First Financial Bankshares (FFIN) 10-K 19 Feb 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Feb. 19, 2019	Jun. 30, 2018
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Trading Symbol	FFIN
Entity Registrant Name	FIRST FINANCIAL BANKSHARES INC
Entity Central Index Key	36,029
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		67,816,714
Entity Public Float			$ 3,280

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
ASSETS
CASH AND DUE FROM BANKS	$ 207,835	$ 209,583
INTEREST-BEARING DEPOSITS IN BANKS	40,812	162,764
Total cash and cash equivalents	248,647	372,347
INTEREST-BEARING TIME DEPOSITS IN BANKS	1,458	1,458
SECURITIES AVAILABLE-FOR-SALE, at fair value	3,158,777	3,087,473
LOANS:
Held for investment	3,953,636	3,485,569
Less - allowance for loan losses	(51,202)	(48,156)
Net loans held for investment	3,902,434	3,437,413
Held-for-sale ($19,185 at fair value at December 31, 2018; none at December 31, 2017)	21,672	15,130
Net loans	3,924,106	3,452,543
BANK PREMISES AND EQUIPMENT, net	133,421	124,026
INTANGIBLE ASSETS	174,683	141,143
OTHER ASSETS	90,762	75,725
Total assets	7,731,854	7,254,715
LIABILITIES AND SHAREHOLDERS' EQUITY
NONINTEREST-BEARING DEPOSITS	2,116,107	2,041,650
INTEREST-BEARING DEPOSITS	4,064,282	3,921,311
Total deposits	6,180,389	5,962,961
DIVIDENDS PAYABLE	14,227	12,589
BORROWINGS	468,706	331,000
OTHER LIABILITIES	15,237	25,397
Total liabilities	6,678,559	6,331,947
COMMITMENTS AND CONTINGENCIES
SHAREHOLDERS' EQUITY:
Common stock - $0.01 par value; authorized 120,000,000 shares; 67,753,133 and 66,260,444 shares issued at December 31, 2018 and 2017, respectively	678	663
Capital surplus	443,114	378,062
Retained earnings	606,658	517,257
Treasury stock (shares at cost: 467,811 and 495,964 at December 31, 2018 and 2017, respectively)	(7,507)	(7,148)
Deferred Compensation	7,507	7,148
Accumulated other comprehensive earnings	2,845	26,786
Total shareholders' equity	1,053,295	922,768
Total liabilities and shareholders' equity	$ 7,731,854	$ 7,254,715

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Loans held-for-sale, fair value	$ 19,185	$ 0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	120,000,000	120,000,000
Common stock, shares issued	67,753,133	66,260,444
Treasury stock, shares	467,811	495,964

Consolidated Statements of Earn

Consolidated Statements of Earnings - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
INTEREST INCOME:
Interest and fees on loans	$ 200,347	$ 166,807	$ 161,018
Interest on investment securities:
Taxable	50,052	32,825	27,626
Exempt from federal income tax	39,661	44,659	43,302
Interest on federal funds sold and interest-bearing deposits in banks	1,630	1,684	342
Total interest income	291,690	245,975	232,288
INTEREST EXPENSE:
Interest on deposits	16,946	8,213	4,503
Other	1,984	1,075	948
Total interest expense	18,930	9,288	5,451
Net interest income	272,760	236,687	226,837
PROVISION FOR LOAN LOSSES	5,665	6,530	10,212
Net interest income after provision for loan losses	267,095	230,157	216,625
NONINTEREST INCOME:
ATM, interchange and credit card fees	28,532	25,686	23,910
Net gain on sale of available-for-sale securities (includes $1,354, $1,828 and $1,270 for the years ended December 31, 2018, 2017 and 2016, respectively, related to accumulated comprehensive earnings reclassifications)	1,354	1,828	1,270
Net gain (loss) on sale of foreclosed assets	116	(50)	456
Net gain (loss) on sale of assets	(147)	(396)	168
Interest on loan recoveries	938	1,128	2,112
Other	5,970	4,602	3,108
Total noninterest income	101,764	91,017	85,132
NONINTEREST EXPENSE:
Salaries and employee benefits	105,189	95,287	90,739
Loss from partial settlement of pension plan	1,546		267
Net occupancy expense	11,173	10,521	10,420
Equipment expense	13,841	13,765	13,479
FDIC insurance premiums	2,333	2,217	2,680
ATM, interchange and credit card expenses	9,282	7,452	7,231
Professional and service fees	8,894	8,063	6,877
Printing, stationery and supplies	1,997	1,989	2,093
Operational and other losses	2,188	3,192	2,170
Amortization of intangible assets	1,272	613	738
Other	32,969	30,887	29,136
Total noninterest expense	190,684	173,986	165,830
EARNINGS BEFORE INCOME TAXES	178,175	147,188	135,927
INCOME TAX EXPENSE (includes $284, $640 and $445 for the years ended December 31, 2018, 2017 and 2016, respectively, related to income tax expense from reclassification items)	27,537	26,817	31,153
NET EARNINGS	$ 150,638	$ 120,371	$ 104,774
NET EARNINGS PER SHARE, BASIC	$ 2.23	$ 1.82	$ 1.59
NET EARNINGS PER SHARE, ASSUMING DILUTION	$ 2.22	$ 1.81	$ 1.59
Trust Fees [Member]
NONINTEREST INCOME:
Revenue from contract with customer	$ 28,181	$ 23,694	$ 19,636
Service Charges on Deposit Accounts [Member]
NONINTEREST INCOME:
Revenue from contract with customer	21,663	19,416	18,386
Real Estate Mortgage Operations [Member]
NONINTEREST INCOME:
Revenue from contract with customer	$ 15,157	$ 15,109	$ 16,086

Consolidated Statements of Ea_2

Consolidated Statements of Earnings (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Reclassifications adjustment for realized gains on investment securities included in net earnings (loss), before income tax	$ 1,354	$ 1,828	$ 1,270
Income tax expense from reclassification items	$ 284	$ 640	$ 445

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Earnings - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net earnings	$ 150,638	$ 120,371	$ 104,774
OTHER ITEMS OF COMPREHENSIVE EARNINGS (LOSS):
Change in unrealized gain (loss) on investment securities available-for-sale, before income tax	(38,185)	23,266	(44,679)
Reclassification adjustment for realized losses (gains) on investment securities included in net earnings, before income tax	(1,354)	(1,828)	(1,270)
Minimum liability pension adjustment, before income tax	1,970	257	1,410
Total other items of comprehensive earnings (losses)	(37,569)	21,695	(44,539)
Income tax benefit (expense) related to: Investment securities
Investment securities	8,303	(13,774)	16,082
Minimum liability pension adjustment	(414)	420	(493)
Total income tax benefit (expense)	7,889	(13,354)	15,589
COMPREHENSIVE EARNINGS	$ 120,958	$ 128,712	$ 75,824

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, 2015	$ 804,986	$ 660	$ 368,925	$ 388,006	$ (6,296)	$ 6,296	$ 47,395
Beginning Balance, Shares at Dec. 31, 2015		65,990,234
Treasury Stock, Beginning Balance, Shares at Dec. 31, 2015					(520,651)
Net earnings	104,774			104,774
Stock option exercises	1,260	$ 1	1,259
Stock option exercises, Shares		82,871
Restricted Stock grant	809		809
Restricted Stock grant, Shares		21,590
Cash dividends declared	(46,246)			(46,246)
Minimum liability pension adjustment, net of related income taxes	917						917
Change in unrealized gain (loss) in investment securities available-for-sale, net of related income taxes	(29,867)						(29,867)
Additional tax benefit related to directors' deferred compensation plan	370		370
Shares purchased (redeemed) in connection with directors' deferred compensation plan, net					$ (375)	375
Shares purchased (redeemed) in connection with directors' deferred compensation plan, net, Shares					13,242
Stock option expense	882		882
Ending Balance at Dec. 31, 2016	837,885	$ 661	372,245	446,534	$ (6,671)	6,671	18,445
Ending Balance, Shares at Dec. 31, 2016		66,094,695
Treasury Stock, Ending Balance, Shares at Dec. 31, 2016					(507,409)
Net earnings	120,371			120,371
Stock option exercises	2,935	$ 2	2,933
Stock option exercises, Shares		140,250
Restricted Stock grant	1,139		1,139
Restricted Stock grant, 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	7,664						7,664
Shares purchased (redeemed) in connection with directors' deferred compensation plan, net					$ (477)	477
Shares purchased (redeemed) in connection with directors' deferred compensation plan, net, Shares					11,445
Stock option expense	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		66,260,444,000
Treasury Stock, Ending Balance, Shares at Dec. 31, 2017	(495,964)				(495,964)
Net earnings	$ 150,638			150,638
Stock option exercises	3,863	$ 2	3,861
Stock option exercises, Shares		173,822
Restricted Stock grant	1,609		1,609
Restricted Stock grant, 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	(31,235)						(31,235)
Shares purchased (redeemed) in connection with directors' deferred compensation plan, net					$ (359)	359
Shares purchased (redeemed) in connection with directors' deferred compensation plan, net, Shares					28,153
Stock option expense	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 Acts 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				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)

Consolidated Statements of Sh_2

Consolidated Statements of Shareholders' Equity (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2016
Retained Earnings [Member]
Cash dividend per share	$ 0.75	$ 0.82	$ 0.70

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
NET EARNINGS	$ 150,638	$ 120,371	$ 104,774
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization	12,549	12,916	11,573
PROVISION FOR LOAN LOSSES	5,665	6,530	10,212
Securities premium amortization, net	27,467	30,310	29,005
Gain on sale of assets, net	(1,216)	(1,167)	(1,894)
Deferred federal income tax expense (benefit)	(250)	(53)	673
Change in loans held for sale	(5,791)	11,769	6,645
Change in other assets	(1,697)	9,313	2,397
Change in other liabilities	1,621	285	(2,643)
Total adjustments	38,348	69,903	55,968
Net cash provided by operating activities	188,986	190,274	160,742
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		249	1,788
Activity in available-for-sale securities:
Sales	220,259	120,576	40,510
Maturities	3,439,028	4,392,131	3,509,113
Purchases	(3,731,821)	(4,768,420)	(3,737,865)
Activity in held-to-maturity securities - maturities		124	157
Net increase in loans	(205,238)	(134,627)	(48,836)
Purchases of bank premises and equipment and other assets	(17,646)	(14,162)	(20,399)
Proceeds from sale of bank premises and equipment and other assets	844	6,085	3,572
Net cash used in investing activities	(275,921)	(398,044)	(251,960)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net increase (decrease) in noninterest-bearing deposits	(87,583)	323,928	(28,230)
Net increase (decrease) in interest-bearing deposits	(36,891)	160,494	316,600
Net increase (decrease) in borrowings	137,706	(114,770)	(169,905)
Common stock transactions:
Proceeds from stock issuances	3,864	2,934	1,260
Dividends paid	(53,861)	(48,955)	(44,907)
Net cash provided by (used in) financing activities	(36,765)	323,631	74,818
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(123,700)	115,861	(16,400)
CASH AND CASH EQUIVALENTS, beginning of year	372,347	256,486	272,886
CASH AND CASH EQUIVALENTS, end of year	$ 248,647	$ 372,347	$ 256,486

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
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, 2018. 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 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. Previously, the Board of Directors had authorized the repurchase of up to 1,500,000 common shares through September 30, 2017. The stock buyback plan authorizes management to repurchase the stock at such time as repurchases are considered beneficial to stockholders. Any repurchase of stock will be made through the open market, block trades or in privately negotiated transactions in accordance with applicable laws and regulations. Under the repurchase plan, there is no minimum number of shares that the Company is required to repurchase. For the years ended December 31, 2018, 2017 and 2016, no shares were repurchased under this 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 The Company records its available-for-sale 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 party pricing services to value its investment securities, which the Company reviews as well as the underlying pricing methodologies for reasonableness and to ensure such prices are aligned with pricing matrices. The Company validates prices supplied by the independent pricing services by comparison to prices obtained from other third party sources on a quarterly basis. 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 nonaccretable difference to accretable yield, which will be recognized prospectively. Decreases in expected cash flows subsequent to acquisition are recognized as impairment. Valuation allowances on these impaired loans reflect only losses incurred after the acquisition. The carrying amount of purchased credit impaired loans at December 31, 2018 and 2017 were $827,000 and $618,000, respectively, compared to a contractual balance of $1,157,000 and $1,865,000, respectively. Other purchased credit impaired loan disclosures were omitted due to immateriality. 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 and $139,971,000, respectively at December 31, 2018 and 2017. There was no impairment recorded for the years ended December 31, 2018, 2017 and 2016. The carrying amount of goodwill arising from acquisitions that qualify as an asset purchase for federal income tax purposes was $22,526,000 and $26,618,000 at December 31, 2018 and 2017, 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 $1,508,000, $1,745,000, and $882,000, for the years ended December 31, 2018, 2017 and 2016, 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 $560,000 and $680,000, respectively, for the year ended December 31, 2018, $483,000 and $562,000, respectively, for the year ended December 31, 2017, and $278,000 and $381,000, respectively, for the year ended December 31, 2016. 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. There were no such anti-dilutive stock options for the years ended December 31, 2018, 2017 and 2016. The following table reconciles the computation of basic EPS to dilutive EPS: Net Weighted Per For the year ended December 31, 2018: Net earnings per share, basic $ 150,638 67,609,367 $ 2.23 Effect of stock options and stock grants — 373,647 (0.01 ) Net earnings per share, assuming dilution $ 150,638 67,983,014 $ 2.22 For the year ended December 31, 2017: Net earnings per share, basic $ 120,371 66,126,863 $ 1.82 Effect of stock options and stock grants — 197,467 (0.01 ) Net earnings per share, assuming dilution $ 120,371 66,324,330 $ 1.81 For the year ended December 31, 2016: Net earnings per share, basic $ 104,774 66,013,004 $ 1.59 Effect of stock options and stock grants — 89,882 — Net earnings per share, assuming dilution $ 104,774 66,102,886 $ 1.59 Recently Issued Authoritative Accounting Guidance Accounting Standards Update (“ASU”) 2014-09, 2014-09 2015-04 2014-09 2014-09, non-interest ASU 2016-01, 2016-01 2016-01, available-for-sale 2016-1 ASU 2016-02, 2016-02 right-of-use 2016-02 ASU 2016-09, 2016-09 2016-09 2016-09 ASU 2016-13, 2016-13 held-to-maturity 2016-13 2016-13 ASU 2017-04, 2017-04 2017-04 ASU 2017-07, 2017-17 2017-17 ASU 2017-08, 2017-08 2017-08 2017-08 ASU 2018-02, 2018-02 2018-02 ASU 2018-13, 2018-13 2018-13 ASU 2018-14, 715-20).” 2018-14 2018-14

