $ 24,582 $ 3,228 $ 27,534 $ 4,069 The Company had $25,770,000 and $29,632,000 in non-accrual, December 31, 2019 2018 Commercial $ 3,093 $ 9,334 Agricultural 1,376 759 Real Estate 19,787 16,714 Consumer 326 727 Total $ 24,582 $ 27,534 No significant additional funds are committed to be advanced in connection with impaired loans as of December 31, 2019. The Company’s impaired loans and related allowance as of December 31, 2019 and 2018 are summarized in the following tables by class of financing receivables (in thousands). No interest income was recognized on impaired loans subsequent to their classification as impaired. December 31, 2019 Unpaid Principal Balance Recorded Recorded Total Related 12 Month Commercial $ 4,511 $ 630 $ 2,463 $ 3,093 $ 1,042 $ 3,488 Agricultural 1,603 658 718 1,376 235 1,644 Real Estate 27,366 7,081 12,706 19,787 1,950 21,726 Consumer 469 — 326 326 1 449 Total $ 33,949 $ 8,369 $ 16,213 $ 24,582 $ 3,228 $ 27,307 * Includes $251,000 of purchased credit impaired loans. December 31, 2018 Unpaid Principal Balance Recorded Recorded Total Related 12 Month Commercial $ 10,808 $ 6,728 $ 2,606 $ 9,334 $ 1,133 $ 7,986 Agricultural 799 213 546 759 170 842 Real Estate 24,072 6,699 10,015 16,714 2,409 16,042 Consumer 935 101 626 727 357 914 Total $ 36,614 $ 13,741 $ 13,793 $ 27,534 $ 4,069 $ 25,784 * Includes $827,000 of purchased credit impaired loans. The Company recognized interest income on impaired loans prior to being recognized as impaired of approximately $750,000, $948,000 and $624,000 during the years ended December 31, 2019, 2018 and 2017, respectively. From a credit risk standpoint, the Company rates its loans in one of four categories: (i) pass, (ii) special mention, (iii) substandard or (iv) doubtful. Loans rated as loss 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 non-accrual. The following summarizes the Company’s internal ratings of its loans held-for-investment December 31, 201 9 Pass Special Substandard Doubtful Total Commercial $ 825,775 $ 20,971 $ 9,580 $ — $ 856,326 Agricultural 101,614 64 1,962 — 103,640 Real Estate 2,717,227 42,036 64,109 — 2,823,372 Consumer 409,698 300 1,633 — 411,631 Total $ 4,054,314 $ 63,371 $ 77,284 $ — $ 4,194,969 December 31, 2018 Pass Special Substandard Doubtful Total Commercial $ 804,584 $ 23,392 $ 16,977 $ — $ 844,953 Agricultural 92,864 46 3,767 — 96,677 Real Estate 2,559,379 26,626 53,341 — 2,639,346 Consumer 370,510 315 1,835 — 372,660 Total $ 3,827,337 $ 50,379 $ 75,920 $ — $ 3,953,636 At December 31, 2019 and 2018, the Company’s past due loans are as follows (dollars in thousands): December 31, 2019 15-59 Past 60-89 Past Greater 90 Total Past Due Total Current Total Loans Total 90 Commercial $ 3,257 $ 557 $ 722 $ 4,536 $ 851,790 $ 856,326 $ 112 Agricultural 183 44 400 627 103,013 103,640 — Real Estate 12,890 288 195 13,373 2,809,999 2,823,372 — Consumer 572 151 45 768 410,863 411,631 41 Total $ 16,902 $ 1,040 $ 1,362 $ 19,304 $ 4,175,665 $ 4,194,969 $ 153 December 31, 2018 15-59 Past 60-89 Past Greater 90 Total Past Due Total Current Total Loans Total 90 Commercial $ 3,546 $ 682 $ 677 $ 4,905 $ 840,048 $ 844,953 $ — Agricultural 791 19 26 836 95,841 96,677 — Real Estate 13,185 881 2,020 16,086 2,623,260 2,639,346 960 Consumer 782 263 54 1,099 371,561 372,660 48 Total $ 18,304 $ 1,845 $ 2,777 $ 22,926 $ 3,930,710 $ 3,953,636 $ 1,008 * The The following table details the allowance for loan losses at December 31, 2019 and 2018 by portfolio segment (in thousands). There were no allowances for purchased credit impaired loans at December 31, 2019 or 2018. Allocation of a portion of the allowance to one category of loans does not preclude its availability to absorb losses in other categories. December 31, 2019 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 1,042 $ 235 $ 1,950 $ 1 $ 3,228 Loan collectively evaluated for impairment 11,080 971 32,024 5,196 49,271 Total $ 12,122 $ 1,206 $ 33,974 $ 5,197 $ 52,499 December 31, 2018 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 1,133 $ 170 $ 2,409 $ 357 $ 4,069 Loan collectively evaluated for impairment 10,815 1,276 29,933 5,109 47,133 Total $ 11,948 $ 1,446 $ 32,342 $ 5,466 $ 51,202 Changes in the allowance for loan losses for the years ended December 31, 2019 and 2018 are summarized as follows (in thousands): December 31, 2019 Commercial Agricultural Real Estate Consumer Total Beginning balance $ 11,948 $ 1,446 $ 32,342 $ 5,466 $ 51,202 Provision for loan losses 398 (79 ) 2,520 126 2,965 Recoveries 1,364 158 404 532 2,458 Charge-offs (1,588 ) (319 ) (1,292 ) (927 ) (4,126 ) Ending balance $ 12,122 $ 1,206 $ 33,974 $ 5,197 $ 52,499 December 31, 2018 Commercial Agricultural Real Estate Consumer Total Beginning balance $ 10,865 $ 1,305 $ 29,896 $ 6,090 $ 48,156 Provision for loan losses 1,662 126 3,463 414 5,665 Recoveries 839 15 462 512 1,828 Charge-offs (1,418 ) — (1,479 ) (1,550 ) (4,447 ) Ending balance $ 11,948 $ 1,446 $ 32,342 $ 5,466 $ 51,202 The Company’s recorded investment in loans as of December 31, 2019 and 2018 related to the balance in the allowance for loan losses on the basis of the Company’s impairment methodology was as follows (in thousands). Purchased credit impaired loans of $251,000 and $827,000, respectively, at December 31, 2019 and 2018 are included in loans individually evaluated for impairment. December 31, 2019 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 3,093 $ 1,376 $ 19,787 $ 326 $ 24,582 Loan collectively evaluated for impairment 853,233 102,264 2,803,585 411,305 4,170,387 Total $ 856,326 $ 103,640 $ 2,823,372 $ 411,631 $ 4,194,969 December 31, 2018 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 9,334 $ 759 $ 16,714 $ 727 $ 27,534 Loan collectively evaluated for impairment 835,619 95,918 2,622,632 371,933 3,926,102 Total $ 844,953 $ 96,677 $ 2,639,346 $ 372,660 $ 3,953,636 The Company’s loans that were modified in the years ended December 31, 2019 and 2018, and considered troubled debt restructurings are as follows (dollars in thousands): Year Ended December 31, 2019 Year Ended December 31, 2018 Number Pre-Modification Recorded Investment Post- Modification Recorded Investment Number Pre-Modification Recorded Post- Commercial 7 $ 551 $ 551 4 $ 864 $ 864 Agricultural 11 812 812 1 4 4 Real Estate 7 1,397 1,397 5 643 643 Consumer — — — 8 209 209 Total 25 $ 2,760 $ 2,760 18 $ 1,720 $ 1,720 The balances below provide information as to how the loans were modified as troubled debt restructured loans during the years ended December 31, 2019 and 2018 (dollars in thousands): Year Ended December 31, 2019 Year Ended December 31, 2018 Adjusted Extended Combined Adjusted Extended Combined Commercial $ — $ 389 $ 162 $ — $ 529 $ 335 Agricultural — 354 458 — — 4 Real Estate — 494 903 — 280 363 Consumer — — — — — 209 Total $ — $ 1,237 $ 1,523 $ — $ 809 $ 911 During the years ended December 31, 2019 and 2018, certain loans were modified as a troubled debt restructured loans 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 or more due or results in the foreclosure and repossession of the applicable collateral. The loans with payment default are as follows (dollars in thousands): Year Ended December 31, 2019 Year Ended December 31, 2018 Number Balance Number Balance Commercial — $ — 1 $ 491 Agriculture 7 267 — — Real Estate — — — — Consumer — — — — Total 7 $ 267 1 $ 491 As of December 31, 2019, the Company has no commitments to lend additional funds to loan customers whose terms have been modified in troubled debt restructurings. An analysis of the changes in loans to officers, directors, principal shareholders, or associates of such persons for the year ended December 31, 2019 (determined as of each respective year-end) Beginning Additional Payments Ending Year ended December 31, 2019 $ 67,394 $ 92,031 $ 74,061 $ 85,364 In the opinion of management, those loans are on substantially the same terms, including interest rates and collateral requirements, as those prevailing at the time for comparable transactions with unaffiliated persons. 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 December 31, 2019, $2,663,321,000 in loans held by our bank subsidiary were subject to blanket liens as security for this line of credit. At December 31, 2019, there were no amounts outstanding under this line of credit.

Loans Held for Sale

Loans Held for Sale	12 Months Ended
Loans Held for Sale	Dec. 31, 2019
Debt Disclosure [Abstract]
Loans Held for Sale	Note 4 - 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 nine 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. Loans held for sale totaled $28,228,000 and $21,672,000 at December 31, 2019 and 2018, respectively. At December 31, 2019 and 2018, $ 5,152,000 and $2,487,000, respectively, are valued at the lower of cost or fair value, and the remaining amount is valued under the fair value option. The change to the fair value option for loans held for sale was effective at June 30, 2018 and was done in conjunction with the Company’s move to mandatory delivery for substantially all loans sold in the secondary market and the purchase of forward mortgage-backed securities to manage the changes in fair value (see note 5 for additional information). 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 10). Interest income on mortgage loans held for sale is recognized based on the contractual rates and reflected in interest income on loans in the consolidated statements of earnings. The Company has no continuing ownership in any of these residential mortgage loans sold.

Derivative Financial Instrument

Derivative Financial Instruments	12 Months Ended
Derivative Financial Instruments	Dec. 31, 2019
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. Beginning in the second quarter of 2018, the Company purchased 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. These financial instruments are not designated as hedging instruments and are used for asset and liability management needs. All derivatives are carried at fair value in either other assets or other liabilities. 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). 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 10), 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 10). The estimated fair values are subject to change primarily due to changes in interest rates. The following table provides the outstanding notional balances and fair values of outstanding derivative positions (dollars in thousands): December 31, 2019: Outstanding Notional Balance Asset Derivative Fair Value Liability Derivative Fair Value IRLCs $ 47,415 $ 886 $ — Forward mortgage-backed securities trades 78,500 — 152 December 31, 2018: Outstanding Notional Balance Asset Derivative Fair Value Liability Derivative Fair Value IRLCs $ 37,088 $ 765 $ — Forward mortgage-backed securities trades 45,500 — 403

Bank Premises and Equipment

Bank Premises and Equipment	12 Months Ended
Bank Premises and Equipment	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Bank Premises and Equipment	6. BANK PREMISES AND EQUIPMENT The following is a summary of bank premises and equipment (in thousands): Useful Life December 31, 2019 2018 Land — $ 30,800 $ 31,190 Buildings 20 to 40 years 138,110 135,335 Furniture and equipment 3 to 10 years 60,200 58,969 Leasehold improvements Lesser of lease term or 5 to 15 years 3,364 3,557 232,474 229,051 Less- accumulated depreciation and amortization (101,452 ) (95,630 ) Total Bank Premises and Equipment $ 131,022 $ 133,421 Depreciation expense for the years ended December 31, 2019, 2018 and 2017 amounted to $9,801,000, $10,130,000 and $9,810,000, respectively, and is included in the captions net occupancy expense and equipment expense in the accompanying consolidated statements of earnings. The Company is lessor for portions of its banking premises. Total rental income for all leases included in net occupancy expense is approximately $2,831,000, $2,682,000 and $2,367,000, for the years ended December 31, 2019, 2018 and 2017, respectively.

Deposits and Borrowings

Deposits and Borrowings	12 Months Ended
Deposits and Borrowings	Dec. 31, 2019
Banking and Thrift [Abstract]
Deposits and Borrowings	7. DEPOSITS AND BORROWINGS: Time deposits of $250,000 or more totaled approximately $117,716,000 and $118,590,000 at December 31, 2019 and 2018, respectively. At December 31, 2019, the scheduled maturities of time deposits (in thousands) were, as follows: Year ending December 31, 2020 351,818 2021 42,445 2022 10,751 2023 7,058 2024 7,941 Thereafter — $ 420,013 Deposits received from related parties at December 31, 2019 and 2018 totaled $87,027,000 and $103,413,000, respectively. Borrowings at December 31, 2019 and 2018 consisted of the following (dollars in thousands): December 31, 2019 2018 Securities sold under agreements with customers to repurchase. $ 375,106 $ 409,631 Federal funds purchased 6,250 4,075 Advances from Federal Home Loan Bank of Dallas — 55,000 Total $ 381,356 $ 468,706 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” At December 31, 2018, the Company had advances from the Federal Home Loan Bank of Dallas of $55,000,000 that were repaid in 2019. There were no

Line of Credit

Line of Credit	12 Months Ended
Line of Credit	Dec. 31, 2019
Debt Disclosure [Abstract]
Line of Credit	8. LINE OF CREDIT: The Company renewed its loan agreement, effective June 30, 2019, with Frost Bank. Under the loan agreement, as renewed and amended, we a 2 will be The Wall Street Journal s s ly 1 2 five years and interest i The Wall Street Journal Prime Rate. non-performing no

Income Taxes

Income Taxes	12 Months Ended
Income Taxes	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	9. INCOME TAXES: On December 22, 2017, the Tax Cuts and Jobs Act was signed into law with sweeping modifications to the Internal Revenue Code. The primary change for the Company was to lower the corporate income tax rate to 21 35 re-measured re-measurement 7,650,000 664,000 No in the fu t ure The Company files a consolidated federal income tax return. Income tax expense is comprised of the following (dollars in thousands): Year Ended December 31, 2019 2018 2017 Current federal income tax $ 33,099 $ 28,359 $ 34,421 Current state income tax 150 92 99 Deferred federal income tax expense (benefit) (29 ) (250 ) (53 ) Restatement of net deferred tax liability due to change in income tax rate — (664 ) (7,650 ) Income tax expense $ 33,220 $ 27,537 $ 26,817 Income tax expense, as a percentage of pretax earnings, differs from the statutory federal income tax rate as follows: As a Percent of Pretax Earnings 2019 2018 2017 Statutory federal income tax rate 21.0 % 21.0 % 35.0 % Restatement of net deferred tax liability due to change in income tax rate — (0.4 ) (5.3 ) Reductions in tax rate resulting from interest income exempt from federal income tax (4.5 ) (5.2 ) (11.5 ) Effect of state income tax 0.1 0.1 0.1 ESOP tax deduction (0.1 ) (0.1 ) (0.2 ) Other 0.3 0.1 0.1 Effective income tax rate 16.8 % 15.5 % 18.2 % The approximate effects of each type of difference that gave rise to the Company’s deferred tax assets and liabilities at December 31, 2019 and 2018 are as follows (dollars in thousands): 2019 2018 Deferred tax assets: Tax basis of loans in excess of financial statement basis $ 12,245 $ 12,010 Minimum liability in defined benefit plan — 352 Recognized for financial reporting purposes but not yet for tax purposes: Deferred compensation 2,254 2,056 Write-downs and adjustments to other real estate owned and repossessed assets 48 49 Other deferred tax assets 157 208 Total deferred tax assets $ 14,704 $ 14,675 Deferred tax liabilities: Financial statement basis of fixed assets in excess of tax basis $ 4,651 $ 4,182 Intangible asset amortization deductible for tax purposes, but not for financial reporting purposes 11,935 11,263 Recognized for financial reporting purposes but not yet for tax purposes: Accretion on investment securities 755 745 Pension plan contributions — 816 Net unrealized gain on investment securities available-for-sale 17,945 1,111 Other deferred tax liabilities 51 34 Total deferred tax liabilities $ 35,337 $ 18,151 Net deferred tax asset (liability) $ (20,633 ) $ (3,476 ) At December 31, 2019 and 2018, management believes that it is more likely than not that all of the deferred tax amounts shown above will be realized and therefore no Current authoritative accounting guidance prescribes a than-not fifty more-likely-than-not more-likely-than-not 6 7 no

