Southside Bancshares (SBSI) 10-Q 1 Aug 19 2019 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2019	Jul. 29, 2019
Cover page.
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2019
Document Transition Report	false
Entity File Number	0-12247
Entity Registrant Name	SOUTHSIDE BANCSHARES INC
Entity Central Index Key	0000705432
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Entity Incorporation, State or Country Code	TX
Entity Tax Identification Number	75-1848732
Entity Address, Address Line One	1201 S. Beckham Avenue,
Entity Address, City or Town	Tyler,
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	75701
City Area Code	903
Local Phone Number	531-7111
Title of 12(b) Security	Common Stock, $1.25 par value
Trading Symbol	SBSI
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		33,756,168
Amendment Flag	false

CONSOLIDATED BALANCE SHEETS (UN

CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($) $ in Thousands		Jun. 30, 2019	Dec. 31, 2018
ASSETS
Cash and due from banks		$ 77,319	$ 87,375
Interest earning deposits		54,642	23,884
Federal funds sold		560	9,460
Total cash and cash equivalents		132,521	120,719
Securities available for sale, at estimated fair value		2,088,787	1,989,436
Securities held to maturity, at carrying value (estimated fair value of $151,307 and $159,781, respectively)		147,091	162,931
Federal Home Loan Bank stock, at cost		44,718	32,583
Equity investments		12,374	12,093
Loans held for sale		1,812	601
Loans:
Loans		3,460,143	3,312,799
Less: Allowance for loan losses	[1]	(24,705)	(27,019)
Net Loans		3,435,438	3,285,780
Premises and equipment, net		140,105	135,972
Operating lease right-of-use assets		9,812	0
Goodwill		201,116	201,116
Other intangible assets, net		15,471	17,779
Interest receivable		25,167	27,287
Deferred tax asset, net		0	9,776
Unsettled issuances of brokered certificates of deposit		0	15,236
Bank owned life insurance		99,294	98,160
Other assets		19,164	14,025
Total assets		6,372,870	6,123,494
Deposits:
Noninterest bearing		1,028,861	994,680
Interest bearing		3,450,395	3,430,350
Total deposits		4,479,256	4,425,030
Other borrowings		26,064	36,810
Federal Home Loan Bank borrowings		823,757	719,065
Subordinated notes, net of unamortized debt issuance costs	[2]	98,490	98,407
Trust preferred subordinated debentures, net of unamortized debt issuance costs		60,248	60,246
Deferred tax liability, net		5,029	0
Unsettled trades to purchase securities		38,569	6,378
Operating lease liabilities		10,204	0
Other liabilities		43,488	46,267
Total liabilities		5,585,105	5,392,203
Off-balance-sheet arrangements, commitments and contingencies (Note 14)
Shareholders’ equity:
Common stock: ($1.25 par value, 80,000,000 shares authorized, 37,866,359 shares issued at June 30, 2019 and 37,845,224 shares issued at December 31, 2018)		47,333	47,307
Paid-in capital		764,220	762,470
Retained earnings		65,183	64,797
Treasury stock: (shares at cost, 4,117,595 at June 30, 2019 and 4,120,475 at December 31, 2018)		(93,906)	(93,055)
Accumulated other comprehensive income (loss)		4,935	(50,228)
Total shareholders’ equity		787,765	731,291
Total liabilities and shareholders’ equity		$ 6,372,870	$ 6,123,494
[1]	The allowance for loan losses recorded on purchased credit impaired (“PCI”) loans totaled $139,000 and $302,000 as of June 30, 2019 and December 31, 2018 , respectively.
[2]	This debt consists of subordinated notes with a remaining maturity greater than one year that qualify under the risk-based capital guidelines as Tier 2 capital, subject to certain limitations.

CONSOLIDATED BALANCE SHEETS (_2

CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Held-to-maturity Securities, Other Disclosure Items [Abstract]
Securities held to maturity, fair value	$ 151,307	$ 159,781
Shareholders' equity:
Common stock, par value (in dollars per share)	$ 1.25	$ 1.25
Common stock, shares authorized (in shares)	80,000,000	80,000,000
Common stock, shares issued (in shares)	37,866,359	37,845,224
Treasury stock (in shares)	4,117,595	4,120,475

CONSOLIDATED STATEMENTS OF INCO

CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Interest income:
Loans		$ 42,982	$ 39,301	$ 84,601	$ 78,131
Taxable investment securities		27	51	55	278
Tax-exempt investment securities		3,527	6,353	7,645	12,734
Mortgage-backed securities		13,246	10,210	25,720	21,104
Federal Home Loan Bank stock and equity investments		440	411	795	825
Other interest earning assets		450	471	883	919
Total interest income		60,672	56,797	119,699	113,991
Interest expense:
Deposits		11,457	8,581	22,698	16,032
Federal Home Loan Bank borrowings		3,899	3,007	8,356	6,639
Subordinated notes		1,410	1,407	2,810	2,805
Trust preferred subordinated debentures		718	658	1,447	1,227
Other borrowings		57	33	132	44
Total interest expense		17,541	13,686	35,443	26,747
Net interest income		43,131	43,111	84,256	87,244
Provision for loan losses	[1]	2,506	1,281	1,588	5,016
Net interest income after provision for loan losses		40,625	41,830	82,668	82,228
Noninterest income:
Deposit services		6,652	6,261	12,638	12,440
Net gain (loss) on sale of securities available for sale		416	(332)	672	(1,159)
Gain on sale of loans		181	173	274	288
Trust fees		1,520	1,931	3,061	3,691
Bank owned life insurance		559	1,185	1,103	1,817
Brokerage services		477	506	994	956
Other		1,449	1,283	2,050	2,584
Total noninterest income		11,254	11,007	20,792	20,617
Noninterest expense:
Salaries and employee benefits		17,891	16,633	35,937	35,192
Net occupancy		3,289	3,360	6,464	6,943
Acquisition expense		0	1,026	0	1,858
Advertising, travel & entertainment		733	775	1,580	1,460
ATM expense		246	243	426	589
Professional fees		1,069	952	2,383	2,022
Software and data processing		1,086	939	2,162	1,962
Communications		489	478	976	1,016
FDIC insurance		437	484	859	981
Amortization of intangibles		1,129	1,328	2,308	2,706
Other		3,331	3,056	6,232	6,212
Total noninterest expense		29,700	29,274	59,327	60,941
Income before income tax expense		22,179	23,563	44,133	41,904
Income tax expense		3,569	3,360	6,706	5,450
Net income		$ 18,610	$ 20,203	$ 37,427	$ 36,454
Earnings per common share - basic (in dollars per share)		$ 0.55	$ 0.58	$ 1.11	$ 1.04
Earnings per common share - diluted (in dollars per share)		0.55	0.57	1.11	1.04
Dividends paid per common share (in dollars per share)		$ 0.31	$ 0.30	$ 0.61	$ 0.58
[1]	Of the $2.5 million and $1.6 million provision for loan losses for the three and six months ended June 30, 2019 , $111,000 and $163,000 related to provision expense reversed on PCI loans, respectively. Of the $1.3 million and $5.0 million recorded in provision for loan losses for the three and six months ended June 30, 2018 , $358,000 related to provision expense on PCI loans.

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 18,610	$ 20,203	$ 37,427	$ 36,454
Securities available for sale and transferred securities:
Change in unrealized holding gain (loss) on available for sale securities during the period	32,196	(10,371)	78,822	(48,154)
Unrealized net gain on securities transferred from held to maturity to available for sale under the transition guidance enumerated in ASU 2017-12	0	0	0	11,881
Change in net unrealized loss on securities transferred from held to maturity to available for sale	0	0	0	401
Reclassification adjustment for amortization related to available for sale and held to maturity debt securities	80	1,252	571	1,390
Reclassification adjustment for net (gain) loss on sale of available for sale securities, included in net income	(416)	332	(672)	1,159
Derivatives:
Change in net unrealized (loss) gain on effective cash flow hedge interest rate swap derivatives	(5,653)	1,725	(8,773)	5,970
Reclassification adjustment of net gain related to derivatives designated as cash flow hedge	(642)	(331)	(1,310)	(458)
Pension plans:
Amortization of net actuarial loss and prior service credit, included in net periodic benefit cost	648	618	1,189	1,091
Other comprehensive income (loss), before tax	26,213	(6,775)	69,827	(26,720)
Income tax (expense) benefit related to items of other comprehensive income (loss)	(5,505)	1,423	(14,664)	5,611
Other comprehensive income (loss), net of tax	20,708	(5,352)	55,163	(21,109)
Comprehensive income	$ 39,318	$ 14,851	$ 92,590	$ 15,345

CONSOLIDATED STATEMENTS OF CHAN

CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Thousands	Total	Common Stock	Paid In Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income (Loss)
Beginning balance, net of tax at Dec. 31, 2017	$ 754,140	$ 47,253	$ 757,439	$ 32,851	$ (47,105)	$ (36,298)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	16,251			16,251
Other comprehensive income (loss)	(15,757)					(15,757)
Issuance of common stock for dividend reinvestment plan (10,035, 10,397, 10,565 and 10,570 shares, respectively)	353	12	341
Stock compensation expense	456		456
Net issuance of common stock under employee stock plans (42,179, 20,872, 23,617 and 20,115 shares, respectively)	761	0	417	(25)	369
Cash dividends paid on common stock ($0.28, $0.30, $0.30 and $0.31 per share, respectively)	(9,808)			(9,808)
Ending balance, net of tax at Mar. 31, 2018	746,396	47,265	758,653	39,184	(46,736)	(51,970)
Beginning balance, net of tax at Dec. 31, 2017	754,140	47,253	757,439	32,851	(47,105)	(36,298)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	36,454
Other comprehensive income (loss)	(21,109)
Ending balance, net of tax at Jun. 30, 2018	751,810	47,278	759,562	48,843	(46,551)	(57,322)
Beginning balance, net of tax at Mar. 31, 2018	746,396	47,265	758,653	39,184	(46,736)	(51,970)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	20,203			20,203
Other comprehensive income (loss)	(5,352)					(5,352)
Issuance of common stock for dividend reinvestment plan (10,035, 10,397, 10,565 and 10,570 shares, respectively)	367	13	354
Stock compensation expense	509		509
Net issuance of common stock under employee stock plans (42,179, 20,872, 23,617 and 20,115 shares, respectively)	204		46	(27)	185
Cash dividends paid on common stock ($0.28, $0.30, $0.30 and $0.31 per share, respectively)	(10,517)			(10,517)
Ending balance, net of tax at Jun. 30, 2018	751,810	47,278	759,562	48,843	(46,551)	(57,322)
Beginning balance, net of tax at Dec. 31, 2018	731,291	47,307	762,470	64,797	(93,055)	(50,228)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	18,817			18,817
Other comprehensive income (loss)	34,455					34,455
Issuance of common stock for dividend reinvestment plan (10,035, 10,397, 10,565 and 10,570 shares, respectively)	355	13	342
Purchase of common stock (40,852 shares)	(1,325)				(1,325)
Stock compensation expense	661		661
Net issuance of common stock under employee stock plans (42,179, 20,872, 23,617 and 20,115 shares, respectively)	338	0	109	(32)	261
Cash dividends paid on common stock ($0.28, $0.30, $0.30 and $0.31 per share, respectively)	(10,107)			(10,107)
Ending balance, net of tax at Mar. 31, 2019	758,033	47,320	763,582	57,023	(94,119)	(15,773)
Beginning balance, net of tax at Dec. 31, 2018	731,291	47,307	762,470	64,797	(93,055)	(50,228)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	37,427
Other comprehensive income (loss)	55,163
Ending balance, net of tax at Jun. 30, 2019	787,765	47,333	764,220	65,183	(93,906)	4,935
Beginning balance, net of tax at Mar. 31, 2019	758,033	47,320	763,582	57,023	(94,119)	(15,773)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	18,610			18,610
Other comprehensive income (loss)	20,708					20,708
Issuance of common stock for dividend reinvestment plan (10,035, 10,397, 10,565 and 10,570 shares, respectively)	349	13	336
Stock compensation expense	571		571
Net issuance of common stock under employee stock plans (42,179, 20,872, 23,617 and 20,115 shares, respectively)	(53)	0	(269)	3	213
Cash dividends paid on common stock ($0.28, $0.30, $0.30 and $0.31 per share, respectively)	(10,453)			(10,453)
Ending balance, net of tax at Jun. 30, 2019	$ 787,765	$ 47,333	$ 764,220	$ 65,183	$ (93,906)	$ 4,935

CONSOLIDATED STATEMENTS OF CH_2

CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (UNAUDITED) (Parenthetical) - $ / shares	3 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018
Statement of Stockholders' Equity [Abstract]
Issuance of common stock - DRIP (in shares)	10,570	10,565	10,397	10,035
Dividends paid on common stock (in dollars per share)	$ 0.31	$ 0.30	$ 0.30	$ 0.28
Treasury stock shares acquired (in shares)		40,852
Net issuance of common stock under employee stock plans (in shares)	20,115	23,617	20,872	42,179

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018
OPERATING ACTIVITIES:
Net income		$ 37,427	$ 36,454
Adjustments to reconcile net income to net cash provided by operations:
Depreciation and net amortization		6,053	7,078
Securities premium amortization (discount accretion), net		5,946	7,557
Loan (discount accretion) premium amortization, net		(940)	(1,712)
Provision for loan losses	[1]	1,588	5,016
Stock compensation expense		1,232	965
Deferred tax expense		142	2,438
Net (gain) loss on sale of securities available for sale		(672)	1,159
Net loss on premises and equipment		220	132
Gross proceeds from sales of loans held for sale		9,745	13,578
Gross originations of loans held for sale		(10,956)	(12,159)
Net (gain) loss on other real estate owned		(90)	258
Net change in:
Interest receivable		2,120	1,391
Other assets		(89)	16,612
Interest payable		1,617	247
Other liabilities		(18,527)	(8,484)
Net cash provided by operating activities		34,816	70,530
Securities available for sale:
Purchases		(784,921)	(195,005)
Sales		713,946	315,656
Maturities, calls and principal repayments		60,288	78,042
Securities held to maturity:
Maturities, calls and principal repayments		15,714	1,767
Proceeds from redemption of Federal Home Loan Bank stock and other investments		8,788	13,377
Purchases of Federal Home Loan Bank stock and other investments		(21,210)	(914)
Net loan (originations) paydowns		(150,798)	19,722
Purchases of premises and equipment		(7,900)	(5,154)
Proceeds from sales of premises and equipment		34	1,905
Proceeds from sales of other real estate owned		490	771
Proceeds from sales of repossessed assets		227	287
Net cash (used in) provided by investing activities		(165,342)	230,454
FINANCING ACTIVITIES:
Net change in deposits		69,276	(6,866)
Net decrease in federal funds purchased and repurchase agreements		(10,746)	(1,211)
Proceeds from Federal Home Loan Bank borrowings		2,959,200	1,718,000
Repayment of Federal Home Loan Bank borrowings		(2,854,506)	(1,958,890)
Proceeds from stock option exercises		534	1,084
Cash paid to tax authority related to tax withholding on share-based awards		(249)	(119)
Purchase of common stock		(1,325)	0
Proceeds from the issuance of common stock for dividend reinvestment plan		704	720
Cash dividends paid		(20,560)	(20,325)
Net cash provided by (used in) financing activities		142,328	(267,607)
Net increase in cash and cash equivalents		11,802	33,377
Cash and cash equivalents at beginning of period		120,719	198,692
Cash and cash equivalents at end of period		132,521	232,069
SUPPLEMENTAL DISCLOSURES FOR CASH FLOW INFORMATION:
Interest paid		33,826	26,499
Income taxes paid		3,500	0
SUPPLEMENTAL DISCLOSURES OF NONCASH INVESTING AND FINANCING ACTIVITIES:
Loans transferred to other repossessed assets and real estate through foreclosure		505	764
Loans transferred from portfolio to held for sale		0	3,984
Transfer of held to maturity securities to available for sale securities		0	743,421
Adjustment to pension liability		(1,189)	(1,091)
Unsettled trades to purchase securities		$ (38,569)	$ (2,279)
[1]	Of the $2.5 million and $1.6 million provision for loan losses for the three and six months ended June 30, 2019 , $111,000 and $163,000 related to provision expense reversed on PCI loans, respectively. Of the $1.3 million and $5.0 million recorded in provision for loan losses for the three and six months ended June 30, 2018 , $358,000 related to provision expense on PCI loans.

Summary of Significant Accounti

Summary of Significant Accounting and Reporting Policies	6 Months Ended
	Jun. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Summary of Significant Accounting and Reporting Policies	Summary of Significant Accounting and Reporting Policies Basis of Presentation In this report, the words “the Company,” “we,” “us,” and “our” refer to the combined entities of Southside Bancshares, Inc. and its subsidiaries, including Southside Bank. The words “Southside” and “Southside Bancshares” refer to Southside Bancshares, Inc. The words “Southside Bank” and “the Bank” refer to Southside Bank. “Diboll” refers to Diboll State Bancshares, Inc., a bank holding company and its wholly-owned subsidiary, First Bank & Trust East Texas, acquired by Southside on November 30, 2017. The accompanying unaudited consolidated financial statements have been prepared in accordance with United States (“U.S.”) generally accepted accounting principles (“GAAP”) for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, not all information required by GAAP for complete financial statements is included in these interim statements. In the opinion of management, all adjustments necessary for a fair presentation of such financial statements have been included. Such adjustments consisted only of normal recurring items. The preparation of these consolidated financial statements in accordance with GAAP requires the use of management’s estimates. These estimates are subjective in nature and involve matters of judgment. Actual amounts could differ from these estimates. Interim results are not necessarily indicative of results for a full year. These financial statements should be read in conjunction with the financial statements and notes thereto in our Annual Report on Form 10-K for the year ended December 31, 2018 . Accounting Changes and Reclassifications Certain prior period amounts may be reclassified to conform to current year presentation. Debt Securities We adopted Accounting Standards Update (“ASU”) 2017-08, “Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities,” on January 1, 2019, the effective date of the guidance. Under previous GAAP, premiums on callable debt securities were generally amortized over the contractual life of the security. ASU 2017-08 requires the premium on callable debt securities to be amortized to the earliest call date. If the debt security is not called at the earliest call date, the holder of the debt security would be required to reset the effective yield on the debt security based on the payment terms required by the debt security. The guidance requires companies to apply the requirements on a modified retrospective basis through a cumulative-effect adjustment directly to retained earnings as of the beginning of the period of adoption. Adoption of this guidance on January 1, 2019, resulted in a cumulative-effect adjustment to reduce retained earnings by $16.5 million , before tax. Subsequent to January 1, 2019, we sold the majority of the securities impacted by ASU 2017-08, and thus, the standard did not materially impact our consolidated net income. Leases We evaluate our contracts at inception to determine if an arrangement is or contains a lease. Operating leases are included in operating lease right-of-use (“ROU”) assets and operating lease liabilities in our consolidated balance sheets. The Company has no finance leases. ROU assets represent our right to use an underlying asset for the lease term, and lease liabilities represent our obligation to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at commencement date based on the present value of lease payments over the lease term. Our leases do not provide an implicit rate, so we use our incremental borrowing rate based on the information available at commencement date in determining the present value of lease payments. The incremental borrowing rate is reevaluated upon lease modification. The operating lease ROU asset also includes any initial direct costs and prepaid lease payments made less any lease incentives. Our lease terms may include options to extend or terminate the lease when it is reasonably certain that we will exercise that option. We adopted ASU 2016-02, “Leases (Topic 842),” on January 1, 2019, the effective date of the guidance, using the practical expedient transition method whereby we did not revise comparative period information or disclosure. The new standard requires lessees to record assets and liabilities on the balance sheet for all leases with terms longer than 12 months. We elected the package of practical expedients permitted under the transition guidance within the new standard, which among other things, allows us to carryforward the historical lease classification. We also elected certain optional practical expedients including the hindsight practical expedient under which we considered the actual outcomes of lease renewals and terminations when measuring the lease term at adoption, and we made an accounting policy election to keep leases with an initial term of 12 months or less off of the balance sheet. We recognize these lease payments in the consolidated statements of income on a straight-line basis over the lease term. We have lease agreements with lease and non-lease components, and we have elected the practical expedient to account for these as a single lease component. Our operating leases relate primarily to bank branches and office space. In conjunction with the adoption of ASU 2016-02 on January 1, 2019, we recognized operating lease liabilities of $10.1 million and related lease assets of $9.8 million on our balance sheet. The difference between the lease assets and lease liabilities primarily consists of deferred rent liabilities reclassified upon adoption to reduce the measurement of the lease assets. The standard did not materially impact our consolidated net income and had no impact on cash flows. Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, “Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments” (“CECL”). ASU 2016-13 introduces an approach based on expected losses to estimate credit losses on certain types of financial instruments. ASU 2016-13 also modifies the impairment model for AFS debt securities and provides for a simplified accounting model for purchased financial assets with credit deterioration since their origination. ASU 2016-13 is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. Early adoption is permitted for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. The guidance requires companies to apply the requirements in the year of adoption through a cumulative-effect adjustment with some aspects of the update requiring a prospective transition approach. We are currently evaluating the potential impact of the pending adoption of ASU 2016-13 on our consolidated financial statements. We plan to adopt ASU 2016-13 on January 1, 2020, the effective date. We have developed a project plan, assigned a project team to complete the analysis needed to implement the guidance and engaged a third party vendor solution to assist with the application of ASU 2016-13. During the second quarter of 2019, the project team entered the parallel phase of the project during which the team will run parallel models to evaluate system processes, data generation and refine aspects of the transition to CECL. In January 2017, the FASB issued ASU 2017-04, “Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment.” ASU 2017-04 is intended to simplify goodwill impairment testing by eliminating the second step of the analysis which requires the calculation of the implied fair value of goodwill to measure a goodwill impairment charge. The update requires entities to compare the fair value of a reporting unit with its carrying amount and recognize an impairment charge for any amount by which the carrying amount exceeds the reporting unit’s fair value, to the extent that the loss recognized does not exceed the amount of goodwill allocated to that reporting unit. ASU 2017-04 is effective for annual and interim goodwill impairment tests performed in periods beginning after December 15, 2019. Early adoption is permitted for annual and interim goodwill impairment testing dates after January 1, 2017. The guidance requires companies to apply the requirements prospectively in the year of adoption. ASU 2017-04 is not expected to have a material impact on our consolidated financial statements.

Acquisition

Acquisition	6 Months Ended
	Jun. 30, 2019
Business Combinations [Abstract]
Business Combination Disclosure	Acquisition On November 30, 2017 , we acquired 100% of the outstanding stock of Diboll State Bancshares, Inc. and its wholly-owned subsidiary First Bank & Trust East Texas (collectively, “Diboll”) headquartered in Diboll, Texas. Diboll operated 17 banking offices in Diboll and surrounding areas. We acquired Diboll to further expand our presence in the East Texas market. The total merger consideration for the Diboll merger was $224.3 million . The operations of Diboll were merged into the Company as of the date of the acquisition. The Company acquired loans, investment securities and deposits with fair values of $621.3 million , $234.4 million and $899.3 million , respectively, at the acquisition date. During 2017, the Company recognized goodwill of $109.7 million . As of June 30, 2019, total goodwill related to the Diboll acquisition was $109.6 million , after recording measurement period adjustments during the third quarter of 2018. The goodwill resulting from the acquisition represents the value expected from the expansion of our markets into the Southeast Texas region and the enhancement of our operations through customer synergies and efficiencies, thereby providing enhanced customer service. Goodwill of $201.1 million as of June 30, 2019 and December 31, 2018 and is not expected to be deductible for tax purposes. We recognized a core deposit intangible of $14.7 million and a trust relationship intangible of $5.4 million , at the date of acquisition, which we are amortizing using an accelerated method over a 9 - and 13 -year weighted average amortization period, respectively, consistent with expected future cash flows.

Earnings Per Share

Earnings Per Share	6 Months Ended
	Jun. 30, 2019
Earnings Per Share [Abstract]
Earnings Per Share	Earnings Per Share Earnings per share on a basic and diluted basis are calculated as follows (in thousands, except per share amounts): Three Months Ended Six Months Ended 2019 2018 2019 2018 Basic and Diluted Earnings: Net income $ 18,610 $ 20,203 $ 37,427 $ 36,454 Basic weighted-average shares outstanding 33,726 35,062 33,711 35,042 Add: Stock awards 150 171 151 175 Diluted weighted-average shares outstanding 33,876 35,233 33,862 35,217 Basic earnings per share: Net Income $ 0.55 $ 0.58 $ 1.11 $ 1.04 Diluted earnings per share: Net Income $ 0.55 $ 0.57 $ 1.11 $ 1.04 For the three and six months ended June 30, 2019 , there were approximately 480,000 and 485,000 anti-dilutive shares, respectively. For the three and six months ended June 30, 2018 , there were approximately 246,000 and 216,000

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	6 Months Ended
	Jun. 30, 2019
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) The changes in accumulated other comprehensive income (loss) by component are as follows (in thousands): Three Months Ended June 30, 2019 Pension Plans Unrealized Gains (Losses) on Securities Unrealized Gains (Losses) on Derivatives Net Prior Service (Cost) Credit Net Gain (Loss) Total Beginning balance, net of tax $ 5,901 $ 4,153 $ (140 ) $ (25,687 ) $ (15,773 ) Other comprehensive income (loss): Other comprehensive income (loss) before reclassifications 32,196 (5,653 ) — — 26,543 Reclassification adjustments included in net income (336 ) (642 ) (3 ) 651 (330 ) Income tax (expense) benefit (6,691 ) 1,322 1 (137 ) (5,505 ) Net current-period other comprehensive income (loss), net of tax 25,169 (4,973 ) (2 ) 514 20,708 Ending balance, net of tax $ 31,070 $ (820 ) $ (142 ) $ (25,173 ) $ 4,935 Six Months Ended June 30, 2019 Pension Plans Unrealized Gains (Losses) on Securities Unrealized Gains (Losses) on Derivatives Net Prior Net Gain (Loss) Total Beginning balance, net of tax $ (31,120 ) $ 7,146 $ (139 ) $ (26,115 ) $ (50,228 ) Other comprehensive income (loss): Other comprehensive income (loss) before reclassifications 78,822 (8,773 ) — — 70,049 Reclassification adjustments included in net income (101 ) (1,310 ) (4 ) 1,193 (222 ) Income tax (expense) benefit (16,531 ) 2,117 1 (251 ) (14,664 ) Net current-period other comprehensive income (loss), net of tax 62,190 (7,966 ) (3 ) 942 55,163 Ending balance, net of tax $ 31,070 $ (820 ) $ (142 ) $ (25,173 ) $ 4,935 Three Months Ended June 30, 2018 Pension Plans Unrealized Gains (Losses) on Securities Unrealized Gains (Losses) on Derivatives Net Prior Service (Cost) Credit Net Gain (Loss) Total Beginning balance, net of tax $ (35,594 ) $ 9,652 $ (134 ) $ (25,894 ) $ (51,970 ) Other comprehensive income (loss): Other comprehensive (loss) income before reclassifications (10,371 ) 1,725 — — (8,646 ) Reclassification adjustments included in net income 1,584 (331 ) (2 ) 620 1,871 Income tax benefit (expense) 1,845 (293 ) 1 (130 ) 1,423 Net current-period other comprehensive (loss) income, net of tax (6,942 ) 1,101 (1 ) 490 (5,352 ) Ending balance, net of tax $ (42,536 ) $ 10,753 $ (135 ) $ (25,404 ) $ (57,322 ) Six Months Ended June 30, 2018 Pension Plans Unrealized Gains (Losses) on Securities Unrealized Gains (Losses) on Derivatives Net Prior Service (Cost) Credit Net Gain (Loss) Total Beginning balance, net of tax $ (16,295 ) $ 6,399 $ (133 ) $ (26,269 ) $ (36,298 ) Cumulative effect of ASU 2016-01 (1) 85 — — — 85 Adjusted beginning balance, net of tax (16,210 ) 6,399 (133 ) (26,269 ) (36,213 ) Other comprehensive income (loss): Other comprehensive (loss) income before reclassifications (35,872 ) 5,970 — — (29,902 ) Reclassification adjustments included in net income 2,549 (458 ) (4 ) 1,095 3,182 Income tax benefit (expense) 6,997 (1,158 ) 2 (230 ) 5,611 Net current-period other comprehensive (loss) income, net of tax (26,326 ) 4,354 (2 ) 865 (21,109 ) Ending balance, net of tax $ (42,536 ) $ 10,753 $ (135 ) $ (25,404 ) $ (57,322 ) (1) The Company adopted ASU 2016-01 on January 1, 2018. This amount includes a reclassification for the cumulative adjustment to retained earnings of $107,000 ( $85,000 , net of tax). The reclassification adjustments out of accumulated other comprehensive income (loss) included in net income are presented below (in thousands): Three Months Ended Six Months Ended 2019 2018 2019 2018 Unrealized losses on securities transferred: Amortization of unrealized losses (1) $ (80 ) $ (1,252 ) $ (571 ) $ (1,390 ) Tax benefit 17 263 120 292 Net of tax (63 ) (989 ) (451 ) (1,098 ) Unrealized gains and losses on available for sale securities: Realized net gain (loss) on sale of securities (2) 416 (332 ) 672 (1,159 ) Tax (expense) benefit (87 ) 70 (141 ) 243 Net of tax 329 (262 ) 531 (916 ) Derivatives: Realized net gain on interest rate swap derivatives (3) 621 309 1,267 415 Tax expense (130 ) (65 ) (266 ) (87 ) Net of tax 491 244 1,001 328 Amortization of unrealized gains on terminated interest rate swap derivatives (3) 21 22 43 43 Tax expense (4 ) (5 ) (9 ) (9 ) Net of tax 17 17 34 34 Amortization of pension plan: Net actuarial loss (4) (651 ) (620 ) (1,193 ) (1,095 ) Prior service credit (4) 3 2 4 4 Total before tax (648 ) (618 ) (1,189 ) (1,091 ) Tax benefit 136 129 250 228 Net of tax (512 ) (489 ) (939 ) (863 ) Total reclassifications for the period, net of tax $ 262 $ (1,479 ) $ 176 $ (2,515 ) (1) Included in interest income on the consolidated statements of income. (2) Listed as net gain (loss) on sale of securities available for sale on the consolidated statements of income. (3) Included in interest expense for Federal Home Loan Bank of Dallas (“FHLB”) borrowings on the consolidated statements of income. (4) These accumulated other comprehensive income components are included in the computation of net periodic pension cost (income) presented in “Note 9 - Employee Benefit Plans.”

