Independent Bank (IBTX) 10-K/A 6 Mar 20 2019 FY Annual report (amended) Financial data

Cover Cover

Cover Cover - USD ($)	12 Months Ended
	Dec. 31, 2019	Feb. 27, 2020	Jun. 30, 2019
Cover page.
Document Type	10-K/A
Document Annual Report	true
Document Period End Date	Dec. 31, 2019
Document Transition Report	false
Entity File Number	001-35854
Entity Registrant Name	Independent Bank Group, Inc.
Entity Incorporation, State or Country Code	TX
Entity Tax Identification Number	13-4219346
Entity Address, Address Line One	7777 Henneman Way
Entity Address, City or Town	McKinney,
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	75070-1711
City Area Code	972
Local Phone Number	562-9004
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	IBTX
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 1,944,702,826
Entity Common Stock, Shares Outstanding		43,040,776
Amendment Flag	true
Amendment Description	Independent Bank Group, Inc. (the “Company”) filed its Annual Report on Form 10-K for the fiscal year ended December 31, 2019 (the “Original Filing”) with the United States Securities and Exchange Commission (the “SEC”) on March 2, 2020. The Company is filing this Amendment No. 1 to the Original Filing solely to correct inadvertent errors by RSM US LLP in the Critical Audit Matters section of its Report of Registered Public Accounting firm (the “Report”) provided with respect to the Company’s consolidated financial statements. Specifically, (1) In the “Allowance for Loan Losses” section of the Report, the opinion previously read: “the Company’s allowance for loan losses totaled $14.8 million.” This number has been corrected to be $51.5 million; and (2) In the “Acquisition of Guaranty Bank” section of the Report, the opinion read: “The fair value of assets acquired in the acquisition totaled $3.9 million, including $2.8 million of loans receivables.” “Million” has been changed to “billion” for both of these numbers. In addition, the Exhibit List included in Item 15 of Part IV has been amended to contain a currently-dated consent of RSM US LLP (Exhibit 23.1) and, pursuant to the rules of the SEC, currently-dated certifications from the Company’s Principal Executive Officer and Principal Financial Officer, as required by Sections 302 and 906 of the Sarbanes-Oxley Act of 2002 (Exhibit 31.1, Exhibit 31.2, Exhibit 32.1 and Exhibit 32.2). Such consent and the certifications of the Company’s Principal Executive Officer and Principal Financial Officer are attached as exhibits to this Amendment No. 1. Except as described above, this Amendment No. 1 speaks as of the original filing date of the Original Filing and does not amend or update any other information contained in the Original Filing to reflect events that may have occurred subsequent to the original filing date. The Company has included a complete copy of the Original Filing, as amended per above, in this filing.
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Central Index Key	0001564618
Current Fiscal Year End Date	--12-31

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Assets
Cash and due from banks	$ 186,299	$ 102,024
Interest-bearing deposits in other banks	378,871	28,755
Cash and cash equivalents	565,170	130,779
Certificates of deposit held in other banks	5,719	1,225
Securities available for sale, at fair value	1,085,936	685,350
Loans held for sale (includes $29,204 and $27,871 carried at fair value, respectively)	35,645	32,727
Loans, net	11,562,814	7,839,695
Premises and equipment, net	242,874	167,866
Other real estate owned	4,819	4,200
Federal Home Loan Bank (FHLB) of Dallas stock and other restricted stock	30,052	26,870
Bank-owned life insurance (BOLI)	215,081	129,521
Deferred tax asset	6,943	13,180
Goodwill	994,021	721,797
Other intangible assets, net	100,741	45,042
Other assets	108,392	51,713
Total assets	14,958,207	9,849,965
Deposits:
Noninterest-bearing	3,240,185	2,145,930
Interest-bearing	8,701,151	5,591,864
Total deposits	11,941,336	7,737,794
FHLB advances	325,000	290,000
Other borrowings	202,251	137,316
Junior subordinated debentures	53,824	27,852
Other liabilities	96,023	50,570
Total liabilities	12,618,434	8,243,532
Commitments and contingencies
Stockholders’ equity:
Preferred stock (0 and 0 shares outstanding, respectively)	0	0
Common stock (42,950,228 and 30,600,582 shares outstanding, respectively)	430	306
Additional paid-in capital	1,926,359	1,317,616
Retained earnings	393,674	296,816
Accumulated other comprehensive income (loss)	19,310	(8,305)
Total stockholders’ equity	2,339,773	1,606,433
Total liabilities and stockholders’ equity	$ 14,958,207	$ 9,849,965

