Southside Bancshares (SBSI) 10-Q 30 Apr 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2019	Apr. 24, 2019
Document and Entity Information [Abstract]
Entity Registrant Name	SOUTHSIDE BANCSHARES INC
Entity Central Index Key	0000705432
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding		33,718,079

CONSOLIDATED BALANCE SHEETS (UN

CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($)		Mar. 31, 2019	Dec. 31, 2018
ASSETS
Cash and due from banks		$ 81,981,000	$ 87,375,000
Interest earning deposits		184,612,000	23,884,000
Federal funds sold		3,350,000	9,460,000
Total cash and cash equivalents		269,943,000	120,719,000
Securities available for sale, at estimated fair value		1,876,255,000	1,989,436,000
Securities held to maturity, at carrying value (estimated fair value of $147,666 and $159,781, respectively)		147,431,000	162,931,000
FHLB stock, at cost		35,269,000	32,583,000
Equity investments		12,182,000	12,093,000
Loans held for sale		384,000	601,000
Loans:
Loans		3,305,110,000	3,312,799,000
Less: Allowance for loan losses	[1]	(24,155,000)	(27,019,000)
Net Loans		3,280,955,000	3,285,780,000
Premises and equipment, net		138,290,000	135,972,000
Operating lease right-of-use assets		9,455,000	0
Goodwill		201,116,000	201,116,000
Other intangible assets, net		16,600,000	17,779,000
Interest receivable		20,017,000	27,287,000
Deferred tax asset, net		491,000	9,776,000
Unsettled trades to sell securities		95,482,000	0
Unsettled issuances of brokered certificates of deposit		0	15,236,000
Bank owned life insurance		98,704,000	98,160,000
Other assets		14,622,000	14,025,000
Total assets		6,217,196,000	6,123,494,000
Deposits:
Noninterest bearing		1,038,116,000	994,680,000
Interest bearing		3,529,777,000	3,430,350,000
Total deposits		4,567,893,000	4,425,030,000
Federal funds purchased and repurchase agreements		8,637,000	36,810,000
FHLB borrowings		619,861,000	719,065,000
Subordinated notes, net of unamortized debt issuance costs		98,448,000	98,407,000
Trust preferred subordinated debentures, net of unamortized debt issuance costs		60,247,000	60,246,000
Unsettled trades to purchase securities		55,826,000	6,378,000
Operating lease liabilities		9,811,000	0
Other liabilities		38,440,000	46,267,000
Total liabilities		5,459,163,000	5,392,203,000
Off-balance-sheet arrangements, commitments and contingencies (Note 14)
Shareholders’ equity:
Common stock: ($1.25 par value, 80,000,000 shares authorized, 37,855,789 shares issued at March 31, 2019 and 37,845,224 shares issued at December 31, 2018)		47,320,000	47,307,000
Paid-in capital		763,582,000	762,470,000
Retained earnings		57,023,000	64,797,000
Treasury stock: (shares at cost, 4,137,710 at March 31, 2019 and 4,120,475 at December 31, 2018)		(94,119,000)	(93,055,000)
Accumulated other comprehensive loss		(15,773,000)	(50,228,000)
Total shareholders’ equity		758,033,000	731,291,000
Total liabilities and shareholders’ equity		$ 6,217,196,000	$ 6,123,494,000
[1]	The allowance for loan loss recorded on purchased credit impaired (“PCI”) loans totaled $250,000 and $302,000 as of March 31, 2019 and December 31, 2018, respectively.

CONSOLIDATED BALANCE SHEETS (_2

CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Held-to-maturity Securities, Other Disclosure Items [Abstract]
Securities held to maturity, fair value	$ 147,666	$ 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)	37,855,789	37,845,224
Treasury stock (in shares)	4,137,710	4,120,475

CONSOLIDATED STATEMENTS OF INCO

CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Interest income:
Loans		$ 41,619	$ 38,830
Investment securities – taxable		28	227
Investment securities – tax-exempt		4,118	6,381
Mortgage-backed securities		12,474	10,894
FHLB stock and equity investments		355	414
Other interest earning assets		433	448
Total interest income		59,027	57,194
Interest expense:
Deposits		11,241	7,451
FHLB borrowings		4,457	3,632
Subordinated notes		1,400	1,398
Trust preferred subordinated debentures		729	569
Other borrowings		75	11
Total interest expense		17,902	13,061
Net interest income		41,125	44,133
Provision for loan losses	[1]	(918)	3,735
Net interest income after provision for loan losses		42,043	40,398
Noninterest income:
Deposit services		5,986	6,179
Net gain (loss) on sale of securities available for sale		256	(827)
Gain on sale of loans		93	115
Trust income		1,541	1,760
Bank owned life insurance income		544	632
Brokerage services		517	450
Other		601	1,301
Total noninterest income		9,538	9,610
Noninterest expense:
Salaries and employee benefits		18,046	18,559
Net occupancy expense		3,175	3,583
Acquisition expense		0	832
Advertising, travel & entertainment		847	685
ATM expense		180	346
Professional fees		1,314	1,070
Software and data processing expense		1,076	1,023
Telephone and communications		487	538
FDIC insurance		422	497
Amortization expense on intangibles		1,179	1,378
Other		2,901	3,156
Total noninterest expense		29,627	31,667
Income before income tax expense		21,954	18,341
Income tax expense		3,137	2,090
Net income		$ 18,817	$ 16,251
Earnings per common share - basic (in dollars per share)		$ 0.56	$ 0.46
Earnings per common share - diluted (in dollars per share)		0.56	0.46
Dividends paid per common share (in dollars per share)		$ 0.30	$ 0.28
[1]	Of the $918,000 reversal of provision for loan losses for the three months ended March 31, 2019, $52,000 related to provision expense reversed on PCI loans. Of the $3.7 million recorded in provision for loan losses for the three months ended March 31, 2018, none related to provision expense on PCI loans.

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 18,817	$ 16,251
Securities available for sale and transferred securities:
Change in unrealized holding gain (loss) on available for sale securities during the period	46,626	(37,783)
Unrealized net gain on securities transferred from held to maturity to available for sale under the transition guidance enumerated in ASU 2017-12	0	11,881
Change in net unrealized loss on securities transferred from held to maturity to available for sale	0	401
Reclassification adjustment for amortization related to available for sale and held to maturity debt securities	491	138
Reclassification adjustment for net (gain) loss on sale of available for sale securities, included in net income	(256)	827
Derivatives:
Change in net unrealized (loss) gain on effective cash flow hedge interest rate swap derivatives	(3,120)	4,245
Reclassification adjustment of net gain related to derivatives designated as cash flow hedge	(668)	(127)
Pension plans:
Amortization of net actuarial loss and prior service credit, included in net periodic benefit cost	541	473
Other comprehensive income (loss), before tax	43,614	(19,945)
Income tax (expense) benefit related to items of other comprehensive income (loss)	(9,159)	4,188
Other comprehensive income (loss), net of tax	34,455	(15,757)
Comprehensive income	$ 53,272	$ 494

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 (10,565 shares in 2019 and 10,035 shares in 2018)	353	12	341
Stock compensation expense	456		456
Net issuance of common stock under employee stock plans (23,617 shares in 2019 and 42,179 shares in 2018)	761	0	417	(25)	369
Cash dividends paid on common stock ($0.30 per share in 2019 and $0.28 per share in 2018)	(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, 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 (10,565 shares in 2019 and 10,035 shares in 2018)	355	13	342
Purchase of common stock (40,852 shares in 2019)	(1,325)				(1,325)
Stock compensation expense	661		661
Net issuance of common stock under employee stock plans (23,617 shares in 2019 and 42,179 shares in 2018)	338	0	109	(32)	261
Cash dividends paid on common stock ($0.30 per share in 2019 and $0.28 per share in 2018)	(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)

CONSOLIDATED STATEMENTS OF CH_2

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

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($)		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
OPERATING ACTIVITIES:
Net income		$ 18,817,000	$ 16,251,000
Adjustments to reconcile net income to net cash provided by operations:
Depreciation and net amortization		3,023,000	3,566,000
Securities premium amortization (discount accretion), net		3,448,000	4,058,000
Loan (discount accretion) premium amortization, net		(438,000)	(1,057,000)
Provision for loan losses	[1]	(918,000)	3,735,000
Stock compensation expense		661,000	456,000
Deferred tax expense (benefit)		126,000	(255,000)
Net (gain) loss on sale of securities available for sale		(256,000)	827,000
Net loss on premises and equipment		5,000	35,000
Gross proceeds from sales of loans held for sale		4,244,000	5,600,000
Gross originations of loans held for sale		(4,027,000)	(5,602,000)
Net (gain) loss on other real estate owned		(92,000)	67,000
Net change in:
Interest receivable		7,270,000	7,827,000
Other assets		3,305,000	1,875,000
Interest payable		(321,000)	(1,219,000)
Other liabilities		(14,373,000)	5,501,000
Net cash provided by operating activities		20,474,000	41,665,000
Securities available for sale:
Purchases		(372,465,000)	(138,581,000)
Sales		436,182,000	237,526,000
Maturities, calls and principal repayments		30,077,000	53,717,000
Securities held to maturity:
Maturities, calls and principal repayments		15,405,000	1,222,000
Proceeds from redemption of FHLB stock and other investments		8,788,000	13,377,000
Purchases of FHLB stock and other investments		(11,551,000)	(638,000)
Net loan paydowns (originations)		5,868,000	(15,154,000)
Purchases of premises and equipment		(4,040,000)	(2,018,000)
Proceeds from sales of premises and equipment		2,000	1,903,000
Proceeds from sales of other real estate owned		470,000	91,000
Proceeds from sales of repossessed assets		137,000	198,000
Net cash provided by investing activities		108,873,000	151,643,000
FINANCING ACTIVITIES:
Net change in deposits		157,991,000	126,372,000
Net decrease in federal funds purchased and repurchase agreements		(28,173,000)	(1,673,000)
Proceeds from FHLB borrowings		1,556,293,000	1,110,000,000
Repayment of FHLB borrowings		(1,655,495,000)	(1,355,194,000)
Proceeds from stock option exercises		412,000	801,000
Cash paid to tax authority related to tax withholding on share-based awards		(74,000)	(40,000)
Purchase of common stock		(1,325,000)	0
Proceeds from the issuance of common stock for dividend reinvestment plan		355,000	353,000
Cash dividends paid		(10,107,000)	(9,808,000)
Net cash provided by (used in) financing activities		19,877,000	(129,189,000)
Net increase in cash and cash equivalents		149,224,000	64,119,000
Cash and cash equivalents at beginning of period		120,719,000	198,692,000
Cash and cash equivalents at end of period		269,943,000	262,811,000
SUPPLEMENTAL DISCLOSURES FOR CASH FLOW INFORMATION:
Interest paid		18,224,000	14,280,000
Income taxes paid		0	0
SUPPLEMENTAL DISCLOSURES OF NONCASH INVESTING AND FINANCING ACTIVITIES:
Loans transferred to other repossessed assets and real estate through foreclosure		336,000	649,000
Transfer of held to maturity securities to available for sale securities		0	743,421,000
Adjustment to pension liability		(541,000)	(473,000)
Unsettled trades to purchase securities		(55,826,000)	(3,646,000)
Unsettled trades to sell securities		$ 95,482,000	$ 35,307,000
[1]	Of the $918,000 reversal of provision for loan losses for the three months ended March 31, 2019, $52,000 related to provision expense reversed on PCI loans. Of the $3.7 million recorded in provision for loan losses for the three months ended March 31, 2018, none related to provision expense on PCI loans.

Summary of Significant Accounti

Summary of Significant Accounting and Reporting Policies	3 Months Ended
	Mar. 31, 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. “Omni” refers to OmniAmerican Bancorp, Inc., a bank holding company, and its wholly-owned subsidiary, OmniAmerican Bank, acquired by Southside on December 17, 2014. “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 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.” 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 on January 1, 2020, the effective date. We have developed a project plan and have assigned a project team to complete the analysis needed to implement the guidance. We are also currently working with a third party vendor solution to assist with the application of ASU 2016-13. The team is currently completing the data collection and anticipates running parallel models during 2019. 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	3 Months Ended
	Mar. 31, 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 fair value of assets acquired, adjusted for subsequent measurement period adjustments, excluding goodwill, totaled $1.03 billion , including total loans of $621.3 million and total investment securities of $234.4 million . Total fair value of the liabilities assumed totaled $910.7 million , including deposits of $899.3 million . We recognized goodwill of $109.6 million associated with Diboll acquisition. 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 was $201.1 million as of March 31, 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 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. The Diboll acquisition was accounted for using the acquisition method of accounting and accordingly, purchased assets, including identifiable intangible assets and assumed liabilities, were recorded at their respective acquisition date fair values. For more information concerning the fair value of the assets acquired and liabilities assumed in relation to the acquisition of Diboll, see “Note 2 - Acquisition” in our Annual Report on Form 10-K for the year ended December 31, 2018.

