Southside Bancshares (SBSI) 10-K 28 Feb 19 2018 FY Annual report Financial data

DOCUMENT AND ENTITY INFORMATION

DOCUMENT AND ENTITY INFORMATION - USD ($)	12 Months Ended
	Dec. 31, 2018	Feb. 25, 2019	Jun. 30, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	SOUTHSIDE BANCSHARES INC
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Entity Central Index Key	705,432
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 1,097,122,089
Entity Common Stock Shares Outstanding (in shares)		33,689,812

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($)		Dec. 31, 2018	Dec. 31, 2017
ASSETS
Cash and due from banks		$ 87,375,000	$ 79,171,000
Interest earning deposits		23,884,000	111,541,000
Federal funds sold		9,460,000	7,980,000
Total cash and cash equivalents		120,719,000	198,692,000
Securities available for sale, at estimated fair value		1,989,436,000
Securities available for sale, at estimated fair value			1,538,755,000
Securities held to maturity, at carrying value (estimated fair value of $159,781 and $921,800, respectively)		162,931,000	909,506,000
FHLB stock, at cost		32,583,000	55,729,000
Equity investments		12,093,000
Equity investments			5,821,000
Loans held for sale		601,000	2,001,000
Loans:
Loans		3,312,799,000	3,294,356,000
Less: Allowance for loan losses	[1]	(27,019,000)	(20,781,000)
Net loans		3,285,780,000	3,273,575,000
Premises and equipment, net		135,972,000	133,640,000
Goodwill		201,116,000	201,246,000
Other intangible assets, net		17,779,000	22,993,000
Interest receivable		27,287,000	28,491,000
Deferred tax asset, net		9,776,000	12,204,000
Unsettled issuances of brokered certificates of deposit		15,236,000	0
Bank owned life insurance		98,160,000	100,368,000
Other assets		14,025,000	15,076,000
Total assets		6,123,494,000	6,498,097,000
Deposits:
Noninterest bearing		994,680,000	1,037,401,000
Interest bearing		3,430,350,000	3,478,046,000
Total deposits		4,425,030,000	4,515,447,000
Federal funds purchased and repurchase agreements		36,810,000	9,498,000
FHLB borrowings		719,065,000	1,017,361,000
Subordinated notes, net of unamortized debt issuance costs	[2]	98,407,000	98,248,000
Trust preferred subordinated debentures, net of unamortized debt issuance costs		60,246,000	60,241,000
Unsettled trades to purchase securities		6,378,000	0
Other liabilities		46,267,000	43,162,000
Total liabilities		5,392,203,000	5,743,957,000
Off-balance-sheet arrangements, commitments and contingencies (Note 17)
Shareholders’ equity:
Common stock: ($1.25 par value, 80,000,000 shares authorized and 37,845,224 shares issued at December 31, 2018 and 40,000,000 shares authorized and 37,802,352 shares issued at December 31, 2017)		47,307,000	47,253,000
Paid-in capital		762,470,000	757,439,000
Retained earnings		64,797,000	32,851,000
Treasury stock, at cost (4,120,475 at December 31, 2018 and 2,802,019 at December 31, 2017)		(93,055,000)	(47,105,000)
Accumulated other comprehensive loss		(50,228,000)	(36,298,000)
Total shareholders’ equity		731,291,000	754,140,000
Total liabilities and shareholders’ equity		$ 6,123,494,000	$ 6,498,097,000
[1]	Loans acquired with the Diboll acquisition were measured at fair value on November 30, 2017, with no carryover of allowance for loan loss. The allowance for loan loss recorded on PCI loans totaled $302,000 as of December 31, 2018. There was no allowance for loan loss recorded on PCI loans as of December 31, 2017
[2]	This debt consists of subordinated notes with a remaining maturity greater than one year that qualify under the risk-based capital guidelines as Tier 2 capital, subject to certain limitations.

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Held to Maturity, fair value	$ 159,781	$ 921,800
Common stock, par value (in dollars per share)	$ 1.25	$ 1.25
Common stock, shares authorized (in shares)	80,000,000	40,000,000
Common stock, shares issued (in shares)	37,845,224	37,802,352
Treasury stock, (in shares)	4,120,475	2,802,019

CONSOLIDATED STATEMENTS OF INCO

CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Interest income
Loans		$ 158,691	$ 117,633	$ 106,564
Investment securities – taxable		417	939	1,057
Investment securities – tax-exempt		24,960	24,529	22,654
Mortgage-backed securities		41,584	41,361	37,450
FHLB stock and equity investments		1,595	1,306	798
Other interest earning assets		1,918	1,706	390
Total interest income		229,165	187,474	168,913
Interest expense
Deposits		35,864	20,736	14,255
FHLB borrowings		12,813	15,106	11,751
Subordinated notes		5,659	5,633	1,628
Trust preferred subordinated debentures		2,610	2,013	1,706
Other borrowings		155	16	8
Total interest expense		57,101	43,504	29,348
Net interest income		172,064	143,970	139,565
Provision for loan losses	[1]	8,437	4,675	9,780
Net interest income after provision for loan losses		163,627	139,295	129,785
Noninterest income
Deposit services		25,082	21,785	20,702
Net (loss) gain on sale of securities available for sale		(1,839)	625	2,836
Gain on sale of loans		692	1,821	2,795
Trust income		6,832	3,818	3,491
Bank owned life insurance income		2,923	2,537	2,626
Brokerage services		1,987	2,422	2,127
Other		5,096	4,465	4,834
Total noninterest income		40,773	37,473	39,411
Noninterest expense
Salaries and employee benefits		70,643	60,779	61,628
Occupancy expense		13,814	12,068	13,722
Acquisition expense		2,413	4,352	0
Advertising, travel & entertainment		2,894	2,219	2,643
ATM and debit card expense		1,090	3,889	3,136
Professional fees		4,035	3,844	4,946
Software and data processing expense		3,996	3,027	2,911
Telephone and communications		1,847	1,905	1,931
FDIC insurance		1,871	1,769	2,141
Amortization expense on intangibles		5,213	1,955	1,940
Other		12,283	10,528	14,524
Total noninterest expense		120,099	106,335	109,522
Income before income tax expense		84,301	70,433	59,674
Income tax expense		10,163	16,121	10,325
Net income		$ 74,138	$ 54,312	$ 49,349
Earnings per common share - basic (in dollars per share)		$ 2.12	$ 1.82	$ 1.82
Earnings per common share - diluted (in dollars per share)		2.11	1.81	1.81
Dividends paid on common stock (in dollars per share)		$ 1.20	$ 1.11	$ 1.01
[1]	Of the $8.4 million in provision for loan losses for the year ended December 31, 2018, $302,000 related to provision expense on PCI loans. Of the $4.7 million and $9.8 million recorded in provision for loan losses for the year ended December 31, 2017 and 2016, respectively, none related to provision expense on PCI loans

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net Income	$ 74,138	$ 54,312	$ 49,349
Securities available for sale and transferred securities:
Change in unrealized (loss) gain on available for sale securities during the period	(34,238)	15,217	(23,459)
Unrealized net gain on securities transferred from held to maturity to available for sale under the transition guidance enumerated in ASU 2017-12	11,881	0	0
Change in net unrealized loss on securities transferred from held to maturity to available for sale	401	0	0
Change in net unrealized loss on securities transferred to held to maturity	0	0	(10,240)
Reclassification adjustment for net loss on equity investments, reclassified to retained earnings with adoption of ASU 2016-01	107	0	0
Reclassification adjustment for amortization related to available for sale and to held to maturity debt securities	1,244	1,255	429
Reclassification adjustment for net loss (gain) on sale of available for sale securities, included in net income	1,839	(625)	(2,836)
Derivatives:
Change in unrealized gain on effective cash flow hedge interest rate swap derivatives	2,351	3	5,255
Change in net unrealized gains on interest rate swap derivatives terminated during the period	0	273	0
Reclassification adjustment from other comprehensive income (loss) related to derivatives designated as cash flow hedge	(1,406)	754	1,815
Pension plans:
Amortization of net actuarial loss and prior service credit, included in net periodic benefit cost	2,182	1,605	1,820
Effect of settlement recognition	0	8	(8)
Prior service cost adjustment due to plan amendments	0	0	(121)
Change in net actuarial loss	(1,994)	(5,218)	(3,132)
Other comprehensive (loss) income, before tax	(17,633)	13,272	(30,477)
Income tax benefit (expense) related to items of other comprehensive income (loss)	3,703	(5,374)	10,667
Other comprehensive (loss) income, net of tax	(13,930)	7,898	(19,810)
Comprehensive income	$ 60,208	$ 62,210	$ 29,539

CONSOLIDATED STATEMENTS OF CHAN

CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - 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, 2015	$ 444,062	$ 34,832	$ 424,078	$ 41,527	$ (37,692)	$ (18,683)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	49,349			49,349
Other comprehensive income (loss)	(19,810)					(19,810)
Issuance of common stock for dividend reinvestment plan (42,872 shares in 2018, 43,650 shares in 2017, 44,575 shares in 2016)	1,411	56	1,355
Net issuance of common stock (2,185,000 shares in 2016)	75,992	2,731	73,261
Tax benefit related to stock awards	332		332
Purchase of common stock (1,459,148 shares in 2018, 443,426 shares in 2016)	(10,199)				(10,199)
Stock compensation expense	1,541		1,541
Net issuance of common stock under employee stock plan (140,692 shares in 2018, 159,356 shares in 2017, 108,255 shares in 2016)	1,559	136	1,473	(50)
Cash dividends paid on common stock ($1.20 per share in 2018, $1.11 per share in 2017, $1.01 per share in 2016)	(25,963)			(25,963)
Stock dividend declared (719,515 shares in 2017, 1,252,353 shares in 2016)	0	1,565	33,200	(34,765)
Ending balance, net of tax at Dec. 31, 2016	518,274	39,320	535,240	30,098	(47,891)	(38,493)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	54,312			54,312
Other comprehensive income (loss)	7,898					7,898
Issuance of common stock for dividend reinvestment plan (42,872 shares in 2018, 43,650 shares in 2017, 44,575 shares in 2016)	1,483	54	1,429
Net issuance of common stock in connection with the acquisition of Diboll State Bancshares, Inc. (5,534,925 shares)	200,087	6,919	193,168
Stock compensation expense	1,815		1,815
Net issuance of common stock under employee stock plan (140,692 shares in 2018, 159,356 shares in 2017, 108,255 shares in 2016)	2,470	61	1,726	(103)	786
Cash dividends paid on common stock ($1.20 per share in 2018, $1.11 per share in 2017, $1.01 per share in 2016)	(32,199)			(32,199)
Stock dividend declared (719,515 shares in 2017, 1,252,353 shares in 2016)	0	899	24,061	(24,960)
Reclassification of certain deferred tax effects	0			5,703		(5,703)
Ending 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	74,138			74,138
Other comprehensive income (loss)	(13,930)					(13,930)
Issuance of common stock for dividend reinvestment plan (42,872 shares in 2018, 43,650 shares in 2017, 44,575 shares in 2016)	1,478	54	1,424
Purchase of common stock (1,459,148 shares in 2018, 443,426 shares in 2016)	(47,193)				(47,193)
Stock compensation expense	2,317		2,317
Net issuance of common stock under employee stock plan (140,692 shares in 2018, 159,356 shares in 2017, 108,255 shares in 2016)	2,405	0	1,290	(128)	1,243
Cash dividends paid on common stock ($1.20 per share in 2018, $1.11 per share in 2017, $1.01 per share in 2016)	(41,979)			(41,979)
Ending 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]
Cumulative effect of ASU 2016-01	$ (85)			$ (85)

CONSOLIDATED STATEMENTS OF CH_2

CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Stockholders' Equity [Abstract]
Issuance of common stock for dividend reinvestment plan (in shares)	42,872	43,650	44,575
Net issuance of common stock (in shares)			2,185,000
Dividends paid on common stock (in dollars per share)	$ 1.20	$ 1.11	$ 1.01
Purchase of common stock (in shares)	1,459,148	0	443,426
Net issuance of common stock under employee stock plan (in shares)	140,692	159,356	108,225
Common Stock Dividends (in shares)		719,515	1,252,353
Net issuance of common stock in connection with the acquisition of Diboll State Bancshares, Inc. (in shares)		5,534,925

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS	12 Months Ended
	Dec. 31, 2018USD ($)		Dec. 31, 2017USD ($)		Dec. 31, 2016USD ($)
OPERATING ACTIVITIES
Net income	$ 74,138,000		$ 54,312,000		$ 49,349,000
Adjustments to reconcile net income to net cash provided by operations:
Depreciation and net amortization	14,045,000		10,208,000		9,084,000
Securities premium amortization (discount accretion), net	13,675,000		17,639,000		19,126,000
Loan (discount accretion) premium amortization, net	(2,333,000)		(1,142,000)		(2,520,000)
Provision for loan losses	8,437,000	[1]	4,675,000	[1]	9,780,000	[1]
Stock compensation expense	2,317,000		1,815,000		1,541,000
Deferred tax expense	6,154,000		3,514,000		1,768,000
Net tax benefit related to stock awards	0		0		(332,000)
Net loss (gain) on sale of securities available for sale	1,839,000		(625,000)		(2,836,000)
Net loss on premises and equipment	768,000		152,000		376,000
Gross proceeds from sales of loans held for sale	24,092,000		58,747,000		82,062,000
Gross originations of loans held for sale	(22,692,000)		(53,107,000)		(85,892,000)
Net loss on other real estate owned	433,000		7,000		219,000
Net gain on sale of customer receivables	(124,000)		0		(194,000)
Net change in:
Interest receivable	1,204,000		(63,000)		(2,483,000)
Other assets	(2,166,000)		(3,909,000)		1,823,000
Interest payable	1,257,000		570,000		2,334,000
Other liabilities	1,358,000		(1,063,000)		3,520,000
Net cash provided by operating activities	122,402,000		91,730,000		86,725,000
Securities available for sale:
Purchases	(306,867,000)		(619,398,000)		(1,001,742,000)
Sales	428,518,000		685,152,000		573,051,000
Maturities, calls and principal repayments	137,883,000		113,183,000		207,500,000
Securities held to maturity:
Purchases	0		(6,260,000)		(44,656,000)
Maturities, calls and principal repayments	3,064,000		28,974,000		31,251,000
Proceeds from redemption of FHLB stock and other investments	24,360,000		6,945,000		3,644,000
Purchases of FHLB stock and other investments	(1,518,000)		(1,233,000)		(13,667,000)
Net loan originations	(24,491,000)		(117,750,000)		(139,607,000)
Proceeds from sales of customer receivables	4,300,000		0		3,325,000
Net cash and cash equivalents acquired in acquisition	0		115,598,000		0
Net cash paid in acquisition	0		(23,941,000)		0
Purchases of premises and equipment	(13,444,000)		(9,633,000)		(6,549,000)
Proceeds from bank owned life insurance	5,956,000		0		0
Proceeds from sales of premises and equipment	1,943,000		12,000		128,000
Proceeds from sales of other real estate owned	1,717,000		659,000		2,024,000
Proceeds from sales of repossessed assets	483,000		429,000		894,000
Net cash provided by (used in) investing activities	261,904,000		172,737,000		(384,404,000)
FINANCING ACTIVITIES:
Net change in deposits	(106,014,000)		82,960,000		78,426,000
Net increase in federal funds purchased and repurchase agreements	27,312,000		2,401,000		4,668,000
Proceeds from FHLB borrowings	4,201,500,000		2,786,476,000		8,158,985,000
Repayment of FHLB borrowings	(4,499,788,000)		(3,078,743,000)		(7,996,913,000)
Net proceeds from issuance of subordinated long-term debt	0		0		98,060,000
Tax benefit related to stock awards	0		0		332,000
Proceeds from stock option exercises	2,653,000		2,692,000		1,663,000
Cash paid to tax authority related to tax withholding on share-based awards	(248,000)		(222,000)		(104,000)
Purchase of common stock	(47,193,000)		0		(10,199,000)
Proceeds from the issuance of common stock for dividend reinvestment plan	1,478,000		1,483,000		1,411,000
Proceeds from the issuance of common stock	0		0		75,992,000
Cash dividends paid	(41,979,000)		(32,199,000)		(25,963,000)
Payments for other financing activities	0		(277,000)		0
Net cash (used in) provided by financing activities	(462,279,000)		(235,429,000)		386,358,000
Net (decrease) increase in cash and cash equivalents	(77,973,000)		29,038,000		88,679,000
Cash and cash equivalents at beginning of period	198,692,000		169,654,000		80,975,000
Cash and cash equivalents at end of period	120,719,000		198,692,000		169,654,000
SUPPLEMENTAL DISCLOSURES FOR CASH FLOW INFORMATION:
Interest paid	55,844,000		42,934,000		27,014,000
Income taxes paid	2,000,000		11,300,000		5,700,000
SUPPLEMENTAL DISCLOSURES OF NONCASH INVESTING AND FINANCING ACTIVITIES:
Loans transferred to other repossessed assets and real estate through foreclosure	2,128,000		574,000		5,777,000
Loans transferred from portfolio to held for sale	3,984,000		0		0
Transfer of held to maturity securities to available for sale securities	743,421,000		0		0
Transfer of available for sale securities to held to maturity securities	0		0		157,083,000
Adjustment to pension liability	188,000		3,605,000		1,441,000
Stock dividend (2.5% for 2017, 5% for 2016)	0		24,960,000		34,765,000
Unsettled trades to purchase securities	(6,378,000)		0		(160,000)
Unsettled issuances of brokered certificates of deposit	15,236,000		0		0
Common stock issued in acquisition	$ 0		$ 200,364,000		$ 0
[1]	Of the $8.4 million in provision for loan losses for the year ended December 31, 2018, $302,000 related to provision expense on PCI loans. Of the $4.7 million and $9.8 million recorded in provision for loan losses for the year ended December 31, 2017 and 2016, respectively, none related to provision expense on PCI loans

CONSOLIDATED STATEMENTS OF CA_2

CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical)	12 Months Ended
	Dec. 31, 2017Rate	Dec. 31, 2016Rate
Statement of Cash Flows [Abstract]
Stock dividend, percentage of common stock	2.50%	5.00%

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING AND REPORTING POLICIES	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING AND REPORTING POLICIES	SUMMARY OF SIGNIFICANT ACCOUNTING AND REPORTING POLICIES Organization . Southside Bancshares, Inc., incorporated in Texas in 1982, is a bank holding company for Southside Bank, a Texas state bank headquartered in Tyler, Texas that was formed in 1960. We operate through 59 branches, 15 of which are located in grocery stores. We consider our primary market areas to be East Texas, Southeast Texas, the greater Fort Worth, Texas area and the greater Austin, Texas area. We are a community-focused financial institution that offers a full range of financial services to individuals, businesses, municipal entities and nonprofit organizations in the communities that we serve. These services include consumer and commercial loans, deposit accounts, wealth management and trust services, brokerage services and safe deposit services. Basis of Presentation and Consolidation . The consolidated financial statements are prepared in conformity with U.S. generally accepted accounting principles (“GAAP”) and include the accounts of Southside Bancshares, Inc. (the “Company”), and its wholly-owned subsidiary, Southside Bank (“Southside Bank” or “the Bank”) and the nonbank subsidiaries. All significant intercompany accounts and transactions are eliminated in consolidation. “Omni” refers to OmniAmerican Bancorp, Inc., a bank holding company acquired by Southside on December 17, 2014. On November 30, 2017, we acquired Diboll State Bancshares, Inc., a Texas corporation (“Diboll”) and the holding company for First Bank & Trust East Texas, a Texas banking association based in Diboll, Texas. See “Note 2 - Acquisition”. We determine if we have a controlling financial interest in an entity by first evaluating whether the entity is a voting interest entity or a variable interest entity (“VIE”) under GAAP. Voting interest entities are entities in which the total equity investment at risk is sufficient to enable the entity to finance itself independently and provides the equity holders with the obligation to absorb losses, the right to receive residual returns and the right to make decisions about the entity’s activities. We consolidate voting interest entities in which we have all, or at least a majority of, the voting interest. As defined in applicable accounting standards, VIEs are entities that lack one or more of the characteristics of a voting interest entity. A controlling financial interest in a VIE is present when an enterprise has both the power to direct the activities of the VIE that most significantly impact the VIEs economic performance and an obligation to absorb losses or the right to receive benefits that could potentially be significant to the VIE. The enterprise with a controlling financial interest, known as the primary beneficiary, consolidates the VIE. Accounting Changes and Reclassifications . Certain prior period amounts have been reclassified to conform to current year presentation. We adopted Accounting Standards Update (“ASU”) 2014-09, “Revenue from Contracts with Customers (Topic 606)” as modified by subsequently issued ASUs 2015-14, 2016-08, 2016-10, 2016-12 and 2016-20, on January 1, 2018, the effective date of the guidance, using the modified retrospective approach. As the majority of the Company’s revenues are not subject to the new guidance, the adoption of ASU 2014-09 did not have a material impact on the Company’s consolidated financial position, results of operations, equity or cash flows. As a result of the guidance, we adjusted the presentation of revenue received from our brokerage services, merchant services, as well as our interchange income associated with debit card services, which were all deemed to be services offered in an agent capacity. These lines of revenue will now be presented on a net basis with the fee income disclosed net of the related costs in the noninterest income section of the consolidated statements of income. In connection with the adoption, for the year ended December 31, 2018 , we netted $4.0 million of debit card expense against deposit services income and $641,000 of brokerage services expense against brokerage services income, respectively. Due to the implementation of the guidance under the modified retrospective method, prior periods have not been adjusted and are not comparative. Refer to our revenue recognition discussion below for more information related to our revenue recognition policies. We adopted ASU 2016-01, “Financial Instruments – Overall (Subtopic 825-10) – Recognition and Measurement of Financial Assets and Financial Liabilities,” on January 1, 2018, the effective date of the guidance. ASU 2016-01, among other things, (i) requires equity investments, with certain exceptions, to be measured at fair value with changes in fair value recognized in net income, (ii) simplifies the impairment assessment of equity investments without readily determinable fair values by requiring a qualitative assessment to identify impairment, (iii) eliminates the requirement for public business entities to disclose the methods and significant assumptions used to estimate the fair value that is required to be disclosed for financial instruments measured at amortized cost on the balance sheet, (iv) requires public business entities to use the exit price notion when measuring the fair value of financial instruments for disclosure purposes, (v) requires an entity to present separately in other comprehensive income the portion of the total change in the fair value of a liability resulting from a change in the instrument-specific credit risk when the entity has elected to measure the liability at fair value in accordance with the fair value option for financial instruments, (vi) requires separate presentation of financial assets and financial liabilities by measurement category and form of financial asset on the balance sheet or the accompanying notes to the financial statements and (vii) clarifies that an entity should evaluate the need for a valuation allowance on a deferred tax asset related to available for sale (“AFS”) securities in combination with the entity’s other deferred tax assets. The guidance requires companies to apply the requirements in the year of adoption, through cumulative adjustment, while the guidance related to equity securities without readily determinable fair values should be applied prospectively. Adoption of this guidance resulted in a cumulative-effect adjustment to retained earnings of $85,000 , net of tax, on January 1, 2018 and an equity security with a carrying value of $5.9 million that was previously recognized in securities AFS, at estimated fair value on our consolidated balance sheet to instead be recognized in equity investments, with subsequent changes in fair value being recognized in income. Also in conjunction with the adoption, our fair value measurement of financial instruments will be based upon an exit price notion as required in ASC 820. The guidance was applied on a prospective approach resulting in prior periods no longer being comparable. We adopted ASU 2017-07, “Compensation - Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost,” on January 1, 2018. ASU 2017-07 requires employers to present the service cost component of net periodic postretirement benefit cost in the same income statement line item as other employee compensation costs arising from services rendered during the period. Employers are required to present the other components of the net periodic benefit cost separately from the line item that includes the service cost and outside of any subtotal of operating income, if one is presented. The guidance requires companies to apply the requirements retrospectively to all prior periods presented. We elected to use the practical expedient that permits us to use the amounts in our pension plan disclosures in our employee benefit footnote for the prior comparative periods as the estimation basis for applying the retrospective presentation requirements, which resulted in an increase of $304,000 and a decrease of $2.4 million in salaries and employee benefits expense and a decrease of $304,000 and an increase of $2.4 million in other noninterest expense for the years ended December 31, 2017 and 2016 , respectively. We early adopted ASU 2017-12, “Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities,” on January 1, 2018. ASU 2017-12 (i) expands hedge accounting for nonfinancial and financial risk components and amends measurement methodologies to more closely align hedge accounting with a company’s risk management activities, (ii) decreases the complexity of preparing and understanding hedge results by eliminating the separate measurement and reporting of hedge ineffectiveness, (iii) enhances transparency, comparability and understanding of hedge results through enhanced disclosures and changing the presentation of hedge results to align the effects of the hedging instrument and the hedged item and (iv) reduces the cost and complexity of applying hedge accounting by simplifying the manner in which assessments of hedge effectiveness may be performed. The guidance also permits a transition election to reclassify held to maturity (“HTM”) securities to AFS securities if a portion of those securities would qualify to be hedged under the new “last-of-layer” approach. The guidance requires companies to apply the requirements to existing hedging relationships on the date of adoption, and the effect of the adoption should be reflected as of the beginning of the fiscal year of adoption. The guidance did not have an impact on our derivatives that qualified as hedges on the date of adoption and thus no adjustment was made to retained earnings. In conjunction with the adoption of ASU 2017-12, we made the transition election to reclassify approximately $743.4 million in book value of securities from HTM to AFS that qualified for the last-of-layer approach described in ASU 2017-12. During the second quarter of 2018, we entered into partial term fair value hedges, as allowed under the recently adopted ASU 2017-12, for certain of our fixed rate callable AFS municipal securities. These hedges are expected to be effective in offsetting changes in the fair value of the hedged securities. 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. Stock Dividend . There were no stock dividends declared or paid during 2018. On May 4, 2017 , our board of directors declared a 2.5% stock dividend to common stock shareholders of record as of May 30, 2017 , which was paid on June 27, 2017 . On May 5, 2016, our board of directors declared a 5.0% stock dividend to common stock shareholders of record as of May 31, 2016, which was paid on June 28, 2016. All share data for all periods presented has been adjusted to give retroactive recognition to these stock dividends unless otherwise indicated. Use of Estimates . In preparing consolidated financial statements in conformity with GAAP, management is required to make estimates and assumptions that affect the reported amounts of assets and liabilities as of the date of the balance sheet and reported amounts of revenues and expenses during the reporting period. These estimates are subjective in nature and involve matters of judgment. Actual results could differ from these estimates. Material estimates that are particularly susceptible to significant change in the near term relate to the determination of the allowance for loan losses, assumptions used in the defined benefit plan and the fair values of financial instruments. The status of contingencies are particularly subject to change and significant assumptions used in periodic evaluation of securities for other-than-temporary impairment. Certain prior period amounts have been reclassified to conform to the current period presentation. Segment Information . Operating segments are components of a business about which separate financial information is available and that are evaluated regularly by the chief operating decision-maker in deciding how to allocate resources and assess performance. Our chief operating decision-maker uses consolidated results to make operating and strategic decisions. Therefore, we have determined that our business is conducted in one reportable segment. Business Combinations. Business combinations are accounted for using the acquisition method of accounting. Under this accounting method, the acquired company’s net assets are recorded at fair value on the date of acquisition, and the results of operations of the acquired company are combined with our results from that date forward. Costs related to the acquisition are expensed as incurred. The difference between the purchase price and the fair value of the net assets acquired (including intangible assets with finite lives) is recorded as goodwill. The accounting policy for goodwill and intangible assets is summarized in this note under the heading “Goodwill and Other Intangibles.” Acquired loans (non-impaired and impaired) are initially measured at fair value as of the acquisition date. The fair value estimates for acquired loans are based on the estimate of expected cash flows, both principal and interest and prepayments, discounted at prevailing market interest rates. Credit discounts representing the principal losses expected over the life of the loan are also a component of the initial fair value; therefore, an allowance for loan losses is not recorded at the acquisition date. We evaluate acquired loans for impairment in accordance with the provisions of ASC 310-30, “Loans and Debt Securities Acquired with Deteriorated Credit Quality” (“ASC 310-30”). Acquired loans are considered impaired if there is evidence of credit deterioration since origination and if it is probable at time of acquisition that all contractually required payments will not be collected. Expected cash flows at the acquisition date in excess of the fair value of the loans is referred to as the accretable yield and recorded as interest income over the life of the loans. Acquired impaired loans are not classified as nonaccrual or nonperforming as they are considered to be performing under the provisions of ASC 310-30. Subsequent to the acquisition date, increases in expected cash flows will generally result in a recovery of any previously recorded allowance for loan loss, to the extent applicable, and/or a reclassification from the nonaccretable difference to accretable yield, which will be recognized prospectively. The present value of any decreases in expected cash flows after the acquisition date will generally result in an impairment charge recorded as a provision for loan losses, resulting in an increase to the allowance for loan loss. For acquired non-impaired loans, the difference between the acquisition date fair value and the contractual amounts due at the acquisition date represents the fair value adjustment. Fair value adjustments may be discounts (or premiums) to a loan’s cost basis and are accreted (or amortized) to interest income over the loan’s remaining contractual life using the level yield method. Cash Equivalents . Cash equivalents, for purposes of reporting cash flow, include cash, amounts due from banks and federal funds sold that have an initial maturity of less than 90 days. We maintain deposits with other institutions in amounts that exceed federal deposit insurance coverage. Management regularly evaluates the credit risk associated with the counterparties to these transactions and believes that we are not exposed to any significant credit risks on cash and cash equivalents. Cash on hand or on deposit with the Federal Reserve Bank of $34.1 million and $32.2 million was required to meet regulatory reserves and clearing requirements at December 31, 2018 and 2017 , respectively. Basic and Diluted Earnings per Common Share . Basic earnings per common share is based on net income divided by the weighted-average number of common shares outstanding during the period. Diluted earnings per common share include the dilutive effect of stock options granted using the treasury stock method. A reconciliation of the weighted-average shares used in calculating basic earnings per common share and the weighted average common shares used in calculating diluted earnings per common share for the reported periods is provided in “Note 3 – Earnings Per Share.” Comprehensive Income . Comprehensive income includes all changes in shareholders’ equity during a period, except those resulting from transactions with shareholders. Besides net income, other components of comprehensive income include the after tax effect of changes in the fair value of AFS securities, changes in the net unrealized loss on securities transferred to/from HTM, changes in the accumulated gain or loss on effective cash flow hedging instruments and changes in the funded status of defined benefit retirement plans. Comprehensive income is reported in the accompanying consolidated statements of comprehensive income and in “Note 4 - Accumulated Other Comprehensive Loss.” Loans . All loans are stated at principal outstanding net of unearned discount and other deferred expenses or fees. Interest income on loans is recognized using the level yield method or simple interest method. Loans receivable that management has the intent and ability to hold for the foreseeable future or until maturity or pay-off are reported at their outstanding principal adjusted for any charge-offs, the allowance for loan losses, and any unamortized deferred fees or costs on originated loans and unamortized premiums or discounts on purchased loans. A loan is considered impaired, based on current information and events, if it is probable that we will be unable to collect the scheduled payments of principal or interest when due according to the contractual terms of the loan agreement. Substantially all of our impaired loans are collateral-dependent, and as such, are measured for impairment based on the fair value of the collateral. Loans Held For Sale . Loans originated and intended for sale in the secondary market are carried at the lower of aggregate cost or fair value, as determined by aggregate outstanding commitments from investors or current investor yield requirements. Net unrealized losses are recognized through a valuation allowance by charges to income. Gains or losses on sales of mortgage loans are recognized based on the difference between the selling price and the carrying value of the related mortgage loans sold. Loan Fees . We treat loan fees, net of direct costs, as an adjustment to the yield of the related loan over its term. Allowance for Loan Losses . An allowance for loan losses is provided through charges to income in the form of a provision for loan losses. Loans which management believes are uncollectible are charged against this account with subsequent recoveries, if any, credited to the account. The amount of the allowance for loan losses is determined by management’s evaluation of the quality and inherent risks in the loan portfolio, economic conditions and other factors which warrant current recognition. Nonaccrual Loans . A loan is placed on nonaccrual when principal or interest is contractually past due 90 days or more unless, in the determination of management, the principal and interest on the loan are well collateralized and in the process of collection. In addition, a loan is placed on nonaccrual when, in the opinion of management, the future collectability of interest and principal is not expected. When classified as nonaccrual, accrued interest receivable on the loan is reversed and the future accrual of interest is suspended. 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. Other Real Estate Owned and Foreclosed Assets . Other Real Estate Owned (“OREO”) includes real estate acquired in full or partial settlement of loan obligations. OREO is initially carried at the fair value of the collateral net of estimated selling costs. Prior to foreclosure, the recorded amount of the loan is written down, if necessary, to the appraised fair value of the real estate to be acquired, less selling costs, by charging the allowance for loan losses. Any subsequent reduction in fair value net of estimated selling costs is charged to noninterest expense. Costs of maintaining and operating foreclosed properties are expensed as incurred and included in other expense in our income statement. Expenditures to complete or improve foreclosed properties are capitalized only if expected to be recovered; otherwise, they are expensed. Other foreclosed assets are held for sale and are initially recorded at fair value less estimated selling costs at the date of foreclosure, by charging the allowance for loan losses. Subsequent to foreclosure, valuations are periodically performed by management and the assets are carried at the lower of carrying amount or fair value less costs to sell. Foreclosed assets are included in other assets in the accompanying consolidated balance sheets. Expenses from operations and changes in the valuation allowance are included in noninterest expense. Securities . Available for Sale (“AFS”). Debt securities that will be held for indefinite periods of time, including securities that may be sold in response to changes in market interest or prepayment rates, needs for liquidity and changes in the availability of and the yield on alternative investments are classified as AFS. These assets are carried at fair value with unrealized gains and losses reported as a separate component of accumulated other comprehensive income (“AOCI”), net of tax. Fair value is determined using quoted market prices as of the close of business on the balance sheet date. If quoted market prices are not available, fair values are based on quoted market prices for similar securities or estimates from independent pricing services. Securities that are hedged with qualifying derivatives are carried at fair value with the change in fair value on both the hedged instrument and the securities recorded in interest income in the consolidated statements of income. Held to Maturity (“HTM”). Debt securities that management has the positive intent and ability to hold until maturity are classified as HTM and are carried at their remaining unpaid principal balance, net of unamortized premiums or unaccreted discounts. Prior to January 1, 2019, premiums were amortized and discounts were accreted to maturity, or in the case of mortgage-backed securities (“MBS”), over the estimated life of the security, using the level yield interest method. Effective January 1, 2019, premium callable securities will be amortized to the earliest call date and securities purchased at a discount will be accreted to maturity. Unrealized gains and losses on AFS securities are excluded from earnings and reported net of tax in AOCI until realized. Declines in the fair value of AFS or HTM securities below their cost that are deemed to be other-than-temporary are reflected in earnings as a realized loss if there is no ability or intent to hold to recovery. If the Company does not intend to sell and will not be required to sell prior to recovery of its amortized cost basis, only the credit component of the impairment is reflected in earnings as a realized loss with the noncredit portion recognized in other comprehensive income. In estimating other-than-temporary impairment losses, we consider (1) the length of time and the extent to which the fair value has been less than cost, (2) the financial condition and near-term prospects of the issuer and (3) our intent and ability to retain our investment in the issuer for a period of time sufficient to allow for any anticipated recovery in fair value. Gains and losses on the sale of securities are recorded in the month of the trade date and are determined using the specific identification method. Equity Investments. Beginning January 1, 2018, upon adoption of ASU 2016-01, equity investments with readily determinable fair values are stated at fair value with the unrealized gains and losses reported in other noninterest income in the consolidated statements of income. For periods prior to January 1, 2018, certain equity investments were classified as AFS and stated at fair value with unrealized gains and losses reported as a separate component of AOCI, net of tax. Equity investments without readily determinable fair values are recorded at cost less impairment, if any. Securities with Limited Marketability. Securities with limited marketability, such as stock in the FHLB, are carried at cost and assessed for other-than-temporary impairment. Premises and Equipment . Land is carried at cost. Bank premises and equipment are stated at cost, net of accumulated depreciation. Depreciation is computed on a straight line basis over the estimated useful lives of the related assets. Useful lives are estimated to be 15 to 40 years for premises and 3 to 10 years for equipment. Leasehold improvements are generally depreciated over the lesser of the term of the respective leases or the estimated useful lives of the improvements. Maintenance and repairs are charged to expense as incurred while major improvements and replacements are capitalized. Bank-Owned Life Insurance . The Company has purchased life insurance policies on certain key executives. Bank-owned life insurance is recorded at the amount that can be realized under the insurance contract at the balance sheet date, which is the cash surrender value adjusted for other charges or other amounts due that are probable at settlement. Changes in the net cash surrender value of the policies, as well as insurance proceeds received are reflected in noninterest income on the consolidated statements of income and are not subject to income taxes. Goodwill and Other Intangibles . Other intangible assets consist primarily of core deposits and trust relationship intangibles. Intangible assets with definite useful lives are amortized on an accelerated basis over their estimated life. Goodwill and intangible assets that have indefinite useful lives are subject to at least an annual impairment test and more frequently if a triggering event occurs. If any such impairment is determined, a write-down is recorded. We have selected October 1 of each year as the measurement date on which we will complete our annual goodwill impairment assessment. As of October 1, 2018 and 2017, the fair value of the reporting unit was greater than the carrying value of the reporting unit. As a result, we did no t record any goodwill impairment for the year ended December 31, 2018 and 2017 , and we had no cumulative goodwill impairment. At December 31, 2018 , core deposit intangible and trust relationship intangible was $13.1 million and $4.5 million , respectively. For the years ended December 31, 2018 and 2017, amortization expense related to our core deposit intangible and trust relationship intangible was $5.1 million and $1.8 million , respectively. For the year ended December 31, 2016, amortization expense related to our core deposit intangible was $1.8 million . Repurchase Agreements . We sell certain securities under agreements to repurchase. The agreements are treated as collateralized financing transactions and the obligations to repurchase securities sold are reflected as a liability in the accompanying consolidated balance sheets. The dollar amount of the securities underlying the agreements remains in the asset account. We determine the type of securities to pledge. Generally we pledge U.S. agency MBS. Derivative Financial Instruments and Hedging Activities . Derivative financial instruments are carried on the consolidated balance sheets as other assets or other liabilities, as applicable, at estimated fair value. The accounting for changes in the fair value (i.e., gains or losses) of a derivative financial instrument is determined by whether it has been designated and qualifies as part of a hedging relationship and, further, by the type of hedging relationship. We present derivative financial instruments at fair value in the consolidated balance sheets on a net basis when a right of offset exists, based on transactions with a single counterparty and any cash collateral paid to and/or received from that counterparty for derivative contracts that are subject to legally enforceable master netting arrangements. For derivative instruments that are designated and qualify as cash flow hedges (i.e., hedging the exposure to variability in expected future cash flows that is attributable to a particular risk), the effective portion of the gain or loss on the derivative instrument is reported as a component of other comprehensive income and reclassified into earnings in the same period or periods during which the hedged transaction affects earnings. The remaining gain or loss on the derivative instrument in excess of the cumulative change in the present value of future cash flows of the hedged item (i.e., the ineffective portion), if any, is recognized in current earnings during the period of change. For derivative instruments not designated as hedging instruments, the gain or loss is recognized in current earnings during the period of change. During the three months ended June 30, 2018, we entered into partial term fair value hedges, as allowed under the recently adopted ASU 2017-12, 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 are 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 are utilized to mitigate the effect of changing interest rates on the hedged securities. The hedging strategy converts a portion of the fixed interest rates on the securities to LIBOR-based variable interest rates. For derivatives designated as hedging instruments at inception, statistical regression analysis is used at inception and for each reporting period thereafter to assess whether the derivative used has been and is expected to be highly effective in offsetting changes in the fair value or cash flows of the hedged item. All components of each derivative instrument’s gain or loss are included in the assessment of hedge effectiveness. Net hedge ineffectiveness is recorded in “other noninterest income” on the consolidated statements of income. Terminated Derivative Financial Instruments . 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 the first quarter of 2017, we terminated two interest rate swap contracts designated as cash flow hedges. At the time of termination, we determined that the underlying hedged forecasted transactions were still probable of occurring. 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. Further information on our derivative instruments and hedging activities is included in “Note 12 - Derivative Financial Instruments and Hedging Activities.” Revenue Recognition. Our revenue consists of net interest income on financial assets and financial liabilities and noninterest income. The classifications of our revenue are presented in the consolidated statements of income. On January 1, 2018, we adopted ASU 2014-09, “Revenue from Contracts with Customers (Topic 606)” using the modified retrospective method. The revenue recognition principle in ASU 2014-09 is that an entity should recognize revenue to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be ent

ACQUISITION

ACQUISITION	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Acquisition	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 operations of Diboll were merged into the Company as of the date of the acquisition. The results of Diboll's operations for November 30 - December 31, 2017 are included in the consolidated financial statements and are not separately quantifiable subsequent to the business combination. Pursuant to the merger agreement, on November 30, 2017 , we issued 5.5 million shares of our common stock and paid $23.9 million in cash for all outstanding shares of Diboll State Bancshares Inc. common stock. In accordance with the merger agreement, each outstanding share of common stock of Diboll State Bancshares, Inc. was converted into (a) 6.5021 shares of common stock of the Company and (b) $28.12 in cash (the “Per Share Merger Consideration”). Pursuant to the Diboll State Bancshares, Inc. Incentive Stock Option 2014 Plan and predecessor plans, and the individual award agreements granted thereunder, all outstanding equity awards terminated as of the effective time of the acquisition and became null and void. Holders of stock options granted under such plans were provided an opportunity to exercise such stock options or take advantage of the cashless exercise feature of such equity awards prior to the effective time of the acquisition. The cash consideration is net of the aggregate after-tax amount paid by Diboll to holders of options to purchase Diboll common stock who utilized the cashless exercise feature immediately prior to the acquisition as outlined in the merger agreement. Based on our closing stock price on November 30, 2017 of $36.20 , the total merger consideration for the Diboll merger was $224.3 million . The components of the consideration paid are shown in the following table (in thousands): Fair value of consideration transferred: Common stock issued $ 200,364 Cash 23,941 Total consideration transferred $ 224,305 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. The purchase price allocation as reported at December 31, 2017 was preliminary and was subject to final determination and valuation of the fair value of assets acquired and liabilities assumed. 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 . Goodwill represents consideration transferred in excess of the fair value of the net assets acquired. In 2017 , the Company recognized initial goodwill of $109.7 million . As of December 31, 2018 , total goodwill related to the Diboll acquisition was $109.6 million , after recording, within the measurement period, an immaterial adjustment to goodwill based on the filing of the short-period Federal Income Tax return for Diboll and its subsidiaries. The measurement period for the Diboll acquisition ended during the fourth quarter of 2018 . The goodwill resulting from the acquisition represents the value expected from the expansion of our markets into the Southeast Texas region and the enhancement of our operations through customer synergies and efficiencies, thereby providing enhanced customer service. Goodwill is not expected to be deductible for tax purposes. The following table reflects the changes in the carrying amount of our goodwill for the year ended December 31, 2018 (in thousands): Goodwill Balance as of December 31, 2017 $ 201,246 Less: measurement period adjustments (130 ) Balance as of December 31, 2018 $ 201,116 The estimated fair values of the assets acquired and liabilities assumed as of the closing date of the transaction adjusted for the subsequent measurement period adjustments are shown in the following table (in thousands): As Originally Reported (1) Measurement Period Adjustments Adjusted Balances Cash, cash equivalents and amounts due from banks $ 115,598 $ — $ 115,598 Other investments 610 — 610 Securities available for sale 234,447 — 234,447 Loans 621,318 — 621,318 Property and equipment 26,256 — 26,256 Other assets 7,052 — 7,052 Core deposit intangible 14,700 — 14,700 Trust relationship intangible 5,400 — 5,400 Goodwill 109,726 (130 ) 109,596 Deposits (899,307 ) — (899,307 ) Deferred tax liability, net (7,802 ) 84 (7,718 ) Other liabilities (3,693 ) 46 (3,647 ) $ 224,305 $ — $ 224,305 (1) The estimated fair value as of the acquisition date, November 30, 2017 , as previously reported in our Form 10-K for the year ended December 31, 2017 . The determination of estimated fair values of the acquired loans required the Company to make certain estimates about discount rates, future expected cash flows, market conditions and other future events that are highly subjective in nature. Based on such factors as past due status, nonaccrual status, bankruptcy status and credit risk ratings, the acquired loans were divided into loans with evidence of credit quality deterioration, which are accounted for under ASC 310-30 (purchased credit impaired “PCI”), and loans that do not meet this criteria, which are accounted for under ASC 310-20 (purchased non-impaired). Expected cash flows, both principal and interest, were estimated based on key assumptions covering such factors as prepayments, default rates and severity of loss given default. These assumptions were developed using both Diboll’s historical experience and the portfolio characteristics as of the acquisition date as well as available market research. The fair value estimates for acquired loans were based on the amount and timing of expected principal, interest and other cash flows, including expected prepayments, discounted at prevailing market interest rates applicable to the types of acquired loans, which we considered to be Level 3 fair value measurements. Deposit liabilities assumed in the acquisition of Diboll were segregated into two categories: time-deposits (i.e., deposit accounts with a stated maturity) and demand deposits, both using Level 2 fair value measurements. In determining fair value of time deposits, the Company discounted the contractual cash flows of the deposit accounts using prevailing market interest rates for time deposit accounts of similar type and duration. For demand deposits, the acquisition date outstanding balance of the assumed demand deposit accounts approximates fair value. Acquisition date fair values for securities available for sale were determined using Level 1 or Level 2 inputs consistent with the methods discussed further in “Note 13 - Fair Value Measurement”. The remaining acquisition date fair values represent either Level 2 fair value measurements (other investments) or Level 3 fair value measurements (property and equipment, core deposit intangible and trust intangible). We recognized a core deposit intangible of $14.7 million and a trust relationship intangible of $5.4 million which will be amortized using an accelerated method over a 9 - and 13 -year weighted average amortization period, respectively, consistent with expected future cash flows. For the year ended December 31, 2017, the Company incurred a total of pre-tax acquisition related expenses associated with the Diboll acquisition of approximately $4.4 million which consisted primarily of $2.4 million of legal and consulting fees and $1.9 million of software expenses due to canceling of contracts. These expenses were recognized in the consolidated statements of income in acquisition expense. We incurred costs of $277,000 directly related to the issuance of the shares related to the acquisition which were offset against additional paid-in-capital in the consolidated statements of changes in equity. We also recorded non-solicitation agreements for $240,000 that will be amortized using the straight-line method over three years in connection with the acquisition. Loans acquired with Diboll were measured at fair value at the acquisition date with no carryover of any allowance for loan losses. Loans were segregated into those loans considered to be performing and those considered PCI. PCI loans are loans acquired with evidence of deteriorated credit quality for which it was probable, at acquisition, that all contractually required cash flows would not be collected. The table below details the PCI loan portfolio at the Diboll acquisition date (in thousands): Purchased Credit Impaired Loans at Acquisition Date Contractually required principal and interest payments $ 59,286 Nonaccretable difference 4,560 Cash flows expected to be collected 54,726 Accretable difference 15,389 Fair value of loans acquired with a deterioration of credit quality $ 39,337 Acquired loans that were considered performing at the Diboll acquisition date and therefore not subject to ASC 310-30 are shown below (in thousands): Fair Value at Acquisition Date Contractual Amounts Receivable Cash Flows Not Expected to be Collected at Acquisition Date (1) Real Estate Loans: Construction $ 40,122 $ 56,905 $ 330 1-4 Family Residential 82,654 130,167 26,894 Commercial 319,623 484,529 97,431 Commercial Loans 82,083 87,688 1,226 Municipal Loans 7,848 9,998 28 Loans to Individuals 49,651 54,687 1,490 Total Loans $ 581,981 $ 823,974 $ 127,399 (1) Cash flows not expected to be collected relate to estimated credit losses and expected prepayments. Unaudited pro forma net income for the years ended December 31, 2017 and 2016 would have been $64.1 million and $58.0 million , respectively, and revenues would have been $270.9 million and $257.8 million for the same years, respectively, had the acquisition occurred as of January 1, 2016.