Securities

Securities	6 Months Ended
	Jun. 30, 2019
Investments, Debt and Equity Securities [Abstract]
Securities	Securities Debt securities The amortized cost, gross unrealized gains and losses and estimated fair value of investment and mortgage-backed securities available for sale (“AFS”) and held to maturity (“HTM”) as of June 30, 2019 and December 31, 2018 are reflected in the tables below (in thousands): June 30, 2019 Amortized Gross Unrealized Gross Unrealized Estimated AVAILABLE FOR SALE Cost Gains Losses Fair Value Investment securities: State and political subdivisions $ 512,575 $ 16,758 $ 478 $ 528,855 Other stocks and bonds 3,000 — 41 2,959 Mortgage-backed securities: (1) Residential 1,296,888 22,944 846 1,318,986 Commercial 233,044 4,963 20 237,987 Total $ 2,045,507 $ 44,665 $ 1,385 $ 2,088,787 HELD TO MATURITY Investment securities: State and political subdivisions $ 3,018 $ 36 $ — $ 3,054 Mortgage-backed securities: (1) Residential 59,756 2,496 144 62,108 Commercial 84,317 1,984 156 86,145 Total $ 147,091 $ 4,516 $ 300 $ 151,307 December 31, 2018 Amortized Gross Unrealized Gross Unrealized Estimated AVAILABLE FOR SALE Cost Gains Losses Fair Value Investment securities: State and political subdivisions $ 728,142 $ 6,115 $ 17,656 $ 716,601 Other stocks and bonds 3,000 — 291 2,709 Mortgage-backed securities: (1) Residential 738,585 3,498 9,111 732,972 Commercial 543,758 941 7,545 537,154 Total $ 2,013,485 $ 10,554 $ 34,603 $ 1,989,436 HELD TO MATURITY Investment securities: State and political subdivisions $ 3,083 $ 5 $ 42 $ 3,046 Mortgage-backed securities: (1) Residential 59,655 154 1,140 58,669 Commercial 100,193 201 2,328 98,066 Total $ 162,931 $ 360 $ 3,510 $ 159,781 (1) All mortgage-backed securities issued and/or guaranteed by U.S. government agencies or U.S. government-sponsored enterprises. From time to time, we have transferred securities from AFS to HTM due to overall balance sheet strategies. The remaining net unamortized, unrealized loss on the transferred securities included in AOCI in the accompanying balance sheets totaled $4.0 million ( $3.1 million , net of tax) at June 30, 2019 and $15.3 million ( $12.1 million , net of tax) at December 31, 2018 . Any net unrealized gain or loss on the transferred securities included in AOCI at the time of transfer will be amortized over the remaining life of the underlying security as an adjustment to the yield on those securities. Securities transferred with losses included in AOCI continue to be included in management’s assessment for other-than-temporary impairment for each individual security. There were no securities transferred from AFS to HTM during the six months ended June 30, 2019 or the year ended December 31, 2018 . On January 1, 2019, we adopted ASU 2017-08, “Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities,” and in conjunction with the adoption recognized a cumulative effect adjustment to reduce retained earnings by $16.5 million , before tax, related to premiums on callable debt securities. Prior to January 1, 2019, premiums were amortized over the contractual life of the security. With the adoption of ASU 2017-08, premiums on debt securities will be amortized to the earliest call date. The following tables represent the estimated fair value and unrealized loss on investment and mortgage-backed securities AFS and HTM as of June 30, 2019 and December 31, 2018 (in thousands): June 30, 2019 Less Than 12 Months More Than 12 Months Total Fair Value Unrealized Loss Fair Value Unrealized Loss Fair Value Unrealized Loss AVAILABLE FOR SALE Investment securities: State and political subdivisions $ 2,281 $ 10 $ 28,087 $ 468 $ 30,368 $ 478 Other stocks and bonds 2,959 41 — — 2,959 41 Mortgage-backed securities: Residential 629 2 91,649 844 92,278 846 Commercial — — 15,033 20 15,033 20 Total $ 5,869 $ 53 $ 134,769 $ 1,332 $ 140,638 $ 1,385 HELD TO MATURITY Mortgage-backed securities: Residential $ — $ — $ 2,579 $ 144 $ 2,579 $ 144 Commercial — — 14,701 156 14,701 156 Total $ — $ — $ 17,280 $ 300 $ 17,280 $ 300 December 31, 2018 Less Than 12 Months More Than 12 Months Total Fair Value Unrealized Fair Value Unrealized Fair Value Unrealized AVAILABLE FOR SALE Investment securities: State and political subdivisions $ 98,112 $ 899 $ 399,205 $ 16,757 $ 497,317 $ 17,656 Other stocks and bonds 2,709 291 — — 2,709 291 Mortgage-backed securities: Residential 5,552 27 488,334 9,084 493,886 9,111 Commercial 9,529 30 457,704 7,515 467,233 7,545 Total $ 115,902 $ 1,247 $ 1,345,243 $ 33,356 $ 1,461,145 $ 34,603 HELD TO MATURITY Investment securities: State and political subdivisions $ 235 $ 1 $ 2,022 $ 41 $ 2,257 $ 42 Mortgage-backed securities: Residential 4,826 60 51,046 1,080 55,872 1,140 Commercial 399 2 89,168 2,326 89,567 2,328 Total $ 5,460 $ 63 $ 142,236 $ 3,447 $ 147,696 $ 3,510 We review those securities in an unrealized loss position for significant differences between fair value and the cost basis to evaluate if a classification of other-than-temporary impairment is warranted. In estimating other-than-temporary impairment losses, management considers, among other things, the length of time and the extent to which the fair value has been less than cost and the financial condition and near-term prospects of the issuer. We consider an other-than-temporary impairment to have occurred when there is an adverse change in expected cash flows. When it is determined that a decline in fair value of AFS and HTM securities is other-than-temporary, the carrying value of the security is reduced to its estimated fair value, with a corresponding charge to earnings for the credit portion and a charge to other comprehensive income for the noncredit portion. Based upon the length of time and the extent to which fair value is less than cost, we believe that none of the securities with an unrealized loss have other-than-temporary impairment at June 30, 2019 . The majority of the securities in an unrealized loss position are highly rated Texas municipal securities and U.S. agency MBS where the unrealized loss is a direct result of the change in interest rates and spreads. For those securities in an unrealized loss position, we do not currently intend to sell the securities and it is not more likely than not that we will be required to sell the securities before the anticipated recovery of their amortized cost basis. To the best of management’s knowledge and based on our consideration of the qualitative factors associated with each security, there were no securities in our investment and MBS portfolio with an other-than-temporary impairment at June 30, 2019 . The following table reflects interest income recognized on securities for the periods presented (in thousands): Three Months Ended 2019 2018 U.S. Treasury $ — $ 23 State and political subdivisions 3,527 6,353 Other stocks and bonds 27 28 Mortgage-backed securities 13,246 10,210 Total interest income on securities $ 16,800 $ 16,614 Six Months Ended 2019 2018 U.S. Treasury $ — $ 131 U.S. government agency debentures — 89 State and political subdivisions 7,645 12,734 Other stocks and bonds 55 58 Mortgage-backed securities 25,720 21,104 Total interest income on securities $ 33,420 $ 34,116 There was a $672,000 net realized gain from the AFS securities portfolio for the six months ended June 30, 2019 , which consisted of $5.5 million in realized gains and $4.9 million in realized losses. There was a $1.2 million net realized loss from the AFS securities portfolio for the six months ended June 30, 2018 , which consisted of $2.7 million in realized losses and $1.5 million in realized gains. There were no sales from the HTM portfolio during the six months ended June 30, 2019 or 2018 . We calculate realized gains and losses on sales of securities under the specific identification method. The amortized cost and estimated fair value of AFS and HTM securities at June 30, 2019 , are presented below by contractual maturity (in thousands). Expected maturities may differ from contractual maturities because issuers may have the right to call or prepay obligations. MBS are presented in total by category due to the fact that MBS typically are issued with stated principal amounts, and the securities are backed by pools of mortgages that have loans with varying maturities. The characteristics of the underlying pool of mortgages, such as fixed-rate or adjustable-rate, as well as prepayment risk, are passed on to the security holder. The term of a mortgage-backed pass-through security thus approximates the term of the underlying mortgages and can vary significantly due to prepayments. June 30, 2019 Amortized Cost Fair Value AVAILABLE FOR SALE Investment securities: Due in one year or less $ 3,349 $ 3,363 Due after one year through five years 8,406 8,469 Due after five years through ten years 28,488 29,573 Due after ten years 475,332 490,409 515,575 531,814 Mortgage-backed securities 1,529,932 1,556,973 Total $ 2,045,507 $ 2,088,787 June 30, 2019 Amortized Cost Fair Value HELD TO MATURITY Investment securities: Due in one year or less $ 115 $ 115 Due after one year through five years 1,658 1,675 Due after five years through ten years 1,245 1,264 Due after ten years — — 3,018 3,054 Mortgage-backed securities: 144,073 148,253 Total $ 147,091 $ 151,307 Investment securities and MBS with carrying values of $949.2 million and $1.08 billion were pledged as of June 30, 2019 and December 31, 2018 , respectively, to collateralize FHLB borrowings, repurchase agreements and public funds or for other purposes as required by law. Equity Investments Equity investments on our consolidated balance sheets include Community Reinvestment Act funds with a readily determinable fair value as well as equity investments without readily determinable fair values. At June 30, 2019 and December 31, 2018 , we had equity investments recorded in our consolidated balance sheets of $12.4 million and $12.1 million , respectively. Any realized and unrealized gains and losses on equity investments are reported in income. Equity investments without readily determinable fair values are recorded at cost less any impairment, if any. The following is a summary of unrealized and realized gains and losses on equity investments recognized in other noninterest income in the consolidated statements of income during the three and six months ended June 30, 2019 and 2018 (in thousands): Three Months Ended Six Months Ended 2019 2018 2019 2018 Net gains (losses) recognized during the period on equity investments $ 87 $ (42 ) $ 163 $ (134 ) Less: Net gains (losses) recognized during the period on equity investments sold during the period — — — — Unrealized gains (losses) recognized during the reporting period on equity investments still held at the reporting date $ 87 $ (42 ) $ 163 $ (134 ) Equity investments are assessed quarterly for other-than-temporary impairment. Based upon that evaluation, management does no t consider any of our equity investments to be other-than-temporarily impaired at June 30, 2019 . FHLB Stock Our FHLB stock, which has limited marketability, is carried at cost and is assessed quarterly for other-than-temporary impairment. Based upon evaluation by management at June 30, 2019 , our FHLB stock was not impaired and thus was no t considered to be other-than-temporarily impaired.

Loans and Allowance for Probabl

Loans and Allowance for Probable Loan Losses	6 Months Ended
	Jun. 30, 2019
Receivables [Abstract]
Loans and Allowance for Probable Loan Losses	Loans and Allowance for Loan Losses Loans in the accompanying consolidated balance sheets are classified as follows (in thousands): June 30, 2019 December 31, 2018 Real estate loans: Construction $ 579,565 $ 507,732 1-4 family residential 782,073 794,499 Commercial 1,251,248 1,194,118 Commercial loans 389,521 356,649 Municipal loans 357,028 353,370 Loans to individuals 100,708 106,431 Total loans 3,460,143 3,312,799 Less: Allowance for loan losses (1) 24,705 27,019 Net loans $ 3,435,438 $ 3,285,780 (1) The allowance for loan losses recorded on purchased credit impaired (“PCI”) loans totaled $139,000 and $302,000 as of June 30, 2019 and December 31, 2018 , respectively. Construction Real Estate Loans Our construction loans are collateralized by property located primarily in or near the market areas we serve. A number of our construction loans will be owner occupied upon completion. Construction loans for non-owner occupied projects are financed, but these typically have cash flows from leases with tenants, secondary sources of repayment, and in some cases, additional collateral. Our construction loans have both adjustable and fixed interest rates during the construction period. Construction loans to individuals are typically priced and made with the intention of granting the permanent loan on the property. Speculative and commercial construction loans are subject to underwriting standards similar to that of the commercial portfolio. Owner occupied 1-4 family residential construction loans are subject to the underwriting standards of the permanent loan. 1-4 Family Residential Real Estate Loans Residential loan originations are generated by our loan officers, in-house origination staff, marketing efforts, present customers, walk-in customers and referrals from real estate agents and builders. We focus our lending efforts primarily on the origination of loans secured by first mortgages on owner occupied 1-4 family residences. Substantially all of our 1-4 family residential originations are secured by properties located in or near our market areas. Our 1-4 family residential loans generally have maturities ranging from five to 30 years. These loans are typically fully amortizing with monthly payments sufficient to repay the total amount of the loan. Our 1-4 family residential loans are made at both fixed and adjustable interest rates. Underwriting for 1-4 family residential loans includes debt-to-income analysis, credit history analysis, appraised value and down payment considerations. Changes in the market value of real estate can affect the potential losses in the portfolio. Commercial Real Estate Loans Commercial real estate loans as of June 30, 2019 consisted of $1.14 billion of owner and non-owner occupied real estate, $96.3 million of loans secured by multi-family properties and $18.1 million of loans secured by farmland. Commercial real estate loans primarily include loans collateralized by retail, commercial office buildings, multi-family residential buildings, medical facilities and offices, senior living, assisted living and skilled nursing facilities, warehouse facilities, hotels and churches. Management does not consider there to be a risk in any one industry type. In determining whether to originate commercial real estate loans, we generally consider such factors as the financial condition of the borrower and the debt service coverage of the property. Commercial real estate loans are made at both fixed and adjustable interest rates for terms generally up to 20 years. Commercial Loans Our commercial loans are diversified loan types including short-term working capital loans for inventory and accounts receivable and short- and medium-term loans for equipment or other business capital expansion. Management does not consider there to be a concentration of risk in any one industry type. In our commercial loan underwriting, we assess the creditworthiness, ability to repay and the value and liquidity of the collateral being offered. Terms of commercial loans are generally commensurate with the useful life of the collateral offered. Municipal Loans We have a specific lending department that makes loans to municipalities and school districts primarily throughout the state of Texas, with a small percentage originating outside of the state. The majority of the loans to municipalities and school districts have tax or revenue pledges and in some cases are additionally supported by collateral. Municipal loans made without a direct pledge of taxes or revenues are usually made based on some type of collateral that represents an essential service. Lending money directly to these municipalities allows us to earn a higher yield than we could if we purchased municipal securities for similar durations. Loans to Individuals Substantially all originations of our loans to individuals are made to consumers in our market areas. The majority of loans to individuals are collateralized by titled equipment, which are primarily automobiles. Loan terms vary according to the type and value of collateral, length of contract and creditworthiness of the borrower. The underwriting standards we employ for consumer loans include an application, a determination of the applicant’s payment history on other debts, with the greatest weight being given to payment history with us and an assessment of the borrower’s ability to meet existing obligations and payments on the proposed loan. Although creditworthiness of the applicant is a primary consideration, the underwriting process also includes a comparison of the value of the collateral, if any, in relation to the proposed loan amount. Most of our loans to individuals are collateralized, which management believes assists in limiting our exposure. Allowance for Loan Losses The allowance for loan losses is based on the most current review of the loan portfolio and is a result of multiple processes. First, we utilize historical net charge-off data to establish general reserve amounts for each class of loans. The historical charge-off figure is further adjusted through qualitative factors that include general trends in past dues, nonaccruals and classified loans to more effectively and promptly react to both positive and negative movements not reflected in the historical data. Second, our lenders have the primary responsibility for identifying problem loans based on customer financial stress and underlying collateral. These recommendations are reviewed by senior loan administration, the special assets department and the loan review department on a monthly basis. Third, the loan review department independently reviews the portfolio on an annual basis. The loan review department follows a board-approved annual loan review scope. The loan review scope encompasses a number of considerations including the size of the loan, the type of credit extended, the seasoning of the loan and the performance of the loan. The loan review scope, as it relates to size, focuses more on larger dollar loan relationships, typically aggregate debt of $500,000 or greater. The loan review officer also reviews specific reserves compared to general reserves to determine trends in comparative reserves as well as losses not reserved for prior to charge-off to determine the effectiveness of the specific reserve process. At each review, a subjective analysis methodology is used to grade the respective loan. Categories of grading vary in severity from loans that do not appear to have a significant probability of loss at the time of review to loans that indicate a probability that the entire balance of the loan will be uncollectible. If at the time of the review we determine it is probable we will not collect the principal and interest cash flows contractually due on the loan, estimates of future expected cash flows or appraisals of the collateral securing the debt are used to determine the necessary allowance. The internal loan review department maintains a list (“Watch List”) of all loans or loan relationships that are graded as having more than the normal degree of risk associated with them. In addition, a list of specifically reserved loans or loan relationships of $150,000 or more is updated on a quarterly basis in order to properly determine necessary allowances and keep management informed on the status of attempts to correct the deficiencies noted with respect to the loans. We calculate historical loss ratios for pools of loans with similar characteristics based on the proportion of actual charge-offs experienced, consistent with the characteristics of remaining loans, to the total population of loans in the pool. The historical gross loss ratios are updated quarterly based on actual charge-off experience and adjusted for qualitative factors. All loans are subject to individual analysis if determined to be impaired with the exception of consumer loans and loans secured by 1-4 family residential loans. Industry and our own experience indicates that a portion of our loans will become delinquent and a portion of our loans will require partial or full charge-off. Regardless of the underwriting criteria utilized, losses may occur as a result of various factors beyond our control, including, among other things, changes in market conditions affecting the value of properties used as collateral for loans and problems affecting the credit worthiness of the borrower and the ability of the borrower to make payments on the loan. Our determination of the appropriateness of the allowance for loan losses is based on various considerations, including an analysis of the risk characteristics of various classifications of loans, previous loan loss experience, specific loans which have loan loss potential, delinquency trends, estimated fair value of the underlying collateral, current economic conditions and geographic and industry loan concentration. Credit Quality Indicators We categorize loans into risk categories on an ongoing basis based on relevant information about the ability of borrowers to service their debt such as: current financial information, historical payment experience, credit documentation, public information and current economic trends, among other factors. We use the following definitions for risk ratings: • Pass (Rating 1 – 4) – This rating is assigned to all satisfactory loans. This category, by definition, consists of acceptable credit. Credit and collateral exceptions should not be present, although their presence would not necessarily prohibit a loan from being rated Pass, if deficiencies are in the process of correction. These loans are not included in the Watch List. • Pass Watch (Rating 5) – These loans require some degree of special treatment, but not due to credit quality. This category does not include loans specially mentioned or adversely classified; however, particular attention is warranted to characteristics such as: ◦ A lack of, or abnormally extended payment program; ◦ A heavy degree of concentration of collateral without sufficient margin; ◦ A vulnerability to competition through lesser or extensive financial leverage; and ◦ A dependence on a single or few customers or sources of supply and materials without suitable substitutes or alternatives. • Special Mention (Rating 6) – A Special Mention loan has potential weaknesses that deserve management’s close attention. If left uncorrected, these potential weaknesses may result in deterioration of the repayment prospects for the loan or in our credit position at some future date. Special Mention loans are not adversely classified and do not expose us to sufficient risk to warrant adverse classification. • Substandard (Rating 7) – Substandard loans are inadequately protected by the current sound worth and paying capacity of the obligor or of the collateral pledged, if any. Loans so classified must have a well-defined weakness or weaknesses that jeopardize the liquidation of the debt. They are characterized by the distinct possibility that the Bank will sustain some loss if the deficiencies are not corrected. • Doubtful (Rating 8) – Loans classified as Doubtful have all the weaknesses inherent in those classified Substandard with the added characteristic that the weaknesses make collection or liquidation, in full, on the basis of currently known facts, conditions and values, highly questionable and improbable. All accruing loans are reserved for as a group of similar type credits and included in the general portion of the allowance for loan losses. Loans to individuals and 1-4 family residential loans, including loans not accruing, are collectively evaluated and included in the general portion of the allowance for loan losses. All loans considered troubled debt restructurings (“TDR”) are evaluated individually for impairment. The general portion of the loan loss allowance is reflective of historical charge-off levels for similar loans adjusted for changes in current conditions and other relevant factors. These factors are likely to cause estimated losses to differ from historical loss experience and include: • Changes in lending policies or procedures, including underwriting, collection, charge-off and recovery procedures; • Changes in local, regional and national economic and business conditions, including entry into new markets; • Changes in the volume or type of credit extended; • Changes in the experience, ability and depth of lending management; • Changes in the volume and severity of past due, nonaccrual, restructured, or classified loans; • Changes in charge-off trends; • Changes in loan review or Board oversight; • Changes in the level of concentrations of credit; and • Changes in external factors, such as competition and legal and regulatory requirements. These factors are also considered for the non-PCI purchased loan portfolio specifically in regards to changes in credit quality, past due, nonaccrual and charge-off trends. The following tables detail activity in the allowance for loan losses by portfolio segment for the periods presented (in thousands): Three Months Ended June 30, 2019 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans Municipal Loans Loans to Individuals Total Balance at beginning of period $ 4,259 $ 3,382 $ 10,660 $ 4,287 $ 508 $ 1,059 $ 24,155 Provision (reversal) for loan losses (2) (660 ) 137 1,516 1,266 22 225 2,506 Loans charged off — — (1,661 ) (130 ) — (606 ) (2,397 ) Recoveries of loans charged off — 3 19 123 — 296 441 Balance at end of period $ 3,599 $ 3,522 $ 10,534 $ 5,546 $ 530 $ 974 $ 24,705 Six Months Ended June 30, 2019 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans Municipal Loans Loans to Individuals Total Balance at beginning of period $ 3,597 $ 3,844 $ 13,968 $ 3,974 $ 525 $ 1,111 $ 27,019 Provision (reversal) for loan losses (2) 2 (310 ) (596 ) 2,000 5 487 1,588 Loans charged off — (18 ) (2,876 ) (581 ) — (1,207 ) (4,682 ) Recoveries of loans charged off — 6 38 153 — 583 780 Balance at end of period $ 3,599 $ 3,522 $ 10,534 $ 5,546 $ 530 $ 974 $ 24,705 Three Months Ended June 30, 2018 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans Municipal Loans Loans to Individuals Total Balance at beginning of period $ 3,597 $ 2,377 $ 14,089 $ 2,385 $ 851 $ 921 $ 24,220 Provision (reversal) for loan losses (2) 244 403 (57 ) 328 8 355 1,281 Loans charged off — (57 ) — (172 ) — (688 ) (917 ) Recoveries of loans charged off — 7 4 19 — 458 488 Balance at end of period $ 3,841 $ 2,730 $ 14,036 $ 2,560 $ 859 $ 1,046 $ 25,072 Six Months Ended June 30, 2018 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans Municipal Loans Loans to Individuals Total Balance at beginning of period (1) $ 3,676 $ 2,445 $ 10,821 $ 2,094 $ 860 $ 885 $ 20,781 Provision (reversal) for loan losses (2) 179 321 3,209 661 (1 ) 647 5,016 Loans charged off (14 ) (57 ) — (257 ) — (1,356 ) (1,684 ) Recoveries of loans charged off — 21 6 62 — 870 959 Balance at end of period $ 3,841 $ 2,730 $ 14,036 $ 2,560 $ 859 $ 1,046 $ 25,072 (1) Loans acquired with the Diboll acquisition were measured at fair value on November 30, 2017 with no carryover of allowance for loan losses. (2) Of the $2.5 million and $1.6 million provision for loan losses for the three and six months ended June 30, 2019 , $111,000 and $163,000 related to provision expense reversed on PCI loans, respectively. Of the $1.3 million and $5.0 million recorded in provision for loan losses for the three and six months ended June 30, 2018 , $358,000 related to provision expense on PCI loans. The following tables present the balance in the allowance for loan losses by portfolio segment based on impairment method (in thousands): June 30, 2019 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans Municipal Loans Loans to Individuals Total Ending balance – individually evaluated for impairment (1) $ 23 $ 66 $ 1,408 $ 782 $ — $ 90 $ 2,369 Ending balance – collectively evaluated for impairment 3,576 3,456 9,126 4,764 530 884 22,336 Balance at end of period $ 3,599 $ 3,522 $ 10,534 $ 5,546 $ 530 $ 974 $ 24,705 December 31, 2018 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans Municipal Loans Loans to Individuals Total Ending balance – individually evaluated for impairment (1) $ 13 $ 40 $ 5,337 $ 368 $ 1 $ 149 $ 5,908 Ending balance – collectively evaluated for impairment 3,584 3,804 8,631 3,606 524 962 21,111 Balance at end of period $ 3,597 $ 3,844 $ 13,968 $ 3,974 $ 525 $ 1,111 $ 27,019 (1) The allowance for loan losses on PCI loans totaled $139,000 and $302,000 as of June 30, 2019 and December 31, 2018 , respectively. The following tables present the recorded investment in loans by portfolio segment based on impairment method (in thousands): June 30, 2019 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans Municipal Loans Loans to Individuals Total Loans individually evaluated for impairment $ 200 $ 1,268 $ 21,361 $ 2,523 $ 429 $ 136 $ 25,917 Loans collectively evaluated for impairment 579,226 772,725 1,198,899 385,322 356,599 100,354 3,393,125 Purchased credit impaired loans 139 8,080 30,988 1,676 — 218 41,101 Total ending loan balance $ 579,565 $ 782,073 $ 1,251,248 $ 389,521 $ 357,028 $ 100,708 $ 3,460,143 December 31, 2018 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans Municipal Loans Loans to Individuals Total Loans individually evaluated for impairment $ 12 $ 1,215 $ 33,013 $ 1,394 $ 429 $ 184 $ 36,247 Loans collectively evaluated for impairment 507,564 782,614 1,128,220 353,036 352,941 105,775 3,230,150 Purchased credit impaired loans 156 10,670 32,885 2,219 — 472 46,402 Total ending loan balance $ 507,732 $ 794,499 $ 1,194,118 $ 356,649 $ 353,370 $ 106,431 $ 3,312,799 The following tables set forth credit quality indicators by class of loans for the periods presented (in thousands): June 30, 2019 Pass Pass Watch (1) Special Mention (1) Substandard (1) Doubtful (1) Total Real estate loans: Construction $ 579,253 $ 47 $ — $ 265 $ — $ 579,565 1-4 family residential 776,375 31 166 4,784 717 782,073 Commercial 1,150,646 55,208 7,444 37,793 157 1,251,248 Commercial loans 375,664 3,362 6,063 4,163 269 389,521 Municipal loans 357,028 — — — — 357,028 Loans to individuals 100,030 — — 380 298 100,708 Total $ 3,338,996 $ 58,648 $ 13,673 $ 47,385 $ 1,441 $ 3,460,143 December 31, 2018 Pass Pass Watch (1) Special Mention (1) Substandard (1) Doubtful (1) Total Real estate loans: Construction $ 507,529 $ 163 $ — $ 28 $ 12 $ 507,732 1-4 family residential 787,516 37 100 5,489 1,357 794,499 Commercial 1,067,874 11,479 26,490 87,767 508 1,194,118 Commercial loans 349,495 520 3,189 2,988 457 356,649 Municipal loans 353,370 — — — — 353,370 Loans to individuals 105,536 4 4 678 209 106,431 Total $ 3,171,320 $ 12,203 $ 29,783 $ 96,950 $ 2,543 $ 3,312,799 (1) Includes PCI loans comprised of $15,000 pass watch, $217,000 special mention, $2.7 million substandard and $305,000 doubtful as of June 30, 2019 . Includes PCI loans comprised of $22,000 pass watch, $859,000 special mention, $3.9 million substandard and $1.2 million doubtful as of December 31, 2018 . Nonperforming Assets and Past Due Loans Nonaccrual loans are loans 90 days or more delinquent and collection in full of both the principal and interest is not expected. Additionally, some loans that are not delinquent or that are delinquent less than 90 days may be placed on nonaccrual status if it is probable that we will not receive contractual principal and interest payments in accordance with the terms of the respective loan agreement. When a loan is categorized as nonaccrual, the accrual of interest is discontinued and any accrued balance is reversed for financial statement purposes. Payments received on nonaccrual loans are applied to the outstanding principal balance. Payments of contractual interest are recognized as income only to the extent that full recovery of the principal balance of the loan is reasonably certain. Loans are returned to accrual status when all the principal and interest amounts contractually due are brought current and future payments are reasonably assured. Other factors, such as the value of collateral securing the loan and the financial condition of the borrower, are considered in judgments as to potential loan loss. Nonaccrual loans and accruing loans past due more than 90 days include both smaller balance homogeneous loans that are collectively evaluated for impairment and individually classified impaired loans. PCI loans are recorded at fair value at acquisition date. Although the PCI loans may be contractually delinquent, we do not classify these loans as past due or nonperforming when the timing and amount of expected cash flows can be reasonably estimated, as the loans were written down to fair value at the acquisition date and the accretable yield is recognized in interest income over the remaining life of the loan. However, subsequent to acquisition, we reassess PCI loans for additional impairment and record additional impairment in the event we conclude it is probable that we will be unable to collect all cash flows originally expected to be collected at acquisition plus any additional cash flows expected to be collected due to changes in estimates after acquisition. All such PCI loans for which we recognize subsequent impairment are reported as impaired loans in the financial statements. The following table sets forth nonperforming assets for the periods presented (in thousands): June 30, 2019 December 31, 2018 Nonaccrual loans (1) (2) $ 16,376 $ 35,770 Accruing loans past due more than 90 days (1) — — Restructured loans (3) 11,918 5,930 Other real estate owned 1,069 1,206 Repossessed assets — — Total nonperforming assets $ 29,363 $ 42,906 (1) Excludes PCI loans measured at fair value at acquisition if the timing and amount of cash flows expected to be collected from those sales can be reasonably estimated. (2) Includes $8.9 million and $10.9 million of restructured loans as of June 30, 2019 and December 31, 2018 , respectively. (3) Includes $776,000 and $3.1 million in PCI loans restructured as of June 30, 2019 and December 31, 2018 , respectively. Foreclosed assets include other real estate owned and repossessed assets. For 1-4 family residential real estate properties, a loan is recognized as a foreclosed property once legal title to the real estate property has been received upon completion of foreclosure or the borrower has conveyed all interest in the residential property through a deed in lieu of foreclosure. There were $12,000 and $147,000 in loans secured by 1-4 family residential properties for which formal foreclosure proceedings were in process as of June 30, 2019 and December 31, 2018 , respectively. The following table sets forth the recorded investment in nonaccrual loans by class of loans for the periods presented (in thousands). The table excludes PCI loans measured at fair value at acquisition: Nonaccrual Loans June 30, 2019 December 31, 2018 Real estate loans: Construction $ 200 $ 12 1-4 family residential 1,418 2,202 Commercial 13,383 32,599 Commercial loans 1,047 639 Loans to individuals 328 318 Total $ 16,376 $ 35,770 Loans are considered impaired if, based on current information and events, it is probable we will be unable to collect the scheduled payments of principal and interest when due according to the contractual terms of the loan agreement. Impairment is evaluated in total for smaller-balance loans of a similar nature and on an individual loan basis for larger loans. The measurement of loss on impaired loans is generally based on the fair value of the collateral less selling costs if repayment is expected solely from the collateral or the present value of the expected future cash flows discounted at the historical effective interest rate stipulated in the loan agreement. In measuring the fair value of the collateral, in addition to relying on third party appraisals, we use assumptions, such as discount rates, and methodologies, such as comparison to the recent selling price of similar assets, consistent with those that would be utilized by unrelated third parties performing a valuation. Loans that are evaluated and determined not to meet the definition of an impaired loan are reserved for at the general reserve rate for its appropriate class. At the time a loss is probable in the collection of contractual amounts, specific reserves are allocated. Loans are charged off to the liquidation value of the collateral net of liquidation costs, if any, when deemed uncollectible or as soon as collection by liquidation is evident. The following tables set forth impaired loans by class of loans, including the unpaid contractual principal balance, the recorded investment and the related allowance for loan losses for the periods presented (in thousands). Impaired loans include restructured and nonaccrual loans for which the allowance was measured in accordance with section 310-10 of ASC Topic 310, “Receivables.” There were no impaired loans recorded without an allowance as of June 30, 2019 or December 31, 2018 . June 30, 2019 Unpaid Contractual Principal Balance Recorded Investment Related Allowance for Loan Losses Real estate loans: Construction $ 356 $ 323 $ 23 1-4 family residential 8,646 7,491 66 Commercial 26,198 22,999 1,408 Commercial loans 4,033 3,449 782 Municipal loans 429 429 — Loans to individuals 481 354 90 Total (1) $ 40,143 $ 35,045 $ 2,369 December 31, 2018 Unpaid Contractual Principal Balance Recorded Investment Related Allowance for Loan Losses Real estate loans: Construction $ 182 $ 148 $ 13 1-4 family residential 6,507 5,923 40 Commercial 36,457 34,744 5,337 Commercial loans 2,874 2,366 368 Municipal loans 429 429 1 Loans to individuals 825 657 149 Total (1) $ 47,274 $ 44,267 $ 5,908 (1) Includes $9.1 million and $8.0 million of PCI loans that experienced deterioration in credit quality subsequent to the acquisition date as of June 30, 2019 and December 31, 2018 , respectively. The following tables present the aging of the recorded investment in past due loans by class of loans (in thousands): June 30, 2019 30-59 Days Past Due 60-89 Days Past Due Greater than 90 Days Past Due Total Past Due Current (1) Total Real estate loans: Construction $ 343 $ 276 $ 193 $ 812 $ 578,753 $ 579,565 1-4 family residential 2,250 1,330 293 3,873 778,200 782,073 Commercial 1,625 425 109 2,159 1,249,089 1,251,248 Commercial loans 2,070 567 619 3,256 386,265 389,521 Municipal loans — — — — 357,028 357,028 Loans to individuals 555 194 137 886 99,822 100,708 Total $ 6,843 $ 2,792 $ 1,351 $ 10,986 $ 3,449,157 $ 3,460,143 December 31, 2018 30-59 Days Past Due 60-89 Days Past Due Greater than 90 Days Past Due Total Past Due Current (1) Total Real estate loans: Construction $ 627 $ 307 $ — $ 934 $ 506,798 $ 507,732 1-4 family residential 7,441 1,258 1,335 10,034 784,465 794,499 Commercial 10,663 7,655 — 18,318 1,175,800 1,194,118 Commercial loans 1,946 705 591 3,242 353,407 356,649 Municipal loans — — — — 353,370 353,370 Loans to individuals 1,289 351 146 1,786 104,645 106,431 Total $ 21,966 $ 10,276 $ 2,072 $ 34,314 $ 3,278,485 $ 3,312,799 (1) Includes PCI loans measured at fair value at acquisition if the timing and amount of cash flows expected to be collected from those sales can be reasonably estimated. The following table sets forth average recorded investment and interest income recognized on impaired loans by class of loans for the periods presented (in thousands). The table excludes PCI loans measured at fair value at acquisition that have not experienced further deterioration in credit quality subsequent to the acquisition date: Three Months Ended June 30, 2019 June 30, 2018 Average Recorded Investment Interest Income Recognized Average Recorded Investment Interest Income Recognized Real estate loans: Construction $ 214 $ 5 $ 140 $ 1 1-4 family residential 7,533 130 3,955 47 Commercial 24,394 153 31,916 5 Commercial loans 2,753 38 2,024 19 Municipal loans 429 6 502 7 Loans to individuals 438 9 242 3 Total $ 35,761 $ 341 $ 38,779 $ 82 Six Months Ended June 30, 2019 June 30, 2018 Average Recorded Investment Interest Income Recognized Average Recorded Interest Income Recognized Real estate loans: Construction $ 200 $ 9 $ 114 $ 1 1-4 family residential 6,271 210 3,945 93 Commercial 30,917 440 20,595 9 Commercial loans 2,699 68 1,900 36 Municipal loans 429 12 502 14 Loans to individuals 517 20 221 4 Total $ 41,033 $ 759 $ 27,277 $ 157 Troubled Debt Restructurings The restructuring of a loan is considered a TDR if both (i) the borrower is experiencing financial difficulties and (ii) the creditor has granted a concession. Concessions may include interest rate reductions or below market interest rates, restructuring amortization schedules and other actions intended to minimize potential losses. We may provide a combination of concessions which may include an extension of the amortization period, interest rate reduction and/or converting the loan to interest-only for a limited period of time. The following tables set forth the recorded balance of loans considered to be TDRs that were restructured and the type of concession by class of loans during the periods presented (dollars in thousands): Three Months Ended June 30, 2019 Extend Amortization Period Interest Rate Reductions Combination Total Modifications Number of Loans Real estate loans: 1-4 family residential $ — $ — $ — $ — — Commercial — — 96 96 1 Commercial loans — — 485 485 4 Loans to individuals — — 25 25 3 Total $ — $ — $ 606 $ 606 8 Six Months Ended June 30, 2019 Extend Amortization Period Interest Rate Reductions Combination Total Modifications Number of Loans Real estate loans: 1-4 family residential $ — $ — $ 111 $ 111 1 Commercial 7,594 — 96 7,690 2 Commercial loans 56 — 485 541 5 Loans to individuals — — 39 39 5 Total $ 7,650 $ — $ 731 $ 8,381 13 Three Months Ended June 30, 2018 Extend Amortization Period Interest Rate Reductions Combination Total Modifications Number of Loans Real estate loans: 1-4 family residential $ — $ 80 $ — $ 80 1 Commercial loans — — 90 90 2 Loans to individuals 9 — 13 22 3 Total $ 9 $ 80 $ 103 $ 192 6 Six Months Ended June 30, 2018 Extend Amortization Period Interest Rate Reductions Combination Total Modifications Number of Loans Real estate loans: 1-4 family residential $ — $ 80 $ — $ 80 1 Commercial loans 132 — 90 222 5 Loans to individuals 106 — 13 119 4 Total $ 238 $ 80 $ 103 $ 421 10 The majority of loans restructured as TDRs during the six months ended June 30, 2019 and 2018 were modified with maturity extensions. Interest continues to be charged on principal balances outstanding during the extended term. Therefore, the financial effects of the recorded investment of loans restructured as TDRs during the six months ended June 30, 2019 and 2018 were not significant. Generally, the loans identified as TDRs were previously reported as impaired loans prior to restructuring, and therefore, the modification did not impact our determination of the allowance for loan losses. On an ongoing basis, the performance of the TDRs is monitored for subsequent payment default. Payment default for TDRs is recognized when the borrower is 90 days or more past due. For the three and six months ended June 30, 2019 and 2018 , the amount of TDRs in default was not significant. Payment defaults for TDRs did not significantly impact the determination of the allowance for loan losses in the periods presented. At June 30, 2019 and 2018 , there were no commitments to lend additional funds to borrowers whose terms had been modified in TDRs. Purchased Credit Impaired Loans The follo