Fair Value Disclosures

Fair Value Disclosures	12 Months Ended
Fair Value Disclosures	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value Disclosures	10. 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 The following table summarizes financial assets and financial liabilities measured at fair value on a recurring basis as of December 31, 2019 and 2018 segregated by the level of the valuation inputs within the fair value hierarchy utilized to measure fair value (in thousands): December 31, 2019 Level 1 Level 2 Inputs Level 3 Inputs Total Fair Value Available-for-sale U.S Treasury securities $ 10,019 $ — $ — $ 10,019 Obligations of state and political subdivisions — 1,288,983 — 1,288,983 Corporate bonds — 230 — 230 Residential mortgage-backed securities — 1,608,863 — 1,608,863 Commercial mortgage-backed securities — 500,744 — 500,744 Other securities 4,478 — — 4,478 Total $ 14,497 $ 3,398,820 $ — $ 3,413,317 Loans held-for-sale $ — $ 23,076 $ — $ 23,076 IRLCs $ — $ 886 $ — $ 886 Forward mortgage-backed securities traded $ — $ (152 ) $ — $ (152 ) December 31, 2018 Level 1 Level 2 Inputs Level 3 Inputs Total Fair Value Available-for-sale U.S Treasury securities $ 9,962 $ — $ — $ 9,962 Obligations of U. S. government sponsored enterprises and agencies — 301 — 301 Obligations of state and political subdivisions — 1,257,871 — 1,257,871 Corporate bonds — 450 — 450 Residential mortgage-backed securities — 1,454,545 — 1,454,545 Commercial mortgage-backed securities — 431,300 — 431,300 Other securities 4,348 — — 4,348 Total $ 14,310 $ 3,144,467 $ — $ 3,158,777 Loans held-for-sale $ — $ 19,185 $ — $ 19,185 IRLCs $ — $ 765 $ — $ 765 Forward mortgage-backed securities traded $ — $ (403 ) $ — $ (403 ) Certain financial assets and financial liabilities are measured at fair value on a nonrecurring basis, that is, the instruments are not measured at fair value on an ongoing basis but are subject to fair value adjustments in certain circumstances (for example, when there is evidence of impairment). Impaired loans are reported at the fair value of the underlying collateral less selling costs if repayment is expected solely from the collateral. Collateral values are estimated using Level 2 inputs based on observable market data. At December 31, 2019, impaired loans with a carrying value of $16,213,000 were reduced by specific valuation reserves totaling $3,228,000 resulting in a net fair value of $12,985,000. Certain non-financial non-financial non-recurring non-financial Non-financial non-recurring re-measured The following table presents other real estate owned that were re-measured Year Ended 2019 2018 Carrying value of other real estate owned prior to re-measurement $ — $ 1,046 Write-downs included in gain (loss) on sale of other real estate owned — (236 ) Fair value $ — $ 810 At December 31, 2019 and 2018, other real estate owned totaled $982,000 and $448,000, 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 at December 31, 2019 and 2018, were as follows (dollars in thousands): 2019 2018 Carrying Estimated Carrying Estimated Fair Value Value Fair Value Value Fair Value Hierarchy Cash and due from banks $ 231,534 $ 231,534 $ 207,835 $ 207,835 Level 1 Federal Funds Sold 3,150 3,150 — — Level 1 Interest-bearing deposits in banks 47,920 47,920 40,812 40,812 Level 1 Interest-bearing time deposits in banks — — 1,458 1,458 Level 2 Available-for-sale 3,413,317 3,413,317 3,158,777 3,158,777 Levels 1 and 2 Loans held-for-investment 4,194,969 4,209,826 3,902,434 3,947,391 Level 3 Loans held-for-sale 28,228 28,343 21,672 21,779 Level 2 Accrued interest receivable 36,894 36,894 36,765 36,765 Level 2 Deposits with stated maturities 420,013 421,397 442,161 441,727 Level 2 Deposits with no stated maturities 6,183,793 6,183,793 5,738,228 5,738,228 Level 1 Borrowings 381,356 381,356 468,706 468,706 Level 2 Accrued interest payable 628 628 408 408 Level 2 IRLCs 886 886 765 765 Level 2 Forward mortgage-backed securities traded 152 152 403 403 Level 2

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
Commitments and Contingencies	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	11. COMMITMENTS AND CONTINGENCIES: The Company is engaged in legal actions arising from the normal course of business. In management’s opinion, the Company has adequate legal defenses with respect to these actions, and as of December 31, 2019 the resolution of these matters is not expected to have material adverse effects upon the results of operations or financial condition of the Company. The Company leases a portion of its bank premises and equipment under operating leases. At December 31, 2019, future minimum lease commitments were: 2020 - $557,000, 2021 - $342,000, 2022 - $145,000 and 2023 and thereafter - $57,000.

Financial Instruments with Off-

Financial Instruments with Off-Balance-Sheet Risk	12 Months Ended
Financial Instruments with Off-Balance-Sheet Risk	Dec. 31, 2019
Text Block [Abstract]
Financial Instruments with Off-Balance-Sheet Risk	12. FINANCIAL INSTRUMENTS WITH OFF-BALANCE-SHEET RISK: We are a party to financial instruments with off-balance-sheet Our exposure to credit loss in the event of nonperformance by the counterparty to the financial instrument for unfunded lines of credit, commitments to extend credit and standby letters of credit is represented by the contractual notional amount of these instruments. We generally use the same credit policies in making commitments and conditional obligations as we do for on-balance-sheet instruments. December 31, 2019 Financial instruments whose contract amounts represent credit risk: Unfunded lines of credit $ 743,595 Unfunded commitments to extend credit 374,158 Standby letters of credit 38,364 Total commercial commitments $ 1,156,117 Unfunded lines of credit and commitments to extend credit are agreements to lend to a customer as long as there is no violation of any condition established in the contract. These commitments generally have fixed expiration dates or other termination clauses and may require payment of a fee. Since many of the commitments are expected to expire without being drawn upon, the total commitment amounts do not necessarily represent future cash requirements. We evaluate each customer’s creditworthiness on a case-by-case Standby letters of credit are conditional commitments we issue to guarantee the performance of a customer to a third party. The credit risk involved in issuing letters of credit is essentially the same as that involved in extending loan facilities to customers. The average collateral value held on letters of credit usually exceeds the contract amount. We believe we have no other off-balance

Concentration of Credit Risk

Concentration of Credit Risk	12 Months Ended
Concentration of Credit Risk	Dec. 31, 2019
Risks and Uncertainties [Abstract]
Concentration of Credit Risk	13. CONCENTRATION OF CREDIT RISK: The Company grants commercial, retail, agriculture and residential real estate loans to customers primarily in North Central, Southeastern and West Texas. Although the Company has a diversified loan portfolio, a substantial portion of its borrowers’ ability to honor their commitments is dependent upon each local economic sector. In addition, the Company holds mortgage related securities which are guaranteed by GNMA, FNMA or FHLMC or are collateralized by loans backed by these agencies.

Pension and Profit Sharing Plan

Pension and Profit Sharing Plans	12 Months Ended
Pension and Profit Sharing Plans	Dec. 31, 2019
Retirement Benefits [Abstract]
Pension and Profit Sharing Plans	14. PENSION AND PROFIT SHARING PLANS: The Company had a defined benefit pension plan that was frozen effective January 1, 2004, whereby no new participants were added to the Plan and no additional years of service accrued to participants. The pension plan covered substantially all of the Company’s employees at the time. The benefits for each employee were based on years of service and a percentage of the employee’s qualifying compensation during the final years of employment. The Company’s funding policy was to contribute annually the amount necessary to satisfy the Internal Revenue Service’s funding standards. Contributions to the pension plan, prior to freezing the plan, were intended to provide not only for benefits attributed to service to date but also for those expected to be earned in the future. The Company made no In December 2018, due to the rising interest rate environment, the Company determined it was in the best interest of its shareholders to work toward terminating its pension obligation. The Company annuitized approximately 53 1,546,000 December 31, 2018. In 2019, the Company continued to take steps to completely settle and terminate its remaining pension obligation and recorded loss associated with the final termination of $2,673,000. The loss incurred included unrealized loss previously recorded in other comprehensive income and refunding to remaining participants for funding balance overages offset by a gain on hedging instrument entered into to minimize interest rate movement during the termination period. At December 31, 2019, all balances in the pension plan are zero and the Company’s obligation has been extinguished. Using an actuarial measurement date of December 31, 2019 and 2018, benefit obligation activity and fair value of plan assets for the years ended December 31, 2019 and 2018, and a statement of the funded status as of December 31, 2019 and 2018, are as follows (dollars in thousands): 2019 2018 Reconciliation of benefit obligations: Benefit obligation at January 1 $ 6,613 $ 15,531 Transfer liability from multiple employer plan 2,929 — Interest cost on projected benefit obligation 393 523 Actuarial (gain) loss, including settlement of all participants balances 1,257 (811 ) Benefits paid, including settlement of participant balances (11,192 ) (8,630 ) Benefit obligation at December 31 $ — $ 6,613 Reconciliation of fair value of plan assets: Fair value of plan assets at January 1 $ 8,781 $ 17,046 Transfer of assets from multiple employer plan 1,829 — Actual return on plan assets 582 365 Employer contributions — — Benefits paid, including settlement of certain participant balances (11,192 ) (8,630 ) Fair value of plan assets at December 31 — 8,781 Funded status $ — $ 2,168 Amounts recognized as a component of accumulated other comprehensive earnings as of year-end 2019 2018 Net actuarial loss $ — $ (1,717 ) Deferred tax benefit — 393 Amounts included in accumulated other comprehensive earnings, net of tax $ — $ (1,324 ) Net periodic benefit cost for the years ended December 31, 2019, 2018 and 2017, are as follows (dollars in thousands): Year Ended December 31, 2019 2018 2017 Service cost - benefits earned during the period $ — $ — $ — Interest cost on projected benefit obligation 393 523 635 Expected return on plan assets (227 ) (1,028 ) (974 ) Amortization of unrecognized net loss 185 186 249 Recognized loss on partial settlement of certain participant balances 2,673 1,546 — Net pension expense (benefit) $ 3,024 $ 1,227 $ (90 ) The following table sets forth the rates used in the actuarial calculations of the present value of benefit obligations and net periodic pension cost and the rate of return on plan assets: 2019 2018 2017 Weighted average discount rate 4.25 % 4.25 % 3.50 % Expected long-term rate of return on assets 2.20 % 6.25 % 6.25 % The weighted average discount rate was estimated based on setting a discount rate to establish an obligation for pension benefits equivalent to an amount that, if invested in high quality fixed income securities, would produce a return that matched the expected benefit payment stream. The expected long-term rate of return on plan assets was based on historical returns and expectations of future returns based on asset mix, after consultation with our investment advisors and actuaries. First Financial Trust & Asset Management Company, National Association, a wholly owned subsidiary of the Company, managed the pension plan assets as well as the profit sharing plan assets (see below). The investment strategy and targeted allocations were based on similar strategies First Financial Trust & Asset Management Company, National Association employed for most of its managed accounts whereby appropriate diversification is achieved. First Financial Trust & Asset Management Company, National Association was prohibited from holding investments deemed to be high risk by the Office of the Comptroller of the Currency. As of December 31, 2018, the pension plan’s total assets included First Financial Bankshares, Inc. common stock valued at approximately $3,373,000. The Company also provides a profit sharing plan, which covers substantially all full-time employees. The profit sharing plan is a defined contribution plan and allows employees to contribute a percentage of their base annual salary. Employees are fully vested to the extent of their contributions and become fully vested in the Company’s contributions over a six In 2004, after freezing our pension plan, we added a safe harbor match to the 401(k) plan. We match a maximum of 4% on employee deferrals of 5% of their employee compensation. Total expense for this matching in 2019, 2018 and 2017 was $2,759,000, $2,588,000 and $2,392,000, respectively, and is included in salaries and employee benefits in the statements of earnings. The Company has a directors’ deferred compensation plan whereby the directors may elect to defer up to 100% of their directors’ fees. All deferred compensation is invested in the Company’s common stock held in a rabbi trust. The stock is held in nominee name of the trustee, and the principal and earnings of the trust are held separate and apart from other funds of the Company, and are used exclusively for the uses and purposes of the deferred compensation agreement. The accounts of the trust have been consolidated in the financial statements of the Company.

Dividends from Subsidiaries

Dividends from Subsidiaries	12 Months Ended
Dividends from Subsidiaries	Dec. 31, 2019
Text Block [Abstract]
Dividends from Subsidiaries	15. DIVIDENDS FROM SUBSIDIARIES: At December 31, 2019, approximately $ 261,416,000

Regulatory Matters

Regulatory Matters	12 Months Ended
Regulatory Matters	Dec. 31, 2019
Banking and Thrift [Abstract]
Regulatory Matters	16. REGULATORY MATTERS: Banking regulators measure capital adequacy by means of the risk-based capital ratios and the leverage ratio under the Basel III regulatory capital framework and prompt corrective action regulations. The risk-based capital rules provide for the weighting of assets and off-balance-sheet quarter-to-date Beginning in January 2016, under the Basel III regulatory capital framework, the implementation of the capital conservation buffer was effective for the Company starting at the 0.625% level and increased 0.625% each year thereafter, until it reaches 2.5% on January 1, 2019. The capital conservation buffer is designed to absorb losses during periods of economic stress and requires increased capital levels for the purpose of capital distributions and other payments. Failure to meet the amount of the buffer will result in restrictions on the Company’s ability to make capital distributions, including dividend payments and stock repurchases, and to pay discretionary bonuses to executive officers. As of December 31, 2019 and 2018, we had a total risk-based capital ratio of 21.13% and 20.61%, a Tier 1 capital to risk-weighted assets ratio of 20.06% and 19.47%; a common equity Tier 1 capital to risk-weighted assets ratio of 20.06% and 19.47%, and a Tier 1 leverage ratio of 12.60% and11.85%, respectively. The regulatory capital ratios as of December 31, 2019 and 2018 were calculated under Basel III rules. There is no threshold for well-capitalized status for bank holding companies. As of December 31, 2019 and 2018, the regulatory capital ratios of the Company and Bank under the Basel III regulatory capital framework are as follows: Actual Minimum Capital Phased-In* Required to be As of December 31, 2019: Amount Ratio Amount Ratio Amount Ratio Total Capital to Risk-Weighted Assets: Consolidated $ 1,051,029 21.13 % $ 522,275 10.50 % — N/A First Financial Bank, N.A $ 908,778 18.31 % $ 521,081 10.50 % $ 496,268 10.00 % Tier 1 Capital to Risk-Weighted Assets: Consolidated $ 997,721 20.06 % $ 422,794 8.50 % — N/A First Financial Bank, N.A $ 855,470 17.24 % $ 421,828 8.50 % $ 397,014 8.00 % Common Equity Tier 1 Capital to Risk-Weighted Assets: Consolidated $ 997,721 20.06 % $ 348,184 7.00 % — N/A First Financial Bank, N.A $ 855,470 17.24 % $ 347,388 7.00 % $ 322,574 6.50 % Leverage Ratio: Consolidated $ 997,721 12.60 % $ 316,850 4.00 % — N/A First Financial Bank, N.A $ 855,470 10.84 % $ 315,570 4.00 % $ 394,463 5.00 % * At December 31, 2019 the Capital Conservative Buffer Basel III has been fully phased-in. Actual Minimum Capital Phase-In Minimum Capital Phased-In Required to be As of December 31, 2018: Amount Ratio Amount Ratio Amount Ratio Amount Ratio Total Capital to Risk-Weighted Assets: Consolidated $ 940,026 20.61 % $ 450,459 9.875 % $ 478,969 10.50 % — N/A First Financial Bank, N.A $ 824,428 18.12 % $ 449,350 9.875 % $ 477,790 10.50 % $ 455,038 10.00 % Tier 1 Capital to Risk-Weighted Assets: Consolidated $ 888,015 19.47 % $ 359,226 7.875 % $ 387,737 8.50 % — N/A First Financial Bank, N.A $ 772,417 16.97 % $ 358,342 7.875 % $ 386,782 8.50 % $ 364,030 8.00 % Common Equity Tier 1 Capital to Risk-Weighted Assets: Consolidated $ 888,015 19.47 % $ 290,802 6.375 % $ 319,312 7.00 % — N/A First Financial Bank, N.A $ 772,417 16.97 % $ 290,087 6.375 % $ 318,526 7.00 % $ 295,775 6.50 % Leverage Ratio: Consolidated $ 888,015 11.85 % $ 299,682 4.00 % $ 299,682 4.00 % — N/A First Financial Bank, N.A $ 772,417 10.35 % $ 298,576 4.00 % $ 298,576 4.00 % $ 373,220 5.00 % In connection with the adoption of the Basel III regulatory capital framework, our subsidiary bank made the election to continue to exclude most accumulated other comprehensive income (“AOCI”) from capital in connection with its March 31, 2015 quarterly financial filing and, in effect, to retain the AOCI treatment under the prior capital rules. In connection with the First Financial Trust & Asset Management Company, National Association’s (the “Trust Company”) application to obtain our trust charter, the Trust Company is required to maintain tangible net assets of $2,000,000 at all times. As of December 31, 2019, our Trust Company had tangible net assets totaling $28,550,000. Our subsidiary bank may be required at times to maintain reserve balances with the Federal Reserve Bank. At December 31, 2019 and 2018, the subsidiary bank’s reserve balances were $17,274,000 and $11,372,000, respectively.

