First Financial Bankshares (FFIN) 10-Q 29 Oct 19 2019 Q3 Quarterly report Financial data

Cover Page

Cover Page - shares	9 Months Ended
	Sep. 30, 2019	Oct. 29, 2019
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31
Document Period End Date	Sep. 30, 2019
Entity Registrant Name	FIRST FINANCIAL BANKSHARES INC
Entity Central Index Key	0000036029
Entity Filer Category	Large Accelerated Filer
Entity Interactive Data Current	Yes
Entity Current Reporting Status	Yes
Entity File Number	0-7674
Entity Incorporation, State or Country Code	TX
Entity Tax Identification Number	75-0944023
Entity Address, Address Line One	400 Pine Street
Entity Address, City or Town	Abilene
Entity Address, State or Province	TX
City Area Code	325
Local Phone Number	627-7155
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Title of 12(b) Security	Common Stock
Trading Symbol	FFIN
Security Exchange Name	NASDAQ
Document Transition Report	false
Document Quarterly Report	true
Entity Address, Postal Zip Code	79601
Entity Common Stock, Shares Outstanding		135,844,644

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
ASSETS
CASH AND DUE FROM BANKS	$ 198,855	$ 207,835	$ 164,998
INTEREST-BEARING DEPOSITS IN BANKS	31,410	40,812	34,511
Total cash and cash equivalents	230,265	248,647	199,509
INTEREST-BEARING TIME DEPOSITS IN BANKS		1,458	1,458
SECURITIES AVAILABLE-FOR-SALE, at fair value	3,397,156	3,158,777	3,144,367
LOANS:
Held for investment	4,100,316	3,953,636	3,867,040
Less - allowance for loan losses	(51,889)	(51,202)	(50,871)
Net loans held for investment	4,048,427	3,902,434	3,816,169
Held-for-sale ($39,735, $15,955 and $19,185 at fair value at September 30, 2019 and 2018 and December 31, 2018, respectively)	40,499	21,672	18,496
Net loans	4,088,926	3,924,106	3,834,665
BANK PREMISES AND EQUIPMENT, net	132,367	133,421	130,815
INTANGIBLE ASSETS	173,905	174,683	174,907
OTHER ASSETS	91,220	90,762	85,510
Total assets	8,113,839	7,731,854	7,571,231
LIABILITIES AND SHAREHOLDERS' EQUITY
NONINTEREST-BEARING DEPOSITS	2,210,997	2,116,107	2,146,984
INTEREST-BEARING DEPOSITS	4,186,686	4,064,282	3,998,298
Total deposits	6,397,683	6,180,389	6,145,282
DIVIDENDS PAYABLE	16,299	14,227	14,216
BORROWINGS	400,155	468,706	380,760
OTHER LIABILITIES	94,604	15,237	35,234
Total liabilities	6,908,741	6,678,559	6,575,492
COMMITMENTS AND CONTINGENCIES
SHAREHOLDERS' EQUITY:
Common stock—($0.01 par value, authorized 200,000,000 shares; 135,822,456, 67,693,586 and 67,753,133 shares issued at September 30, 2019 and 2018 and December 31, 2018, respectively)	1,358	678	677
Capital surplus	448,968	443,114	440,589
Retained earnings	682,575	606,658	582,449
Treasury stock (shares at cost: 928,287, 471,070 and 467,811 at September 30, 2019 and 2018 and December 31, 2018, respectively)	(8,042)	(7,507)	(7,512)
Deferred compensation	8,042	7,507	7,512
Accumulated other comprehensive earnings (loss)	72,197	2,845	(27,976)
Total shareholders' equity	1,205,098	1,053,295	995,739
Total liabilities and shareholders' equity	$ 8,113,839	$ 7,731,854	$ 7,571,231

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Statement of Financial Position [Abstract]
Loans held-for-sale, fair value	$ 39,735	$ 19,185	$ 15,955
Common stock, par value	$ 0.01	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000	200,000,000
Common stock, shares issued	135,822,456	67,753,133	67,693,586
Treasury stock, shares	928,287	467,811	471,070

Consolidated Statements of Earn

Consolidated Statements of Earnings - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
INTEREST INCOME:
Interest and fees on loans	$ 57,123	$ 51,428	$ 166,095	$ 147,279
Interest on investment securities:
Taxable	14,292	12,593	41,505	36,666
Exempt from federal income tax	8,795	9,558	27,801	29,882
Interest on federal funds sold and interest-bearing deposits in banks	381	470	1,668	1,382
Total interest income	80,591	74,049	237,069	215,209
INTEREST EXPENSE:
Interest on deposits	7,123	4,330	21,070	11,854
Other	830	293	2,231	869
Total interest expense	7,953	4,623	23,301	12,723
Net interest income	72,638	69,426	213,768	202,486
PROVISION FOR LOAN LOSSES	450	1,450	2,015	3,865
Net interest income after provision for loan losses	72,188	67,976	211,753	198,621
NONINTEREST INCOME:
Trust fees	7,051	7,291	21,057	21,265
Service charges on deposit accounts	5,629	5,690	16,179	15,950
ATM, interchange and credit card fees	7,728	7,533	21,920	21,570
Real estate mortgage operations	5,733	4,834	13,928	11,718
Net gain on sale of available-for-sale securities (includes $52 and $58 for the three months ended September 30, 2019 and 2018, respectively, and $728 and $1,346 for the nine months ended September 30, 2019 and 2018, respectively, related to accumulated other comprehensive earnings reclassifications)	52	58	728	1,346
Net gain on sale of foreclosed assets	71	84	193	201
Net gain (loss) on sale of assets	235	(61)	241	(152)
Interest on loan recoveries	575	199	1,815	607
Other	1,595	1,427	5,020	4,461
Total noninterest income	28,669	27,055	81,081	76,966
NONINTEREST EXPENSE:
Salaries and employee benefits	28,550	26,377	82,468	79,442
Loss from partial settlement of pension plan			900
Net occupancy expense	2,830	2,900	8,372	8,589
Equipment expense	2,225	2,629	7,009	7,548
FDIC insurance premiums	15	570	1,091	1,768
ATM, interchange and credit card expenses	2,627	2,344	7,437	6,692
Professional and service fees	1,902	2,174	5,721	6,613
Printing, stationery and supplies	480	387	1,348	1,485
Operational and other losses	507	981	1,253	1,852
Software amortization and expense	1,767	1,393	5,147	4,433
Amortization of intangible assets	246	279	778	1,049
Other	7,761	7,472	23,059	22,977
Total noninterest expense	48,910	47,506	144,583	142,448
EARNINGS BEFORE INCOME TAXES	51,947	47,525	148,251	133,139
INCOME TAX EXPENSE (includes $11 and $12 for the three months ended September 30, 2019 and 2018, respectively, and $153 and $283 for the nine months ended September 30, 2019 and 2018, respectively, related to income tax expense from reclassification items)	8,867	7,475	24,827	20,937
NET EARNINGS	$ 43,080	$ 40,050	$ 123,424	$ 112,202
EARNINGS PER SHARE, BASIC	$ 0.32	$ 0.30	$ 0.91	$ 0.83
EARNINGS PER SHARE, ASSUMING DILUTION	0.32	0.29	0.91	0.83
DIVIDENDS PER SHARE	$ 0.12	$ 0.11	$ 0.35	$ 0.31

Consolidated Statements of Ea_2

Consolidated Statements of Earnings (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Reclassifications adjustment for realized gains on investment securities included in net earnings (loss), before income tax	$ 52	$ 58	$ 728	$ 1,346
Income tax expense from reclassification items	$ 11	$ 12	$ 153	$ 283

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Earnings - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
NET EARNINGS	$ 43,080	$ 40,050	$ 123,424	$ 112,202
OTHER ITEMS OF COMPREHENSIVE EARNINGS (LOSS):
Change in unrealized gain (loss) on investment securities available-for-sale, before income taxes	16,446	(20,930)	88,517	(75,236)
Reclassification adjustment for realized gains on investment securities included in net earnings, before income tax	(52)	(58)	(728)	(1,346)
Total other items of comprehensive earnings	16,394	(20,988)	87,789	(76,582)
Income tax benefit (expense) related to other items of comprehensive earnings	(3,444)	4,407	(18,437)	16,082
Reclassification of certain income tax effects related to the change in the U.S. statutory federal income tax rate under the Tax Cuts and Jobs Act to retained earnings				5,759
COMPREHENSIVE EARNINGS	$ 56,030	$ 23,469	$ 192,776	$ 57,461

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, 2017	$ 922,768	$ 663	$ 378,062	$ 517,257	$ (7,148)	$ 7,148	$ 26,786
Beginning Balance, Shares at Dec. 31, 2017		66,260,444
Treasury Stock, Beginning Balance, Shares at Dec. 31, 2017					(495,964)
Net earnings (unaudited)	112,202			112,202
Stock option exercises (unaudited)	2,800	$ 1	2,799
Stock option exercises, Shares		133,061
Restricted stock grant (unaudited)	523		523
Restricted stock grant (unaudited), Shares		10,710
Cash dividends declared	(41,272)			(41,272)
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
Change in unrealized gain (loss) in investment securities available-for-sale, net of related income taxes (unaudited)	(60,500)						(60,500)
Shares purchased (redeemed) in connection with directors' deferred compensation plan, net (unaudited)					$ (364)	364
Shares purchased (redeemed) in connection with directors' deferred compensation plan, net, Shares					24,894
Stock option expense (unaudited)	1,131		1,131
Reclassification of certain income tax effects related to the change in the U.S. statutory federal income tax rate under the Tax Cuts and Jobs Act to retained earnings				(5,759)			5,759
Reclassification of unrealized gain in equity securities at December 31, 2017 from accumulated other comprehensive earnings to retained earnings (unaudited)				21			(21)
Ending Balance at Sep. 30, 2018	$ 995,739	$ 677	440,589	582,449	$ (7,512)	7,512	(27,976)
Ending Balance, Shares at Sep. 30, 2018		67,693,586
Treasury Stock, Ending Balance, Shares at Sep. 30, 2018	(471,070)				(471,070)
Beginning Balance at Jun. 30, 2018	$ 985,628	$ 677	439,731	556,615	$ (7,419)	7,419	(11,395)
Beginning Balance, Shares at Jun. 30, 2018		67,669,658
Treasury Stock, Beginning Balance, Shares at Jun. 30, 2018					(491,170)
Net earnings (unaudited)	40,050			40,050
Stock option exercises (unaudited)	481		481
Stock option exercises, Shares		23,928
Cash dividends declared	(14,216)			(14,216)
Change in unrealized gain (loss) in investment securities available-for-sale, net of related income taxes (unaudited)	(16,581)						(16,581)
Shares purchased (redeemed) in connection with directors' deferred compensation plan, net (unaudited)					$ (93)	93
Shares purchased (redeemed) in connection with directors' deferred compensation plan, net, Shares					20,100
Stock option expense (unaudited)	377		377
Ending Balance at Sep. 30, 2018	$ 995,739	$ 677	440,589	582,449	$ (7,512)	7,512	(27,976)
Ending Balance, Shares at Sep. 30, 2018		67,693,586
Treasury Stock, Ending Balance, Shares at Sep. 30, 2018	(471,070)				(471,070)
Beginning Balance at Dec. 31, 2018	$ 1,053,295	$ 678	443,114	606,658	$ (7,507)	7,507	2,845
Beginning Balance, Shares at Dec. 31, 2018		67,753,133
Treasury Stock, Beginning Balance, Shares at Dec. 31, 2018	(467,811)				(467,811)
Net earnings (unaudited)	$ 123,424			123,424
Stock option exercises (unaudited)	3,493	$ 2	3,491
Stock option exercises, Shares		185,779
Restricted stock grant (unaudited)	1,307		1,307
Restricted stock grant (unaudited), Shares		43,334
Cash dividends declared	(46,829)			(46,829)
Change in unrealized gain (loss) in investment securities available-for-sale, net of related income taxes (unaudited)	69,352						69,352
Shares purchased (redeemed) in connection with directors' deferred compensation plan, net (unaudited)					$ (535)	535
Shares purchased (redeemed) in connection with directors' deferred compensation plan, net, Shares					3,863
Stock option expense (unaudited)	1,056		1,056
Two-for-one stock spllit in the form of a 100% stock dividend (unaudited)		$ 678		(678)
Two-for-one stock spllit in the form of a 100% stock dividend (unaudited), shares		67,840,210			(464,339)
Ending Balance at Sep. 30, 2019	$ 1,205,098	$ 1,358	448,968	682,575	$ (8,042)	8,042	72,197
Ending Balance, Shares at Sep. 30, 2019		135,822,456
Treasury Stock, Ending Balance, Shares at Sep. 30, 2019	(928,287)				(928,287)
Beginning Balance at Jun. 30, 2019	$ 1,164,748	$ 1,358	448,349	655,794	$ (7,823)	7,823	59,247
Beginning Balance, Shares at Jun. 30, 2019		135,809,224
Treasury Stock, Beginning Balance, Shares at Jun. 30, 2019					(929,441)
Net earnings (unaudited)	43,080			43,080
Stock option exercises (unaudited)	188		188
Stock option exercises, Shares		13,232
Cash dividends declared	(16,299)			(16,299)
Change in unrealized gain (loss) in investment securities available-for-sale, net of related income taxes (unaudited)	12,950						12,950
Shares purchased (redeemed) in connection with directors' deferred compensation plan, net (unaudited)					$ (219)	219
Shares purchased (redeemed) in connection with directors' deferred compensation plan, net, Shares					1,154
Stock option expense (unaudited)	431		431
Ending Balance at Sep. 30, 2019	$ 1,205,098	$ 1,358	$ 448,968	$ 682,575	$ (8,042)	$ 8,042	$ 72,197
Ending Balance, Shares at Sep. 30, 2019		135,822,456
Treasury Stock, Ending Balance, Shares at Sep. 30, 2019	(928,287)				(928,287)

Consolidated Statements of Sh_2

Consolidated Statements of Shareholders' Equity (Parenthetical) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Cash dividend per share	$ 0.12	$ 0.11	$ 0.35	$ 0.31
Common Stock Dividend Percentage			100.00%
Retained Earnings [Member]
Cash dividend per share	$ 0.12	$ 0.11	$ 0.35	$ 0.31