EARNINGS PER SHARE

EARNINGS PER SHARE	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
EARNINGS PER SHARE	EARNINGS PER SHARE Earnings per share on a basic and diluted basis has been adjusted to give retroactive recognition to stock dividends and is calculated as follows (in thousands, except per share amounts): Years Ended December 31, 2018 2017 2016 Basic and Diluted Earnings: Net Income $ 74,138 $ 54,312 $ 49,349 Basic weighted-average shares outstanding 34,951 29,841 27,118 Add: Stock awards 165 206 129 Diluted weighted-average shares outstanding 35,116 30,047 27,247 Basic Earnings Per Share: Net Income $ 2.12 $ 1.82 $ 1.82 Diluted Earnings Per Share: Net Income $ 2.11 $ 1.81 $ 1.81 For the year ended December 31, 2018 , there were approximately 356,000 antidilutive options. For the years ended December 31, 2017 and 2016 there were approximately 154,000 and 359,000 antidilutive options, respectively.

ACCUMULATED OTHER COMPREHENSIVE

ACCUMULATED OTHER COMPREHENSIVE LOSS	12 Months Ended
	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
ACCUMULATED OTHER COMPREHENSIVE LOSS	ACCUMULATED OTHER COMPREHENSIVE LOSS The changes in accumulated other comprehensive loss by component are as follows for the years presented (in thousands): Year Ended December 31, 2018 Pension Plans Unrealized Gains (Losses) on Securities Unrealized Gains (Losses) on Derivatives Net Prior Net Gain (Loss) Total Beginning balance, net of tax $ (16,295 ) $ 6,399 $ (133 ) $ (26,269 ) $ (36,298 ) Other comprehensive (loss) income: Other comprehensive (loss) income before reclassifications (21,956 ) 2,351 — (1,994 ) (21,599 ) Reclassified from accumulated other comprehensive income (1) 3,190 (1,406 ) (7 ) 2,189 3,966 Income tax benefit (expense) 3,941 (198 ) 1 (41 ) 3,703 Net current-period other comprehensive (loss) income, net of tax (14,825 ) 747 (6 ) 154 (13,930 ) Ending balance, net of tax $ (31,120 ) $ 7,146 $ (139 ) $ (26,115 ) $ (50,228 ) Year Ended December 31, 2017 Pension Plans Unrealized Gains (Losses) on Securities Unrealized Gains (Losses) on Derivatives Net Prior Net Gain (Loss) Total Beginning balance, net of tax $ (23,708 ) $ 4,595 $ (133 ) $ (19,247 ) $ (38,493 ) Other comprehensive (loss) income: Other comprehensive income (loss) before reclassifications 15,217 276 8 (5,218 ) 10,283 Reclassified from accumulated other comprehensive income 630 754 (8 ) 1,613 2,989 Income tax (expense) benefit (5,546 ) (360 ) — 532 (5,374 ) Net current-period other comprehensive income (loss), net of tax 10,301 670 — (3,073 ) 7,898 Reclassification of certain deferred tax effects (2) (2,888 ) 1,134 — (3,949 ) (5,703 ) Ending balance, net of tax $ (16,295 ) $ 6,399 $ (133 ) $ (26,269 ) $ (36,298 ) (1) As discussed in “Note 1 – Summary of Significant Accounting and Reporting Policies,” 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). (2) Amounts reclassified to retained earnings due to early adoption of ASU 2018-02. See “Note 1 – Summary of Significant Accounting and Reporting Policies” for further information. Year Ended December 31, 2016 Pension Plans Unrealized Gains (Losses) on Securities Unrealized Gains (Losses) on Derivatives Net Prior Net Gain (Loss) Total Beginning balance, net of tax $ (239 ) $ — $ (44 ) $ (18,400 ) $ (18,683 ) Other comprehensive (loss) income: Other comprehensive (loss) income before reclassifications (33,699 ) 5,255 (129 ) (3,132 ) (31,705 ) Reclassified from accumulated other comprehensive income (2,407 ) 1,815 (8 ) 1,828 1,228 Income tax benefit (expense) 12,637 (2,475 ) 48 457 10,667 Net current-period other comprehensive (loss) income, net of tax (23,469 ) 4,595 (89 ) (847 ) (19,810 ) Ending balance, net of tax $ (23,708 ) $ 4,595 $ (133 ) $ (19,247 ) $ (38,493 ) The reclassifications out of accumulated other comprehensive (loss) income into net income are presented below (in thousands): Year Ended December 31, 2018 2017 2016 Unrealized losses on securities transferred: Amortization of unrealized losses (1) $ (1,244 ) $ (1,255 ) $ (429 ) Tax benefit 261 439 150 Net of tax $ (983 ) $ (816 ) $ (279 ) Unrealized gains and losses on available for sale securities: Realized net (loss) gain on sale of securities (2) $ (1,839 ) $ 625 $ 2,836 Tax benefit (expense) 386 (219 ) (993 ) Net of tax $ (1,453 ) $ 406 $ 1,843 Derivatives: Realized net gain (loss) on interest rate swap derivatives (3) $ 1,319 $ (828 ) $ (1,815 ) Tax (expense) benefit (277 ) 290 635 Net of tax $ 1,042 $ (538 ) $ (1,180 ) Amortization of unrealized gains on terminated interest rate swap derivatives (3) $ 87 $ 74 $ — Tax expense (18 ) (26 ) — Net of tax $ 69 $ 48 $ — Amortization of pension plan: Net actuarial loss (4) $ (2,189 ) $ (1,613 ) $ (1,828 ) Prior service credit (4) 7 8 8 Total before tax (2,182 ) (1,605 ) (1,820 ) Tax benefit 459 562 637 Net of tax $ (1,723 ) $ (1,043 ) $ (1,183 ) Total reclassifications for the period, net of tax $ (3,048 ) $ (1,943 ) $ (799 ) (1) Included in interest income on the consolidated statements of income. (2) Listed as net (loss) gain 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 11 - Employee Benefits.”

SECURITIES

SECURITIES	12 Months Ended
	Dec. 31, 2018
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 December 31, 2018 and 2017 are reflected in the tables below (in thousands): 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 December 31, 2017 Amortized Gross Unrealized Gross Unrealized Estimated AVAILABLE FOR SALE Cost Gains Losses Fair Value Investment Securities: U.S. Government Agency Debentures $ 108,869 $ — $ — $ 108,869 State and Political Subdivisions 392,760 3,895 3,991 392,664 Other Stocks and Bonds 5,024 31 — 5,055 Other Equity Securities (2) 6,027 — 107 5,920 Mortgage-backed Securities: (1) Residential 720,930 4,476 7,377 718,029 Commercial 308,357 761 900 308,218 Total $ 1,541,967 $ 9,163 $ 12,375 $ 1,538,755 HELD TO MATURITY Investment Securities: State and Political Subdivisions $ 413,632 $ 10,879 $ 2,583 $ 421,928 Mortgage-backed Securities: (1) Residential 129,044 1,631 239 130,436 Commercial 366,830 3,812 1,206 369,436 Total $ 909,506 $ 16,322 $ 4,028 $ 921,800 (1) All mortgage-backed securities issued and/or guaranteed by U.S. government agencies or U.S. government-sponsored enterprises. (2) See “Note 1 - Summary of Significant Accounting and Reporting Policies” for further information. 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 $15.3 million ( $12.1 million , net of tax) at December 31, 2018 and $17.4 million ( $13.8 million , net of tax) at December 31, 2017 . 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 years ended December 31, 2018 or 2017 . On January 1, 2018, we early-adopted ASU 2017-12, “Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities,” and in conjunction with the adoption took the one-time transition election to reclassify approximately $743.4 million book value of securities from HTM to AFS that qualified for hedging under the last-of-layer approach. The unrealized gain of $11.9 million ( $9.4 million , net of tax) on the transferred securities was recognized in other comprehensive income on the date of transfer. The following tables represent the estimated fair value and unrealized loss on investment and mortgage-backed securities AFS and HTM as of December 31, 2018 and December 31, 2017 (in thousands): December 31, 2018 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 $ 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 December 31, 2017 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 $ 32,341 $ 121 $ 172,006 $ 3,870 $ 204,347 $ 3,991 Other Equity Securities (1) 5,920 107 — — 5,920 107 Mortgage-backed Securities: Residential 429,742 3,232 102,973 4,145 532,715 7,377 Commercial 146,796 419 13,134 481 159,930 900 Total $ 614,799 $ 3,879 $ 288,113 $ 8,496 $ 902,912 $ 12,375 HELD TO MATURITY Investment Securities: State and Political Subdivisions $ 85,608 $ 807 $ 56,736 $ 1,776 $ 142,344 $ 2,583 Mortgage-backed Securities: Residential 24,707 157 2,736 82 27,443 239 Commercial 136,491 782 13,552 424 150,043 1,206 Total $ 246,806 $ 1,746 $ 73,024 $ 2,282 $ 319,830 $ 4,028 (1) See “Note 1 – Summary of Significant Accounting and Reporting Policies” for further information. 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 December 31, 2018 . 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 December 31, 2018 . The following tables reflect interest income recognized on securities for the periods presented (in thousands): Years Ended December 31, 2018 2017 2016 U.S. Treasury $ 218 $ 519 $ 739 U.S. Government Agency Debentures 89 178 — State and Political Subdivisions 24,960 24,530 22,654 Other Stocks and Bonds 110 125 195 Other Equity Securities (1) — 116 123 Mortgage-backed Securities 41,584 41,361 37,450 Total interest income on securities $ 66,961 $ 66,829 $ 61,161 (1) See “Note 1 - Summary of Significant Accounting and Reporting Policies” for further information. Of the $1.8 million in net securities loss from the AFS portfolio for the year ended December 31, 2018 , there were $3.8 million in realized loss position and $2.0 million in a realized gain position. Of the $625,000 in net securities gains from the AFS portfolio for the year ended December 31, 2017 , there were $5.0 million in realized gain position and $4.4 million in realized loss position. Of the $2.8 million in net securities gains from the AFS portfolio for the year ended December 31, 2016 , there were $6.3 million in a realized gain position and $3.4 million in a realized loss position. There were no sales from the HTM portfolio during the years ended December 31, 2018 , 2017 or 2016 . 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 December 31, 2018 , 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. December 31, 2018 Amortized Cost Fair Value AVAILABLE FOR SALE Investment Securities: Due in one year or less $ 3,559 $ 3,602 Due after one year through five years 39,169 40,055 Due after five years through ten years 176,316 175,181 Due after ten years 512,098 500,472 731,142 719,310 Mortgage-backed Securities 1,282,343 1,270,126 Total $ 2,013,485 $ 1,989,436 December 31, 2018 Amortized Cost Fair Value HELD TO MATURITY Investment Securities: Due in one year or less $ 116 $ 115 Due after one year through five years 1,696 1,674 Due after five years through ten years 1,271 1,257 Due after ten years — — 3,083 3,046 Mortgage-backed Securities: 159,848 156,735 Total $ 162,931 $ 159,781 Investment securities and MBS with carrying values of $1.08 billion and $1.24 billion were pledged as of December 31, 2018 and 2017 , 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 sheet include Community Reinvestment Act funds with a readily determinable fair value as well as equity investments without readily determinable fair values. At December 31, 2018 , we had equity investments recorded in our consolidated balance sheet of $12.1 million . At December 31, 2017 , we had $5.8 million in equity investments without readily determinable fair values recorded at cost. Beginning January 1, 2018, upon adoption of ASU 2016-01, equity investments with readily determinable fair values are stated at fair value with realized and unrealized gains and losses reported in income. For periods prior to January 1, 2018, these equity investments were classified as AFS and stated at fair value with unrealized gains and losses reported as a separate component of AOCI, net of tax. Equity investments without readily determinable fair values are recorded at cost less impairment, if any. At December 31, 2017, we had $5.9 million in equity investments included in AFS securities and recorded at fair value, with net unrealized losses of $85,000 , net of tax, recognized in AOCI. On January 1, 2018, these unrealized losses were reclassified out of AOCI and into retained earnings with subsequent changes in fair value being recognized in net income. 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 year ended December 31, 2018 (in thousands): Year Ended December 31, 2018 Net losses recognized during the period on equity investments $ (117 ) Less: Net gains (losses) recognized during the period on equity investments sold during the period — Unrealized losses recognized during the reporting period on equity investments still held at the reporting date $ (117 ) 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 December 31, 2018 . 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	12 Months Ended
	Dec. 31, 2018
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): December 31, 2018 December 31, 2017 Real Estate Loans: Construction $ 507,732 $ 475,867 1-4 Family Residential 794,499 805,341 Commercial 1,194,118 1,265,159 Commercial Loans 356,649 266,422 Municipal Loans 353,370 345,798 Loans to Individuals 106,431 135,769 Total Loans 3,312,799 3,294,356 Less: Allowance for Loan Losses (1) 27,019 20,781 Net Loans $ 3,285,780 $ 3,273,575 (1) Loans acquired with the Diboll acquisition were measured at fair value on November 30, 2017 , with no carryover of allowance for loan loss. The allowance for loan loss recorded on PCI loans totaled $302,000 as of December 31, 2018 . There was no allowance for loan loss recorded on PCI loans as of December 31, 2017 . Loans to Affiliated Parties In the normal course of business, we make loans to certain of our executive officers and directors and their related interests. As of December 31, 2018 and 2017 , these loans totaled $4.0 million and $5.5 million , respectively. These loans represented 0.6% and 0.7% of shareholders’ equity as of December 31, 2018 and 2017 , 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 December 31, 2018 consisted of $1.13 billion of owner and non-owner occupied real estate, $49.2 million of loans secured by multi-family properties and $15.8 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. 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 review we determine it is probable that 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): Year Ended December 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) (72 ) 1,134 3,894 2,392 (335 ) 1,424 8,437 Loans charged off (14 ) (91 ) (783 ) (756 ) — (2,602 ) (4,246 ) Recoveries of loans charged off 7 356 36 244 — 1,404 2,047 Balance at end of period $ 3,597 $ 3,844 $ 13,968 $ 3,974 $ 525 $ 1,111 $ 27,019 Year Ended December 31, 2017 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans Municipal Loans Loans to Individuals Total Balance at beginning of period $ 4,147 $ 2,665 $ 7,204 $ 2,263 $ 750 $ 882 $ 17,911 Provision (reversal) for loan losses (2) (437 ) 65 3,604 242 110 1,091 4,675 Loans charged off (35 ) (304 ) — (723 ) — (2,391 ) (3,453 ) Recoveries of loans charged off 1 19 13 312 — 1,303 1,648 Balance at end of period (1) $ 3,676 $ 2,445 $ 10,821 $ 2,094 $ 860 $ 885 $ 20,781 Year Ended December 31, 2016 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans (3) Municipal Loans Loans to Individuals Total Balance at beginning of period $ 4,350 $ 2,595 $ 4,577 $ 6,596 $ 725 $ 893 $ 19,736 Provision (reversal) for loan losses (2) (472 ) (28 ) 2,604 6,397 (224 ) 1,503 9,780 Loans charged off (3) — (43 ) — (11,396 ) — (2,948 ) (14,387 ) Recoveries of loans charged off 269 141 23 666 249 1,434 2,782 Balance at end of period $ 4,147 $ 2,665 $ 7,204 $ 2,263 $ 750 $ 882 $ 17,911 (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 $8.4 million in provision for loan losses for the year ended December 31, 2018 , $302,000 related to provision expense on PCI loans. Of the $4.7 million and $9.8 million recorded in provision for loan losses for the year ended December 31, 2017 and 2016 , respectively, none related to provision expense on PCI loans. (3) Of the $11.4 million in commercial charge-offs recorded for the year ended December 31, 2016 , $10.9 million relates to the charge-off of two large commercial borrowing relationships. The following tables present the balance in the allowance for loan losses by portfolio segment based on impairment method (in thousands): 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 December 31, 2017 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans Municipal Loans Loans to Individuals Total Ending balance – individually evaluated for impairment (1) $ 12 $ 14 $ 14 $ 252 $ 10 $ 51 $ 353 Ending balance – collectively evaluated for impairment 3,664 2,431 10,807 1,842 850 834 20,428 Balance at end of period $ 3,676 $ 2,445 $ 10,821 $ 2,094 $ 860 $ 885 $ 20,781 (1) The allowance for loan loss on PCI loans totaled $302,000 as of December 31, 2018 . There was no allowance for loan losses associated with PCI loans as of December 31, 2017 . The following tables present the recorded investment in loans by portfolio segment based on impairment method (in thousands): 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 (1) 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 December 31, 2017 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans Municipal Loans Loans to Individuals Total Loans individually evaluated for impairment $ 86 $ 1,581 $ 895 $ 1,429 $ 502 $ 205 $ 4,698 Loans collectively evaluated for impairment 475,505 797,111 1,232,327 259,745 345,296 134,441 3,244,425 Purchased credit impaired loans 276 6,649 31,937 5,248 — 1,123 45,233 Total ending loan balance $ 475,867 $ 805,341 $ 1,265,159 $ 266,422 $ 345,798 $ 135,769 $ 3,294,356 (1) At December 31, 2018 , PCI totals include approximately $14.0 million in new funds to a borrower that has since been upgraded to a Pass credit. The following tables set forth credit quality indicators by class of loans for the periods presented (in thousands): 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 December 31, 2017 Pass Pass Watch (1) Special Mention (1) Substandard (1) Doubtful (1) Total Real Estate Loans: Construction $ 471,446 $ 3,329 $ 77 $ 982 $ 33 $ 475,867 1-4 Family Residential 796,639 559 857 6,610 676 805,341 Commercial 1,136,576 26,275 25,301 76,625 382 1,265,159 Commercial Loans 247,430 9,625 3,956 5,203 208 266,422 Municipal Loans 344,366 — 930 502 — 345,798 Loans to Individuals 134,694 20 102 707 246 135,769 Total $ 3,131,151 $ 39,808 $ 31,223 $ 90,629 $ 1,545 $ 3,294,356 (1) 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 . Includes PCI loans comprised of $362,000 pass watch, $6.0 million special mention, $10.5 million substandard and $925,000 doubtful as of December 31, 2017 . 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): December 31, 2018 December 31, 2017 Nonaccrual loans (1) (2) $ 35,770 $ 2,937 Accruing loans past due more than 90 days (1) — 1 Restructured loans (3) 5,930 5,767 Other real estate owned 1,206 1,613 Repossessed assets — 154 Total Nonperforming Assets $ 42,906 $ 10,472 (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. The increase in nonaccrual loans was primarily due to the addition of four commercial real estate loans to nonaccrual status during the year, one of which was added during the fourth quarter . (2) Includes $10.9 million and $1.3 million of restructured loans as of December 31, 2018 and 2017 , respectively. (3) Includes $3.1 million and $2.9 million in PCI loans restructured as of December 31, 2018 and 2017 , 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 $147,000 and $154,000 in loans secured by 1-4 family residential properties for which formal foreclosure proceedings were in process as of December 31, 2018 and December 31, 2017 , 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 December 31, 2018 December 31, 2017 Real Estate Loans: Construction $ 12 $ 86 1-4 Family Residential 2,202 1,098 Commercial 32,599 595 Commercial Loans 639 903 Loans to Individuals 318 255 Total $ 35,770 $ 2,937 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 for the years ended December 31, 2018 or 2017 . 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 December 31, 2017 Unpaid Contractual Principal Balance Recorded Related Allowance for Loan Losses Real Estate Loans: Construction $ 91 $ 86 $ 12 1-4 Family Residential 4,141 3,952 14 Commercial 1,353 1,199 14 Commercial Loans 1,665 1,605 252 Municipal Loans 502 502 10 Loans to Individuals 237 205 51 Total (1) $ 7,989 $ 7,549 $ 353 (1) Includes $8.0 million and $2.9 million of PCI loans that experienced deterioration in credit quality subsequent to the acquisition date as of December 31, 2018 and December 31, 2017 , respectively. The following tables present the aging of the recorded investment in past due loans by class of loans (in thousands): 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 December 31, 2017 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 $ 1,302 $ 1,530 $ 68 $ 2,900 $ 472,967 $ 475,867 1-4 Family Residential 8,508 1,574 862 10,944 794,397 805,341 Commercial 1,357 24 5 1,386 1,263,773 1,265,159 Commercial Loans 662 400 333 1,395 265,027 266,422 Municipal Loans 422 — — 422 345,376 345,798 Loans to Individuals 1,526 373 93 1,992 133,777 135,769 Total $ 13,777 $ 3,901 $ 1,361 $ 19,039 $ 3,275,317 $ 3,294,356 (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: Years Ended December 31, 2018 2017 2016 Average Recorded Investment Interest Income Recognized Average Recorded Investment Interest Income Recognized Average Recorded Investment Interest Income Recognized Real Estate Loans: Construction $ 149 $ 7 $ 251 $ — $ 510 $ 22 1-4 Family Residential 4,193 208 4,264 197 3,247 169 Commercial 26,186 65 1,338 30 4,490 63 Commercial Loans 2,131 102 2,862 59 13,481 48 Municipal Loans 474 26 545 30 612 33 Loans to Individuals 250 9 244 9 257 9 Total $ 33,383 $ 417 $ 9,504 $ 325 $ 22,597 $ 344 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 during the periods presented (dollars in thousands): December 31, 2018 Extend Amortization Period Interest Rate Reductions Combination Total Modifications Number of Contracts Real Estate Loans: 1-4 Family Residential $ — $ 79 $ — $ 79 1 Commercial 10,398 — 274 10,672 3 Commercial Loans 211 — 215 426 13 Loans to Individuals 8 33 51 92 5 Total $ 10,617 $ 112 $ 540 $ 11,269 22 December 31, 2017 Extend Amortization Period Interest Rate Reductions Combination Total Modifications Number of Contracts Commercial Loans $ 778 $ — $ 241 $ 1,019 4 Loans to Individuals 23 — 52 75 6 Total $ 801 $ — $ 293 $ 1,094 10 The majority of loans restructured as TDRs during the year ended December 31, 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 year ended December 31, 2018 and 2017 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 years ended December 31, 2018 and 2017 , there were $216,000 and $138,000 , respectively, of TDRs in default. Payment defaults for TDRs did not significantly impact the determination of the allowance for loan loss in either period presented. At December 31, 2018 and 2017 , 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): December 31, 2018 December 31, 2017 Outstanding principal balance (1) $ 51,388 $ 52,426 Carrying amount (1) $ 46,402 $ 45,233 (1) At December 31, 2018 , PCI totals include approximately $14.0 million in new funds to a borrower that has since been upgraded to a Pass credit. The following table presents the changes in the accretable yield during the periods fo

PREMISES AND EQUIPMENT

PREMISES AND EQUIPMENT	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
PREMISES AND EQUIPMENT	PREMISES AND EQUIPMENT December 31, 2018 December 31, 2017 (in thousands) Premises $ 166,128 $ 158,817 Furniture and equipment 41,810 40,565 207,938 199,382 Less: accumulated depreciation 71,966 65,742 Total $ 135,972 $ 133,640 Assets with accumulated depreciation of $2.2 million and $915,000 were written off for the years ended December 31, 2018 and 2017 , respectively. Depreciation expense was $8.4 million , $8.1 million and $8.0 million for the years ended December 31, 2018 , 2017 and 2016 , respectively.

DEPOSITS

DEPOSITS	12 Months Ended
	Dec. 31, 2018
Deposits [Abstract]
DEPOSITS	DEPOSITS December 31, 2018 December 31, 2017 (in thousands) Noninterest bearing demand deposits: Private accounts $ 967,096 $ 995,685 Public accounts 27,584 41,716 Total noninterest bearing demand deposits 994,680 1,037,401 Interest bearing deposits: Private accounts: Savings deposits 360,007 356,857 Money market demand deposits 440,442 443,015 Platinum money market deposits 344,546 308,105 Interest bearing checking 662,911 686,816 NOW demand deposits 23,451 20,142 Certificates and other time deposits of $250,000 or more 84,564 87,195 Certificates and other time deposits under $250,000 680,282 534,220 Total private accounts 2,596,203 2,436,350 Public accounts: Savings deposits 320 304 Money market demand deposits 15,513 19,560 Platinum money market deposits 329,695 360,006 Interest bearing checking 56,694 55,902 NOW demand deposits 141,200 114,401 Certificates and other time deposits of $250,000 or more 281,204 462,941 Certificates and other time deposits under $250,000 9,521 28,582 Total public accounts 834,147 1,041,696 Total interest bearing deposits 3,430,350 3,478,046 Total deposits $ 4,425,030 $ 4,515,447 For the years ended December 31, 2018 , 2017 and 2016 , interest expense on time deposits of $250,000 or more was $8.5 million , $5.0 million and $3.2 million , respectively. At December 31, 2018 , the scheduled maturities of certificates and other time deposits, including public accounts, were as follows (in thousands): 2019 $ 845,661 2020 116,542 2021 42,254 2022 20,003 2023 25,931 2024 and thereafter 5,180 $ 1,055,571 At December 31, 2018 , we had $238.1 million in brokered certificates of deposit (“CDs”) that represented 5.4% of our deposits. Our brokered CDs had a weighted average cost of 223 basis points with maturities of less than one year . These brokered CDs are reflected in the CDs under $250,000 category. At December 31, 2017 , we had $60.2 million in brokered CDs. We utilized brokered CDs, because they better matched overall ALCO objectives at the time of issuance. Our current policy allows for a maximum of $300 million in brokered CDs. At December 31, 2018 and 2017 , we had approximately $16.2 million and $31.7 million , respectively, in deposits from related parties, including directors and named executive officers. The aggregate amount of demand deposit overdrafts that have been reclassified as loans were $1.6 million and $1.3 million at December 31, 2018 and 2017 , respectively.

BORROWING ARRANGEMENTS

BORROWING ARRANGEMENTS	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
BORROWING ARRANGEMENTS	BORROWING ARRANGEMENTS Information related to borrowings is provided in the table below (dollars in thousands): December 31, 2018 December 31, 2017 Federal funds purchased and repurchase agreements: Balance at end of period $ 36,810 $ 9,498 Average amount outstanding during the period (1) 10,880 8,120 Maximum amount outstanding during the period (2) 36,810 9,498 Weighted average interest rate during the period (3) 1.4 % 0.2 % Interest rate at end of period (4) 2.1 % 0.2 % FHLB borrowings: Balance at end of period $ 719,065 $ 1,017,361 Average amount outstanding during the period (1) 720,785 1,222,033 Maximum amount outstanding during the period (2) 957,231 1,414,453 Weighted average interest rate during the period (3) 1.8 % 1.2 % Interest rate at end of period (4) 2.3 % 1.4 % (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 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 December 31, 2018 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 $ 36,686 $ 124 $ — $ — $ — $ — $ 36,810 FHLB borrowings 336,502 365,165 11,483 — — 5,915 719,065 Total obligations $ 373,188 $ 365,289 $ 11,483 $ — $ — $ 5,915 $ 755,875 FHLB borrowings represent borrowings with fixed and floating interest rates ranging from 1.37% to 4.799% and with remaining maturities of overnight to 9.5 years at December 31, 2018. FHLB borrowings may be collateralized by FHLB stock, nonspecified loans and/or securities. From time to time, the Company may enter into various variable rate advance agreements with the FHLB. These advance agreements totaled $310.0 million at December 31, 2018 and $280.0 million December 31, 2017 . Two of the variable rate advance agreements have interest rates of three-month LIBOR plus 0.021% , and one has an interest rate of three-month LIBOR minus 0.003% . The remaining variable rate advance agreements have interest rates ranging from one-month LIBOR plus 0.072% to one-month LIBOR plus 0.164% . In connection with obtaining these variable rate advance agreements, the Company also entered into various interest rate swap contracts that are treated as cash flow hedges under ASC Topic 815, “Derivatives and Hedging” that effectively converted the variable rate advance agreements to fixed interest rates ranging from 0.932% to 2.833% and original terms ranging from four years to ten years. The cash flows from the swaps are expected to be effective in hedging the variability in future cash flows attributable to fluctuations in the one-month and three-month LIBOR interest rates. During the first quarter of 2017 , we terminated two interest rate swap contracts designated as cash flow hedges having a total notional value of $40.0 million . At the time of termination, we determined that the underlying hedged forecasted transactions were still probable of occurring. 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. Refer to “Note 12 - 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 $28.0 million federal funds purchased at December 31, 2018 . There were no federal funds purchased at December 31, 2017 . Southside Bank has a $5.0 million line of credit with Frost Bank to be used to issue letters of credit, and at December 31, 2018 , we had one outstanding letter of credit for $195,000 . At December 31, 2018 , the amount of additional funding Southside Bank could obtain from FHLB, collateralized by securities, FHLB stock and nonspecified loans, was approximately $1.17 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 $8.8 million and $9.5 million at December 31, 2018 and 2017 , 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 OBLIGATIONS

LONG-TERM OBLIGATIONS	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
LONG-TERM OBLIGATIONS	LONG-TERM DEBT December 31, 2018 December 31, (in thousands) Subordinated notes: (1) 5.50% Subordinated Notes, net of unamortized debt issuance costs (2) $ 98,407 $ 98,248 Total Subordinated notes 98,407 98,248 Trust preferred subordinated debentures: (3) Southside Statutory Trust III, net of unamortized debt issuance costs (4) 20,554 20,549 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 60,246 60,241 Total Long-term debt $ 158,653 $ 158,489 (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 December 31, 2018 and $1.8 million at December 31, 2017 . (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 $65,000 at December 31, 2018 and $70,000 at December 31, 2017 . As of December 31, 2018 , 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 BENEFITS