Stock Option Plan and Restricte

Stock Option Plan and Restricted Stock Plan	12 Months Ended
Stock Option Plan and Restricted Stock Plan	Dec. 31, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock Option Plan and Restricted Stock Plan	17. STOCK OPTION PLAN AND RESTRICTED STOCK PLAN: The Company has an incentive stock plan to provide for the granting of options to employees of the Company at prices not less than market at the date of grant. At December 31, 2019, the Company had allocated 5,673,000 20 10 Shares Weighted- Weighted- Aggregate Intrinsic Outstanding, beginning of year 2,171,086 $ 17.27 Granted 398,850 29.70 Exercised (328,802 ) 13.06 Cancelled (102,938 ) 19.84 Outstanding, end of year 2,138,196 20.12 6.39 $ 32,040 Exercisable at end of year 885,206 $ 16.08 4.88 $ 16,836 The options outstanding at December 31, 2019 had exercise prices ranging between $7.87 and $29.70. Stock options have been adjusted retroactively for the effects of stock dividends and splits. The following table summarizes information concerning outstanding and vested stock options as of December 31, 2019: Exercise Price Number Outstanding Remaining Number Vested $ 7.87 97,456 1.8 97,456 $ 15.43 336,500 3.8 336,500 $ 16.95 564,440 5.8 303,160 $ 21.18 747,450 7.5 148,090 $ 29.70 392,350 9.5 — The fair value of the options granted during 2019 and 2017 were estimated using the Black-Scholes options pricing model with the following weighted-average assumptions: risk-free interest rate of %, %, respectively; expected dividend yield of % and %, respectively; expected life of years and years, respectively; and expected volatility of % %, respectively. The weighted-average grant-date fair value of options granted during 2019 and 2017 was $7.31 and $4.95, respectively. There were no grants during 2018. The total intrinsic value of options exercised during the years ended December 31, 2019, 2018 and 2017, was $5,742,000, $5,476,000 and $3,082,000, respectively. As of December 31, 2019, there was $4,943,000 of total unrecognized compensation cost related to nonvested share-based compensation arrangements granted under the Plan. That cost is expected to be recognized over a weighted-average period of 2.28 years. The total fair value of shares vested during the years ended December 31, 2019, 2018 and 2017 was $1,693,000, $888,000 and $1,246,000. The aggregate intrinsic value of vested stock options at December 31, 2019 totaled $14,234,000. On April 28, 2015, shareholders of the Company approved a restricted stock plan for selected employees, officers, non-employee On April 26, 2016, upon re-election ten non-employee re-election ten non-employee re-election nine nine non-employee non-employee On October 27, 2015, the Company granted 31,273 shares with a total value of $1,060,000 to certain officers that is being expensed over the vesting period of three years. On October 25, 2016, the Company granted 15,405 shares with a total value of $560,000 to certain officers that is being expensed over the vesting period of three years. On October 24, 2017, the Company granted 14,191 restricted shares with a total value of $655,000 to certain officers that is being expensed over the vesting period of one three years. three $ certain officers that will be expensed over a three 22,188 restricted shares with a total value of $ 785,000 three 995,000 680,000 562,000

Condensed Financial Information

Condensed Financial Information - Parent Company	12 Months Ended
Condensed Financial Information - Parent Company	Dec. 31, 2019
Condensed Financial Information Disclosure [Abstract]
Condensed Financial Information - Parent Company	18. CONDENSED FINANCIAL INFORMATION - PARENT COMPANY: Condensed Balance Sheets-December 31, 2019 and 2018 2019 2018 ASSETS Cash in subsidiary bank $ 44,422 $ 16,981 Cash in unaffiliated banks 2 2 Interest-bearing deposits in subsidiary bank 80,652 84,279 Total cash and cash equivalents 125,076 101,262 Securities available-for-sale, 6,297 6,276 Investment in and advances to subsidiaries, at equity 1,111,955 959,352 Intangible assets 723 723 Other assets 2,701 2,647 Total assets $ 1,246,752 $ 1,070,260 LIABILITIES AND SHAREHOLDERS’ EQUITY Total liabilities $ 19,555 $ 16,965 Shareholders’ equity: Common stock 1,359 678 Capital surplus 450,676 443,114 Retained earnings 707,656 606,658 Treasury stock (8,222 ) (7,507 ) Deferred compensation 8,222 7,507 Accumulated other comprehensive earnings 67,506 2,845 Total shareholders’ equity 1,227,197 1,053,295 Total liabilities and shareholders’ equity $ 1,246,752 $ 1,070,260 Condensed Statements of Earnings- For the Years Ended December 31, 2019, 2018 and 2017 2019 2018 2017 Income: Cash dividends from subsidiaries $ 84,500 $ 74,100 $ 30,800 Excess of earnings over dividends of subsidiaries 86,956 82,323 92,929 Other 7,937 7,269 6,590 Total income 179,393 163,692 130,319 Expenses: Salaries and employee benefits 11,963 9,966 8,606 Other operating expenses 4,756 4,781 3,871 Total expense 16,719 14,747 12,477 Earnings before income taxes 162,674 148,945 117,842 Income tax benefit 2,138 1,693 2,529 Net earnings $ 164,812 $ 150,638 $ 120,371 Condensed Statements of Cash Flows- For the Years Ended December 31, 2019, 2018 and 2017 2019 2018 2017 Cash flows from operating activities: Net earnings $ 164,812 $ 150,638 $ 120,371 Adjustments to reconcile net earnings to net cash provided by operating activities: Excess of earnings over dividends of subsidiary bank (86,956 ) (82,323 ) (92,929 ) Depreciation and amortization, net 246 331 207 Decrease (increase) in other assets 1,508 560 438 Increase (decrease) in other liabilities 990 1,932 183 Other — (2 ) 2 Net cash provided by operating activities 80,600 71,136 28,272 Cash flows from investing activities: Cash received in connection with acquisition of banks — — — Maturity of available-for-sale — 2,000 2,997 Purchases of bank premises and equipment and software (24 ) (346 ) (30 ) Net cash provided by (used in) investing activities (24 ) 1,654 2,967 Cash flows from financing activities: Proceeds of stock issuances 4,294 3,864 2,934 Cash dividends paid (61,056 ) (53,861 ) (48,955 ) Net cash used in financing activities (56,762 ) (49,997 ) (46,021 ) Net increase (decrease) in cash and cash equivalents 23,814 22,793 (14,782 ) Cash and cash equivalents, beginning of year 101,262 78,469 93,251 Cash and cash equivalents, end of year $ 125,076 $ 101,262 $ 78,469

Cash Flow Information

Cash Flow Information	12 Months Ended
Cash Flow Information	Dec. 31, 2019
Supplemental Cash Flow Elements [Abstract]
Cash Flow Information	19. CASH FLOW INFORMATION: Year Ended December 31, 2019 2018 2017 Supplemental cash flow information: Interest paid $ 29,882 $ 18,709 $ 9,316 Federal income taxes paid 30,726 26,578 29,695 Schedule of noncash investing and financing activities: Assets acquired through foreclosure 1,463 126 2,211 Investment securities purchased but not settled — — — Restricted stock grant to officers and directors 1,781 1,609 1,139

Acquisition

Acquisition	12 Months Ended
Acquisition	Dec. 31, 2019
Business Combinations [Abstract]
Acquisition	20. ACQUISITION On October 12, 2017 At closing, Commercial Bancshares, Inc. was merged into the Company and Commercial State Bank, Kingwood, Texas, was merged into First Financial Bank, National Association, Abilene, Texas, a wholly owned subsidiary of the Company. The primary purpose of the acquisition was to expand the Company’s market share around Houston. Factors that contributed to a purchase price resulting in goodwill include Commercial State Bank’s 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, 2018. The following table presents the amounts recorded on the consolidated balance sheet on the acquisition date (dollars in thousands): Fair value of consideration paid: Common stock issued ( 1,289,371 $ 58,087 Fair value of identifiable assets acquired: Cash and cash equivalents 18,653 Securities available-for-sale 64,501 Loans 266,327 Identifiable intangible assets 3,167 Other assets 15,375 Total identifiable assets acquired 368,023 Fair value of liabilities assumed: Deposits 341,902 Other liabilities (373 ) Total liabilities assumed 341,529 Fair value of net identifiable assets acquired 26,494 Goodwill resulting from acquisition $ 31,593 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 $266,327,000 at acquisition compared to contractual amounts of $271,714,000. The fair value of purchased credit impaired loans at acquisition was $3,013,000 compared to contractual amounts of $3,806,000. Additional purchased credit impaired loan disclosures were omitted due to immateriality. All other acquired loans were considered performing loans. Commercial State Bank had branches in Kingwood, Fulshear, El Campo and Palacios, all located around Houston, Texas.

Subsequent Events

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2019
Subsequent Events [Abstract]
Subsequent Events	21. SUBSEQUENT EVENT On January 1, 2020, the Com pany acquired % of the outstanding capital stock of TB&T , Inc. through the merger of a wholly owned subsidiary with and into TB&T , Inc. Following such merger, TB&T , Inc. and its wholly owned subsidiary, The Bank & Trust of Bryan/College Station, Texas, were merged into the Company and First Financial Bank, National Association, respectively. Considerations paid to the shareholders of TB&T , Inc. totaled approximately shares of the Company’s common stock with an aggregate value of $ at January 1, 2020. In addition, TB&T Bancshares, Inc. made a $1,920,000 special dividend to its shareholders prior to closing of the transaction. At December 31, 2019, The Bank & Trust of Bryan/College Station, Texas had gross loans totaling $455,400,000, total deposits of $551,900,000 and total assets of $631,100,000.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2019
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 73 locations located in Texas as of December 31, 2019. The subsidiary bank is First Financial Bank, National Association, Abilene, Texas. The bank’s primary source of revenue is providing loans and banking services to consumers and commercial customers in the market area in which the subsidiary is located. In addition, the Company also owns First Financial Trust & Asset Management Company, National Association, First Financial Insurance Agency, Inc., and First Technology Services, Inc. A summary of significant accounting policies of Bankshares 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 U.S. 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 U.S. 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 loan losses and its valuation of financial instruments.
Consolidation	Consolidation The accompanying consolidated financial statements include the accounts of Bankshares and its subsidiaries, all of which are wholly-owned. All significant intercompany accounts and transactions have been eliminated.
Stock Split and Increase in Authorized Shares	Stock Split and Increase in Authorized Shares On April 23, 2019, the Company’s Board of Directors declared a two-for-one stock split of the Company’s outstanding common shares effective on June 3, 2019. In addition, the shareholders of the Company approved an amendment to the Amended and Restated Certificate of Formation to increase the number of authorized shares to 200,000,000. All per share amounts in the annual report on Form 10-K have been restated to reflect this stock split. An amount equal to the par value of the additional common shares to be issued pursuant to the stock split was reflected as a transfer from retained earnings to common stock in the consolidated financial statements as of and for the year ended December 31, 2019.
Stock Repurchase	Stock Repurchase On June 25, 2017, the Company’s Board of Directors authorized the repurchase of up to 2,000,000 common shares through September 30, 2020 shares were repurchased under this repurchase plan or the prior authorization that expired September 30, 2017.
Acquisition	Acquisition On January 1, 2018, the Company acquired 100% of the outstanding capital stock of Commercial Bancshares, Inc. through the merger of a wholly-owned subsidiary with and into Commercial Bancshares, Inc. Following such merger, Commercial Bancshares, Inc. and its wholly-owned subsidiary, Commercial State Bank, Kingwood, Texas were merged into the Company and First Financial Bank, National Association, respectively. The results of operations of Commercial Bancshares, Inc. subsequent to the acquisition date, are include in the consolidated earnings of the Company. See Note 20 for additional information.
Investment Securities	Investment Securities Management classifies debt and equity securities as held-to-maturity, available-for-sale, held-to-maturity held-to-maturity available-for-sale Available-for-sale available-for-sale Effective January 1, 2018, in accordance with ASU 2016-01 decreases in available-for-sale The Company records its available-for-sale debt When the fair value of a debt security is below its amortized cost, and depending on the length of time the condition exists and the extent the fair value is below amortized cost, additional analysis is performed to determine whether an other-than-temporary impairment condition exists. Available-for-sale held-to-maturity The Company’s investment portfolio consists of U.S. Treasury securities, obligations of U.S. government sponsored enterprises and agencies, 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 - -
Loans and Allowance for Loan Losses	Loans Held-for-Investment Loans held for investment are stated at the amount of unpaid principal, reduced by unearned income and an allowance for loan losses. 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. The allowance for loan losses is established through a provision for loan losses charged to expense. Loans are charged against the allowance for loan losses when management believes the collectability of the principal is unlikely. The allowance for loan losses is an amount which represents management’s best estimate of probable losses that are inherent in the Company’s loan portfolio as of the balance sheet date. The allowance for loan losses is comprised of three elements: (i) specific reserves determined based on probable losses on specific classified loans; (ii) a historical valuation reserve component that considers historical loss rates and estimated loss emergence periods; and (iii) qualitative reserves based upon general economic conditions and other qualitative risk factors both internal and external to the Company. The allowance for loan losses is increased by charges to income and decreased by charge-offs Although we believe we use the best information available to make loan loss allowance determinations, future adjustments could be necessary if circumstances or economic conditions differ substantially from the assumptions used in making our initial determinations. A decline in the economy could result in increased levels of non-performing Accrual of interest is discontinued on a loan and payments are applied to principal when management believes, after considering economic and business conditions and collection efforts, the borrower’s financial condition is such that collection of interest is doubtful. Except consumer loans, generally all loans past due greater than 90 days, based on contractual terms, are placed on non-accrual. charged-off charge-off Loans are considered impaired when, based on current information and events, management determines that it is probable we will be unable to collect all amounts due in accordance with the loan agreement, including scheduled principal and interest payments. If a loan is impaired, a specific valuation allowance is allocated, if necessary. Interest payments on impaired loans are typically applied to principal unless collectability of the principal amount is reasonably assured, in which case interest is recognized on a cash basis. Impaired loans, or portions thereof, are charged off when deemed uncollectable. The Company’s policy requires measurement of the allowance for an impaired, collateral dependent loan based on the fair value of the collateral less cost to sell. Other loan impairments for non-collateral From time to time, the Company modifies its loan agreement with a borrower. A modified loan is considered a troubled debt restructuring when two conditions are met: (i) the borrower is experiencing financial difficulty and (ii) concessions are made by the Company that would not otherwise be considered for a borrower with similar credit risk characteristics. Modifications to loan terms may include a lower interest rate, a reduction of principal, or a longer term to maturity. For all impaired loans, including the Company’s troubled debt restructurings, the Company performs a periodic, well-documented credit evaluation of the borrower’s financial condition and prospects for repayment to assess the likelihood that all principal and interest payments required under the terms of the agreement will be collected in full. When doubt exists about the ultimate collectability of principal and interest, the troubled debt restructuring remains on non-accrual non-accrual The Company originates certain mortgage loans for sale in the secondary market. Accordingly, these loans are classified as held-for-sale Loans acquired, including loans acquired in a business combination, are initially recorded at fair value with no valuation allowance. Acquired loans are segregated between those considered to be credit impaired and those deemed performing. To make this determination, management considers such factors as past due status, non-accrual Purchased credit impaired loans are those loans that showed evidence of deterioration of credit quality since origination and for which it is probable, at acquisition, that the Company will be unable to collect all amounts contractually owed. Their acquisition fair value, which includes a credit component at the acquisition date, was based on the estimate of cash flows, both principal and interest, expected to be collected or estimated collateral values if cash flows are not estimable, discounted at prevailing market rates of interest. The difference between the discounted cash flows expected at acquisition and the investment in the loan is recognized as interest income on a level-yield method over the life of the loan, unless management was unable to reasonably forecast cash flows in which case the loans were placed on nonaccrual. Subsequent to the acquisition date, increases in expected cash flows will generally result in a recovery of any previously recorded allowance for loan loss, to the extent applicable, and/or a reclassification from the non-accretable
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 loan 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 and totaled $ 171,565,000 The carrying amount of goodwill arising from acquisitions that qualify as an asset purchase for federal income tax purposes was $18,680,000 and $22,526,000 at December 31, 2019 and 2018, respectively, and is deductible for federal income tax purposes. For the year ended December 31, 2017, the Company sold its mortgage servicing rights totaling $1,795,000 to an unrelated third party resulting in a loss on sale of approximately $215,000.
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 deposits in banks with original maturity of 90 days or less, and federal funds sold.
Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (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 Company recorded stock option expense totaling $1,489,000, $1,508,000 and $1,745,000 for the years ended December 31, 2019, 2018 and 2017, respectively. The Company also grants restricted stock for a fixed number of shares. The Company recorded expenses associated with its director and officer restricted stock grants totaling $620,000, $560,000 and $483,000 and $995,000, $
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 stock shares outstanding during the period. The Company calculates dilutive EPS assuming all outstanding stock options to purchase common stock have been exercised 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 restricted stock are assumed to be used to purchase common stock at the average market price during the respective year. Anti-dilutive shares are excluded from the computation of EPS . Net Earnings Weighted Per For the year ended December 31, 2019: Net earnings per share, basic $ 164,812 135,647,354 $ 1.22 Effect of stock options and stock grants — 698,665 (0.01 ) Net earnings per share, assuming dilution $ 164,812 136,346,019 $ 1.21 For the year ended December 31, 2018: Net earnings per share, basic $ 150,638 135,218,734 $ 1.11 Effect of stock options and stock grants — 747,294 — Net earnings per share, assuming dilution $ 150,638 135,966,028 $ 1.11 For the year ended December 31, 2017: Net earnings per share, basic $ 120,371 132,253,726 $ 0.91 Effect of stock options and stock grants — 394,934 — Net earnings per share, assuming dilution $ 120,371 132,648,660 $ 0.91
Recently Issued and Effective Authoritative Accounting Guidance	Recently Issued and Effective Authoritative Accounting Guidance Accounting Standards Update (“ASU”) 2014-09, “Revenue from Contracts with Customers 2014-09 2015-04 2014-09 2014-09, non-interest ASU 2016-01, ASU 2016-01 “Financial Instruments – Overall: Recognition and Measurement of Financial Assets and Financial Liabilities 2016-01, available-for-sale 2016-1 ASU 2016-02, “Leases 2016-02 right-of-use 2016-02 ASU 2016-09, “Compensation – Stock Compensation: Improvements to Employee Share-Based Payment Accounting 2016-09 income statement during the period in which they occur. Previously, such amounts were recorded in capital surplus. Additionally, excess tax benefits are classified along with other income tax cash flows as an operating activity rather than a financing activity, as was previously the case. ASU 2016-09 2016-09 ASU 2016-15, “Statement of Cash Flows (Topic 230) – Classification of Certain Cash Receipts and Cash Payments.” 2016-15 2016-15 ASU 2017-08, “Receivables – Nonrefundable Fees and Other Costs: Premium Amortization on Purchased Callable Debt Securities.” 2017-08 2017-08 2017-08 ASU 2017-09, Compensation – Stock Compensation (Topic 718) – Scope of Modification Accounting 2017-09 2017-09, 2017-09 ASU 2018-02, “Income Statement – Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income.” 2018-02 2018-02 2018-02

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
Summary of Significant Accounting Policies (Tables)	Dec. 31, 2019
Accounting Policies [Abstract]
Computation of Basic EPS to Dilutive EPS	The following table reconciles the computation of basic EPS to dilutive EPS: Net Earnings Weighted Per For the year ended December 31, 2019: Net earnings per share, basic $ 164,812 135,647,354 $ 1.22 Effect of stock options and stock grants — 698,665 (0.01 ) Net earnings per share, assuming dilution $ 164,812 136,346,019 $ 1.21 For the year ended December 31, 2018: Net earnings per share, basic $ 150,638 135,218,734 $ 1.11 Effect of stock options and stock grants — 747,294 — Net earnings per share, assuming dilution $ 150,638 135,966,028 $ 1.11 For the year ended December 31, 2017: Net earnings per share, basic $ 120,371 132,253,726 $ 0.91 Effect of stock options and stock grants — 394,934 — Net earnings per share, assuming dilution $ 120,371 132,648,660 $ 0.91