Interest-bearing Time Deposits

Interest-bearing Time Deposits in Banks and Securities	12 Months Ended
	Dec. 31, 2018
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 both December 31, 2018 and 2017 and at December 31, 2018, have original maturities within twelve months. A summary of the Company’s available-for-sale December 31, 2018 Amortized Gross Gross 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 December 31, 2017 Amortized Gross Gross Estimated Securities available-for-sale: Obligations of U.S. government sponsored enterprises and agencies $ 60,516 $ — $ (186 ) $ 60,330 Obligations of state and political subdivisions 1,369,295 52,491 (936 ) 1,420,850 Corporate bonds and other 11,421 43 (5 ) 11,459 Residential mortgage-backed securities 1,223,452 4,561 (8,916 ) 1,219,097 Commercial mortgage-backed securities 377,934 263 (2,460 ) 375,737 Total securities available-for-sale $ 3,042,618 $ 57,358 $ (12,503 ) $ 3,087,473 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, 2018, were computed by using scheduled amortization of balances and historical prepayment rates. At December 31, 2018 and 2017, 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 $ 187,600 $ 188,914 Due after one year through five years 547,868 563,679 Due after five years through ten years 507,792 518,317 Due after ten years 1,714 2,022 Mortgage-backed securities 1,908,594 1,885,845 Total $ 3,153,568 $ 3,158,777 The following tables disclose, as of December 31, 2018 and 2017, the Company’s investment securities that have been in a continuous unrealized-loss Less than 12 Months 12 Months or Longer Total December 31, 2018 Fair Unrealized Fair Unrealized Fair 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 Less than 12 Months 12 Months or Longer Total December 31, 2017 Fair Unrealized Fair Unrealized Fair Unrealized Obligations of U.S. government sponsored enterprises and agencies $ 60,329 $ 186 $ — $ — $ 60,329 $ 186 Obligations of state and political subdivisions 66,361 219 44,938 717 111,299 936 Corporate bonds and other 224 2 237 3 461 5 Residential mortgage-backed securities 701,252 3,988 239,641 4,928 940,893 8,916 Commercial mortgage-backed securities 239,548 1,500 92,549 960 332,097 2,460 Total $ 1,067,714 $ 5,895 $ 377,365 $ 6,608 $ 1,445,079 $ 12,503 The number of investments in an unrealized loss position totaled 366 at December 31, 2018. 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, 2018 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, 2018, 84.70% of our available-for-sale Securities, carried at approximately $1,988,579,000 and $2,018,420,000 at December 31, 2018 and 2017, respectively, were pledged as collateral for public or trust fund deposits, repurchase agreements and for other purposes required or permitted by law. During 2018, 2017 and 2016, 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
	Dec. 31, 2018
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, 2018 2017 Commercial $ 844,953 $ 684,099 Agricultural 96,677 94,543 Real estate 2,639,346 2,302,998 Consumer 372,660 403,929 Total loans held-for-investment $ 3,953,636 $ 3,485,569 The Company’s non-accrual December 31, 2018 2017 Non-accrual $ 27,534 $ 17,670 Loans still accruing and past due 90 days or more 1,008 288 Troubled debt restructured loans** 513 627 Total $ 29,055 $ 18,585 * Includes $827,000 and $618,000, respectively, of purchased credit impaired loans as of December 31, 2018 and 2017. ** Our troubled debt restructured loans of $3,840,000 and $4,629,000, 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, 2018 December 31, 2017 Recorded Investment Valuation Recorded Valuation $ 27,534 $ 4,069 $ 17,670 $ 3,996 The Company had $29,632,000 and $20,117,000 in non-accrual, Non-accrual December 31, 2018 2017 Commercial $ 9,334 $ 3,612 Agricultural 759 134 Real Estate 16,714 12,838 Consumer 727 1,086 Total $ 27,534 $ 17,670 No significant additional funds are committed to be advanced in connection with impaired loans as of December 31, 2018. The Company’s impaired loans and related allowance as of December 31, 2018 and 2017 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, 2018 Unpaid 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. December 31, 2017 Unpaid Recorded Recorded Total Related 12 Month Commercial $ 5,597 $ 518 $ 3,094 $ 3,612 $ 1,194 $ 4,849 Agricultural 147 — 134 134 31 120 Real Estate 16,823 2,348 10,490 12,838 2,316 13,835 Consumer 1,284 143 943 1,086 455 1,258 Total $ 23,851 $ 3,009 $ 14,661 $ 17,670 $ 3,996 $ 20,062 * Includes $618,000 of purchased credit impaired loans. The Company recognized interest income on impaired loans prior to being recognized as impaired of approximately $948,000, $624,000 and $829,000 during the years ended December 31, 2018, 2017 and 2016, 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, 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 December 31, 2017 Pass Special Substandard Doubtful Total Commercial $ 649,166 $ 6,282 $ 28,651 $ — $ 684,099 Agricultural 90,457 1,527 2,559 — 94,543 Real Estate 2,227,302 29,089 46,607 — 2,302,998 Consumer 401,434 181 2,314 — 403,929 Total $ 3,368,359 $ 37,079 $ 80,131 $ — $ 3,485,569 At December 31, 2018 and 2017, the Company’s past due loans are as follows (dollars in thousands): December 31, 2018 15-59 60-89 Greater Total Past Total Total 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 December 31, 2017 15-59 60-89 Greater Total Past Total Total Total 90 Commercial $ 2,039 $ 1,104 $ 1,081 $ 4,224 $ 679,875 $ 684,099 $ 7 Agricultural 640 — — 640 93,903 94,543 — Real Estate 12,308 511 1,198 14,017 2,288,981 2,302,998 216 Consumer 1,360 361 135 1,856 402,073 403,929 65 Total $ 16,347 $ 1,976 $ 2,414 $ 20,737 $ 3,464,832 $ 3,485,569 $ 288 * The Company monitors commercial, agricultural and real estate loans after such loans are 15 days past due. Consumer loans are monitored after such loans are 30 days past due. The following table details the allowance for loan losses at December 31, 2018 and 2017 by portfolio segment (in thousands). There were no allowances for purchased credit impaired loans at December 31, 2018 or 2017. 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, 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 December 31, 2017 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 1,194 $ 31 $ 2,316 $ 455 $ 3,996 Loan collectively evaluated for impairment 9,671 1,274 27,580 5,635 44,160 Total $ 10,865 $ 1,305 $ 29,896 $ 6,090 $ 48,156 Changes in the allowance for loan losses for the years ended December 31, 2018 and 2017 are summarized as follows (in thousands): 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 December 31, 2017 Commercial Agricultural Real Estate Consumer Total Beginning balance $ 11,707 $ 1,101 $ 26,864 $ 6,107 $ 45,779 Provision for loan losses 1,233 243 4,055 999 6,530 Recoveries 943 32 192 501 1,668 Charge-offs (3,018 ) (71 ) (1,215 ) (1,517 ) (5,821 ) Ending balance $ 10,865 $ 1,305 $ 29,896 $ 6,090 $ 48,156 The Company’s recorded investment in loans as of December 31, 2018 and 2017 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 $827,000 and $618,000, respectively, at December 31, 2018 and 2017 are included in loans individually evaluated for impairment. 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 December 31, 2017 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 3,612 $ 134 $ 12,838 $ 1,086 $ 17,670 Loan collectively evaluated for impairment 680,487 94,409 2,290,160 402,843 3,467,899 Total $ 684,099 $ 94,543 $ 2,302,998 $ 403,929 $ 3,485,569 The Company’s loans that were modified in the years ended December 31, 2018 and 2017, and considered troubled debt restructurings are as follows (dollars in thousands): Year Ended December 31, 2018 Year Ended December 31, 2017 Number Pre-Modification Post- Number Pre-Modification Post- Commercial 4 $ 864 $ 864 11 $ 895 $ 895 Agricultural 1 4 4 — — — Real Estate 5 643 643 5 625 625 Consumer 8 209 209 1 25 25 Total 18 $ 1,720 $ 1,720 17 $ 1,545 $ 1,545 The balances below provide information as to how the loans were modified as troubled debt restructured loans during the years ended December 31, 2018 and 2017 (dollars in thousands): Year Ended December 31, 2018 Year Ended December 31, 2017 Adjusted Extended Combined Adjusted Extended Combined Commercial $ — $ 529 $ 335 $ — $ 195 $ 700 Agricultural — — 4 — — — Real Estate — 280 363 — 312 313 Consumer — — 209 — 25 — Total $ — $ 809 $ 911 $ — $ 532 $ 1,013 During the years ended December 31, 2018 and 2017, 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, 2018 Year Ended December 31, 2017 Number Balance Number Balance Commercial 1 $ 491 2 $ 88 Agriculture — — — — Real Estate — — — — Consumer — — — — Total 1 $ 491 2 $ 88 As of December 31, 2018, 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, 2018 (determined as of each respective year-end) Beginning Additional Payments Ending Year ended December 31, 2018 $ 55,904 $ 55,678 $ 44,188 $ 67,394 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, 2018, $2,495,150,000 in loans held by our bank subsidiary were subject to blanket liens as security for this line of credit. At December 31, 2018, there was $55,000,000 outstanding under this line of credit.

Loans Held for Sale

Loans Held for Sale	12 Months Ended
	Dec. 31, 2018
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 $21,672,000 and $15,130,000 at December 31, 2018 and 2017, respectively. At December 31, 2018, $2,487,000 is valued at the lower of cost or fair value, and the remaining amount is valued under the fair value option. All of the amounts for December 31, 2017 were valued at the lower of cost or fair value. 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 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
	Dec. 31, 2018
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, 2018: Outstanding Asset Liability IRLCs $ 37,088 $ 765 $ — Forward mortgage-backed securities trades 45,500 — 403 December 31, 2017: Outstanding Asset Liability IRLCs $ 37,589 $ 500 $ —

Bank Premises and Equipment

Bank Premises and Equipment	12 Months Ended
	Dec. 31, 2018
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, 2018 2017 Land – $ 31,190 $ 29,508 Buildings 20 to 40 years 135,335 119,728 Furniture and equipment 3 to 10 years 58,969 58,672 Leasehold improvements Lesser of lease term or 5 to 15 years 3,557 4,118 229,051 212,026 Less- accumulated depreciation and amortization (95,630 ) (88,000 ) Total Bank Premises and Equipment $ 133,421 $ 124,026 Depreciation expense for the years ended December 31, 2018, 2017 and 2016 amounted to $10,130,000, $9,810,000 and $9,390,000, 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 $2,682,000, $2,367,000 and $2,139,000, for the years ended December 31, 2018, 2017 and 2016, respectively. During the years ended December 31, 2018, 2017 and 2016, the Company recorded gains (losses) on sale of the bank premises and equipment totaling ($147,000), ($396,000) and $168,000. In 2017, the Company sold its San Angelo main region branch building for $1,586,000 and recorded a gain of $210,000 and cancelled its San Angelo grocery store branch lease and recorded a write off of leasehold improvements of $360,000. In 2016, the Company sold its Weatherford and Orange main region branch building for $1,385,000 and $2,000,000 and recorded a gain of $560,000 and a loss of $31,000, respectively.

Deposits and Borrowings

Deposits and Borrowings	12 Months Ended
	Dec. 31, 2018
Banking and Thrift [Abstract]
Deposits and Borrowings	7. DEPOSITS AND BORROWINGS: Time deposits of $250,000 or more totaled approximately $118,590,000 and $115,203,000 at December 31, 2018 and 2017, respectively. At December 31, 2018, the scheduled maturities of time deposits (in thousands) were, as follows: Year ending December 31, 2019 $ 373,359 2020 42,801 2021 11,406 2022 8,066 2023 6,475 Thereafter 54 $442,161 Deposits received from related parties at December 31, 2018 and 2017 totaled $103,413,000 and $74,270,000, respectively. Borrowings at December 31, 2018 and 2017 consisted of the following (dollars in thousands): December 31, 2018 2017 Securities sold under agreements with customers to repurchase $ 409,631 $ 320,450 Federal funds purchased 4,075 10,550 Advances from Federal Home Loan Bank of Dallas 55,000 — Total $ 468,706 $ 331,000 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 will be repaid in 2019. The interest rate on this advance was 2.65% at December 31, 2018. There were no such advances outstanding at December 31, 2017.

Line of Credit

Line of Credit	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Line of Credit	8. LINE OF CREDIT: The Company renewed its loan agreement, effective June 30, 2017, with Frost Bank. Under the loan agreement, as renewed and amended, we are permitted to draw up to $25,000,000 on a revolving line of credit. Prior to June 30, 2019, interest is paid quarterly at The Wall Street Journal The Wall Street Journal non-performing

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
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% from 35%. The Company’s deferred tax assets and liabilities were re-measured re-measurement The Company files a consolidated federal income tax return. Income tax expense is comprised of the following (dollars in thousands): Year Ended December 31 , 2018 2017 2016 Current federal income tax $ 28,359 $ 34,421 $ 30,381 Current state income tax 92 99 99 Deferred federal income tax expense (benefit) (250 ) (53 ) 673 Restatement of net deferred tax liability due to change in income tax rate (664 ) (7,650 ) — Income tax expense $ 27,537 $ 26,817 $ 31,153 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 2018 2017 2016 Statutory federal income tax rate 21.0 % 35.0 % 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 (5.2 ) (11.5 ) (12.1 ) Effect of state income tax 0.1 0.1 0.1 ESOP tax deduction (0.1 ) (0.2 ) (0.2 ) Other 0.1 0.1 0.1 Effective income tax rate 15.5 % 18.2 % 22.9 % The approximate effects of each type of difference that gave rise to the Company’s deferred tax assets and liabilities at December 31, 2018 and 2017 are as follows (dollars in thousands): 2018 2017 Deferred tax assets: Tax basis of loans in excess of financial statement basis $ 12,010 $ 10,550 Minimum liability in defined benefit plan 352 766 Recognized for financial reporting purposes but not yet for tax purposes: Deferred compensation 2,056 1,818 Write-downs and adjustments to other real estate owned and repossessed assets 49 11 Other deferred tax assets 208 79 Total deferred tax assets $ 14,675 $ 13,224 Deferred tax liabilities: Financial statement basis of fixed assets in excess of tax basis $ 4,182 3,343 Intangible asset amortization deductible for tax purposes, but not for financial reporting purposes 11,263 9,926 Recognized for financial reporting purposes but not yet for tax purposes: Accretion on investment securities 745 1,039 Pension plan contributions 816 1,086 Net unrealized gain on investment securities available-for-sale 1,111 9,420 Other deferred tax liabilities 34 31 Total deferred tax liabilities $ 18,151 $ 24,845 Net deferred tax asset (liability) $ (3,476 ) $ (11,621 ) At December 31, 2018 and 2017, management believes that it is more likely than not that all of the deferred tax amounts shown above will be realized and therefore no valuation allowance was recorded. Current authoritative accounting guidance prescribes a more-likely-than-not more-likely-than-not more-likely-than-not

Fair Value Disclosures

Fair Value Disclosures	12 Months Ended
	Dec. 31, 2018
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, IRLCs and forward mortgage-backed securities traded. There were no transfers between Level 2 and Level 3 during the years ended December 31, 2018, 2017 and 2016. The following table summarizes financial assets and financial liabilities measured at fair value on a recurring basis as of December 31, 2018 and 2017 segregated by the level of the valuation inputs within the fair value hierarchy utilized to measure fair value (in thousands): December 31, 2018 Level 1 Level 2 Level 3 Total Fair 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 December 31, 2017 Level 1 Level 2 Level 3 Total Fair Available-for-sale Obligations of U. S. government sponsored enterprises and agencies $ — $ 60,330 $ — $ 60,330 Obligations of state and political subdivisions — 1,420,850 — 1,420,850 Corporate bonds — 7,031 — 7,031 Residential mortgage-backed securities — 1,219,097 — 1,219,097 Commercial mortgage-backed securities — 375,737 — 375,737 Other securities 4,428 — — 4,428 Total $ 4,428 $ 3,083,045 $ — $ 3,087,473 IRLCs $ — $ 500 $ — $ 500 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). Financial assets and financial liabilities measured at fair value on a non-recurring Impaired Loans – 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, 2018, impaired loans with a carrying value of $13,793,000 were reduced by specific valuation reserves totaling $4,069,000 resulting in a net fair value of $9,724,000. The Company also had impaired loans of $13,741,000 with no specific valuation reserve at December 31, 2018, due to the loans carrying value generally being lower than the value of the collateral associated with the loan. Loans Held-for-Sale held-for-sale Certain non-financial non-financial non-recurring non-financial Non-financial non-recurring re-measured re-measured Year Ended December 31, 2018 2017 Carrying value of other real estate owned prior to re-measurement $ 1,046 $ 1,067 Write-downs included in gain (loss) on sale of other real estate owned (236 ) (306 ) Fair value $ 810 $ 761 At December 31, 2018 and 2017, other real estate owned totaled $448,000 and $1,347,000, 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, 2018 and 2017, were as follows (dollars in thousands): 2018 2017 Carrying Estimated Carrying Estimated Fair Value Value Fair Value Value Fair Value Hierarchy Cash and due from banks $ 207,835 $ 207,835 $ 209,583 $ 209,583 Level 1 Interest-bearing deposits in banks 40,812 40,812 162,764 162,764 Level 1 Interest-bearing time deposits in banks 1,458 1,458 1,458 1,458 Level 2 Available-for-sale 3,158,777 3,158,777 3,087,473 3,087,473 Levels 1 and 2 Loans held-for-investment 3,902,434 3,947,391 3,437,413 3,455,003 Level 3 Loans held-for-sale 21,672 21,779 15,130 15,314 Level 2 Accrued interest receivable 36,765 36,765 36,081 36,081 Level 2 Deposits with stated maturities 442,161 441,727 451,255 452,000 Level 2 Deposits with no stated maturities 5,738,228 5,738,228 5,511,706 5,511,706 Level 1 Borrowings 468,706 468,706 331,000 331,000 Level 2 Accrued interest payable 408 408 197 197 Level 2 IRLCs 765 765 500 500 Level 2 Forward mortgage-backed securities traded 403 403 — — Level 2

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2018
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, 2018 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, 2018, future minimum lease commitments were: 2019—$610,000, 2020—$409,000, 2021—$224,000, 2022—$27,000 and 2023 and thereafter—$5,000.

