Simmons First National (SFNC) 10-Q 7 Nov 18 2018 Q3 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 26, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	SIMMONS FIRST NATIONAL CORP
Entity Central Index Key	90,498
Trading Symbol	sfnc
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Current Reporting Status	Yes
Entity Common Stock, Shares Outstanding		92,303,093
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Emerging Growth Company	false
Entity Small Business	false

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands		Sep. 30, 2018	Dec. 31, 2017
ASSETS
Cash and non-interest bearing balances due from banks		$ 125,231	$ 205,025
Interest bearing balances due from banks and federal funds sold		388,573	393,017
Cash and cash equivalents		513,804	598,042
Interest bearing balances due from banks - time		3,954	3,314
Investment securities:
Held-to-maturity		323,306	368,058
Available-for-sale securities		1,997,814	1,589,517
Total investments		2,321,120	1,957,575
Mortgage loans held for sale		48,195	24,038
Other assets held for sale		5,136	165,780
Loans:
Legacy loans		8,123,274	5,705,609
Allowance for loan losses		(55,358)	(41,668)
Loans acquired, net of discount and allowance		3,734,921	5,074,076
Net loans		11,802,837	10,738,017
Premises and equipment		287,246	287,249
Foreclosed assets and other real estate owned		22,664	32,118
Interest receivable		51,509	43,528
Bank owned life insurance		192,680	185,984
Goodwill		845,687	842,651
Other intangible assets		93,975	106,071
Other assets		92,457	71,439
Total assets		16,281,264	15,055,806
Deposits:
Non-interest bearing transaction accounts		2,778,670	2,665,249
Interest bearing transaction accounts and savings deposits		6,776,330	6,494,896
Time deposits		2,533,506	1,932,730
Total deposits		12,088,506	11,092,875
Federal funds purchased and securities sold under agreements to repurchase		109,213	122,444
Other borrowings		1,420,917	1,380,024
Subordinated notes and debentures		372,934	140,565
Other liabilities held for sale		424	157,366
Accrued interest and other liabilities		105,951	77,968
Total liabilities		14,097,945	12,971,242
Stockholders’ equity:
Common stock, Class A, $0.01 par value; 175,000,000 and 120,000,000 shares authorized at September 30, 2018 and December 31, 2017, respectively (1); 92,291,070 and 92,029,118 shares issued and outstanding at September 30, 2018 and December 31, 2017, respectively	[1]	923	920
Surplus		1,597,261	1,586,034
Undivided profits		633,175	514,874
Accumulated other comprehensive loss		(48,040)	(17,264)
Total stockholders’ equity		2,183,319	2,084,564
Total liabilities and stockholders’ equity		$ 16,281,264	$ 15,055,806
[1]	On April 19, 2018, shareholders of the Company approved an increase in the number of authorized shares from 120,000,000 to 175,000,000.

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Common stock, Class A, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, Class A, shares authorized (in shares)	175,000,000	120,000,000
Common stock, Class A, shares issued (in shares)	92,291,070	92,029,118
Common stock, Class A, shares outstanding (in shares)	92,291,070	92,029,118

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
INTEREST INCOME
Loans		$ 162,438	$ 77,457	$ 456,041	$ 219,734
Interest bearing balances due from banks and federal funds sold		1,405	650	3,828	986
Investment securities		14,640	9,218	41,558	28,659
Mortgage loans held for sale		501	159	964	430
TOTAL INTEREST INCOME		178,984	87,484	502,391	249,809
INTEREST EXPENSE
Deposits		24,390	6,030	58,448	15,050
Federal funds purchased and securities sold under agreements to repurchase		104	83	302	250
Other borrowings		6,240	1,875	16,520	4,628
Subordinated notes and debentures		5,282	677	12,350	1,870
TOTAL INTEREST EXPENSE		36,016	8,665	87,620	21,798
NET INTEREST INCOME		142,968	78,819	414,771	228,011
Provision for loan losses		10,345	5,462	28,528	16,792
NET INTEREST INCOME AFTER PROVISION FOR LOAN LOSSES		132,623	73,357	386,243	211,219
NON-INTEREST INCOME
Investment banking income		664	680	2,312	2,007
Bank owned life insurance income		1,105	725	3,310	2,402
Gain on sale of securities, net		54	3	53	2,302
Other income		4,942	7,276	14,151	15,178
TOTAL NON-INTEREST INCOME		33,725	36,332	109,308	102,136
NON-INTEREST EXPENSE
Salaries and employee benefits		55,515	35,285	167,550	105,026
Occupancy expense, net		7,713	4,928	22,594	14,459
Furniture and equipment expense		3,761	4,840	12,184	13,833
Other real estate and foreclosure expense		538	1,071	2,940	2,177
Deposit insurance		2,248	1,020	6,232	2,480
Merger related costs		804	752	3,980	7,879
Other operating expenses		29,674	18,263	81,353	58,035
TOTAL NON-INTEREST EXPENSE		100,253	66,159	296,833	203,889
INCOME BEFORE INCOME TAXES		66,095	43,530	198,718	109,466
Provision for income taxes		10,902	14,678	38,651	35,429
NET INCOME		$ 55,193	$ 28,852	$ 160,067	$ 74,037
BASIC EARNINGS PER SHARE (in dollars per share)	[1]	$ 0.60	$ 0.45	$ 1.74	$ 1.16
DILUTED EARNINGS PER SHARE (in dollars per share)	[1]	$ 0.59	$ 0.44	$ 1.72	$ 1.16
Trust income
NON-INTEREST INCOME
Non-interest income		$ 6,277	$ 4,225	$ 17,148	$ 12,550
Service charges on deposit accounts
NON-INTEREST INCOME
Non-interest income		10,837	8,907	31,245	25,492
Other service charges and fees
NON-INTEREST INCOME
Non-interest income		1,201	2,433	5,968	7,145
Mortgage and SBA lending income
NON-INTEREST INCOME
Non-interest income		1,825	3,219	9,400	9,603
Debit and credit card fees
NON-INTEREST INCOME
Non-interest income		$ 6,820	$ 8,864	$ 25,721	$ 25,457
[1]	All per share amounts have been restated to reflect the effect of the two-for-one stock split on February 8, 2018.

Consolidated Statements of In_2

Consolidated Statements of Income (Parentheticals)	Feb. 08, 2018
Income Statement [Abstract]
Conversion ratio	2

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
NET INCOME	$ 55,193	$ 28,852	$ 160,067	$ 74,037
OTHER COMPREHENSIVE (LOSS) INCOME
Unrealized holding (losses) gains arising during the period on available-for-sale securities	(10,583)	1,107	(41,612)	9,807
Less: Reclassification adjustment for realized gains included in net income	54	3	53	2,302
Other comprehensive (loss) gain, before tax effect	(10,637)	1,104	(41,665)	7,505
Less: Tax effect of other comprehensive (loss) income	(2,780)	433	(10,889)	2,944
TOTAL OTHER COMPREHENSIVE (LOSS) INCOME	(7,857)	671	(30,776)	4,561
COMPREHENSIVE INCOME	$ 47,336	$ 29,523	$ 129,291	$ 78,598

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
OPERATING ACTIVITIES
Net income	$ 160,067	$ 74,037
Adjustments to reconcile net income to net cash (used in) provided by operating activities:
Depreciation and amortization	20,810	14,589
Provision for loan losses	28,528	16,792
Gain on sale of investments	(53)	(2,302)
Net accretion of investment securities and assets	(41,423)	(19,472)
Net (accretion) amortization on borrowings	(471)	319
Stock-based compensation expense	8,448	5,675
Gain on sale of premises and equipment, net of impairment	0	(615)
Loss (gain) on sale of foreclosed assets held for sale	150	(801)
Gain on sale of mortgage loans held for sale	(9,675)	(8,809)
Gain on sale of loans	(10)	(18)
Fair value write-down of closed branches	954	325
Deferred income taxes	7,316	4,962
Increase in cash surrender value of bank owned life insurance	(3,310)	(2,402)
Originations of mortgage loans held for sale	(424,751)	(353,714)
Proceeds from sale of mortgage loans held for sale	410,269	377,697
Changes in assets and liabilities:
Interest receivable	(7,798)	(1,129)
Assets held in trading accounts	0	(8)
Other assets	(24,695)	8,249
Accrued interest and other liabilities	23,821	(9,738)
Income taxes payable	3,956	4,819
Net cash provided by operating activities	152,133	108,456
INVESTING ACTIVITIES
Net originations of loans	(1,034,175)	(448,476)
Proceeds from sale of loans	24,977	20,705
(Increase) decrease in due from banks - time	(640)	2,488
Purchases of premises and equipment, net	(17,084)	(28,971)
Proceeds from sale of premises and equipment	0	3,475
Purchases of other real estate owned	0	(1,021)
Proceeds from sale of foreclosed assets held for sale	20,739	11,401
Proceeds from sale of available-for-sale securities	7,726	327,218
Proceeds from maturities of available-for-sale securities	197,464	76,615
Purchases of available-for-sale securities	(634,791)	(380,308)
Proceeds from maturities of held-to-maturity securities	46,515	57,896
Purchases of held-to-maturity securities	(1,172)	(860)
Purchases of bank owned life insurance	(4,000)	(143)
Proceeds from bank owned life insurance death benefits	616	0
Proceeds from the sale of insurance lines of business	0	3,707
Cash paid in business combinations, net of cash received	0	(22,000)
Disposition of assets and liabilities held for sale	(58,295)	0
Net cash used in investing activities	(1,452,120)	(378,274)
FINANCING ACTIVITIES
Net change in deposits	995,631	201,395
Proceeds from issuance of subordinated notes	326,355	0
Repayments of subordinated debentures	(94,915)	0
Dividends paid on common stock	(41,766)	(23,986)
Net change in other borrowed funds	40,893	246,382
Net change in federal funds purchased and securities sold under agreements to repurchase	(13,231)	(10,505)
Net shares issued under stock compensation plans	1,756	2,545
Shares issued under employee stock purchase plan	1,026	618
Net cash provided by financing activities	1,215,749	416,449
(DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	(84,238)	146,631
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	598,042	285,659
CASH AND CASH EQUIVALENTS, END OF PERIOD	$ 513,804	$ 432,290

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands		Total	Common Stock	Surplus	Accumulated Other Comprehensive Income (Loss)	Undivided Profits	Hardeman County Investment Company, Inc.	Hardeman County Investment Company, Inc.Common Stock	Hardeman County Investment Company, Inc.Surplus	OKSB Merger	OKSB MergerCommon Stock	OKSB MergerSurplus	First Texas Merger	First Texas MergerCommon Stock	First Texas MergerSurplus
Balance at Dec. 31, 2016		$ 1,151,111	$ 626	$ 711,663	$ (15,212)	$ 454,034
Comprehensive income		78,598			4,561	74,037
Stock issued for employee stock purchase plan		618		618
Stock-based compensation plans, net		8,220	2	8,218
Stock issued for acquisition							$ 42,638	$ 16	$ 42,622
Dividends on common stock	[1]	(23,986)				(23,986)
Balance at Sep. 30, 2017		1,257,199	644	763,121	(10,651)	504,085
Comprehensive income		15,306			(3,597)	18,903
Reclassify stranded tax effects due to 2017 tax law changes		0			(3,016)	3,016
Stock-based compensation plans, net		4,721	1	4,720
Stock issued for acquisition										$ 431,398	$ 145	$ 431,253	$ 387,070	$ 130	$ 386,940
Dividends on common stock	[1]	(11,130)				(11,130)
Balance at Dec. 31, 2017		2,084,564	920	1,586,034	(17,264)	514,874
Comprehensive income		129,291			(30,776)	160,067
Stock issued for employee stock purchase plan		1,026		1,026
Stock-based compensation plans, net		10,204	3	10,201
Dividends on common stock	[1]	(41,766)				(41,766)
Balance at Sep. 30, 2018		$ 2,183,319	$ 923	$ 1,597,261	$ (48,040)	$ 633,175
[1]	All share and per share amounts have been restated to reflect the effect of the two-for-one stock split on February 8, 2018.

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Parenthetical)	3 Months Ended	9 Months Ended
	Dec. 31, 2017$ / sharesshares	Sep. 30, 2018$ / sharesshares	Sep. 30, 2017$ / sharesshares
Stock issued for employee stock purchase plan, shares (in shares)		39,782	26,002
Stock issued for compensation plans, shares (in shares)	116,190	226,715	243,096
Cash dividends per share (in dollars per share) | $ / shares	$ 0.125	$ 0.45	$ 0.375
Hardeman County Investment Company, Inc.
Stock issued for acquisition (in shares)			1,599,940
OKSB Merger
Stock issued for acquisition (in shares)	14,488,604
First Texas Merger
Stock issued for acquisition (in shares)	12,999,840

Preparation of Interim Financia

Preparation of Interim Financial Statements	9 Months Ended
	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Preparation of Interim Financial Statements	PREPARATION OF INTERIM FINANCIAL STATEMENTS Organizational Structure Simmons First National Corporation (the “Company”) is a publicly traded financial holding company that trades on the NASDAQ Global Select Market (“NASDAQ”) under the ticker symbol “SFNC” and the parent of Simmons Bank, an Arkansas state-chartered bank that began as a community bank in 1903. Simmons Bank is the parent of Simmons First Investment Group, Inc. (a dually registered broker-dealer and investment adviser), Simmons First Insurance Services, Inc. (an insurance agency), and Simmons First Insurance Services of TN, LLC (an insurance agency). Description of Business The Company is headquartered in Pine Bluff, Arkansas and conducts banking operations in communities throughout Arkansas, Colorado, Kansas, Missouri, Oklahoma, Tennessee and Texas. The Company, through its subsidiaries, offers consumer, real estate and commercial loans, checking, savings and time deposits from 191 financial centers conveniently located throughout its market areas. Additionally, the Company offers specialized products and services such as credit cards, trust and fiduciary services, investments, agricultural finance lending, equipment lending, insurance and small business administration (“SBA”) lending. Basis of Presentation The accompanying unaudited consolidated financial statements have been prepared based upon Securities and Exchange Commission (“SEC”) rules that permit reduced disclosures for interim periods. Certain information and footnote disclosures have been condensed or omitted in accordance with those rules and regulations. The accompanying consolidated balance sheet as of December 31, 2017 , was derived from audited financial statements. In the opinion of management, these financial statements reflect all adjustments that are necessary for a fair presentation of interim results of operations, including normal recurring accruals. Significant intercompany accounts and transactions have been eliminated in consolidation. The results for the interim periods are not necessarily indicative of results for the full year. For a more complete discussion of significant accounting policies and certain other information, this report should be read in conjunction with the consolidated financial statements and accompanying notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 , which was filed with the SEC on February 28, 2018 . The preparation of financial statements, in accordance with accounting principles generally accepted in the United States (“US GAAP”), requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, income items and expenses and disclosure of contingent assets and liabilities. The estimates and assumptions used in the accompanying consolidated financial statements are based upon management’s evaluation of the relevant facts and circumstances as of the date of the consolidated financial statements and actual results may differ from these estimates. Such estimates include, but are not limited to, the Company’s allowance for loan losses. Certain prior year amounts have been reclassified to conform to the current year financial statement presentation. These changes and reclassifications did not impact previously reported net income or comprehensive income. Recently Adopted Accounting Standards Reporting Comprehensive Income – In February 2018, the Financial Accounting Standards Board (“FASB”) issued Accounting Standard Update (“ASU”) No. 2018-02, Income Statement-Reporting Comprehensive Income (Topic 220) (“ASU 2018-02”), that allows a reclassification from accumulated other comprehensive income (“AOCI”) to retained earnings for stranded tax effects resulting from the tax reform legislation signed into law in December 2017 (“2017 Act”). Current US GAAP requires the remeasurement of deferred tax assets and liabilities as a result of a change in tax laws or rates to be presented in net income from continuing operations. Consequently, the original deferred tax amount recorded through AOCI at the old rate will remain in AOCI despite the fact that its related deferred tax asset/liability will be reduced through continuing operations to reflect the new rate, resulting in “stranded” tax effects in AOCI. ASU 2018-02 requires a reclassification from AOCI to retained earnings for those stranded tax effects resulting from the newly enacted federal corporate income tax rate. The amount of reclassification would be the difference between 1) the amount initially charged or credited directly to other comprehensive income at the previous enacted federal corporate income tax rate that remains in AOCI and 2) the amount that would have been charged or credited using the newly enacted federal corporate income tax rate, excluding the effect of any valuation allowance previously charged to income from continuing operations. The effective date is for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. As permitted, the Company elected to early adopt the provisions of ASU 2018-02 during the fourth quarter 2017 , which resulted in a reclassification from AOCI to retained earnings in the amount of $3.0 million related to the change in federal corporate tax rate. Stock Compensation: Scope of Modification Accounting – In May 2017, the FASB issued ASU No. 2017-09, Compensation – Stock Compensation (Topic 718): Scope of Modification Accounting (“ASU 2017-09”), that provides clarity and reduces both (1) diversity in practice and (2) cost and complexity when applying the guidance in Topic 718, to a change to the terms or conditions of a share-based payment award. An entity may change the terms or conditions of a share-based payment award for many different reasons, and the nature and effect of the change can vary significantly. The guidance clarifies which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting and the guidance should be applied prospectively to an award modified on or after the adoption date. ASU 2017-09 is effective for interim and annual reporting periods beginning after December 15, 2017, with early adoption permitted. Currently, the Company has not modified any existing awards nor has any plans to do so, therefore the adoption of ASU 2017-09 has not had a material effect on the Company’s results of operations, financial position or disclosures. Premium Amortization on Purchased Callable Debt Securities – In March 2017, the FASB issued ASU No. 2017-08, Receivables – Nonrefundable Fees and Other Costs (Topic 310-20): Premium Amortization on Purchased Callable Debt Securities (“ASU 2017-08”), that amends the amortization period for certain purchased callable debt securities held at a premium. Specifically, the amendments shorten the amortization period by requiring that the premium be amortized to the earliest call date. Under previous US GAAP, entities generally amortize the premium as an adjustment of yield over the contractual life of the instrument. The amendments do not require an accounting change for securities held at a discount; the discount continues to be amortized to maturity. The effective date is for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. As permitted, the Company elected to early adopt the provisions of ASU 2017-08 during the first quarter 2017. The adoption of this standard did not have a material effect on the Company’s results of operations, financial position or disclosures. Statement of Cash Flows – In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments (“ASU 2016-15”), designed to address the diversity in how certain cash receipts and cash payments are presented and classified in the statement of cash flows, including debt prepayment or extinguishment costs, settlement of certain debt instruments, contingent consideration payments made after a business combination, proceeds from the settlement of insurance claims, and distributions received from equity method investees. The amendments also provide guidance on when an entity should separate or aggregate cash flows based on the predominance principle. The effective date is for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. The new standard is required to be applied retrospectively, but may be applied prospectively if retrospective application would be impracticable. The adoption of 2016-15 did not have a material impact on the Company’s results of operations, financial position or disclosures since the amendment applies to the classification of cash flows. The adoption did not have a material impact on the consolidated statement of cash flows. Financial Assets and Financial Liabilities – In January 2016, the FASB issued ASU No. 2016-01, Financial Instruments – Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities (“ASU 2016-01”), that makes changes primarily affecting the accounting for equity investments, financial liabilities under the fair value option, and the presentation and disclosure requirements for financial instruments. In addition, the FASB clarified guidance related to the valuation allowance assessment when recognizing deferred tax assets resulting from unrealized losses on available-for-sale debt securities. In February 2018, the FASB issued 2018-03 that clarified certain guidance and contained narrow scope amendments. The effective date is for fiscal periods beginning after December 15, 2017, including interim periods within those fiscal years. ASU 2016-01 did not have a material impact on the Company’s results of operations or financial position. However, this new guidance requires the disclosed estimated fair value of the Company’s loan portfolio to be based on an exit price calculation, which considers liquidity, credit and nonperformance risk of its loans. The adoption of 2016-01 did not have a material impact on the Company’s fair value disclosures. Revenue Recognition – In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASU 2014-09”), that outlines a single comprehensive revenue recognition model for entities to follow in accounting for revenue from contracts with customers. The core principle of this revenue model is that an entity should recognize revenue for the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled to receive for those goods or services. In July 2015, the FASB issued ASU No. 2015-14, deferring the effective date to annual and interim periods beginning after December 15, 2017. The guidance does not apply to revenue associated with financial instruments, including loans and securities that are accounted for under other US GAAP, which comprises a significant portion of the Company’s revenue stream. However, the updated guidance affects the revenue recognition pattern for certain revenue streams, including service charges on deposit accounts, gains/losses on sale of other real estate owned (“OREO”), and trust income. The adoption of this standard did not have a material effect on the Company’s results of operations, financial position or disclosures. See below “Revenue from Contracts with Customers” for additional information. Recently Issued Accounting Standards Cloud Computing Arrangements – In August 2018, the FASB issued ASU No. 2018-15, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That is a Service Contract (“ASU 2018-15”), that amends the definition of a hosting arrangement and requires a customer in a hosting arrangement that is a service contract to capitalize certain implementation costs as if the arrangement was an internal-use software project. The internal-use software guidance states that only qualifying costs incurred during the application development stage can be capitalized. The effective date is for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years, with early adoption permitted. Entities have the option to apply the guidance prospectively to all implementation costs incurred after the date of adoption or retrospectively in accordance with the applicable guidance. At the time of adoption, entities will be required to disclose the nature of its hosting arrangements that are service contracts and provide disclosures as if the deferred implementation costs were a separate, major depreciable asset class. The Company is beginning to evaluate its cloud computing arrangements and has not yet determined how it will apply or the impact of this new standard. Fair Value Measurement Disclosures – In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement (“ASU 2018-13”), that eliminates, amends and adds disclosure requirements for fair value measurements. These amendments are part of FASB’s disclosure review project and they are expected to reduce costs for preparers while providing more decision-useful information for financial statement users. The eliminated disclosure requirements include the 1) the amount of, and reasons for, transfers between Level 1 and Level 2 of the fair value hierarchy; 2) the policy of timing of transfers between levels of the fair value hierarchy; and 3) the valuation processes for Level 3 fair value measurements. Among other modifications, the amended disclosure requirements remove the term “at a minimum” from the phrase “an entity shall disclose at a minimum” to promote the appropriate exercise of discretion by entities and clarifies that the measurement uncertainty disclosure is to communicate information about the uncertainty in measurement as of the reporting date. Under the new disclosure requirements, entities must disclose the changes in unrealized gains or losses included in other comprehensive income for recurring Level 3 fair value measurements held at the end of the reporting period and the range and weighted average used to develop significant unobservable inputs for Level 3 fair value measurements. ASU 2018-13 is effective for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years, with early adoption permitted. The Company is currently evaluating the impact this standard will have on its fair value disclosures. Derivatives and Hedging: Targeted Improvements – In August 2017, the FASB issued ASU No. 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities (“ASU 2017-12”), that changes both the designation and measurement guidance for qualifying hedging relationships and the presentation of hedge results in order to better align a company’s risk management activities and financial reporting for hedging relationships. In summary, this amendment 1) expands the types of transactions eligible for hedge accounting; 2) eliminates the separate measurement and presentation of hedge ineffectiveness; 3) simplifies the requirements around the assessment of hedge effectiveness; 4) provides companies more time to finalize hedge documentation; and 5) enhances presentation and disclosure requirements. The effective date is for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years, with early adoption permitted. All transition requirements and elections should be applied to existing hedging relationships on the date of adoption and the effects should be reflected as of the beginning of the fiscal year of adoption. The Company has evaluated the impact this standard will have on its results of operations, financial position or disclosures, and it is not expected to have a material impact. Goodwill Impairment – In January 2017, the FASB issued ASU No. 2017-04, Intangibles – Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment (“ASU 2017-04”), that eliminates Step 2 from the goodwill impairment test which required entities to compare the implied fair value of goodwill to its carrying amount. Under the amendments, the goodwill impairment will be measured as the excess of the reporting unit’s carrying amount over its fair value. An impairment charge should be recognized for the amount by which the carrying amount exceeds the reporting unit’s fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. The effective date is for fiscal years beginning after December 15, 2019, with early adoption permitted for interim or annual impairment tests beginning in 2017. ASU 2017-04 is not expected to have a material effect on the Company’s results of operations, financial position or disclosures. Credit Losses on Financial Instruments – In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”), which requires earlier measurement of credit losses, expands the range of information considered in determining expected credit losses and enhances disclosures. The main objective of ASU 2016-13 is to provide financial statement users with more decision-useful information about the expected credit losses on financial instruments and other commitments to extend credit held by a reporting entity at each reporting date. The amendments replace the incurred loss impairment methodology in current US GAAP with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. The effective date for these amendments is for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. The Company has formed a cross functional team that continues to assess its data and system needs and evaluate the potential impact of adopting the new guidance. The Company anticipates a significant change in the processes and procedures to calculate the loan losses, including changes in assumptions and estimates to consider expected credit losses over the life of the loan versus the current accounting practice that utilizes the incurred loss model. The Company expects to recognize a one-time cumulative effect adjustment to the allowance for loan losses as of the beginning of the first reporting period in which the new standard is effective, but has not yet determined the magnitude of any such one-time adjustment or the overall impact on its results of operations, financial position or disclosures. However, the Company is continuing its efforts in developing processes and procedures to ensure it is fully compliant at the required adoption date. Among other things, the Company continues to gather data and develop forecast models for asset quality, loan balances, and portfolio net charge-offs and has chosen a software vendor in preparation for the implementation of this standard. Model development and testing is projected to take place during the fourth quarter 2018 in anticipation of developing a range of potential impact as well as allowing parallel model calculations through 2019 up to the date of adoption. Leases – In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) (“ASU 2016-02”), that establishes the principles to report transparent and economically neutral information about the assets and liabilities that arise from leases. The new guidance results in a more consistent representation of the rights and obligations arising from leases by requiring lessees to recognize the lease asset and lease liabilities that arise from leases in the statement of financial position and to disclose qualitative and quantitative information about lease transactions, such as information about variable lease payments and options to renew and terminate leases. The effective date is for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. ASU 2016-02 requires entities to adopt the new lease standard using a modified retrospective transition method, meaning an entity initially applies the new lease standard at the beginning of the earliest period presented in the financial statements. Due to complexities associated with using this method, in July 2018, the FASB issued ASU No. 2018-11, Leases (Topic 842): Targeted Improvements , to relieve entities of the requirement to present prior comparative years’ results when they adopt the new lease standard and giving entities the option to recognize the cumulative effect of applying the new standard as an adjustment to the opening balance of retained earnings. The Company has substantially completed the identification of all of its leases that will need to be measured and reported in the statement of financial position and is currently working with its selected lease implementation vendor to set up and test the accounting for the lease contracts on the lease administrative system. Based upon leases that were outstanding as of September 30, 2018 , the Company does not expect the new standard to have a material impact on its results of operations, but anticipates increases in its assets and liabilities. Decisions to repurchase, modify or renew leases prior to the implementation date will impact the level of materiality. There have been no other significant changes to the Company’s accounting policies from the 2017 Form 10-K. Presently, the Company is not aware of any other changes to the Accounting Standards Codification that will have a material impact on its present or future financial position or results of operations. Revenue from Contracts with Customers Accounting Standards Codification (“ASC”) Topic 606, Revenue from Contracts with Customers , applies to all contracts with customers to provide goods or services in the ordinary course of business. However, Topic 606 specifically does not apply to revenue related to financial instruments, guarantees, insurance contracts, leases, or nonmonetary exchanges. Given these scope exceptions, interest income recognition and measurement related to loans and investments securities, the Company’s two largest sources of revenue, are not accounted for under Topic 606. Also, the Company does not use Topic 606 to account for gains or losses on its investments in securities, loans, and derivatives due to the scope exceptions. Certain revenue streams, such as service charges on deposit accounts, gains or losses on the sale of OREO, and trust income, fall under the scope of Topic 606 and the Company must recognize revenue at an amount that reflects the consideration to which the Company expects to be entitled in exchange for transferring goods or services to a customer. Topic 606 is applied using five steps: 1) identify the contract with the customer, 2) identify the performance obligations in the contract, 3) determine the transaction price, 4) allocate the transaction price to the performance obligations in the contract, and 5) recognize revenue when (or as) the entity satisfies a performance obligation. The Company has evaluated the nature of all contracts with customers that fall under the scope of Topic 606 and determined that further disaggregation of revenue from contracts with customers into categories was not necessary. There has not been significant revenue recognized in the current reporting periods resulting from performance obligations satisfied in previous periods. In addition, there has not been a significant change in timing of revenues received from customers. A description of performance obligations for each type of contract with customers is as follows: Service charges on deposit accounts – The Company’s primary source of funding comes from deposit accounts with its customers. Customers pay certain fees to access their cash on deposit including, but not limited to, non-transactional fees such as account maintenance, dormancy or statement rendering fees, and certain transaction-based fees such as ATM, wire transfer, overdraft or returned check fees. The Company generally satisfies its performance obligations as services are rendered. The transaction prices are fixed, and are charged either on a periodic basis or based on activity. Sale of OREO – In the normal course of business, the Company will enter into contracts with customers to sell OREO, which has generally been foreclosed upon by the Company. The Company generally satisfies its performance obligation upon conveyance of property from the Company to the customer, generally by way of an executed agreement. The transaction price is fixed, and on occasion the Company will finance a portion of the proceeds the customers uses to purchase the property. These properties are generally sold without recourse or warranty. Trust Income – The Company enters into contracts with its customers to manage assets for investment, and/or transact on their accounts. The Company generally satisfies its performance obligations as services are rendered. The management fee is a fixed percentage-based fee calculated upon the average balance of assets under management and is charged to customers on a monthly basis. Acquisition Accounting, Loans Acquired The Company accounts for its acquisitions under ASC Topic 805, Business Combinations , which requires the use of the acquisition method of accounting. All identifiable assets acquired, including loans, are recorded at fair value. No allowance for loan losses related to the loans acquired is recorded on the acquisition date as the fair value of the loans acquired incorporates assumptions regarding credit risk. Loans acquired are recorded at fair value in accordance with the fair value methodology prescribed in ASC Topic 820, Fair Value Measurement . The fair value estimates associated with the loans include estimates related to expected prepayments and the amount and timing of undiscounted expected principal, interest and other cash flows. The Company evaluates non-impaired loans acquired in accordance with the provisions of ASC Topic 310-20, Nonrefundable Fees and Other Costs . The fair value discount on these loans is accreted into interest income over the weighted average life of the loans using a constant yield method. The Company evaluates purchased impaired loans in accordance with the provisions of ASC Topic 310-30, Loans and Debt Securities Acquired with Deteriorated Credit Quality . Purchased loans are considered impaired if there is evidence of credit deterioration since origination and if it is probable that not all contractually required payments will be collected. For impaired loans accounted for under ASC Topic 310-30, the Company continues to estimate cash flows expected to be collected on purchased credit impaired loans. The Company evaluates, at each balance sheet date, whether the present value of the purchased credit impaired loans determined using the effective interest rates has decreased significantly and if so, recognize a provision for loan loss in the consolidated statement of income. For any significant increases in cash flows expected to be collected, the Company adjusts the amount of accretable yield recognized on a prospective basis over the remaining life of the purchased credit impaired loan. For further discussion of acquisition and loan accounting, see Note 2, Acquisitions, and Note 6, Loans Acquired.

Acquisitions

Acquisitions	9 Months Ended
	Sep. 30, 2018
Business Combinations [Abstract]
Acquisitions	ACQUISITIONS Southwest Bancorp, Inc. On October 19, 2017, the Company completed the acquisition of Southwest Bancorp, Inc. (“OKSB”) headquartered in Stillwater, Oklahoma, including its wholly-owned bank subsidiary, Bank SNB. The Company issued 14,488,604 shares of its common stock valued at approximately $431.4 million as of October 19, 2017, plus $94.9 million in cash in exchange for all outstanding shares of OKSB common stock. Prior to the acquisition, OKSB conducted banking business from 29 branches located in Texas, Oklahoma, Kansas and Colorado. In addition, OKSB owned a loan production office in Denver, Colorado. Including the effects of the acquisition method accounting adjustments, the Company acquired approximately $2.7 billion in assets, including approximately $2.0 billion in loans (inclusive of loan discounts) and approximately $2.0 billion in deposits. The Company completed the systems conversion and merged Bank SNB into Simmons Bank in May 2018. Goodwill of $229.1 million was recorded as a result of the transaction. The acquisition allowed the Company to enter the Texas, Oklahoma, and Colorado banking markets and it also strengthened the Company’s Kansas franchise and its product offerings in the healthcare and real estate industries, all of which gave rise to the goodwill recorded. The goodwill will not be deductible for tax purposes. A summary, at fair value, of the assets acquired and liabilities assumed in the OKSB transaction, as of the acquisition date, is as follows: (In thousands) Acquired from OKSB Fair Value Adjustments Fair Value Assets Acquired Cash and due from banks $ 79,517 $ — $ 79,517 Investment securities 485,468 (1,295 ) 484,173 Loans acquired 2,039,524 (43,071 ) 1,996,453 Allowance for loan losses (26,957 ) 26,957 — Foreclosed assets 6,284 (1,127 ) 5,157 Premises and equipment 21,210 5,457 26,667 Bank owned life insurance 28,704 — 28,704 Goodwill 13,545 (13,545 ) — Core deposit intangible 1,933 40,191 42,124 Other intangibles 3,806 — 3,806 Other assets 33,455 (9,141 ) 24,314 Total assets acquired $ 2,686,489 $ 4,426 $ 2,690,915 Liabilities Assumed Deposits: Non-interest bearing transaction accounts $ 485,971 $ — $ 485,971 Interest bearing transaction accounts and savings deposits 869,252 — 869,252 Time deposits 613,345 (2,213 ) 611,132 Total deposits 1,968,568 (2,213 ) 1,966,355 Securities sold under agreement to repurchase 11,256 — 11,256 Other borrowings 347,000 — 347,000 Subordinated debentures 46,393 — 46,393 Accrued interest and other liabilities 17,440 5,364 22,804 Total liabilities assumed 2,390,657 3,151 2,393,808 Equity 295,832 (295,832 ) — Total equity assumed 295,832 (295,832 ) — Total liabilities and equity assumed $ 2,686,489 $ (292,681 ) $ 2,393,808 Net assets acquired 297,107 Purchase price 526,251 Goodwill $ 229,144 During 2018 , the Company finalized its analysis of the loans acquired along with other acquired assets and assumed liabilities. The Company’s operating results for all periods presented include the operating results of the acquired assets and assumed liabilities of OKSB subsequent to the acquisition date. First Texas BHC, Inc. On October 19, 2017, the Company completed the acquisition of First Texas BHC, Inc. (“First Texas”) headquartered in Fort Worth, Texas, including its wholly-owned bank subsidiary, Southwest Bank. The Company issued 12,999,840 shares of its common stock valued at approximately $387.1 million as of October 19, 2017, plus $70.0 million in cash in exchange for all outstanding shares of First Texas common stock. Prior to the acquisition, First Texas operated 15 banking centers, a trust office and a limited service branch in north Texas and a loan production office in Austin, Texas. Including the effects of the acquisition method accounting adjustments, the Company acquired approximately $2.4 billion in assets, including approximately $2.2 billion in loans (inclusive of loan discounts) and approximately $1.9 billion in deposits. The Company completed the systems conversion and merged Southwest Bank into Simmons Bank in February 2018. Goodwill of $240.8 million was recorded as a result of the transaction. The acquisition allowed the Company to enter the Texas banking markets and it also strengthened the Company’s specialty product offerings in the area of SBA lending and trust services, all of which gave rise to the goodwill recorded. The goodwill will not be deductible for tax purposes. A summary, at fair value, of the assets acquired and liabilities assumed in the First Texas transaction, as of the acquisition date, is as follows: (In thousands) Acquired from First Texas Fair Value Adjustments Fair Value Assets Acquired Cash and due from banks $ 59,277 $ — $ 59,277 Investment securities 81,114 (596 ) 80,518 Loans acquired 2,246,212 (37,834 ) 2,208,378 Allowance for loan losses (20,864 ) 20,664 (200 ) Premises and equipment 24,864 10,123 34,987 Bank owned life insurance 7,190 — 7,190 Goodwill 37,227 (37,227 ) — Core deposit intangible — 7,328 7,328 Other assets 18,263 11,485 29,748 Total assets acquired $ 2,453,283 $ (26,057 ) $ 2,427,226 Liabilities Assumed Deposits: Non-interest bearing transaction accounts $ 74,410 $ — $ 74,410 Interest bearing transaction accounts and savings deposits 1,683,298 — 1,683,298 Time deposits 124,233 (283 ) 123,950 Total deposits 1,881,941 (283 ) 1,881,658 Securities sold under agreement to repurchase 50,000 — 50,000 Other borrowings 235,000 — 235,000 Subordinated debentures 30,323 589 30,912 Accrued interest and other liabilities 11,727 1,669 13,396 Total liabilities assumed 2,208,991 1,975 2,210,966 Equity 244,292 (244,292 ) — Total equity assumed 244,292 (244,292 ) — Total liabilities and equity assumed $ 2,453,283 $ (242,317 ) $ 2,210,966 Net assets acquired 216,260 Purchase price 457,103 Goodwill $ 240,843 During 2018 , the Company finalized its analysis of the loans acquired along with other acquired assets and assumed liabilities. The Company’s operating results for all periods presented include the operating results of the acquired assets and assumed liabilities of First Texas subsequent to the acquisition date. Summary of Unaudited Pro forma Information The unaudited pro forma information below for the years ended December 31, 2017 and 2016 gives effect to the OKSB and First Texas acquisitions as if the acquisitions had occurred on January 1, 2016. Pro forma earnings for the year ended December 31, 2017 were adjusted to exclude $9.4 million of acquisition-related costs, net of tax, incurred by Simmons during 2017 . The pro forma financial information is not necessarily indicative of the results of operations if the acquisitions had been effective as of this date. (In thousands, except per share data) 2017 2016 Revenue (1) $ 654,358 $ 620,461 Net income $ 130,947 $ 136,199 Diluted earnings per share $ 1.43 $ 1.52 _________________________________________ (1) Net interest income plus non-interest income. Consolidated year-to-date 2017 results included approximately $29.2 million of revenue and $10.5 million of net income attributable to the OKSB acquisition and $27.6 million of revenue and $5.7 million of net income attributable to the First Texas acquisition. Hardeman County Investment Company, Inc. On May 15, 2017, the Company completed the acquisition of Hardeman County Investment Company, Inc. (“Hardeman”), headquartered in Jackson, Tennessee, including its wholly-owned bank subsidiary, First South Bank. The Company issued 1,599,940 shares of its common stock valued at approximately $42.6 million as of May 15, 2017, plus $30.0 million in cash in exchange for all outstanding shares of Hardeman common stock. Prior to the acquisition, Hardeman conducted banking business from 10 branches located in western Tennessee. Including the effects of the acquisition method accounting adjustments, the Company acquired approximately $462.9 million in assets, including approximately $251.6 million in loans (inclusive of loan discounts) and approximately $389.0 million in deposits. The Company completed the systems conversion and merged First South Bank into Simmons Bank in September 2017. As part of the systems conversion, five existing Simmons Bank and First South Bank branches were consolidated or closed. Goodwill of $29.4 million was recorded as a result of the transaction. The merger strengthened the Company’s position in the western Tennessee market, and the Company will be able to achieve cost savings by integrating the two companies and combining accounting, data processing, and other administrative functions, all of which gave rise to the goodwill recorded. The goodwill will not be deductible for tax purposes. A summary, at fair value, of the assets acquired and liabilities assumed in the Hardeman transaction, as of the acquisition date, is as follows: (In thousands) Acquired from Hardeman Fair Value Adjustments Fair Value Assets Acquired Cash and due from banks $ 8,001 $ — $ 8,001 Interest bearing balances due from banks - time 1,984 — 1,984 Investment securities 170,654 (285 ) 170,369 Loans acquired 257,641 (5,992 ) 251,649 Allowance for loan losses (2,382 ) 2,382 — Foreclosed assets 1,083 (452 ) 631 Premises and equipment 9,905 1,258 11,163 Bank owned life insurance 7,819 — 7,819 Goodwill 11,485 (11,485 ) — Core deposit intangible — 7,840 7,840 Other intangibles — 830 830 Other assets 2,639 (1 ) 2,638 Total assets acquired $ 468,829 $ (5,905 ) $ 462,924 Liabilities Assumed Deposits: Non-interest bearing transaction accounts $ 76,555 $ — $ 76,555 Interest bearing transaction accounts and savings deposits 214,872 — 214,872 Time deposits 97,917 (368 ) 97,549 Total deposits 389,344 (368 ) 388,976 Securities sold under agreement to repurchase 17,163 — 17,163 Other borrowings 3,000 — 3,000 Subordinated debentures 6,702 — 6,702 Accrued interest and other liabilities 1,891 1,924 3,815 Total liabilities assumed 418,100 1,556 419,656 Equity 50,729 (50,729 ) — Total equity assumed 50,729 (50,729 ) — Total liabilities and equity assumed $ 468,829 $ (49,173 ) $ 419,656 Net assets acquired 43,268 Purchase price 72,639 Goodwill $ 29,371 During 2018 , the Company finalized its analysis of the loans acquired along with other acquired assets and assumed liabilities. The Company’s operating results for all periods presented include the operating results of the acquired assets and assumed liabilities of Hardeman subsequent to the acquisition date. The following is a description of the methods used to determine the fair values of significant assets and liabilities presented in the acquisitions above. Cash and due from banks and time deposits due from banks – The carrying amount of these assets is a reasonable estimate of fair value based on the short-term nature of these assets. Investment securities – Investment securities were acquired with an adjustment to fair value based upon quoted market prices if material. Otherwise, the carrying amount of these assets was deemed to be a reasonable estimate of fair value. Loans acquired – Fair values for loans were based on a discounted cash flow methodology that considered factors including the type of loan and related collateral, classification status, fixed or variable interest rate, term of loan and whether or not the loan was amortizing, and current discount rates. The discount rates used for loans are based on current market rates for new originations of comparable loans and include adjustments for liquidity concerns. The discount rate does not include a factor for credit losses as that has been included in the estimated cash flows. Loans were grouped together according to similar characteristics and were treated in the aggregate when applying various valuation techniques. Foreclosed assets – These assets are presented at the estimated present values that management expects to receive when the properties are sold, net of related costs of disposal. Premises and equipment – Bank premises and equipment were acquired with an adjustment to fair value, which represents the difference between the Company’s current analysis of property and equipment values completed in connection with the acquisition and book value acquired. Bank owned life insurance – Bank owned life insurance is carried at its current cash surrender value, which is the most reasonable estimate of fair value. Goodwill – The consideration paid as a result of the acquisition exceeded the fair value of the assets acquired, resulting in an intangible asset, goodwill. Goodwill established prior to the acquisitions, if applicable, was written off. Core deposit intangible – This intangible asset represents the value of the relationships that the acquired banks had with their deposit customers. The fair value of this intangible asset was estimated based on a discounted cash flow methodology that gave appropriate consideration to expected customer attrition rates, cost of the deposit base and the net maintenance cost attributable to customer deposits. Core deposit intangible established prior to the acquisitions, if applicable, was written off. Other intangibles – Other intangible assets represent the value of the relationships that Hardeman had with its insurance customers and the mortgage servicing rights acquired with OKSB. The fair value of Hardeman’s insurance customer relationships was estimated based on a combination of discounted cash flow methodology and a market valuation approach. Other intangibles established prior to the acquisitions, if applicable, were written off. Other assets – The fair value adjustment results from certain assets whose value was estimated to be less than book value, such as certain prepaid assets, receivables and other miscellaneous assets. Otherwise, the carrying amount of these assets was deemed to be a reasonable estimate of fair value. Deposits – The fair values used for the demand and savings deposits that comprise the transaction accounts acquired, by definition equal the amount payable on demand at the acquisition date. The Company performed a fair value analysis of the estimated weighted average interest rate of the certificates of deposits compared to the current market rates and recorded a fair value adjustment for the difference when material. Securities sold under agreement to repurchase – The carrying amount of securities sold under agreement to repurchase is a reasonable estimate of fair value based on the short-term nature of these liabilities. FHLB and other borrowings – The fair value of Federal Home Loan Bank and other borrowings is estimated based on borrowing rates currently available to the Company for borrowings with similar terms and maturities. Subordinated debentures – The fair value of subordinated debentures is estimated based on borrowing rates currently available to the Company for borrowings with similar terms and maturities. Due to the floating rate nature of the debenture, the fair value approximates book value as of the date acquired. Accrued interest and other liabilities – The adjustment establishes a liability for unfunded commitments equal to the fair value of that liability at the date of acquisition.