Borrowing Arrangements

Borrowing Arrangements	6 Months Ended
	Jun. 30, 2019
Debt Disclosure [Abstract]
Borrowing Arrangements	Borrowing Arrangements Information related to borrowings is provided in the table below (dollars in thousands): June 30, December 31, 2018 Other borrowings: Balance at end of period $ 26,064 $ 36,810 Average amount outstanding during the period (1) 15,653 10,880 Maximum amount outstanding during the period (2) 28,354 36,810 Weighted average interest rate during the period (3) 1.7 % 1.4 % Interest rate at end of period (4) 2.0 % 2.1 % Federal Home Loan Bank borrowings: Balance at end of period $ 823,757 $ 719,065 Average amount outstanding during the period (1) 785,901 720,785 Maximum amount outstanding during the period (2) 1,004,997 957,231 Weighted average interest rate during the period (3) 2.1 % 1.8 % Interest rate at end of period (4) 2.4 % 2.3 % (1) The average amount outstanding during the period was computed by dividing the total daily outstanding principal balances by the number of days in the period. (2) The maximum amount outstanding at any month-end during the period. (3) The weighted average interest rate during the period was computed by dividing the actual interest expense (annualized for interim periods) by the average amount outstanding during the period. The weighted average interest rate on the FHLB borrowings includes the effect of interest rate swaps. (4) Stated rate. Maturities of the obligations associated with our borrowing arrangements based on scheduled repayments at June 30, 2019 are as follows (in thousands): Payments Due by Period Less than 1 Year 1-2 Years 2-3 Years 3-4 Years 4-5 Years Thereafter Total Other borrowings $ 25,931 $ 133 $ — $ — $ — $ — $ 26,064 Federal Home Loan Bank borrowings 796,765 21,374 — — — 5,618 823,757 Total obligations $ 822,696 $ 21,507 $ — $ — $ — $ 5,618 $ 849,821 Other borrowings include federal funds purchased and repurchase agreements. Southside Bank has three unsecured lines of credit for the purchase of overnight federal funds at prevailing rates with Frost Bank, TIB – The Independent Bankers Bank and Comerica Bank for $40.0 million , $15.0 million and $7.5 million , respectively. There were $18.0 million and $28.0 million federal funds purchased at June 30, 2019 and December 31, 2018 , respectively. Southside Bank has a $5.0 million line of credit with Frost Bank to be used to issue letters of credit, and at June 30, 2019 , the line had no outstanding letters of credit. At June 30, 2019 , the amount of additional funding Southside Bank could obtain from FHLB, collateralized by securities, FHLB stock and nonspecified loans and securities, was approximately $1.26 billion , net of FHLB stock purchases required. Southside Bank currently has no outstanding letters of credit from FHLB held as collateral for its public fund deposits. Southside Bank enters into sales of securities under repurchase agreements. These repurchase agreements totaled $8.1 million and $8.8 million at June 30, 2019 and December 31, 2018 , respectively, and had maturities of less than thirteen months . These repurchase agreements are secured by investment securities and are stated at the amount of cash received in connection with the transaction. FHLB borrowings represent borrowings with fixed and floating interest rates ranging from 1.37% to 4.799% and with remaining maturities of 2 days to 9 years at June 30, 2019 . FHLB borrowings may be collateralized by FHLB stock, nonspecified loans and/or securities. Southside Bank has entered into various variable rate advance agreements with the FHLB. These advance agreements totaled $310.0 million at both June 30, 2019 and December 31, 2018 . Three of the variable rate advance agreements have interest rates tied to three-month LIBOR and the remaining agreements have interest rates tied to one-month LIBOR . In connection with $270.0 million of these variable rate advance agreements, Southside Bank also entered into various interest rate swap contracts that are treated as cash flow hedges under ASC Topic 815, “Derivatives and Hedging” that effectively convert the variable rate advance agreements to fixed interest rates. The interest rate swap contracts had an average interest rate of 1.58% with an average weighted maturity of 4.3 years at June 30, 2019 . Refer to “Note 10 - Derivative Financial Instruments and Hedging Activities” in our consolidated financial statements included in this report for a detailed description of our hedging policy and methodology related to derivative instruments.

Long-term Debt Long-term Obliga

Long-term Debt Long-term Obligations	6 Months Ended
	Jun. 30, 2019
Debt Disclosure [Abstract]
Long-term Obligations	Long-term Debt June 30, December 31, (in thousands) Subordinated notes: (1) 5.50% Subordinated Notes, net of unamortized debt issuance costs (2) $ 98,490 $ 98,407 Total Subordinated notes 98,490 98,407 Trust preferred subordinated debentures: (3) Southside Statutory Trust III, net of unamortized debt issuance costs (4) 20,556 20,554 Southside Statutory Trust IV 23,196 23,196 Southside Statutory Trust V 12,887 12,887 Magnolia Trust Company I 3,609 3,609 Total Trust preferred subordinated debentures 60,248 60,246 Total Long-term debt $ 158,738 $ 158,653 (1) This debt consists of subordinated notes with a remaining maturity greater than one year that qualify under the risk-based capital guidelines as Tier 2 capital, subject to certain limitations. (2) The unamortized discount and debt issuance costs reflected in the carrying amount of the subordinated notes totaled approximately $1.5 million at June 30, 2019 and $1.6 million at December 31, 2018 . (3) This debt consists of trust preferred securities that qualify under the risk-based capital guidelines as Tier 1 capital, subject to certain limitations. (4) The unamortized debt issuance costs reflected in the carrying amount of the Southside Statutory Trust III junior subordinated debentures totaled $63,000 at June 30, 2019 and $65,000 at December 31, 2018 . As of June 30, 2019 , the details of the subordinated notes and the trust preferred subordinated debentures are summarized below (dollars in thousands): Date Issued Amount Issued Fixed or Floating Rate Interest Rate Maturity Date 5.50% Subordinated Notes September 19, 2016 $ 100,000 Fixed-to-Floating 5.50% September 30, 2026 Southside Statutory Trust III September 4, 2003 $ 20,619 Floating 3 month LIBOR + 2.94% September 4, 2033 Southside Statutory Trust IV August 8, 2007 $ 23,196 Floating 3 month LIBOR + 1.30% October 30, 2037 Southside Statutory Trust V August 10, 2007 $ 12,887 Floating 3 month LIBOR + 2.25% September 15, 2037 Magnolia Trust Company I (1) October 10, 2007 $ 3,609 Floating 3 month LIBOR + 1.80% November 23, 2035 (1) On October 10, 2007, as part of an acquisition we assumed $3.6 million of floating rate junior subordinated debentures issued in 2005 to Magnolia Trust Company I. On September 19, 2016 , the Company issued $100.0 million aggregate principal amount of fixed-to-floating rate subordinated notes that mature on September 30, 2026 . This debt initially bears interest at a fixed rate of 5.50% through September 29, 2021 and thereafter, adjusts quarterly at a floating rate equal to three-month LIBOR plus 429.7 basis points.

Employee Benefit Plans

Employee Benefit Plans	6 Months Ended
	Jun. 30, 2019
Defined Contribution Plan [Abstract]
Employee Benefit Plans	Employee Benefit Plans The components of net periodic benefit cost (income) related to our employee benefit plans are as follows (in thousands): Three Months Ended June 30, Defined Benefit Defined Benefit Pension Plan Acquired Restoration 2019 2018 2019 2018 2019 2018 Service cost $ 394 $ 390 $ — $ — $ 110 $ 84 Interest cost 919 839 43 41 195 165 Expected return on assets (1,511 ) (1,622 ) (73 ) (72 ) — — Net loss amortization 470 372 — — 181 248 Prior service (credit) cost amortization (4 ) (4 ) — — 1 2 Net periodic benefit cost (income) $ 268 $ (25 ) $ (30 ) $ (31 ) $ 487 $ 499 Six Months Ended June 30, Defined Benefit Defined Benefit Pension Plan Acquired Restoration 2019 2018 2019 2018 2019 2018 Service cost $ 710 $ 774 $ — $ — $ 170 $ 147 Interest cost 1,827 1,696 84 82 356 298 Expected return on assets (3,015 ) (3,242 ) (146 ) (145 ) — — Net loss amortization 913 756 — — 280 339 Prior service (credit) cost amortization (7 ) (7 ) — — 3 3 Net periodic benefit cost (income) $ 428 $ (23 ) $ (62 ) $ (63 ) $ 809 $ 787 The service cost component is recorded on our consolidated income statements as salaries and employee benefits in noninterest expense while all other components other than service cost are recorded in other noninterest expense.

Derivative Financial Instrument

Derivative Financial Instruments and Hedging Activities	6 Months Ended
	Jun. 30, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments and Hedging Activities	Derivative Financial Instruments and Hedging Activities Our hedging policy allows the use of interest rate derivative instruments to manage our exposure to interest rate risk or hedge specified assets and liabilities. These instruments may include interest rate swaps and interest rate caps and floors. All derivative instruments are carried on the balance sheet at their estimated fair value and are recorded in other assets or other liabilities, as appropriate. Derivative instruments may be designated as cash flow hedges of variable rate assets or liabilities, cash flow hedges of forecasted transactions or fair value hedges of a recognized asset or liability or as non-hedging instruments. Gains and losses on derivative instruments designated as cash flow hedges are recorded in AOCI to the extent that they are effective. The amount recorded in other comprehensive income is reclassified to earnings in the same periods that the hedged cash flows impact earnings. The ineffective portion of changes in fair value is reported in current earnings. Gains and losses on derivative instruments designated as fair value hedges, as well as the change in fair value on the hedged item, are recorded in interest income in the consolidated statements of income. Gains and losses due to changes in fair value of the interest rate swap agreements completely offset changes in the fair value of the hedged portion of the hedged item. For derivative instruments not designated as hedging instruments, the gain or loss is recognized in current earnings during the period of change. We have entered into certain interest rate swap contracts on specific variable rate FHLB advance agreements. These interest rate swap contracts were designated as hedging instruments in cash flow hedges under ASC Topic 815. The objective of the interest rate swap contracts is to manage the expected future cash flows on $270.0 million of variable rate advance agreements with the FHLB. The cash flows from the swap are expected to be effective in hedging the variability in future cash flows attributable to fluctuations in the underlying LIBOR interest rate. During 2018, we entered into partial-term fair value hedges for certain of our fixed rate callable AFS municipal securities. These partial-term hedges of selected cash flows covering the time periods to the call dates of the hedged securities were expected to be effective in offsetting changes in the fair value of the hedged securities. Interest rate swaps designated as partial-term fair value hedges were utilized to mitigate the effect of changing interest rates on the hedged securities. The hedging strategy converted a portion of the fixed interest rates on the securities to LIBOR-based variable interest rates. During the first quarter of 2019, our fair value hedging relationships were ineffective due to the sale of the hedged items. As a result of the sale, the cumulative adjustments to the carrying amount was a fair value loss recognized in earnings and recorded in interest income. The remaining fair value loss from the date of the sale of the hedged items through March 31, 2019, was recognized in earnings and recorded in noninterest income. As of March 31, 2019, the interest rate swaps were considered non-hedging instruments and were subsequently terminated on April 12, 2019. In accordance with ASC Topic 815, if a hedging item is terminated prior to maturity for a cash settlement, the existing gain or loss within AOCI will continue to be reclassified into earnings during the period or periods in which the hedged forecasted transaction affects earnings unless it is probable that the forecasted transaction will not occur by the end of the originally specified time period. If the forecasted transaction is deemed probable to not occur, the derivative gain or loss reported in AOCI shall be reclassified into earnings immediately. During 2017, we terminated two interest rate swap contracts designated as cash flow hedges. At the time of termination, we determined the underlying hedged forecasted transactions were still probable of occurring. The existing gain in AOCI will be reclassified into earnings in the same periods the hedged forecasted transaction affects earnings. These transactions are reevaluated on a monthly basis to determine if the hedged forecasted transactions are still probable of occurring. If at a subsequent evaluation, it is determined that the transactions will not occur, any related gains or losses recorded in AOCI are immediately recognized in earnings. From time to time, we may enter into certain interest rate swaps, cap and floor contracts that are not designated as hedging instruments. These interest rate derivative contracts relate to transactions in which we enter into an interest rate swap, cap, or floor with a customer while concurrently entering into an offsetting interest rate swap, cap, or floor with a third-party financial institution. We agree to pay interest to the customer on a notional amount at a variable rate and receive interest from the customer on a similar notional amount at a fixed interest rate. At the same time, we agree to pay a third-party financial institution the same fixed interest rate on the same notional amount and receive the same variable interest rate on the same notional amount. These interest rate derivative contracts allow our customers to effectively convert a variable rate loan to a fixed rate loan. The changes in the fair value of the underlying derivative contracts primarily offset each other and do not significantly impact our results of operations. We recognized swap fee income associated with these derivative contracts immediately based upon the difference in the bid/ask spread of the underlying transactions with the customer and the third-party financial institution. The swap fee income is included in other noninterest income in our consolidated statements of income. At June 30, 2019 , net derivative liabilities included $7.4 million of cash collateral held by a counterparty to a master netting agreement. The notional amounts of the derivative instruments represent the contractual cash flows pertaining to the underlying agreements. These amounts are not exchanged and are not reflected in the consolidated balance sheets. The fair value of the interest rate swaps are presented at net in other assets and other liabilities when a right of offset exists, based on transactions with a single counterparty that are subject to a legally enforceable master netting agreement. The following tables present the notional and estimated fair value amount of derivative positions outstanding (in thousands): June 30, 2019 December 31, 2018 Estimated Fair Value Estimated Fair Value Notional (1) Asset Derivative Liability Derivative Notional (1) Asset Derivative Liability Derivative Derivatives designated as hedging instruments Interest rate contracts: Swaps-Cash flow Hedge-Financial institution counterparties $ 270,000 $ 2,334 $ 3,442 $ 270,000 $ 9,388 $ 457 Swaps-Fair Value Hedge-Financial institution counterparties — — — 21,100 — 657 Derivatives designated as non-hedging instruments Interest rate contracts: Swaps-Financial institution counterparties 110,699 16 6,614 93,967 1,119 1,087 Swaps-Customer counterparties 110,699 6,614 16 93,967 1,087 1,119 Gross derivatives 8,964 10,072 11,594 3,320 Offsetting derivative assets/liabilities (2,350 ) (2,350 ) (2,201 ) (2,201 ) Cash collateral received/posted — (7,420 ) (8,306 ) — Net derivatives included in the consolidated balance sheets (2) $ 6,614 $ 302 $ 1,087 $ 1,119 (1) Notional amounts, which represent the extent of involvement in the derivatives market, are used to determine the contractual cash flows required in accordance with the terms of the agreement. These amounts are typically not exchanged, significantly exceed amounts subject to credit or market risk and are not reflected in the consolidated balance sheets. (2) Net derivative assets are included in other assets and net derivative liabilities are included in other liabilities on the consolidated balance sheets. Included in the fair value of net derivative assets and net derivative liabilities are credit valuation adjustments reflecting counterparty credit risk and our credit risk. We had no credit exposure related to interest rate swaps with financial institutions and $6.6 million related to interest rate swaps with customers at June 30, 2019 . We had no credit exposure related to interest rate swaps with financial institutions and $1.1 million related to interest rate swaps with customers at December 31, 2018 . The credit risk associated with customer transactions is partially mitigated as these are generally secured by the non-cash collateral securing the underlying transaction being hedged. The summarized expected weighted average remaining maturity of the notional amount of interest rate swaps and the weighted average interest rates associated with the amounts expected to be received or paid on interest rate swap agreements are presented below (dollars in thousands). Variable rates received on pay fixed swaps are based on one-month or three-month LIBOR rates in effect at June 30, 2019 and December 31, 2018 : June 30, 2019 December 31, 2018 Weighted Average Weighted Average Notional Amount Remaining Maturity (in years) Receive Rate Pay Rate Notional Amount Remaining Maturity Receive Rate Pay Swaps-Cash flow hedge Financial institution counterparties $ 270,000 4.3 2.44 % 1.58 % $ 270,000 4.8 2.45 % 1.58 % Swaps-Fair value hedge Financial institution counterparties — — — — 21,100 7.5 2.56 3.00 Swaps-Non-hedging Financial institution counterparties 110,699 11.6 2.42 2.57 93,967 11.6 2.36 2.58 Customer counterparties 110,699 11.6 2.57 2.42 93,967 11.6 2.58 2.36