Earnings Per Share

Earnings Per Share	3 Months Ended
	Mar. 31, 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 2019 2018 Basic and Diluted Earnings: Net income $ 18,817 $ 16,251 Basic weighted-average shares outstanding 33,697 35,022 Add: Stock awards 149 178 Diluted weighted-average shares outstanding 33,846 35,200 Basic earnings per share: Net Income $ 0.56 $ 0.46 Diluted earnings per share: Net Income $ 0.56 $ 0.46 For the three months ended March 31, 2019 and 2018 , there were approximately 490,000 and 186,000 anti-dilutive shares, respectively.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	3 Months Ended
	Mar. 31, 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 March 31, 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 46,626 (3,120 ) — — 43,506 Reclassified from accumulated other comprehensive income (loss) 235 (668 ) (1 ) 542 108 Income tax (expense) benefit (9,840 ) 795 — (114 ) (9,159 ) Net current-period other comprehensive income (loss), net of tax 37,021 (2,993 ) (1 ) 428 34,455 Ending balance, net of tax $ 5,901 $ 4,153 $ (140 ) $ (25,687 ) $ (15,773 ) Three Months Ended March 31, 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 income (loss) before reclassifications (25,501 ) 4,245 — — (21,256 ) Reclassified from accumulated other comprehensive income (loss) 965 (127 ) (2 ) 475 1,311 Income tax benefit (expense) 5,152 (865 ) 1 (100 ) 4,188 Net current-period other comprehensive (loss) income, net of tax (19,384 ) 3,253 (1 ) 375 (15,757 ) Ending balance, net of tax $ (35,594 ) $ 9,652 $ (134 ) $ (25,894 ) $ (51,970 ) (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 reclassifications out of accumulated other comprehensive income (loss) into net income are presented below (in thousands): Three Months Ended 2019 2018 Unrealized losses on securities transferred: Amortization of unrealized losses (1) $ (491 ) $ (138 ) Tax benefit 103 29 Net of tax $ (388 ) $ (109 ) Unrealized gains and losses on available for sale securities: Realized net gain (loss) on sale of securities (2) $ 256 $ (827 ) Tax (expense) benefit (54 ) 174 Net of tax $ 202 $ (653 ) Derivatives: Realized net gain on interest rate swap derivatives (3) $ 646 $ 106 Tax expense (136 ) (22 ) Net of tax $ 510 $ 84 Amortization of unrealized gains on terminated interest rate swap derivatives (3) $ 22 $ 21 Tax expense (5 ) (4 ) Net of tax $ 17 $ 17 Amortization of pension plan: Net actuarial loss (4) $ (542 ) $ (475 ) Prior service credit (4) 1 2 Total before tax (541 ) (473 ) Tax benefit 114 99 Net of tax (427 ) (374 ) Total reclassifications for the period, net of tax $ (86 ) $ (1,035 ) (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 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	3 Months Ended
	Mar. 31, 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 and held to maturity as of March 31, 2019 and December 31, 2018 are reflected in the tables below (in thousands): March 31, 2019 Amortized Gross Unrealized Gross Unrealized Estimated AVAILABLE FOR SALE Cost Gains Losses Fair Value Investment securities: State and political subdivisions $ 446,006 $ 9,130 $ 1,865 $ 453,271 Other stocks and bonds 3,000 — 79 2,921 Mortgage-backed securities: (1) Residential 999,201 8,669 4,168 1,003,702 Commercial 416,618 910 1,167 416,361 Total $ 1,864,825 $ 18,709 $ 7,279 $ 1,876,255 HELD TO MATURITY Investment securities: State and political subdivisions $ 3,025 $ 29 $ — $ 3,054 Mortgage-backed securities: (1) Residential 59,720 962 413 60,269 Commercial 84,686 514 857 84,343 Total $ 147,431 $ 1,505 $ 1,270 $ 147,666 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 March 31, 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 three months ended March 31, 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 March 31, 2019 and December 31, 2018 (in thousands): March 31, 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 $ 241 $ — $ 91,310 $ 1,865 $ 91,551 $ 1,865 Other stocks and bonds 2,921 79 — — 2,921 79 Mortgage-backed securities: Residential 14,666 83 314,543 4,085 329,209 4,168 Commercial — — 186,267 1,167 186,267 1,167 Total $ 17,828 $ 162 $ 592,120 $ 7,117 $ 609,948 $ 7,279 HELD TO MATURITY Mortgage-backed securities: Residential $ 1,213 $ 18 $ 4,759 $ 395 $ 5,972 $ 413 Commercial — — 44,916 857 44,916 857 Total $ 1,213 $ 18 $ 49,675 $ 1,252 $ 50,888 $ 1,270 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 March 31, 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 March 31, 2019 . The following table reflects interest income recognized on securities for the periods presented (in thousands): Three Months Ended 2019 2018 U.S. Treasury $ — $ 108 U.S. government agency debentures — 89 State and political subdivisions 4,118 6,381 Other stocks and bonds 28 30 Mortgage-backed securities 12,474 10,894 Total interest income on securities $ 16,620 $ 17,502 There was a $256,000 net realized gain from the AFS securities portfolio for the three months ended March 31, 2019 , which consisted of $5.0 million in realized gains and $4.8 million in realized losses. There was an $827,000 net realized loss from the AFS securities portfolio for the three months ended March 31, 2018 , which consisted of $1.8 million in realized losses and $941,000 in realized gains. There were no sales from the HTM portfolio during the three months ended March 31, 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 March 31, 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. March 31, 2019 Amortized Cost Fair Value AVAILABLE FOR SALE Investment securities: Due in one year or less $ 3,827 $ 3,866 Due after one year through five years 7,743 7,741 Due after five years through ten years 29,416 30,332 Due after ten years 408,020 414,253 449,006 456,192 Mortgage-backed securities 1,415,819 1,420,063 Total $ 1,864,825 $ 1,876,255 March 31, 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 1,663 1,676 Due after five years through ten years 1,247 1,263 Due after ten years — — 3,025 3,054 Mortgage-backed securities: 144,406 144,612 Total $ 147,431 $ 147,666 Investment securities and MBS with carrying values of $1.03 billion and $1.08 billion were pledged as of March 31, 2019 and December 31, 2018 , respectively, to collateralize Federal Home Loan Bank of Dallas (“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 March 31, 2019 and December 31, 2018 , we had equity investments recorded in our consolidated balance sheets of $12.2 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 months ended March 31, 2019 (in thousands): Three Months Ended 2019 2018 Net gains (losses) recognized during the period on equity investments $ 76 $ (92 ) 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 $ 76 $ (92 ) 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 March 31, 2019 . Federal Home Loan Bank Stock Our FHLB stock, which has limited marketability, is carried at cost.

Loans and Allowance for Probabl

Loans and Allowance for Probable Loan Losses	3 Months Ended
	Mar. 31, 2019
Receivables [Abstract]
Loans and Allowance for Probable Loan Losses	Loans and Allowance for Probable Loan Losses Loans in the accompanying consolidated balance sheets are classified as follows (in thousands): March 31, 2019 December 31, 2018 Real estate loans: Construction $ 603,411 $ 507,732 1-4 family residential 786,198 794,499 Commercial 1,104,378 1,194,118 Commercial loans 367,995 356,649 Municipal loans 343,026 353,370 Loans to individuals 100,102 106,431 Total loans 3,305,110 3,312,799 Less: Allowance for loan losses (1) 24,155 27,019 Net loans $ 3,280,955 $ 3,285,780 (1) The allowance for loan loss recorded on purchased credit impaired (“PCI”) loans totaled $250,000 and $302,000 as of March 31, 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 March 31, 2019 consisted of $1.05 billion of owner and non-owner occupied real estate, $34.9 million of loans secured by multi-family properties and $17.3 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 March 31, 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) 662 (447 ) (2,112 ) 734 (17 ) 262 (918 ) Loans charged off — (18 ) (1,215 ) (451 ) — (601 ) (2,285 ) Recoveries of loans charged off — 3 19 30 — 287 339 Balance at end of period $ 4,259 $ 3,382 $ 10,660 $ 4,287 $ 508 $ 1,059 $ 24,155 Three Months Ended March 31, 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) (65 ) (82 ) 3,266 333 (9 ) 292 3,735 Loans charged off (14 ) — — (85 ) — (668 ) (767 ) Recoveries of loans charged off — 14 2 43 — 412 471 Balance at end of period $ 3,597 $ 2,377 $ 14,089 $ 2,385 $ 851 $ 921 $ 24,220 (1) Loans acquired with the Diboll acquisition were measured at fair value on November 30, 2017 with no carryover of allowance for loan loss. (2) Of the $918,000 reversal of provision for loan losses for the three months ended March 31, 2019 , $52,000 related to provision expense reversed on PCI loans. Of the $3.7 million recorded in provision for loan losses for the three months ended March 31, 2018 , none 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): March 31, 2019 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans Municipal Loans Loans to Individuals Total Ending balance – individually evaluated for impairment (1) $ 13 $ 83 $ 3,100 $ 403 $ 1 $ 150 $ 3,750 Ending balance – collectively evaluated for impairment 4,246 3,299 7,560 3,884 507 909 20,405 Balance at end of period $ 4,259 $ 3,382 $ 10,660 $ 4,287 $ 508 $ 1,059 $ 24,155 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 loss on PCI loans totaled $250,000 and $302,000 as of March 31, 2019 and December 31, 2018 , respectively. The following tables present the recorded investment in loans by portfolio segment based on impairment method (in thousands): March 31, 2019 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans Municipal Loans Loans to Individuals Total Loans individually evaluated for impairment $ 8 $ 1,295 $ 23,282 $ 1,914 $ 429 $ 142 $ 27,070 Loans collectively evaluated for impairment 603,257 776,725 1,049,049 364,363 342,597 99,618 3,235,609 Purchased credit impaired loans 146 8,178 32,047 1,718 — 342 42,431 Total ending loan balance $ 603,411 $ 786,198 $ 1,104,378 $ 367,995 $ 343,026 $ 100,102 $ 3,305,110 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): March 31, 2019 Pass Pass Watch (1) Special Mention (1) Substandard (1) Doubtful (1) Total Real estate loans: Construction $ 603,239 $ 23 $ — $ 149 $ — $ 603,411 1-4 family residential 780,827 35 98 4,439 799 786,198 Commercial 1,004,085 25,844 26,948 47,341 160 1,104,378 Commercial loans 360,398 1,131 3,251 3,129 86 367,995 Municipal loans 343,026 — — — — 343,026 Loans to individuals 99,504 — 2 414 182 100,102 Total $ 3,191,079 $ 27,033 $ 30,299 $ 55,472 $ 1,227 $ 3,305,110 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 $21,000 pass watch, $308,000 special mention, $2.9 million substandard and $317,000 doubtful as of March 31, 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): March 31, 2019 December 31, 2018 Nonaccrual loans (1) (2) $ 17,691 $ 35,770 Accruing loans past due more than 90 days (1) (3) 7,927 — Restructured loans (4) 11,490 5,930 Other real estate owned 978 1,206 Repossessed assets 25 — Total nonperforming assets $ 38,111 $ 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 $10.7 million and $10.9 million of restructured loans as of March 31, 2019 and December 31, 2018 , respectively. (3) The relationship comprising this figure subsequently paid off in the second quarter of 2019. (4) Includes $719,000 and $3.1 million in PCI loans restructured as of March 31, 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 $155,000 and $147,000 in loans secured by 1-4 family residential properties for which formal foreclosure proceedings were in process as of March 31, 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 March 31, 2019 December 31, 2018 Real estate loans: Construction $ 8 $ 12 1-4 family residential 1,395 2,202 Commercial 15,266 32,599 Commercial loans 758 639 Loans to individuals 264 318 Total $ 17,691 $ 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 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 March 31, 2019 or December 31, 2018 . March 31, 2019 Unpaid Contractual Principal Balance Recorded Investment Related Allowance for Loan Losses Real estate loans: Construction $ 169 $ 136 $ 13 1-4 family residential 8,742 7,576 83 Commercial 26,333 24,965 3,100 Commercial loans 3,139 2,527 403 Municipal loans 429 429 1 Loans to individuals 636 484 150 Total (1) $ 39,448 $ 36,117 $ 3,750 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 $9.0 million and $8.0 million of PCI loans that experienced deterioration in credit quality subsequent to the acquisition date as of March 31, 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): March 31, 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 $ 5,894 $ 72 $ — $ 5,966 $ 597,445 $ 603,411 1-4 family residential 11,506 270 305 12,081 774,117 786,198 Commercial 895 — 7,939 8,834 1,095,544 1,104,378 Commercial loans 1,722 492 503 2,717 365,278 367,995 Municipal loans — — — — 343,026 343,026 Loans to individuals 1,144 206 62 1,412 98,690 100,102 Total $ 21,161 $ 1,040 $ 8,809 $ 31,010 $ 3,274,100 $ 3,305,110 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 March 31, 2019 March 31, 2018 Average Recorded Investment Interest Income Recognized Average Recorded Interest Income Recognized Real estate loans: Construction $ 170 $ 5 $ 78 $ — 1-4 family residential 5,336 79 3,923 41 Commercial 35,951 277 11,970 3 Commercial loans 2,602 31 1,623 17 Municipal loans 429 6 502 7 Loans to individuals 589 9 211 2 Total $ 45,077 $ 407 $ 18,307 $ 70 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 March 31, 2019 Extend Amortization Period Interest Rate Reductions Combination Total Modifications Number of Loans Real estate loans: 1-4 family residential $ — $ — $ 113 $ 113 1 Commercial 7,627 — — 7,627 1 Commercial loans 57 — — 57 1 Loans to individuals — — 15 15 2 Total $ 7,684 $ — $ 128 $ 7,812 5 Three Months Ended March 31, 2018 Extend Amortization Period Interest Rate Reductions Combination Total Modifications Number of Loans Commercial loans $ 207 $ — $ — $ 207 3 Loans to individuals 104 — — 104 1 Total $ 311 $ — $ — $ 311 4 The majority of loans restructured as TDRs during the three months ended March 31, 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 three months ended March 31, 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 months ended March 31, 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 loss in either period presented. At March 31, 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 following table presents the outstanding principal balance and carrying value for PCI loans for the periods presented (in thousands): March 31, 2019 December 31, 2018 Outstanding principal balance $ 47,034 $ 51,388 Carrying amount $ 42,431 $ 46,402 The following table presents the changes in the accretable yield during the periods for PCI loans (in thousands): Three Months Ended 2019 2018 Balance at beginning of period $ 15,054 $ 18,721 Changes in expected cash flows not affecting non-accretable differences — (1,445 ) Reclassifications (to) from nonaccretable discount 262 (320 ) Accretion (796 ) (1,138 ) Balance at end of period $ 14,520 $ 15,818