Investment Securities

Investment Securities	9 Months Ended
	Sep. 30, 2018
Investments, Debt and Equity Securities [Abstract]
Investment Securities	INVESTMENT SECURITIES The amortized cost and fair value of investment securities that are classified as held-to-maturity (“HTM”) and available-for-sale (“AFS”) are as follows: September 30, 2018 December 31, 2017 (In thousands) Amortized Cost Gross Unrealized Gains Gross Unrealized (Losses) Estimated Fair Value Amortized Cost Gross Unrealized Gains Gross Unrealized (Losses) Estimated Fair Value Held-to-Maturity U.S. Government agencies $ 34,983 $ — $ (113 ) $ 34,870 $ 46,945 $ 7 $ (228 ) $ 46,724 Mortgage-backed securities 13,933 — (698 ) 13,235 16,132 8 (287 ) 15,853 State and political subdivisions 272,396 2,369 (2,020 ) 272,745 301,491 5,962 (222 ) 307,231 Other securities 1,994 — (6 ) 1,988 3,490 — — 3,490 Total HTM $ 323,306 $ 2,369 $ (2,837 ) $ 322,838 $ 368,058 $ 5,977 $ (737 ) $ 373,298 Available-for-Sale U.S. Government agencies $ 145,808 $ — $ (4,348 ) $ 141,460 $ 141,559 $ 116 $ (1,951 ) $ 139,724 Mortgage-backed securities 1,471,687 127 (52,188 ) 1,419,626 1,208,017 246 (20,946 ) 1,187,317 State and political subdivisions 291,731 12 (9,304 ) 282,439 144,642 532 (2,009 ) 143,165 Other securities 151,572 2,718 (1 ) 154,289 118,106 1,206 (1 ) 119,311 Total AFS $ 2,060,798 $ 2,857 $ (65,841 ) $ 1,997,814 $ 1,612,324 $ 2,100 $ (24,907 ) $ 1,589,517 Securities with limited marketability, such as stock in the Federal Reserve Bank and the Federal Home Loan Bank, are carried at cost and are reported as other AFS securities in the table above. Certain investment securities are valued at less than their historical cost. Total fair value of these investments at September 30, 2018 and December 31, 2017 , was $2.0 billion and $1.4 billion , which is approximately 86.0% and 73.5% , respectively, of the Company’s combined AFS and HTM investment portfolios. The following table shows the gross unrealized losses and fair value of the Company’s investments with unrealized losses, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position at September 30, 2018 : Less Than 12 Months 12 Months or More Total (In thousands) Estimated Fair Value Gross Unrealized Losses Estimated Fair Value Gross Unrealized Losses Estimated Fair Value Gross Unrealized Losses Held-to-Maturity U.S. Government agencies $ 3,972 $ (11 ) $ 30,898 $ (102 ) $ 34,870 $ (113 ) Mortgage-backed securities 3,830 (106 ) 9,404 (592 ) 13,234 (698 ) State and political subdivisions 123,574 (1,682 ) 8,539 (338 ) 132,113 (2,020 ) Other securities 1,166 (6 ) — — 1,166 (6 ) Total HTM $ 132,542 $ (1,805 ) $ 48,841 $ (1,032 ) $ 181,383 $ (2,837 ) Available-for-Sale U.S. Government agencies $ 56,785 $ (689 ) $ 84,675 $ (3,659 ) $ 141,460 $ (4,348 ) Mortgage-backed securities 586,783 (11,469 ) 808,969 (40,719 ) 1,395,752 (52,188 ) State and political subdivisions 182,036 (4,510 ) 95,076 (4,794 ) 277,112 (9,304 ) Other securities — — 99 (1 ) 99 (1 ) Total AFS $ 825,604 $ (16,668 ) $ 988,819 $ (49,173 ) $ 1,814,423 $ (65,841 ) These declines primarily resulted from the rate for these investments yielding less than current market rates. Based on evaluation of available evidence, management believes the declines in fair value for these securities are temporary. Management does not have the intent to sell these securities and management believes it is more likely than not the Company will not have to sell these securities before recovery of their amortized cost basis less any current period credit losses. Declines in the fair value of HTM and AFS securities below their cost that are deemed to be other than temporary are reflected in earnings as realized losses. In estimating other-than-temporary impairment losses, management considers, among other things, (i) the length of time and the extent to which the fair value has been less than cost, (ii) the financial condition and near-term prospects of the issuer, and (iii) the intent and ability of the Company to retain its investment in the issuer for a period of time sufficient to allow for any anticipated recovery in fair value. Management has the ability and intent to hold the securities classified as HTM until they mature, at which time the Company expects to receive full value for the securities. Furthermore, as of September 30, 2018 , management also had the ability and intent to hold the securities classified as AFS for a period of time sufficient for a recovery of cost. The unrealized losses are largely due to increases in market interest rates over the yields available at the time the underlying securities were purchased. The fair value is expected to recover as the bonds approach their maturity date or repricing date or if market yields for such investments decline. Management does not believe any of the securities are impaired due to reasons of credit quality. Accordingly, as of September 30, 2018 , management believes the impairments detailed in the table above are temporary. Should the impairment of any of these securities become other than temporary, the cost basis of the investment will be reduced and the resulting loss recognized in net income in the period the other-than-temporary impairment is identified. Income earned on securities for the three and nine months ended September 30, 2018 and 2017 , is as follows: Three Months Ended September 30, Nine Months Ended September 30, (In thousands) 2018 2017 2018 2017 Taxable: Held-to-maturity $ 528 $ 625 $ 1,641 $ 1,922 Available-for-sale 10,364 5,949 29,614 18,003 Non-taxable: Held-to-maturity 1,828 2,135 5,661 6,635 Available-for-sale 1,920 509 4,642 2,099 Total $ 14,640 $ 9,218 $ 41,558 $ 28,659 The amortized cost and estimated fair value by maturity of securities are shown in the following table. Securities are classified according to their contractual maturities without consideration of principal amortization, potential prepayments or call options. Accordingly, actual maturities may differ from contractual maturities. Held-to-Maturity Available-for-Sale (In thousands) Amortized Cost Fair Value Amortized Cost Fair Value One year or less $ 50,503 $ 50,366 $ 120 $ 119 After one through five years 60,633 60,313 35,703 34,714 After five through ten years 91,862 91,364 22,485 21,698 After ten years 106,375 107,560 379,331 367,466 Securities not due on a single maturity date 13,933 13,235 1,471,687 1,419,626 Other securities (no maturity) — — 151,472 154,191 Total $ 323,306 $ 322,838 $ 2,060,798 $ 1,997,814 The carrying value, which approximates the fair value, of securities pledged as collateral, to secure public deposits and for other purposes, amounted to $933.5 million at September 30, 2018 and $1.2 billion at December 31, 2017 . There were approximately $41,000 of gross realized gains and no gross realized losses from the sale of securities during the three months ended September 30, 2018 , and approximately $54,000 of gross realized gains and $1,000 of gross realized losses from the sale of securities during the nine months ended September 30, 2018 . There were approximately $3,000 of gross realized gains and no realized losses from the sale of securities during the three months ended September 30, 2017 , and approximately $2.3 million of gross realized gains and $5,000 of gross realized losses from the sale of securities during the nine months ended September 30, 2017 . The state and political subdivision debt obligations are predominately non-rated bonds representing small issuances, primarily in Arkansas, Missouri, Oklahoma, Tennessee and Texas issues, which are evaluated on an ongoing basis.

Other Assets and Other Liabilit

Other Assets and Other Liabilities Held for Sale	9 Months Ended
	Sep. 30, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Other Assets and Other Liabilities Held for Sale	OTHER ASSETS AND OTHER LIABILITIES HELD FOR SALE In August 2017, the Company, through its bank subsidiary, Simmons Bank, acquired the stock of Heartland Bank (“Heartland”) at a public auction held to satisfy certain indebtedness of Heartland’s former holding company, Rock Bancshares, Inc. In March 2018 , Heartland sold $141.0 million of branches and loans, as well as $154.6 million of deposits and other liabilities. At the end of the third quarter 2018 , other assets held for sale of $5.1 million and other liabilities held for sale of $424,000 related to Heartland, both recorded at fair value, remained at the Company. The Company will continue to work through the disposition of Heartland’s few remaining assets.

Loans and Allowance for Loan Lo

Loans and Allowance for Loan Losses	9 Months Ended
	Sep. 30, 2018
Receivables [Abstract]
Loans and Allowance for Loan Losses	LOANS AND ALLOWANCE FOR LOAN LOSSES At September 30, 2018 , the Company’s loan portfolio was $11.86 billion , compared to $10.78 billion at December 31, 2017 . The various categories of loans are summarized as follows: (In thousands) September 30, 2018 December 31, 2017 Consumer: Credit cards $ 182,137 $ 185,422 Other consumer 259,581 280,094 Total consumer 441,718 465,516 Real Estate: Construction 1,229,888 614,155 Single family residential 1,401,991 1,094,633 Other commercial 3,077,188 2,530,824 Total real estate 5,709,067 4,239,612 Commercial: Commercial 1,608,342 825,217 Agricultural 218,778 148,302 Total commercial 1,827,120 973,519 Other 145,369 26,962 Loans 8,123,274 5,705,609 Loans acquired, net of discount and allowance (1) 3,734,921 5,074,076 Total loans $ 11,858,195 $ 10,779,685 _____________________________ (1) See Note 6, Loans Acquired, for segregation of loans acquired by loan class. Loan Origination/Risk Management – The Company seeks to manage its credit risk by diversifying its loan portfolio, determining that borrowers have adequate sources of cash flow for loan repayment without liquidation of collateral; obtaining and monitoring collateral; providing an adequate allowance for loans losses by regularly reviewing loans through the internal loan review process. The loan portfolio is diversified by borrower, purpose and industry. The Company seeks to use diversification within the loan portfolio to reduce its credit risk, thereby minimizing the adverse impact on the portfolio, if weaknesses develop in either the economy or a particular segment of borrowers. Collateral requirements are based on credit assessments of borrowers and may be used to recover the debt in case of default. Furthermore, a factor that influenced the Company’s judgment regarding the allowance for loan losses consists of an eight-year historical loss average segregated by each primary loan sector. On an annual basis, historical loss rates are calculated for each sector. Consumer – The consumer loan portfolio consists of credit card loans and other consumer loans. Credit card loans are diversified by geographic region to reduce credit risk and minimize any adverse impact on the portfolio. Although they are regularly reviewed to facilitate the identification and monitoring of creditworthiness, credit card loans are unsecured loans, making them more susceptible to be impacted by economic downturns resulting in increasing unemployment. Other consumer loans include direct and indirect installment loans and overdrafts. Loans in this portfolio segment are sensitive to unemployment and other key consumer economic measures. Real estate – The real estate loan portfolio consists of construction loans, single family residential loans and commercial loans. Construction and development loans (“C&D”) and commercial real estate loans (“CRE”) can be particularly sensitive to valuation of real estate. Commercial real estate cycles are inevitable. The long planning and production process for new properties and rapid shifts in business conditions and employment create an inherent tension between supply and demand for commercial properties. While general economic trends often move individual markets in the same direction over time, the timing and magnitude of changes are determined by other forces unique to each market. CRE cycles tend to be local in nature and longer than other credit cycles. Factors influencing the CRE market are traditionally different from those affecting residential real estate markets; thereby making predictions for one market based on the other difficult. Additionally, submarkets within commercial real estate – such as office, industrial, apartment, retail and hotel – also experience different cycles, providing an opportunity to lower the overall risk through diversification across types of CRE loans. Management realizes that local demand and supply conditions will also mean that different geographic areas will experience cycles of different amplitude and length. The Company monitors these loans closely. Commercial – The commercial loan portfolio includes commercial and agricultural loans, representing loans to commercial customers and farmers for use in normal business or farming operations to finance working capital needs, equipment purchases or other expansion projects. Collection risk in this portfolio is driven by the creditworthiness of the underlying borrowers, particularly cash flow from customers’ business or farming operations. The Company continues its efforts to keep loan terms short, reducing the negative impact of upward movement in interest rates. Term loans are generally set up with one or three year balloons, and the Company has instituted a pricing mechanism for commercial loans. It is standard practice to require personal guaranties on all commercial loans for closely-held or limited liability entities. Nonaccrual and Past Due Loans – Loans are considered past due if the required principal and interest payments have not been received as of the date such payments were due. Loans are placed on nonaccrual status when, in management’s opinion, the borrower may be unable to meet payment obligations as they become due, as well as when required by regulatory provisions. Loans may be placed on nonaccrual status regardless if such loans are considered past due. When interest accrual is discontinued, all unpaid accrued interest is reversed. Interest income is subsequently recognized only to the extent cash payments are received in excess of principal due. Loans are returned to accrual status when all the principal and interest amounts contractually due are brought current and future payments are reasonably assured. Nonaccrual loans, excluding loans acquired, segregated by class of loans, are as follows: (In thousands) September 30, 2018 December 31, 2017 Consumer: Credit cards $ 328 $ 170 Other consumer 3,317 4,605 Total consumer 3,645 4,775 Real estate: Construction 1,289 2,242 Single family residential 11,508 13,431 Other commercial 9,639 16,054 Total real estate 22,436 31,727 Commercial: Commercial 11,932 6,980 Agricultural 2,492 2,160 Total commercial 14,424 9,140 Total $ 40,505 $ 45,642 An age analysis of past due loans, excluding loans acquired, segregated by class of loans, is as follows: (In thousands) Gross 30-89 Days Past Due 90 Days or More Past Due Total Past Due Current Total Loans 90 Days Past Due & Accruing September 30, 2018 Consumer: Credit cards $ 777 $ 517 $ 1,294 $ 180,843 $ 182,137 $ 188 Other consumer 3,341 1,921 5,262 254,319 259,581 1 Total consumer 4,118 2,438 6,556 435,162 441,718 189 Real estate: Construction 1,033 397 1,430 1,228,458 1,229,888 — Single family residential 5,180 4,212 9,392 1,392,599 1,401,991 92 Other commercial 4,555 4,152 8,707 3,068,481 3,077,188 — Total real estate 10,768 8,761 19,529 5,689,538 5,709,067 92 Commercial: Commercial 4,568 5,873 10,441 1,597,901 1,608,342 — Agricultural 128 2,253 2,381 216,397 218,778 — Total commercial 4,696 8,126 12,822 1,814,298 1,827,120 — Other — — — 145,369 145,369 — Total $ 19,582 $ 19,325 $ 38,907 $ 8,084,367 $ 8,123,274 $ 281 December 31, 2017 Consumer: Credit cards $ 707 $ 672 $ 1,379 $ 184,043 $ 185,422 $ 332 Other consumer 5,009 3,298 8,307 271,787 280,094 10 Total consumer 5,716 3,970 9,686 455,830 465,516 342 Real estate: Construction 411 1,210 1,621 612,534 614,155 — Single family residential 8,071 6,460 14,531 1,080,102 1,094,633 1 Other commercial 2,388 8,031 10,419 2,520,405 2,530,824 — Total real estate 10,870 15,701 26,571 4,213,041 4,239,612 1 Commercial: Commercial 1,523 6,125 7,648 817,569 825,217 — Agricultural 50 2,120 2,170 146,132 148,302 — Total commercial 1,573 8,245 9,818 963,701 973,519 — Other — — — 26,962 26,962 — Total $ 18,159 $ 27,916 $ 46,075 $ 5,659,534 $ 5,705,609 $ 343 Impaired Loans – A loan is considered impaired when it is probable that the Company will not receive all amounts due according to the contractual terms of the loans, including scheduled principal and interest payments. This includes loans that are delinquent 90 days or more, nonaccrual loans and certain other loans identified by management. Certain other loans identified by management consist of performing loans with specific allocations of the allowance for loan losses. Impaired loans are carried at the present value of estimated future cash flows using the loan’s existing rate, or the fair value of the collateral if the loan is collateral dependent. Impairment is evaluated in total for smaller-balance loans of a similar nature and on an individual loan basis for other loans. Impaired loans, or portions thereof, are charged-off when deemed uncollectible. Impaired loans, net of government guarantees and excluding loans acquired, segregated by class of loans, are as follows: (In thousands) Unpaid Contractual Principal Balance Recorded Investment With No Allowance Recorded Investment With Allowance Total Recorded Investment Related Allowance Average Investment in Impaired Loans Interest Income Recognized Average Investment in Impaired Loans Interest Income Recognized September 30, 2018 Three Months Ended Nine Months Ended Consumer: Credit cards $ 328 $ 328 $ — $ 328 $ — $ 283 $ 35 $ 259 $ 60 Other consumer 3,528 3,317 — 3,317 — 3,561 28 4,109 96 Total consumer 3,856 3,645 — 3,645 — 3,844 63 4,368 156 Real estate: Construction 879 800 490 1,290 232 1,411 11 1,747 41 Single family residential 11,771 11,023 715 11,738 36 13,577 98 13,550 315 Other commercial 7,909 5,942 7,431 13,373 — 12,282 108 14,284 332 Total real estate 20,559 17,765 8,636 26,401 268 27,270 217 29,581 688 Commercial: Commercial 11,777 9,786 6,062 15,848 191 11,840 108 9,533 222 Agricultural 3,507 1,460 — 1,460 — 1,355 12 1,470 34 Total commercial 15,284 11,246 6,062 17,308 191 13,195 120 11,003 256 Total $ 39,699 $ 32,656 $ 14,698 $ 47,354 $ 459 $ 44,309 $ 400 $ 44,952 $ 1,100 December 31, 2017 Three Months Ended Nine Months Ended Consumer: Credit cards $ 170 $ 170 $ — $ 170 $ — $ 283 $ 12 $ 292 $ 23 Other consumer 4,755 4,605 — 4,605 — 3,314 23 2,711 53 Total consumer 4,925 4,775 — 4,775 — 3,597 35 3,003 76 Real estate: Construction 2,522 1,347 895 2,242 249 2,582 17 2,828 56 Single family residential 14,347 12,725 706 13,431 53 12,878 85 12,772 251 Other commercial 22,308 6,732 9,133 15,865 36 19,306 121 19,313 380 Total real estate 39,177 20,804 10,734 31,538 338 34,766 223 34,913 687 Commercial: Commercial 9,954 4,306 2,269 6,575 — 14,543 84 12,943 255 Agricultural 3,278 1,035 — 1,035 — 1,562 8 1,645 32 Total commercial 13,232 5,341 2,269 7,610 — 16,105 92 14,588 287 Total $ 57,334 $ 30,920 $ 13,003 $ 43,923 $ 338 $ 54,468 $ 350 $ 52,504 $ 1,050 At September 30, 2018 , and December 31, 2017 , impaired loans, net of government guarantees and excluding loans acquired, totaled $47.4 million and $43.9 million , respectively. Allocations of the allowance for loan losses relative to impaired loans were $459,000 and $338,000 at September 30, 2018 and December 31, 2017 , respectively. Approximately $400,000 and $1,100,000 of interest income was recognized on average impaired loans of $44.3 million and $45.0 million for the three and nine months ended September 30, 2018 . Interest income recognized on impaired loans on a cash basis during the three and nine months ended September 30, 2018 and 2017 was not material. Included in certain impaired loan categories are troubled debt restructurings (“TDRs”). When the Company restructures a loan to a borrower that is experiencing financial difficulty and grants a concession that it would not otherwise consider, a “troubled debt restructuring” results and the Company classifies the loan as a TDR. The Company grants various types of concessions, primarily interest rate reduction and/or payment modifications or extensions, with an occasional forgiveness of principal. Under ASC Topic 310-10-35 – Subsequent Measurement , a TDR is considered to be impaired, and an impairment analysis must be performed. The Company assesses the exposure for each modification, either by collateral discounting or by calculation of the present value of future cash flows, and determines if a specific allocation to the allowance for loan losses is needed. Once an obligation has been restructured because of such credit problems, it continues to be considered a TDR until paid in full; or, if an obligation yields a market interest rate and no longer has any concession regarding payment amount or amortization, then it is not considered a TDR at the beginning of the calendar year after the year in which the improvement takes place. The Company returns TDRs to accrual status only if (1) all contractual amounts due can reasonably be expected to be repaid within a prudent period, and (2) repayment has been in accordance with the contract for a sustained period, typically at least six months. The following table presents a summary of troubled debt restructurings, excluding loans acquired, segregated by class of loans. Accruing TDR Loans Nonaccrual TDR Loans Total TDR Loans (Dollars in thousands) Number Balance Number Balance Number Balance September 30, 2018 Real estate: Construction — $ — 3 $ 490 3 $ 490 Single-family residential 7 318 10 631 17 949 Other commercial 2 3,365 3 2,953 5 6,318 Total real estate 9 3,683 16 4,074 25 7,757 Commercial: Commercial 6 4,730 6 753 12 5,483 Total commercial 6 4,730 6 753 12 5,483 Total 15 $ 8,413 22 $ 4,827 37 $ 13,240 December 31, 2017 Real estate: Construction — $ — 1 $ 420 1 $ 420 Single-family residential 4 141 15 954 19 1,095 Other commercial 4 4,322 5 3,712 9 8,034 Total real estate 8 4,463 21 5,086 29 9,549 Commercial: Commercial 5 2,644 6 745 11 3,389 Total commercial 5 2,644 6 745 11 3,389 Total 13 $ 7,107 27 $ 5,831 40 $ 12,938 The following table presents loans that were restructured as TDRs during the three and nine months ended September 30, 2018 and 2017 , excluding loans acquired, segregated by class of loans. Modification Type (Dollars in thousands) Number of Loans Balance Prior to TDR Balance at September 30, Change in Maturity Date Change in Rate Financial Impact on Date of Restructure Three Months Ended September 30, 2018 Real estate: Other commercial 2 $ 392 $ 390 $ 390 $ — $ 212 Total real estate 2 392 390 390 — 212 Commercial: Commercial 3 2,363 2,358 2,358 — 190 Total commercial 3 2,363 2,358 2,358 — 190 Total 5 $ 2,755 $ 2,748 $ 2,748 $ — $ 402 Three Months Ended September 30, 2017 Commercial: Commercial 1 $ 608 $ 607 $ 607 $ — $ — Total commercial 1 608 607 607 — — Total 1 $ 608 $ 607 $ 607 $ — $ — Nine Months Ended September 30, 2018 Consumer: Other consumer 1 $ 91 $ 91 $ 91 $ — $ — Total consumer 1 91 91 91 — — Real estate: Single-family residential 1 61 62 62 — — Other commercial 2 392 390 390 — 212 Total real estate 3 453 452 452 — 212 Commercial: Commercial 3 2,363 2,358 2,358 — 190 Total commercial 3 2,363 2,358 2,358 — 190 Total 7 $ 2,907 $ 2,901 $ 2,901 $ — $ 402 Nine Months Ended September 30, 2017 Real estate: Construction 1 $ 456 $ 456 $ 456 $ — $ — Other commercial 2 7,362 7,362 7,362 — 33 Total real estate 3 7,818 7,818 7,818 — 33 Commercial: Commercial 10 1,419 1,407 1,368 39 — Total commercial 10 1,419 1,407 1,368 39 — Total 13 $ 9,237 $ 9,225 $ 9,186 $ 39 $ 33 During the three months ended September 30, 2018 , the Company modified 5 loans with a recorded investment of $2.8 million , prior to modification that was deemed troubled debt restructuring. The restructured loans were modified by deferring amortized principal payments, changing the maturity date and requiring interest only payments for a period of up to 12 months. Based on the fair value of the collateral, a specific reserve of $402,000 was determined necessary for these loans. Also, there was no immediate financial impact from the restructuring of these loans, as it was not considered necessary to charge-off interest or principal on the date of restructure. During the nine months ended September 30, 2018 , the Company modified 7 loans with a recorded investment of $2.9 million prior to modification which were deemed troubled debt restructuring. The restructured loans were modified by deferring amortized principal payments, changing the maturity date and requiring interest only payments for a period of up to 12 months. Based on the fair value of the collateral, a specific reserve of $402,000 was determined necessary for these loans. Also, there was no immediate financial impact from the restructuring of these loans, as it was not considered necessary to charge-off interest or principal on the date of restructure. During the three months ended September 30, 2017 , the Company modified 1 loan with a recorded investment of $608,000 and during the nine months ended September 30, 2017 , the Company modified 13 loans with a recorded investment of $9.2 million prior to modification which were deemed troubled debt restructuring. The restructured loans were modified by changing various terms, including changing the interest rate, deferring amortized principal payments, changing the maturity date and requiring interest only payments for a period of 12 months. Based on the fair value of the collateral, a specific reserve of $33,000 was determined necessary for these loans and recorded during the nine months ended September 30, 2017 . Also, there was no immediate financial impact from the restructuring of these loans, as it was not considered necessary to charge-off interest or principal on the date of restructure. There was one commercial real estate loan considered a TDR for which a payment default occurred during the nine months ended September 30, 2018 . A charge-off of $66,300 was recorded for this loan and $294,300 was transferred to OREO. There was one commercial real estate loan for which a payment default occurred during the nine months ended September 30, 2017 . The Company defines a payment default as a payment received more than 90 days after its due date. In addition to the TDRs that occurred during the periods provided in the preceding tables, the Company had TDRs with pre-modification loan balances of $294,300 and $117,000 at September 30, 2018 and 2017 , respectively, for which OREO was received in full or partial satisfaction of the loans. The majority of such TDRs were in commercial real estate and residential real estate. At September 30, 2018 and December 31, 2017 , the Company had $2,262,000 and $5,057,000 , respectively, of consumer mortgage loans secured by residential real estate properties for which formal foreclosure proceedings are in process. At September 30, 2018 and December 31, 2017 , the Company had $3,610,000 and $3,828,000 , respectively, of OREO secured by residential real estate properties. Credit Quality Indicators – As part of the on-going monitoring of the credit quality of the Company’s loan portfolio, management tracks certain credit quality indicators including trends related to (i) the weighted-average risk rating of commercial and real estate loans, (ii) the level of classified commercial and real estate loans, (iii) net charge-offs, (iv) non-performing loans (see details above) and (v) the general economic conditions in the States of Arkansas, Colorado, Kansas, Missouri, Oklahoma, Tennessee and Texas. The Company utilizes a risk rating matrix to assign a risk rate to each of its commercial and real estate loans. Loans are rated on a scale of 1 to 8. A description of the general characteristics of the 8 risk ratings is as follows: • Risk Rate 1 – Pass (Excellent) – This category includes loans which are virtually free of credit risk. Borrowers in this category represent the highest credit quality and greatest financial strength. • Risk Rate 2 – Pass (Good) - Loans under this category possess a nominal risk of default. This category includes borrowers with strong financial strength and superior financial ratios and trends. These loans are generally fully secured by cash or equivalents (other than those rated “excellent”). • Risk Rate 3 – Pass (Acceptable – Average) - Loans in this category are considered to possess a normal level of risk. Borrowers in this category have satisfactory financial strength and adequate cash flow coverage to service debt requirements. If secured, the perfected collateral should be of acceptable quality and within established borrowing parameters. • Risk Rate 4 – Pass (Monitor) - Loans in the Watch (Monitor) category exhibit an overall acceptable level of risk, but that risk may be increased by certain conditions, which represent “red flags”. These “red flags” require a higher level of supervision or monitoring than the normal “Pass” rated credit. The borrower may be experiencing these conditions for the first time, or it may be recovering from weakness, which at one time justified a higher rating. These conditions may include: weaknesses in financial trends; marginal cash flow; one-time negative operating results; non-compliance with policy or borrowing agreements; poor diversity in operations; lack of adequate monitoring information or lender supervision; questionable management ability/stability. • Risk Rate 5 – Special Mention - A loan in this category 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 asset or in the institution’s credit position at some future date. Special Mention loans are not adversely classified (although they are “criticized”) and do not expose an institution to sufficient risk to warrant adverse classification. Borrowers may be experiencing adverse operating trends, or an ill-proportioned balance sheet. Non-financial characteristics of a Special Mention rating may include management problems, pending litigation, a non-existent, or ineffective loan agreement or other material structural weakness, and/or other significant deviation from prudent lending practices. • Risk Rate 6 – Substandard - A Substandard loan is inadequately protected by the current sound worth and paying capacity of the borrower 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. The loans are characterized by the distinct possibility that the Company will sustain some loss if the deficiencies are not corrected. This does not imply ultimate loss of the principal, but may involve burdensome administrative expenses and the accompanying cost to carry the loan. • Risk Rate 7 – Doubtful – A loan classified Doubtful has all the weaknesses inherent in a substandard loan except that the weaknesses make collection or liquidation in full (on the basis of currently existing facts, conditions, and values) highly questionable and improbable. Doubtful borrowers are usually in default, lack adequate liquidity, or capital, and lack the resources necessary to remain an operating entity. The possibility of loss is extremely high, but because of specific pending events that may strengthen the asset, its classification as loss is deferred. Pending factors include: proposed merger or acquisition; liquidation procedures; capital injection; perfection of liens on additional collateral; and refinancing plans. Loans classified as Doubtful are placed on nonaccrual status. • Risk Rate 8 – Loss - Loans classified Loss are considered uncollectible and of such little value that their continuance as bankable assets is not warranted. This classification does not mean that the loans has absolutely no recovery or salvage value, but rather it is not practical or desirable to defer writing off this basically worthless loan, even though partial recovery may be affected in the future. Borrowers in the Loss category are often in bankruptcy, have formally suspended debt repayments, or have otherwise ceased normal business operations. Loans should be classified as Loss and charged-off in the period in which they become uncollectible. Loans acquired are evaluated using this internal grading system. Loans acquired are evaluated individually and include purchased credit impaired loans of $5.0 million and $17.1 million that are accounted for under ASC Topic 310-30 and are classified as substandard (Risk Rating 6) as of September 30, 2018 and December 31, 2017 , respectively. Of the remaining loans acquired and accounted for under ASC Topic 310-20, $61.5 million and $76.3 million were classified (Risk Ratings 6, 7 and 8 – see classified loans discussion below) at September 30, 2018 and December 31, 2017 , respectively. Purchased credit impaired loans are loans that showed evidence of deterioration of credit quality since origination and for which it is probable, at acquisition, that the Company will be unable to collect all amounts contractually owed. Their fair value was initially based on the estimate of cash flows, both principal and interest, expected to be collected or estimated collateral values if cash flows are not estimable, discounted at prevailing market rates of interest. The difference between the undiscounted cash flows expected at acquisition and the fair value at acquisition is recognized as interest income on a level-yield method over the life of the loan. Contractually required payments for interest and principal that exceed the undiscounted cash flows expected at acquisition are not recognized as a yield adjustment. Increases in expected cash flows subsequent to the initial investment are recognized prospectively through adjustment of the yield on the loan over its remaining life. Decreases in expected cash flows are recognized as impairment. Classified loans for the Company include loans in Risk Ratings 6, 7 and 8. Loans may be classified, but not considered impaired, due to one of the following reasons: (1)The Company has established minimum dollar amount thresholds for loan impairment testing. Loans rated 6 – 8 that fall under the threshold amount are not tested for impairment and therefore are not included in impaired loans. (2) Of the loans that are above the threshold amount and tested for impairment, after testing, some are considered to not be impaired and are not included in impaired loans. Total classified loans, excluding loans accounted for under ASC Topic 310-30, were $145.3 million and $175.6 million , as of September 30, 2018 and December 31, 2017 , respectively. The following table presents a summary of loans by credit risk rating as of September 30, 2018 and December 31, 2017 , segregated by class of loans. Loans accounted for under ASC Topic 310-30 are all included in Risk Rate 1-4 in this table. (In thousands) Risk Rate 1-4 Risk Rate 5 Risk Rate 6 Risk Rate 7 Risk Rate 8 Total September 30, 2018 Consumer: Credit cards $ 181,620 $ — $ 517 $ — $ — $ 182,137 Other consumer 255,857 — 3,724 — — 259,581 Total consumer 437,477 — 4,241 — — 441,718 Real estate: Construction 1,225,481 2,286 2,121 — — 1,229,888 Single family residential 1,382,655 843 18,256 237 — 1,401,991 Other commercial 3,047,514 9,304 20,370 — — 3,077,188 Total real estate 5,655,650 12,433 40,747 237 — 5,709,067 Commercial: Commercial 1,569,357 8,250 30,735 — — 1,608,342 Agricultural 215,742 155 2,881 — — 218,778 Total commercial 1,785,099 8,405 33,616 — — 1,827,120 Other 145,369 — — — — 145,369 Loans acquired 3,620,803 47,672 66,087 359 — 3,734,921 Total $ 11,644,398 $ 68,510 $ 144,691 $ 596 $ — $ 11,858,195 (In thousands) Risk Rate 1-4 Risk Rate 5 Risk Rate 6 Risk Rate 7 Risk Rate 8 Total December 31, 2017 Consumer: Credit cards $ 184,920 $ — $ 502 $ — $ — $ 185,422 Other consumer 275,160 — 4,934 — — 280,094 Total consumer 460,080 — 5,436 — — 465,516 Real estate: Construction 603,126 5,795 5,218 16 — 614,155 Single family residential 1,066,902 3,954 23,490 287 — 1,094,633 Other commercial 2,480,293 19,581 30,950 — — 2,530,824 Total real estate 4,150,321 29,330 59,658 303 — 4,239,612 Commercial: Commercial 736,377 74,254 14,402 50 134 825,217 Agricultural 146,065 24 2,190 23 — 148,302 Total commercial 882,442 74,278 16,592 73 134 973,519 Other 26,962 — — — — 26,962 Loans acquired 4,918,570 62,128 93,378 — — 5,074,076 Total $ 10,438,375 $ 165,736 $ 175,064 $ 376 $ 134 $ 10,779,685 Allowance for Loan Losses Allowance for Loan Losses – The allowance for loan losses is a reserve established through a provision for loan losses charged to expense, which represents management’s best estimate of probable losses that have been incurred within the existing portfolio of loans. The allowance, in the judgment of management, is necessary to reserve for estimated loan losses and risks inherent in the loan portfolio. The Company’s allowance for loan loss methodology includes allowance allocations calculated in accordance with ASC Topic 310-10, Receivables , and allowance allocations calculated in accordance with ASC Topic 450-20, Loss Contingencies . Accordingly, the methodology is based on the Company’s internal grading system, specific impairment analysis, qualitative and quantitative factors. As mentioned above, allocations to the allowance for loan losses are categorized as either specific allocations or general allocations. A loan is considered impaired when it is probable that the Company will not receive all amounts due according to the contractual terms of the loan, including scheduled principal and interest payments. For a collateral dependent loan, the Company’s evaluation process includes a valuation by appraisal or other collateral analysis. This valuation is compared to the remaining outstanding principal balance of the loan. If a loss is determined to be probable, the loss is included in the allowance for loan losses as a specific allocation. If the loan is not collateral dependent, the measurement of loss is based on the difference between the expected and contractual future cash flows of the loan. The general allocation is calculated monthly based on management’s assessment of several factors such as (1) historical loss experience based on volumes and types, (2) volume and trends in delinquencies and nonaccruals, (3) lending policies and procedures including those for loan losses, collections and recoveries, (4) national, state and local economic trends and conditions, (5) external factors and pressure from competition, (6) the experience, ability and depth of lending management and staff, (7) seasoning of new products obtained and new markets entered through acquisition and (8) other factors and trends that will affect specific loans and categories of loans. The Company establishes general allocations for each major loan category. This category also includes allocations to loans which are collectively evaluated for loss such as credit cards, one-to-four family owner occupied residential real estate loans and other consumer loans. The following table details activity in the allowance for loan losses by portfolio segment for legacy loans for the three and nine months ended September 30, 2018 . Allocation of a portion of the allowance to one category of loans does not preclude its availability to absorb losses in other categories. (In thousands) Commercial Real Estate Credit Card Other Consumer and Other Total Three Months Ended September 30, 2018 Balance, beginning of period (2) $ 15,767 $ 28,904 $ 3,822 $ 3,239 $ 51,732 Provision for loan losses (1) 3,589 5,308 719 729 10,345 Charge-offs (592 ) (4,952 ) (919 ) (1,321 ) (7,784 ) Recoveries 450 210 229 176 1,065 Net charge-offs (142 ) (4,742 ) (690 ) (1,145 ) (6,719 ) Balance, September 30, 2018 (2) $ 19,214 $ 29,470 $ 3,851 $ 2,823 $ 55,358 Nine Months Ended September 30, 2018 Balance, beginning of period (2) $ 7,007 $ 27,281 $ 3,784 $ 3,596 $ 41,668 Provision for loan losses (1) 14,772 7,133 2,219 2,567 26,691 Charge-offs (3,143 ) (5,568 ) (2,930 ) (3,743 ) (15,384 ) Recoveries 578 624 778 403 2,383 Net charge-offs (2,565 ) (4,944 ) (2,152 ) (3,340 ) (13,001 ) Balance, September 30, 2018 (2) $ 19,214 $ 29,470 $ 3,851 $ 2,823 $ 55,358 Period-end amount allocated to: Loans individually evaluated for impairment $ 191 $ 268 $ — $ — $ 459 Loans collectively evaluated for impairment 19,023 29,202 3,851 2,823 54,899 Balance, September 30, 2018 (2) $ 19,214 $ 29,470 $ 3,851 $ 2,823 $ 55,358 ______________________ (1) Provision for loan losses of $1,837,000 attributable to loans acquired was excluded from this table for the nine months ended September 30, 2018 (total provision for loan losses for the three and nine months ended September 30, 2018 was $10,345,000 and $28,528,000 ). There were $699,000 and $910,000 in charge-offs for loans acquired during the three and nine months ended September 30, 2018 , respectively, resulting in an ending balance in the allowance related to