Financial Instruments with Off-

Financial Instruments with Off-Balance-Sheet Risk	12 Months Ended
	Dec. 31, 2018
Text Block [Abstract]
Financial Instruments with Off-Balance-Sheet Risk	12. FINANCIAL INSTRUMENTS WITH OFF-BALANCE-SHEET 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 December 31, 2018 (in thousands) Financial instruments whose contract amounts represent credit risk: Unfunded lines of credit $ 632,667 Unfunded commitments to extend credit 301,616 Standby letters of credit 26,641 Total commercial commitments $ 960,924 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
	Dec. 31, 2018
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
	Dec. 31, 2018
Retirement Benefits [Abstract]
Pension and Profit Sharing Plans	14. PENSION AND PROFIT SHARING PLANS: The Company’s defined benefit pension plan was frozen effective January 1, 2004, whereby no new participants will be added to the Plan and no additional years of service will accrue to participants, unless the pension plan is reinstated at a future date. 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 and is 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. As a result of the Pension Protection Act of 2006 (the “Protection Act”), the Company will be required to contribute amounts in future years to fund any shortfalls. The Company has evaluated the provisions of the Protection Act as well as the Internal Revenue Service’s funding standards to develop a plan for funding in future years. As a result, the Company made no contribution in 2018 and 2017, and is continuing to evaluate future funding amounts. In December 2018, due to the rising interest rate environment, the Company determined it was in the best interest of its shareholders to settle its pension obligation to its retiree group in payout, approximately 53% of the pension benefit obligation on that date, and recorded a loss on settlement totaling $1,546,000 for the year ended December 31, 2018. In 2019, the Company began steps to terminate and settle the remaining obligation in its pension plan. Termination of the plan is expected to be in late 2019 but is subject to regulatory approval and changes in interest rates and, therefore there is no certainty that it will be consummated. Using an actuarial measurement date of December 31, 2018 and 2017, benefit obligation activity and fair value of plan assets for the years ended December 31, 2018 and 2017, and a statement of the funded status as of December 31, 2018 and 2017, are as follows (dollars in thousands): 2018 2017 Reconciliation of benefit obligations: Benefit obligation at January 1 $ 15,531 $ 15,453 Interest cost on projected benefit obligation 523 635 Actuarial (gain) loss (811 ) 486 Benefits paid, including settlement of certain participant balances (8,630 ) (1,043 ) Benefit obligation at December 31 $ 6,613 $ 15,531 Reconciliation of fair value of plan assets: Fair value of plan assets at January 1 $ 17,046 $ 15,787 Actual return on plan assets 365 2,302 Employer contributions — — Benefits paid, including settlement of certain participant balances (8,630 ) (1,043 ) Fair value of plan assets at December 31 8,781 17,046 Funded status $ 2,168 $ 1,515 Amounts recognized as a component of accumulated other comprehensive earnings as of year-end 2018 2017 Net actuarial loss $ (1,717 ) $ (3,597 ) Deferred tax benefit 393 1,227 Amounts included in accumulated other comprehensive earnings, net of tax $ (1,324 ) $ (2,370 ) Net periodic benefit cost for the years ended December 31, 2018, 2017 and 2016, are as follows (dollars in thousands): Year Ended December 31, 2018 2017 2016 Service cost—benefits earned during the period $ — $ — $ — Interest cost on projected benefit obligation 523 635 665 Expected return on plan assets (1,028 ) (974 ) (912 ) Amortization of unrecognized net loss 186 249 375 Recognized loss on partial settlement of certain participant balances 1,546 — 267 Net periodic pension benefit expense (benefit) $ 1,227 $ (90 ) $ 395 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: 2018 2017 2016 Weighted average discount rate 4.25 % 3.50 % 4.25 % Expected long-term rate of return on assets 6.25 % 6.25 % 6.25 % The weighted average discount rate is 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 matches the expected benefit payment stream. The expected long-term rate of return on plan assets is based on historical returns and expectations of future returns based on asset mix, after consultation with our investment advisors and actuaries. The major type of plan assets in the pension plan and the targeted allocation percentage as of December 31, 2018 and 2017 is as follows: December 31, 2018 December 31, 2017 Targeted Equity securities 72 % 75 % 75 % Debt securities 27 % 24 % 25 % Cash and equivalents 1 % 1 % — The range and weighted average final maturities of debt securities held in the pension plan as of December 31, 2018 are 2.54 to 18.76 years and approximately 6.91 years, respectively. Assets held in the pension plan are considered either Level 1 consisting of the money market funds, publicly traded common stocks and publically traded mutual funds or Level 2 consisting of obligations of state and political subdivisions, corporate bonds and mortgage-backed securities. There were no Level 3 securities. See note 10 for a discussion of the fair value hierarchy. The breakdown by level is as follows (dollars in thousands): Level 1 Level 2 Level 3 Total Fair Money market fund $ 87 $ — $ — $ 87 Obligations of state and political subdivisions — 208 — 208 Corporate bonds — 449 — 449 Mortgage-backed securities — 901 — 901 Corporate stocks and mutual funds 7,136 — — 7,136 Total $ 7,223 $ 1,558 $ — $ 8,781 First Financial Trust & Asset Management Company, National Association, a wholly owned subsidiary of the Company, manages the pension plan assets as well as the profit sharing plan assets (see below). The investment strategy and targeted allocations are based on similar strategies First Financial Trust & Asset Management Company, National Association employs for most of its managed accounts whereby appropriate diversification is achieved. First Financial Trust & Asset Management Company, National Association is prohibited from holding investments deemed to be high risk by the Office of the Comptroller of the Currency. An estimate of the undiscounted projected future payments to eligible participants for the next five years and the following five years in the aggregate is as follows (dollars in thousands): Year Ending December 31, 2019 $ 837 2020 $ 318 2021 $ 388 2022 $ 398 2023 $ 333 2024 forward $ 2,339 As of December 31, 2018 and 2017, the pension plan’s total assets included First Financial Bankshares, Inc. common stock valued at approximately $3,373,000 and $2,776,000, respectively. 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-year 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 2018, 2017 and 2016 was $2,588,000, $2,392,000 and $2,331,000, 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
	Dec. 31, 2018
Text Block [Abstract]
Dividends from Subsidiaries	15. DIVIDENDS FROM SUBSIDIARIES: At December 31, 2018, approximately $233,956,000 was available for the declaration of dividends by the Company’s subsidiaries without the prior approval of regulatory agencies.

Regulatory Matters

Regulatory Matters	12 Months Ended
	Dec. 31, 2018
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 increasing 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, 2018 and 2017, we had a total risk-based capital ratio of 20.61% and 19.85%, a Tier 1 capital to risk-weighted assets ratio of 19.47% and 18.66%; a common equity Tier 1 capital to risk-weighted assets ratio of 19.47% and 18.66%, and a Tier 1 leverage ratio of 11.85% and 11.09%, respectively. The regulatory capital ratios as of December 31, 2018 and 2017 were calculated under Basel III rules. There is no threshold for well-capitalized status for bank holding companies. As of December 31, 2018 and 2017, the regulatory capital ratios of the Company and Bank under the Basel III regulatory capital framework are as follows: 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 % Actual Minimum Capital Phase-In Minimum Capital Phased-In Required to be As of December 31, 2017: Amount Ratio Amount Ratio Amount Ratio Amount Ratio Total Capital to Risk-Weighted Assets: Consolidated $ 814,634 19.85 % $ 379,578 9.250 % $ 430,872 10.50 % — N/A First Financial Bank, N.A $ 723,563 17.68 % $ 378,614 9.250 % $ 429,777 10.50 % $ 409,312 10.00 % Tier 1 Capital to Risk-Weighted Assets: Consolidated $ 765,882 18.66 % $ 297,507 7.250 % $ 348,801 8.50 % — N/A First Financial Bank, N.A $ 674,811 16.49 % $ 296,751 7.250 % $ 347,915 8.50 % $ 327,450 8.00 % Common Equity Tier 1 Capital to Risk-Weighted Assets: Consolidated $ 765,882 18.66 % $ 235,954 5.750 % $ 287,248 7.00 % — N/A First Financial Bank, N.A $ 674,811 16.49 % $ 235,354 5.750 % $ 286,518 7.00 % $ 266,053 6.50 % Leverage Ratio: Consolidated $ 765,882 11.09 % $ 276,296 4.000 % $ 276,296 4.00 % — N/A First Financial Bank, N.A $ 674,811 9.80 % $ 275,320 4.000 % $ 275,320 4.00 % $ 344,151 5.00 % We have performed a preliminary assessment using the regulatory capital estimation tool made available by the OCC and believe the Company and Bank are prepared to meet the new requirements upon full adoption of Basel III that will be effective in 2019. 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, 2018, our Trust Company had tangible net assets totaling $22,503,000. Our subsidiary bank may be required at times to maintain reserve balances with the Federal Reserve Bank. At December 31, 2018 and 2017, the subsidiary bank’s reserve balances were $11,372,000 and $11,504,000, respectively.

Stock Option Plan and Restricte

Stock Option Plan and Restricted Stock Plan	12 Months Ended
	Dec. 31, 2018
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, 2018, the Company had allocated 3,003,000 shares of stock for issuance under the plan. The plan provides that options granted are exercisable after two years from date of grant at a rate of 20% each year cumulatively during the 10-year Shares Weighted- Weighted- Aggregate Intrinsic Outstanding, beginning of year 1,325,965 $ 33.01 Granted — — Exercised (173,822 ) 22.23 Cancelled (66,600 ) 36.25 Outstanding, end of year 1,085,543 34.54 6.55 $ 25,135 Exercisable at end of year 407,463 $ 27.41 4.65 $ 12,337 The options outstanding at December 31, 2018 had exercise prices ranging between $16.78 and $42.35. 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, 2018: Exercise Price Number Remaining Number Vested $ 16.78 29,823 0.4 29,823 15.73 90,265 2.8 90,265 30.85 211,355 4.8 161,135 33.89 341,250 6.8 126,240 $ 42.35 412,850 8.5 — The fair value of the options granted during 2017 was estimated using the Black-Scholes options pricing model with the following weighted-average assumptions: risk-free interest rate of 1.89%; expected dividend yield of 1.79%; expected life of 6.24 years; and expected volatility of 26.51%. The weighted-average grant-date fair value of options granted during 2017 was $9.90. There were no grants during 2018 and 2016. The total intrinsic value of options exercised during the years ended December 31, 2018, 2017 and 2016, was $5,476,000, $3,082,000 and $1,226,000, respectively. As of December 31, 2018, there was $3,522,000 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 1.89 years. The total fair value of shares vested during the years ended December 31, 2018, 2017 and 2016 was $888,000, $1,246,000 and $592,000. The aggregate intrinsic value of vested stock options at December 31, 2018 totaled $11,170,000. On April 28, 2015, shareholders of the Company approved a restricted stock plan for selected employees, officers, non-employee On July 21, 2015, upon re-election non-employee re-election non-employee re-election non-employee re-election 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 to three years. On October 23, 2018, the Company granted 26,021 restricted shares with a total value of $1,440,000 to certain officers that will be expensed over a three year vesting period. The Company recorded restricted stock expense for officers of $680,000, $562,000 and $381,000, respectively, for the year ended December 31, 2018, 2017 and 2016.

Condensed Financial Information

Condensed Financial Information - Parent Company	12 Months Ended
	Dec. 31, 2018
Condensed Financial Information Disclosure [Abstract]
Condensed Financial Information - Parent Company	18. CONDENSED FINANCIAL INFORMATION—PARENT COMPANY: Condensed Balance Sheets-December 31, 2018 and 2017 2018 2017 ASSETS Cash in subsidiary bank $ 16,981 $ 14,272 Cash in unaffiliated banks 2 2 Interest-bearing deposits in subsidiary bank 84,279 64,195 Total cash and cash equivalents 101,262 78,469 Securities available-for-sale, 6,276 8,515 Investment in and advances to subsidiaries, at equity 959,352 847,445 Intangible assets 723 723 Other assets 2,647 2,654 Total assets $ 1,070,260 $ 937,806 LIABILITIES AND SHAREHOLDERS’ EQUITY Total liabilities $ 16,965 $ 15,038 Shareholders’ equity: Common stock 678 663 Capital surplus 443,114 378,062 Retained earnings 606,658 517,257 Treasury stock (7,507 ) (7,148 ) Deferred compensation 7,507 7,148 Accumulated other comprehensive earnings 2,845 26,786 Total shareholders’ equity 1,053,295 922,768 Total liabilities and shareholders’ equity $ 1,070,260 $ 937,806 Condensed Statements of Earnings- For the Years Ended December 31, 2018, 2017 and 2016 2018 2017 2016 Income: Cash dividends from subsidiaries $ 74,100 $ 30,800 $ 48,800 Excess of earnings over dividends of subsidiaries 82,323 92,929 58,809 Other 7,269 6,590 4,184 Total income 163,692 130,319 111,793 Expenses: Salaries and employee benefits 9,966 8,606 5,655 Other operating expenses 4,781 3,871 3,531 Total expense 14,747 12,477 9,186 Earnings before income taxes 148,945 117,842 102,607 Income tax benefit 1,693 2,529 2,167 Net earnings $ 150,638 $ 120,371 $ 104,774 Condensed Statements of Cash Flows- For the Years Ended December 31, 2018, 2017 and 2016 2018 2017 2016 Cash flows from operating activities: Net earnings $ 150,638 $ 120,371 $ 104,774 Adjustments to reconcile net earnings to net cash provided by operating activities: Excess of earnings over dividends of subsidiary bank (82,323 ) (92,929 ) (58,809 ) Depreciation and amortization, net 331 207 208 Decrease (increase) in other assets 560 438 1,702 Increase (decrease) in other liabilities 1,932 183 (1,374 ) Other (2 ) 2 8 Net cash provided by operating activities 71,136 28,272 46,509 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 (346 ) (30 ) (94 ) Other — — 10 Net cash provided by (used in) investing activities 1,654 2,967 (84 ) Cash flows from financing activities: Proceeds of stock issuances 3,864 2,934 1,260 Cash dividends paid (53,861 ) (48,955 ) (44,907 ) Net cash used in financing activities (49,997 ) (46,021 ) (43,647 ) Net increase (decrease) in cash and cash equivalents 22,793 (14,782 ) 2,778 Cash and cash equivalents, beginning of year 78,469 93,251 90,473 Cash and cash equivalents, end of year $ 101,262 $ 78,469 $ 93,251