Interest-bearing Time Deposit_2

Interest-bearing Time Deposits in Banks and Securities (Tables)	12 Months Ended
	Dec. 31, 2019
Cash and Cash Equivalents [Abstract]
Summary of Available-for-Sale Securities	A summary of the Company’s available-for-sale December 31, 2019 Amortized Gross Gross Estimated Securities available-for-sale: U.S. Treasury securities $ 9,997 $ 22 $ — $ 10,019 Obligations of state and political subdivisions 1,231,619 57,764 (400 ) 1,288,983 Corporate bonds and other 4,643 65 — 4,708 Residential mortgage-backed 1,586,872 23,139 (1,148 ) 1,608,863 Commercial mortgage-backed securities 494,674 6,356 (286 ) 500,744 Total securities available-for-sale $ 3,327,805 $ 87,346 $ (1,834 ) $ 3,413,317 December 31, 201 8 Gross Gross Unrealized Estimated Securities available-for-sale: U.S. Treasury securities $ 9,970 $ — $ (8 ) $ 9,962 Obligations of U.S. government sponsored enterprises and agencies 301 — — 301 Obligations of state and political subdivisions 1,229,828 30,013 (1,970 ) 1,257,871 Corporate bonds and other 4,875 — (77 ) 4,798 Residential mortgage-backed securities 1,472,228 3,928 (21,611 ) 1,454,545 Commercial mortgage-backed securities 436,366 670 (5,736 ) 431,300 Total securities available-for-sale $ 3,153,568 $ 34,611 $ (29,402 ) $ 3,158,777
Amortized Cost and Estimated Fair Value of Available-for-Sale Securities	The amortized cost and estimated fair value of available-for-sale Amortized Estimated Due within one year $ 150,912 $ 152,445 Due after one year through five years 485,838 510,783 Due after five years through ten years 607,770 638,239 Due after ten years 1,739 2,243 Mortgage-backed securities 2,081,546 2,109,607 Total $ 3,327,805 $ 3,413,317
Continuous Unrealized-Loss Position of Available-for-Sale Securities	The following tables disclose, as of December 31, 2019 and 2018, the Company’s investment securities that have been in a continuous unrealized-loss Less than 12 Months 12 Months or Longer Total December 31, 2019 Fair Unrealized Fair Value Unrealized Fair Value Unrealized Obligations of state and political subdivisions $ 65,787 $ 400 $ 326 $ — $ 66,113 $ 400 Residential mortgage-backed securities 100,004 306 103,983 842 203,987 1,148 Commercial mortgage-backed securities 74,560 178 35,178 108 109,738 286 Total $ 240,351 $ 884 $ 139,487 $ 950 $ 379,838 $ 1,834 Less than 12 Months 12 Months or Longer Total December 31, 2018 Fair Unrealized Fair Value Unrealized Fair Value Unrealized U.S. Treasury securities $ 9,962 $ 8 $ — $ — $ 9,962 $ 8 Obligations of U.S. government sponsored enterprises and agencies — — 301 — 301 — Obligations of state and political subdivisions 27,489 107 114,461 1,863 141,950 1,970 Corporate bonds and other 4,348 68 450 9 4,798 77 Residential mortgage-backed securities 119,584 483 922,289 21,128 1,041,873 21,611 Commercial mortgage-backed securities 1,994 5 343,015 5,731 345,009 5,736 Total $ 163,377 $ 671 $ 1,380,516 $ 28,731 $ 1,543,893 $ 29,402

Loans Held for Investment and_2

Loans Held for Investment and Allowance for Loan Losses (Tables)	12 Months Ended
	Dec. 31, 2019
Receivables [Abstract]
Loans Held-for-Investment by Class of Financing Receivables	Loans held-for-investment December 31, 2019 2018 Commercial $ 856,326 $ 844,953 Agricultural 103,640 96,677 Real estate 2,823,372 2,639,346 Consumer 411,631 372,660 Total loans held-for-investment $ 4,194,969 $ 3,953,636
Non-Accrual Loans, Loans Still Accruing and Past Due 90 Days or More and Restructured Loans	The Company’s non-accrual December 31, 2019 2018 Non-accrual $ 24,582 $ 27,534 Loans still accruing and past due 90 days or more 153 1,008 Troubled debt restructured loans** 26 513 Total $ 24,761 $ 29,055 * Includes $251,000 and $827,000, respectively, of purchased credit impaired loans as of December 31, 2019 and 2018. ** Our troubled debt restructured loans of $4,791,000 and $3,840,000, whose interest collection, after considering economic and business conditions and collection efforts, is doubtful are included in non-accrual
Recorded Investment in Impaired Loans and Related Valuation Allowance	The Company’s recorded investment in impaired loans and the related valuation allowance are as follows (dollars in thousands): December 31, 2019 December 31, 2018 Recorded Investment Valuation Allowance Recorded Investment Valuation Allowance $ 24,582 $ 3,228 $ 27,534 $ 4,069
Schedule of Non-Accrual Loans	Non-accrual loans totaled $24,582,000 and $27,534,000 at December 31, 2019 and 2018, respectively, and consisted of the following amounts by type (dollars in thousands): December 31, 2019 2018 Commercial $ 3,093 $ 9,334 Agricultural 1,376 759 Real Estate 19,787 16,714 Consumer 326 727 Total $ 24,582 $ 27,534
Schedule of Impaired Loans and Related Allowance	The Company’s impaired loans and related allowance as of December 31, 2019 and 2018 are summarized in the following tables by class of financing receivables (in thousands). No interest income was recognized on impaired loans subsequent to their classification as impaired. December 31, 2019 Unpaid Principal Balance Recorded Recorded Total Related 12 Month Commercial $ 4,511 $ 630 $ 2,463 $ 3,093 $ 1,042 $ 3,488 Agricultural 1,603 658 718 1,376 235 1,644 Real Estate 27,366 7,081 12,706 19,787 1,950 21,726 Consumer 469 — 326 326 1 449 Total $ 33,949 $ 8,369 $ 16,213 $ 24,582 $ 3,228 $ 27,307 * Includes $251,000 of purchased credit impaired loans. December 31, 2018 Unpaid Principal Balance Recorded Recorded Total Related 12 Month Commercial $ 10,808 $ 6,728 $ 2,606 $ 9,334 $ 1,133 $ 7,986 Agricultural 799 213 546 759 170 842 Real Estate 24,072 6,699 10,015 16,714 2,409 16,042 Consumer 935 101 626 727 357 914 Total $ 36,614 $ 13,741 $ 13,793 $ 27,534 $ 4,069 $ 25,784 * Includes $827,000 of purchased credit impaired loans.
Schedule of Internal Ratings of Loans	The following summarizes the Company’s internal ratings of its loans held-for-investment December 31, 201 9 Pass Special Substandard Doubtful Total Commercial $ 825,775 $ 20,971 $ 9,580 $ — $ 856,326 Agricultural 101,614 64 1,962 — 103,640 Real Estate 2,717,227 42,036 64,109 — 2,823,372 Consumer 409,698 300 1,633 — 411,631 Total $ 4,054,314 $ 63,371 $ 77,284 $ — $ 4,194,969 December 31, 2018 Pass Special Substandard Doubtful Total Commercial $ 804,584 $ 23,392 $ 16,977 $ — $ 844,953 Agricultural 92,864 46 3,767 — 96,677 Real Estate 2,559,379 26,626 53,341 — 2,639,346 Consumer 370,510 315 1,835 — 372,660 Total $ 3,827,337 $ 50,379 $ 75,920 $ — $ 3,953,636
Schedule of Past Due Loans	At December 31, 2019 and 2018, the Company’s past due loans are as follows (dollars in thousands): December 31, 2019 15-59 Past 60-89 Past Greater 90 Total Past Due Total Current Total Loans Total 90 Commercial $ 3,257 $ 557 $ 722 $ 4,536 $ 851,790 $ 856,326 $ 112 Agricultural 183 44 400 627 103,013 103,640 — Real Estate 12,890 288 195 13,373 2,809,999 2,823,372 — Consumer 572 151 45 768 410,863 411,631 41 Total $ 16,902 $ 1,040 $ 1,362 $ 19,304 $ 4,175,665 $ 4,194,969 $ 153 December 31, 2018 15-59 Past 60-89 Past Greater 90 Total Past Due Total Current Total Loans Total 90 Commercial $ 3,546 $ 682 $ 677 $ 4,905 $ 840,048 $ 844,953 $ — Agricultural 791 19 26 836 95,841 96,677 — Real Estate 13,185 881 2,020 16,086 2,623,260 2,639,346 960 Consumer 782 263 54 1,099 371,561 372,660 48 Total $ 18,304 $ 1,845 $ 2,777 $ 22,926 $ 3,930,710 $ 3,953,636 $ 1,008 * The
Schedule of Allowance for Loan Losses by Portfolio Segment	The following table details the allowance for loan losses at December 31, 2019 and 2018 by portfolio segment (in thousands). There were no allowances for purchased credit impaired loans at December 31, 2019 or 2018. Allocation of a portion of the allowance to one category of loans does not preclude its availability to absorb losses in other categories. December 31, 2019 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 1,042 $ 235 $ 1,950 $ 1 $ 3,228 Loan collectively evaluated for impairment 11,080 971 32,024 5,196 49,271 Total $ 12,122 $ 1,206 $ 33,974 $ 5,197 $ 52,499 December 31, 2018 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 1,133 $ 170 $ 2,409 $ 357 $ 4,069 Loan collectively evaluated for impairment 10,815 1,276 29,933 5,109 47,133 Total $ 11,948 $ 1,446 $ 32,342 $ 5,466 $ 51,202
Changes in Allowance for Loan Losses	Changes in the allowance for loan losses for the years ended December 31, 2019 and 2018 are summarized as follows (in thousands): December 31, 2019 Commercial Agricultural Real Estate Consumer Total Beginning balance $ 11,948 $ 1,446 $ 32,342 $ 5,466 $ 51,202 Provision for loan losses 398 (79 ) 2,520 126 2,965 Recoveries 1,364 158 404 532 2,458 Charge-offs (1,588 ) (319 ) (1,292 ) (927 ) (4,126 ) Ending balance $ 12,122 $ 1,206 $ 33,974 $ 5,197 $ 52,499 December 31, 2018 Commercial Agricultural Real Estate Consumer Total Beginning balance $ 10,865 $ 1,305 $ 29,896 $ 6,090 $ 48,156 Provision for loan losses 1,662 126 3,463 414 5,665 Recoveries 839 15 462 512 1,828 Charge-offs (1,418 ) — (1,479 ) (1,550 ) (4,447 ) Ending balance $ 11,948 $ 1,446 $ 32,342 $ 5,466 $ 51,202
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 December 31, 2019 and 2018 related to the balance in the allowance for loan losses on the basis of the Company’s impairment methodology was as follows (in thousands). Purchased credit impaired loans of $251,000 and $827,000, respectively, at December 31, 2019 and 2018 are included in loans individually evaluated for impairment. December 31, 2019 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 3,093 $ 1,376 $ 19,787 $ 326 $ 24,582 Loan collectively evaluated for impairment 853,233 102,264 2,803,585 411,305 4,170,387 Total $ 856,326 $ 103,640 $ 2,823,372 $ 411,631 $ 4,194,969 December 31, 2018 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 9,334 $ 759 $ 16,714 $ 727 $ 27,534 Loan collectively evaluated for impairment 835,619 95,918 2,622,632 371,933 3,926,102 Total $ 844,953 $ 96,677 $ 2,639,346 $ 372,660 $ 3,953,636
Schedule of Loans Modified and Considered Troubled Debt Restructurings	The Company’s loans that were modified in the years ended December 31, 2019 and 2018, and considered troubled debt restructurings are as follows (dollars in thousands): Year Ended December 31, 2019 Year Ended December 31, 2018 Number Pre-Modification Recorded Investment Post- Modification Recorded Investment Number Pre-Modification Recorded Post- Commercial 7 $ 551 $ 551 4 $ 864 $ 864 Agricultural 11 812 812 1 4 4 Real Estate 7 1,397 1,397 5 643 643 Consumer — — — 8 209 209 Total 25 $ 2,760 $ 2,760 18 $ 1,720 $ 1,720
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 during the years ended December 31, 2019 and 2018 (dollars in thousands): Year Ended December 31, 2019 Year Ended December 31, 2018 Adjusted Extended Combined Adjusted Extended Combined Commercial $ — $ 389 $ 162 $ — $ 529 $ 335 Agricultural — 354 458 — — 4 Real Estate — 494 903 — 280 363 Consumer — — — — — 209 Total $ — $ 1,237 $ 1,523 $ — $ 809 $ 911
Schedule of Troubled Debt Restructurings	The loans with payment default are as follows (dollars in thousands): Year Ended December 31, 2019 Year Ended December 31, 2018 Number Balance Number Balance Commercial — $ — 1 $ 491 Agriculture 7 267 — — Real Estate — — — — Consumer — — — — Total 7 $ 267 1 $ 491
Analysis of Changes in Loans to Officers, Directors, Principal Shareholders, or Associates of Such Persons	An analysis of the changes in loans to officers, directors, principal shareholders, or associates of such persons for the year ended December 31, 2019 (determined as of each respective year-end) Beginning Additional Payments Ending Year ended December 31, 2019 $ 67,394 $ 92,031 $ 74,061 $ 85,364

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	12 Months Ended
Derivative Financial Instruments (Tables)	Dec. 31, 2019
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 (dollars in thousands): December 31, 2019: Outstanding Notional Balance Asset Derivative Fair Value Liability Derivative Fair Value IRLCs $ 47,415 $ 886 $ — Forward mortgage-backed securities trades 78,500 — 152 December 31, 2018: Outstanding Notional Balance Asset Derivative Fair Value Liability Derivative Fair Value IRLCs $ 37,088 $ 765 $ — Forward mortgage-backed securities trades 45,500 — 403

Bank Premises and Equipment (Ta

Bank Premises and Equipment (Tables)	12 Months Ended
Bank Premises and Equipment (Tables)	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Summary of Bank Premises and Equipment	The following is a summary of bank premises and equipment (in thousands): Useful Life December 31, 2019 2018 Land — $ 30,800 $ 31,190 Buildings 20 to 40 years 138,110 135,335 Furniture and equipment 3 to 10 years 60,200 58,969 Leasehold improvements Lesser of lease term or 5 to 15 years 3,364 3,557 232,474 229,051 Less- accumulated depreciation and amortization (101,452 ) (95,630 ) Total Bank Premises and Equipment $ 131,022 $ 133,421

Deposits and Borrowings (Tables

Deposits and Borrowings (Tables)	12 Months Ended
Deposits and Borrowings (Tables)	Dec. 31, 2019
Banking and Thrift [Abstract]
Scheduled Maturities of Time Deposits	At December 31, 2019, the scheduled maturities of time deposits (in thousands) were, as follows: Year ending December 31, 2020 351,818 2021 42,445 2022 10,751 2023 7,058 2024 7,941 Thereafter — $ 420,013
Schedule of Borrowings	Borrowings at December 31, 2019 and 2018 consisted of the following (dollars in thousands): December 31, 2019 2018 Securities sold under agreements with customers to repurchase. $ 375,106 $ 409,631 Federal funds purchased 6,250 4,075 Advances from Federal Home Loan Bank of Dallas — 55,000 Total $ 381,356 $ 468,706

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
Income Taxes (Tables)	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income Tax Expense	The Company files a consolidated federal income tax return. Income tax expense is comprised of the following (dollars in thousands): Year Ended December 31, 2019 2018 2017 Current federal income tax $ 33,099 $ 28,359 $ 34,421 Current state income tax 150 92 99 Deferred federal income tax expense (benefit) (29 ) (250 ) (53 ) Restatement of net deferred tax liability due to change in income tax rate — (664 ) (7,650 ) Income tax expense $ 33,220 $ 27,537 $ 26,817
Percentage of Pretax Earnings, Differs from Statutory Federal Income Tax Rate	Income tax expense, as a percentage of pretax earnings, differs from the statutory federal income tax rate as follows: As a Percent of Pretax Earnings 2019 2018 2017 Statutory federal income tax rate 21.0 % 21.0 % 35.0 % Restatement of net deferred tax liability due to change in income tax rate — (0.4 ) (5.3 ) Reductions in tax rate resulting from interest income exempt from federal income tax (4.5 ) (5.2 ) (11.5 ) Effect of state income tax 0.1 0.1 0.1 ESOP tax deduction (0.1 ) (0.1 ) (0.2 ) Other 0.3 0.1 0.1 Effective income tax rate 16.8 % 15.5 % 18.2 %
Schedule of Deferred Tax Assets and Liabilities	The approximate effects of each type of difference that gave rise to the Company’s deferred tax assets and liabilities at December 31, 2019 and 2018 are as follows (dollars in thousands): 2019 2018 Deferred tax assets: Tax basis of loans in excess of financial statement basis $ 12,245 $ 12,010 Minimum liability in defined benefit plan — 352 Recognized for financial reporting purposes but not yet for tax purposes: Deferred compensation 2,254 2,056 Write-downs and adjustments to other real estate owned and repossessed assets 48 49 Other deferred tax assets 157 208 Total deferred tax assets $ 14,704 $ 14,675 Deferred tax liabilities: Financial statement basis of fixed assets in excess of tax basis $ 4,651 $ 4,182 Intangible asset amortization deductible for tax purposes, but not for financial reporting purposes 11,935 11,263 Recognized for financial reporting purposes but not yet for tax purposes: Accretion on investment securities 755 745 Pension plan contributions — 816 Net unrealized gain on investment securities available-for-sale 17,945 1,111 Other deferred tax liabilities 51 34 Total deferred tax liabilities $ 35,337 $ 18,151 Net deferred tax asset (liability) $ (20,633 ) $ (3,476 )

Fair Value Disclosures (Tables)