Loans Acquired

Loans Acquired	9 Months Ended
	Sep. 30, 2018
Receivables [Abstract]
Loans Acquired	LOANS ACQUIRED During the fourth quarter of 2017 , the Company evaluated $1.985 billion of net loans ( $2.021 billion gross loans less $36.3 million discount) purchased in conjunction with the acquisition of OKSB, described in Note 2, Acquisitions, in accordance with the provisions of ASC Topic 310-20, Nonrefundable Fees and Other Costs . The fair value discount is being accreted into interest income over the weighted average life of the loans using a constant yield method. These loans are not considered to be impaired loans. The Company evaluated the remaining $11.4 million of net loans ( $18.1 million gross loans less $6.7 million discount) purchased in conjunction with the acquisition of OKSB for impairment in accordance with the provisions of ASC Topic 310-30, Loans and Debt Securities Acquired with Deteriorated Credit Quality . Purchased loans are considered impaired if there is evidence of credit deterioration since origination and if it is probable that not all contractually required payments will be collected. Also during the fourth quarter of 2017 , the Company evaluated $2.208 billion of net loans ( $2.246 billion gross loans less $37.8 million discount) purchased in conjunction with the acquisition of First Texas, described in Note 2, Acquisitions, in accordance with the provisions of ASC Topic 310-20, Nonrefundable Fees and Other Costs . The fair value discount is being accreted into interest income over the weighted average life of the loans using a constant yield method. These loans are not considered to be impaired loans. During the second quarter of 2017 , the Company evaluated $249.2 million of net loans ( $254.2 million gross loans less $5.0 million discount) purchased in conjunction with the acquisition of Hardeman, described in Note 2, Acquisitions, in accordance with the provisions of ASC Topic 310-20, Nonrefundable Fees and Other Costs . The fair value discount is being accreted into interest income over the weighted average life of the loans using a constant yield method. These loans are not considered to be impaired loans. The Company evaluated the remaining $2.4 million of net loans ( $3.4 million gross loans less $990,000 discount) purchased in conjunction with the acquisition of Hardeman for impairment in accordance with the provisions of ASC Topic 310-30, Loans and Debt Securities Acquired with Deteriorated Credit Quality . See Note 2, Acquisitions, for further discussion of loans acquired. The following table reflects the carrying value of all loans acquired as of September 30, 2018 and December 31, 2017 : Loans Acquired (In thousands) September 30, 2018 December 31, 2017 Consumer: Other consumer $ 21,278 $ 51,467 Real estate: Construction 467,895 637,032 Single family residential 606,866 793,228 Other commercial 2,040,189 2,387,777 Total real estate 3,114,950 3,818,037 Commercial: Commercial 596,641 995,587 Agricultural 2,052 66,576 Total commercial 598,693 1,062,163 Other — 142,409 Total loans acquired (1) $ 3,734,921 $ 5,074,076 _____________________________________________________________________________________ (1) Loans acquired are reported net of a $1,345,000 and $418,000 allowance at September 30, 2018 and December 31, 2017 , respectively. Nonaccrual loans acquired, excluding purchased credit impaired loans accounted for under ASC Topic 310-30, segregated by class of loans, are as follows (see Note 5, Loans and Allowance for Loan Losses, for discussion of nonaccrual loans): (In thousands) September 30, 2018 December 31, 2017 Consumer: Other consumer $ 293 $ 334 Real estate: Construction 279 1,767 Single family residential 9,053 12,151 Other commercial 1,354 7,401 Total real estate 10,686 21,319 Commercial: Commercial 4,964 1,748 Agricultural 38 84 Total commercial 5,002 1,832 Total $ 15,981 $ 23,485 An age analysis of past due loans acquired segregated by class of loans, is as follows (see Note 5, Loans and Allowance for Loan Losses, for discussion of past due loans): (In thousands) Gross 30-89 Days Past Due 90 Days or More Past Due Total Past Due Current Total Loans 90 Days Past Due & Accruing September 30, 2018 Consumer: Other consumer $ 213 $ 214 $ 427 $ 20,851 $ 21,278 $ — Real estate: Construction 117 207 324 467,571 467,895 — Single family residential 2,459 5,948 8,407 598,459 606,866 1 Other commercial 2,491 4,157 6,648 2,033,541 2,040,189 — Total real estate 5,067 10,312 15,379 3,099,571 3,114,950 1 Commercial: Commercial 1,471 4,020 5,491 591,150 596,641 — Agricultural 27 5 32 2,020 2,052 — Total commercial 1,498 4,025 5,523 593,170 598,693 — Total $ 6,778 $ 14,551 $ 21,329 $ 3,713,592 $ 3,734,921 $ 1 December 31, 2017 Consumer: Other consumer $ 889 $ 260 $ 1,149 $ 50,318 $ 51,467 $ 108 Real estate: Construction 2,577 1,448 4,025 633,007 637,032 279 Single family residential 12,936 3,302 16,238 776,990 793,228 126 Other commercial 17,176 5,647 22,823 2,364,954 2,387,777 2,565 Total real estate 32,689 10,397 43,086 3,774,951 3,818,037 2,970 Commercial: Commercial 2,344 1,039 3,383 992,204 995,587 67 Agricultural 51 — 51 66,525 66,576 — Total commercial 2,395 1,039 3,434 1,058,729 1,062,163 67 Other 15 — 15 142,394 142,409 — Total $ 35,988 $ 11,696 $ 47,684 $ 5,026,392 $ 5,074,076 $ 3,145 The following table presents a summary of loans acquired by credit risk rating, segregated by class of loans (see Note 5, Loans and Allowance for Loan Losses, for discussion of loan risk rating). Loans accounted for under ASC Topic 310-30 are all included in Risk Rate 1-4 in this table. (In thousands) Risk Rate 1-4 Risk Rate 5 Risk Rate 6 Risk Rate 7 Risk Rate 8 Total September 30, 2018 Consumer: Other consumer $ 20,813 $ 9 $ 456 $ — $ — $ 21,278 Real estate: Construction 440,881 18,011 9,003 — — 467,895 Single family residential 590,003 2,475 14,029 359 — 606,866 Other commercial 2,006,371 12,283 21,535 — — 2,040,189 Total real estate 3,037,255 32,769 44,567 359 — 3,114,950 Commercial: Commercial 560,791 14,894 20,956 — — 596,641 Agricultural 1,944 — 108 — — 2,052 Total commercial 562,735 14,894 21,064 — — 598,693 Total $ 3,620,803 $ 47,672 $ 66,087 $ 359 $ — $ 3,734,921 December 31, 2017 Consumer: Other consumer $ 50,625 $ 21 $ 821 $ — $ — $ 51,467 Real estate: Construction 604,796 30,524 1,712 — — 637,032 Single family residential 770,954 2,618 19,656 — — 793,228 Other commercial 2,337,097 15,064 35,616 — — 2,387,777 Total real estate 3,712,847 48,206 56,984 — — 3,818,037 Commercial: Commercial 946,322 13,901 35,364 — — 995,587 Agricultural 66,367 — 209 — — 66,576 Total commercial 1,012,689 13,901 35,573 — — 1,062,163 Other 142,409 — — — — 142,409 Total $ 4,918,570 $ 62,128 $ 93,378 $ — $ — $ 5,074,076 Loans acquired were individually evaluated and recorded at estimated fair value, including estimated credit losses, at the time of acquisition. These loans are systematically reviewed by the Company to determine the risk of losses that may exceed those identified at the time of the acquisition. Techniques used in determining risk of loss are similar to the Company’s legacy loan portfolio, with most focus being placed on those loans which include the larger loan relationships and those loans which exhibit higher risk characteristics. In addition to the accretable yield on loans acquired not considered to be impaired, the amount of the estimated cash flows expected to be received from the purchased credit impaired loans in excess of the fair values recorded for the purchased credit impaired loans is referred to as the accretable yield. The accretable yield is recognized as interest income over the estimated lives of the loans. Each quarter, the Company estimates the cash flows expected to be collected from the acquired purchased credit impaired loans, and adjustments may or may not be required. This has resulted in an increase in interest income that is spread on a level-yield basis over the remaining expected lives of the loans. The impact of these adjustments on the Company’s financial results for the three and nine months ended September 30, 2018 and 2017 is shown below: Three Months Ended Nine Months Ended (In thousands) 2018 2017 2018 2017 Impact on net interest income and pre-tax income $ 629 $ 23 $ 1,105 $ 2,596 Impact, net of taxes $ 464 $ 14 $ 814 $ 1,578 These adjustments will be recognized over the remaining lives of the purchased credit impaired loans. The accretable yield adjustments recorded in future periods will change as the Company continues to evaluate expected cash flows from the purchased credit impaired loans. Changes in the carrying amount of the accretable yield for all purchased impaired loans were as follows for the three and nine months ended September 30, 2018 and 2017 . Three Months Ended Nine Months Ended (In thousands) Accretable Yield Carrying Amount of Loans Accretable Yield Carrying Amount of Loans Beginning balance $ 1,382 $ 13,995 $ 620 $ 17,116 Additions — — — — Accretable yield adjustments 717 — 1,895 — Accretion (635 ) 635 (1,051 ) 1,051 Payments and other reductions, net — (9,664 ) — (13,201 ) Balance, ending $ 1,464 $ 4,966 $ 1,464 $ 4,966 Three Months Ended Nine Months Ended (In thousands) Accretable Yield Carrying Amount of Loans Accretable Yield Carrying Amount of Loans Beginning balance $ 766 $ 8,448 $ 1,655 $ 17,802 Additions — — — 2,388 Accretable yield adjustments 52 — 2,698 — Accretion (408 ) 408 (3,943 ) 3,943 Payments and other reductions, net — (980 ) — (16,257 ) Balance, ending $ 410 $ 7,876 $ 410 $ 7,876 Purchased impaired loans are evaluated on an individual borrower basis. Because some loans evaluated by the Company were determined to have experienced impairment in the estimated credit quality or cash flows, the Company recorded a provision and established an allowance for loan loss for loans acquired resulting in a total allowance on loans acquired of $1,345,000 at September 30, 2018 and $418,000 at December 31, 2017 . The provision on loans acquired for the nine months ended September 30, 2018 and 2017 was $1,837,000 and $1,464,000 , respectively. There was no provision on loans acquired for the three months ended September 30, 2018 and 2017 .

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	9 Months Ended
	Sep. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangible Assets	GOODWILL AND OTHER INTANGIBLE ASSETS Goodwill is tested annually, or more often than annually, if circumstances warrant, for impairment. If the implied fair value of goodwill is lower than its carrying amount, goodwill impairment is indicated, and goodwill is written down to its implied fair value. Subsequent increases in goodwill value are not recognized in the financial statements. Goodwill totaled $845.7 million at September 30, 2018 and $842.7 million at December 31, 2017 . The Company recorded $229.1 million , $240.8 million and $29.4 million of goodwill as a result of its acquisitions of OKSB, First Texas and Hardeman, respectively. Goodwill impairment was neither indicated nor recorded during the nine months ended September 30, 2018 or the year ended December 31, 2017 . Core deposit premiums are amortized over periods ranging from 10 to 15 years and are periodically evaluated, at least annually, as to the recoverability of their carrying value. Core deposit premiums of $42.1 million , $7.3 million , and $7.8 million were recorded during 2017 as part of the OKSB, First Texas and Hardeman acquisitions, respectively. Intangible assets are being amortized over various periods ranging from 10 to 15 years. The Company recorded $830,000 of intangible assets during 2017 related to the insurance operations in the Hardeman acquisition. The Company recorded $3.8 million of other intangible assets during 2017 as part of the OKSB acquisition which were subsequently sold in first quarter 2018 . The Company’s goodwill and other intangibles (carrying basis and accumulated amortization) at September 30, 2018 and December 31, 2017 , were as follows: (In thousands) September 30, 2018 December 31, 2017 Goodwill $ 845,687 $ 842,651 Core deposit premiums: Gross carrying amount 105,984 105,984 Accumulated amortization (23,802 ) (16,659 ) Core deposit premiums, net 82,182 89,325 Books of business intangible: Gross carrying amount 15,234 15,414 Accumulated amortization (3,441 ) (2,827 ) Books of business intangible, net 11,793 12,587 Other intangibles: Gross carrying amount 2,068 6,037 Accumulated amortization (2,068 ) (1,878 ) Other intangibles, net — 4,159 Other intangible assets, net 93,975 106,071 Total goodwill and other intangible assets $ 939,662 $ 948,722 The Company’s estimated remaining amortization expense on intangibles as of September 30, 2018 is as follows: (In thousands) Year Amortization Expense Remainder of 2018 $ 2,642 2019 10,565 2020 10,552 2021 10,490 2022 10,438 Thereafter 49,288 Total $ 93,975

Time Deposits

Time Deposits	9 Months Ended
	Sep. 30, 2018
Banking and Thrift [Abstract]
Time Deposits	TIME DEPOSITS Time deposits include approximately $1.364 billion and $736.0 million of certificates of deposit of $100,000 or more at September 30, 2018 , and December 31, 2017 , respectively. Of this total approximately $702.5 million and $396.8 million of certificates of deposit were over $250,000 at September 30, 2018 and December 31, 2017 , respectively.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES The provision for income taxes is comprised of the following components for the periods indicated below: Three Months Ended Nine Months Ended (In thousands) 2018 2017 2018 2017 Income taxes currently payable $ 5,638 $ 11,946 $ 31,335 $ 30,467 Deferred income taxes 5,264 2,732 7,316 4,962 Provision for income taxes $ 10,902 $ 14,678 $ 38,651 $ 35,429 The tax effects of temporary differences between the tax basis of assets and liabilities and their financial reporting amounts that give rise to deferred income tax assets and liabilities, and their appropriate tax effects, are as follows: (In thousands) September 30, 2018 December 31, 2017 Deferred tax assets: Loans acquired $ 12,092 $ 19,885 Allowance for loan losses 12,601 10,773 Valuation of foreclosed assets 2,709 2,852 Tax NOLs from acquisition 6,962 7,821 Deferred compensation payable 2,645 2,433 Accrued equity and other compensation 6,605 5,302 Acquired securities 549 578 Unrealized loss on available-for-sale securities 16,221 6,107 Other 5,890 8,813 Gross deferred tax assets 66,274 64,564 Deferred tax liabilities: Goodwill and other intangible amortization (30,645 ) (32,572 ) Accumulated depreciation (11,778 ) (8,945 ) Other (2,197 ) (4,413 ) Gross deferred tax liabilities (44,620 ) (45,930 ) Net deferred tax asset, included in other assets $ 21,654 $ 18,634 A reconciliation of income tax expense at the statutory rate to the Company’s actual income tax expense is shown for the periods indicated below: Three Months Ended Nine Months Ended (In thousands) 2018 2017 2018 2017 Computed at the statutory rate (1) $ 13,880 $ 15,235 $ 41,731 $ 38,313 Increase (decrease) in taxes resulting from: State income taxes, net of federal tax benefit 986 342 4,073 1,117 Discrete items related to ASU 2016-09 (31 ) 5 (2,567 ) (1,372 ) Tax exempt interest income (833 ) (955 ) (2,292 ) (3,160 ) Tax exempt earnings on BOLI (186 ) (178 ) (562 ) (616 ) Other differences, net (2,914 ) 229 (1,732 ) 1,147 Actual tax provision $ 10,902 $ 14,678 $ 38,651 $ 35,429 ________________________ (1) The statutory rate was 21% for 2018 compared to 35% for 2017 . The Company follows ASC Topic 740, Income Taxes , which prescribes a recognition threshold and a measurement attribute for the financial statement recognition and measurement of a tax position taken or expected to be taken in a tax return. Benefits from tax positions should be recognized in the financial statements only when it is more likely than not that the tax position will be sustained upon examination by the appropriate taxing authority that would have full knowledge of all relevant information. A tax position that meets the more-likely-than-not recognition threshold is measured at the largest amount of benefit that is greater than fifty percent likely of being realized upon ultimate settlement. Tax positions that previously failed to meet the more-likely-than-not recognition threshold should be recognized in the first subsequent financial reporting period in which that threshold is met. Previously recognized tax positions that no longer meet the more-likely-than-not recognition threshold should be derecognized in the first subsequent financial reporting period in which that threshold is no longer met. ASC Topic 740 also provides guidance on the accounting for and disclosure of unrecognized tax benefits, interest and penalties. The Company has no history of expiring net operating loss carryforwards and is projecting significant pre-tax and financial taxable income in 2018 and in future years. The Company expects to fully realize its deferred tax assets in the future. Income tax expense was lower in the third quarter due largely to discrete tax benefits related to tax accounting for a cost segregation study, excess tax benefits related to restricted stock and a state tax deferred tax asset (“DTA”) adjustment. The purpose of the cost segregation study was to analyze the costs included in various projects and recognize the benefit of recording tax depreciation in 2017 when the federal rate was higher. The purpose of the state DTA adjustment was due to an analysis of projected state apportionment after the 2017 acquisitions of First South Bank, Bank SNB and Southwest Bank were merged into Simmons Bank in 2018. On December 22, 2017, the President signed tax reform legislation (the “2017 Act”) which includes a broad range of tax reform proposals affecting businesses, including corporate tax rates, business deductions, and international tax provisions. The 2017 Act reduces the corporate tax rate from 35% to 21% for tax years beginning after December 31, 2017 . Under US GAAP, deferred tax assets and liabilities are required to be measured at the enacted tax rate expected to apply when temporary differences are to be realized or settled and the effect of a change in tax law is recorded discretely as a component of the income tax provision related to continuing operations in the period of enactment. As a result, the Company was required to remeasure its deferred taxes as of December 22, 2017 based upon the new 21% tax rate and the change was recorded in the 2017 income tax provision in the fourth quarter. On December 22, 2017, the SEC issued Staff Accounting Bulletin No. 118 (“SAB 118”), which provides guidance on accounting for the tax effects of the 2017 Act. SAB 118 provides a measurement period that should not extend beyond one year from the 2017 Act enactment date for companies to complete the accounting under ASC 740, Income Taxes . As such, the company’s 2017 financial results reflect the income tax effects for the 2017 Act for which the accounting under ASC 740 is complete and provisional amounts for those specific income tax effects of the 2017 Act for which the accounting under ASC 740 is incomplete but a reasonable estimate could be determined. The company did not identify items for which the income tax effects of the 2017 Act have not been completed and a reasonable estimate could not be determined as of December 31, 2017 . The tax expense recorded in 2017 is a reasonable estimate based on published guidance available at this time and is considered provisional. The ultimate impact of the 2017 Act may differ from these estimates due to changes in interpretations and assumptions made by the Company, as well as additional regulatory guidance. Any adjustments will be reflected in the Company’s financial statements in future periods. The amount of unrecognized tax benefits may increase or decrease in the future for various reasons including adding amounts for current tax year positions, expiration of open income tax returns due to the statutes of limitation, changes in management’s judgment about the level of uncertainty, status of examinations, litigation and legislative activity and the addition or elimination of uncertain tax positions. Section 382 of the Internal Revenue Code imposes an annual limit on the ability of a corporation that undergoes an “ownership change” to use its U.S. net operating losses to reduce its tax liability. The Company closed a stock acquisition in a prior year that invoked the Section 382 annual limitation. Approximately $35.6 million of federal net operating losses subject to the IRC Sec 382 annual limitation are expected to be utilized by the Company. The net operating loss carryforwards expire between 2028 and 2035. The Company files income tax returns in the U.S. federal jurisdiction. The Company’s U.S. federal income tax returns are open and subject to examinations from the 2014 tax year and forward. The Company’s various state income tax returns are generally open from the 2014 and later tax return years based on individual state statute of limitations.

Securities Sold Under Agreement

Securities Sold Under Agreements to Repurchase	9 Months Ended
	Sep. 30, 2018
Banking and Thrift [Abstract]
Securities Sold Under Agreements to Repurchase	SECURITIES SOLD UNDER AGREEMENTS TO REPURCHASE The Company utilizes securities sold under agreements to repurchase to facilitate the needs of its customers and to facilitate secured short-term funding needs. Securities sold under agreements to repurchase are stated at the amount of cash received in connection with the transaction. The Company monitors collateral levels on a continuous basis. The Company may be required to provide additional collateral based on the fair value of the underlying securities. Securities pledged as collateral under repurchase agreements are maintained with safekeeping agents. The gross amount of recognized liabilities for repurchase agreements was $109.0 million and $122.0 million at September 30, 2018 and December 31, 2017 , respectively. The remaining contractual maturity of the securities sold under agreements to repurchase in the consolidated balance sheets as of September 30, 2018 and December 31, 2017 is presented in the following tables. Remaining Contractual Maturity of the Agreements (In thousands) Overnight and Continuous Up to 30 Days 30-90 Days Greater than 90 Days Total September 30, 2018 Repurchase agreements: U.S. Government agencies $ 108,963 $ — $ — $ — $ 108,963 December 31, 2017 Repurchase agreements: U.S. Government agencies $ 122,019 $ — $ — $ — $ 122,019

Other Borrowings and Subordinat

Other Borrowings and Subordinated Notes and Debentures	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Other Borrowings and Subordinated Notes and Debentures	OTHER BORROWINGS AND SUBORDINATED NOTES AND DEBENTURES Debt at September 30, 2018 and December 31, 2017 consisted of the following components: (In thousands) September 30, 2018 December 31, 2017 Other Borrowings FHLB advances, net of discount, due 2018 to 2033, 1.38% to 7.37% secured by residential real estate loans $ 1,420,917 $ 1,261,642 Revolving credit agreement, due 10/5/2018, floating rate of 1.50% above the one month LIBOR rate, unsecured — 75,000 Notes payable, due 10/15/2020, 3.85%, fixed rate, unsecured — 43,382 Total other borrowings 1,420,917 1,380,024 Subordinated Notes and Debentures Subordinated notes payable, due 4/1/2028, fixed-to-floating rate (fixed rate of 5.00% through 3/31/2023, floating rate of 2.15% above the three month LIBOR rate, reset quarterly) 330,000 — Trust preferred securities, due 12/30/2033, floating rate of 2.80% above the three month LIBOR rate, reset quarterly, callable without penalty — 20,620 Trust preferred securities, net of discount, due 6/30/2035, floating rate of 1.75% above the three month LIBOR rate, reset quarterly, callable without penalty — 9,327 Trust preferred securities, net of discount, due 9/15/2037, floating rate of 1.37% above the three month LIBOR rate, reset quarterly 10,310 10,284 Trust preferred securities, net of discount, due 12/5/2033, floating rate of 2.88% above the three month LIBOR rate, reset quarterly, callable without penalty — 5,156 Trust preferred securities, net of discount, due 10/18/2034, floating rate of 2.00% above the three month LIBOR rate, reset quarterly, callable without penalty — 5,148 Trust preferred securities, net of discount, due 6/6/2037, floating rate of 1.57% above the three month LIBOR rate, reset quarterly, callable without penalty 10,310 10,288 Trust preferred securities, due 12/15/2035, floating rate of 1.45% above the three month LIBOR rate, reset quarterly, callable without penalty 6,702 6,702 Trust preferred securities, due 6/26/2033, floating rate of 3.10% above the three month LIBOR rate, reset quarterly, callable without penalty — 20,619 Trust preferred securities, due 10/7/2033, floating rate of 2.85% above the three month LIBOR rate, reset quarterly, callable without penalty — 25,774 Trust preferred securities, due 9/15/2037, floating rate of 2.00% above the three month LIBOR rate, reset quarterly, callable without penalty — 8,248 Other subordinated debentures, net of discount, called 9/30/2018, floating rate equal to daily average of prime rate, reset quarterly 19,075 18,399 Unamortized debt issuance costs (3,463 ) — Total subordinated notes and debentures 372,934 140,565 Total other borrowings and subordinated debt $ 1,793,851 $ 1,520,589 In March 2018 , the Company issued $330.0 million in aggregate principal amount, of 5.00% Fixed-to-Floating Rate Subordinated Notes (“the Notes”) at a public offering price equal to 100% of the aggregate principal amount of the Notes. The Company incurred $3.6 million in debt issuance costs related to the offering during March. The Notes will mature on April 1, 2028 and will bear interest at an initial fixed rate of 5.00% per annum, payable semi-annually in arrears. From and including April 1, 2023 to, but excluding, the maturity date or the date of earlier redemption, the interest rate will reset quarterly to an annual interest rate equal to the then-current three month LIBOR rate plus 215 basis points, payable quarterly in arrears. The Notes will be subordinated in right of payment to the payment of the Company’s other existing and future senior indebtedness, including all of its general creditors. The Notes are obligations of Simmons First National Corporation only and are not obligations of, and are not guaranteed by, any of its subsidiaries. During the first nine months of 2018 , the Company used a portion of the net proceeds from the sale of the Notes to repay certain outstanding indebtedness, including the amounts borrowed under the Revolving Credit Agreement (the “Credit Agreement”), certain trust preferred securities, both discussed below, and unsecured debt from correspondent banks. The subordinated notes qualify for Tier 2 capital treatment. In October 2017, the Company entered into the Credit Agreement with U.S. Bank National Association and executed an unsecured Revolving Credit Note pursuant to which the Company may borrow, prepay and re-borrow up to $75.0 million , the proceeds of which were primarily used to pay off amounts outstanding under a term note assumed with the First Texas acquisition. The Credit Agreement contained customary representations, warranties, and covenants of the Company, including, among other things, covenants that impose various financial ratio requirements. In October 2018, the Company and U.S. Bank National Association entered into a First Amendment to the Credit Agreement, which extended the expiration date from October 5, 2018 to October 4, 2019, reduced the $75.0 million to $50.0 million , and increased the commitment fee on the unused portion from an annual rate of 0.25% to 0.30% . In October 2019, all amounts borrowed, together with applicable interest, fees, and other amounts owed by the Company are due and payable. The balance due under the Credit Agreement at September 30, 2018 was zero . At September 30, 2018 , the Company had $1.4 billion of Federal Home Loan Bank (“FHLB”) advances outstanding with original maturities of one year or less, of which $675.0 million are FHLB Owns the Option (“FOTO”) advances. FOTO advances are a low cost, fixed-rate source of funding in return for granting to FHLB the flexibility to choose a termination date earlier than the maturity date. Typically, FOTO exercise dates follow a specified lockout period at the beginning of the term when FHLB cannot terminate the FOTO advance. If FHLB exercises its option to terminate the FOTO advance at one of the specified option exercise dates, there is no termination or prepayment fee, and replacement funding will be available at then-prevailing market rates, subject to FHLB’s credit and collateral requirements. The Company’s FOTO advances outstanding at the end of the third quarter have ten to fifteen year maturity dates with lockout periods that vary but do not exceed one year. These FOTO advances are considered and monitored by the Company as short-term advances due to the likelihood of FHLB exercising the options within a year of the settlement dates based upon the rising rate environment and the short lockout periods. The Company had total FHLB advances of $1.4 billion at September 30, 2018 , with approximately $885.4 million of additional advances available from the FHLB. The FHLB advances are secured by mortgage loans and investment securities totaling approximately $3.9 billion at September 30, 2018 . The trust preferred securities are tax-advantaged issues that qualified for Tier 1 capital treatment until December 31, 2017 , when the Company reached $15 billion in assets. They still qualify for inclusion as Tier 2 capital at September 30, 2018 . Distributions on these securities are included in interest expense on long-term debt. Each of the trusts is a statutory business trust organized for the sole purpose of issuing trust securities and investing the proceeds thereof in junior subordinated debentures of the Company, the sole asset of each trust. The preferred securities of each trust represent preferred beneficial interests in the assets of the respective trusts and are subject to mandatory redemption upon payment of the junior subordinated debentures held by the trust. The common securities of each trust are wholly-owned by the Company. Each trust’s ability to pay amounts due on the trust preferred securities is solely dependent upon the Company making payments on the related junior subordinated debentures. The Company’s obligations under the junior subordinated securities and other relevant trust agreements, in aggregate, constitute a full and unconditional guarantee by the Company of each respective trust’s obligations under the trust securities issued by each respective trust. The other subordinated debentures were called as of September 30, 2018 and as a result are classified as short-term at the end of the quarter. Principal and interest will be paid to the holders of the subordinated debt beginning on October 1, 2018. The Company’s long-term debt includes subordinated debt, notes payable and FHLB advances with an original maturity of greater than one year. Aggregate annual maturities of long-term debt at September 30, 2018 , are as follows: (In thousands) Year Annual Maturities 2018 $ 376 2019 2,135 2020 2,109 2021 1,800 2022 949 Thereafter 362,404 Total $ 369,773

Contingent Liabilities

Contingent Liabilities	9 Months Ended
	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Contingent Liabilities	CONTINGENT LIABILITIES The Company and/or its subsidiaries have various unrelated legal proceedings, which, in the aggregate, are not expected to have a material adverse effect on the financial position of the Company and its subsidiaries.

Common Stock

Common Stock	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
Common Stock	COMMON STOCK On January 18, 2018, the board of directors of the Company approved a two-for-one stock split of the Corporation’s outstanding Class A common stock (“Common Stock”) in the form of a 100% stock dividend for shareholders of record as of the close of business on January 30, 2018 (“Record Date”). The new shares were distributed by the Company’s transfer agent, Computershare, and the Company’s common stock began trading on a split-adjusted basis on the NASDAQ Global Select Market on February 9, 2018. All previously reported share and per share data included in filings subsequent to February 8, 2018 are restated to reflect the retroactive effect of this two -for-one stock split. On April 19, 2018, shareholders of the Company approved an increase in the number of authorized shares from 120,000,000 to 175,000,000 . On July 23, 2012, the Company approved a stock repurchase program which authorized the repurchase of up to 1,700,000 shares (split adjusted) of Class A common stock, or approximately 2% of the shares outstanding. Under the current plan, the Company can repurchase an additional 308,272 shares. The shares are to be purchased from time to time at prevailing market prices, through open market or unsolicited negotiated transactions, depending upon market conditions. Under the repurchase program, there is no time limit for the stock repurchases, nor is there a minimum number of shares that the Company intends to repurchase. The Company may discontinue purchases at any time that management determines additional purchases are not warranted. The Company intends to use the repurchased shares to satisfy stock option exercises, payment of future stock awards and dividends and general corporate purposes. The Company had no repurchases of its common stock during the three and nine month periods ended September 30, 2018 .

Undivided Profits

Undivided Profits	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
Undivided Profits	UNDIVIDED PROFITS The Company’s subsidiary bank is subject to legal limitations on dividends that can be paid to the parent company without prior approval of the applicable regulatory agencies. The approval of the Commissioner of the Arkansas State Bank Department is required if the total of all dividends declared by an Arkansas state bank in any calendar year exceeds seventy-five percent ( 75% ) of the total of its net profits, as defined, for that year combined with seventy-five percent ( 75% ) of its retained net profits of the preceding year. At September 30, 2018 , the Company’s subsidiary bank had approximately $1.6 million available for payment of dividends to the Company, without prior regulatory approval. The risk-based capital guidelines of the Federal Reserve Board and the Arkansas State Bank Department include the definitions for (1) a well-capitalized institution, (2) an adequately-capitalized institution, and (3) an undercapitalized institution. Under the Basel III Rules effective January 1, 2015, the criteria for a well-capitalized institution are: a 5% “Tier l leverage capital” ratio, an 8% “Tier 1 risk-based capital” ratio, 10% “total risk-based capital” ratio; and a 6.50% “common equity Tier 1 (CET1)” ratio. The Company and Bank must hold a capital conservation buffer composed of CET1 capital above its minimum risk-based capital requirements. The implementation of the capital conservation buffer began on January 1, 2016, at the 0.625% level and will phase in over a four -year period (increasing by that amount on each subsequent January 1 until it reaches 2.5% on January 1, 2019). As of September 30, 2018 , the Company and its subsidiary bank met all capital adequacy requirements under the Basel III Capital Rules, and management believes the Company and its subsidiary bank would meet all Capital Rules on a fully phased-in basis if such requirements were currently effective. The Company’s CET1 ratio was 9.82% at September 30, 2018 .

Stock Based Compensation

Stock Based Compensation	9 Months Ended
	Sep. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock Based Compensation	STOCK BASED COMPENSATION The Company’s Board of Directors has adopted various stock-based compensation plans. The plans provide for the grant of incentive stock options, nonqualified stock options, stock appreciation rights, restricted stock awards, restricted stock units, and performance stock units. Pursuant to the plans, shares are reserved for future issuance by the Company upon exercise of stock options or awarding of bonus shares granted to directors, officers and other key employees. Share and per share information regarding Stock-Based Compensation Plans has been adjusted to reflect the effects of the Company’s two -for-one stock split which became effective on February 8, 2018. The table below summarizes the transactions under the Company’s active stock compensation plans for the nine months ended September 30, 2018 : Stock Options Outstanding Non-vested Stock Awards Outstanding Non-vested Stock Units Outstanding Number of Shares (000) Weighted Average Exercise Price Number of Shares (000) Weighted Average Exercise Price Number of Shares (000) Weighted Average Exercise Price Balance, January 1, 2018 812 $ 21.98 162 $ 20.86 652 $ 27.92 Granted — — — — 343 29.31 Stock Options Exercised (111 ) 19.22 — — — — Stock Awards/Units Vested — — (55 ) 18.95 (175 ) 27.74 Forfeited/Expired (6 ) 21.73 (10 ) 20.12 (91 ) 28.37 Balance, September 30, 2018 695 $ 22.42 97 $ 22.00 729 $ 28.56 Exercisable, September 30, 2018 661 $ 22.37 The following table summarizes information about stock options under the plans outstanding at September 30, 2018 : Options Outstanding Options Exercisable Range of Exercise Prices Number of Shares (000) Weighted Average Remaining Contractual Life (Years) Weighted Average Exercise Price Number of Shares (000) Weighted Average Exercise Price $ 9.46 — $ 9.46 1 3.30 $9.46 1 $9.46 10.65 — 10.65 4 4.32 10.65 4 10.65 10.76 — 10.76 2 1.30 10.76 2 10.76 20.29 — 20.29 71 6.25 20.29 71 20.29 20.36 — 20.36 3 6.13 20.36 1 20.36 22.20 — 22.20 74 6.48 22.20 74 22.20 22.75 — 22.75 436 6.86 22.75 436 22.75 23.51 — 23.51 97 7.30 23.51 65 23.51 24.07 — 24.07 7 6.96 24.07 7 24.07 $ 9.46 — $ 24.07 695 6.78 $22.42 661 $22.37 Stock-based compensation expense was $9,818,000 and $6,486,000 during the nine months ended September 30, 2018 and 2017 , respectively. Stock-based compensation expense is recognized ratably over the requisite service period for all stock-based awards. There was $56,000 of unrecognized stock-based compensation expense related to stock options at September 30, 2018 . Unrecognized stock-based compensation expense related to non-vested stock awards was $21,129,000 at September 30, 2018 . At such date, the weighted-average period over which this unrecognized expense is expected to be recognized was 1.9 years. The intrinsic value of stock options outstanding and stock options exercisable at September 30, 2018 was $4,884,000 and $4,680,000 . Aggregate intrinsic value represents the difference between the Company’s closing stock price on the last trading day of the period, which was $29.45 as of September 30, 2018 , and the exercise price multiplied by the number of options outstanding. The total intrinsic value of stock options exercised during the nine months ended September 30, 2018 and September 30, 2017 , was $1,155,000 and $1,012,000 , respectively. The fair value of the Company’s employee stock options granted is estimated on the date of grant using the Black-Scholes option-pricing model. This model requires the input of highly subjective assumptions, changes to which can materially affect the fair value estimate. There were no stock options granted during the nine months ended September 30, 2018 and 2017 .

Earnings Per Share ("EPS")

Earnings Per Share ("EPS")	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Earnings Per Share (EPS)	EARNINGS PER SHARE (“EPS”) Basic EPS is computed based on the weighted average number of shares outstanding during each period. Diluted EPS is computed using the weighted average common shares and all potential dilutive common shares outstanding during the period. The share and per share amounts for 2017 have been restated to reflect the effect of the two -for-one stock split during February 2018. Following is the computation of earnings per share for the three and nine months ended September 30, 2018 and 2017 : Three Months Ended Nine Months Ended (In thousands, except per share data) 2018 2017 2018 2017 Net income $ 55,193 $ 28,852 $ 160,067 $ 74,037 Average common shares outstanding 92,290 64,427 92,246 63,594 Average potential dilutive common shares 551 420 551 420 Average diluted common shares 92,841 64,847 92,797 64,014 Basic earnings per share $ 0.60 $ 0.45 $ 1.74 $ 1.16 Diluted earnings per share $ 0.59 $ 0.44 $ 1.72 $ 1.16 There were no stock options excluded from the earnings per share calculation due to the related exercise price exceeding the average market price for the three and nine months ended September 30, 2018 and 2017 .