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net earnings	$ 123,424	$ 112,202
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization	8,730	9,554
Provision for loan losses	2,015	3,865
Securities premium amortization (discount accretion), net	18,690	21,005
Gain on sale of assets, net	(1,312)	(1,254)
Deferred federal income tax benefit	1,720	8,107
Change in loans held-for-sale	(18,491)	(2,928)
Change in other assets	1,789	2,699
Change in other liabilities	9,097	5,653
Total adjustments	22,238	46,701
Net cash provided by operating activities	145,662	158,903
CASH FLOWS FROM INVESTING ACTIVITIES:
Cash received in acquisition of Commercial Bancshares, Inc.		18,653
Net decrease in interest-bearing time deposits in banks	1,458
Activity in available-for-sale securities:
Sales	67,404	220,259
Maturities	4,342,074	3,354,571
Purchases	(4,526,709)	(3,650,127)
Net increase in loans	(149,553)	(116,860)
Purchases of bank premises and equipment and other assets	(7,541)	(12,381)
Proceeds from sale of bank premises and equipment and other assets	1,344	810
Net cash used in investing activities	(271,523)	(185,075)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net increase (decrease) in noninterest-bearing deposits	94,890	(56,706)
Net increase (decrease) in interest-bearing deposits	122,404	(102,875)
Net increase (decrease) in borrowings	(68,551)	49,760
Common stock transactions:
Proceeds from stock issuances	3,493	2,800
Dividends paid	(44,757)	(39,645)
Net cash provided by (used in) financing activities	107,479	(146,666)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(18,382)	(172,838)
CASH AND CASH EQUIVALENTS, beginning of period	248,647	372,347
CASH AND CASH EQUIVALENTS, end of period	230,265	199,509
SUPPLEMENTAL INFORMATION AND NONCASH TRANSACTIONS:
Interest paid	22,963	12,617
Federal income taxes paid	22,141	20,351
Transfer of loans and bank premises to other real estate	1,208	126
Investment securities purchased but not settled	51,181	13,453
Restricted stock grant to officers and directors	$ 1,307	523
Stocks issued in acquisition of Commercial Bancshares, Inc.		$ 58,087

Basis of Presentation

Basis of Presentation	9 Months Ended
	Sep. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Note 1 — Basis of Presentation The unaudited interim consolidated financial statements include the accounts of the Company, a Texas corporation and a financial holding company registered under the Bank Holding Company Act of 1956, as amended, or BHCA, and its wholly-owned subsidiaries: First Financial Bank, National Association, Abilene, Texas; First Technology Services, Inc.; First Financial Trust & Asset Management Company, National Association; First Financial Investments, Inc.; and First Financial Insurance Agency, Inc. Through our subsidiary bank, we conduct a full-service commercial banking business. Our banking centers are located primarily in Central, North Central, Southeast and West Texas. As of September 30, 2019, we had 73 financial centers across Texas, with eleven locations in Abilene, three locations in Weatherford, two locations in Cleburne, Conroe, San Angelo, Stephenville and Granbury, and one location each in Acton, Albany, Aledo, Alvarado, Beaumont, Boyd, Bridgeport, Brock, Burleson, Cisco, Clyde, Cut and Shoot, Decatur, Eastland, El Campo, Fort Worth, Fulshear, Glen Rose, Grapevine, Hereford, Huntsville, Keller, Kingwood, Magnolia, Mauriceville, Merkel, Midlothian, Mineral Wells, Montgomery, Moran, New Waverly, Newton, Odessa, Orange, Palacios, Port Arthur, Ranger, Rising Star, Roby, Southlake, Spring, Sweetwater, Tomball, Trent, Trophy Club, Vidor, Waxahachie, Willis and Willow Park, all in Texas. Our trust subsidiary has eight locations which are located in Abilene, Fort Worth, Houston, Odessa, Beaumont, San Angelo, Stephenville and Sweetwater. In the opinion of management, the unaudited interim consolidated financial statements reflect all adjustments necessary for a fair presentation of the Company’s financial position and unaudited results of operations and should be read in conjunction with the Company’s audited consolidated financial statements and notes thereto in the Company’s Annual Report on Form 10-K, In addition, certain reclassifications have been made to the 2018 statements of earnings to conform to the 2019 presentation. Goodwill and other intangible assets are evaluated annually for impairment as of the end of the second quarter. No such impairment has been noted in connection with the current or any prior evaluations.

Stock Split and Stock Repurchas

Stock Split and Stock Repurchase	9 Months Ended
	Sep. 30, 2019
Equity [Abstract]
Stock Repurchase	Note 2 – On April 23, 2019, the Company’s Board of Directors declared a two-for-one stock split of a the Company’s outstanding common shares with On July 25, 2017, the Company’s Board of Directors authorized the repurchase of up to 2,000,000 common shares through September 30, 2020. The shares buyback plan authorizes management to repurchase the shares at such time as repurchases are considered beneficial to shareholders. Any repurchase of shares will be made through the open market, block trades or in privately negotiated transactions in accordance with applicable laws and regulations. Under the repurchase plan, there is no minimum number of shares that the Company is required to repurchase. Through September 30, 2019, no shares were repurchased under this authorization.

Earnings Per Share

Earnings Per Share	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Earnings Per Share	Note 3—Earnings Per Share Basic earnings per common share is computed by dividing net income available to common shareholders by the weighted average number of shares outstanding during the periods presented. In computing diluted earnings per common share for the three months ended September 30, 2019 and 2018, the Company assumes that all dilutive outstanding options to purchase common shares have been exercised at the beginning of the period (or the time of issuance, if later). The dilutive effect of these outstanding options and the restricted shares is reflected by application of the treasury stock method, whereby the proceeds from exercised options and restricted shares are assumed to be used to purchase common shares at the average market price during the respective periods. The weighted average common shares outstanding used in computing basic earnings per common share for the three months ended September 30, 2019 and 2018 were 135,693,901 and 135,270,116 shares, respectively. The weighted average common shares outstanding used in computing basic earnings per common share for the nine months ended September 30, 2019 and 2018 were 135,613,646 and 135,173,686. The weighted average common shares outstanding used in computing fully diluted earnings per common share for the three months ended September 30, 2019 and 2018 were 136,369,328 and 136,107,448 shares, respectively. The weighted average common shares outstanding used in computing fully diluted earnings per common share for the nine months ended September 30, 2019 and 2018 were 136,274,342 and 135,896,840. For the three and nine months ended September 30, 2019 and 2018, there were no stock options that were anti-dilutive that have been excluded from the EPS calculation.

Interest-bearing Time Deposits

Interest-bearing Time Deposits in Banks and Securities	9 Months Ended
	Sep. 30, 2019
Cash and Cash Equivalents [Abstract]
Interest-bearing Time Deposits in Banks and Securities	Note 4—Interest-bearing Time Deposits in Banks and Securities Interest-bearing time deposits in banks totaled $ 1,458 respectively, and had original maturities ranging from one 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. Often, the information available to conduct these assessments is limited and rapidly changing, making estimates of fair value subject to judgment. If actual information or conditions are different than estimated, the extent of the impairment of the debt security may be different than previously estimated, which could have a material effect on the Company’s results of operations and financial condition. The Company’s investment portfolio consists of U.S. Treasury securities, 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. A summary of the Company’s available-for-sale September 30, 2019 Gross Gross Amortized Unrealized Unrealized Estimated Cost Basis Holding Gains Holding Losses Fair Value U.S. Treasury securities $ 9,990 $ 31 $ — $ 10,021 Obligations of states and political subdivisions 1,182,549 59,734 (86 ) 1,242,197 Corporate bonds and other 4,643 87 — 4,730 Residential mortgage-backed securities 1,597,807 27,001 (1,428 ) 1,623,380 Commercial mortgage-backed securities 509,019 8,069 (260 ) 516,828 Total securities available-for-sale $ 3,304,008 $ 94,922 $ (1,774 ) $ 3,397,156 September 30, 2018 Gross Gross Amortized Unrealized Unrealized Estimated Cost Basis Holding Gains Holding Losses Fair Value U.S. Treasury securities $ 9,964 $ — $ (35 ) $ 9,929 Obligations of U.S. government sponsored enterprises and agencies 303 — (1 ) 302 Obligations of states and political subdivisions 1,174,320 21,664 (4,097 ) 1,191,887 Corporate bonds and other 4,860 — (121 ) 4,739 Residential mortgage-backed securities 1,533,302 912 (39,908 ) 1,494,306 Commercial mortgage-backed securities 453,495 8 (10,299 ) 443,204 Total securities available-for-sale $ 3,176,244 $ 22,584 $ (54,461 ) $ 3,144,367 December 31, 2018 Gross Gross Amortized Unrealized Unrealized Estimated Cost Basis Holding Gains Holding Losses Fair Value U.S. Treasury securities $ 9,970 $ — $ (8 ) $ 9,962 Obligations of U.S. government sponsored enterprises and agencies 301 — — 301 Obligations of states and political subdivisions 1,229,828 30,013 (1,970 ) 1,257,871 Corporate bonds and other 4,875 — (77 ) 4,798 Residential mortgage-backed securities 1,472,228 3,928 (21,611 ) 1,454,545 Commercial mortgage-backed securities 436,366 670 (5,736 ) 431,300 Total securities available-for-sale $ 3,153,568 $ 34,611 $ (29,402 ) $ 3,158,777 The Company invests in mortgage-backed securities that have expected maturities that differ from their contractual maturities. These differences arise because borrowers may have the right to call or prepay obligations with or without a prepayment penalty. These securities include collateralized mortgage obligations (CMOs) and other asset backed securities. The expected maturities of these securities at September 30, 2019 were computed by using scheduled amortization of balances and historical prepayment rates. At September 30, 2019 and 2018, and December 31, 2018, the Company did not hold CMOs that entail higher risks than standard mortgage-backed securities. The amortized cost and estimated fair value of available-for-sale Amortized Estimated Cost Basis Fair Value Due within one year $ 207,121 $ 208,899 Due after one year through five years 494,764 520,494 Due after five years through ten years 493,565 525,301 Due after ten years 1,732 2,254 Mortgage-backed securities 2,106,826 2,140,208 Total $ 3,304,008 $ 3,397,156 The following tables disclose the Company’s investment securities that have been in a continuous unrealized-loss Less than 12 Months 12 Months or Longer Total September 30, 2019 Fair Value Unrealized Loss Fair Value Unrealized Loss Fair Value Unrealized Loss Obligations of states and political subdivisions $ 11,140 $ 86 $ 828 $ — $ 11,968 $ 86 Residential mortgage-backed securities 91,850 75 146,449 1,353 238,299 1,428 Commercial mortgage-backed securities 42,310 115 74,873 145 117,183 260 Total $ 145,300 $ 276 $ 222,150 $ 1,498 $ 367,450 $ 1,774 Less than 12 Months 12 Months or Longer Total September 30, 2018 Fair Value Unrealized Loss Fair Value Unrealized Loss Fair Value Unrealized Loss U.S. Treasury Securities $ 9,929 $ 35 $ — $ — $ 9,929 $ 35 Obligations of U.S. government sponsored enterprises and agencies 302 1 — — 302 1 Obligations of states and political subdivisions 184,265 2,165 44,750 1,932 229,015 4,097 Corporate bonds and other 4,399 110 449 11 4,848 121 Residential mortgage-backed securities 962,320 20,850 461,227 19,058 1,423,547 39,908 Commercial mortgage-backed securities 270,375 5,908 167,368 4,391 437,743 10,299 Total $ 1,431,590 $ 29,069 $ 673,794 $ 25,392 $ 2,105,384 $ 54,461 Less than 12 Months 12 Months or Longer Total December 31, 2018 Fair Value Unrealized Loss Fair Value Unrealized Loss Fair Value Unrealized Loss U.S. Treasury securities $ 9,962 $ 8 $ — $ — $ 9,962 $ 8 Obligations of U.S. government sponsored enterprises and agencies — — 301 — 301 — Obligations of state and political subdivisions 27,489 107 114,461 1,863 141,950 1,970 Corporate bonds and other 4,348 68 450 9 4,798 77 Residential mortgage-backed securities 119,584 483 922,289 21,128 1,041,873 21,611 Commercial mortgage-backed securities 1,994 5 343,015 5,731 345,009 5,736 Total $ 163,377 $ 671 $ 1,380,516 $ 28,731 $ 1,543,893 $ 29,402 The number of investments in an unrealized loss position totaled 77 at September 30, 2019. We do not believe these unrealized losses are “other-than-temporary” as (i) we do not 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. In making this determination, we also consider the length of time and extent to which fair value has been less than cost and the financial condition of the issuer. The unrealized losses noted are interest rate related due to the level of interest rates at September 30, 2019 compared to the time of purchase. We have reviewed the ratings of the issuers and have not identified any issues related to the ultimate repayment of principal as a result of credit concerns on these securities. Our mortgage related securities are backed by GNMA, FNMA and FHLMC or are collateralized by securities backed by these agencies. At September 30, 2019, 85.33% of our available-for-sale At September 30, 2019, $2,112,193,000 of the Company’s securities were pledged as collateral for public or trust fund deposits, repurchase agreements and for other purposes required or permitted by law. During the three months ended September 30, 2019 and 2018, sales of investment securities that were classified as available-for-sale During the nine months ended September 30, 2019 and 2018, sales of investment securities classified as available-for-sale The specific identification method was used to determine cost in order to compute the realized gains and losses.