EMPLOYEE BENEFITS	12 Months Ended
	Dec. 31, 2018
Employee Benefits Including Defined Benefit Plans and Share-based Compensation Plans [Abstract]
EMPLOYEE BENEFITS	EMPLOYEE BENEFITS Deferred Compensation Agreements Southside Bank has deferred compensation agreements with 17 of its executive officers, which generally provide for payment of an aggregate amount of $6.9 million over a maximum period of 15 years after retirement or death. Of the 17 executives included in the agreements, payments have commenced to nine former executives and/or their beneficiaries. Three executive officers became eligible to receive payments in 2016 as a result of the acceptance of an early retirement package offered in late December of 2015. Deferred compensation expense was $201,000 , $353,000 and $357,000 for the years ended December 31, 2018 , 2017 and 2016 , respectively. At December 31, 2018 and 2017 , the deferred compensation plan liability totaled $3.4 million and $3.5 million , respectively. Health Insurance We provide accident and health insurance for substantially all employees through a self-funded insurance program. The cost of health care benefits was $6.5 million , $5.6 million and $4.9 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. Our healthcare plan was amended to provide health insurance coverage for any retiree having 50 years of service with the Company. In addition, the eligible retiree must have Medicare coverage, including part A, part B and part D. There was one retiree participating in the health insurance plan as of December 31, 2018 . There were two retirees participating in the health insurance plan as of December 31, 2017 and 2016 . Employee Stock Ownership Plan We have an Employee Stock Ownership Plan (the “ESOP”) which covers substantially all employees. Contributions to the ESOP are at the sole discretion of the board of directors. We contributed $700,000 to the ESOP for the year ended December 31, 2018 and $350,000 for the years ended December 31, 2017 and 2016 . At December 31, 2018 and 2017 , the ESOP owned 277,492 and 280,542 shares of common stock, respectively. The number of shares has been adjusted as a result of stock dividends. These shares are treated as externally held shares for dividend and earnings per share calculations. Long-term Disability We have an officer’s long-term disability income policy which provides coverage in the event they become disabled as defined under its terms. Individuals are automatically covered under the policy if they (a) have been elected as an officer, (b) have been an employee of Southside Bank for three years and (c) receive earnings of $50,000 or more on an annual basis. The policy provides, among other things, that should a covered individual become totally disabled he would receive two-thirds of his current salary, not to exceed $15,000 per month. The benefits paid out of the policy are limited by the benefits paid to the individual under the terms of our other Company-sponsored benefit plans. Split Dollar Agreements We originally entered into split dollar agreements with eight of our executive officers. The agreements provide we will be the beneficiary of bank owned life insurance (“BOLI”) insuring the executives’ lives. The agreements provide the executives the right to designate the beneficiaries of the death benefits guaranteed in each agreement. The agreements originally provided for death benefits of an initial aggregate amount of $4.5 million . Prior to an executive’s retirement, his individual amount is increased annually on the anniversary date of the agreement by inflation adjustment factors of either 3% or 5% . As of December 31, 2018 , three of the executives remain actively employed with us. Death benefits under this agreement were paid during 2018 for one retired covered officer and during 2013 for one active covered officer. As of December 31, 2018 , the estimated death benefits for the six executives total $4.1 million . The agreements also state that after the executive’s retirement, we shall also pay an annual gross-up bonus to the executive in an amount sufficient to enable the executive to pay federal income tax on both the economic benefit and on the gross-up bonus. The expense required to record the post retirement liability associated with the split dollar post retirement bonuses was $172,000 for the year ended December 31, 2016 , and a credit to expense of $250,000 and $3,000 for the years ended December 31, 2018 and 2017 , respectively. For the years ended December 31, 2018 and 2017 , the split dollar liability totaled $1.4 million and $1.9 million , respectively. 401(k) Plan We have a 401(k) defined contribution plan (the “401(k) Plan”) covering substantially all employees that permits each participant to make before- or after-tax contributions subject to certain limits imposed by the Internal Revenue Code. Beginning January 1, 2017, eligible employees may participate in the 401(k) Plan after they have worked at least 30 days with the Company. For the years ended December 31, 2018 , 2017 and 2016 , expense attributable to the 401(k) Plan amounted to $1.5 million , $613,000 and $562,000 , respectively. Pension Plans We have a defined benefit pension plan (the “Plan”) pursuant to which participants are entitled to benefits based on final average monthly compensation and years of credited service determined in accordance with plan provisions. Entrance into the Plan by new employees was frozen effective December 31, 2005. Employees hired after December 31, 2005 are not eligible to participate in the Plan. All participants in the Plan are fully vested. Benefits are payable monthly commencing on the later of age 65 or the participant’s date of retirement. Eligible participants may retire at reduced benefit levels after reaching age 55 . We contribute amounts to the pension fund sufficient to satisfy funding requirements of the Employee Retirement Income Security Act. Plan assets included 240,666 shares of our stock at December 31, 2018 and 2017 . Our stock included in the Plan assets was purchased at fair value. The number of shares has been adjusted as a result of stock dividends, if applicable. During 2018 , our funded status improved and at December 31, 2018 , we had an unfunded status of $1.1 million compared to an unfunded status of $3.0 million at December 31, 2017 . The improvement was a result of an increase in the discount rate at December 31, 2018 compared to December 31, 2017 to better reflect current market conditions, contributions to the plan since December 31, 2017 and the updated mortality assumption at December 31, 2018 compared to December 31, 2017 , partially offset by a less than expected return on the fair value of plan assets since December 31, 2017 . In late December 2015, we offered an early retirement package to 24 of our employees, of which 16 accepted the early retirement offer by the acceptance deadline of January 29, 2016. During 2016, the Plan provided special and contractual termination benefits of $1.5 million to 15 employees that accepted an early retirement package during the year ended December 31, 2016. In connection with the acquisition of Omni, we acquired the OmniAmerican Bank Defined Benefit Plan (the “Acquired Plan”) which was remeasured at fair value. The Acquired Plan originally called for benefits to be paid to eligible employees at retirement based primarily upon years of service and the compensation levels at retirement. As of December 31, 2006, the benefits under the Acquired Plan were frozen by Omni. No further benefits will be earned by employees after that date. In addition, no new participants may be added to the Acquired Plan after December 31, 2006. During 2018 , our funded status improved, and at December 31, 2018 , we had a funded status of $197,000 compared to an unfunded status of $361,000 at December 31, 2017 . The improvement was a result of an increase in the discount rate at December 31, 2018 compared to December 31, 2017 to better reflect the current market conditions, contributions to the plan since December 31, 2017 and the updated mortality assumption at December 31, 2018 compared to December 31, 2017 , partially offset by a less than expected return on the fair value of plan assets since December 31, 2017 . We have a nonfunded supplemental retirement plan (the “Restoration Plan”) for our employees whose benefits under the principal retirement plan are reduced because of compensation deferral elections or limitations under federal tax laws. Both the Plan and the Restoration Plan were amended effective January 1, 2013 to change the formula for determining death benefits for participants who die while in service of the employer and who are early retirement eligible on their date of death. We use a measurement date of December 31 for our plans. Year Ended December 31, 2018 2017 2016 Defined Benefit Pension Plan Defined Restoration Plan Defined Benefit Pension Plan Defined Restoration Plan Defined Benefit Pension Plan Defined Restoration Plan (in thousands) Change in Projected Benefit Obligation: Benefit obligation at end of prior year $ 94,276 $ 4,392 $ 14,642 $ 88,071 $ 4,238 $ 12,723 $ 80,040 $ 4,685 $ 12,024 Service cost 1,548 — 293 1,398 — 247 1,375 — 207 Interest cost 3,392 163 597 3,601 177 567 3,731 212 535 Actuarial (gain) loss (9,399 ) (480 ) 344 5,404 418 1,751 4,978 275 237 Benefits paid (3,622 ) (183 ) (576 ) (4,128 ) (43 ) (646 ) (3,632 ) (31 ) (280 ) Expenses paid (203 ) (19 ) — (70 ) (47 ) — (91 ) (39 ) — Plan amendments — — — — — — 121 — — Settlements — — — — (351 ) — — (864 ) — Special and contractual termination benefits — — — — — — 1,549 — — Benefit obligation at end of year 85,992 3,873 15,300 94,276 4,392 14,642 88,071 4,238 12,723 Change in Plan Assets: Fair value of plan assets at end of prior year 91,233 4,031 — 85,293 2,993 — 76,355 3,740 — Actual return (4,497 ) (259 ) — 8,138 479 — 7,661 187 — Employer contributions 2,000 500 576 2,000 1,000 646 5,000 — 280 Benefits paid (3,622 ) (183 ) (576 ) (4,128 ) (43 ) (646 ) (3,632 ) (31 ) (280 ) Expenses paid (203 ) (19 ) — (70 ) (47 ) — (91 ) (39 ) — Settlements — — — — (351 ) — — (864 ) — Fair value of plan assets at end of year 84,911 4,070 — 91,233 4,031 — 85,293 2,993 — (Un)Funded status at end of year (1,081 ) 197 (15,300 ) (3,043 ) (361 ) (14,642 ) (2,778 ) (1,245 ) (12,723 ) Accrued benefit (liability) asset recognized $ (1,081 ) $ 197 $ (15,300 ) $ (3,043 ) $ (361 ) $ (14,642 ) $ (2,778 ) $ (1,245 ) $ (12,723 ) Accumulated benefit obligation at end of year $ 77,888 $ 3,873 $ 13,403 $ 83,802 $ 4,392 $ 13,246 $ 77,639 $ 4,238 $ 11,133 Amounts related to our defined benefit pension plans and restoration plan recognized as a component of other comprehensive (loss) income were as follows (in thousands): Year Ended December 31, 2018 2017 2016 Defined Defined Restoration Defined Defined Restoration Defined Defined Restoration Recognition of net loss $ 1,512 $ — $ 677 $ 1,312 $ — $ 301 $ 1,642 $ — $ 186 Recognition of prior service (credit) cost (14 ) — 7 (14 ) — 6 (14 ) — 6 Recognition of loss (gain) due to settlement — — — — 8 — — (8 ) — Net (loss) gain occurring during the year (1,581 ) (69 ) (344 ) (3,317 ) (150 ) (1,751 ) (2,541 ) (354 ) (237 ) Net prior service cost occurring during the year — — — — — — (121 ) — — (83 ) (69 ) 340 (2,019 ) (142 ) (1,444 ) (1,034 ) (362 ) (45 ) Deferred tax benefit (expense) 17 14 (71 ) 241 30 259 362 127 16 Other comprehensive (loss) income, net of tax $ (66 ) $ (55 ) $ 269 $ (1,778 ) $ (112 ) $ (1,185 ) $ (672 ) $ (235 ) $ (29 ) Net amounts recognized in net periodic benefit cost and other comprehensive loss were as follows (in thousands): December 31, 2018 December 31, 2017 Defined Benefit Pension Plan Defined Restoration Plan Defined Defined Restoration Plan Net loss $ 1,512 $ — $ 677 $ 1,312 $ — $ 301 Prior service (credit) cost (14 ) — 7 (14 ) — 6 Loss (gain) recognized due to settlement — — — — 8 — 1,498 — 684 1,298 8 307 Deferred tax (expense) benefit (315 ) — (144 ) (454 ) (2 ) (107 ) Accumulated other comprehensive income (loss), net of tax $ 1,183 $ — $ 540 $ 844 $ 6 $ 200 Amounts recognized as a component of accumulated other comprehensive loss were as follows (in thousands): December 31, 2018 December 31, 2017 Defined Defined Restoration Defined Defined Restoration Net (loss) gain $ (28,928 ) $ (171 ) $ (3,984 ) $ (28,859 ) $ (102 ) $ (4,317 ) Prior service cost (123 ) — (24 ) (109 ) — (31 ) (29,051 ) (171 ) (4,008 ) (28,968 ) (102 ) (4,348 ) Deferred tax benefit (expense) 6,100 35 841 9,674 15 1,276 Reclassification of certain deferred tax effects (1) — — — (3,591 ) 6 (364 ) Accumulated other comprehensive (loss) income, net of tax $ (22,951 ) $ (136 ) $ (3,167 ) $ (22,885 ) $ (81 ) $ (3,436 ) (1) Amounts reclassified to retained earnings due to early adoption of ASU 2018-02. See “Note 1 – Summary of Significant Accounting and Reporting Policies” for further information. Net periodic pension cost and postretirement benefit cost included the following components (in thousands): Year Ended December 31, 2018 2017 2016 Defined Benefit Pension Plan: Service cost $ 1,548 $ 1,398 $ 1,375 Interest cost 3,392 3,601 3,731 Expected return on assets (6,483 ) (6,050 ) (5,224 ) Net loss amortization 1,512 1,312 1,642 Prior service credit amortization (14 ) (14 ) (14 ) Special and contractual termination benefits — — 1,549 Net periodic benefit cost $ (45 ) $ 247 $ 3,059 Defined Benefit Pension Plan Acquired: Service cost $ — $ — $ — Interest cost 163 177 212 Expected return on assets (290 ) (212 ) (265 ) Net loss amortization — — — Prior service credit amortization — — — Loss (gain) recognized due to settlement — 8 (8 ) Net periodic benefit cost $ (127 ) $ (27 ) $ (61 ) Restoration Plan: Service cost $ 293 $ 247 $ 207 Interest cost 597 567 535 Net loss amortization 677 301 186 Prior service cost amortization 7 6 6 Net periodic benefit cost $ 1,574 $ 1,121 $ 934 The amounts in accumulated other comprehensive income (loss) that are expected to be recognized as components of net periodic benefit cost during 2019 are as follows (in thousands): Defined Benefit Pension Plan Defined Restoration Net loss $ 1,774 $ — $ 398 Prior service (credit) cost (14 ) — 6 1,760 — 404 Deferred tax benefit (370 ) — (85 ) Accumulated other comprehensive loss, net of tax $ 1,390 $ — $ 319 The Plan and Acquired Plan assets, which consist primarily of marketable equity and debt instruments, are valued using market quotations in active markets for identical assets, market quotations for similar assets in active or non-active markets or the net asset value (“NAV”) provided by the plan administrator. The Plans’ obligations and the annual pension expense are determined by independent actuaries and through the use of a number of assumptions. Key assumptions in measuring the Plans’ obligations include the discount rate, the rate of salary increases and the estimated future return on plan assets. In determining the discount rate, we utilized a cash flow matching analysis to determine a range of appropriate discount rates for the defined benefit pension plan and restoration plan. In developing the cash flow matching analysis, we had our actuaries construct a portfolio of high quality noncallable bonds to match as closely as possible the timing of future benefit payments of the plans at December 31, 2018 . We utilized a bond selection-settlement approach that selects a portfolio of bonds from a universe of high quality corporate bonds rated AA by at least half of the rating agencies available. Based on the results of this cash flow matching analysis, we were able to determine an appropriate discount rate. Salary increase assumptions are based upon historical experience and anticipated future management actions. The expected long-term rate of return assumption reflects the average return expected based on the investment strategies and asset allocation of the assets invested to provide for the Plans’ liabilities. We considered broad equity and bond indices, long-term return projections and actual long-term historical Plan performance when evaluating the expected long-term rate of return assumption. The assumptions used to determine the benefit obligation were as follows: December 31, 2018 December 31, 2017 Defined Benefit Defined Restoration Defined Defined Restoration Discount rate 4.32 % 4.32 % 4.32 % 3.71 % 3.71 % 3.71 % Compensation increase rate 3.50 % — 3.50 % 3.50 % — 3.50 % The assumptions used to determine net periodic pension cost and postretirement benefit cost were as follows: Year Ended December 31, 2018 2017 2016 Defined Benefit Pension Plan: Discount rate 3.71 % 4.23 % 4.56 % Expected long-term rate of return on plan assets 7.25 % 7.25 % 7.25 % Compensation increase rate 3.50 % 3.50 % 3.50 % Defined Benefit Pension Plan Acquired Discount rate 3.71 % 4.23 % 4.56 % Expected long-term rate of return on plan assets 7.25 % 7.25 % 7.25 % Compensation increase rate — — — Restoration Plan: Discount rate 3.71 % 4.23 % 4.56 % Compensation increase rate 3.50 % 3.50 % 3.50 % Material changes in pension benefit costs may occur in the future due to changes in these assumptions. Future annual amounts could be impacted by changes in the number of SSB Plan participants, changes in the level of benefits provided, changes in the discount rates, changes in the expected long-term rate of return, changes in the level of contributions to the Plan and other factors. The major categories of assets in our Plan and the Acquired Plan are presented in the following table (in thousands). Assets are segregated by the level of the valuation inputs within the fair value hierarchy established by ASC Topic 820 “Fair Value Measurements and Disclosures,” utilized to measure fair value (see “Note 13 – Fair Value Measurement”). Our Restoration Plan is unfunded. December 31, 2018 December 31, 2017 Defined Defined Defined Defined Level 1: Cash $ 278 $ — $ 423 $ — Equity Securities: U.S. large cap (1) 5,204 — 6,198 — U.S. mid cap (2) 18,913 — 21,379 — U.S. small cap (3) 9,900 — 10,706 — Fixed Income Securities: International developed (4) 6,733 — 8,601 — International emerging (2) 3,464 — 4,308 — Level 2: Cash Equivalents 15,025 — 13,256 — Equity Securities: U.S. large cap (1) — 1,360 — 1,440 U.S. mid cap (2) — 152 — 167 U.S. small cap (3) — 72 — 84 International (5) — 735 — 712 Fixed Income Securities: Corporate bonds (6) 952 407 1,118 378 U.S. government agencies (6) 20,182 — 19,303 — Municipal bonds (6) 3,991 — 5,595 — U.S. agency mortgage-backed securities (7) 269 — 346 — Asset-backed securities (8) — 743 — 717 Real estate (9) — 286 — 241 Balanced Asset Allocation (10) — 84 — 81 Other (11) — 231 — 211 Total fair value of plan assets $ 84,911 $ 4,070 $ 91,233 $ 4,031 (1) For the defined benefit pension plan, this category is comprised of individual securities that are actively managed and a broadly diversified “passive” mutual fund. The Acquired Plan assets in this category consist of pooled separate accounts invested in mutual funds and domestic stocks. (2) For the defined benefit pension plan, this category is comprised of broadly diversified “passive” mutual funds. The Acquired Plan assets in this category consist of pooled separate accounts invested in mutual funds and domestic stocks. (3) For the defined benefit pension plan, this category is comprised of broadly diversified “passive” mutual funds and shares of Southside Bancshares stock that is owned in the Plan. The Acquired Plan assets in this category consist of pooled separate accounts invested in mutual funds and domestic stocks. (4) This category is comprised of individual securities that are actively managed and a broadly diversified “passive” mutual fund. (5) This category is comprised of pooled separate accounts invested in mutual funds and international stocks. (6) For the defined benefit pension plan, this category is comprised of individual investment grade securities that are generally held to maturity in the Plan. The Acquired Plan assets in this category consist of pooled separate accounts invested in investment grade and below investment grade bonds. (7) This category is comprised of individual securities that are generally not held to maturity. (8) This category is mainly comprised of a pooled separate account invested in asset backed securities, residential mortgage backed securities, commercial mortgage backed securities and corporate bonds. (9) This category is comprised of a pooled separate account invested in commercial real estate and includes mortgage loans which are backed by the associated properties. (10) This category is comprised of a pooled separate account invested in a single mutual fund invested in a combination of fixed income and equity investment options. (11) This category is comprised of a pooled separate account invested in a broad range of instruments including, but not limited to, equities, bonds, currencies, convertible securities and derivatives such as futures, options, swaps and forwards. We did not have any plan assets with Level 3 input fair value measurements at December 31, 2018 or 2017 . Our overall investment strategy is to realize long-term growth of the Plan within acceptable risk parameters, while funding benefit payments from dividend and interest income, to the extent possible. The target allocations for plan assets are 55.0% equities, 44.5% fixed income and 0.5% cash equivalents. Equity securities are diversified among U.S. and international (both developed and emerging), large, mid and small caps, value and growth securities and real estate investment trusts (“REITs”). The investment objective of equity funds is long-term capital appreciation with current income. Fixed income securities include government agencies, CDs, corporate bonds, municipal bonds and MBS. The investment objective of fixed income funds is to maximize investment return while preserving investment principal. Mutual funds are primarily used because of the superior diversification they provide. As of December 31, 2018 , expected future benefit payments related to the Plan, the Acquired Plan and the Restoration Plan were as follows (in thousands): Defined Benefit Pension Plan Defined Benefit Restoration 2019 $ 3,836 $ 66 $ 723 2020 3,951 229 780 2021 4,142 129 916 2022 4,354 90 1,031 2023 4,520 92 1,005 2024 through 2028 25,008 897 5,521 $ 45,811 $ 1,503 $ 9,976 We do no t expect to make additional contributions to the Plan, the Acquired Plan or the Restoration Plan in 2019 . Share-based Incentive Plans 2017 Incentive Plan On May 10, 2017, our shareholders approved the Southside Bancshares, Inc. 2017 Incentive Plan (the “2017 Incentive Plan”), which is a stock-based incentive compensation plan. A total of 2,460,000 shares of our common stock were reserved and available for issuance pursuant to awards granted under the 2017 Incentive Plan. This amount includes a number of additional shares (not to exceed 410,000 ) underlying awards outstanding as of May 10, 2017 under the Company’s 2009 Incentive Plan that thereafter terminate or expire unexercised, or are cancelled, forfeited or lapse for any reason. Under the 2017 Incentive Plan, we are authorized to grant stock options, stock appreciation rights, restricted stock, restricted stock units, performance awards and qualified performance-based awards or any combination thereof to selected employees, officers, directors and consultants of the Company and its affiliates. As of December 31, 2018 , there were 1,675,607 shares remaining available for grant for future awards. All share data for all periods presented has been adjusted to give retroactive recognition to stock dividends unless otherwise indicated. Reference to incentive plans refers to the 2017 Incentive Plan and predecessor incentive plans. As of December 31, 2018 , 2017 and 2016 , there were 612,740 , 366,292 and 599,498 unvested awards outstanding, respectively. For the years ended December 31, 2018 , 2017 and 2016 , there was $2.3 million , $1.8 million and $1.5 million of share-based compensation expense related to the incentive plans, respectively, and $487,000 , $635,000 and $539,000 of income tax benefit related to the stock compensation expense, respectively. As of December 31, 2018 , 2017 and 2016 , there was $5.8 million , $3.8 million and $5.6 million of unrecognized compensation cost related to the incentive plans, respectively. The remaining cost at December 31, 2018 is expected to be recognized over a weighted-average period of 2.79 years . The nonqualified stock options (“NQSOs”) have contractual terms of 10 years and vest in equal annual installments over either a three - or four -year period. The fair value of each restricted stock units (“RSUs”) is the ending stock price on the date of grant. The RSUs vest in equal annual installments over a three - or four -year period. Each award is evidenced by an award agreement that specifies the option price, if applicable, the duration of the award, the number of shares to which the award pertains and such other provisions as the Board determines. Historically, shares issued in connection with stock compensation awards have been issued from available authorized shares. Beginning in the second quarter of 2017, shares were issued from available treasury shares. Shares issued in connection with stock compensation awards along with other related information are presented in the following table without the retroactive recognition of stock dividends (in thousands, except share amounts): Year Ended December 31, 2018 2017 2016 New shares issued from available authorized shares — 48,311 108,225 New shares issued from available treasury shares 140,692 111,045 — Total 140,692 159,356 108,225 Proceeds from stock option exercises $ 2,653 $ 2,692 $ 1,663 The estimated weighted-average grant-date fair value per option and the underlying Black-Scholes option-pricing model assumptions are summarized in the following table for years in which we granted NQSOs pursuant to the incentive plans: Years Ended December 31, 2018 2017 2016 Weighted-average grant date fair value per option $6.78 — $7.18 Weighted-average assumptions: Risk-free interest rates 2.81% — 1.79% Expected dividend yield 1.10% — 2.69% Expected volatility factors of the market price of Southside Bancshares common stock 25.41% — 27.02% Expected option life (in years) 6.2 — 6.2 A combined summary of activity in our share-based plans as of December 31, 2018 is presented below: Restricted Stock Units Outstanding Stock Options Outstanding Number of Shares Weighted- Average Grant-Date Fair Value Number of Shares Weighted- Average Exercise Price Weighted- Average Grant-Date Fair Value Balance, January 1, 2018 78,253 $ 32.04 690,312 $ 26.02 $ 6.19 Granted 64,358 34.28 356,849 34.52 6.78 Stock options exercised — — (115,277 ) 23.02 5.69 Stock awards vested (29,752 ) 31.14 — — — Forfeited (3,109 ) 32.93 (16,980 ) 32.51 6.67 Canceled/expired — — (5,553 ) 30.06 6.68 Balance, December 31, 2018 109,750 $ 33.57 909,351 $ 29.59 $ 6.47 Other information regarding options outstanding and exercisable as of December 31, 2018 is as follows: Options Outstanding Options Exercisable Range of Exercise Prices Number Weighted- Weighted- Number Weighted- $ 14.67 - $20.00 110,291 $ 15.89 3.03 110,291 $ 15.89 20.01 - 25.00 106,826 22.92 5.43 82,747 23.01 25.01 - 30.00 202,009 26.68 6.47 136,613 26.58 30.01 - 35.00 346,965 34.52 9.41 — — 35.01 - 37.28 143,260 37.28 7.90 76,710 37.28 Total 909,351 $ 29.59 7.28 406,361 $ 24.97 The total intrinsic value of outstanding in-the-money stock options and outstanding in-the-money exercisable stock options was $3.7 million and $3.2 million at December 31, 2018 , respectively. The weighted-average remaining contractual life of options exercisable at December 31, 2018 was 5.49 years . The total intrinsic value of stock options exercised during the years ended December 31, 2018 , 2017 and 2016 was $1.4 million , $1.8 million and $1.3 million , respectively. Due to adoption of ASU 2016-09 “Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting,” during 2017, there was no tax benefit realized for the deductions related to stock awards for the years ended December 31, 2018 or 2017 . However, prior to adoption of the ASU, the tax benefit realized for the deductions related to stock awards was $332,000 for the year ended December 31, 2016.

DERIVATIVE FINANCIAL INSTRUMENT

DERIVATIVE FINANCIAL INSTRUMENTS AND HEDGING ACTIVITIES	12 Months Ended
	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
DERIVATIVES INSTRUMENTS AND HEDGING ACTIVITIES DISCLOSURE	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, 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 accumulated other comprehensive income 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. Therefore, no gain or loss has been recognized due to hedge ineffectiveness. For derivative instruments not designated as hedging instruments, the gain or loss is recognized in current earnings during the period of change. From time to time, we enter into certain interest rate swap contracts on specific variable rate advance agreements with the FHLB. 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 the three months ended June 30, 2018, we entered into partial term fair value hedges, as allowed under the recently adopted ASU 2017-12, 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 are expected to be effective in offsetting changes in the fair value of the hedged securities. As of December 31, 2018 , hedged securities with a carrying amount of $23.7 million are included in our AFS securities portfolio in our consolidated balance sheets. Interest rate swaps designated as partial-term fair value hedges are utilized to mitigate the effect of changing interest rates on the hedged securities. The hedging strategy converts a portion of the fixed interest rates on the securities to LIBOR-based variable interest rates. 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 accumulated other comprehensive income 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 accumulated other comprehensive income shall be reclassified into earnings immediately. During the first quarter of 2017, we terminated two interest rate swap contracts designated as cash flow hedges. At the time of termination, we determined that 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 December 31, 2018 , net derivative assets included $8.3 million of cash collateral received from counterparties under master netting agreements. 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): December 31, 2018 December 31, 2017 Estimated Fair Value Estimated Fair Value Notional Amount (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 $ 9,388 $ 457 $ 240,000 $ 7,922 $ 22 Swaps-Fair Value Hedge-Financial institution counterparties 21,100 — 657 — — — Derivatives designated as non-hedging instruments Interest rate contracts: Swaps-Financial institution counterparties 93,967 1,119 1,087 67,220 92 612 Swaps-Customer counterparties 93,967 1,087 1,119 67,220 612 92 Gross derivatives 11,594 3,320 8,626 726 Offsetting derivative assets/liabilities (2,201 ) (2,201 ) (114 ) (114 ) Cash collateral received/posted (8,306 ) — (7,900 ) (520 ) Net derivatives included in the consolidated balance sheets (2) $ 1,087 $ 1,119 $ 612 $ 92 (1) Notional amounts, which represent the extent of involvement in the derivatives market, are used to determine the contractual cash flows required in accordance with the terms of the agreement. These amounts are typically not exchanged, significantly exceed amounts subject to credit or market risk and are not reflected in the consolidated balance sheets. (2) Net derivative assets are included in other assets and net derivative liabilities are included in other liabilities on the consolidated balance sheets. Included in the fair value of net derivative assets and net derivative liabilities are credit valuation adjustments reflecting counterparty credit risk and our credit risk. We had no credit exposure related to interest rate swaps with financial institutions and $1.1 million related to interest rate swaps with customers at December 31, 2018 . We had net credit exposure of $30,000 related to interest rate swaps with financial institutions and $612,000 related to interest rate swaps with customers at December 31, 2017 . 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 December 31, 2018 and December 31, 2017 : December 31, 2018 December 31, 2017 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 4.8 2.45 % 1.58 % $ 240,000 5.3 1.44 % 1.43 % Swaps-Fair Value Hedge Financial institution counterparties 21,100 7.5 2.56 3.00 — — — — Swaps-Non-Hedging Financial institution counterparties 93,967 11.6 2.36 2.58 67,220 12.7 1.39 2.37 Customer counterparties 93,967 11.6 2.58 2.36 67,220 12.7 2.37 1.39

FAIR VALUE MEASUREMENT

FAIR VALUE MEASUREMENT	12 Months Ended
	Dec. 31, 2018
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 December 31, 2018 and 2017 , 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 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 December 31, 2018 and 2017 . 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 December 31, 2018 and 2017 , 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): 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 (2) 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 (3) 37,813 — — 37,813 Total asset nonrecurring fair value measurements $ 39,019 $ — $ — $ 39,019 December 31, 2017 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: U.S. Government Agency Debentures $ 108,869 $ — $ 108,869 $ — State and Political Subdivisions 392,664 — 392,664 — Other Stocks and Bonds 5,055 — 5,055 — Equity Investments (2) 5,920 5,920 — — Mortgage-backed Securities: (1) Residential 718,029 — 718,029 — Commercial 308,218 — 308,218 — Derivative assets: Interest rate swaps 8,626 — 8,626 — Total asset recurring fair value measurements $ 1,547,381 $ 5,920 $ 1,541,461 $ — Derivative liabilities: Interest rate swaps $ 726 $ — $ 726 $ — Total liability recurring fair value measurements $ 726 $ — $ 726 $ — Nonrecurring fair value measurements Foreclosed assets $ 1,767 $ — $ — $ 1,767 Impaired loans (3) 6,536 — — 6,536 Total asset nonrecurring fair value measurements $ 8,303 $ — $ — $ 8,303 (1) All mortgage-backed securities are issued and/or guaranteed by U.S. government agencies or U.S. government-sponsored enterprises. (2) With the adoption of ASU 2016-01 on January 1, 2018, these investments are included in equity investments on our consolidated balance sheets. The guidance was applied on a prospective approach resulting in prior-periods no longer being comparable. See “Note 1 - Summary of Significant Accounting and Reporting Policies” for further information. (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. 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 - With the adoption of ASU 2016-01 on January 1, 2018, we refined our methodology to estimate the fair value of our loan portfolio to an exit price notion with adjustments for liquidity, credit and prepayment factors. The guidance was applied on a prospective approach resulting in prior-periods no longer being comparable. See “Note 1 – Summary of Significant Accounting and Reporting Policies” for further information. For December 31, 2017, a djustable rate loans that repriced frequently and with no significant change in credit risk, the carrying amounts were a reasonable estimate of those assets’ fair value, and the fair value of fixed rate loans were estimated by discounting the future cash flows using the current rates at which similar loans would be made to borrowers with similar credit ratings and for the same remaining maturities. Nonperforming loans continue to be 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. 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 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 — Estimated Fair Value December 31, 2017 Carrying Total Level 1 Level 2 Level 3 Financial Assets: Cash and cash equivalents $ 198,692 $ 198,692 $ 198,692 $ — $ — Investment Securities: Held to maturity, at carrying value 413,632 421,928 — 421,928 — Mortgage-backed Securities: Held to maturity, at carrying value 495,874 499,872 — 499,872 — FHLB stock, at cost 55,729 55,729 — 55,729 — Equity investments 5,821 5,821 — 5,821 — Loans, net of allowance for loan losses 3,273,575 3,269,316 — — 3,269,316 Loans held for sale 2,001 2,001 — 2,001 — Financial Liabilities: Deposits $ 4,515,447 $ 4,506,133 $ — $ 4,506,133 $ — Federal funds purchased and repurchase agreements 9,498 9,498 — 9,498 — FHLB borrowings 1,017,361 1,008,292 — 1,008,292 — Subordinated notes, net of unamortized debt issuance costs 98,248 99,665 — 99,665 — Trust preferred subordinated debentures, net of unamortized debt issuance costs 60,241 47,622 — 47,622 — 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.

SHAREHOLDERS' EQUITY

SHAREHOLDERS' EQUITY	12 Months Ended
	Dec. 31, 2018
Regulatory Capital Requirements [Abstract]
SHAREHOLDERS' EQUITY	SHAREHOLDERS’ EQUITY Cash dividends declared and paid were $1.20 , $1.11 and $1.01 per share for the years ended December 31, 2018 , 2017 and 2016 , respectively. Future dividends will depend on our earnings, financial condition and other factors which the board of directors considers to be relevant. Our dividend policy requires that any cash dividend payments made may not exceed consolidated earnings for that year. On December 6, 2016, we entered into an underwriting agreement, pursuant to which we sold 2,185,000 shares of our common stock at a price of $36.50 per share. We received $200.1 million in net proceeds, after deducting underwriting discounts and costs. These net proceeds were used primarily for general corporate purposes. We are subject to various regulatory capital requirements administered by the federal banking agencies. Failure to meet minimum capital requirements can initiate certain mandatory and possibly additional discretionary actions by regulators that, if undertaken, could have a direct material effect on our financial statements. Under capital adequacy guidelines and the regulatory framework for prompt corrective action, we must meet specific capital guidelines that involve quantitative measures of our assets, liabilities and certain off-balance-sheet items as calculated under regulatory accounting practices. Our capital amounts and classification are also subject to qualitative judgments by the regulators regarding components, risk weightings and other factors. Quantitative measures established by regulation to ensure capital adequacy require us to maintain minimum amounts and ratios (set forth in the table below) of Common Equity Tier 1, Tier 1 and Total Capital (as defined in the regulations) to risk-weighted assets (as defined) and of Tier 1 Capital (as defined) to average assets (as defined). At December 31, 2018 , we exceeded all regulatory minimum capital requirements. As of December 31, 2018 , the most recent notification from the FDIC categorized us as well capitalized under the regulatory framework for prompt corrective action. To be categorized as well capitalized we must maintain minimum Common Equity Tier 1 risk-based, Tier 1 risk-based, Total risk-based and Tier 1 leverage ratios as set forth in the table below. There are no conditions or events since that notification that management believes have changed our category. Actual For Capital Adequacy Purposes To Be Well Capitalized Under Prompt Corrective Actions Provisions Amount Ratio Amount Ratio Amount Ratio December 31, 2018: (dollars in thousands) Common Equity Tier 1 (to Risk Weighted Assets) Consolidated $ 568,283 14.77 % $ 173,174 4.50 % N/A N/A Bank Only $ 714,991 18.59 % $ 173,095 4.50 % $ 250,026 6.50 % Tier 1 Capital (to Risk Weighted Assets) Consolidated $ 626,718 16.29 % $ 230,899 6.00 % N/A N/A Bank Only $ 714,991 18.59 % $ 230,793 6.00 % $ 307,725 8.00 % Total Capital (to Risk Weighted Assets) Consolidated $ 754,034 19.59 % $ 307,865 8.00 % N/A N/A Bank Only $ 743,900 19.34 % $ 307,725 8.00 % $ 384,656 10.00 % Tier 1 Capital (to Average Assets) (1) Consolidated $ 626,718 10.64 % $ 235,689 4.00 % N/A N/A Bank Only $ 714,991 12.14 % $ 235,532 4.00 % $ 294,415 5.00 % December 31, 2017: Common Equity Tier 1 (to Risk Weighted Assets) Consolidated $ 570,610 14.65 % $ 175,216 4.50 % N/A N/A Bank Only $ 711,157 18.27 % $ 175,145 4.50 % $ 252,987 6.50 % Tier 1 Capital (to Risk Weighted Assets) Consolidated $ 627,532 16.12 % $ 233,621 6.00 % N/A N/A Bank Only $ 711,157 18.27 % $ 233,527 6.00 % $ 311,369 8.00 % Total Capital (to Risk Weighted Assets) Consolidated $ 748,532 19.22 % $ 311,495 8.00 % N/A N/A Bank Only $ 733,909 18.86 % $ 311,369 8.00 % $ 389,211 10.00 % Tier 1 Capital (to Average Assets) (1) Consolidated $ 627,532 11.16 % $ 224,844 4.00 % N/A N/A Bank Only $ 711,157 12.66 % $ 224,741 4.00 % $ 280,926 5.00 % (1) Refers to quarterly average assets as calculated in accordance with policies established by bank regulatory agencies. Our payment of dividends is limited under regulation. The amount that can be paid in any calendar year without prior approval of our regulatory agencies cannot exceed the lesser of net profits (as defined) for that year plus the net profits for the preceding two calendar years or retained earnings.

DIVIDEND REINVESTMENT AND COMMO

DIVIDEND REINVESTMENT AND COMMON STOCK REPURCHASE PLAN	12 Months Ended
	Dec. 31, 2018
Dividend Reinvestment and Common Stock Repurchase Plan [Abstract]
DIVIDEND REINVESTMENT AND COMMON STOCK REPURCHASE PLAN	DIVIDEND REINVESTMENT AND COMMON STOCK REPURCHASE PLAN We have in effect a Dividend Reinvestment Plan (“DRIP”) which allows enrolled shareholders to reinvest dividends paid to them by the Company into new shares of the our stock. The DRIP is funded by stock authorized but not yet issued. For the year ended December 31, 2018 , 42,872 shares were issued under this plan at an average price of $34.45 per share, reflective of other trades at the time of each sale. For the year ended December 31, 2017 , 43,650 shares were issued under this plan at an average price of $33.99 per share, reflective of other trades at the time of each sale. Our board continually evaluates the Company’s capital needs and those of Southside Bank and may, at their discretion, initiate, modify or discontinue an authorized stock repurchase plan. Repurchased shares are designated as treasury shares and are available for general corporate purposes, which may include possible use in connection with our share-based incentive plans and other distributions. During 2018, 1,459,148 shares of common stock were repurchased under an authorized stock repurchase plan at a cost of $47.2 million . During 2016, 443,426 shares of common stock were repurchased under a previously authorized stock repurchase plan at a cost of $10.2 million . No shares were repurchased during 2017. Subsequent to December 31, 2018 and through January 7, 2019, we repurchased 40,852 shares of common stock at an average price of $32.42 , at which time our 2018 stock repurchase authorization expired.

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The income tax expense included in the accompanying statements of income consists of the following (in thousands): Years Ended December 31, 2018 2017 2016 Current income tax expense $ 4,009 $ 12,607 $ 8,557 Deferred income tax expense 6,154 3,514 1,768 Income tax expense $ 10,163 $ 16,121 $ 10,325 The components of the net deferred tax asset (liability) as of December 31, 2018 and 2017 are summarized below (in thousands): Assets Liabilities Allowance for loan losses $ 5,673 $ Retirement and other benefit plans (2,519 ) Premises and equipment (6,360 ) Core deposit intangible (2,748 ) Unrealized losses on securities available for sale 7,926 Effective hedging derivatives (1,761 ) Fair value adjustment on loans 1,894 Fair value adjustment on time deposits (6 ) Unfunded status of defined benefit plan 6,979 State business tax credit 483 Stock-based compensation 797 Other (582 ) Gross deferred tax assets (liabilities) 23,752 (13,976 ) Net deferred tax asset at December 31, 2018 $ 9,776 Allowance for loan losses $ 4,364 $ Retirement and other benefit plans (2,102 ) Premises and equipment (5,716 ) Core deposit intangible (3,660 ) Unrealized losses on securities available for sale 4,285 Effective hedging derivatives (1,701 ) Fair value adjustment on loans 2,607 Fair value adjustment on time deposits (54 ) Alternative minimum tax credit 6,943 Unfunded status of defined benefit plan 7,018 State business tax credit 544 Stock-based compensation 642 Other (966 ) Gross deferred tax assets (liabilities) 26,403 (14,199 ) Net deferred tax asset at December 31, 2017 $ 12,204 A reconciliation of tax at statutory rates and total tax expense is as follows (dollars in thousands): Years Ended December 31, 2018 2017 2016 Amount Percent of Pre-Tax Income Amount Percent of Pre-Tax Income Amount Percent of Pre-Tax Income Statutory tax expense $ 17,703 21.0 % $ 24,652 35.0 % $ 20,886 35.0 % Increase (decrease) in taxes from: Tax rate changes (767 ) (0.9 )% 2,416 3.4 % — — Tax exempt interest (6,257 ) (7.4 )% (10,195 ) (14.5 )% (9,879 ) (16.6 )% Bank owned life insurance (613 ) (0.7 )% (885 ) (1.2 )% (915 ) (1.5 )% Share-based compensation (191 ) (0.2 )% (482 ) (0.7 )% — — Acquisition costs — — 467 0.7 % — — State business tax 297 0.3 % 68 0.1 % 71 0.1 % Other, net (9 ) — 80 0.1 % 162 0.3 % Income tax expense $ 10,163 12.1 % $ 16,121 22.9 % $ 10,325 17.3 % The Tax Cuts and Jobs Act (“Tax Act”) was enacted on December 22, 2017. The Tax Act reduced the U.S. federal corporate tax rate from 35% to 21%. We remeasured certain deferred tax assets and liabilities as of December 22, 2017 based on the rates at which they are expected to reverse in the future, which is generally 21%, by recording a provisional amount of $2.4 million . At December 31, 2018 , we had completed our accounting for all of the enactment-date income tax effects of the Tax Act. During 2018, we recognized a benefit of $767,000 made to the provisional amounts recorded as of December 22, 2017 with the remeasurement of the net deferred tax asset. The Tax Act also repealed the existing Alternative Minimum Tax (“AMT”). As of December 31, 2018 , we had fully realized the remaining AMT tax credit of $ 7.8 million . We file income tax returns in the U.S. federal jurisdiction 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. No valuation allowance for deferred tax assets was recorded at December 31, 2018 or 2017 as management believes it is more likely than not that all of the deferred tax assets will be realized in future years. Unrecognized tax benefits were not material at December 31, 2018 or 2017 .

OFF-BALANCE-SHEET ARRANGEMENTS,

OFF-BALANCE-SHEET ARRANGEMENTS, COMMITMENTS AND CONTINGENCIES	12 Months Ended
	Dec. 31, 2018
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): December 31, 2018 December 31, 2017 Unused commitments: Commitments to extend credit $ 874,557 $ 804,715 Standby letters of credit 27,438 14,890 Total $ 901,995 $ 819,605 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. Lease Commitments . We lease certain branch facilities and office equipment under operating leases. It is expected that certain leases will be renewed, or equipment replaced with new leased equipment, as these leases expire. Future minimum rental commitments due under non-cancelable operating leases at December 31, 2018 were as follows (in thousands): 2019 $ 1,265 2020 1,158 2021 906 2022 742 2023 560 2024 and thereafter 1,352 $ 5,983 Rent expense for branch facilities was $1.8 million , $1.7 million and $3.9 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. Rent expense for leased equipment was $160,000 , $178,000 and $261,000 for the years ended December 31, 2018 , 2017 and 2016 , respectively. It is expected that certain leases will be renewed, or equipment replaced with new leased equipment, as these leases expire. With the adoption of ASU 2016-02, “Leases (Topic 842),” we recognized a lease liability of $10.1 million and a related right-of-use asset of $9.8 million on our balance sheet as of January 1, 2019. See “Note 1 – Summary of Significant Accounting and Reporting Policies” for further information. We acquired a 202,000 square-foot office building in Fort Worth, Texas upon completion of the Omni acquisition 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. Gross rental income from these leases was $3.0 million for the year ended December 31, 2018 and $3.1 million for both years ended December 31, 2017 and 2016 . At December 31, 2018 , non-cancelable operating leases for the building with future minimum lease payments are as follows (in thousands): 2019 $ 2,574 2020 2,427 2021 1,374 2022 1,352 2023 1,119 2024 and thereafter 3,996 $ 12,842 Securities . In the normal course of business we buy and sell securities. At December 31, 2018 , there were $6.4 million of unsettled trades to purchase securities and no unsettled trades to sell securities. As of December 31, 2017 , there were no unsettled trades to purchase securities and no unsettled trades to sell securities. Deposits. There were $15.2 million of unsettled issuances of brokered CDs at December 31, 2018 . There were no unsettled issuances of brokered CDs at December 31, 2017 . 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.

SIGNIFICANT GROUP CONCENTRATION

SIGNIFICANT GROUP CONCENTRATIONS OF CREDIT RISK	12 Months Ended
	Dec. 31, 2018
Risks and Uncertainties [Abstract]
SIGNIFICANT GROUP CONCENTRATIONS OF CREDIT RISK	SIGNIFICANT GROUP CONCENTRATIONS OF CREDIT RISK Although we have a diversified loan portfolio, a significant portion of our loans are collateralized by real estate. Repayment of these loans is in part dependent upon the economic conditions in the market area. See “Item 1. Business – Market Area.” Part of the risk associated with real estate loans has been mitigated since 31.8% of this group represents loans collateralized by residential dwellings that are primarily owner occupied. Losses on this type of loan have historically been less than those on speculative properties. Many of the remaining real estate loans are collateralized primarily with non-owner occupied commercial real estate. The MBS we hold consist exclusively of U.S. agency pass-through securities which are either directly or indirectly backed by the full faith and credit of the United States Government or guaranteed by GSEs. The Government National Mortgage Association (“GNMA”) MBS are backed by the full faith and credit of the United States Government. The Fannie Mae and Freddie Mac U.S. agency GSE guaranteed MBS are not backed by the full faith and credit of the United States government.