Cash Flow Information

Cash Flow Information	12 Months Ended
	Dec. 31, 2018
Supplemental Cash Flow Elements [Abstract]
Cash Flow Information	19. CASH FLOW INFORMATION: Supplemental information on cash flows and noncash transactions is as follows (dollars in thousands): Year Ended December 31, 2018 2017 2016 Supplemental cash flow information: Interest paid $ 18,709 $ 9,316 $ 5,465 Federal income taxes paid 26,578 29,695 28,348 Schedule of noncash investing and financing activities: Assets acquired through foreclosure 126 2,211 2,269 Investment securities purchased but not settled — — 12,381 Restricted stock grant to officers and directors 1,609 1,139 810

Acquisition

Acquisition	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Acquisition	20. ACQUISITION On October 12, 2017, we entered into an agreement and plan of reorganization to acquire Commercial Bancshares, Inc. and its wholly owned bank subsidiary, Commercial State Bank, Kingwood, Texas. On January 1, 2018, the transaction was completed. Pursuant to the agreement, we issued 1,289,371 shares of the Company’s common stock in exchange for all of the outstanding shares of Commercial Bancshares, Inc. In addition, Commercial Bancshares, Inc. made a $22,075,000 special dividend to its shareholders prior to closing of the transaction, which was increased for the amount by which Commercial Bancshares, Inc.’s consolidated shareholders’ equity as of January 1, 2018 exceeded $42,402,000, after certain adjustments per the merger agreement. 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 shares) $ 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.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
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, 2018. 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 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. Previously, the Board of Directors had authorized the repurchase of up to 1,500,000 common shares through September 30, 2017. The stock buyback plan authorizes management to repurchase the stock at such time as repurchases are considered beneficial to stockholders. Any repurchase of stock will be made through the open market, block trades or in privately negotiated transactions in accordance with applicable laws and regulations. Under the repurchase plan, there is no minimum number of shares that the Company is required to repurchase. For the years ended December 31, 2018, 2017 and 2016, no shares were repurchased under this 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 The Company records its available-for-sale 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 party pricing services to value its investment securities, which the Company reviews as well as the underlying pricing methodologies for reasonableness and to ensure such prices are aligned with pricing matrices. The Company validates prices supplied by the independent pricing services by comparison to prices obtained from other third party sources on a quarterly basis.
Loans Held-for-Investment 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 nonaccretable difference to accretable yield, which will be recognized prospectively. Decreases in expected cash flows subsequent to acquisition are recognized as impairment. Valuation allowances on these impaired loans reflect only losses incurred after the acquisition. The carrying amount of purchased credit impaired loans at December 31, 2018 and 2017 were $827,000 and $618,000, respectively, compared to a contractual balance of $1,157,000 and $1,865,000, respectively. Other purchased credit impaired loan disclosures were omitted due to immateriality.
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 and $139,971,000, respectively at December 31, 2018 and 2017. There was no impairment recorded for the years ended December 31, 2018, 2017 and 2016. The carrying amount of goodwill arising from acquisitions that qualify as an asset purchase for federal income tax purposes was $22,526,000 and $26,618,000 at December 31, 2018 and 2017, 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 $1,508,000, $1,745,000, and $882,000, for the years ended December 31, 2018, 2017 and 2016, 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 $560,000 and $680,000, respectively, for the year ended December 31, 2018, $483,000 and $562,000, respectively, for the year ended December 31, 2017, and $278,000 and $381,000, respectively, for the year ended December 31, 2016.
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. There were no such anti-dilutive stock options for the years ended December 31, 2018, 2017 and 2016. The following table reconciles the computation of basic EPS to dilutive EPS: Net Weighted Per For the year ended December 31, 2018: Net earnings per share, basic $ 150,638 67,609,367 $ 2.23 Effect of stock options and stock grants — 373,647 (0.01 ) Net earnings per share, assuming dilution $ 150,638 67,983,014 $ 2.22 For the year ended December 31, 2017: Net earnings per share, basic $ 120,371 66,126,863 $ 1.82 Effect of stock options and stock grants — 197,467 (0.01 ) Net earnings per share, assuming dilution $ 120,371 66,324,330 $ 1.81 For the year ended December 31, 2016: Net earnings per share, basic $ 104,774 66,013,004 $ 1.59 Effect of stock options and stock grants — 89,882 — Net earnings per share, assuming dilution $ 104,774 66,102,886 $ 1.59
Recently Issued Authoritative Accounting Guidance	Recently Issued Authoritative Accounting Guidance Accounting Standards Update (“ASU”) 2014-09, 2014-09 2015-04 2014-09 2014-09, non-interest ASU 2016-01, 2016-01 2016-01, available-for-sale 2016-1 ASU 2016-02, 2016-02 right-of-use 2016-02 ASU 2016-09, 2016-09 2016-09 2016-09 ASU 2016-13, 2016-13 held-to-maturity 2016-13 2016-13 ASU 2017-04, 2017-04 2017-04 ASU 2017-07, 2017-17 2017-17 ASU 2017-08, 2017-08 2017-08 2017-08 ASU 2018-02, 2018-02 2018-02 ASU 2018-13, 2018-13 2018-13 ASU 2018-14, 715-20).” 2018-14 2018-14

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Computation of Basic EPS to Dilutive EPS	The following table reconciles the computation of basic EPS to dilutive EPS: Net Weighted Per For the year ended December 31, 2018: Net earnings per share, basic $ 150,638 67,609,367 $ 2.23 Effect of stock options and stock grants — 373,647 (0.01 ) Net earnings per share, assuming dilution $ 150,638 67,983,014 $ 2.22 For the year ended December 31, 2017: Net earnings per share, basic $ 120,371 66,126,863 $ 1.82 Effect of stock options and stock grants — 197,467 (0.01 ) Net earnings per share, assuming dilution $ 120,371 66,324,330 $ 1.81 For the year ended December 31, 2016: Net earnings per share, basic $ 104,774 66,013,004 $ 1.59 Effect of stock options and stock grants — 89,882 — Net earnings per share, assuming dilution $ 104,774 66,102,886 $ 1.59

Interest-bearing Time Deposit_2

Interest-bearing Time Deposits in Banks and Securities (Tables)	12 Months Ended
	Dec. 31, 2018
Cash and Cash Equivalents [Abstract]
Summary of Available-for-Sale Securities	A summary of the Company’s available-for-sale December 31, 2018 Amortized Gross Gross 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 December 31, 2017 Amortized Gross Gross Estimated Securities available-for-sale: Obligations of U.S. government sponsored enterprises and agencies $ 60,516 $ — $ (186 ) $ 60,330 Obligations of state and political subdivisions 1,369,295 52,491 (936 ) 1,420,850 Corporate bonds and other 11,421 43 (5 ) 11,459 Residential mortgage-backed securities 1,223,452 4,561 (8,916 ) 1,219,097 Commercial mortgage-backed securities 377,934 263 (2,460 ) 375,737 Total securities available-for-sale $ 3,042,618 $ 57,358 $ (12,503 ) $ 3,087,473
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 $ 187,600 $ 188,914 Due after one year through five years 547,868 563,679 Due after five years through ten years 507,792 518,317 Due after ten years 1,714 2,022 Mortgage-backed securities 1,908,594 1,885,845 Total $ 3,153,568 $ 3,158,777
Continuous Unrealized-Loss Position of Available-for-Sale Securities	The following tables disclose, as of December 31, 2018 and 2017, the Company’s investment securities that have been in a continuous unrealized-loss Less than 12 Months 12 Months or Longer Total December 31, 2018 Fair Unrealized Fair Unrealized Fair 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 Less than 12 Months 12 Months or Longer Total December 31, 2017 Fair Unrealized Fair Unrealized Fair Unrealized Obligations of U.S. government sponsored enterprises and agencies $ 60,329 $ 186 $ — $ — $ 60,329 $ 186 Obligations of state and political subdivisions 66,361 219 44,938 717 111,299 936 Corporate bonds and other 224 2 237 3 461 5 Residential mortgage-backed securities 701,252 3,988 239,641 4,928 940,893 8,916 Commercial mortgage-backed securities 239,548 1,500 92,549 960 332,097 2,460 Total $ 1,067,714 $ 5,895 $ 377,365 $ 6,608 $ 1,445,079 $ 12,503

Loans Held for Investment and_2

Loans Held for Investment and Allowance for Loan Losses (Tables)	12 Months Ended
	Dec. 31, 2018
Receivables [Abstract]
Loans Held-for-Investment by Class of Financing Receivables	Loans held-for-investment December 31, 2018 2017 Commercial $ 844,953 $ 684,099 Agricultural 96,677 94,543 Real estate 2,639,346 2,302,998 Consumer 372,660 403,929 Total loans held-for-investment $ 3,953,636 $ 3,485,569
Non-Accrual Loans, Loans Still Accruing and Past Due 90 Days or More and Restructured Loans	The Company’s non-accrual December 31, 2018 2017 Non-accrual $ 27,534 $ 17,670 Loans still accruing and past due 90 days or more 1,008 288 Troubled debt restructured loans** 513 627 Total $ 29,055 $ 18,585 * Includes $827,000 and $618,000, respectively, of purchased credit impaired loans as of December 31, 2018 and 2017. ** Our troubled debt restructured loans of $3,840,000 and $4,629,000, 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, 2018 December 31, 2017 Recorded Investment Valuation Recorded Valuation $ 27,534 $ 4,069 $ 17,670 $ 3,996
Schedule of Non-Accrual Loans	Non-accrual December 31, 2018 2017 Commercial $ 9,334 $ 3,612 Agricultural 759 134 Real Estate 16,714 12,838 Consumer 727 1,086 Total $ 27,534 $ 17,670
Schedule of Impaired Loans and Related Allowance	The Company’s impaired loans and related allowance as of December 31, 2018 and 2017 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, 2018 Unpaid 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. December 31, 2017 Unpaid Recorded Recorded Total Related 12 Month Commercial $ 5,597 $ 518 $ 3,094 $ 3,612 $ 1,194 $ 4,849 Agricultural 147 — 134 134 31 120 Real Estate 16,823 2,348 10,490 12,838 2,316 13,835 Consumer 1,284 143 943 1,086 455 1,258 Total $ 23,851 $ 3,009 $ 14,661 $ 17,670 $ 3,996 $ 20,062 * Includes $618,000 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, 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 December 31, 2017 Pass Special Substandard Doubtful Total Commercial $ 649,166 $ 6,282 $ 28,651 $ — $ 684,099 Agricultural 90,457 1,527 2,559 — 94,543 Real Estate 2,227,302 29,089 46,607 — 2,302,998 Consumer 401,434 181 2,314 — 403,929 Total $ 3,368,359 $ 37,079 $ 80,131 $ — $ 3,485,569
Schedule of Past Due Loans	At December 31, 2018 and 2017, the Company’s past due loans are as follows (dollars in thousands): December 31, 2018 15-59 60-89 Greater Total Past Total Total 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 December 31, 2017 15-59 60-89 Greater Total Past Total Total Total 90 Commercial $ 2,039 $ 1,104 $ 1,081 $ 4,224 $ 679,875 $ 684,099 $ 7 Agricultural 640 — — 640 93,903 94,543 — Real Estate 12,308 511 1,198 14,017 2,288,981 2,302,998 216 Consumer 1,360 361 135 1,856 402,073 403,929 65 Total $ 16,347 $ 1,976 $ 2,414 $ 20,737 $ 3,464,832 $ 3,485,569 $ 288 * The Company monitors commercial, agricultural and real estate loans after such loans are 15 days past due. Consumer loans are monitored after such loans are 30 days past due.
Schedule of Allowance for Loan Losses by Portfolio Segment	The following table details the allowance for loan losses at December 31, 2018 and 2017 by portfolio segment (in thousands). There were no allowances for purchased credit impaired loans at December 31, 2018 or 2017. 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, 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 December 31, 2017 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 1,194 $ 31 $ 2,316 $ 455 $ 3,996 Loan collectively evaluated for impairment 9,671 1,274 27,580 5,635 44,160 Total $ 10,865 $ 1,305 $ 29,896 $ 6,090 $ 48,156
Changes in Allowance for Loan Losses	Changes in the allowance for loan losses for the years ended December 31, 2018 and 2017 are summarized as follows (in thousands): 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 December 31, 2017 Commercial Agricultural Real Estate Consumer Total Beginning balance $ 11,707 $ 1,101 $ 26,864 $ 6,107 $ 45,779 Provision for loan losses 1,233 243 4,055 999 6,530 Recoveries 943 32 192 501 1,668 Charge-offs (3,018 ) (71 ) (1,215 ) (1,517 ) (5,821 ) Ending balance $ 10,865 $ 1,305 $ 29,896 $ 6,090 $ 48,156
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, 2018 and 2017 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 $827,000 and $618,000, respectively, at December 31, 2018 and 2017 are included in loans individually evaluated for impairment. 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 December 31, 2017 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 3,612 $ 134 $ 12,838 $ 1,086 $ 17,670 Loan collectively evaluated for impairment 680,487 94,409 2,290,160 402,843 3,467,899 Total $ 684,099 $ 94,543 $ 2,302,998 $ 403,929 $ 3,485,569
Schedule of Loans Modified and Considered Troubled Debt Restructurings	The Company’s loans that were modified in the years ended December 31, 2018 and 2017, and considered troubled debt restructurings are as follows (dollars in thousands): Year Ended December 31, 2018 Year Ended December 31, 2017 Number Pre-Modification Post- Number Pre-Modification Post- Commercial 4 $ 864 $ 864 11 $ 895 $ 895 Agricultural 1 4 4 — — — Real Estate 5 643 643 5 625 625 Consumer 8 209 209 1 25 25 Total 18 $ 1,720 $ 1,720 17 $ 1,545 $ 1,545
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, 2018 and 2017 (dollars in thousands): Year Ended December 31, 2018 Year Ended December 31, 2017 Adjusted Extended Combined Adjusted Extended Combined Commercial $ — $ 529 $ 335 $ — $ 195 $ 700 Agricultural — — 4 — — — Real Estate — 280 363 — 312 313 Consumer — — 209 — 25 — Total $ — $ 809 $ 911 $ — $ 532 $ 1,013
Schedule of Troubled Debt Restructurings	The loans with payment default are as follows (dollars in thousands): Year Ended December 31, 2018 Year Ended December 31, 2017 Number Balance Number Balance Commercial 1 $ 491 2 $ 88 Agriculture — — — — Real Estate — — — — Consumer — — — — Total 1 $ 491 2 $ 88
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, 2018 (determined as of each respective year-end) Beginning Additional Payments Ending Year ended December 31, 2018 $ 55,904 $ 55,678 $ 44,188 $ 67,394

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018: Outstanding Asset Liability IRLCs $ 37,088 $ 765 $ — Forward mortgage-backed securities trades 45,500 — 403 December 31, 2017: Outstanding Asset Liability IRLCs $ 37,589 $ 500 $ —

Bank Premises and Equipment (Ta

Bank Premises and Equipment (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 2017 Land – $ 31,190 $ 29,508 Buildings 20 to 40 years 135,335 119,728 Furniture and equipment 3 to 10 years 58,969 58,672 Leasehold improvements Lesser of lease term or 5 to 15 years 3,557 4,118 229,051 212,026 Less- accumulated depreciation and amortization (95,630 ) (88,000 ) Total Bank Premises and Equipment $ 133,421 $ 124,026