Loans Held for Investment and A

Loans Held for Investment and Allowance for Loan Losses	9 Months Ended
	Sep. 30, 2019
Receivables [Abstract]
Loans Held for Investment and Allowance for Loan Losses	Note 5 – Loans Held for Investment and Allowance for Loan Losses 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 Company has certain lending policies and procedures in place that are designed to maximize loan income with an acceptable level of risk. Management reviews and approves these policies and procedures on an annual basis and makes changes as appropriate. Management receives and reviews monthly reports related to loan originations, quality, concentrations, delinquencies, nonperforming and potential problem loans. Diversification in the loan portfolio is a means of managing risk associated with fluctuations in economic conditions, both by type of loan and geographic location. Commercial loans are underwritten after evaluating and understanding the borrower’s ability to operate profitably and effectively. Underwriting standards are designed to determine whether the borrower possesses sound business ethics and practices and to evaluate current and projected cash flows to determine the ability of the borrower to repay their obligations as agreed. Commercial loans are primarily made based on the identified cash flows of the borrower and, secondarily, on the underlying collateral provided by the borrower. Most commercial loans are secured by the assets being financed or other business assets, such as accounts receivable or inventory, and include personal guarantees. Agricultural loans are subject to underwriting standards and processes similar to commercial loans. These agricultural loans are based primarily on the identified cash flows of the borrower and secondarily on the underlying collateral provided by the borrower. Most agricultural loans are secured by the agriculture related assets being financed, such as farm land, cattle or equipment, and include personal guarantees. Real estate loans are also subject to underwriting standards and processes similar to commercial and agricultural loans. These loans are underwritten primarily based on projected cash flows and, secondarily, as loans secured by real estate. The repayment of real estate loans is generally largely dependent on the successful operation of the property securing the loans or the business conducted on the property securing the loan. Real estate loans may be more adversely affected by conditions in the real estate markets or in the general economy. The properties securing the Company’s real estate portfolio are generally diverse in terms of type and geographic location within Texas. This diversity helps reduce the exposure to adverse economic events that affect any single market or industry. Generally, real estate loans are owner occupied which further reduces the Company’s risk. Consumer loan underwriting utilizes methodical credit standards and analysis to supplement the Company’s underwriting policies and procedures. The Company’s loan policy addresses types of consumer loans that may be originated and the collateral, if secured, which must be perfected. The relatively smaller individual dollar amounts of consumer loans that are spread over numerous individual borrowers also minimize the Company’s risk. 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 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 September 30, 2019 and 2018 and December 31, 2018 were $342,000, $2,947,000 and $827,000, respectively, compared to a contractual balance of $605,000, $3,898,000 and $1,157,000, respectively. Other purchased credit impaired loan disclosures were omitted due to immateriality. Loans held-for-investment September 30, December 31, 2019 2018 2018 Commercial $ 836,644 $ 773,924 $ 844,953 Agricultural 102,054 93,953 96,677 Real estate 2,749,552 2,614,929 2,639,346 Consumer 412,066 384,234 372,660 Total loans held-for-investment $ 4,100,316 $ 3,867,040 $ 3,953,636 The Company’s non-accrual September 30, December 31, 2019 2018 2018 Non-accrual $ 25,717 $ 25,587 $ 27,534 Loans still accruing and past due 90 days or more 104 88 1,008 Troubled debt restructured loans** 27 513 513 Total $ 25,848 $ 26,188 $ 29,055 * Includes $342,000, $2,947,000 and $827,000 of purchased credit impaired loans as of September 30, 2019 and 2018, and December 31, 2018, respectively. ** Troubled debt restructured loans of $3,983,000, $4,577,000 and $3,840,000, whose interest collection, after considering economic ​​​​​​​and business conditions and collection efforts, is doubtful are included in non-accrual The Company’s recorded investment in impaired loans and the related valuation allowance are as follows (in thousands): September 30, 2019 September 30, 2018 December 31, 2018 Re Investment Valuation Recorded Valuation Recorded Valuation $ 25,717 $ 4,194 $ 25,587 $ 4,988 $ 27,534 $ 4,069 The Company had $27,212,000, $26,859,000 and $29,632,000 in non-accrual, Non-accrual September 30, December 31, 2019 2018 2018 Commercial $ 8,802 $ 6,961 $ 9,334 Agricultural 1,502 1,046 759 Real estate 15,095 16,682 16,714 Consumer 318 898 727 Total $ 25,717 $ 25,587 $ 27,534 No significant additional funds are committed to be advanced in connection with impaired loans as of September 30, 2019. The Company’s impaired loans and related allowance 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. September 30, 2019 Unpaid Principal Balance Recorded Recorded Total Related Year –to- D Average Three- Commercial $ 10,250 $ 5,885 $ 2,917 $ 8,802 $ 1,448 $ 9,586 $ 9,263 Agricultural 1,701 406 1,096 1,502 247 1,707 1,609 Real Estate 22,535 4,143 10,952 15,095 2,314 16,739 15,577 Consumer 444 9 309 318 185 416 346 Total $ 34,930 $ 10,443 $ 15,274 $ 25,717 $ 4,194 $ 28,448 $ 26,795 * Includes $342,000 of purchased credit impaired loans. September 30, 201 8 Unpaid Principal Balance Recorded Recorded Total Related Year –to-Date Average Three- Commercial $ 9,276 $ 3,467 $ 3,494 $ 6,961 $ 1,412 $ 8,339 $ 7,669 Agricultural 1,062 — 1,046 1,046 528 1,506 1,101 Real Estate 22,513 4,215 12,467 16,682 2,652 18,688 17,762 Consumer 1,088 50 848 898 396 1,012 942 Total $ 33,939 $ 7,732 $ 17,855 $ 25,587 $ 4,988 $ 29,545 $ 27,474 * Includes $2,947,000 of purchased credit impaired loans. December 31, 2018 Unpaid Principal Balance Recorded Recorded Total Related 12 Month Commercial $ 10,808 $ 6,728 $ 2,606 $ 9,334 $ 1,133 $ 7,986 Agricultural 799 213 546 759 170 842 Real Estate 24,072 6,699 10,015 16,714 2,409 16,042 Consumer 935 101 626 727 357 914 Total $ 36,614 $ 13,741 $ 13,793 $ 27,534 $ 4,069 $ 25,784 * Includes $827,000 of purchased credit impaired loans. The Company recognized interest income on impaired loans prior to being recognized as impaired of approximately $948,000 during the year ended December 31, 2018. Such amounts for the three-month and nine-month periods ended September 30, 2019 and 2018 were not significant. 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 September 30, 2019 Pass Special Substandard Doubtful Total Commercial $ 797,444 $ 24,836 $ 14,364 $ — $ 836,644 Agricultural 99,586 61 2,407 — 102,054 Real Estate 2,673,591 21,171 54,790 — 2,749,552 Consumer 410,491 232 1,343 — 412,066 Total $ 3,981,112 $ 46,300 $ 72,904 $ — $ 4,100,316 September 30, 2018 Pass Special Substandard Doubtful Total Commercial $ 747,758 $ 8,817 $ 17,349 $ — $ 773,924 Agricultural 89,314 68 4,571 — 93,953 Real Estate 2,530,673 27,241 57,015 — 2,614,929 Consumer 381,772 324 2,138 — 384,234 Total $ 3,749,517 $ 36,450 $ 81,073 $ — $ 3,867,040 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 The Company’s past due loans are as follows (in thousands): September 30, 2019 15-59 Past Due* 60-89 Past Due Greater Total Current Total Loans 90 Days Past Accruing Commercial $ 2,740 $ 815 $ 619 $ 4,174 $ 832,470 $ 836,644 $ — Agricultural 605 232 202 1,039 101,015 102,054 — Real Estate 14,216 1,563 239 16,018 2,733,534 2,749,552 69 Consumer 595 164 40 799 411,267 412,066 35 Total $ 18,156 $ 2,774 $ 1,100 $ 22,030 $ 4,078,286 $ 4,100,316 $ 104 September 30, 2018 15-59 Past Due* 60-89 Past Due Greater Total Current Total Loans 90 Days Past Accruing Commercial $ 3,850 $ 420 $ 3,331 $ 7,601 $ 766,323 $ 773,924 $ — Agricultural 442 — 287 729 93,224 93,953 — Real Estate 15,542 2,583 661 18,786 2,596,143 2,614,929 — Consumer 749 173 145 1,067 383,167 384,234 88 Total $ 20,583 $ 3,176 $ 4,424 $ 28,183 $ 3,838,857 $ 3,867,040 $ 88 December 31, 2018 15-59 Past Due* 60-89 Past Due Greater Total Current Total Loans Total 90 Past Due Accruing Commercial $ 3,546 $ 682 $ 677 $ 4,905 $ 840,048 $ 844,953 $ — Agricultural 791 19 26 836 95,841 96,677 — Real Estate 13,185 881 2,020 16,086 2,623,260 2,639,346 960 Consumer 782 263 54 1,099 371,561 372,660 48 Total $ 18,304 $ 1,845 $ 2,777 $ 22,926 $ 3,930,710 $ 3,953,636 $ 1,008 * The 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 by portfolio segment (in thousands). There were no allowances for purchased credit impaired loans at September 30, 2019 and 2018, and December 31, 2018. Allocation of a portion of the allowance to one category of loans does not preclude its availability to absorb losses in other categories. September 30, 2019 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 1,448 $ 247 $ 2,314 $ 185 $ 4,194 Loans collectively evaluated for impairment 11,018 1,000 30,022 5,655 47,695 Total $ 12,466 $ 1,247 $ 32,336 $ 5,840 $ 51,889 September 30, 2018 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 1,412 $ 528 $ 2,652 $ 396 $ 4,988 Loans collectively evaluated for impairment 7,549 1,106 31,713 5,515 45,883 Total $ 8,961 $ 1,634 $ 34,365 $ 5,911 $ 50,871 December 31, 2018 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 1,133 $ 170 $ 2,409 $ 357 $ 4,069 Loans collectively evaluated for impairment 10,815 1,276 29,933 5,109 47,133 Total $ 11,948 $ 1,446 $ 32,342 $ 5,466 $ 51,202 Changes in the allowance for loan losses are summarized as follows by portfolio segment (in thousands): Three months ended September 30, 2019 Commercial Agricultural Real Estate Consumer Total Beginning balance $ 13,899 $ 1,360 $ 30,799 $ 5,762 $ 51,820 Provision for loan losses (1,174 ) (32 ) 1,531 125 450 Recoveries 90 85 100 111 386 Charge-offs (349 ) (166 ) (94 ) (158 ) (767 ) Ending balance $ 12,466 $ 1,247 $ 32,336 $ 5,840 $ 51,889 Three months ended September 30, 2018 Commercial Agricultural Real Estate Consumer Total Beginning balance $ 9,218 $ 1,402 $ 33,243 $ 6,088 $ 49,951 Provision for loan losses (24 ) 229 1,091 154 1,450 Recoveries 192 3 85 135 415 Charge-offs (425 ) — (54 ) (466 ) (945 ) Ending balance $ 8,961 $ 1,634 $ 34,365 $ 5,911 $ 50,871 Nine months ended September 30, 2019 Commercial Agricultural Real Estate Consumer Total Beginning balance $ 11,948 $ 1,446 $ 32,342 $ 5,466 $ 51,202 Provision for loan losses 439 10 998 568 2,015 Recoveries 1,163 92 250 459 1,964 Charge-offs (1,084 ) (301 ) (1,254 ) (653 ) (3,292 ) Ending balance $ 12,466 $ 1,247 $ 32,336 $ 5,840 $ 51,889 Nine months ended September 30, 2018 Commercial Agricultural Real Estate Consumer Total Beginning balance $ 10,865 $ 1,305 $ 29,896 $ 6,090 $ 48,156 Provision for loan losses (1,316 ) 317 4,325 539 3,865 Recoveries 476 12 345 382 1,215 Charge-offs (1,064 ) — (201 ) (1,100 ) (2,365 ) Ending balance $ 8,961 $ 1,634 $ 34,365 $ 5,911 $ 50,871 The Company’s recorded investment in loans related to the balance in the allowance for loan losses on the basis of the Company’s impairment methodology is as follows (in thousands). Purchased credit impaired loans of $342,000, $2,947,000 and $827,000 at September 30, 2019 and 2018, and December 31, 2018, respectively, are included in loans individually evaluated for impairment. September 30, 2019 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 8,802 $ 1,502 $ 15,095 $ 318 $ 25,717 Loans collectively evaluated for impairment 827,842 100,552 2,734,457 411,748 4,074,599 Total $ 836,644 $ 102,054 $ 2,749,552 $ 412,066 $ 4,100,316 September 30, 2018 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 6,961 $ 1,046 $ 16,682 $ 898 $ 25,587 Loans collectively evaluated for impairment 766,963 92,907 2,598,247 383,336 3,841,453 Total $ 773,924 $ 93,953 $ 2,614,929 $ 384,234 $ 3,867,040 December 31, 2018 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 9,334 $ 759 $ 16,714 $ 727 $ 27,534 Loan collectively evaluated for impairment 835,619 95,918 2,622,632 371,933 3,926,102 Total $ 844,953 $ 96,677 $ 2,639,346 $ 372,660 $ 3,953,636 The Company’s loans that were modified and considered troubled debt restructurings are as follows (in thousands): Three Months Ended September 30, 2019 Nine Months Ended September 30, 2019 Pre-Modification Post- Pre-Modification Post- Recorded Recorded Recorded Recorded Number Investment Investment Number Investment Investment Commercial 2 $ 100 $ 100 5 $ 379 $ 379 Agricultural — — — 10 619 619 Real Estate 1 42 42 5 692 692 Consumer — — — — — — Total 3 $ 142 $ 142 20 $ 1,690 $ 1,690 Three Months Ended September 30, 2018 Nine Months Ended September 30, 2018 Pre-Modification Post- Pre-Modification Post- Recorded Recorded Recorded Recorded Number Investment Investment Number Investment Investment Commercial 2 $ 547 $ 547 3 $ 826 $ 826 Agricultural — — — 1 4 4 Real Estate 1 117 117 5 642 642 Consumer — — — 6 113 113 Total 3 $ 664 $ 664 15 $ 1,585 $ 1,585 The balances below provide information as to how the loans were modified as troubled debt restructured loans (in thousands): Three Months Ended September 30, 2019 Nine Months Ended September 30, 2019 Adjusted Extended Combined Maturity Adjusted Extended Combined Maturity Commercial $ — $ — $ 100 $ — $ 279 $ 100 Agricultural — — — — 354 265 Real Estate — — 42 — 202 490 Consumer — — — — — — Total $ — $ — $ 142 $ — $ 835 $ 855 Three Months Ended September 30, 2018 Nine Months Ended September 30, 2018 Adjusted Extended Combined Maturity Adjusted Extended Combined Maturity Commercial $ — $ 491 $ 56 $ — $ 491 $ 335 Agricultural — — — — — 4 Real Estate — 117 — — 279 363 Consumer — — — — — 113 Total $ — $ 608 $ 56 $ — $ 770 $ 815 During the three and nine months ended September 30, 2019, two loans totaling $28,000 As of September 30, 2019, the Company has no commitments to lend additional funds to loan customers whose terms have been modified in troubled debt restructurings. 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 September 30, 2019, $2,616,319,000 in loans held by our bank subsidiary were subject to blanket liens as security for this line of credit. At September 30, 2019, there was $35,000,000

Loans Held for Sale

Loans Held for Sale	9 Months Ended
	Sep. 30, 2019
Debt Disclosure [Abstract]
Loans Held for Sale	Note 6 - 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 $ 40,499 18,496 21,672

Derivative Financial Instrument

Derivative Financial Instruments	9 Months Ended
	Sep. 30, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments	Note 7 - 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 12), 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 12). 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): September 30, 2019: Outstanding Notional Balance Asset Derivative Fair Value Liability Derivative Fair Value IRLCs $ 82,330 $ 1,320 $ — Forward mortgage-backed securities trades 126,500 41 — September 30, 2018: Outstanding Notional Balance Asset Derivative Fair Value Liability Derivative Fair Value IRLCs $ 48,311 $ 715 $ — Forward mortgage-backed securities trades 42,500 143 — December 31, 2018: Outstanding Notional Balance Asset Derivative Fair Value Liability Derivative Fair Value IRLCs $ 37,088 $ 765 $ — Forward mortgage-backed securities trades 45,500 — 403

Borrowings

Borrowings	9 Months Ended
	Sep. 30, 2019
Debt Disclosure [Abstract]
Borrowings	Note 8 – Borrowings Borrowings consisted of the following (dollars in thousands): September 30, December 31, 2019 2018 2018 Securities sold under agreements with customers to repurchase $ 358,155 $ 378,460 $ 409,631 Federal funds purchased 7,000 2,300 4,075 Advances from Federal Home Loan Bank of Dallas 35,000 — 55,000 Total $ 400,155 $ 380,760 $ 468,706 Securities sold under repurchase agreements are generally with significant customers of the Company that require short-term liquidity for their funds for which the Company pledges certain securities that have a fair value equal to at least the amount of the borrowings. The agreements mature daily and therefore the risk arising from a decline in the fair value of the collateral pledged is minimal. The securities pledged are mortgage-backed securities. These agreements do not include “right of set-off”