Additional Cash Flow Informatio

Additional Cash Flow Information	9 Months Ended
	Sep. 30, 2018
Supplemental Cash Flow Information [Abstract]
Additional Cash Flow Information	ADDITIONAL CASH FLOW INFORMATION The following is a summary of the Company’s additional cash flow information during the nine months ended: Nine Months Ended (In thousands) 2018 2017 Interest paid $ 78,987 $ 21,531 Income taxes paid 25,576 21,718 Transfers of loans to foreclosed assets held for sale 7,745 5,311 Transfers of premises to foreclosed assets and other real estate owned 3,690 3,188

Other Operating Expenses

Other Operating Expenses	9 Months Ended
	Sep. 30, 2018
Other Income and Expenses [Abstract]
Other Operating Expenses	OTHER OPERATING EXPENSES Other operating expenses consist of the following: Three Months Ended September 30, Nine Months Ended (In thousands) 2018 2017 2018 2017 Professional services $ 4,616 $ 3,946 $ 13,896 $ 13,079 Postage 1,262 1,091 4,103 3,427 Telephone 1,248 943 4,217 3,003 Credit card expense 3,405 3,137 9,820 9,081 Marketing 2,912 1,219 6,334 4,253 Operating supplies 585 592 1,917 1,406 Amortization of intangibles 2,772 1,724 8,394 4,828 Branch right sizing expense 970 153 1,049 370 Other expense 11,904 5,458 31,623 18,588 Total other operating expenses $ 29,674 $ 18,263 $ 81,353 $ 58,035

Certain Transactions

Certain Transactions	9 Months Ended
	Sep. 30, 2018
Related Party Transactions [Abstract]
Certain Transactions	CERTAIN TRANSACTIONS From time to time the Company and its subsidiaries have made loans and other extensions of credit to directors, officers, their associates and members of their immediate families. From time to time directors, officers and their associates and members of their immediate families have placed deposits with the Company’s subsidiary bank, Simmons Bank. Such loans, other extensions of credit and deposits were made in the ordinary course of business, on substantially the same terms (including interest rates and collateral) as those prevailing at the time for comparable transactions with other persons not related to the lender and did not involve more than normal risk of collectability or present other unfavorable features.

Commitments and Credit Risk

Commitments and Credit Risk	9 Months Ended
	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Credit Risk	COMMITMENTS AND CREDIT RISK The Company grants agri-business, commercial and residential loans to customers primarily throughout Arkansas, Colorado, Kansas, Missouri, Oklahoma, Tennessee and Texas, along with credit card loans to customers throughout the United States. Commitments to extend credit are agreements to lend to a customer as long as there is no violation of any condition established in the contract. Commitments generally have fixed expiration dates or other termination clauses and may require payment of a fee. Since a portion of the commitments may expire without being drawn upon, the total commitment amounts do not necessarily represent future cash requirements. Each customer’s creditworthiness is evaluated on a case-by-case basis. The amount of collateral obtained, if deemed necessary, is based on management’s credit evaluation of the counterparty. Collateral held varies, but may include accounts receivable, inventory, property, plant and equipment, commercial real estate and residential real estate. At September 30, 2018 , the Company had outstanding commitments to extend credit aggregating approximately $568,117,000 and $3,430,361,000 for credit card commitments and other loan commitments. At December 31, 2017 , the Company had outstanding commitments to extend credit aggregating approximately $564,592,000 and $3,086,696,000 for credit card commitments and other loan commitments, respectively. Standby letters of credit are conditional commitments issued by the Company to guarantee the performance of a customer to a third party. Those guarantees are primarily issued to support public and private borrowing arrangements, including commercial paper, bond financing, and similar transactions. The credit risk involved in issuing letters of credit is essentially the same as that involved in extending loans to customers. The Company had total outstanding letters of credit amounting to $34,518,000 and $47,621,000 at September 30, 2018 , and December 31, 2017 , respectively, with terms ranging from 9 months to 15 years. At September 30, 2018 and December 31, 2017 , the Company had no deferred revenue under standby letter of credit agreements.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	FAIR VALUE MEASUREMENTS ASC Topic 820, Fair Value Measurements defines fair value, establishes a framework for measuring fair value and expands disclosures about fair value measurements. ASC Topic 820 defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The guidance also establishes a fair value hierarchy that requires the use of observable inputs and minimizes the use of unobservable inputs when measuring fair value. Topic 820 describes three levels of inputs that may be used to measure fair value: • Level 1 Inputs – Quoted prices in active markets for identical assets or liabilities. • Level 2 Inputs – Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities in active markets; quoted prices for similar assets or liabilities in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. • Level 3 Inputs – Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. In general, fair value is based upon quoted market prices, where available. If such quoted market prices are not available, fair value is based upon internally developed models that primarily use, as inputs, observable market-based parameters. Valuation adjustments may be made to ensure that financial instruments are recorded at fair value. These adjustments may include amounts to reflect counterparty credit quality and the Company’s creditworthiness, among other things, as well as unobservable parameters. Any such valuation adjustments are applied consistently over time. The Company’s valuation methodologies may produce a fair value calculation that may not be indicative of net realizable value or reflective of future fair values. While management believes the Company’s valuation methodologies are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different estimate of fair value at the reporting date. Furthermore, the reported fair value amounts have not been comprehensively revalued since the presentation dates, and therefore, estimates of fair value after the balance sheet date may differ significantly from the amounts presented herein. A more detailed 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. Following is a description of the inputs and valuation methodologies used for assets measured at fair value on a recurring basis and recognized in the accompanying consolidated balance sheets, as well as the general classification of such assets pursuant to the valuation hierarchy. Available-for-sale securities – Where quoted market prices are available in an active market, securities are classified within Level 1 of the valuation hierarchy. Level 1 securities would include highly liquid government bonds, mortgage products and exchange traded equities. Other securities classified as available-for-sale are reported at fair value utilizing Level 2 inputs. For these securities, the Company obtains fair value measurements from an independent pricing service. 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 security’s terms and conditions, among other things. In order to ensure the fair values are consistent with ASC Topic 820, the Company periodically checks the fair values by comparing them to another pricing source, such as Bloomberg. The availability of pricing confirms Level 2 classification in the fair value hierarchy. The third-party pricing service is subject to an annual review of internal controls (SSAE 16), which is made available for the Company’s review. In certain cases where Level 1 or Level 2 inputs are not available, securities are classified within Level 3 of the hierarchy. The Company’s investment in U.S. Treasury securities, if any, is reported at fair value utilizing Level 1 inputs. The remainder of the Company’s available-for-sale securities are reported at fair value utilizing Level 2 inputs. Derivative instruments – The Company’s derivative instruments are reported at fair value utilizing Level 2 inputs. The Company obtains fair value measurements from dealer quotes. Other assets and liabilities held for sale – The Company’s other assets and liabilities held for sale are reported at fair value utilizing Level 3 inputs. See Note 4 - Other assets and other liabilities held for sale. The following table sets forth the Company’s financial assets by level within the fair value hierarchy that were measured at fair value on a recurring basis as of September 30, 2018 and December 31, 2017 . Fair Value Measurements Using (In thousands) Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) September 30, 2018 Available-for-sale securities U.S. Government agencies $ 141,460 $ — $ 141,460 $ — Mortgage-backed securities 1,419,626 — 1,419,626 — State and political subdivisions 282,439 — 282,439 — Other securities 154,289 — 154,289 — Other assets held for sale 5,136 — — 5,136 Derivative asset 9,691 — 9,691 — Other liabilities held for sale (424 ) — — (424 ) Derivative liability (7,940 ) — (7,940 ) — December 31, 2017 Available-for-sale securities U.S. Government agencies $ 139,724 $ — $ 139,724 $ — Mortgage-backed securities 1,187,317 — 1,187,317 — States and political subdivisions 143,165 — 143,165 — Other securities 119,311 — 119,311 — Other assets held for sale 165,780 — — 165,780 Derivative asset 3,634 — 3,634 — Other liabilities held for sale (157,366 ) — — (157,366 ) Derivative liability (3,068 ) — (3,068 ) — Certain financial assets and liabilities are measured at fair value on a nonrecurring basis; that is, the instruments are not measured at fair value on an ongoing basis but are subject to fair value adjustments in certain circumstances (for example, when there is evidence of impairment). Financial assets and liabilities measured at fair value on a nonrecurring basis include the following: Impaired loans (collateral dependent) – Loan impairment is reported when full payment under the loan terms is not expected. Allowable methods for determining the amount of impairment include estimating fair value using the fair value of the collateral for collateral-dependent loans. If the impaired loan is identified as collateral dependent, then the fair value method of measuring the amount of impairment is utilized. This method requires obtaining a current independent appraisal of the collateral and applying a discount factor to the value. A portion of the allowance for loan losses is allocated to impaired loans if the value of such loans is deemed to be less than the unpaid balance. If these allocations cause the allowance for loan losses to require an increase, such increase is reported as a component of the provision for loan losses. Loan losses are charged against the allowance when management believes the uncollectability of a loan is confirmed. Impaired loans that are collateral dependent are classified within Level 3 of the fair value hierarchy when impairment is determined using the fair value method. Appraisals are updated at renewal, if not more frequently, for all collateral dependent loans that are deemed impaired by way of impairment testing. Impairment testing is performed on all loans over $1.5 million rated Substandard or worse, all existing impaired loans regardless of size and all TDRs. All collateral dependent impaired loans meeting these thresholds have had updated appraisals or internally prepared evaluations within the last one to two years and these updated valuations are considered in the quarterly review and discussion of the corporate Special Asset Committee. On targeted CRE loans, appraisals/internally prepared valuations may be updated before the typical 1-3 year balloon/maturity period. If an updated valuation results in decreased value, a specific (ASC 310) impairment is placed against the loan, or a partial charge-down is initiated, depending on the circumstances and anticipation of the loan’s ability to remain a going concern, possibility of foreclosure, certain market factors, etc. Foreclosed assets and other real estate owned – Foreclosed assets and other real estate owned are reported at fair value, less estimated costs to sell. At foreclosure, if the fair value, less estimated costs to sell, of the real estate acquired is less than the Company’s recorded investment in the related loan, a write-down is recognized through a charge to the allowance for loan losses. Additionally, valuations are periodically performed by management and any subsequent reduction in value is recognized by a charge to income. The fair value of foreclosed assets and other real estate owned is estimated using Level 3 inputs based on unobservable market data. As of September 30, 2018 and December 31, 2017 , the fair value of foreclosed assets and other real estate owned less estimated costs to sell was $22.7 million and $32.1 million , respectively. The significant unobservable inputs (Level 3) used in the fair value measurement of collateral for collateral-dependent impaired loans and foreclosed assets primarily relate to the specialized discounting criteria applied to the borrower’s reported amount of collateral. The amount of the collateral discount depends upon the condition and marketability of the collateral, as well as other factors which may affect the collectability of the loan. Management’s assessment of the significance of a particular input to the fair value measurement in its entirety requires judgment and considers factors specific to the asset. It is reasonably possible that a change in the estimated fair value for instruments measured using Level 3 inputs could occur in the future. As the Company’s primary objective in the event of default would be to liquidate the collateral to settle the outstanding balance of the loan, collateral that is less marketable would receive a larger discount. During the reported periods, collateral discounts ranged from 10% to 40% for commercial and residential real estate collateral. Mortgage loans held for sale – Mortgage loans held for sale are reported at fair value if, on an aggregate basis, the fair value of the loans is less than cost. In determining whether the fair value of loans held for sale is less than cost when quoted market prices are not available, the Company may consider outstanding investor commitments, discounted cash flow analyses with market assumptions or the fair value of the collateral if the loan is collateral dependent. Such loans are classified within either Level 2 or Level 3 of the fair value hierarchy. Where assumptions are made using significant unobservable inputs, such loans held for sale are classified as Level 3. At September 30, 2018 and December 31, 2017 , the aggregate fair value of mortgage loans held for sale exceeded their cost. Accordingly, no mortgage loans held for sale were marked down and reported at fair value. The following table sets forth the Company’s financial assets by level within the fair value hierarchy that were measured at fair value on a nonrecurring basis as of September 30, 2018 and December 31, 2017 . Fair Value Measurements Using (In thousands) Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) September 30, 2018 Impaired loans (1) (2) (collateral dependent) $ 17,789 $ — $ — $ 17,789 Foreclosed assets and other real estate owned (1) 14,643 — — 14,643 December 31, 2017 Impaired loans (1) (2) (collateral dependent) $ 11,229 $ — $ — $ 11,229 Foreclosed assets and other real estate owned (1) 24,093 — — 24,093 ________________________ (1) These amounts represent the resulting carrying amounts on the Consolidated Balance Sheets for impaired collateral dependent loans and foreclosed assets and other real estate owned for which fair value re-measurements took place during the period. (2) Specific allocations of $2,738,000 and $2,195,000 were related to the impaired collateral dependent loans for which fair value re-measurements took place during the periods ended September 30, 2018 and December 31, 2017 , respectively. ASC Topic 825, Financial Instruments , requires disclosure in annual and interim financial statements of the fair value of financial assets and financial liabilities, including those financial assets and financial liabilities that are not measured and reported at fair value on a recurring basis or nonrecurring basis. The following methods and assumptions were used to estimate the fair value of each class of financial instruments not previously disclosed. Cash and cash equivalents – The carrying amount for cash and cash equivalents approximates fair value (Level 1). Interest bearing balances due from banks – The fair value of interest bearing balances due from banks – time is estimated using a discounted cash flow calculation that applies the rates currently offered on deposits of similar remaining maturities (Level 2). Held-to-maturity securities – Fair values for held-to-maturity securities equal quoted market prices, if available, such as for highly liquid government bonds (Level 1). If quoted market prices are not available, fair values are estimated based on quoted market prices of similar securities. For these securities, the Company obtains fair value measurements from an independent pricing service. 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 security’s terms and conditions, among other things (Level 2). In certain cases where Level 1 or Level 2 inputs are not available, securities are classified within Level 3 of the hierarchy. Loans – The fair value of loans is 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. Additional factors considered include the type of loan and related collateral, variable or fixed rate, classification status, remaining term, interest rate, historical delinquencies, loan to value ratios, current market rates and remaining loan balance. The loans were grouped together according to similar characteristics and were treated in the aggregate when applying various valuation techniques. The discount rates used for loans were based on current market rates for new originations of similar loans. Estimated credit losses were also factored into the projected cash flows of the loans (Level 3). Deposits – The fair value of demand deposits, savings accounts and money market deposits is the amount payable on demand at the reporting date (i.e., their carrying amount) (Level 2). The fair value of fixed-maturity time deposits is estimated using a discounted cash flow calculation that applies the rates currently offered for deposits of similar remaining maturities (Level 3). Federal Funds purchased, securities sold under agreement to repurchase and short-term debt – The carrying amount for Federal funds purchased, securities sold under agreement to repurchase and short-term debt are a reasonable estimate of fair value (Level 2). Other borrowings – For short-term instruments, the carrying amount is a reasonable estimate of fair value. For long-term debt, rates currently available to the Company for debt with similar terms and remaining maturities are used to estimate the fair value (Level 2). Subordinated debentures – The fair value of subordinated debentures is estimated using the rates that would be charged for subordinated debentures of similar remaining maturities (Level 2). Accrued interest receivable/payable – The carrying amounts of accrued interest approximated fair value (Level 2). Commitments to extend credit, letters of credit and lines of credit – The fair value of commitments is estimated using the fees currently charged to enter into similar agreements, taking into account the remaining terms of the agreements and the present creditworthiness of the counterparties. For fixed rate loan commitments, fair value also considers the difference between current levels of interest rates and the committed rates. The fair values of letters of credit and lines of credit are based on fees currently charged for similar agreements or on the estimated cost to terminate or otherwise settle the obligations with the counterparties at the reporting date. The fair value of a financial instrument is the current amount that would be exchanged between willing parties, other than in a forced liquidation. Fair value is best determined based upon quoted market prices. However, in many instances, there are no quoted market prices for the Company’s various financial instruments. In cases where quoted market prices are not available, fair values are based on estimates using present value or other valuation techniques. Those techniques are significantly affected by the assumptions used, including the discount rate and estimates of future cash flows. Accordingly, the fair value estimates may not be realized in an immediate settlement of the instrument. The estimated fair values, and related carrying amounts, of the Company’s financial instruments are as follows: Carrying Fair Value Measurements (In thousands) Amount Level 1 Level 2 Level 3 Total September 30, 2018 Financial assets: Cash and cash equivalents $ 513,804 $ 513,804 $ — $ — $ 513,804 Interest bearing balances due from banks - time 3,954 — 3,954 — 3,954 Held-to-maturity securities 323,306 — 322,838 — 322,838 Mortgage loans held for sale 48,195 — — 48,195 48,195 Interest receivable 51,509 — 51,509 — 51,509 Legacy loans, net 8,067,916 — — 7,996,273 7,996,273 Loans acquired, net 3,734,921 — — 3,701,755 3,701,755 Financial liabilities: Non-interest bearing transaction accounts 2,778,670 — 2,778,670 — 2,778,670 Interest bearing transaction accounts and savings deposits 6,776,330 — 6,776,330 — 6,776,330 Time deposits 2,533,506 — — 2,508,228 2,508,228 Federal funds purchased and securities sold under agreements to repurchase 109,213 — 109,213 — 109,213 Other borrowings 1,420,917 — 1,417,166 — 1,417,166 Subordinated notes and debentures 372,934 — 310,701 — 310,701 Interest payable 13,197 — 13,197 — 13,197 December 31, 2017 Financial assets: Cash and cash equivalents $ 598,042 $ 598,042 $ — $ — $ 598,042 Interest bearing balances due from banks - time 3,314 — 3,314 — 3,314 Held-to-maturity securities 368,058 — 373,298 — 373,298 Mortgage loans held for sale 24,038 — — 24,038 24,038 Interest receivable 43,528 — 43,528 — 43,528 Legacy loans, net 5,663,941 — — 5,646,505 5,646,505 Loans acquired, net 5,074,076 — — 5,058,455 5,058,455 Financial liabilities: Non-interest bearing transaction accounts 2,665,249 — 2,665,249 — 2,665,249 Interest bearing transaction accounts and savings deposits 6,494,896 — 6,494,896 — 6,494,896 Time deposits 1,932,730 — — 1,915,539 1,915,539 Federal funds purchased and securities sold under agreements to repurchase 122,444 — 122,444 — 122,444 Other borrowings 1,380,024 — 1,381,365 — 1,381,365 Subordinated debentures 140,565 — 136,474 — 136,474 Interest payable 4,564 — 4,564 — 4,564 The fair value of commitments to extend credit, letters of credit and lines of credit is not presented since management believes the fair value to be insignificant.

Preparation of Interim Financ_2

Preparation of Interim Financial Statements (Policies)	9 Months Ended
	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited consolidated financial statements have been prepared based upon Securities and Exchange Commission (“SEC”) rules that permit reduced disclosures for interim periods. Certain information and footnote disclosures have been condensed or omitted in accordance with those rules and regulations. The accompanying consolidated balance sheet as of December 31, 2017 , was derived from audited financial statements. In the opinion of management, these financial statements reflect all adjustments that are necessary for a fair presentation of interim results of operations, including normal recurring accruals. Significant intercompany accounts and transactions have been eliminated in consolidation. The results for the interim periods are not necessarily indicative of results for the full year. For a more complete discussion of significant accounting policies and certain other information, this report should be read in conjunction with the consolidated financial statements and accompanying notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 , which was filed with the SEC on February 28, 2018 . The preparation of financial statements, in accordance with accounting principles generally accepted in the United States (“US GAAP”), requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, income items and expenses and disclosure of contingent assets and liabilities. The estimates and assumptions used in the accompanying consolidated financial statements are based upon management’s evaluation of the relevant facts and circumstances as of the date of the consolidated financial statements and actual results may differ from these estimates. Such estimates include, but are not limited to, the Company’s allowance for loan losses.
Reclassification	Certain prior year amounts have been reclassified to conform to the current year financial statement presentation. These changes and reclassifications did not impact previously reported net income or comprehensive income.
Recently Adopted and Issued Accounting Standards	Recently Adopted Accounting Standards Reporting Comprehensive Income – In February 2018, the Financial Accounting Standards Board (“FASB”) issued Accounting Standard Update (“ASU”) No. 2018-02, Income Statement-Reporting Comprehensive Income (Topic 220) (“ASU 2018-02”), that allows a reclassification from accumulated other comprehensive income (“AOCI”) to retained earnings for stranded tax effects resulting from the tax reform legislation signed into law in December 2017 (“2017 Act”). Current US GAAP requires the remeasurement of deferred tax assets and liabilities as a result of a change in tax laws or rates to be presented in net income from continuing operations. Consequently, the original deferred tax amount recorded through AOCI at the old rate will remain in AOCI despite the fact that its related deferred tax asset/liability will be reduced through continuing operations to reflect the new rate, resulting in “stranded” tax effects in AOCI. ASU 2018-02 requires a reclassification from AOCI to retained earnings for those stranded tax effects resulting from the newly enacted federal corporate income tax rate. The amount of reclassification would be the difference between 1) the amount initially charged or credited directly to other comprehensive income at the previous enacted federal corporate income tax rate that remains in AOCI and 2) the amount that would have been charged or credited using the newly enacted federal corporate income tax rate, excluding the effect of any valuation allowance previously charged to income from continuing operations. The effective date is for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. As permitted, the Company elected to early adopt the provisions of ASU 2018-02 during the fourth quarter 2017 , which resulted in a reclassification from AOCI to retained earnings in the amount of $3.0 million related to the change in federal corporate tax rate. Stock Compensation: Scope of Modification Accounting – In May 2017, the FASB issued ASU No. 2017-09, Compensation – Stock Compensation (Topic 718): Scope of Modification Accounting (“ASU 2017-09”), that provides clarity and reduces both (1) diversity in practice and (2) cost and complexity when applying the guidance in Topic 718, to a change to the terms or conditions of a share-based payment award. An entity may change the terms or conditions of a share-based payment award for many different reasons, and the nature and effect of the change can vary significantly. The guidance clarifies which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting and the guidance should be applied prospectively to an award modified on or after the adoption date. ASU 2017-09 is effective for interim and annual reporting periods beginning after December 15, 2017, with early adoption permitted. Currently, the Company has not modified any existing awards nor has any plans to do so, therefore the adoption of ASU 2017-09 has not had a material effect on the Company’s results of operations, financial position or disclosures. Premium Amortization on Purchased Callable Debt Securities – In March 2017, the FASB issued ASU No. 2017-08, Receivables – Nonrefundable Fees and Other Costs (Topic 310-20): Premium Amortization on Purchased Callable Debt Securities (“ASU 2017-08”), that amends the amortization period for certain purchased callable debt securities held at a premium. Specifically, the amendments shorten the amortization period by requiring that the premium be amortized to the earliest call date. Under previous US GAAP, entities generally amortize the premium as an adjustment of yield over the contractual life of the instrument. The amendments do not require an accounting change for securities held at a discount; the discount continues to be amortized to maturity. The effective date is for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. As permitted, the Company elected to early adopt the provisions of ASU 2017-08 during the first quarter 2017. The adoption of this standard did not have a material effect on the Company’s results of operations, financial position or disclosures. Statement of Cash Flows – In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments (“ASU 2016-15”), designed to address the diversity in how certain cash receipts and cash payments are presented and classified in the statement of cash flows, including debt prepayment or extinguishment costs, settlement of certain debt instruments, contingent consideration payments made after a business combination, proceeds from the settlement of insurance claims, and distributions received from equity method investees. The amendments also provide guidance on when an entity should separate or aggregate cash flows based on the predominance principle. The effective date is for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. The new standard is required to be applied retrospectively, but may be applied prospectively if retrospective application would be impracticable. The adoption of 2016-15 did not have a material impact on the Company’s results of operations, financial position or disclosures since the amendment applies to the classification of cash flows. The adoption did not have a material impact on the consolidated statement of cash flows. Financial Assets and Financial Liabilities – In January 2016, the FASB issued ASU No. 2016-01, Financial Instruments – Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities (“ASU 2016-01”), that makes changes primarily affecting the accounting for equity investments, financial liabilities under the fair value option, and the presentation and disclosure requirements for financial instruments. In addition, the FASB clarified guidance related to the valuation allowance assessment when recognizing deferred tax assets resulting from unrealized losses on available-for-sale debt securities. In February 2018, the FASB issued 2018-03 that clarified certain guidance and contained narrow scope amendments. The effective date is for fiscal periods beginning after December 15, 2017, including interim periods within those fiscal years. ASU 2016-01 did not have a material impact on the Company’s results of operations or financial position. However, this new guidance requires the disclosed estimated fair value of the Company’s loan portfolio to be based on an exit price calculation, which considers liquidity, credit and nonperformance risk of its loans. The adoption of 2016-01 did not have a material impact on the Company’s fair value disclosures. Revenue Recognition – In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASU 2014-09”), that outlines a single comprehensive revenue recognition model for entities to follow in accounting for revenue from contracts with customers. The core principle of this revenue model is that an entity should recognize revenue for the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled to receive for those goods or services. In July 2015, the FASB issued ASU No. 2015-14, deferring the effective date to annual and interim periods beginning after December 15, 2017. The guidance does not apply to revenue associated with financial instruments, including loans and securities that are accounted for under other US GAAP, which comprises a significant portion of the Company’s revenue stream. However, the updated guidance affects the revenue recognition pattern for certain revenue streams, including service charges on deposit accounts, gains/losses on sale of other real estate owned (“OREO”), and trust income. The adoption of this standard did not have a material effect on the Company’s results of operations, financial position or disclosures. See below “Revenue from Contracts with Customers” for additional information. Recently Issued Accounting Standards Cloud Computing Arrangements – In August 2018, the FASB issued ASU No. 2018-15, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That is a Service Contract (“ASU 2018-15”), that amends the definition of a hosting arrangement and requires a customer in a hosting arrangement that is a service contract to capitalize certain implementation costs as if the arrangement was an internal-use software project. The internal-use software guidance states that only qualifying costs incurred during the application development stage can be capitalized. The effective date is for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years, with early adoption permitted. Entities have the option to apply the guidance prospectively to all implementation costs incurred after the date of adoption or retrospectively in accordance with the applicable guidance. At the time of adoption, entities will be required to disclose the nature of its hosting arrangements that are service contracts and provide disclosures as if the deferred implementation costs were a separate, major depreciable asset class. The Company is beginning to evaluate its cloud computing arrangements and has not yet determined how it will apply or the impact of this new standard. Fair Value Measurement Disclosures – In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement (“ASU 2018-13”), that eliminates, amends and adds disclosure requirements for fair value measurements. These amendments are part of FASB’s disclosure review project and they are expected to reduce costs for preparers while providing more decision-useful information for financial statement users. The eliminated disclosure requirements include the 1) the amount of, and reasons for, transfers between Level 1 and Level 2 of the fair value hierarchy; 2) the policy of timing of transfers between levels of the fair value hierarchy; and 3) the valuation processes for Level 3 fair value measurements. Among other modifications, the amended disclosure requirements remove the term “at a minimum” from the phrase “an entity shall disclose at a minimum” to promote the appropriate exercise of discretion by entities and clarifies that the measurement uncertainty disclosure is to communicate information about the uncertainty in measurement as of the reporting date. Under the new disclosure requirements, entities must disclose the changes in unrealized gains or losses included in other comprehensive income for recurring Level 3 fair value measurements held at the end of the reporting period and the range and weighted average used to develop significant unobservable inputs for Level 3 fair value measurements. ASU 2018-13 is effective for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years, with early adoption permitted. The Company is currently evaluating the impact this standard will have on its fair value disclosures. Derivatives and Hedging: Targeted Improvements – In August 2017, the FASB issued ASU No. 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities (“ASU 2017-12”), that changes both the designation and measurement guidance for qualifying hedging relationships and the presentation of hedge results in order to better align a company’s risk management activities and financial reporting for hedging relationships. In summary, this amendment 1) expands the types of transactions eligible for hedge accounting; 2) eliminates the separate measurement and presentation of hedge ineffectiveness; 3) simplifies the requirements around the assessment of hedge effectiveness; 4) provides companies more time to finalize hedge documentation; and 5) enhances presentation and disclosure requirements. The effective date is for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years, with early adoption permitted. All transition requirements and elections should be applied to existing hedging relationships on the date of adoption and the effects should be reflected as of the beginning of the fiscal year of adoption. The Company has evaluated the impact this standard will have on its results of operations, financial position or disclosures, and it is not expected to have a material impact. Goodwill Impairment – In January 2017, the FASB issued ASU No. 2017-04, Intangibles – Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment (“ASU 2017-04”), that eliminates Step 2 from the goodwill impairment test which required entities to compare the implied fair value of goodwill to its carrying amount. Under the amendments, the goodwill impairment will be measured as the excess of the reporting unit’s carrying amount over its fair value. An impairment charge should be recognized for the amount by which the carrying amount exceeds the reporting unit’s fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. The effective date is for fiscal years beginning after December 15, 2019, with early adoption permitted for interim or annual impairment tests beginning in 2017. ASU 2017-04 is not expected to have a material effect on the Company’s results of operations, financial position or disclosures. Credit Losses on Financial Instruments – In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”), which requires earlier measurement of credit losses, expands the range of information considered in determining expected credit losses and enhances disclosures. The main objective of ASU 2016-13 is to provide financial statement users with more decision-useful information about the expected credit losses on financial instruments and other commitments to extend credit held by a reporting entity at each reporting date. The amendments replace the incurred loss impairment methodology in current US GAAP with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. The effective date for these amendments is for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. The Company has formed a cross functional team that continues to assess its data and system needs and evaluate the potential impact of adopting the new guidance. The Company anticipates a significant change in the processes and procedures to calculate the loan losses, including changes in assumptions and estimates to consider expected credit losses over the life of the loan versus the current accounting practice that utilizes the incurred loss model. The Company expects to recognize a one-time cumulative effect adjustment to the allowance for loan losses as of the beginning of the first reporting period in which the new standard is effective, but has not yet determined the magnitude of any such one-time adjustment or the overall impact on its results of operations, financial position or disclosures. However, the Company is continuing its efforts in developing processes and procedures to ensure it is fully compliant at the required adoption date. Among other things, the Company continues to gather data and develop forecast models for asset quality, loan balances, and portfolio net charge-offs and has chosen a software vendor in preparation for the implementation of this standard. Model development and testing is projected to take place during the fourth quarter 2018 in anticipation of developing a range of potential impact as well as allowing parallel model calculations through 2019 up to the date of adoption. Leases – In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) (“ASU 2016-02”), that establishes the principles to report transparent and economically neutral information about the assets and liabilities that arise from leases. The new guidance results in a more consistent representation of the rights and obligations arising from leases by requiring lessees to recognize the lease asset and lease liabilities that arise from leases in the statement of financial position and to disclose qualitative and quantitative information about lease transactions, such as information about variable lease payments and options to renew and terminate leases. The effective date is for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. ASU 2016-02 requires entities to adopt the new lease standard using a modified retrospective transition method, meaning an entity initially applies the new lease standard at the beginning of the earliest period presented in the financial statements. Due to complexities associated with using this method, in July 2018, the FASB issued ASU No. 2018-11, Leases (Topic 842): Targeted Improvements , to relieve entities of the requirement to present prior comparative years’ results when they adopt the new lease standard and giving entities the option to recognize the cumulative effect of applying the new standard as an adjustment to the opening balance of retained earnings. The Company has substantially completed the identification of all of its leases that will need to be measured and reported in the statement of financial position and is currently working with its selected lease implementation vendor to set up and test the accounting for the lease contracts on the lease administrative system. Based upon leases that were outstanding as of September 30, 2018 , the Company does not expect the new standard to have a material impact on its results of operations, but anticipates increases in its assets and liabilities. Decisions to repurchase, modify or renew leases prior to the implementation date will impact the level of materiality. There have been no other significant changes to the Company’s accounting policies from the 2017 Form 10-K. Presently, the Company is not aware of any other changes to the Accounting Standards Codification that will have a material impact on its present or future financial position or results of operations.
Revenue from Contracts with Customers	Revenue from Contracts with Customers Accounting Standards Codification (“ASC”) Topic 606, Revenue from Contracts with Customers , applies to all contracts with customers to provide goods or services in the ordinary course of business. However, Topic 606 specifically does not apply to revenue related to financial instruments, guarantees, insurance contracts, leases, or nonmonetary exchanges. Given these scope exceptions, interest income recognition and measurement related to loans and investments securities, the Company’s two largest sources of revenue, are not accounted for under Topic 606. Also, the Company does not use Topic 606 to account for gains or losses on its investments in securities, loans, and derivatives due to the scope exceptions. Certain revenue streams, such as service charges on deposit accounts, gains or losses on the sale of OREO, and trust income, fall under the scope of Topic 606 and the Company must recognize revenue at an amount that reflects the consideration to which the Company expects to be entitled in exchange for transferring goods or services to a customer. Topic 606 is applied using five steps: 1) identify the contract with the customer, 2) identify the performance obligations in the contract, 3) determine the transaction price, 4) allocate the transaction price to the performance obligations in the contract, and 5) recognize revenue when (or as) the entity satisfies a performance obligation. The Company has evaluated the nature of all contracts with customers that fall under the scope of Topic 606 and determined that further disaggregation of revenue from contracts with customers into categories was not necessary. There has not been significant revenue recognized in the current reporting periods resulting from performance obligations satisfied in previous periods. In addition, there has not been a significant change in timing of revenues received from customers. A description of performance obligations for each type of contract with customers is as follows: Service charges on deposit accounts – The Company’s primary source of funding comes from deposit accounts with its customers. Customers pay certain fees to access their cash on deposit including, but not limited to, non-transactional fees such as account maintenance, dormancy or statement rendering fees, and certain transaction-based fees such as ATM, wire transfer, overdraft or returned check fees. The Company generally satisfies its performance obligations as services are rendered. The transaction prices are fixed, and are charged either on a periodic basis or based on activity. Sale of OREO – In the normal course of business, the Company will enter into contracts with customers to sell OREO, which has generally been foreclosed upon by the Company. The Company generally satisfies its performance obligation upon conveyance of property from the Company to the customer, generally by way of an executed agreement. The transaction price is fixed, and on occasion the Company will finance a portion of the proceeds the customers uses to purchase the property. These properties are generally sold without recourse or warranty. Trust Income – The Company enters into contracts with its customers to manage assets for investment, and/or transact on their accounts. The Company generally satisfies its performance obligations as services are rendered. The management fee is a fixed percentage-based fee calculated upon the average balance of assets under management and is charged to customers on a monthly basis.
Acquisition Accounting, Loans Acquired	Acquisition Accounting, Loans Acquired The Company accounts for its acquisitions under ASC Topic 805, Business Combinations , which requires the use of the acquisition method of accounting. All identifiable assets acquired, including loans, are recorded at fair value. No allowance for loan losses related to the loans acquired is recorded on the acquisition date as the fair value of the loans acquired incorporates assumptions regarding credit risk. Loans acquired are recorded at fair value in accordance with the fair value methodology prescribed in ASC Topic 820, Fair Value Measurement . The fair value estimates associated with the loans include estimates related to expected prepayments and the amount and timing of undiscounted expected principal, interest and other cash flows. The Company evaluates non-impaired loans acquired in accordance with the provisions of ASC Topic 310-20, Nonrefundable Fees and Other Costs . The fair value discount on these loans is accreted into interest income over the weighted average life of the loans using a constant yield method. The Company evaluates purchased impaired loans in accordance with the provisions of ASC Topic 310-30, Loans and Debt Securities Acquired with Deteriorated Credit Quality . Purchased loans are considered impaired if there is evidence of credit deterioration since origination and if it is probable that not all contractually required payments will be collected. For impaired loans accounted for under ASC Topic 310-30, the Company continues to estimate cash flows expected to be collected on purchased credit impaired loans. The Company evaluates, at each balance sheet date, whether the present value of the purchased credit impaired loans determined using the effective interest rates has decreased significantly and if so, recognize a provision for loan loss in the consolidated statement of income. For any significant increases in cash flows expected to be collected, the Company adjusts the amount of accretable yield recognized on a prospective basis over the remaining life of the purchased credit impaired loan. For further discussion of acquisition and loan accounting, see Note 2, Acquisitions, and Note 6, Loans Acquired.
Income Taxes	The Company follows ASC Topic 740, Income Taxes , which prescribes a recognition threshold and a measurement attribute for the financial statement recognition and measurement of a tax position taken or expected to be taken in a tax return. Benefits from tax positions should be recognized in the financial statements only when it is more likely than not that the tax position will be sustained upon examination by the appropriate taxing authority that would have full knowledge of all relevant information. A tax position that meets the more-likely-than-not recognition threshold is measured at the largest amount of benefit that is greater than fifty percent likely of being realized upon ultimate settlement. Tax positions that previously failed to meet the more-likely-than-not recognition threshold should be recognized in the first subsequent financial reporting period in which that threshold is met. Previously recognized tax positions that no longer meet the more-likely-than-not recognition threshold should be derecognized in the first subsequent financial reporting period in which that threshold is no longer met. ASC Topic 740 also provides guidance on the accounting for and disclosure of unrecognized tax benefits, interest and penalties. The Company has no history of expiring net operating loss carryforwards and is projecting significant pre-tax and financial taxable income in 2018 and in future years. The Company expects to fully realize its deferred tax assets in the future. Income tax expense was lower in the third quarter due largely to discrete tax benefits related to tax accounting for a cost segregation study, excess tax benefits related to restricted stock and a state tax deferred tax asset (“DTA”) adjustment. The purpose of the cost segregation study was to analyze the costs included in various projects and recognize the benefit of recording tax depreciation in 2017 when the federal rate was higher. The purpose of the state DTA adjustment was due to an analysis of projected state apportionment after the 2017 acquisitions of First South Bank, Bank SNB and Southwest Bank were merged into Simmons Bank in 2018. On December 22, 2017, the President signed tax reform legislation (the “2017 Act”) which includes a broad range of tax reform proposals affecting businesses, including corporate tax rates, business deductions, and international tax provisions. The 2017 Act reduces the corporate tax rate from 35% to 21% for tax years beginning after December 31, 2017 . Under US GAAP, deferred tax assets and liabilities are required to be measured at the enacted tax rate expected to apply when temporary differences are to be realized or settled and the effect of a change in tax law is recorded discretely as a component of the income tax provision related to continuing operations in the period of enactment. As a result, the Company was required to remeasure its deferred taxes as of December 22, 2017 based upon the new 21% tax rate and the change was recorded in the 2017 income tax provision in the fourth quarter. On December 22, 2017, the SEC issued Staff Accounting Bulletin No. 118 (“SAB 118”), which provides guidance on accounting for the tax effects of the 2017 Act. SAB 118 provides a measurement period that should not extend beyond one year from the 2017 Act enactment date for companies to complete the accounting under ASC 740, Income Taxes .