Fair Value Measurement

Fair Value Measurement	6 Months Ended
	Jun. 30, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurement	Fair Value Measurement Fair value is the price that would be received upon the sale of an asset or paid to transfer a liability (exit price) 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 is not 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. Valuation techniques including the market approach, the income approach and/or the cost approach are utilized to determine fair value. Inputs to valuation techniques refer to the assumptions that market participants would use in pricing the asset or liability. Valuation policies and procedures are determined by our investment department and reported to our Asset/Liability Committee (“ALCO”) for review. An entity must consider all aspects of nonperforming risk, including the entity’s own credit standing, when measuring fair value of a liability. Inputs may be observable, meaning those that reflect the assumptions market participants would use in pricing the asset or liability developed based on market data obtained from independent sources, or unobservable, meaning those that reflect the reporting entity’s own assumptions about the assumptions market participants would use in pricing the asset or liability developed based on the best information available in the circumstances. A fair value hierarchy for valuation inputs gives the highest priority to quoted prices in active markets for identical assets or liabilities and the lowest priority to unobservable inputs. The fair value hierarchy is as follows: Level 1 Inputs - Unadjusted quoted prices in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. Level 2 Inputs - Inputs other than quoted prices included in Level 1 that are observable for the asset or liability, either directly or indirectly. These might 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 (such as interest rates, volatilities, prepayment speeds, credit risks, etc.) or inputs that are derived principally from or corroborated by market data by correlation or other means. Level 3 Inputs - Unobservable inputs for determining the fair values of assets or liabilities that reflect an entity’s own assumptions about the assumptions that market participants would use in pricing the assets or liabilities. Level 3 assets recorded at fair value on a nonrecurring basis at June 30, 2019 and December 31, 2018 included loans for which a specific allowance was established based on the fair value of collateral and commercial real estate for which fair value of the properties was less than the cost basis. For both asset classes, the unobservable inputs were the additional adjustments applied by management to the appraised values to reflect such factors as non-current appraisals and revisions to estimated time to sell. These adjustments are determined based on qualitative judgments made by management on a case-by-case basis and are not quantifiable inputs, although they are used in the determination of fair value. 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. Certain financial assets are measured at fair value in accordance with GAAP. Adjustments to the fair value of these assets usually result from the application of fair value accounting or write-downs of individual assets. Transfers between levels of the fair value hierarchy are recognized on the actual date of the event or circumstances that caused the transfer, which generally coincides with our monthly and/or quarterly valuation process. There were no transfers between Level 1 and Level 2 during the six months ended June 30, 2019 or the year ended December 31, 2018 . Securities Available for Sale and Equity Investments with readily determinable fair values – U.S. Treasury securities and equity investments with readily determinable fair values are reported at fair value utilizing Level 1 inputs. Other securities classified as available for sale are reported at fair value utilizing Level 2 inputs. For these securities, we obtain fair value measurements from independent pricing services and obtain an understanding of the pricing methodologies used by these independent pricing services. The fair value measurements consider observable data that may include dealer quotes, market spreads, cash flows, the U.S. Treasury yield curve, live trading levels, trade execution data, market consensus prepayment speeds, credit information and the bond’s terms and conditions, among other things, as stated in the pricing methodologies of the independent pricing services. We review and validate the prices supplied by the independent pricing services for reasonableness by comparison to prices obtained from, in most cases, two additional third party sources. For securities where prices are outside a reasonable range, we further review those securities, based on internal ALCO approved procedures, to determine what a reasonable fair value measurement is for those securities, given available data. Derivatives – Derivatives are reported at fair value utilizing Level 2 inputs. We obtain fair value measurements from three sources including an independent pricing service and the counterparty to the derivatives designated as hedges. The fair value measurements consider observable data that may include dealer quotes, market spreads, the U.S. Treasury yield curve, live trading levels, trade execution data, credit information and the derivatives’ terms and conditions, among other things. We review the prices supplied by the sources for reasonableness. In addition, we obtain a basic understanding of their underlying pricing methodology. We validate prices supplied by the sources by comparison to one another. Certain nonfinancial assets and nonfinancial liabilities measured at fair value on a recurring basis include reporting units measured at fair value and tested for goodwill impairment. Certain financial assets and financial liabilities are measured at fair value on a nonrecurring basis, which means that the instruments are not measured at fair value on an ongoing basis but are subject to fair value adjustments in certain circumstances (for example, when there is evidence of impairment). Financial assets and financial liabilities measured at fair value on a nonrecurring basis included foreclosed assets and impaired loans at June 30, 2019 and December 31, 2018 . Foreclosed Assets – Foreclosed assets are initially recorded at fair value less costs to sell. The fair value measurements of foreclosed assets can include Level 2 measurement inputs such as real estate appraisals and comparable real estate sales information, in conjunction with Level 3 measurement inputs such as cash flow projections, qualitative adjustments and sales cost estimates. As a result, the categorization of foreclosed assets is Level 3 of the fair value hierarchy. In connection with the measurement and initial recognition of certain foreclosed assets, we may recognize charge-offs through the allowance for loan losses. Impaired Loans – Certain impaired loans may be reported at the fair value of the underlying collateral if repayment is expected solely from the collateral. Collateral values are estimated using Level 3 inputs based on customized discounting criteria or appraisals. At June 30, 2019 and December 31, 2018 , the impact of loans with specific reserves based on the fair value of the collateral was reflected in our allowance for loan losses. The following tables summarize assets measured at fair value on a recurring and nonrecurring basis segregated by the level of the valuation inputs within the fair value hierarchy utilized to measure fair value (in thousands): June 30, 2019 Fair Value Measurements at the End of the Reporting Period Using Carrying Amount Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Recurring fair value measurements Investment securities: State and political subdivisions $ 528,855 $ — $ 528,855 $ — Other stocks and bonds 2,959 — 2,959 — Mortgage-backed securities: (1) Residential 1,318,986 — 1,318,986 — Commercial 237,987 — 237,987 — Equity investments: Equity investments 5,948 5,948 — — Derivative assets: Interest rate swaps 8,964 — 8,964 — Total asset recurring fair value measurements $ 2,103,699 $ 5,948 $ 2,097,751 $ — Derivative liabilities: Interest rate swaps $ 10,072 $ — $ 10,072 $ — Total liability recurring fair value measurements $ 10,072 $ — $ 10,072 $ — Nonrecurring fair value measurements Foreclosed assets $ 1,069 $ — $ — $ 1,069 Impaired loans (2) 32,148 — — 32,148 Total asset nonrecurring fair value measurements $ 33,217 $ — $ — $ 33,217 December 31, 2018 Fair Value Measurements at the End of the Reporting Period Using Carrying Amount Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Recurring fair value measurements Investment securities: State and political subdivisions $ 716,601 $ — $ 716,601 $ — Other stocks and bonds 2,709 — 2,709 — Mortgage-backed securities: (1) Residential 732,972 — 732,972 — Commercial 537,154 — 537,154 — Equity investments: Equity investments 5,791 5,791 — — Derivative assets: Interest rate swaps 11,594 — 11,594 — Total asset recurring fair value measurements $ 2,006,821 $ 5,791 $ 2,001,030 $ — Derivative liabilities: Interest rate swaps $ 3,320 $ — $ 3,320 $ — Total liability recurring fair value measurements $ 3,320 $ — $ 3,320 $ — Nonrecurring fair value measurements Foreclosed assets $ 1,206 $ — $ — $ 1,206 Impaired loans (2) 37,813 — — 37,813 Total asset nonrecurring fair value measurements $ 39,019 $ — $ — $ 39,019 (1) All mortgage-backed securities are issued and/or guaranteed by U.S. government agencies or U.S. government-sponsored enterprises. (2) Impaired loans represent collateral-dependent loans with a specific valuation allowance. Losses on these loans represent charge-offs which are netted against the allowance for loan losses. Disclosure of fair value information about financial instruments, whether or not recognized in the balance sheet, is required when it is practicable to estimate that value. In cases where quoted market prices are not available, fair values are based on estimates using present value or other estimation techniques. Those techniques are significantly affected by the assumptions used, including the discount rate and estimates of future cash flows. Such techniques and assumptions, as they apply to individual categories of our financial instruments, are as follows: Cash and cash equivalents - The carrying amount for cash and cash equivalents is a reasonable estimate of those assets’ fair value. Investment and mortgage-backed securities held to maturity - Fair values for these securities are based on quoted market prices, where available. If quoted market prices are not available, fair values are based on quoted market prices for similar securities or estimates from independent pricing services. FHLB stock - The carrying amount of FHLB stock is a reasonable estimate of the fair value of those assets. Equity investments - The carrying value of equity investments without readily determinable fair values are measured at cost less impairment, if any, adjusted for observable price changes for an identical or similar investment of the same issuer. This carrying value is a reasonable estimate of the fair value of those assets. Loans receivable - We estimate the fair value of our loan portfolio to an exit price notion with adjustments for liquidity, credit and prepayment factors. Nonperforming loans are estimated using discounted cash flow analyses or the underlying value of the collateral where applicable. Loans held for sale – The fair value of loans held for sale is determined based on expected proceeds, which are based on sales contracts and commitments. Deposit liabilities - The fair value of demand deposits, savings accounts and certain money market deposits is the amount on demand at the reporting date, which is the carrying value. Fair values for fixed rate CDs are estimated using a discounted cash flow calculation that applies interest rates currently being offered for deposits of similar remaining maturities. Other borrowings - Federal funds purchased generally have original terms to maturity of one day and repurchase agreements generally have terms of less than one year, and therefore both are considered short-term borrowings. Consequently, their carrying value is a reasonable estimate of fair value. FHLB borrowings - The fair value of these borrowings is estimated by discounting the future cash flows using rates at which borrowings would be made to borrowers with similar credit ratings and for the same remaining maturities. Subordinated notes - The fair value of the subordinated notes is estimated by discounting future cash flows using estimated rates at which long-term debt would be made to borrowers with similar credit ratings and for the remaining maturities. Trust preferred subordinated debentures - The fair value of the long-term debt is estimated by discounting future cash flows using estimated rates at which long-term debt would be made to borrowers with similar credit ratings and for the remaining maturities. The fair value estimate of financial instruments for which quoted market prices are unavailable is dependent upon the assumptions used. Consequently, those estimates cannot be substantiated by comparison to independent markets and, in many cases, could not be realized in immediate settlement of the instruments. Accordingly, the aggregate fair value amounts presented in the following fair value tables do not necessarily represent their underlying value. The following tables present our financial assets and financial liabilities measured on a nonrecurring basis at both their respective carrying amounts and estimated fair value (in thousands): Estimated Fair Value June 30, 2019 Carrying Total Level 1 Level 2 Level 3 Financial assets: Cash and cash equivalents $ 132,521 $ 132,521 $ 132,521 $ — $ — Investment securities: Held to maturity, at carrying value 3,018 3,054 — 3,054 — Mortgage-backed securities: Held to maturity, at carrying value 144,073 148,253 — 148,253 — Federal Home Loan Bank stock, at cost 44,718 44,718 — 44,718 — Equity investments 6,426 6,426 — 6,426 — Loans, net of allowance for loan losses 3,435,438 3,493,559 — — 3,493,559 Loans held for sale 1,812 1,812 — 1,812 — Financial liabilities: Deposits $ 4,479,256 $ 4,478,936 $ — $ 4,478,936 $ — Other borrowings 26,064 26,064 — 26,064 — Federal Home Loan Bank borrowings 823,757 825,450 — 825,450 — Subordinated notes, net of unamortized debt issuance costs 98,490 98,964 — 98,964 — Trust preferred subordinated debentures, net of unamortized debt issuance costs 60,248 58,819 — 58,819 — Estimated Fair Value December 31, 2018 Carrying Total Level 1 Level 2 Level 3 Financial assets: Cash and cash equivalents $ 120,719 $ 120,719 $ 120,719 $ — $ — Investment securities: Held to maturity, at carrying value 3,083 3,046 — 3,046 — Mortgage-backed securities: Held to maturity, at carrying value 159,848 156,735 — 156,735 — Federal Home Loan Bank stock, at cost 32,583 32,583 — 32,583 — Equity investments 6,302 6,302 — 6,302 — Loans, net of allowance for loan losses 3,285,780 3,251,923 — — 3,251,923 Loans held for sale 601 601 — 601 — Financial liabilities: Deposits $ 4,425,030 $ 4,417,902 $ — $ 4,417,902 $ — Other borrowings 36,810 36,810 — 36,810 — Federal Home Loan Bank borrowings 719,065 708,904 — 708,904 — Subordinated notes, net of unamortized debt issuance costs 98,407 97,611 — 97,611 — Trust preferred subordinated debentures, net of unamortized debt issuance costs 60,246 54,729 — 54,729 —

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2019
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The income tax expense included in the accompanying consolidated statements of income consists of the following (in thousands): Three Months Ended Six Months Ended 2019 2018 2019 2018 Current income tax expense $ 3,553 $ 667 $ 6,564 $ 3,012 Deferred income tax expense 16 2,693 142 2,438 Income tax expense $ 3,569 $ 3,360 $ 6,706 $ 5,450 The net deferred tax liability totaled $5.0 million at June 30, 2019 as compared to a net deferred asset of $9.8 million at December 31, 2018 . No valuation allowance was recorded at June 30, 2019 or December 31, 2018 , as management believes it is more likely than not that all of the deferred tax asset items will be realized in future years. Unrecognized tax benefits were not material at June 30, 2019 or December 31, 2018 . We recognized income tax expense of $3.6 million and $6.7 million , for an effective tax rate (“ETR”) of 16.1% and 15.2% for the three and six months ended June 30, 2019 , respectively, compared to income tax expense of $3.4 million and $5.5 million , for an ETR of 14.3% and 13.0% , for the three and six months ended June 30, 2018 , respectively. The higher ETR for the three and six months ended June 30, 2019 was mainly due to a decrease in tax-exempt income as a percentage of pre-tax income as compared to the same periods in 2018. The ETR differs from the stated rate of 21% for the three and six months ended June 30, 2019 and 2018 primarily due to the effect of tax-exempt income from municipal loans and securities, as well as bank owned life insurance. We file income tax returns in the U.S. federal jurisdictions and in certain states. We are no longer subject to U.S. federal income tax examinations by tax authorities for years before 2015 or Texas state tax examinations by tax authorities for years before 2014

Leases

Leases	6 Months Ended
	Jun. 30, 2019
Leases [Abstract]
Leases	Leases We lease certain retail- and full-service branch locations, ATM locations, certain equipment and a loan production office . Leases with an initial term of twelve months or less are not recorded on the balance sheet. Operating lease cost, which is comprised of the amortization of the ROU asset and the implicit interest accreted on the operating lease liability, is recognized on a straight-line basis over the lease term and is included in net occupancy expense on our consolidated statements of income. We evaluate the lease term by assuming the exercise of options to extend that are reasonably assured and those option periods covered by an option to terminate the lease, if deemed not reasonably certain to be exercised. The lease term is used to determine the straight-line expense and limits the depreciable life of any related leasehold improvements. Certain leases require us to pay real estate taxes, insurance, maintenance and other operating expenses associated with the leased premises. These expenses are classified in net occupancy expense on our consolidated statements of income, consistent with similar costs for owned locations, but is not included in operating lease cost below. Our leases have remaining lease terms ranging from 4 months to 19.9 years , some of which include options to extend the leases for up to 10 years , and some of which include options to terminate the leases within 2 years . We calculate the lease liability using a discount rate that represents our incremental borrowing rate at the lease commencement date. We are also party to operating leases where we lease properties we own to third parties. Operating lease income received from tenants who rent our properties is reported as a reduction to occupancy expense on our consolidated statements of income. The underlying assets associated with these operating leases are included in premises and equipment on our consolidated balance sheets. Balance sheet information related to leases was as follows (in thousands): June 30, 2019 Operating leases: Operating lease right-of-use assets $ 9,812 Operating lease liabilities $ 10,204 The components of lease cost were as follows (in thousands): Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 Operating lease cost $ 395 $ 789 Supplemental cash flow information related to leases was as follows (in thousands): Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 Cash paid for amounts included in the measurement of the lease liabilities: Operating cash flows from operating leases $ 360 $ 700 Right-of-use assets obtained in exchange for new operating lease liabilities $ 654 $ 654 Additional information related to leases was as follows: June 30, 2019 Weighted average remaining lease term (in years) 12.5 Weighted average discount rate 3.88 % Future minimum rental commitments due under non-cancelable operating leases at June 30, 2019 were as follows (in thousands): Year ending December 31, 2019 (excluding the six months ended June 30, 2019) $ 625 2020 1,338 2021 1,232 2022 1,193 2023 1,044 2024 and thereafter 7,866 Total lease payments (1) 13,298 Less: Interest (3,094 ) Present value of lease liabilities $ 10,204 (1) Excludes $9.1 million of lease payments for a lease executed but not yet commenced. Lease will commence in 2020 with a lease term of 20.4 years . We also lease certain of our owned facilities or portions thereof to third parties. Our primary leased facility is a 202,000 square-foot office building in Fort Worth, Texas that is used for a branch location and certain bank operations. We occupy approximately 41,000 square feet of the building and lease the remaining space to various tenants. Some of these leases contain options to renew and options to terminate at the discretion of the tenant. Gross rental income from these leases were as follows (in thousands): Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 Gross rental income $ 742 $ 1,487 At June 30, 2019 , non-cancelable operating leases with future minimum lease payments are as follows (in thousands): Year ending December 31, 2019 (excluding the six months ended June 30, 2019) $ 1,388 2020 2,693 2021 1,576 2022 1,553 2023 1,316 2024 and thereafter 4,098 Total lease payments $ 12,624
Leases	Leases We lease certain retail- and full-service branch locations, ATM locations, certain equipment and a loan production office . Leases with an initial term of twelve months or less are not recorded on the balance sheet. Operating lease cost, which is comprised of the amortization of the ROU asset and the implicit interest accreted on the operating lease liability, is recognized on a straight-line basis over the lease term and is included in net occupancy expense on our consolidated statements of income. We evaluate the lease term by assuming the exercise of options to extend that are reasonably assured and those option periods covered by an option to terminate the lease, if deemed not reasonably certain to be exercised. The lease term is used to determine the straight-line expense and limits the depreciable life of any related leasehold improvements. Certain leases require us to pay real estate taxes, insurance, maintenance and other operating expenses associated with the leased premises. These expenses are classified in net occupancy expense on our consolidated statements of income, consistent with similar costs for owned locations, but is not included in operating lease cost below. Our leases have remaining lease terms ranging from 4 months to 19.9 years , some of which include options to extend the leases for up to 10 years , and some of which include options to terminate the leases within 2 years . We calculate the lease liability using a discount rate that represents our incremental borrowing rate at the lease commencement date. We are also party to operating leases where we lease properties we own to third parties. Operating lease income received from tenants who rent our properties is reported as a reduction to occupancy expense on our consolidated statements of income. The underlying assets associated with these operating leases are included in premises and equipment on our consolidated balance sheets. Balance sheet information related to leases was as follows (in thousands): June 30, 2019 Operating leases: Operating lease right-of-use assets $ 9,812 Operating lease liabilities $ 10,204 The components of lease cost were as follows (in thousands): Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 Operating lease cost $ 395 $ 789 Supplemental cash flow information related to leases was as follows (in thousands): Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 Cash paid for amounts included in the measurement of the lease liabilities: Operating cash flows from operating leases $ 360 $ 700 Right-of-use assets obtained in exchange for new operating lease liabilities $ 654 $ 654 Additional information related to leases was as follows: June 30, 2019 Weighted average remaining lease term (in years) 12.5 Weighted average discount rate 3.88 % Future minimum rental commitments due under non-cancelable operating leases at June 30, 2019 were as follows (in thousands): Year ending December 31, 2019 (excluding the six months ended June 30, 2019) $ 625 2020 1,338 2021 1,232 2022 1,193 2023 1,044 2024 and thereafter 7,866 Total lease payments (1) 13,298 Less: Interest (3,094 ) Present value of lease liabilities $ 10,204 (1) Excludes $9.1 million of lease payments for a lease executed but not yet commenced. Lease will commence in 2020 with a lease term of 20.4 years . We also lease certain of our owned facilities or portions thereof to third parties. Our primary leased facility is a 202,000 square-foot office building in Fort Worth, Texas that is used for a branch location and certain bank operations. We occupy approximately 41,000 square feet of the building and lease the remaining space to various tenants. Some of these leases contain options to renew and options to terminate at the discretion of the tenant. Gross rental income from these leases were as follows (in thousands): Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 Gross rental income $ 742 $ 1,487 At June 30, 2019 , non-cancelable operating leases with future minimum lease payments are as follows (in thousands): Year ending December 31, 2019 (excluding the six months ended June 30, 2019) $ 1,388 2020 2,693 2021 1,576 2022 1,553 2023 1,316 2024 and thereafter 4,098 Total lease payments $ 12,624

Off-Balance-Sheet Arrangements,

Off-Balance-Sheet Arrangements, Commitments and Contingencies	6 Months Ended
	Jun. 30, 2019
Commitments and Contingencies Disclosure [Abstract]
Off-Balance-Sheet Arrangements, Commitments and Contingencies	Off-Balance-Sheet Arrangements, Commitments and Contingencies Financial Instruments with Off-Balance-Sheet Risk . In the normal course of business, we are a party to certain financial instruments with off-balance-sheet risk to meet the financing needs of our customers. These off-balance-sheet instruments include commitments to extend credit and standby letters of credit. These instruments involve, to varying degrees, elements of credit and interest rate risk in excess of the amount reflected in the financial statements. The contract or notional amounts of these instruments reflect the extent of involvement and exposure to credit loss that we have in these particular classes of financial instruments. Commitments to extend credit are agreements to lend to a customer provided that the terms established in the contract are met. Commitments generally have fixed expiration dates and may require the payment of fees. Since some commitments are expected to expire without being drawn upon, the total commitment amounts do not necessarily represent future cash requirements. Standby letters of credit are conditional commitments issued to guarantee the performance of a customer to a third party. These guarantees are primarily issued to support public and private borrowing arrangements. The credit risk involved in issuing letters of credit is essentially the same as that involved in extending loan commitments to customers and similarly do not necessarily represent future cash obligations. Financial instruments with off-balance-sheet risk were as follows (in thousands): June 30, 2019 December 31, 2018 Unused commitments: Commitments to extend credit $ 1,024,034 $ 874,557 Standby letters of credit 27,463 27,438 Total $ 1,051,497 $ 901,995 We apply the same credit policies in making commitments and standby letters of credit as we do for on-balance-sheet instruments. We evaluate each customer’s creditworthiness on a case-by-case basis. The amount of collateral obtained, if deemed necessary, upon extension of credit is based on management’s credit evaluation of the borrower. Collateral held varies but may include cash or cash equivalents, negotiable instruments, real estate, accounts receivable, inventory, oil, gas and mineral interests, property, plant and equipment. Securities . In the normal course of business we buy and sell securities. At June 30, 2019 , there were $38.6 million of unsettled trades to purchase securities and no unsettled trades to sell securities. At December 31, 2018 , there were $6.4 million unsettled trades to purchase securities and no unsettled trades to sell securities. Deposits . There were no unsettled issuances of brokered certificates of deposits (“CD”) at June 30, 2019 . There were $15.2 million unsettled issuances of brokered CDs at December 31, 2018 . Litigation . We are involved with various litigation in the normal course of business. Management, after consulting with our legal counsel, believes that any liability resulting from litigation will not have a material effect on our financial position, results of operations or liquidity.

Summary of Significant Accoun_2

Summary of Significant Accounting and Reporting Policies (Policies)	6 Months Ended
	Jun. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation In this report, the words “the Company,” “we,” “us,” and “our” refer to the combined entities of Southside Bancshares, Inc. and its subsidiaries, including Southside Bank. The words “Southside” and “Southside Bancshares” refer to Southside Bancshares, Inc. The words “Southside Bank” and “the Bank” refer to Southside Bank. “Diboll” refers to Diboll State Bancshares, Inc., a bank holding company and its wholly-owned subsidiary, First Bank & Trust East Texas, acquired by Southside on November 30, 2017. The accompanying unaudited consolidated financial statements have been prepared in accordance with United States (“U.S.”) generally accepted accounting principles (“GAAP”) for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, not all information required by GAAP for complete financial statements is included in these interim statements. In the opinion of management, all adjustments necessary for a fair presentation of such financial statements have been included. Such adjustments consisted only of normal recurring items. The preparation of these consolidated financial statements in accordance with GAAP requires the use of management’s estimates. These estimates are subjective in nature and involve matters of judgment. Actual amounts could differ from these estimates. Interim results are not necessarily indicative of results for a full year. These financial statements should be read in conjunction with the financial statements and notes thereto in our Annual Report on Form 10-K for the year ended December 31, 2018 . Accounting Changes and Reclassifications Certain prior period amounts may be reclassified to conform to current year presentation. Debt Securities We adopted Accounting Standards Update (“ASU”) 2017-08, “Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities,” on January 1, 2019, the effective date of the guidance. Under previous GAAP, premiums on callable debt securities were generally amortized over the contractual life of the security. ASU 2017-08 requires the premium on callable debt securities to be amortized to the earliest call date. If the debt security is not called at the earliest call date, the holder of the debt security would be required to reset the effective yield on the debt security based on the payment terms required by the debt security. The guidance requires companies to apply the requirements on a modified retrospective basis through a cumulative-effect adjustment directly to retained earnings as of the beginning of the period of adoption. Adoption of this guidance on January 1, 2019, resulted in a cumulative-effect adjustment to reduce retained earnings by $16.5 million , before tax. Subsequent to January 1, 2019, we sold the majority of the securities impacted by ASU 2017-08, and thus, the standard did not materially impact our consolidated net income.
Leases	Leases We evaluate our contracts at inception to determine if an arrangement is or contains a lease. Operating leases are included in operating lease right-of-use (“ROU”) assets and operating lease liabilities in our consolidated balance sheets. The Company has no finance leases. ROU assets represent our right to use an underlying asset for the lease term, and lease liabilities represent our obligation to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at commencement date based on the present value of lease payments over the lease term. Our leases do not provide an implicit rate, so we use our incremental borrowing rate based on the information available at commencement date in determining the present value of lease payments. The incremental borrowing rate is reevaluated upon lease modification. The operating lease ROU asset also includes any initial direct costs and prepaid lease payments made less any lease incentives. Our lease terms may include options to extend or terminate the lease when it is reasonably certain that we will exercise that option. We adopted ASU 2016-02, “Leases (Topic 842),” on January 1, 2019, the effective date of the guidance, using the practical expedient transition method whereby we did not revise comparative period information or disclosure. The new standard requires lessees to record assets and liabilities on the balance sheet for all leases with terms longer than 12 months. We elected the package of practical expedients permitted under the transition guidance within the new standard, which among other things, allows us to carryforward the historical lease classification. We also elected certain optional practical expedients including the hindsight practical expedient under which we considered the actual outcomes of lease renewals and terminations when measuring the lease term at adoption, and we made an accounting policy election to keep leases with an initial term of 12 months or less off of the balance sheet. We recognize these lease payments in the consolidated statements of income on a straight-line basis over the lease term. We have lease agreements with lease and non-lease components, and we have elected the practical expedient to account for these as a single lease component. Our operating leases relate primarily to bank branches and office space. In conjunction with the adoption of ASU 2016-02 on January 1, 2019, we recognized operating lease liabilities of $10.1 million and related lease assets of $9.8 million on our balance sheet. The difference between the lease assets and lease liabilities primarily consists of deferred rent liabilities reclassified upon adoption to reduce the measurement of the lease assets. The standard did not materially impact our consolidated net income and had no impact on cash flows.
Accounting Pronouncements	Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, “Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments” (“CECL”). ASU 2016-13 introduces an approach based on expected losses to estimate credit losses on certain types of financial instruments. ASU 2016-13 also modifies the impairment model for AFS debt securities and provides for a simplified accounting model for purchased financial assets with credit deterioration since their origination. ASU 2016-13 is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. Early adoption is permitted for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. The guidance requires companies to apply the requirements in the year of adoption through a cumulative-effect adjustment with some aspects of the update requiring a prospective transition approach. We are currently evaluating the potential impact of the pending adoption of ASU 2016-13 on our consolidated financial statements. We plan to adopt ASU 2016-13 on January 1, 2020, the effective date. We have developed a project plan, assigned a project team to complete the analysis needed to implement the guidance and engaged a third party vendor solution to assist with the application of ASU 2016-13. During the second quarter of 2019, the project team entered the parallel phase of the project during which the team will run parallel models to evaluate system processes, data generation and refine aspects of the transition to CECL. In January 2017, the FASB issued ASU 2017-04, “Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment.” ASU 2017-04 is intended to simplify goodwill impairment testing by eliminating the second step of the analysis which requires the calculation of the implied fair value of goodwill to measure a goodwill impairment charge. The update requires entities to compare the fair value of a reporting unit with its carrying amount and recognize an impairment charge for any amount by which the carrying amount exceeds the reporting unit’s fair value, to the extent that the loss recognized does not exceed the amount of goodwill allocated to that reporting unit. ASU 2017-04 is effective for annual and interim goodwill impairment tests performed in periods beginning after December 15, 2019. Early adoption is permitted for annual and interim goodwill impairment testing dates after January 1, 2017. The guidance requires companies to apply the requirements prospectively in the year of adoption. ASU 2017-04 is not expected to have a material impact on our consolidated financial statements.