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Income Taxes	Note 9 - Income Taxes Income tax expense was $ 8,867 7,475 24,827 20,937 30,

Stock Option Plan and Restricte

Stock Option Plan and Restricted Stock Plan	9 Months Ended
	Sep. 30, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock Option Plan and Restricted Stock Plan	Note 10 - Stock Option Plan and Restricted Stock Plan The Company grants incentive stock options for a fixed number of shares with an exercise price equal to the fair value of the shares at the date of grant to employees. On June 26, 2019, the Company granted 398,850 incentive stock options with an exercise price of $29.70 per share. The fair value of the options was $7.31 per share and was estimated using the Black-Scholes options pricing model with the following weighted average assumptions: risk free interest rate of 1.83%; expected dividend yield of 1.62%; expected life of 6.64 years; and expected volatility of 26.69%. No options were granted in 2018. The Company recorded stock option expense totaling $431,000 and $377,000 for the three-month periods ended September 30, 2019 and 2018, respectively. The Company recorded stock option expense totaling $1,056,000 and $1,131,000 for the nine months ended September 30, 2019 and 2018, respectively. The additional disclosure requirements under authoritative accounting guidance have been omitted due to the amounts being insignificant. On April 25, 2017, upon re-election non-employee re-election non-employee re-election non-employee On October 27, 2015, the Company granted 62,546 restricted shares with a total value of $1,060,000 to certain officers that were are are are being three t are b eing expensed over the vesting period of three years. On October 22, 2019, the Company granted 22,188 restricted shares with a total value of $785,000 to certain officers that will be

Pension Plan

Pension Plan	9 Months Ended
	Sep. 30, 2019
Retirement Benefits [Abstract]
Pension Plan	Note 11 - Pension Plan The Company’s defined benefit pension plan was frozen effective January 1, 2004, whereby no new participants were added to the plan and no additional years of service were accrued to participants. The pension plan covered substantially all of the Company’s employees at the time. The benefits for each employee were based on years of service and a percentage of the employee’s qualifying compensation during the final years of employment. The Company’s funding policy was and is to contribute annually the amount necessary to satisfy the Internal Revenue Service’s funding standards. As a result of its evaluation of its funding status, the Company made no contribution in 2018, and has not made a contribution through September 30, 2019. 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 made a decision to terminate and settle the remaining obligation in its pension plan with an effective termination date of June In addition, the Company had a multiple employer pension plan related to its acquisition of Orange Savings Bank in 2013. This plan was likewise frozen. During the first quarter of 2019, the Company made a decision to remove this plan from the multiple employer plan and merge it into the Company’s existing pension plan. The Company recorded $900,000 in pension merger expense for the three months ended March 31, 2019 in connection with this merger of the Orange pension plan. In May 2019, the Company assumed the Orange pension obligation of $2,740,000 and received related assets totaling $1,829,000. Net periodic benefit costs totaling $31,000 and $65,000 were recorded for the three months ended September 30, 2019 and 2018, respectively. Net periodic benefit costs totaling $973,000 and $177,000 were recorded for the nine months ended September 30, 2019 and 2018, respectively, which includes the Orange pension merger costs discussed above.

Fair Value Disclosures

Fair Value Disclosures	9 Months Ended
	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Fair Value Disclosures	Note 12 - 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 • 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 6 and 7 related to the determination of fair value for loans held-for-sale, There were no transfers between Level 1 and Level 2 or Level 2 and Level 3 during the three and nine months ended September 30, 2019 and 2018, and the year ended December 31, 2018. The following table summarizes the Company’s available-for-sale September 30, 2019 Level 1 Inputs Level 2 Inputs Level 3 Inputs Total Fair Value Available-for-sale U.S. Treasury securities $ 10,021 $ — $ — $ 10,021 Obligations of states and political subdivisions — 1,242,197 — 1,242,197 Corporate bonds — 229 — 229 Residential mortgage-backed securities — 1,623,380 — 1,623,380 Commercial mortgage-backed securities — 516,828 — 516,828 Other securities 4,501 — — 4,501 Total $ 14,522 $ 3,382,634 $ — $ 3,397,156 Loans held-for-sale $ — $ 39,735 $ — $ 39,735 IRLCs $ — $ 1,320 $ — $ 1,320 Forward mortgage-backed securities trades $ — $ 41 $ — $ 41 September 30, 2018 Level 1 Inputs Level 2 Inputs Level 3 Inputs Total Fair Value U.S. Treasury securities $ 9,929 $ — $ — $ 9,929 Obligations of U. S. government sponsored enterprises and agencies — 302 — 302 Obligations of states and political subdivisions — 1,191,887 — 1,191,887 Corporate bonds — 450 — 450 Residential mortgage-backed securities — 1,494,306 — 1,494,306 Commercial mortgage-backed securities — 443,204 — 443,204 Other securities 4,289 — — 4,289 Total $ 14,218 $ 3,130,149 $ — $ 3,144,367 Loans held-for-sale $ — $ 15,955 $ — $ 15,955 IRLCs $ — $ 715 $ — $ 715 Forward mortgage-backed securities trades $ — $ 143 $ — $ 143 December 31, 2018 Level 1 Inputs Level 2 Inputs Level 3 Inputs Total Fair Value Available-for-sale U.S. Treasury securities $ 9,962 $ — $ — $ 9,962 Obligations of U. S. government sponsored enterprises and agencies — 301 — 301 Obligations of states 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 trades $ — $ (403 ) $ — $ (403 ) Certain financial assets and financial liabilities are measured at fair value on a nonrecurring basis, that is, the instruments are not measured at fair value on an ongoing basis but are subject to fair value adjustments in certain circumstances (for example, when there is evidence of impairment). Impaired loans are reported at the fair value of the underlying collateral less selling costs if repayment is expected solely from the collateral. Collateral values are estimated using Level 2 inputs based on observable market data. At September 30, 2019, impaired loans with a carrying value of $15,274,000 were reduced by specific valuation reserves totaling $4,194,000 resulting in a net fair value of $11,080,000. The Company also had impaired loans of $ 10,443 Certain non-financial non-financial non-recurring non-financial Non-financial non-recurring re-measured Re-evaluation The following table presents other real estate owned that were re-measured Three Months Ended September 30, 2019 2018 Carrying value of other real estate owned prior to re-measurement $ — $ — Write-downs included in gain (loss) on sale of other real estate owned — — Fair value $ — $ — Nine Months Ended September 30, 2019 2018 Carrying value of other real estate owned prior to re-measurement $ — $ 526 Write-downs included in gain (loss) on sale of other real estate owned — (126 ) Fair value $ — $ 400 At September 30, 2019 and 2018, and December 31, 2018, other real estate owned totaled $1,329,000, $593,000 and $448,000, The Company is required under current authoritative accounting guidance to disclose the estimated fair value of their financial instrument assets and liabilities including those subject to the requirements discussed above. For the Company, as for most financial institutions, substantially all of its assets and liabilities are considered financial instruments. Many of the Company’s financial instruments, however, lack an available trading market as characterized by a willing buyer and willing seller engaging in an exchange transaction. The estimated fair value amounts of financial instruments have been determined by the Company using available market information and appropriate valuation methodologies. However, considerable judgment is required to interpret data to develop the estimates of fair value. Accordingly, the estimates presented herein are not necessarily indicative of the amounts the Company could realize in a current market exchange. The use of different market assumptions and/or estimation methodologies may have a material effect on the estimated fair value amounts. In addition, reasonable comparability between financial institutions may not be likely due to the wide range of permitted valuation techniques and numerous estimates that must be made given the absence of active secondary markets for many of the financial instruments. This lack of uniform valuation methodologies also introduces a greater degree of subjectivity to these estimated fair values. Cash and due from banks, federal funds sold, interest-bearing deposits and time deposits in banks and accrued interest receivable and payable are liquid in nature and considered Levels 1 or 2 of the fair value hierarchy. Financial instruments with stated maturities have been valued using a present value discounted cash flow with a discount rate approximating current market for similar assets and liabilities and are considered Levels 2 and 3 of the fair value hierarchy. Financial instrument liabilities with no stated maturities have an estimated fair value equal to both the amount payable on demand and the carrying value and are considered Level 1 of the fair value hierarchy. The carrying value and the estimated fair value of the Company’s contractual off-balance-sheet The estimated fair values and carrying values of all financial instruments under current authoritative guidance were as follows (in thousands). September 30, December 31, 2019 2018 2018 Carrying Estimated Carrying Estimated Carrying Estimated Fair Value Cash and due from banks $ 198,855 $ 198,855 $ 164,998 $ 164,998 $ 207,835 $ 207,835 Level 1 Interest-bearing deposits in banks 31,410 31,410 34,511 34,511 40,812 40,812 Level 1 Interest-bearing time deposits in banks — — 1,458 1,458 1,458 1,458 Level 2 Available-for-sale 3,397,156 3,397,156 3,144,367 3,144,367 3,158,777 3,158,777 Levels 1 and 2 Loans held for investment 4,048,427 4,068,755 3,816,169 3,857,059 3,902,434 3,947,391 Level 3 Loans held for sale 40,499 40,542 18,496 18,517 21,672 21,779 Level 2 Accrued interest receivable 29,606 29,606 28,990 28,990 36,765 36,765 Level 2 Deposits with stated maturities 428,192 429,522 450,667 450,409 442,161 441,727 Level 2 Deposits with no stated maturities 5,969,491 5,969,491 5,694,615 5,694,615 5,738,228 5,738,228 Level 1 Borrowings 400,155 400,155 380,760 380,760 468,706 468,706 Level 2 Accrued interest payable 746 746 303 303 408 408 Level 2 IRLCs 1,320 1,320 715 715 765 765 Level 2 Forward mortgage backed securities trades 41 41 143 143 (403 ) (403 ) Level 2

Recently Issued Authoritative A

Recently Issued Authoritative Accounting Guidance	9 Months Ended
	Sep. 30, 2019
Accounting Changes and Error Corrections [Abstract]
Recently Issued Authoritative Accounting Guidance	Note 13—Recently Issued Authoritative Accounting Guidance Accounting Standards Update (“ASU”) 2014-09, “Revenue from Contracts with Customers 2014-09 2015-4 2014-09 2014-09, non-interest ASU 2016-01, ASU 2016-01 “Financial Instruments – Overall: Recognition and Measurement of Financial Assets and Financial Liabilities 2016-01, available-for-sale 2016-1 ASU 2016-02, “Leases 2016-02 right-of-use 2016-02 ASU 2016-13, “Financial Instruments – Credit Losses 2016-13 2016-13 2016-13 available-for-sale 2016-13 2016-13. 2016-13 ASU 2017-04, “Intangibles – Goodwill and Other 2017-04 2017-04 ASU 2018-02, “Income Statement – Reporting Comprehensive Income: Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income.” 2018-02 2018-02 ASU 2018-13, “Fair Value Measurement – Changes to the Disclosure Requirements for Fair Value Measurement 2018-13 2018-13

Acquisition and Proposed Acquis

Acquisition and Proposed Acquisition	9 Months Ended
	Sep. 30, 2019
Business Combinations [Abstract]
Acquisition and Proposed Acquisition	Note 14 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. On September 19, 2019, we entered into an agreement and $445,600,000, total deposits of $538,200,000 and total assets of $624,500,000. Pending regulatory and shareholder approvals, the acquisition is expected to close in the first quarter of 2020.

Summary of Significant Accounti

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Investment Securities	Management classifies debt and equity securities as held-to-maturity, available-for-sale, held-to-maturity held-to-maturity available-for-sale 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. Often, the information available to conduct these assessments is limited and rapidly changing, making estimates of fair value subject to judgment. If actual information or conditions are different than estimated, the extent of the impairment of the debt security may be different than previously estimated, which could have a material effect on the Company’s results of operations and financial condition. The Company’s investment portfolio consists of U.S. Treasury securities, 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 and Allowance for Loan Losses	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 Company has certain lending policies and procedures in place that are designed to maximize loan income with an acceptable level of risk. Management reviews and approves these policies and procedures on an annual basis and makes changes as appropriate. Management receives and reviews monthly reports related to loan originations, quality, concentrations, delinquencies, nonperforming and potential problem loans. Diversification in the loan portfolio is a means of managing risk associated with fluctuations in economic conditions, both by type of loan and geographic location. Commercial loans are underwritten after evaluating and understanding the borrower’s ability to operate profitably and effectively. Underwriting standards are designed to determine whether the borrower possesses sound business ethics and practices and to evaluate current and projected cash flows to determine the ability of the borrower to repay their obligations as agreed. Commercial loans are primarily made based on the identified cash flows of the borrower and, secondarily, on the underlying collateral provided by the borrower. Most commercial loans are secured by the assets being financed or other business assets, such as accounts receivable or inventory, and include personal guarantees. Real estate loans are also subject to underwriting standards and processes similar to commercial and agricultural loans. These loans are underwritten primarily based on projected cash flows and, secondarily, as loans secured by real estate. The repayment of real estate loans is generally largely dependent on the successful operation of the property securing the loans or the business conducted on the property securing the loan. Real estate loans may be more adversely affected by conditions in the real estate markets or in the general economy. The properties securing the Company’s real estate portfolio are generally diverse in terms of type and geographic location within Texas. This diversity helps reduce the exposure to adverse economic events that affect any single market or industry. Generally, real estate loans are owner occupied which further reduces the Company’s risk. Consumer loan underwriting utilizes methodical credit standards and analysis to supplement the Company’s underwriting policies and procedures. The Company’s loan policy addresses types of consumer loans that may be originated and the collateral, if secured, which must be perfected. The relatively smaller individual dollar amounts of consumer loans that are spread over numerous individual borrowers also minimize the Company’s risk. 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 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
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 • 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
Recently Issued Authoritative Accounting Guidance	Accounting Standards Update (“ASU”) 2014-09, “Revenue from Contracts with Customers 2014-09 2015-4 2014-09 2014-09, non-interest ASU 2016-01, ASU 2016-01 “Financial Instruments – Overall: Recognition and Measurement of Financial Assets and Financial Liabilities 2016-01, available-for-sale 2016-1 ASU 2016-02, “Leases 2016-02 right-of-use 2016-02 ASU 2016-13, “Financial Instruments – Credit Losses 2016-13 2016-13 2016-13 available-for-sale 2016-13 2016-13. 2016-13 ASU 2017-04, “Intangibles – Goodwill and Other 2017-04 2017-04 ASU 2018-02, “Income Statement – Reporting Comprehensive Income: Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income.” 2018-02 2018-02 ASU 2018-13, “Fair Value Measurement – Changes to the Disclosure Requirements for Fair Value Measurement 2018-13 2018-13