Borrowing Arrangements

Borrowing Arrangements	3 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
Borrowing Arrangements	Borrowing Arrangements Information related to borrowings is provided in the table below (dollars in thousands): March 31, 2019 December 31, 2018 Federal funds purchased and repurchase agreements: Balance at end of period $ 8,637 $ 36,810 Average amount outstanding during the period (1) 16,788 10,880 Maximum amount outstanding during the period (2) 28,354 36,810 Weighted average interest rate during the period (3) 1.8 % 1.4 % Interest rate at end of period (4) 1.1 % 2.1 % FHLB borrowings: Balance at end of period $ 619,861 $ 719,065 Average amount outstanding during the period (1) 816,389 720,785 Maximum amount outstanding during the period (2) 1,004,997 957,231 Weighted average interest rate during the period (3) 2.2 % 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 March 31, 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 Federal funds purchased and repurchase agreements $ 8,505 $ 132 $ — $ — $ — $ — $ 8,637 FHLB borrowings 462,665 145,429 6,000 — — 5,767 619,861 Total obligations $ 471,170 $ 145,561 $ 6,000 $ — $ — $ 5,767 $ 628,498 FHLB borrowings represent borrowings with fixed and floating interest rates ranging from 1.37% to 4.799% and with remaining maturities of 5 days to 9.3 years at March 31, 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 March 31, 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 that average 1.58% with an average weighted maturity of 4.6 years at March 31, 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. 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 no federal funds purchased at March 31, 2019 . There were $28.0 million federal funds purchased at December 31, 2018 . Southside Bank has a $5.0 million line of credit with Frost Bank to be used to issue letters of credit, and at March 31, 2019 , we had one outstanding letter of credit for $195,000 . At March 31, 2019 , the amount of additional funding Southside Bank could obtain from FHLB, collateralized by securities, FHLB stock and nonspecified loans and securities, was approximately $1.34 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 agreements to repurchase (“repurchase agreements”). These repurchase agreements totaled $8.6 million and $8.8 million at March 31, 2019 and December 31, 2018 , respectively, and had maturities of less than two years. These repurchase agreements are secured by investment securities and are stated at the amount of cash received in connection with the transaction.

Long-term Debt Long-term Obliga

Long-term Debt Long-term Obligations	3 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
Long-term Obligations	Long-term Debt March 31, 2019 December 31, (in thousands) Subordinated notes: (1) 5.50% Subordinated Notes, net of unamortized debt issuance costs (2) $ 98,448 $ 98,407 Total Subordinated notes 98,448 98,407 Trust preferred subordinated debentures: (3) Southside Statutory Trust III, net of unamortized debt issuance costs (4) 20,555 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 60,247 60,246 Total Long-term debt $ 158,695 $ 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 $1.6 million at March 31, 2019 and 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 $64,000 at March 31, 2019 and $65,000 at December 31, 2018 . As of March 31, 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. The proceeds from the sale of the subordinated notes were used for general corporate purposes, which included advances to the Bank to finance its activities.

Employee Benefit Plans

Employee Benefit Plans	3 Months Ended
	Mar. 31, 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 March 31, Defined Benefit Defined Benefit Pension Plan Acquired Restoration 2019 2018 2019 2018 2019 2018 Service cost $ 316 $ 384 $ — $ — $ 60 $ 63 Interest cost 908 857 41 41 161 133 Expected return on assets (1,504 ) (1,620 ) (73 ) (73 ) — — Net loss amortization 443 384 — — 99 91 Prior service (credit) cost amortization (3 ) (3 ) — — 2 1 Net periodic benefit cost (income) $ 160 $ 2 $ (32 ) $ (32 ) $ 322 $ 288 The service cost component is recorded on our consolidated income statement 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	3 Months Ended
	Mar. 31, 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 available for sale 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 for the quarter ended March 31, 2019 . 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 March 31, 2019 , net derivative assets included $3.4 million of cash collateral received from counterparties under master netting agreements and net derivative liabilities included $2.2 million of cash collateral held by a counterparty to a master netting agreement. At March 31, 2019 , we had $531,000 of cash collateral receivable that was not offset against derivative liabilities. 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): March 31, 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 $ 6,408 $ 1,243 $ 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 114,348 75 3,180 93,967 1,119 1,087 Swaps-Customer counterparties 93,248 2,244 75 93,967 1,087 1,119 Gross derivatives 8,727 4,498 11,594 3,320 Offsetting derivative assets/liabilities (2,254 ) (2,254 ) (2,201 ) (2,201 ) Cash collateral received/posted (3,350 ) (2,169 ) (8,306 ) — Net derivatives included in the consolidated balance sheets (2) $ 3,123 $ 75 $ 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 $1.4 million credit exposure related to interest rate swaps with financial institutions and $2.2 million related to interest rate swaps with customers at March 31, 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 March 31, 2019 and December 31, 2018 : March 31, 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 4.6 2.54 % 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 114,348 10.6 2.53 2.65 93,967 11.6 2.36 2.58 Customer counterparties 93,248 11.4 2.58 2.49 93,967 11.6 2.58 2.36

Fair Value Measurement

Fair Value Measurement	3 Months Ended
	Mar. 31, 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 March 31, 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 three months ended March 31, 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 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 March 31, 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 March 31, 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): March 31, 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 $ 453,271 $ — $ 453,271 $ — Other stocks and bonds 2,921 — 2,921 — Mortgage-backed securities: (1) Residential 1,003,702 — 1,003,702 — Commercial 416,361 — 416,361 — Equity investments: Equity investments 5,864 5,864 — — Derivative assets: Interest rate swaps 8,727 — 8,727 — Total asset recurring fair value measurements $ 1,890,846 $ 5,864 $ 1,884,982 $ — Derivative liabilities: Interest rate swaps $ 4,498 $ — $ 4,498 $ — Total liability recurring fair value measurements $ 4,498 $ — $ 4,498 $ — Nonrecurring fair value measurements Foreclosed assets $ 1,003 $ — $ — $ 1,003 Impaired loans (2) 31,680 — — 31,680 Total asset nonrecurring fair value measurements $ 32,683 $ — $ — $ 32,683 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 - Equity investments with readily determinable fair values are presented at fair value based upon the currently available bid-and-ask quotations publicly available on a market or exchange. The carrying value of other 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. Federal funds purchased and repurchase agreements - 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 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 March 31, 2019 Carrying Total Level 1 Level 2 Level 3 Financial assets: Cash and cash equivalents $ 269,943 $ 269,943 $ 269,943 $ — $ — Investment securities: Held to maturity, at carrying value 3,025 3,054 — 3,054 — Mortgage-backed securities: Held to maturity, at carrying value 144,406 144,612 — 144,612 — FHLB stock, at cost 35,269 35,269 — 35,269 — Equity investments 6,318 6,318 — 6,318 — Loans, net of allowance for loan losses 3,280,955 3,293,896 — — 3,293,896 Loans held for sale 384 384 — 384 — Financial liabilities: Deposits $ 4,567,893 $ 4,563,629 $ — $ 4,563,629 $ — Federal funds purchased and repurchase agreements 8,637 8,637 — 8,637 — FHLB borrowings 619,861 614,247 — 614,247 — Subordinated notes, net of unamortized debt issuance costs 98,448 98,400 — 98,400 — Trust preferred subordinated debentures, net of unamortized debt issuance costs 60,247 57,637 — 57,637 — 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 — FHLB 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 $ — Federal funds purchased and repurchase agreements 36,810 36,810 — 36,810 — FHLB 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 — 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 above fair value tables do not necessarily represent their underlying value.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 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 2019 2018 Current income tax expense $ 3,011 $ 2,345 Deferred income tax expense (benefit) 126 (255 ) Income tax expense $ 3,137 $ 2,090 Net deferred tax assets totaled $491,000 at March 31, 2019 and $9.8 million at December 31, 2018 . No valuation allowance for the net deferred tax asset was recorded at March 31, 2019 or December 31, 2018 , as management believes it is more likely than not that all of the net deferred tax asset will be realized in future years. Unrecognized tax benefits were not material at March 31, 2019 or December 31, 2018 . We recognized income tax expense of $3.1 million , for an effective tax rate (“ETR”) of 14.3% for the three months ended March 31, 2019 , compared to income tax expense of $2.1 million , for an ETR of 11.4% , for the three months ended March 31, 2018 . The higher ETR for the three months ended March 31, 2019 was mainly due to a decrease in tax-exempt income as a percentage of pre-tax income as compared to the same period in 2018. The ETR differs from the stated rate of 21% for the three months ended March 31, 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	3 Months Ended
	Mar. 31, 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 7 months to 20.1 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): March 31, 2019 Operating leases: Operating lease right-of-use assets $ 9,455 Operating lease liabilities $ 9,811 The components of lease cost were as follows (in thousands): Three Months Ended Operating lease cost $ 394 Supplemental cash flow information related to leases was as follows (in thousands): Three Months Ended Cash paid for amounts included in the measurement of the lease liabilities: Operating cash flows from operating leases $ 340 Right-of-use assets obtained in exchange for new operating lease liabilities $ — Additional information related to leases was as follows: March 31, 2019 Weighted average remaining lease term (in years) 12.3 Weighted average discount rate 3.91 % Future minimum rental commitments due under non-cancelable operating leases at March 31, 2019 were as follows (in thousands): Year ending December 31, 2019 (excluding the three months ended March 31, 2019) $ 977 2020 1,287 2021 1,180 2022 1,142 2023 992 2024 and thereafter 7,219 Total lease payments 12,797 Less: Interest (2,986 ) Present value of lease liabilities $ 9,811 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 Gross rental income $ 745 At March 31, 2019 , non-cancelable operating leases with future minimum lease payments are as follows (in thousands): Year ending December 31, 2019 (excluding the three months ended March 31, 2019) $ 2,050 2020 2,572 2021 1,487 2022 1,466 2023 1,227 2024 and thereafter 4,048 Total lease payments $ 12,850
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 7 months to 20.1 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): March 31, 2019 Operating leases: Operating lease right-of-use assets $ 9,455 Operating lease liabilities $ 9,811 The components of lease cost were as follows (in thousands): Three Months Ended Operating lease cost $ 394 Supplemental cash flow information related to leases was as follows (in thousands): Three Months Ended Cash paid for amounts included in the measurement of the lease liabilities: Operating cash flows from operating leases $ 340 Right-of-use assets obtained in exchange for new operating lease liabilities $ — Additional information related to leases was as follows: March 31, 2019 Weighted average remaining lease term (in years) 12.3 Weighted average discount rate 3.91 % Future minimum rental commitments due under non-cancelable operating leases at March 31, 2019 were as follows (in thousands): Year ending December 31, 2019 (excluding the three months ended March 31, 2019) $ 977 2020 1,287 2021 1,180 2022 1,142 2023 992 2024 and thereafter 7,219 Total lease payments 12,797 Less: Interest (2,986 ) Present value of lease liabilities $ 9,811 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 Gross rental income $ 745 At March 31, 2019 , non-cancelable operating leases with future minimum lease payments are as follows (in thousands): Year ending December 31, 2019 (excluding the three months ended March 31, 2019) $ 2,050 2020 2,572 2021 1,487 2022 1,466 2023 1,227 2024 and thereafter 4,048 Total lease payments $ 12,850

Off-Balance-Sheet Arrangements,

Off-Balance-Sheet Arrangements, Commitments and Contingencies	3 Months Ended
	Mar. 31, 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): March 31, 2019 December 31, 2018 Unused commitments: Commitments to extend credit $ 900,422 $ 874,557 Standby letters of credit 26,826 27,438 Total $ 927,248 $ 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 March 31, 2019 , there were $55.8 million of unsettled trades to purchase securities and $95.5 million 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 March 31, 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)	3 Months Ended
	Mar. 31, 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. “Omni” refers to OmniAmerican Bancorp, Inc., a bank holding company, and its wholly-owned subsidiary, OmniAmerican Bank, acquired by Southside on December 17, 2014. “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 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.” 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 on January 1, 2020, the effective date. We have developed a project plan and have assigned a project team to complete the analysis needed to implement the guidance. We are also currently working with a third party vendor solution to assist with the application of ASU 2016-13. The team is currently completing the data collection and anticipates running parallel models during 2019. 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)	3 Months Ended
	Mar. 31, 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 2019 2018 Basic and Diluted Earnings: Net income $ 18,817 $ 16,251 Basic weighted-average shares outstanding 33,697 35,022 Add: Stock awards 149 178 Diluted weighted-average shares outstanding 33,846 35,200 Basic earnings per share: Net Income $ 0.56 $ 0.46 Diluted earnings per share: Net Income $ 0.56 $ 0.46