PARENT COMPANY FINANCIAL INFORM

PARENT COMPANY FINANCIAL INFORMATION	12 Months Ended
	Dec. 31, 2018
Condensed Financial Information Disclosure [Abstract]
PARENT COMPANY FINANCIAL INFORMATION	PARENT COMPANY FINANCIAL INFORMATION Condensed financial information for Southside Bancshares, Inc. (parent company only) was as follows (in thousands, except share amounts): CONDENSED BALANCE SHEETS December 31, 2018 2017 ASSETS Cash and due from banks $ 11,431 $ 8,483 Investment in bank subsidiaries at equity in underlying net assets 875,814 894,010 Investment in nonbank subsidiaries at equity in underlying net assets 1,826 1,826 Other assets 4,290 10,350 Total assets $ 893,361 $ 914,669 LIABILITIES Subordinated notes, net of unamortized debt issuance costs $ 98,407 $ 98,248 Trust preferred subordinated debentures, net of unamortized debt issuance costs 60,246 60,241 Other liabilities 3,417 2,040 Total liabilities 162,070 160,529 SHAREHOLDERS’ EQUITY Common stock: ($1.25 par value, 80,000,000 shares authorized, 37,845,224 shares issued at December 31, 2018 and 40,000,000 shares authorized and 37,802,352 shares issued at December 31, 2017) 47,307 47,253 Paid-in capital 762,470 757,439 Retained earnings 64,797 32,851 Treasury stock, at cost (4,120,475 at December 31, 2018 and 2,802,019 at December 31, 2017) (93,055 ) (47,105 ) Accumulated other comprehensive loss (50,228 ) (36,298 ) Total shareholders’ equity 731,291 754,140 Total liabilities and shareholders’ equity $ 893,361 $ 914,669 CONDENSED STATEMENTS OF INCOME Years Ended December 31, 2018 2017 2016 Income Dividends from subsidiary $ 90,000 $ 27,000 $ 30,000 Interest income 78 60 51 Total income 90,078 27,060 30,051 Expense Interest expense 8,269 7,646 3,334 Other 3,662 5,869 3,227 Total expense 11,931 13,515 6,561 Income before income tax expense 78,147 13,545 23,490 Income tax benefit 2,489 4,242 2,278 Income before equity in undistributed earnings of subsidiaries 80,636 17,787 25,768 Equity in undistributed earnings of subsidiaries (6,498 ) 36,525 23,581 Net income $ 74,138 $ 54,312 $ 49,349 CONDENSED STATEMENTS OF CASH FLOWS Years Ended December 31, 2018 2017 2016 OPERATING ACTIVITIES: Net Income $ 74,138 $ 54,312 $ 49,349 Adjustments to reconcile net income to net cash provided by operations: Amortization 164 153 45 Equity in undistributed earnings of subsidiaries 6,498 (36,525 ) (23,581 ) Decrease (increase) in other assets 6,060 (2,113 ) (1,035 ) Increase (decrease) in other liabilities 1,377 (155 ) 1,564 Net cash provided by operating activities 88,237 15,672 26,342 INVESTING ACTIVITIES: Investment in subsidiaries — 890 (126,000 ) Net cash paid in acquisition — (22,801 ) — Net cash used in investing activities — (21,911 ) (126,000 ) FINANCING ACTIVITIES: Net proceeds from issuance of subordinated long-term debt — — 98,060 Purchase of common stock (47,193 ) — (10,199 ) Proceeds from issuance of common stock 3,883 3,953 78,962 Cash dividends paid (41,979 ) (32,199 ) (25,963 ) Net cash (used in) provided by financing activities (85,289 ) (28,246 ) 140,860 Net increase (decrease) in cash and cash equivalents 2,948 (34,485 ) 41,202 Cash and cash equivalents at beginning of period 8,483 42,968 1,766 Cash and cash equivalents at end of period $ 11,431 $ 8,483 $ 42,968

QUARTERLY FINANCIAL INFORMATION

QUARTERLY FINANCIAL INFORMATION OF REGISTRANT	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
QUARTERLY FINANCIAL INFORMATION OF REGISTRANT NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (UNAUDITED)	QUARTERLY FINANCIAL INFORMATION OF REGISTRANT NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (UNAUDITED) (in thousands, except share amounts) 2018 Fourth Third Second First Interest income $ 58,022 $ 57,152 $ 56,797 $ 57,194 Interest expense 15,612 14,742 13,686 13,061 Net interest income 42,410 42,410 43,111 44,133 Provision for loan losses 2,446 975 1,281 3,735 Net gain (loss) on sale of securities available for sale 61 (741 ) (332 ) (827 ) Noninterest income excluding net gain (loss) on sale of securities 10,073 10,763 11,339 10,437 Noninterest expense 30,196 28,962 29,274 31,667 Income before income tax expense 19,902 22,495 23,563 18,341 Income tax expense 2,521 2,192 3,360 2,090 Net income 17,381 20,303 20,203 16,251 Earnings per common share Basic $ 0.50 $ 0.58 $ 0.58 $ 0.46 Diluted $ 0.50 $ 0.58 $ 0.57 $ 0.46 Cash dividends paid per common share $ 0.32 $ 0.30 $ 0.30 $ 0.28 2017 Fourth Third Second First Interest income $ 50,104 $ 46,473 $ 46,009 $ 44,888 Interest expense 11,798 11,513 10,585 9,608 Net interest income 38,306 34,960 35,424 35,280 Provision for loan losses 1,271 960 1,346 1,098 Net (loss) gain on sale of securities available for sale (249 ) 627 (75 ) 322 Noninterest income excluding net gain (loss) on sale of securities 9,348 8,781 9,368 9,351 Noninterest expense 29,933 25,007 25,537 25,858 Income before income tax expense 16,201 18,401 17,834 17,997 Income tax expense 5,870 3,890 3,353 3,008 Net income 10,331 14,511 14,481 14,989 Earnings per common share Basic $ 0.33 $ 0.49 $ 0.49 $ 0.51 Diluted $ 0.33 $ 0.49 $ 0.49 $ 0.51 Cash dividends paid per common share $ 0.30 $ 0.28 $ 0.28 $ 0.25

SUMMARY OF SIGNIFICANT ACCOUN_2

SUMMARY OF SIGNIFICANT ACCOUNTING AND REPORTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation and Consolidation	Basis of Presentation and Consolidation . The consolidated financial statements are prepared in conformity with U.S. generally accepted accounting principles (“GAAP”) and include the accounts of Southside Bancshares, Inc. (the “Company”), and its wholly-owned subsidiary, Southside Bank (“Southside Bank” or “the Bank”) and the nonbank subsidiaries. All significant intercompany accounts and transactions are eliminated in consolidation. “Omni” refers to OmniAmerican Bancorp, Inc., a bank holding company acquired by Southside on December 17, 2014. On November 30, 2017, we acquired Diboll State Bancshares, Inc., a Texas corporation (“Diboll”) and the holding company for First Bank & Trust East Texas, a Texas banking association based in Diboll, Texas. See “Note 2 - Acquisition”. We determine if we have a controlling financial interest in an entity by first evaluating whether the entity is a voting interest entity or a variable interest entity (“VIE”) under GAAP. Voting interest entities are entities in which the total equity investment at risk is sufficient to enable the entity to finance itself independently and provides the equity holders with the obligation to absorb losses, the right to receive residual returns and the right to make decisions about the entity’s activities. We consolidate voting interest entities in which we have all, or at least a majority of, the voting interest. As defined in applicable accounting standards, VIEs are entities that lack one or more of the characteristics of a voting interest entity. A controlling financial interest in a VIE is present when an enterprise has both the power to direct the activities of the VIE that most significantly impact the VIEs economic performance and an obligation to absorb losses or the right to receive benefits that could potentially be significant to the VIE. The enterprise with a controlling financial interest, known as the primary beneficiary, consolidates the VIE.
Use of Estimates	Use of Estimates . In preparing consolidated financial statements in conformity with GAAP, management is required to make estimates and assumptions that affect the reported amounts of assets and liabilities as of the date of the balance sheet and reported amounts of revenues and expenses during the reporting period. These estimates are subjective in nature and involve matters of judgment. Actual results could differ from these estimates. Material estimates that are particularly susceptible to significant change in the near term relate to the determination of the allowance for loan losses, assumptions used in the defined benefit plan and the fair values of financial instruments. The status of contingencies are particularly subject to change and significant assumptions used in periodic evaluation of securities for other-than-temporary impairment. Certain prior period amounts have been reclassified to conform to the current period presentation.
Segment Information	Segment Information . Operating segments are components of a business about which separate financial information is available and that are evaluated regularly by the chief operating decision-maker in deciding how to allocate resources and assess performance. Our chief operating decision-maker uses consolidated results to make operating and strategic decisions. Therefore, we have determined that our business is conducted in one reportable segment.
Business Combinations	Business Combinations. Business combinations are accounted for using the acquisition method of accounting. Under this accounting method, the acquired company’s net assets are recorded at fair value on the date of acquisition, and the results of operations of the acquired company are combined with our results from that date forward. Costs related to the acquisition are expensed as incurred. The difference between the purchase price and the fair value of the net assets acquired (including intangible assets with finite lives) is recorded as goodwill. The accounting policy for goodwill and intangible assets is summarized in this note under the heading “Goodwill and Other Intangibles.” Acquired loans (non-impaired and impaired) are initially measured at fair value as of the acquisition date. The fair value estimates for acquired loans are based on the estimate of expected cash flows, both principal and interest and prepayments, discounted at prevailing market interest rates. Credit discounts representing the principal losses expected over the life of the loan are also a component of the initial fair value; therefore, an allowance for loan losses is not recorded at the acquisition date. We evaluate acquired loans for impairment in accordance with the provisions of ASC 310-30, “Loans and Debt Securities Acquired with Deteriorated Credit Quality” (“ASC 310-30”). Acquired loans are considered impaired if there is evidence of credit deterioration since origination and if it is probable at time of acquisition that all contractually required payments will not be collected. Expected cash flows at the acquisition date in excess of the fair value of the loans is referred to as the accretable yield and recorded as interest income over the life of the loans. Acquired impaired loans are not classified as nonaccrual or nonperforming as they are considered to be performing under the provisions of ASC 310-30. Subsequent to the acquisition date, increases in expected cash flows will generally result in a recovery of any previously recorded allowance for loan loss, to the extent applicable, and/or a reclassification from the nonaccretable difference to accretable yield, which will be recognized prospectively. The present value of any decreases in expected cash flows after the acquisition date will generally result in an impairment charge recorded as a provision for loan losses, resulting in an increase to the allowance for loan loss. For acquired non-impaired loans, the difference between the acquisition date fair value and the contractual amounts due at the acquisition date represents the fair value adjustment. Fair value adjustments may be discounts (or premiums) to a loan’s cost basis and are accreted (or amortized) to interest income over the loan’s remaining contractual life using the level yield method.
Cash Equivalents	Cash Equivalents . Cash equivalents, for purposes of reporting cash flow, include cash, amounts due from banks and federal funds sold that have an initial maturity of less than 90 days. We maintain deposits with other institutions in amounts that exceed federal deposit insurance coverage. Management regularly evaluates the credit risk associated with the counterparties to these transactions and believes that we are not exposed to any significant credit risks on cash and cash equivalents.
Basic and Diluted Earnings per Common Share	Basic and Diluted Earnings per Common Share . Basic earnings per common share is based on net income divided by the weighted-average number of common shares outstanding during the period. Diluted earnings per common share include the dilutive effect of stock options granted using the treasury stock method.
Comprehensive Income	Comprehensive Income . Comprehensive income includes all changes in shareholders’ equity during a period, except those resulting from transactions with shareholders. Besides net income, other components of comprehensive income include the after tax effect of changes in the fair value of AFS securities, changes in the net unrealized loss on securities transferred to/from HTM, changes in the accumulated gain or loss on effective cash flow hedging instruments and changes in the funded status of defined benefit retirement plans.
Loans	Loans . All loans are stated at principal outstanding net of unearned discount and other deferred expenses or fees. Interest income on loans is recognized using the level yield method or simple interest method. Loans receivable that management has the intent and ability to hold for the foreseeable future or until maturity or pay-off are reported at their outstanding principal adjusted for any charge-offs, the allowance for loan losses, and any unamortized deferred fees or costs on originated loans and unamortized premiums or discounts on purchased loans. A loan is considered impaired, based on current information and events, if it is probable that we will be unable to collect the scheduled payments of principal or interest when due according to the contractual terms of the loan agreement. Substantially all of our impaired loans are collateral-dependent, and as such, are measured for impairment based on the fair value of the collateral.
Loans Held For Sale	Loans Held For Sale . Loans originated and intended for sale in the secondary market are carried at the lower of aggregate cost or fair value, as determined by aggregate outstanding commitments from investors or current investor yield requirements. Net unrealized losses are recognized through a valuation allowance by charges to income. Gains or losses on sales of mortgage loans are recognized based on the difference between the selling price and the carrying value of the related mortgage loans sold.
Loan Fees	Loan Fees . We treat loan fees, net of direct costs, as an adjustment to the yield of the related loan over its term.
Allowance for Loan Losses	Allowance for Loan Losses . An allowance for loan losses is provided through charges to income in the form of a provision for loan losses. Loans which management believes are uncollectible are charged against this account with subsequent recoveries, if any, credited to the account. The amount of the allowance for loan losses is determined by management’s evaluation of the quality and inherent risks in the loan portfolio, economic conditions and other factors which warrant current recognition.
Nonaccrual Loans	Nonaccrual Loans . A loan is placed on nonaccrual when principal or interest is contractually past due 90 days or more unless, in the determination of management, the principal and interest on the loan are well collateralized and in the process of collection. In addition, a loan is placed on nonaccrual when, in the opinion of management, the future collectability of interest and principal is not expected. When classified as nonaccrual, accrued interest receivable on the loan is reversed and the future accrual of interest is suspended. 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.
Other Real Estate Owned	Other Real Estate Owned and Foreclosed Assets . Other Real Estate Owned (“OREO”) includes real estate acquired in full or partial settlement of loan obligations. OREO is initially carried at the fair value of the collateral net of estimated selling costs. Prior to foreclosure, the recorded amount of the loan is written down, if necessary, to the appraised fair value of the real estate to be acquired, less selling costs, by charging the allowance for loan losses. Any subsequent reduction in fair value net of estimated selling costs is charged to noninterest expense. Costs of maintaining and operating foreclosed properties are expensed as incurred and included in other expense in our income statement. Expenditures to complete or improve foreclosed properties are capitalized only if expected to be recovered; otherwise, they are expensed.
Foreclosed Assets	Other foreclosed assets are held for sale and are initially recorded at fair value less estimated selling costs at the date of foreclosure, by charging the allowance for loan losses. Subsequent to foreclosure, valuations are periodically performed by management and the assets are carried at the lower of carrying amount or fair value less costs to sell. Foreclosed assets are included in other assets in the accompanying consolidated balance sheets. Expenses from operations and changes in the valuation allowance are included in noninterest expense.
Securities	Securities . Available for Sale (“AFS”). Debt securities that will be held for indefinite periods of time, including securities that may be sold in response to changes in market interest or prepayment rates, needs for liquidity and changes in the availability of and the yield on alternative investments are classified as AFS. These assets are carried at fair value with unrealized gains and losses reported as a separate component of accumulated other comprehensive income (“AOCI”), net of tax. Fair value is determined using quoted market prices as of the close of business on the balance sheet date. If quoted market prices are not available, fair values are based on quoted market prices for similar securities or estimates from independent pricing services. Securities that are hedged with qualifying derivatives are carried at fair value with the change in fair value on both the hedged instrument and the securities recorded in interest income in the consolidated statements of income. Held to Maturity (“HTM”). Debt securities that management has the positive intent and ability to hold until maturity are classified as HTM and are carried at their remaining unpaid principal balance, net of unamortized premiums or unaccreted discounts. Prior to January 1, 2019, premiums were amortized and discounts were accreted to maturity, or in the case of mortgage-backed securities (“MBS”), over the estimated life of the security, using the level yield interest method. Effective January 1, 2019, premium callable securities will be amortized to the earliest call date and securities purchased at a discount will be accreted to maturity. Unrealized gains and losses on AFS securities are excluded from earnings and reported net of tax in AOCI until realized. Declines in the fair value of AFS or HTM securities below their cost that are deemed to be other-than-temporary are reflected in earnings as a realized loss if there is no ability or intent to hold to recovery. If the Company does not intend to sell and will not be required to sell prior to recovery of its amortized cost basis, only the credit component of the impairment is reflected in earnings as a realized loss with the noncredit portion recognized in other comprehensive income. In estimating other-than-temporary impairment losses, we consider (1) the length of time and the extent to which the fair value has been less than cost, (2) the financial condition and near-term prospects of the issuer and (3) our intent and ability to retain our investment in the issuer for a period of time sufficient to allow for any anticipated recovery in fair value. Gains and losses on the sale of securities are recorded in the month of the trade date and are determined using the specific identification method. Equity Investments. Beginning January 1, 2018, upon adoption of ASU 2016-01, equity investments with readily determinable fair values are stated at fair value with the unrealized gains and losses reported in other noninterest income in the consolidated statements of income. For periods prior to January 1, 2018, certain equity investments were classified as AFS and stated at fair value with unrealized gains and losses reported as a separate component of AOCI, net of tax. Equity investments without readily determinable fair values are recorded at cost less impairment, if any.
Securities with Limited Marketability	Securities with Limited Marketability. Securities with limited marketability, such as stock in the FHLB, are carried at cost and assessed for other-than-temporary impairment.
Premises and Equipment	Premises and Equipment . Land is carried at cost. Bank premises and equipment are stated at cost, net of accumulated depreciation. Depreciation is computed on a straight line basis over the estimated useful lives of the related assets. Useful lives are estimated to be 15 to 40 years for premises and 3 to 10 years for equipment. Leasehold improvements are generally depreciated over the lesser of the term of the respective leases or the estimated useful lives of the improvements. Maintenance and repairs are charged to expense as incurred while major improvements and replacements are capitalized.
Bank Owned Life Insurance	Bank-Owned Life Insurance . The Company has purchased life insurance policies on certain key executives. Bank-owned life insurance is recorded at the amount that can be realized under the insurance contract at the balance sheet date, which is the cash surrender value adjusted for other charges or other amounts due that are probable at settlement. Changes in the net cash surrender value of the policies, as well as insurance proceeds received are reflected in noninterest income on the consolidated statements of income and are not subject to income taxes.
Goodwill and Other Intangibles	Goodwill and Other Intangibles . Other intangible assets consist primarily of core deposits and trust relationship intangibles. Intangible assets with definite useful lives are amortized on an accelerated basis over their estimated life. Goodwill and intangible assets that have indefinite useful lives are subject to at least an annual impairment test and more frequently if a triggering event occurs. If any such impairment is determined, a write-down is recorded.
Repurchase Agreements	Repurchase Agreements . We sell certain securities under agreements to repurchase. The agreements are treated as collateralized financing transactions and the obligations to repurchase securities sold are reflected as a liability in the accompanying consolidated balance sheets. The dollar amount of the securities underlying the agreements remains in the asset account. We determine the type of securities to pledge. Generally we pledge U.S. agency MBS.
Derivative Financial Instruments and Hedging Activities	Derivative Financial Instruments and Hedging Activities . Derivative financial instruments are carried on the consolidated balance sheets as other assets or other liabilities, as applicable, at estimated fair value. The accounting for changes in the fair value (i.e., gains or losses) of a derivative financial instrument is determined by whether it has been designated and qualifies as part of a hedging relationship and, further, by the type of hedging relationship. We present derivative financial instruments at fair value in the consolidated balance sheets on a net basis when a right of offset exists, based on transactions with a single counterparty and any cash collateral paid to and/or received from that counterparty for derivative contracts that are subject to legally enforceable master netting arrangements. For derivative instruments that are designated and qualify as cash flow hedges (i.e., hedging the exposure to variability in expected future cash flows that is attributable to a particular risk), the effective portion of the gain or loss on the derivative instrument is reported as a component of other comprehensive income and reclassified into earnings in the same period or periods during which the hedged transaction affects earnings. The remaining gain or loss on the derivative instrument in excess of the cumulative change in the present value of future cash flows of the hedged item (i.e., the ineffective portion), if any, is recognized in current earnings during the period of change. For derivative instruments not designated as hedging instruments, the gain or loss is recognized in current earnings during the period of change. During the three months ended June 30, 2018, we entered into partial term fair value hedges, as allowed under the recently adopted ASU 2017-12, 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 are 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 are utilized to mitigate the effect of changing interest rates on the hedged securities. The hedging strategy converts a portion of the fixed interest rates on the securities to LIBOR-based variable interest rates. For derivatives designated as hedging instruments at inception, statistical regression analysis is used at inception and for each reporting period thereafter to assess whether the derivative used has been and is expected to be highly effective in offsetting changes in the fair value or cash flows of the hedged item. All components of each derivative instrument’s gain or loss are included in the assessment of hedge effectiveness. Net hedge ineffectiveness is recorded in “other noninterest income” on the consolidated statements of income.
Terminated Derivative Financial Instruments	Terminated Derivative Financial Instruments . 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 the first quarter of 2017, we terminated two interest rate swap contracts designated as cash flow hedges. At the time of termination, we determined that the underlying hedged forecasted transactions were still probable of occurring. 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.
Revenue Recognition	Revenue Recognition. Our revenue consists of net interest income on financial assets and financial liabilities and noninterest income. The classifications of our revenue are presented in the consolidated statements of income. On January 1, 2018, we adopted ASU 2014-09, “Revenue from Contracts with Customers (Topic 606)” using the modified retrospective method. The revenue recognition principle in ASU 2014-09 is that an entity should recognize revenue to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. ASU 2014-09 permits an entity to recognize the incremental costs of obtaining a contract as an expense when incurred if the amortization period of the asset would have been one year or less. We generally expense sales commissions when incurred because the amortization period is within one year or less. These costs are recorded within salaries and employee benefits on the consolidated statements of income. Revenue is recognized when obligations under the terms of a contract with our customer are satisfied; generally this occurs with the transfer of control of goods or services. Under ASU 2014-09’s practical expedient to recognize revenue equal to the amounts for which we have a right to invoice, revenue is measured as the amount of consideration we expect to receive in exchange for the transfer of those goods or services. The following summarizes our revenue recognition policies as they relate to revenue from contracts with customers under ASU 2014-09: • Deposit services . Service charges on deposit accounts include fees for banking services provided, overdrafts and non-sufficient funds. Revenue is generally recognized in accordance with published deposit account agreements for retail accounts or contractual agreements for commercial accounts. Our deposit services also include our ATM and debit card interchange revenue that is presented net of the associated costs. Interchange revenue is generated by our deposit customers’ usage and volume of activity. Interchange rates are not controlled by the Company, which effectively acts as processor that collects and remits payments associated with customer debit card transactions. • Trust income. Trust income includes fees and commissions from investment management, administrative and advisory services primarily for individuals, and to a lesser extent, partnerships and corporations. Revenue is recognized on an accrual basis at the time the services are performed and when we have a right to invoice and are based on either the market value of the assets managed or the services provided. • Brokerage services. Brokerage services income includes fees and commissions charged when we arrange for another party to transfer brokerage services to a customer. The fees and commissions under this agent relationship are based upon stated fee schedules based upon the type of transaction, volume and value of the services provided. • Other noninterest income . Other noninterest income includes among other things, merchant services income. Merchant services revenue is derived from third party vendors that process credit card transactions on behalf of our merchant customers. Merchant services revenue is primarily comprised of residual fee income based on the referred merchant’s processing volumes and/or margin.
Income Taxes	Income Taxes . We file a consolidated federal income tax return. Income tax expense represents the taxes expected to be paid or returned for current year taxes adjusted for the change in deferred tax assets and liabilities. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of changes in tax rates is recognized in income in the period the change occurs. Uncertain tax positions arise when it is more likely than not that the tax position taken will be sustained upon examination by the appropriate tax authority. Any income tax benefit as well as penalties and interest related to income tax expense are recorded as a component of income tax expense.
Fair Value of Financial Instruments	Fair Value of Financial Instruments . Fair values of financial instruments are estimated using relevant market information and other assumptions. Fair value estimates involve uncertainties and matters of significant judgment. 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.
Defined Benefit Pension Plan	Defined Benefit Pension Plan . Defined benefit pension obligations and the annual pension costs are determined by independent actuaries and through the use of a number of assumptions that are reviewed by management. These assumptions include a compensation rate increase, a discount rate used to determine the current benefit obligation and a long-term expected rate of return on plan assets. Net periodic defined benefit pension expense includes service cost, interest cost based on the assumed discount rate, an expected return on plan assets, amortization of prior service cost and amortization of net actuarial gains or losses. Prior service costs include the impact of plan amendments on the liabilities and are amortized over the future service periods of active employees expected to receive benefits under the plan. Actuarial gains and losses result from experience different from that assumed and from changes in assumptions. Amortization of actuarial gains and losses is included as a component of net periodic defined benefit pension cost. 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.
Share-Based Awards	Share-Based Awards . Share-based compensation transactions are recognized as compensation cost in the income statement based on their fair values on the date of the grant and recorded over the vesting period.
Loss Contingencies	Loss Contingencies . Loss contingencies, including claims and legal actions arising in the ordinary course of business are recorded as liabilities when the likelihood of loss is probable and an amount or range of loss can be reasonably estimated.
Trust Assets	Wealth Management and Trust Assets . Our wealth management and trust assets, other than cash on deposit at Southside Bank, are not included in the accompanying financial statements, because they are not our assets.
Accounting Pronouncements	Accounting Pronouncements : In February 2016, the FASB issued ASU 2016-02, “Leases (Topic 842).” ASU 2016-02 requires most leases to be recognized on the balance sheet and requires enhanced disclosures. Consistent with legacy GAAP, the recognition, measurement and presentation of expenses and cash flows arising from a lease by a lessee primarily will depend on its classification as a finance or operating lease. However, unlike legacy GAAP which requires only capital leases to be recognized on the balance sheet, the new ASU 2016-02 will require both finance (formerly known as “capital”) and operating leases to be recognized on the balance sheet. ASU 2016-02 is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. The guidance originally required companies to apply the requirements in the year of adoption using a modified retrospective approach beginning in the earliest period presented; however, in July 2018, the FASB issued ASU 2018-11 “Leases (Topic 842): Targeted Improvements,” which provides lessees the option to apply the new leasing standard by recognizing a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. We adopted ASU 2016-02 on January 1, 2019, the effective date of the guidance, using the cumulative-effect adjustment option and did not revise comparative period information or disclosure. 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. Our operating leases relate primarily to bank branches and office space. In conjunction with the adoption, on January 1, 2019, we recognized 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 adoption of the new standard will result in additional quantitative and qualitative disclosures. 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 significant impact on our consolidated financial statements. In March 2017, the FASB issued ASU 2017-08, “Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities.” Under current GAAP, premiums on callable debt securities are 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. ASU 2017-08 is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. 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. We adopted the new standard on January 1, 2019, the effective date of the guidance, and recognized a cumulative-effect adjustment to reduce retained earnings by $16.5 million , before tax.

ACQUISITION (Tables)

ACQUISITION (Tables)	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Schedule of consideration paid	The components of the consideration paid are shown in the following table (in thousands): Fair value of consideration transferred: Common stock issued $ 200,364 Cash 23,941 Total consideration transferred $ 224,305
Schedule of Goodwill	The following table reflects the changes in the carrying amount of our goodwill for the year ended December 31, 2018 (in thousands): Goodwill Balance as of December 31, 2017 $ 201,246 Less: measurement period adjustments (130 ) Balance as of December 31, 2018 $ 201,116
Schedule of assets acquired and liabilities assumed	The estimated fair values of the assets acquired and liabilities assumed as of the closing date of the transaction adjusted for the subsequent measurement period adjustments are shown in the following table (in thousands): As Originally Reported (1) Measurement Period Adjustments Adjusted Balances Cash, cash equivalents and amounts due from banks $ 115,598 $ — $ 115,598 Other investments 610 — 610 Securities available for sale 234,447 — 234,447 Loans 621,318 — 621,318 Property and equipment 26,256 — 26,256 Other assets 7,052 — 7,052 Core deposit intangible 14,700 — 14,700 Trust relationship intangible 5,400 — 5,400 Goodwill 109,726 (130 ) 109,596 Deposits (899,307 ) — (899,307 ) Deferred tax liability, net (7,802 ) 84 (7,718 ) Other liabilities (3,693 ) 46 (3,647 ) $ 224,305 $ — $ 224,305 (1) The estimated fair value as of the acquisition date, November 30, 2017 , as previously reported in our Form 10-K for the year ended December 31, 2017 .
Schedule of acquired PCI loans	The table below details the PCI loan portfolio at the Diboll acquisition date (in thousands): Purchased Credit Impaired Loans at Acquisition Date Contractually required principal and interest payments $ 59,286 Nonaccretable difference 4,560 Cash flows expected to be collected 54,726 Accretable difference 15,389 Fair value of loans acquired with a deterioration of credit quality $ 39,337 The following table presents the outstanding principal balance and carrying value for PCI loans for the periods presented (in thousands): December 31, 2018 December 31, 2017 Outstanding principal balance (1) $ 51,388 $ 52,426 Carrying amount (1) $ 46,402 $ 45,233 (1) At December 31, 2018 , PCI totals include approximately $14.0 million in new funds to a borrower that has since been upgraded to a Pass credit.
Schedule of acquired loans that were considered performing	Acquired loans that were considered performing at the Diboll acquisition date and therefore not subject to ASC 310-30 are shown below (in thousands): Fair Value at Acquisition Date Contractual Amounts Receivable Cash Flows Not Expected to be Collected at Acquisition Date (1) Real Estate Loans: Construction $ 40,122 $ 56,905 $ 330 1-4 Family Residential 82,654 130,167 26,894 Commercial 319,623 484,529 97,431 Commercial Loans 82,083 87,688 1,226 Municipal Loans 7,848 9,998 28 Loans to Individuals 49,651 54,687 1,490 Total Loans $ 581,981 $ 823,974 $ 127,399 (1) Cash flows not expected to be collected relate to estimated credit losses and expected prepayments.

EARNINGS PER SHARE (Tables)

EARNINGS PER SHARE (Tables)	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Earnings per share on a basic and diluted basis	Earnings per share on a basic and diluted basis has been adjusted to give retroactive recognition to stock dividends and is calculated as follows (in thousands, except per share amounts): Years Ended December 31, 2018 2017 2016 Basic and Diluted Earnings: Net Income $ 74,138 $ 54,312 $ 49,349 Basic weighted-average shares outstanding 34,951 29,841 27,118 Add: Stock awards 165 206 129 Diluted weighted-average shares outstanding 35,116 30,047 27,247 Basic Earnings Per Share: Net Income $ 2.12 $ 1.82 $ 1.82 Diluted Earnings Per Share: Net Income $ 2.11 $ 1.81 $ 1.81

ACCUMULATED OTHER COMPREHENSI_2

ACCUMULATED OTHER COMPREHENSIVE LOSS (Tables)	12 Months Ended
	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Schedule of accumulated other comprehensive income (loss) by component	The changes in accumulated other comprehensive loss by component are as follows for the years presented (in thousands): Year Ended December 31, 2018 Pension Plans Unrealized Gains (Losses) on Securities Unrealized Gains (Losses) on Derivatives Net Prior Net Gain (Loss) Total Beginning balance, net of tax $ (16,295 ) $ 6,399 $ (133 ) $ (26,269 ) $ (36,298 ) Other comprehensive (loss) income: Other comprehensive (loss) income before reclassifications (21,956 ) 2,351 — (1,994 ) (21,599 ) Reclassified from accumulated other comprehensive income (1) 3,190 (1,406 ) (7 ) 2,189 3,966 Income tax benefit (expense) 3,941 (198 ) 1 (41 ) 3,703 Net current-period other comprehensive (loss) income, net of tax (14,825 ) 747 (6 ) 154 (13,930 ) Ending balance, net of tax $ (31,120 ) $ 7,146 $ (139 ) $ (26,115 ) $ (50,228 ) Year Ended December 31, 2017 Pension Plans Unrealized Gains (Losses) on Securities Unrealized Gains (Losses) on Derivatives Net Prior Net Gain (Loss) Total Beginning balance, net of tax $ (23,708 ) $ 4,595 $ (133 ) $ (19,247 ) $ (38,493 ) Other comprehensive (loss) income: Other comprehensive income (loss) before reclassifications 15,217 276 8 (5,218 ) 10,283 Reclassified from accumulated other comprehensive income 630 754 (8 ) 1,613 2,989 Income tax (expense) benefit (5,546 ) (360 ) — 532 (5,374 ) Net current-period other comprehensive income (loss), net of tax 10,301 670 — (3,073 ) 7,898 Reclassification of certain deferred tax effects (2) (2,888 ) 1,134 — (3,949 ) (5,703 ) Ending balance, net of tax $ (16,295 ) $ 6,399 $ (133 ) $ (26,269 ) $ (36,298 ) (1) As discussed in “Note 1 – Summary of Significant Accounting and Reporting Policies,” 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). (2) Amounts reclassified to retained earnings due to early adoption of ASU 2018-02. See “Note 1 – Summary of Significant Accounting and Reporting Policies” for further information. Year Ended December 31, 2016 Pension Plans Unrealized Gains (Losses) on Securities Unrealized Gains (Losses) on Derivatives Net Prior Net Gain (Loss) Total Beginning balance, net of tax $ (239 ) $ — $ (44 ) $ (18,400 ) $ (18,683 ) Other comprehensive (loss) income: Other comprehensive (loss) income before reclassifications (33,699 ) 5,255 (129 ) (3,132 ) (31,705 ) Reclassified from accumulated other comprehensive income (2,407 ) 1,815 (8 ) 1,828 1,228 Income tax benefit (expense) 12,637 (2,475 ) 48 457 10,667 Net current-period other comprehensive (loss) income, net of tax (23,469 ) 4,595 (89 ) (847 ) (19,810 ) Ending balance, net of tax $ (23,708 ) $ 4,595 $ (133 ) $ (19,247 ) $ (38,493 )
Reclassification out of Accumulated Other Comprehensive Income	The reclassifications out of accumulated other comprehensive (loss) income into net income are presented below (in thousands): Year Ended December 31, 2018 2017 2016 Unrealized losses on securities transferred: Amortization of unrealized losses (1) $ (1,244 ) $ (1,255 ) $ (429 ) Tax benefit 261 439 150 Net of tax $ (983 ) $ (816 ) $ (279 ) Unrealized gains and losses on available for sale securities: Realized net (loss) gain on sale of securities (2) $ (1,839 ) $ 625 $ 2,836 Tax benefit (expense) 386 (219 ) (993 ) Net of tax $ (1,453 ) $ 406 $ 1,843 Derivatives: Realized net gain (loss) on interest rate swap derivatives (3) $ 1,319 $ (828 ) $ (1,815 ) Tax (expense) benefit (277 ) 290 635 Net of tax $ 1,042 $ (538 ) $ (1,180 ) Amortization of unrealized gains on terminated interest rate swap derivatives (3) $ 87 $ 74 $ — Tax expense (18 ) (26 ) — Net of tax $ 69 $ 48 $ — Amortization of pension plan: Net actuarial loss (4) $ (2,189 ) $ (1,613 ) $ (1,828 ) Prior service credit (4) 7 8 8 Total before tax (2,182 ) (1,605 ) (1,820 ) Tax benefit 459 562 637 Net of tax $ (1,723 ) $ (1,043 ) $ (1,183 ) Total reclassifications for the period, net of tax $ (3,048 ) $ (1,943 ) $ (799 ) (1) Included in interest income on the consolidated statements of income. (2) Listed as net (loss) gain 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 11 - Employee Benefits.”

SECURITIES (Tables)

SECURITIES (Tables)	12 Months Ended
	Dec. 31, 2018
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 December 31, 2018 and 2017 are reflected in the tables below (in thousands): 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 December 31, 2017 Amortized Gross Unrealized Gross Unrealized Estimated AVAILABLE FOR SALE Cost Gains Losses Fair Value Investment Securities: U.S. Government Agency Debentures $ 108,869 $ — $ — $ 108,869 State and Political Subdivisions 392,760 3,895 3,991 392,664 Other Stocks and Bonds 5,024 31 — 5,055 Other Equity Securities (2) 6,027 — 107 5,920 Mortgage-backed Securities: (1) Residential 720,930 4,476 7,377 718,029 Commercial 308,357 761 900 308,218 Total $ 1,541,967 $ 9,163 $ 12,375 $ 1,538,755 HELD TO MATURITY Investment Securities: State and Political Subdivisions $ 413,632 $ 10,879 $ 2,583 $ 421,928 Mortgage-backed Securities: (1) Residential 129,044 1,631 239 130,436 Commercial 366,830 3,812 1,206 369,436 Total $ 909,506 $ 16,322 $ 4,028 $ 921,800 (1) All mortgage-backed securities issued and/or guaranteed by U.S. government agencies or U.S. government-sponsored enterprises. (2) See “Note 1 - Summary of Significant Accounting and Reporting Policies” for further information.
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 December 31, 2018 and December 31, 2017 (in thousands): December 31, 2018 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 $ 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 December 31, 2017 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 $ 32,341 $ 121 $ 172,006 $ 3,870 $ 204,347 $ 3,991 Other Equity Securities (1) 5,920 107 — — 5,920 107 Mortgage-backed Securities: Residential 429,742 3,232 102,973 4,145 532,715 7,377 Commercial 146,796 419 13,134 481 159,930 900 Total $ 614,799 $ 3,879 $ 288,113 $ 8,496 $ 902,912 $ 12,375 HELD TO MATURITY Investment Securities: State and Political Subdivisions $ 85,608 $ 807 $ 56,736 $ 1,776 $ 142,344 $ 2,583 Mortgage-backed Securities: Residential 24,707 157 2,736 82 27,443 239 Commercial 136,491 782 13,552 424 150,043 1,206 Total $ 246,806 $ 1,746 $ 73,024 $ 2,282 $ 319,830 $ 4,028 (1) See “Note 1 – Summary of Significant Accounting and Reporting Policies” for further information.
Interest income recognized on securities	The following tables reflect interest income recognized on securities for the periods presented (in thousands): Years Ended December 31, 2018 2017 2016 U.S. Treasury $ 218 $ 519 $ 739 U.S. Government Agency Debentures 89 178 — State and Political Subdivisions 24,960 24,530 22,654 Other Stocks and Bonds 110 125 195 Other Equity Securities (1) — 116 123 Mortgage-backed Securities 41,584 41,361 37,450 Total interest income on securities $ 66,961 $ 66,829 $ 61,161 (1) See “Note 1 - Summary of Significant Accounting and Reporting Policies” for further information.
Amortized cost and fair value of securities presented by contractual maturity	The amortized cost and estimated fair value of AFS and HTM securities at December 31, 2018 , 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. December 31, 2018 Amortized Cost Fair Value AVAILABLE FOR SALE Investment Securities: Due in one year or less $ 3,559 $ 3,602 Due after one year through five years 39,169 40,055 Due after five years through ten years 176,316 175,181 Due after ten years 512,098 500,472 731,142 719,310 Mortgage-backed Securities 1,282,343 1,270,126 Total $ 2,013,485 $ 1,989,436 December 31, 2018 Amortized Cost Fair Value HELD TO MATURITY Investment Securities: Due in one year or less $ 116 $ 115 Due after one year through five years 1,696 1,674 Due after five years through ten years 1,271 1,257 Due after ten years — — 3,083 3,046 Mortgage-backed Securities: 159,848 156,735 Total $ 162,931 $ 159,781
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 year ended December 31, 2018 (in thousands): Year Ended December 31, 2018 Net losses recognized during the period on equity investments $ (117 ) Less: Net gains (losses) recognized during the period on equity investments sold during the period — Unrealized losses recognized during the reporting period on equity investments still held at the reporting date $ (117 )

LOANS AND ALLOWANCE FOR PROBA_2

LOANS AND ALLOWANCE FOR PROBABLE LOAN LOSSES (Tables)	12 Months Ended
	Dec. 31, 2018
Receivables [Abstract]
Classification of loans in the consolidated balance sheets	Loans in the accompanying consolidated balance sheets are classified as follows (in thousands): December 31, 2018 December 31, 2017 Real Estate Loans: Construction $ 507,732 $ 475,867 1-4 Family Residential 794,499 805,341 Commercial 1,194,118 1,265,159 Commercial Loans 356,649 266,422 Municipal Loans 353,370 345,798 Loans to Individuals 106,431 135,769 Total Loans 3,312,799 3,294,356 Less: Allowance for Loan Losses (1) 27,019 20,781 Net Loans $ 3,285,780 $ 3,273,575 (1) Loans acquired with the Diboll acquisition were measured at fair value on November 30, 2017 , with no carryover of allowance for loan loss. The allowance for loan loss recorded on PCI loans totaled $302,000 as of December 31, 2018 . There was no allowance for loan loss recorded on PCI loans as of December 31, 2017 .
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): Year Ended December 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) (72 ) 1,134 3,894 2,392 (335 ) 1,424 8,437 Loans charged off (14 ) (91 ) (783 ) (756 ) — (2,602 ) (4,246 ) Recoveries of loans charged off 7 356 36 244 — 1,404 2,047 Balance at end of period $ 3,597 $ 3,844 $ 13,968 $ 3,974 $ 525 $ 1,111 $ 27,019 Year Ended December 31, 2017 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans Municipal Loans Loans to Individuals Total Balance at beginning of period $ 4,147 $ 2,665 $ 7,204 $ 2,263 $ 750 $ 882 $ 17,911 Provision (reversal) for loan losses (2) (437 ) 65 3,604 242 110 1,091 4,675 Loans charged off (35 ) (304 ) — (723 ) — (2,391 ) (3,453 ) Recoveries of loans charged off 1 19 13 312 — 1,303 1,648 Balance at end of period (1) $ 3,676 $ 2,445 $ 10,821 $ 2,094 $ 860 $ 885 $ 20,781 Year Ended December 31, 2016 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans (3) Municipal Loans Loans to Individuals Total Balance at beginning of period $ 4,350 $ 2,595 $ 4,577 $ 6,596 $ 725 $ 893 $ 19,736 Provision (reversal) for loan losses (2) (472 ) (28 ) 2,604 6,397 (224 ) 1,503 9,780 Loans charged off (3) — (43 ) — (11,396 ) — (2,948 ) (14,387 ) Recoveries of loans charged off 269 141 23 666 249 1,434 2,782 Balance at end of period $ 4,147 $ 2,665 $ 7,204 $ 2,263 $ 750 $ 882 $ 17,911 (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 $8.4 million in provision for loan losses for the year ended December 31, 2018 , $302,000 related to provision expense on PCI loans. Of the $4.7 million and $9.8 million recorded in provision for loan losses for the year ended December 31, 2017 and 2016 , respectively, none related to provision expense on PCI loans. (3) Of the $11.4 million in commercial charge-offs recorded for the year ended December 31, 2016 , $10.9 million relates to the charge-off of two large commercial borrowing relationships.
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): 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 December 31, 2017 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans Municipal Loans Loans to Individuals Total Ending balance – individually evaluated for impairment (1) $ 12 $ 14 $ 14 $ 252 $ 10 $ 51 $ 353 Ending balance – collectively evaluated for impairment 3,664 2,431 10,807 1,842 850 834 20,428 Balance at end of period $ 3,676 $ 2,445 $ 10,821 $ 2,094 $ 860 $ 885 $ 20,781 (1) The allowance for loan loss on PCI loans totaled $302,000 as of December 31, 2018 . There was no allowance for loan losses associated with PCI loans as of December 31, 2017
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): 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 (1) 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 December 31, 2017 Real Estate Construction 1-4 Family Residential Commercial Commercial Loans Municipal Loans Loans to Individuals Total Loans individually evaluated for impairment $ 86 $ 1,581 $ 895 $ 1,429 $ 502 $ 205 $ 4,698 Loans collectively evaluated for impairment 475,505 797,111 1,232,327 259,745 345,296 134,441 3,244,425 Purchased credit impaired loans 276 6,649 31,937 5,248 — 1,123 45,233 Total ending loan balance $ 475,867 $ 805,341 $ 1,265,159 $ 266,422 $ 345,798 $ 135,769 $ 3,294,356 (1) At December 31, 2018 , PCI totals include approximately $14.0 million in new funds to a borrower that has since been upgraded to a Pass credit.
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): 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 December 31, 2017 Pass Pass Watch (1) Special Mention (1) Substandard (1) Doubtful (1) Total Real Estate Loans: Construction $ 471,446 $ 3,329 $ 77 $ 982 $ 33 $ 475,867 1-4 Family Residential 796,639 559 857 6,610 676 805,341 Commercial 1,136,576 26,275 25,301 76,625 382 1,265,159 Commercial Loans 247,430 9,625 3,956 5,203 208 266,422 Municipal Loans 344,366 — 930 502 — 345,798 Loans to Individuals 134,694 20 102 707 246 135,769 Total $ 3,131,151 $ 39,808 $ 31,223 $ 90,629 $ 1,545 $ 3,294,356 (1) 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 . Includes PCI loans comprised of $362,000 pass watch, $6.0 million special mention, $10.5 million substandard and $925,000 doubtful as of December 31, 2017 .
Summary of nonperforming assets for the period	The following table sets forth nonperforming assets for the periods presented (in thousands): December 31, 2018 December 31, 2017 Nonaccrual loans (1) (2) $ 35,770 $ 2,937 Accruing loans past due more than 90 days (1) — 1 Restructured loans (3) 5,930 5,767 Other real estate owned 1,206 1,613 Repossessed assets — 154 Total Nonperforming Assets $ 42,906 $ 10,472 (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. The increase in nonaccrual loans was primarily due to the addition of four commercial real estate loans to nonaccrual status during the year, one of which was added during the fourth quarter . (2) Includes $10.9 million and $1.3 million of restructured loans as of December 31, 2018 and 2017 , respectively. (3) Includes $3.1 million and $2.9 million in PCI loans restructured as of December 31, 2018 and 2017 , 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 December 31, 2018 December 31, 2017 Real Estate Loans: Construction $ 12 $ 86 1-4 Family Residential 2,202 1,098 Commercial 32,599 595 Commercial Loans 639 903 Loans to Individuals 318 255 Total $ 35,770 $ 2,937
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 for the years ended December 31, 2018 or 2017 . 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 December 31, 2017 Unpaid Contractual Principal Balance Recorded Related Allowance for Loan Losses Real Estate Loans: Construction $ 91 $ 86 $ 12 1-4 Family Residential 4,141 3,952 14 Commercial 1,353 1,199 14 Commercial Loans 1,665 1,605 252 Municipal Loans 502 502 10 Loans to Individuals 237 205 51 Total (1) $ 7,989 $ 7,549 $ 353 (1) Includes $8.0 million and $2.9 million of PCI loans that experienced deterioration in credit quality subsequent to the acquisition date as of December 31, 2018 and December 31, 2017 , 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): 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 December 31, 2017 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 $ 1,302 $ 1,530 $ 68 $ 2,900 $ 472,967 $ 475,867 1-4 Family Residential 8,508 1,574 862 10,944 794,397 805,341 Commercial 1,357 24 5 1,386 1,263,773 1,265,159 Commercial Loans 662 400 333 1,395 265,027 266,422 Municipal Loans 422 — — 422 345,376 345,798 Loans to Individuals 1,526 373 93 1,992 133,777 135,769 Total $ 13,777 $ 3,901 $ 1,361 $ 19,039 $ 3,275,317 $ 3,294,356 (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: Years Ended December 31, 2018 2017 2016 Average Recorded Investment Interest Income Recognized Average Recorded Investment Interest Income Recognized Average Recorded Investment Interest Income Recognized Real Estate Loans: Construction $ 149 $ 7 $ 251 $ — $ 510 $ 22 1-4 Family Residential 4,193 208 4,264 197 3,247 169 Commercial 26,186 65 1,338 30 4,490 63 Commercial Loans 2,131 102 2,862 59 13,481 48 Municipal Loans 474 26 545 30 612 33 Loans to Individuals 250 9 244 9 257 9 Total $ 33,383 $ 417 $ 9,504 $ 325 $ 22,597 $ 344
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 during the periods presented (dollars in thousands): December 31, 2018 Extend Amortization Period Interest Rate Reductions Combination Total Modifications Number of Contracts Real Estate Loans: 1-4 Family Residential $ — $ 79 $ — $ 79 1 Commercial 10,398 — 274 10,672 3 Commercial Loans 211 — 215 426 13 Loans to Individuals 8 33 51 92 5 Total $ 10,617 $ 112 $ 540 $ 11,269 22 December 31, 2017 Extend Amortization Period Interest Rate Reductions Combination Total Modifications Number of Contracts Commercial Loans $ 778 $ — $ 241 $ 1,019 4 Loans to Individuals 23 — 52 75 6 Total $ 801 $ — $ 293 $ 1,094 10
Schedule of acquired PCI loans	The table below details the PCI loan portfolio at the Diboll acquisition date (in thousands): Purchased Credit Impaired Loans at Acquisition Date Contractually required principal and interest payments $ 59,286 Nonaccretable difference 4,560 Cash flows expected to be collected 54,726 Accretable difference 15,389 Fair value of loans acquired with a deterioration of credit quality $ 39,337 The following table presents the outstanding principal balance and carrying value for PCI loans for the periods presented (in thousands): December 31, 2018 December 31, 2017 Outstanding principal balance (1) $ 51,388 $ 52,426 Carrying amount (1) $ 46,402 $ 45,233 (1) At December 31, 2018 , PCI totals include approximately $14.0 million in new funds to a borrower that has since been upgraded to a Pass credit.
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): December 31, 2018 December 31, 2017 Balance at beginning of period $ 18,721 $ 2,480 Additions due to acquisition — 15,389 Changes in expected cash flows not affecting non-accretable differences (1,445 ) — Reclassifications (to) from nonaccretable discount 1,211 1,720 Accretion (3,433 ) (868 ) Balance at end of period $ 15,054 $ 18,721