Deposits and Borrowings (Tables

Deposits and Borrowings (Tables)	12 Months Ended
	Dec. 31, 2018
Banking and Thrift [Abstract]
Scheduled Maturities of Time Deposits	At December 31, 2018, the scheduled maturities of time deposits (in thousands) were, as follows: Year ending December 31, 2019 $ 373,359 2020 42,801 2021 11,406 2022 8,066 2023 6,475 Thereafter 54 $442,161
Schedule of Borrowings	Borrowings at December 31, 2018 and 2017 consisted of the following (dollars in thousands): December 31, 2018 2017 Securities sold under agreements with customers to repurchase $ 409,631 $ 320,450 Federal funds purchased 4,075 10,550 Advances from Federal Home Loan Bank of Dallas 55,000 — Total $ 468,706 $ 331,000

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
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 , 2018 2017 2016 Current federal income tax $ 28,359 $ 34,421 $ 30,381 Current state income tax 92 99 99 Deferred federal income tax expense (benefit) (250 ) (53 ) 673 Restatement of net deferred tax liability due to change in income tax rate (664 ) (7,650 ) — Income tax expense $ 27,537 $ 26,817 $ 31,153
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 2018 2017 2016 Statutory federal income tax rate 21.0 % 35.0 % 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 (5.2 ) (11.5 ) (12.1 ) Effect of state income tax 0.1 0.1 0.1 ESOP tax deduction (0.1 ) (0.2 ) (0.2 ) Other 0.1 0.1 0.1 Effective income tax rate 15.5 % 18.2 % 22.9 %
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, 2018 and 2017 are as follows (dollars in thousands): 2018 2017 Deferred tax assets: Tax basis of loans in excess of financial statement basis $ 12,010 $ 10,550 Minimum liability in defined benefit plan 352 766 Recognized for financial reporting purposes but not yet for tax purposes: Deferred compensation 2,056 1,818 Write-downs and adjustments to other real estate owned and repossessed assets 49 11 Other deferred tax assets 208 79 Total deferred tax assets $ 14,675 $ 13,224 Deferred tax liabilities: Financial statement basis of fixed assets in excess of tax basis $ 4,182 3,343 Intangible asset amortization deductible for tax purposes, but not for financial reporting purposes 11,263 9,926 Recognized for financial reporting purposes but not yet for tax purposes: Accretion on investment securities 745 1,039 Pension plan contributions 816 1,086 Net unrealized gain on investment securities available-for-sale 1,111 9,420 Other deferred tax liabilities 34 31 Total deferred tax liabilities $ 18,151 $ 24,845 Net deferred tax asset (liability) $ (3,476 ) $ (11,621 )

Fair Value Disclosures (Tables)

Fair Value Disclosures (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 and 2017 segregated by the level of the valuation inputs within the fair value hierarchy utilized to measure fair value (in thousands): December 31, 2018 Level 1 Level 2 Level 3 Total Fair 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 December 31, 2017 Level 1 Level 2 Level 3 Total Fair Available-for-sale Obligations of U. S. government sponsored enterprises and agencies $ — $ 60,330 $ — $ 60,330 Obligations of state and political subdivisions — 1,420,850 — 1,420,850 Corporate bonds — 7,031 — 7,031 Residential mortgage-backed securities — 1,219,097 — 1,219,097 Commercial mortgage-backed securities — 375,737 — 375,737 Other securities 4,428 — — 4,428 Total $ 4,428 $ 3,083,045 $ — $ 3,087,473 IRLCs $ — $ 500 $ — $ 500
Other Real Estate Owned	circumstances arise. The following table presents other real estate owned that were re-measured Year Ended December 31, 2018 2017 Carrying value of other real estate owned prior to re-measurement $ 1,046 $ 1,067 Write-downs included in gain (loss) on sale of other real estate owned (236 ) (306 ) Fair value $ 810 $ 761
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, 2018 and 2017, were as follows (dollars in thousands): 2018 2017 Carrying Estimated Carrying Estimated Fair Value Value Fair Value Value Fair Value Hierarchy Cash and due from banks $ 207,835 $ 207,835 $ 209,583 $ 209,583 Level 1 Interest-bearing deposits in banks 40,812 40,812 162,764 162,764 Level 1 Interest-bearing time deposits in banks 1,458 1,458 1,458 1,458 Level 2 Available-for-sale 3,158,777 3,158,777 3,087,473 3,087,473 Levels 1 and 2 Loans held-for-investment 3,902,434 3,947,391 3,437,413 3,455,003 Level 3 Loans held-for-sale 21,672 21,779 15,130 15,314 Level 2 Accrued interest receivable 36,765 36,765 36,081 36,081 Level 2 Deposits with stated maturities 442,161 441,727 451,255 452,000 Level 2 Deposits with no stated maturities 5,738,228 5,738,228 5,511,706 5,511,706 Level 1 Borrowings 468,706 468,706 331,000 331,000 Level 2 Accrued interest payable 408 408 197 197 Level 2 IRLCs 765 765 500 500 Level 2 Forward mortgage-backed securities traded 403 403 — — Level 2

Financial Instruments with Of_2

Financial Instruments with Off-Balance-Sheet Risk (Tables)	12 Months Ended
	Dec. 31, 2018
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 December 31, 2018 (in thousands) Financial instruments whose contract amounts represent credit risk: Unfunded lines of credit $ 632,667 Unfunded commitments to extend credit 301,616 Standby letters of credit 26,641 Total commercial commitments $ 960,924

Pension and Profit Sharing Pl_2

Pension and Profit Sharing Plans (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 and 2017, benefit obligation activity and fair value of plan assets for the years ended December 31, 2018 and 2017, and a statement of the funded status as of December 31, 2018 and 2017, are as follows (dollars in thousands): 2018 2017 Reconciliation of benefit obligations: Benefit obligation at January 1 $ 15,531 $ 15,453 Interest cost on projected benefit obligation 523 635 Actuarial (gain) loss (811 ) 486 Benefits paid, including settlement of certain participant balances (8,630 ) (1,043 ) Benefit obligation at December 31 $ 6,613 $ 15,531 Reconciliation of fair value of plan assets: Fair value of plan assets at January 1 $ 17,046 $ 15,787 Actual return on plan assets 365 2,302 Employer contributions — — Benefits paid, including settlement of certain participant balances (8,630 ) (1,043 ) Fair value of plan assets at December 31 8,781 17,046 Funded status $ 2,168 $ 1,515
Component of Accumulated Other Comprehensive Earnings	Amounts recognized as a component of accumulated other comprehensive earnings as of year-end 2018 2017 Net actuarial loss $ (1,717 ) $ (3,597 ) Deferred tax benefit 393 1,227 Amounts included in accumulated other comprehensive earnings, net of tax $ (1,324 ) $ (2,370 )
Net Periodic Pension Cost	Net periodic benefit cost for the years ended December 31, 2018, 2017 and 2016, are as follows (dollars in thousands): Year Ended December 31, 2018 2017 2016 Service cost—benefits earned during the period $ — $ — $ — Interest cost on projected benefit obligation 523 635 665 Expected return on plan assets (1,028 ) (974 ) (912 ) Amortization of unrecognized net loss 186 249 375 Recognized loss on partial settlement of certain participant balances 1,546 — 267 Net periodic pension benefit expense (benefit) $ 1,227 $ (90 ) $ 395
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: 2018 2017 2016 Weighted average discount rate 4.25 % 3.50 % 4.25 % Expected long-term rate of return on assets 6.25 % 6.25 % 6.25 %
Pension Plan and Targeted Allocation Percentage	The major type of plan assets in the pension plan and the targeted allocation percentage as of December 31, 2018 and 2017 is as follows: December 31, 2018 December 31, 2017 Targeted Equity securities 72 % 75 % 75 % Debt securities 27 % 24 % 25 % Cash and equivalents 1 % 1 % —
Breakdown by Level	hierarchy. The breakdown by level is as follows (dollars in thousands): Level 1 Level 2 Level 3 Total Fair Money market fund $ 87 $ — $ — $ 87 Obligations of state and political subdivisions — 208 — 208 Corporate bonds — 449 — 449 Mortgage-backed securities — 901 — 901 Corporate stocks and mutual funds 7,136 — — 7,136 Total $ 7,223 $ 1,558 $ — $ 8,781
Estimate of Undiscounted Projected Future Payments	An estimate of the undiscounted projected future payments to eligible participants for the next five years and the following five years in the aggregate is as follows (dollars in thousands): Year Ending December 31, 2019 $ 837 2020 $ 318 2021 $ 388 2022 $ 398 2023 $ 333 2024 forward $ 2,339

Regulatory Matters (Tables)

Regulatory Matters (Tables)	12 Months Ended
	Dec. 31, 2018
Banking and Thrift [Abstract]
Schedule of Regulatory Capital Ratios Under the Basel III Regulatory Capital Framework	As of December 31, 2018 and 2017, the regulatory capital ratios of the Company and Bank under the Basel III regulatory capital framework are as follows: 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 % Actual Minimum Capital Phase-In Minimum Capital Phased-In Required to be As of December 31, 2017: Amount Ratio Amount Ratio Amount Ratio Amount Ratio Total Capital to Risk-Weighted Assets: Consolidated $ 814,634 19.85 % $ 379,578 9.250 % $ 430,872 10.50 % — N/A First Financial Bank, N.A $ 723,563 17.68 % $ 378,614 9.250 % $ 429,777 10.50 % $ 409,312 10.00 % Tier 1 Capital to Risk-Weighted Assets: Consolidated $ 765,882 18.66 % $ 297,507 7.250 % $ 348,801 8.50 % — N/A First Financial Bank, N.A $ 674,811 16.49 % $ 296,751 7.250 % $ 347,915 8.50 % $ 327,450 8.00 % Common Equity Tier 1 Capital to Risk-Weighted Assets: Consolidated $ 765,882 18.66 % $ 235,954 5.750 % $ 287,248 7.00 % — N/A First Financial Bank, N.A $ 674,811 16.49 % $ 235,354 5.750 % $ 286,518 7.00 % $ 266,053 6.50 % Leverage Ratio: Consolidated $ 765,882 11.09 % $ 276,296 4.000 % $ 276,296 4.00 % — N/A First Financial Bank, N.A $ 674,811 9.80 % $ 275,320 4.000 % $ 275,320 4.00 % $ 344,151 5.00 %

Stock Option Plan and Restric_2

Stock Option Plan and Restricted Stock Plan (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 is presented in the table and narrative below: Shares Weighted- Weighted- Aggregate Intrinsic Outstanding, beginning of year 1,325,965 $ 33.01 Granted — — Exercised (173,822 ) 22.23 Cancelled (66,600 ) 36.25 Outstanding, end of year 1,085,543 34.54 6.55 $ 25,135 Exercisable at end of year 407,463 $ 27.41 4.65 $ 12,337
Schedule of Information Concerning Outstanding and Vested Stock Options	The following table summarizes information concerning outstanding and vested stock options as of December 31, 2018: Exercise Price Number Remaining Number Vested $ 16.78 29,823 0.4 29,823 15.73 90,265 2.8 90,265 30.85 211,355 4.8 161,135 33.89 341,250 6.8 126,240 $ 42.35 412,850 8.5 —

Condensed Financial Informati_2

Condensed Financial Information - Parent Company (Tables)	12 Months Ended
	Dec. 31, 2018
Condensed Financial Information Disclosure [Abstract]
Condensed Balance Sheets	Condensed Balance Sheets-December 31, 2018 and 2017 2018 2017 ASSETS Cash in subsidiary bank $ 16,981 $ 14,272 Cash in unaffiliated banks 2 2 Interest-bearing deposits in subsidiary bank 84,279 64,195 Total cash and cash equivalents 101,262 78,469 Securities available-for-sale, 6,276 8,515 Investment in and advances to subsidiaries, at equity 959,352 847,445 Intangible assets 723 723 Other assets 2,647 2,654 Total assets $ 1,070,260 $ 937,806 LIABILITIES AND SHAREHOLDERS’ EQUITY Total liabilities $ 16,965 $ 15,038 Shareholders’ equity: Common stock 678 663 Capital surplus 443,114 378,062 Retained earnings 606,658 517,257 Treasury stock (7,507 ) (7,148 ) Deferred compensation 7,507 7,148 Accumulated other comprehensive earnings 2,845 26,786 Total shareholders’ equity 1,053,295 922,768 Total liabilities and shareholders’ equity $ 1,070,260 $ 937,806
Condensed Statements of Earnings	Condensed Statements of Earnings- For the Years Ended December 31, 2018, 2017 and 2016 2018 2017 2016 Income: Cash dividends from subsidiaries $ 74,100 $ 30,800 $ 48,800 Excess of earnings over dividends of subsidiaries 82,323 92,929 58,809 Other 7,269 6,590 4,184 Total income 163,692 130,319 111,793 Expenses: Salaries and employee benefits 9,966 8,606 5,655 Other operating expenses 4,781 3,871 3,531 Total expense 14,747 12,477 9,186 Earnings before income taxes 148,945 117,842 102,607 Income tax benefit 1,693 2,529 2,167 Net earnings $ 150,638 $ 120,371 $ 104,774
Condensed Statements of Cash Flows	Condensed Statements of Cash Flows- For the Years Ended December 31, 2018, 2017 and 2016 2018 2017 2016 Cash flows from operating activities: Net earnings $ 150,638 $ 120,371 $ 104,774 Adjustments to reconcile net earnings to net cash provided by operating activities: Excess of earnings over dividends of subsidiary bank (82,323 ) (92,929 ) (58,809 ) Depreciation and amortization, net 331 207 208 Decrease (increase) in other assets 560 438 1,702 Increase (decrease) in other liabilities 1,932 183 (1,374 ) Other (2 ) 2 8 Net cash provided by operating activities 71,136 28,272 46,509 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 (346 ) (30 ) (94 ) Other — — 10 Net cash provided by (used in) investing activities 1,654 2,967 (84 ) Cash flows from financing activities: Proceeds of stock issuances 3,864 2,934 1,260 Cash dividends paid (53,861 ) (48,955 ) (44,907 ) Net cash used in financing activities (49,997 ) (46,021 ) (43,647 ) Net increase (decrease) in cash and cash equivalents 22,793 (14,782 ) 2,778 Cash and cash equivalents, beginning of year 78,469 93,251 90,473 Cash and cash equivalents, end of year $ 101,262 $ 78,469 $ 93,251

Cash Flow Information (Tables)

Cash Flow Information (Tables)	12 Months Ended
	Dec. 31, 2018
Supplemental Cash Flow Elements [Abstract]
Supplemental Information on Cash Flows and Noncash Transactions	Supplemental information on cash flows and noncash transactions is as follows (dollars in thousands): Year Ended December 31, 2018 2017 2016 Supplemental cash flow information: Interest paid $ 18,709 $ 9,316 $ 5,465 Federal income taxes paid 26,578 29,695 28,348 Schedule of noncash investing and financing activities: Assets acquired through foreclosure 126 2,211 2,269 Investment securities purchased but not settled — — 12,381 Restricted stock grant to officers and directors 1,609 1,139 810

Acquisition (Tables)