Acquisitions (Tables)

Acquisitions (Tables)	9 Months Ended
	Sep. 30, 2018
Business Combinations [Abstract]
Fair Value of Assets Acquired and Liabilities Assumed	A summary, at fair value, of the assets acquired and liabilities assumed in the Hardeman transaction, as of the acquisition date, is as follows: (In thousands) Acquired from Hardeman Fair Value Adjustments Fair Value Assets Acquired Cash and due from banks $ 8,001 $ — $ 8,001 Interest bearing balances due from banks - time 1,984 — 1,984 Investment securities 170,654 (285 ) 170,369 Loans acquired 257,641 (5,992 ) 251,649 Allowance for loan losses (2,382 ) 2,382 — Foreclosed assets 1,083 (452 ) 631 Premises and equipment 9,905 1,258 11,163 Bank owned life insurance 7,819 — 7,819 Goodwill 11,485 (11,485 ) — Core deposit intangible — 7,840 7,840 Other intangibles — 830 830 Other assets 2,639 (1 ) 2,638 Total assets acquired $ 468,829 $ (5,905 ) $ 462,924 Liabilities Assumed Deposits: Non-interest bearing transaction accounts $ 76,555 $ — $ 76,555 Interest bearing transaction accounts and savings deposits 214,872 — 214,872 Time deposits 97,917 (368 ) 97,549 Total deposits 389,344 (368 ) 388,976 Securities sold under agreement to repurchase 17,163 — 17,163 Other borrowings 3,000 — 3,000 Subordinated debentures 6,702 — 6,702 Accrued interest and other liabilities 1,891 1,924 3,815 Total liabilities assumed 418,100 1,556 419,656 Equity 50,729 (50,729 ) — Total equity assumed 50,729 (50,729 ) — Total liabilities and equity assumed $ 468,829 $ (49,173 ) $ 419,656 Net assets acquired 43,268 Purchase price 72,639 Goodwill $ 29,371 A summary, at fair value, of the assets acquired and liabilities assumed in the First Texas transaction, as of the acquisition date, is as follows: (In thousands) Acquired from First Texas Fair Value Adjustments Fair Value Assets Acquired Cash and due from banks $ 59,277 $ — $ 59,277 Investment securities 81,114 (596 ) 80,518 Loans acquired 2,246,212 (37,834 ) 2,208,378 Allowance for loan losses (20,864 ) 20,664 (200 ) Premises and equipment 24,864 10,123 34,987 Bank owned life insurance 7,190 — 7,190 Goodwill 37,227 (37,227 ) — Core deposit intangible — 7,328 7,328 Other assets 18,263 11,485 29,748 Total assets acquired $ 2,453,283 $ (26,057 ) $ 2,427,226 Liabilities Assumed Deposits: Non-interest bearing transaction accounts $ 74,410 $ — $ 74,410 Interest bearing transaction accounts and savings deposits 1,683,298 — 1,683,298 Time deposits 124,233 (283 ) 123,950 Total deposits 1,881,941 (283 ) 1,881,658 Securities sold under agreement to repurchase 50,000 — 50,000 Other borrowings 235,000 — 235,000 Subordinated debentures 30,323 589 30,912 Accrued interest and other liabilities 11,727 1,669 13,396 Total liabilities assumed 2,208,991 1,975 2,210,966 Equity 244,292 (244,292 ) — Total equity assumed 244,292 (244,292 ) — Total liabilities and equity assumed $ 2,453,283 $ (242,317 ) $ 2,210,966 Net assets acquired 216,260 Purchase price 457,103 Goodwill $ 240,843 A summary, at fair value, of the assets acquired and liabilities assumed in the OKSB transaction, as of the acquisition date, is as follows: (In thousands) Acquired from OKSB Fair Value Adjustments Fair Value Assets Acquired Cash and due from banks $ 79,517 $ — $ 79,517 Investment securities 485,468 (1,295 ) 484,173 Loans acquired 2,039,524 (43,071 ) 1,996,453 Allowance for loan losses (26,957 ) 26,957 — Foreclosed assets 6,284 (1,127 ) 5,157 Premises and equipment 21,210 5,457 26,667 Bank owned life insurance 28,704 — 28,704 Goodwill 13,545 (13,545 ) — Core deposit intangible 1,933 40,191 42,124 Other intangibles 3,806 — 3,806 Other assets 33,455 (9,141 ) 24,314 Total assets acquired $ 2,686,489 $ 4,426 $ 2,690,915 Liabilities Assumed Deposits: Non-interest bearing transaction accounts $ 485,971 $ — $ 485,971 Interest bearing transaction accounts and savings deposits 869,252 — 869,252 Time deposits 613,345 (2,213 ) 611,132 Total deposits 1,968,568 (2,213 ) 1,966,355 Securities sold under agreement to repurchase 11,256 — 11,256 Other borrowings 347,000 — 347,000 Subordinated debentures 46,393 — 46,393 Accrued interest and other liabilities 17,440 5,364 22,804 Total liabilities assumed 2,390,657 3,151 2,393,808 Equity 295,832 (295,832 ) — Total equity assumed 295,832 (295,832 ) — Total liabilities and equity assumed $ 2,686,489 $ (292,681 ) $ 2,393,808 Net assets acquired 297,107 Purchase price 526,251 Goodwill $ 229,144
Pro Forma Information	The unaudited pro forma information below for the years ended December 31, 2017 and 2016 gives effect to the OKSB and First Texas acquisitions as if the acquisitions had occurred on January 1, 2016. Pro forma earnings for the year ended December 31, 2017 were adjusted to exclude $9.4 million of acquisition-related costs, net of tax, incurred by Simmons during 2017 . The pro forma financial information is not necessarily indicative of the results of operations if the acquisitions had been effective as of this date. (In thousands, except per share data) 2017 2016 Revenue (1) $ 654,358 $ 620,461 Net income $ 130,947 $ 136,199 Diluted earnings per share $ 1.43 $ 1.52 _________________________________________ (1) Net interest income plus non-interest income.

Investment Securities (Tables)

Investment Securities (Tables)	9 Months Ended
	Sep. 30, 2018
Investments, Debt and Equity Securities [Abstract]
Investment Securities	The amortized cost and fair value of investment securities that are classified as held-to-maturity (“HTM”) and available-for-sale (“AFS”) are as follows: September 30, 2018 December 31, 2017 (In thousands) Amortized Cost Gross Unrealized Gains Gross Unrealized (Losses) Estimated Fair Value Amortized Cost Gross Unrealized Gains Gross Unrealized (Losses) Estimated Fair Value Held-to-Maturity U.S. Government agencies $ 34,983 $ — $ (113 ) $ 34,870 $ 46,945 $ 7 $ (228 ) $ 46,724 Mortgage-backed securities 13,933 — (698 ) 13,235 16,132 8 (287 ) 15,853 State and political subdivisions 272,396 2,369 (2,020 ) 272,745 301,491 5,962 (222 ) 307,231 Other securities 1,994 — (6 ) 1,988 3,490 — — 3,490 Total HTM $ 323,306 $ 2,369 $ (2,837 ) $ 322,838 $ 368,058 $ 5,977 $ (737 ) $ 373,298 Available-for-Sale U.S. Government agencies $ 145,808 $ — $ (4,348 ) $ 141,460 $ 141,559 $ 116 $ (1,951 ) $ 139,724 Mortgage-backed securities 1,471,687 127 (52,188 ) 1,419,626 1,208,017 246 (20,946 ) 1,187,317 State and political subdivisions 291,731 12 (9,304 ) 282,439 144,642 532 (2,009 ) 143,165 Other securities 151,572 2,718 (1 ) 154,289 118,106 1,206 (1 ) 119,311 Total AFS $ 2,060,798 $ 2,857 $ (65,841 ) $ 1,997,814 $ 1,612,324 $ 2,100 $ (24,907 ) $ 1,589,517
Gross Unrealized Losses and Fair Value of Investments	The following table shows the gross unrealized losses and fair value of the Company’s investments with unrealized losses, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position at September 30, 2018 : Less Than 12 Months 12 Months or More Total (In thousands) Estimated Fair Value Gross Unrealized Losses Estimated Fair Value Gross Unrealized Losses Estimated Fair Value Gross Unrealized Losses Held-to-Maturity U.S. Government agencies $ 3,972 $ (11 ) $ 30,898 $ (102 ) $ 34,870 $ (113 ) Mortgage-backed securities 3,830 (106 ) 9,404 (592 ) 13,234 (698 ) State and political subdivisions 123,574 (1,682 ) 8,539 (338 ) 132,113 (2,020 ) Other securities 1,166 (6 ) — — 1,166 (6 ) Total HTM $ 132,542 $ (1,805 ) $ 48,841 $ (1,032 ) $ 181,383 $ (2,837 ) Available-for-Sale U.S. Government agencies $ 56,785 $ (689 ) $ 84,675 $ (3,659 ) $ 141,460 $ (4,348 ) Mortgage-backed securities 586,783 (11,469 ) 808,969 (40,719 ) 1,395,752 (52,188 ) State and political subdivisions 182,036 (4,510 ) 95,076 (4,794 ) 277,112 (9,304 ) Other securities — — 99 (1 ) 99 (1 ) Total AFS $ 825,604 $ (16,668 ) $ 988,819 $ (49,173 ) $ 1,814,423 $ (65,841 )
Income Earned on Securities	Income earned on securities for the three and nine months ended September 30, 2018 and 2017 , is as follows: Three Months Ended September 30, Nine Months Ended September 30, (In thousands) 2018 2017 2018 2017 Taxable: Held-to-maturity $ 528 $ 625 $ 1,641 $ 1,922 Available-for-sale 10,364 5,949 29,614 18,003 Non-taxable: Held-to-maturity 1,828 2,135 5,661 6,635 Available-for-sale 1,920 509 4,642 2,099 Total $ 14,640 $ 9,218 $ 41,558 $ 28,659
Amortized Cost and Estimated Fair Value by Maturity of Securities	The amortized cost and estimated fair value by maturity of securities are shown in the following table. Securities are classified according to their contractual maturities without consideration of principal amortization, potential prepayments or call options. Accordingly, actual maturities may differ from contractual maturities. Held-to-Maturity Available-for-Sale (In thousands) Amortized Cost Fair Value Amortized Cost Fair Value One year or less $ 50,503 $ 50,366 $ 120 $ 119 After one through five years 60,633 60,313 35,703 34,714 After five through ten years 91,862 91,364 22,485 21,698 After ten years 106,375 107,560 379,331 367,466 Securities not due on a single maturity date 13,933 13,235 1,471,687 1,419,626 Other securities (no maturity) — — 151,472 154,191 Total $ 323,306 $ 322,838 $ 2,060,798 $ 1,997,814

Loans and Allowance for Loan _2

Loans and Allowance for Loan Losses (Tables)	9 Months Ended
	Sep. 30, 2018
Receivables [Abstract]
Loan Portfolio	The various categories of loans are summarized as follows: (In thousands) September 30, 2018 December 31, 2017 Consumer: Credit cards $ 182,137 $ 185,422 Other consumer 259,581 280,094 Total consumer 441,718 465,516 Real Estate: Construction 1,229,888 614,155 Single family residential 1,401,991 1,094,633 Other commercial 3,077,188 2,530,824 Total real estate 5,709,067 4,239,612 Commercial: Commercial 1,608,342 825,217 Agricultural 218,778 148,302 Total commercial 1,827,120 973,519 Other 145,369 26,962 Loans 8,123,274 5,705,609 Loans acquired, net of discount and allowance (1) 3,734,921 5,074,076 Total loans $ 11,858,195 $ 10,779,685 _____________________________ (1) See Note 6, Loans Acquired, for segregation of loans acquired by loan class. The impact of these adjustments on the Company’s financial results for the three and nine months ended September 30, 2018 and 2017 is shown below: Three Months Ended Nine Months Ended (In thousands) 2018 2017 2018 2017 Impact on net interest income and pre-tax income $ 629 $ 23 $ 1,105 $ 2,596 Impact, net of taxes $ 464 $ 14 $ 814 $ 1,578 The following table reflects the carrying value of all loans acquired as of September 30, 2018 and December 31, 2017 : Loans Acquired (In thousands) September 30, 2018 December 31, 2017 Consumer: Other consumer $ 21,278 $ 51,467 Real estate: Construction 467,895 637,032 Single family residential 606,866 793,228 Other commercial 2,040,189 2,387,777 Total real estate 3,114,950 3,818,037 Commercial: Commercial 596,641 995,587 Agricultural 2,052 66,576 Total commercial 598,693 1,062,163 Other — 142,409 Total loans acquired (1) $ 3,734,921 $ 5,074,076 _____________________________________________________________________________________ (1) Loans acquired are reported net of a $1,345,000 and $418,000 allowance at September 30, 2018 and December 31, 2017 , respectively. Changes in the carrying amount of the accretable yield for all purchased impaired loans were as follows for the three and nine months ended September 30, 2018 and 2017 . Three Months Ended Nine Months Ended (In thousands) Accretable Yield Carrying Amount of Loans Accretable Yield Carrying Amount of Loans Beginning balance $ 1,382 $ 13,995 $ 620 $ 17,116 Additions — — — — Accretable yield adjustments 717 — 1,895 — Accretion (635 ) 635 (1,051 ) 1,051 Payments and other reductions, net — (9,664 ) — (13,201 ) Balance, ending $ 1,464 $ 4,966 $ 1,464 $ 4,966 Three Months Ended Nine Months Ended (In thousands) Accretable Yield Carrying Amount of Loans Accretable Yield Carrying Amount of Loans Beginning balance $ 766 $ 8,448 $ 1,655 $ 17,802 Additions — — — 2,388 Accretable yield adjustments 52 — 2,698 — Accretion (408 ) 408 (3,943 ) 3,943 Payments and other reductions, net — (980 ) — (16,257 ) Balance, ending $ 410 $ 7,876 $ 410 $ 7,876
Nonaccrual Loans	Nonaccrual loans, excluding loans acquired, segregated by class of loans, are as follows: (In thousands) September 30, 2018 December 31, 2017 Consumer: Credit cards $ 328 $ 170 Other consumer 3,317 4,605 Total consumer 3,645 4,775 Real estate: Construction 1,289 2,242 Single family residential 11,508 13,431 Other commercial 9,639 16,054 Total real estate 22,436 31,727 Commercial: Commercial 11,932 6,980 Agricultural 2,492 2,160 Total commercial 14,424 9,140 Total $ 40,505 $ 45,642 Nonaccrual loans acquired, excluding purchased credit impaired loans accounted for under ASC Topic 310-30, segregated by class of loans, are as follows (see Note 5, Loans and Allowance for Loan Losses, for discussion of nonaccrual loans): (In thousands) September 30, 2018 December 31, 2017 Consumer: Other consumer $ 293 $ 334 Real estate: Construction 279 1,767 Single family residential 9,053 12,151 Other commercial 1,354 7,401 Total real estate 10,686 21,319 Commercial: Commercial 4,964 1,748 Agricultural 38 84 Total commercial 5,002 1,832 Total $ 15,981 $ 23,485
Past Due Loans	An age analysis of past due loans, excluding loans acquired, segregated by class of loans, is as follows: (In thousands) Gross 30-89 Days Past Due 90 Days or More Past Due Total Past Due Current Total Loans 90 Days Past Due & Accruing September 30, 2018 Consumer: Credit cards $ 777 $ 517 $ 1,294 $ 180,843 $ 182,137 $ 188 Other consumer 3,341 1,921 5,262 254,319 259,581 1 Total consumer 4,118 2,438 6,556 435,162 441,718 189 Real estate: Construction 1,033 397 1,430 1,228,458 1,229,888 — Single family residential 5,180 4,212 9,392 1,392,599 1,401,991 92 Other commercial 4,555 4,152 8,707 3,068,481 3,077,188 — Total real estate 10,768 8,761 19,529 5,689,538 5,709,067 92 Commercial: Commercial 4,568 5,873 10,441 1,597,901 1,608,342 — Agricultural 128 2,253 2,381 216,397 218,778 — Total commercial 4,696 8,126 12,822 1,814,298 1,827,120 — Other — — — 145,369 145,369 — Total $ 19,582 $ 19,325 $ 38,907 $ 8,084,367 $ 8,123,274 $ 281 December 31, 2017 Consumer: Credit cards $ 707 $ 672 $ 1,379 $ 184,043 $ 185,422 $ 332 Other consumer 5,009 3,298 8,307 271,787 280,094 10 Total consumer 5,716 3,970 9,686 455,830 465,516 342 Real estate: Construction 411 1,210 1,621 612,534 614,155 — Single family residential 8,071 6,460 14,531 1,080,102 1,094,633 1 Other commercial 2,388 8,031 10,419 2,520,405 2,530,824 — Total real estate 10,870 15,701 26,571 4,213,041 4,239,612 1 Commercial: Commercial 1,523 6,125 7,648 817,569 825,217 — Agricultural 50 2,120 2,170 146,132 148,302 — Total commercial 1,573 8,245 9,818 963,701 973,519 — Other — — — 26,962 26,962 — Total $ 18,159 $ 27,916 $ 46,075 $ 5,659,534 $ 5,705,609 $ 343 An age analysis of past due loans acquired segregated by class of loans, is as follows (see Note 5, Loans and Allowance for Loan Losses, for discussion of past due loans): (In thousands) Gross 30-89 Days Past Due 90 Days or More Past Due Total Past Due Current Total Loans 90 Days Past Due & Accruing September 30, 2018 Consumer: Other consumer $ 213 $ 214 $ 427 $ 20,851 $ 21,278 $ — Real estate: Construction 117 207 324 467,571 467,895 — Single family residential 2,459 5,948 8,407 598,459 606,866 1 Other commercial 2,491 4,157 6,648 2,033,541 2,040,189 — Total real estate 5,067 10,312 15,379 3,099,571 3,114,950 1 Commercial: Commercial 1,471 4,020 5,491 591,150 596,641 — Agricultural 27 5 32 2,020 2,052 — Total commercial 1,498 4,025 5,523 593,170 598,693 — Total $ 6,778 $ 14,551 $ 21,329 $ 3,713,592 $ 3,734,921 $ 1 December 31, 2017 Consumer: Other consumer $ 889 $ 260 $ 1,149 $ 50,318 $ 51,467 $ 108 Real estate: Construction 2,577 1,448 4,025 633,007 637,032 279 Single family residential 12,936 3,302 16,238 776,990 793,228 126 Other commercial 17,176 5,647 22,823 2,364,954 2,387,777 2,565 Total real estate 32,689 10,397 43,086 3,774,951 3,818,037 2,970 Commercial: Commercial 2,344 1,039 3,383 992,204 995,587 67 Agricultural 51 — 51 66,525 66,576 — Total commercial 2,395 1,039 3,434 1,058,729 1,062,163 67 Other 15 — 15 142,394 142,409 — Total $ 35,988 $ 11,696 $ 47,684 $ 5,026,392 $ 5,074,076 $ 3,145
Impaired Loans	Impaired loans, net of government guarantees and excluding loans acquired, segregated by class of loans, are as follows: (In thousands) Unpaid Contractual Principal Balance Recorded Investment With No Allowance Recorded Investment With Allowance Total Recorded Investment Related Allowance Average Investment in Impaired Loans Interest Income Recognized Average Investment in Impaired Loans Interest Income Recognized September 30, 2018 Three Months Ended Nine Months Ended Consumer: Credit cards $ 328 $ 328 $ — $ 328 $ — $ 283 $ 35 $ 259 $ 60 Other consumer 3,528 3,317 — 3,317 — 3,561 28 4,109 96 Total consumer 3,856 3,645 — 3,645 — 3,844 63 4,368 156 Real estate: Construction 879 800 490 1,290 232 1,411 11 1,747 41 Single family residential 11,771 11,023 715 11,738 36 13,577 98 13,550 315 Other commercial 7,909 5,942 7,431 13,373 — 12,282 108 14,284 332 Total real estate 20,559 17,765 8,636 26,401 268 27,270 217 29,581 688 Commercial: Commercial 11,777 9,786 6,062 15,848 191 11,840 108 9,533 222 Agricultural 3,507 1,460 — 1,460 — 1,355 12 1,470 34 Total commercial 15,284 11,246 6,062 17,308 191 13,195 120 11,003 256 Total $ 39,699 $ 32,656 $ 14,698 $ 47,354 $ 459 $ 44,309 $ 400 $ 44,952 $ 1,100 December 31, 2017 Three Months Ended Nine Months Ended Consumer: Credit cards $ 170 $ 170 $ — $ 170 $ — $ 283 $ 12 $ 292 $ 23 Other consumer 4,755 4,605 — 4,605 — 3,314 23 2,711 53 Total consumer 4,925 4,775 — 4,775 — 3,597 35 3,003 76 Real estate: Construction 2,522 1,347 895 2,242 249 2,582 17 2,828 56 Single family residential 14,347 12,725 706 13,431 53 12,878 85 12,772 251 Other commercial 22,308 6,732 9,133 15,865 36 19,306 121 19,313 380 Total real estate 39,177 20,804 10,734 31,538 338 34,766 223 34,913 687 Commercial: Commercial 9,954 4,306 2,269 6,575 — 14,543 84 12,943 255 Agricultural 3,278 1,035 — 1,035 — 1,562 8 1,645 32 Total commercial 13,232 5,341 2,269 7,610 — 16,105 92 14,588 287 Total $ 57,334 $ 30,920 $ 13,003 $ 43,923 $ 338 $ 54,468 $ 350 $ 52,504 $ 1,050
Troubled Debt Restructuring	The following table presents loans that were restructured as TDRs during the three and nine months ended September 30, 2018 and 2017 , excluding loans acquired, segregated by class of loans. Modification Type (Dollars in thousands) Number of Loans Balance Prior to TDR Balance at September 30, Change in Maturity Date Change in Rate Financial Impact on Date of Restructure Three Months Ended September 30, 2018 Real estate: Other commercial 2 $ 392 $ 390 $ 390 $ — $ 212 Total real estate 2 392 390 390 — 212 Commercial: Commercial 3 2,363 2,358 2,358 — 190 Total commercial 3 2,363 2,358 2,358 — 190 Total 5 $ 2,755 $ 2,748 $ 2,748 $ — $ 402 Three Months Ended September 30, 2017 Commercial: Commercial 1 $ 608 $ 607 $ 607 $ — $ — Total commercial 1 608 607 607 — — Total 1 $ 608 $ 607 $ 607 $ — $ — Nine Months Ended September 30, 2018 Consumer: Other consumer 1 $ 91 $ 91 $ 91 $ — $ — Total consumer 1 91 91 91 — — Real estate: Single-family residential 1 61 62 62 — — Other commercial 2 392 390 390 — 212 Total real estate 3 453 452 452 — 212 Commercial: Commercial 3 2,363 2,358 2,358 — 190 Total commercial 3 2,363 2,358 2,358 — 190 Total 7 $ 2,907 $ 2,901 $ 2,901 $ — $ 402 Nine Months Ended September 30, 2017 Real estate: Construction 1 $ 456 $ 456 $ 456 $ — $ — Other commercial 2 7,362 7,362 7,362 — 33 Total real estate 3 7,818 7,818 7,818 — 33 Commercial: Commercial 10 1,419 1,407 1,368 39 — Total commercial 10 1,419 1,407 1,368 39 — Total 13 $ 9,237 $ 9,225 $ 9,186 $ 39 $ 33 The following table presents a summary of troubled debt restructurings, excluding loans acquired, segregated by class of loans. Accruing TDR Loans Nonaccrual TDR Loans Total TDR Loans (Dollars in thousands) Number Balance Number Balance Number Balance September 30, 2018 Real estate: Construction — $ — 3 $ 490 3 $ 490 Single-family residential 7 318 10 631 17 949 Other commercial 2 3,365 3 2,953 5 6,318 Total real estate 9 3,683 16 4,074 25 7,757 Commercial: Commercial 6 4,730 6 753 12 5,483 Total commercial 6 4,730 6 753 12 5,483 Total 15 $ 8,413 22 $ 4,827 37 $ 13,240 December 31, 2017 Real estate: Construction — $ — 1 $ 420 1 $ 420 Single-family residential 4 141 15 954 19 1,095 Other commercial 4 4,322 5 3,712 9 8,034 Total real estate 8 4,463 21 5,086 29 9,549 Commercial: Commercial 5 2,644 6 745 11 3,389 Total commercial 5 2,644 6 745 11 3,389 Total 13 $ 7,107 27 $ 5,831 40 $ 12,938
Loans by Credit Risk Ratings	The following table presents a summary of loans by credit risk rating as of September 30, 2018 and December 31, 2017 , segregated by class of loans. Loans accounted for under ASC Topic 310-30 are all included in Risk Rate 1-4 in this table. (In thousands) Risk Rate 1-4 Risk Rate 5 Risk Rate 6 Risk Rate 7 Risk Rate 8 Total September 30, 2018 Consumer: Credit cards $ 181,620 $ — $ 517 $ — $ — $ 182,137 Other consumer 255,857 — 3,724 — — 259,581 Total consumer 437,477 — 4,241 — — 441,718 Real estate: Construction 1,225,481 2,286 2,121 — — 1,229,888 Single family residential 1,382,655 843 18,256 237 — 1,401,991 Other commercial 3,047,514 9,304 20,370 — — 3,077,188 Total real estate 5,655,650 12,433 40,747 237 — 5,709,067 Commercial: Commercial 1,569,357 8,250 30,735 — — 1,608,342 Agricultural 215,742 155 2,881 — — 218,778 Total commercial 1,785,099 8,405 33,616 — — 1,827,120 Other 145,369 — — — — 145,369 Loans acquired 3,620,803 47,672 66,087 359 — 3,734,921 Total $ 11,644,398 $ 68,510 $ 144,691 $ 596 $ — $ 11,858,195 (In thousands) Risk Rate 1-4 Risk Rate 5 Risk Rate 6 Risk Rate 7 Risk Rate 8 Total December 31, 2017 Consumer: Credit cards $ 184,920 $ — $ 502 $ — $ — $ 185,422 Other consumer 275,160 — 4,934 — — 280,094 Total consumer 460,080 — 5,436 — — 465,516 Real estate: Construction 603,126 5,795 5,218 16 — 614,155 Single family residential 1,066,902 3,954 23,490 287 — 1,094,633 Other commercial 2,480,293 19,581 30,950 — — 2,530,824 Total real estate 4,150,321 29,330 59,658 303 — 4,239,612 Commercial: Commercial 736,377 74,254 14,402 50 134 825,217 Agricultural 146,065 24 2,190 23 — 148,302 Total commercial 882,442 74,278 16,592 73 134 973,519 Other 26,962 — — — — 26,962 Loans acquired 4,918,570 62,128 93,378 — — 5,074,076 Total $ 10,438,375 $ 165,736 $ 175,064 $ 376 $ 134 $ 10,779,685 The following table presents a summary of loans acquired by credit risk rating, segregated by class of loans (see Note 5, Loans and Allowance for Loan Losses, for discussion of loan risk rating). Loans accounted for under ASC Topic 310-30 are all included in Risk Rate 1-4 in this table. (In thousands) Risk Rate 1-4 Risk Rate 5 Risk Rate 6 Risk Rate 7 Risk Rate 8 Total September 30, 2018 Consumer: Other consumer $ 20,813 $ 9 $ 456 $ — $ — $ 21,278 Real estate: Construction 440,881 18,011 9,003 — — 467,895 Single family residential 590,003 2,475 14,029 359 — 606,866 Other commercial 2,006,371 12,283 21,535 — — 2,040,189 Total real estate 3,037,255 32,769 44,567 359 — 3,114,950 Commercial: Commercial 560,791 14,894 20,956 — — 596,641 Agricultural 1,944 — 108 — — 2,052 Total commercial 562,735 14,894 21,064 — — 598,693 Total $ 3,620,803 $ 47,672 $ 66,087 $ 359 $ — $ 3,734,921 December 31, 2017 Consumer: Other consumer $ 50,625 $ 21 $ 821 $ — $ — $ 51,467 Real estate: Construction 604,796 30,524 1,712 — — 637,032 Single family residential 770,954 2,618 19,656 — — 793,228 Other commercial 2,337,097 15,064 35,616 — — 2,387,777 Total real estate 3,712,847 48,206 56,984 — — 3,818,037 Commercial: Commercial 946,322 13,901 35,364 — — 995,587 Agricultural 66,367 — 209 — — 66,576 Total commercial 1,012,689 13,901 35,573 — — 1,062,163 Other 142,409 — — — — 142,409 Total $ 4,918,570 $ 62,128 $ 93,378 $ — $ — $ 5,074,076
Allowance for Loan Losses	The Company’s recorded investment in loans, excluding loans acquired, related to each balance in the allowance for loan losses by portfolio segment on the basis of the Company’s impairment methodology was as follows: (In thousands) Commercial Real Estate Credit Card Other Consumer and Other Total September 30, 2018 Loans individually evaluated for impairment $ 17,308 $ 26,401 $ 328 $ 3,317 $ 47,354 Loans collectively evaluated for impairment 1,809,812 5,682,666 181,809 401,633 8,075,920 Balance, end of period $ 1,827,120 $ 5,709,067 $ 182,137 $ 404,950 $ 8,123,274 December 31, 2017 Loans individually evaluated for impairment $ 7,610 $ 31,538 $ 170 $ 4,605 $ 43,923 Loans collectively evaluated for impairment 965,909 4,208,074 185,252 302,451 5,661,686 Balance, end of period $ 973,519 $ 4,239,612 $ 185,422 $ 307,056 $ 5,705,609 The following table details activity in the allowance for loan losses by portfolio segment for legacy loans for the three and nine months ended September 30, 2018 . Allocation of a portion of the allowance to one category of loans does not preclude its availability to absorb losses in other categories. (In thousands) Commercial Real Estate Credit Card Other Consumer and Other Total Three Months Ended September 30, 2018 Balance, beginning of period (2) $ 15,767 $ 28,904 $ 3,822 $ 3,239 $ 51,732 Provision for loan losses (1) 3,589 5,308 719 729 10,345 Charge-offs (592 ) (4,952 ) (919 ) (1,321 ) (7,784 ) Recoveries 450 210 229 176 1,065 Net charge-offs (142 ) (4,742 ) (690 ) (1,145 ) (6,719 ) Balance, September 30, 2018 (2) $ 19,214 $ 29,470 $ 3,851 $ 2,823 $ 55,358 Nine Months Ended September 30, 2018 Balance, beginning of period (2) $ 7,007 $ 27,281 $ 3,784 $ 3,596 $ 41,668 Provision for loan losses (1) 14,772 7,133 2,219 2,567 26,691 Charge-offs (3,143 ) (5,568 ) (2,930 ) (3,743 ) (15,384 ) Recoveries 578 624 778 403 2,383 Net charge-offs (2,565 ) (4,944 ) (2,152 ) (3,340 ) (13,001 ) Balance, September 30, 2018 (2) $ 19,214 $ 29,470 $ 3,851 $ 2,823 $ 55,358 Period-end amount allocated to: Loans individually evaluated for impairment $ 191 $ 268 $ — $ — $ 459 Loans collectively evaluated for impairment 19,023 29,202 3,851 2,823 54,899 Balance, September 30, 2018 (2) $ 19,214 $ 29,470 $ 3,851 $ 2,823 $ 55,358 ______________________ (1) Provision for loan losses of $1,837,000 attributable to loans acquired was excluded from this table for the nine months ended September 30, 2018 (total provision for loan losses for the three and nine months ended September 30, 2018 was $10,345,000 and $28,528,000 ). There were $699,000 and $910,000 in charge-offs for loans acquired during the three and nine months ended September 30, 2018 , respectively, resulting in an ending balance in the allowance related to loans acquired of $1,345,000 . (2) Allowance for loan losses at September 30, 2018 includes $1,345,000 allowance for loans acquired (not shown in the table above). Allowance for loan losses at June 30, 2018 and December 31, 2017 includes $2,044,000 and $418,000 , respectively, of allowance for loans acquired (not shown in the table above). The total allowance for loan losses at September 30, 2018 was $56,703,000 and total allowance for loan losses at June 30, 2018 and December 31, 2017 was $53,776,000 and $42,086,000 , respectively. Activity in the allowance for loan losses for the three and nine months ended September 30, 2017 was as follows: (In thousands) Commercial Real Estate Credit Card Other Consumer and Other Total Three Months Ended September 30, 2017 Balance, beginning of period (4) $ 8,105 $ 25,731 $ 3,754 $ 3,789 $ 41,379 Provision for loan losses (3) 2,310 2,150 761 241 5,462 Charge-offs (2,442 ) (896 ) (1,017 ) (819 ) (5,174 ) Recoveries 21 309 275 445 1,050 Net charge-offs (2,421 ) (587 ) (742 ) (374 ) (4,124 ) Balance, September 30, 2017 (4) $ 7,994 $ 27,294 $ 3,773 $ 3,656 $ 42,717 Nine Months Ended September 30, 2017 Balance, beginning of period (4) $ 7,739 $ 21,817 $ 3,779 $ 2,951 $ 36,286 Provision for loan losses (3) 3,255 7,984 2,168 1,920 15,327 Charge-offs (3,083 ) (3,264 ) (2,962 ) (2,986 ) (12,295 ) Recoveries 83 757 788 1,771 3,399 Net charge-offs (3,000 ) (2,507 ) (2,174 ) (1,215 ) (8,896 ) Balance, September 30, 2017 (4) $ 7,994 $ 27,294 $ 3,773 $ 3,656 $ 42,717 Period-end amount allocated to: Loans individually evaluated for impairment $ 3,996 $ 2,325 $ — $ — $ 6,321 Loans collectively evaluated for impairment 3,998 24,969 3,773 3,656 36,396 Balance, September 30, 2017 (4) $ 7,994 $ 27,294 $ 3,773 $ 3,656 $ 42,717 Period-end amount allocated to: Loans individually evaluated for impairment $ — $ 338 $ — $ — $ 338 Loans collectively evaluated for impairment 7,007 26,943 3,784 3,596 41,330 Balance, December 31, 2017 (5) $ 7,007 $ 27,281 $ 3,784 $ 3,596 $ 41,668 ______________________ (3) Provision for loan losses of $1,464,000 attributable to loans acquired was excluded from this table for the nine months ended September 30, 2017 (total provision for loan losses for the three and nine months ended September 30, 2017 was $5,462,000 and $16,792,000 , respectively). There were $2.0 million in charge-offs for loans acquired during the nine months ended September 30, 2017 , respectively, resulting in an ending balance in the allowance related to loans acquired of $391,000 . (4) Allowance for loan losses at September 30, 2017 and June 30, 2017 includes $391,000 allowance for loans acquired (not shown in the table above) and December 31, 2016 includes $954,000 allowance for loans acquired (not shown in the table above). The total allowance for loan losses at September 30, 2017 , June 30, 2017 and December 31, 2016 was $43,108,000 , $41,770,000 and $37,240,000 , respectively. (5) Allowance for loan losses at December 31, 2017 includes $418,000 allowance for loans acquired (not shown in the table above). The total allowance for loan losses at December 31, 2017 was $42,086,000 .