Earnings Per Share (Tables)

Earnings Per Share (Tables)	6 Months Ended
	Jun. 30, 2019
Earnings Per Share [Abstract]
Earnings per share on a basic and diluted basis	Earnings per share on a basic and diluted basis are calculated as follows (in thousands, except per share amounts): Three Months Ended Six Months Ended 2019 2018 2019 2018 Basic and Diluted Earnings: Net income $ 18,610 $ 20,203 $ 37,427 $ 36,454 Basic weighted-average shares outstanding 33,726 35,062 33,711 35,042 Add: Stock awards 150 171 151 175 Diluted weighted-average shares outstanding 33,876 35,233 33,862 35,217 Basic earnings per share: Net Income $ 0.55 $ 0.58 $ 1.11 $ 1.04 Diluted earnings per share: Net Income $ 0.55 $ 0.57 $ 1.11 $ 1.04

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Tables)	6 Months Ended
	Jun. 30, 2019
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Schedule of accumulated other comprehensive income (loss) by component	The changes in accumulated other comprehensive income (loss) by component are as follows (in thousands): Three Months Ended June 30, 2019 Pension Plans Unrealized Gains (Losses) on Securities Unrealized Gains (Losses) on Derivatives Net Prior Service (Cost) Credit Net Gain (Loss) Total Beginning balance, net of tax $ 5,901 $ 4,153 $ (140 ) $ (25,687 ) $ (15,773 ) Other comprehensive income (loss): Other comprehensive income (loss) before reclassifications 32,196 (5,653 ) — — 26,543 Reclassification adjustments included in net income (336 ) (642 ) (3 ) 651 (330 ) Income tax (expense) benefit (6,691 ) 1,322 1 (137 ) (5,505 ) Net current-period other comprehensive income (loss), net of tax 25,169 (4,973 ) (2 ) 514 20,708 Ending balance, net of tax $ 31,070 $ (820 ) $ (142 ) $ (25,173 ) $ 4,935 Six Months Ended June 30, 2019 Pension Plans Unrealized Gains (Losses) on Securities Unrealized Gains (Losses) on Derivatives Net Prior Net Gain (Loss) Total Beginning balance, net of tax $ (31,120 ) $ 7,146 $ (139 ) $ (26,115 ) $ (50,228 ) Other comprehensive income (loss): Other comprehensive income (loss) before reclassifications 78,822 (8,773 ) — — 70,049 Reclassification adjustments included in net income (101 ) (1,310 ) (4 ) 1,193 (222 ) Income tax (expense) benefit (16,531 ) 2,117 1 (251 ) (14,664 ) Net current-period other comprehensive income (loss), net of tax 62,190 (7,966 ) (3 ) 942 55,163 Ending balance, net of tax $ 31,070 $ (820 ) $ (142 ) $ (25,173 ) $ 4,935 Three Months Ended June 30, 2018 Pension Plans Unrealized Gains (Losses) on Securities Unrealized Gains (Losses) on Derivatives Net Prior Service (Cost) Credit Net Gain (Loss) Total Beginning balance, net of tax $ (35,594 ) $ 9,652 $ (134 ) $ (25,894 ) $ (51,970 ) Other comprehensive income (loss): Other comprehensive (loss) income before reclassifications (10,371 ) 1,725 — — (8,646 ) Reclassification adjustments included in net income 1,584 (331 ) (2 ) 620 1,871 Income tax benefit (expense) 1,845 (293 ) 1 (130 ) 1,423 Net current-period other comprehensive (loss) income, net of tax (6,942 ) 1,101 (1 ) 490 (5,352 ) Ending balance, net of tax $ (42,536 ) $ 10,753 $ (135 ) $ (25,404 ) $ (57,322 ) Six Months Ended June 30, 2018 Pension Plans Unrealized Gains (Losses) on Securities Unrealized Gains (Losses) on Derivatives Net Prior Service (Cost) Credit Net Gain (Loss) Total Beginning balance, net of tax $ (16,295 ) $ 6,399 $ (133 ) $ (26,269 ) $ (36,298 ) Cumulative effect of ASU 2016-01 (1) 85 — — — 85 Adjusted beginning balance, net of tax (16,210 ) 6,399 (133 ) (26,269 ) (36,213 ) Other comprehensive income (loss): Other comprehensive (loss) income before reclassifications (35,872 ) 5,970 — — (29,902 ) Reclassification adjustments included in net income 2,549 (458 ) (4 ) 1,095 3,182 Income tax benefit (expense) 6,997 (1,158 ) 2 (230 ) 5,611 Net current-period other comprehensive (loss) income, net of tax (26,326 ) 4,354 (2 ) 865 (21,109 ) Ending balance, net of tax $ (42,536 ) $ 10,753 $ (135 ) $ (25,404 ) $ (57,322 ) (1) The Company adopted ASU 2016-01 on January 1, 2018. This amount includes a reclassification for the cumulative adjustment to retained earnings of $107,000 ( $85,000 , net of tax).
Reclassifications out of accumulated other comprehensive income	The reclassification adjustments out of accumulated other comprehensive income (loss) included in net income are presented below (in thousands): Three Months Ended Six Months Ended 2019 2018 2019 2018 Unrealized losses on securities transferred: Amortization of unrealized losses (1) $ (80 ) $ (1,252 ) $ (571 ) $ (1,390 ) Tax benefit 17 263 120 292 Net of tax (63 ) (989 ) (451 ) (1,098 ) Unrealized gains and losses on available for sale securities: Realized net gain (loss) on sale of securities (2) 416 (332 ) 672 (1,159 ) Tax (expense) benefit (87 ) 70 (141 ) 243 Net of tax 329 (262 ) 531 (916 ) Derivatives: Realized net gain on interest rate swap derivatives (3) 621 309 1,267 415 Tax expense (130 ) (65 ) (266 ) (87 ) Net of tax 491 244 1,001 328 Amortization of unrealized gains on terminated interest rate swap derivatives (3) 21 22 43 43 Tax expense (4 ) (5 ) (9 ) (9 ) Net of tax 17 17 34 34 Amortization of pension plan: Net actuarial loss (4) (651 ) (620 ) (1,193 ) (1,095 ) Prior service credit (4) 3 2 4 4 Total before tax (648 ) (618 ) (1,189 ) (1,091 ) Tax benefit 136 129 250 228 Net of tax (512 ) (489 ) (939 ) (863 ) Total reclassifications for the period, net of tax $ 262 $ (1,479 ) $ 176 $ (2,515 ) (1) Included in interest income on the consolidated statements of income. (2) Listed as net gain (loss) on sale of securities available for sale on the consolidated statements of income. (3) Included in interest expense for Federal Home Loan Bank of Dallas (“FHLB”) borrowings on the consolidated statements of income. (4) These accumulated other comprehensive income components are included in the computation of net periodic pension cost (income) presented in “Note 9 - Employee Benefit Plans.”

Securities (Tables)

Securities (Tables)	6 Months Ended
	Jun. 30, 2019
Investments, Debt and Equity Securities [Abstract]
Amortized cost and estimated fair value of investment and mortgage-backed securities	The amortized cost, gross unrealized gains and losses and estimated fair value of investment and mortgage-backed securities available for sale (“AFS”) and held to maturity (“HTM”) as of June 30, 2019 and December 31, 2018 are reflected in the tables below (in thousands): June 30, 2019 Amortized Gross Unrealized Gross Unrealized Estimated AVAILABLE FOR SALE Cost Gains Losses Fair Value Investment securities: State and political subdivisions $ 512,575 $ 16,758 $ 478 $ 528,855 Other stocks and bonds 3,000 — 41 2,959 Mortgage-backed securities: (1) Residential 1,296,888 22,944 846 1,318,986 Commercial 233,044 4,963 20 237,987 Total $ 2,045,507 $ 44,665 $ 1,385 $ 2,088,787 HELD TO MATURITY Investment securities: State and political subdivisions $ 3,018 $ 36 $ — $ 3,054 Mortgage-backed securities: (1) Residential 59,756 2,496 144 62,108 Commercial 84,317 1,984 156 86,145 Total $ 147,091 $ 4,516 $ 300 $ 151,307 December 31, 2018 Amortized Gross Unrealized Gross Unrealized Estimated AVAILABLE FOR SALE Cost Gains Losses Fair Value Investment securities: State and political subdivisions $ 728,142 $ 6,115 $ 17,656 $ 716,601 Other stocks and bonds 3,000 — 291 2,709 Mortgage-backed securities: (1) Residential 738,585 3,498 9,111 732,972 Commercial 543,758 941 7,545 537,154 Total $ 2,013,485 $ 10,554 $ 34,603 $ 1,989,436 HELD TO MATURITY Investment securities: State and political subdivisions $ 3,083 $ 5 $ 42 $ 3,046 Mortgage-backed securities: (1) Residential 59,655 154 1,140 58,669 Commercial 100,193 201 2,328 98,066 Total $ 162,931 $ 360 $ 3,510 $ 159,781 (1) All mortgage-backed securities issued and/or guaranteed by U.S. government agencies or U.S. government-sponsored enterprises.
Unrealized loss on securities	The following tables represent the estimated fair value and unrealized loss on investment and mortgage-backed securities AFS and HTM as of June 30, 2019 and December 31, 2018 (in thousands): June 30, 2019 Less Than 12 Months More Than 12 Months Total Fair Value Unrealized Loss Fair Value Unrealized Loss Fair Value Unrealized Loss AVAILABLE FOR SALE Investment securities: State and political subdivisions $ 2,281 $ 10 $ 28,087 $ 468 $ 30,368 $ 478 Other stocks and bonds 2,959 41 — — 2,959 41 Mortgage-backed securities: Residential 629 2 91,649 844 92,278 846 Commercial — — 15,033 20 15,033 20 Total $ 5,869 $ 53 $ 134,769 $ 1,332 $ 140,638 $ 1,385 HELD TO MATURITY Mortgage-backed securities: Residential $ — $ — $ 2,579 $ 144 $ 2,579 $ 144 Commercial — — 14,701 156 14,701 156 Total $ — $ — $ 17,280 $ 300 $ 17,280 $ 300 December 31, 2018 Less Than 12 Months More Than 12 Months Total Fair Value Unrealized Fair Value Unrealized Fair Value Unrealized AVAILABLE FOR SALE Investment securities: State and political subdivisions $ 98,112 $ 899 $ 399,205 $ 16,757 $ 497,317 $ 17,656 Other stocks and bonds 2,709 291 — — 2,709 291 Mortgage-backed securities: Residential 5,552 27 488,334 9,084 493,886 9,111 Commercial 9,529 30 457,704 7,515 467,233 7,545 Total $ 115,902 $ 1,247 $ 1,345,243 $ 33,356 $ 1,461,145 $ 34,603 HELD TO MATURITY Investment securities: State and political subdivisions $ 235 $ 1 $ 2,022 $ 41 $ 2,257 $ 42 Mortgage-backed securities: Residential 4,826 60 51,046 1,080 55,872 1,140 Commercial 399 2 89,168 2,326 89,567 2,328 Total $ 5,460 $ 63 $ 142,236 $ 3,447 $ 147,696 $ 3,510
Interest income recognized on securities	The following table reflects interest income recognized on securities for the periods presented (in thousands): Three Months Ended 2019 2018 U.S. Treasury $ — $ 23 State and political subdivisions 3,527 6,353 Other stocks and bonds 27 28 Mortgage-backed securities 13,246 10,210 Total interest income on securities $ 16,800 $ 16,614 Six Months Ended 2019 2018 U.S. Treasury $ — $ 131 U.S. government agency debentures — 89 State and political subdivisions 7,645 12,734 Other stocks and bonds 55 58 Mortgage-backed securities 25,720 21,104 Total interest income on securities $ 33,420 $ 34,116
Amortized cost, carrying value and fair value of securities presented by contractual maturity	The amortized cost and estimated fair value of AFS and HTM securities at June 30, 2019 , are presented below by contractual maturity (in thousands). Expected maturities may differ from contractual maturities because issuers may have the right to call or prepay obligations. MBS are presented in total by category due to the fact that MBS typically are issued with stated principal amounts, and the securities are backed by pools of mortgages that have loans with varying maturities. The characteristics of the underlying pool of mortgages, such as fixed-rate or adjustable-rate, as well as prepayment risk, are passed on to the security holder. The term of a mortgage-backed pass-through security thus approximates the term of the underlying mortgages and can vary significantly due to prepayments. June 30, 2019 Amortized Cost Fair Value AVAILABLE FOR SALE Investment securities: Due in one year or less $ 3,349 $ 3,363 Due after one year through five years 8,406 8,469 Due after five years through ten years 28,488 29,573 Due after ten years 475,332 490,409 515,575 531,814 Mortgage-backed securities 1,529,932 1,556,973 Total $ 2,045,507 $ 2,088,787 June 30, 2019 Amortized Cost Fair Value HELD TO MATURITY Investment securities: Due in one year or less $ 115 $ 115 Due after one year through five years 1,658 1,675 Due after five years through ten years 1,245 1,264 Due after ten years — — 3,018 3,054 Mortgage-backed securities: 144,073 148,253 Total $ 147,091 $ 151,307
Unrealized and realized gains (losses) recognized in net income on equity investments	The following is a summary of unrealized and realized gains and losses on equity investments recognized in other noninterest income in the consolidated statements of income during the three and six months ended June 30, 2019 and 2018 (in thousands): Three Months Ended Six Months Ended 2019 2018 2019 2018 Net gains (losses) recognized during the period on equity investments $ 87 $ (42 ) $ 163 $ (134 ) Less: Net gains (losses) recognized during the period on equity investments sold during the period — — — — Unrealized gains (losses) recognized during the reporting period on equity investments still held at the reporting date $ 87 $ (42 ) $ 163 $ (134 )

Loans and Allowance for Proba_2

Loans and Allowance for Probable Loan Losses (Tables)	6 Months Ended
	Jun. 30, 2019
Receivables [Abstract]
Classification of loans in the consolidated balance sheets	Loans in the accompanying consolidated balance sheets are classified as follows (in thousands): June 30, 2019 December 31, 2018 Real estate loans: Construction $ 579,565 $ 507,732 1-4 family residential 782,073 794,499 Commercial 1,251,248 1,194,118 Commercial loans 389,521 356,649 Municipal loans 357,028 353,370 Loans to individuals 100,708 106,431 Total loans 3,460,143 3,312,799 Less: Allowance for loan losses (1) 24,705 27,019 Net loans $ 3,435,438 $ 3,285,780 (1) The allowance for loan losses recorded on purchased credit impaired (“PCI”) loans totaled $139,000 and $302,000 as of June 30, 2019 and December 31, 2018 , respectively.
Activity in the allowance for loan losses by portfolio segment	The following tables detail activity in the allowance for loan losses by portfolio segment for the periods presented (in thousands): Three Months Ended June 30, 2019 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans Municipal Loans Loans to Individuals Total Balance at beginning of period $ 4,259 $ 3,382 $ 10,660 $ 4,287 $ 508 $ 1,059 $ 24,155 Provision (reversal) for loan losses (2) (660 ) 137 1,516 1,266 22 225 2,506 Loans charged off — — (1,661 ) (130 ) — (606 ) (2,397 ) Recoveries of loans charged off — 3 19 123 — 296 441 Balance at end of period $ 3,599 $ 3,522 $ 10,534 $ 5,546 $ 530 $ 974 $ 24,705 Six Months Ended June 30, 2019 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans Municipal Loans Loans to Individuals Total Balance at beginning of period $ 3,597 $ 3,844 $ 13,968 $ 3,974 $ 525 $ 1,111 $ 27,019 Provision (reversal) for loan losses (2) 2 (310 ) (596 ) 2,000 5 487 1,588 Loans charged off — (18 ) (2,876 ) (581 ) — (1,207 ) (4,682 ) Recoveries of loans charged off — 6 38 153 — 583 780 Balance at end of period $ 3,599 $ 3,522 $ 10,534 $ 5,546 $ 530 $ 974 $ 24,705 Three Months Ended June 30, 2018 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans Municipal Loans Loans to Individuals Total Balance at beginning of period $ 3,597 $ 2,377 $ 14,089 $ 2,385 $ 851 $ 921 $ 24,220 Provision (reversal) for loan losses (2) 244 403 (57 ) 328 8 355 1,281 Loans charged off — (57 ) — (172 ) — (688 ) (917 ) Recoveries of loans charged off — 7 4 19 — 458 488 Balance at end of period $ 3,841 $ 2,730 $ 14,036 $ 2,560 $ 859 $ 1,046 $ 25,072 Six Months Ended June 30, 2018 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans Municipal Loans Loans to Individuals Total Balance at beginning of period (1) $ 3,676 $ 2,445 $ 10,821 $ 2,094 $ 860 $ 885 $ 20,781 Provision (reversal) for loan losses (2) 179 321 3,209 661 (1 ) 647 5,016 Loans charged off (14 ) (57 ) — (257 ) — (1,356 ) (1,684 ) Recoveries of loans charged off — 21 6 62 — 870 959 Balance at end of period $ 3,841 $ 2,730 $ 14,036 $ 2,560 $ 859 $ 1,046 $ 25,072 (1) Loans acquired with the Diboll acquisition were measured at fair value on November 30, 2017 with no carryover of allowance for loan losses. (2) Of the $2.5 million and $1.6 million provision for loan losses for the three and six months ended June 30, 2019 , $111,000 and $163,000 related to provision expense reversed on PCI loans, respectively. Of the $1.3 million and $5.0 million recorded in provision for loan losses for the three and six months ended June 30, 2018 , $358,000 related to provision expense on PCI loans.
Balance in the allowance for loan losses by portfolio segment based on impairment method	The following tables present the balance in the allowance for loan losses by portfolio segment based on impairment method (in thousands): June 30, 2019 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans Municipal Loans Loans to Individuals Total Ending balance – individually evaluated for impairment (1) $ 23 $ 66 $ 1,408 $ 782 $ — $ 90 $ 2,369 Ending balance – collectively evaluated for impairment 3,576 3,456 9,126 4,764 530 884 22,336 Balance at end of period $ 3,599 $ 3,522 $ 10,534 $ 5,546 $ 530 $ 974 $ 24,705 December 31, 2018 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans Municipal Loans Loans to Individuals Total Ending balance – individually evaluated for impairment (1) $ 13 $ 40 $ 5,337 $ 368 $ 1 $ 149 $ 5,908 Ending balance – collectively evaluated for impairment 3,584 3,804 8,631 3,606 524 962 21,111 Balance at end of period $ 3,597 $ 3,844 $ 13,968 $ 3,974 $ 525 $ 1,111 $ 27,019 (1) The allowance for loan losses on PCI loans totaled $139,000 and $302,000 as of June 30, 2019 and December 31, 2018 , respectively.
Balance in recorded investments in loans by portfolio segment based on impairment method	The following tables present the recorded investment in loans by portfolio segment based on impairment method (in thousands): June 30, 2019 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans Municipal Loans Loans to Individuals Total Loans individually evaluated for impairment $ 200 $ 1,268 $ 21,361 $ 2,523 $ 429 $ 136 $ 25,917 Loans collectively evaluated for impairment 579,226 772,725 1,198,899 385,322 356,599 100,354 3,393,125 Purchased credit impaired loans 139 8,080 30,988 1,676 — 218 41,101 Total ending loan balance $ 579,565 $ 782,073 $ 1,251,248 $ 389,521 $ 357,028 $ 100,708 $ 3,460,143 December 31, 2018 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans Municipal Loans Loans to Individuals Total Loans individually evaluated for impairment $ 12 $ 1,215 $ 33,013 $ 1,394 $ 429 $ 184 $ 36,247 Loans collectively evaluated for impairment 507,564 782,614 1,128,220 353,036 352,941 105,775 3,230,150 Purchased credit impaired loans 156 10,670 32,885 2,219 — 472 46,402 Total ending loan balance $ 507,732 $ 794,499 $ 1,194,118 $ 356,649 $ 353,370 $ 106,431 $ 3,312,799
Summary of loans by credit quality indicators	The following tables set forth credit quality indicators by class of loans for the periods presented (in thousands): June 30, 2019 Pass Pass Watch (1) Special Mention (1) Substandard (1) Doubtful (1) Total Real estate loans: Construction $ 579,253 $ 47 $ — $ 265 $ — $ 579,565 1-4 family residential 776,375 31 166 4,784 717 782,073 Commercial 1,150,646 55,208 7,444 37,793 157 1,251,248 Commercial loans 375,664 3,362 6,063 4,163 269 389,521 Municipal loans 357,028 — — — — 357,028 Loans to individuals 100,030 — — 380 298 100,708 Total $ 3,338,996 $ 58,648 $ 13,673 $ 47,385 $ 1,441 $ 3,460,143 December 31, 2018 Pass Pass Watch (1) Special Mention (1) Substandard (1) Doubtful (1) Total Real estate loans: Construction $ 507,529 $ 163 $ — $ 28 $ 12 $ 507,732 1-4 family residential 787,516 37 100 5,489 1,357 794,499 Commercial 1,067,874 11,479 26,490 87,767 508 1,194,118 Commercial loans 349,495 520 3,189 2,988 457 356,649 Municipal loans 353,370 — — — — 353,370 Loans to individuals 105,536 4 4 678 209 106,431 Total $ 3,171,320 $ 12,203 $ 29,783 $ 96,950 $ 2,543 $ 3,312,799 (1) Includes PCI loans comprised of $15,000 pass watch, $217,000 special mention, $2.7 million substandard and $305,000 doubtful as of June 30, 2019 . Includes PCI loans comprised of $22,000 pass watch, $859,000 special mention, $3.9 million substandard and $1.2 million doubtful as of December 31, 2018 .
Summary of nonperforming assets for the period	The following table sets forth nonperforming assets for the periods presented (in thousands): June 30, 2019 December 31, 2018 Nonaccrual loans (1) (2) $ 16,376 $ 35,770 Accruing loans past due more than 90 days (1) — — Restructured loans (3) 11,918 5,930 Other real estate owned 1,069 1,206 Repossessed assets — — Total nonperforming assets $ 29,363 $ 42,906 (1) Excludes PCI loans measured at fair value at acquisition if the timing and amount of cash flows expected to be collected from those sales can be reasonably estimated. (2) Includes $8.9 million and $10.9 million of restructured loans as of June 30, 2019 and December 31, 2018 , respectively. (3) Includes $776,000 and $3.1 million in PCI loans restructured as of June 30, 2019 and December 31, 2018 , respectively.
Recorded investment in nonaccrual by class of loans	The following table sets forth the recorded investment in nonaccrual loans by class of loans for the periods presented (in thousands). The table excludes PCI loans measured at fair value at acquisition: Nonaccrual Loans June 30, 2019 December 31, 2018 Real estate loans: Construction $ 200 $ 12 1-4 family residential 1,418 2,202 Commercial 13,383 32,599 Commercial loans 1,047 639 Loans to individuals 328 318 Total $ 16,376 $ 35,770
Summary of impaired loans by class of loans for the period	The following tables set forth impaired loans by class of loans, including the unpaid contractual principal balance, the recorded investment and the related allowance for loan losses for the periods presented (in thousands). Impaired loans include restructured and nonaccrual loans for which the allowance was measured in accordance with section 310-10 of ASC Topic 310, “Receivables.” There were no impaired loans recorded without an allowance as of June 30, 2019 or December 31, 2018 . June 30, 2019 Unpaid Contractual Principal Balance Recorded Investment Related Allowance for Loan Losses Real estate loans: Construction $ 356 $ 323 $ 23 1-4 family residential 8,646 7,491 66 Commercial 26,198 22,999 1,408 Commercial loans 4,033 3,449 782 Municipal loans 429 429 — Loans to individuals 481 354 90 Total (1) $ 40,143 $ 35,045 $ 2,369 December 31, 2018 Unpaid Contractual Principal Balance Recorded Investment Related Allowance for Loan Losses Real estate loans: Construction $ 182 $ 148 $ 13 1-4 family residential 6,507 5,923 40 Commercial 36,457 34,744 5,337 Commercial loans 2,874 2,366 368 Municipal loans 429 429 1 Loans to individuals 825 657 149 Total (1) $ 47,274 $ 44,267 $ 5,908 (1) Includes $9.1 million and $8.0 million of PCI loans that experienced deterioration in credit quality subsequent to the acquisition date as of June 30, 2019 and December 31, 2018 , respectively.
Aging of recorded investment in past due loans by class of loans	The following tables present the aging of the recorded investment in past due loans by class of loans (in thousands): June 30, 2019 30-59 Days Past Due 60-89 Days Past Due Greater than 90 Days Past Due Total Past Due Current (1) Total Real estate loans: Construction $ 343 $ 276 $ 193 $ 812 $ 578,753 $ 579,565 1-4 family residential 2,250 1,330 293 3,873 778,200 782,073 Commercial 1,625 425 109 2,159 1,249,089 1,251,248 Commercial loans 2,070 567 619 3,256 386,265 389,521 Municipal loans — — — — 357,028 357,028 Loans to individuals 555 194 137 886 99,822 100,708 Total $ 6,843 $ 2,792 $ 1,351 $ 10,986 $ 3,449,157 $ 3,460,143 December 31, 2018 30-59 Days Past Due 60-89 Days Past Due Greater than 90 Days Past Due Total Past Due Current (1) Total Real estate loans: Construction $ 627 $ 307 $ — $ 934 $ 506,798 $ 507,732 1-4 family residential 7,441 1,258 1,335 10,034 784,465 794,499 Commercial 10,663 7,655 — 18,318 1,175,800 1,194,118 Commercial loans 1,946 705 591 3,242 353,407 356,649 Municipal loans — — — — 353,370 353,370 Loans to individuals 1,289 351 146 1,786 104,645 106,431 Total $ 21,966 $ 10,276 $ 2,072 $ 34,314 $ 3,278,485 $ 3,312,799 (1) Includes PCI loans measured at fair value at acquisition if the timing and amount of cash flows expected to be collected from those sales can be reasonably estimated.
Average recorded investment and interest income on impaired loans	The following table sets forth average recorded investment and interest income recognized on impaired loans by class of loans for the periods presented (in thousands). The table excludes PCI loans measured at fair value at acquisition that have not experienced further deterioration in credit quality subsequent to the acquisition date: Three Months Ended June 30, 2019 June 30, 2018 Average Recorded Investment Interest Income Recognized Average Recorded Investment Interest Income Recognized Real estate loans: Construction $ 214 $ 5 $ 140 $ 1 1-4 family residential 7,533 130 3,955 47 Commercial 24,394 153 31,916 5 Commercial loans 2,753 38 2,024 19 Municipal loans 429 6 502 7 Loans to individuals 438 9 242 3 Total $ 35,761 $ 341 $ 38,779 $ 82 Six Months Ended June 30, 2019 June 30, 2018 Average Recorded Investment Interest Income Recognized Average Recorded Interest Income Recognized Real estate loans: Construction $ 200 $ 9 $ 114 $ 1 1-4 family residential 6,271 210 3,945 93 Commercial 30,917 440 20,595 9 Commercial loans 2,699 68 1,900 36 Municipal loans 429 12 502 14 Loans to individuals 517 20 221 4 Total $ 41,033 $ 759 $ 27,277 $ 157
Schedule of recorded investment in loans modified	The following tables set forth the recorded balance of loans considered to be TDRs that were restructured and the type of concession by class of loans during the periods presented (dollars in thousands): Three Months Ended June 30, 2019 Extend Amortization Period Interest Rate Reductions Combination Total Modifications Number of Loans Real estate loans: 1-4 family residential $ — $ — $ — $ — — Commercial — — 96 96 1 Commercial loans — — 485 485 4 Loans to individuals — — 25 25 3 Total $ — $ — $ 606 $ 606 8 Six Months Ended June 30, 2019 Extend Amortization Period Interest Rate Reductions Combination Total Modifications Number of Loans Real estate loans: 1-4 family residential $ — $ — $ 111 $ 111 1 Commercial 7,594 — 96 7,690 2 Commercial loans 56 — 485 541 5 Loans to individuals — — 39 39 5 Total $ 7,650 $ — $ 731 $ 8,381 13 Three Months Ended June 30, 2018 Extend Amortization Period Interest Rate Reductions Combination Total Modifications Number of Loans Real estate loans: 1-4 family residential $ — $ 80 $ — $ 80 1 Commercial loans — — 90 90 2 Loans to individuals 9 — 13 22 3 Total $ 9 $ 80 $ 103 $ 192 6 Six Months Ended June 30, 2018 Extend Amortization Period Interest Rate Reductions Combination Total Modifications Number of Loans Real estate loans: 1-4 family residential $ — $ 80 $ — $ 80 1 Commercial loans 132 — 90 222 5 Loans to individuals 106 — 13 119 4 Total $ 238 $ 80 $ 103 $ 421 10
Schedule of PCI Loans	The following table presents the outstanding principal balance and carrying value for PCI loans for the periods presented (in thousands): June 30, 2019 December 31, 2018 Outstanding principal balance $ 45,430 $ 51,388 Carrying amount $ 41,101 $ 46,402
Schedule of changes in accretable yield for pci loans	The following table presents the changes in the accretable yield for PCI loans during the periods presented (in thousands): Three Months Ended Six Months Ended 2019 2018 2019 2018 Balance at beginning of period $ 14,520 $ 15,818 $ 15,054 $ 18,721 Changes in expected cash flows not affecting non-accretable differences — — — (1,445 ) Reclassifications (to) from nonaccretable discount 812 1,090 1,074 770 Accretion (776 ) (803 ) (1,572 ) (1,941 ) Balance at end of period $ 14,556 $ 16,105 $ 14,556 $ 16,105

Borrowing Arrangements (Tables)

Borrowing Arrangements (Tables)	6 Months Ended
	Jun. 30, 2019
Debt Disclosure [Abstract]
Schedule of Debt	Information related to borrowings is provided in the table below (dollars in thousands): June 30, December 31, 2018 Other borrowings: Balance at end of period $ 26,064 $ 36,810 Average amount outstanding during the period (1) 15,653 10,880 Maximum amount outstanding during the period (2) 28,354 36,810 Weighted average interest rate during the period (3) 1.7 % 1.4 % Interest rate at end of period (4) 2.0 % 2.1 % Federal Home Loan Bank borrowings: Balance at end of period $ 823,757 $ 719,065 Average amount outstanding during the period (1) 785,901 720,785 Maximum amount outstanding during the period (2) 1,004,997 957,231 Weighted average interest rate during the period (3) 2.1 % 1.8 % Interest rate at end of period (4) 2.4 % 2.3 % (1) The average amount outstanding during the period was computed by dividing the total daily outstanding principal balances by the number of days in the period. (2) The maximum amount outstanding at any month-end during the period. (3) The weighted average interest rate during the period was computed by dividing the actual interest expense (annualized for interim periods) by the average amount outstanding during the period. The weighted average interest rate on the FHLB borrowings includes the effect of interest rate swaps. (4) Stated rate.
Schedule of Maturities of Borrowings	Maturities of the obligations associated with our borrowing arrangements based on scheduled repayments at June 30, 2019 are as follows (in thousands): Payments Due by Period Less than 1 Year 1-2 Years 2-3 Years 3-4 Years 4-5 Years Thereafter Total Other borrowings $ 25,931 $ 133 $ — $ — $ — $ — $ 26,064 Federal Home Loan Bank borrowings 796,765 21,374 — — — 5,618 823,757 Total obligations $ 822,696 $ 21,507 $ — $ — $ — $ 5,618 $ 849,821

Long-term Debt Long-term Obli_2

Long-term Debt Long-term Obligations (Tables)	6 Months Ended
	Jun. 30, 2019
Debt Disclosure [Abstract]
Schedule of Long-term Debt Instruments [Table Text Block]	June 30, December 31, (in thousands) Subordinated notes: (1) 5.50% Subordinated Notes, net of unamortized debt issuance costs (2) $ 98,490 $ 98,407 Total Subordinated notes 98,490 98,407 Trust preferred subordinated debentures: (3) Southside Statutory Trust III, net of unamortized debt issuance costs (4) 20,556 20,554 Southside Statutory Trust IV 23,196 23,196 Southside Statutory Trust V 12,887 12,887 Magnolia Trust Company I 3,609 3,609 Total Trust preferred subordinated debentures 60,248 60,246 Total Long-term debt $ 158,738 $ 158,653 (1) This debt consists of subordinated notes with a remaining maturity greater than one year that qualify under the risk-based capital guidelines as Tier 2 capital, subject to certain limitations. (2) The unamortized discount and debt issuance costs reflected in the carrying amount of the subordinated notes totaled approximately $1.5 million at June 30, 2019 and $1.6 million at December 31, 2018 . (3) This debt consists of trust preferred securities that qualify under the risk-based capital guidelines as Tier 1 capital, subject to certain limitations. (4) The unamortized debt issuance costs reflected in the carrying amount of the Southside Statutory Trust III junior subordinated debentures totaled $63,000 at June 30, 2019 and $65,000 at December 31, 2018 .
Schedule of Subordinated Borrowing [Table Text Block]	As of June 30, 2019 , the details of the subordinated notes and the trust preferred subordinated debentures are summarized below (dollars in thousands): Date Issued Amount Issued Fixed or Floating Rate Interest Rate Maturity Date 5.50% Subordinated Notes September 19, 2016 $ 100,000 Fixed-to-Floating 5.50% September 30, 2026 Southside Statutory Trust III September 4, 2003 $ 20,619 Floating 3 month LIBOR + 2.94% September 4, 2033 Southside Statutory Trust IV August 8, 2007 $ 23,196 Floating 3 month LIBOR + 1.30% October 30, 2037 Southside Statutory Trust V August 10, 2007 $ 12,887 Floating 3 month LIBOR + 2.25% September 15, 2037 Magnolia Trust Company I (1) October 10, 2007 $ 3,609 Floating 3 month LIBOR + 1.80% November 23, 2035 (1) On October 10, 2007, as part of an acquisition we assumed $3.6 million of floating rate junior subordinated debentures issued in 2005 to Magnolia Trust Company I.