Interest-bearing Time Deposit_2

Interest-bearing Time Deposits in Banks and Securities (Tables)	9 Months Ended
	Sep. 30, 2019
Cash and Cash Equivalents [Abstract]
Summary of Available-for-Sale Securities	A summary of the Company’s available-for-sale September 30, 2019 Gross Gross Amortized Unrealized Unrealized Estimated Cost Basis Holding Gains Holding Losses Fair Value U.S. Treasury securities $ 9,990 $ 31 $ — $ 10,021 Obligations of states and political subdivisions 1,182,549 59,734 (86 ) 1,242,197 Corporate bonds and other 4,643 87 — 4,730 Residential mortgage-backed securities 1,597,807 27,001 (1,428 ) 1,623,380 Commercial mortgage-backed securities 509,019 8,069 (260 ) 516,828 Total securities available-for-sale $ 3,304,008 $ 94,922 $ (1,774 ) $ 3,397,156 September 30, 2018 Gross Gross Amortized Unrealized Unrealized Estimated Cost Basis Holding Gains Holding Losses Fair Value U.S. Treasury securities $ 9,964 $ — $ (35 ) $ 9,929 Obligations of U.S. government sponsored enterprises and agencies 303 — (1 ) 302 Obligations of states and political subdivisions 1,174,320 21,664 (4,097 ) 1,191,887 Corporate bonds and other 4,860 — (121 ) 4,739 Residential mortgage-backed securities 1,533,302 912 (39,908 ) 1,494,306 Commercial mortgage-backed securities 453,495 8 (10,299 ) 443,204 Total securities available-for-sale $ 3,176,244 $ 22,584 $ (54,461 ) $ 3,144,367 December 31, 2018 Gross Gross Amortized Unrealized Unrealized Estimated Cost Basis Holding Gains Holding Losses Fair Value U.S. Treasury securities $ 9,970 $ — $ (8 ) $ 9,962 Obligations of U.S. government sponsored enterprises and agencies 301 — — 301 Obligations of states and political subdivisions 1,229,828 30,013 (1,970 ) 1,257,871 Corporate bonds and other 4,875 — (77 ) 4,798 Residential mortgage-backed securities 1,472,228 3,928 (21,611 ) 1,454,545 Commercial mortgage-backed securities 436,366 670 (5,736 ) 431,300 Total securities available-for-sale $ 3,153,568 $ 34,611 $ (29,402 ) $ 3,158,777
Amortized Cost and Estimated Fair Value of Available-for-Sale Securities	The amortized cost and estimated fair value of available-for-sale Amortized Estimated Cost Basis Fair Value Due within one year $ 207,121 $ 208,899 Due after one year through five years 494,764 520,494 Due after five years through ten years 493,565 525,301 Due after ten years 1,732 2,254 Mortgage-backed securities 2,106,826 2,140,208 Total $ 3,304,008 $ 3,397,156
Continuous Unrealized-Loss Position of Available-for-Sale Securities	The following tables disclose the Company’s investment securities that have been in a continuous unrealized-loss Less than 12 Months 12 Months or Longer Total September 30, 2019 Fair Value Unrealized Loss Fair Value Unrealized Loss Fair Value Unrealized Loss Obligations of states and political subdivisions $ 11,140 $ 86 $ 828 $ — $ 11,968 $ 86 Residential mortgage-backed securities 91,850 75 146,449 1,353 238,299 1,428 Commercial mortgage-backed securities 42,310 115 74,873 145 117,183 260 Total $ 145,300 $ 276 $ 222,150 $ 1,498 $ 367,450 $ 1,774 Less than 12 Months 12 Months or Longer Total September 30, 2018 Fair Value Unrealized Loss Fair Value Unrealized Loss Fair Value Unrealized Loss U.S. Treasury Securities $ 9,929 $ 35 $ — $ — $ 9,929 $ 35 Obligations of U.S. government sponsored enterprises and agencies 302 1 — — 302 1 Obligations of states and political subdivisions 184,265 2,165 44,750 1,932 229,015 4,097 Corporate bonds and other 4,399 110 449 11 4,848 121 Residential mortgage-backed securities 962,320 20,850 461,227 19,058 1,423,547 39,908 Commercial mortgage-backed securities 270,375 5,908 167,368 4,391 437,743 10,299 Total $ 1,431,590 $ 29,069 $ 673,794 $ 25,392 $ 2,105,384 $ 54,461 Less than 12 Months 12 Months or Longer Total December 31, 2018 Fair Value Unrealized Loss Fair Value Unrealized Loss Fair Value Unrealized Loss U.S. Treasury securities $ 9,962 $ 8 $ — $ — $ 9,962 $ 8 Obligations of U.S. government sponsored enterprises and agencies — — 301 — 301 — Obligations of state and political subdivisions 27,489 107 114,461 1,863 141,950 1,970 Corporate bonds and other 4,348 68 450 9 4,798 77 Residential mortgage-backed securities 119,584 483 922,289 21,128 1,041,873 21,611 Commercial mortgage-backed securities 1,994 5 343,015 5,731 345,009 5,736 Total $ 163,377 $ 671 $ 1,380,516 $ 28,731 $ 1,543,893 $ 29,402

Loans Held for Investment and_2

Loans Held for Investment and Allowance for Loan Losses (Tables)	9 Months Ended
	Sep. 30, 2019
Receivables [Abstract]
Loans Held-for-Investment by Class of Financing Receivables	Loans held-for-investment September 30, December 31, 2019 2018 2018 Commercial $ 836,644 $ 773,924 $ 844,953 Agricultural 102,054 93,953 96,677 Real estate 2,749,552 2,614,929 2,639,346 Consumer 412,066 384,234 372,660 Total loans held-for-investment $ 4,100,316 $ 3,867,040 $ 3,953,636
Non-Accrual Loans, Loans Still Accruing and Past Due 90 Days or More and Restructured Loans	The Company’s non-accrual September 30, December 31, 2019 2018 2018 Non-accrual $ 25,717 $ 25,587 $ 27,534 Loans still accruing and past due 90 days or more 104 88 1,008 Troubled debt restructured loans** 27 513 513 Total $ 25,848 $ 26,188 $ 29,055 * Includes $342,000, $2,947,000 and $827,000 of purchased credit impaired loans as of September 30, 2019 and 2018, and December 31, 2018, respectively. ** Troubled debt restructured loans of $3,983,000, $4,577,000 and $3,840,000, whose interest collection, after considering economic ​​​​​​​and business conditions and collection efforts, is doubtful are included in non-accrual
Recorded Investment in Impaired Loans and Related Valuation Allowance	The Company’s recorded investment in impaired loans and the related valuation allowance are as follows (in thousands): September 30, 2019 September 30, 2018 December 31, 2018 Re Investment Valuation Recorded Valuation Recorded Valuation $ 25,717 $ 4,194 $ 25,587 $ 4,988 $ 27,534 $ 4,069
Schedule of Non-Accrual Loans	Non-accrual September 30, December 31, 2019 2018 2018 Commercial $ 8,802 $ 6,961 $ 9,334 Agricultural 1,502 1,046 759 Real estate 15,095 16,682 16,714 Consumer 318 898 727 Total $ 25,717 $ 25,587 $ 27,534
Schedule of Impaired Loans and Related Allowance	The Company’s impaired loans and related allowance 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. September 30, 2019 Unpaid Principal Balance Recorded Recorded Total Related Year –to- D Average Three- Commercial $ 10,250 $ 5,885 $ 2,917 $ 8,802 $ 1,448 $ 9,586 $ 9,263 Agricultural 1,701 406 1,096 1,502 247 1,707 1,609 Real Estate 22,535 4,143 10,952 15,095 2,314 16,739 15,577 Consumer 444 9 309 318 185 416 346 Total $ 34,930 $ 10,443 $ 15,274 $ 25,717 $ 4,194 $ 28,448 $ 26,795 * Includes $342,000 of purchased credit impaired loans. September 30, 201 8 Unpaid Principal Balance Recorded Recorded Total Related Year –to-Date Average Three- Commercial $ 9,276 $ 3,467 $ 3,494 $ 6,961 $ 1,412 $ 8,339 $ 7,669 Agricultural 1,062 — 1,046 1,046 528 1,506 1,101 Real Estate 22,513 4,215 12,467 16,682 2,652 18,688 17,762 Consumer 1,088 50 848 898 396 1,012 942 Total $ 33,939 $ 7,732 $ 17,855 $ 25,587 $ 4,988 $ 29,545 $ 27,474 * Includes $2,947,000 of purchased credit impaired loans. December 31, 2018 Unpaid Principal Balance Recorded Recorded Total Related 12 Month Commercial $ 10,808 $ 6,728 $ 2,606 $ 9,334 $ 1,133 $ 7,986 Agricultural 799 213 546 759 170 842 Real Estate 24,072 6,699 10,015 16,714 2,409 16,042 Consumer 935 101 626 727 357 914 Total $ 36,614 $ 13,741 $ 13,793 $ 27,534 $ 4,069 $ 25,784 * Includes $827,000 of purchased credit impaired loans.
Schedule of Internal Ratings of Loans	The following summarizes the Company’s internal ratings of its loans held-for-investment September 30, 2019 Pass Special Substandard Doubtful Total Commercial $ 797,444 $ 24,836 $ 14,364 $ — $ 836,644 Agricultural 99,586 61 2,407 — 102,054 Real Estate 2,673,591 21,171 54,790 — 2,749,552 Consumer 410,491 232 1,343 — 412,066 Total $ 3,981,112 $ 46,300 $ 72,904 $ — $ 4,100,316 September 30, 2018 Pass Special Substandard Doubtful Total Commercial $ 747,758 $ 8,817 $ 17,349 $ — $ 773,924 Agricultural 89,314 68 4,571 — 93,953 Real Estate 2,530,673 27,241 57,015 — 2,614,929 Consumer 381,772 324 2,138 — 384,234 Total $ 3,749,517 $ 36,450 $ 81,073 $ — $ 3,867,040 December 31, 2018 Pass Special Substandard Doubtful Total Commercial $ 804,584 $ 23,392 $ 16,977 $ — $ 844,953 Agricultural 92,864 46 3,767 — 96,677 Real Estate 2,559,379 26,626 53,341 — 2,639,346 Consumer 370,510 315 1,835 — 372,660 Total $ 3,827,337 $ 50,379 $ 75,920 $ — $ 3,953,636
Schedule of Past Due Loans	The Company’s past due loans are as follows (in thousands): September 30, 2019 15-59 Past Due* 60-89 Past Due Greater Total Current Total Loans 90 Days Past Accruing Commercial $ 2,740 $ 815 $ 619 $ 4,174 $ 832,470 $ 836,644 $ — Agricultural 605 232 202 1,039 101,015 102,054 — Real Estate 14,216 1,563 239 16,018 2,733,534 2,749,552 69 Consumer 595 164 40 799 411,267 412,066 35 Total $ 18,156 $ 2,774 $ 1,100 $ 22,030 $ 4,078,286 $ 4,100,316 $ 104 September 30, 2018 15-59 Past Due* 60-89 Past Due Greater Total Current Total Loans 90 Days Past Accruing Commercial $ 3,850 $ 420 $ 3,331 $ 7,601 $ 766,323 $ 773,924 $ — Agricultural 442 — 287 729 93,224 93,953 — Real Estate 15,542 2,583 661 18,786 2,596,143 2,614,929 — Consumer 749 173 145 1,067 383,167 384,234 88 Total $ 20,583 $ 3,176 $ 4,424 $ 28,183 $ 3,838,857 $ 3,867,040 $ 88 December 31, 2018 15-59 Past Due* 60-89 Past Due Greater Total Current Total Loans Total 90 Past Due Accruing Commercial $ 3,546 $ 682 $ 677 $ 4,905 $ 840,048 $ 844,953 $ — Agricultural 791 19 26 836 95,841 96,677 — Real Estate 13,185 881 2,020 16,086 2,623,260 2,639,346 960 Consumer 782 263 54 1,099 371,561 372,660 48 Total $ 18,304 $ 1,845 $ 2,777 $ 22,926 $ 3,930,710 $ 3,953,636 $ 1,008 * The 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 by portfolio segment (in thousands). There were no allowances for purchased credit impaired loans at September 30, 2019 and 2018, and December 31, 2018. Allocation of a portion of the allowance to one category of loans does not preclude its availability to absorb losses in other categories. September 30, 2019 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 1,448 $ 247 $ 2,314 $ 185 $ 4,194 Loans collectively evaluated for impairment 11,018 1,000 30,022 5,655 47,695 Total $ 12,466 $ 1,247 $ 32,336 $ 5,840 $ 51,889 September 30, 2018 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 1,412 $ 528 $ 2,652 $ 396 $ 4,988 Loans collectively evaluated for impairment 7,549 1,106 31,713 5,515 45,883 Total $ 8,961 $ 1,634 $ 34,365 $ 5,911 $ 50,871 December 31, 2018 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 1,133 $ 170 $ 2,409 $ 357 $ 4,069 Loans collectively evaluated for impairment 10,815 1,276 29,933 5,109 47,133 Total $ 11,948 $ 1,446 $ 32,342 $ 5,466 $ 51,202
Changes in Allowance for Loan Losses	Changes in the allowance for loan losses are summarized as follows by portfolio segment (in thousands): Three months ended September 30, 2019 Commercial Agricultural Real Estate Consumer Total Beginning balance $ 13,899 $ 1,360 $ 30,799 $ 5,762 $ 51,820 Provision for loan losses (1,174 ) (32 ) 1,531 125 450 Recoveries 90 85 100 111 386 Charge-offs (349 ) (166 ) (94 ) (158 ) (767 ) Ending balance $ 12,466 $ 1,247 $ 32,336 $ 5,840 $ 51,889 Three months ended September 30, 2018 Commercial Agricultural Real Estate Consumer Total Beginning balance $ 9,218 $ 1,402 $ 33,243 $ 6,088 $ 49,951 Provision for loan losses (24 ) 229 1,091 154 1,450 Recoveries 192 3 85 135 415 Charge-offs (425 ) — (54 ) (466 ) (945 ) Ending balance $ 8,961 $ 1,634 $ 34,365 $ 5,911 $ 50,871 Nine months ended September 30, 2019 Commercial Agricultural Real Estate Consumer Total Beginning balance $ 11,948 $ 1,446 $ 32,342 $ 5,466 $ 51,202 Provision for loan losses 439 10 998 568 2,015 Recoveries 1,163 92 250 459 1,964 Charge-offs (1,084 ) (301 ) (1,254 ) (653 ) (3,292 ) Ending balance $ 12,466 $ 1,247 $ 32,336 $ 5,840 $ 51,889 Nine months ended September 30, 2018 Commercial Agricultural Real Estate Consumer Total Beginning balance $ 10,865 $ 1,305 $ 29,896 $ 6,090 $ 48,156 Provision for loan losses (1,316 ) 317 4,325 539 3,865 Recoveries 476 12 345 382 1,215 Charge-offs (1,064 ) — (201 ) (1,100 ) (2,365 ) Ending balance $ 8,961 $ 1,634 $ 34,365 $ 5,911 $ 50,871
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 related to the balance in the allowance for loan losses on the basis of the Company’s impairment methodology is as follows (in thousands). Purchased credit impaired loans of $342,000, $2,947,000 and $827,000 at September 30, 2019 and 2018, and December 31, 2018, respectively, are included in loans individually evaluated for impairment. September 30, 2019 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 8,802 $ 1,502 $ 15,095 $ 318 $ 25,717 Loans collectively evaluated for impairment 827,842 100,552 2,734,457 411,748 4,074,599 Total $ 836,644 $ 102,054 $ 2,749,552 $ 412,066 $ 4,100,316 September 30, 2018 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 6,961 $ 1,046 $ 16,682 $ 898 $ 25,587 Loans collectively evaluated for impairment 766,963 92,907 2,598,247 383,336 3,841,453 Total $ 773,924 $ 93,953 $ 2,614,929 $ 384,234 $ 3,867,040 December 31, 2018 Commercial Agricultural Real Estate Consumer Total Loans individually evaluated for impairment $ 9,334 $ 759 $ 16,714 $ 727 $ 27,534 Loan collectively evaluated for impairment 835,619 95,918 2,622,632 371,933 3,926,102 Total $ 844,953 $ 96,677 $ 2,639,346 $ 372,660 $ 3,953,636
Schedule of Loans Modified and Considered Troubled Debt Restructurings	The Company’s loans that were modified and considered troubled debt restructurings are as follows (in thousands): Three Months Ended September 30, 2019 Nine Months Ended September 30, 2019 Pre-Modification Post- Pre-Modification Post- Recorded Recorded Recorded Recorded Number Investment Investment Number Investment Investment Commercial 2 $ 100 $ 100 5 $ 379 $ 379 Agricultural — — — 10 619 619 Real Estate 1 42 42 5 692 692 Consumer — — — — — — Total 3 $ 142 $ 142 20 $ 1,690 $ 1,690 Three Months Ended September 30, 2018 Nine Months Ended September 30, 2018 Pre-Modification Post- Pre-Modification Post- Recorded Recorded Recorded Recorded Number Investment Investment Number Investment Investment Commercial 2 $ 547 $ 547 3 $ 826 $ 826 Agricultural — — — 1 4 4 Real Estate 1 117 117 5 642 642 Consumer — — — 6 113 113 Total 3 $ 664 $ 664 15 $ 1,585 $ 1,585
Schedule of How Loans Were Modified as Troubled Debt Restructured Loans	The balances below provide information as to how the loans were modified as troubled debt restructured loans (in thousands): Three Months Ended September 30, 2019 Nine Months Ended September 30, 2019 Adjusted Extended Combined Maturity Adjusted Extended Combined Maturity Commercial $ — $ — $ 100 $ — $ 279 $ 100 Agricultural — — — — 354 265 Real Estate — — 42 — 202 490 Consumer — — — — — — Total $ — $ — $ 142 $ — $ 835 $ 855 Three Months Ended September 30, 2018 Nine Months Ended September 30, 2018 Adjusted Extended Combined Maturity Adjusted Extended Combined Maturity Commercial $ — $ 491 $ 56 $ — $ 491 $ 335 Agricultural — — — — — 4 Real Estate — 117 — — 279 363 Consumer — — — — — 113 Total $ — $ 608 $ 56 $ — $ 770 $ 815