Loans Acquired (Tables)

Loans Acquired (Tables)	9 Months Ended
	Sep. 30, 2018
Receivables [Abstract]
Loans Acquired	The various categories of loans are summarized as follows: (In thousands) September 30, 2018 December 31, 2017 Consumer: Credit cards $ 182,137 $ 185,422 Other consumer 259,581 280,094 Total consumer 441,718 465,516 Real Estate: Construction 1,229,888 614,155 Single family residential 1,401,991 1,094,633 Other commercial 3,077,188 2,530,824 Total real estate 5,709,067 4,239,612 Commercial: Commercial 1,608,342 825,217 Agricultural 218,778 148,302 Total commercial 1,827,120 973,519 Other 145,369 26,962 Loans 8,123,274 5,705,609 Loans acquired, net of discount and allowance (1) 3,734,921 5,074,076 Total loans $ 11,858,195 $ 10,779,685 _____________________________ (1) See Note 6, Loans Acquired, for segregation of loans acquired by loan class. The impact of these adjustments on the Company’s financial results for the three and nine months ended September 30, 2018 and 2017 is shown below: Three Months Ended Nine Months Ended (In thousands) 2018 2017 2018 2017 Impact on net interest income and pre-tax income $ 629 $ 23 $ 1,105 $ 2,596 Impact, net of taxes $ 464 $ 14 $ 814 $ 1,578 The following table reflects the carrying value of all loans acquired as of September 30, 2018 and December 31, 2017 : Loans Acquired (In thousands) September 30, 2018 December 31, 2017 Consumer: Other consumer $ 21,278 $ 51,467 Real estate: Construction 467,895 637,032 Single family residential 606,866 793,228 Other commercial 2,040,189 2,387,777 Total real estate 3,114,950 3,818,037 Commercial: Commercial 596,641 995,587 Agricultural 2,052 66,576 Total commercial 598,693 1,062,163 Other — 142,409 Total loans acquired (1) $ 3,734,921 $ 5,074,076 _____________________________________________________________________________________ (1) Loans acquired are reported net of a $1,345,000 and $418,000 allowance at September 30, 2018 and December 31, 2017 , respectively. Changes in the carrying amount of the accretable yield for all purchased impaired loans were as follows for the three and nine months ended September 30, 2018 and 2017 . Three Months Ended Nine Months Ended (In thousands) Accretable Yield Carrying Amount of Loans Accretable Yield Carrying Amount of Loans Beginning balance $ 1,382 $ 13,995 $ 620 $ 17,116 Additions — — — — Accretable yield adjustments 717 — 1,895 — Accretion (635 ) 635 (1,051 ) 1,051 Payments and other reductions, net — (9,664 ) — (13,201 ) Balance, ending $ 1,464 $ 4,966 $ 1,464 $ 4,966 Three Months Ended Nine Months Ended (In thousands) Accretable Yield Carrying Amount of Loans Accretable Yield Carrying Amount of Loans Beginning balance $ 766 $ 8,448 $ 1,655 $ 17,802 Additions — — — 2,388 Accretable yield adjustments 52 — 2,698 — Accretion (408 ) 408 (3,943 ) 3,943 Payments and other reductions, net — (980 ) — (16,257 ) Balance, ending $ 410 $ 7,876 $ 410 $ 7,876
Nonaccrual Loans	Nonaccrual loans, excluding loans acquired, segregated by class of loans, are as follows: (In thousands) September 30, 2018 December 31, 2017 Consumer: Credit cards $ 328 $ 170 Other consumer 3,317 4,605 Total consumer 3,645 4,775 Real estate: Construction 1,289 2,242 Single family residential 11,508 13,431 Other commercial 9,639 16,054 Total real estate 22,436 31,727 Commercial: Commercial 11,932 6,980 Agricultural 2,492 2,160 Total commercial 14,424 9,140 Total $ 40,505 $ 45,642 Nonaccrual loans acquired, excluding purchased credit impaired loans accounted for under ASC Topic 310-30, segregated by class of loans, are as follows (see Note 5, Loans and Allowance for Loan Losses, for discussion of nonaccrual loans): (In thousands) September 30, 2018 December 31, 2017 Consumer: Other consumer $ 293 $ 334 Real estate: Construction 279 1,767 Single family residential 9,053 12,151 Other commercial 1,354 7,401 Total real estate 10,686 21,319 Commercial: Commercial 4,964 1,748 Agricultural 38 84 Total commercial 5,002 1,832 Total $ 15,981 $ 23,485
Past Due Loans	An age analysis of past due loans, excluding loans acquired, segregated by class of loans, is as follows: (In thousands) Gross 30-89 Days Past Due 90 Days or More Past Due Total Past Due Current Total Loans 90 Days Past Due & Accruing September 30, 2018 Consumer: Credit cards $ 777 $ 517 $ 1,294 $ 180,843 $ 182,137 $ 188 Other consumer 3,341 1,921 5,262 254,319 259,581 1 Total consumer 4,118 2,438 6,556 435,162 441,718 189 Real estate: Construction 1,033 397 1,430 1,228,458 1,229,888 — Single family residential 5,180 4,212 9,392 1,392,599 1,401,991 92 Other commercial 4,555 4,152 8,707 3,068,481 3,077,188 — Total real estate 10,768 8,761 19,529 5,689,538 5,709,067 92 Commercial: Commercial 4,568 5,873 10,441 1,597,901 1,608,342 — Agricultural 128 2,253 2,381 216,397 218,778 — Total commercial 4,696 8,126 12,822 1,814,298 1,827,120 — Other — — — 145,369 145,369 — Total $ 19,582 $ 19,325 $ 38,907 $ 8,084,367 $ 8,123,274 $ 281 December 31, 2017 Consumer: Credit cards $ 707 $ 672 $ 1,379 $ 184,043 $ 185,422 $ 332 Other consumer 5,009 3,298 8,307 271,787 280,094 10 Total consumer 5,716 3,970 9,686 455,830 465,516 342 Real estate: Construction 411 1,210 1,621 612,534 614,155 — Single family residential 8,071 6,460 14,531 1,080,102 1,094,633 1 Other commercial 2,388 8,031 10,419 2,520,405 2,530,824 — Total real estate 10,870 15,701 26,571 4,213,041 4,239,612 1 Commercial: Commercial 1,523 6,125 7,648 817,569 825,217 — Agricultural 50 2,120 2,170 146,132 148,302 — Total commercial 1,573 8,245 9,818 963,701 973,519 — Other — — — 26,962 26,962 — Total $ 18,159 $ 27,916 $ 46,075 $ 5,659,534 $ 5,705,609 $ 343 An age analysis of past due loans acquired segregated by class of loans, is as follows (see Note 5, Loans and Allowance for Loan Losses, for discussion of past due loans): (In thousands) Gross 30-89 Days Past Due 90 Days or More Past Due Total Past Due Current Total Loans 90 Days Past Due & Accruing September 30, 2018 Consumer: Other consumer $ 213 $ 214 $ 427 $ 20,851 $ 21,278 $ — Real estate: Construction 117 207 324 467,571 467,895 — Single family residential 2,459 5,948 8,407 598,459 606,866 1 Other commercial 2,491 4,157 6,648 2,033,541 2,040,189 — Total real estate 5,067 10,312 15,379 3,099,571 3,114,950 1 Commercial: Commercial 1,471 4,020 5,491 591,150 596,641 — Agricultural 27 5 32 2,020 2,052 — Total commercial 1,498 4,025 5,523 593,170 598,693 — Total $ 6,778 $ 14,551 $ 21,329 $ 3,713,592 $ 3,734,921 $ 1 December 31, 2017 Consumer: Other consumer $ 889 $ 260 $ 1,149 $ 50,318 $ 51,467 $ 108 Real estate: Construction 2,577 1,448 4,025 633,007 637,032 279 Single family residential 12,936 3,302 16,238 776,990 793,228 126 Other commercial 17,176 5,647 22,823 2,364,954 2,387,777 2,565 Total real estate 32,689 10,397 43,086 3,774,951 3,818,037 2,970 Commercial: Commercial 2,344 1,039 3,383 992,204 995,587 67 Agricultural 51 — 51 66,525 66,576 — Total commercial 2,395 1,039 3,434 1,058,729 1,062,163 67 Other 15 — 15 142,394 142,409 — Total $ 35,988 $ 11,696 $ 47,684 $ 5,026,392 $ 5,074,076 $ 3,145
Loans by Credit Risk Ratings	The following table presents a summary of loans by credit risk rating as of September 30, 2018 and December 31, 2017 , segregated by class of loans. Loans accounted for under ASC Topic 310-30 are all included in Risk Rate 1-4 in this table. (In thousands) Risk Rate 1-4 Risk Rate 5 Risk Rate 6 Risk Rate 7 Risk Rate 8 Total September 30, 2018 Consumer: Credit cards $ 181,620 $ — $ 517 $ — $ — $ 182,137 Other consumer 255,857 — 3,724 — — 259,581 Total consumer 437,477 — 4,241 — — 441,718 Real estate: Construction 1,225,481 2,286 2,121 — — 1,229,888 Single family residential 1,382,655 843 18,256 237 — 1,401,991 Other commercial 3,047,514 9,304 20,370 — — 3,077,188 Total real estate 5,655,650 12,433 40,747 237 — 5,709,067 Commercial: Commercial 1,569,357 8,250 30,735 — — 1,608,342 Agricultural 215,742 155 2,881 — — 218,778 Total commercial 1,785,099 8,405 33,616 — — 1,827,120 Other 145,369 — — — — 145,369 Loans acquired 3,620,803 47,672 66,087 359 — 3,734,921 Total $ 11,644,398 $ 68,510 $ 144,691 $ 596 $ — $ 11,858,195 (In thousands) Risk Rate 1-4 Risk Rate 5 Risk Rate 6 Risk Rate 7 Risk Rate 8 Total December 31, 2017 Consumer: Credit cards $ 184,920 $ — $ 502 $ — $ — $ 185,422 Other consumer 275,160 — 4,934 — — 280,094 Total consumer 460,080 — 5,436 — — 465,516 Real estate: Construction 603,126 5,795 5,218 16 — 614,155 Single family residential 1,066,902 3,954 23,490 287 — 1,094,633 Other commercial 2,480,293 19,581 30,950 — — 2,530,824 Total real estate 4,150,321 29,330 59,658 303 — 4,239,612 Commercial: Commercial 736,377 74,254 14,402 50 134 825,217 Agricultural 146,065 24 2,190 23 — 148,302 Total commercial 882,442 74,278 16,592 73 134 973,519 Other 26,962 — — — — 26,962 Loans acquired 4,918,570 62,128 93,378 — — 5,074,076 Total $ 10,438,375 $ 165,736 $ 175,064 $ 376 $ 134 $ 10,779,685 The following table presents a summary of loans acquired by credit risk rating, segregated by class of loans (see Note 5, Loans and Allowance for Loan Losses, for discussion of loan risk rating). Loans accounted for under ASC Topic 310-30 are all included in Risk Rate 1-4 in this table. (In thousands) Risk Rate 1-4 Risk Rate 5 Risk Rate 6 Risk Rate 7 Risk Rate 8 Total September 30, 2018 Consumer: Other consumer $ 20,813 $ 9 $ 456 $ — $ — $ 21,278 Real estate: Construction 440,881 18,011 9,003 — — 467,895 Single family residential 590,003 2,475 14,029 359 — 606,866 Other commercial 2,006,371 12,283 21,535 — — 2,040,189 Total real estate 3,037,255 32,769 44,567 359 — 3,114,950 Commercial: Commercial 560,791 14,894 20,956 — — 596,641 Agricultural 1,944 — 108 — — 2,052 Total commercial 562,735 14,894 21,064 — — 598,693 Total $ 3,620,803 $ 47,672 $ 66,087 $ 359 $ — $ 3,734,921 December 31, 2017 Consumer: Other consumer $ 50,625 $ 21 $ 821 $ — $ — $ 51,467 Real estate: Construction 604,796 30,524 1,712 — — 637,032 Single family residential 770,954 2,618 19,656 — — 793,228 Other commercial 2,337,097 15,064 35,616 — — 2,387,777 Total real estate 3,712,847 48,206 56,984 — — 3,818,037 Commercial: Commercial 946,322 13,901 35,364 — — 995,587 Agricultural 66,367 — 209 — — 66,576 Total commercial 1,012,689 13,901 35,573 — — 1,062,163 Other 142,409 — — — — 142,409 Total $ 4,918,570 $ 62,128 $ 93,378 $ — $ — $ 5,074,076

Goodwill and Other Intangible_2

Goodwill and Other Intangible Assets (Tables)	9 Months Ended
	Sep. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangibles	The Company’s goodwill and other intangibles (carrying basis and accumulated amortization) at September 30, 2018 and December 31, 2017 , were as follows: (In thousands) September 30, 2018 December 31, 2017 Goodwill $ 845,687 $ 842,651 Core deposit premiums: Gross carrying amount 105,984 105,984 Accumulated amortization (23,802 ) (16,659 ) Core deposit premiums, net 82,182 89,325 Books of business intangible: Gross carrying amount 15,234 15,414 Accumulated amortization (3,441 ) (2,827 ) Books of business intangible, net 11,793 12,587 Other intangibles: Gross carrying amount 2,068 6,037 Accumulated amortization (2,068 ) (1,878 ) Other intangibles, net — 4,159 Other intangible assets, net 93,975 106,071 Total goodwill and other intangible assets $ 939,662 $ 948,722
Estimated Remaining Amortization Expense	The Company’s estimated remaining amortization expense on intangibles as of September 30, 2018 is as follows: (In thousands) Year Amortization Expense Remainder of 2018 $ 2,642 2019 10,565 2020 10,552 2021 10,490 2022 10,438 Thereafter 49,288 Total $ 93,975

Income Taxes (Tables)

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Provision for Income Taxes	The provision for income taxes is comprised of the following components for the periods indicated below: Three Months Ended Nine Months Ended (In thousands) 2018 2017 2018 2017 Income taxes currently payable $ 5,638 $ 11,946 $ 31,335 $ 30,467 Deferred income taxes 5,264 2,732 7,316 4,962 Provision for income taxes $ 10,902 $ 14,678 $ 38,651 $ 35,429
Schedule of Deferred Tax Assets and Liabilities	The tax effects of temporary differences between the tax basis of assets and liabilities and their financial reporting amounts that give rise to deferred income tax assets and liabilities, and their appropriate tax effects, are as follows: (In thousands) September 30, 2018 December 31, 2017 Deferred tax assets: Loans acquired $ 12,092 $ 19,885 Allowance for loan losses 12,601 10,773 Valuation of foreclosed assets 2,709 2,852 Tax NOLs from acquisition 6,962 7,821 Deferred compensation payable 2,645 2,433 Accrued equity and other compensation 6,605 5,302 Acquired securities 549 578 Unrealized loss on available-for-sale securities 16,221 6,107 Other 5,890 8,813 Gross deferred tax assets 66,274 64,564 Deferred tax liabilities: Goodwill and other intangible amortization (30,645 ) (32,572 ) Accumulated depreciation (11,778 ) (8,945 ) Other (2,197 ) (4,413 ) Gross deferred tax liabilities (44,620 ) (45,930 ) Net deferred tax asset, included in other assets $ 21,654 $ 18,634
Reconciliation of Income Tax Expense	A reconciliation of income tax expense at the statutory rate to the Company’s actual income tax expense is shown for the periods indicated below: Three Months Ended Nine Months Ended (In thousands) 2018 2017 2018 2017 Computed at the statutory rate (1) $ 13,880 $ 15,235 $ 41,731 $ 38,313 Increase (decrease) in taxes resulting from: State income taxes, net of federal tax benefit 986 342 4,073 1,117 Discrete items related to ASU 2016-09 (31 ) 5 (2,567 ) (1,372 ) Tax exempt interest income (833 ) (955 ) (2,292 ) (3,160 ) Tax exempt earnings on BOLI (186 ) (178 ) (562 ) (616 ) Other differences, net (2,914 ) 229 (1,732 ) 1,147 Actual tax provision $ 10,902 $ 14,678 $ 38,651 $ 35,429 ________________________ (1) The statutory rate was 21% for 2018 compared to 35% for 2017 .

Securities Sold Under Agreeme_2

Securities Sold Under Agreements to Repurchase (Tables)	9 Months Ended
	Sep. 30, 2018
Banking and Thrift [Abstract]
Contractual Maturity of Securities Sold Under Agreements to Repurchase	The remaining contractual maturity of the securities sold under agreements to repurchase in the consolidated balance sheets as of September 30, 2018 and December 31, 2017 is presented in the following tables. Remaining Contractual Maturity of the Agreements (In thousands) Overnight and Continuous Up to 30 Days 30-90 Days Greater than 90 Days Total September 30, 2018 Repurchase agreements: U.S. Government agencies $ 108,963 $ — $ — $ — $ 108,963 December 31, 2017 Repurchase agreements: U.S. Government agencies $ 122,019 $ — $ — $ — $ 122,019

Other Borrowings and Subordin_2

Other Borrowings and Subordinated Notes and Debentures (Tables)	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Debt	Debt at September 30, 2018 and December 31, 2017 consisted of the following components: (In thousands) September 30, 2018 December 31, 2017 Other Borrowings FHLB advances, net of discount, due 2018 to 2033, 1.38% to 7.37% secured by residential real estate loans $ 1,420,917 $ 1,261,642 Revolving credit agreement, due 10/5/2018, floating rate of 1.50% above the one month LIBOR rate, unsecured — 75,000 Notes payable, due 10/15/2020, 3.85%, fixed rate, unsecured — 43,382 Total other borrowings 1,420,917 1,380,024 Subordinated Notes and Debentures Subordinated notes payable, due 4/1/2028, fixed-to-floating rate (fixed rate of 5.00% through 3/31/2023, floating rate of 2.15% above the three month LIBOR rate, reset quarterly) 330,000 — Trust preferred securities, due 12/30/2033, floating rate of 2.80% above the three month LIBOR rate, reset quarterly, callable without penalty — 20,620 Trust preferred securities, net of discount, due 6/30/2035, floating rate of 1.75% above the three month LIBOR rate, reset quarterly, callable without penalty — 9,327 Trust preferred securities, net of discount, due 9/15/2037, floating rate of 1.37% above the three month LIBOR rate, reset quarterly 10,310 10,284 Trust preferred securities, net of discount, due 12/5/2033, floating rate of 2.88% above the three month LIBOR rate, reset quarterly, callable without penalty — 5,156 Trust preferred securities, net of discount, due 10/18/2034, floating rate of 2.00% above the three month LIBOR rate, reset quarterly, callable without penalty — 5,148 Trust preferred securities, net of discount, due 6/6/2037, floating rate of 1.57% above the three month LIBOR rate, reset quarterly, callable without penalty 10,310 10,288 Trust preferred securities, due 12/15/2035, floating rate of 1.45% above the three month LIBOR rate, reset quarterly, callable without penalty 6,702 6,702 Trust preferred securities, due 6/26/2033, floating rate of 3.10% above the three month LIBOR rate, reset quarterly, callable without penalty — 20,619 Trust preferred securities, due 10/7/2033, floating rate of 2.85% above the three month LIBOR rate, reset quarterly, callable without penalty — 25,774 Trust preferred securities, due 9/15/2037, floating rate of 2.00% above the three month LIBOR rate, reset quarterly, callable without penalty — 8,248 Other subordinated debentures, net of discount, called 9/30/2018, floating rate equal to daily average of prime rate, reset quarterly 19,075 18,399 Unamortized debt issuance costs (3,463 ) — Total subordinated notes and debentures 372,934 140,565 Total other borrowings and subordinated debt $ 1,793,851 $ 1,520,589
Aggregate Annual Maturities of Long-term Debt	Aggregate annual maturities of long-term debt at September 30, 2018 , are as follows: (In thousands) Year Annual Maturities 2018 $ 376 2019 2,135 2020 2,109 2021 1,800 2022 949 Thereafter 362,404 Total $ 369,773

Stock Based Compensation (Table

Stock Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock Compensation Plans	The table below summarizes the transactions under the Company’s active stock compensation plans for the nine months ended September 30, 2018 : Stock Options Outstanding Non-vested Stock Awards Outstanding Non-vested Stock Units Outstanding Number of Shares (000) Weighted Average Exercise Price Number of Shares (000) Weighted Average Exercise Price Number of Shares (000) Weighted Average Exercise Price Balance, January 1, 2018 812 $ 21.98 162 $ 20.86 652 $ 27.92 Granted — — — — 343 29.31 Stock Options Exercised (111 ) 19.22 — — — — Stock Awards/Units Vested — — (55 ) 18.95 (175 ) 27.74 Forfeited/Expired (6 ) 21.73 (10 ) 20.12 (91 ) 28.37 Balance, September 30, 2018 695 $ 22.42 97 $ 22.00 729 $ 28.56 Exercisable, September 30, 2018 661 $ 22.37
Stock Options	The following table summarizes information about stock options under the plans outstanding at September 30, 2018 : Options Outstanding Options Exercisable Range of Exercise Prices Number of Shares (000) Weighted Average Remaining Contractual Life (Years) Weighted Average Exercise Price Number of Shares (000) Weighted Average Exercise Price $ 9.46 — $ 9.46 1 3.30 $9.46 1 $9.46 10.65 — 10.65 4 4.32 10.65 4 10.65 10.76 — 10.76 2 1.30 10.76 2 10.76 20.29 — 20.29 71 6.25 20.29 71 20.29 20.36 — 20.36 3 6.13 20.36 1 20.36 22.20 — 22.20 74 6.48 22.20 74 22.20 22.75 — 22.75 436 6.86 22.75 436 22.75 23.51 — 23.51 97 7.30 23.51 65 23.51 24.07 — 24.07 7 6.96 24.07 7 24.07 $ 9.46 — $ 24.07 695 6.78 $22.42 661 $22.37

Earnings Per Share ("EPS") (Tab

Earnings Per Share ("EPS") (Tables)	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Computation of Earnings Per Share	Following is the computation of earnings per share for the three and nine months ended September 30, 2018 and 2017 : Three Months Ended Nine Months Ended (In thousands, except per share data) 2018 2017 2018 2017 Net income $ 55,193 $ 28,852 $ 160,067 $ 74,037 Average common shares outstanding 92,290 64,427 92,246 63,594 Average potential dilutive common shares 551 420 551 420 Average diluted common shares 92,841 64,847 92,797 64,014 Basic earnings per share $ 0.60 $ 0.45 $ 1.74 $ 1.16 Diluted earnings per share $ 0.59 $ 0.44 $ 1.72 $ 1.16

Additional Cash Flow Informat_2

Additional Cash Flow Information (Tables)	9 Months Ended
	Sep. 30, 2018
Supplemental Cash Flow Information [Abstract]
Additional Cash Flow Information	The following is a summary of the Company’s additional cash flow information during the nine months ended: Nine Months Ended (In thousands) 2018 2017 Interest paid $ 78,987 $ 21,531 Income taxes paid 25,576 21,718 Transfers of loans to foreclosed assets held for sale 7,745 5,311 Transfers of premises to foreclosed assets and other real estate owned 3,690 3,188

Other Operating Expenses (Table

Other Operating Expenses (Tables)	9 Months Ended
	Sep. 30, 2018
Other Income and Expenses [Abstract]
Other Operating Expenses	Other operating expenses consist of the following: Three Months Ended September 30, Nine Months Ended (In thousands) 2018 2017 2018 2017 Professional services $ 4,616 $ 3,946 $ 13,896 $ 13,079 Postage 1,262 1,091 4,103 3,427 Telephone 1,248 943 4,217 3,003 Credit card expense 3,405 3,137 9,820 9,081 Marketing 2,912 1,219 6,334 4,253 Operating supplies 585 592 1,917 1,406 Amortization of intangibles 2,772 1,724 8,394 4,828 Branch right sizing expense 970 153 1,049 370 Other expense 11,904 5,458 31,623 18,588 Total other operating expenses $ 29,674 $ 18,263 $ 81,353 $ 58,035

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Financial Instruments Measured on Recurring Basis	The following table sets forth the Company’s financial assets by level within the fair value hierarchy that were measured at fair value on a recurring basis as of September 30, 2018 and December 31, 2017 . Fair Value Measurements Using (In thousands) Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) September 30, 2018 Available-for-sale securities U.S. Government agencies $ 141,460 $ — $ 141,460 $ — Mortgage-backed securities 1,419,626 — 1,419,626 — State and political subdivisions 282,439 — 282,439 — Other securities 154,289 — 154,289 — Other assets held for sale 5,136 — — 5,136 Derivative asset 9,691 — 9,691 — Other liabilities held for sale (424 ) — — (424 ) Derivative liability (7,940 ) — (7,940 ) — December 31, 2017 Available-for-sale securities U.S. Government agencies $ 139,724 $ — $ 139,724 $ — Mortgage-backed securities 1,187,317 — 1,187,317 — States and political subdivisions 143,165 — 143,165 — Other securities 119,311 — 119,311 — Other assets held for sale 165,780 — — 165,780 Derivative asset 3,634 — 3,634 — Other liabilities held for sale (157,366 ) — — (157,366 ) Derivative liability (3,068 ) — (3,068 ) —
Financial Assets Measure on Nonrecurring Basis	The following table sets forth the Company’s financial assets by level within the fair value hierarchy that were measured at fair value on a nonrecurring basis as of September 30, 2018 and December 31, 2017 . Fair Value Measurements Using (In thousands) Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) September 30, 2018 Impaired loans (1) (2) (collateral dependent) $ 17,789 $ — $ — $ 17,789 Foreclosed assets and other real estate owned (1) 14,643 — — 14,643 December 31, 2017 Impaired loans (1) (2) (collateral dependent) $ 11,229 $ — $ — $ 11,229 Foreclosed assets and other real estate owned (1) 24,093 — — 24,093 ________________________ (1) These amounts represent the resulting carrying amounts on the Consolidated Balance Sheets for impaired collateral dependent loans and foreclosed assets and other real estate owned for which fair value re-measurements took place during the period. (2) Specific allocations of $2,738,000 and $2,195,000 were related to the impaired collateral dependent loans for which fair value re-measurements took place during the periods ended September 30, 2018 and December 31, 2017 , respectively.
Estimated Fair Values and Related Carrying Amounts	The estimated fair values, and related carrying amounts, of the Company’s financial instruments are as follows: Carrying Fair Value Measurements (In thousands) Amount Level 1 Level 2 Level 3 Total September 30, 2018 Financial assets: Cash and cash equivalents $ 513,804 $ 513,804 $ — $ — $ 513,804 Interest bearing balances due from banks - time 3,954 — 3,954 — 3,954 Held-to-maturity securities 323,306 — 322,838 — 322,838 Mortgage loans held for sale 48,195 — — 48,195 48,195 Interest receivable 51,509 — 51,509 — 51,509 Legacy loans, net 8,067,916 — — 7,996,273 7,996,273 Loans acquired, net 3,734,921 — — 3,701,755 3,701,755 Financial liabilities: Non-interest bearing transaction accounts 2,778,670 — 2,778,670 — 2,778,670 Interest bearing transaction accounts and savings deposits 6,776,330 — 6,776,330 — 6,776,330 Time deposits 2,533,506 — — 2,508,228 2,508,228 Federal funds purchased and securities sold under agreements to repurchase 109,213 — 109,213 — 109,213 Other borrowings 1,420,917 — 1,417,166 — 1,417,166 Subordinated notes and debentures 372,934 — 310,701 — 310,701 Interest payable 13,197 — 13,197 — 13,197 December 31, 2017 Financial assets: Cash and cash equivalents $ 598,042 $ 598,042 $ — $ — $ 598,042 Interest bearing balances due from banks - time 3,314 — 3,314 — 3,314 Held-to-maturity securities 368,058 — 373,298 — 373,298 Mortgage loans held for sale 24,038 — — 24,038 24,038 Interest receivable 43,528 — 43,528 — 43,528 Legacy loans, net 5,663,941 — — 5,646,505 5,646,505 Loans acquired, net 5,074,076 — — 5,058,455 5,058,455 Financial liabilities: Non-interest bearing transaction accounts 2,665,249 — 2,665,249 — 2,665,249 Interest bearing transaction accounts and savings deposits 6,494,896 — 6,494,896 — 6,494,896 Time deposits 1,932,730 — — 1,915,539 1,915,539 Federal funds purchased and securities sold under agreements to repurchase 122,444 — 122,444 — 122,444 Other borrowings 1,380,024 — 1,381,365 — 1,381,365 Subordinated debentures 140,565 — 136,474 — 136,474 Interest payable 4,564 — 4,564 — 4,564

Preparation of Interim Financ_3

Preparation of Interim Financial Statements (Details) $ in Millions	3 Months Ended
	Dec. 31, 2017USD ($)	Sep. 30, 2018financial_center
Number of financial centers | financial_center		191
Accounting Standards Update 2018-02
Cumulative effect of new accounting principle in period of adoption | $	$ 3

Acquisitions - Textual (Details

Acquisitions - Textual (Details) $ in Thousands	Oct. 19, 2017USD ($)financial_centerbranchshares	May 15, 2017USD ($)branchshares	Dec. 31, 2017USD ($)	Sep. 30, 2018USD ($)	Oct. 18, 2017USD ($)	Jun. 30, 2017USD ($)	May 14, 2017USD ($)
Business Acquisition [Line Items]
Goodwill			$ 842,651	$ 845,687
OKSB Merger
Business Acquisition [Line Items]
Shares issued (in shares) | shares	14,488,604
Shares issued	$ 431,400
Payments to acquire businesses, gross	$ 94,900
Number of bank branches | branch	29
Total assets acquired	$ 2,690,915				$ 2,686,489
Gross value of loans acquired	1,996,453		2,021,000		2,039,524
Total deposits acquired	1,966,355				1,968,568
Goodwill	$ 229,144				13,545
Revenue attributable to acquisition			29,200
Net income attributable to acquisition			10,500
First Texas Merger
Business Acquisition [Line Items]
Shares issued (in shares) | shares	12,999,840
Shares issued	$ 387,100
Payments to acquire businesses, gross	$ 70,000
Number of bank branches | financial_center	15
Total assets acquired	$ 2,427,226				2,453,283
Gross value of loans acquired	2,208,378		2,246,000		2,246,212
Total deposits acquired	1,881,658				1,881,941
Goodwill	$ 240,843				$ 37,227
Revenue attributable to acquisition			27,600
Net income attributable to acquisition			5,700
OKSB and First Texas Acquisitions
Business Acquisition [Line Items]
Acquisition related costs			$ 9,400
Hardeman County Investment Company, Inc.
Business Acquisition [Line Items]
Shares issued (in shares) | shares		1,599,940
Shares issued		$ 42,600
Payments to acquire businesses, gross		$ 30,000
Number of bank branches | branch		10
Total assets acquired		$ 462,924					$ 468,829
Gross value of loans acquired		251,649				$ 254,200	257,641
Total deposits acquired		388,976					389,344
Goodwill		$ 29,371					$ 11,485

Acquisitions - Assets Acquired

Acquisitions - Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Oct. 19, 2017	May 15, 2017	Sep. 30, 2018	Dec. 31, 2017	Oct. 18, 2017	Jun. 30, 2017	May 14, 2017
Assets Acquired
Goodwill			$ 845,687	$ 842,651
Liabilities Assumed
Goodwill			$ 845,687	842,651
OKSB Merger
Assets Acquired
Cash and due from banks	$ 79,517				$ 79,517
Investment securities	484,173				485,468
Loans acquired	1,996,453			2,021,000	2,039,524
Allowance for loan losses	0				(26,957)
Foreclosed assets	5,157				6,284
Premises and equipment	26,667				21,210
Bank owned life insurance	28,704				28,704
Goodwill	229,144				13,545
Other assets	24,314				33,455
Total assets acquired	2,690,915				2,686,489
Liabilities Assumed
Non-interest bearing transaction accounts	485,971				485,971
Interest bearing transaction accounts and savings deposits	869,252				869,252
Time deposits	611,132				613,345
Total deposits	1,966,355				1,968,568
Securities sold under agreement to repurchase	11,256				11,256
Other borrowings	347,000				347,000
Subordinated debentures	46,393				46,393
Accrued interest and other liabilities	22,804				17,440
Total liabilities assumed	2,393,808				2,390,657
Total equity assumed					295,832
Total liabilities and equity assumed	2,393,808				2,686,489
Net assets acquired	297,107
Purchase price	526,251
Goodwill	229,144				13,545
OKSB Merger | Core deposit intangible
Assets Acquired
Intangibles	42,124				1,933
OKSB Merger | Other intangibles
Assets Acquired
Intangibles	3,806				3,806
OKSB Merger | Fair Value Adjustments
Assets Acquired
Cash and due from banks	0
Investment securities	(1,295)
Loans acquired	(43,071)
Allowance for loan losses	26,957
Foreclosed assets	(1,127)
Premises and equipment	5,457
Bank owned life insurance	0
Goodwill	(13,545)
Other assets	(9,141)
Total assets acquired	4,426
Liabilities Assumed
Non-interest bearing transaction accounts	0
Interest bearing transaction accounts and savings deposits	0
Time deposits	(2,213)
Total deposits	(2,213)
Securities sold under agreement to repurchase	0
Other borrowings	0
Subordinated debentures	0
Accrued interest and other liabilities	5,364
Total liabilities assumed	3,151
Total equity assumed	(295,832)
Total liabilities and equity assumed	(292,681)
Goodwill	(13,545)
OKSB Merger | Fair Value Adjustments | Core deposit intangible
Assets Acquired
Intangibles	40,191
OKSB Merger | Fair Value Adjustments | Other intangibles
Assets Acquired
Intangibles	0
First Texas Merger
Assets Acquired
Cash and due from banks	59,277				59,277
Investment securities	80,518				81,114
Loans acquired	2,208,378			$ 2,246,000	2,246,212
Allowance for loan losses	(200)				(20,864)
Premises and equipment	34,987				24,864
Bank owned life insurance	7,190				7,190
Goodwill	240,843				37,227
Other assets	29,748				18,263
Total assets acquired	2,427,226				2,453,283
Liabilities Assumed
Non-interest bearing transaction accounts	74,410				74,410
Interest bearing transaction accounts and savings deposits	1,683,298				1,683,298
Time deposits	123,950				124,233
Total deposits	1,881,658				1,881,941
Securities sold under agreement to repurchase	50,000				50,000
Other borrowings	235,000				235,000
Subordinated debentures	30,912				30,323
Accrued interest and other liabilities	13,396				11,727
Total liabilities assumed	2,210,966				2,208,991
Total equity assumed					244,292
Total liabilities and equity assumed	2,210,966				2,453,283
Net assets acquired	216,260
Purchase price	457,103
Goodwill	240,843				37,227
First Texas Merger | Core deposit intangible
Assets Acquired
Intangibles	7,328				$ 0
First Texas Merger | Fair Value Adjustments
Assets Acquired
Cash and due from banks	0
Investment securities	(596)
Loans acquired	(37,834)
Allowance for loan losses	20,664
Premises and equipment	10,123
Bank owned life insurance	0
Goodwill	(37,227)
Other assets	11,485
Total assets acquired	(26,057)
Liabilities Assumed
Non-interest bearing transaction accounts	0
Interest bearing transaction accounts and savings deposits	0
Time deposits	(283)
Total deposits	(283)
Securities sold under agreement to repurchase	0
Other borrowings	0
Subordinated debentures	589
Accrued interest and other liabilities	1,669
Total liabilities assumed	1,975
Total equity assumed	(244,292)
Total liabilities and equity assumed	(242,317)
Goodwill	(37,227)
First Texas Merger | Fair Value Adjustments | Core deposit intangible
Assets Acquired
Intangibles	$ 7,328
Hardeman County Investment Company, Inc.
Assets Acquired
Cash and due from banks		$ 8,001					$ 8,001
Interest bearing balances due from banks - time		1,984					1,984
Investment securities		170,369					170,654
Loans acquired		251,649				$ 254,200	257,641
Allowance for loan losses							(2,382)
Foreclosed assets		631					1,083
Premises and equipment		11,163					9,905
Bank owned life insurance		7,819					7,819
Goodwill		29,371					11,485
Other assets		2,638					2,639
Total assets acquired		462,924					468,829
Liabilities Assumed
Non-interest bearing transaction accounts		76,555					76,555
Interest bearing transaction accounts and savings deposits		214,872					214,872
Time deposits		97,549					97,917
Total deposits		388,976					389,344
Securities sold under agreement to repurchase		17,163					17,163
Other borrowings		3,000					3,000
Subordinated debentures		6,702					6,702
Accrued interest and other liabilities		3,815					1,891
Total liabilities assumed		419,656					418,100
Total equity assumed							50,729
Total liabilities and equity assumed		419,656					468,829
Net assets acquired		43,268
Purchase price		72,639
Goodwill		29,371					11,485
Hardeman County Investment Company, Inc. | Core deposit intangible
Assets Acquired
Intangibles		7,840					0
Hardeman County Investment Company, Inc. | Other intangibles
Assets Acquired
Intangibles		830					$ 0
Hardeman County Investment Company, Inc. | Fair Value Adjustments
Assets Acquired
Cash and due from banks		0
Interest bearing balances due from banks - time		0
Investment securities		(285)
Loans acquired		(5,992)
Allowance for loan losses		2,382
Foreclosed assets		(452)
Premises and equipment		1,258
Bank owned life insurance		0
Goodwill		(11,485)
Other assets		(1)
Total assets acquired		(5,905)
Liabilities Assumed
Non-interest bearing transaction accounts		0
Interest bearing transaction accounts and savings deposits		0
Time deposits		(368)
Total deposits		(368)
Securities sold under agreement to repurchase		0
Other borrowings		0
Subordinated debentures		0
Accrued interest and other liabilities		1,924
Total liabilities assumed		1,556
Total equity assumed		(50,729)
Total liabilities and equity assumed		(49,173)
Goodwill		(11,485)
Hardeman County Investment Company, Inc. | Fair Value Adjustments | Core deposit intangible
Assets Acquired
Intangibles		7,840
Hardeman County Investment Company, Inc. | Fair Value Adjustments | Other intangibles
Assets Acquired
Intangibles		$ 830

Acquisitions - Summary of Unaud

Acquisitions - Summary of Unaudited Pro Forma Information (Details) - OKSB and First Texas Acquisitions - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Revenue	$ 654,358	$ 620,461
Net income	$ 130,947	$ 136,199
Diluted earnings per share (in dollars per share)	$ 1.43	$ 1.52

Investment Securities - Summary

Investment Securities - Summary of Investment Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Held-to-Maturity
Amortized Cost	$ 323,306	$ 368,058
Gross Unrealized Gains	2,369	5,977
Gross Unrealized (Losses)	(2,837)	(737)
Estimated Fair Value	322,838	373,298
Available-for-Sale
Amortized Cost	2,060,798	1,612,324
Gross Unrealized Gains	2,857	2,100
Gross Unrealized (Losses)	(65,841)	(24,907)
Estimated Fair Value	1,997,814	1,589,517
U.S. Government agencies
Held-to-Maturity
Amortized Cost	34,983	46,945
Gross Unrealized Gains	0	7
Gross Unrealized (Losses)	(113)	(228)
Estimated Fair Value	34,870	46,724
Available-for-Sale
Amortized Cost	145,808	141,559
Gross Unrealized Gains	0	116
Gross Unrealized (Losses)	(4,348)	(1,951)
Estimated Fair Value	141,460	139,724
Mortgage-backed securities
Held-to-Maturity
Amortized Cost	13,933	16,132
Gross Unrealized Gains	0	8
Gross Unrealized (Losses)	(698)	(287)
Estimated Fair Value	13,235	15,853
Available-for-Sale
Amortized Cost	1,471,687	1,208,017
Gross Unrealized Gains	127	246
Gross Unrealized (Losses)	(52,188)	(20,946)
Estimated Fair Value	1,419,626	1,187,317
State and political subdivisions
Held-to-Maturity
Amortized Cost	272,396	301,491
Gross Unrealized Gains	2,369	5,962
Gross Unrealized (Losses)	(2,020)	(222)
Estimated Fair Value	272,745	307,231
Available-for-Sale
Amortized Cost	291,731	144,642
Gross Unrealized Gains	12	532
Gross Unrealized (Losses)	(9,304)	(2,009)
Estimated Fair Value	282,439	143,165
Other securities
Held-to-Maturity
Amortized Cost	1,994	3,490
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	(6)	0
Estimated Fair Value	1,988	3,490
Available-for-Sale
Amortized Cost	151,572	118,106
Gross Unrealized Gains	2,718	1,206
Gross Unrealized (Losses)	(1)	(1)
Estimated Fair Value	$ 154,289	$ 119,311

Investment Securities - Textual

Investment Securities - Textual (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Securities valued at less than historical cost, amount	$ 2,000,000,000		$ 2,000,000,000		$ 1,400,000,000
Securities valued at less than historical cost (as percent)	86.00%		86.00%		73.50%
Securities pledged as collateral	$ 933,500,000		$ 933,500,000		$ 1,200,000,000
Realized gains	41,000	$ 3,000	54,000	$ 2,300,000
Realized losses	$ 0	$ 0	$ 1,000	$ 5,000

Investment Securities - Securit

Investment Securities - Securities With Unrealized Losses (Details) $ in Thousands	Sep. 30, 2018USD ($)
Held-to-Maturity
Held-to-maturity, less than 12 months, estimated fair value	$ 132,542
Held-to-maturity, less than 12 months, gross unrealized losses	(1,805)
Held-to-maturity, 12 months or more, estimated fair value	48,841
Held-to-maturity, 12 months or more, gross unrealized losses	(1,032)
Held-to-maturity, total, estimated fair value	181,383
Held-to-maturity, total, gross unrealized losses	(2,837)
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	825,604
Available-for-sale, less than 12 months, gross unrealized losses	(16,668)
Available-for-sale, 12 months or more, estimated fair value	988,819
Available-for-sale, 12 months or more, gross unrealized losses	(49,173)
Available-for-sale, total, estimated fair value	1,814,423
Available-for-sale, total, gross unrealized losses	(65,841)
U.S. Government agencies
Held-to-Maturity
Held-to-maturity, less than 12 months, estimated fair value	3,972
Held-to-maturity, less than 12 months, gross unrealized losses	(11)
Held-to-maturity, 12 months or more, estimated fair value	30,898
Held-to-maturity, 12 months or more, gross unrealized losses	(102)
Held-to-maturity, total, estimated fair value	34,870
Held-to-maturity, total, gross unrealized losses	(113)
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	56,785
Available-for-sale, less than 12 months, gross unrealized losses	(689)
Available-for-sale, 12 months or more, estimated fair value	84,675
Available-for-sale, 12 months or more, gross unrealized losses	(3,659)
Available-for-sale, total, estimated fair value	141,460
Available-for-sale, total, gross unrealized losses	(4,348)
Mortgage-backed securities
Held-to-Maturity
Held-to-maturity, less than 12 months, estimated fair value	3,830
Held-to-maturity, less than 12 months, gross unrealized losses	(106)
Held-to-maturity, 12 months or more, estimated fair value	9,404
Held-to-maturity, 12 months or more, gross unrealized losses	(592)
Held-to-maturity, total, estimated fair value	13,234
Held-to-maturity, total, gross unrealized losses	(698)
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	586,783
Available-for-sale, less than 12 months, gross unrealized losses	(11,469)
Available-for-sale, 12 months or more, estimated fair value	808,969
Available-for-sale, 12 months or more, gross unrealized losses	(40,719)
Available-for-sale, total, estimated fair value	1,395,752
Available-for-sale, total, gross unrealized losses	(52,188)
State and political subdivisions
Held-to-Maturity
Held-to-maturity, less than 12 months, estimated fair value	123,574
Held-to-maturity, less than 12 months, gross unrealized losses	(1,682)
Held-to-maturity, 12 months or more, estimated fair value	8,539
Held-to-maturity, 12 months or more, gross unrealized losses	(338)
Held-to-maturity, total, estimated fair value	132,113
Held-to-maturity, total, gross unrealized losses	(2,020)
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	182,036
Available-for-sale, less than 12 months, gross unrealized losses	(4,510)
Available-for-sale, 12 months or more, estimated fair value	95,076
Available-for-sale, 12 months or more, gross unrealized losses	(4,794)
Available-for-sale, total, estimated fair value	277,112
Available-for-sale, total, gross unrealized losses	(9,304)
Other securities
Held-to-Maturity
Held-to-maturity, less than 12 months, estimated fair value	1,166
Held-to-maturity, less than 12 months, gross unrealized losses	(6)
Held-to-maturity, 12 months or more, estimated fair value	0
Held-to-maturity, 12 months or more, gross unrealized losses	0
Held-to-maturity, total, estimated fair value	1,166
Held-to-maturity, total, gross unrealized losses	(6)
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	0
Available-for-sale, less than 12 months, gross unrealized losses	0
Available-for-sale, 12 months or more, estimated fair value	99
Available-for-sale, 12 months or more, gross unrealized losses	(1)
Available-for-sale, total, estimated fair value	99
Available-for-sale, total, gross unrealized losses	$ (1)

Investment Securities - Income

Investment Securities - Income Earned on Securities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Non-taxable:
Total	$ 14,640	$ 9,218	$ 41,558	$ 28,659
Held-to-maturity
Taxable:
Taxable	528	625	1,641	1,922
Non-taxable:
Non-taxable	1,828	2,135	5,661	6,635
Available-for-sale
Taxable:
Taxable	10,364	5,949	29,614	18,003
Non-taxable:
Non-taxable	$ 1,920	$ 509	$ 4,642	$ 2,099