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Tables)	3 Months Ended
	Mar. 31, 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 March 31, 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 46,626 (3,120 ) — — 43,506 Reclassified from accumulated other comprehensive income (loss) 235 (668 ) (1 ) 542 108 Income tax (expense) benefit (9,840 ) 795 — (114 ) (9,159 ) Net current-period other comprehensive income (loss), net of tax 37,021 (2,993 ) (1 ) 428 34,455 Ending balance, net of tax $ 5,901 $ 4,153 $ (140 ) $ (25,687 ) $ (15,773 ) Three Months Ended March 31, 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 income (loss) before reclassifications (25,501 ) 4,245 — — (21,256 ) Reclassified from accumulated other comprehensive income (loss) 965 (127 ) (2 ) 475 1,311 Income tax benefit (expense) 5,152 (865 ) 1 (100 ) 4,188 Net current-period other comprehensive (loss) income, net of tax (19,384 ) 3,253 (1 ) 375 (15,757 ) Ending balance, net of tax $ (35,594 ) $ 9,652 $ (134 ) $ (25,894 ) $ (51,970 ) (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 reclassifications out of accumulated other comprehensive income (loss) into net income are presented below (in thousands): Three Months Ended 2019 2018 Unrealized losses on securities transferred: Amortization of unrealized losses (1) $ (491 ) $ (138 ) Tax benefit 103 29 Net of tax $ (388 ) $ (109 ) Unrealized gains and losses on available for sale securities: Realized net gain (loss) on sale of securities (2) $ 256 $ (827 ) Tax (expense) benefit (54 ) 174 Net of tax $ 202 $ (653 ) Derivatives: Realized net gain on interest rate swap derivatives (3) $ 646 $ 106 Tax expense (136 ) (22 ) Net of tax $ 510 $ 84 Amortization of unrealized gains on terminated interest rate swap derivatives (3) $ 22 $ 21 Tax expense (5 ) (4 ) Net of tax $ 17 $ 17 Amortization of pension plan: Net actuarial loss (4) $ (542 ) $ (475 ) Prior service credit (4) 1 2 Total before tax (541 ) (473 ) Tax benefit 114 99 Net of tax (427 ) (374 ) Total reclassifications for the period, net of tax $ (86 ) $ (1,035 ) (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 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)	3 Months Ended
	Mar. 31, 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 and held to maturity as of March 31, 2019 and December 31, 2018 are reflected in the tables below (in thousands): March 31, 2019 Amortized Gross Unrealized Gross Unrealized Estimated AVAILABLE FOR SALE Cost Gains Losses Fair Value Investment securities: State and political subdivisions $ 446,006 $ 9,130 $ 1,865 $ 453,271 Other stocks and bonds 3,000 — 79 2,921 Mortgage-backed securities: (1) Residential 999,201 8,669 4,168 1,003,702 Commercial 416,618 910 1,167 416,361 Total $ 1,864,825 $ 18,709 $ 7,279 $ 1,876,255 HELD TO MATURITY Investment securities: State and political subdivisions $ 3,025 $ 29 $ — $ 3,054 Mortgage-backed securities: (1) Residential 59,720 962 413 60,269 Commercial 84,686 514 857 84,343 Total $ 147,431 $ 1,505 $ 1,270 $ 147,666 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 March 31, 2019 and December 31, 2018 (in thousands): March 31, 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 $ 241 $ — $ 91,310 $ 1,865 $ 91,551 $ 1,865 Other stocks and bonds 2,921 79 — — 2,921 79 Mortgage-backed securities: Residential 14,666 83 314,543 4,085 329,209 4,168 Commercial — — 186,267 1,167 186,267 1,167 Total $ 17,828 $ 162 $ 592,120 $ 7,117 $ 609,948 $ 7,279 HELD TO MATURITY Mortgage-backed securities: Residential $ 1,213 $ 18 $ 4,759 $ 395 $ 5,972 $ 413 Commercial — — 44,916 857 44,916 857 Total $ 1,213 $ 18 $ 49,675 $ 1,252 $ 50,888 $ 1,270 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 $ — $ 108 U.S. government agency debentures — 89 State and political subdivisions 4,118 6,381 Other stocks and bonds 28 30 Mortgage-backed securities 12,474 10,894 Total interest income on securities $ 16,620 $ 17,502
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 March 31, 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. March 31, 2019 Amortized Cost Fair Value AVAILABLE FOR SALE Investment securities: Due in one year or less $ 3,827 $ 3,866 Due after one year through five years 7,743 7,741 Due after five years through ten years 29,416 30,332 Due after ten years 408,020 414,253 449,006 456,192 Mortgage-backed securities 1,415,819 1,420,063 Total $ 1,864,825 $ 1,876,255 March 31, 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 1,663 1,676 Due after five years through ten years 1,247 1,263 Due after ten years — — 3,025 3,054 Mortgage-backed securities: 144,406 144,612 Total $ 147,431 $ 147,666
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 months ended March 31, 2019 (in thousands): Three Months Ended 2019 2018 Net gains (losses) recognized during the period on equity investments $ 76 $ (92 ) 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 $ 76 $ (92 )

Loans and Allowance for Proba_2

Loans and Allowance for Probable Loan Losses (Tables)	3 Months Ended
	Mar. 31, 2019
Receivables [Abstract]
Classification of loans in the consolidated balance sheets	Loans in the accompanying consolidated balance sheets are classified as follows (in thousands): March 31, 2019 December 31, 2018 Real estate loans: Construction $ 603,411 $ 507,732 1-4 family residential 786,198 794,499 Commercial 1,104,378 1,194,118 Commercial loans 367,995 356,649 Municipal loans 343,026 353,370 Loans to individuals 100,102 106,431 Total loans 3,305,110 3,312,799 Less: Allowance for loan losses (1) 24,155 27,019 Net loans $ 3,280,955 $ 3,285,780 (1) The allowance for loan loss recorded on purchased credit impaired (“PCI”) loans totaled $250,000 and $302,000 as of March 31, 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 March 31, 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) 662 (447 ) (2,112 ) 734 (17 ) 262 (918 ) Loans charged off — (18 ) (1,215 ) (451 ) — (601 ) (2,285 ) Recoveries of loans charged off — 3 19 30 — 287 339 Balance at end of period $ 4,259 $ 3,382 $ 10,660 $ 4,287 $ 508 $ 1,059 $ 24,155 Three Months Ended March 31, 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) (65 ) (82 ) 3,266 333 (9 ) 292 3,735 Loans charged off (14 ) — — (85 ) — (668 ) (767 ) Recoveries of loans charged off — 14 2 43 — 412 471 Balance at end of period $ 3,597 $ 2,377 $ 14,089 $ 2,385 $ 851 $ 921 $ 24,220 (1) Loans acquired with the Diboll acquisition were measured at fair value on November 30, 2017 with no carryover of allowance for loan loss. (2) Of the $918,000 reversal of provision for loan losses for the three months ended March 31, 2019 , $52,000 related to provision expense reversed on PCI loans. Of the $3.7 million recorded in provision for loan losses for the three months ended March 31, 2018 , none 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): March 31, 2019 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans Municipal Loans Loans to Individuals Total Ending balance – individually evaluated for impairment (1) $ 13 $ 83 $ 3,100 $ 403 $ 1 $ 150 $ 3,750 Ending balance – collectively evaluated for impairment 4,246 3,299 7,560 3,884 507 909 20,405 Balance at end of period $ 4,259 $ 3,382 $ 10,660 $ 4,287 $ 508 $ 1,059 $ 24,155 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 loss on PCI loans totaled $250,000 and $302,000 as of March 31, 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): March 31, 2019 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans Municipal Loans Loans to Individuals Total Loans individually evaluated for impairment $ 8 $ 1,295 $ 23,282 $ 1,914 $ 429 $ 142 $ 27,070 Loans collectively evaluated for impairment 603,257 776,725 1,049,049 364,363 342,597 99,618 3,235,609 Purchased credit impaired loans 146 8,178 32,047 1,718 — 342 42,431 Total ending loan balance $ 603,411 $ 786,198 $ 1,104,378 $ 367,995 $ 343,026 $ 100,102 $ 3,305,110 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): March 31, 2019 Pass Pass Watch (1) Special Mention (1) Substandard (1) Doubtful (1) Total Real estate loans: Construction $ 603,239 $ 23 $ — $ 149 $ — $ 603,411 1-4 family residential 780,827 35 98 4,439 799 786,198 Commercial 1,004,085 25,844 26,948 47,341 160 1,104,378 Commercial loans 360,398 1,131 3,251 3,129 86 367,995 Municipal loans 343,026 — — — — 343,026 Loans to individuals 99,504 — 2 414 182 100,102 Total $ 3,191,079 $ 27,033 $ 30,299 $ 55,472 $ 1,227 $ 3,305,110 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 $21,000 pass watch, $308,000 special mention, $2.9 million substandard and $317,000 doubtful as of March 31, 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): March 31, 2019 December 31, 2018 Nonaccrual loans (1) (2) $ 17,691 $ 35,770 Accruing loans past due more than 90 days (1) (3) 7,927 — Restructured loans (4) 11,490 5,930 Other real estate owned 978 1,206 Repossessed assets 25 — Total nonperforming assets $ 38,111 $ 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 $10.7 million and $10.9 million of restructured loans as of March 31, 2019 and December 31, 2018 , respectively. (3) The relationship comprising this figure subsequently paid off in the second quarter of 2019. (4) Includes $719,000 and $3.1 million in PCI loans restructured as of March 31, 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 March 31, 2019 December 31, 2018 Real estate loans: Construction $ 8 $ 12 1-4 family residential 1,395 2,202 Commercial 15,266 32,599 Commercial loans 758 639 Loans to individuals 264 318 Total $ 17,691 $ 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 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 March 31, 2019 or December 31, 2018 . March 31, 2019 Unpaid Contractual Principal Balance Recorded Investment Related Allowance for Loan Losses Real estate loans: Construction $ 169 $ 136 $ 13 1-4 family residential 8,742 7,576 83 Commercial 26,333 24,965 3,100 Commercial loans 3,139 2,527 403 Municipal loans 429 429 1 Loans to individuals 636 484 150 Total (1) $ 39,448 $ 36,117 $ 3,750 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 $9.0 million and $8.0 million of PCI loans that experienced deterioration in credit quality subsequent to the acquisition date as of March 31, 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): March 31, 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 $ 5,894 $ 72 $ — $ 5,966 $ 597,445 $ 603,411 1-4 family residential 11,506 270 305 12,081 774,117 786,198 Commercial 895 — 7,939 8,834 1,095,544 1,104,378 Commercial loans 1,722 492 503 2,717 365,278 367,995 Municipal loans — — — — 343,026 343,026 Loans to individuals 1,144 206 62 1,412 98,690 100,102 Total $ 21,161 $ 1,040 $ 8,809 $ 31,010 $ 3,274,100 $ 3,305,110 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 March 31, 2019 March 31, 2018 Average Recorded Investment Interest Income Recognized Average Recorded Interest Income Recognized Real estate loans: Construction $ 170 $ 5 $ 78 $ — 1-4 family residential 5,336 79 3,923 41 Commercial 35,951 277 11,970 3 Commercial loans 2,602 31 1,623 17 Municipal loans 429 6 502 7 Loans to individuals 589 9 211 2 Total $ 45,077 $ 407 $ 18,307 $ 70
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 March 31, 2019 Extend Amortization Period Interest Rate Reductions Combination Total Modifications Number of Loans Real estate loans: 1-4 family residential $ — $ — $ 113 $ 113 1 Commercial 7,627 — — 7,627 1 Commercial loans 57 — — 57 1 Loans to individuals — — 15 15 2 Total $ 7,684 $ — $ 128 $ 7,812 5 Three Months Ended March 31, 2018 Extend Amortization Period Interest Rate Reductions Combination Total Modifications Number of Loans Commercial loans $ 207 $ — $ — $ 207 3 Loans to individuals 104 — — 104 1 Total $ 311 $ — $ — $ 311 4
Schedule of PCI Loans	The following table presents the outstanding principal balance and carrying value for PCI loans for the periods presented (in thousands): March 31, 2019 December 31, 2018 Outstanding principal balance $ 47,034 $ 51,388 Carrying amount $ 42,431 $ 46,402
Schedule of changes in accretable yield for pci loans	The following table presents the changes in the accretable yield during the periods for PCI loans (in thousands): Three Months Ended 2019 2018 Balance at beginning of period $ 15,054 $ 18,721 Changes in expected cash flows not affecting non-accretable differences — (1,445 ) Reclassifications (to) from nonaccretable discount 262 (320 ) Accretion (796 ) (1,138 ) Balance at end of period $ 14,520 $ 15,818

Borrowing Arrangements (Tables)

Borrowing Arrangements (Tables)	3 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
Schedule of Debt	Information related to borrowings is provided in the table below (dollars in thousands): March 31, 2019 December 31, 2018 Federal funds purchased and repurchase agreements: Balance at end of period $ 8,637 $ 36,810 Average amount outstanding during the period (1) 16,788 10,880 Maximum amount outstanding during the period (2) 28,354 36,810 Weighted average interest rate during the period (3) 1.8 % 1.4 % Interest rate at end of period (4) 1.1 % 2.1 % FHLB borrowings: Balance at end of period $ 619,861 $ 719,065 Average amount outstanding during the period (1) 816,389 720,785 Maximum amount outstanding during the period (2) 1,004,997 957,231 Weighted average interest rate during the period (3) 2.2 % 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 March 31, 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 Federal funds purchased and repurchase agreements $ 8,505 $ 132 $ — $ — $ — $ — $ 8,637 FHLB borrowings 462,665 145,429 6,000 — — 5,767 619,861 Total obligations $ 471,170 $ 145,561 $ 6,000 $ — $ — $ 5,767 $ 628,498