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Summary of Outstanding Notional Balances and Fair Values of Outstanding Derivative Positions	The following table provides the outstanding notional balances and fair values of outstanding derivative positions (dollars in thousands): September 30, 2019: Outstanding Notional Balance Asset Derivative Fair Value Liability Derivative Fair Value IRLCs $ 82,330 $ 1,320 $ — Forward mortgage-backed securities trades 126,500 41 — September 30, 2018: Outstanding Notional Balance Asset Derivative Fair Value Liability Derivative Fair Value IRLCs $ 48,311 $ 715 $ — Forward mortgage-backed securities trades 42,500 143 — December 31, 2018: Outstanding Notional Balance Asset Derivative Fair Value Liability Derivative Fair Value IRLCs $ 37,088 $ 765 $ — Forward mortgage-backed securities trades 45,500 — 403

Borrowings (Tables)

Borrowings (Tables)	9 Months Ended
	Sep. 30, 2019
Debt Disclosure [Abstract]
Schedule of Borrowings	Borrowings consisted of the following (dollars in thousands): September 30, December 31, 2019 2018 2018 Securities sold under agreements with customers to repurchase $ 358,155 $ 378,460 $ 409,631 Federal funds purchased 7,000 2,300 4,075 Advances from Federal Home Loan Bank of Dallas 35,000 — 55,000 Total $ 400,155 $ 380,760 $ 468,706

Fair Value Disclosures (Tables)

Fair Value Disclosures (Tables)	9 Months Ended
	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Financial Assets and Financial Liabilities Measured at Fair Value on Recurring Basis	The following table summarizes the Company’s available-for-sale September 30, 2019 Level 1 Inputs Level 2 Inputs Level 3 Inputs Total Fair Value Available-for-sale U.S. Treasury securities $ 10,021 $ — $ — $ 10,021 Obligations of states and political subdivisions — 1,242,197 — 1,242,197 Corporate bonds — 229 — 229 Residential mortgage-backed securities — 1,623,380 — 1,623,380 Commercial mortgage-backed securities — 516,828 — 516,828 Other securities 4,501 — — 4,501 Total $ 14,522 $ 3,382,634 $ — $ 3,397,156 Loans held-for-sale $ — $ 39,735 $ — $ 39,735 IRLCs $ — $ 1,320 $ — $ 1,320 Forward mortgage-backed securities trades $ — $ 41 $ — $ 41 September 30, 2018 Level 1 Inputs Level 2 Inputs Level 3 Inputs Total Fair Value U.S. Treasury securities $ 9,929 $ — $ — $ 9,929 Obligations of U. S. government sponsored enterprises and agencies — 302 — 302 Obligations of states and political subdivisions — 1,191,887 — 1,191,887 Corporate bonds — 450 — 450 Residential mortgage-backed securities — 1,494,306 — 1,494,306 Commercial mortgage-backed securities — 443,204 — 443,204 Other securities 4,289 — — 4,289 Total $ 14,218 $ 3,130,149 $ — $ 3,144,367 Loans held-for-sale $ — $ 15,955 $ — $ 15,955 IRLCs $ — $ 715 $ — $ 715 Forward mortgage-backed securities trades $ — $ 143 $ — $ 143 December 31, 2018 Level 1 Inputs Level 2 Inputs Level 3 Inputs Total Fair Value Available-for-sale U.S. Treasury securities $ 9,962 $ — $ — $ 9,962 Obligations of U. S. government sponsored enterprises and agencies — 301 — 301 Obligations of states 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 trades $ — $ (403 ) $ — $ (403 )
Other Real Estate Owned	The following table presents other real estate owned that were re-measured Three Months Ended September 30, 2019 2018 Carrying value of other real estate owned prior to re-measurement $ — $ — Write-downs included in gain (loss) on sale of other real estate owned — — Fair value $ — $ — Nine Months Ended September 30, 2019 2018 Carrying value of other real estate owned prior to re-measurement $ — $ 526 Write-downs included in gain (loss) on sale of other real estate owned — (126 ) Fair value $ — $ 400
Schedule of Estimated Fair Values and Carrying Values of All Financial Instruments	The estimated fair values and carrying values of all financial instruments under current authoritative guidance were as follows (in thousands). September 30, December 31, 2019 2018 2018 Carrying Estimated Carrying Estimated Carrying Estimated Fair Value Cash and due from banks $ 198,855 $ 198,855 $ 164,998 $ 164,998 $ 207,835 $ 207,835 Level 1 Interest-bearing deposits in banks 31,410 31,410 34,511 34,511 40,812 40,812 Level 1 Interest-bearing time deposits in banks — — 1,458 1,458 1,458 1,458 Level 2 Available-for-sale 3,397,156 3,397,156 3,144,367 3,144,367 3,158,777 3,158,777 Levels 1 and 2 Loans held for investment 4,048,427 4,068,755 3,816,169 3,857,059 3,902,434 3,947,391 Level 3 Loans held for sale 40,499 40,542 18,496 18,517 21,672 21,779 Level 2 Accrued interest receivable 29,606 29,606 28,990 28,990 36,765 36,765 Level 2 Deposits with stated maturities 428,192 429,522 450,667 450,409 442,161 441,727 Level 2 Deposits with no stated maturities 5,969,491 5,969,491 5,694,615 5,694,615 5,738,228 5,738,228 Level 1 Borrowings 400,155 400,155 380,760 380,760 468,706 468,706 Level 2 Accrued interest payable 746 746 303 303 408 408 Level 2 IRLCs 1,320 1,320 715 715 765 765 Level 2 Forward mortgage backed securities trades 41 41 143 143 (403 ) (403 ) Level 2

Acquisition and Proposed Acqu_2

Acquisition and Proposed Acquisition (Tables)	9 Months Ended
	Sep. 30, 2019
Schedule of Preliminary Estimated Fair Value Amounts Assigned to Major Asset and Liability Categories at 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 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

Stock Split and Stock Repurch_2

Stock Split and Stock Repurchase - Additional Information (Detail) - shares	Apr. 23, 2019	Sep. 30, 2019	Jul. 25, 2017
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program expiration date		Sep. 30, 2020
Stock repurchased under authorization		0
Stockholders' Equity Note, Stock Split	two-for-one stock split
Dividends Payable, Date of Record	May 15, 2019
Dividends Payable, Date to be Paid	Jun. 3, 2019
Maximum [Member]
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, number of shares authorized to be repurchased			2,000,000
Minimum [Member]
Equity, Class of Treasury Stock [Line Items]
Minimum number of shares that company is required to repurchase		0

Earnings Per Share - Additional

Earnings Per Share - Additional Information (Detail) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Weighted average common shares outstanding, basic	135,693,901	135,270,116	135,613,646	135,173,686
Weighted average common shares outstanding, diluted	136,369,328	136,107,448	136,274,342	135,896,840

Interest-bearing Time Deposit_3

Interest-bearing Time Deposits in Banks and Securities - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2019USD ($)Investment	Sep. 30, 2018USD ($)	Sep. 30, 2019USD ($)Investment	Sep. 30, 2018USD ($)	Dec. 31, 2018USD ($)
Interest Bearing Time Deposits In Banks And Securities [Line Items]
INTEREST-BEARING TIME DEPOSITS IN BANKS		$ 1,458,000		$ 1,458,000	$ 1,458,000
Number of investment positions | Investment	77		77
Securities pledged as collateral	$ 2,112,193,000		$ 2,112,193,000
Sales of investment securities available-for-sale	1,352,000	71,134,000	67,404,000	220,259,000
Gross realized gains from security sales	54,000	348,000	747,000	1,877,000
Gross realized losses from security sales or calls	$ 2,000	$ 290,000	$ 19,000	$ 531,000
Maximum [Member]
Interest Bearing Time Deposits In Banks And Securities [Line Items]
Interest-bearing time deposits, maturity period, years			6 months
Minimum [Member]
Interest Bearing Time Deposits In Banks And Securities [Line Items]
Interest-bearing time deposits, maturity period, years			1 year
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	36.22%		36.22%
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]
Percentage of available for sale securities	85.33%		85.33%

Interest-bearing Time Deposit_4

Interest-bearing Time Deposits in Banks and Securities - Summary of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	$ 3,304,008	$ 3,153,568	$ 3,176,244
Securities available-for-sale, Gross Unrealized Holding Gains	94,922	34,611	22,584
Securities available-for-sale, Gross Unrealized Holding Losses	(1,774)	(29,402)	(54,461)
Securities available-for-sale, Estimated Fair Value	3,397,156	3,158,777	3,144,367
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	9,990	9,970	9,964
Securities available-for-sale, Gross Unrealized Holding Gains	31
Securities available-for-sale, Gross Unrealized Holding Losses		(8)	(35)
Securities available-for-sale, Estimated Fair Value	10,021	9,962	9,929
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	303
Securities available-for-sale, Gross Unrealized Holding Losses			(1)
Securities available-for-sale, Estimated Fair Value		301	302
Obligations of State and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	1,182,549	1,229,828	1,174,320
Securities available-for-sale, Gross Unrealized Holding Gains	59,734	30,013	21,664
Securities available-for-sale, Gross Unrealized Holding Losses	(86)	(1,970)	(4,097)
Securities available-for-sale, Estimated Fair Value	1,242,197	1,257,871	1,191,887
Corporate Bonds and Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	4,643	4,875	4,860
Securities available-for-sale, Gross Unrealized Holding Gains	87
Securities available-for-sale, Gross Unrealized Holding Losses		(77)	(121)
Securities available-for-sale, Estimated Fair Value	4,730	4,798	4,739
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	1,597,807	1,472,228	1,533,302
Securities available-for-sale, Gross Unrealized Holding Gains	27,001	3,928	912
Securities available-for-sale, Gross Unrealized Holding Losses	(1,428)	(21,611)	(39,908)
Securities available-for-sale, Estimated Fair Value	1,623,380	1,454,545	1,494,306
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	509,019	436,366	453,495
Securities available-for-sale, Gross Unrealized Holding Gains	8,069	670	8
Securities available-for-sale, Gross Unrealized Holding Losses	(260)	(5,736)	(10,299)
Securities available-for-sale, Estimated Fair Value	$ 516,828	$ 431,300	$ 443,204

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	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Investments, Debt and Equity Securities [Abstract]
Available-for-Sale, Amortized Cost Basis, Due within one year	$ 207,121
Available-for-Sale, Amortized Cost Basis, Due after one year through five years	494,764
Available-for-Sale, Amortized Cost Basis, Due after five years through ten years	493,565
Available-for-Sale, Amortized Cost Basis, Due after ten years	1,732
Available-for-Sale, Amortized Cost Basis, Mortgage-backed securities	2,106,826
Available-for-Sale, Amortized Cost Basis, Total	3,304,008	$ 3,153,568	$ 3,176,244
Available-for-Sale, Estimated Fair Value, Due within one year	208,899
Available-for-Sale, Estimated Fair Value, Due after one year through five years	520,494
Available-for-Sale, Estimated Fair Value, Due after five years through ten years	525,301
Available-for-Sale, Estimated Fair Value, Due after ten years	2,254
Available-for-Sale, Estimated Fair Value, Mortgage-backed securities	2,140,208
Securities available-for-sale, Estimated Fair Value, Total	$ 3,397,156	$ 3,158,777	$ 3,144,367