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	6 Months Ended
	Jun. 30, 2019
Defined Contribution Plan [Abstract]
The components of net periodic benefit cost	The components of net periodic benefit cost (income) related to our employee benefit plans are as follows (in thousands): Three Months Ended June 30, Defined Benefit Defined Benefit Pension Plan Acquired Restoration 2019 2018 2019 2018 2019 2018 Service cost $ 394 $ 390 $ — $ — $ 110 $ 84 Interest cost 919 839 43 41 195 165 Expected return on assets (1,511 ) (1,622 ) (73 ) (72 ) — — Net loss amortization 470 372 — — 181 248 Prior service (credit) cost amortization (4 ) (4 ) — — 1 2 Net periodic benefit cost (income) $ 268 $ (25 ) $ (30 ) $ (31 ) $ 487 $ 499 Six Months Ended June 30, Defined Benefit Defined Benefit Pension Plan Acquired Restoration 2019 2018 2019 2018 2019 2018 Service cost $ 710 $ 774 $ — $ — $ 170 $ 147 Interest cost 1,827 1,696 84 82 356 298 Expected return on assets (3,015 ) (3,242 ) (146 ) (145 ) — — Net loss amortization 913 756 — — 280 339 Prior service (credit) cost amortization (7 ) (7 ) — — 3 3 Net periodic benefit cost (income) $ 428 $ (23 ) $ (62 ) $ (63 ) $ 809 $ 787

Derivative Financial Instrume_2

Derivative Financial Instruments and Hedging Activities (Tables)	6 Months Ended
	Jun. 30, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block]	The following tables present the notional and estimated fair value amount of derivative positions outstanding (in thousands): June 30, 2019 December 31, 2018 Estimated Fair Value Estimated Fair Value Notional (1) Asset Derivative Liability Derivative Notional (1) Asset Derivative Liability Derivative Derivatives designated as hedging instruments Interest rate contracts: Swaps-Cash flow Hedge-Financial institution counterparties $ 270,000 $ 2,334 $ 3,442 $ 270,000 $ 9,388 $ 457 Swaps-Fair Value Hedge-Financial institution counterparties — — — 21,100 — 657 Derivatives designated as non-hedging instruments Interest rate contracts: Swaps-Financial institution counterparties 110,699 16 6,614 93,967 1,119 1,087 Swaps-Customer counterparties 110,699 6,614 16 93,967 1,087 1,119 Gross derivatives 8,964 10,072 11,594 3,320 Offsetting derivative assets/liabilities (2,350 ) (2,350 ) (2,201 ) (2,201 ) Cash collateral received/posted — (7,420 ) (8,306 ) — Net derivatives included in the consolidated balance sheets (2) $ 6,614 $ 302 $ 1,087 $ 1,119 (1) Notional amounts, which represent the extent of involvement in the derivatives market, are used to determine the contractual cash flows required in accordance with the terms of the agreement. These amounts are typically not exchanged, significantly exceed amounts subject to credit or market risk and are not reflected in the consolidated balance sheets. (2) Net derivative assets are included in other assets and net derivative liabilities are included in other liabilities on the consolidated balance sheets. Included in the fair value of net derivative assets and net derivative liabilities are credit valuation adjustments reflecting counterparty credit risk and our credit risk. We had no credit exposure related to interest rate swaps with financial institutions and $6.6 million related to interest rate swaps with customers at June 30, 2019 . We had no credit exposure related to interest rate swaps with financial institutions and $1.1 million related to interest rate swaps with customers at December 31, 2018
Weighted Average Maturity And Interest Rates On Risk Management Interest Rate Swaps [Table Text Block]	The summarized expected weighted average remaining maturity of the notional amount of interest rate swaps and the weighted average interest rates associated with the amounts expected to be received or paid on interest rate swap agreements are presented below (dollars in thousands). Variable rates received on pay fixed swaps are based on one-month or three-month LIBOR rates in effect at June 30, 2019 and December 31, 2018 : June 30, 2019 December 31, 2018 Weighted Average Weighted Average Notional Amount Remaining Maturity (in years) Receive Rate Pay Rate Notional Amount Remaining Maturity Receive Rate Pay Swaps-Cash flow hedge Financial institution counterparties $ 270,000 4.3 2.44 % 1.58 % $ 270,000 4.8 2.45 % 1.58 % Swaps-Fair value hedge Financial institution counterparties — — — — 21,100 7.5 2.56 3.00 Swaps-Non-hedging Financial institution counterparties 110,699 11.6 2.42 2.57 93,967 11.6 2.36 2.58 Customer counterparties 110,699 11.6 2.57 2.42 93,967 11.6 2.58 2.36

Fair Value Measurement (Tables)

Fair Value Measurement (Tables)	6 Months Ended
	Jun. 30, 2019
Fair Value Disclosures [Abstract]
Summary of fair value measurement on recurring and nonrecurring basis segregated by level of valuation inputs within fair value hierarchy utilized to measure fair value	The following tables summarize assets measured at fair value on a recurring and nonrecurring basis segregated by the level of the valuation inputs within the fair value hierarchy utilized to measure fair value (in thousands): June 30, 2019 Fair Value Measurements at the End of the Reporting Period Using Carrying Amount Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Recurring fair value measurements Investment securities: State and political subdivisions $ 528,855 $ — $ 528,855 $ — Other stocks and bonds 2,959 — 2,959 — Mortgage-backed securities: (1) Residential 1,318,986 — 1,318,986 — Commercial 237,987 — 237,987 — Equity investments: Equity investments 5,948 5,948 — — Derivative assets: Interest rate swaps 8,964 — 8,964 — Total asset recurring fair value measurements $ 2,103,699 $ 5,948 $ 2,097,751 $ — Derivative liabilities: Interest rate swaps $ 10,072 $ — $ 10,072 $ — Total liability recurring fair value measurements $ 10,072 $ — $ 10,072 $ — Nonrecurring fair value measurements Foreclosed assets $ 1,069 $ — $ — $ 1,069 Impaired loans (2) 32,148 — — 32,148 Total asset nonrecurring fair value measurements $ 33,217 $ — $ — $ 33,217 December 31, 2018 Fair Value Measurements at the End of the Reporting Period Using Carrying Amount Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Recurring fair value measurements Investment securities: State and political subdivisions $ 716,601 $ — $ 716,601 $ — Other stocks and bonds 2,709 — 2,709 — Mortgage-backed securities: (1) Residential 732,972 — 732,972 — Commercial 537,154 — 537,154 — Equity investments: Equity investments 5,791 5,791 — — Derivative assets: Interest rate swaps 11,594 — 11,594 — Total asset recurring fair value measurements $ 2,006,821 $ 5,791 $ 2,001,030 $ — Derivative liabilities: Interest rate swaps $ 3,320 $ — $ 3,320 $ — Total liability recurring fair value measurements $ 3,320 $ — $ 3,320 $ — Nonrecurring fair value measurements Foreclosed assets $ 1,206 $ — $ — $ 1,206 Impaired loans (2) 37,813 — — 37,813 Total asset nonrecurring fair value measurements $ 39,019 $ — $ — $ 39,019 (1) All mortgage-backed securities are issued and/or guaranteed by U.S. government agencies or U.S. government-sponsored enterprises. (2) Impaired loans represent collateral-dependent loans with a specific valuation allowance. Losses on these loans represent charge-offs which are netted against the allowance for loan losses.
Financial assets, financial liabilities, and unrecognized financial instruments at carrying amount and fair value	The following tables present our financial assets and financial liabilities measured on a nonrecurring basis at both their respective carrying amounts and estimated fair value (in thousands): Estimated Fair Value June 30, 2019 Carrying Total Level 1 Level 2 Level 3 Financial assets: Cash and cash equivalents $ 132,521 $ 132,521 $ 132,521 $ — $ — Investment securities: Held to maturity, at carrying value 3,018 3,054 — 3,054 — Mortgage-backed securities: Held to maturity, at carrying value 144,073 148,253 — 148,253 — Federal Home Loan Bank stock, at cost 44,718 44,718 — 44,718 — Equity investments 6,426 6,426 — 6,426 — Loans, net of allowance for loan losses 3,435,438 3,493,559 — — 3,493,559 Loans held for sale 1,812 1,812 — 1,812 — Financial liabilities: Deposits $ 4,479,256 $ 4,478,936 $ — $ 4,478,936 $ — Other borrowings 26,064 26,064 — 26,064 — Federal Home Loan Bank borrowings 823,757 825,450 — 825,450 — Subordinated notes, net of unamortized debt issuance costs 98,490 98,964 — 98,964 — Trust preferred subordinated debentures, net of unamortized debt issuance costs 60,248 58,819 — 58,819 — Estimated Fair Value December 31, 2018 Carrying Total Level 1 Level 2 Level 3 Financial assets: Cash and cash equivalents $ 120,719 $ 120,719 $ 120,719 $ — $ — Investment securities: Held to maturity, at carrying value 3,083 3,046 — 3,046 — Mortgage-backed securities: Held to maturity, at carrying value 159,848 156,735 — 156,735 — Federal Home Loan Bank stock, at cost 32,583 32,583 — 32,583 — Equity investments 6,302 6,302 — 6,302 — Loans, net of allowance for loan losses 3,285,780 3,251,923 — — 3,251,923 Loans held for sale 601 601 — 601 — Financial liabilities: Deposits $ 4,425,030 $ 4,417,902 $ — $ 4,417,902 $ — Other borrowings 36,810 36,810 — 36,810 — Federal Home Loan Bank borrowings 719,065 708,904 — 708,904 — Subordinated notes, net of unamortized debt issuance costs 98,407 97,611 — 97,611 — Trust preferred subordinated debentures, net of unamortized debt issuance costs 60,246 54,729 — 54,729 —

Income Taxes Income Taxes (Tab

Income Taxes Income Taxes (Tables)	6 Months Ended
	Jun. 30, 2019
Income Tax Disclosure [Abstract]
Income Taxes	The income tax expense included in the accompanying consolidated statements of income consists of the following (in thousands): Three Months Ended Six Months Ended 2019 2018 2019 2018 Current income tax expense $ 3,553 $ 667 $ 6,564 $ 3,012 Deferred income tax expense 16 2,693 142 2,438 Income tax expense $ 3,569 $ 3,360 $ 6,706 $ 5,450

Leases (Tables)

Leases (Tables)	6 Months Ended
	Jun. 30, 2019
Leases [Abstract]
Leases Balance Sheet Information	Balance sheet information related to leases was as follows (in thousands): June 30, 2019 Operating leases: Operating lease right-of-use assets $ 9,812 Operating lease liabilities $ 10,204 Additional information related to leases was as follows: June 30, 2019 Weighted average remaining lease term (in years) 12.5 Weighted average discount rate 3.88 %
Lease Expense	The components of lease cost were as follows (in thousands): Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 Operating lease cost $ 395 $ 789 Supplemental cash flow information related to leases was as follows (in thousands): Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 Cash paid for amounts included in the measurement of the lease liabilities: Operating cash flows from operating leases $ 360 $ 700 Right-of-use assets obtained in exchange for new operating lease liabilities $ 654 $ 654
Lessee, Operating Lease, Liability, Maturity	Future minimum rental commitments due under non-cancelable operating leases at June 30, 2019 were as follows (in thousands): Year ending December 31, 2019 (excluding the six months ended June 30, 2019) $ 625 2020 1,338 2021 1,232 2022 1,193 2023 1,044 2024 and thereafter 7,866 Total lease payments (1) 13,298 Less: Interest (3,094 ) Present value of lease liabilities $ 10,204 (1) Excludes $9.1 million of lease payments for a lease executed but not yet commenced. Lease will commence in 2020 with a lease term of 20.4 years .
Gross Rental Income	Gross rental income from these leases were as follows (in thousands): Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 Gross rental income $ 742 $ 1,487
Lessor, Operating Lease, Payments to be Received, Maturity	At June 30, 2019 , non-cancelable operating leases with future minimum lease payments are as follows (in thousands): Year ending December 31, 2019 (excluding the six months ended June 30, 2019) $ 1,388 2020 2,693 2021 1,576 2022 1,553 2023 1,316 2024 and thereafter 4,098 Total lease payments $ 12,624

Off-Balance-Sheet Arrangement_2

Off-Balance-Sheet Arrangements, Commitments and Contingencies (Tables)	6 Months Ended
	Jun. 30, 2019
Commitments and Contingencies Disclosure [Abstract]
Schedule of unused commitments	Financial instruments with off-balance-sheet risk were as follows (in thousands): June 30, 2019 December 31, 2018 Unused commitments: Commitments to extend credit $ 1,024,034 $ 874,557 Standby letters of credit 27,463 27,438 Total $ 1,051,497 $ 901,995

Summary of Significant Accoun_3

Summary of Significant Accounting and Reporting Policies - Reclassifications (Details) - USD ($) $ in Thousands	Jan. 01, 2019	Jun. 30, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease liabilities		$ 10,204	$ 0
Right-of-Use assets obtained in exchange for operating lease liabilities		$ 9,812	$ 0
Accounting Standards Update 2017-08
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect on Retained Earnings, before tax	$ (16,500)
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease liabilities	10,100
Right-of-Use assets obtained in exchange for operating lease liabilities	$ 9,800

Acquisition (Details)

Acquisition (Details) $ in Thousands	Nov. 30, 2017USD ($)banking_offices	Jun. 30, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Business Acquisition [Line Items]
Goodwill		$ 201,116	$ 201,116
Diboll State Bancshares, Inc.
Business Acquisition [Line Items]
Voting interests acquired	100.00%
Number of branches | banking_offices	17
Acquisition, Total merger consideration	$ 224,300
Acquisition, Loans	621,300
Acquisition, Investment securities	234,400
Acquisition, Deposits	899,300
Goodwill		$ 109,600		$ 109,700
Core Deposits | Diboll State Bancshares, Inc.
Business Acquisition [Line Items]
Acquisition, Finite-lived intangible assets	$ 14,700
Amortization period	9 years
Trust Relationship Intangible | Diboll State Bancshares, Inc.
Business Acquisition [Line Items]
Acquisition, Finite-lived intangible assets	$ 5,400
Amortization period	13 years

Earnings Per Share (Details)

Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Basic and Diluted Earnings:
Net income	$ 18,610	$ 18,817	$ 20,203	$ 16,251	$ 37,427	$ 36,454
Basic weighted-average shares outstanding (in shares)	33,726		35,062		33,711	35,042
Add: Stock awards (in shares)	150		171		151	175
Diluted weighted-average shares outstanding (in shares)	33,876		35,233		33,862	35,217
Basic Earnings Per Share:
Earnings per common share - basic (in dollars per share)	$ 0.55		$ 0.58		$ 1.11	$ 1.04
Diluted Earnings Per Share:
Earnings per common share - diluted (in dollars per share)	$ 0.55		$ 0.57		$ 1.11	$ 1.04
Antidilutive securities excluded from calculating earnings
Number of antidilutive options (in shares)	480		246		485	216

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Loss) - Accumulated Other Comprehensive Income, Changes In (Details) - USD ($)		Jan. 01, 2019	Jan. 01, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
AOCI Attributable to Parent, Net of Tax
Beginning balance, net of tax		$ 731,291,000	$ 754,140,000	$ 758,033,000	$ 746,396,000	$ 731,291,000	$ 754,140,000
Cumulative effect of accounting change		(16,452,000)	0
Adjusted beginning balance, net of tax		714,839,000	754,140,000
Income tax (expense) benefit				(5,505,000)	1,423,000	(14,664,000)	5,611,000
Ending balance, net of tax				787,765,000	751,810,000	787,765,000	751,810,000
Retained Earnings
AOCI Attributable to Parent, Net of Tax
Beginning balance, net of tax		64,797,000	32,851,000	57,023,000	39,184,000	64,797,000	32,851,000
Cumulative effect of accounting change		(16,452,000)	(85,000)
Adjusted beginning balance, net of tax		48,345,000	32,766,000
Ending balance, net of tax				65,183,000	48,843,000	65,183,000	48,843,000
Unrealized Gains (Losses) on Securities
AOCI Attributable to Parent, Net of Tax
Beginning balance, net of tax		(31,120,000)	(16,295,000)	5,901,000	(35,594,000)	(31,120,000)	(16,295,000)
Adjusted beginning balance, net of tax			(16,210,000)
Other comprehensive income (loss) before reclassifications				32,196,000	(10,371,000)	78,822,000	(35,872,000)
Reclassification adjustments included in net income				(336,000)	1,584,000	(101,000)	2,549,000
Income tax (expense) benefit				(6,691,000)	1,845,000	(16,531,000)	6,997,000
Net current-period other comprehensive income (loss), net of tax				25,169,000	(6,942,000)	62,190,000	(26,326,000)
Ending balance, net of tax				31,070,000	(42,536,000)	31,070,000	(42,536,000)
Unrealized Gains (Losses) on Derivatives
AOCI Attributable to Parent, Net of Tax
Beginning balance, net of tax		7,146,000	6,399,000	4,153,000	9,652,000	7,146,000	6,399,000
Adjusted beginning balance, net of tax			6,399,000
Other comprehensive income (loss) before reclassifications				(5,653,000)	1,725,000	(8,773,000)	5,970,000
Reclassification adjustments included in net income				(642,000)	(331,000)	(1,310,000)	(458,000)
Income tax (expense) benefit				1,322,000	(293,000)	2,117,000	(1,158,000)
Net current-period other comprehensive income (loss), net of tax				(4,973,000)	1,101,000	(7,966,000)	4,354,000
Ending balance, net of tax				(820,000)	10,753,000	(820,000)	10,753,000
Net Prior Service (Cost) Credit
AOCI Attributable to Parent, Net of Tax
Reclassification adjustments included in net income	[1]			(3,000)	(2,000)	(4,000)	(4,000)
Net Gain (Loss)
AOCI Attributable to Parent, Net of Tax
Reclassification adjustments included in net income	[1]			651,000	620,000	1,193,000	1,095,000
Total
AOCI Attributable to Parent, Net of Tax
Beginning balance, net of tax		(50,228,000)	(36,298,000)	(15,773,000)	(51,970,000)	(50,228,000)	(36,298,000)
Cumulative effect of accounting change			85,000
Adjusted beginning balance, net of tax		(50,228,000)	(36,213,000)
Other comprehensive income (loss) before reclassifications				26,543,000	(8,646,000)	70,049,000	(29,902,000)
Reclassification adjustments included in net income				(330,000)	1,871,000	(222,000)	3,182,000
Income tax (expense) benefit				(5,505,000)	1,423,000	(14,664,000)	5,611,000
Net current-period other comprehensive income (loss), net of tax				20,708,000	(5,352,000)	55,163,000	(21,109,000)
Ending balance, net of tax				4,935,000	(57,322,000)	4,935,000	(57,322,000)
Accounting Standards Update 2016-01 | Retained Earnings
AOCI Attributable to Parent, Net of Tax
Cumulative effect of accounting change			(85,000)
Cumulative Effect on Retained Earnings, before Tax			(107,000)
Accounting Standards Update 2016-01 | Unrealized Gains (Losses) on Securities
AOCI Attributable to Parent, Net of Tax
Cumulative effect of accounting change	[2]		85,000
Accounting Standards Update 2016-01 | Unrealized Gains (Losses) on Derivatives
AOCI Attributable to Parent, Net of Tax
Cumulative effect of accounting change			0
Accounting Standards Update 2016-01 | Total
AOCI Attributable to Parent, Net of Tax
Cumulative effect of accounting change	[2]		85,000
Defined Benefit Pension Plan | Net Prior Service (Cost) Credit
AOCI Attributable to Parent, Net of Tax
Beginning balance, net of tax		(139,000)	(133,000)	(140,000)	(134,000)	(139,000)	(133,000)
Adjusted beginning balance, net of tax			(133,000)
Other comprehensive income (loss) before reclassifications				0	0	0	0
Reclassification adjustments included in net income				(3,000)	(2,000)	(4,000)	(4,000)
Income tax (expense) benefit				1,000	1,000	1,000	2,000
Net current-period other comprehensive income (loss), net of tax				(2,000)	(1,000)	(3,000)	(2,000)
Ending balance, net of tax				(142,000)	(135,000)	(142,000)	(135,000)
Defined Benefit Pension Plan | Net Gain (Loss)
AOCI Attributable to Parent, Net of Tax
Beginning balance, net of tax		$ (26,115,000)	(26,269,000)	(25,687,000)	(25,894,000)	(26,115,000)	(26,269,000)
Adjusted beginning balance, net of tax			(26,269,000)
Other comprehensive income (loss) before reclassifications				0	0	0	0
Reclassification adjustments included in net income				651,000	620,000	1,193,000	1,095,000
Income tax (expense) benefit				(137,000)	(130,000)	(251,000)	(230,000)
Net current-period other comprehensive income (loss), net of tax				514,000	490,000	942,000	865,000
Ending balance, net of tax				$ (25,173,000)	$ (25,404,000)	$ (25,173,000)	$ (25,404,000)
Defined Benefit Pension Plan | Accounting Standards Update 2016-01 | Net Prior Service (Cost) Credit
AOCI Attributable to Parent, Net of Tax
Cumulative effect of accounting change			0
Defined Benefit Pension Plan | Accounting Standards Update 2016-01 | Net Gain (Loss)
AOCI Attributable to Parent, Net of Tax
Cumulative effect of accounting change			$ 0
[1]	These accumulated other comprehensive income components are included in the computation of net periodic pension cost (income) presented in “Note 9 - Employee Benefit Plans.”
[2]	The Company adopted ASU 2016-01 on January 1, 2018. This amount includes a reclassification for the cumulative adjustment to retained earnings of $107,000 ( $85,000 , net of tax).

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Income (Loss) - Reclassifications out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of unrealized losses		$ 80	$ 1,252	$ 571	$ 1,390
Tax benefit (expense)		(3,569)	(3,360)	(6,706)	(5,450)
Total reclassifications for the period, net of tax		262	(1,479)	176	(2,515)
Unrealized gains (losses)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassified from accumulated other comprehensive income		336	(1,584)	101	(2,549)
Realized net loss on interest rate swap derivatives
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassified from accumulated other comprehensive income		642	331	1,310	458
Net actuarial loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassified from accumulated other comprehensive income	[1]	(651)	(620)	(1,193)	(1,095)
Prior service credit
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassified from accumulated other comprehensive income	[1]	3	2	4	4
Amortization of pension plan
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassified from accumulated other comprehensive income		(648)	(618)	(1,189)	(1,091)
Tax benefit		136	129	250	228
Total reclassifications for the period, net of tax		(512)	(489)	(939)	(863)
Unrealized losses on securities transferred from held to maturity to available for sale: | Reclassification out of accumulated other comprehensive income | Unrealized gains (losses)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of unrealized losses	[2]	(80)	(1,252)	(571)	(1,390)
Tax benefit (expense)		17	263	120	292
Net of tax		(63)	(989)	(451)	(1,098)
Unrealized gains and losses on available for sale securities | Reclassification out of accumulated other comprehensive income | Unrealized gains (losses)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax benefit (expense)		(87)	70	(141)	243
Net of tax		329	(262)	531	(916)
Realized net (loss) gain on sale of securities	[3]	416	(332)	672	(1,159)
Interest rate swap derivatives | Reclassification out of accumulated other comprehensive income | Realized net loss on interest rate swap derivatives
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax benefit (expense)		(130)	(65)	(266)	(87)
Net of tax		491	244	1,001	328
Realized net gain (loss) on interest rate swap derivatives	[4]	621	309	1,267	415
Interest rate swap derivatives | Reclassification out of accumulated other comprehensive income | Amortization of unrealized gains on terminated interest rate swap derivatives
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax benefit (expense)		(4)	(5)	(9)	(9)
Net of tax		17	17	34	34
Realized net gain (loss) on interest rate swap derivatives	[4]	$ 21	$ 22	$ 43	$ 43
[1]	These accumulated other comprehensive income components are included in the computation of net periodic pension cost (income) presented in “Note 9 - Employee Benefit Plans.”
[2]	Included in interest income on the consolidated statements of income.
[3]	Listed as net gain (loss) on sale of securities available for sale on the consolidated statements of income.
[4]	Included in interest expense for Federal Home Loan Bank of Dallas (“FHLB”) borrowings on the consolidated statements of income.

Securities - Schedule of Debt

Securities - Schedule of Debt Securities Components (Details) - USD ($) $ in Thousands		Jun. 30, 2019	Dec. 31, 2018
AVAILABLE FOR SALE
Amortized Cost		$ 2,045,507	$ 2,013,485
Gross unrealized gains		44,665	10,554
Gross unrealized losses		1,385	34,603
Estimated fair value		2,088,787	1,989,436
HELD TO MATURITY
Amortized cost		147,091	162,931
Gross unrealized gains		4,516	360
Gross unrealized losses		300	3,510
Estimated Fair Value		151,307	159,781
State and political subdivisions
AVAILABLE FOR SALE
Amortized Cost		512,575	728,142
Gross unrealized gains		16,758	6,115
Gross unrealized losses		478	17,656
Estimated fair value		528,855	716,601
HELD TO MATURITY
Amortized cost		3,018	3,083
Gross unrealized gains		36	5
Gross unrealized losses		0	42
Estimated Fair Value		3,054	3,046
Other stocks and bonds
AVAILABLE FOR SALE
Amortized Cost		3,000	3,000
Gross unrealized gains		0	0
Gross unrealized losses		41	291
Estimated fair value		2,959	2,709
Residential
AVAILABLE FOR SALE
Amortized Cost	[1]	1,296,888	738,585
Gross unrealized gains	[1]	22,944	3,498
Gross unrealized losses	[1]	846	9,111
Estimated fair value	[1]	1,318,986	732,972
HELD TO MATURITY
Amortized cost	[1]	59,756	59,655
Gross unrealized gains	[1]	2,496	154
Gross unrealized losses	[1]	144	1,140
Estimated Fair Value	[1]	62,108	58,669
Commercial
AVAILABLE FOR SALE
Amortized Cost	[1]	233,044	543,758
Gross unrealized gains	[1]	4,963	941
Gross unrealized losses	[1]	20	7,545
Estimated fair value	[1]	237,987	537,154
HELD TO MATURITY
Amortized cost	[1]	84,317	100,193
Gross unrealized gains	[1]	1,984	201
Gross unrealized losses	[1]	156	2,328
Estimated Fair Value	[1]	$ 86,145	$ 98,066
[1]	All mortgage-backed securities issued and/or guaranteed by U.S. government agencies or U.S. government-sponsored enterprises.