Long-term Debt Long-term Obli_2

Long-term Debt Long-term Obligations (Tables)	3 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
Schedule of Long-term Debt Instruments [Table Text Block]	March 31, 2019 December 31, (in thousands) Subordinated notes: (1) 5.50% Subordinated Notes, net of unamortized debt issuance costs (2) $ 98,448 $ 98,407 Total Subordinated notes 98,448 98,407 Trust preferred subordinated debentures: (3) Southside Statutory Trust III, net of unamortized debt issuance costs (4) 20,555 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 60,247 60,246 Total Long-term debt $ 158,695 $ 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 $1.6 million at March 31, 2019 and 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 $64,000 at March 31, 2019 and $65,000 at December 31, 2018 .
Schedule of Subordinated Borrowing [Table Text Block]	As of March 31, 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)	3 Months Ended
	Mar. 31, 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 March 31, Defined Benefit Defined Benefit Pension Plan Acquired Restoration 2019 2018 2019 2018 2019 2018 Service cost $ 316 $ 384 $ — $ — $ 60 $ 63 Interest cost 908 857 41 41 161 133 Expected return on assets (1,504 ) (1,620 ) (73 ) (73 ) — — Net loss amortization 443 384 — — 99 91 Prior service (credit) cost amortization (3 ) (3 ) — — 2 1 Net periodic benefit cost (income) $ 160 $ 2 $ (32 ) $ (32 ) $ 322 $ 288

Derivative Financial Instrume_2

Derivative Financial Instruments and Hedging Activities (Tables)	3 Months Ended
	Mar. 31, 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): March 31, 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 $ 6,408 $ 1,243 $ 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 114,348 75 3,180 93,967 1,119 1,087 Swaps-Customer counterparties 93,248 2,244 75 93,967 1,087 1,119 Gross derivatives 8,727 4,498 11,594 3,320 Offsetting derivative assets/liabilities (2,254 ) (2,254 ) (2,201 ) (2,201 ) Cash collateral received/posted (3,350 ) (2,169 ) (8,306 ) — Net derivatives included in the consolidated balance sheets (2) $ 3,123 $ 75 $ 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 $1.4 million credit exposure related to interest rate swaps with financial institutions and $2.2 million related to interest rate swaps with customers at March 31, 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
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 March 31, 2019 and December 31, 2018 : March 31, 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 4.6 2.54 % 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 114,348 10.6 2.53 2.65 93,967 11.6 2.36 2.58 Customer counterparties 93,248 11.4 2.58 2.49 93,967 11.6 2.58 2.36

Fair Value Measurement (Tables)

Fair Value Measurement (Tables)	3 Months Ended
	Mar. 31, 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): March 31, 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 $ 453,271 $ — $ 453,271 $ — Other stocks and bonds 2,921 — 2,921 — Mortgage-backed securities: (1) Residential 1,003,702 — 1,003,702 — Commercial 416,361 — 416,361 — Equity investments: Equity investments 5,864 5,864 — — Derivative assets: Interest rate swaps 8,727 — 8,727 — Total asset recurring fair value measurements $ 1,890,846 $ 5,864 $ 1,884,982 $ — Derivative liabilities: Interest rate swaps $ 4,498 $ — $ 4,498 $ — Total liability recurring fair value measurements $ 4,498 $ — $ 4,498 $ — Nonrecurring fair value measurements Foreclosed assets $ 1,003 $ — $ — $ 1,003 Impaired loans (2) 31,680 — — 31,680 Total asset nonrecurring fair value measurements $ 32,683 $ — $ — $ 32,683 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 March 31, 2019 Carrying Total Level 1 Level 2 Level 3 Financial assets: Cash and cash equivalents $ 269,943 $ 269,943 $ 269,943 $ — $ — Investment securities: Held to maturity, at carrying value 3,025 3,054 — 3,054 — Mortgage-backed securities: Held to maturity, at carrying value 144,406 144,612 — 144,612 — FHLB stock, at cost 35,269 35,269 — 35,269 — Equity investments 6,318 6,318 — 6,318 — Loans, net of allowance for loan losses 3,280,955 3,293,896 — — 3,293,896 Loans held for sale 384 384 — 384 — Financial liabilities: Deposits $ 4,567,893 $ 4,563,629 $ — $ 4,563,629 $ — Federal funds purchased and repurchase agreements 8,637 8,637 — 8,637 — FHLB borrowings 619,861 614,247 — 614,247 — Subordinated notes, net of unamortized debt issuance costs 98,448 98,400 — 98,400 — Trust preferred subordinated debentures, net of unamortized debt issuance costs 60,247 57,637 — 57,637 — 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 — FHLB 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 $ — Federal funds purchased and repurchase agreements 36,810 36,810 — 36,810 — FHLB 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 (Tables)

Income Taxes (Tables)	3 Months Ended
	Mar. 31, 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 2019 2018 Current income tax expense $ 3,011 $ 2,345 Deferred income tax expense (benefit) 126 (255 ) Income tax expense $ 3,137 $ 2,090

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Leases Balance Sheet Information	Balance sheet information related to leases was as follows (in thousands): March 31, 2019 Operating leases: Operating lease right-of-use assets $ 9,455 Operating lease liabilities $ 9,811 Additional information related to leases was as follows: March 31, 2019 Weighted average remaining lease term (in years) 12.3 Weighted average discount rate 3.91 %
Lease Expense	Supplemental cash flow information related to leases was as follows (in thousands): Three Months Ended Cash paid for amounts included in the measurement of the lease liabilities: Operating cash flows from operating leases $ 340 Right-of-use assets obtained in exchange for new operating lease liabilities $ — The components of lease cost were as follows (in thousands): Three Months Ended Operating lease cost $ 394
Lessee, Operating Lease, Liability, Maturity	Future minimum rental commitments due under non-cancelable operating leases at March 31, 2019 were as follows (in thousands): Year ending December 31, 2019 (excluding the three months ended March 31, 2019) $ 977 2020 1,287 2021 1,180 2022 1,142 2023 992 2024 and thereafter 7,219 Total lease payments 12,797 Less: Interest (2,986 ) Present value of lease liabilities $ 9,811
Gross Rental Income	Gross rental income from these leases were as follows (in thousands): Three Months Ended Gross rental income $ 745
Lessor, Operating Lease, Payments to be Received, Maturity	At March 31, 2019 , non-cancelable operating leases with future minimum lease payments are as follows (in thousands): Year ending December 31, 2019 (excluding the three months ended March 31, 2019) $ 2,050 2020 2,572 2021 1,487 2022 1,466 2023 1,227 2024 and thereafter 4,048 Total lease payments $ 12,850

Off-Balance-Sheet Arrangement_2

Off-Balance-Sheet Arrangements, Commitments and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Schedule of unused commitments	Financial instruments with off-balance-sheet risk were as follows (in thousands): March 31, 2019 December 31, 2018 Unused commitments: Commitments to extend credit $ 900,422 $ 874,557 Standby letters of credit 26,826 27,438 Total $ 927,248 $ 901,995

Summary of Significant Accoun_3

Summary of Significant Accounting and Reporting Policies - Reclassifications (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Mar. 31, 2019	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease liabilities	$ 0	$ 9,811
Right-of-Use assets obtained in exchange for operating lease liabilities	0	$ 9,455
Accounting Standards Update 2017-08
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect on Retained Earnings, before tax	$ (16,452)
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 ($)banking_offices	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)
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, Assets	1,030,000
Acquisition, Loans	621,300
Acquisition, Investment securities	234,400
Acquisition, Liabilities assumed	910,700
Acquisition, Deposits	899,300
Goodwill		$ 109,600
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
	Mar. 31, 2019	Mar. 31, 2018
Basic and Diluted Earnings:
Net income	$ 18,817	$ 16,251
Basic weighted-average shares outstanding (in shares)	33,697	35,022
Add: Stock awards (in shares)	149	178
Diluted weighted-average shares outstanding (in shares)	33,846	35,200
Basic Earnings Per Share:
Earnings per common share - basic (in dollars per share)	$ 0.56	$ 0.46
Diluted Earnings Per Share:
Earnings per common share - diluted (in dollars per share)	$ 0.56	$ 0.46
Antidilutive securities excluded from calculating earnings
Number of antidilutive options (in shares)	490	186

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Loss) - Accumulated Other Comprehensive Income, Changes In (Details) - USD ($)		Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2019	Mar. 31, 2018	Jan. 01, 2019	Jan. 01, 2018
AOCI Attributable to Parent, Net of Tax
Beginning balance, net of tax				$ 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				(9,159,000)	4,188,000
Ending balance, net of tax		$ 731,291,000	$ 754,140,000	758,033,000	746,396,000
Retained Earnings
AOCI Attributable to Parent, Net of Tax
Beginning balance, net of tax				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		64,797,000	32,851,000	57,023,000	39,184,000
Unrealized Gains (Losses) on Securities
AOCI Attributable to Parent, Net of Tax
Beginning balance, net of tax				(31,120,000)	(16,295,000)
Adjusted beginning balance, net of tax							(16,210,000)
Other comprehensive income (loss) before reclassifications				46,626,000	(25,501,000)
Reclassified from accumulated other comprehensive income				235,000	965,000
Income tax (expense) benefit				(9,840,000)	5,152,000
Net current-period other comprehensive income (loss), net of tax				37,021,000	(19,384,000)
Ending balance, net of tax		(31,120,000)	(16,295,000)	5,901,000	(35,594,000)
Unrealized Gains (Losses) on Derivatives
AOCI Attributable to Parent, Net of Tax
Beginning balance, net of tax				7,146,000	6,399,000
Adjusted beginning balance, net of tax							6,399,000
Other comprehensive income (loss) before reclassifications				(3,120,000)	4,245,000
Reclassified from accumulated other comprehensive income				(668,000)	(127,000)
Income tax (expense) benefit				795,000	(865,000)
Net current-period other comprehensive income (loss), net of tax				(2,993,000)	3,253,000
Ending balance, net of tax		7,146,000	6,399,000	4,153,000	9,652,000
Net Prior Service (Cost) Credit
AOCI Attributable to Parent, Net of Tax
Reclassified from accumulated other comprehensive income	[1]			(1,000)	(2,000)
Net Gain (Loss)
AOCI Attributable to Parent, Net of Tax
Reclassified from accumulated other comprehensive income	[1]			542,000	475,000
Total
AOCI Attributable to Parent, Net of Tax
Beginning balance, net of tax				(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				43,506,000	(21,256,000)
Reclassified from accumulated other comprehensive income				108,000	1,311,000
Income tax (expense) benefit				(9,159,000)	4,188,000
Net current-period other comprehensive income (loss), net of tax				34,455,000	(15,757,000)
Ending balance, net of tax		(50,228,000)	(36,298,000)	(15,773,000)	(51,970,000)
Accounting Standards Update 2017-08
AOCI Attributable to Parent, Net of Tax
Cumulative Effect on Retained Earnings, before Tax		(16,452,000)
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)
Adjusted beginning balance, net of tax							(133,000)
Other comprehensive income (loss) before reclassifications				0	0
Reclassified from accumulated other comprehensive income				(1,000)	(2,000)
Income tax (expense) benefit				0	1,000
Net current-period other comprehensive income (loss), net of tax				(1,000)	(1,000)
Ending balance, net of tax		(139,000)	(133,000)	(140,000)	(134,000)
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)
Adjusted beginning balance, net of tax							(26,269,000)
Other comprehensive income (loss) before reclassifications				0	0
Reclassified from accumulated other comprehensive income				542,000	475,000
Income tax (expense) benefit				(114,000)	(100,000)
Net current-period other comprehensive income (loss), net of tax				428,000	375,000
Ending balance, net of tax		$ (26,115,000)	$ (26,269,000)	$ (25,687,000)	$ (25,894,000)
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
		Mar. 31, 2019	Mar. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of unrealized losses		$ 491	$ 138
Tax benefit (expense)		(3,137)	(2,090)
Total reclassifications for the period, net of tax		(86)	(1,035)
Unrealized gains (losses)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassified from accumulated other comprehensive income		(235)	(965)
Realized net loss on interest rate swap derivatives
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassified from accumulated other comprehensive income		668	127
Net actuarial loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassified from accumulated other comprehensive income	[1]	(542)	(475)
Prior service credit
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassified from accumulated other comprehensive income	[1]	1	2
Amortization of pension plan
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassified from accumulated other comprehensive income		(541)	(473)
Tax benefit		114	99
Total reclassifications for the period, net of tax		(427)	(374)
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]	(491)	(138)
Tax benefit (expense)		103	29
Net of tax		(388)	(109)
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)		(54)	174
Net of tax		202	(653)
Realized net (loss) gain on sale of securities	[3]	256	(827)
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)		(136)	(22)
Net of tax		510	84
Realized net gain (loss) on interest rate swap derivatives	[4]	646	106
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)		(5)	(4)
Net of tax		17	17
Realized net gain (loss) on interest rate swap derivatives	[4]	$ 22	$ 21
[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 FHLB borrowings on the consolidated statements of income.