Acquisition (Tables) - FBC Bancshares, Inc. and First Bank, N.A. [Member]	12 Months Ended
	Dec. 31, 2018
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 shares) $ 58,087
Schedule of Preliminary Estimated Fair Value Amounts Assigned to Major Asset and Liability Categories at Acquisition Date	Fair value of consideration paid: Common stock issued (1,289,371 shares) $ 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)	12 Months Ended
	Dec. 31, 2018USD ($)Locationshares	Dec. 31, 2017USD ($)shares	Dec. 31, 2016USD ($)shares	Jan. 01, 2018	Sep. 02, 2017shares	Jun. 25, 2017shares
Equity, Class of Treasury Stock [Line Items]
Number of locations | Location	73
Stock repurchase program expiration date	Sep. 30, 2020
Minimum number of shares that company is required to repurchase | shares	0
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	$ 27,534,000	$ 17,670,000
Contractual balance	36,614,000	23,851,000
Impairment recorded	$ 0	0	$ 0
Other identifiable intangible assets, amortized period (years)	7 years
Goodwill and intangible assets with indefinite lives	$ 171,565,000	139,971,000
Carrying amount of goodwill arising from acquisitions, is deductible for federal income tax purposes	$ 22,526,000	26,618,000
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	$ 4,169,000	29,156,000
Minimum pension liability, included in accumulated other comprehensive income	(1,324,000)	(2,370,000)
Stock compensation expense	$ 1,508,000	$ 1,745,000	$ 882,000
Federal statutory tax rate	21.00%	35.00%	35.00%
Purchased Credit Impaired Loans [Member]
Equity, Class of Treasury Stock [Line Items]
Loans individually evaluated for impairment	$ 827,000	$ 618,000
Contractual balance	1,157,000	1,865,000
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	560,000	483,000	$ 278,000
Officers [Member]
Equity, Class of Treasury Stock [Line Items]
Restricted stock expense	$ 680,000	$ 562,000	$ 381,000
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, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net earnings	$ 150,638	$ 120,371	$ 104,774
Effect of stock options and stock grants, Net Earnings	0	0	0
Net earnings per share, assuming dilution, Net Earnings	$ 150,638	$ 120,371	$ 104,774
Net earnings per share, basic, Weighted Average Shares	67,609,367	66,126,863	66,013,004
Effect of stock options and stock grants, Weighted Average Shares	373,647	197,467	89,882
Net earnings per share, assuming dilution, Weighted Average Shares	67,983,014	66,324,330	66,102,886
Net earnings per share, basic, Per Share Amount	$ 2.23	$ 1.82	$ 1.59
Effect of stock options and stock grants, Per Share Amount	(0.01)	(0.01)
Net earnings per share, assuming dilution, Per Share Amount	$ 2.22	$ 1.81	$ 1.59

Interest-bearing Time Deposit_3

Interest-bearing Time Deposits in Banks and Securities - Additional Information (Detail) $ in Thousands	Dec. 31, 2018USD ($)Investment	Dec. 31, 2018USD ($)Investment	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Interest Bearing Time Deposits In Banks And Securities [Line Items]
INTEREST-BEARING TIME DEPOSITS IN BANKS	$ 1,458	$ 1,458	$ 1,458
Interest-bearing time deposits, maturity period, years		12 months
Number of investment positions | Investment	366	366
Securities pledged as collateral	$ 1,988,579	$ 1,988,579	2,018,420
Sales of investment securities available-for-sale		220,259	120,576	$ 40,510
Gross realized gains from security sales		1,847	2,643	1,579
Gross realized losses from security sales or calls		$ 493	$ 815	$ 309
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	32.65%	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	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	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	$ 3,153,568	$ 3,153,568	$ 3,042,618
Securities available-for-sale, Gross Unrealized Holding Gains	34,611		57,358
Securities available-for-sale, Gross Unrealized Holding Losses	(29,402)		(12,503)
Securities available-for-sale, Estimated Fair Value	3,158,777	$ 3,158,777	3,087,473
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	9,970
Securities available-for-sale, Gross Unrealized Holding Losses	(8)
Securities available-for-sale, Estimated Fair Value	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		60,516
Securities available-for-sale, Gross Unrealized Holding Losses			(186)
Securities available-for-sale, Estimated Fair Value	301		60,330
Obligations of State and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	1,229,828		1,369,295
Securities available-for-sale, Gross Unrealized Holding Gains	30,013		52,491
Securities available-for-sale, Gross Unrealized Holding Losses	(1,970)		(936)
Securities available-for-sale, Estimated Fair Value	1,257,871		1,420,850
Corporate Bonds and Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	4,875		11,421
Securities available-for-sale, Gross Unrealized Holding Gains			43
Securities available-for-sale, Gross Unrealized Holding Losses	(77)		(5)
Securities available-for-sale, Estimated Fair Value	4,798		11,459
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	1,472,228		1,223,452
Securities available-for-sale, Gross Unrealized Holding Gains	3,928		4,561
Securities available-for-sale, Gross Unrealized Holding Losses	(21,611)		(8,916)
Securities available-for-sale, Estimated Fair Value	1,454,545		1,219,097
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	436,366		377,934
Securities available-for-sale, Gross Unrealized Holding Gains	670		263
Securities available-for-sale, Gross Unrealized Holding Losses	(5,736)		(2,460)
Securities available-for-sale, Estimated Fair Value	$ 431,300		$ 375,737

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	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Available-for-Sale, Amortized Cost Basis, Due within one year		$ 187,600
Available-for-Sale, Amortized Cost Basis, Due after one year through five years		547,868
Available-for-Sale, Amortized Cost Basis, Due after five years through ten years		507,792
Available-for-Sale, Amortized Cost Basis, Due after ten years		1,714
Available-for-Sale, Amortized Cost Basis, Mortgage-backed securities		1,908,594
Available-for-Sale, Amortized Cost Basis, Total	$ 3,153,568	3,153,568	$ 3,042,618
Available-for-Sale, Estimated Fair Value, Due within one year		188,914
Available-for-Sale, Estimated Fair Value, Due after one year through five years		563,679
Available-for-Sale, Estimated Fair Value, Due after five years through ten years		518,317
Available-for-Sale, Estimated Fair Value, Due after ten years		2,022
Available-for-Sale, Estimated Fair Value, Mortgage-backed securities		1,885,845
Securities available-for-sale, Estimated Fair Value, Total	$ 3,158,777	$ 3,158,777	$ 3,087,473

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, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Fair Value	$ 163,377	$ 1,067,714
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	671	5,895
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	1,380,516	377,365
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	28,731	6,608
Available-for-sale securities, continuous unrealized loss position, Fair Value	1,543,893	1,445,079
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	29,402	12,503
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 Less than 12 Months, Fair Value		60,329
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss		186
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	60,329
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss		186
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	27,489	66,361
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	107	219
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	114,461	44,938
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	1,863	717
Available-for-sale securities, continuous unrealized loss position, Fair Value	141,950	111,299
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	1,970	936
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	224
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	68	2
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	450	237
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	9	3
Available-for-sale securities, continuous unrealized loss position, Fair Value	4,798	461
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	77	5
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	119,584	701,252
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	483	3,988
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	922,289	239,641
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	21,128	4,928
Available-for-sale securities, continuous unrealized loss position, Fair Value	1,041,873	940,893
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	21,611	8,916
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	1,994	239,548
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	5	1,500
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	343,015	92,549
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	5,731	960
Available-for-sale securities, continuous unrealized loss position, Fair Value	345,009	332,097
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	5,736	$ 2,460
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

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, 2018	Dec. 31, 2017
Loans and Leases Receivable Disclosure [Line Items]
Total	$ 3,953,636	$ 3,485,569
Commercial [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total	844,953	684,099
Agriculture [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total	96,677	94,543
Real Estate [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total	2,639,346	2,302,998
Consumer [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total	$ 372,660	$ 403,929

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, 2018	Dec. 31, 2017
Receivables [Abstract]
Non-accrual loans	$ 27,534	$ 17,670
Loans still accruing and past due 90 days or more	1,008	288
Troubled debt restructured loans	513	627
Total	$ 29,055	$ 18,585

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, 2018	Dec. 31, 2017
Loans and Leases Receivable Disclosure [Line Items]
Non-accrual loans	$ 27,534,000	$ 17,670,000
Troubled debt restructured loans	513,000	627,000
Doubtful [Member]
Loans and Leases Receivable Disclosure [Line Items]
Troubled debt restructured loans	3,840,000	4,629,000
Purchased Credit Impaired Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Non-accrual loans	$ 827,000	$ 618,000

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, 2018	Dec. 31, 2017
Receivables [Abstract]
Recorded Investment	$ 27,534	$ 17,670
Valuation Allowance	$ 4,069	$ 3,996

Loans Held for Investment and_7

Loans Held for Investment and Allowance for Loan Losses - Additional Information (Detail) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual, past due 90 days or more and still accruing, restructured loans and foreclosed assets	$ 29,632,000	$ 20,117,000	$ 29,632,000	$ 20,117,000
Non accrual loans	27,534,000	17,670,000	27,534,000	17,670,000
Additional funds advanced in connection with impaired loans	0		0
Interest income recognized on impaired loans	0	0
Interest income recognized on impaired loans			948,000	624,000	$ 829,000
Allowance for loan losses	51,202,000	48,156,000	51,202,000	48,156,000	$ 45,779,000
Loans individually evaluated for impairment	27,534,000	17,670,000	$ 27,534,000	$ 17,670,000
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		$ 0
Loans held by subsidiaries subject to blanket liens	2,495,150,000		2,495,150,000
Letters of credit outstanding	55,000,000		55,000,000
Advances from Federal Home Loan Bank of Dallas	55,000,000	0	55,000,000	$ 0
Purchased Credit Impaired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non accrual loans	827,000	618,000	827,000	618,000
Allowance for loan losses	0	0	0	0
Loans individually evaluated for impairment	$ 827,000	$ 618,000	$ 827,000	$ 618,000

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, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	$ 27,534	$ 17,670
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	9,334	3,612
Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	759	134
Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	16,714	12,838
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	$ 727	$ 1,086

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, 2018	Dec. 31, 2017
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	$ 36,614	$ 23,851
Recorded Investment With No Allowance	13,741	3,009
Recorded Investment With Allowance	13,793	14,661
Total Recorded Investment	27,534	17,670
Related Allowance	4,069	3,996
Average Recorded Investment	25,784	20,062
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	10,808	5,597
Recorded Investment With No Allowance	6,728	518
Recorded Investment With Allowance	2,606	3,094
Total Recorded Investment	9,334	3,612
Related Allowance	1,133	1,194
Average Recorded Investment	7,986	4,849
Agriculture [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	799	147
Recorded Investment With No Allowance	213
Recorded Investment With Allowance	546	134
Total Recorded Investment	759	134
Related Allowance	170	31
Average Recorded Investment	842	120
Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	24,072	16,823
Recorded Investment With No Allowance	6,699	2,348
Recorded Investment With Allowance	10,015	10,490
Total Recorded Investment	16,714	12,838
Related Allowance	2,409	2,316
Average Recorded Investment	16,042	13,835
Consumer [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	935	1,284
Recorded Investment With No Allowance	101	143
Recorded Investment With Allowance	626	943
Total Recorded Investment	727	1,086
Related Allowance	357	455
Average Recorded Investment	$ 914	$ 1,258

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, 2018	Dec. 31, 2017
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Allowance	$ 13,741	$ 3,009
Purchased Credit Impaired Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Allowance	$ 827	$ 618

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, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	$ 3,953,636	$ 3,485,569
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	844,953	684,099
Agriculture [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	96,677	94,543
Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	2,639,346	2,302,998
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	372,660	403,929
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	3,827,337	3,368,359
Pass [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	804,584	649,166
Pass [Member] | Agriculture [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	92,864	90,457
Pass [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	2,559,379	2,227,302
Pass [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	370,510	401,434
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	50,379	37,079
Special Mention [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	23,392	6,282
Special Mention [Member] | Agriculture [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	46	1,527
Special Mention [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	26,626	29,089
Special Mention [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	315	181
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	75,920	80,131
Substandard [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	16,977	28,651
Substandard [Member] | Agriculture [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	3,767	2,559
Substandard [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	53,341	46,607
Substandard [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	$ 1,835	$ 2,314

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, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 22,926	$ 20,737
Total Current	3,930,710	3,464,832
Total Loans	3,953,636	3,485,569
Total 90 Days Past Due Still Accruing	1,008	288
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,905	4,224
Total Current	840,048	679,875
Total Loans	844,953	684,099
Total 90 Days Past Due Still Accruing		7
Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	836	640
Total Current	95,841	93,903
Total Loans	96,677	94,543
Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	16,086	14,017
Total Current	2,623,260	2,288,981
Total Loans	2,639,346	2,302,998
Total 90 Days Past Due Still Accruing	960	216
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,099	1,856
Total Current	371,561	402,073
Total Loans	372,660	403,929
Total 90 Days Past Due Still Accruing	48	65
15-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	18,304	16,347
15-59 Days Past Due [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,546	2,039
15-59 Days Past Due [Member] | Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	791	640
15-59 Days Past Due [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	13,185	12,308
15-59 Days Past Due [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	782	1,360
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,845	1,976
60-89 Days Past Due [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	682	1,104
60-89 Days Past Due [Member] | Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	19
60-89 Days Past Due [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	881	511
60-89 Days Past Due [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	263	361
Greater than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,777	2,414
Greater than 90 Days [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	677	1,081
Greater than 90 Days [Member] | Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	26
Greater than 90 Days [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,020	1,198
Greater than 90 Days [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 54	$ 135

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	$ 4,069	$ 3,996
Loan collectively evaluated for impairment	47,133	44,160
Total allowance for loan losses	51,202	48,156	$ 45,779
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	1,133	1,194
Loan collectively evaluated for impairment	10,815	9,671
Total allowance for loan losses	11,948	10,865	11,707
Agriculture [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	170	31
Loan collectively evaluated for impairment	1,276	1,274
Total allowance for loan losses	1,446	1,305	1,101
Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	2,409	2,316
Loan collectively evaluated for impairment	29,933	27,580
Total allowance for loan losses	32,342	29,896	26,864
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	357	455
Loan collectively evaluated for impairment	5,109	5,635
Total allowance for loan losses	$ 5,466	$ 6,090	$ 6,107

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, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 48,156	$ 45,779
Provision for loan losses	5,665	6,530
Recoveries	1,828	1,668
Charge-offs	(4,447)	(5,821)
Ending balance	51,202	48,156
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	10,865	11,707
Provision for loan losses	1,662	1,233
Recoveries	839	943
Charge-offs	(1,418)	(3,018)
Ending balance	11,948	10,865
Agriculture [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,305	1,101
Provision for loan losses	126	243
Recoveries	15	32
Charge-offs		(71)
Ending balance	1,446	1,305
Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	29,896	26,864
Provision for loan losses	3,463	4,055
Recoveries	462	192
Charge-offs	(1,479)	(1,215)
Ending balance	32,342	29,896
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	6,090	6,107
Provision for loan losses	414	999
Recoveries	512	501
Charge-offs	(1,550)	(1,517)
Ending balance	$ 5,466	$ 6,090

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, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	$ 27,534	$ 17,670
Loan collectively evaluated for impairment	3,926,102	3,467,899
Total	3,953,636	3,485,569
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	9,334	3,612
Loan collectively evaluated for impairment	835,619	680,487
Total	844,953	684,099
Agriculture [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	759	134
Loan collectively evaluated for impairment	95,918	94,409
Total	96,677	94,543
Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	16,714	12,838
Loan collectively evaluated for impairment	2,622,632	2,290,160
Total	2,639,346	2,302,998
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	727	1,086
Loan collectively evaluated for impairment	371,933	402,843
Total	$ 372,660	$ 403,929

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	1 Months Ended	12 Months Ended
	Dec. 31, 2017USD ($)SecurityLoan	Dec. 31, 2018USD ($)
Financing Receivable, Modifications [Line Items]
Number	17	18
Pre-Modification Recorded Investment	$ 1,545	$ 1,720
Post-Modification Recorded Investment	$ 1,545	$ 1,720
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number	11	4
Pre-Modification Recorded Investment	$ 895	$ 864
Post-Modification Recorded Investment	$ 895	$ 864
Agriculture [Member]
Financing Receivable, Modifications [Line Items]
Number		1
Pre-Modification Recorded Investment		$ 4
Post-Modification Recorded Investment		$ 4
Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number	5	5
Pre-Modification Recorded Investment	$ 625	$ 643
Post-Modification Recorded Investment	$ 625	$ 643
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Number	1	8
Pre-Modification Recorded Investment	$ 25	$ 209
Post-Modification Recorded Investment	$ 25	$ 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	1 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	$ 1,545	$ 1,720
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	895	864
Agriculture [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		4
Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	625	643
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	$ 25	209
Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		809	$ 532
Extended Maturity [Member] | Commercial [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		529	195
Extended Maturity [Member] | Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		280	312
Extended Maturity [Member] | Consumer [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans			25
Combined Rate and Maturity [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		911	1,013
Combined Rate and Maturity [Member] | Commercial [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		335	700
Combined Rate and Maturity [Member] | Agriculture [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		4
Combined Rate and Maturity [Member] | Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		363	$ 313
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, 2018USD ($)Contract	Dec. 31, 2017USD ($)Contract
Financing Receivable, Modifications [Line Items]
Number | Contract	1	2
Balance | $	$ 491	$ 88
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number | Contract	1	2
Balance | $	$ 491	$ 88