Fair Value Disclosures (Tables)	12 Months Ended
Fair Value Disclosures (Tables)	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Financial Assets and Financial Liabilities Measured at Fair Value on Recurring Basis	The following table summarizes financial assets and financial liabilities measured at fair value on a recurring basis as of December 31, 2019 and 2018 segregated by the level of the valuation inputs within the fair value hierarchy utilized to measure fair value (in thousands): December 31, 2019 Level 1 Level 2 Inputs Level 3 Inputs Total Fair Value Available-for-sale U.S Treasury securities $ 10,019 $ — $ — $ 10,019 Obligations of state and political subdivisions — 1,288,983 — 1,288,983 Corporate bonds — 230 — 230 Residential mortgage-backed securities — 1,608,863 — 1,608,863 Commercial mortgage-backed securities — 500,744 — 500,744 Other securities 4,478 — — 4,478 Total $ 14,497 $ 3,398,820 $ — $ 3,413,317 Loans held-for-sale $ — $ 23,076 $ — $ 23,076 IRLCs $ — $ 886 $ — $ 886 Forward mortgage-backed securities traded $ — $ (152 ) $ — $ (152 ) December 31, 2018 Level 1 Level 2 Inputs Level 3 Inputs Total Fair Value Available-for-sale U.S Treasury securities $ 9,962 $ — $ — $ 9,962 Obligations of U. S. government sponsored enterprises and agencies — 301 — 301 Obligations of state and political subdivisions — 1,257,871 — 1,257,871 Corporate bonds — 450 — 450 Residential mortgage-backed securities — 1,454,545 — 1,454,545 Commercial mortgage-backed securities — 431,300 — 431,300 Other securities 4,348 — — 4,348 Total $ 14,310 $ 3,144,467 $ — $ 3,158,777 Loans held-for-sale $ — $ 19,185 $ — $ 19,185 IRLCs $ — $ 765 $ — $ 765 Forward mortgage-backed securities traded $ — $ (403 ) $ — $ (403 )
Other Real Estate Owned	The following table presents other real estate owned that were re-measured Year Ended 2019 2018 Carrying value of other real estate owned prior to re-measurement $ — $ 1,046 Write-downs included in gain (loss) on sale of other real estate owned — (236 ) Fair value $ — $ 810
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 at December 31, 2019 and 2018, were as follows (dollars in thousands): 2019 2018 Carrying Estimated Carrying Estimated Fair Value Value Fair Value Value Fair Value Hierarchy Cash and due from banks $ 231,534 $ 231,534 $ 207,835 $ 207,835 Level 1 Federal Funds Sold 3,150 3,150 — — Level 1 Interest-bearing deposits in banks 47,920 47,920 40,812 40,812 Level 1 Interest-bearing time deposits in banks — — 1,458 1,458 Level 2 Available-for-sale 3,413,317 3,413,317 3,158,777 3,158,777 Levels 1 and 2 Loans held-for-investment 4,194,969 4,209,826 3,902,434 3,947,391 Level 3 Loans held-for-sale 28,228 28,343 21,672 21,779 Level 2 Accrued interest receivable 36,894 36,894 36,765 36,765 Level 2 Deposits with stated maturities 420,013 421,397 442,161 441,727 Level 2 Deposits with no stated maturities 6,183,793 6,183,793 5,738,228 5,738,228 Level 1 Borrowings 381,356 381,356 468,706 468,706 Level 2 Accrued interest payable 628 628 408 408 Level 2 IRLCs 886 886 765 765 Level 2 Forward mortgage-backed securities traded 152 152 403 403 Level 2

Financial Instruments with Of_2

Financial Instruments with Off-Balance-Sheet Risk (Tables)	12 Months Ended
Financial Instruments with Off-Balance-Sheet Risk (Tables)	Dec. 31, 2019
Text Block [Abstract]
Schedule of Financial Instruments with Off-Balance-Sheet Risk	We generally use the same credit policies in making commitments and conditional obligations as we do for on-balance-sheet instruments. December 31, 2019 Financial instruments whose contract amounts represent credit risk: Unfunded lines of credit $ 743,595 Unfunded commitments to extend credit 374,158 Standby letters of credit 38,364 Total commercial commitments $ 1,156,117

Pension and Profit Sharing Pl_2

Pension and Profit Sharing Plans (Tables)	12 Months Ended
Pension and Profit Sharing Plans (Tables)	Dec. 31, 2019
Retirement Benefits [Abstract]
Benefit Obligation Activity and Fair Value of Plan Assets and Statement of Funded Status	Using an actuarial measurement date of December 31, 2019 and 2018, benefit obligation activity and fair value of plan assets for the years ended December 31, 2019 and 2018, and a statement of the funded status as of December 31, 2019 and 2018, are as follows (dollars in thousands): 2019 2018 Reconciliation of benefit obligations: Benefit obligation at January 1 $ 6,613 $ 15,531 Transfer liability from multiple employer plan 2,929 — Interest cost on projected benefit obligation 393 523 Actuarial (gain) loss, including settlement of all participants balances 1,257 (811 ) Benefits paid, including settlement of participant balances (11,192 ) (8,630 ) Benefit obligation at December 31 $ — $ 6,613 Reconciliation of fair value of plan assets: Fair value of plan assets at January 1 $ 8,781 $ 17,046 Transfer of assets from multiple employer plan 1,829 — Actual return on plan assets 582 365 Employer contributions — — Benefits paid, including settlement of certain participant balances (11,192 ) (8,630 ) Fair value of plan assets at December 31 — 8,781 Funded status $ — $ 2,168
Component of Accumulated Other Comprehensive Earnings	Amounts recognized as a component of accumulated other comprehensive earnings as of year-end 2019 2018 Net actuarial loss $ — $ (1,717 ) Deferred tax benefit — 393 Amounts included in accumulated other comprehensive earnings, net of tax $ — $ (1,324 )
Net Periodic Pension Cost	Net periodic benefit cost for the years ended December 31, 2019, 2018 and 2017, are as follows (dollars in thousands): Year Ended December 31, 2019 2018 2017 Service cost - benefits earned during the period $ — $ — $ — Interest cost on projected benefit obligation 393 523 635 Expected return on plan assets (227 ) (1,028 ) (974 ) Amortization of unrecognized net loss 185 186 249 Recognized loss on partial settlement of certain participant balances 2,673 1,546 — Net pension expense (benefit) $ 3,024 $ 1,227 $ (90 )
Benefit Obligations and Net Periodic Pension Cost and Rate of Return on Plan Assets	The following table sets forth the rates used in the actuarial calculations of the present value of benefit obligations and net periodic pension cost and the rate of return on plan assets: 2019 2018 2017 Weighted average discount rate 4.25 % 4.25 % 3.50 % Expected long-term rate of return on assets 2.20 % 6.25 % 6.25 %

Regulatory Matters (Tables)

Regulatory Matters (Tables)	12 Months Ended
Regulatory Matters (Tables)	Dec. 31, 2019
Banking and Thrift [Abstract]
Schedule of Regulatory Capital Ratios Under the Basel III Regulatory Capital Framework	As of December 31, 2019 and 2018, the regulatory capital ratios of the Company and Bank under the Basel III regulatory capital framework are as follows: Actual Minimum Capital Phased-In* Required to be As of December 31, 2019: Amount Ratio Amount Ratio Amount Ratio Total Capital to Risk-Weighted Assets: Consolidated $ 1,051,029 21.13 % $ 522,275 10.50 % — N/A First Financial Bank, N.A $ 908,778 18.31 % $ 521,081 10.50 % $ 496,268 10.00 % Tier 1 Capital to Risk-Weighted Assets: Consolidated $ 997,721 20.06 % $ 422,794 8.50 % — N/A First Financial Bank, N.A $ 855,470 17.24 % $ 421,828 8.50 % $ 397,014 8.00 % Common Equity Tier 1 Capital to Risk-Weighted Assets: Consolidated $ 997,721 20.06 % $ 348,184 7.00 % — N/A First Financial Bank, N.A $ 855,470 17.24 % $ 347,388 7.00 % $ 322,574 6.50 % Leverage Ratio: Consolidated $ 997,721 12.60 % $ 316,850 4.00 % — N/A First Financial Bank, N.A $ 855,470 10.84 % $ 315,570 4.00 % $ 394,463 5.00 % Actual Minimum Capital Phase-In Minimum Capital Phased-In Required to be As of December 31, 2018: Amount Ratio Amount Ratio Amount Ratio Amount Ratio Total Capital to Risk-Weighted Assets: Consolidated $ 940,026 20.61 % $ 450,459 9.875 % $ 478,969 10.50 % — N/A First Financial Bank, N.A $ 824,428 18.12 % $ 449,350 9.875 % $ 477,790 10.50 % $ 455,038 10.00 % Tier 1 Capital to Risk-Weighted Assets: Consolidated $ 888,015 19.47 % $ 359,226 7.875 % $ 387,737 8.50 % — N/A First Financial Bank, N.A $ 772,417 16.97 % $ 358,342 7.875 % $ 386,782 8.50 % $ 364,030 8.00 % Common Equity Tier 1 Capital to Risk-Weighted Assets: Consolidated $ 888,015 19.47 % $ 290,802 6.375 % $ 319,312 7.00 % — N/A First Financial Bank, N.A $ 772,417 16.97 % $ 290,087 6.375 % $ 318,526 7.00 % $ 295,775 6.50 % Leverage Ratio: Consolidated $ 888,015 11.85 % $ 299,682 4.00 % $ 299,682 4.00 % — N/A First Financial Bank, N.A $ 772,417 10.35 % $ 298,576 4.00 % $ 298,576 4.00 % $ 373,220 5.00 %

Stock Option Plan and Restric_2

Stock Option Plan and Restricted Stock Plan (Tables)	12 Months Ended
Stock Option Plan and Restricted Stock Plan (Tables)	Dec. 31, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Analysis of Stock Option Activity	An analysis of stock option activity for the year ended December 31, 2019 is presented in the table and narrative below: Shares Weighted- Weighted- Aggregate Intrinsic Outstanding, beginning of year 2,171,086 $ 17.27 Granted 398,850 29.70 Exercised (328,802 ) 13.06 Cancelled (102,938 ) 19.84 Outstanding, end of year 2,138,196 20.12 6.39 $ 32,040 Exercisable at end of year 885,206 $ 16.08 4.88 $ 16,836
Schedule of Information Concerning Outstanding and Vested Stock Options	The following table summarizes information concerning outstanding and vested stock options as of December 31, 2019: Exercise Price Number Outstanding Remaining Number Vested $ 7.87 97,456 1.8 97,456 $ 15.43 336,500 3.8 336,500 $ 16.95 564,440 5.8 303,160 $ 21.18 747,450 7.5 148,090 $ 29.70 392,350 9.5 — The fair value of the options granted during 2019 and 2017 were estimated using the Black-Scholes options pricing model with the following weighted-average assumptions: risk-free interest rate of %, %, respectively; expected dividend yield of % and %, respectively; expected life of years and years, respectively; and expected volatility of % %, respectively.

Condensed Financial Informati_2

Condensed Financial Information - Parent Company (Tables)	12 Months Ended
Condensed Financial Information - Parent Company (Tables)	Dec. 31, 2019
Condensed Financial Information Disclosure [Abstract]
Condensed Balance Sheets	Condensed Balance Sheets-December 31, 2019 and 2018 2019 2018 ASSETS Cash in subsidiary bank $ 44,422 $ 16,981 Cash in unaffiliated banks 2 2 Interest-bearing deposits in subsidiary bank 80,652 84,279 Total cash and cash equivalents 125,076 101,262 Securities available-for-sale, 6,297 6,276 Investment in and advances to subsidiaries, at equity 1,111,955 959,352 Intangible assets 723 723 Other assets 2,701 2,647 Total assets $ 1,246,752 $ 1,070,260 LIABILITIES AND SHAREHOLDERS’ EQUITY Total liabilities $ 19,555 $ 16,965 Shareholders’ equity: Common stock 1,359 678 Capital surplus 450,676 443,114 Retained earnings 707,656 606,658 Treasury stock (8,222 ) (7,507 ) Deferred compensation 8,222 7,507 Accumulated other comprehensive earnings 67,506 2,845 Total shareholders’ equity 1,227,197 1,053,295 Total liabilities and shareholders’ equity $ 1,246,752 $ 1,070,260
Condensed Statements of Earnings	Condensed Statements of Earnings- For the Years Ended December 31, 2019, 2018 and 2017 2019 2018 2017 Income: Cash dividends from subsidiaries $ 84,500 $ 74,100 $ 30,800 Excess of earnings over dividends of subsidiaries 86,956 82,323 92,929 Other 7,937 7,269 6,590 Total income 179,393 163,692 130,319 Expenses: Salaries and employee benefits 11,963 9,966 8,606 Other operating expenses 4,756 4,781 3,871 Total expense 16,719 14,747 12,477 Earnings before income taxes 162,674 148,945 117,842 Income tax benefit 2,138 1,693 2,529 Net earnings $ 164,812 $ 150,638 $ 120,371
Condensed Statements of Cash Flows	Condensed Statements of Cash Flows- For the Years Ended December 31, 2019, 2018 and 2017 2019 2018 2017 Cash flows from operating activities: Net earnings $ 164,812 $ 150,638 $ 120,371 Adjustments to reconcile net earnings to net cash provided by operating activities: Excess of earnings over dividends of subsidiary bank (86,956 ) (82,323 ) (92,929 ) Depreciation and amortization, net 246 331 207 Decrease (increase) in other assets 1,508 560 438 Increase (decrease) in other liabilities 990 1,932 183 Other — (2 ) 2 Net cash provided by operating activities 80,600 71,136 28,272 Cash flows from investing activities: Cash received in connection with acquisition of banks — — — Maturity of available-for-sale — 2,000 2,997 Purchases of bank premises and equipment and software (24 ) (346 ) (30 ) Net cash provided by (used in) investing activities (24 ) 1,654 2,967 Cash flows from financing activities: Proceeds of stock issuances 4,294 3,864 2,934 Cash dividends paid (61,056 ) (53,861 ) (48,955 ) Net cash used in financing activities (56,762 ) (49,997 ) (46,021 ) Net increase (decrease) in cash and cash equivalents 23,814 22,793 (14,782 ) Cash and cash equivalents, beginning of year 101,262 78,469 93,251 Cash and cash equivalents, end of year $ 125,076 $ 101,262 $ 78,469

Cash Flow Information (Tables)

Cash Flow Information (Tables)	12 Months Ended
Cash Flow Information (Tables)	Dec. 31, 2019
Supplemental Cash Flow Elements [Abstract]
Supplemental Information on Cash Flows and Noncash Transactions	19. CASH FLOW INFORMATION: Supplemental information on cash flows and noncash transactions is as follows (dollars in thousands): Year Ended December 31, 2019 2018 2017 Supplemental cash flow information: Interest paid $ 29,882 $ 18,709 $ 9,316 Federal income taxes paid 30,726 26,578 29,695 Schedule of noncash investing and financing activities: Assets acquired through foreclosure 1,463 126 2,211 Investment securities purchased but not settled — — — Restricted stock grant to officers and directors 1,781 1,609 1,139

Acquisition (Tables)

Acquisition (Tables)	12 Months Ended
Acquisition (Tables)	Dec. 31, 2019
Schedule of Amounts Recorded on Consolidated Balance Sheet on Acquisition Date	The following table presents the amounts recorded on the consolidated balance sheet on the acquisition date (dollars in thousands): Fair value of consideration paid: Common stock issued ( 1,289,371 $ 58,087 Fair value of identifiable assets acquired: Cash and cash equivalents 18,653 Securities available-for-sale 64,501 Loans 266,327 Identifiable intangible assets 3,167 Other assets 15,375 Total identifiable assets acquired 368,023 Fair value of liabilities assumed: Deposits 341,902 Other liabilities (373 ) Total liabilities assumed 341,529 Fair value of net identifiable assets acquired 26,494 Goodwill resulting from acquisition $ 31,593

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail)	Apr. 23, 2019shares	Dec. 31, 2019USD ($)Locationshares	Dec. 31, 2018USD ($)shares	Dec. 31, 2017USD ($)shares	Jan. 01, 2018	Sep. 02, 2017shares	Jun. 25, 2017shares
Equity, Class of Treasury Stock [Line Items]
Number of locations \| Location		73
Stockholders' Equity Note, Stock Split	two-for-one stock split
Common stock, shares authorized \| shares	200,000,000	200,000,000	200,000,000
Minimum number of shares that company is required to repurchase \| shares		0
Stock repurchase program expiration date		Sep. 30, 2020
Stock repurchased under authorization \| shares		0	0	0
Minimum number of days to consider the loans as non-accrual		90 days
Loans individually evaluated for impairment		$ 24,582,000	$ 27,534,000
Contractual balance		33,949,000	36,614,000
Impairment recorded		$ 0	0	$ 0
Other identifiable intangible assets, amortized period (years)		7 years
Goodwill and intangible assets with indefinite lives		$ 171,565,000	171,565,000
Carrying amount of goodwill arising from acquisitions, is deductible for federal income tax purposes		$ 18,680,000	22,526,000
Other intangible assets mortgage servicing rights				1,795,000
Loss on sale of mortgage servicing rights				(215,000)
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		$ 67,506,000	4,169,000
Minimum pension liability, included in accumulated other comprehensive income		0	(1,324,000)
Stock compensation expense		$ 1,489,000	$ 1,508,000	$ 1,745,000
Federal statutory tax rate		21.00%	21.00%	35.00%
Purchased Credit Impaired Loans [Member]
Equity, Class of Treasury Stock [Line Items]
Loans individually evaluated for impairment		$ 251,000	$ 827,000
Contractual balance		345,000	1,157,000
Accounting Standards Update 2018-02 [Member]
Equity, Class of Treasury Stock [Line Items]
Reclassification of standard tax debit within accumulated other comprehensive income to retained earnings		5,759,000
Director [Member]
Equity, Class of Treasury Stock [Line Items]
Restricted stock expense		620,000	560,000	$ 483,000
Officers [Member]
Equity, Class of Treasury Stock [Line Items]
Restricted stock expense		$ 995,000	$ 680,000	$ 562,000
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						1,500,000	2,000,000

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Computation of Basic EPS to Dilutive EPS (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Net earnings	$ 164,812	$ 150,638	$ 120,371
Effect of stock options and stock grants, Net Earnings	0	0	0
Net earnings per share, assuming dilution, Net Earnings	$ 164,812	$ 150,638	$ 120,371
Net earnings per share, basic, Weighted Average Shares	135,647,354	135,218,734	132,253,726
Effect of stock options and stock grants, Weighted Average Shares	698,665	747,294	394,934
Net earnings per share, assuming dilution, Weighted Average Shares	136,346,019	135,966,028	132,648,660
Net earnings per share, basic, Per Share Amount	$ 1.22	$ 1.11	$ 0.91
Effect of stock options and stock grants, Per Share Amount	(0.01)
Net earnings per share, assuming dilution, Per Share Amount	$ 1.21	$ 1.11	$ 0.91