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	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Fair Value	$ 145,300	$ 163,377	$ 1,431,590
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	276	671	29,069
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	222,150	1,380,516	673,794
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	1,498	28,731	25,392
Available-for-sale securities, continuous unrealized loss position, Fair Value	367,450	1,543,893	2,105,384
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	1,774	29,402	54,461
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	9,929
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss		8	35
Available-for-sale securities, continuous unrealized loss position, Fair Value		9,962	9,929
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss		8	35
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			302
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss			1
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	302
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss			1
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	11,140	27,489	184,265
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	86	107	2,165
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	828	114,461	44,750
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss		1,863	1,932
Available-for-sale securities, continuous unrealized loss position, Fair Value	11,968	141,950	229,015
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	86	1,970	4,097
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	4,399
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss		68	110
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value		450	449
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss		9	11
Available-for-sale securities, continuous unrealized loss position, Fair Value		4,798	4,848
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss		77	121
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	91,850	119,584	962,320
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	75	483	20,850
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	146,449	922,289	461,227
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	1,353	21,128	19,058
Available-for-sale securities, continuous unrealized loss position, Fair Value	238,299	1,041,873	1,423,547
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	1,428	21,611	39,908
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	42,310	1,994	270,375
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	115	5	5,908
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	74,873	343,015	167,368
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	145	5,731	4,391
Available-for-sale securities, continuous unrealized loss position, Fair Value	117,183	345,009	437,743
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	$ 260	$ 5,736	$ 10,299

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	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Loans and Leases Receivable Disclosure [Line Items]
Total	$ 4,100,316	$ 3,953,636	$ 3,867,040
Commercial [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total	836,644	844,953	773,924
Agriculture [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total	102,054	96,677	93,953
Real Estate [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total	2,749,552	2,639,346	2,614,929
Consumer [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total	$ 412,066	$ 372,660	$ 384,234

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		Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Receivables [Abstract]
Non-accrual loans	[1]	$ 25,717	$ 27,534	$ 25,587
Loans still accruing and past due 90 days or more		104	1,008	88
Troubled debt restructured loans	[2]	27	513	513
Total		$ 25,848	$ 29,055	$ 26,188
[1]	Includes $342,000, $2,947,000 and $827,000 of purchased credit impaired loans as of September 30, 2019 and 2018, and December 31, 2018, respectively.
[2]	Troubled debt restructured loans of $3,983,000, $4,577,000 and $3,840,000, whose interest collection, after considering economic and business conditions and collection efforts, is doubtful are included in non-accrual loans at September 30, 2019 and 2018, and December 31, 2018, respectively.

Loans Held for Investment and_5

Loans Held for Investment and Allowance for Loan Losses - Non-Accrual Loans, Loans Still Accruing and Past Due 90 Days or More and Restructured Loans (Parenthetical) (Detail) - USD ($)		Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Loans and Leases Receivable Disclosure [Line Items]
Non-accrual loans	[1]	$ 25,717,000	$ 27,534,000	$ 25,587,000
Troubled debt restructured loans	[2]	27,000	513,000	513,000
Doubtful [Member]
Loans and Leases Receivable Disclosure [Line Items]
Troubled debt restructured loans		3,983,000	3,840,000	4,577,000
Purchased Credit Impaired Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Non-accrual loans		$ 342,000	$ 827,000	$ 2,947,000
[1]	Includes $342,000, $2,947,000 and $827,000 of purchased credit impaired loans as of September 30, 2019 and 2018, and December 31, 2018, respectively.
[2]	Troubled debt restructured loans of $3,983,000, $4,577,000 and $3,840,000, whose interest collection, after considering economic and business conditions and collection efforts, is doubtful are included in non-accrual loans at September 30, 2019 and 2018, and December 31, 2018, respectively.

Loans Held for Investment and_6

Loans Held for Investment and Allowance for Loan Losses - Recorded Investment in Impaired Loans and Related Valuation Allowance (Detail) - USD ($) $ in Thousands		Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Receivables [Abstract]
Recorded Investment	[1]	$ 25,717	$ 27,534	$ 25,587
Valuation Allowance		$ 4,194	$ 4,069	$ 4,988
[1]	Includes $342,000, $2,947,000 and $827,000 of purchased credit impaired loans as of September 30, 2019 and 2018, and December 31, 2018, respectively.

Loans Held for Investment and_7

Loans Held for Investment and Allowance for Loan Losses - Additional Information (Detail)		3 Months Ended		9 Months Ended		12 Months Ended
		Sep. 30, 2019USD ($)Contract	Sep. 30, 2018USD ($)Contract	Sep. 30, 2019USD ($)Contract	Sep. 30, 2018USD ($)Contract	Dec. 31, 2018USD ($)	Jun. 30, 2019USD ($)	Jun. 30, 2018USD ($)	Dec. 31, 2017USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual, past due 90 days or more and still accruing, restructured loans and foreclosed assets		$ 27,212,000	$ 26,859,000	$ 27,212,000	$ 26,859,000	$ 29,632,000
Non accrual loans	[1]	25,717,000	25,587,000	25,717,000	25,587,000	27,534,000
Additional funds advanced in connection with impaired loans		0		0
Interest income recognized on impaired loans						948,000
Allowance for loan losses		51,889,000	50,871,000	51,889,000	50,871,000	51,202,000	$ 51,820,000	$ 49,951,000	$ 48,156,000
Loans individually evaluated for impairment		$ 25,717,000	25,587,000	25,717,000	25,587,000	27,534,000
Default for purposes of this disclosure is a troubled debt restructured loan		90 days
Commitments to lend additional funds to borrowers with loan that have been modified as TDRs		$ 0		0
Loans held by subsidiaries subject to blanket liens		2,616,319,000		2,616,319,000
Letters of credit outstanding		35,000,000		35,000,000
Impaired Financing Receivable, Unpaid Principal Balance		$ 34,930,000	$ 33,939,000	$ 34,930,000	$ 33,939,000	36,614,000
Number of loans modified | Contract		2	0	2	0
Loans modified as troubled debt restructured loan , value		$ 28,000		$ 28,000
Purchased Credit Impaired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non accrual loans		342,000	$ 2,947,000	342,000	$ 2,947,000	827,000
Allowance for loan losses		0	0	0	0	0
Loans individually evaluated for impairment		342,000	2,947,000	342,000	2,947,000	827,000
Impaired Financing Receivable, Unpaid Principal Balance		$ 605,000	$ 3,898,000	$ 605,000	$ 3,898,000	$ 1,157,000
[1]	Includes $342,000, $2,947,000 and $827,000 of purchased credit impaired loans as of September 30, 2019 and 2018, and December 31, 2018, respectively.

Loans Held for Investment and_8

Loans Held for Investment and Allowance for Loan Losses - Schedule of Non-Accrual Loans (Detail) - USD ($) $ in Thousands		Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	[1]	$ 25,717	$ 27,534	$ 25,587
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans		8,802	9,334	6,961
Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans		1,502	759	1,046
Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans		15,095	16,714	16,682
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans		$ 318	$ 727	$ 898
[1]	Includes $342,000, $2,947,000 and $827,000 of purchased credit impaired loans as of September 30, 2019 and 2018, and December 31, 2018, respectively.

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	3 Months Ended				9 Months Ended				12 Months Ended
	Sep. 30, 2019		Sep. 30, 2018		Sep. 30, 2019		Sep. 30, 2018		Dec. 31, 2018
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	$ 34,930		$ 33,939		$ 34,930		$ 33,939		$ 36,614
Recorded Investment With No Allowance	10,443	[1]	7,732	[2]	10,443	[1]	7,732	[2]	13,741	[3]
Recorded Investment With Allowance	15,274		17,855		15,274		17,855		13,793
Total Recorded Investment	25,717		25,587		25,717		25,587		27,534
Related Allowance	4,194		4,988		4,194		4,988		4,069
Average Recorded Investment	26,795		27,474		28,448		29,545		25,784
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	10,250		9,276		10,250		9,276		10,808
Recorded Investment With No Allowance	5,885	[1]	3,467	[2]	5,885	[1]	3,467	[2]	6,728	[3]
Recorded Investment With Allowance	2,917		3,494		2,917		3,494		2,606
Total Recorded Investment	8,802		6,961		8,802		6,961		9,334
Related Allowance	1,448		1,412		1,448		1,412		1,133
Average Recorded Investment	9,263		7,669		9,586		8,339		7,986
Agriculture [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	1,701		1,062		1,701		1,062		799
Recorded Investment With No Allowance	406	[1]	0	[2]	406	[1]	0	[2]	213	[3]
Recorded Investment With Allowance	1,096		1,046		1,096		1,046		546
Total Recorded Investment	1,502		1,046		1,502		1,046		759
Related Allowance	247		528		247		528		170
Average Recorded Investment	1,609		1,101		1,707		1,506		842
Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	22,535		22,513		22,535		22,513		24,072
Recorded Investment With No Allowance	4,143	[1]	4,215	[2]	4,143	[1]	4,215	[2]	6,699	[3]
Recorded Investment With Allowance	10,952		12,467		10,952		12,467		10,015
Total Recorded Investment	15,095		16,682		15,095		16,682		16,714
Related Allowance	2,314		2,652		2,314		2,652		2,409
Average Recorded Investment	15,577		17,762		16,739		18,688		16,042
Consumer [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	444		1,088		444		1,088		935
Recorded Investment With No Allowance	9	[1]	50	[2]	9	[1]	50	[2]	101	[3]
Recorded Investment With Allowance	309		848		309		848		626
Total Recorded Investment	318		898		318		898		727
Related Allowance	185		396		185		396		357
Average Recorded Investment	$ 346		$ 942		$ 416		$ 1,012		$ 914
[1]	Includes $342,000 of purchased credit impaired loans.
[2]	Includes $2,947,000 of purchased credit impaired loans.
[3]	Includes $827,000 of purchased credit impaired loans.

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	Sep. 30, 2019		Dec. 31, 2018		Sep. 30, 2018
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Allowance	$ 10,443	[1]	$ 13,741	[2]	$ 7,732	[3]
Purchased Credit Impaired Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Allowance	$ 342,000		$ 827,000		$ 2,947,000
[1]	Includes $342,000 of purchased credit impaired loans.
[2]	Includes $827,000 of purchased credit impaired loans.
[3]	Includes $2,947,000 of purchased credit impaired loans.

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	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	$ 4,100,316	$ 3,953,636	$ 3,867,040
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	836,644	844,953	773,924
Agriculture [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	102,054	96,677	93,953
Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	2,749,552	2,639,346	2,614,929
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	412,066	372,660	384,234
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	3,981,112	3,827,337	3,749,517
Pass [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	797,444	804,584	747,758
Pass [Member] | Agriculture [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	99,586	92,864	89,314
Pass [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	2,673,591	2,559,379	2,530,673
Pass [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	410,491	370,510	381,772
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	46,300	50,379	36,450
Special Mention [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	24,836	23,392	8,817
Special Mention [Member] | Agriculture [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	61	46	68
Special Mention [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	21,171	26,626	27,241
Special Mention [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	232	315	324
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	72,904	75,920	81,073
Substandard [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	14,364	16,977	17,349
Substandard [Member] | Agriculture [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	2,407	3,767	4,571
Substandard [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	54,790	53,341	57,015
Substandard [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Internal ratings of loan	$ 1,343	$ 1,835	$ 2,138

Loans Held for Investment an_12

Loans Held for Investment and Allowance for Loan Losses - Schedule of Past Due Loans (Detail) - USD ($) $ in Thousands		Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		$ 22,030	$ 22,926	$ 28,183
Total Current		4,078,286	3,930,710	3,838,857
Total Loans		4,100,316	3,953,636	3,867,040
Total 90 Days Past Due Still Accruing		104	1,008	88
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		4,174	4,905	7,601
Total Current		832,470	840,048	766,323
Total Loans		836,644	844,953	773,924
Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		1,039	836	729
Total Current		101,015	95,841	93,224
Total Loans		102,054	96,677	93,953
Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		16,018	16,086	18,786
Total Current		2,733,534	2,623,260	2,596,143
Total Loans		2,749,552	2,639,346	2,614,929
Total 90 Days Past Due Still Accruing		69	960
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		799	1,099	1,067
Total Current		411,267	371,561	383,167
Total Loans		412,066	372,660	384,234
Total 90 Days Past Due Still Accruing		35	48	88
15-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	[1]	18,156	18,304	20,583
15-59 Days Past Due [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	[1]	2,740	3,546	3,850
15-59 Days Past Due [Member] | Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	[1]	605	791	442
15-59 Days Past Due [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	[1]	14,216	13,185	15,542
15-59 Days Past Due [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	[1]	595	782	749
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		2,774	1,845	3,176
60-89 Days Past Due [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		815	682	420
60-89 Days Past Due [Member] | Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		232	19	0
60-89 Days Past Due [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		1,563	881	2,583
60-89 Days Past Due [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		164	263	173
Greater than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		1,100	2,777	4,424
Greater than 90 Days [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		619	677	3,331
Greater than 90 Days [Member] | Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		202	26	287
Greater than 90 Days [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		239	2,020	661
Greater than 90 Days [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		$ 40	$ 54	$ 145
[1]	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.