PREMISES AND EQUIPMENT (Tables)

PREMISES AND EQUIPMENT (Tables)	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Schedule of premises and equipment	December 31, 2018 December 31, 2017 (in thousands) Premises $ 166,128 $ 158,817 Furniture and equipment 41,810 40,565 207,938 199,382 Less: accumulated depreciation 71,966 65,742 Total $ 135,972 $ 133,640

DEPOSITS (Tables)

DEPOSITS (Tables)	12 Months Ended
	Dec. 31, 2018
Deposits [Abstract]
Schedule of deposits at year-end	December 31, 2018 December 31, 2017 (in thousands) Noninterest bearing demand deposits: Private accounts $ 967,096 $ 995,685 Public accounts 27,584 41,716 Total noninterest bearing demand deposits 994,680 1,037,401 Interest bearing deposits: Private accounts: Savings deposits 360,007 356,857 Money market demand deposits 440,442 443,015 Platinum money market deposits 344,546 308,105 Interest bearing checking 662,911 686,816 NOW demand deposits 23,451 20,142 Certificates and other time deposits of $250,000 or more 84,564 87,195 Certificates and other time deposits under $250,000 680,282 534,220 Total private accounts 2,596,203 2,436,350 Public accounts: Savings deposits 320 304 Money market demand deposits 15,513 19,560 Platinum money market deposits 329,695 360,006 Interest bearing checking 56,694 55,902 NOW demand deposits 141,200 114,401 Certificates and other time deposits of $250,000 or more 281,204 462,941 Certificates and other time deposits under $250,000 9,521 28,582 Total public accounts 834,147 1,041,696 Total interest bearing deposits 3,430,350 3,478,046 Total deposits $ 4,425,030 $ 4,515,447
Schedule of maturities of time deposits	At December 31, 2018 , the scheduled maturities of certificates and other time deposits, including public accounts, were as follows (in thousands): 2019 $ 845,661 2020 116,542 2021 42,254 2022 20,003 2023 25,931 2024 and thereafter 5,180 $ 1,055,571

BORROWING ARRANGEMENTS (Tables)

BORROWING ARRANGEMENTS (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Schedule of debt	Information related to borrowings is provided in the table below (dollars in thousands): December 31, 2018 December 31, 2017 Federal funds purchased and repurchase agreements: Balance at end of period $ 36,810 $ 9,498 Average amount outstanding during the period (1) 10,880 8,120 Maximum amount outstanding during the period (2) 36,810 9,498 Weighted average interest rate during the period (3) 1.4 % 0.2 % Interest rate at end of period (4) 2.1 % 0.2 % FHLB borrowings: Balance at end of period $ 719,065 $ 1,017,361 Average amount outstanding during the period (1) 720,785 1,222,033 Maximum amount outstanding during the period (2) 957,231 1,414,453 Weighted average interest rate during the period (3) 1.8 % 1.2 % Interest rate at end of period (4) 2.3 % 1.4 % (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 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 December 31, 2018 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 $ 36,686 $ 124 $ — $ — $ — $ — $ 36,810 FHLB borrowings 336,502 365,165 11,483 — — 5,915 719,065 Total obligations $ 373,188 $ 365,289 $ 11,483 $ — $ — $ 5,915 $ 755,875

LONG-TERM OBLIGATIONS (Tables)

LONG-TERM OBLIGATIONS (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Schedule of long-term debt by entity	December 31, 2018 December 31, (in thousands) Subordinated notes: (1) 5.50% Subordinated Notes, net of unamortized debt issuance costs (2) $ 98,407 $ 98,248 Total Subordinated notes 98,407 98,248 Trust preferred subordinated debentures: (3) Southside Statutory Trust III, net of unamortized debt issuance costs (4) 20,554 20,549 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 60,246 60,241 Total Long-term debt $ 158,653 $ 158,489 (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 December 31, 2018 and $1.8 million at December 31, 2017 . (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 $65,000 at December 31, 2018 and $70,000 at December 31, 2017 .
Schedule of subordinated borrowing	As of December 31, 2018 , 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 BENEFITS (Tables)

EMPLOYEE BENEFITS (Tables)	12 Months Ended
	Dec. 31, 2018
Employee Benefits Including Defined Benefit Plans and Share-based Compensation Plans [Abstract]
Schedule of changes in projected benefit obligation and fair value of plan assets	Year Ended December 31, 2018 2017 2016 Defined Benefit Pension Plan Defined Restoration Plan Defined Benefit Pension Plan Defined Restoration Plan Defined Benefit Pension Plan Defined Restoration Plan (in thousands) Change in Projected Benefit Obligation: Benefit obligation at end of prior year $ 94,276 $ 4,392 $ 14,642 $ 88,071 $ 4,238 $ 12,723 $ 80,040 $ 4,685 $ 12,024 Service cost 1,548 — 293 1,398 — 247 1,375 — 207 Interest cost 3,392 163 597 3,601 177 567 3,731 212 535 Actuarial (gain) loss (9,399 ) (480 ) 344 5,404 418 1,751 4,978 275 237 Benefits paid (3,622 ) (183 ) (576 ) (4,128 ) (43 ) (646 ) (3,632 ) (31 ) (280 ) Expenses paid (203 ) (19 ) — (70 ) (47 ) — (91 ) (39 ) — Plan amendments — — — — — — 121 — — Settlements — — — — (351 ) — — (864 ) — Special and contractual termination benefits — — — — — — 1,549 — — Benefit obligation at end of year 85,992 3,873 15,300 94,276 4,392 14,642 88,071 4,238 12,723 Change in Plan Assets: Fair value of plan assets at end of prior year 91,233 4,031 — 85,293 2,993 — 76,355 3,740 — Actual return (4,497 ) (259 ) — 8,138 479 — 7,661 187 — Employer contributions 2,000 500 576 2,000 1,000 646 5,000 — 280 Benefits paid (3,622 ) (183 ) (576 ) (4,128 ) (43 ) (646 ) (3,632 ) (31 ) (280 ) Expenses paid (203 ) (19 ) — (70 ) (47 ) — (91 ) (39 ) — Settlements — — — — (351 ) — — (864 ) — Fair value of plan assets at end of year 84,911 4,070 — 91,233 4,031 — 85,293 2,993 — (Un)Funded status at end of year (1,081 ) 197 (15,300 ) (3,043 ) (361 ) (14,642 ) (2,778 ) (1,245 ) (12,723 ) Accrued benefit (liability) asset recognized $ (1,081 ) $ 197 $ (15,300 ) $ (3,043 ) $ (361 ) $ (14,642 ) $ (2,778 ) $ (1,245 ) $ (12,723 ) Accumulated benefit obligation at end of year $ 77,888 $ 3,873 $ 13,403 $ 83,802 $ 4,392 $ 13,246 $ 77,639 $ 4,238 $ 11,133
Schedule of amounts recognized in other comprehensive income (loss)	Amounts related to our defined benefit pension plans and restoration plan recognized as a component of other comprehensive (loss) income were as follows (in thousands): Year Ended December 31, 2018 2017 2016 Defined Defined Restoration Defined Defined Restoration Defined Defined Restoration Recognition of net loss $ 1,512 $ — $ 677 $ 1,312 $ — $ 301 $ 1,642 $ — $ 186 Recognition of prior service (credit) cost (14 ) — 7 (14 ) — 6 (14 ) — 6 Recognition of loss (gain) due to settlement — — — — 8 — — (8 ) — Net (loss) gain occurring during the year (1,581 ) (69 ) (344 ) (3,317 ) (150 ) (1,751 ) (2,541 ) (354 ) (237 ) Net prior service cost occurring during the year — — — — — — (121 ) — — (83 ) (69 ) 340 (2,019 ) (142 ) (1,444 ) (1,034 ) (362 ) (45 ) Deferred tax benefit (expense) 17 14 (71 ) 241 30 259 362 127 16 Other comprehensive (loss) income, net of tax $ (66 ) $ (55 ) $ 269 $ (1,778 ) $ (112 ) $ (1,185 ) $ (672 ) $ (235 ) $ (29 )
Schedule of amounts in accumulated other comprehensive income (loss) recognized in net periodic benefit cost during period	Net amounts recognized in net periodic benefit cost and other comprehensive loss were as follows (in thousands): December 31, 2018 December 31, 2017 Defined Benefit Pension Plan Defined Restoration Plan Defined Defined Restoration Plan Net loss $ 1,512 $ — $ 677 $ 1,312 $ — $ 301 Prior service (credit) cost (14 ) — 7 (14 ) — 6 Loss (gain) recognized due to settlement — — — — 8 — 1,498 — 684 1,298 8 307 Deferred tax (expense) benefit (315 ) — (144 ) (454 ) (2 ) (107 ) Accumulated other comprehensive income (loss), net of tax $ 1,183 $ — $ 540 $ 844 $ 6 $ 200
Schedule of amounts recognized as a component of accumulated other comprehensive loss	Amounts recognized as a component of accumulated other comprehensive loss were as follows (in thousands): December 31, 2018 December 31, 2017 Defined Defined Restoration Defined Defined Restoration Net (loss) gain $ (28,928 ) $ (171 ) $ (3,984 ) $ (28,859 ) $ (102 ) $ (4,317 ) Prior service cost (123 ) — (24 ) (109 ) — (31 ) (29,051 ) (171 ) (4,008 ) (28,968 ) (102 ) (4,348 ) Deferred tax benefit (expense) 6,100 35 841 9,674 15 1,276 Reclassification of certain deferred tax effects (1) — — — (3,591 ) 6 (364 ) Accumulated other comprehensive (loss) income, net of tax $ (22,951 ) $ (136 ) $ (3,167 ) $ (22,885 ) $ (81 ) $ (3,436 ) (1) Amounts reclassified to retained earnings due to early adoption of ASU 2018-02. See “Note 1 – Summary of Significant Accounting and Reporting Policies” for further information.
Schedule of components of net periodic pension cost and postretirement benefit cost	Net periodic pension cost and postretirement benefit cost included the following components (in thousands): Year Ended December 31, 2018 2017 2016 Defined Benefit Pension Plan: Service cost $ 1,548 $ 1,398 $ 1,375 Interest cost 3,392 3,601 3,731 Expected return on assets (6,483 ) (6,050 ) (5,224 ) Net loss amortization 1,512 1,312 1,642 Prior service credit amortization (14 ) (14 ) (14 ) Special and contractual termination benefits — — 1,549 Net periodic benefit cost $ (45 ) $ 247 $ 3,059 Defined Benefit Pension Plan Acquired: Service cost $ — $ — $ — Interest cost 163 177 212 Expected return on assets (290 ) (212 ) (265 ) Net loss amortization — — — Prior service credit amortization — — — Loss (gain) recognized due to settlement — 8 (8 ) Net periodic benefit cost $ (127 ) $ (27 ) $ (61 ) Restoration Plan: Service cost $ 293 $ 247 $ 207 Interest cost 597 567 535 Net loss amortization 677 301 186 Prior service cost amortization 7 6 6 Net periodic benefit cost $ 1,574 $ 1,121 $ 934
Schedule of amounts in accumulated other comprehensive income (loss) that is expected to be recognized as a component of net periodic benefit cost during the next fiscal year	The amounts in accumulated other comprehensive income (loss) that are expected to be recognized as components of net periodic benefit cost during 2019 are as follows (in thousands): Defined Benefit Pension Plan Defined Restoration Net loss $ 1,774 $ — $ 398 Prior service (credit) cost (14 ) — 6 1,760 — 404 Deferred tax benefit (370 ) — (85 ) Accumulated other comprehensive loss, net of tax $ 1,390 $ — $ 319
Schedule of assumptions used to determine benefit obligation and net periodic benefit cost	The assumptions used to determine the benefit obligation were as follows: December 31, 2018 December 31, 2017 Defined Benefit Defined Restoration Defined Defined Restoration Discount rate 4.32 % 4.32 % 4.32 % 3.71 % 3.71 % 3.71 % Compensation increase rate 3.50 % — 3.50 % 3.50 % — 3.50 % The assumptions used to determine net periodic pension cost and postretirement benefit cost were as follows: Year Ended December 31, 2018 2017 2016 Defined Benefit Pension Plan: Discount rate 3.71 % 4.23 % 4.56 % Expected long-term rate of return on plan assets 7.25 % 7.25 % 7.25 % Compensation increase rate 3.50 % 3.50 % 3.50 % Defined Benefit Pension Plan Acquired Discount rate 3.71 % 4.23 % 4.56 % Expected long-term rate of return on plan assets 7.25 % 7.25 % 7.25 % Compensation increase rate — — — Restoration Plan: Discount rate 3.71 % 4.23 % 4.56 % Compensation increase rate 3.50 % 3.50 % 3.50 %
Schedule of allocation of plan assets	The major categories of assets in our Plan and the Acquired Plan are presented in the following table (in thousands). Assets are segregated by the level of the valuation inputs within the fair value hierarchy established by ASC Topic 820 “Fair Value Measurements and Disclosures,” utilized to measure fair value (see “Note 13 – Fair Value Measurement”). Our Restoration Plan is unfunded. December 31, 2018 December 31, 2017 Defined Defined Defined Defined Level 1: Cash $ 278 $ — $ 423 $ — Equity Securities: U.S. large cap (1) 5,204 — 6,198 — U.S. mid cap (2) 18,913 — 21,379 — U.S. small cap (3) 9,900 — 10,706 — Fixed Income Securities: International developed (4) 6,733 — 8,601 — International emerging (2) 3,464 — 4,308 — Level 2: Cash Equivalents 15,025 — 13,256 — Equity Securities: U.S. large cap (1) — 1,360 — 1,440 U.S. mid cap (2) — 152 — 167 U.S. small cap (3) — 72 — 84 International (5) — 735 — 712 Fixed Income Securities: Corporate bonds (6) 952 407 1,118 378 U.S. government agencies (6) 20,182 — 19,303 — Municipal bonds (6) 3,991 — 5,595 — U.S. agency mortgage-backed securities (7) 269 — 346 — Asset-backed securities (8) — 743 — 717 Real estate (9) — 286 — 241 Balanced Asset Allocation (10) — 84 — 81 Other (11) — 231 — 211 Total fair value of plan assets $ 84,911 $ 4,070 $ 91,233 $ 4,031 (1) For the defined benefit pension plan, this category is comprised of individual securities that are actively managed and a broadly diversified “passive” mutual fund. The Acquired Plan assets in this category consist of pooled separate accounts invested in mutual funds and domestic stocks. (2) For the defined benefit pension plan, this category is comprised of broadly diversified “passive” mutual funds. The Acquired Plan assets in this category consist of pooled separate accounts invested in mutual funds and domestic stocks. (3) For the defined benefit pension plan, this category is comprised of broadly diversified “passive” mutual funds and shares of Southside Bancshares stock that is owned in the Plan. The Acquired Plan assets in this category consist of pooled separate accounts invested in mutual funds and domestic stocks. (4) This category is comprised of individual securities that are actively managed and a broadly diversified “passive” mutual fund. (5) This category is comprised of pooled separate accounts invested in mutual funds and international stocks. (6) For the defined benefit pension plan, this category is comprised of individual investment grade securities that are generally held to maturity in the Plan. The Acquired Plan assets in this category consist of pooled separate accounts invested in investment grade and below investment grade bonds. (7) This category is comprised of individual securities that are generally not held to maturity. (8) This category is mainly comprised of a pooled separate account invested in asset backed securities, residential mortgage backed securities, commercial mortgage backed securities and corporate bonds. (9) This category is comprised of a pooled separate account invested in commercial real estate and includes mortgage loans which are backed by the associated properties. (10) This category is comprised of a pooled separate account invested in a single mutual fund invested in a combination of fixed income and equity investment options. (11) This category is comprised of a pooled separate account invested in a broad range of instruments including, but not limited to, equities, bonds, currencies, convertible securities and derivatives such as futures, options, swaps and forwards.
Schedule of expected future benefit payments related to pension and postretirement plans	As of December 31, 2018 , expected future benefit payments related to the Plan, the Acquired Plan and the Restoration Plan were as follows (in thousands): Defined Benefit Pension Plan Defined Benefit Restoration 2019 $ 3,836 $ 66 $ 723 2020 3,951 229 780 2021 4,142 129 916 2022 4,354 90 1,031 2023 4,520 92 1,005 2024 through 2028 25,008 897 5,521 $ 45,811 $ 1,503 $ 9,976
Schedule of shares issued in connection with stock compensation awards	Shares issued in connection with stock compensation awards along with other related information are presented in the following table without the retroactive recognition of stock dividends (in thousands, except share amounts): Year Ended December 31, 2018 2017 2016 New shares issued from available authorized shares — 48,311 108,225 New shares issued from available treasury shares 140,692 111,045 — Total 140,692 159,356 108,225 Proceeds from stock option exercises $ 2,653 $ 2,692 $ 1,663
Schedule of stock option valuation assumptions	The estimated weighted-average grant-date fair value per option and the underlying Black-Scholes option-pricing model assumptions are summarized in the following table for years in which we granted NQSOs pursuant to the incentive plans: Years Ended December 31, 2018 2017 2016 Weighted-average grant date fair value per option $6.78 — $7.18 Weighted-average assumptions: Risk-free interest rates 2.81% — 1.79% Expected dividend yield 1.10% — 2.69% Expected volatility factors of the market price of Southside Bancshares common stock 25.41% — 27.02% Expected option life (in years) 6.2 — 6.2
Schedule of stock options and restricted stock units award activity	A combined summary of activity in our share-based plans as of December 31, 2018 is presented below: Restricted Stock Units Outstanding Stock Options Outstanding Number of Shares Weighted- Average Grant-Date Fair Value Number of Shares Weighted- Average Exercise Price Weighted- Average Grant-Date Fair Value Balance, January 1, 2018 78,253 $ 32.04 690,312 $ 26.02 $ 6.19 Granted 64,358 34.28 356,849 34.52 6.78 Stock options exercised — — (115,277 ) 23.02 5.69 Stock awards vested (29,752 ) 31.14 — — — Forfeited (3,109 ) 32.93 (16,980 ) 32.51 6.67 Canceled/expired — — (5,553 ) 30.06 6.68 Balance, December 31, 2018 109,750 $ 33.57 909,351 $ 29.59 $ 6.47
Schedule of shares stock option exercise price range	Other information regarding options outstanding and exercisable as of December 31, 2018 is as follows: Options Outstanding Options Exercisable Range of Exercise Prices Number Weighted- Weighted- Number Weighted- $ 14.67 - $20.00 110,291 $ 15.89 3.03 110,291 $ 15.89 20.01 - 25.00 106,826 22.92 5.43 82,747 23.01 25.01 - 30.00 202,009 26.68 6.47 136,613 26.58 30.01 - 35.00 346,965 34.52 9.41 — — 35.01 - 37.28 143,260 37.28 7.90 76,710 37.28 Total 909,351 $ 29.59 7.28 406,361 $ 24.97

DERIVATIVE FINANCIAL INSTRUME_2

DERIVATIVE FINANCIAL INSTRUMENTS AND HEDGING ACTIVITIES (Tables)	12 Months Ended
	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of derivative instruments in statement of financial position, fair value	The following tables present the notional and estimated fair value amount of derivative positions outstanding (in thousands): December 31, 2018 December 31, 2017 Estimated Fair Value Estimated Fair Value Notional Amount (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 $ 9,388 $ 457 $ 240,000 $ 7,922 $ 22 Swaps-Fair Value Hedge-Financial institution counterparties 21,100 — 657 — — — Derivatives designated as non-hedging instruments Interest rate contracts: Swaps-Financial institution counterparties 93,967 1,119 1,087 67,220 92 612 Swaps-Customer counterparties 93,967 1,087 1,119 67,220 612 92 Gross derivatives 11,594 3,320 8,626 726 Offsetting derivative assets/liabilities (2,201 ) (2,201 ) (114 ) (114 ) Cash collateral received/posted (8,306 ) — (7,900 ) (520 ) Net derivatives included in the consolidated balance sheets (2) $ 1,087 $ 1,119 $ 612 $ 92 (1) Notional amounts, which represent the extent of involvement in the derivatives market, are used to determine the contractual cash flows required in accordance with the terms of the agreement. These amounts are typically not exchanged, significantly exceed amounts subject to credit or market risk and are not reflected in the consolidated balance sheets. (2) Net derivative assets are included in other assets and net derivative liabilities are included in other liabilities on the consolidated balance sheets. Included in the fair value of net derivative assets and net derivative liabilities are credit valuation adjustments reflecting counterparty credit risk and our credit risk. We had no credit exposure related to interest rate swaps with financial institutions and $1.1 million related to interest rate swaps with customers at December 31, 2018 . We had net credit exposure of $30,000 related to interest rate swaps with financial institutions and $612,000 related to interest rate swaps with customers at December 31, 2017 . 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	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 December 31, 2018 and December 31, 2017 : December 31, 2018 December 31, 2017 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 4.8 2.45 % 1.58 % $ 240,000 5.3 1.44 % 1.43 % Swaps-Fair Value Hedge Financial institution counterparties 21,100 7.5 2.56 3.00 — — — — Swaps-Non-Hedging Financial institution counterparties 93,967 11.6 2.36 2.58 67,220 12.7 1.39 2.37 Customer counterparties 93,967 11.6 2.58 2.36 67,220 12.7 2.37 1.39

FAIR VALUE MEASUREMENT (Tables)

FAIR VALUE MEASUREMENT (Tables)	12 Months Ended
	Dec. 31, 2018
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	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 (2) 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 (3) 37,813 — — 37,813 Total asset nonrecurring fair value measurements $ 39,019 $ — $ — $ 39,019 December 31, 2017 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: U.S. Government Agency Debentures $ 108,869 $ — $ 108,869 $ — State and Political Subdivisions 392,664 — 392,664 — Other Stocks and Bonds 5,055 — 5,055 — Equity Investments (2) 5,920 5,920 — — Mortgage-backed Securities: (1) Residential 718,029 — 718,029 — Commercial 308,218 — 308,218 — Derivative assets: Interest rate swaps 8,626 — 8,626 — Total asset recurring fair value measurements $ 1,547,381 $ 5,920 $ 1,541,461 $ — Derivative liabilities: Interest rate swaps $ 726 $ — $ 726 $ — Total liability recurring fair value measurements $ 726 $ — $ 726 $ — Nonrecurring fair value measurements Foreclosed assets $ 1,767 $ — $ — $ 1,767 Impaired loans (3) 6,536 — — 6,536 Total asset nonrecurring fair value measurements $ 8,303 $ — $ — $ 8,303 (1) All mortgage-backed securities are issued and/or guaranteed by U.S. government agencies or U.S. government-sponsored enterprises. (2) With the adoption of ASU 2016-01 on January 1, 2018, these investments are included in equity investments on our consolidated balance sheets. The guidance was applied on a prospective approach resulting in prior-periods no longer being comparable. See “Note 1 - Summary of Significant Accounting and Reporting Policies” for further information. (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.
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 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 — Estimated Fair Value December 31, 2017 Carrying Total Level 1 Level 2 Level 3 Financial Assets: Cash and cash equivalents $ 198,692 $ 198,692 $ 198,692 $ — $ — Investment Securities: Held to maturity, at carrying value 413,632 421,928 — 421,928 — Mortgage-backed Securities: Held to maturity, at carrying value 495,874 499,872 — 499,872 — FHLB stock, at cost 55,729 55,729 — 55,729 — Equity investments 5,821 5,821 — 5,821 — Loans, net of allowance for loan losses 3,273,575 3,269,316 — — 3,269,316 Loans held for sale 2,001 2,001 — 2,001 — Financial Liabilities: Deposits $ 4,515,447 $ 4,506,133 $ — $ 4,506,133 $ — Federal funds purchased and repurchase agreements 9,498 9,498 — 9,498 — FHLB borrowings 1,017,361 1,008,292 — 1,008,292 — Subordinated notes, net of unamortized debt issuance costs 98,248 99,665 — 99,665 — Trust preferred subordinated debentures, net of unamortized debt issuance costs 60,241 47,622 — 47,622 —

SHAREHOLDERS' EQUITY (Tables)

SHAREHOLDERS' EQUITY (Tables)	12 Months Ended
	Dec. 31, 2018
Regulatory Capital Requirements [Abstract]
Schedule of compliance with regulatory capital requirements under ranking regulations	As of December 31, 2018 , the most recent notification from the FDIC categorized us as well capitalized under the regulatory framework for prompt corrective action. To be categorized as well capitalized we must maintain minimum Common Equity Tier 1 risk-based, Tier 1 risk-based, Total risk-based and Tier 1 leverage ratios as set forth in the table below. There are no conditions or events since that notification that management believes have changed our category. Actual For Capital Adequacy Purposes To Be Well Capitalized Under Prompt Corrective Actions Provisions Amount Ratio Amount Ratio Amount Ratio December 31, 2018: (dollars in thousands) Common Equity Tier 1 (to Risk Weighted Assets) Consolidated $ 568,283 14.77 % $ 173,174 4.50 % N/A N/A Bank Only $ 714,991 18.59 % $ 173,095 4.50 % $ 250,026 6.50 % Tier 1 Capital (to Risk Weighted Assets) Consolidated $ 626,718 16.29 % $ 230,899 6.00 % N/A N/A Bank Only $ 714,991 18.59 % $ 230,793 6.00 % $ 307,725 8.00 % Total Capital (to Risk Weighted Assets) Consolidated $ 754,034 19.59 % $ 307,865 8.00 % N/A N/A Bank Only $ 743,900 19.34 % $ 307,725 8.00 % $ 384,656 10.00 % Tier 1 Capital (to Average Assets) (1) Consolidated $ 626,718 10.64 % $ 235,689 4.00 % N/A N/A Bank Only $ 714,991 12.14 % $ 235,532 4.00 % $ 294,415 5.00 % December 31, 2017: Common Equity Tier 1 (to Risk Weighted Assets) Consolidated $ 570,610 14.65 % $ 175,216 4.50 % N/A N/A Bank Only $ 711,157 18.27 % $ 175,145 4.50 % $ 252,987 6.50 % Tier 1 Capital (to Risk Weighted Assets) Consolidated $ 627,532 16.12 % $ 233,621 6.00 % N/A N/A Bank Only $ 711,157 18.27 % $ 233,527 6.00 % $ 311,369 8.00 % Total Capital (to Risk Weighted Assets) Consolidated $ 748,532 19.22 % $ 311,495 8.00 % N/A N/A Bank Only $ 733,909 18.86 % $ 311,369 8.00 % $ 389,211 10.00 % Tier 1 Capital (to Average Assets) (1) Consolidated $ 627,532 11.16 % $ 224,844 4.00 % N/A N/A Bank Only $ 711,157 12.66 % $ 224,741 4.00 % $ 280,926 5.00 % (1) Refers to quarterly average assets as calculated in accordance with policies established by bank regulatory agencies.

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Schedule of components of income tax provision	The income tax expense included in the accompanying statements of income consists of the following (in thousands): Years Ended December 31, 2018 2017 2016 Current income tax expense $ 4,009 $ 12,607 $ 8,557 Deferred income tax expense 6,154 3,514 1,768 Income tax expense $ 10,163 $ 16,121 $ 10,325
Schedule of net deferred tax assets and liabilities	The components of the net deferred tax asset (liability) as of December 31, 2018 and 2017 are summarized below (in thousands): Assets Liabilities Allowance for loan losses $ 5,673 $ Retirement and other benefit plans (2,519 ) Premises and equipment (6,360 ) Core deposit intangible (2,748 ) Unrealized losses on securities available for sale 7,926 Effective hedging derivatives (1,761 ) Fair value adjustment on loans 1,894 Fair value adjustment on time deposits (6 ) Unfunded status of defined benefit plan 6,979 State business tax credit 483 Stock-based compensation 797 Other (582 ) Gross deferred tax assets (liabilities) 23,752 (13,976 ) Net deferred tax asset at December 31, 2018 $ 9,776 Allowance for loan losses $ 4,364 $ Retirement and other benefit plans (2,102 ) Premises and equipment (5,716 ) Core deposit intangible (3,660 ) Unrealized losses on securities available for sale 4,285 Effective hedging derivatives (1,701 ) Fair value adjustment on loans 2,607 Fair value adjustment on time deposits (54 ) Alternative minimum tax credit 6,943 Unfunded status of defined benefit plan 7,018 State business tax credit 544 Stock-based compensation 642 Other (966 ) Gross deferred tax assets (liabilities) 26,403 (14,199 ) Net deferred tax asset at December 31, 2017 $ 12,204
Schedule of income tax reconciliation	A reconciliation of tax at statutory rates and total tax expense is as follows (dollars in thousands): Years Ended December 31, 2018 2017 2016 Amount Percent of Pre-Tax Income Amount Percent of Pre-Tax Income Amount Percent of Pre-Tax Income Statutory tax expense $ 17,703 21.0 % $ 24,652 35.0 % $ 20,886 35.0 % Increase (decrease) in taxes from: Tax rate changes (767 ) (0.9 )% 2,416 3.4 % — — Tax exempt interest (6,257 ) (7.4 )% (10,195 ) (14.5 )% (9,879 ) (16.6 )% Bank owned life insurance (613 ) (0.7 )% (885 ) (1.2 )% (915 ) (1.5 )% Share-based compensation (191 ) (0.2 )% (482 ) (0.7 )% — — Acquisition costs — — 467 0.7 % — — State business tax 297 0.3 % 68 0.1 % 71 0.1 % Other, net (9 ) — 80 0.1 % 162 0.3 % Income tax expense $ 10,163 12.1 % $ 16,121 22.9 % $ 10,325 17.3 %

OFF-BALANCE-SHEET ARRANGEMENT_2

OFF-BALANCE-SHEET ARRANGEMENTS, COMMITMENTS AND CONTINGENCIES (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Scheduled maturities of unused commitments	Financial instruments with off-balance-sheet risk were as follows (in thousands): December 31, 2018 December 31, 2017 Unused commitments: Commitments to extend credit $ 874,557 $ 804,715 Standby letters of credit 27,438 14,890 Total $ 901,995 $ 819,605
Future minimum commitments of non-cancelable operating leases	Future minimum rental commitments due under non-cancelable operating leases at December 31, 2018 were as follows (in thousands): 2019 $ 1,265 2020 1,158 2021 906 2022 742 2023 560 2024 and thereafter 1,352 $ 5,983
Schedule of future minimum rental payments receivable under non-cancelable operating leases	At December 31, 2018 , non-cancelable operating leases for the building with future minimum lease payments are as follows (in thousands): 2019 $ 2,574 2020 2,427 2021 1,374 2022 1,352 2023 1,119 2024 and thereafter 3,996 $ 12,842

PARENT COMPANY FINANCIAL INFO_2

PARENT COMPANY FINANCIAL INFORMATION (Tables)	12 Months Ended
	Dec. 31, 2018
Condensed Financial Information Disclosure [Abstract]
Condensed balance sheets	Condensed financial information for Southside Bancshares, Inc. (parent company only) was as follows (in thousands, except share amounts): CONDENSED BALANCE SHEETS December 31, 2018 2017 ASSETS Cash and due from banks $ 11,431 $ 8,483 Investment in bank subsidiaries at equity in underlying net assets 875,814 894,010 Investment in nonbank subsidiaries at equity in underlying net assets 1,826 1,826 Other assets 4,290 10,350 Total assets $ 893,361 $ 914,669 LIABILITIES Subordinated notes, net of unamortized debt issuance costs $ 98,407 $ 98,248 Trust preferred subordinated debentures, net of unamortized debt issuance costs 60,246 60,241 Other liabilities 3,417 2,040 Total liabilities 162,070 160,529 SHAREHOLDERS’ EQUITY Common stock: ($1.25 par value, 80,000,000 shares authorized, 37,845,224 shares issued at December 31, 2018 and 40,000,000 shares authorized and 37,802,352 shares issued at December 31, 2017) 47,307 47,253 Paid-in capital 762,470 757,439 Retained earnings 64,797 32,851 Treasury stock, at cost (4,120,475 at December 31, 2018 and 2,802,019 at December 31, 2017) (93,055 ) (47,105 ) Accumulated other comprehensive loss (50,228 ) (36,298 ) Total shareholders’ equity 731,291 754,140 Total liabilities and shareholders’ equity $ 893,361 $ 914,669
Condensed statements of income	CONDENSED STATEMENTS OF INCOME Years Ended December 31, 2018 2017 2016 Income Dividends from subsidiary $ 90,000 $ 27,000 $ 30,000 Interest income 78 60 51 Total income 90,078 27,060 30,051 Expense Interest expense 8,269 7,646 3,334 Other 3,662 5,869 3,227 Total expense 11,931 13,515 6,561 Income before income tax expense 78,147 13,545 23,490 Income tax benefit 2,489 4,242 2,278 Income before equity in undistributed earnings of subsidiaries 80,636 17,787 25,768 Equity in undistributed earnings of subsidiaries (6,498 ) 36,525 23,581 Net income $ 74,138 $ 54,312 $ 49,349
Condensed statements of cash flows	CONDENSED STATEMENTS OF CASH FLOWS Years Ended December 31, 2018 2017 2016 OPERATING ACTIVITIES: Net Income $ 74,138 $ 54,312 $ 49,349 Adjustments to reconcile net income to net cash provided by operations: Amortization 164 153 45 Equity in undistributed earnings of subsidiaries 6,498 (36,525 ) (23,581 ) Decrease (increase) in other assets 6,060 (2,113 ) (1,035 ) Increase (decrease) in other liabilities 1,377 (155 ) 1,564 Net cash provided by operating activities 88,237 15,672 26,342 INVESTING ACTIVITIES: Investment in subsidiaries — 890 (126,000 ) Net cash paid in acquisition — (22,801 ) — Net cash used in investing activities — (21,911 ) (126,000 ) FINANCING ACTIVITIES: Net proceeds from issuance of subordinated long-term debt — — 98,060 Purchase of common stock (47,193 ) — (10,199 ) Proceeds from issuance of common stock 3,883 3,953 78,962 Cash dividends paid (41,979 ) (32,199 ) (25,963 ) Net cash (used in) provided by financing activities (85,289 ) (28,246 ) 140,860 Net increase (decrease) in cash and cash equivalents 2,948 (34,485 ) 41,202 Cash and cash equivalents at beginning of period 8,483 42,968 1,766 Cash and cash equivalents at end of period $ 11,431 $ 8,483 $ 42,968

QUARTERLY FINANCIAL INFORMATI_2

QUARTERLY FINANCIAL INFORMATION OF REGISTRANT (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Schedule of quarterly financial information	2018 Fourth Third Second First Interest income $ 58,022 $ 57,152 $ 56,797 $ 57,194 Interest expense 15,612 14,742 13,686 13,061 Net interest income 42,410 42,410 43,111 44,133 Provision for loan losses 2,446 975 1,281 3,735 Net gain (loss) on sale of securities available for sale 61 (741 ) (332 ) (827 ) Noninterest income excluding net gain (loss) on sale of securities 10,073 10,763 11,339 10,437 Noninterest expense 30,196 28,962 29,274 31,667 Income before income tax expense 19,902 22,495 23,563 18,341 Income tax expense 2,521 2,192 3,360 2,090 Net income 17,381 20,303 20,203 16,251 Earnings per common share Basic $ 0.50 $ 0.58 $ 0.58 $ 0.46 Diluted $ 0.50 $ 0.58 $ 0.57 $ 0.46 Cash dividends paid per common share $ 0.32 $ 0.30 $ 0.30 $ 0.28 2017 Fourth Third Second First Interest income $ 50,104 $ 46,473 $ 46,009 $ 44,888 Interest expense 11,798 11,513 10,585 9,608 Net interest income 38,306 34,960 35,424 35,280 Provision for loan losses 1,271 960 1,346 1,098 Net (loss) gain on sale of securities available for sale (249 ) 627 (75 ) 322 Noninterest income excluding net gain (loss) on sale of securities 9,348 8,781 9,368 9,351 Noninterest expense 29,933 25,007 25,537 25,858 Income before income tax expense 16,201 18,401 17,834 17,997 Income tax expense 5,870 3,890 3,353 3,008 Net income 10,331 14,511 14,481 14,989 Earnings per common share Basic $ 0.33 $ 0.49 $ 0.49 $ 0.51 Diluted $ 0.33 $ 0.49 $ 0.49 $ 0.51 Cash dividends paid per common share $ 0.30 $ 0.28 $ 0.28 $ 0.25

SUMMARY OF SIGNIFICANT ACCOUN_3

SUMMARY OF SIGNIFICANT ACCOUNTING AND REPORTING POLICIES (Details)	12 Months Ended
	Dec. 31, 2018USD ($)banking_officessegment	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Organization and Basis of Presentation [Abstract]
Number of branches | banking_offices	59
Number of branches in grocery stores | banking_offices	15
Segment Information [Abstract]
Number of reportable segments | segment	1
Cash and Cash Equivalents [Abstract]
Cash on deposit with the Federal Reserve required to meet regulatory reserve and clearing requirements	$ 34,100,000	$ 32,200,000
Goodwill and Other Intangible Assets [Abstract]
Goodwill impairment loss	0	0
Amortization expense of intangible assets	5,213,000	1,955,000	$ 1,940,000
Core deposit intangible
Goodwill and Other Intangible Assets [Abstract]
Intangible assets, net	13,100,000
Amortization expense of intangible assets			$ 1,800,000
Trust relationship intangible
Goodwill and Other Intangible Assets [Abstract]
Intangible assets, net	4,500,000
Core Deposit Intangible and Trust Relationship Intangible [Member]
Goodwill and Other Intangible Assets [Abstract]
Amortization expense of intangible assets	$ 5,100,000	$ 1,800,000
Premises | Minimum
Premises and Equipment [Abstract]
Estimated useful life	15 years
Premises | Maximum
Premises and Equipment [Abstract]
Estimated useful life	40 years
Equipment | Minimum
Premises and Equipment [Abstract]
Estimated useful life	3 years
Equipment | Maximum
Premises and Equipment [Abstract]
Estimated useful life	10 years

SUMMARY OF SIGNIFICANT ACCOUN_4

SUMMARY OF SIGNIFICANT ACCOUNTING AND REPORTING POLICIES - Reclassifications (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Amortization expense on intangibles	$ 5,213,000	$ 1,955,000	$ 1,940,000
Securities available for sale, at estimated fair value		1,538,755,000
Securities held to maturity, at carrying value (estimated fair value of $159,781 and $921,800, respectively)	162,931,000	909,506,000
Decrease in debit card expense	1,090,000	3,889,000	3,136,000
Decrease in deposit services income	25,082,000	21,785,000	20,702,000
Decrease in brokerage services income	1,987,000	2,422,000	2,127,000
Cumulative effect of ASU 2016-01	(85,000)
Increase (decrease) in salaries and employee benefits expense	70,643,000	60,779,000	61,628,000
(Decrease) increase in other noninterest expense	12,283,000	10,528,000	14,524,000
Securities available for sale	2,013,485,000
Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in debit card expense	4,000,000
Decrease in deposit services income	4,030,000
Decrease in brokerage expense	641,000
Decrease in brokerage services income	641,000
Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Securities available for sale, at estimated fair value				$ (5,900,000)
Equity investments				5,900,000
Accounting Standards Update 2017-07
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase (decrease) in salaries and employee benefits expense		304,000	(2,400,000)
(Decrease) increase in other noninterest expense		(304,000)	$ 2,400,000
New Accounting Pronouncement, Early Adoption, Effect | Accounting Standards Update 2017-12
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Securities held to maturity, at carrying value (estimated fair value of $159,781 and $921,800, respectively)				(743,400,000)
Securities available for sale				743,400,000
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of ASU 2016-01	(85,000)
Retained Earnings | Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of ASU 2016-01				$ (85,000)
Core Deposit Intangible and Trust Relationship Intangible [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Amortization expense on intangibles	$ 5,100,000	$ 1,800,000