Securities - Schedule of Debt

Securities - Schedule of Debt Securities Components (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
AVAILABLE FOR SALE
Amortized Cost	$ 1,864,825	$ 2,013,485
Gross unrealized gains	18,709	10,554
Gross unrealized losses	7,279	34,603
Estimated fair value	1,876,255	1,989,436
HELD TO MATURITY
Amortized cost	147,431	162,931
Gross unrealized gains	1,505	360
Gross unrealized losses	1,270	3,510
Estimated Fair Value	147,666	159,781
State and political subdivisions
AVAILABLE FOR SALE
Amortized Cost	446,006	728,142
Gross unrealized gains	9,130	6,115
Gross unrealized losses	1,865	17,656
Estimated fair value	453,271	716,601
HELD TO MATURITY
Amortized cost	3,025	3,083
Gross unrealized gains	29	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	79	291
Estimated fair value	2,921	2,709
Residential
AVAILABLE FOR SALE
Amortized Cost	999,201	738,585
Gross unrealized gains	8,669	3,498
Gross unrealized losses	4,168	9,111
Estimated fair value	1,003,702	732,972
HELD TO MATURITY
Amortized cost	59,720	59,655
Gross unrealized gains	962	154
Gross unrealized losses	413	1,140
Estimated Fair Value	60,269	58,669
Commercial
AVAILABLE FOR SALE
Amortized Cost	416,618	543,758
Gross unrealized gains	910	941
Gross unrealized losses	1,167	7,545
Estimated fair value	416,361	537,154
HELD TO MATURITY
Amortized cost	84,686	100,193
Gross unrealized gains	514	201
Gross unrealized losses	857	2,328
Estimated Fair Value	$ 84,343	$ 98,066

Securities - Unrealized Loss o

Securities - Unrealized Loss on Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Available-for-sale, Unrealized Loss Position [Abstract]
Less than 12 Months, fair value	$ 17,828	$ 115,902
More than 12 Months, fair value	592,120	1,345,243
Total fair value	609,948	1,461,145
Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Less than 12 Months, unrealized loss	162	1,247
More than 12 Months, unrealized Loss	7,117	33,356
Total unrealized loss	7,279	34,603
Held-to-maturity, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	1,213	5,460
More than 12 Months, fair value	49,675	142,236
Total fair value	50,888	147,696
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Losses [Abstract]
Less than 12 months, unrealized loss	18	63
More than 12 months, unrealized loss	1,252	3,447
Total unrealized loss	1,270	3,510
State and political subdivisions
Available-for-sale, Unrealized Loss Position [Abstract]
Less than 12 Months, fair value	241	98,112
More than 12 Months, fair value	91,310	399,205
Total fair value	91,551	497,317
Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Less than 12 Months, unrealized loss	0	899
More than 12 Months, unrealized Loss	1,865	16,757
Total unrealized loss	1,865	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	2,921	2,709
More than 12 Months, fair value	0	0
Total fair value	2,921	2,709
Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Less than 12 Months, unrealized loss	79	291
More than 12 Months, unrealized Loss	0	0
Total unrealized loss	79	291
Residential
Available-for-sale, Unrealized Loss Position [Abstract]
Less than 12 Months, fair value	14,666	5,552
More than 12 Months, fair value	314,543	488,334
Total fair value	329,209	493,886
Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Less than 12 Months, unrealized loss	83	27
More than 12 Months, unrealized Loss	4,085	9,084
Total unrealized loss	4,168	9,111
Held-to-maturity, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	1,213	4,826
More than 12 Months, fair value	4,759	51,046
Total fair value	5,972	55,872
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Losses [Abstract]
Less than 12 months, unrealized loss	18	60
More than 12 months, unrealized loss	395	1,080
Total unrealized loss	413	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	186,267	457,704
Total fair value	186,267	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	1,167	7,515
Total unrealized loss	1,167	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	44,916	89,168
Total fair value	44,916	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	857	2,326
Total unrealized loss	$ 857	$ 2,328

Securities - Interest Income o

Securities - Interest Income on Securities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Investments, Debt Securities [Abstract]
U.S. Treasury	$ 0	$ 108
U.S. government agency debentures	0	89
State and political subdivisions	4,118	6,381
Other stocks and bonds	28	30
Mortgage-backed securities	12,474	10,894
Total interest income on securities	$ 16,620	$ 17,502

Securities - Amortized Cost an

Securities - Amortized Cost and Estimated Fair Value of Investments in Debt Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Available for sale, Amortized Cost
Due in one year or less	$ 3,827
Due after one year through five years	7,743
Due after five years through ten years	29,416
Due after ten years	408,020
Total available-for-sale investment securities	449,006
Mortgage-backed securities	1,415,819
Amortized Cost	1,864,825	$ 2,013,485
Available for sale, Fair Value
Due in one year or less	3,866
Due after one year through five years	7,741
Due after five years through ten years	30,332
Due after ten years	414,253
Total available-for-sale investment securities	456,192
Mortgage-backed securities	1,420,063
Total	1,876,255	1,989,436
Held to maturity, Amortized Cost
Due in one year or less	115
Due after one year through five years	1,663
Due after five years through ten years	1,247
Due after ten years	0
Total held-to-maturity investment securities	3,025
Mortgage-backed securities	144,406
Amortized cost	147,431	162,931
Held to maturity, Fair Value
Due in one year or less	115
Due after one year through five years	1,676
Due after five years through ten years	1,263
Due after ten years	0
Total held-to-maturity investment securities	3,054
Mortgage-backed securities	144,612
Total	$ 147,666	$ 159,781

Securities - Unrealized and R

Securities - Unrealized and Realized Gain (Loss) Recognized in Net Income on Equity Investments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Gain (Loss) on Securities [Line Items]
Net gains (losses) recognized during the period on equity investments	$ 76	$ (92)
Less: Net gains (losses) recognized during the period on equity investments sold during the period	0	0
Unrealized gains (losses) recognized during the reporting period on equity investments still held at the reporting date	$ 76	$ (92)

Securities - Narrative (Detail

Securities - Narrative (Details)	Dec. 31, 2018USD ($)	Mar. 31, 2019USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2018USD ($)
Investment [Line Items]
Transferred Securities, Unrealized Loss, Before Tax	$ 15,300,000	$ 4,000,000		$ 15,300,000
Securities transferred, Unrealized Loss, Net of Tax	12,100,000	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		$ 256,000	$ (827,000)
Gross realized gains on AFS securities		5,000,000	941,000
Gross realized losses on AFS securities		4,800,000	1,800,000
Carrying value of investment securities pledged as collateral	1,080,000,000	1,030,000,000		1,080,000,000
Equity investments	12,093,000	$ 12,182,000		$ 12,093,000
Equity investments 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	$ (16,452,000)

Loans and Allowance for Proba_3

Loans and Allowance for Probable Loan Losses - Loans by Portfolio Segment (Details) - USD ($) $ in Thousands		Mar. 31, 2019	Dec. 31, 2018
Loans and Leases Receivable Disclosure [Abstract]
Total ending loan balance		$ 3,305,110	$ 3,312,799
Less: Allowance for loan losses	[1]	24,155	27,019
Net Loans		3,280,955	3,285,780
Construction Real Estate Loans
Loans and Leases Receivable Disclosure [Abstract]
Total ending loan balance		603,411	507,732
1-4 Family Residential Real Estate Loans
Loans and Leases Receivable Disclosure [Abstract]
Total ending loan balance		786,198	794,499
Commercial Real Estate Loans
Loans and Leases Receivable Disclosure [Abstract]
Total ending loan balance		1,104,378	1,194,118
Commercial loans
Loans and Leases Receivable Disclosure [Abstract]
Total ending loan balance		367,995	356,649
Municipal loans
Loans and Leases Receivable Disclosure [Abstract]
Total ending loan balance		343,026	353,370
Loans to individuals
Loans and Leases Receivable Disclosure [Abstract]
Total ending loan balance		100,102	106,431
Purchase Credit Impaired (PCI) Loans
Loans and Leases Receivable Disclosure [Abstract]
Less: Allowance for loan losses	[1]	$ 250	$ 302
[1]	The allowance for loan loss recorded on purchased credit impaired (“PCI”) loans totaled $250,000 and $302,000 as of March 31, 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 ($)		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Allowances for Loan Losses [Roll Forward]
Balance at beginning of period		$ 27,019,000	$ 20,781,000	[1]
Provision (reversal) for loan losses	[2]	(918,000)	3,735,000
Loans charged off		(2,285,000)	(767,000)
Recoveries of loans charged off		339,000	471,000
Balance at end of period		24,155,000	24,220,000
Provision (reversal) for PCI Loans		(52,000)	0
Construction Real Estate Loans
Allowances for Loan Losses [Roll Forward]
Balance at beginning of period		3,597,000	3,676,000	[1]
Provision (reversal) for loan losses		662,000	(65,000)
Loans charged off		0	(14,000)
Recoveries of loans charged off		0	0
Balance at end of period		4,259,000	3,597,000
1-4 Family Residential Real Estate Loans
Allowances for Loan Losses [Roll Forward]
Balance at beginning of period		3,844,000	2,445,000	[1]
Provision (reversal) for loan losses		(447,000)	(82,000)
Loans charged off		(18,000)	0
Recoveries of loans charged off		3,000	14,000
Balance at end of period		3,382,000	2,377,000
Commercial Real Estate Loans
Allowances for Loan Losses [Roll Forward]
Balance at beginning of period		13,968,000	10,821,000	[1]
Provision (reversal) for loan losses		(2,112,000)	3,266,000
Loans charged off		(1,215,000)	0
Recoveries of loans charged off		19,000	2,000
Balance at end of period		10,660,000	14,089,000
Commercial loans
Allowances for Loan Losses [Roll Forward]
Balance at beginning of period		3,974,000	2,094,000	[1]
Provision (reversal) for loan losses		734,000	333,000
Loans charged off		(451,000)	(85,000)
Recoveries of loans charged off		30,000	43,000
Balance at end of period		4,287,000	2,385,000
Municipal loans
Allowances for Loan Losses [Roll Forward]
Balance at beginning of period		525,000	860,000	[1]
Provision (reversal) for loan losses		(17,000)	(9,000)
Loans charged off		0	0
Recoveries of loans charged off		0	0
Balance at end of period		508,000	851,000
Loans to individuals
Allowances for Loan Losses [Roll Forward]
Balance at beginning of period		1,111,000	885,000	[1]
Provision (reversal) for loan losses		262,000	292,000
Loans charged off		(601,000)	(668,000)
Recoveries of loans charged off		287,000	412,000
Balance at end of period		$ 1,059,000	$ 921,000
[1]	Loans acquired with the Diboll acquisition were measured at fair value on November 30, 2017 with no carryover of allowance for loan loss.
[2]	Of the $918,000 reversal of provision for loan losses for the three months ended March 31, 2019, $52,000 related to provision expense reversed on PCI loans. Of the $3.7 million recorded in provision for loan losses for the three months ended March 31, 2018, none 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		Mar. 31, 2019	Dec. 31, 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]	$ 3,750	$ 5,908
Ending balance - collectively evaluated for impairment		20,405	21,111
Balance at end of period		24,155	27,019	$ 24,220	$ 20,781
Loans and Leases Receivable, Allowance	[3]	24,155	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]	13	13
Ending balance - collectively evaluated for impairment		4,246	3,584
Balance at end of period		4,259	3,597	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]	83	40
Ending balance - collectively evaluated for impairment		3,299	3,804
Balance at end of period		3,382	3,844	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]	3,100	5,337
Ending balance - collectively evaluated for impairment		7,560	8,631
Balance at end of period		10,660	13,968	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]	403	368
Ending balance - collectively evaluated for impairment		3,884	3,606
Balance at end of period		4,287	3,974	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]	1	1
Ending balance - collectively evaluated for impairment		507	524
Balance at end of period		508	525	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]	150	149
Ending balance - collectively evaluated for impairment		909	962
Balance at end of period		1,059	1,111	$ 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]	$ 250	$ 302
[1]	The allowance for loan loss on PCI loans totaled $250,000 and $302,000 as of March 31, 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 loss.
[3]	The allowance for loan loss recorded on purchased credit impaired (“PCI”) loans totaled $250,000 and $302,000 as of March 31, 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	Mar. 31, 2019	Dec. 31, 2018
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Loans individually evaluated for impairment	$ 27,070	$ 36,247
Loans collectively evaluated for impairment	3,235,609	3,230,150
Purchased credit impaired loans	42,431	46,402
Total ending loan balance	3,305,110	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	8	12
Loans collectively evaluated for impairment	603,257	507,564
Purchased credit impaired loans	146	156
Total ending loan balance	603,411	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	1,295	1,215
Loans collectively evaluated for impairment	776,725	782,614
Purchased credit impaired loans	8,178	10,670
Total ending loan balance	786,198	794,499
Commercial Real Estate Loans
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Loans individually evaluated for impairment	23,282	33,013
Loans collectively evaluated for impairment	1,049,049	1,128,220
Purchased credit impaired loans	32,047	32,885
Total ending loan balance	1,104,378	1,194,118
Commercial loans
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Loans individually evaluated for impairment	1,914	1,394
Loans collectively evaluated for impairment	364,363	353,036
Purchased credit impaired loans	1,718	2,219
Total ending loan balance	367,995	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	342,597	352,941
Purchased credit impaired loans	0	0
Total ending loan balance	343,026	353,370
Loans to individuals
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Loans individually evaluated for impairment	142	184
Loans collectively evaluated for impairment	99,618	105,775
Purchased credit impaired loans	342	472
Total ending loan balance	$ 100,102	$ 106,431