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	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	$ 4,194		$ 4,069	$ 4,988
Loans collectively evaluated for impairment	47,695		47,133	45,883
Total allowance for loan losses	51,889	$ 51,820	51,202	50,871	$ 49,951	$ 48,156
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	1,448		1,133	1,412
Loans collectively evaluated for impairment	11,018		10,815	7,549
Total allowance for loan losses	12,466	13,899	11,948	8,961	9,218	10,865
Agriculture [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	247		170	528
Loans collectively evaluated for impairment	1,000		1,276	1,106
Total allowance for loan losses	1,247	1,360	1,446	1,634	1,402	1,305
Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	2,314		2,409	2,652
Loans collectively evaluated for impairment	30,022		29,933	31,713
Total allowance for loan losses	32,336	30,799	32,342	34,365	33,243	29,896
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	185		357	396
Loans collectively evaluated for impairment	5,655		5,109	5,515
Total allowance for loan losses	$ 5,840	$ 5,762	$ 5,466	$ 5,911	$ 6,088	$ 6,090

Loans Held for Investment an_14

Loans Held for Investment and Allowance for Loan Losses - Changes in Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 51,820	$ 49,951	$ 51,202	$ 48,156
Provision for loan losses	450	1,450	2,015	3,865
Recoveries	386	415	1,964	1,215
Charge-offs	(767)	(945)	(3,292)	(2,365)
Ending balance	51,889	50,871	51,889	50,871
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	13,899	9,218	11,948	10,865
Provision for loan losses	(1,174)	(24)	439	(1,316)
Recoveries	90	192	1,163	476
Charge-offs	(349)	(425)	(1,084)	(1,064)
Ending balance	12,466	8,961	12,466	8,961
Agriculture [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,360	1,402	1,446	1,305
Provision for loan losses	(32)	229	10	317
Recoveries	85	3	92	12
Charge-offs	(166)		(301)
Ending balance	1,247	1,634	1,247	1,634
Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	30,799	33,243	32,342	29,896
Provision for loan losses	1,531	1,091	998	4,325
Recoveries	100	85	250	345
Charge-offs	(94)	(54)	(1,254)	(201)
Ending balance	32,336	34,365	32,336	34,365
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	5,762	6,088	5,466	6,090
Provision for loan losses	125	154	568	539
Recoveries	111	135	459	382
Charge-offs	(158)	(466)	(653)	(1,100)
Ending balance	$ 5,840	$ 5,911	$ 5,840	$ 5,911

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	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	$ 25,717	$ 27,534	$ 25,587
Loan collectively evaluated for impairment	4,074,599	3,926,102	3,841,453
Total	4,100,316	3,953,636	3,867,040
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	8,802	9,334	6,961
Loan collectively evaluated for impairment	827,842	835,619	766,963
Total	836,644	844,953	773,924
Agriculture [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	1,502	759	1,046
Loan collectively evaluated for impairment	100,552	95,918	92,907
Total	102,054	96,677	93,953
Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	15,095	16,714	16,682
Loan collectively evaluated for impairment	2,734,457	2,622,632	2,598,247
Total	2,749,552	2,639,346	2,614,929
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	318	727	898
Loan collectively evaluated for impairment	411,748	371,933	383,336
Total	$ 412,066	$ 372,660	$ 384,234

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	3 Months Ended		9 Months Ended
	Sep. 30, 2019USD ($)SecurityLoan	Sep. 30, 2018USD ($)SecurityLoan	Sep. 30, 2019USD ($)SecurityLoan	Sep. 30, 2018USD ($)SecurityLoan
Financing Receivable, Modifications [Line Items]
Number | SecurityLoan	3	3	20	15
Pre-Modification Recorded Investment	$ 142	$ 664	$ 1,690	$ 1,585
Post-Modification Recorded Investment	$ 142	$ 664	$ 1,690	$ 1,585
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number | SecurityLoan	2	2	5	3
Pre-Modification Recorded Investment	$ 100	$ 547	$ 379	$ 826
Post-Modification Recorded Investment	$ 100	$ 547	$ 379	$ 826
Agriculture [Member]
Financing Receivable, Modifications [Line Items]
Number | SecurityLoan			10	1
Pre-Modification Recorded Investment			$ 619	$ 4
Post-Modification Recorded Investment			$ 619	$ 4
Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number | SecurityLoan	1	1	5	5
Pre-Modification Recorded Investment	$ 42	$ 117	$ 692	$ 642
Post-Modification Recorded Investment	$ 42	$ 117	$ 692	$ 642
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Number | SecurityLoan				6
Pre-Modification Recorded Investment				$ 113
Post-Modification Recorded Investment				$ 113

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	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	$ 142	$ 664	$ 1,690	$ 1,585
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	100	547	379	826
Agriculture [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans			619	4
Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	42	117	692	642
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans				113
Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		608	835	770
Extended Maturity [Member] | Commercial [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		491	279	491
Extended Maturity [Member] | Agriculture [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans			354
Extended Maturity [Member] | Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		117	202	279
Combined Rate and Maturity [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	142	56	855	815
Combined Rate and Maturity [Member] | Commercial [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	100	56	100	335
Combined Rate and Maturity [Member] | Agriculture [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans			265	4
Combined Rate and Maturity [Member] | Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	$ 42		$ 490	363
Combined Rate and Maturity [Member] | Consumer [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		$ 0		$ 113

Loans Held for Sale - Additiona

Loans Held for Sale - Additional Information (Detail) - USD ($)	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Loans Receivables Held For Sale Net [Abstract]
Loans held for sale	$ 40,499,000	$ 21,672,000	$ 18,496,000
Loans held-for-sale at the lower of cost or fair value	$ 764,000	$ 2,487,000	$ 2,541,000

Derivative Financial Instrume_3

Derivative Financial Instruments - Summary of Outstanding Notional Balances and Fair Values of Outstanding Derivative Positions (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
IRLCs [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Outstanding Notional Balance	$ 82,330	$ 37,088	$ 48,311
Asset Derivative Fair Value	1,320	765	715
Forward Mortgage-Backed Securities Trades [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Outstanding Notional Balance	126,500	45,500	42,500
Asset Derivative Fair Value	$ 41		$ 143
Liability Derivative Fair Value		$ 403

Borrowings - Schedule of Borrow

Borrowings - Schedule of Borrowings (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Debt Disclosure [Abstract]
Securities sold under agreements with customers to repurchase	$ 358,155	$ 409,631	$ 378,460
Federal funds purchased	7,000	4,075	2,300
Advances from Federal Home Loan Bank of Dallas	35,000	55,000
Total	$ 400,155	$ 468,706	$ 380,760

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Federal statutory tax rate			21.00%		35.00%
Income tax expense	$ 8,867	$ 7,475	$ 24,827	$ 20,937
Effective tax rates on pre-tax income	17.07%	15.73%	16.75%	15.73%

Stock Option Plan and Restric_2

Stock Option Plan and Restricted Stock Plan - Additional Information (Detail) - USD ($)	Oct. 22, 2019	Jun. 26, 2019	Apr. 23, 2019	Oct. 23, 2018	Apr. 24, 2018	Oct. 24, 2017	Apr. 25, 2017	Oct. 25, 2016	Oct. 27, 2015	Jun. 26, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares vesting period				3 years
Risk-free interest rate										1.83%
Expected dividend yield										1.62%
Expected life										6 years 7 months 20 days
Expected volatility										26.69%
Weighted-average grant-date fair value of options granted										$ 7.31
Stock compensation expense											$ 431,000	$ 377,000	$ 1,056,000	$ 1,131,000
Granted, Shares										398,850					0
Granted the period exercise price										$ 29.70
Restricted Stock [Member] | Non-Employee Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares granted			660,000		21,420		29,300
Restricted shares value			$ 21,714		$ 523,000		$ 600,000
Restricted Stock [Member] | Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense											185,000	135,000	455,000	425,000
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	22,188	23,428		52,042		28,382		30,810	62,546
Restricted shares value	$ 785,000	$ 695,000		$ 1,440,000		$ 655,000		$ 560,000	$ 1,060,000
Stock compensation expense											$ 248,000	$ 175,000	$ 661,000	$ 501,000

Pension Plan - Additional Infor

Pension Plan - Additional Information (Detail) - USD ($)	May 31, 2019	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
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
Net periodic benefit costs, total		$ 31,000		$ 65,000	$ 973,000	$ 177,000
Orange pension plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension merger expense			$ 900,000
Defined Benefit Plan, Benefit Obligation, Business Combination	$ 2,740,000
Defined Benefit Plan, Plan Assets, Business Combination	$ 1,829,000

Fair Value Disclosures - Additi

Fair Value Disclosures - Additional Information (Detail)	Sep. 30, 2019USD ($)		Dec. 31, 2018USD ($)		Sep. 30, 2018USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans carrying value, recorded investment with allowance	$ 15,274,000		$ 13,793,000		$ 17,855,000
Impaired loans valuation reserves	4,194,000		4,069,000		4,988,000
Impaired loans net fair value	11,080,000
Recorded Investment With No Allowance	10,443,000	[1]	13,741,000	[2]	7,732,000	[3]
Other real estate owned, total	1,329,000		$ 448,000		$ 593,000
Level 2 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans carrying value, recorded investment with allowance	15,274,000
Impaired loans valuation reserves	$ 4,194,000
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
[1]	Includes $342,000 of purchased credit impaired loans.
[2]	Includes $827,000 of purchased credit impaired loans.
[3]	Includes $2,947,000 of purchased credit impaired loans.

Fair Value Disclosures - Financ

Fair Value Disclosures - Financial Assets and Financial Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	$ 3,397,156	$ 3,158,777	$ 3,144,367
Loans held-for-sale	40,499	21,672	18,496
U.S. Treasury Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	10,021	9,962	9,929
Obligations of U.S. Government Sponsored Enterprises and Agencies [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value		301	302
Obligations of State and Political Subdivisions [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	1,242,197	1,257,871	1,191,887
Residential Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	1,623,380	1,454,545	1,494,306
Commercial Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	516,828	431,300	443,204
IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	1,320	765	715
Forward Mortgage-Backed Securities Trades [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	41		143
Forward mortgage-backed securities trades		403
Fair Value, Measurements, Recurring [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	3,397,156	3,158,777	3,144,367
Loans held-for-sale	39,735	19,185	15,955
Fair Value, Measurements, Recurring [Member] | U.S. Treasury Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	10,021	9,962	9,929
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	302
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	1,242,197	1,257,871	1,191,887
Fair Value, Measurements, Recurring [Member] | Residential Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	1,623,380	1,454,545	1,494,306
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	516,828	431,300	443,204
Fair Value, Measurements, Recurring [Member] | IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	1,320	765	715
Fair Value, Measurements, Recurring [Member] | Forward Mortgage-Backed Securities Trades [Member]
Available-for-sale investment securities:
Forward mortgage-backed securities trades	41	(403)	143
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	229	450	450
Fair Value, Measurements, Recurring [Member] | Other Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	4,501	4,348	4,289
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	14,522	14,310	14,218
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member] | U.S. Treasury Securities [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	10,021	9,962	9,929
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	4,501	4,348	4,289
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member]
Available-for-sale investment securities:
Available-for-sale investment securities, Total Fair Value	3,382,634	3,144,467	3,130,149
Loans held-for-sale	39,735	19,185	15,955
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	302
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	1,242,197	1,257,871	1,191,887
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	1,623,380	1,454,545	1,494,306
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	516,828	431,300	443,204
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	1,320	765	715
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Forward Mortgage-Backed Securities Trades [Member]
Available-for-sale investment securities:
Forward mortgage-backed securities trades	41	(403)	143
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	$ 229	$ 450	$ 450

Fair Value Disclosures - Other

Fair Value Disclosures - Other Real Estate Owned (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Carrying value of other real estate owned prior to re-measurement		$ 526		$ 526
Write-downs included in gain (loss) on sale of other real estate owned	0	0	0	(126)
Other real estate owned, fair value		$ 400		$ 400

Fair Value Disclosures - Schedu

Fair Value Disclosures - Schedule of Estimated Fair Values and Carrying Values of All Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	$ 198,855	$ 207,835	$ 164,998
Interest-bearing deposits in banks	31,410	40,812	34,511
Interest-bearing time deposits in banks		1,458	1,458
Available-for-sale securities	3,397,156	3,158,777	3,144,367
Loans held for investment	4,048,427	3,902,434	3,816,169
Loans held for sale	40,499	21,672	18,496
Borrowings	400,155	468,706	380,760
IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset Derivative Fair Value	1,320	765	715
Forward Mortgage-Backed Securities Trades [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset Derivative Fair Value	41		143
Forward mortgage-backed securities trades		403
Carrying Value [Member] | Level 1 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	198,855	207,835	164,998
Interest-bearing deposits in banks	31,410	40,812	34,511
Deposits with no stated maturities	5,969,491	5,738,228	5,694,615
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	29,606	36,765	28,990
Deposits with stated maturities	428,192	442,161	450,667
Borrowings	400,155	468,706	380,760
Accrued interest payable	746	408	303
Carrying Value [Member] | Level 2 Inputs [Member] | IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset Derivative Fair Value	1,320	765	715
Carrying Value [Member] | Level 2 Inputs [Member] | Forward Mortgage-Backed Securities Trades [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Forward mortgage-backed securities trades	41	(403)	143
Carrying Value [Member] | Levels 1 and 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale securities	3,397,156	3,158,777	3,144,367
Carrying Value [Member] | Level 3 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for investment	4,048,427	3,902,434	3,816,169
Loans held for sale	40,499	21,672	18,496
Estimated Fair Value [Member] | Level 1 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	198,855	207,835	164,998
Interest-bearing deposits in banks	31,410	40,812	34,511
Deposits with no stated maturities	5,969,491	5,738,228	5,694,615
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	29,606	36,765	28,990
Deposits with stated maturities	429,522	441,727	450,409
Borrowings	400,155	468,706	380,760
Accrued interest payable	746	408	303
Estimated Fair Value [Member] | Level 2 Inputs [Member] | IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset Derivative Fair Value	1,320	765	715
Estimated Fair Value [Member] | Level 2 Inputs [Member] | Forward Mortgage-Backed Securities Trades [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Forward mortgage-backed securities trades	41	(403)	143
Estimated Fair Value [Member] | Levels 1 and 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale securities	3,397,156	3,158,777	3,144,367
Estimated Fair Value [Member] | Level 3 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for investment	4,068,755	3,947,391	3,857,059
Loans held for sale	$ 40,542	$ 21,779	$ 18,517

Recently Issued Authoritative_2

Recently Issued Authoritative Accounting Guidance - Additional Information (Detail) - USD ($)	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2018	Sep. 30, 2019	Dec. 31, 2017
Summary Of Significant Accounting Policies [Line Items]
Federal statutory tax rate		21.00%	35.00%
Accounting Standards Update 2018-02 [Member]
Summary Of Significant Accounting Policies [Line Items]
Reclassification of standard tax debit within accumulated other comprehensive income to retained earnings	$ 5,759,000

Acquisition and Proposed Acqu_3

Acquisition and Proposed Acquisition - Additional Information (Detail) - USD ($)	Sep. 19, 2019	Jan. 02, 2018	Oct. 12, 2017	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Business Acquisition [Line Items]
Fair value of total loans				$ 266,327,000
Fair value of purchased credit impaired loans				25,717,000		$ 27,534,000	$ 25,587,000
Contractual amounts				34,930,000		36,614,000	33,939,000
Purchased Credit Impaired Loans [Member]
Business Acquisition [Line Items]
Contractual amounts				605,000		$ 1,157,000	$ 3,898,000
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
Deposits				341,902,000
Total identifiable assets acquired				368,023,000
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
The Bank And Trust Bancshares [Member]
Business Acquisition [Line Items]
Payment for all outstanding shares of acquired entity by shares	6,275,806
Fair value of total loans					$ 445,600,000
Deposits					538,200,000
Total identifiable assets acquired					$ 624,500,000

Acquisition and Proposed Acqu_4

Acquisition and Proposed 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 and Proposed Acqu_5

Acquisition and Proposed 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 and Proposed Acqu_6

Acquisition and Proposed Acquisition - Schedule of Preliminary Estimated Fair Value Amounts Assigned to Major Asset and Liability Categories at Acquisition Date (Detail) $ in Thousands	Sep. 30, 2019USD ($)
Business Acquisition [Line Items]
Loans	$ 266,327
FBC Bancshares, Inc. and First Bank, N.A. [Member]
Business Acquisition [Line Items]
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
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