SUMMARY OF SIGNIFICANT ACCOUN_5

SUMMARY OF SIGNIFICANT ACCOUNTING AND REPORTING POLICIES - Stock Dividend (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Dividends, Common Stock [Abstract]
Stock dividends declared or paid	$ 0	$ 24,960,000	$ 34,765,000
Stock dividend, percentage of common stock		2.50%	5.00%

SUMMARY OF SIGNIFICANT ACCOUN_6

SUMMARY OF SIGNIFICANT ACCOUNTING AND REPORTING POLICIES - Accounting Pronouncements (Details) - Subsequent Event $ in Millions	Jan. 01, 2019USD ($)
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in Operating Liabilities	$ 10.1
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	9.8
Accounting Standards Update 2017-08
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect on Retained Earnings, before Tax	$ (16.5)

ACQUISITION - Narrative (Detail

ACQUISITION - Narrative (Details) $ / shares in Units, $ in Thousands	Nov. 30, 2017USD ($)banking_offices$ / sharesshares	Dec. 31, 2018USD ($)banking_offices	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Business Acquisition [Line Items]
Number of branches | banking_offices		59
Acquisition, goodwill		$ 201,116	$ 201,246
Acquisition expense		2,413	4,352	$ 0
Acquisition, legal and consulting fees		4,035	3,844	4,946
Acquisition, software and data processing expense		3,996	3,027	2,911
Diboll State Bancshares, Inc.
Business Acquisition [Line Items]
Percentage of company acquired	100.00%
Number of branches | banking_offices	17
Acquisition, number of shares issued | shares	5,500,000
Company stock consideration, stock issued per each share of acquiree stock (in shares) | shares	6.5021
Cash consideration, per share of acquiree stock (in dollars per share) | $ / shares	$ 28.12
Acquisition, closing stock price per share (in dollars per share) | $ / shares	$ 36.2
Acquisition, total merger consideration	$ 224,305
Acquisition, assets	1,030,000
Acquisition, loans	621,318	621,318
Acquisition, investment securities	234,447	234,447
Acquisition, liabilities assumed	910,700
Acquisition, deposits	899,300
Acquisition, goodwill	109,726	109,596	109,726
Acquisition expense		4,400
Acquisition, legal and consulting fees		2,400
Acquisition, software and data processing expense		$ 1,900
Cost related to issuance of shares related to the merger	277
Pro forma net income (loss)			64,100	58,000
Pro forma revenue			$ 270,900	$ 257,800
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
Non-solicitation Agreements | Diboll State Bancshares, Inc.
Business Acquisition [Line Items]
Acquisition, finite-lived intangible assets	$ 240
Amortization period	3 years

ACQUISITION - Schedule of Comp

ACQUISITION - Schedule of Components of Consideration Paid (Details) - USD ($) $ in Thousands	Nov. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Common stock issued		$ 0	$ 200,364	$ 0
Cash		$ 0	$ 23,941	$ 0
Diboll State Bancshares, Inc.
Business Acquisition [Line Items]
Common stock issued	$ 200,364
Cash	23,941
Total consideration transferred	$ 224,305

ACQUISITION - Goodwill (Detail

ACQUISITION - Goodwill (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)
Goodwill [Roll Forward]
Balance as of December 31, 2017	$ 201,246
Less: measurement period adjustments	(130)
Balance as of December 31, 2018	$ 201,116

ACQUISITION - Assets Acquired

ACQUISITION - Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	12 Months Ended
	Nov. 29, 2018	Dec. 31, 2018	Dec. 31, 2017	Nov. 30, 2017
Assets of acquired bank:
Goodwill		$ 201,116	$ 201,246
Diboll State Bancshares, Inc.
Assets of acquired bank:
Cash, cash equivalents and amounts due from banks		115,598		$ 115,598
Other investments		610		610
Securities available for sale		234,447		234,447
Loans		621,318		621,318
Property and equipment		26,256		26,256
Other assets		7,052		7,052
Core deposit intangible		14,700		14,700
Trust relationship intangible		5,400		5,400
Goodwill		109,596	$ 109,726	109,726
Liabilities of acquired bank:
Deposits		(899,307)		(899,307)
Deferred tax liability, net		(7,718)		(7,802)
Other liabilities		(3,647)		(3,693)
Fair value of assets acquired net of liabilities assumed		$ 224,305		$ 224,305
Measurement Period Adjustments
Cash, cash equivalents and amounts due from banks	$ 0
Other investments	0
Securities available for sale	0
Loans	0
Property and equipment	0
Other assets	0
Core deposit intangible	0
Trust relationship intangible	0
Goodwill	(130)
Deposits	0
Deferred tax liability, net	(84)
Other liabilities	(46)
Fair value of assets acquired net of liabilities assumed	$ 0

ACQUISITION - PCI Loans (Detai

ACQUISITION - PCI Loans (Details) - Diboll State Bancshares, Inc. $ in Thousands	Nov. 30, 2017USD ($)
Business Acquisition [Line Items]
Contractually required principal and interest payments	$ 59,286
Nonaccretable difference	4,560
Cash flows expected to be collected	54,726
Accretable difference	15,389
Fair value of loans acquired with a deterioration of credit quality	$ 39,337

ACQUISITION - Acquired Perform

ACQUISITION - Acquired Performing Loans (Details) - Diboll State Bancshares, Inc. - Performing loans $ in Thousands	Nov. 30, 2017USD ($)
Business Acquisition [Line Items]
Fair Value at Acquisition Date	$ 581,981
Contractual Amounts Receivable	823,974
Cash Flows Not Expected to be Collected at Acquisition Date	127,399	[1]
Construction Real Estate Loans
Business Acquisition [Line Items]
Fair Value at Acquisition Date	40,122
Contractual Amounts Receivable	56,905
Cash Flows Not Expected to be Collected at Acquisition Date	330	[1]
1-4 Family Residential Real Estate Loans
Business Acquisition [Line Items]
Fair Value at Acquisition Date	82,654
Contractual Amounts Receivable	130,167
Cash Flows Not Expected to be Collected at Acquisition Date	26,894	[1]
Commercial Real Estate Loans
Business Acquisition [Line Items]
Fair Value at Acquisition Date	319,623
Contractual Amounts Receivable	484,529
Cash Flows Not Expected to be Collected at Acquisition Date	97,431	[1]
Commercial Loans
Business Acquisition [Line Items]
Fair Value at Acquisition Date	82,083
Contractual Amounts Receivable	87,688
Cash Flows Not Expected to be Collected at Acquisition Date	1,226	[1]
Municipal Loans
Business Acquisition [Line Items]
Fair Value at Acquisition Date	7,848
Contractual Amounts Receivable	9,998
Cash Flows Not Expected to be Collected at Acquisition Date	28
Loans to Individuals
Business Acquisition [Line Items]
Fair Value at Acquisition Date	49,651
Contractual Amounts Receivable	54,687
Cash Flows Not Expected to be Collected at Acquisition Date	$ 1,490	[1]
[1]	Cash flows not expected to be collected relate to estimated credit losses and expected prepayments.

EARNINGS PER SHARE (Details)

EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Basic and Diluted Earnings:
Net Income	$ 17,381	$ 20,303	$ 20,203	$ 16,251	$ 10,331	$ 14,511	$ 14,481	$ 14,989	$ 74,138	$ 54,312	$ 49,349
Basic weighted-average shares outstanding (in shares)									34,951	29,841	27,118
Add: Stock options (in shares)									165	206	129
Diluted weighted-average shares outstanding (in shares)									35,116	30,047	27,247
Basic Earnings Per Share:
Earnings per common share - basic (in dollars per share)	$ 0.50	$ 0.58	$ 0.58	$ 0.46	$ 0.33	$ 0.49	$ 0.49	$ 0.51	$ 2.12	$ 1.82	$ 1.82
Diluted Earnings Per Share:
Earnings per common share - diluted (in dollars per share)	$ 0.50	$ 0.58	$ 0.57	$ 0.46	$ 0.33	$ 0.49	$ 0.49	$ 0.51	$ 2.11	$ 1.81	$ 1.81
Antidilutive securities from non-qualified stock options excluded from calculating earnings
Number of antidilutive options (in shares)									356	154	359

ACCUMULATED OTHER COMPREHENSI_3

ACCUMULATED OTHER COMPREHENSIVE LOSS - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
AOCI Attributable to Parent, Net of Tax
Beginning balance, net of tax		$ 754,140		$ 518,274	$ 444,062
Income tax benefit (expense)		3,703		(5,374)	10,667
Ending balance, net of tax		731,291		754,140	518,274
Cumulative effect of ASU 2016-01, net of tax		(85)
Retained Earnings
AOCI Attributable to Parent, Net of Tax
Beginning balance, net of tax		32,851		30,098	41,527
Ending balance, net of tax		64,797		32,851	30,098
Cumulative effect of ASU 2016-01, net of tax		(85)
Unrealized Gains (Losses) on Securities
AOCI Attributable to Parent, Net of Tax
Beginning balance, net of tax		(16,295)		(23,708)	(239)
Other comprehensive (loss) income before reclassifications		(21,956)		15,217	(33,699)
Reclassified from accumulated other comprehensive income		3,190	[1]	630	(2,407)
Income tax benefit (expense)		3,941		(5,546)	12,637
Net current-period other comprehensive (loss) income, net of tax		(14,825)		10,301	(23,469)
Reclassification of certain deferred tax effects	[2]			(2,888)
Ending balance, net of tax		(31,120)		(16,295)	(23,708)
Unrealized Gains (Losses) on Derivatives
AOCI Attributable to Parent, Net of Tax
Beginning balance, net of tax		6,399		4,595	0
Other comprehensive (loss) income before reclassifications		2,351		276	5,255
Reclassified from accumulated other comprehensive income		(1,406)		754	1,815
Income tax benefit (expense)		(198)		(360)	(2,475)
Net current-period other comprehensive (loss) income, net of tax		747		670	4,595
Reclassification of certain deferred tax effects	[2]			1,134
Ending balance, net of tax		7,146		6,399	4,595
Net Prior Service (Cost) Credit
AOCI Attributable to Parent, Net of Tax
Reclassified from accumulated other comprehensive income	[3]	(7)		(8)	(8)
Net Gain (Loss)
AOCI Attributable to Parent, Net of Tax
Reclassified from accumulated other comprehensive income	[3]	2,189		1,613	1,828
Total
AOCI Attributable to Parent, Net of Tax
Beginning balance, net of tax		(36,298)		(38,493)	(18,683)
Other comprehensive (loss) income before reclassifications		(21,599)		10,283	(31,705)
Reclassified from accumulated other comprehensive income		3,966	[1]	2,989	1,228
Income tax benefit (expense)		3,703		(5,374)	10,667
Net current-period other comprehensive (loss) income, net of tax		(13,930)		7,898	(19,810)
Reclassification of certain deferred tax effects	[2]			(5,703)
Ending balance, net of tax		(50,228)		(36,298)	(38,493)
Accounting Standards Update 2016-01 | Retained Earnings
AOCI Attributable to Parent, Net of Tax
Cumulative Effect of New Accounting Principle in Period of Adoption, Before Tax						$ (107)
Cumulative effect of ASU 2016-01, net of tax						$ (85)
Defined Benefit Pension Plan | Net Prior Service (Cost) Credit
AOCI Attributable to Parent, Net of Tax
Beginning balance, net of tax		(133)		(133)	(44)
Other comprehensive (loss) income before reclassifications		0		8	(129)
Reclassified from accumulated other comprehensive income		(7)		(8)	(8)
Income tax benefit (expense)		1		0	48
Net current-period other comprehensive (loss) income, net of tax		(6)		0	(89)
Reclassification of certain deferred tax effects	[2]			0
Ending balance, net of tax		(139)		(133)	(133)
Defined Benefit Pension Plan | Net Gain (Loss)
AOCI Attributable to Parent, Net of Tax
Beginning balance, net of tax		(26,269)		(19,247)	(18,400)
Other comprehensive (loss) income before reclassifications		(1,994)		(5,218)	(3,132)
Reclassified from accumulated other comprehensive income		2,189		1,613	1,828
Income tax benefit (expense)		(41)		532	457
Net current-period other comprehensive (loss) income, net of tax		154		(3,073)	(847)
Reclassification of certain deferred tax effects	[2]			(3,949)
Ending balance, net of tax		$ (26,115)		$ (26,269)	$ (19,247)
[1]	As discussed in “Note 1 – Summary of Significant Accounting and Reporting Policies,” 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).
[2]	Amounts reclassified to retained earnings due to early adoption of ASU 2018-02. See “Note 1 – Summary of Significant Accounting and Reporting Policies” for further information.
[3]	These accumulated other comprehensive income components are included in the computation of net periodic pension cost (income) presented in “Note 11 - Employee Benefits.”

ACCUMULATED OTHER COMPREHENSI_4

ACCUMULATED OTHER COMPREHENSIVE LOSS - Reclassifications out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of unrealized losses										$ 1,244		$ 1,255	$ 429
Tax benefit (expense)		$ (2,521)	$ (2,192)	$ (3,360)	$ (2,090)	$ (5,870)	$ (3,890)	$ (3,353)	$ (3,008)	(10,163)		(16,121)	(10,325)
Total reclassifications for the period, net of tax										(3,048)		(1,943)	(799)
Unrealized gains (losses)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassified from accumulated other comprehensive income (loss)										(3,190)	[1]	(630)	2,407
Realized net gain (loss) on interest rate swap derivatives
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassified from accumulated other comprehensive income (loss)										1,406		(754)	(1,815)
Net actuarial loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassified from accumulated other comprehensive income (loss)	[2]									(2,189)		(1,613)	(1,828)
Prior service credit
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassified from accumulated other comprehensive income (loss)	[2]									7		8	8
Amortization of pension plan
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassified from accumulated other comprehensive income (loss)										(2,182)		(1,605)	(1,820)
Tax benefit										459		562	637
Total reclassifications for the period, net of tax										(1,723)		(1,043)	(1,183)
Unrealized losses on securities transferred | Reclassification out of accumulated other comprehensive income | Unrealized gains (losses)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of unrealized losses	[3]									(1,244)		(1,255)	(429)
Tax benefit (expense)										261		439	150
Net of tax										(983)		(816)	(279)
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)										386		(219)	(993)
Net of tax										(1,453)		406	1,843
Realized net (loss) gain on sale of securities	[4]									(1,839)		625	2,836
Interest Rate Swaps | Reclassification out of accumulated other comprehensive income | Realized net gain (loss) on interest rate swap derivatives
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax benefit (expense)										(277)		290	635
Net of tax										1,042		(538)	(1,180)
Realized net gain (loss) on interest rate swaps	[5]									1,319		(828)	(1,815)
Interest Rate Swaps | Reclassification out of accumulated other comprehensive income | Amortization of unrealized gains on terminated interest rate swaps
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax benefit (expense)										(18)		(26)	0
Net of tax										69		48	0
Realized net gain (loss) on interest rate swaps	[5]									$ 87		$ 74	$ 0
[1]	As discussed in “Note 1 – Summary of Significant Accounting and Reporting Policies,” 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).
[2]	These accumulated other comprehensive income components are included in the computation of net periodic pension cost (income) presented in “Note 11 - Employee Benefits.”
[3]	Included in interest income on the consolidated statements of income.
[4]	Listed as net (loss) gain on sale of securities available for sale on the consolidated statements of income.
[5]	Included in interest expense for FHLB borrowings on the consolidated statements of income.

SECURITIES - Schedule of Debt

SECURITIES - Schedule of Debt and Equity Securities Components (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
AVAILABLE FOR SALE:
Amortized cost	$ 2,013,485
Gross unrealized gain	10,554
Gross unrealized loss	34,603
Estimated fair value	1,989,436
Amortized cost		$ 1,541,967
Gross unrealized gains		9,163
Gross unrealized loss		12,375
Estimated fair value		1,538,755
HELD TO MATURITY:
Amortized cost	162,931	909,506
Gross unrealized gains	360	16,322
Gross unrealized losses	3,510	4,028
Estimated fair value	159,781	921,800
U.S. Government Agency Debentures
AVAILABLE FOR SALE:
Amortized cost		108,869
Gross unrealized gains		0
Gross unrealized loss		0
Estimated fair value		108,869
State and Political Subdivisions
AVAILABLE FOR SALE:
Amortized cost	728,142
Gross unrealized gain	6,115
Gross unrealized loss	17,656
Estimated fair value	716,601
Amortized cost		392,760
Gross unrealized gains		3,895
Gross unrealized loss		3,991
Estimated fair value		392,664
HELD TO MATURITY:
Amortized cost	3,083	413,632
Gross unrealized gains	5	10,879
Gross unrealized losses	42	2,583
Estimated fair value	3,046	421,928
Other Stocks and Bonds
AVAILABLE FOR SALE:
Amortized cost	3,000
Gross unrealized gain	0
Gross unrealized loss	291
Estimated fair value	2,709
Amortized cost		5,024
Gross unrealized gains		31
Gross unrealized loss		0
Estimated fair value		5,055
Other Equity Securities
AVAILABLE FOR SALE:
Amortized cost		6,027
Gross unrealized gains		0
Gross unrealized loss		107
Estimated fair value		5,920
Residential
AVAILABLE FOR SALE:
Amortized cost	738,585
Gross unrealized gain	3,498
Gross unrealized loss	9,111
Estimated fair value	732,972
Amortized cost		720,930
Gross unrealized gains		4,476
Gross unrealized loss		7,377
Estimated fair value		718,029
HELD TO MATURITY:
Amortized cost	59,655	129,044
Gross unrealized gains	154	1,631
Gross unrealized losses	1,140	239
Estimated fair value	58,669	130,436
Commercial
AVAILABLE FOR SALE:
Amortized cost	543,758
Gross unrealized gain	941
Gross unrealized loss	7,545
Estimated fair value	537,154
Amortized cost		308,357
Gross unrealized gains		761
Gross unrealized loss		900
Estimated fair value		308,218
HELD TO MATURITY:
Amortized cost	100,193	366,830
Gross unrealized gains	201	3,812
Gross unrealized losses	2,328	1,206
Estimated fair value	$ 98,066	$ 369,436

SECURITIES - Unrealized Loss o

SECURITIES - Unrealized Loss on Securities (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Available-for-sale, Unrealized Loss Position [Abstract]
Less than 12 Months, fair value		$ 115,902
Less than 12 months, fair value			$ 614,799
More than 12 Months, fair value		1,345,243
More than 12 months, fair value			288,113
Total fair value		1,461,145
Total fair value			902,912
Available-for-sale Securities, Unrealized Loss Position, Accumulated Loss)
Less than 12 Months, unrealized loss		1,247
Less than 12 months, unrealized loss			3,879
More than 12 Months, unrealized loss		33,356
More than 12 months, unrealized loss			8,496
Total unrealized loss		34,603
Total unrealized loss			12,375
Held-to-maturity, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value		5,460	246,806
More than 12 months, fair value		142,236	73,024
Total fair value		147,696	319,830
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Less than 12 Months, unrealized loss position		63	1,746
More than 12 Months, unrealized loss position		3,447	2,282
Unrealized loss position		3,510	4,028
State and Political Subdivisions
Available-for-sale, Unrealized Loss Position [Abstract]
Less than 12 Months, fair value		98,112
Less than 12 months, fair value			32,341
More than 12 Months, fair value		399,205
More than 12 months, fair value			172,006
Total fair value		497,317
Total fair value			204,347
Available-for-sale Securities, Unrealized Loss Position, Accumulated Loss)
Less than 12 Months, unrealized loss		899
Less than 12 months, unrealized loss			121
More than 12 Months, unrealized loss		16,757
More than 12 months, unrealized loss			3,870
Total unrealized loss		17,656
Total unrealized loss			3,991
Held-to-maturity, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value		235	85,608
More than 12 months, fair value		2,022	56,736
Total fair value		2,257	142,344
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Less than 12 Months, unrealized loss position		1	807
More than 12 Months, unrealized loss position		41	1,776
Unrealized loss position		42	2,583
Other Stocks and Bonds
Available-for-sale, Unrealized Loss Position [Abstract]
Less than 12 Months, fair value		2,709
More than 12 Months, fair value		0
Total fair value		2,709
Available-for-sale Securities, Unrealized Loss Position, Accumulated Loss)
Less than 12 Months, unrealized loss		291
More than 12 Months, unrealized loss		0
Total unrealized loss		291
Other Equity Securities
Available-for-sale, Unrealized Loss Position [Abstract]
Less than 12 months, fair value	[1]		5,920
More than 12 months, fair value	[1]		0
Total fair value	[1]		5,920
Available-for-sale Securities, Unrealized Loss Position, Accumulated Loss)
Less than 12 months, unrealized loss	[1]		107
More than 12 months, unrealized loss	[1]		0
Total unrealized loss	[1]		107
Residential
Available-for-sale, Unrealized Loss Position [Abstract]
Less than 12 Months, fair value		5,552
Less than 12 months, fair value			429,742
More than 12 Months, fair value		488,334
More than 12 months, fair value			102,973
Total fair value		493,886
Total fair value			532,715
Available-for-sale Securities, Unrealized Loss Position, Accumulated Loss)
Less than 12 Months, unrealized loss		27
Less than 12 months, unrealized loss			3,232
More than 12 Months, unrealized loss		9,084
More than 12 months, unrealized loss			4,145
Total unrealized loss		9,111
Total unrealized loss			7,377
Held-to-maturity, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value		4,826	24,707
More than 12 months, fair value		51,046	2,736
Total fair value		55,872	27,443
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Less than 12 Months, unrealized loss position		60	157
More than 12 Months, unrealized loss position		1,080	82
Unrealized loss position		1,140	239
Commercial
Available-for-sale, Unrealized Loss Position [Abstract]
Less than 12 Months, fair value		9,529
Less than 12 months, fair value			146,796
More than 12 Months, fair value		457,704
More than 12 months, fair value			13,134
Total fair value		467,233
Total fair value			159,930
Available-for-sale Securities, Unrealized Loss Position, Accumulated Loss)
Less than 12 Months, unrealized loss		30
Less than 12 months, unrealized loss			419
More than 12 Months, unrealized loss		7,515
More than 12 months, unrealized loss			481
Total unrealized loss		7,545
Total unrealized loss			900
Held-to-maturity, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value		399	136,491
More than 12 months, fair value		89,168	13,552
Total fair value		89,567	150,043
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Less than 12 Months, unrealized loss position		2	782
More than 12 Months, unrealized loss position		2,326	424
Unrealized loss position		$ 2,328	$ 1,206
[1]	See “Note 1 – Summary of Significant Accounting and Reporting Policies” for further information.

SECURITIES - Interest Income o

SECURITIES - Interest Income on Securities (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Interest Income Recognized on Securities [Abstract]
U.S. Treasury		$ 218	$ 519	$ 739
U.S. Government Agency Debentures		89	178	0
State and Political Subdivisions		24,960	24,530	22,654
Other Stocks and Bonds		110	125	195
Other Equity Securities	[1]	0	116	123
Mortgage-backed Securities		41,584	41,361	37,450
Total interest income on securities		$ 66,961	$ 66,829	$ 61,161
[1]	See “Note 1 - Summary of Significant Accounting and Reporting Policies” for further information.

SECURITIES - Amortized Cost an

SECURITIES - Amortized Cost and Estimated Fair Value of Investments in Debt Securities By Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Available for sale, Amortized Cost
Due in one year or less	$ 3,559
Due after one year through five years	39,169
Due after five years through ten years	176,316
Due after ten years	512,098
Total available-for-sale investment securities	731,142
Mortgage-backed Securities	1,282,343
Amortized cost	2,013,485
Available for sale Securities, Fair Value
Due in one year or less	3,602
Due after one year through five years	40,055
Due after five years through ten years	175,181
Due after ten years	500,472
Subtotal	719,310
Mortgage-backed Securities and Other Equity Securities	1,270,126
Total	1,989,436
Held to Maturity, Amortized Cost
Due in one year or less	116
Due after one year through five years	1,696
Due after five years through ten years	1,271
Due after ten years	0
Subtotal	3,083
Mortgage-backed Securities	159,848
Amortized cost	162,931	$ 909,506
Held to Maturity, Fair Value
Due in one year or less	115
Due after one year through five years	1,674
Due after five years through ten years	1,257
Due after ten years	0
Subtotal	3,046
Mortgage-backed Securities	156,735
Total	$ 159,781	$ 921,800

SECURITIES - Unrealized and Re

SECURITIES - Unrealized and Realized Gain (Loss) Recognized in Net Income on Equity Investments (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)
Gain (Loss) on Securities [Line Items]
Net losses recognized during the period on equity investments	$ (117)
Less: Net gains (losses) recognized during the period on equity investments sold during the period	0
Unrealized losses recognized during the reporting period on equity investments still held at the reporting date	$ (117)

SECURITIES - Narrative (Detail

SECURITIES - Narrative (Details)	Jan. 01, 2018USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Investment [Line Items]
Transferred Securities, Unrealized Loss, Before Tax		$ 15,300,000	$ 17,400,000
Securities transferred, Unrealized Loss, Net of Tax		12,100,000	13,800,000
Fair value of securities transferred from AFS to HTM		0	0	$ 157,083,000
Securities available for sale, at estimated fair value		1,989,436,000
Unrealized net gain on securities transferred from held to maturity to available for sale under the transition guidance enumerated in ASU 2017-12		$ 11,881,000	0	0
AFS securities and HTM securities with other-than-temporary impairment		0
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Net realized (loss) gain on AFS securities		$ (1,800,000)
Gross realized gains on AFS securities		2,000,000
Gross realized loss on AFS securities		3,800,000
Net realized (loss) gain on AFS securities			625,000	2,800,000
Gross realized gains on AFS securities			5,000,000	6,300,000
Gross realized loss on AFS securities			4,400,000	3,400,000
Carrying value of investment securities pledged as collateral		1,080,000,000	1,240,000,000
Equity investments		$ 12,093,000
Equity investments without readily determinable fair value			5,821,000
Securities available for sale, at estimated fair value			1,538,755,000
Equity investments with other-than-temporary impairment		0
Proceeds from sale of held-to-maturity securities		$ 0	0	$ 0
New Accounting Pronouncement, Early Adoption, Effect | Accounting Standards Update 2017-12
Investment [Line Items]
Securities available for sale, at estimated fair value	$ 743,400,000
Unrealized net gain on securities transferred from held to maturity to available for sale under the transition guidance enumerated in ASU 2017-12	11,900,000
Unrealized net gain on securities transferred from held to maturity to available for sale, net of tax	$ 9,400,000
Other Equity Securities
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Securities available for sale, at estimated fair value			5,920,000
Unrealized losses on equity investment included in AFS securities			$ 85,000

LOANS AND ALLOWANCE FOR PROBA_3

LOANS AND ALLOWANCE FOR PROBABLE LOAN LOSSES - Narrative (Details) - USD ($)		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable, Gross, Allowance, and Net [Abstract]
Loans to related parties		$ 4,000,000	$ 5,500,000
Related party loans as a percent of stockholders' equity		0.60%	0.70%
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired loans without an allowance		$ 0	$ 0
Nonaccrual loans	[1],[2]	35,770,000	2,937,000
Troubled Debt Restructurings (TDR) in Default		216,000	138,000
Commitments to lend additional funds on Troubled Debt Restructurings (TDR)		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
1-4 Family Residential Real Estate Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonaccrual loans		2,202,000	1,098,000
Loans for which formal foreclosure proceedings were in process		147,000	154,000
Commercial Real Estate Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans secured by owner and non-owner occupied commercial real estate		1,130,000,000
Loans secured by multi-family properties		49,200,000
Loans secured by farmland		15,800,000
Nonaccrual loans		$ 32,599,000	$ 595,000
[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. The increase in nonaccrual loans was primarily due to the addition of four commercial real estate loans to nonaccrual status during the year, one of which was added during the fourth quarter.
[2]	Includes $10.9 million and $1.3 million of restructured loans as of December 31, 2018 and 2017, respectively.

LOANS AND ALLOWANCE FOR PROBA_4

LOANS AND ALLOWANCE FOR PROBABLE LOAN LOSSES - Loans by Portfolio Segment (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Loans and Leases Receivable Disclosure [Abstract]
Total ending loan balance		$ 3,312,799	$ 3,294,356
Less: Allowance for loan losses	[1]	27,019	20,781
Net loans		3,285,780	3,273,575
Construction Real Estate Loans
Loans and Leases Receivable Disclosure [Abstract]
Total ending loan balance		507,732	475,867
1-4 Family Residential Real Estate Loans
Loans and Leases Receivable Disclosure [Abstract]
Total ending loan balance		794,499	805,341
Commercial Real Estate Loans
Loans and Leases Receivable Disclosure [Abstract]
Total ending loan balance		1,194,118	1,265,159
Commercial Loans
Loans and Leases Receivable Disclosure [Abstract]
Total ending loan balance		356,649	266,422
Municipal Loans
Loans and Leases Receivable Disclosure [Abstract]
Total ending loan balance		353,370	345,798
Loans to Individuals
Loans and Leases Receivable Disclosure [Abstract]
Total ending loan balance		106,431	135,769
Purchased Credit Impaired (PCI) Loans
Loans and Leases Receivable Disclosure [Abstract]
Less: Allowance for loan losses		$ 302	$ 0
[1]	Loans acquired with the Diboll acquisition were measured at fair value on November 30, 2017, with no carryover of allowance for loan loss. The allowance for loan loss recorded on PCI loans totaled $302,000 as of December 31, 2018. There was no allowance for loan loss recorded on PCI loans as of December 31, 2017

LOANS AND ALLOWANCE FOR PROBA_5

LOANS AND ALLOWANCE FOR PROBABLE LOAN LOSSES - Allowance for Loan Losses Activity by Portfolio Segment (Details)		3 Months Ended										12 Months Ended
		Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)		Dec. 31, 2017USD ($)		Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2018USD ($)		Dec. 31, 2017USD ($)		Dec. 31, 2016USD ($)Loan
Change in Allowances for Loan Losses [Abstract]
Balance at beginning of period					$ 20,781,000	[1]					$ 17,911,000	$ 20,781,000	[1]	$ 17,911,000		$ 19,736,000
Provision (reversal) for loan losses		$ 2,446,000	$ 975,000	$ 1,281,000	3,735,000		$ 1,271,000		$ 960,000	$ 1,346,000	1,098,000	8,437,000	[2]	4,675,000	[2]	9,780,000	[2]
Loans charged off												(4,246,000)		(3,453,000)		(14,387,000)
Recoveries of loans charged off												2,047,000		1,648,000		2,782,000
Balance at end of period		27,019,000					20,781,000	[1]				27,019,000		20,781,000	[1]	17,911,000
Provision expense on PCI Loans												302,000		0		0
Construction Real Estate Loans
Change in Allowances for Loan Losses [Abstract]
Balance at beginning of period					3,676,000	[1]					4,147,000	3,676,000	[1]	4,147,000		4,350,000
Provision (reversal) for loan losses												(72,000)		(437,000)		(472,000)
Loans charged off												(14,000)		(35,000)		0
Recoveries of loans charged off												7,000		1,000		269,000
Balance at end of period		3,597,000					3,676,000	[1]				3,597,000		3,676,000	[1]	4,147,000
1-4 Family Residential Real Estate Loans
Change in Allowances for Loan Losses [Abstract]
Balance at beginning of period					2,445,000	[1]					2,665,000	2,445,000	[1]	2,665,000		2,595,000
Provision (reversal) for loan losses												1,134,000		65,000		(28,000)
Loans charged off												(91,000)		(304,000)		(43,000)
Recoveries of loans charged off												356,000		19,000		141,000
Balance at end of period		3,844,000					2,445,000	[1]				3,844,000		2,445,000	[1]	2,665,000
Commercial Real Estate Loans
Change in Allowances for Loan Losses [Abstract]
Balance at beginning of period					10,821,000	[1]					7,204,000	10,821,000	[1]	7,204,000		4,577,000
Provision (reversal) for loan losses												3,894,000		3,604,000		2,604,000
Loans charged off												(783,000)		0		0
Recoveries of loans charged off												36,000		13,000		23,000
Balance at end of period		13,968,000					10,821,000	[1]				13,968,000		10,821,000	[1]	7,204,000
Commercial Loans
Change in Allowances for Loan Losses [Abstract]
Balance at beginning of period					2,094,000	[1]					2,263,000	2,094,000	[1]	2,263,000		6,596,000
Provision (reversal) for loan losses												2,392,000		242,000		6,397,000
Loans charged off												(756,000)		(723,000)		(11,396,000)	[3]
Recoveries of loans charged off												244,000		312,000		666,000
Balance at end of period		3,974,000					2,094,000	[1]				3,974,000		2,094,000	[1]	2,263,000
Charge-off of large commercial borrowing relationships	[3]															$ 10,900,000
Number of loans partially charged-off | Loan	[3]															2
Municipal Loans
Change in Allowances for Loan Losses [Abstract]
Balance at beginning of period					860,000	[1]					750,000	860,000	[1]	750,000		$ 725,000
Provision (reversal) for loan losses												(335,000)		110,000		(224,000)
Loans charged off												0		0		0
Recoveries of loans charged off												0		0		249,000
Balance at end of period		525,000					860,000	[1]				525,000		860,000	[1]	750,000
Loans to Individuals
Change in Allowances for Loan Losses [Abstract]
Balance at beginning of period					$ 885,000	[1]					$ 882,000	885,000	[1]	882,000		893,000
Provision (reversal) for loan losses												1,424,000		1,091,000		1,503,000
Loans charged off												(2,602,000)		(2,391,000)		(2,948,000)
Recoveries of loans charged off												1,404,000		1,303,000		1,434,000
Balance at end of period		$ 1,111,000					$ 885,000	[1]				$ 1,111,000		$ 885,000	[1]	$ 882,000
[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 $8.4 million in provision for loan losses for the year ended December 31, 2018, $302,000 related to provision expense on PCI loans. Of the $4.7 million and $9.8 million recorded in provision for loan losses for the year ended December 31, 2017 and 2016, respectively, none related to provision expense on PCI loans
[3]	Of the $11.4 million in commercial charge-offs recorded for the year ended December 31, 2016, $10.9 million relates to the charge-off of two large commercial borrowing relationships.

LOANS AND ALLOWANCE FOR PROBA_6

LOANS AND ALLOWANCE FOR PROBABLE LOAN LOSSES - Allowance Balance, by Impairment Method, Reserve (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Schedule of Allowance For Loan Losses, Allowance Balance, by Impairment Method [Line Items]
Ending balance - individually evaluated for impairment	[1]	$ 5,908	$ 353
Ending balance - collectively evaluated for impairment		21,111	20,428
Balance at end of period		27,019	20,781	[2]	$ 17,911	$ 19,736
Loans and Leases Receivable, Allowance	[3]	27,019	20,781
Construction Real Estate Loans
Schedule of Allowance For Loan Losses, Allowance Balance, by Impairment Method [Line Items]
Ending balance - individually evaluated for impairment		13	12
Ending balance - collectively evaluated for impairment		3,584	3,664
Balance at end of period		3,597	3,676	[2]	4,147	4,350
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		40	14
Ending balance - collectively evaluated for impairment		3,804	2,431
Balance at end of period		3,844	2,445	[2]	2,665	2,595
Commercial Real Estate Loans
Schedule of Allowance For Loan Losses, Allowance Balance, by Impairment Method [Line Items]
Ending balance - individually evaluated for impairment		5,337	14
Ending balance - collectively evaluated for impairment		8,631	10,807
Balance at end of period		13,968	10,821	[2]	7,204	4,577
Commercial Loans
Schedule of Allowance For Loan Losses, Allowance Balance, by Impairment Method [Line Items]
Ending balance - individually evaluated for impairment		368	252
Ending balance - collectively evaluated for impairment		3,606	1,842
Balance at end of period		3,974	2,094	[2]	2,263	6,596
Municipal Loans
Schedule of Allowance For Loan Losses, Allowance Balance, by Impairment Method [Line Items]
Ending balance - individually evaluated for impairment		1	10
Ending balance - collectively evaluated for impairment		524	850
Balance at end of period		525	860	[2]	750	725
Loans to Individuals
Schedule of Allowance For Loan Losses, Allowance Balance, by Impairment Method [Line Items]
Ending balance - individually evaluated for impairment		149	51
Ending balance - collectively evaluated for impairment		962	834
Balance at end of period		1,111	885	[2]	$ 882	$ 893
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		$ 302	$ 0
[1]	The allowance for loan loss on PCI loans totaled $302,000 as of December 31, 2018. There was no allowance for loan losses associated with PCI loans as of December 31, 2017.
[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]	Loans acquired with the Diboll acquisition were measured at fair value on November 30, 2017, with no carryover of allowance for loan loss. The allowance for loan loss recorded on PCI loans totaled $302,000 as of December 31, 2018. There was no allowance for loan loss recorded on PCI loans as of December 31, 2017

LOANS AND ALLOWANCE FOR PROBA_7

LOANS AND ALLOWANCE FOR PROBABLE LOAN LOSSES - Allowance for Loan Losses, Loan Portfolio, by Impairment Method (Details) - USD ($) $ in Thousands	Dec. 31, 2018		Dec. 31, 2017
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Loans individually evaluated for impairment	$ 36,247		$ 4,698
Loans collectively evaluated for impairment	3,230,150		3,244,425
Purchased credit impaired loans	46,402	[1],[2]	45,233
Total ending loan balance	3,312,799		3,294,356
Construction Real Estate Loans
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Loans individually evaluated for impairment	12		86
Loans collectively evaluated for impairment	507,564		475,505
Purchased credit impaired loans	156		276
Total ending loan balance	507,732		475,867
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	1,215		1,581
Loans collectively evaluated for impairment	782,614		797,111
Purchased credit impaired loans	10,670		6,649
Total ending loan balance	794,499		805,341
Commercial Real Estate Loans
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Loans individually evaluated for impairment	33,013		895
Loans collectively evaluated for impairment	1,128,220		1,232,327
Purchased credit impaired loans	32,885		31,937
Total ending loan balance	1,194,118		1,265,159
Commercial Loans
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Loans individually evaluated for impairment	1,394		1,429
Loans collectively evaluated for impairment	353,036		259,745
Purchased credit impaired loans	2,219		5,248
Total ending loan balance	356,649		266,422
Municipal Loans
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Loans individually evaluated for impairment	429		502
Loans collectively evaluated for impairment	352,941		345,296
Purchased credit impaired loans	0		0
Total ending loan balance	353,370		345,798
Loans to Individuals
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Loans individually evaluated for impairment	184		205
Loans collectively evaluated for impairment	105,775		134,441
Purchased credit impaired loans	472		1,123
Total ending loan balance	106,431		135,769
Pass
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Total ending loan balance	3,171,320		3,131,151
Purchased credit impaired loans, new funds to borrower	14,000
Pass | Construction Real Estate Loans
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Total ending loan balance	507,529		471,446
Pass | 1-4 Family Residential Real Estate Loans
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Total ending loan balance	787,516		796,639
Pass | Commercial Real Estate Loans
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Total ending loan balance	1,067,874		1,136,576
Pass | Commercial Loans
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Total ending loan balance	349,495		247,430
Pass | Municipal Loans
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Total ending loan balance	353,370		344,366
Pass | Loans to Individuals
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Total ending loan balance	$ 105,536		$ 134,694
[1]	At December 31, 2018, PCI totals include approximately $14.0 million in new funds to a borrower that has since been upgraded to a Pass credit.
[2]	At December 31, 2018, PCI totals include approximately $14.0 million in new funds to a borrower that has since been upgraded to a Pass credit.

LOANS AND ALLOWANCE FOR PROBA_8

LOANS AND ALLOWANCE FOR PROBABLE LOAN LOSSES - Loans by Credit Quality Indicator (Details) - USD ($) $ in Thousands		Dec. 31, 2018		Dec. 31, 2017
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance		$ 3,312,799		$ 3,294,356
PCI loans		46,402	[1],[2]	45,233
Pass
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance		3,171,320		3,131,151
Pass Watch
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	12,203		39,808
PCI loans		22		362
Special Mention
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	29,783		31,223
PCI loans		859		6,000
Substandard
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	96,950		90,629
PCI loans		3,900		10,500
Doubtful
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	2,543		1,545
PCI loans		1,200		925
Construction Real Estate Loans
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance		507,732		475,867
PCI loans		156		276
Construction Real Estate Loans | Pass
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance		507,529		471,446
Construction Real Estate Loans | Pass Watch
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	163		3,329
Construction Real Estate Loans | Special Mention
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	0		77
Construction Real Estate Loans | Substandard
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	28		982
Construction Real Estate Loans | Doubtful
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	12		33
1-4 Family Residential Real Estate Loans
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance		794,499		805,341
PCI loans		10,670		6,649
1-4 Family Residential Real Estate Loans | Pass
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance		787,516		796,639
1-4 Family Residential Real Estate Loans | Pass Watch
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	37		559
1-4 Family Residential Real Estate Loans | Special Mention
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	100		857
1-4 Family Residential Real Estate Loans | Substandard
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	5,489		6,610
1-4 Family Residential Real Estate Loans | Doubtful
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	1,357		676
Commercial Real Estate Loans
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance		1,194,118		1,265,159
PCI loans		32,885		31,937
Commercial Real Estate Loans | Pass
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance		1,067,874		1,136,576
Commercial Real Estate Loans | Pass Watch
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	11,479		26,275
Commercial Real Estate Loans | Special Mention
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	26,490		25,301
Commercial Real Estate Loans | Substandard
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	87,767		76,625
Commercial Real Estate Loans | Doubtful
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	508		382
Commercial Loans
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance		356,649		266,422
PCI loans		2,219		5,248
Commercial Loans | Pass
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance		349,495		247,430
Commercial Loans | Pass Watch
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	520		9,625
Commercial Loans | Special Mention
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	3,189		3,956
Commercial Loans | Substandard
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	2,988		5,203
Commercial Loans | Doubtful
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	457		208
Municipal Loans
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance		353,370		345,798
PCI loans		0		0
Municipal Loans | Pass
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance		353,370		344,366
Municipal Loans | Pass Watch
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	0		0
Municipal Loans | Special Mention
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	0		930
Municipal Loans | Substandard
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	0		502
Municipal Loans | Doubtful
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	0		0
Loans to Individuals
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance		106,431		135,769
PCI loans		472		1,123
Loans to Individuals | Pass
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance		105,536		134,694
Loans to Individuals | Pass Watch
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	4		20
Loans to Individuals | Special Mention
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	4		102
Loans to Individuals | Substandard
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	678		707
Loans to Individuals | Doubtful
Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract]
Total ending loan balance	[3]	$ 209		$ 246
[1]	At December 31, 2018, PCI totals include approximately $14.0 million in new funds to a borrower that has since been upgraded to a Pass credit.
[2]	At December 31, 2018, PCI totals include approximately $14.0 million in new funds to a borrower that has since been upgraded to a Pass credit.
[3]	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. Includes PCI loans comprised of $362,000 pass watch, $6.0 million special mention, $10.5 million substandard and $925,000 doubtful as of December 31, 2017.