Loans and Allowance for Proba_7

Loans and Allowance for Probable Loan Losses - Loans by Credit Quality Indicator (Details) - USD ($) $ in Thousands		Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans		$ 3,305,110	$ 3,312,799
Purchased credit impaired loans		42,431	46,402
Pass
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans		3,191,079	3,171,320
Pass Watch
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	27,033	12,203
Purchased credit impaired loans		21	22
Special Mention
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	30,299	29,783
Purchased credit impaired loans		308	859
Substandard
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	55,472	96,950
Purchased credit impaired loans		2,926	3,900
Doubtful
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	1,227	2,543
Purchased credit impaired loans		317	1,200
Construction Real Estate Loans
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans		603,411	507,732
Purchased credit impaired loans		146	156
Construction Real Estate Loans | Pass
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans		603,239	507,529
Construction Real Estate Loans | Pass Watch
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	23	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]	149	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		786,198	794,499
Purchased credit impaired loans		8,178	10,670
1-4 Family Residential Real Estate Loans | Pass
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans		780,827	787,516
1-4 Family Residential Real Estate Loans | Pass Watch
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	35	37
1-4 Family Residential Real Estate Loans | Special Mention
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	98	100
1-4 Family Residential Real Estate Loans | Substandard
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	4,439	5,489
1-4 Family Residential Real Estate Loans | Doubtful
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	799	1,357
Commercial Real Estate Loans
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans		1,104,378	1,194,118
Purchased credit impaired loans		32,047	32,885
Commercial Real Estate Loans | Pass
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans		1,004,085	1,067,874
Commercial Real Estate Loans | Pass Watch
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	25,844	11,479
Commercial Real Estate Loans | Special Mention
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	26,948	26,490
Commercial Real Estate Loans | Substandard
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	47,341	87,767
Commercial Real Estate Loans | Doubtful
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	160	508
Commercial loans
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans		367,995	356,649
Purchased credit impaired loans		1,718	2,219
Commercial loans | Pass
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans		360,398	349,495
Commercial loans | Pass Watch
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	1,131	520
Commercial loans | Special Mention
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	3,251	3,189
Commercial loans | Substandard
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	3,129	2,988
Commercial loans | Doubtful
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	86	457
Municipal loans
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans		343,026	353,370
Purchased credit impaired loans		0	0
Municipal loans | Pass
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans		343,026	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		100,102	106,431
Purchased credit impaired loans		342	472
Loans to individuals | Pass
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans		99,504	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]	2	4
Loans to individuals | Substandard
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	414	678
Loans to individuals | Doubtful
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Loans	[1]	$ 182	$ 209
[1]	Includes PCI loans comprised of $21,000 pass watch, $308,000 special mention, $2.9 million substandard and $317,000 doubtful as of March 31, 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 ($)		Mar. 31, 2019	Dec. 31, 2018
Nonperforming Assets by Asset Class [Abstract]
Nonaccrual loans	[1],[2]	$ 17,691,000	$ 35,770,000
Accruing loans past due more than 90 days	[1],[3]	7,927,000	0
Restructured loans	[4]	11,490,000	5,930,000
Other real estate owned		978,000	1,206,000
Repossessed assets		25,000	0
Total nonperforming assets		38,111,000	42,906,000
Restructured nonaccrual loans		10,700,000	10,900,000
PCI loans restructured		$ 719,000	$ 3,100,000
[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 $10.7 million and $10.9 million of restructured loans as of March 31, 2019 and December 31, 2018, respectively.
[3]	The relationship comprising this figure subsequently paid off in the second quarter of 2019.
[4]	Includes $719,000 and $3.1 million in PCI loans restructured as of March 31, 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		Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	[1],[2]	$ 17,691	$ 35,770
Construction Real Estate Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans		8	12
1-4 Family Residential Real Estate Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans		1,395	2,202
Commercial Real Estate Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans		15,266	32,599
Commercial loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans		758	639
Loans to individuals
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans		$ 264	$ 318
[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 $10.7 million and $10.9 million of restructured loans as of March 31, 2019 and December 31, 2018, respectively.

Loans and Allowance for Prob_10

Loans and Allowance for Probable Loan Losses - Impaired Loans by Class of Loan (Details) - USD ($) $ in Thousands		Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	[1]	$ 39,448	$ 47,274
Recorded Investment	[1]	36,117	44,267
Related Allowance for Loan Losses	[1]	3,750	5,908
PCI loans that experienced deterioration in credit quality subsequent to acquisition		9,000	8,000
Construction Real Estate Loans
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance		169	182
Recorded Investment		136	148
Related Allowance for Loan Losses		13	13
1-4 Family Residential Real Estate Loans
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance		8,742	6,507
Recorded Investment		7,576	5,923
Related Allowance for Loan Losses		83	40
Commercial Real Estate Loans
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance		26,333	36,457
Recorded Investment		24,965	34,744
Related Allowance for Loan Losses		3,100	5,337
Commercial loans
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance		3,139	2,874
Recorded Investment		2,527	2,366
Related Allowance for Loan Losses		403	368
Municipal loans
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance		429	429
Recorded Investment		429	429
Related Allowance for Loan Losses		1	1
Loans to individuals
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance		636	825
Recorded Investment		484	657
Related Allowance for Loan Losses		$ 150	$ 149
[1]	Includes $9.0 million and $8.0 million of PCI loans that experienced deterioration in credit quality subsequent to the acquisition date as of March 31, 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		Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		$ 31,010	$ 34,314
Current	[1]	3,274,100	3,278,485
Total ending loan balance		3,305,110	3,312,799
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		21,161	21,966
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		1,040	10,276
Greater than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		8,809	2,072
Construction Real Estate Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		5,966	934
Current	[1]	597,445	506,798
Total ending loan balance		603,411	507,732
Construction Real Estate Loans | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		5,894	627
Construction Real Estate Loans | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		72	307
Construction Real Estate Loans | Greater than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		0	0
1-4 Family Residential Real Estate Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		12,081	10,034
Current	[1]	774,117	784,465
Total ending loan balance		786,198	794,499
1-4 Family Residential Real Estate Loans | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		11,506	7,441
1-4 Family Residential Real Estate Loans | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		270	1,258
1-4 Family Residential Real Estate Loans | Greater than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		305	1,335
Commercial Real Estate Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		8,834	18,318
Current	[1]	1,095,544	1,175,800
Total ending loan balance		1,104,378	1,194,118
Commercial Real Estate Loans | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		895	10,663
Commercial Real Estate Loans | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		0	7,655
Commercial Real Estate Loans | Greater than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		7,939	0
Commercial loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		2,717	3,242
Current	[1]	365,278	353,407
Total ending loan balance		367,995	356,649
Commercial loans | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		1,722	1,946
Commercial loans | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		492	705
Commercial loans | Greater than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		503	591
Municipal loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		0	0
Current	[1]	343,026	353,370
Total ending loan balance		343,026	353,370
Municipal loans | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		0	0
Municipal loans | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		0	0
Municipal loans | Greater than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		0	0
Loans to individuals
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		1,412	1,786
Current	[1]	98,690	104,645
Total ending loan balance		100,102	106,431
Loans to individuals | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		1,144	1,289
Loans to individuals | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		206	351
Loans to individuals | Greater than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		$ 62	$ 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
	Mar. 31, 2019	Mar. 31, 2018
Financing Receivable, Impaired [Line Items]
Average recorded investment	$ 45,077	$ 18,307
Interest income recognized	407	70
Construction Real Estate Loans
Financing Receivable, Impaired [Line Items]
Average recorded investment	170	78
Interest income recognized	5	0
1-4 Family Residential Real Estate Loans
Financing Receivable, Impaired [Line Items]
Average recorded investment	5,336	3,923
Interest income recognized	79	41
Commercial Real Estate Loans
Financing Receivable, Impaired [Line Items]
Average recorded investment	35,951	11,970
Interest income recognized	277	3
Commercial loans
Financing Receivable, Impaired [Line Items]
Average recorded investment	2,602	1,623
Interest income recognized	31	17
Municipal loans
Financing Receivable, Impaired [Line Items]
Average recorded investment	429	502
Interest income recognized	6	7
Loans to individuals
Financing Receivable, Impaired [Line Items]
Average recorded investment	589	211
Interest income recognized	$ 9	$ 2

Loans and Allowance for Prob_13

Loans and Allowance for Probable Loan Losses - Troubled Debt Restructurings (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)contract	Mar. 31, 2018USD ($)contract
Financing Receivable, Modifications [Line Items]
Extend Amortization Period	$ 7,684	$ 311
Interest Rate Reductions	0	0
Combination	128	0
Total Modifications	$ 7,812	$ 311
Number of Loans | contract	5	4
1-4 Family Residential Real Estate Loans
Financing Receivable, Modifications [Line Items]
Extend Amortization Period	$ 0
Interest Rate Reductions	0
Combination	113
Total Modifications	$ 113
Number of Loans | contract	1
Commercial Real Estate Loans
Financing Receivable, Modifications [Line Items]
Extend Amortization Period	$ 7,627
Interest Rate Reductions	0
Combination	0
Total Modifications	$ 7,627
Number of Loans | contract	1
Commercial loans
Financing Receivable, Modifications [Line Items]
Extend Amortization Period	$ 57	$ 207
Interest Rate Reductions	0	0
Combination	0	0
Total Modifications	$ 57	$ 207
Number of Loans | contract	1	3
Loans to individuals
Financing Receivable, Modifications [Line Items]
Extend Amortization Period	$ 0	$ 104
Interest Rate Reductions	0	0
Combination	15	0
Total Modifications	$ 15	$ 104
Number of Loans | contract	2	1

Loans and Allowance for Prob_14

Loans and Allowance for Probable Loan Losses - Purchased Credit Impaired (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Purchased Credit Impaired [Abstract]
Outstanding principal balance	$ 47,034		$ 51,388
Carrying amount	42,431		$ 46,402
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	15,054	$ 18,721
Changes in expected cash flows not affecting non-accretable differences	0	(1,445)
Reclassifications (to) from nonaccretable discount	262	(320)
Accretion	(796)	(1,138)
Balance at end of period	$ 14,520	$ 15,818

Loans and Allowance for Prob_15

Loans and Allowance for Probable Loan Losses - Narrative (Details) - USD ($)	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans in process of foreclosure	$ 155,000	$ 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 Losses [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 Losses [Line Items]
Owner and nonowner-occupied real estate	1,050,000,000
Loans secured by multi-family properties	34,900,000
Loans secured by farmland	$ 17,300,000

Borrowing Arrangements (Details

Borrowing Arrangements (Details) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
		Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Federal funds purchased and repurchase agreements		$ 8,637	$ 36,810
FHLB borrowings		619,861	719,065
Federal funds purchased and repurchase agreements:
Debt Instrument [Line Items]
Federal funds purchased and repurchase agreements		8,637	36,810
Average amount outstanding during the period	[1]	16,788	10,880
Maximum amount outstanding during the period	[2]	$ 28,354	$ 36,810
Weighted average interest rate during the period	[3]	1.80%	1.40%
Interest rate at end of the period	[4]	1.10%	2.10%
FHLB borrowings:
Debt Instrument [Line Items]
FHLB borrowings		$ 619,861	$ 719,065
Average amount outstanding during the period	[1]	816,389	720,785
Maximum amount outstanding during the period	[2]	$ 1,004,997	$ 957,231
Weighted average interest rate during the period	[3]	2.20%	1.80%
Interest rate at end of the period	[4]	2.40%	2.30%
Minimum
Debt Instrument [Line Items]
FHLB borrowings maturities		5 days
[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	Mar. 31, 2019USD ($)
Debt Instrument [Line Items]
Less than 1 Year	$ 471,170
1-2 Years	145,561
2-3 Years	6,000
3-4 Years	0
4-5 Years	0
Thereafter	5,767
Total	628,498
Federal funds purchased and repurchase agreements:
Debt Instrument [Line Items]
Less than 1 Year	8,505
1-2 Years	132
2-3 Years	0
3-4 Years	0
4-5 Years	0
Thereafter	0
Total	8,637
FHLB borrowings:
Debt Instrument [Line Items]
Less than 1 Year	462,665
1-2 Years	145,429
2-3 Years	6,000
3-4 Years	0
4-5 Years	0
Thereafter	5,767
Total	$ 619,861

Borrowing Arrangements Narrativ

Borrowing Arrangements Narrative (Details)	3 Months Ended
	Mar. 31, 2019USD ($)Oustanding_Letters_of_Creditcredit_lineagreementRate	Mar. 31, 2017contract	Dec. 31, 2018USD ($)
Line of Credit Facility [Line Items]
FHLB borrowings with variable interest rate, face amount	$ 270,000,000
Number of credit lines maintained by the Company | credit_line	3
Federal funds purchased	$ 0		$ 28,000,000
Number of outstanding letters of credit | Oustanding_Letters_of_Credit	1
Letters of credit outstanding, amount	$ 195,000
FHLB borrowings, additional funding available	1,340,000,000
Letters of Credit, FHLB, as collateral	0
Securities sold under agreements to repurchase	$ 8,600,000		8,800,000
Maturity of repurchase agreements (less than)	2 years
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
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]
FHLB borrowings interest rates	1.37%
FHLB borrowings maturities	5 days
Maximum
Line of Credit Facility [Line Items]
FHLB borrowings interest rates	4.799%
FHLB borrowings maturities	9 years 3 months
Variable Rate Advance Agreements
Line of Credit Facility [Line Items]
FHLB 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]
FHLB 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
One-Month London Interbank Offered Rate (LIBOR) | Variable Rate Advance Agreements
Line of Credit Facility [Line Items]
FHLB borrowings, description of variable rate basis	one-month LIBOR
Interest rate swap derivatives
Line of Credit Facility [Line Items]
Derivative, instruments terminated | contract		2
Cash flow hedging | Variable Rate Advance Agreements
Line of Credit Facility [Line Items]
FHLB 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 7 months
Terminated cash flow hedging | Variable Rate Advance Agreements
Line of Credit Facility [Line Items]
FHLB borrowings with variable interest rate, face amount	$ 40,000,000