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, 2018USD ($)
Receivables [Abstract]
Beginning Balance	$ 55,904
Additional Loans	55,678
Payments	44,188
Ending Balance	$ 67,394

Loans Held for Sale - Additiona

Loans Held for Sale - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group [Abstract]
Loans held for sale	$ 21,672	$ 15,130
Loans held-for-sale at the lower of cost or fair value	$ 2,487

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, 2018	Dec. 31, 2017
IRLCs [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Outstanding Notional Balance	$ 37,088	$ 37,589
Asset Derivative Fair Value	765	$ 500
Forward Mortgage-Backed Securities Traded [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Outstanding Notional Balance	45,500
Liability Derivative Fair Value	$ 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, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Land	$ 31,190	$ 29,508
Buildings	135,335	119,728
Furniture and equipment	58,969	58,672
Leasehold improvements	3,557	4,118
Gross	229,051	212,026
Less- accumulated depreciation and amortization	(95,630)	(88,000)
Total Bank Premises and Equipment	$ 133,421	$ 124,026
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, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 10,130,000	$ 9,810,000	$ 9,390,000
Rental income for leases included in net occupancy expense	2,682,000	2,367,000	2,139,000
Gain (loss) on sale the of bank premises and equipment	(147,000)	(396,000)	168,000
Gain (loss) on sale of building	$ 1,216,000	1,167,000	1,894,000
Weatherford [Member]
Property, Plant and Equipment [Line Items]
Proceeds from Sale of Building			1,385,000
Gain (loss) on sale of building			560,000
Orange [Member]
Property, Plant and Equipment [Line Items]
Proceeds from Sale of Building			2,000,000
Gain (loss) on sale of building			$ (31,000)
San Angelo [Member]
Property, Plant and Equipment [Line Items]
Proceeds from Sale of Building		1,586,000
Gain (loss) on sale of building		210,000
Write off of leasehold improvements		$ 360,000

Deposits and Borrowings - Addit

Deposits and Borrowings - Additional Information (Detail) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Banking and Thrift [Abstract]
Time deposit threshold amount	$ 250,000
Time deposits of $250,000 or more totaled	118,590,000	$ 115,203,000
Deposits received from related parties	103,413,000	74,270,000
Advances from Federal Home Loan Bank of Dallas, maturing during 2018	$ 55,000,000	$ 0
Interest rate on advance	2.65%

Deposits and Borrowings - Sched

Deposits and Borrowings - Scheduled Maturities of Time Deposits (Detail) $ in Thousands	Dec. 31, 2018USD ($)
Banking and Thrift [Abstract]
2,019	$ 373,359
2,020	42,801
2,021	11,406
2,022	8,066
2,023	6,475
Thereafter	54
Time deposits	$ 442,161

Deposits and Borrowings - Sch_2

Deposits and Borrowings - Schedule of Borrowings (Detail) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Debt Disclosure [Abstract]
Securities sold under agreements with customers to repurchase	$ 409,631,000	$ 320,450,000
Federal funds purchased	4,075,000	10,550,000
Advances from Federal Home Loan Bank of Dallas	55,000,000	0
Total	$ 468,706,000	$ 331,000,000

Line of Credit - Additional Inf

Line of Credit - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Line of Credit Facility [Line Items]
Revolving line of credit, permitted	$ 25,000,000
Line of credit, maturity date	Jun. 30, 2019
Term facility payable (in years)	Five
Interest paid on basis points	Prime Rate plus 50 basis points or LIBOR plus 250 basis points.
Percentage of restricted dividend payments	55.00%
Line of credit	$ 0	$ 0
Prime Rate [Member]
Line of Credit Facility [Line Items]
Interest rate spread above benchmark rate	0.50%
LIBOR [Member]
Line of Credit Facility [Line Items]
Interest rate spread above benchmark rate	2.50%
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
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Federal statutory tax rate	21.00%	35.00%	35.00%
Restatement of deferred tax liability due to change in tax rate	$ 8,314,000	$ 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, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Current federal income tax	$ 28,359	$ 34,421	$ 30,381
Current state income tax	92	99	99
Deferred federal income tax expense (benefit)	(250)	(53)	673
Restatement of net deferred tax liability due to change in income tax rate	(664)	(7,650)
Income tax expense	$ 27,537	$ 26,817	$ 31,153

Income Taxes - Percentage of Pr

Income Taxes - Percentage of Pretax Earnings, Differs from Statutory Federal Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Statutory federal income tax rate	21.00%	35.00%	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	(5.20%)	(11.50%)	(12.10%)
Effect of state income tax	0.10%	0.10%	0.10%
ESOP tax deduction	(0.10%)	(0.20%)	(0.20%)
Other	0.10%	0.10%	0.10%
Effective income tax rate	15.50%	18.20%	22.90%

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Tax basis of loans in excess of financial statement basis	$ 12,010	$ 10,550
Minimum liability in defined benefit plan	352	766
Deferred compensation	2,056	1,818
Write-downs and adjustments to other real estate owned and repossessed assets	49	11
Other deferred tax assets	208	79
Total deferred tax assets	14,675	13,224
Deferred tax liabilities:
Financial statement basis of fixed assets in excess of tax basis	4,182	3,343
Intangible asset amortization deductible for tax purposes, but not for financial reporting purposes	11,263	9,926
Accretion on investment securities	745	1,039
Pension plan contributions	816	1,086
Net unrealized gain on investment securities available-for-sale	1,111	9,420
Other deferred tax liabilities	34	31
Total deferred tax liabilities	18,151	24,845
Net deferred tax asset (liability)	$ (3,476)	$ (11,621)

Fair Value Disclosures - Additi

Fair Value Disclosures - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
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	13,793,000	14,661,000
Impaired loans valuation reserves	4,069,000	3,996,000
Impaired loans net fair value	9,724,000
Recorded Investment With No Allowance	13,741,000	3,009,000
Loans held-for-sale at the lower of cost or fair value	2,487,000
Loans held for sale under fair value	19,185,000	0
Other real estate owned, total	448,000	$ 1,347,000
Level 2 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale at the lower of cost or fair value	2,487,000
Loans held for sale under fair value	$ 2,594,000
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	Dec. 31, 2017
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	$ 3,158,777	$ 3,158,777	$ 3,087,473
Loans held-for-sale		21,672	15,130
U.S. Treasury Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	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		60,330
Obligations of State and Political Subdivisions [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	1,257,871		1,420,850
Residential Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	1,454,545		1,219,097
Commercial Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	$ 431,300		375,737
IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value		765	500
Forward Mortgage-Backed Securities Traded [Member]
Available-for-sale investment securities:
Forward mortgage-backed securities traded		403
Fair Value, Measurements, Recurring [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value		3,158,777	3,087,473
Loans held-for-sale		19,185
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value		450	7,031
Fair Value, Measurements, Recurring [Member] | U.S. Treasury Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value		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	60,330
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		1,257,871	1,420,850
Fair Value, Measurements, Recurring [Member] | Residential Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value		1,454,545	1,219,097
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value		431,300	375,737
Fair Value, Measurements, Recurring [Member] | IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value		765	500
Fair Value, Measurements, Recurring [Member] | Forward Mortgage-Backed Securities Traded [Member]
Available-for-sale investment securities:
Forward mortgage-backed securities traded		403
Fair Value, Measurements, Recurring [Member] | Other Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value		4,348	4,428
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value		14,310	4,428
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		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		4,348	4,428
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value		3,144,467	3,083,045
Loans held-for-sale		19,185
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		450	7,031
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	60,330
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		1,257,871	1,420,850
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		1,454,545	1,219,097
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		431,300	375,737
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value		765	$ 500
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Forward Mortgage-Backed Securities Traded [Member]
Available-for-sale investment securities:
Forward mortgage-backed securities traded		$ 403

Fair Value Disclosures - Other

Fair Value Disclosures - Other Real Estate Owned (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Carrying value of other real estate owned prior to re-measurement	$ 1,046	$ 1,067
Write-downs included in gain (loss) on sale of other real estate owned	(236)	(306)
Other real estate owned, fair value	$ 810	$ 761

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	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
CASH AND DUE FROM BANKS		$ 207,835	$ 209,583
INTEREST-BEARING DEPOSITS IN BANKS		40,812	162,764
INTEREST-BEARING TIME DEPOSITS IN BANKS		1,458	1,458
Available-for-sale securities	$ 3,158,777	3,158,777	3,087,473
Loans held for investment		3,902,434	3,437,413
Loans held for sale		21,672	15,130
Deposits with stated maturities		442,161
BORROWINGS		468,706	331,000
IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset Derivative Fair Value		765	500
Forward Mortgage-Backed Securities Traded [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Forward mortgage-backed securities traded		403
Carrying Value [Member] | IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset Derivative Fair Value		765	500
Carrying Value [Member] | Forward Mortgage-Backed Securities Traded [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Forward mortgage-backed securities traded		403
Carrying Value [Member] | Level 1 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
CASH AND DUE FROM BANKS		207,835	209,583
INTEREST-BEARING DEPOSITS IN BANKS		40,812	162,764
Deposits with no stated maturities		5,738,228	5,511,706
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	1,458
Accrued interest receivable		36,765	36,081
Deposits with stated maturities		442,161	451,255
BORROWINGS		468,706	331,000
Accrued interest payable		408	197
Carrying Value [Member] | Levels 1 and 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale securities		3,158,777	3,087,473
Carrying Value [Member] | Level 3 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for investment		3,902,434	3,437,413
Loans held for sale		21,672	15,130
Estimated Fair Value [Member] | IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset Derivative Fair Value		765	500
Estimated Fair Value [Member] | Forward Mortgage-Backed Securities Traded [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Forward mortgage-backed securities traded		403
Estimated Fair Value [Member] | Level 1 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
CASH AND DUE FROM BANKS		207,835	209,583
INTEREST-BEARING DEPOSITS IN BANKS		40,812	162,764
Deposits with no stated maturities		5,738,228	5,511,706
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	1,458
Accrued interest receivable		36,765	36,081
Deposits with stated maturities		441,727	452,000
BORROWINGS		468,706	331,000
Accrued interest payable		408	197
Estimated Fair Value [Member] | Levels 1 and 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale securities		3,158,777	3,087,473
Estimated Fair Value [Member] | Level 3 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for investment		3,947,391	3,455,003
Loans held for sale		$ 21,779	$ 15,314

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	Dec. 31, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
Future minimum lease commitments, 2019	$ 610,000
Future minimum lease commitments, 2020	409,000
Future minimum lease commitments, 2021	224,000
Future minimum lease commitments, 2022	27,000
Future minimum lease commitments, 2023 and thereafter	$ 5,000

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, 2018USD ($)
Concentration Risk [Line Items]
Financial instruments whose contract amounts represent credit risk	$ 960,924
Unfunded Lines of Credit [Member]
Concentration Risk [Line Items]
Financial instruments whose contract amounts represent credit risk	632,667
Unfunded Commitments to Extend Credit [Member]
Concentration Risk [Line Items]
Financial instruments whose contract amounts represent credit risk	301,616
Standby Letters of Credit [Member]
Concentration Risk [Line Items]
Financial instruments whose contract amounts represent credit risk	$ 26,641

Pension and Profit Sharing Pl_3

Pension and Profit Sharing Plans - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Contributions to the plan	$ 0	$ 0
Defined benefit plan pension obligation retirement benefit percentage	53.00%
Defined benefit plan pension obligation, loss on settlement	$ 1,546,000
Weighted average final maturities of debt securities held in the pension plan, Years	6 years 10 months 28 days
Level 3 securities	0
Common stock value	$ 678,000	663,000
Vesting period	6 years
Defined contribution plan cost	$ 7,049,000	4,735,000	$ 3,221,000
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	$ 68,855,000	55,796,000
Pension Plan's Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Common stock value	3,373,000	2,776,000
Safe Harbor 401(k) Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan cost	$ 2,588,000	$ 2,392,000	$ 2,331,000
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted average final maturities of debt securities held in the pension plan, Years	2 years 6 months 14 days
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted average final maturities of debt securities held in the pension plan, Years	18 years 9 months 3 days

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Interest cost on projected benefit obligation	$ 523,000	$ 635,000	$ 665,000
Actuarial (gain) loss	(1,717,000)	(3,597,000)
Benefits paid, including settlement of certain participant balances	(1,546,000)
Employer contributions	0	0
Fair value of plan assets at December 31	8,781,000
Reconciliation of Benefit Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at January 1	15,531,000	15,453,000
Interest cost on projected benefit obligation	523,000	635,000
Actuarial (gain) loss	(811,000)	486,000
Benefits paid, including settlement of certain participant balances	(8,630,000)	(1,043,000)
Benefit obligation at December 31	6,613,000	15,531,000	15,453,000
Reconciliation of Fair Value of Plan Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at January 1	17,046,000	15,787,000
Actual return on plan assets	365,000	2,302,000
Employer contributions	0	0
Benefits paid, including settlement of certain participant balances	(8,630,000)	(1,043,000)
Fair value of plan assets at December 31	8,781,000	17,046,000	$ 15,787,000
Funded status	$ 2,168,000	$ 1,515,000

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, 2018	Dec. 31, 2017
Retirement Benefits [Abstract]
Net actuarial loss	$ (1,717)	$ (3,597)
Deferred tax benefit	393	1,227
Amounts included in accumulated other comprehensive earnings, net of tax	$ (1,324)	$ (2,370)

Pension and Profit Sharing Pl_6

Pension and Profit Sharing Plans - Net Periodic Pension Cost (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Service cost-benefits earned during the period	$ 0	$ 0	$ 0
Interest cost on projected benefit obligation	523	635	665
Expected return on plan assets	(1,028)	(974)	(912)
Amortization of unrecognized net loss	186	249	375
Recognized loss on partial settlement of certain participant balances	1,546		267
Net periodic pension benefit expense (benefit)	$ 1,227	$ (90)	$ 395

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Weighted average discount rate	4.25%	3.50%	4.25%
Expected long-term rate of return on assets	6.25%	6.25%	6.25%

Pension and Profit Sharing Pl_8

Pension and Profit Sharing Plans - Pension Plan and Targeted Allocation Percentage (Detail)	Dec. 31, 2018	Dec. 31, 2017
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Allocation	72.00%	75.00%
Targeted Allocation	75.00%
Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Allocation	27.00%	24.00%
Targeted Allocation	25.00%
Cash and Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Allocation	1.00%	1.00%

Pension and Profit Sharing Pl_9

Pension and Profit Sharing Plans - Breakdown by Level (Detail) $ in Thousands	Dec. 31, 2018USD ($)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 8,781
Money Market Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	87
Obligations of State and Political Subdivisions [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	208
Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	449
Mortgage-backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	901
Corporate Stocks and Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	7,136
Level 1 Inputs [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	7,223
Level 1 Inputs [Member] | Money Market Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	87
Level 1 Inputs [Member] | Corporate Stocks and Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	7,136
Level 2 Inputs [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	1,558
Level 2 Inputs [Member] | Obligations of State and Political Subdivisions [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	208
Level 2 Inputs [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	449
Level 2 Inputs [Member] | Mortgage-backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 901