LOANS AND ALLOWANCE FOR PROBA_9

LOANS AND ALLOWANCE FOR PROBABLE LOAN LOSSES - Nonperforming Assets by Asset Class (Details) $ in Thousands		3 Months Ended	12 Months Ended
		Dec. 31, 2018USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Nonperforming Assets by Asset Class [Abstract]
Nonaccrual loans	[1],[2]	$ 35,770	$ 35,770	$ 2,937
Accruing loans past due more than 90 days	[1]	0	0	1
Restructured loans	[3]	5,930	5,930	5,767
Other real estate owned		1,206	1,206	1,613
Repossessed assets		0	0	154
Total Nonperforming Assets		$ 42,906	$ 42,906	10,472
Number of commercial real estate loans added to nonaccrual		1	4
Restructured nonaccrual loans		$ 10,900	$ 10,900	1,300
PCI loans restructured		$ 3,100	$ 3,100	$ 2,900
[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. The increase in nonaccrual loans was primarily due to the addition of four commercial real estate loans to nonaccrual status during the year, one of which was added during the fourth quarter.
[2]	Includes $10.9 million and $1.3 million of restructured loans as of December 31, 2018 and 2017, respectively.
[3]	Includes $3.1 million and $2.9 million in PCI loans restructured as of December 31, 2018 and 2017, respectively.

LOANS AND ALLOWANCE FOR PROB_10

LOANS AND ALLOWANCE FOR PROBABLE LOAN LOSSES - Nonaccrual Loans by Class (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	[1],[2]	$ 35,770	$ 2,937
Construction Real Estate Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans		12	86
1-4 Family Residential Real Estate Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans		2,202	1,098
Commercial Real Estate Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans		32,599	595
Commercial Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans		639	903
Loans to Individuals
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans		$ 318	$ 255
[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. The increase in nonaccrual loans was primarily due to the addition of four commercial real estate loans to nonaccrual status during the year, one of which was added during the fourth quarter.
[2]	Includes $10.9 million and $1.3 million of restructured loans as of December 31, 2018 and 2017, respectively.

LOANS AND ALLOWANCE FOR PROB_11

LOANS AND ALLOWANCE FOR PROBABLE LOAN LOSSES - Impaired Loans by Class of Loan (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Impaired Financing Receivable, Recorded Investment [Abstract]
Unpaid Contractual Principal Balance	[1]	$ 47,274	$ 7,989
Recorded Investment	[1]	44,267	7,549
Related Allowance for Loan Losses	[1]	5,908	353
PCI loans that experienced deterioration in credit quality subsequent to acquisition		8,000	2,900
Construction Real Estate Loans
Impaired Financing Receivable, Recorded Investment [Abstract]
Unpaid Contractual Principal Balance		182	91
Recorded Investment		148	86
Related Allowance for Loan Losses		13	12
1-4 Family Residential Real Estate Loans
Impaired Financing Receivable, Recorded Investment [Abstract]
Unpaid Contractual Principal Balance		6,507	4,141
Recorded Investment		5,923	3,952
Related Allowance for Loan Losses		40	14
Commercial Real Estate Loans
Impaired Financing Receivable, Recorded Investment [Abstract]
Unpaid Contractual Principal Balance		36,457	1,353
Recorded Investment		34,744	1,199
Related Allowance for Loan Losses		5,337	14
Commercial Loans
Impaired Financing Receivable, Recorded Investment [Abstract]
Unpaid Contractual Principal Balance		2,874	1,665
Recorded Investment		2,366	1,605
Related Allowance for Loan Losses		368	252
Municipal Loans
Impaired Financing Receivable, Recorded Investment [Abstract]
Unpaid Contractual Principal Balance		429	502
Recorded Investment		429	502
Related Allowance for Loan Losses		1	10
Loans to Individuals
Impaired Financing Receivable, Recorded Investment [Abstract]
Unpaid Contractual Principal Balance		825	237
Recorded Investment		657	205
Related Allowance for Loan Losses		$ 149	$ 51
[1]	Includes $8.0 million and $2.9 million of PCI loans that experienced deterioration in credit quality subsequent to the acquisition date as of December 31, 2018 and December 31, 2017, respectively.

LOANS AND ALLOWANCE FOR PROB_12

LOANS AND ALLOWANCE FOR PROBABLE LOAN LOSSES - Aging of Past Due Loans By Class of Loan (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		$ 34,314	$ 19,039
Current	[1]	3,278,485	3,275,317
Total ending loans balance		3,312,799	3,294,356
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		21,966	13,777
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		10,276	3,901
Greater than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		2,072	1,361
Construction Real Estate Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		934	2,900
Current	[1]	506,798	472,967
Total ending loans balance		507,732	475,867
Construction Real Estate Loans | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		627	1,302
Construction Real Estate Loans | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		307	1,530
Construction Real Estate Loans | Greater than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		0	68
1-4 Family Residential Real Estate Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		10,034	10,944
Current	[1]	784,465	794,397
Total ending loans balance		794,499	805,341
1-4 Family Residential Real Estate Loans | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		7,441	8,508
1-4 Family Residential Real Estate Loans | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		1,258	1,574
1-4 Family Residential Real Estate Loans | Greater than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		1,335	862
Commercial Real Estate Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		18,318	1,386
Current	[1]	1,175,800	1,263,773
Total ending loans balance		1,194,118	1,265,159
Commercial Real Estate Loans | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		10,663	1,357
Commercial Real Estate Loans | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		7,655	24
Commercial Real Estate Loans | Greater than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		0	5
Commercial Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		3,242	1,395
Current	[1]	353,407	265,027
Total ending loans balance		356,649	266,422
Commercial Loans | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		1,946	662
Commercial Loans | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		705	400
Commercial Loans | Greater than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		591	333
Municipal Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		0	422
Current	[1]	353,370	345,376
Total ending loans balance		353,370	345,798
Municipal Loans | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		0	422
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		1,786	1,992
Current	[1]	104,645	133,777
Total ending loans balance		106,431	135,769
Loans to Individuals | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		1,289	1,526
Loans to Individuals | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		351	373
Loans to Individuals | Greater than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		$ 146	$ 93
[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_13

LOANS AND ALLOWANCE FOR PROBABLE LOAN LOSSES - Interest Income on Impaired Loans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Impaired Financing Receivable, Average Recorded Investment and Interest [Abstract]
Average Recorded Investment	$ 33,383	$ 9,504	$ 22,597
Interest Income Recognized	417	325	344
Construction Real Estate Loans
Impaired Financing Receivable, Average Recorded Investment and Interest [Abstract]
Average Recorded Investment	149	251	510
Interest Income Recognized	7	0	22
1-4 Family Residential Real Estate Loans
Impaired Financing Receivable, Average Recorded Investment and Interest [Abstract]
Average Recorded Investment	4,193	4,264	3,247
Interest Income Recognized	208	197	169
Commercial Real Estate Loans
Impaired Financing Receivable, Average Recorded Investment and Interest [Abstract]
Average Recorded Investment	26,186	1,338	4,490
Interest Income Recognized	65	30	63
Commercial Loans
Impaired Financing Receivable, Average Recorded Investment and Interest [Abstract]
Average Recorded Investment	2,131	2,862	13,481
Interest Income Recognized	102	59	48
Municipal Loans
Impaired Financing Receivable, Average Recorded Investment and Interest [Abstract]
Average Recorded Investment	474	545	612
Interest Income Recognized	26	30	33
Loans to Individuals
Impaired Financing Receivable, Average Recorded Investment and Interest [Abstract]
Average Recorded Investment	250	244	257
Interest Income Recognized	$ 9	$ 9	$ 9

LOANS AND ALLOWANCE FOR PROB_14

LOANS AND ALLOWANCE FOR PROBABLE LOAN LOSSES - Troubled Debt Restructurings (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)contract	Dec. 31, 2017USD ($)contract
Troubled Debt Restructuring [Abstract]
Extend Amortization Period	$ 10,617	$ 801
Interest Rate Reductions	112	0
Combination	540	293
Total Modifications	$ 11,269	$ 1,094
Number of Contracts | contract	22	10
1-4 Family Residential Real Estate Loans
Troubled Debt Restructuring [Abstract]
Extend Amortization Period	$ 0
Interest Rate Reductions	79
Combination	0
Total Modifications	$ 79
Number of Contracts | contract	1
Commercial Real Estate Loans
Troubled Debt Restructuring [Abstract]
Extend Amortization Period	$ 10,398
Interest Rate Reductions	0
Combination	274
Total Modifications	$ 10,672
Number of Contracts | contract	3
Commercial Loans
Troubled Debt Restructuring [Abstract]
Extend Amortization Period	$ 211	$ 778
Interest Rate Reductions	0	0
Combination	215	241
Total Modifications	$ 426	$ 1,019
Number of Contracts | contract	13	4
Loans to Individuals
Troubled Debt Restructuring [Abstract]
Extend Amortization Period	$ 8	$ 23
Interest Rate Reductions	33	0
Combination	51	52
Total Modifications	$ 92	$ 75
Number of Contracts | contract	5	6

LOANS AND ALLOWANCE FOR PROB_15

LOANS AND ALLOWANCE FOR PROBABLE LOAN LOSSES - Purchased Credit Impaired (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018		Dec. 31, 2017
Purchased Credit Impaired [Abstract]
Outstanding principal balance	$ 51,388	[1]	$ 52,426
Carrying amount	46,402	[1],[2]	45,233
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	18,721		2,480
Additions due to acquisition	0		15,389
Changes in expected cash flows not affecting non-accretable differences	(1,445)		0
Reclassifications (to) from nonaccretable discount	1,211		1,720
Accretion	(3,433)		(868)
Balance at end of period	15,054		$ 18,721
Pass
Purchased Credit Impaired [Abstract]
Purchased credit impaired loans, new funds to borrower	$ 14,000
[1]	At December 31, 2018, PCI totals include approximately $14.0 million in new funds to a borrower that has since been upgraded to a Pass credit.
[2]	At December 31, 2018, PCI totals include approximately $14.0 million in new funds to a borrower that has since been upgraded to a Pass credit.

PREMISES AND EQUIPMENT (Details

PREMISES AND EQUIPMENT (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Premises	$ 166,128	$ 158,817
Furniture and equipment	41,810	40,565
Premises and equipment, gross	207,938	199,382
Less: accumulated depreciation	71,966	65,742
Premises and equipment, net	135,972	133,640
Depreciation [Abstract]
Accumulated depreciation of assets written off	2,200	915
Depreciation expense	$ 8,400	$ 8,100	$ 8,000

DEPOSITS - Types and Component

DEPOSITS - Types and Components of Deposit Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Noninterest bearing demand deposits:
Noninterest bearing demand deposits	$ 994,680	$ 1,037,401
Interest bearing deposits:
Total interest bearing deposits	3,430,350	3,478,046
Total deposits	4,425,030	4,515,447
Private accounts
Noninterest bearing demand deposits:
Noninterest bearing demand deposits	967,096	995,685
Interest bearing deposits:
Savings deposits	360,007	356,857
Money market demand deposits	440,442	443,015
Platinum money market deposits	344,546	308,105
Interest bearing checking	662,911	686,816
NOW demand deposits	23,451	20,142
Certificates and other time deposits, $250,000 or more	84,564	87,195
Certificates and other time deposits under $250,000	680,282	534,220
Total interest bearing deposits	2,596,203	2,436,350
Public accounts
Noninterest bearing demand deposits:
Noninterest bearing demand deposits	27,584	41,716
Interest bearing deposits:
Savings deposits	320	304
Money market demand deposits	15,513	19,560
Platinum money market deposits	329,695	360,006
Interest bearing checking	56,694	55,902
NOW demand deposits	141,200	114,401
Certificates and other time deposits, $250,000 or more	281,204	462,941
Certificates and other time deposits under $250,000	9,521	28,582
Total interest bearing deposits	$ 834,147	$ 1,041,696

DEPOSITS - Scheduled Maturitie

DEPOSITS - Scheduled Maturities of Time Deposits (Details) $ in Thousands	Dec. 31, 2018USD ($)
Time Deposits, Fiscal Year Maturity [Abstract]
2,019	$ 845,661
2,020	116,542
2,021	42,254
2,022	20,003
2,023	25,931
2024 and thereafter	5,180
Total	$ 1,055,571

DEPOSITS - Narrative (Details)

DEPOSITS - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deposit Liabilities Disclosures [Line Items]
Time deposits threshold	$ 250,000
Interest expense on time deposits of $250,000 or more	8,500,000	$ 5,000,000	$ 3,200,000
Maximum brokered certificates of deposit balance allowed per company policy	300,000,000
Related party deposit liabilities	16,200,000	31,700,000
Demand deposit overdrafts reclassified as loans	1,600,000	1,300,000
Certificates of deposit - CDs
Deposit Liabilities Disclosures [Line Items]
Brokered certificates of deposit	$ 238,100,000	$ 60,200,000
Brokered certificates of deposit, as a percent of total deposits	5.40%
Weighted average cost, domestic deposit, brokered	2.23%
Brokered certificates of deposit, maturity period	1 year
Category under which brokered certificates of deposit are reported	$ 250,000

BORROWING ARRANGEMENTS (Details

BORROWING ARRANGEMENTS (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Federal funds purchased and repurchase agreements		$ 36,810	$ 9,498
FHLB borrowings		719,065	1,017,361
Federal funds purchased and repurchase agreements:
Debt Instrument [Line Items]
Federal funds purchased and repurchase agreements		36,810	9,498
Average amount outstanding during the period	[1]	10,880	8,120
Maximum amount outstanding during the period	[2]	$ 36,810	$ 9,498
Weighted average interest rate during the period	[3]	1.40%	0.20%
Interest rate at end of period	[4]	2.10%	0.20%
FHLB borrowings:
Debt Instrument [Line Items]
FHLB borrowings		$ 719,065	$ 1,017,361
Average amount outstanding during the period	[1]	720,785	1,222,033
Maximum amount outstanding during the period	[2]	$ 957,231	$ 1,414,453
Weighted average interest rate during the period	[3]	1.80%	1.20%
Interest rate at end of period	[4]	2.30%	1.40%
[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 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.

BORROWING ARRANGEMENTS - Matur

BORROWING ARRANGEMENTS - Maturities Table (Details) $ in Thousands	Dec. 31, 2018USD ($)
Debt Instrument [Line Items]
Less than 1 Year	$ 373,188
1-2 Years	365,289
2-3 Years	11,483
3-4 Years	0
4-5 Years	0
Thereafter	5,915
Total	755,875
Federal funds purchased and repurchase agreements:
Debt Instrument [Line Items]
Less than 1 Year	36,686
1-2 Years	124
2-3 Years	0
3-4 Years	0
4-5 Years	0
Thereafter	0
Total	36,810
FHLB borrowings:
Debt Instrument [Line Items]
Less than 1 Year	336,502
1-2 Years	365,165
2-3 Years	11,483
3-4 Years	0
4-5 Years	0
Thereafter	5,915
Total	$ 719,065

BORROWING ARRANGEMENTS - Addit

BORROWING ARRANGEMENTS - Additional Information (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2017USD ($)contract	Dec. 31, 2018USD ($)credit_lineagreementOustanding_Letters_of_CreditRate	Dec. 31, 2017USD ($)
Line of Credit Facility [Line Items]
Debt face amount		$ 270,000,000
Number of credit lines maintained by the Company | credit_line		3
Federal funds purchased		$ 28,000,000	$ 0
Number of outstanding letters of credit | Oustanding_Letters_of_Credit		1
Letters of credit outstanding		$ 195,000
FHLB Advances, unused funds		1,170,000,000
Letters of credit, FHLB, as collateral		0
Securities sold under agreements to repurchase		$ 8,800,000	9,500,000
Maturity of repurchase agreements		2 years
Frost Bank
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity		$ 40,000,000
Line of credit facility, 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]
Federal home loan bank, advances, general debt obligations, disclosures, interest rate at period end		1.37%
Maximum
Line of Credit Facility [Line Items]
Federal home loan bank, advances, general debt obligations, disclosures, interest rate at period end		4.799%
Maturity range of FHLB advances		9 years 6 months 3 days
Variable Rate Advance Agreements
Line of Credit Facility [Line Items]
Debt face amount		$ 310,000,000	$ 280,000,000
Three-Month London Interbank Offered Rate (LIBOR) | Variable Rate Advance Agreements
Line of Credit Facility [Line Items]
Description of variable rate basis		three-month LIBOR
Three-Month London Interbank Offered Rate (LIBOR) | Variable Rate Advance Agreements | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable rate | Rate		(0.003%)
Three-Month London Interbank Offered Rate (LIBOR) | Variable Rate Advance Agreements | Maximum
Line of Credit Facility [Line Items]
Number of variable rate advance agreements | agreement		2
Basis spread on variable rate | Rate		0.021%
One-Month London Interbank Offered Rate (LIBOR) | Variable Rate Advance Agreements
Line of Credit Facility [Line Items]
Description of variable rate basis		one-month LIBOR
One-Month London Interbank Offered Rate (LIBOR) | Variable Rate Advance Agreements | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable rate | Rate		0.072%
One-Month London Interbank Offered Rate (LIBOR) | Variable Rate Advance Agreements | Maximum
Line of Credit Facility [Line Items]
Basis spread on variable rate | Rate		0.164%
Interest Rate Swaps
Line of Credit Facility [Line Items]
Derivative, instruments terminated | contract	2
Derivative, terminated, notional amount	$ 40,000,000
Interest Rate Swaps | Minimum
Line of Credit Facility [Line Items]
Derivative, fixed interest rate		0.932%
Derivative, term of contract		4 years
Interest Rate Swaps | Maximum
Line of Credit Facility [Line Items]
Derivative, fixed interest rate		2.833%
Derivative, term of contract		10 years

LONG-TERM DEBT - Other Long-te

LONG-TERM DEBT - Other Long-term Obligations (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018		Dec. 31, 2017		Oct. 10, 2007	[5]	Aug. 10, 2007	Aug. 08, 2007
Debt Instruments [Abstract]
Subordinated notes, net of unamortized debt issuance costs	[1]	$ 98,407		$ 98,248
Trust preferred subordinated debentures	[2]	60,246		60,241
Total long-term obligations		158,653		158,489
5.50% Subordinated Notes
Debt Instruments [Abstract]
Subordinated notes, net of unamortized debt issuance costs	[1],[3]	98,407		98,248
Unamortized debt issuance expense		1,600		1,800
Southside Statutory Trust III, net of unamortized debt issuance costs
Debt Instruments [Abstract]
Trust preferred subordinated debentures	[2],[4]	20,554		20,549
Unamortized debt issuance expense		65		70
Southside Statutory Trust IV
Debt Instruments [Abstract]
Trust preferred subordinated debentures		23,196	[2]	23,196	[2]				$ 23,196
Southside Statutory Trust V
Debt Instruments [Abstract]
Trust preferred subordinated debentures		12,887	[2]	12,887	[2]			$ 12,887
Magnolia Trust Company I
Debt Instruments [Abstract]
Trust preferred subordinated debentures		$ 3,609	[2]	$ 3,609	[2]	$ 3,609
Minimum | 5.50% Subordinated Notes
Debt Instruments [Abstract]
Long-term debt, remaining maturity		1 year
[1]	This debt consists of subordinated notes with a remaining maturity greater than one year that qualify under the risk-based capital guidelines as Tier 2 capital, subject to certain limitations.
[2]	This debt consists of trust preferred securities that qualify under the risk-based capital guidelines as Tier 1 capital, subject to certain limitations.
[3]	The unamortized discount and debt issuance costs reflected in the carrying amount of the subordinated notes totaled approximately $1.6 million at December 31, 2018 and $1.8 million at December 31, 2017.
[4]	The unamortized debt issuance costs reflected in the carrying amount of the Southside Statutory Trust III junior subordinated debentures totaled $65,000 at December 31, 2018 and $70,000 at December 31, 2017.
[5]	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.

LONG-TERM DEBT - LT Debt Inter

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

Dec. 31, 2018

Dec. 31, 2017

Debt Instrument [Line Items]

Other long-term debt

[1]

$ 60,246

$ 60,241

5.50% Subordinated Notes

Debt Instrument [Line Items]

Amount issued

$ 100,000

Stated interest rate

5.50%

Southside Statutory Trust III

Debt Instrument [Line Items]

Amount issued

$ 20,619

Other long-term debt

[1],[2]

20,554

20,549

Southside Statutory Trust III | Three-Month London Interbank Offered Rate (LIBOR)

Debt Instrument [Line Items]

Basis spread on variable rate

2.94%

Southside Statutory Trust IV

Debt Instrument [Line Items]

Other long-term debt

$ 23,196

23,196

[1]

23,196

[1]

Southside Statutory Trust IV | Three-Month London Interbank Offered Rate (LIBOR)

Debt Instrument [Line Items]

Basis spread on variable rate

1.30%

Southside Statutory Trust V

Debt Instrument [Line Items]

Other long-term debt

$ 12,887

12,887

[1]

12,887

[1]

Southside Statutory Trust V | Three-Month London Interbank Offered Rate (LIBOR)

Debt Instrument [Line Items]

Basis spread on variable rate

2.25%

Magnolia Trust Company I

Debt Instrument [Line Items]

Other long-term debt

$ 3,609

[3]

$ 3,609

[1]

$ 3,609

[1]

Magnolia Trust Company I | Three-Month London Interbank Offered Rate (LIBOR)

Debt Instrument [Line Items]

Basis spread on variable rate

[3]

1.80%

Scenario, Forecast [Member] | 5.50% Subordinated Notes | Three-Month London Interbank Offered Rate (LIBOR)

Debt Instrument [Line Items]

Basis spread on variable rate

4.297%

[1]

This debt consists of trust preferred securities that qualify under the risk-based capital guidelines as Tier 1 capital, subject to certain limitations.

[2]

The unamortized debt issuance costs reflected in the carrying amount of the Southside Statutory Trust III junior subordinated debentures totaled $65,000 at December 31, 2018 and $70,000 at December 31, 2017.

[3]

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 BENEFITS - Narrative

EMPLOYEE BENEFITS - Narrative (Details)	12 Months Ended
	Dec. 31, 2018USD ($)executive_officerRateshares	Dec. 31, 2017USD ($)shares	Dec. 31, 2016USD ($)executive_officershares	Dec. 31, 2015	Dec. 31, 2013executive_officer
Health Insurance Coverage [Abstract]
Cost of health care benefits	$ 6,500,000	$ 5,600,000	$ 4,900,000
Health coverage eligibility for retiring employees, minimum years of service	50 years
Retirees participating in health insurance	1	2	2
Employee Stock Ownership Plan (ESOP) [Abstract]
Contributions to the employee stock ownership plan (ESOP)	$ 700,000	$ 350,000	$ 350,000
Shares owned by the ESOP (in shares) | shares	277,492	280,542
Supplemental Unemployment Benefits [Abstract]
Long-term disability coverage, minimum years of service rendered for officers to automatically qualify	3 years
Long-term disability coverage, minimum annual salary level for officers to automatically qualify	$ 50,000
Long-term disability coverage, maximum benefit provided, per month	$ 15,000
Long-term disability coverage, maximum benefit provided, as a ratio of final salary | Rate	66.66667%
401(k) [Abstract]
Requisite service period	30 days
401(k) Plan expense	$ 1,500,000	$ 613,000	562,000
Share-based Compensation [Abstract]
Tax benefit (expense) realized for deductions related to stock option exercises			332,000
Defined Benefit Pension Plan
Defined Benefit Plan [Abstract]
Defined benefit pension plan, minimum eligibility age	65 years
Early retirement election at reduced benefit levels, minimum eligibility age	55 years
Number of shares of Company stock included in plan assets (in shares) | shares	240,666	240,666
Funded (under funded) status	$ (1,081,000)	$ (3,043,000)	$ (2,778,000)
Number of employees offered early retirement			24
Total number of employees that accepted early retirement offer			15	16
Special and contractual termination benefits	0	0	$ 1,549,000
Accrued benefit (liability) asset recognized	(1,081,000)	(3,043,000)	(2,778,000)
Expected future employer contributions, next fiscal year	0
Defined Benefit Pension Plan Acquired
Defined Benefit Plan [Abstract]
Funded (under funded) status	197,000	(361,000)	(1,245,000)
Special and contractual termination benefits	0	0	0
Accrued benefit (liability) asset recognized	197,000	(361,000)	(1,245,000)
Expected future employer contributions, next fiscal year	0
Restoration Plan
Defined Benefit Plan [Abstract]
Funded (under funded) status	(15,300,000)	(14,642,000)	(12,723,000)
Special and contractual termination benefits	0	0	0
Accrued benefit (liability) asset recognized	(15,300,000)	$ (14,642,000)	$ (12,723,000)
Expected future employer contributions, next fiscal year	$ 0
Other Equity Securities | Defined Benefit Pension Plan
Defined Benefit Plan [Abstract]
Target allocation	55.00%
Fixed Income Securities | Defined Benefit Pension Plan
Defined Benefit Plan [Abstract]
Target allocation	44.50%
Cash equivalents | Defined Benefit Pension Plan
Defined Benefit Plan [Abstract]
Target allocation	0.50%
Restricted Stock Units (RSUs)
Share-based Compensation [Abstract]
Nonvested awards outstanding (in shares) | shares	109,750	78,253
Incentive Plan 2009
Share-based Compensation [Abstract]
Number of additional shares (in shares) | shares	410,000
Incentive Plan 2017
Share-based Compensation [Abstract]
Common stock shares reserved and available for issuance (in shares) | shares	2,460,000
Shares remaining available for grant for future awards (in shares) | shares	1,675,607
Incentive Plan
Share-based Compensation [Abstract]
Nonvested awards outstanding (in shares) | shares	612,740	366,292	599,498
Share-based compensation expense	$ 2,300,000	$ 1,800,000	$ 1,500,000
Tax benefit from share-based compensation expense	487,000	635,000	539,000
Unrecognized compensation expense	$ 5,800,000	3,800,000	5,600,000
Unrecognized compensation, weighted-average period for recognition	2 years 9 months 14 days
Incentive Plan | Stock options
Share-based Compensation [Abstract]
Awards contractual term	10 years
Total intrinsic value of outstanding stock options	$ 3,700,000
Total intrinsic value of exercisable stock options	$ 3,200,000
Weighted-average remaining contractual life of options exercisable	5 years 5 months 28 days
Total intrinsic value of stock options exercised during period	$ 1,400,000	1,800,000	1,300,000
Tax benefit (expense) realized for deductions related to stock option exercises	$ 0	0	$ 332,000
Incentive Plan | Stock options | Minimum
Share-based Compensation [Abstract]
Awards vesting period	3 years
Incentive Plan | Stock options | Maximum
Share-based Compensation [Abstract]
Awards vesting period	4 years
Incentive Plan | Restricted Stock Units (RSUs) | Minimum
Share-based Compensation [Abstract]
Awards vesting period	3 years
Incentive Plan | Restricted Stock Units (RSUs) | Maximum
Share-based Compensation [Abstract]
Awards vesting period	4 years
Executive officers
Deferred Compensation Arrangements [Abstract]
Number of employees included in the deferred compensation agreement with the Company | executive_officer	17
Aggregate payment amount provided in the deferred compensation agreements	$ 6,900,000
Maximum benefit period after retirement or death	15 years
Number of individuals receiving payments | executive_officer	9
Number of individuals that accepted the retirement package | executive_officer			3
Deferred compensation expense	$ 201,000	353,000	$ 357,000
Total deferred compensation plan liability	$ 3,400,000	3,500,000
Split Dollar Life Insurance Agreements [Abstract]
Number of employees originally covered by the split dollar agreements | executive_officer	8
Aggregate death benefit amount provided in agreement, before inflation adjustment	$ 4,500,000
Number of employees covered by the split dollar agreements, Actively employed with us | executive_officer	3
Number of retired covered officers death benefits were paid | executive_officer	1
Number of active covered officers death benefits were paid | executive_officer					1
Number of remaining employees covered by the split dollar agreements | executive_officer	6
Aggregate death benefits, inflation adjusted	$ 4,100,000
Expense of split dollar retirement bonus	(250,000)	(3,000)	$ 172,000
Total split dollar liability	$ 1,400,000	$ 1,900,000
Executive officers | Minimum
Split Dollar Life Insurance Agreements [Abstract]
Inflation adjustment factor applied to benefits, annual	3.00%
Executive officers | Maximum
Split Dollar Life Insurance Agreements [Abstract]
Inflation adjustment factor applied to benefits, annual	5.00%

EMPLOYEE BENEFITS - Change in

EMPLOYEE BENEFITS - Change in Projected Benefit Obligation and Plan Assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Pension Plan
Change in Projected Benefit Obligation:
Benefit obligation at end of prior year	$ 94,276,000	$ 88,071,000	$ 80,040,000
Service cost	1,548,000	1,398,000	1,375,000
Interest cost	3,392,000	3,601,000	3,731,000
Actuarial (gain) loss	(9,399,000)	5,404,000	4,978,000
Benefits Paid	(3,622,000)	(4,128,000)	(3,632,000)
Expenses paid	(203,000)	(70,000)	(91,000)
Plan Amendments	0	0	121,000
Settlements	0	0	0
Special and contractual termination benefits	0	0	1,549,000
Benefit obligation at end of year	85,992,000	94,276,000	88,071,000
Change in Plan Assets:
Fair value of plan assets at end of prior year	91,233,000	85,293,000	76,355,000
Actual return	(4,497,000)	8,138,000	7,661,000
Employer contributions	2,000,000	2,000,000	5,000,000
Benefits paid	(3,622,000)	(4,128,000)	(3,632,000)
Expenses paid	(203,000)	(70,000)	(91,000)
Settlements	0	0	0
Fair value of plan assets at end of year	84,911,000	91,233,000	85,293,000
(Un)Funded status at end of year	(1,081,000)	(3,043,000)	(2,778,000)
Accrued benefit (liability) asset recognized	(1,081,000)	(3,043,000)	(2,778,000)
Accumulated benefit obligation at end of year	77,888,000	83,802,000	77,639,000
Defined Benefit Pension Plan Acquired
Change in Projected Benefit Obligation:
Benefit obligation at end of prior year	4,392,000	4,238,000	4,685,000
Service cost	0	0	0
Interest cost	163,000	177,000	212,000
Actuarial (gain) loss	(480,000)	418,000	275,000
Benefits Paid	(183,000)	(43,000)	(31,000)
Expenses paid	(19,000)	(47,000)	(39,000)
Plan Amendments	0	0	0
Settlements	0	(351,000)	(864,000)
Special and contractual termination benefits	0	0	0
Benefit obligation at end of year	3,873,000	4,392,000	4,238,000
Change in Plan Assets:
Fair value of plan assets at end of prior year	4,031,000	2,993,000	3,740,000
Actual return	(259,000)	479,000	187,000
Employer contributions	500,000	1,000,000	0
Benefits paid	(183,000)	(43,000)	(31,000)
Expenses paid	(19,000)	(47,000)	(39,000)
Settlements	0	(351,000)	(864,000)
Fair value of plan assets at end of year	4,070,000	4,031,000	2,993,000
(Un)Funded status at end of year	197,000	(361,000)	(1,245,000)
Accrued benefit (liability) asset recognized	197,000	(361,000)	(1,245,000)
Accumulated benefit obligation at end of year	3,873,000	4,392,000	4,238,000
Restoration Plan
Change in Projected Benefit Obligation:
Benefit obligation at end of prior year	14,642,000	12,723,000	12,024,000
Service cost	293,000	247,000	207,000
Interest cost	597,000	567,000	535,000
Actuarial (gain) loss	344,000	1,751,000	237,000
Benefits Paid	(576,000)	(646,000)	(280,000)
Expenses paid	0	0	0
Plan Amendments	0	0	0
Settlements	0	0	0
Special and contractual termination benefits	0	0	0
Benefit obligation at end of year	15,300,000	14,642,000	12,723,000
Change in Plan Assets:
Fair value of plan assets at end of prior year	0	0	0
Actual return	0	0	0
Employer contributions	576,000	646,000	280,000
Benefits paid	(576,000)	(646,000)	(280,000)
Expenses paid	0	0	0
Settlements	0	0	0
Fair value of plan assets at end of year	0	0	0
(Un)Funded status at end of year	(15,300,000)	(14,642,000)	(12,723,000)
Accrued benefit (liability) asset recognized	(15,300,000)	(14,642,000)	(12,723,000)
Accumulated benefit obligation at end of year	$ 13,403,000	$ 13,246,000	$ 11,133,000

EMPLOYEE BENEFITS - Amounts Re

EMPLOYEE BENEFITS - Amounts Recognized as a Component of Other Comprehensive Income (loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Net (loss) gain occurring during the year	$ 1,994	$ 5,218	$ 3,132
Net prior service (cost) credit occurring during the year	0	0	121
Defined Benefit Pension Plan
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Recognition of net loss	1,512	1,312	1,642
Recognition of prior service (credit) cost	(14)	(14)	(14)
Recognition of loss (gain) due to settlements	0	0	0
Net (loss) gain occurring during the year	(1,581)	(3,317)	(2,541)
Net prior service (cost) credit occurring during the year	0	0	(121)
Total adjustment during the year	(83)	(2,019)	(1,034)
Deferred tax benefit (expense)	17	241	362
Other comprehensive (loss) income, net of tax	(66)	(1,778)	(672)
Defined Benefit Pension Plan Acquired
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Recognition of net loss	0	0	0
Recognition of prior service (credit) cost	0	0	0
Recognition of loss (gain) due to settlements	0	8	(8)
Net (loss) gain occurring during the year	(69)	(150)	(354)
Net prior service (cost) credit occurring during the year	0	0	0
Total adjustment during the year	(69)	(142)	(362)
Deferred tax benefit (expense)	14	30	127
Other comprehensive (loss) income, net of tax	(55)	(112)	(235)
Restoration Plan
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Recognition of net loss	677	301	186
Recognition of prior service (credit) cost	7	6	6
Recognition of loss (gain) due to settlements	0	0	0
Net (loss) gain occurring during the year	(344)	(1,751)	(237)
Net prior service (cost) credit occurring during the year	0	0	0
Total adjustment during the year	340	(1,444)	(45)
Deferred tax benefit (expense)	(71)	259	16
Other comprehensive (loss) income, net of tax	$ 269	$ (1,185)	$ (29)

EMPLOYEE BENEFITS - Amounts in

EMPLOYEE BENEFITS - Amounts in Accumulated Other Comprehensive Income (Loss) Recognized in Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Net loss	$ 1,512	$ 1,312	$ 1,642
Prior service (credit) cost	(14)	(14)	(14)
Loss (gain) recognized due to settlement	0	0	0
Total amount in other comprehensive income recognized in net periodic benefit cost, before tax	1,498	1,298
Deferred tax (expense) benefit	(315)	(454)
Accumulated other comprehensive income (loss), net of tax	1,183	844
Defined Benefit Pension Plan Acquired
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Net loss	0	0	0
Prior service (credit) cost	0	0	0
Loss (gain) recognized due to settlement	0	8	(8)
Total amount in other comprehensive income recognized in net periodic benefit cost, before tax	0	8
Deferred tax (expense) benefit	0	(2)
Accumulated other comprehensive income (loss), net of tax	0	6
Restoration Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Net loss	677	301	186
Prior service (credit) cost	7	6	6
Loss (gain) recognized due to settlement	0	0	$ 0
Total amount in other comprehensive income recognized in net periodic benefit cost, before tax	684	307
Deferred tax (expense) benefit	(144)	(107)
Accumulated other comprehensive income (loss), net of tax	$ 540	$ 200

EMPLOYEE BENEFITS - Amounts _2

EMPLOYEE BENEFITS - Amounts Recognized as a Component of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Pension Plan
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax [Abstract]
Net (loss) gain		$ (28,928)	$ (28,859)
Prior service cost		(123)	(109)
Accumulated other comprehensive (loss) income, before tax		(29,051)	(28,968)
Deferred tax benefit (expense)		6,100	9,674
Reclassification of Certain Tax Effects	[1]	0	(3,591)
Accumulated other comprehensive (loss) income, net of tax		(22,951)	(22,885)
Defined Benefit Pension Plan Acquired
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax [Abstract]
Net (loss) gain		(171)	(102)
Prior service cost		0	0
Accumulated other comprehensive (loss) income, before tax		(171)	(102)
Deferred tax benefit (expense)		35	15
Reclassification of Certain Tax Effects	[1]	0	6
Accumulated other comprehensive (loss) income, net of tax		(136)	(81)
Restoration Plan
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax [Abstract]
Net (loss) gain		(3,984)	(4,317)
Prior service cost		(24)	(31)
Accumulated other comprehensive (loss) income, before tax		(4,008)	(4,348)
Deferred tax benefit (expense)		841	1,276
Reclassification of Certain Tax Effects	[1]	0	(364)
Accumulated other comprehensive (loss) income, net of tax		$ (3,167)	$ (3,436)
[1]	Amounts reclassified to retained earnings due to early adoption of ASU 2018-02. See “Note 1 – Summary of Significant Accounting and Reporting Policies” for further information.

EMPLOYEE BENEFITS - Net Period

EMPLOYEE BENEFITS - Net Periodic Benefit Cost and Postretirement Benefit Cost (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Pension Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 1,548,000	$ 1,398,000	$ 1,375,000
Interest cost	3,392,000	3,601,000	3,731,000
Expected return on assets	(6,483,000)	(6,050,000)	(5,224,000)
Net loss amortization	1,512,000	1,312,000	1,642,000
Prior service cost (credit) amortization	(14,000)	(14,000)	(14,000)
Special and contractual termination benefits	0	0	1,549,000
Loss (gain) recognized due to settlement	0	0	0
Net periodic benefit cost	(45,000)	247,000	3,059,000
Defined Benefit Pension Plan Acquired
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	0	0	0
Interest cost	163,000	177,000	212,000
Expected return on assets	(290,000)	(212,000)	(265,000)
Net loss amortization	0	0	0
Prior service cost (credit) amortization	0	0	0
Special and contractual termination benefits	0	0	0
Loss (gain) recognized due to settlement	0	8,000	(8,000)
Net periodic benefit cost	(127,000)	(27,000)	(61,000)
Restoration Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	293,000	247,000	207,000
Interest cost	597,000	567,000	535,000
Net loss amortization	677,000	301,000	186,000
Prior service cost (credit) amortization	7,000	6,000	6,000
Special and contractual termination benefits	0	0	0
Loss (gain) recognized due to settlement	0	0	0
Net periodic benefit cost	$ 1,574,000	$ 1,121,000	$ 934,000

EMPLOYEE BENEFITS - Amounts th

EMPLOYEE BENEFITS - Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in next fiscal year (Details) $ in Thousands	Dec. 31, 2018USD ($)
Defined Benefit Pension Plan
Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year [Abstract]
Net loss	$ 1,774
Prior service (credit) cost	(14)
Total amount that will be amortized from accumulated other comprehensive income	1,760
Deferred tax benefit	(370)
Accumulated other comprehensive loss, net of tax	1,390
Defined Benefit Pension Plan Acquired
Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year [Abstract]
Net loss	0
Prior service (credit) cost	0
Total amount that will be amortized from accumulated other comprehensive income	0
Deferred tax benefit	0
Accumulated other comprehensive loss, net of tax	0
Restoration Plan
Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year [Abstract]
Net loss	398
Prior service (credit) cost	6
Total amount that will be amortized from accumulated other comprehensive income	404
Deferred tax benefit	(85)
Accumulated other comprehensive loss, net of tax	$ 319

EMPLOYEE BENEFITS - Assumption

EMPLOYEE BENEFITS - Assumptions Used to Calculate Benefit Obligation, Net Periodic Benefit Cost and Postretirement Benefit (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Pension Plan
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	4.32%	3.71%
Compensation increase rate	3.50%	3.50%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate	3.71%	4.23%	4.56%
Expected long-term rate of return on plan assets	7.25%	7.25%	7.25%
Compensation increase rate	3.50%	3.50%	3.50%
Defined Benefit Pension Plan Acquired
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	4.32%	3.71%
Compensation increase rate	0.00%	0.00%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate	3.71%	4.23%	4.56%
Expected long-term rate of return on plan assets	7.25%	7.25%	7.25%
Compensation increase rate	0.00%	0.00%	0.00%
Restoration Plan
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	4.32%	3.71%
Compensation increase rate	3.50%	3.50%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate	3.71%	4.23%	4.56%
Compensation increase rate	3.50%	3.50%	3.50%

EMPLOYEE BENEFITS - Pension Pl

EMPLOYEE BENEFITS - Pension Plan Asset Categories (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Pension Plan
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets		$ 84,911	$ 91,233	$ 85,293	$ 76,355
Defined Benefit Pension Plan Acquired
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets		4,070	4,031	$ 2,993	$ 3,740
Level 1 | Defined Benefit Pension Plan | Cash
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets		278	423
Level 1 | Defined Benefit Pension Plan | U.S. large cap equities
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[1]	5,204	6,198
Level 1 | Defined Benefit Pension Plan | U.S. mid cap equities
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[2]	18,913	21,379
Level 1 | Defined Benefit Pension Plan | U.S. small cap equities
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[3]	9,900	10,706
Level 1 | Defined Benefit Pension Plan | International developed
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[4]	6,733	8,601
Level 1 | Defined Benefit Pension Plan | International emerging
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[2]	3,464	4,308
Level 1 | Defined Benefit Pension Plan Acquired | Cash
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets		0	0
Level 1 | Defined Benefit Pension Plan Acquired | U.S. large cap equities
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[1]	0	0
Level 1 | Defined Benefit Pension Plan Acquired | U.S. mid cap equities
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[2]	0	0
Level 1 | Defined Benefit Pension Plan Acquired | U.S. small cap equities
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[3]	0	0
Level 1 | Defined Benefit Pension Plan Acquired | International developed
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[4]	0	0
Level 1 | Defined Benefit Pension Plan Acquired | International emerging
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[2]	0	0
Level 2 | Defined Benefit Pension Plan | Cash equivalents
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets		15,025	13,256
Level 2 | Defined Benefit Pension Plan | U.S. large cap equities
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[1]	0	0
Level 2 | Defined Benefit Pension Plan | U.S. mid cap equities
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[2]	0	0
Level 2 | Defined Benefit Pension Plan | U.S. small cap equities
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[3]	0	0
Level 2 | Defined Benefit Pension Plan | International
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[5]	0	0
Level 2 | Defined Benefit Pension Plan | Corporate bonds
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[6]	952	1,118
Level 2 | Defined Benefit Pension Plan | U.S. government agencies
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[6]	20,182	19,303
Level 2 | Defined Benefit Pension Plan | Municipal bonds
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[6]	3,991	5,595
Level 2 | Defined Benefit Pension Plan | U.S. agency mortgage-backed securities
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[7]	269	346
Level 2 | Defined Benefit Pension Plan | Asset-backed Securities
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[8]	0	0
Level 2 | Defined Benefit Pension Plan | Real Estate
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[9]	0	0
Level 2 | Defined Benefit Pension Plan | Balanced Asset Allocation
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[10]	0	0
Level 2 | Defined Benefit Pension Plan | Other
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[11]	0	0
Level 2 | Defined Benefit Pension Plan Acquired | Cash equivalents
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets		0	0
Level 2 | Defined Benefit Pension Plan Acquired | U.S. large cap equities
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[1]	1,360	1,440
Level 2 | Defined Benefit Pension Plan Acquired | U.S. mid cap equities
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[2]	152	167
Level 2 | Defined Benefit Pension Plan Acquired | U.S. small cap equities
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[3]	72	84
Level 2 | Defined Benefit Pension Plan Acquired | International
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[5]	735	712
Level 2 | Defined Benefit Pension Plan Acquired | Corporate bonds
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[6]	407	378
Level 2 | Defined Benefit Pension Plan Acquired | U.S. government agencies
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[6]	0	0
Level 2 | Defined Benefit Pension Plan Acquired | Municipal bonds
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[6]	0	0
Level 2 | Defined Benefit Pension Plan Acquired | U.S. agency mortgage-backed securities
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[7]	0	0
Level 2 | Defined Benefit Pension Plan Acquired | Asset-backed Securities
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[8]	743	717
Level 2 | Defined Benefit Pension Plan Acquired | Real Estate
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[9]	286	241
Level 2 | Defined Benefit Pension Plan Acquired | Balanced Asset Allocation
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[10]	84	81
Level 2 | Defined Benefit Pension Plan Acquired | Other
Defined Benefit Plan, Categories of Plan Assets [Abstract]
Total fair value of plan assets	[11]	$ 231	$ 211
[1]	For the defined benefit pension plan, this category is comprised of individual securities that are actively managed and a broadly diversified “passive” mutual fund. The Acquired Plan assets in this category consist of pooled separate accounts invested in mutual funds and domestic stocks.
[2]	For the defined benefit pension plan, this category is comprised of broadly diversified “passive” mutual funds. The Acquired Plan assets in this category consist of pooled separate accounts invested in mutual funds and domestic stocks.
[3]	For the defined benefit pension plan, this category is comprised of broadly diversified “passive” mutual funds and shares of Southside Bancshares stock that is owned in the Plan. The Acquired Plan assets in this category consist of pooled separate accounts invested in mutual funds and domestic stocks.
[4]	This category is comprised of individual securities that are actively managed and a broadly diversified “passive” mutual fund.
[5]	This category is comprised of pooled separate accounts invested in mutual funds and international stocks.
[6]	For the defined benefit pension plan, this category is comprised of individual investment grade securities that are generally held to maturity in the Plan. The Acquired Plan assets in this category consist of pooled separate accounts invested in investment grade and below investment grade bonds.
[7]	This category is comprised of individual securities that are generally not held to maturity.
[8]	This category is mainly comprised of a pooled separate account invested in asset backed securities, residential mortgage backed securities, commercial mortgage backed securities and corporate bonds.
[9]	This category is comprised of a pooled separate account invested in commercial real estate and includes mortgage loans which are backed by the associated properties.
[10]	This category is comprised of a pooled separate account invested in a single mutual fund invested in a combination of fixed income and equity investment options.
[11]	This category is comprised of a pooled separate account invested in a broad range of instruments including, but not limited to, equities, bonds, currencies, convertible securities and derivatives such as futures, options, swaps and forwards.