Long-term Debt Other Long-term

Long-term Debt Other Long-term Obligations (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Oct. 10, 2007	Aug. 10, 2007	Aug. 08, 2007
Debt Instruments [Abstract]
Subordinated notes, net of unamortized debt issuance costs:	$ 98,448,000	$ 98,407,000
Trust preferred subordinated debentures	60,247,000	60,246,000
Total long-term obligations	158,695,000	158,653,000
5.50% Subordinated Notes
Debt Instruments [Abstract]
Subordinated notes, net of unamortized debt issuance costs:	98,448,000	98,407,000
Unamortized Debt Issuance Expense	1,600,000	1,600,000
Southside Statutory Trust III, net of unamortized debt issuance costs [Member]
Debt Instruments [Abstract]
Trust preferred subordinated debentures	20,555,000	20,554,000
Unamortized Debt Issuance Expense	64,000	65,000
Southside Statutory Trust IV
Debt Instruments [Abstract]
Trust preferred subordinated debentures	23,196,000	23,196,000			$ 23,196,000
Southside Statutory Trust V
Debt Instruments [Abstract]
Trust preferred subordinated debentures	12,887,000	12,887,000		$ 12,887,000
Magnolia Trust Company I
Debt Instruments [Abstract]
Trust preferred subordinated debentures	$ 3,609,000	$ 3,609,000	$ 3,609,000
Minimum | 5.50% Subordinated Notes
Debt Instruments [Abstract]
Long-term debt, remaining maturity	1 year

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	Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Other long-term debt							$ 60,247	$ 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							20,555	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	23,196
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	12,887
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	$ 3,609
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%

Employee Benefit Plans (Details

Employee Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Defined Benefit Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 316	$ 384
Interest cost	908	857
Expected return on assets	(1,504)	(1,620)
Net loss amortization	443	384
Prior service (credit) cost amortization	(3)	(3)
Net periodic benefit cost (income)	160	2
Defined Benefit Pension Plan Acquired
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost	41	41
Expected return on assets	(73)	(73)
Net loss amortization	0	0
Prior service (credit) cost amortization	0	0
Net periodic benefit cost (income)	(32)	(32)
Restoration Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	60	63
Interest cost	161	133
Expected return on assets	0	0
Net loss amortization	99	91
Prior service (credit) cost amortization	2	1
Net periodic benefit cost (income)	$ 322	$ 288

Derivative Financial Instrume_3

Derivative Financial Instruments and Hedging Activities - Schedule Of Derivative Instruments (Details) - USD ($)		Mar. 31, 2019	Dec. 31, 2018
Asset Derivative
Gross derivatives		$ 8,727,000	$ 11,594,000
Offsetting derivative assets		(2,254,000)	(2,201,000)
Cash collateral received/posted		(3,350,000)	(8,306,000)
Net derivatives included in the consolidated balance sheets	[1]	3,123,000	1,087,000
Liability Derivative
Gross derivatives		4,498,000	3,320,000
Offsetting derivative liabilities		(2,254,000)	(2,201,000)
Cash collateral received/posted		(2,169,000)	0
Net derivatives included in the consolidated balance sheets	[1]	75,000	1,119,000
Financial Institution Counterparties
Liability Derivative
Net credit exposure		1,400,000	0
Financial Institution Counterparties | Designated as Hedging Instrument | Cash Flow Hedging | Interest Rate Swap
Derivatives, Fair Value [Line Items]
Notional Amount	[2]	270,000,000	270,000,000
Asset Derivative
Gross derivatives		6,408,000	9,388,000
Liability Derivative
Gross derivatives		1,243,000	457,000
Financial Institution Counterparties | Designated as Hedging Instrument | Fair Value Hedging [Member] | Interest Rate Swap
Derivatives, Fair Value [Line Items]
Notional Amount	[2]	0	21,100,000
Asset Derivative
Gross derivatives		0	0
Liability Derivative
Gross derivatives		0	657,000
Financial Institution Counterparties | Not Designated as Hedging Instrument | Interest Rate Swap
Derivatives, Fair Value [Line Items]
Notional Amount	[2]	114,348,000	93,967,000
Asset Derivative
Gross derivatives		75,000	1,119,000
Liability Derivative
Gross derivatives		3,180,000	1,087,000
Customer Counterparties
Liability Derivative
Net credit exposure		2,244,000	1,087,000
Customer Counterparties | Not Designated as Hedging Instrument | Interest Rate Swap
Derivatives, Fair Value [Line Items]
Notional Amount	[2]	93,248,000	93,967,000
Asset Derivative
Gross derivatives		2,244,000	1,087,000
Liability Derivative
Gross derivatives		$ 75,000	$ 1,119,000
[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 $1.4 million credit exposure related to interest rate swaps with financial institutions and $2.2 million related to interest rate swaps with customers at March 31, 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		3 Months Ended	12 Months Ended
		Mar. 31, 2019	Dec. 31, 2018
Financial Institution Counterparties | Not Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	[1]	$ 114,348	$ 93,967
Remaining Maturity (in years)		10 years 7 months 21 days	11 years 7 months 21 days
Weighted Average Receive Rate		2.53%	2.36%
Weighted Average Pay Rate		2.65%	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 6 months 29 days	4 years 9 months 28 days
Weighted Average Receive Rate		2.54%	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 1 day
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]	$ 93,248	$ 93,967
Remaining Maturity (in years)		11 years 4 months 25 days	11 years 7 months 21 days
Weighted Average Receive Rate		2.58%	2.58%
Weighted Average Pay Rate		2.49%	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)	3 Months Ended
	Mar. 31, 2017contract	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Derivative [Line Items]
Debt instrument, face amount		$ 270,000,000
Cash collateral received from counterparties under master netting agreements		3,350,000	$ 8,306,000
Cash collateral held by a counterparty to a master netting agreement		2,169,000
Cash collateral received that was not offset against derivative liabilities		$ 531,000
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		Mar. 31, 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		$ 1,876,255	$ 1,989,436
Derivative assets	[1]	3,123	1,087
Derivative liabilities	[1]	75	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		453,271	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		2,921	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		1,003,702	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		416,361	537,154
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity investments		5,864	5,791
Total asset fair value measurements		1,890,846	2,006,821
Total liability fair value measurements		4,498	3,320
Fair Value, Measurements, 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		453,271	716,601
Fair Value, Measurements, 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		2,921	2,709
Fair Value, Measurements, 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	[2]	1,003,702	732,972
Fair Value, Measurements, 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	[2]	416,361	537,154
Fair Value, Measurements, Recurring [Member] | Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		8,727	11,594
Derivative liabilities		4,498	3,320
Fair Value, Measurements, 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		5,864	5,791
Total asset fair value measurements		5,864	5,791
Total liability fair value measurements		0	0
Fair Value, Measurements, 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, Measurements, 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, Measurements, 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	[2]	0	0
Fair Value, Measurements, 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	[2]	0	0
Fair Value, Measurements, 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, Measurements, 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		1,884,982	2,001,030
Total liability fair value measurements		4,498	3,320
Fair Value, Measurements, 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		453,271	716,601
Fair Value, Measurements, 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		2,921	2,709
Fair Value, Measurements, 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	[2]	1,003,702	732,972
Fair Value, Measurements, 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	[2]	416,361	537,154
Fair Value, Measurements, 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		8,727	11,594
Derivative liabilities		4,498	3,320
Fair Value, Measurements, 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, Measurements, 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, Measurements, 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, Measurements, 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	[2]	0	0
Fair Value, Measurements, 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	[2]	0	0
Fair Value, Measurements, 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, Measurements, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreclosed assets		1,003	1,206
Impaired loans	[3]	31,680	37,813
Total asset fair value measurements		32,683	39,019
Fair Value, Measurements, 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	[3]	0	0
Total asset fair value measurements		0	0
Fair Value, Measurements, 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	[3]	0	0
Total asset fair value measurements		0	0
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreclosed assets		1,003	1,206
Impaired loans	[3]	31,680	37,813
Total asset fair value measurements		$ 32,683	$ 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 $1.4 million credit exposure related to interest rate swaps with financial institutions and $2.2 million related to interest rate swaps with customers at March 31, 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 are issued and/or guaranteed by U.S. government agencies or U.S. government-sponsored enterprises.
[3]	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	Mar. 31, 2019	Dec. 31, 2018
Carrying Amount
Financial assets:
Cash and cash equivalents	$ 269,943	$ 120,719
Investment securities:
Held to maturity, at carrying value	3,025	3,083
Mortgage-backed securities:
Held to maturity, at carrying value	144,406	159,848
FHLB stock, at cost	35,269	32,583
Equity investments	6,318	6,302
Loans, net of allowance for loan losses	3,280,955	3,285,780
Loans held for sale	384	601
Financial liabilities:
Deposits	4,567,893	4,425,030
Federal funds purchased and repurchase agreements	8,637	36,810
FHLB borrowings	619,861	719,065
Subordinated notes, net of unamortized debt issuance costs	98,448	98,407
Trust preferred subordinated debentures, net of unamortized debt issuance costs	60,247	60,246
Estimated Fair Value
Financial assets:
Cash and cash equivalents	269,943	120,719
Investment securities:
Held to maturity, at carrying value	3,054	3,046
Mortgage-backed securities:
Held to maturity, at carrying value	144,612	156,735
FHLB stock, at cost	35,269	32,583
Equity investments	6,318	6,302
Loans, net of allowance for loan losses	3,293,896	3,251,923
Loans held for sale	384	601
Financial liabilities:
Deposits	4,563,629	4,417,902
Federal funds purchased and repurchase agreements	8,637	36,810
FHLB borrowings	614,247	708,904
Subordinated notes, net of unamortized debt issuance costs	98,400	97,611
Trust preferred subordinated debentures, net of unamortized debt issuance costs	57,637	54,729
Estimated Fair Value | Level 1
Financial assets:
Cash and cash equivalents	269,943	120,719
Investment securities:
Held to maturity, at carrying value	0	0
Mortgage-backed securities:
Held to maturity, at carrying value	0	0
FHLB 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
Federal funds purchased and repurchase agreements	0	0
FHLB 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	144,612	156,735
FHLB stock, at cost	35,269	32,583
Equity investments	6,318	6,302
Loans, net of allowance for loan losses	0	0
Loans held for sale	384	601
Financial liabilities:
Deposits	4,563,629	4,417,902
Federal funds purchased and repurchase agreements	8,637	36,810
FHLB borrowings	614,247	708,904
Subordinated notes, net of unamortized debt issuance costs	98,400	97,611
Trust preferred subordinated debentures, net of unamortized debt issuance costs	57,637	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
FHLB stock, at cost	0	0
Equity investments	0	0
Loans, net of allowance for loan losses	3,293,896	3,251,923
Loans held for sale	0	0
Financial liabilities:
Deposits	0	0
Federal funds purchased and repurchase agreements	0	0
FHLB 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)	3 Months Ended
	Mar. 31, 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
	Mar. 31, 2019	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Current income tax expense	$ 3,011	$ 2,345
Deferred income tax expense (benefit)	126	(255)
Income tax expense	$ 3,137	$ 2,090

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Net deferred tax assets	$ 491,000		$ 9,800,000
Deferred tax assets, valuation allowance	0		$ 0
Income tax expense	$ 3,137,000	$ 2,090,000
Effective income tax rate, percent	14.30%	11.40%

Leases - Narrative (Details)

Leases - Narrative (Details)	3 Months Ended
	Mar. 31, 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	7 months
Maximum
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Remaining Lease Term	20 years 1 month
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	Mar. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Operating lease right-of-use assets	$ 9,455	$ 0
Operating lease liabilities	$ 9,811	$ 0

Leases - Components of Lease Ex

Leases - Components of Lease Expense (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Leases [Abstract]
Operating lease cost	$ 394

Leases - Supplemental Cash Flow

Leases - Supplemental Cash Flow Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Leases [Abstract]
Operating cash flows from operating leases	$ 340
Right-of-use assets obtained in exchange for new operating lease liabilities	$ 0

Leases - Weighted Average Lease

Leases - Weighted Average Lease Information (Details)	Mar. 31, 2019Rate
Leases [Abstract]
Weighted average remaining lease term	12 years 3 months 15 days
Weighted average discount rate	3.91%

Leases - Future Operating Lease

Leases - Future Operating Lease Obligations (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Leases [Abstract]
2019 (excluding the three months ended March 31, 2019)	$ 977
2020	1,287
2021	1,180
2021	1,142
2023	992
2024 and thereafter	7,219
Total lease payments	12,797
Less: Interest	(2,986)
Present value of lease liabilities	$ 9,811	$ 0

Leases - Rental Income (Details

Leases - Rental Income (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Lessor, Operating Lease, Description [Abstract]
Gross rental income	$ 745

Leases - Future Operating Lea_2

Leases - Future Operating Lease Receivable (Details) $ in Thousands	Mar. 31, 2019USD ($)
Leases [Abstract]
2019 (excluding the three months ended March 31, 2019)	$ 2,050
2020	2,572
2021	1,487
2022	1,466
2023	1,227
2024 and thereafter	4,048
Total lease payments	$ 12,850

Off-Balance-Sheet Arrangement_3

Off-Balance-Sheet Arrangements, Commitments and Contingencies (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance-sheet risk, at fair value	$ 927,248	$ 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	900,422	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	$ 26,826	$ 27,438

Off-Balance-Sheet Arrangement_4

Off-Balance-Sheet Arrangements, Commitments and Contingencies Narrative (Details) - USD ($)	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Securities:
Unsettled trades to purchase securities	$ 55,826,000	$ 6,378,000	$ 3,646,000
Unsettled trades to sell securities	95,482,000	0	$ 35,307,000
Deposits:
Unsettled Issuances of Brokered CDs	$ 0	$ 15,236,000

Uncategorized Items - sbsi-2019

Label	Element	Value
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)
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	47,253,000
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAdjustedBalance1	$ 47,307,000