Interest-bearing Time Deposit_3

Interest-bearing Time Deposits in Banks and Securities - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)Investment	Dec. 31, 2018USD ($)Investment	Dec. 31, 2017USD ($)
Interest Bearing Time Deposits In Banks And Securities [Line Items]
INTEREST-BEARING TIME DEPOSITS IN BANKS	$ 0	$ 1,458
Interest-bearing time deposits, maturity period, years	12 months
Number of investment positions \| Investment	93	93
Securities pledged as collateral	$ 2,329,784	$ 1,988,579
Sales of investment securities available-for-sale	67,414	220,259	$ 120,576
Gross realized gains from security sales	752	1,847	2,643
Gross realized losses from security sales or calls	$ 19	$ 493	$ 815
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	41.35%	32.65%
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	86.34%	84.70%

Interest-bearing Time Deposit_4

Interest-bearing Time Deposits in Banks and Securities - Summary of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	$ 3,327,805	$ 3,153,568
Securities available-for-sale, Gross Unrealized Holding Gains	87,346	34,611
Securities available-for-sale, Gross Unrealized Holding Losses	(1,834)	(29,402)
Securities available-for-sale, Estimated Fair Value	3,413,317	3,158,777
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	9,997	9,970
Securities available-for-sale, Gross Unrealized Holding Gains	22
Securities available-for-sale, Gross Unrealized Holding Losses		(8)
Securities available-for-sale, Estimated Fair Value	10,019	9,962
Obligations of U.S. Government Sponsored Enterprises and Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total		301
Securities available-for-sale, Estimated Fair Value		301
Obligations of State and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	1,231,619	1,229,828
Securities available-for-sale, Gross Unrealized Holding Gains	57,764	30,013
Securities available-for-sale, Gross Unrealized Holding Losses	(400)	(1,970)
Securities available-for-sale, Estimated Fair Value	1,288,983	1,257,871
Corporate Bonds and Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	4,643	4,875
Securities available-for-sale, Gross Unrealized Holding Gains	65
Securities available-for-sale, Gross Unrealized Holding Losses		(77)
Securities available-for-sale, Estimated Fair Value	4,708	4,798
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	1,586,872	1,472,228
Securities available-for-sale, Gross Unrealized Holding Gains	23,139	3,928
Securities available-for-sale, Gross Unrealized Holding Losses	(1,148)	(21,611)
Securities available-for-sale, Estimated Fair Value	1,608,863	1,454,545
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	494,674	436,366
Securities available-for-sale, Gross Unrealized Holding Gains	6,356	670
Securities available-for-sale, Gross Unrealized Holding Losses	(286)	(5,736)
Securities available-for-sale, Estimated Fair Value	$ 500,744	$ 431,300

Interest-bearing Time Deposit_5

Interest-bearing Time Deposits in Banks and Securities - Amortized Cost and Estimated Fair Value of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Available-for-Sale, Amortized Cost Basis, Due within one year	$ 150,912
Available-for-Sale, Amortized Cost Basis, Due after one year through five years	485,838
Available-for-Sale, Amortized Cost Basis, Due after five years through ten years	607,770
Available-for-Sale, Amortized Cost Basis, Due after ten years	1,739
Available-for-Sale, Amortized Cost Basis, Mortgage-backed securities	2,081,546
Available-for-Sale, Amortized Cost Basis, Total	3,327,805	$ 3,153,568
Available-for-Sale, Estimated Fair Value, Due within one year	152,445
Available-for-Sale, Estimated Fair Value, Due after one year through five years	510,783
Available-for-Sale, Estimated Fair Value, Due after five years through ten years	638,239
Available-for-Sale, Estimated Fair Value, Due after ten years	2,243
Available-for-Sale, Estimated Fair Value, Mortgage-backed securities	2,109,607
Securities available-for-sale, Estimated Fair Value, Total	$ 3,413,317	$ 3,158,777

Interest-bearing Time Deposit_6

Interest-bearing Time Deposits in Banks and Securities - Continuous Unrealized-Loss Position of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Fair Value	$ 240,351	$ 163,377
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	884	671
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	139,487	1,380,516
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	950	28,731
Available-for-sale securities, continuous unrealized loss position, Fair Value	379,838	1,543,893
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	1,834	29,402
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Fair Value		9,962
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss		8
Available-for-sale securities, continuous unrealized loss position, Fair Value		9,962
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss		8
Obligations of U.S. Government Sponsored Enterprises and Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value		301
Available-for-sale securities, continuous unrealized loss position, Fair Value		301
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	65,787	27,489
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	400	107
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	326	114,461
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss		1,863
Available-for-sale securities, continuous unrealized loss position, Fair Value	66,113	141,950
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	400	1,970
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		4,348
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss		68
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value		450
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss		9
Available-for-sale securities, continuous unrealized loss position, Fair Value		4,798
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss		77
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	100,004	119,584
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	306	483
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	103,983	922,289
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	842	21,128
Available-for-sale securities, continuous unrealized loss position, Fair Value	203,987	1,041,873
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	1,148	21,611
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	74,560	1,994
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	178	5
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	35,178	343,015
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	108	5,731
Available-for-sale securities, continuous unrealized loss position, Fair Value	109,738	345,009
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	$ 286	$ 5,736

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	Dec. 31, 2019	Dec. 31, 2018
Loans and Leases Receivable Disclosure [Line Items]
Total	$ 4,194,969	$ 3,953,636
Commercial [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total	856,326	844,953
Agriculture [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total	103,640	96,677
Real Estate [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total	2,823,372	2,639,346
Consumer [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total	$ 411,631	$ 372,660

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		Dec. 31, 2019	Dec. 31, 2018
Receivables [Abstract]
Non-accrual loans	[1]	$ 24,582	$ 27,534
Loans still accruing and past due 90 days or more		153	1,008
Troubled debt restructured loans	[2]	26	513
Total		$ 24,761	$ 29,055

[1]	Includes $251,000 and $827,000, respectively, of purchased credit impaired loans as of December 31, 2019 and 2018.
[2]	Our troubled debt restructured loans of $4,791,000 and $3,840,000, whose interest collection, after considering economic and business conditions and collection efforts, is doubtful are included in non-accrual loans as of December 31, 2019 and 2018, respectively.

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 ($)		Dec. 31, 2019	Dec. 31, 2018
Loans and Leases Receivable Disclosure [Line Items]
Non-accrual loans	[1]	$ 24,582,000	$ 27,534,000
Troubled debt restructured loans	[2]	26,000	513,000
Doubtful [Member]
Loans and Leases Receivable Disclosure [Line Items]
Troubled debt restructured loans		4,791,000	3,840,000
Purchased Credit Impaired Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Non-accrual loans		$ 251,000	$ 827,000

[1]	Includes $251,000 and $827,000, respectively, of purchased credit impaired loans as of December 31, 2019 and 2018.
[2]	Our troubled debt restructured loans of $4,791,000 and $3,840,000, whose interest collection, after considering economic and business conditions and collection efforts, is doubtful are included in non-accrual loans as of December 31, 2019 and 2018, respectively.

Loans Held for Investment and_6

Loans Held for Investment and Allowance for Loan Losses - Recorded Investment in Impaired Loans and Related Valuation Allowance (Detail) - USD ($) $ in Thousands		Dec. 31, 2019	Dec. 31, 2018
Receivables [Abstract]
Recorded Investment	[1]	$ 24,582	$ 27,534
Valuation Allowance		$ 3,228	$ 4,069

[1]	Includes $251,000 and $827,000, respectively, of purchased credit impaired loans as of December 31, 2019 and 2018.

Loans Held for Investment and_7

Loans Held for Investment and Allowance for Loan Losses - Additional Information (Detail) - USD ($)		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual, past due 90 days or more and still accruing, restructured loans and foreclosed assets		$ 25,770,000	$ 29,632,000
Non accrual loans	[1]	24,582,000	27,534,000
Additional funds advanced in connection with impaired loans		0
Interest income recognized on impaired loans		0
Interest income recognized on impaired loans		750,000	948,000	$ 624,000
Allowance for loan losses		52,499,000	51,202,000	$ 48,156,000
Loans individually evaluated for impairment		$ 24,582,000	$ 27,534,000
Default for purposes of this disclosure is a troubled debt restructured loan		90 days	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		2,663,321,000
Letters of credit outstanding		0
Advances from Federal Home Loan Bank of Dallas		0	$ 55,000,000
Purchased Credit Impaired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non accrual loans		251,000	827,000
Allowance for loan losses		0	0
Loans individually evaluated for impairment		$ 251,000	$ 827,000

[1]	Includes $251,000 and $827,000, respectively, of purchased credit impaired loans as of December 31, 2019 and 2018.

Loans Held for Investment and_8

Loans Held for Investment and Allowance for Loan Losses - Schedule of Non-Accrual Loans (Detail) - USD ($) $ in Thousands		Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	[1]	$ 24,582	$ 27,534
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans		3,093	9,334
Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans		1,376	759
Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans		19,787	16,714
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans		$ 326	$ 727

[1]	Includes $251,000 and $827,000, respectively, of purchased credit impaired loans as of December 31, 2019 and 2018.

Loans Held for Investment and_9

Loans Held for Investment and Allowance for Loan Losses - Schedule of Impaired Loans and Related Allowance (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	$ 33,949	$ 36,614
Recorded Investment With No Allowance	8,369	13,741
Recorded Investment With Allowance	16,213	13,793
Total Recorded Investment	24,582	27,534
Related Allowance	3,228	4,069
Average Recorded Investment	27,307	25,784
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	4,511	10,808
Recorded Investment With No Allowance	630	6,728
Recorded Investment With Allowance	2,463	2,606
Total Recorded Investment	3,093	9,334
Related Allowance	1,042	1,133
Average Recorded Investment	3,488	7,986
Agriculture [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	1,603	799
Recorded Investment With No Allowance	658	213
Recorded Investment With Allowance	718	546
Total Recorded Investment	1,376	759
Related Allowance	235	170
Average Recorded Investment	1,644	842
Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	27,366	24,072
Recorded Investment With No Allowance	7,081	6,699
Recorded Investment With Allowance	12,706	10,015
Total Recorded Investment	19,787	16,714
Related Allowance	1,950	2,409
Average Recorded Investment	21,726	16,042
Consumer [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	469	935
Recorded Investment With No Allowance	0	101
Recorded Investment With Allowance	326	626
Total Recorded Investment	326	727
Related Allowance	1	357
Average Recorded Investment	$ 449	$ 914

Loans Held for Investment an_10

Loans Held for Investment and Allowance for Loan Losses - Schedule of Impaired Loans and Related Allowance (Parenthetical) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Allowance	$ 8,369	$ 13,741
Purchased Credit Impaired Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Allowance	$ 251,000	$ 827,000

Loans Held for Investment an_11

Loans Held for Investment and Allowance for Loan Losses - Schedule of Internal Ratings of Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	$ 4,194,969	$ 3,953,636
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	856,326	844,953
Agriculture [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	103,640	96,677
Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	2,823,372	2,639,346
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	411,631	372,660
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	4,054,314	3,827,337
Pass [Member] \| Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	825,775	804,584
Pass [Member] \| Agriculture [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	101,614	92,864
Pass [Member] \| Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	2,717,227	2,559,379
Pass [Member] \| Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	409,698	370,510
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	63,371	50,379
Special Mention [Member] \| Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	20,971	23,392
Special Mention [Member] \| Agriculture [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	64	46
Special Mention [Member] \| Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	42,036	26,626
Special Mention [Member] \| Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	300	315
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	77,284	75,920
Substandard [Member] \| Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	9,580	16,977
Substandard [Member] \| Agriculture [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	1,962	3,767
Substandard [Member] \| Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	64,109	53,341
Substandard [Member] \| Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	$ 1,633	$ 1,835

Loans Held for Investment an_12

Loans Held for Investment and Allowance for Loan Losses - Schedule of Past Due Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 19,304	$ 22,926
Total Current	4,175,665	3,930,710
Total Loans	4,194,969	3,953,636
Total 90 Days Past Due Still Accruing	153	1,008
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,536	4,905
Total Current	851,790	840,048
Total Loans	856,326	844,953
Total 90 Days Past Due Still Accruing	112
Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	627	836
Total Current	103,013	95,841
Total Loans	103,640	96,677
Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	13,373	16,086
Total Current	2,809,999	2,623,260
Total Loans	2,823,372	2,639,346
Total 90 Days Past Due Still Accruing		960
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	768	1,099
Total Current	410,863	371,561
Total Loans	411,631	372,660
Total 90 Days Past Due Still Accruing	41	48
15-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	16,902	18,304
15-59 Days Past Due [Member] \| Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,257	3,546
15-59 Days Past Due [Member] \| Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	183	791
15-59 Days Past Due [Member] \| Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	12,890	13,185
15-59 Days Past Due [Member] \| Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	572	782
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,040	1,845
60-89 Days Past Due [Member] \| Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	557	682
60-89 Days Past Due [Member] \| Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	44	19
60-89 Days Past Due [Member] \| Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	288	881
60-89 Days Past Due [Member] \| Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	151	263
Greater than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,362	2,777
Greater than 90 Days [Member] \| Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	722	677
Greater than 90 Days [Member] \| Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	400	26
Greater than 90 Days [Member] \| Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	195	2,020
Greater than 90 Days [Member] \| Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 45	$ 54

Loans Held for Investment an_13

Loans Held for Investment and Allowance for Loan Losses - Schedule of Allowance for Loan Losses by Portfolio Segment (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	$ 3,228	$ 4,069
Loan collectively evaluated for impairment	49,271	47,133
Total allowance for loan losses	52,499	51,202	$ 48,156
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	1,042	1,133
Loan collectively evaluated for impairment	11,080	10,815
Total allowance for loan losses	12,122	11,948	10,865
Agriculture [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	235	170
Loan collectively evaluated for impairment	971	1,276
Total allowance for loan losses	1,206	1,446	1,305
Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	1,950	2,409
Loan collectively evaluated for impairment	32,024	29,933
Total allowance for loan losses	33,974	32,342	29,896
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	1	357
Loan collectively evaluated for impairment	5,196	5,109
Total allowance for loan losses	$ 5,197	$ 5,466	$ 6,090

Loans Held for Investment an_14

Loans Held for Investment and Allowance for Loan Losses - Changes in Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 51,202	$ 48,156
Provision for loan losses	2,965	5,665
Recoveries	2,458	1,828
Charge-offs	(4,126)	(4,447)
Ending balance	52,499	51,202
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	11,948	10,865
Provision for loan losses	398	1,662
Recoveries	1,364	839
Charge-offs	(1,588)	(1,418)
Ending balance	12,122	11,948
Agriculture [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,446	1,305
Provision for loan losses	(79)	126
Recoveries	158	15
Charge-offs	(319)
Ending balance	1,206	1,446
Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	32,342	29,896
Provision for loan losses	2,520	3,463
Recoveries	404	462
Charge-offs	(1,292)	(1,479)
Ending balance	33,974	32,342
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	5,466	6,090
Provision for loan losses	126	414
Recoveries	532	512
Charge-offs	(927)	(1,550)
Ending balance	$ 5,197	$ 5,466

Loans Held for Investment an_15

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	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	$ 24,582	$ 27,534
Loan collectively evaluated for impairment	4,170,387	3,926,102
Total	4,194,969	3,953,636
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	3,093	9,334
Loan collectively evaluated for impairment	853,233	835,619
Total	856,326	844,953
Agriculture [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	1,376	759
Loan collectively evaluated for impairment	102,264	95,918
Total	103,640	96,677
Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	19,787	16,714
Loan collectively evaluated for impairment	2,803,585	2,622,632
Total	2,823,372	2,639,346
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	326	727
Loan collectively evaluated for impairment	411,305	371,933
Total	$ 411,631	$ 372,660

Loans Held for Investment an_16

Loans Held for Investment and Allowance for Loan Losses - Schedule of Loans Modified and Considered Troubled Debt Restructurings (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)SecurityLoan	Dec. 31, 2018USD ($)SecurityLoan
Financing Receivable, Modifications [Line Items]
Number \| SecurityLoan	25	18
Pre-Modification Recorded Investment	$ 2,760	$ 1,720
Post-Modification Recorded Investment	$ 2,760	$ 1,720
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number \| SecurityLoan	7	4
Pre-Modification Recorded Investment	$ 551	$ 864
Post-Modification Recorded Investment	$ 551	$ 864
Agriculture [Member]
Financing Receivable, Modifications [Line Items]
Number \| SecurityLoan	11	1
Pre-Modification Recorded Investment	$ 812	$ 4
Post-Modification Recorded Investment	$ 812	$ 4
Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number \| SecurityLoan	7	5
Pre-Modification Recorded Investment	$ 1,397	$ 643
Post-Modification Recorded Investment	$ 1,397	$ 643
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Number \| SecurityLoan		8
Pre-Modification Recorded Investment		$ 209
Post-Modification Recorded Investment		$ 209

Loans Held for Investment an_17

Loans Held for Investment and Allowance for Loan Losses - Schedule of How Loans Were Modified as Troubled Debt Restructured Loans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	$ 2,760	$ 1,720
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	551	864
Agriculture [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	812	4
Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	1,397	643
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		209
Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	1,237	809
Extended Maturity [Member] \| Commercial [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	389	529
Extended Maturity [Member] \| Agriculture [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	354
Extended Maturity [Member] \| Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	494	280
Combined Rate and Maturity [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	1,523	911
Combined Rate and Maturity [Member] \| Commercial [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	162	335
Combined Rate and Maturity [Member] \| Agriculture [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	458	4
Combined Rate and Maturity [Member] \| Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	$ 903	363
Combined Rate and Maturity [Member] \| Consumer [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		$ 209

Loans Held for Investment an_18

Loans Held for Investment and Allowance for Loan Losses - Schedule of Troubled Debt Restructurings (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)Contract	Dec. 31, 2018USD ($)Contract
Financing Receivable, Modifications [Line Items]
Number \| Contract	7	1
Balance \| $	$ 267	$ 491
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number \| Contract		1
Balance \| $		$ 491
Agriculture [Member]
Financing Receivable, Modifications [Line Items]
Number \| Contract	7
Balance \| $	$ 267

Loans and Allowance for Loan Lo

Loans and Allowance for Loan Losses - Analysis of Changes in Loans to Officers, Directors, Principal Shareholders, or Associates of Such Persons (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
Receivables [Abstract]
Beginning Balance	$ 67,394
Additional Loans	92,031
Payments	74,061
Ending Balance	$ 85,364