EMPLOYEE BENEFITS - Expected F

EMPLOYEE BENEFITS - Expected Future Benefit Payments (Details) $ in Thousands	Dec. 31, 2018USD ($)
Defined Benefit Pension Plan
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
2,019	$ 3,836
2,020	3,951
2,021	4,142
2,022	4,354
2,023	4,520
2024 through 2028	25,008
Total expected future payments	45,811
Defined Benefit Pension Plan Acquired
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
2,019	66
2,020	229
2,021	129
2,022	90
2,023	92
2024 through 2028	897
Total expected future payments	1,503
Restoration Plan
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
2,019	723
2,020	780
2,021	916
2,022	1,031
2,023	1,005
2024 through 2028	5,521
Total expected future payments	$ 9,976

EMPLOYEE BENEFITS - Schedule o

EMPLOYEE BENEFITS - Schedule of Shares Issued in Connection with Stock Compensation Awards (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
New shares issued (in shares)	140,692	159,356	108,225
Proceeds from stock options exercised	$ 2,653	$ 2,692	$ 1,663
New shares issued from authorized shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
New shares issued (in shares)	0	48,311	108,225
New shares issued from available treasury shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
New shares issued (in shares)	140,692	111,045	0

EMPLOYEE BENEFITS - Stock Opti

EMPLOYEE BENEFITS - Stock Option Valuation Assumptions (Details) - Stock options - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant date fair value per option (in dollars per share)	$ 6.78	$ 7.18
Weighted-average assumptions:
Risk-free interest rates	2.81%	1.79%
Expected dividend yield	1.10%	2.69%
Expected volatility factors of the market price of Southside Bancshares common stock	25.41%	27.02%
Expected option life (in years)	6 years 2 months 16 days	6 years 2 months 16 days

EMPLOYEE BENEFITS - Summary of

EMPLOYEE BENEFITS - Summary of Activity of Share-based Plans (Details)	12 Months Ended
	Dec. 31, 2018$ / sharesshares
Restricted Stock Units Outstanding
Number of Shares
Balance, January 1, 2018 (shares) | shares	78,253
Granted (shares) | shares	64,358
Stock awards vested (shares) | shares	(29,752)
Forfeited (shares) | shares	(3,109)
Canceled/expired (shares) | shares	0
Balance, December 31, 2018 (shares) | shares	109,750
Weighted- Average Grant-Date Fair Value
Balance, January 1, 2018 (in dollars per share)	$ 32.04
Granted (in dollars per share)	34.28
Stock awards vested (in dollars per share)	31.14
Forfeited (in dollars per share)	32.93
Canceled/expired (in dollars per share)	0
Balance, December 31, 2018 (in dollars per share)	$ 33.57
Stock Options Outstanding
Number of Shares
Balance, January 1, 2018 (shares) | shares	690,312
Granted (shares) | shares	356,849
Stock options exercised (shares) | shares	(115,277)
Forfeited (shares) | shares	(16,980)
Canceled/expired (shares) | shares	(5,553)
Balance, December 31, 2018 (shares) | shares	909,351
Weighted- Average Exercise Price
Balance, January 1, 2018 (in dollars per share)	$ 26.02
Granted (in dollars per share)	34.52
Stock options exercised (in dollars per share)	23.02
Forfeited (in dollars per share)	32.51
Canceled/expired (in dollars per share)	30.06
Balance, December 31, 2018 (in dollars per share)	29.59
Weighted- Average Grant-Date Fair Value
Balance, January 1, 2018 (in dollars per share)	6.19
Granted (in dollars per share)	6.78
Stock options exercised (in dollars per share)	5.69
Forfeited (in dollars per share)	6.67
Canceled/expired (in dollars per share)	6.68
Balance, December 31, 2018 (in dollars per share)	$ 6.47

EMPLOYEE BENEFITS - Stock Op_2

EMPLOYEE BENEFITS - Stock Options Exercise Price Range (Details)	12 Months Ended
	Dec. 31, 2018$ / sharesshares
Options Outstanding
Number of Shares (in shares) | shares	909,351
Weighted- Average Exercise Price (in dollars per share)	$ 29.59
Weighted- Average Remaining Contractual Life in Years	7 years 3 months 10 days
Options Exercisable
Number of Shares (in shares) | shares	406,361
Weighted- Average Exercise Price (in dollars per share)	$ 24.97
$14.67 - $20.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices - Lower Range Limit (in dollars per share)	14.67
Range of Exercise Prices - Upper Range Limit (in dollars per share)	$ 20
Options Outstanding
Number of Shares (in shares) | shares	110,291
Weighted- Average Exercise Price (in dollars per share)	$ 15.89
Weighted- Average Remaining Contractual Life in Years	3 years 12 days
Options Exercisable
Number of Shares (in shares) | shares	110,291
Weighted- Average Exercise Price (in dollars per share)	$ 15.89
$20.01 - $25.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices - Lower Range Limit (in dollars per share)	20.01
Range of Exercise Prices - Upper Range Limit (in dollars per share)	$ 25
Options Outstanding
Number of Shares (in shares) | shares	106,826
Weighted- Average Exercise Price (in dollars per share)	$ 22.92
Weighted- Average Remaining Contractual Life in Years	5 years 5 months 6 days
Options Exercisable
Number of Shares (in shares) | shares	82,747
Weighted- Average Exercise Price (in dollars per share)	$ 23.01
$25.01 - $30.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices - Lower Range Limit (in dollars per share)	25.01
Range of Exercise Prices - Upper Range Limit (in dollars per share)	$ 30
Options Outstanding
Number of Shares (in shares) | shares	202,009
Weighted- Average Exercise Price (in dollars per share)	$ 26.68
Weighted- Average Remaining Contractual Life in Years	6 years 5 months 20 days
Options Exercisable
Number of Shares (in shares) | shares	136,613
Weighted- Average Exercise Price (in dollars per share)	$ 26.58
$30.01 - $35.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices - Lower Range Limit (in dollars per share)	30.01
Range of Exercise Prices - Upper Range Limit (in dollars per share)	$ 35
Options Outstanding
Number of Shares (in shares) | shares	346,965
Weighted- Average Exercise Price (in dollars per share)	$ 34.52
Weighted- Average Remaining Contractual Life in Years	9 years 4 months 28 days
Options Exercisable
Number of Shares (in shares) | shares	0
Weighted- Average Exercise Price (in dollars per share)	$ 0
$35.01 - $37.28
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices - Lower Range Limit (in dollars per share)	35.01
Range of Exercise Prices - Upper Range Limit (in dollars per share)	$ 37.28
Options Outstanding
Number of Shares (in shares) | shares	143,260
Weighted- Average Exercise Price (in dollars per share)	$ 37.28
Weighted- Average Remaining Contractual Life in Years	7 years 10 months 25 days
Options Exercisable
Number of Shares (in shares) | shares	76,710
Weighted- Average Exercise Price (in dollars per share)	$ 37.28

DERIVATIVE FINANCIAL INSTRUME_3

DERIVATIVE FINANCIAL INSTRUMENTS AND HEDGING ACTIVITIES - Narrative (Details)	3 Months Ended
	Mar. 31, 2017contract	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Derivative [Line Items]
Debt face amount		$ 270,000,000
Cash collateral received		8,306,000	$ 7,900,000
Interest Rate Swaps
Derivative [Line Items]
Derivative, instruments terminated | contract	2
Available-for-sale Securities [Member] | Fixed rate callable securities [Member]
Derivative [Line Items]
Hedged Asset, Fair Value Hedge		$ 23,700,000

DERIVATIVE FINANCIAL INSTRUME_4

DERIVATIVE FINANCIAL INSTRUMENTS AND HEDGING ACTIVITIES - Schedule of Derivative Instruments (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Derivative Asset [Abstract]
Gross derivatives	$ 11,594,000	$ 8,626,000
Offsetting derivative assets/liabilities	(2,201,000)	(114,000)
Cash collateral received/posted	(8,306,000)	(7,900,000)
Net derivatives included in the consolidated balance sheets	1,087,000	612,000
Derivative Liability [Abstract]
Gross derivatives	3,320,000	726,000
Offsetting derivative assets/liabilities	(2,201,000)	(114,000)
Cash collateral received/posted	0	(520,000)
Net derivatives included in the consolidated balance sheets	1,119,000	92,000
Financial institution counterparties
Derivative Liability [Abstract]
Net credit exposure	0	30,000
Financial institution counterparties | Derivatives designated as hedging instruments | Cash Flow Hedging | Interest Rate Swaps
Derivatives, Fair Value [Line Items]
Notional Amount	270,000,000	240,000,000
Derivative Asset [Abstract]
Gross derivatives	9,388,000	7,922,000
Derivative Liability [Abstract]
Gross derivatives	457,000	22,000
Financial institution counterparties | Derivatives designated as hedging instruments | Fair Value Hedging [Member] | Interest Rate Swaps
Derivatives, Fair Value [Line Items]
Notional Amount	21,100,000	0
Derivative Asset [Abstract]
Gross derivatives	0	0
Derivative Liability [Abstract]
Gross derivatives	657,000	0
Financial institution counterparties | Derivatives designated as non-hedging instruments | Interest Rate Swaps
Derivatives, Fair Value [Line Items]
Notional Amount	93,967,000	67,220,000
Derivative Asset [Abstract]
Gross derivatives	1,119,000	92,000
Derivative Liability [Abstract]
Gross derivatives	1,087,000	612,000
Customer counterparties
Derivative Liability [Abstract]
Net credit exposure	1,100,000	612,000
Customer counterparties | Derivatives designated as non-hedging instruments | Interest Rate Swaps
Derivatives, Fair Value [Line Items]
Notional Amount	93,967,000	67,220,000
Derivative Asset [Abstract]
Gross derivatives	1,087,000	612,000
Derivative Liability [Abstract]
Gross derivatives	$ 1,119,000	$ 92,000

DERIVATIVE FINANCIAL INSTRUME_5

DERIVATIVE FINANCIAL INSTRUMENTS AND HEDGING ACTIVITIES - Weighted Average Remaining Maturity, Lives, and Rates of Interest Rate Swaps (Details) - Interest Rate Swaps - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Financial institution counterparties | Not Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	$ 93,967	$ 67,220
Remaining Maturity	11 years 7 months 21 days	12 years 8 months 15 days
Receive Rate	2.36%	1.39%
Pay Rate	2.58%	2.37%
Financial institution counterparties | Cash Flow Hedging | Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	$ 270,000	$ 240,000
Remaining Maturity	4 years 9 months 28 days	5 years 3 months
Receive Rate	2.45%	1.44%
Pay Rate	1.58%	1.43%
Financial institution counterparties | Fair Value Hedging [Member] | Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	$ 21,100	$ 0
Remaining Maturity	7 years 6 months 1 day
Receive Rate	2.56%
Pay Rate	3.00%
Customer counterparties | Not Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	$ 93,967	$ 67,220
Remaining Maturity	11 years 7 months 21 days	12 years 8 months 15 days
Receive Rate	2.58%	2.37%
Pay Rate	2.36%	1.39%

FAIR VALUE MEASUREMENT - Fair

FAIR VALUE MEASUREMENT - Fair Value Measurements, Recurring and Nonrecurring Basis (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value		$ 1,989,436
Securities available for sale, at estimated fair value			$ 1,538,755
Derivative assets: Interest rate swaps		1,087	612
Derivative liabilities: Interest rate swaps		1,119	92
U.S. Government Agency Debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value			108,869
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		716,601
Securities available for sale, at estimated fair value			392,664
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		2,709
Securities available for sale, at estimated fair value			5,055
Residential MBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value		732,972
Securities available for sale, at estimated fair value			718,029
Commercial MBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value		537,154
Securities available for sale, at estimated fair value			308,218
Equity Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value			5,920
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity investments	[1]	5,791
Total asset fair value measurements		2,006,821	1,547,381
Total liability fair value measurements		3,320	726
Fair Value, Measurements, Recurring [Member] | U.S. Government Agency Debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value			108,869
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		716,601
Securities available for sale, at estimated fair value			392,664
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		2,709
Securities available for sale, at estimated fair value			5,055
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]	732,972
Securities available for sale, at estimated fair value	[2]		718,029
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]	537,154
Securities available for sale, at estimated fair value	[2]		308,218
Fair Value, Measurements, Recurring [Member] | Equity Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	[1]		5,920
Fair Value, Measurements, Recurring [Member] | Interest Rate Swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets: Interest rate swaps		11,594	8,626
Derivative liabilities: Interest rate swaps		3,320	726
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	[1]	5,791
Total asset fair value measurements		5,791	5,920
Total liability fair value measurements		0	0
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Government Agency Debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value			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
Securities available for sale, at estimated fair value			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
Securities available for sale, at estimated fair value			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
Securities available for sale, at estimated fair value	[2]		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
Securities available for sale, at estimated fair value	[2]		0
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	[1]		5,920
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Interest Rate Swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets: Interest rate swaps		0	0
Derivative liabilities: Interest rate swaps		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	[1]	0
Total asset fair value measurements		2,001,030	1,541,461
Total liability fair value measurements		3,320	726
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | U.S. Government Agency Debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value			108,869
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		716,601
Securities available for sale, at estimated fair value			392,664
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		2,709
Securities available for sale, at estimated fair value			5,055
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]	732,972
Securities available for sale, at estimated fair value	[2]		718,029
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]	537,154
Securities available for sale, at estimated fair value	[2]		308,218
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Equity Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	[1]		0
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Interest Rate Swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets: Interest rate swaps		11,594	8,626
Derivative liabilities: Interest rate swaps		3,320	726
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	[1]	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) | U.S. Government Agency Debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value			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
Securities available for sale, at estimated fair value			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
Securities available for sale, at estimated fair value			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
Securities available for sale, at estimated fair value	[2]		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
Securities available for sale, at estimated fair value	[2]		0
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) | Equity Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	[1]		0
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) | Interest Rate Swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets: Interest rate swaps		0	0
Derivative liabilities: Interest rate swaps		0	0
Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreclosed assets		1,206	1,767
Impaired loans	[3]	37,813	6,536
Total asset fair value measurements		39,019	8,303
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		1,206	1,767
Impaired loans	[3]	37,813	6,536
Total asset fair value measurements		$ 39,019	$ 8,303
[1]	With the adoption of ASU 2016-01 on January 1, 2018, these investments are included in equity investments on our consolidated balance sheets. The guidance was applied on a prospective approach resulting in prior-periods no longer being comparable. See “Note 1 - Summary of Significant Accounting and Reporting Policies” for further information.
[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 - Fai_2

FAIR VALUE MEASUREMENT - Fair Value, Balance Sheet Grouping (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Carrying Amount
Financial Assets
Cash and cash equivalents	$ 120,719	$ 198,692
Investment Securities:
Held to maturity, at carrying value	3,083	413,632
Mortgage-backed securities:
Held to maturity, at carrying value	159,848	495,874
FHLB stock, at cost	32,583	55,729
Equity investments	6,302	5,821
Loans, net of allowance for loan losses	3,285,780	3,273,575
Loans held for sale	601	2,001
Financial Liabilities:
Deposits	4,425,030	4,515,447
Federal funds purchased and repurchase agreements	36,810	9,498
FHLB borrowings	719,065	1,017,361
Subordinated notes, net of unamortized debt issuance costs	98,407	98,248
Trust preferred subordinated debentures, net of unamortized debt issuance costs	60,246	60,241
Estimated Fair Value
Financial Assets
Cash and cash equivalents	120,719	198,692
Investment Securities:
Held to maturity, at carrying value	3,046	421,928
Mortgage-backed securities:
Held to maturity, at carrying value	156,735	499,872
FHLB stock, at cost	32,583	55,729
Equity investments	6,302	5,821
Loans, net of allowance for loan losses	3,251,923	3,269,316
Loans held for sale	601	2,001
Financial Liabilities:
Deposits	4,417,902	4,506,133
Federal funds purchased and repurchase agreements	36,810	9,498
FHLB borrowings	708,904	1,008,292
Subordinated notes, net of unamortized debt issuance costs	97,611	99,665
Trust preferred subordinated debentures, net of unamortized debt issuance costs	54,729	47,622
Estimated Fair Value | Level 1
Financial Assets
Cash and cash equivalents	120,719	198,692
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	3,046	421,928
Mortgage-backed securities:
Held to maturity, at carrying value	156,735	499,872
FHLB stock, at cost	32,583	55,729
Equity investments	6,302	5,821
Loans, net of allowance for loan losses	0	0
Loans held for sale	601	2,001
Financial Liabilities:
Deposits	4,417,902	4,506,133
Federal funds purchased and repurchase agreements	36,810	9,498
FHLB borrowings	708,904	1,008,292
Subordinated notes, net of unamortized debt issuance costs	97,611	99,665
Trust preferred subordinated debentures, net of unamortized debt issuance costs	54,729	47,622
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	3,251,923	3,269,316
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 - Fai_3

FAIR VALUE MEASUREMENT - Fair Value Measurements, Narrative (Details)	12 Months Ended
	Dec. 31, 2018source
Available-for-sale Securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Number of third party sources used to validate prices	2
Derivative [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Number of third party sources used to validate prices	3

SHAREHOLDERS' EQUITY - Regulat

SHAREHOLDERS' EQUITY - Regulatory Capital Requirements (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Consolidated
Common Equity Tier 1 (to Risk Weighted Assets)
Common Equity Tier 1 Capital		$ 568,283	$ 570,610
Common Equity Tier 1 Capital for Capital Adequacy Purposes		$ 173,174	$ 175,216
Common Equity Tier 1 (to Risk Weighted Assets) Ratios [Abstract]
Common Equity Tier 1 Capital to Risk Weighted Assets		14.77%	14.65%
Common Equity TIer 1 Required for Capital Adequacy Purposes to Risk Weighted Assets		4.50%	4.50%
Tier 1 Capital (to Risk Weighted Assets)
Tier 1 Capital		$ 626,718	$ 627,532
Tier 1 Capital Required for Capital Adequacy Purposes		$ 230,899	$ 233,621
Tier 1 Capital (to Risk Weighted Assets) Ratios
Tier 1 Capital to Risk Weighted Assets		16.29%	16.12%
Tier 1 Capital Required for Capital Adequacy Purposes to Risk Weighted Assets		6.00%	6.00%
Total Capital (to Risk Weighted Assets)
Total Capital		$ 754,034	$ 748,532
Total Capital Required for Capital Adequacy Purposes		$ 307,865	$ 311,495
Total Capital (to Risk Weighted Assets) Ratios
Total Capital to Risk Weighted Assets		19.59%	19.22%
Total Capital Required for Capital Adequacy Purposes to Risk Weighted Assets		8.00%	8.00%
Tier 1 Capital (to Average Assets)
Tier 1 Capital	[1]	$ 626,718	$ 627,532
Tier 1 Capital Required for Capital Adequacy Purposes	[1]	$ 235,689	$ 224,844
Tier 1 Capital (to Average Assets) Ratios
Tier 1 Capital to Average Assets	[1]	10.64%	11.16%
Tier 1 Capital Required for Capital Adequacy Purposes to Average Assets	[1]	4.00%	4.00%
Bank Only
Common Equity Tier 1 (to Risk Weighted Assets)
Common Equity Tier 1 Capital		$ 714,991	$ 711,157
Common Equity Tier 1 Capital for Capital Adequacy Purposes		173,095	175,145
Common Equity Tier 1 Capital to be Well Capitalized		$ 250,026	$ 252,987
Common Equity Tier 1 (to Risk Weighted Assets) Ratios [Abstract]
Common Equity Tier 1 Capital to Risk Weighted Assets		18.59%	18.27%
Common Equity TIer 1 Required for Capital Adequacy Purposes to Risk Weighted Assets		4.50%	4.50%
Common Equity Tier 1 Capital Required to be Well Capitalized to Risk Weighted Assets		6.50%	6.50%
Tier 1 Capital (to Risk Weighted Assets)
Tier 1 Capital		$ 714,991	$ 711,157
Tier 1 Capital Required for Capital Adequacy Purposes		230,793	233,527
Tier 1 Capital Required to be Well Capitalized		$ 307,725	$ 311,369
Tier 1 Capital (to Risk Weighted Assets) Ratios
Tier 1 Capital to Risk Weighted Assets		18.59%	18.27%
Tier 1 Capital Required for Capital Adequacy Purposes to Risk Weighted Assets		6.00%	6.00%
Tier 1 Capital Required to be Well Capitalized to Risk Weighted Assets		8.00%	8.00%
Total Capital (to Risk Weighted Assets)
Total Capital		$ 743,900	$ 733,909
Total Capital Required for Capital Adequacy Purposes		307,725	311,369
Total Capital Required to be Well Capitalized		$ 384,656	$ 389,211
Total Capital (to Risk Weighted Assets) Ratios
Total Capital to Risk Weighted Assets		19.34%	18.86%
Total Capital Required for Capital Adequacy Purposes to Risk Weighted Assets		8.00%	8.00%
Total Capital Required to be Well Capitalized to Risk Weighted Assets		10.00%	10.00%
Tier 1 Capital (to Average Assets)
Tier 1 Capital	[1]	$ 714,991	$ 711,157
Tier 1 Capital Required for Capital Adequacy Purposes	[1]	235,532	224,741
Tier 1 Capital Required to be Well Capitalized	[1]	$ 294,415	$ 280,926
Tier 1 Capital (to Average Assets) Ratios
Tier 1 Capital to Average Assets	[1]	12.14%	12.66%
Tier 1 Capital Required for Capital Adequacy Purposes to Average Assets	[1]	4.00%	4.00%
Tier 1 Capital Required to be Well Capitalized to Average Assets	[1]	5.00%	5.00%
[1]	Refers to quarterly average assets as calculated in accordance with policies established by bank regulatory agencies.

SHAREHOLDERS' EQUITY - Narrati

SHAREHOLDERS' EQUITY - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	Dec. 06, 2016	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Payments of Ordinary Dividends [Abstract]
Dividends paid on common stock (in dollars per share)		$ 0.32	$ 0.3	$ 0.3	$ 0.28	$ 0.3	$ 0.28	$ 0.28	$ 0.25	$ 1.20	$ 1.11	$ 1.01
Net issuance of common stock (in shares)	2,185,000											2,185,000
Price of shares issued (in dollars per share)	$ 36.50
Value of stock issued during the period	$ 200,100											$ 75,992

DIVIDEND REINVESTMENT AND COM_2

DIVIDEND REINVESTMENT AND COMMON STOCK REPURCHASE PLAN (Details) - USD ($) $ / shares in Units, $ in Thousands	Jan. 07, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Stock issued during period under dividend reinvestment plan (in shares)		42,872	43,650	44,575
Stock issued during period under dividend reinvestment plan, average price per share (in dollars per share)		$ 34.45	$ 33.99
Purchase of common stock (in shares)		1,459,148	0	443,426
Repurchase of common stock, cost		$ 47,193		$ 10,199
Subsequent Event
Class of Stock [Line Items]
Purchase of common stock (in shares)	40,852
Average cost per share (in usd per share)	$ 32.42

INCOME TAXES - Provision for I

INCOME TAXES - Provision for Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Current income tax expense									$ 4,009	$ 12,607	$ 8,557
Deferred income tax expense									6,154	3,514	1,768
Income tax expense	$ 2,521	$ 2,192	$ 3,360	$ 2,090	$ 5,870	$ 3,890	$ 3,353	$ 3,008	$ 10,163	$ 16,121	$ 10,325

INCOME TAXES - Summary of Net

INCOME TAXES - Summary of Net Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Assets
Allowance for loan losses	$ 5,673	$ 4,364
Unrealized losses on securities available for sale	7,926	4,285
Fair value adjustment on loans	1,894	2,607
Alternative minimum tax credit		6,943
Unfunded status of defined benefit plan	6,979	7,018
State business tax credit	483	544
Stock-based compensation	797	642
Gross deferred tax assets	23,752	26,403
Liabilities
Retirement and other benefit plans	(2,519)	(2,102)
Premises and equipment	(6,360)	(5,716)
Core deposit intangible	(2,748)	(3,660)
Effective hedging derivatives	(1,761)	(1,701)
Fair value adjustment on time deposits	(6)	(54)
Other	(582)	(966)
Gross deferred tax liabilities	(13,976)	(14,199)
Net deferred tax asset at year-end	$ 9,776	$ 12,204

INCOME TAXES - Income Tax Expe

INCOME TAXES - Income Tax Expense Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Amount
Statutory tax expense									$ 17,703	$ 24,652	$ 20,886
Increase (decrease) in taxes from:
Tax rate changes									(767)	2,416	0
Tax exempt interest									(6,257)	(10,195)	(9,879)
Bank Owned Life Insurance									(613)	(885)	(915)
Share-based compensation									(191)	(482)	0
Acquisition costs									0	467	0
State Business Tax									297	68	71
Other, net									(9)	80	162
Income tax expense	$ 2,521	$ 2,192	$ 3,360	$ 2,090	$ 5,870	$ 3,890	$ 3,353	$ 3,008	$ 10,163	$ 16,121	$ 10,325
Percent of Pre-Tax Income
Statutory tax expense									21.00%	35.00%	35.00%
Increase (Decrease) in Taxes From:
Percent of Pre-tax income, tax rate changes									(0.90%)	3.40%	0.00%
Percent of Pre-tax income, Tax exempt interest									(7.40%)	(14.50%)	(16.60%)
Percent of Pre-tax income, Bank Owned Life Insurance									(0.70%)	(1.20%)	(1.50%)
Percent of Pre-tax income, Share based compensation									(0.20%)	(0.70%)	0.00%
Percent of Pre-tax income, Acquisition Costs									0.00%	0.70%	0.00%
Percent of Pre-tax income, State Business Tax									0.30%	0.10%	0.10%
Percent of Pre-tax income, Other Net									0.00%	0.10%	0.30%
Percent of Pre-tax income, Income tax expense									12.10%	22.90%	17.30%

INCOME TAXES Narrative (Details

INCOME TAXES Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Narrative [Abstract]
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax Credit Recognized	$ 7,800,000
Deferred tax asset valuation allowance	$ 0	$ 0

OFF-BALANCE-SHEET ARRANGEMENT_3

OFF-BALANCE-SHEET ARRANGEMENTS, COMMITMENTS AND CONTINGENCIES - Off-Balance Sheet Arrangements, Commitments and Contingencies (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance sheet risk, at fair value	$ 901,995	$ 819,605
Commitments to extend credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance sheet risk, at fair value	874,557	804,715
Standby letters of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance sheet risk, at fair value	$ 27,438	$ 14,890

OFF-BALANCE-SHEET ARRANGEMENT_4

OFF-BALANCE-SHEET ARRANGEMENTS, COMMITMENTS AND CONTINGENCIES - Operating Lease Commitments and Rent Expense (Details) $ in Thousands	Dec. 31, 2018USD ($)
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,019	$ 1,265
2,020	1,158
2,021	906
2,022	742
2,023	560
2024 and thereafter	1,352
Total future minimum payments due	$ 5,983

OFF-BALANCE-SHEET ARRANGEMENT_5

OFF-BALANCE-SHEET ARRANGEMENTS, COMMITMENTS AND CONTINGENCIES - Operating Lease - Lessor (Details) $ in Thousands	Dec. 31, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,019	$ 2,574
2,020	2,427
2,021	1,374
2,022	1,352
2,023	1,119
2024 and thereafter	3,996
Future minimum payments receivable	$ 12,842

OFF-BALANCE-SHEET ARRANGEMENT_6

OFF-BALANCE-SHEET ARRANGEMENTS, COMMITMENTS AND CONTINGENCIES - Narrative (Details) ft² in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)ft²	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Jan. 01, 2019USD ($)
Long-term Purchase Commitment [Line Items]
Number of square feet in building acquired | ft²	202
Number of square feet occupied | ft²	41
Lease revenue	$ 3,000,000	$ 3,100,000	$ 3,100,000
Securities
Unsettled trades to purchase securities	6,378,000	0	160,000
Unsettled trades to sell securities	0	0
Deposits [Abstract]
Unsettled issuances of brokered certificates of deposit	15,236,000	0	0
Land, Buildings and Improvements
Long-term Purchase Commitment [Line Items]
Rent expense	1,800,000	1,700,000	3,900,000
Office Equipment
Long-term Purchase Commitment [Line Items]
Rent expense	$ 160,000	$ 178,000	$ 261,000
Subsequent Event | Accounting Standards Update 2016-02
Long-term Purchase Commitment [Line Items]
Increase in Operating Liabilities				$ 10,100,000
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability				$ 9,800,000

SIGNIFICANT GROUP CONCENTRATI_2

SIGNIFICANT GROUP CONCENTRATIONS OF CREDIT RISK (Details)	12 Months Ended
	Dec. 31, 2018Rate
Residential Real Estate [Member] | Credit Concentration Risk
Concentration Risk [Line Items]
Concentration risk percentage	31.80%

PARENT COMPANY FINANCIAL INFO_3

PARENT COMPANY FINANCIAL INFORMATION - BALANCE SHEETS (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
ASSETS
Cash and due from banks		$ 87,375	$ 79,171
Other assets		14,025	15,076
Total assets		6,123,494	6,498,097
Liabilities [Abstract]
Subordinated notes, net of unamortized debt issuance costs	[1]	98,407	98,248
Trust preferred subordinated debentures, net of unamortized debt issuance costs		60,246	60,241
Other liabilities		46,267	43,162
Total liabilities		5,392,203	5,743,957
Stockholders' Equity Attributable to Parent [Abstract]
Common stock: ($1.25 par value, 80,000,000 shares authorized and 37,845,224 shares issued at December 31, 2018 and 40,000,000 shares authorized and 37,802,352 shares issued at December 31, 2017)		47,307	47,253
Paid-in capital		762,470	757,439
Retained earnings		64,797	32,851
Treasury stock, at cost (4,120,475 at December 31, 2018 and 2,802,019 at December 31, 2017)		(93,055)	(47,105)
Accumulated other comprehensive loss		(50,228)	(36,298)
Total shareholders’ equity		731,291	754,140	$ 518,274	$ 444,062
Total liabilities and shareholders’ equity		6,123,494	6,498,097
Parent
ASSETS
Cash and due from banks		11,431	8,483
Other assets		4,290	10,350
Total assets		893,361	914,669
Liabilities [Abstract]
Subordinated notes, net of unamortized debt issuance costs		98,407	98,248
Trust preferred subordinated debentures, net of unamortized debt issuance costs		60,246	60,241
Other liabilities		3,417	2,040
Total liabilities		162,070	160,529
Stockholders' Equity Attributable to Parent [Abstract]
Common stock: ($1.25 par value, 80,000,000 shares authorized and 37,845,224 shares issued at December 31, 2018 and 40,000,000 shares authorized and 37,802,352 shares issued at December 31, 2017)		47,307	47,253
Paid-in capital		762,470	757,439
Retained earnings		64,797	32,851
Treasury stock, at cost (4,120,475 at December 31, 2018 and 2,802,019 at December 31, 2017)		(93,055)	(47,105)
Accumulated other comprehensive loss		(50,228)	(36,298)
Total shareholders’ equity		731,291	754,140
Total liabilities and shareholders’ equity		893,361	914,669
Parent | Bank subsidiaries
ASSETS
Investment in subsidiaries at equity in underlying net assets		875,814	894,010
Parent | Nonbank subsidiaries
ASSETS
Investment in subsidiaries at equity in underlying net assets		$ 1,826	$ 1,826
[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.

PARENT COMPANY FINANCIAL INFO_4

PARENT COMPANY FINANCIAL INFORMATION - BALANCE SHEETS SHARE INFORMATION (Details) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Common stock, par value (in dollars per share)	$ 1.25	$ 1.25
Common stock, shares authorized (in shares)	80,000,000	40,000,000
Common stock, shares issued (in shares)	37,845,224	37,802,352
Treasury stock, (in shares)	4,120,475	2,802,019
Parent
Common stock, par value (in dollars per share)	$ 1.25	$ 1.25
Common stock, shares authorized (in shares)	80,000,000	40,000,000
Common stock, shares issued (in shares)	37,845,224	37,802,352
Treasury stock, (in shares)	4,120,475	2,802,019

PARENT COMPANY FINANCIAL INFO_5

PARENT COMPANY FINANCIAL INFORMATION - INCOME STATEMENT (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income
Total interest income	$ 58,022	$ 57,152	$ 56,797	$ 57,194	$ 50,104	$ 46,473	$ 46,009	$ 44,888	$ 229,165	$ 187,474	$ 168,913
Expense
Interest expense	15,612	14,742	13,686	13,061	11,798	11,513	10,585	9,608	57,101	43,504	29,348
Income tax benefit	(2,521)	(2,192)	(3,360)	(2,090)	(5,870)	(3,890)	(3,353)	(3,008)	(10,163)	(16,121)	(10,325)
Net income	$ 17,381	$ 20,303	$ 20,203	$ 16,251	$ 10,331	$ 14,511	$ 14,481	$ 14,989	74,138	54,312	49,349
Parent
Income
Dividends from subsidiary									90,000	27,000	30,000
Interest income									78	60	51
Total interest income									90,078	27,060	30,051
Expense
Interest expense									8,269	7,646	3,334
Other									3,662	5,869	3,227
Total expense									11,931	13,515	6,561
Income before income tax expense									78,147	13,545	23,490
Income tax benefit									2,489	4,242	2,278
Income before equity in undistributed earnings of subsidiaries									80,636	17,787	25,768
Equity in undistributed earnings of subsidiaries									(6,498)	36,525	23,581
Net income									$ 74,138	$ 54,312	$ 49,349

PARENT COMPANY FINANCIAL INFO_6

PARENT COMPANY FINANCIAL INFORMATION - CASH FLOWS (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
OPERATING ACTIVITIES:
Net Income	$ 17,381	$ 20,303	$ 20,203	$ 16,251	$ 10,331	$ 14,511	$ 14,481	$ 14,989	$ 74,138	$ 54,312	$ 49,349
Adjustments to reconcile net income to net cash provided by operations:
Decrease (increase) in other assets									(2,166)	(3,909)	1,823
Increase (decrease) in other liabilities									1,358	(1,063)	3,520
Net cash provided by operating activities									122,402	91,730	86,725
INVESTING ACTIVITIES:
Net cash provided by (used in) investing activities									261,904	172,737	(384,404)
FINANCING ACTIVITIES:
Net proceeds from issuance of subordinated long-term debt									0	0	98,060
Purchase of common stock									(47,193)	0	(10,199)
Proceeds from issuance of common stock									0	0	75,992
Cash dividends paid									(41,979)	(32,199)	(25,963)
Net cash (used in) provided by financing activities									(462,279)	(235,429)	386,358
Net increase (decrease) in cash and cash equivalents									(77,973)	29,038	88,679
Cash and cash equivalents at beginning of period				198,692				169,654	198,692	169,654	80,975
Cash and cash equivalents at end of period	120,719				198,692				120,719	198,692	169,654
Parent
OPERATING ACTIVITIES:
Net Income									74,138	54,312	49,349
Adjustments to reconcile net income to net cash provided by operations:
Amortization									164	153	45
Equity in undistributed earnings of subsidiaries									6,498	(36,525)	(23,581)
Decrease (increase) in other assets									6,060	(2,113)	(1,035)
Increase (decrease) in other liabilities									1,377	(155)	1,564
Net cash provided by operating activities									88,237	15,672	26,342
INVESTING ACTIVITIES:
Investment in subsidiaries									0	890	(126,000)
Net cash paid in acquisition									0	(22,801)	0
Net cash provided by (used in) investing activities									0	(21,911)	(126,000)
FINANCING ACTIVITIES:
Net proceeds from issuance of subordinated long-term debt									0	0	98,060
Purchase of common stock									(47,193)	0	(10,199)
Proceeds from issuance of common stock									3,883	3,953	78,962
Cash dividends paid									(41,979)	(32,199)	(25,963)
Net cash (used in) provided by financing activities									(85,289)	(28,246)	140,860
Net increase (decrease) in cash and cash equivalents									2,948	(34,485)	41,202
Cash and cash equivalents at beginning of period				$ 8,483				$ 42,968	8,483	42,968	1,766
Cash and cash equivalents at end of period	$ 11,431				$ 8,483				$ 11,431	$ 8,483	$ 42,968

QUARTERLY FINANCIAL INFORMATI_3

QUARTERLY FINANCIAL INFORMATION OF REGISTRANT (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 58,022	$ 57,152	$ 56,797	$ 57,194	$ 50,104	$ 46,473	$ 46,009	$ 44,888	$ 229,165		$ 187,474		$ 168,913
Interest expense	15,612	14,742	13,686	13,061	11,798	11,513	10,585	9,608	57,101		43,504		29,348
Net interest income	42,410	42,410	43,111	44,133	38,306	34,960	35,424	35,280	172,064		143,970		139,565
Provision for loan losses	2,446	975	1,281	3,735	1,271	960	1,346	1,098	8,437	[1]	4,675	[1]	9,780	[1]
Net gain (loss) on sale of securities available for sale	61	(741)	(332)	(827)	(249)	627	(75)	322	(1,839)		625		2,836
Noninterest income excluding net gain (loss) on sale of securities	10,073	10,763	11,339	10,437	9,348	8,781	9,368	9,351	40,773		37,473		39,411
Noninterest expense	30,196	28,962	29,274	31,667	29,933	25,007	25,537	25,858	120,099		106,335		109,522
Income before income tax expense	19,902	22,495	23,563	18,341	16,201	18,401	17,834	17,997	84,301		70,433		59,674
Income tax expense	2,521	2,192	3,360	2,090	5,870	3,890	3,353	3,008	10,163		16,121		10,325
Net income	$ 17,381	$ 20,303	$ 20,203	$ 16,251	$ 10,331	$ 14,511	$ 14,481	$ 14,989	$ 74,138		$ 54,312		$ 49,349
Earnings (loss) per common share
Earnings (loss) per common share - basic (in dollars per share)	$ 0.50	$ 0.58	$ 0.58	$ 0.46	$ 0.33	$ 0.49	$ 0.49	$ 0.51	$ 2.12		$ 1.82		$ 1.82
Earnings (loss) per common share - diluted (in dollars per share)	0.50	0.58	0.57	0.46	0.33	0.49	0.49	0.51	2.11		1.81		1.81
Dividends paid on common stock (in dollars per share)	$ 0.32	$ 0.3	$ 0.3	$ 0.28	$ 0.3	$ 0.28	$ 0.28	$ 0.25	$ 1.20		$ 1.11		$ 1.01
[1]	Of the $8.4 million in provision for loan losses for the year ended December 31, 2018, $302,000 related to provision expense on PCI loans. Of the $4.7 million and $9.8 million recorded in provision for loan losses for the year ended December 31, 2017 and 2016, respectively, none related to provision expense on PCI loans