Pension and Profit Sharing P_10

Pension and Profit Sharing Plans - Estimate of Undiscounted Projected Future Payments (Detail) $ in Thousands	Dec. 31, 2018USD ($)
Retirement Benefits [Abstract]
2,019	$ 837
2,020	318
2,021	388
2,022	398
2,023	333
2024 forward	$ 2,339

Dividends from Subsidiaries - A

Dividends from Subsidiaries - Additional Information (Detail)	Dec. 31, 2018USD ($)
Equity [Abstract]
Amount available for the declaration of dividends by subsidiary banks without prior approval of regulatory agencies	$ 233,956,000

Regulatory Matters - Additional

Regulatory Matters - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
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	20.61%	19.85%
Tier1 Capital (to Risk-Weighted Assets), Actual Ratio	19.47%	18.66%
Common Tier1 Capital (to Risk-Weighted Assets), Actual Ratio	19.47%	18.66%
Tier1 Leverage ratio, Actual Ratio	11.85%	11.09%
Required tangible net assets	$ 2,000,000
Tangible net assets, total	22,503,000
Subsidiary bank's reserve balance	$ 11,372,000	$ 11,504,000
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, 2018	Dec. 24, 2018	Dec. 31, 2017
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Risk-Weighted Assets, Actual Ratio	20.61%		19.85%
Tier1 Capital to Risk-Weighted Assets, Actual Ratio	19.47%		18.66%
Leverage Ratio, Actual Ratio	11.85%		11.09%
Consolidated [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Risk-Weighted Assets, Actual Amount	$ 940,026		$ 814,634
Tier1 Capital to Risk-Weighted Assets, Actual Amount	888,015		765,882
Common Equity Tier1 Capital to Risk-Weighted Assets, Actual Amount	888,015		765,882
Leverage Ratio, Actual Amount	$ 888,015		$ 765,882
Total Capital to Risk-Weighted Assets, Actual Ratio	20.61%		19.85%
Tier1 Capital to Risk-Weighted Assets, Actual Ratio	19.47%		18.66%
Common Equity Tier1 Capital to Risk-Weighted Assets, Actual Ratio	19.47%		18.66%
Leverage Ratio, Actual Ratio	11.85%		11.09%
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	$ 478,969	$ 430,872
Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required	387,737	348,801
Common Equity Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required	319,312	287,248
Leverage Ratio, Minimum Capital Required	$ 299,682	276,296
Total Capital to Risk-Weighted Assets, Minimum Capital Required	10.50%		10.50%
Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required	8.50%		8.50%
Common Equity Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required, Ratio	7.00%		7.00%
Leverage Ratio, Minimum Capital Required, Ratio	4.00%		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		$ 379,578
Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required	359,226		297,507
Common Equity Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required	290,802		235,954
Leverage Ratio, Minimum Capital Required	$ 299,682		$ 276,296
Total Capital to Risk-Weighted Assets, Minimum Capital Required	9.875%		9.25%
Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required	7.875%		7.25%
Common Equity Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required, Ratio	6.375%		5.75%
Leverage Ratio, Minimum Capital Required, Ratio	4.00%		4.00%
Parent Company [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Risk-Weighted Assets, Actual Amount	$ 824,428		$ 723,563
Tier1 Capital to Risk-Weighted Assets, Actual Amount	772,417		674,811
Common Equity Tier1 Capital to Risk-Weighted Assets, Actual Amount	772,417		674,811
Leverage Ratio, Actual Amount	$ 772,417		$ 674,811
Total Capital to Risk-Weighted Assets, Actual Ratio	18.12%		17.68%
Tier1 Capital to Risk-Weighted Assets, Actual Ratio	16.97%		16.49%
Common Equity Tier1 Capital to Risk-Weighted Assets, Actual Ratio	16.97%		16.49%
Leverage Ratio, Actual Ratio	10.35%		9.80%
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	$ 455,038		$ 409,312
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	$ 364,030		$ 327,450
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	$ 295,775		$ 266,053
Leverage Ratio, Required To Be Considered Well Capitalized , Ratio	5.00%		5.00%
Leverage Ratio, Required To Be Considered Well Capitalized, Amount	$ 373,220		$ 344,151
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	477,790	429,777
Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required	386,782	347,915
Common Equity Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required	318,526	286,518
Leverage Ratio, Minimum Capital Required	$ 298,576	$ 275,320
Total Capital to Risk-Weighted Assets, Minimum Capital Required	10.50%		10.50%
Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required	8.50%		8.50%
Common Equity Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required, Ratio	7.00%		7.00%
Leverage Ratio, Minimum Capital Required, Ratio	4.00%		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		$ 378,614
Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required	358,342		296,751
Common Equity Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required	290,087		235,354
Leverage Ratio, Minimum Capital Required	$ 298,576		$ 275,320
Total Capital to Risk-Weighted Assets, Minimum Capital Required	9.875%		9.25%
Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required	7.875%		7.25%
Common Equity Tier1 Capital to Risk-Weighted Assets, Minimum Capital Required, Ratio	6.375%		5.75%
Leverage Ratio, Minimum Capital Required, Ratio	4.00%		4.00%

Stock Option Plan and Restric_3

Stock Option Plan and Restricted Stock Plan - Additional Information (Detail)	Oct. 23, 2018USD ($)shares	Apr. 24, 2018USD ($)Non_Employee_Directorsshares	Oct. 24, 2017USD ($)shares	Apr. 25, 2017USD ($)Non_Employee_Directorsshares	Oct. 25, 2016USD ($)shares	Apr. 26, 2016USD ($)Non_Employee_Directorsshares	Oct. 27, 2015USD ($)shares	Jul. 21, 2015USD ($)Non_Employee_Directorsshares	Dec. 31, 2018USD ($)$ / sharesshares	Dec. 31, 2017USD ($)$ / shares	Dec. 31, 2016USD ($)$ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of stock for issuance under the plan | shares									3,003,000
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 | $ / shares									$ 16.78
Stock options outstanding, exercise price range, upper | $ / shares									42.35
Fair value assumptions method used										Black-Scholes options pricing model
Risk-free interest rate										1.89%
Expected dividend yield										1.79%
Expected life										6 years 2 months 26 days
Expected volatility										26.51%
Weighted-average grant-date fair value of options granted | $ / shares									$ 0	$ 9.90	$ 0
Total intrinsic value of options exercised									$ 5,476,000	$ 3,082,000	$ 1,226,000
Total unrecognized compensation cost related to nonvested share-based compensation arrangements granted under the Plan									$ 3,522,000
Weighted-average period of unrecognized compensation cost recognition, years									1 year 10 months 20 days
Total fair value of shares vested									$ 888,000	1,246,000	592,000
Aggregate intrinsic value of vested stock options									11,170,000
Stock compensation expense									$ 1,508,000	1,745,000	882,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of stock for issuance under the plan | shares									379,000
Number of non employee directors | Non_Employee_Directors		9		10		10		10
Restricted Stock [Member] | Non-Employee Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares granted | shares		10,710		14,650		7,660		7,070
Restricted shares value		$ 540,000		$ 600,000		$ 250,000		$ 250,000
Restricted Stock [Member] | Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense									$ 560,000	483,000	278,000
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
Restricted shares granted | shares	26,021		14,191		15,405		31,273
Restricted shares value	$ 1,440,000		$ 655,000		$ 560,000		$ 1,060,000
Stock compensation expense									$ 680,000	$ 562,000	$ 381,000
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 Analysis of Stock Option Activity (Detail) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)$ / sharesshares
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Outstanding, beginning of year, Shares | shares	1,325,965
Granted, Shares | shares	0
Exercised, Shares | shares	(173,822)
Cancelled, Shares | shares	(66,600)
Outstanding, end of year, Shares | shares	1,085,543
Exercisable at end of year, Shares | shares	407,463
Outstanding, beginning of year, Weighted-Average Ex. Price | $ / shares	$ 33.01
Granted, Weighted-Average Ex. Price | $ / shares	0
Exercised, Weighted-Average Ex. Price | $ / shares	22.23
Cancelled, Weighted-Average Ex. Price | $ / shares	36.25
Outstanding, end of year, Weighted-Average Ex. Price | $ / shares	34.54
Exercisable at end of year, Weighted-Average Ex. Price | $ / shares	$ 27.41
Outstanding, end of year, Weighted-Average Remaining Contractual Term (Years)	6 years 6 months 18 days
Exercisable at end of year, Weighted-Average Remaining Contractual Term (Years)	4 years 7 months 24 days
Outstanding, end of year, Aggregate Intrinsic Value | $	$ 25,135
Exercisable at end of year, Aggregate Intrinsic Value | $	$ 12,337

Stock Option Plan and Restric_5

Stock Option Plan and Restricted Stock Plan - Schedule of Information Concerning Outstanding and Vested Stock Options (Detail)	12 Months Ended
	Dec. 31, 2018$ / sharesshares
Exercise Price $16.78 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise Price | $ / shares	$ 16.78
Number Outstanding	29,823
Number Vested	29,823
Remaining Contracted Life (Years)	4 months 24 days
Exercise Price $15.73 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise Price | $ / shares	$ 15.73
Number Outstanding	90,265
Number Vested	90,265
Remaining Contracted Life (Years)	2 years 9 months 18 days
Exercise Price $30.85 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise Price | $ / shares	$ 30.85
Number Outstanding	211,355
Number Vested	161,135
Remaining Contracted Life (Years)	4 years 9 months 18 days
Exercise Price $33.89 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise Price | $ / shares	$ 33.89
Number Outstanding	341,250
Number Vested	126,240
Remaining Contracted Life (Years)	6 years 9 months 18 days
Exercise Price $42.35 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise Price | $ / shares	$ 42.35
Number Outstanding	412,850
Remaining Contracted Life (Years)	8 years 6 months

Condensed Financial Informati_3

Condensed Financial Information - Parent Company - Condensed Balance Sheets (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
ASSETS
Interest-bearing deposits in subsidiary bank	$ 40,812	$ 162,764
Total cash and cash equivalents	248,647	372,347	$ 256,486	$ 272,886
OTHER ASSETS	90,762	75,725
Total assets	7,731,854	7,254,715
LIABILITIES AND SHAREHOLDERS' EQUITY
Total liabilities	6,678,559	6,331,947
SHAREHOLDERS' EQUITY:
Common stock	678	663
Capital surplus	443,114	378,062
Retained earnings	606,658	517,257
Accumulated other comprehensive earnings	2,845	26,786
Total shareholders' equity	1,053,295	922,768	837,885	804,986
Total liabilities and shareholders' equity	7,731,854	7,254,715
Subsidiary Bank [Member]
ASSETS
Cash in banks	16,981	14,272
Interest-bearing deposits in subsidiary bank	84,279	64,195
Unaffiliated Banks [Member]
ASSETS
Cash in banks	2	2
Parent Company [Member]
ASSETS
Total cash and cash equivalents	101,262	78,469	$ 93,251	$ 90,473
SECURITIES AVAILABLE-FOR-SALE, at fair value	6,276	8,515
Investment in and advances to subsidiaries, at equity	959,352	847,445
INTANGIBLE ASSETS	723	723
OTHER ASSETS	2,647	2,654
Total assets	1,070,260	937,806
LIABILITIES AND SHAREHOLDERS' EQUITY
Total liabilities	16,965	15,038
SHAREHOLDERS' EQUITY:
Common stock	678	663
Capital surplus	443,114	378,062
Retained earnings	606,658	517,257
Treasury stock	(7,507)	(7,148)
Deferred compensation	7,507	7,148
Accumulated other comprehensive earnings	2,845	26,786
Total shareholders' equity	1,053,295	922,768
Total liabilities and shareholders' equity	$ 1,070,260	$ 937,806

Condensed Financial Informati_4

Condensed Financial Information - Parent Company - Condensed Statements of Earnings (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income:
Total interest income	$ 291,690	$ 245,975	$ 232,288
Expenses:
Salaries and employee benefits	105,189	95,287	90,739
EARNINGS BEFORE INCOME TAXES	178,175	147,188	135,927
Income tax benefit	(27,537)	(26,817)	(31,153)
Net earnings	150,638	120,371	104,774
Parent Company [Member]
Income:
Cash dividends from subsidiaries	74,100	30,800	48,800
Excess of earnings over dividends of subsidiaries	82,323	92,929	58,809
Other	7,269	6,590	4,184
Total interest income	163,692	130,319	111,793
Expenses:
Salaries and employee benefits	9,966	8,606	5,655
Other operating expenses	4,781	3,871	3,531
Total Expense	14,747	12,477	9,186
EARNINGS BEFORE INCOME TAXES	148,945	117,842	102,607
Income tax benefit	1,693	2,529	2,167
Net earnings	$ 150,638	$ 120,371	$ 104,774

Condensed Financial Informati_5

Condensed Financial Information - Parent Company - Condensed Statements of Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net earnings	$ 150,638	$ 120,371	$ 104,774
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization, net	12,549	12,916	11,573
Decrease (increase) in other assets	(1,697)	9,313	2,397
Increase (decrease) in other liabilities	1,621	285	(2,643)
CASH FLOWS FROM INVESTING ACTIVITIES:
Cash received in connection with acquisition of banks	18,653
Maturity of available-for-sale security	3,439,028	4,392,131	3,509,113
Purchases of bank premises and equipment and software	(17,646)	(14,162)	(20,399)
Cash flows from financing activities:
Proceeds of stock issuances	3,864	2,934	1,260
Cash dividends paid	(53,861)	(48,955)	(44,907)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(123,700)	115,861	(16,400)
CASH AND CASH EQUIVALENTS, beginning of year	372,347	256,486	272,886
CASH AND CASH EQUIVALENTS, end of year	248,647	372,347	256,486
Parent Company [Member]
Cash flows from operating activities:
Net earnings	150,638	120,371	104,774
Adjustments to reconcile net earnings to net cash provided by operating activities:
Excess of earnings over dividends of subsidiary bank	(82,323)	(92,929)	(58,809)
Depreciation and amortization, net	331	207	208
Decrease (increase) in other assets	560	438	1,702
Increase (decrease) in other liabilities	1,932	183	(1,374)
Other	(2)	2	8
Net cash provided by operating activities	71,136	28,272	46,509
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	(346)	(30)	(94)
Other			10
Net cash provided by (used in) investing activities	1,654	2,967	(84)
Cash flows from financing activities:
Proceeds of stock issuances	3,864	2,934	1,260
Cash dividends paid	(53,861)	(48,955)	(44,907)
Net cash used in financing activities	(49,997)	(46,021)	(43,647)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	22,793	(14,782)	2,778
CASH AND CASH EQUIVALENTS, beginning of year	78,469	93,251	90,473
CASH AND CASH EQUIVALENTS, end of year	$ 101,262	$ 78,469	$ 93,251

Cash Flow Information - Supplem

Cash Flow Information - Supplemental Information on Cash Flows and Noncash Transactions (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental cash flow information:
Interest paid	$ 18,709	$ 9,316	$ 5,465
Federal income taxes paid	26,578	29,695	28,348
Schedule of noncash investing and financing activities:
Assets acquired through foreclosure	126	2,211	2,269
Investment securities purchased but not settled			12,381
Restricted stock grant to officers and directors	$ 1,609	$ 1,139	$ 810

Acquisition - Additional Inform

Acquisition - Additional Information (Detail) - USD ($)	Jan. 01, 2018	Oct. 12, 2017	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Fair value of purchased credit impaired loans			$ 27,534,000	$ 17,670,000
Contractual amounts			36,614,000	23,851,000
Purchased Credit Impaired Loans [Member]
Business Acquisition [Line Items]
Contractual amounts			1,157,000	$ 1,865,000
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, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill resulting from acquisition	$ 171,565,000	$ 139,971,000
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