Investment Securities - Maturit

Investment Securities - Maturities of Investment Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Held-to-maturity, amortized cost, one year or less	$ 50,503
Held-to-maturity, amortized cost, after one through five years	60,633
Held-to-maturity, amortized cost, after five through ten years	91,862
Held-to-maturity, amortized cost, after ten years	106,375
Held-to-maturity, amortized cost, securities not due on a single maturity date	13,933
Amortized Cost	323,306	$ 368,058
Held-to-maturity, fair value, one year or less	50,366
Held-to-maturity, fair value, after one through five years	60,313
Held-to-maturity, fair value, after five through ten years	91,364
Held-to-maturity, fair value, after ten years	107,560
Held-to-maturity, fair value, securities not due on a single maturity date	13,235
Held-to-maturity, fair value, total	322,838	373,298
Available-for-sale, amortized cost, one year or less	120
Available-for-sale, amortized cost, after one through five years	35,703
Available-for-sale, amortized cost, after five through ten years	22,485
Available-for-sale, amortized cost, after ten years	379,331
Available-for-sale, amortized cost, securities not due on a single maturity date	1,471,687
Available-for-sale, amortized cost, other securities (no maturity)	151,472
Amortized Cost	2,060,798	1,612,324
Available-for-sale, fair value, one year or less	119
Available-for-sale, fair value, after one through five years	34,714
Available-for-sale, fair value, after five through ten years	21,698
Available-for-sale, fair value, after ten years	367,466
Available-for-sale, fair value, securities not due on a single maturity date	1,419,626
Available-for-sale, fair value, other securities (no maturity)	154,191
Available-for-sale, fair value, total	$ 1,997,814	$ 1,589,517

Other Assets and Other Liabil_2

Other Assets and Other Liabilities Held for Sale (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Other assets held for sale	$ 5,136		$ 165,780
Other liabilities held for sale	$ 424		$ 157,366
Heartland
Business Acquisition [Line Items]
Branches and loans acquired		$ 141,000
Deposits and liabilities		$ 154,600

Loans and Allowance for Loan _3

Loans and Allowance for Loan Losses - Textual (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2018USD ($)loan	Sep. 30, 2017USD ($)loan	Sep. 30, 2018USD ($)loan	Sep. 30, 2017USD ($)loan	Dec. 31, 2017USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 11,860,000,000		$ 11,860,000,000		$ 10,780,000,000
Recorded investment	47,354,000		47,354,000		43,923,000
Impaired loan, related allowance	459,000		459,000		338,000
Interest income recognized	400,000	$ 350,000	1,100,000	$ 1,050,000
Average Investment in Impaired Loans	$ 44,309,000	$ 54,468,000	$ 44,952,000	$ 52,504,000
Troubled debt, number of contracts | loan	5	1	7	13
Balance prior to TDR	$ 2,755,000	$ 608,000	$ 2,907,000	$ 9,237,000
Reserve	402,000		402,000	33,000
Foreclosed assets and other real estate owned	22,664,000		22,664,000		32,118,000
Risk Rate 6 | Financial Asset Acquired with Credit Deterioration
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired	5,000,000		5,000,000		17,100,000
Risk Ratings 6,7, and 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired excluding loans accounted for under ASC Topic 310-30	145,300,000		145,300,000		175,600,000
Risk Ratings 6,7, and 8 | Financial Asset Acquired with Credit Deterioration
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired excluding loans accounted for under ASC Topic 310-30	61,500,000		61,500,000		76,300,000
Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans in process of foreclosure, amount	2,262,000		2,262,000		5,057,000
OREO Received in Full or Partial Satisfaction of Loans | Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Foreclosed assets and other real estate owned	3,610,000		3,610,000		3,828,000
Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	5,709,067,000		5,709,067,000		4,239,612,000
Recorded investment	26,401,000		26,401,000		31,538,000
Impaired loan, related allowance	268,000		268,000		$ 338,000
Interest income recognized	217,000	223,000	688,000	687,000
Average Investment in Impaired Loans	$ 27,270,000	$ 34,766,000	$ 29,581,000	$ 34,913,000
Troubled debt, number of contracts | loan	2		3	3
Balance prior to TDR	$ 392,000		$ 453,000	$ 7,818,000
Real estate | OREO Received in Full or Partial Satisfaction of Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance prior to TDR			$ 294,300	$ 117,000
Commercial Real Estate | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans with subsequent default | loan			1	1
Write-down of impaired loans			$ 66,300
Transfers of loans			$ 294,300

Loans and Allowance for Loan _4

Loans and Allowance for Loan Losses - Loan Portfolio by Categories (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 11,860,000	$ 10,780,000
Loans acquired, net of discount and allowance	3,734,921	5,074,076
Total loans	11,858,195	10,779,685
Loans, Excluding Acquired Loans
Loans and Leases Receivable Disclosure [Line Items]
Loans	8,123,274	5,705,609
Consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans	441,718	465,516
Consumer | Credit cards
Loans and Leases Receivable Disclosure [Line Items]
Loans	182,137	185,422
Consumer | Other consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans	259,581	280,094
Real estate
Loans and Leases Receivable Disclosure [Line Items]
Loans	5,709,067	4,239,612
Real estate | Construction
Loans and Leases Receivable Disclosure [Line Items]
Loans	1,229,888	614,155
Real estate | Single family residential
Loans and Leases Receivable Disclosure [Line Items]
Loans	1,401,991	1,094,633
Real estate | Other commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans	3,077,188	2,530,824
Commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans	1,827,120	973,519
Commercial | Commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans	1,608,342	825,217
Commercial | Agricultural
Loans and Leases Receivable Disclosure [Line Items]
Loans	218,778	148,302
Other
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 145,369	$ 26,962

Loans and Allowance for Loan _5

Loans and Allowance for Loan Losses - Nonaccrual Loans, Excluding Loans Acquired, Segregated by Class of Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	$ 40,505	$ 45,642
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	3,645	4,775
Consumer | Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	328	170
Consumer | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	3,317	4,605
Real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	22,436	31,727
Real estate | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	1,289	2,242
Real estate | Single family residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	11,508	13,431
Real estate | Other commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	9,639	16,054
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	14,424	9,140
Commercial | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	11,932	6,980
Commercial | Agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	$ 2,492	$ 2,160

Loans and Allowance for Loan _6

Loans and Allowance for Loan Losses - Age Analysis of Past Due Loans, Excluding Loans Acquired, Segregated by Class of Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	$ 11,858,195	$ 10,779,685
Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	38,907	46,075
Current	8,084,367	5,659,534
Total Loans	8,123,274	5,705,609
90 Days Past Due & Accruing	281	343
Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	19,582	18,159
90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	19,325	27,916
Consumer | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	6,556	9,686
Current	435,162	455,830
Total Loans	441,718	465,516
90 Days Past Due & Accruing	189	342
Consumer | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,118	5,716
Consumer | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,438	3,970
Consumer | Credit cards | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,294	1,379
Current	180,843	184,043
Total Loans	182,137	185,422
90 Days Past Due & Accruing	188	332
Consumer | Credit cards | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	777	707
Consumer | Credit cards | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	517	672
Consumer | Other consumer | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,262	8,307
Current	254,319	271,787
Total Loans	259,581	280,094
90 Days Past Due & Accruing	1	10
Consumer | Other consumer | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,341	5,009
Consumer | Other consumer | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,921	3,298
Real estate | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	19,529	26,571
Current	5,689,538	4,213,041
Total Loans	5,709,067	4,239,612
90 Days Past Due & Accruing	92	1
Real estate | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	10,768	10,870
Real estate | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	8,761	15,701
Real estate | Construction | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,430	1,621
Current	1,228,458	612,534
Total Loans	1,229,888	614,155
90 Days Past Due & Accruing	0	0
Real estate | Construction | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,033	411
Real estate | Construction | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	397	1,210
Real estate | Single family residential | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	9,392	14,531
Current	1,392,599	1,080,102
Total Loans	1,401,991	1,094,633
90 Days Past Due & Accruing	92	1
Real estate | Single family residential | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,180	8,071
Real estate | Single family residential | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,212	6,460
Real estate | Other commercial | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	8,707	10,419
Current	3,068,481	2,520,405
Total Loans	3,077,188	2,530,824
90 Days Past Due & Accruing	0	0
Real estate | Other commercial | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,555	2,388
Real estate | Other commercial | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,152	8,031
Commercial | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	12,822	9,818
Current	1,814,298	963,701
Total Loans	1,827,120	973,519
90 Days Past Due & Accruing	0	0
Commercial | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,696	1,573
Commercial | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	8,126	8,245
Commercial | Commercial | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	10,441	7,648
Current	1,597,901	817,569
Total Loans	1,608,342	825,217
90 Days Past Due & Accruing	0	0
Commercial | Commercial | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,568	1,523
Commercial | Commercial | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,873	6,125
Commercial | Agricultural | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,381	2,170
Current	216,397	146,132
Total Loans	218,778	148,302
90 Days Past Due & Accruing	0	0
Commercial | Agricultural | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	128	50
Commercial | Agricultural | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,253	2,120
Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans		26,962
Other | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Current	145,369	26,962
Total Loans	145,369	26,962
90 Days Past Due & Accruing	0	$ 0
Other | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0
Other | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 0

Loans and Allowance for Loan _7

Loans and Allowance for Loan Losses - Impaired Loans, Net of Government Guarantees and Excluding Loans Acquired, Segregated by Class of Loans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	$ 39,699		$ 39,699		$ 57,334
Recorded Investment With No Allowance	32,656		32,656		30,920
Recorded Investment With Allowance	14,698		14,698		13,003
Total Recorded Investment	47,354		47,354		43,923
Related Allowance	459		459		338
Average Investment in Impaired Loans	44,309	$ 54,468	44,952	$ 52,504
Interest Income Recognized	400	350	1,100	1,050
Consumer
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	3,856		3,856		4,925
Recorded Investment With No Allowance	3,645		3,645		4,775
Recorded Investment With Allowance	0		0		0
Total Recorded Investment	3,645		3,645		4,775
Related Allowance	0		0		0
Average Investment in Impaired Loans	3,844	3,597	4,368	3,003
Interest Income Recognized	63	35	156	76
Consumer | Credit cards
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	328		328		170
Recorded Investment With No Allowance	328		328		170
Recorded Investment With Allowance	0		0		0
Total Recorded Investment	328		328		170
Related Allowance	0		0		0
Average Investment in Impaired Loans	283	283	259	292
Interest Income Recognized	35	12	60	23
Consumer | Other consumer
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	3,528		3,528		4,755
Recorded Investment With No Allowance	3,317		3,317		4,605
Recorded Investment With Allowance	0		0		0
Total Recorded Investment	3,317		3,317		4,605
Related Allowance	0		0		0
Average Investment in Impaired Loans	3,561	3,314	4,109	2,711
Interest Income Recognized	28	23	96	53
Real estate
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	20,559		20,559		39,177
Recorded Investment With No Allowance	17,765		17,765		20,804
Recorded Investment With Allowance	8,636		8,636		10,734
Total Recorded Investment	26,401		26,401		31,538
Related Allowance	268		268		338
Average Investment in Impaired Loans	27,270	34,766	29,581	34,913
Interest Income Recognized	217	223	688	687
Real estate | Construction
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	879		879		2,522
Recorded Investment With No Allowance	800		800		1,347
Recorded Investment With Allowance	490		490		895
Total Recorded Investment	1,290		1,290		2,242
Related Allowance	232		232		249
Average Investment in Impaired Loans	1,411	2,582	1,747	2,828
Interest Income Recognized	11	17	41	56
Real estate | Single family residential
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	11,771		11,771		14,347
Recorded Investment With No Allowance	11,023		11,023		12,725
Recorded Investment With Allowance	715		715		706
Total Recorded Investment	11,738		11,738		13,431
Related Allowance	36		36		53
Average Investment in Impaired Loans	13,577	12,878	13,550	12,772
Interest Income Recognized	98	85	315	251
Real estate | Other commercial
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	7,909		7,909		22,308
Recorded Investment With No Allowance	5,942		5,942		6,732
Recorded Investment With Allowance	7,431		7,431		9,133
Total Recorded Investment	13,373		13,373		15,865
Related Allowance	0		0		36
Average Investment in Impaired Loans	12,282	19,306	14,284	19,313
Interest Income Recognized	108	121	332	380
Commercial
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	15,284		15,284		13,232
Recorded Investment With No Allowance	11,246		11,246		5,341
Recorded Investment With Allowance	6,062		6,062		2,269
Total Recorded Investment	17,308		17,308		7,610
Related Allowance	191		191		0
Average Investment in Impaired Loans	13,195	16,105	11,003	14,588
Interest Income Recognized	120	92	256	287
Commercial | Commercial
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	11,777		11,777		9,954
Recorded Investment With No Allowance	9,786		9,786		4,306
Recorded Investment With Allowance	6,062		6,062		2,269
Total Recorded Investment	15,848		15,848		6,575
Related Allowance	191		191		0
Average Investment in Impaired Loans	11,840	14,543	9,533	12,943
Interest Income Recognized	108	84	222	255
Commercial | Agricultural
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	3,507		3,507		3,278
Recorded Investment With No Allowance	1,460		1,460		1,035
Recorded Investment With Allowance	0		0		0
Total Recorded Investment	1,460		1,460		1,035
Related Allowance	0		0		$ 0
Average Investment in Impaired Loans	1,355	1,562	1,470	1,645
Interest Income Recognized	$ 12	$ 8	$ 34	$ 32

Loans and Allowance for Loan _8

Loans and Allowance for Loan Losses - Troubled Debt Restructurings, Excluding Loans Acquired, Segregated by Class of Loans (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018USD ($)loan	Sep. 30, 2017loan	Sep. 30, 2018USD ($)loan	Sep. 30, 2017loan	Dec. 31, 2017USD ($)loan
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	5	1	7	13
Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			37		40
Troubled debt, balance | $	$ 13,240		$ 13,240		$ 12,938
Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			15		13
Troubled debt, balance | $	8,413		$ 8,413		$ 7,107
Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			22		27
Troubled debt, balance | $	$ 4,827		$ 4,827		$ 5,831
Real estate
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	2		3	3
Real estate | Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			25		29
Troubled debt, balance | $	$ 7,757		$ 7,757		$ 9,549
Real estate | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			9		8
Troubled debt, balance | $	3,683		$ 3,683		$ 4,463
Real estate | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			16		21
Troubled debt, balance | $	4,074		$ 4,074		$ 5,086
Real estate | Construction
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts				1
Real estate | Construction | Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			3		1
Troubled debt, balance | $	490		$ 490		$ 420
Real estate | Construction | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			0		0
Troubled debt, balance | $	0		$ 0		$ 0
Real estate | Construction | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			3		1
Troubled debt, balance | $	490		$ 490		$ 420
Real estate | Single family residential
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			1
Real estate | Single family residential | Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			17		19
Troubled debt, balance | $	949		$ 949		$ 1,095
Real estate | Single family residential | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			7		4
Troubled debt, balance | $	318		$ 318		$ 141
Real estate | Single family residential | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			10		15
Troubled debt, balance | $	$ 631		$ 631		$ 954
Real estate | Other commercial
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	2		2	2
Real estate | Other commercial | Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			5		9
Troubled debt, balance | $	$ 6,318		$ 6,318		$ 8,034
Real estate | Other commercial | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			2		4
Troubled debt, balance | $	3,365		$ 3,365		$ 4,322
Real estate | Other commercial | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			3		5
Troubled debt, balance | $	$ 2,953		$ 2,953		$ 3,712
Commercial
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	3	1	3	10
Commercial | Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			12		11
Troubled debt, balance | $	$ 5,483		$ 5,483		$ 3,389
Commercial | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			6		5
Troubled debt, balance | $	4,730		$ 4,730		$ 2,644
Commercial | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			6		6
Troubled debt, balance | $	$ 753		$ 753		$ 745
Commercial | Commercial
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	3	1	3	10
Commercial | Commercial | Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			12		11
Troubled debt, balance | $	$ 5,483		$ 5,483		$ 3,389
Commercial | Commercial | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			6		5
Troubled debt, balance | $	4,730		$ 4,730		$ 2,644
Commercial | Commercial | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			6		6
Troubled debt, balance | $	$ 753		$ 753		$ 745

Loans and Allowance for Loan _9

Loans and Allowance for Loan Losses - Loans Restructured as TDRs, Excluding Loans Acquired, Segregated by Class of Loans (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018USD ($)loan	Sep. 30, 2017USD ($)loan	Sep. 30, 2018USD ($)loan	Sep. 30, 2017USD ($)loan
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	5	1	7	13
Balance Prior to TDR	$ 2,755	$ 608	$ 2,907	$ 9,237
Balance	2,748	607	2,901	9,225
Financial Impact on Date of Restructure	402	0	402	33
Change in Maturity Date
Financing Receivable, Modifications [Line Items]
Balance	2,748	607	2,901	9,186
Change in Rate
Financing Receivable, Modifications [Line Items]
Balance	$ 0	$ 0	$ 0	$ 39
Consumer
Financing Receivable, Modifications [Line Items]
Number of Loans | loan			1
Balance Prior to TDR			$ 91
Balance			91
Financial Impact on Date of Restructure			0
Consumer | Change in Maturity Date
Financing Receivable, Modifications [Line Items]
Balance			91
Consumer | Change in Rate
Financing Receivable, Modifications [Line Items]
Balance			$ 0
Consumer | Other consumer
Financing Receivable, Modifications [Line Items]
Number of Loans | loan			1
Balance Prior to TDR			$ 91
Balance			91
Financial Impact on Date of Restructure			0
Consumer | Other consumer | Change in Maturity Date
Financing Receivable, Modifications [Line Items]
Balance			91
Consumer | Other consumer | Change in Rate
Financing Receivable, Modifications [Line Items]
Balance			$ 0
Real estate
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	2		3	3
Balance Prior to TDR	$ 392		$ 453	$ 7,818
Balance	390		452	7,818
Financial Impact on Date of Restructure	212		212	33
Real estate | Change in Maturity Date
Financing Receivable, Modifications [Line Items]
Balance	390		452	7,818
Real estate | Change in Rate
Financing Receivable, Modifications [Line Items]
Balance	$ 0		$ 0	$ 0
Real estate | Single family residential
Financing Receivable, Modifications [Line Items]
Number of Loans | loan			1
Balance Prior to TDR			$ 61
Balance			62
Financial Impact on Date of Restructure			0
Real estate | Single family residential | Change in Maturity Date
Financing Receivable, Modifications [Line Items]
Balance			62
Real estate | Single family residential | Change in Rate
Financing Receivable, Modifications [Line Items]
Balance			$ 0
Real estate | Construction
Financing Receivable, Modifications [Line Items]
Number of Loans | loan				1
Balance Prior to TDR				$ 456
Balance				456
Financial Impact on Date of Restructure				0
Real estate | Construction | Change in Maturity Date
Financing Receivable, Modifications [Line Items]
Balance				456
Real estate | Construction | Change in Rate
Financing Receivable, Modifications [Line Items]
Balance				$ 0
Real estate | Other commercial
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	2		2	2
Balance Prior to TDR	$ 392		$ 392	$ 7,362
Balance	390		390	7,362
Financial Impact on Date of Restructure	212		212	33
Real estate | Other commercial | Change in Maturity Date
Financing Receivable, Modifications [Line Items]
Balance	390		390	7,362
Real estate | Other commercial | Change in Rate
Financing Receivable, Modifications [Line Items]
Balance	$ 0		$ 0	$ 0
Commercial
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	3	1	3	10
Balance Prior to TDR	$ 2,363	$ 608	$ 2,363	$ 1,419
Balance	2,358	607	2,358	1,407
Financial Impact on Date of Restructure	190	0	190	0
Commercial | Change in Maturity Date
Financing Receivable, Modifications [Line Items]
Balance	2,358	607	2,358	1,368
Commercial | Change in Rate
Financing Receivable, Modifications [Line Items]
Balance	$ 0	$ 0	$ 0	$ 39
Commercial | Commercial
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	3	1	3	10
Balance Prior to TDR	$ 2,363	$ 608	$ 2,363	$ 1,419
Balance	2,358	607	2,358	1,407
Financial Impact on Date of Restructure	190	0	190	0
Commercial | Commercial | Change in Maturity Date
Financing Receivable, Modifications [Line Items]
Balance	2,358	607	2,358	1,368
Commercial | Commercial | Change in Rate
Financing Receivable, Modifications [Line Items]
Balance	$ 0	$ 0	$ 0	$ 39

Loans and Allowance for Loan_10

Loans and Allowance for Loan Losses - Loans by Credit Risk Rating, Segregated by Class of Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 11,858,195	$ 10,779,685
Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	11,644,398	10,438,375
Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	68,510	165,736
Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	144,691	175,064
Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	596	376
Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	134
Other
Financing Receivable, Recorded Investment [Line Items]
Loans		26,962
Other | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans		26,962
Other | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Other | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Other | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Other | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	8,123,274	5,705,609
Loans, Excluding Acquired Loans | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	441,718	465,516
Loans, Excluding Acquired Loans | Consumer | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	437,477	460,080
Loans, Excluding Acquired Loans | Consumer | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	4,241	5,436
Loans, Excluding Acquired Loans | Consumer | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Credit cards
Financing Receivable, Recorded Investment [Line Items]
Loans	182,137	185,422
Loans, Excluding Acquired Loans | Consumer | Credit cards | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	181,620	184,920
Loans, Excluding Acquired Loans | Consumer | Credit cards | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Credit cards | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	517	502
Loans, Excluding Acquired Loans | Consumer | Credit cards | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Credit cards | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Other consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	259,581	280,094
Loans, Excluding Acquired Loans | Consumer | Other consumer | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	255,857	275,160
Loans, Excluding Acquired Loans | Consumer | Other consumer | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Other consumer | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	3,724	4,934
Loans, Excluding Acquired Loans | Consumer | Other consumer | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Other consumer | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	5,709,067	4,239,612
Loans, Excluding Acquired Loans | Real estate | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	5,655,650	4,150,321
Loans, Excluding Acquired Loans | Real estate | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	12,433	29,330
Loans, Excluding Acquired Loans | Real estate | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	40,747	59,658
Loans, Excluding Acquired Loans | Real estate | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	237	303
Loans, Excluding Acquired Loans | Real estate | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Real estate | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	1,229,888	614,155
Loans, Excluding Acquired Loans | Real estate | Construction | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	1,225,481	603,126
Loans, Excluding Acquired Loans | Real estate | Construction | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	2,286	5,795
Loans, Excluding Acquired Loans | Real estate | Construction | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	2,121	5,218
Loans, Excluding Acquired Loans | Real estate | Construction | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	0	16
Loans, Excluding Acquired Loans | Real estate | Construction | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Real estate | Single family residential
Financing Receivable, Recorded Investment [Line Items]
Loans	1,401,991	1,094,633
Loans, Excluding Acquired Loans | Real estate | Single family residential | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	1,382,655	1,066,902
Loans, Excluding Acquired Loans | Real estate | Single family residential | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	843	3,954
Loans, Excluding Acquired Loans | Real estate | Single family residential | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	18,256	23,490
Loans, Excluding Acquired Loans | Real estate | Single family residential | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	237	287
Loans, Excluding Acquired Loans | Real estate | Single family residential | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Real estate | Other commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	3,077,188	2,530,824
Loans, Excluding Acquired Loans | Real estate | Other commercial | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	3,047,514	2,480,293
Loans, Excluding Acquired Loans | Real estate | Other commercial | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	9,304	19,581
Loans, Excluding Acquired Loans | Real estate | Other commercial | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	20,370	30,950
Loans, Excluding Acquired Loans | Real estate | Other commercial | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Real estate | Other commercial | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	1,827,120	973,519
Loans, Excluding Acquired Loans | Commercial | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	1,785,099	882,442
Loans, Excluding Acquired Loans | Commercial | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	8,405	74,278
Loans, Excluding Acquired Loans | Commercial | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	33,616	16,592
Loans, Excluding Acquired Loans | Commercial | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	0	73
Loans, Excluding Acquired Loans | Commercial | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	134
Loans, Excluding Acquired Loans | Commercial | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	1,608,342	825,217
Loans, Excluding Acquired Loans | Commercial | Commercial | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	1,569,357	736,377
Loans, Excluding Acquired Loans | Commercial | Commercial | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	8,250	74,254
Loans, Excluding Acquired Loans | Commercial | Commercial | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	30,735	14,402
Loans, Excluding Acquired Loans | Commercial | Commercial | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	0	50
Loans, Excluding Acquired Loans | Commercial | Commercial | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	134
Loans, Excluding Acquired Loans | Commercial | Agricultural
Financing Receivable, Recorded Investment [Line Items]
Loans	218,778	148,302
Loans, Excluding Acquired Loans | Commercial | Agricultural | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	215,742	146,065
Loans, Excluding Acquired Loans | Commercial | Agricultural | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	155	24
Loans, Excluding Acquired Loans | Commercial | Agricultural | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	2,881	2,190
Loans, Excluding Acquired Loans | Commercial | Agricultural | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	0	23
Loans, Excluding Acquired Loans | Commercial | Agricultural | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Other
Financing Receivable, Recorded Investment [Line Items]
Loans	145,369	26,962
Loans, Excluding Acquired Loans | Other | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	145,369
Loans, Excluding Acquired Loans | Other | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	0
Loans, Excluding Acquired Loans | Other | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	0
Loans, Excluding Acquired Loans | Other | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	0
Loans, Excluding Acquired Loans | Other | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0
Loans Acquired
Financing Receivable, Recorded Investment [Line Items]
Loans	3,734,921	5,074,076
Loans Acquired | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	3,620,803	4,918,570
Loans Acquired | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	47,672	62,128
Loans Acquired | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	66,087	93,378
Loans Acquired | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	359	0
Loans Acquired | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Consumer | Other consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	21,278	51,467
Loans Acquired | Consumer | Other consumer | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	20,813	50,625
Loans Acquired | Consumer | Other consumer | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	9	21
Loans Acquired | Consumer | Other consumer | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	456	821
Loans Acquired | Consumer | Other consumer | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Consumer | Other consumer | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	3,114,950	3,818,037
Loans Acquired | Real estate | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	3,037,255	3,712,847
Loans Acquired | Real estate | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	32,769	48,206
Loans Acquired | Real estate | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	44,567	56,984
Loans Acquired | Real estate | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	359	0
Loans Acquired | Real estate | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Real estate | Other consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	2,040,189	2,387,777
Loans Acquired | Real estate | Other consumer | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	2,006,371
Loans Acquired | Real estate | Other consumer | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	12,283
Loans Acquired | Real estate | Other consumer | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	21,535
Loans Acquired | Real estate | Other consumer | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	0
Loans Acquired | Real estate | Other consumer | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0
Loans Acquired | Real estate | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	467,895	637,032
Loans Acquired | Real estate | Construction | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	440,881	604,796
Loans Acquired | Real estate | Construction | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	18,011	30,524
Loans Acquired | Real estate | Construction | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	9,003	1,712
Loans Acquired | Real estate | Construction | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Real estate | Construction | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Real estate | Single family residential
Financing Receivable, Recorded Investment [Line Items]
Loans	606,866	793,228
Loans Acquired | Real estate | Single family residential | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	590,003	770,954
Loans Acquired | Real estate | Single family residential | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	2,475	2,618
Loans Acquired | Real estate | Single family residential | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	14,029	19,656
Loans Acquired | Real estate | Single family residential | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	359	0
Loans Acquired | Real estate | Single family residential | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Real estate | Other commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	2,040,189	2,387,777
Loans Acquired | Real estate | Other commercial | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans		2,337,097
Loans Acquired | Real estate | Other commercial | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans		15,064
Loans Acquired | Real estate | Other commercial | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans		35,616
Loans Acquired | Real estate | Other commercial | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Loans Acquired | Real estate | Other commercial | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Loans Acquired | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	598,693	1,062,163
Loans Acquired | Commercial | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	562,735	1,012,689
Loans Acquired | Commercial | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	14,894	13,901
Loans Acquired | Commercial | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	21,064	35,573
Loans Acquired | Commercial | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Commercial | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Commercial | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	596,641	995,587
Loans Acquired | Commercial | Commercial | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	560,791	946,322
Loans Acquired | Commercial | Commercial | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	14,894	13,901
Loans Acquired | Commercial | Commercial | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	20,956	35,364
Loans Acquired | Commercial | Commercial | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Commercial | Commercial | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Commercial | Agricultural
Financing Receivable, Recorded Investment [Line Items]
Loans	2,052	66,576
Loans Acquired | Commercial | Agricultural | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	1,944	66,367
Loans Acquired | Commercial | Agricultural | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Commercial | Agricultural | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	108	209
Loans Acquired | Commercial | Agricultural | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Commercial | Agricultural | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Other
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 0	142,409
Loans Acquired | Other | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans		142,409
Loans Acquired | Other | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Loans Acquired | Other | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Loans Acquired | Other | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Loans Acquired | Other | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans		$ 0

Loans and Allowance for Loan_11

Loans and Allowance for Loan Losses - Activity in the Allowance for Loan Losses, by Portfolio Segment, for the Current Year (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of period	$ 53,776,000	$ 41,770,000	$ 42,086,000	$ 37,240,000
Provision for loan losses	10,345,000	5,462,000	28,528,000	16,792,000
Balance, end of year	56,703,000	43,108,000	56,703,000	43,108,000
Loans, Excluding Acquired Loans
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of period	51,732,000	41,379,000	41,668,000	36,286,000
Provision for loan losses	10,345,000	5,462,000	26,691,000	15,327,000
Charge-offs	(7,784,000)	(5,174,000)	(15,384,000)	(12,295,000)
Recoveries	1,065,000	1,050,000	2,383,000	3,399,000
Net charge-offs	(6,719,000)	(4,124,000)	(13,001,000)	(8,896,000)
Balance, end of year	55,358,000	42,717,000	55,358,000	42,717,000
Period-end amount allocated to:
Loans individually evaluated for impairment	459,000	6,321,000	459,000	6,321,000	$ 338,000
Loans collectively evaluated for impairment	54,899,000	36,396,000	54,899,000	36,396,000	41,330,000
Loans, Excluding Acquired Loans | Other Consumer and Other
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of period	3,239,000	3,789,000	3,596,000	2,951,000
Provision for loan losses	729,000	241,000	2,567,000	1,920,000
Charge-offs	(1,321,000)	(819,000)	(3,743,000)	(2,986,000)
Recoveries	176,000	445,000	403,000	1,771,000
Net charge-offs	(1,145,000)	(374,000)	(3,340,000)	(1,215,000)
Balance, end of year	2,823,000	3,656,000	2,823,000	3,656,000
Period-end amount allocated to:
Loans individually evaluated for impairment	0	0	0	0	0
Loans collectively evaluated for impairment	2,823,000	3,656,000	2,823,000	3,656,000	3,596,000
Loans, Excluding Acquired Loans | Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of period	15,767,000	8,105,000	7,007,000	7,739,000
Provision for loan losses	3,589,000	2,310,000	14,772,000	3,255,000
Charge-offs	(592,000)	(2,442,000)	(3,143,000)	(3,083,000)
Recoveries	450,000	21,000	578,000	83,000
Net charge-offs	(142,000)	(2,421,000)	(2,565,000)	(3,000,000)
Balance, end of year	19,214,000	7,994,000	19,214,000	7,994,000
Period-end amount allocated to:
Loans individually evaluated for impairment	191,000	3,996,000	191,000	3,996,000	0
Loans collectively evaluated for impairment	19,023,000	3,998,000	19,023,000	3,998,000	7,007,000
Loans, Excluding Acquired Loans | Real estate
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of period	28,904,000	25,731,000	27,281,000	21,817,000
Provision for loan losses	5,308,000	2,150,000	7,133,000	7,984,000
Charge-offs	(4,952,000)	(896,000)	(5,568,000)	(3,264,000)
Recoveries	210,000	309,000	624,000	757,000
Net charge-offs	(4,742,000)	(587,000)	(4,944,000)	(2,507,000)
Balance, end of year	29,470,000	27,294,000	29,470,000	27,294,000
Period-end amount allocated to:
Loans individually evaluated for impairment	268,000	2,325,000	268,000	2,325,000	338,000
Loans collectively evaluated for impairment	29,202,000	24,969,000	29,202,000	24,969,000	26,943,000
Loans, Excluding Acquired Loans | Consumer | Credit cards
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of period	3,822,000	3,754,000	3,784,000	3,779,000
Provision for loan losses	719,000	761,000	2,219,000	2,168,000
Charge-offs	(919,000)	(1,017,000)	(2,930,000)	(2,962,000)
Recoveries	229,000	275,000	778,000	788,000
Net charge-offs	(690,000)	(742,000)	(2,152,000)	(2,174,000)
Balance, end of year	3,851,000	3,773,000	3,851,000	3,773,000
Period-end amount allocated to:
Loans individually evaluated for impairment	0	0	0	0	0
Loans collectively evaluated for impairment	3,851,000	3,773,000	3,851,000	3,773,000	$ 3,784,000
Loans Acquired
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of period	2,044,000		418,000	954,000
Provision for loan losses	0	0	1,837,000	1,464,000
Charge-offs	(699,000)		(910,000)	(2,000,000)
Balance, end of year	$ 1,345,000	$ 391,000	$ 1,345,000	$ 391,000

Loans and Allowance for Loan_12

Loans and Allowance for Loan Losses - Recorded Investment in Loans, Excluding Loans Acquired (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	$ 11,858,195	$ 10,779,685
Loans, Excluding Acquired Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	47,354	43,923
Loans collectively evaluated for impairment	8,075,920	5,661,686
Total Loans	8,123,274	5,705,609
Loans, Excluding Acquired Loans | Other Consumer and Other
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	3,317	4,605
Loans collectively evaluated for impairment	401,633	302,451
Total Loans	404,950	307,056
Loans, Excluding Acquired Loans | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	17,308	7,610
Loans collectively evaluated for impairment	1,809,812	965,909
Total Loans	1,827,120	973,519
Loans, Excluding Acquired Loans | Real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	26,401	31,538
Loans collectively evaluated for impairment	5,682,666	4,208,074
Total Loans	5,709,067	4,239,612
Loans, Excluding Acquired Loans | Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	441,718	465,516
Loans, Excluding Acquired Loans | Consumer | Credit cards
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	328	170
Loans collectively evaluated for impairment	181,809	185,252
Total Loans	$ 182,137	$ 185,422

Loans Acquired - Textual (Detai

Loans Acquired - Textual (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2018	Dec. 31, 2017	Oct. 19, 2017	Oct. 18, 2017	Jun. 30, 2017	May 15, 2017	May 14, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 11,858,195,000		$ 11,858,195,000			$ 10,779,685,000
Allowance for loan losses	56,703,000	$ 43,108,000	56,703,000	$ 43,108,000	$ 53,776,000	42,086,000			$ 41,770,000			$ 37,240,000
Provision for loan losses	10,345,000	5,462,000	28,528,000	16,792,000
Loans acquired, net
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	3,734,921,000		3,734,921,000			5,074,076,000
Allowance for loan losses	1,345,000	391,000	1,345,000	391,000	$ 2,044,000	418,000						$ 954,000
Provision for loan losses	$ 0	$ 0	$ 1,837,000	$ 1,464,000
OKSB Merger
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans						1,985,000,000
Gross value of loans acquired						2,021,000,000	$ 1,996,453,000	$ 2,039,524,000
Loans acquired discount						36,300,000
OKSB Merger | Financial Asset Acquired with Credit Deterioration
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans						11,400,000
Gross value of loans acquired						18,100,000
Loans acquired discount						6,700,000
First Texas Merger
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans						2,208,000,000
Gross value of loans acquired						2,246,000,000	$ 2,208,378,000	$ 2,246,212,000
Loans acquired discount						$ 37,800,000
Hardeman County Investment Company, Inc.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans									249,200,000
Gross value of loans acquired									254,200,000	$ 251,649,000	$ 257,641,000
Loans acquired discount									5,000,000
Hardeman County Investment Company, Inc. | Financial Asset Acquired with Credit Deterioration
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans									2,400,000
Gross value of loans acquired									3,400,000
Loans acquired discount									$ 990,000

Loans Acquired - Carrying Value

Loans Acquired - Carrying Value of all Acquired Impaired Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Acquired loans	$ 11,858,195		$ 10,779,685
Allowance for loan losses	56,703	$ 53,776	42,086	$ 43,108	$ 41,770	$ 37,240
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Acquired loans			26,962
Loans Acquired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Acquired loans	3,734,921		5,074,076
Allowance for loan losses	1,345	$ 2,044	418	$ 391		$ 954
Loans Acquired | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Acquired loans	21,278		51,467
Loans Acquired | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Acquired loans	3,114,950		3,818,037
Loans Acquired | Real estate | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Acquired loans	2,040,189		2,387,777
Loans Acquired | Real estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Acquired loans	467,895		637,032
Loans Acquired | Real estate | Single family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Acquired loans	606,866		793,228
Loans Acquired | Real estate | Other commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Acquired loans	2,040,189		2,387,777
Loans Acquired | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Acquired loans	598,693		1,062,163
Loans Acquired | Commercial | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Acquired loans	596,641		995,587
Loans Acquired | Commercial | Agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Acquired loans	2,052		66,576
Loans Acquired | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Acquired loans	$ 0		$ 142,409

Loans Acquired - Nonaccrual Acq

Loans Acquired - Nonaccrual Acquired Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	$ 40,505	$ 45,642
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	3,645	4,775
Consumer | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	3,317	4,605
Real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	22,436	31,727
Real estate | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	1,289	2,242
Real estate | Single family residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	11,508	13,431
Real estate | Other commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	9,639	16,054
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	14,424	9,140
Commercial | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	11,932	6,980
Commercial | Agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	2,492	2,160
Loans Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	15,981	23,485
Loans Acquired | Consumer | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	293	334
Loans Acquired | Real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	10,686	21,319
Loans Acquired | Real estate | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	279	1,767
Loans Acquired | Real estate | Single family residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	9,053	12,151
Loans Acquired | Real estate | Other commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	1,354	7,401
Loans Acquired | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	5,002	1,832
Loans Acquired | Commercial | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	4,964	1,748
Loans Acquired | Commercial | Agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	$ 38	$ 84