Loans Held for Sale - Additiona

Loans Held for Sale - Additional Information (Detail) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Loans Receivables Held For Sale Net [Abstract]
Loans held for sale	$ 28,228,000	$ 21,672,000
Loans held-for-sale at the lower of cost or fair value	$ 5,152,000	$ 2,487,000

Derivative Financial Instrume_3

Derivative Financial Instruments - Summary of Outstanding Notional Balances and Fair Values of Outstanding Derivative Positions (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
IRLCs [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Outstanding Notional Balance	$ 47,415	$ 37,088
Asset Derivative Fair Value	886	765
Forward Mortgage-Backed Securities Trades [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Outstanding Notional Balance	78,500	45,500
Liability Derivative Fair Value	$ 152	$ 403

Bank Premises and Equipment - S

Bank Premises and Equipment - Summary of Bank Premises and Equipment (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Land	$ 30,800	$ 31,190
Buildings	138,110	135,335
Furniture and equipment	60,200	58,969
Leasehold improvements	3,364	3,557
Gross	232,474	229,051
Less- accumulated depreciation and amortization	(101,452)	(95,630)
Total Bank Premises and Equipment	$ 131,022	$ 133,421
Minimum [Member] \| Buildings [Member]
Property, Plant and Equipment [Line Items]
Useful Life in years	20 years
Minimum [Member] \| Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Useful Life in years	3 years
Minimum [Member] \| Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Useful Life in years	5 years
Maximum [Member] \| Buildings [Member]
Property, Plant and Equipment [Line Items]
Useful Life in years		40 years
Maximum [Member] \| Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Useful Life in years		10 years
Maximum [Member] \| Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Useful Life in years		15 years

Bank Premises and Equipment - A

Bank Premises and Equipment - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 9,801,000	$ 10,130,000	$ 9,810,000
Rental income for leases included in net occupancy expense	$ 2,831,000	$ 2,682,000	$ 2,367,000

Deposits and Borrowings - Addit

Deposits and Borrowings - Additional Information (Detail) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Banking and Thrift [Abstract]
Time deposit threshold amount	$ 250,000
Time deposits of $250,000 or more totaled	117,716,000	$ 118,590,000
Deposits received from related parties	87,027,000	103,413,000
Advances from Federal Home Loan Bank of Dallas, maturing during 2018	$ 0	$ 55,000,000

Deposits and Borrowings - Sched

Deposits and Borrowings - Scheduled Maturities of Time Deposits (Detail) $ in Thousands	Dec. 31, 2019USD ($)
Banking and Thrift [Abstract]
2020	$ 351,818
2021	42,445
2022	10,751
2023	7,058
2024	7,941
Thereafter	0
Time deposits	$ 420,013

Deposits and Borrowings - Sch_2

Deposits and Borrowings - Schedule of Borrowings (Detail) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Debt Disclosure [Abstract]
Securities sold under agreements with customers to repurchase	$ 375,106,000	$ 409,631,000
Federal funds purchased	6,250,000	4,075,000
Advances from Federal Home Loan Bank of Dallas	0	55,000,000
Total	$ 381,356,000	$ 468,706,000

Line of Credit - Additional Inf

Line of Credit - Additional Information (Detail) - USD ($)	12 Months Ended
Line of Credit - Additional Information (Detail) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Revolving line of credit, permitted	$ 25,000,000
Line of credit, maturity date	Jun. 30, 2021
Term facility payable (in years)	five years
Percentage of restricted dividend payments	55.00%
Line of credit	$ 0	$ 0
Minimum [Member]
Line of Credit Facility [Line Items]
Percentage of stock dividend declared	37.00%
Maximum [Member]
Line of Credit Facility [Line Items]
Percentage of stock dividend declared	53.00%

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
Income Taxes - Additional Information (Detail) - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Federal statutory tax rate	21.00%	21.00%	35.00%
Restatement of deferred tax liability due to change in tax rate	$ 0	$ 664,000	$ 7,650,000
Deferred tax amounts, valuation allowance recorded	0	0
Uncertain tax positions	$ 0	$ 0
Minimum [Member]
Income Taxes [Line Items]
Tax position measured if more-likely-than-not threshold is exceeded, percentage		50.00%

Income Taxes - Income Tax Expen

Income Taxes - Income Tax Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Current federal income tax	$ 33,099	$ 28,359	$ 34,421
Current state income tax	150	92	99
Deferred federal income tax expense (benefit)	(29)	(250)	(53)
Restatement of net deferred tax liability due to change in income tax rate		(664)	(7,650)
Income tax expense	$ 33,220	$ 27,537	$ 26,817

Income Taxes - Percentage of Pr

Income Taxes - Percentage of Pretax Earnings, Differs from Statutory Federal Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Statutory federal income tax rate	21.00%	21.00%	35.00%
Restatement of net deferred tax liability due to change in income tax rate		(0.40%)	(5.30%)
Reductions in tax rate resulting from interest income exempt from federal income tax	(4.50%)	(5.20%)	(11.50%)
Effect of state income tax	0.10%	0.10%	0.10%
ESOP tax deduction	(0.10%)	(0.10%)	(0.20%)
Other	0.30%	0.10%	0.10%
Effective income tax rate	16.80%	15.50%	18.20%

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Tax basis of loans in excess of financial statement basis	$ 12,245	$ 12,010
Minimum liability in defined benefit plan		352
Deferred compensation	2,254	2,056
Write-downs and adjustments to other real estate owned and repossessed assets	48	49
Other deferred tax assets	157	208
Total deferred tax assets	14,704	14,675
Deferred tax liabilities:
Financial statement basis of fixed assets in excess of tax basis	4,651	4,182
Intangible asset amortization deductible for tax purposes, but not for financial reporting purposes	11,935	11,263
Accretion on investment securities	755	745
Pension plan contributions		816
Net unrealized gain on investment securities available-for-sale	17,945	1,111
Other deferred tax liabilities	51	34
Total deferred tax liabilities	35,337	18,151
Net deferred tax asset (liability)	$ (20,633)	$ (3,476)

Fair Value Disclosures - Additi

Fair Value Disclosures - Additional Information (Detail)	12 Months Ended
Fair Value Disclosures - Additional Information (Detail)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets transfer between Level 2 and Level 3	$ 0	$ 0	$ 0
Impaired loans carrying value, recorded investment with allowance	16,213,000	13,793,000
Impaired loans valuation reserves	3,228,000	4,069,000
Impaired loans net fair value	12,985,000
Other real estate owned, total	$ 982,000	$ 448,000
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	Dec. 31, 2019	Dec. 31, 2018
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	$ 3,413,317	$ 3,158,777
Loans held-for-sale	28,228	21,672
U.S. Treasury Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	10,019	9,962
Obligations of U.S. Government Sponsored Enterprises and Agencies [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value		301
Obligations of State and Political Subdivisions [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	1,288,983	1,257,871
Residential Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	1,608,863	1,454,545
Commercial Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	500,744	431,300
IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	886	765
Forward Mortgage-Backed Securities Trades [Member]
Available-for-sale investment securities:
Forward mortgage-backed securities trades	152	403
Fair Value, Measurements, Recurring [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	3,413,317	3,158,777
Loans held-for-sale	23,076	19,185
Fair Value, Measurements, Recurring [Member] \| U.S. Treasury Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	10,019	9,962
Fair Value, Measurements, Recurring [Member] \| Obligations of U.S. Government Sponsored Enterprises and Agencies [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value		301
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	1,288,983	1,257,871
Fair Value, Measurements, Recurring [Member] \| Residential Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	1,608,863	1,454,545
Fair Value, Measurements, Recurring [Member] \| Commercial Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	500,744	431,300
Fair Value, Measurements, Recurring [Member] \| IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	886	765
Fair Value, Measurements, Recurring [Member] \| Forward Mortgage-Backed Securities Trades [Member]
Available-for-sale investment securities:
Forward mortgage-backed securities trades	(152)	(403)
Fair Value, Measurements, Recurring [Member] \| Corporate Bonds [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	230	450
Fair Value, Measurements, Recurring [Member] \| Other Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	4,478	4,348
Fair Value, Measurements, Recurring [Member] \| Level 1 Inputs [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	14,497	14,310
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	10,019	9,962
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	4,478	4,348
Fair Value, Measurements, Recurring [Member] \| Level 2 Inputs [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	3,398,820	3,144,467
Loans held-for-sale	23,076	19,185
Fair Value, Measurements, Recurring [Member] \| Level 2 Inputs [Member] \| Obligations of U.S. Government Sponsored Enterprises and Agencies [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value		301
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	1,288,983	1,257,871
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	1,608,863	1,454,545
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	500,744	431,300
Fair Value, Measurements, Recurring [Member] \| Level 2 Inputs [Member] \| IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	886	765
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	(152)	(403)
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	230	$ 450
Fair Value, Measurements, Recurring [Member] \| Level 3 Inputs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	$ 0

Fair Value Disclosures - Other

Fair Value Disclosures - Other Real Estate Owned (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Carrying value of other real estate owned prior to re-measurement		$ 1,046
Write-downs included in gain (loss) on sale of other real estate owned	$ 0	(236)
Other real estate owned, fair value		$ 810

Fair Value Disclosures - Schedu

Fair Value Disclosures - Schedule of Estimated Fair Values and Carrying Values of All Financial Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	$ 231,534	$ 207,835
Federal funds sold	3,150
Interest-bearing deposits in banks	47,920	40,812
Interest-bearing time deposits in banks	0	1,458
Available-for-sale securities	3,413,317	3,158,777
Loans held for investment	4,142,470	3,902,434
Loans held for sale	28,228	21,672
Deposits with stated maturities	420,013
Borrowings	381,356	468,706
IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset Derivative Fair Value	886	765
Forward Mortgage-Backed Securities Trades [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Forward mortgage-backed securities trades	152	403
Carrying Value [Member] \| Level 1 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	231,534	207,835
Federal funds sold	3,150
Interest-bearing deposits in banks	47,920	40,812
Deposits with no stated maturities	6,183,793	5,738,228
Carrying Value [Member] \| Level 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest-bearing time deposits in banks		1,458
Loans held for sale	28,228	21,672
Accrued interest receivable	36,894	36,765
Deposits with stated maturities	420,013	442,161
Borrowings	381,356	468,706
Accrued interest payable	628	408
Carrying Value [Member] \| Level 2 Inputs [Member] \| IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset Derivative Fair Value	886	765
Carrying Value [Member] \| Level 2 Inputs [Member] \| Forward Mortgage-Backed Securities Trades [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Forward mortgage-backed securities trades	152	403
Carrying Value [Member] \| Levels 1 and 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale securities	3,413,317	3,158,777
Carrying Value [Member] \| Level 3 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for investment	4,194,969	3,902,434
Estimated Fair Value [Member] \| Level 1 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	231,534	207,835
Federal funds sold	3,150
Interest-bearing deposits in banks	47,920	40,812
Deposits with no stated maturities	6,183,793	5,738,228
Estimated Fair Value [Member] \| Level 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest-bearing time deposits in banks		1,458
Loans held for sale	28,343	21,779
Accrued interest receivable	36,894	36,765
Deposits with stated maturities	421,397	441,727
Borrowings	381,356	468,706
Accrued interest payable	628	408
Asset Derivative Fair Value	886
Forward mortgage-backed securities trades	152
Estimated Fair Value [Member] \| Level 2 Inputs [Member] \| IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset Derivative Fair Value		765
Estimated Fair Value [Member] \| Level 2 Inputs [Member] \| Forward Mortgage-Backed Securities Trades [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Forward mortgage-backed securities trades		403
Estimated Fair Value [Member] \| Levels 1 and 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale securities	3,413,317	3,158,777
Estimated Fair Value [Member] \| Level 3 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for investment	$ 4,209,826	$ 3,947,391

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	Dec. 31, 2019USD ($)
Commitments and Contingencies Disclosure [Abstract]
Future minimum lease commitments, 2020	$ 557,000
Future minimum lease commitments, 2021	342,000
Future minimum lease commitments, 2022	145,000
Future minimum lease commitments, 2023 and thereafter	$ 57,000

Financial Instruments with Of_3

Financial Instruments with Off-Balance-Sheet Risk - Schedule of Financial Instruments with Off-Balance-sheet Risk (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
Concentration Risk [Line Items]
Financial instruments whose contract amounts represent credit risk	$ 1,156,117
Unfunded Lines of Credit [Member]
Concentration Risk [Line Items]
Financial instruments whose contract amounts represent credit risk	743,595
Unfunded Commitments to Extend Credit [Member]
Concentration Risk [Line Items]
Financial instruments whose contract amounts represent credit risk	374,158
Standby Letters of Credit [Member]
Concentration Risk [Line Items]
Financial instruments whose contract amounts represent credit risk	$ 38,364

Pension and Profit Sharing Pl_3

Pension and Profit Sharing Plans - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Contributions to the plan	$ 0	$ 0	$ 0
Defined benefit plan pension obligation retirement benefit percentage		53.00%
Defined benefit plan pension obligation, loss on settlement	2,673,000	$ 1,546,000
Common stock value	$ 1,359,000	678,000
Vesting period	6 years
Defined contribution plan cost	$ 7,661,000	7,049,000	4,735,000
Employee deferrals	4.00%
Employee compensation	5.00%
Directors' fees	100.00%
Profit Sharing Plan's Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Common stock value	$ 83,014,000	68,855,000
Pension Plan's Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Common stock value		3,373,000
Safe Harbor 401(k) Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan cost	$ 2,759,000	$ 2,588,000	$ 2,392,000

Pension and Profit Sharing Pl_4

Pension and Profit Sharing Plans - Benefit Obligation Activity and Fair Value of Plan Assets and Statement of Funded Status (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Interest cost on projected benefit obligation	$ 393,000	$ 523,000	$ 635,000
Actuarial (gain) loss, including settlement of all participants balances	0	(1,717,000)
Benefits paid, including settlement of certain participant balances	(2,673,000)	(1,546,000)
Employer contributions	0	0	0
Reconciliation of Benefit Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at January 1	6,613,000	15,531,000
Transfer liability from multiple employer plan	2,929,000
Interest cost on projected benefit obligation	393,000	523,000
Actuarial (gain) loss, including settlement of all participants balances	1,257,000	(811,000)
Benefits paid, including settlement of certain participant balances	(11,192,000)	(8,630,000)
Benefit obligation at December 31		6,613,000	15,531,000
Reconciliation of Fair Value of Plan Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at January 1	8,781,000	17,046,000
Transfer of assets from multiple employer plan	1,829,000
Actual return on plan assets	582,000	365,000
Benefits paid, including settlement of certain participant balances	$ (11,192,000)	(8,630,000)
Fair value of plan assets at December 31		8,781,000	$ 17,046,000
Funded status		$ 2,168,000

Pension and Profit Sharing Pl_5

Pension and Profit Sharing Plans - Component of Accumulated other Comprehensive Earnings (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Retirement Benefits [Abstract]
Net actuarial loss	$ 0	$ (1,717)
Deferred tax benefit	0	393
Amounts included in accumulated other comprehensive earnings, net of tax	$ 0	$ (1,324)

Pension and Profit Sharing Pl_6

Pension and Profit Sharing Plans - Net Periodic Pension Cost (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Retirement Benefits [Abstract]
Service cost-benefits earned during the period	$ 0	$ 0	$ 0
Interest cost on projected benefit obligation	393	523	635
Expected return on plan assets	(227)	(1,028)	(974)
Amortization of unrecognized net loss	185	186	249
Recognized loss on partial settlement of certain participant balances	2,673	1,546	0
Net periodic pension benefit expense (benefit)	$ 3,024	$ 1,227	$ (90)

Pension and Profit Sharing Pl_7

Pension and Profit Sharing Plans - Benefit Obligations and Net Periodic Pension Cost and Rate of Return on Plan Assets (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Retirement Benefits [Abstract]
Weighted average discount rate	4.25%	4.25%	3.50%
Expected long-term rate of return on assets	2.20%	6.25%	6.25%

Dividends from Subsidiaries - A

Dividends from Subsidiaries - Additional Information (Detail)	Dec. 31, 2019USD ($)
Equity [Abstract]
Amount available for the declaration of dividends by subsidiary banks without prior approval of regulatory agencies	$ 261,416,000

Regulatory Matters - Additional

Regulatory Matters - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Periodic increase of capital conservation buffer	0.625%
Total risk-based capital ratio, Actual Ratio	21.13%	20.61%
Tier1 Capital (to Risk-Weighted Assets), Actual Ratio	20.06%	19.47%
Common Tier1 Capital (to Risk-Weighted Assets), Actual Ratio	20.06%	19.47%
Tier1 Leverage ratio, Actual Ratio	12.60%	11.85%
Required tangible net assets	$ 28,550,000	$ 2,000,000
Subsidiary bank's reserve balance	$ 17,274,000	$ 11,372,000
Minimum [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital conservation buffer	0.625%
Maximum [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital conservation buffer	2.50%