Securities - Unrealized Loss o

Securities - Unrealized Loss on Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Available-for-sale, Unrealized Loss Position [Abstract]
Less than 12 Months, fair value	$ 5,869	$ 115,902
More than 12 Months, fair value	134,769	1,345,243
Total fair value	140,638	1,461,145
Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Less than 12 Months, unrealized loss	53	1,247
More than 12 Months, unrealized Loss	1,332	33,356
Total unrealized loss	1,385	34,603
Held-to-maturity, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	0	5,460
More than 12 Months, fair value	17,280	142,236
Total fair value	17,280	147,696
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Losses [Abstract]
Less than 12 months, unrealized loss	0	63
More than 12 months, unrealized loss	300	3,447
Total unrealized loss	300	3,510
State and political subdivisions
Available-for-sale, Unrealized Loss Position [Abstract]
Less than 12 Months, fair value	2,281	98,112
More than 12 Months, fair value	28,087	399,205
Total fair value	30,368	497,317
Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Less than 12 Months, unrealized loss	10	899
More than 12 Months, unrealized Loss	468	16,757
Total unrealized loss	478	17,656
Held-to-maturity, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value		235
More than 12 Months, fair value		2,022
Total fair value		2,257
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Losses [Abstract]
Less than 12 months, unrealized loss		1
More than 12 months, unrealized loss		41
Total unrealized loss		42
Other stocks and bonds
Available-for-sale, Unrealized Loss Position [Abstract]
Less than 12 Months, fair value	2,959	2,709
More than 12 Months, fair value	0	0
Total fair value	2,959	2,709
Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Less than 12 Months, unrealized loss	41	291
More than 12 Months, unrealized Loss	0	0
Total unrealized loss	41	291
Residential
Available-for-sale, Unrealized Loss Position [Abstract]
Less than 12 Months, fair value	629	5,552
More than 12 Months, fair value	91,649	488,334
Total fair value	92,278	493,886
Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Less than 12 Months, unrealized loss	2	27
More than 12 Months, unrealized Loss	844	9,084
Total unrealized loss	846	9,111
Held-to-maturity, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	0	4,826
More than 12 Months, fair value	2,579	51,046
Total fair value	2,579	55,872
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Losses [Abstract]
Less than 12 months, unrealized loss	0	60
More than 12 months, unrealized loss	144	1,080
Total unrealized loss	144	1,140
Commercial
Available-for-sale, Unrealized Loss Position [Abstract]
Less than 12 Months, fair value	0	9,529
More than 12 Months, fair value	15,033	457,704
Total fair value	15,033	467,233
Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Less than 12 Months, unrealized loss	0	30
More than 12 Months, unrealized Loss	20	7,515
Total unrealized loss	20	7,545
Held-to-maturity, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	0	399
More than 12 Months, fair value	14,701	89,168
Total fair value	14,701	89,567
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Losses [Abstract]
Less than 12 months, unrealized loss	0	2
More than 12 months, unrealized loss	156	2,326
Total unrealized loss	$ 156	$ 2,328

Securities - Interest Income o

Securities - Interest Income on Securities (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Investments, Debt Securities [Abstract]
U.S. Treasury	$ 0	$ 23	$ 0	$ 131
U.S. government agency debentures			0	89
State and political subdivisions	3,527	6,353	7,645	12,734
Other stocks and bonds	27	28	55	58
Mortgage-backed securities	13,246	10,210	25,720	21,104
Total interest income on securities	$ 16,800	$ 16,614	$ 33,420	$ 34,116

Securities - Amortized Cost an

Securities - Amortized Cost and Estimated Fair Value of Investments in Debt Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Available for sale, Amortized Cost
Due in one year or less	$ 3,349
Due after one year through five years	8,406
Due after five years through ten years	28,488
Due after ten years	475,332
Total available-for-sale investment securities	515,575
Mortgage-backed securities	1,529,932
Amortized Cost	2,045,507	$ 2,013,485
Available for sale, Fair Value
Due in one year or less	3,363
Due after one year through five years	8,469
Due after five years through ten years	29,573
Due after ten years	490,409
Total available-for-sale investment securities	531,814
Mortgage-backed securities	1,556,973
Total	2,088,787	1,989,436
Held to maturity, Amortized Cost
Due in one year or less	115
Due after one year through five years	1,658
Due after five years through ten years	1,245
Due after ten years	0
Total held-to-maturity investment securities	3,018
Mortgage-backed securities	144,073
Amortized cost	147,091	162,931
Held to maturity, Fair Value
Due in one year or less	115
Due after one year through five years	1,675
Due after five years through ten years	1,264
Due after ten years	0
Total held-to-maturity investment securities	3,054
Mortgage-backed securities	148,253
Total	$ 151,307	$ 159,781

Securities - Unrealized and Re

Securities - Unrealized and Realized Gain (Loss) Recognized in Net Income on Equity Investments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Gain (Loss) on Securities [Line Items]
Net gains (losses) recognized during the period on equity investments	$ 87	$ (42)	$ 163	$ (134)
Less: Net gains (losses) recognized during the period on equity investments sold during the period	0	0	0	0
Unrealized gains (losses) recognized during the reporting period on equity investments still held at the reporting date	$ 87	$ (42)	$ 163	$ (134)

Securities - Narrative (Detail

Securities - Narrative (Details)	Jan. 01, 2019USD ($)	Jun. 30, 2019USD ($)	Jun. 30, 2018USD ($)	Dec. 31, 2018USD ($)
Investment [Line Items]
Transferred Securities, Unrealized Loss, Before Tax		$ 4,000,000		$ 15,300,000
Securities transferred, Unrealized Loss, Net of Tax		3,100,000		12,100,000
Fair value of securities transferred from AFS to HTM		$ 0		0
AFS securities and HTM securities with other-than-temporary impairment		0
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Net realized gain (loss) on AFS securities		$ 672,000	$ (1,200,000)
Gross realized gains on AFS securities		5,500,000	1,500,000
Gross realized losses on AFS securities		4,900,000	2,700,000
Carrying value of investment securities pledged as collateral		949,200,000		1,080,000,000
Equity investments		$ 12,374,000		$ 12,093,000
Equity investments with other-than-temporary impairment		0
Federal Home Loan Bank stock with other-than-temporary impairment		0
Debt Securities, Held-to-maturity, Sale or Transfer of Investment [Abstract]
Sale of HTM portfolio		$ 0	$ 0
Accounting Standards Update 2017-08
Investment [Line Items]
Cumulative effect on Retained Earnings, before tax	$ (16,500,000)

Loans and Allowance for Proba_3

Loans and Allowance for Probable Loan Losses - Loans by Portfolio Segment (Details) - USD ($) $ in Thousands		Jun. 30, 2019	Dec. 31, 2018
Loans and Leases Receivable Disclosure [Abstract]
Total ending loan balance		$ 3,460,143	$ 3,312,799
Less: Allowance for loan losses	[1]	24,705	27,019
Net Loans		3,435,438	3,285,780
Construction Real Estate Loans
Loans and Leases Receivable Disclosure [Abstract]
Total ending loan balance		579,565	507,732
1-4 Family Residential Real Estate Loans
Loans and Leases Receivable Disclosure [Abstract]
Total ending loan balance		782,073	794,499
Commercial Real Estate Loans
Loans and Leases Receivable Disclosure [Abstract]
Total ending loan balance		1,251,248	1,194,118
Commercial loans
Loans and Leases Receivable Disclosure [Abstract]
Total ending loan balance		389,521	356,649
Municipal loans
Loans and Leases Receivable Disclosure [Abstract]
Total ending loan balance		357,028	353,370
Loans to individuals
Loans and Leases Receivable Disclosure [Abstract]
Total ending loan balance		100,708	106,431
Purchase Credit Impaired (PCI) Loans
Loans and Leases Receivable Disclosure [Abstract]
Less: Allowance for loan losses	[1]	$ 139	$ 302
[1]	The allowance for loan losses recorded on purchased credit impaired (“PCI”) loans totaled $139,000 and $302,000 as of June 30, 2019 and December 31, 2018 , respectively.

Loans and Allowance for Proba_4

Loans and Allowance for Probable Loan Losses - Allowance for Loan Losses Activity by Portfolio Segment (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Allowances for Loan Losses [Roll Forward]
Balance at beginning of period		$ 24,155	$ 24,220	$ 27,019	$ 20,781	[1]
Provision (reversal) for loan losses	[2]	2,506	1,281	1,588	5,016
Loans charged off		(2,397)	(917)	(4,682)	(1,684)
Recoveries of loans charged off		441	488	780	959
Balance at end of period		24,705	25,072	24,705	25,072
Provision (reversal) for PCI Loans		(111)	358	(163)	358
Construction Real Estate Loans
Allowances for Loan Losses [Roll Forward]
Balance at beginning of period		4,259	3,597	3,597	3,676	[1]
Provision (reversal) for loan losses		(660)	244	2	179
Loans charged off		0	0	0	(14)
Recoveries of loans charged off		0	0	0	0
Balance at end of period		3,599	3,841	3,599	3,841
1-4 Family Residential Real Estate Loans
Allowances for Loan Losses [Roll Forward]
Balance at beginning of period		3,382	2,377	3,844	2,445	[1]
Provision (reversal) for loan losses		137	403	(310)	321
Loans charged off		0	(57)	(18)	(57)
Recoveries of loans charged off		3	7	6	21
Balance at end of period		3,522	2,730	3,522	2,730
Commercial Real Estate Loans
Allowances for Loan Losses [Roll Forward]
Balance at beginning of period		10,660	14,089	13,968	10,821	[1]
Provision (reversal) for loan losses		1,516	(57)	(596)	3,209
Loans charged off		(1,661)	0	(2,876)	0
Recoveries of loans charged off		19	4	38	6
Balance at end of period		10,534	14,036	10,534	14,036
Commercial loans
Allowances for Loan Losses [Roll Forward]
Balance at beginning of period		4,287	2,385	3,974	2,094	[1]
Provision (reversal) for loan losses		1,266	328	2,000	661
Loans charged off		(130)	(172)	(581)	(257)
Recoveries of loans charged off		123	19	153	62
Balance at end of period		5,546	2,560	5,546	2,560
Municipal loans
Allowances for Loan Losses [Roll Forward]
Balance at beginning of period		508	851	525	860	[1]
Provision (reversal) for loan losses		22	8	5	(1)
Loans charged off		0	0	0	0
Recoveries of loans charged off		0	0	0	0
Balance at end of period		530	859	530	859
Loans to individuals
Allowances for Loan Losses [Roll Forward]
Balance at beginning of period		1,059	921	1,111	885	[1]
Provision (reversal) for loan losses		225	355	487	647
Loans charged off		(606)	(688)	(1,207)	(1,356)
Recoveries of loans charged off		296	458	583	870
Balance at end of period		$ 974	$ 1,046	$ 974	$ 1,046
[1]	Loans acquired with the Diboll acquisition were measured at fair value on November 30, 2017 with no carryover of allowance for loan losses.
[2]	Of the $2.5 million and $1.6 million provision for loan losses for the three and six months ended June 30, 2019 , $111,000 and $163,000 related to provision expense reversed on PCI loans, respectively. Of the $1.3 million and $5.0 million recorded in provision for loan losses for the three and six months ended June 30, 2018 , $358,000 related to provision expense on PCI loans.

Loans and Allowance for Proba_5

Loans and Allowance for Probable Loan Losses - Allowance Balance, by Impairment Method (Details) - USD ($) $ in Thousands		Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	[2]
Schedule of Allowance For Loan Losses, Allowance Balance, by Impairment Method [Line Items]
Ending balance - individually evaluated for impairment	[1]	$ 2,369		$ 5,908
Ending balance - collectively evaluated for impairment		22,336		21,111
Balance at end of period		24,705	$ 24,155	27,019	$ 25,072	$ 24,220	$ 20,781
Loans and Leases Receivable, Allowance	[3]	24,705		27,019
Construction Real Estate Loans
Schedule of Allowance For Loan Losses, Allowance Balance, by Impairment Method [Line Items]
Ending balance - individually evaluated for impairment	[1]	23		13
Ending balance - collectively evaluated for impairment		3,576		3,584
Balance at end of period		3,599	4,259	3,597	3,841	3,597	3,676
1-4 Family Residential Real Estate Loans
Schedule of Allowance For Loan Losses, Allowance Balance, by Impairment Method [Line Items]
Ending balance - individually evaluated for impairment	[1]	66		40
Ending balance - collectively evaluated for impairment		3,456		3,804
Balance at end of period		3,522	3,382	3,844	2,730	2,377	2,445
Commercial Real Estate Loans
Schedule of Allowance For Loan Losses, Allowance Balance, by Impairment Method [Line Items]
Ending balance - individually evaluated for impairment	[1]	1,408		5,337
Ending balance - collectively evaluated for impairment		9,126		8,631
Balance at end of period		10,534	10,660	13,968	14,036	14,089	10,821
Commercial loans
Schedule of Allowance For Loan Losses, Allowance Balance, by Impairment Method [Line Items]
Ending balance - individually evaluated for impairment	[1]	782		368
Ending balance - collectively evaluated for impairment		4,764		3,606
Balance at end of period		5,546	4,287	3,974	2,560	2,385	2,094
Municipal loans
Schedule of Allowance For Loan Losses, Allowance Balance, by Impairment Method [Line Items]
Ending balance - individually evaluated for impairment	[1]	0		1
Ending balance - collectively evaluated for impairment		530		524
Balance at end of period		530	508	525	859	851	860
Loans to individuals
Schedule of Allowance For Loan Losses, Allowance Balance, by Impairment Method [Line Items]
Ending balance - individually evaluated for impairment	[1]	90		149
Ending balance - collectively evaluated for impairment		884		962
Balance at end of period		974	$ 1,059	1,111	$ 1,046	$ 921	$ 885
Financial Asset Acquired with Credit Deterioration [Member]
Schedule of Allowance For Loan Losses, Allowance Balance, by Impairment Method [Line Items]
Loans and Leases Receivable, Allowance	[3]	$ 139		$ 302
[1]	The allowance for loan losses on PCI loans totaled $139,000 and $302,000 as of June 30, 2019 and December 31, 2018 , respectively.
[2]	Loans acquired with the Diboll acquisition were measured at fair value on November 30, 2017 with no carryover of allowance for loan losses.
[3]	The allowance for loan losses recorded on purchased credit impaired (“PCI”) loans totaled $139,000 and $302,000 as of June 30, 2019 and December 31, 2018 , respectively.

Loans and Allowance for Proba_6

Loans and Allowance for Probable Loan Losses - Allowance for Loan Losses, Loan Portfolio, by Impairment Method (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Loans individually evaluated for impairment	$ 25,917	$ 36,247
Loans collectively evaluated for impairment	3,393,125	3,230,150
Purchased credit impaired loans	41,101	46,402
Total ending loan balance	3,460,143	3,312,799
Construction Real Estate Loans
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Loans individually evaluated for impairment	200	12
Loans collectively evaluated for impairment	579,226	507,564
Purchased credit impaired loans	139	156
Total ending loan balance	579,565	507,732
1-4 Family Residential Real Estate Loans
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Loans individually evaluated for impairment	1,268	1,215
Loans collectively evaluated for impairment	772,725	782,614
Purchased credit impaired loans	8,080	10,670
Total ending loan balance	782,073	794,499
Commercial Real Estate Loans
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Loans individually evaluated for impairment	21,361	33,013
Loans collectively evaluated for impairment	1,198,899	1,128,220
Purchased credit impaired loans	30,988	32,885
Total ending loan balance	1,251,248	1,194,118
Commercial loans
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Loans individually evaluated for impairment	2,523	1,394
Loans collectively evaluated for impairment	385,322	353,036
Purchased credit impaired loans	1,676	2,219
Total ending loan balance	389,521	356,649
Municipal loans
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Loans individually evaluated for impairment	429	429
Loans collectively evaluated for impairment	356,599	352,941
Purchased credit impaired loans	0	0
Total ending loan balance	357,028	353,370
Loans to individuals
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Loans individually evaluated for impairment	136	184
Loans collectively evaluated for impairment	100,354	105,775
Purchased credit impaired loans	218	472
Total ending loan balance	$ 100,708	$ 106,431

Loans and Allowance for Proba_7

Loans and Allowance for Probable Loan Losses - Loans by Credit Quality Indicator (Details) - USD ($) $ in Thousands		Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans		$ 3,460,143	$ 3,312,799
Purchased credit impaired loans		41,101	46,402
Pass
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans		3,338,996	3,171,320
Pass Watch
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	58,648	12,203
Purchased credit impaired loans		15	22
Special Mention
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	13,673	29,783
Purchased credit impaired loans		217	859
Substandard
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	47,385	96,950
Purchased credit impaired loans		2,700	3,900
Doubtful
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	1,441	2,543
Purchased credit impaired loans		305	1,200
Construction Real Estate Loans
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans		579,565	507,732
Purchased credit impaired loans		139	156
Construction Real Estate Loans | Pass
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans		579,253	507,529
Construction Real Estate Loans | Pass Watch
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	47	163
Construction Real Estate Loans | Special Mention
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	0	0
Construction Real Estate Loans | Substandard
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	265	28
Construction Real Estate Loans | Doubtful
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	0	12
1-4 Family Residential Real Estate Loans
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans		782,073	794,499
Purchased credit impaired loans		8,080	10,670
1-4 Family Residential Real Estate Loans | Pass
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans		776,375	787,516
1-4 Family Residential Real Estate Loans | Pass Watch
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	31	37
1-4 Family Residential Real Estate Loans | Special Mention
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	166	100
1-4 Family Residential Real Estate Loans | Substandard
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	4,784	5,489
1-4 Family Residential Real Estate Loans | Doubtful
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	717	1,357
Commercial Real Estate Loans
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans		1,251,248	1,194,118
Purchased credit impaired loans		30,988	32,885
Commercial Real Estate Loans | Pass
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans		1,150,646	1,067,874
Commercial Real Estate Loans | Pass Watch
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	55,208	11,479
Commercial Real Estate Loans | Special Mention
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	7,444	26,490
Commercial Real Estate Loans | Substandard
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	37,793	87,767
Commercial Real Estate Loans | Doubtful
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	157	508
Commercial loans
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans		389,521	356,649
Purchased credit impaired loans		1,676	2,219
Commercial loans | Pass
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans		375,664	349,495
Commercial loans | Pass Watch
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	3,362	520
Commercial loans | Special Mention
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	6,063	3,189
Commercial loans | Substandard
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	4,163	2,988
Commercial loans | Doubtful
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	269	457
Municipal loans
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans		357,028	353,370
Purchased credit impaired loans		0	0
Municipal loans | Pass
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans		357,028	353,370
Municipal loans | Pass Watch
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	0	0
Municipal loans | Special Mention
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	0	0
Municipal loans | Substandard
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	0	0
Municipal loans | Doubtful
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	0	0
Loans to individuals
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans		100,708	106,431
Purchased credit impaired loans		218	472
Loans to individuals | Pass
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans		100,030	105,536
Loans to individuals | Pass Watch
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	0	4
Loans to individuals | Special Mention
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	0	4
Loans to individuals | Substandard
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	380	678
Loans to individuals | Doubtful
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	$ 298	$ 209
[1]	Includes PCI loans comprised of $15,000 pass watch, $217,000 special mention, $2.7 million substandard and $305,000 doubtful as of June 30, 2019 . Includes PCI loans comprised of $22,000 pass watch, $859,000 special mention, $3.9 million substandard and $1.2 million doubtful as of December 31, 2018 .

Loans and Allowance for Proba_8

Loans and Allowance for Probable Loan Losses - Nonperforming Assets by Asset Class (Details) - USD ($)		Jun. 30, 2019	Dec. 31, 2018
Nonperforming Assets by Asset Class [Abstract]
Nonaccrual loans	[1],[2]	$ 16,376,000	$ 35,770,000
Accruing loans past due more than 90 days	[2]	0	0
Restructured loans	[3]	11,918,000	5,930,000
Other real estate owned		1,069,000	1,206,000
Repossessed assets		0	0
Total nonperforming assets		29,363,000	42,906,000
Restructured nonaccrual loans		8,900,000	10,900,000
PCI loans restructured		$ 776,000	$ 3,100,000
[1]	Includes $8.9 million and $10.9 million of restructured loans as of June 30, 2019 and December 31, 2018 , respectively.
[2]	Excludes PCI loans measured at fair value at acquisition if the timing and amount of cash flows expected to be collected from those sales can be reasonably estimated.
[3]	Includes $776,000 and $3.1 million in PCI loans restructured as of June 30, 2019 and December 31, 2018 , respectively.

Loans and Allowance for Proba_9

Loans and Allowance for Probable Loan Losses - Nonaccrual by Class of Loans (Details) - USD ($) $ in Thousands		Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	[1],[2]	$ 16,376	$ 35,770
Construction Real Estate Loans
Financing Receivable, Past Due [Line Items]
Nonaccrual loans		200	12
1-4 Family Residential Real Estate Loans
Financing Receivable, Past Due [Line Items]
Nonaccrual loans		1,418	2,202
Commercial Real Estate Loans
Financing Receivable, Past Due [Line Items]
Nonaccrual loans		13,383	32,599
Commercial loans
Financing Receivable, Past Due [Line Items]
Nonaccrual loans		1,047	639
Loans to individuals
Financing Receivable, Past Due [Line Items]
Nonaccrual loans		$ 328	$ 318
[1]	Includes $8.9 million and $10.9 million of restructured loans as of June 30, 2019 and December 31, 2018 , respectively.
[2]	Excludes PCI loans measured at fair value at acquisition if the timing and amount of cash flows expected to be collected from those sales can be reasonably estimated.

Loans and Allowance for Prob_10

Loans and Allowance for Probable Loan Losses - Impaired Loans by Class of Loan (Details) - USD ($) $ in Thousands		Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	[1]	$ 40,143	$ 47,274
Recorded Investment	[1]	35,045	44,267
Related Allowance for Loan Losses	[1]	2,369	5,908
PCI loans that experienced deterioration in credit quality subsequent to acquisition		9,100	8,000
Construction Real Estate Loans
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance		356	182
Recorded Investment		323	148
Related Allowance for Loan Losses		23	13
1-4 Family Residential Real Estate Loans
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance		8,646	6,507
Recorded Investment		7,491	5,923
Related Allowance for Loan Losses		66	40
Commercial Real Estate Loans
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance		26,198	36,457
Recorded Investment		22,999	34,744
Related Allowance for Loan Losses		1,408	5,337
Commercial loans
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance		4,033	2,874
Recorded Investment		3,449	2,366
Related Allowance for Loan Losses		782	368
Municipal loans
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance		429	429
Recorded Investment		429	429
Related Allowance for Loan Losses		0	1
Loans to individuals
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance		481	825
Recorded Investment		354	657
Related Allowance for Loan Losses		$ 90	$ 149
[1]	Includes $9.1 million and $8.0 million of PCI loans that experienced deterioration in credit quality subsequent to the acquisition date as of June 30, 2019 and December 31, 2018 , respectively.

Loans and Allowance for Prob_11

Loans and Allowance for Probable Loan Losses - Aging of Past Due Loans by Class of Loan (Details) - USD ($) $ in Thousands		Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Past Due [Line Items]
Total Past Due		$ 10,986	$ 34,314
Current	[1]	3,449,157	3,278,485
Total ending loan balance		3,460,143	3,312,799
30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		6,843	21,966
60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		2,792	10,276
Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		1,351	2,072
Construction Real Estate Loans
Financing Receivable, Past Due [Line Items]
Total Past Due		812	934
Current	[1]	578,753	506,798
Total ending loan balance		579,565	507,732
Construction Real Estate Loans | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		343	627
Construction Real Estate Loans | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		276	307
Construction Real Estate Loans | Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		193	0
1-4 Family Residential Real Estate Loans
Financing Receivable, Past Due [Line Items]
Total Past Due		3,873	10,034
Current	[1]	778,200	784,465
Total ending loan balance		782,073	794,499
1-4 Family Residential Real Estate Loans | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		2,250	7,441
1-4 Family Residential Real Estate Loans | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		1,330	1,258
1-4 Family Residential Real Estate Loans | Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		293	1,335
Commercial Real Estate Loans
Financing Receivable, Past Due [Line Items]
Total Past Due		2,159	18,318
Current	[1]	1,249,089	1,175,800
Total ending loan balance		1,251,248	1,194,118
Commercial Real Estate Loans | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		1,625	10,663
Commercial Real Estate Loans | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		425	7,655
Commercial Real Estate Loans | Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		109	0
Commercial loans
Financing Receivable, Past Due [Line Items]
Total Past Due		3,256	3,242
Current	[1]	386,265	353,407
Total ending loan balance		389,521	356,649
Commercial loans | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		2,070	1,946
Commercial loans | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		567	705
Commercial loans | Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		619	591
Municipal loans
Financing Receivable, Past Due [Line Items]
Total Past Due		0	0
Current	[1]	357,028	353,370
Total ending loan balance		357,028	353,370
Municipal loans | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		0	0
Municipal loans | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		0	0
Municipal loans | Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		0	0
Loans to individuals
Financing Receivable, Past Due [Line Items]
Total Past Due		886	1,786
Current	[1]	99,822	104,645
Total ending loan balance		100,708	106,431
Loans to individuals | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		555	1,289
Loans to individuals | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		194	351
Loans to individuals | Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		$ 137	$ 146
[1]	Includes PCI loans measured at fair value at acquisition if the timing and amount of cash flows expected to be collected from those sales can be reasonably estimated.