Loans Acquired - Age Analysis o

Loans Acquired - Age Analysis of Past Due Acquired Loans, Excluding Loans Covered by Loss Share (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	$ 11,858,195	$ 10,779,685
Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans		26,962
Loans Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	21,329	47,684
Current	3,713,592	5,026,392
Total Loans	3,734,921	5,074,076
90 Days Past Due & Accruing	1	3,145
Loans Acquired | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	6,778	35,988
Loans Acquired | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	14,551	11,696
Loans Acquired | Consumer | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	427	1,149
Current	20,851	50,318
Total Loans	21,278	51,467
90 Days Past Due & Accruing	0	108
Loans Acquired | Consumer | Other consumer | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	213	889
Loans Acquired | Consumer | Other consumer | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	214	260
Loans Acquired | Real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	15,379	43,086
Current	3,099,571	3,774,951
Total Loans	3,114,950	3,818,037
90 Days Past Due & Accruing	1	2,970
Loans Acquired | Real estate | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,067	32,689
Loans Acquired | Real estate | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	10,312	10,397
Loans Acquired | Real estate | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	6,648	22,823
Current	2,033,541	2,364,954
Total Loans	2,040,189	2,387,777
90 Days Past Due & Accruing	0	2,565
Loans Acquired | Real estate | Other consumer | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,491	17,176
Loans Acquired | Real estate | Other consumer | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,157	5,647
Loans Acquired | Real estate | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	324	4,025
Current	467,571	633,007
Total Loans	467,895	637,032
90 Days Past Due & Accruing	0	279
Loans Acquired | Real estate | Construction | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	117	2,577
Loans Acquired | Real estate | Construction | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	207	1,448
Loans Acquired | Real estate | Single family residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	8,407	16,238
Current	598,459	776,990
Total Loans	606,866	793,228
90 Days Past Due & Accruing	1	126
Loans Acquired | Real estate | Single family residential | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,459	12,936
Loans Acquired | Real estate | Single family residential | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,948	3,302
Loans Acquired | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,523	3,434
Current	593,170	1,058,729
Total Loans	598,693	1,062,163
90 Days Past Due & Accruing	0	67
Loans Acquired | Commercial | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,498	2,395
Loans Acquired | Commercial | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,025	1,039
Loans Acquired | Commercial | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,491	3,383
Current	591,150	992,204
Total Loans	596,641	995,587
90 Days Past Due & Accruing	0	67
Loans Acquired | Commercial | Commercial | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,471	2,344
Loans Acquired | Commercial | Commercial | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,020	1,039
Loans Acquired | Commercial | Agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	32	51
Current	2,020	66,525
Total Loans	2,052	66,576
90 Days Past Due & Accruing	0	0
Loans Acquired | Commercial | Agricultural | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	27	51
Loans Acquired | Commercial | Agricultural | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5	0
Loans Acquired | Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		15
Current		142,394
Total Loans	$ 0	142,409
90 Days Past Due & Accruing		0
Loans Acquired | Other | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		15
Loans Acquired | Other | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		$ 0

Loans Acquired - Summary of Acq

Loans Acquired - Summary of Acquired Loans, Excluding Loans Covered by Loss Share (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 11,858,195	$ 10,779,685
Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	3,734,921	5,074,076
Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	11,644,398	10,438,375
Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	3,620,803	4,918,570
Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	68,510	165,736
Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	47,672	62,128
Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	144,691	175,064
Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	66,087	93,378
Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	596	376
Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	359	0
Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	134
Risk Rate 8 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Consumer | Other consumer | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	21,278	51,467
Consumer | Other consumer | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	20,813	50,625
Consumer | Other consumer | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	9	21
Consumer | Other consumer | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	456	821
Consumer | Other consumer | Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Consumer | Other consumer | Risk Rate 8 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Real estate | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	3,114,950	3,818,037
Real estate | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	3,037,255	3,712,847
Real estate | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	32,769	48,206
Real estate | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	44,567	56,984
Real estate | Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	359	0
Real estate | Risk Rate 8 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Real estate | Other consumer | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	2,040,189	2,387,777
Real estate | Other consumer | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	2,006,371
Real estate | Other consumer | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	12,283
Real estate | Other consumer | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	21,535
Real estate | Other consumer | Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0
Real estate | Other consumer | Risk Rate 8 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0
Real estate | Construction | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	467,895	637,032
Real estate | Construction | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	440,881	604,796
Real estate | Construction | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	18,011	30,524
Real estate | Construction | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	9,003	1,712
Real estate | Construction | Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Real estate | Construction | Risk Rate 8 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Real estate | Single family residential | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	606,866	793,228
Real estate | Single family residential | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	590,003	770,954
Real estate | Single family residential | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	2,475	2,618
Real estate | Single family residential | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	14,029	19,656
Real estate | Single family residential | Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	359	0
Real estate | Single family residential | Risk Rate 8 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Real estate | Other commercial | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	2,040,189	2,387,777
Real estate | Other commercial | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans		2,337,097
Real estate | Other commercial | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans		15,064
Real estate | Other commercial | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans		35,616
Real estate | Other commercial | Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Real estate | Other commercial | Risk Rate 8 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Commercial | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	598,693	1,062,163
Commercial | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	562,735	1,012,689
Commercial | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	14,894	13,901
Commercial | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	21,064	35,573
Commercial | Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial | Risk Rate 8 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial | Commercial | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	596,641	995,587
Commercial | Commercial | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	560,791	946,322
Commercial | Commercial | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	14,894	13,901
Commercial | Commercial | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	20,956	35,364
Commercial | Commercial | Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial | Commercial | Risk Rate 8 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial | Agricultural | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	2,052	66,576
Commercial | Agricultural | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	1,944	66,367
Commercial | Agricultural | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial | Agricultural | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	108	209
Commercial | Agricultural | Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial | Agricultural | Risk Rate 8 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Other
Financing Receivable, Recorded Investment [Line Items]
Loans		26,962
Other | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 0	142,409
Other | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans		26,962
Other | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans		142,409
Other | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Other | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Other | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Other | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Other | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Other | Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Other | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Other | Risk Rate 8 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans		$ 0

Loans Acquired - Impact of the

Loans Acquired - Impact of the Adjustments on the Company's Financial Results for the Following Reporting Periods (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Receivables [Abstract]
Impact on net interest income and pre-tax income	$ 629	$ 23	$ 1,105	$ 2,596
Impact, net of taxes	$ 464	$ 14	$ 814	$ 1,578

Loans Acquired - Changes in the

Loans Acquired - Changes in the Carrying Amount of the Accretable Yield for All Purchased Impaired and Non-impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accretable Yield
Beginning balance	$ 1,382	$ 766	$ 620	$ 1,655
Additions	0	0	0	0
Accretable yield adjustments	717	52	1,895	2,698
Accretion	(635)	(408)	(1,051)	(3,943)
Payments and other reductions, net	0	0	0	0
Balance, ending	1,464	410	1,464	410
Carrying Amount of Loans
Beginning balance	13,995	8,448	17,116	17,802
Additions	0	0	0	2,388
Accretion	635	408	1,051	3,943
Payments and other reductions, net	(9,664)	(980)	(13,201)	(16,257)
Balance, ending	$ 4,966	$ 7,876	$ 4,966	$ 7,876

Goodwill and Other Intangible_3

Goodwill and Other Intangible Assets - Textual (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Oct. 19, 2017	Oct. 18, 2017	May 15, 2017	May 14, 2017
Goodwill [Line Items]
Goodwill	$ 845,687	$ 842,651
Minimum
Finite-Lived Intangible Assets [Line Items]
Useful life	10 years
Maximum
Finite-Lived Intangible Assets [Line Items]
Useful life	15 years
Core Deposit Premium | Minimum
Finite-Lived Intangible Assets [Line Items]
Useful life	10 years
Core Deposit Premium | Maximum
Finite-Lived Intangible Assets [Line Items]
Useful life	15 years
OKSB Merger
Goodwill [Line Items]
Goodwill			$ 229,144	$ 13,545
OKSB Merger | Core Deposit Premium
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired		42,100
OKSB Merger | Other intangibles, net
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired		3,800
First Texas BHC, Inc.
Goodwill [Line Items]
Goodwill			$ 240,800
First Texas BHC, Inc. | Core Deposit Premium
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired		7,300
Hardeman County Investment Company, Inc.
Goodwill [Line Items]
Goodwill					$ 29,371	$ 11,485
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired		830
Hardeman County Investment Company, Inc. | Core Deposit Premium
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired		$ 7,800

Goodwill and Other Intangible_4

Goodwill and Other Intangible Assets - Goodwill and Other Intangibles (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	$ 845,687	$ 842,651
Finite-Lived Intangible Assets [Line Items]
Other intangible assets, net	93,975	106,071
Total goodwill and other intangible assets	939,662	948,722
Core Deposit Premium
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	105,984	105,984
Accumulated amortization	(23,802)	(16,659)
Other intangible assets, net	82,182	89,325
Books of Business Intangible
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	15,234	15,414
Accumulated amortization	(3,441)	(2,827)
Other intangible assets, net	11,793	12,587
Other intangibles, net
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	2,068	6,037
Accumulated amortization	(2,068)	(1,878)
Other intangible assets, net	$ 0	$ 4,159

Goodwill and Other Intangible_5

Goodwill and Other Intangible Assets - Amortization Expense (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Remainder of 2018	$ 2,642
2,019	10,565
2,020	10,552
2,021	10,490
2,022	10,438
Thereafter	49,288
Other intangible assets, net	$ 93,975	$ 106,071

Time Deposits - Textual (Detail

Time Deposits - Textual (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Banking and Thrift [Abstract]
Time deposits certificates of $100,000 or more	$ 1,364	$ 736
Time deposits certificates over $250,000	$ 702.5	$ 396.8

Income Taxes - Provision for In

Income Taxes - Provision for Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Income taxes currently payable	$ 5,638	$ 11,946	$ 31,335	$ 30,467
Deferred income taxes	5,264	2,732	7,316	4,962
Provision for income taxes	$ 10,902	$ 14,678	$ 38,651	$ 35,429

Income Taxes - Tax Effects of T

Income Taxes - Tax Effects of Temporary Differences Related to Deferred Taxes Included in Other Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Deferred tax assets:
Loans acquired	$ 12,092	$ 19,885
Allowance for loan losses	12,601	10,773
Valuation of foreclosed assets	2,709	2,852
Tax NOLs from acquisition	6,962	7,821
Deferred compensation payable	2,645	2,433
Accrued equity and other compensation	6,605	5,302
Acquired securities	549	578
Unrealized loss on available-for-sale securities	16,221	6,107
Other	5,890	8,813
Gross deferred tax assets	66,274	64,564
Deferred tax liabilities:
Goodwill and other intangible amortization	(30,645)	(32,572)
Accumulated depreciation	(11,778)	(8,945)
Other	(2,197)	(4,413)
Gross deferred tax liabilities	(44,620)	(45,930)
Net deferred tax asset, included in other assets	$ 21,654	$ 18,634

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Income Tax Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Computed at the statutory rate	$ 13,880	$ 15,235	$ 41,731	$ 38,313
State income taxes, net of federal tax benefit	986	342	4,073	1,117
Discrete items related to ASU 2016-09	(31)	5	(2,567)	(1,372)
Tax exempt interest income	(833)	(955)	(2,292)	(3,160)
Tax exempt earnings on BOLI	(186)	(178)	(562)	(616)
Other differences, net	(2,914)	229	(1,732)	1,147
Provision for income taxes	$ 10,902	$ 14,678	$ 38,651	$ 35,429

Income Taxes - Textual (Details

Income Taxes - Textual (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018USD ($)
U.S. federal | Earliest Tax Year
Operating Loss Carryforwards [Line Items]
Open tax year	2,014
State | Earliest Tax Year
Operating Loss Carryforwards [Line Items]
Open tax year	2,014
Metropolitan
Operating Loss Carryforwards [Line Items]
Net operating losses	$ 35.6

Securities Sold Under Agreeme_3

Securities Sold Under Agreements to Repurchase - Textual (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Banking and Thrift [Abstract]
Repurchase agreements	$ 109	$ 122

Securities Sold Under Agreeme_4

Securities Sold Under Agreements to Repurchase - Contractual Maturity of the Agreements (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	$ 109,000	$ 122,000
U.S. Government agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	108,963	122,019
U.S. Government agencies | Overnight and Continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	108,963	122,019
U.S. Government agencies | Up to 30 Days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	0	0
U.S. Government agencies | 30-90 Days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	0	0
U.S. Government agencies | Greater than 90 Days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	$ 0	$ 0

Other Borrowings and Subordin_3

Other Borrowings and Subordinated Notes and Debentures - Debt Components (Details) - USD ($) $ in Thousands	1 Months Ended	9 Months Ended
	Mar. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Total other borrowings and subordinated debt		$ 1,793,851	$ 1,520,589
U.S. Bank National Association | Revolving credit facility
Debt Instrument [Line Items]
Total other borrowings and subordinated debt		$ 0	75,000
U.S. Bank National Association | Revolving credit facility | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)		1.50%
Total other borrowings
Debt Instrument [Line Items]
Total other borrowings and subordinated debt		$ 1,420,917	1,380,024
FHLB advances, net of discount, due 2018 to 2033, 1.38% to 7.37% secured by residential real estate loans
Debt Instrument [Line Items]
Total other borrowings and subordinated debt		$ 1,420,917	1,261,642
FHLB advances, net of discount, due 2018 to 2033, 1.38% to 7.37% secured by residential real estate loans | Minimum
Debt Instrument [Line Items]
Fixed rate (as percent)		1.38%
FHLB advances, net of discount, due 2018 to 2033, 1.38% to 7.37% secured by residential real estate loans | Maximum
Debt Instrument [Line Items]
Fixed rate (as percent)		7.37%
Notes payable, due 10/15/2020, 3.85%, fixed rate, unsecured
Debt Instrument [Line Items]
Total other borrowings and subordinated debt		$ 0	43,382
Fixed rate (as percent)		3.85%
Subordinated Notes and Debentures
Debt Instrument [Line Items]
Unamortized debt issuance costs		$ (3,463)	0
Total other borrowings and subordinated debt		372,934	140,565
Subordinated notes payable, due 4/1/2028, fixed-to-floating rate (fixed rate of 5.00% through 3/31/2023, floating rate of 2.15% above the three month LIBOR rate, reset quarterly)
Debt Instrument [Line Items]
Long-term debt, gross		$ 330,000	0
Fixed rate (as percent)	5.00%	5.00%
Subordinated notes payable, due 4/1/2028, fixed-to-floating rate (fixed rate of 5.00% through 3/31/2023, floating rate of 2.15% above the three month LIBOR rate, reset quarterly) | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)	2.15%
Debentures | Trust preferred securities, due 12/30/2033, floating rate of 2.80% above the three month LIBOR rate, reset quarterly, callable without penalty
Debt Instrument [Line Items]
Long-term debt, gross		$ 0	20,620
Debentures | Trust preferred securities, due 12/30/2033, floating rate of 2.80% above the three month LIBOR rate, reset quarterly, callable without penalty | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)		2.80%
Debentures | Trust preferred securities, net of discount, due 6/30/2035, floating rate of 1.75% above the three month LIBOR rate, reset quarterly, callable without penalty
Debt Instrument [Line Items]
Long-term debt, gross		$ 0	9,327
Debentures | Trust preferred securities, net of discount, due 6/30/2035, floating rate of 1.75% above the three month LIBOR rate, reset quarterly, callable without penalty | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)		1.75%
Debentures | Trust preferred securities, net of discount, due 9/15/2037, floating rate of 1.37% above the three month LIBOR rate, reset quarterly
Debt Instrument [Line Items]
Long-term debt, gross		$ 10,310	10,284
Debentures | Trust preferred securities, net of discount, due 9/15/2037, floating rate of 1.37% above the three month LIBOR rate, reset quarterly | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)		1.37%
Debentures | Trust preferred securities, net of discount, due 12/5/2033, floating rate of 2.88% above the three month LIBOR rate, reset quarterly, callable without penalty
Debt Instrument [Line Items]
Long-term debt, gross		$ 0	5,156
Debentures | Trust preferred securities, net of discount, due 12/5/2033, floating rate of 2.88% above the three month LIBOR rate, reset quarterly, callable without penalty | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)		2.88%
Debentures | Trust preferred securities, net of discount, due 10/18/2034, floating rate of 2.00% above the three month LIBOR rate, reset quarterly, callable without penalty
Debt Instrument [Line Items]
Long-term debt, gross		$ 0	5,148
Debentures | Trust preferred securities, net of discount, due 10/18/2034, floating rate of 2.00% above the three month LIBOR rate, reset quarterly, callable without penalty | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)		2.00%
Debentures | Trust preferred securities, net of discount, due 6/6/2037, floating rate of 1.57% above the three month LIBOR rate, reset quarterly, callable without penalty
Debt Instrument [Line Items]
Long-term debt, gross		$ 10,310	10,288
Debentures | Trust preferred securities, net of discount, due 6/6/2037, floating rate of 1.57% above the three month LIBOR rate, reset quarterly, callable without penalty | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)		1.57%
Debentures | Trust preferred securities, due 12/15/2035, floating rate of 1.45% above the three month LIBOR rate, reset quarterly, callable without penalty
Debt Instrument [Line Items]
Long-term debt, gross		$ 6,702	6,702
Debentures | Trust preferred securities, due 12/15/2035, floating rate of 1.45% above the three month LIBOR rate, reset quarterly, callable without penalty | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)		1.45%
Debentures | Trust preferred securities, due 6/26/2033, floating rate of 3.10% above the three month LIBOR rate, reset quarterly, callable without penalty
Debt Instrument [Line Items]
Long-term debt, gross		$ 0	20,619
Debentures | Trust preferred securities, due 6/26/2033, floating rate of 3.10% above the three month LIBOR rate, reset quarterly, callable without penalty | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)		3.10%
Debentures | Trust preferred securities, due 10/7/2033, floating rate of 2.85% above the three month LIBOR rate, reset quarterly, callable without penalty
Debt Instrument [Line Items]
Long-term debt, gross		$ 0	25,774
Debentures | Trust preferred securities, due 10/7/2033, floating rate of 2.85% above the three month LIBOR rate, reset quarterly, callable without penalty | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)		2.85%
Debentures | Trust preferred securities, due 9/15/2037, floating rate of 2.00% above the three month LIBOR rate, reset quarterly, callable without penalty
Debt Instrument [Line Items]
Long-term debt, gross		$ 0	8,248
Debentures | Trust preferred securities, due 9/15/2037, floating rate of 2.00% above the three month LIBOR rate, reset quarterly, callable without penalty | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)		2.00%
Debentures | Other subordinated debentures, net of discount, called 9/30/2018, floating rate equal to daily average of prime rate, reset quarterly
Debt Instrument [Line Items]
Long-term debt, gross		$ 19,075	$ 18,399

Other Borrowings and Subordin_4

Other Borrowings and Subordinated Notes and Debentures - Textual (Details) - USD ($)	1 Months Ended			9 Months Ended	12 Months Ended
	Oct. 31, 2018	Mar. 31, 2018	Oct. 31, 2017	Sep. 30, 2018	Dec. 31, 2017
Short-term Debt [Line Items]
FHLB advances outstanding				$ 1,400,000,000
Lockout period				1 year
FHLB advances				$ 1,400,000,000
Additional advances from FHLB				885,400,000
Debt Instrument [Line Items]
Commitment fee on unused portion (as percent)			0.25%
Long-term debt				1,793,851,000	$ 1,520,589,000
Mortgage loans and investment securities securing FHLB advances				3,900,000,000
Assets				16,281,264,000	15,055,806,000
U.S. Bank National Association | Revolving credit facility
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 75,000,000
Long-term debt				$ 0	$ 75,000,000
Subsequent Event | U.S. Bank National Association | Revolving credit facility
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 50,000,000
Commitment fee on unused portion (as percent)	0.30%
London Interbank Offered Rate (LIBOR) | U.S. Bank National Association | Revolving credit facility
Debt Instrument [Line Items]
Floating rate (as percent)				1.50%
Federal Home Loan Bank Owns the Options (FOTO) Advances
Short-term Debt [Line Items]
FHLB advances outstanding				$ 675,000,000
Federal Home Loan Bank Owns the Options (FOTO) Advances | Minimum
Short-term Debt [Line Items]
Debt term				10 years
Federal Home Loan Bank Owns the Options (FOTO) Advances | Maximum
Short-term Debt [Line Items]
Debt term				15 years
Federal Home Loan Bank Advances
Short-term Debt [Line Items]
Debt term					1 year
Subordinated debt
Debt Instrument [Line Items]
Subordinated debentures		$ 330,000,000			$ 0
Fixed rate (as percent)		5.00%		5.00%
Debt issuance costs		$ 3,600,000
Subordinated debt | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)		2.15%

Other Borrowings and Subordin_5

Other Borrowings and Subordinated Notes and Debentures - Aggregate Annual Maturities of Long-term Debt (Details) $ in Thousands	Sep. 30, 2018USD ($)
Debt Disclosure [Abstract]
2,018	$ 376
2,019	2,135
2,020	2,109
2,021	1,800
2,022	949
Thereafter	362,404
Total	$ 369,773

Common Stock - Textual (Details

Common Stock - Textual (Details)	Feb. 08, 2018	Jul. 23, 2012shares	Sep. 30, 2018shares	Sep. 30, 2018shares	Apr. 19, 2018shares	Apr. 18, 2018shares	Dec. 31, 2017shares
Equity [Abstract]
Conversion ratio	2
Common stock, shares authorized (in shares)			175,000,000	175,000,000	175,000,000	120,000,000	120,000,000
Number of shares authorized to be repurchased (in shares)		1,700,000
Percent of outstanding stock (as percent)		2.00%
Number of additional shares to be repurchased (in shares)		308,272
Repurchase of common stock (in shares)			0	0

Undivided Profits - Textual (De

Undivided Profits - Textual (Details) $ in Millions	3 Months Ended
	Sep. 30, 2018USD ($)
Equity [Abstract]
Threshold percentage of net profits exceeded by dividends declared, any calendar year (as percent)	75.00%
Threshold percentage of net profits exceeded by dividends declared, combined with preceding year (as percent)	75.00%
Statutory accounting practices, statutory amount available for dividend payments without regulatory approval	$ 1.6
Tier 1 leverage capital required to be well capitalized to average assets (as percent)	5.00%
Tier 1 risk-based capital required to be well capitalized to risk weighted assets (as percent)	8.00%
Capital required to be well-capitalized to risk weighted assets (as percent)	10.00%
Common equity Tier 1 ratio required to be well capitalized (as percent)	6.50%
Capital conservation buffer phase in amount	0.625%
Capital conservation buffer phase in period	4 years
Capital conservation buffer (as percent)	2.50%
CET1 ratio (as percent)	9.82%

Stock Based Compensation - Text

Stock Based Compensation - Textual (Details) $ / shares in Units, $ in Thousands	Feb. 08, 2018	Sep. 30, 2018USD ($)$ / sharesshares	Sep. 30, 2017USD ($)shares
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Conversion ratio	2
Stock-based compensation expense		$ 9,818	$ 6,486
Unrecognized stock-based compensation expense related to stock options		56
Unrecognized stock-based compensation expense related to non-vested stock awards		$ 21,129
Period unrecognized expenses is expected to be recognized		1 year 10 months 24 days
Intrinsic value of stock options outstanding		$ 4,884
Intrinsic value of stock options exercisable		$ 4,680
Share price (in dollars per share) | $ / shares		$ 29.45
Stock options exercised		$ 1,155	$ 1,012
Stock options granted | shares		0	0

Stock Based Compensation - Stoc

Stock Based Compensation - Stock Compensation Plans (Details) - $ / shares	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Stock Options Outstanding
Stock options outstanding, number of shares, balance (in shares)	812,000
Stock options outstanding, granted (in shares)	0	0
Stock options exercised, exercised (in shares)	(111,000)
Stock options outstanding, forfeited/expired (in shares)	(6,000)
Stock options outstanding, number of shares, balance (in shares)	695,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Stock options, weighted average exercise price, balance (in dollars per share)	$ 21.98
Stock options, weighted average exercise price, granted (in dollars per share)	0
Stock options, weighted average exercise price, exercised (in dollars per share)	19.22
Stock options, weighted average exercise price, forfeited/expired (in dollars per share)	21.73
Stock options, weighted average exercise price, balance (in dollars per share)	$ 22.42
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Stock options outstanding, number of shares, exercisable (in shares)	661,000
Stock options outstanding, weighted average exercise price, exercisable (in dollars per share)	$ 22.37
Non-vested Stock Awards Outstanding
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Non-vested shares outstanding, balance (in shares)	162,000
Non-vested shares outstanding, granted (in shares)	0
Non-vested shares outstanding, vested (in shares)	(55,000)
Non-vested shares outstanding, forfeited (in shares)	(10,000)
Non-vested shares outstanding, balance (in shares)	97,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Non-vested shares outstanding. weighted-average exercise price, balance (in dollars per share)	$ 20.86
Non-vested shares outstanding. weighted-average exercise price, granted (in dollars per share)	0
Non-vested shares outstanding. weighted-average exercise price, vested (in dollars per share)	18.95
Non-vested shares outstanding. weighted-average exercise price, forfeited/expired (in dollars per share)	20.12
Non-vested shares outstanding. weighted-average exercise price, balance (in dollars per share)	$ 22
Non-vested Stock Units Outstanding
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Non-vested shares outstanding, balance (in shares)	652,000
Non-vested shares outstanding, granted (in shares)	343,000
Non-vested shares outstanding, vested (in shares)	(175,000)
Non-vested shares outstanding, forfeited (in shares)	(91,000)
Non-vested shares outstanding, balance (in shares)	729,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Non-vested shares outstanding. weighted-average exercise price, balance (in dollars per share)	$ 27.92
Non-vested shares outstanding. weighted-average exercise price, granted (in dollars per share)	29.31
Non-vested shares outstanding. weighted-average exercise price, vested (in dollars per share)	27.74
Non-vested shares outstanding. weighted-average exercise price, forfeited/expired (in dollars per share)	28.37
Non-vested shares outstanding. weighted-average exercise price, balance (in dollars per share)	$ 28.56

Stock Based Compensation - St_2

Stock Based Compensation - Stock Options (Details) shares in Thousands	3 Months Ended
	Sep. 30, 2018$ / sharesshares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, range of exercise prices, minimum (in dollars per share)	$ 9.46
Options outstanding, range of exercise prices, maximum (in dollars per share)	$ 24.07
Options outstanding, number of shares (in shares) | shares	695
Options outstanding, weighted average remaining contractual life	6 years 9 months 11 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 22.42
Options exercisable, number of shares (in shares) | shares	661
Options exercisable, weighted average exercise price (in dollars per share)	$ 22.37
Range 1
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, range of exercise prices, minimum (in dollars per share)	9.46
Options outstanding, range of exercise prices, maximum (in dollars per share)	$ 9.46
Options outstanding, number of shares (in shares) | shares	1
Options outstanding, weighted average remaining contractual life	3 years 3 months 18 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 9.46
Options exercisable, number of shares (in shares) | shares	1
Options exercisable, weighted average exercise price (in dollars per share)	$ 9.46
Range 2
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, range of exercise prices, minimum (in dollars per share)	10.65
Options outstanding, range of exercise prices, maximum (in dollars per share)	$ 10.65
Options outstanding, number of shares (in shares) | shares	4
Options outstanding, weighted average remaining contractual life	4 years 3 months 26 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 10.65
Options exercisable, number of shares (in shares) | shares	4
Options exercisable, weighted average exercise price (in dollars per share)	$ 10.65
Range 3
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, range of exercise prices, minimum (in dollars per share)	10.76
Options outstanding, range of exercise prices, maximum (in dollars per share)	$ 10.76
Options outstanding, number of shares (in shares) | shares	2
Options outstanding, weighted average remaining contractual life	1 year 3 months 18 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 10.76
Options exercisable, number of shares (in shares) | shares	2
Options exercisable, weighted average exercise price (in dollars per share)	$ 10.76
Range 4
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, range of exercise prices, minimum (in dollars per share)	20.29
Options outstanding, range of exercise prices, maximum (in dollars per share)	$ 20.29
Options outstanding, number of shares (in shares) | shares	71
Options outstanding, weighted average remaining contractual life	6 years 3 months
Options outstanding, weighted average exercise price (in dollars per share)	$ 20.29
Options exercisable, number of shares (in shares) | shares	71
Options exercisable, weighted average exercise price (in dollars per share)	$ 20.29
Range 5
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, range of exercise prices, minimum (in dollars per share)	20.36
Options outstanding, range of exercise prices, maximum (in dollars per share)	$ 20.36
Options outstanding, number of shares (in shares) | shares	3
Options outstanding, weighted average remaining contractual life	6 years 1 month 17 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 20.36
Options exercisable, number of shares (in shares) | shares	1
Options exercisable, weighted average exercise price (in dollars per share)	$ 20.36
Range 6
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, range of exercise prices, minimum (in dollars per share)	22.20
Options outstanding, range of exercise prices, maximum (in dollars per share)	$ 22.20
Options outstanding, number of shares (in shares) | shares	74
Options outstanding, weighted average remaining contractual life	6 years 5 months 23 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 22.20
Options exercisable, number of shares (in shares) | shares	74
Options exercisable, weighted average exercise price (in dollars per share)	$ 22.20
Range 7
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, range of exercise prices, minimum (in dollars per share)	22.75
Options outstanding, range of exercise prices, maximum (in dollars per share)	$ 22.75
Options outstanding, number of shares (in shares) | shares	436
Options outstanding, weighted average remaining contractual life	6 years 10 months 10 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 22.75
Options exercisable, number of shares (in shares) | shares	436
Options exercisable, weighted average exercise price (in dollars per share)	$ 22.75
Range 8
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, range of exercise prices, minimum (in dollars per share)	23.51
Options outstanding, range of exercise prices, maximum (in dollars per share)	$ 23.51
Options outstanding, number of shares (in shares) | shares	97
Options outstanding, weighted average remaining contractual life	7 years 3 months 18 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 23.51
Options exercisable, number of shares (in shares) | shares	65
Options exercisable, weighted average exercise price (in dollars per share)	$ 23.51
Range 9
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, range of exercise prices, minimum (in dollars per share)	24.07
Options outstanding, range of exercise prices, maximum (in dollars per share)	$ 24.07
Options outstanding, number of shares (in shares) | shares	7
Options outstanding, weighted average remaining contractual life	6 years 11 months 16 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 24.07
Options exercisable, number of shares (in shares) | shares	7
Options exercisable, weighted average exercise price (in dollars per share)	$ 24.07

Earnings Per Share ("EPS") - Te

Earnings Per Share ("EPS") - Textual (Details)	Feb. 08, 2018	Sep. 30, 2018shares	Sep. 30, 2017shares	Sep. 30, 2018shares	Sep. 30, 2017shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Conversion ratio	2
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares excluded from earnings per share calculation (in shares)		0	0	0	0

Earnings Per Share ("EPS") (Det

Earnings Per Share ("EPS") (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income		$ 55,193	$ 28,852	$ 160,067	$ 74,037
Average common shares outstanding (in shares)		92,290	64,427	92,246	63,594
Average potential dilutive common shares (in shares)		551	420	551	420
Average diluted common shares (in shares)		92,841	64,847	92,797	64,014
Basic earnings per share (in dollars per share)	[1]	$ 0.60	$ 0.45	$ 1.74	$ 1.16
Diluted earnings per share (in dollars per share)	[1]	$ 0.59	$ 0.44	$ 1.72	$ 1.16
[1]	All per share amounts have been restated to reflect the effect of the two-for-one stock split on February 8, 2018.

Additional Cash Flow Informat_3

Additional Cash Flow Information (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Other Significant Noncash Transactions [Line Items]
Interest paid	$ 78,987	$ 21,531
Income taxes paid	25,576	21,718
Transfers of loans to foreclosed assets held for sale
Other Significant Noncash Transactions [Line Items]
Transfers of loans	7,745	5,311
Transfers of premises to foreclosed assets and other real estate owned
Other Significant Noncash Transactions [Line Items]
Transfers of loans	$ 3,690	$ 3,188

Other Operating Expenses (Detai

Other Operating Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other Income and Expenses [Abstract]
Professional services	$ 4,616	$ 3,946	$ 13,896	$ 13,079
Postage	1,262	1,091	4,103	3,427
Telephone	1,248	943	4,217	3,003
Credit card expense	3,405	3,137	9,820	9,081
Marketing	2,912	1,219	6,334	4,253
Operating supplies	585	592	1,917	1,406
Amortization of intangibles	2,772	1,724	8,394	4,828
Branch right sizing expense	970	153	1,049	370
Other expense	11,904	5,458	31,623	18,588
Total other operating expenses	$ 29,674	$ 18,263	$ 81,353	$ 58,035

Commitments and Credit Risk - T

Commitments and Credit Risk - Textual (Details) - USD ($)	3 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Other Commitments [Line Items]
Outstanding letters of credit	$ 34,518,000	$ 47,621,000
Standby Letters of Credit
Other Commitments [Line Items]
Deferred revenue	$ 0	0
Minimum
Other Commitments [Line Items]
Term of letter of credit	9 months
Maximum
Other Commitments [Line Items]
Term of letter of credit	15 years
Credit card commitments
Other Commitments [Line Items]
Outstanding commitments	$ 568,117,000	564,592,000
Other loan commitments
Other Commitments [Line Items]
Outstanding commitments	$ 3,430,361,000	$ 3,086,696,000

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value of Financial Assets Measure on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	$ 1,997,814	$ 1,589,517
U.S. Government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	141,460	139,724
Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,419,626	1,187,317
State and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	282,439	143,165
Other securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	154,289	119,311
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets held for sale	5,136	165,780
Derivative asset	9,691	3,634
Other liabilities held for sale	(424)	(157,366)
Derivative liability	(7,940)	(3,068)
Fair Value, Measurements, Recurring | U.S. Government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	141,460	139,724
Fair Value, Measurements, Recurring | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,419,626	1,187,317
Fair Value, Measurements, Recurring | State and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	282,439	143,165
Fair Value, Measurements, Recurring | Other securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities	154,289	119,311
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets held for sale	0	0
Derivative asset	0	0
Other liabilities held for sale	0	0
Derivative liability	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring | 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]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities	0	0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets held for sale	0	0
Derivative asset	9,691	3,634
Other liabilities held for sale	0	0
Derivative liability	(7,940)	(3,068)
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | U.S. Government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	141,460	139,724
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,419,626	1,187,317
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | State and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	282,439	143,165
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities	154,289	119,311
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets held for sale	5,136	165,780
Derivative asset	0	0
Other liabilities held for sale	(424)	(157,366)
Derivative liability	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | U.S. Government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | State and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Other securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities	$ 0	$ 0

Fair Value Measurements - Textu

Fair Value Measurements - Textual (Details) $ in Thousands	3 Months Ended
	Sep. 30, 2018USD ($)	Dec. 31, 2017USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreclosed assets and other real estate owned	$ 22,664	$ 32,118
Impaired loan, related allowance	459	338
Collateral dependent
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loan, related allowance	$ 2,738	2,195
Commercial Real Estate | Discount Rate | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input (as percent)	0.10
Commercial Real Estate | Discount Rate | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input (as percent)	0.40
Residential Real Estate | Discount Rate | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input (as percent)	0.10
Residential Real Estate | Discount Rate | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input (as percent)	0.40
Foreclosed Assets Not Covered By FDIC Loss Share
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreclosed assets and other real estate owned	$ 22,700	$ 32,100
Ratings of Substandard or worse
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Threshold value for performing impairment testing on loans	$ 1,500

Fair Value Measurements - Fai_2

Fair Value Measurements - Fair Value of Financial Assets Measured on a Nonrecurring Basis (Details) - Fair Value, Measurements, Nonrecurring - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans (collateral dependent)	$ 17,789	$ 11,229
Foreclosed assets and other real estate owned	14,643	24,093
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans (collateral dependent)	0	0
Foreclosed assets and other real estate owned	0	0
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans (collateral dependent)	0	0
Foreclosed assets and other real estate owned	0	0
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans (collateral dependent)	17,789	11,229
Foreclosed assets and other real estate owned	$ 14,643	$ 24,093

Fair Value Measurements - Estim

Fair Value Measurements - Estimated Fair Values and Related Carrying Amounts of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities	$ 322,838	$ 373,298
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	513,804	598,042
Interest bearing balances due from banks - time	3,954	3,314
Held-to-maturity securities	323,306	368,058
Mortgage loans held for sale	48,195	24,038
Interest receivable	51,509	43,528
Federal funds purchased and securities sold under agreements to repurchase	109,213	122,444
Other borrowings	1,420,917	1,380,024
Subordinated notes and debentures	372,934	140,565
Interest payable	13,197	4,564
Carrying Amount | Non-interest bearing transaction accounts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	2,778,670	2,665,249
Carrying Amount | Interest bearing transaction accounts and savings deposits
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	6,776,330	6,494,896
Carrying Amount | Time deposits
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	2,533,506	1,932,730
Carrying Amount | Legacy loans, net
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	8,067,916	5,663,941
Carrying Amount | Loans acquired, net
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	3,734,921	5,074,076
Fair Value Measurements
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	513,804	598,042
Interest bearing balances due from banks - time	3,954	3,314
Held-to-maturity securities	322,838	373,298
Mortgage loans held for sale	48,195	24,038
Interest receivable	51,509	43,528
Federal funds purchased and securities sold under agreements to repurchase	109,213	122,444
Other borrowings	1,417,166	1,381,365
Subordinated notes and debentures	310,701	136,474
Interest payable	13,197	4,564
Fair Value Measurements | Non-interest bearing transaction accounts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	2,778,670	2,665,249
Fair Value Measurements | Interest bearing transaction accounts and savings deposits
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	6,776,330	6,494,896
Fair Value Measurements | Time deposits
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	2,508,228	1,915,539
Fair Value Measurements | Legacy loans, net
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	7,996,273	5,646,505
Fair Value Measurements | Loans acquired, net
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	3,701,755	5,058,455
Fair Value Measurements | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	513,804	598,042
Interest bearing balances due from banks - time	0	0
Held-to-maturity securities	0	0
Mortgage loans held for sale	0	0
Interest receivable	0	0
Federal funds purchased and securities sold under agreements to repurchase	0	0
Other borrowings	0	0
Subordinated notes and debentures	0	0
Interest payable	0	0
Fair Value Measurements | Quoted Prices in Active Markets for Identical Assets (Level 1) | Non-interest bearing transaction accounts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	0	0
Fair Value Measurements | Quoted Prices in Active Markets for Identical Assets (Level 1) | Interest bearing transaction accounts and savings deposits
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	0	0
Fair Value Measurements | Quoted Prices in Active Markets for Identical Assets (Level 1) | Time deposits
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	0	0
Fair Value Measurements | Quoted Prices in Active Markets for Identical Assets (Level 1) | Legacy loans, net
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	0	0
Fair Value Measurements | Quoted Prices in Active Markets for Identical Assets (Level 1) | Loans acquired, net
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	0	0
Fair Value Measurements | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Interest bearing balances due from banks - time	3,954	3,314
Held-to-maturity securities	322,838	373,298
Mortgage loans held for sale	0	0
Interest receivable	51,509	43,528
Federal funds purchased and securities sold under agreements to repurchase	109,213	122,444
Other borrowings	1,417,166	1,381,365
Subordinated notes and debentures	310,701	136,474
Interest payable	13,197	4,564
Fair Value Measurements | Significant Other Observable Inputs (Level 2) | Non-interest bearing transaction accounts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	2,778,670	2,665,249
Fair Value Measurements | Significant Other Observable Inputs (Level 2) | Interest bearing transaction accounts and savings deposits
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	6,776,330	6,494,896
Fair Value Measurements | Significant Other Observable Inputs (Level 2) | Time deposits
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	0	0
Fair Value Measurements | Significant Other Observable Inputs (Level 2) | Legacy loans, net
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	0	0
Fair Value Measurements | Significant Other Observable Inputs (Level 2) | Loans acquired, net
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	0	0
Fair Value Measurements | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Interest bearing balances due from banks - time	0	0
Held-to-maturity securities	0	0
Mortgage loans held for sale	48,195	24,038
Interest receivable	0	0
Federal funds purchased and securities sold under agreements to repurchase	0	0
Other borrowings	0	0
Subordinated notes and debentures	0	0
Interest payable	0	0
Fair Value Measurements | Significant Unobservable Inputs (Level 3) | Non-interest bearing transaction accounts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	0	0
Fair Value Measurements | Significant Unobservable Inputs (Level 3) | Interest bearing transaction accounts and savings deposits
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	0	0
Fair Value Measurements | Significant Unobservable Inputs (Level 3) | Time deposits
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	2,508,228	1,915,539
Fair Value Measurements | Significant Unobservable Inputs (Level 3) | Legacy loans, net
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	7,996,273	5,646,505
Fair Value Measurements | Significant Unobservable Inputs (Level 3) | Loans acquired, net
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	$ 3,701,755	$ 5,058,455