Regulatory Matters - Schedule o

Regulatory Matters - Schedule of Regulatory Capital Ratios Under the Basel III Regulatory Capital Framework (Detail) - USD ($) $ in Thousands	Dec. 31, 2019		Dec. 31, 2018
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Risk-Weighted Assets, Actual Ratio	21.13%		20.61%
Tier1 Capital to Risk-Weighted Assets, Actual Ratio	20.06%		19.47%
Leverage Ratio, Actual Ratio	12.60%		11.85%
Consolidated [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Risk-Weighted Assets, Actual Amount	$ 1,051,029		$ 940,026
Tier1 Capital to Risk-Weighted Assets, Actual Amount	997,721		888,015
Common Equity Tier1 Capital to Risk-Weighted Assets, Actual Amount	997,721		888,015
Leverage Ratio, Actual Amount	$ 997,721		$ 888,015
Total Capital to Risk-Weighted Assets, Actual Ratio	21.13%		20.61%
Tier1 Capital to Risk-Weighted Assets, Actual Ratio	20.06%		19.47%
Common Equity Tier1 Capital to Risk-Weighted Assets, Actual Ratio	20.06%		19.47%
Leverage Ratio, Actual Ratio	12.60%		11.85%
Consolidated [Member] \| Minimum [Member] \| Basel III Fully Phased-In [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Risk-Weighted Assets, Minimum Capital Required	$ 522,275	[1]	$ 478,969
Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required	422,794	[1]	387,737
Common Equity Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required	348,184	[1]	319,312
Leverage Ratio, Minimum Capital Required	$ 316,850	[1]	$ 299,682
Total Capital to Risk-Weighted Assets, Minimum Capital Required	10.50%	[1]	10.50%
Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required	8.50%	[1]	8.50%
Common Equity Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required, Ratio	7.00%	[1]	7.00%
Leverage Ratio, Minimum Capital Required, Ratio	4.00%	[1]	4.00%
Consolidated [Member] \| Minimum [Member] \| Basel III Phase-In [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Risk-Weighted Assets, Minimum Capital Required			$ 450,459
Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required			359,226
Common Equity Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required			290,802
Leverage Ratio, Minimum Capital Required			$ 299,682
Total Capital to Risk-Weighted Assets, Minimum Capital Required			9.875%
Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required			7.875%
Common Equity Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required, Ratio			6.375%
Leverage Ratio, Minimum Capital Required, Ratio			4.00%
Parent Company [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Risk-Weighted Assets, Actual Amount	$ 908,778		$ 824,428
Tier1 Capital to Risk-Weighted Assets, Actual Amount	855,470		772,417
Common Equity Tier1 Capital to Risk-Weighted Assets, Actual Amount	855,470		772,417
Leverage Ratio, Actual Amount	$ 855,470		$ 772,417
Total Capital to Risk-Weighted Assets, Actual Ratio	18.31%		18.12%
Tier1 Capital to Risk-Weighted Assets, Actual Ratio	17.24%		16.97%
Common Equity Tier1 Capital to Risk-Weighted Assets, Actual Ratio	17.24%		16.97%
Leverage Ratio, Actual Ratio	10.84%		10.35%
Parent Company [Member] \| Minimum [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Risk-Weighted Assets, Required To Be Considered Well Capitalized , Ratio	10.00%		10.00%
Total Capital to Risk-Weighted Assets, Required To Be Considered Well Capitalized, Amount	$ 496,268		$ 455,038
Tier1 Capital to Risk-Weighted Assets, Required To Be Considered Well Capitalized , Ratio	8.00%		8.00%
Tier1 Capital to Risk-Weighted Assets, Required To Be Considered Well Capitalized, Amount	$ 397,014		$ 364,030
Common Equity Tier1 Capital to Risk-Weighted Assets, Required To Be Considered Well Capitalized , Ratio	6.50%		6.50%
Common Equity Tier1 Capital to Risk-Weighted Assets, Required To Be Considered Well Capitalized, Amount	$ 322,574		$ 295,775
Leverage Ratio, Required To Be Considered Well Capitalized , Ratio	5.00%		5.00%
Leverage Ratio, Required To Be Considered Well Capitalized, Amount	$ 394,463		$ 373,220
Parent Company [Member] \| Minimum [Member] \| Basel III Fully Phased-In [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Risk-Weighted Assets, Minimum Capital Required	521,081	[1]	477,790
Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required	421,828	[1]	386,782
Common Equity Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required	347,388	[1]	318,526
Leverage Ratio, Minimum Capital Required	$ 315,570	[1]	$ 298,576
Total Capital to Risk-Weighted Assets, Minimum Capital Required	10.50%	[1]	10.50%
Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required	8.50%	[1]	8.50%
Common Equity Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required, Ratio	7.00%	[1]	7.00%
Leverage Ratio, Minimum Capital Required, Ratio	4.00%	[1]	4.00%
Parent Company [Member] \| Minimum [Member] \| Basel III Phase-In [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Risk-Weighted Assets, Minimum Capital Required			$ 449,350
Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required			358,342
Common Equity Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required			290,087
Leverage Ratio, Minimum Capital Required			$ 298,576
Total Capital to Risk-Weighted Assets, Minimum Capital Required			9.875%
Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required			7.875%
Common Equity Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required, Ratio			6.375%
Leverage Ratio, Minimum Capital Required, Ratio			4.00%

[1]	At December 31, 2019 the Capital Conservative Buffer Basel III has been fully phased-in.

Stock Option Plan and Restric_3

Stock Option Plan and Restricted Stock Plan - Additional Information (Detail) - USD ($)	Apr. 28, 2020	Oct. 22, 2019	Jun. 26, 2019	Oct. 23, 2018	Apr. 24, 2018	Oct. 24, 2017	Apr. 25, 2017	Oct. 25, 2016	Oct. 27, 2015	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of stock for issuance under the plan										5,673,000
Restricted shares vesting period										6 years
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										$ 29.70
Fair value assumptions method used										Black-Scholes options pricing model		Black-Scholes options pricing model
Risk-free interest rate										1.83%		1.89%
Expected dividend yield										1.62%		1.79%
Expected life										6 years 7 months 20 days		6 years 2 months 26 days
Expected volatility										26.69%		26.51%
Weighted-average grant-date fair value of options granted										$ 7.31		$ 4.95
Total intrinsic value of options exercised										$ 5,742,000	$ 5,476,000	$ 3,082,000
Total unrecognized compensation cost related to nonvested share-based compensation arrangements granted under the Plan										$ 4,943,000
Weighted-average period of unrecognized compensation cost recognition, years										2 years 3 months 10 days
Total fair value of shares vested										$ 1,693,000	888,000	1,246,000
Aggregate intrinsic value of vested stock options										14,234,000
Stock compensation expense										$ 1,489,000	1,508,000	1,745,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of stock for issuance under the plan										686,000
Restricted Stock [Member] \| Non-Employee Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares granted	21,714				14,650		7,660			10,710
Restricted shares value	$ 660,000				$ 600,000		$ 250,000			$ 540,000
Restricted Stock [Member] \| Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense										620,000	560,000	483,000
Restricted Stock [Member] \| Officers [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares vesting period		3 years	3 years	3 years				3 years	3 years
Restricted shares granted		22,188	23,428	26,021		14,191		15,405	31,273
Restricted shares value		$ 785,000	$ 695,000	$ 1,440,000		$ 655,000		$ 560,000	$ 1,060,000
Stock compensation expense										$ 995,000	$ 680,000	$ 562,000
Restricted Stock [Member] \| Officers [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares vesting period						1 year
Restricted Stock [Member] \| Officers [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares vesting period						3 years
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 Information Concerning Outstanding and Vested Stock Options (Detail)	12 Months Ended
	Dec. 31, 2019$ / sharesshares
Exercise Price $7.87 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise Price \| $ / shares	$ 7.87
Number Outstanding	97,456
Number Vested	97,456
Remaining Contracted Life (Years)	1 year 9 months 18 days
Exercise Price $15.43 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise Price \| $ / shares	$ 15.43
Number Outstanding	336,500
Number Vested	336,500
Remaining Contracted Life (Years)	3 years 9 months 18 days
Exercise Price $16.95 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise Price \| $ / shares	$ 16.95
Number Outstanding	564,440
Number Vested	303,160
Remaining Contracted Life (Years)	5 years 9 months 18 days
Exercise Price $21.18 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise Price \| $ / shares	$ 21.18
Number Outstanding	747,450
Number Vested	148,090
Remaining Contracted Life (Years)	7 years 6 months
Exercise Price $29.70 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise Price \| $ / shares	$ 29.70
Number Outstanding	392,350
Remaining Contracted Life (Years)	9 years 6 months

Stock Option Plan and Restric_5

Stock Option Plan and Restricted Stock Plan - Schedule of Analysis of Stock Option Activity (Detail) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)$ / sharesshares
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Outstanding, beginning of year, Shares \| shares	2,171,086
Granted, Shares \| shares	398,850
Exercised, Shares \| shares	(328,802)
Cancelled, Shares \| shares	(102,938)
Outstanding, end of year, Shares \| shares	2,138,196
Exercisable at end of year, Shares \| shares	885,206
Outstanding, beginning of year, Weighted-Average Ex. Price \| $ / shares	$ 17.27
Granted, Weighted-Average Ex. Price \| $ / shares	29.70
Exercised, Weighted-Average Ex. Price \| $ / shares	13.06
Cancelled, Weighted-Average Ex. Price \| $ / shares	19.84
Outstanding, end of year, Weighted-Average Ex. Price \| $ / shares	20.12
Exercisable at end of year, Weighted-Average Ex. Price \| $ / shares	$ 16.08
Outstanding, end of year, Weighted-Average Remaining Contractual Term (Years)	6 years 4 months 20 days
Exercisable at end of year, Weighted-Average Remaining Contractual Term (Years)	4 years 10 months 17 days
Outstanding, end of year, Aggregate Intrinsic Value \| $	$ 32,040
Exercisable at end of year, Aggregate Intrinsic Value \| $	$ 16,836

Condensed Financial Informati_3

Condensed Financial Information - Parent Company - Condensed Balance Sheets (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
ASSETS
Interest-bearing deposits in subsidiary bank	$ 47,920	$ 40,812
Total cash and cash equivalents	282,604	248,647	$ 372,347	$ 256,486
OTHER ASSETS	90,919	90,762
Total assets	8,262,227	7,731,854
LIABILITIES AND SHAREHOLDERS' EQUITY
Total liabilities	7,035,030	6,678,559
SHAREHOLDERS' EQUITY:
Common stock	1,359	678
Capital surplus	450,676	443,114
Retained earnings	707,656	606,658
Accumulated other comprehensive earnings	67,506	2,845
Total shareholders' equity	1,227,197	1,053,295	922,768	837,885
Total liabilities and shareholders' equity	8,262,227	7,731,854
Subsidiary Bank [Member]
ASSETS
Cash in banks	44,422	16,981
Interest-bearing deposits in subsidiary bank	80,652	84,279
Unaffiliated Banks [Member]
ASSETS
Cash in banks	2	2
Parent Company [Member]
ASSETS
Total cash and cash equivalents	125,076	101,262	$ 78,469	$ 93,251
SECURITIES AVAILABLE-FOR-SALE, at fair value	6,297	6,276
Investment in and advances to subsidiaries, at equity	1,111,955	959,352
INTANGIBLE ASSETS	723	723
OTHER ASSETS	2,701	2,647
Total assets	1,246,752	1,070,260
LIABILITIES AND SHAREHOLDERS' EQUITY
Total liabilities	19,555	16,965
SHAREHOLDERS' EQUITY:
Common stock	1,359	678
Capital surplus	450,676	443,114
Retained earnings	707,656	606,658
Treasury stock	(8,222)	(7,507)
Deferred compensation	8,222	7,507
Accumulated other comprehensive earnings	67,506	2,845
Total shareholders' equity	1,227,197	1,053,295
Total liabilities and shareholders' equity	$ 1,246,752	$ 1,070,260

Condensed Financial Informati_4

Condensed Financial Information - Parent Company - Condensed Statements of Earnings (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income:
Total interest income	$ 319,192	$ 291,690	$ 245,975
Expenses:
Salaries and employee benefits	112,336	105,189	95,287
EARNINGS BEFORE INCOME TAXES	198,032	178,175	147,188
Income tax benefit	(33,220)	(27,537)	(26,817)
Net earnings	164,812	150,638	120,371
Parent Company [Member]
Income:
Cash dividends from subsidiaries	84,500	74,100	30,800
Excess of earnings over dividends of subsidiaries	86,956	82,323	92,929
Other	7,937	7,269	6,590
Total interest income	179,393	163,692	130,319
Expenses:
Salaries and employee benefits	11,963	9,966	8,606
Other operating expenses	4,756	4,781	3,871
Total Expense	16,719	14,747	12,477
EARNINGS BEFORE INCOME TAXES	162,674	148,945	117,842
Income tax benefit	2,138	1,693	2,529
Net earnings	$ 164,812	$ 150,638	$ 120,371

Condensed Financial Informati_5

Condensed Financial Information - Parent Company - Condensed Statements of Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net earnings	$ 164,812	$ 150,638	$ 120,371
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization, net	11,665	12,549	12,916
Decrease (increase) in other assets	1,851	(1,697)	9,313
Increase (decrease) in other liabilities	4,374	1,621	285
CASH FLOWS FROM INVESTING ACTIVITIES:
Cash received in connection with acquisition of banks		18,653
Maturity of available-for-sale security	4,460,703	3,439,028	4,392,131
Purchases of bank premises and equipment and software	(8,671)	(17,646)	(14,162)
Cash flows from financing activities:
Proceeds of stock issuances	4,294	3,864	2,934
Cash dividends paid	(61,056)	(53,861)	(48,955)
NET DECREASE IN CASH AND CASH EQUIVALENTS	33,957	(123,700)	115,861
CASH AND CASH EQUIVALENTS, beginning of year	248,647	372,347	256,486
CASH AND CASH EQUIVALENTS, end of year	282,604	248,647	372,347
Parent Company [Member]
Cash flows from operating activities:
Net earnings	164,812	150,638	120,371
Adjustments to reconcile net earnings to net cash provided by operating activities:
Excess of earnings over dividends of subsidiary bank	(86,956)	(82,323)	(92,929)
Depreciation and amortization, net	246	331	207
Decrease (increase) in other assets	1,508	560	438
Increase (decrease) in other liabilities	990	1,932	183
Other	0	(2)	2
Net cash provided by operating activities	80,600	71,136	28,272
CASH FLOWS FROM INVESTING ACTIVITIES:
Cash received in connection with acquisition of banks	0	0	0
Maturity of available-for-sale security		2,000	2,997
Purchases of bank premises and equipment and software	(24)	(346)	(30)
Net cash provided by (used in) investing activities	(24)	1,654	2,967
Cash flows from financing activities:
Proceeds of stock issuances	4,294	3,864	2,934
Cash dividends paid	(61,056)	(53,861)	(48,955)
Net cash used in financing activities	(56,762)	(49,997)	(46,021)
NET DECREASE IN CASH AND CASH EQUIVALENTS	23,814	22,793	(14,782)
CASH AND CASH EQUIVALENTS, beginning of year	101,262	78,469	93,251
CASH AND CASH EQUIVALENTS, end of year	$ 125,076	$ 101,262	$ 78,469

Cash Flow Information - Supplem

Cash Flow Information - Supplemental Information on Cash Flows and Noncash Transactions (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Supplemental cash flow information:
Interest paid	$ 29,882	$ 18,709	$ 9,316
Federal income taxes paid	30,726	26,578	29,695
Schedule of noncash investing and financing activities:
Assets acquired through foreclosure	1,463	126	2,211
Investment securities purchased but not settled
Restricted stock grant to officers and directors	$ 1,781	$ 1,609	$ 1,139

Acquisition - Additional Inform

Acquisition - Additional Information (Detail) - USD ($)	Jan. 01, 2018	Oct. 12, 2017	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Fair value of total loans			$ 266,327,000
Fair value of purchased credit impaired loans			24,582,000	$ 27,534,000
Contractual amounts			33,949,000	36,614,000
Purchased Credit Impaired Loans [Member]
Business Acquisition [Line Items]
Contractual amounts			345,000	$ 1,157,000
FBC Bancshares, Inc. and First Bank, N.A. [Member]
Business Acquisition [Line Items]
Payment for all outstanding shares of acquired entity by shares		1,289,371
Fair value of total loans			266,327,000
Total loans of contractual amounts			271,714,000
FBC Bancshares, Inc. and First Bank, N.A. [Member] \| Purchased Credit Impaired Loans [Member]
Business Acquisition [Line Items]
Fair value of purchased credit impaired loans			3,013,000
Contractual amounts			$ 3,806,000
Commercial Bancshares, Inc [Member]
Business Acquisition [Line Items]
Business acquisition, agreement date			Oct. 12, 2017
Payment for all outstanding shares of acquired entity by shares	1,289,371
Business acquisition, special dividend	$ 22,075,000
Increase decrease in business acquisition, special dividend	$ 42,402,000

Acquisition - Schedule of Amoun

Acquisition - Schedule of Amounts Recorded on Consolidated Balance Sheet on Acquisition Date (Detail) $ in Thousands	Oct. 12, 2017USD ($)
FBC Bancshares, Inc. and First Bank, N.A. [Member]
Business Acquisition [Line Items]
Common stock issued (1,289,371 shares)	$ 58,087

Acquisition - Schedule of Amo_2

Acquisition - Schedule of Amounts Recorded on Consolidated Balance Sheet on Acquisition Date (Parenthetical) (Detail)	Oct. 12, 2017shares
FBC Bancshares, Inc. and First Bank, N.A. [Member]
Business Acquisition [Line Items]
Common stock issued shares	1,289,371

Acquisition - Schedule of Preli

Acquisition - Schedule of Preliminary Estimated Fair Value Amounts Assigned to Major Asset and Liability Categories at Acquisition Date (Detail) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Loans	$ 266,327,000
Goodwill resulting from acquisition	171,565,000	$ 171,565,000
FBC Bancshares, Inc. and First Bank, N.A. [Member]
Business Acquisition [Line Items]
Cash and cash equivalents	18,653,000
Securities available-for-sale	64,501,000
Loans	266,327,000
Identifiable intangible assets	3,167,000
Other assets	15,375,000
Total identifiable assets acquired	368,023,000
Deposits	341,902,000
Other liabilities	(373,000)
Total liabilities assumed	341,529,000
Fair value of net identifiable assets acquired	26,494,000
Goodwill resulting from acquisition	$ 31,593,000

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) - USD ($)	Jan. 01, 2020	Dec. 31, 2019	Dec. 31, 2018
Subsequent Event [Line Items]
Gross loans		$ 4,194,969,000	$ 3,953,636,000
Deposits		6,603,806,000	6,180,389,000
Assets		8,262,227,000	$ 7,731,854,000
TB And T Bancshares Inc [Member]
Subsequent Event [Line Items]
payment of special dividend		1,920,000
Bank And Trust of Bryan College Station [Member]
Subsequent Event [Line Items]
Gross loans		455,400,000
Deposits		551,900,000
Assets		$ 631,100,000
Subsequent Event [Member] \| TB And T Bancshares Inc [Member]
Subsequent Event [Line Items]
Percentage of voting shares acquired	100.00%
Number of shares issued or issuable for business acquisition	6,276,000
Value of shares issued or issuable for business acquisition	$ 220,300,000