Loans and Allowance for Prob_12

Loans and Allowance for Probable Loan Losses - Interest Income on Impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Financing Receivable, Impaired [Line Items]
Average recorded investment	$ 35,761	$ 38,779	$ 41,033	$ 27,277
Interest income recognized	341	82	759	157
Construction Real Estate Loans
Financing Receivable, Impaired [Line Items]
Average recorded investment	214	140	200	114
Interest income recognized	5	1	9	1
1-4 Family Residential Real Estate Loans
Financing Receivable, Impaired [Line Items]
Average recorded investment	7,533	3,955	6,271	3,945
Interest income recognized	130	47	210	93
Commercial Real Estate Loans
Financing Receivable, Impaired [Line Items]
Average recorded investment	24,394	31,916	30,917	20,595
Interest income recognized	153	5	440	9
Commercial loans
Financing Receivable, Impaired [Line Items]
Average recorded investment	2,753	2,024	2,699	1,900
Interest income recognized	38	19	68	36
Municipal loans
Financing Receivable, Impaired [Line Items]
Average recorded investment	429	502	429	502
Interest income recognized	6	7	12	14
Loans to individuals
Financing Receivable, Impaired [Line Items]
Average recorded investment	438	242	517	221
Interest income recognized	$ 9	$ 3	$ 20	$ 4

Loans and Allowance for Prob_13

Loans and Allowance for Probable Loan Losses - Troubled Debt Restructurings (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019USD ($)contract	Jun. 30, 2018USD ($)contract	Jun. 30, 2019USD ($)contract	Jun. 30, 2018USD ($)contract
Financing Receivable, Troubled Debt Restructuring [Line Items]
Extend Amortization Period	$ 0	$ 9	$ 7,650	$ 238
Interest Rate Reductions	0	80	0	80
Combination	606	103	731	103
Total Modifications	$ 606	$ 192	$ 8,381	$ 421
Number of Loans | contract	8	6	13	10
1-4 Family Residential Real Estate Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Extend Amortization Period	$ 0	$ 0	$ 0	$ 0
Interest Rate Reductions	0	80	0	80
Combination	0	0	111	0
Total Modifications	$ 0	$ 80	$ 111	$ 80
Number of Loans | contract	0	1	1	1
Commercial Real Estate Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Extend Amortization Period	$ 0		$ 7,594
Interest Rate Reductions	0		0
Combination	96		96
Total Modifications	$ 96		$ 7,690
Number of Loans | contract	1		2
Commercial loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Extend Amortization Period	$ 0	$ 0	$ 56	$ 132
Interest Rate Reductions	0	0	0	0
Combination	485	90	485	90
Total Modifications	$ 485	$ 90	$ 541	$ 222
Number of Loans | contract	4	2	5	5
Loans to individuals
Financing Receivable, Troubled Debt Restructuring [Line Items]
Extend Amortization Period	$ 0	$ 9	$ 0	$ 106
Interest Rate Reductions	0	0	0	0
Combination	25	13	39	13
Total Modifications	$ 25	$ 22	$ 39	$ 119
Number of Loans | contract	3	3	5	4

Loans and Allowance for Prob_14

Loans and Allowance for Probable Loan Losses - Purchased Credit Impaired (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Purchased Credit Impaired [Abstract]
Outstanding principal balance	$ 45,430		$ 45,430		$ 51,388
Carrying amount	41,101		41,101		$ 46,402
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	14,520	$ 15,818	15,054	$ 18,721
Changes in expected cash flows not affecting non-accretable differences	0	0	0	(1,445)
Reclassifications (to) from nonaccretable discount	812	1,090	1,074	770
Accretion	(776)	(803)	(1,572)	(1,941)
Balance at end of period	$ 14,556	$ 16,105	$ 14,556	$ 16,105

Loans and Allowance for Prob_15

Loans and Allowance for Probable Loan Losses - Narrative (Details) - USD ($)	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans in process of foreclosure	$ 12,000	$ 147,000
Commitments to lend additional funds on Troubled Debt Restructurings (TDR)	0		$ 0
Impaired loans without an allowance	0	$ 0
Minimum
Financing Receivable, Allowance for Credit Loss [Line Items]
Loan review larger dollar loan relationship scope, aggregate debt	500,000
Specifically reserved loans or loan relationships threshold	150,000
Commercial Real Estate Loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Owner and nonowner-occupied real estate	1,140,000,000
Loans secured by multi-family properties	96,300,000
Loans secured by farmland	$ 18,100,000

Borrowing Arrangements (Details

Borrowing Arrangements (Details) - USD ($) $ in Thousands		6 Months Ended	12 Months Ended
		Jun. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Other borrowings		$ 26,064	$ 36,810
Federal Home Loan Bank borrowings		823,757	719,065
Other borrowings:
Debt Instrument [Line Items]
Other borrowings		26,064	36,810
Average amount outstanding during the period	[1]	15,653	10,880
Maximum amount outstanding during the period	[2]	$ 28,354	$ 36,810
Weighted average interest rate during the period	[3]	1.70%	1.40%
Interest rate at end of the period	[4]	2.00%	2.10%
Federal Home Loan Bank borrowings:
Debt Instrument [Line Items]
Federal Home Loan Bank borrowings		$ 823,757	$ 719,065
Average amount outstanding during the period	[1]	785,901	720,785
Maximum amount outstanding during the period	[2]	$ 1,004,997	$ 957,231
Weighted average interest rate during the period	[3]	2.10%	1.80%
Interest rate at end of the period	[4]	2.40%	2.30%
[1]	The average amount outstanding during the period was computed by dividing the total daily outstanding principal balances by the number of days in the period.
[2]	The maximum amount outstanding at any month-end during the period.
[3]	The weighted average interest rate during the period was computed by dividing the actual interest expense (annualized for interim periods) by the average amount outstanding during the period. The weighted average interest rate on the FHLB borrowings includes the effect of interest rate swaps.
[4]	Stated rate.

Borrowings Maturities Table (De

Borrowings Maturities Table (Details) $ in Thousands	Jun. 30, 2019USD ($)
Debt Instrument [Line Items]
Less than 1 Year	$ 822,696
1-2 Years	21,507
2-3 Years	0
3-4 Years	0
4-5 Years	0
Thereafter	5,618
Total	849,821
Other borrowings:
Debt Instrument [Line Items]
Less than 1 Year	25,931
1-2 Years	133
2-3 Years	0
3-4 Years	0
4-5 Years	0
Thereafter	0
Total	26,064
Federal Home Loan Bank borrowings:
Debt Instrument [Line Items]
Less than 1 Year	796,765
1-2 Years	21,374
2-3 Years	0
3-4 Years	0
4-5 Years	0
Thereafter	5,618
Total	$ 823,757

Borrowing Arrangements Narrativ

Borrowing Arrangements Narrative (Details)	6 Months Ended
	Jun. 30, 2019USD ($)Oustanding_Letters_of_Creditcredit_lineagreementRate	Dec. 31, 2018USD ($)
Line of Credit Facility [Line Items]
Federal Home Loan Bank borrowings with variable interest rate, face amount	$ 270,000,000
Number of credit lines maintained by the Company | credit_line	3
Federal funds purchased	$ 18,000,000	$ 28,000,000
Federal Home Loan Bank borrowings, additional funding available	1,260,000,000
Letters of Credit, Federal Home Loan Bank, as collateral	0
Securities sold under repurchase agreements	$ 8,100,000	8,800,000
Maturity of repurchase agreements (less than)	13 months
Frost Bank
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity	$ 40,000,000
Line of credit, capacity available for issuance of letters of credit	$ 5,000,000
Number of outstanding letters of credit | Oustanding_Letters_of_Credit	0
TIB - The Independent Bankers Bank
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity	$ 15,000,000
Comerica Bank
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity	$ 7,500,000
Minimum
Line of Credit Facility [Line Items]
Federal Home Loan Bank borrowings interest rates	1.37%
Federal Home Loan Bank borrowings maturities	2 days
Maximum
Line of Credit Facility [Line Items]
Federal Home Loan Bank borrowings interest rates	4.799%
Federal Home Loan Bank borrowings maturities	9 years
Variable Rate Advance Agreements
Line of Credit Facility [Line Items]
Federal Home Loan Bank borrowings with variable interest rate, face amount	$ 310,000,000	$ 310,000,000
Three-Month London Interbank Offered Rate (LIBOR) | Variable Rate Advance Agreements
Line of Credit Facility [Line Items]
Federal Home Loan Bank borrowings, description of variable rate basis	three-month LIBOR
Three-Month London Interbank Offered Rate (LIBOR) | Variable Rate Advance Agreements | Maximum
Line of Credit Facility [Line Items]
Debt Instrument, Number Of Variable Rate Advance Agreements | agreement	3
Cash flow hedging | Variable Rate Advance Agreements
Line of Credit Facility [Line Items]
Federal Home Loan Bank borrowings with variable interest rate, face amount	$ 270,000,000
Debt Instrument, Interest Rate During Period | Rate	1.58%
Derivative, Average Remaining Maturity	4 years 3 months 18 days

Long-term Debt Other Long-term

Long-term Debt Other Long-term Obligations (Details) - USD ($)		6 Months Ended
		Jun. 30, 2019		Dec. 31, 2018		Oct. 10, 2007	Aug. 10, 2007	Aug. 08, 2007
Debt Instruments [Abstract]
Subordinated notes, net of unamortized debt issuance costs:	[1]	$ 98,490,000		$ 98,407,000
Trust preferred subordinated debentures	[2]	60,248,000		60,246,000
Total long-term debt		158,738,000		158,653,000
5.50% Subordinated Notes
Debt Instruments [Abstract]
Subordinated notes, net of unamortized debt issuance costs:	[1],[3]	98,490,000		98,407,000
Unamortized Debt Issuance Expense		1,500,000		1,600,000
Southside Statutory Trust III, net of unamortized debt issuance costs [Member]
Debt Instruments [Abstract]
Trust preferred subordinated debentures	[2],[4]	20,556,000		20,554,000
Unamortized Debt Issuance Expense		63,000		65,000
Southside Statutory Trust IV
Debt Instruments [Abstract]
Trust preferred subordinated debentures		23,196,000	[2]	23,196,000	[2]			$ 23,196,000
Southside Statutory Trust V
Debt Instruments [Abstract]
Trust preferred subordinated debentures		12,887,000	[2]	12,887,000	[2]		$ 12,887,000
Magnolia Trust Company I
Debt Instruments [Abstract]
Trust preferred subordinated debentures		$ 3,609,000	[2]	$ 3,609,000	[2]	$ 3,609,000
Minimum | 5.50% Subordinated Notes
Debt Instruments [Abstract]
Long-term debt, remaining maturity, greater than		1 year
[1]	This debt consists of subordinated notes with a remaining maturity greater than one year that qualify under the risk-based capital guidelines as Tier 2 capital, subject to certain limitations.
[2]	This debt consists of trust preferred securities that qualify under the risk-based capital guidelines as Tier 1 capital, subject to certain limitations.
[3]	The unamortized discount and debt issuance costs reflected in the carrying amount of the subordinated notes totaled approximately $1.5 million at June 30, 2019 and $1.6 million at December 31, 2018 .
[4]	The unamortized debt issuance costs reflected in the carrying amount of the Southside Statutory Trust III junior subordinated debentures totaled $63,000 at June 30, 2019 and $65,000 at December 31, 2018 .

Long-term Debt LT Debt Interest

Long-term Debt LT Debt Interest Rates (Details) - USD ($) $ in Thousands		Sep. 29, 2021	Sep. 19, 2016	Oct. 10, 2007	Aug. 10, 2007	Aug. 08, 2007	Sep. 04, 2003	Jun. 30, 2019		Dec. 31, 2018
Debt Instrument [Line Items]
Other long-term debt	[1]							$ 60,248		$ 60,246
5.50% Subordinated Notes
Debt Instrument [Line Items]
Amount issued			$ 100,000
Stated interest rate			5.50%
Southside Statutory Trust III
Debt Instrument [Line Items]
Amount issued							$ 20,619
Other long-term debt	[1],[2]							20,556		20,554
Southside Statutory Trust III | Three-Month London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis on variable rate							2.94%
Southside Statutory Trust IV
Debt Instrument [Line Items]
Other long-term debt						$ 23,196		23,196	[1]	23,196	[1]
Southside Statutory Trust IV | Three-Month London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis on variable rate						1.30%
Southside Statutory Trust V
Debt Instrument [Line Items]
Other long-term debt					$ 12,887			12,887	[1]	12,887	[1]
Southside Statutory Trust V | Three-Month London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis on variable rate					2.25%
Magnolia Trust Company I
Debt Instrument [Line Items]
Other long-term debt				$ 3,609				$ 3,609	[1]	$ 3,609	[1]
Magnolia Trust Company I | Three-Month London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis on variable rate				1.80%
Scenario, Forecast | 5.50% Subordinated Notes | Three-Month London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis on variable rate		4.297%
[1]	This debt consists of trust preferred securities that qualify under the risk-based capital guidelines as Tier 1 capital, subject to certain limitations.
[2]	The unamortized debt issuance costs reflected in the carrying amount of the Southside Statutory Trust III junior subordinated debentures totaled $63,000 at June 30, 2019 and $65,000 at December 31, 2018 .

Employee Benefit Plans (Details

Employee Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Defined Benefit Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 394	$ 390	$ 710	$ 774
Interest cost	919	839	1,827	1,696
Expected return on assets	(1,511)	(1,622)	(3,015)	(3,242)
Net loss amortization	470	372	913	756
Prior service (credit) cost amortization	(4)	(4)	(7)	(7)
Net periodic benefit cost (income)	268	(25)	428	(23)
Defined Benefit Pension Plan Acquired
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	43	41	84	82
Expected return on assets	(73)	(72)	(146)	(145)
Net loss amortization	0	0	0	0
Prior service (credit) cost amortization	0	0	0	0
Net periodic benefit cost (income)	(30)	(31)	(62)	(63)
Restoration Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	110	84	170	147
Interest cost	195	165	356	298
Expected return on assets	0	0	0	0
Net loss amortization	181	248	280	339
Prior service (credit) cost amortization	1	2	3	3
Net periodic benefit cost (income)	$ 487	$ 499	$ 809	$ 787

Derivative Financial Instrume_3

Derivative Financial Instruments and Hedging Activities - Schedule Of Derivative Instruments (Details) - USD ($) $ in Thousands		Jun. 30, 2019	Dec. 31, 2018
Asset Derivative
Gross derivatives		$ 8,964	$ 11,594
Offsetting derivative assets		(2,350)	(2,201)
Cash collateral received/posted		0	(8,306)
Net derivatives included in the consolidated balance sheets	[1]	6,614	1,087
Liability Derivative
Gross derivatives		10,072	3,320
Offsetting derivative liabilities		(2,350)	(2,201)
Cash collateral received/posted		(7,420)	0
Net derivatives included in the consolidated balance sheets	[1]	302	1,119
Financial Institution Counterparties
Liability Derivative
Net credit exposure		0	0
Financial Institution Counterparties | Designated as Hedging Instrument | Cash Flow Hedging | Interest Rate Swap
Derivatives, Fair Value [Line Items]
Notional Amount	[2]	270,000	270,000
Asset Derivative
Gross derivatives		2,334	9,388
Liability Derivative
Gross derivatives		3,442	457
Financial Institution Counterparties | Designated as Hedging Instrument | Fair Value Hedging [Member] | Interest Rate Swap
Derivatives, Fair Value [Line Items]
Notional Amount	[2]	0	21,100
Asset Derivative
Gross derivatives		0	0
Liability Derivative
Gross derivatives		0	657
Financial Institution Counterparties | Not Designated as Hedging Instrument | Interest Rate Swap
Derivatives, Fair Value [Line Items]
Notional Amount	[2]	110,699	93,967
Asset Derivative
Gross derivatives		16	1,119
Liability Derivative
Gross derivatives		6,614	1,087
Customer Counterparties
Liability Derivative
Net credit exposure		6,600	1,100
Customer Counterparties | Not Designated as Hedging Instrument | Interest Rate Swap
Derivatives, Fair Value [Line Items]
Notional Amount	[2]	110,699	93,967
Asset Derivative
Gross derivatives		6,614	1,087
Liability Derivative
Gross derivatives		$ 16	$ 1,119
[1]	Net derivative assets are included in other assets and net derivative liabilities are included in other liabilities on the consolidated balance sheets. Included in the fair value of net derivative assets and net derivative liabilities are credit valuation adjustments reflecting counterparty credit risk and our credit risk. We had no credit exposure related to interest rate swaps with financial institutions and $6.6 million related to interest rate swaps with customers at June 30, 2019 . We had no credit exposure related to interest rate swaps with financial institutions and $1.1 million related to interest rate swaps with customers at December 31, 2018 . The credit risk associated with customer transactions is partially mitigated as these are generally secured by the non-cash collateral securing the underlying transaction being hedged.
[2]	Notional amounts, which represent the extent of involvement in the derivatives market, are used to determine the contractual cash flows required in accordance with the terms of the agreement. These amounts are typically not exchanged, significantly exceed amounts subject to credit or market risk and are not reflected in the consolidated balance sheets.

Derivative Financial Instrume_4

Derivative Financial Instruments and Hedging Activities - Weighted Average Remaining Maturity, Lives, and Rates of Interest Rate Swaps (Details) - Interest Rate Swap - USD ($) $ in Thousands		6 Months Ended	12 Months Ended
		Jun. 30, 2019	Dec. 31, 2018
Financial Institution Counterparties | Not Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	[1]	$ 110,699	$ 93,967
Remaining Maturity (in years)		11 years 7 months 6 days	11 years 7 months 6 days
Weighted Average Receive Rate		2.42%	2.36%
Weighted Average Pay Rate		2.57%	2.58%
Financial Institution Counterparties | Cash Flow Hedging | Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	[1]	$ 270,000	$ 270,000
Remaining Maturity (in years)		4 years 3 months 18 days	4 years 9 months 18 days
Weighted Average Receive Rate		2.44%	2.45%
Weighted Average Pay Rate		1.58%	1.58%
Financial Institution Counterparties | Fair Value Hedging [Member] | Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	[1]	$ 0	$ 21,100
Remaining Maturity (in years)			7 years 6 months
Weighted Average Receive Rate		0.00%	2.56%
Weighted Average Pay Rate		0.00%	3.00%
Customer Counterparties | Not Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	[1]	$ 110,699	$ 93,967
Remaining Maturity (in years)		11 years 7 months 6 days	11 years 7 months 6 days
Weighted Average Receive Rate		2.57%	2.58%
Weighted Average Pay Rate		2.42%	2.36%
[1]	Notional amounts, which represent the extent of involvement in the derivatives market, are used to determine the contractual cash flows required in accordance with the terms of the agreement. These amounts are typically not exchanged, significantly exceed amounts subject to credit or market risk and are not reflected in the consolidated balance sheets.

Derivative Financial Instrume_5

Derivative Financial Instruments and Hedging Activities - Narrative (Details)	12 Months Ended
	Dec. 31, 2017contract	Jun. 30, 2019USD ($)
Derivative [Line Items]
Debt instrument, face amount		$ 270,000,000
Cash collateral held by a counterparty to a master netting agreement		$ 7,400,000
Interest Rate Swap
Derivative [Line Items]
Derivative, instruments terminated | contract	2

Fair Value Measurement - Recur

Fair Value Measurement - Recurring and Nonrecurring Basis (Details) - USD ($) $ in Thousands		Jun. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value		$ 2,088,787	$ 1,989,436
Derivative assets	[1]	6,614	1,087
Derivative liabilities	[1]	302	1,119
State and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value		528,855	716,601
Other stocks and bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value		2,959	2,709
Residential MBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	[2]	1,318,986	732,972
Commercial MBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	[2]	237,987	537,154
Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity investments		5,948	5,791
Total asset fair value measurements		2,103,699	2,006,821
Total liability fair value measurements		10,072	3,320
Fair Value, Recurring [Member] | State and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value		528,855	716,601
Fair Value, Recurring [Member] | Other stocks and bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value		2,959	2,709
Fair Value, Recurring [Member] | Residential MBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	[3]	1,318,986	732,972
Fair Value, Recurring [Member] | Commercial MBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	[3]	237,987	537,154
Fair Value, Recurring [Member] | Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		8,964	11,594
Derivative liabilities		10,072	3,320
Fair Value, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity investments		5,948	5,791
Total asset fair value measurements		5,948	5,791
Total liability fair value measurements		0	0
Fair Value, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | State and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value		0	0
Fair Value, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other stocks and bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value		0	0
Fair Value, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Residential MBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	[3]	0	0
Fair Value, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Commercial MBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	[3]	0	0
Fair Value, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		0	0
Derivative liabilities		0	0
Fair Value, Recurring [Member] | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity investments		0	0
Total asset fair value measurements		2,097,751	2,001,030
Total liability fair value measurements		10,072	3,320
Fair Value, Recurring [Member] | Significant Other Observable Inputs (Level 2) | State and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value		528,855	716,601
Fair Value, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Other stocks and bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value		2,959	2,709
Fair Value, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Residential MBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	[3]	1,318,986	732,972
Fair Value, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Commercial MBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	[3]	237,987	537,154
Fair Value, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		8,964	11,594
Derivative liabilities		10,072	3,320
Fair Value, Recurring [Member] | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity investments		0	0
Total asset fair value measurements		0	0
Total liability fair value measurements		0	0
Fair Value, Recurring [Member] | Significant Unobservable Inputs (Level 3) | State and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value		0	0
Fair Value, Recurring [Member] | Significant Unobservable Inputs (Level 3) | Other stocks and bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value		0	0
Fair Value, Recurring [Member] | Significant Unobservable Inputs (Level 3) | Residential MBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	[3]	0	0
Fair Value, Recurring [Member] | Significant Unobservable Inputs (Level 3) | Commercial MBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	[3]	0	0
Fair Value, Recurring [Member] | Significant Unobservable Inputs (Level 3) | Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		0	0
Derivative liabilities		0	0
Fair Value, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreclosed assets		1,069	1,206
Impaired loans	[4]	32,148	37,813
Total asset fair value measurements		33,217	39,019
Fair Value, Nonrecurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreclosed assets		0	0
Impaired loans	[4]	0	0
Total asset fair value measurements		0	0
Fair Value, Nonrecurring [Member] | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreclosed assets		0	0
Impaired loans	[4]	0	0
Total asset fair value measurements		0	0
Fair Value, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreclosed assets		1,069	1,206
Impaired loans	[4]	32,148	37,813
Total asset fair value measurements		$ 33,217	$ 39,019
[1]	Net derivative assets are included in other assets and net derivative liabilities are included in other liabilities on the consolidated balance sheets. Included in the fair value of net derivative assets and net derivative liabilities are credit valuation adjustments reflecting counterparty credit risk and our credit risk. We had no credit exposure related to interest rate swaps with financial institutions and $6.6 million related to interest rate swaps with customers at June 30, 2019 . We had no credit exposure related to interest rate swaps with financial institutions and $1.1 million related to interest rate swaps with customers at December 31, 2018 . The credit risk associated with customer transactions is partially mitigated as these are generally secured by the non-cash collateral securing the underlying transaction being hedged.
[2]	All mortgage-backed securities issued and/or guaranteed by U.S. government agencies or U.S. government-sponsored enterprises.
[3]	All mortgage-backed securities are issued and/or guaranteed by U.S. government agencies or U.S. government-sponsored enterprises.
[4]	Impaired loans represent collateral-dependent loans with a specific valuation allowance. Losses on these loans represent charge-offs which are netted against the allowance for loan losses.

Fair Value Measurement - Balan

Fair Value Measurement - Balance Sheet Grouping (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Carrying Amount
Financial assets:
Cash and cash equivalents	$ 132,521	$ 120,719
Investment securities:
Held to maturity, at carrying value	3,018	3,083
Mortgage-backed securities:
Held to maturity, at carrying value	144,073	159,848
Federal Home Loan Bank stock, at cost	44,718	32,583
Equity investments	6,426	6,302
Loans, net of allowance for loan losses	3,435,438	3,285,780
Loans held for sale	1,812	601
Financial liabilities:
Deposits	4,479,256	4,425,030
Other borrowings	26,064	36,810
Federal Home Loan Bank borrowings	823,757	719,065
Subordinated notes, net of unamortized debt issuance costs	98,490	98,407
Trust preferred subordinated debentures, net of unamortized debt issuance costs	60,248	60,246
Estimated Fair Value
Financial assets:
Cash and cash equivalents	132,521	120,719
Investment securities:
Held to maturity, at carrying value	3,054	3,046
Mortgage-backed securities:
Held to maturity, at carrying value	148,253	156,735
Federal Home Loan Bank stock, at cost	44,718	32,583
Equity investments	6,426	6,302
Loans, net of allowance for loan losses	3,493,559	3,251,923
Loans held for sale	1,812	601
Financial liabilities:
Deposits	4,478,936	4,417,902
Other borrowings	26,064	36,810
Federal Home Loan Bank borrowings	825,450	708,904
Subordinated notes, net of unamortized debt issuance costs	98,964	97,611
Trust preferred subordinated debentures, net of unamortized debt issuance costs	58,819	54,729
Estimated Fair Value | Level 1
Financial assets:
Cash and cash equivalents	132,521	120,719
Investment securities:
Held to maturity, at carrying value	0	0
Mortgage-backed securities:
Held to maturity, at carrying value	0	0
Federal Home Loan Bank stock, at cost	0	0
Equity investments	0	0
Loans, net of allowance for loan losses	0	0
Loans held for sale	0	0
Financial liabilities:
Deposits	0	0
Other borrowings	0	0
Federal Home Loan Bank borrowings	0	0
Subordinated notes, net of unamortized debt issuance costs	0	0
Trust preferred subordinated debentures, net of unamortized debt issuance costs	0	0
Estimated Fair Value | Level 2
Financial assets:
Cash and cash equivalents	0	0
Investment securities:
Held to maturity, at carrying value	3,054	3,046
Mortgage-backed securities:
Held to maturity, at carrying value	148,253	156,735
Federal Home Loan Bank stock, at cost	44,718	32,583
Equity investments	6,426	6,302
Loans, net of allowance for loan losses	0	0
Loans held for sale	1,812	601
Financial liabilities:
Deposits	4,478,936	4,417,902
Other borrowings	26,064	36,810
Federal Home Loan Bank borrowings	825,450	708,904
Subordinated notes, net of unamortized debt issuance costs	98,964	97,611
Trust preferred subordinated debentures, net of unamortized debt issuance costs	58,819	54,729
Estimated Fair Value | Level 3
Financial assets:
Cash and cash equivalents	0	0
Investment securities:
Held to maturity, at carrying value	0	0
Mortgage-backed securities:
Held to maturity, at carrying value	0	0
Federal Home Loan Bank stock, at cost	0	0
Equity investments	0	0
Loans, net of allowance for loan losses	3,493,559	3,251,923
Loans held for sale	0	0
Financial liabilities:
Deposits	0	0
Other borrowings	0	0
Federal Home Loan Bank borrowings	0	0
Subordinated notes, net of unamortized debt issuance costs	0	0
Trust preferred subordinated debentures, net of unamortized debt issuance costs	$ 0	$ 0

Fair Value Measurement Narrativ

Fair Value Measurement Narrative (Details)	6 Months Ended
	Jun. 30, 2019source
Available-for-sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of third party sources used to validate prices	2
Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of third party sources used to validate prices	3

Income Taxes - Provision for I

Income Taxes - Provision for Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Tax Disclosure [Abstract]
Current income tax expense	$ 3,553	$ 667	$ 6,564	$ 3,012
Deferred income tax expense	16	2,693	142	2,438
Income tax expense	$ 3,569	$ 3,360	$ 6,706	$ 5,450

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Deferred tax liability, net	$ 5,029,000		$ 5,029,000		$ 0
Net deferred tax assets					9,800,000
Deferred tax assets, valuation allowance	0		0		$ 0
Income tax expense	$ 3,569,000	$ 3,360,000	$ 6,706,000	$ 5,450,000
Effective income tax rate, percent	16.10%	14.30%	15.20%	13.00%

Leases - Narrative (Details)

Leases - Narrative (Details)	6 Months Ended
	Jun. 30, 2019ft²
Lessee, Lease, Description [Line Items]
Building Acquired, Number of Square Feet	202,000
Number of Square Feet Occupied	41,000
Minimum
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Remaining Lease Term	4 months
Maximum
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Remaining Lease Term	19 years 10 months 24 days
Lessee, Operating Lease, Option to Extend	10 years
Lessee, Operating Lease, Option to Terminate	2 years

Leases - Balance Sheet Informat

Leases - Balance Sheet Information (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Leases [Abstract]
Operating lease right-of-use assets	$ 9,812	$ 0
Operating lease liabilities	$ 10,204	$ 0

Leases - Components of Lease Ex

Leases - Components of Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Leases [Abstract]
Operating lease cost	$ 395	$ 789

Leases - Supplemental Cash Flow

Leases - Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Leases [Abstract]
Operating cash flows from operating leases	$ 360	$ 700
Right-of-use assets obtained in exchange for new operating lease liabilities	$ 654	$ 654

Leases - Weighted Average Lease

Leases - Weighted Average Lease Information (Details)	Jun. 30, 2019Rate
Leases [Abstract]
Weighted average remaining lease term	12 years 6 months
Weighted average discount rate	3.88%

Leases - Future Operating Lease

Leases - Future Operating Lease Obligations (Details) - USD ($) $ in Thousands		6 Months Ended
		Jun. 30, 2019	Dec. 31, 2018
Leases [Abstract]
Lessee, Operating Lease, Lease Not Yet Commenced, Payments, Due		$ 9,100
2019 (excluding the six months ended June 30, 2019)		625
2020		1,338
2021		1,232
2021		1,193
2023		1,044
2024 and thereafter		7,866
Total lease payments	[1]	13,298
Less: Interest		(3,094)
Present value of lease liabilities		$ 10,204	$ 0
Lessee, Operating Lease, Not Yet Commenced, Lease Term		20 years 4 months 24 days
[1]	Excludes $9.1 million of lease payments for a lease executed but not yet commenced. Lease will commence in 2020 with a lease term of 20.4 years .

Leases - Rental Income (Details

Leases - Rental Income (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Lessor, Operating Lease, Description [Abstract]
Gross rental income	$ 742	$ 1,487

Leases - Future Operating Lea_2

Leases - Future Operating Lease Receivable (Details) $ in Thousands	Jun. 30, 2019USD ($)
Leases [Abstract]
2019 (excluding the six months ended June 30, 2019)	$ 1,388
2020	2,693
2021	1,576
2022	1,553
2023	1,316
2024 and thereafter	4,098
Total lease payments	$ 12,624

Off-Balance-Sheet Arrangement_3

Off-Balance-Sheet Arrangements, Commitments and Contingencies (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance-sheet risk, at fair value	$ 1,051,497	$ 901,995
Commitments to extend credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance-sheet risk, at fair value	1,024,034	874,557
Standby letters of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance-sheet risk, at fair value	$ 27,463	$ 27,438

Off-Balance-Sheet Arrangement_4

Off-Balance-Sheet Arrangements, Commitments and Contingencies Narrative (Details) - USD ($)	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Securities:
Unsettled trades to purchase securities	$ 38,569,000	$ 6,378,000	$ 2,279,000
Unsettled trades to sell securities	0	0
Deposits:
Unsettled Issuances of Brokered CDs	$ 0	$ 15,236,000

Uncategorized Items - sbsi10-q0

Label	Element	Value
Additional Paid-in Capital [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAdjustedBalance1	$ 757,439,000
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAdjustedBalance1	762,470,000
Common Stock [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAdjustedBalance1	47,307,000
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAdjustedBalance1	47,253,000
Treasury Stock [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAdjustedBalance1	(47,105,000)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAdjustedBalance1	$ (93,055,000)