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Preferred stock, shares outstanding (shares)	0	0
Common stock (42,950,228 and 30,600,582 shares outstanding, respectively)	42,950,228	30,600,582
Loans held for sale (includes $29,204 and $27,871 carried at fair value, respectively)	$ 29,204	$ 27,871

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Interest income:
Interest and fees on loans	$ 611,589	$ 384,791	$ 290,357
Interest on taxable securities	21,324	14,007	8,229
Interest on nontaxable securities	8,482	4,580	3,877
Interest on interest-bearing deposits and other	11,537	3,912	5,451
Total interest income	652,932	407,290	307,914
Interest expense:
Interest on deposits	123,384	60,767	28,518
Interest on FHLB advances	10,173	10,264	5,858
Interest on other borrowings and repurchase agreements	11,590	8,398	6,898
Interest on junior subordinated debentures	3,028	1,609	1,162
Total interest expense	148,175	81,038	42,436
Net interest income	504,757	326,252	265,478
Provision for loan losses	14,805	9,860	8,265
Net interest income after provision for loan losses	489,952	316,392	257,213
Noninterest income:
Service charges on deposit accounts	24,500	14,224	12,955
Investment management and trust	9,330	0	0
Mortgage banking revenue	15,461	15,512	13,755
Gain on sale of loans	6,779	0	351
Gain on sale of branches	1,549	0	2,917
Gain on sale of trust business	1,319	0	0
Gain (loss) on sale of other real estate	875	269	(160)
Gain on sale of repossessed assets	0	0	1,010
Gain (loss) on sale of securities available for sale	275	(581)	124
(Loss) gain on sale of premises and equipment	(585)	123	(21)
Increase in cash surrender value of BOLI	5,525	3,170	2,748
Other	13,148	9,507	7,608
Total noninterest income	78,176	42,224	41,287
Noninterest expense:
Salaries and employee benefits	162,683	111,697	95,741
Occupancy	37,654	24,786	22,079
Data processing	17,103	10,754	8,597
FDIC assessment	1,065	3,306	4,311
Advertising and public relations	2,527	1,907	1,452
Communications	5,145	3,353	2,860
Other real estate owned expenses, net	418	318	304
Impairment of other real estate	1,801	85	1,412
Amortization of other intangible assets	12,880	5,739	4,639
Professional fees	7,936	4,556	4,564
Acquisition expense, including legal	33,445	6,157	12,898
Other	39,207	25,961	17,956
Total noninterest expense	321,864	198,619	176,813
Income before taxes	246,264	159,997	121,687
Income tax expense	53,528	31,738	45,175
Net income	$ 192,736	$ 128,259	$ 76,512
Basic earnings per share (usd per share)	$ 4.46	$ 4.33	$ 2.98
Diluted earnings per share (usd per share)	$ 4.46	$ 4.33	$ 2.97

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 192,736	$ 128,259	$ 76,512
Other comprehensive income (loss) before tax:
Change in net unrealized gains (losses) on available for sale securities during the year	35,620	(10,182)	1,067
Reclassification for amount realized through sales of securities available for sale included in net income	(275)	581	(124)
Other comprehensive income (loss) before tax	35,345	(9,601)	943
Income tax expense (benefit)	7,730	(2,016)	330
Other comprehensive income (loss), net of tax	27,615	(7,585)	613
Comprehensive income	$ 220,351	$ 120,674	$ 77,125

Consolidated Statements of Chan

Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Preferred Stock $.01 Par Value 10 million shares authorized	Common Stock $.01 Par Value 100 million shares authorized	Additional Paid in Capital	Retained Earnings	Accumulated Other Comprehensive (Loss) Income
Beginning balance (in shares) at Dec. 31, 2016			18,870,312
Beginning balance at Dec. 31, 2016	$ 672,365	$ 0	$ 189	$ 555,325	$ 117,951	$ (1,100)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	76,512				76,512
Other comprehensive income (loss), net of tax	613					613
Stock issued for acquisition of bank, net of offering costs (in shares)			8,804,699
Stock issued for acquisition of bank, net of offering costs of $804 for 2019, $209 for 2018 and $942 for 2017	565,200		$ 88	565,112
Common stock issued, net of offering costs (in shares)			448,500
Common stock issued, net of offering costs of $525 in 2017	26,816		$ 5	26,811
Restricted stock forfeited (in shares)			(2,543)
Restricted stock forfeited	0
Restricted stock granted (in shares)			130,722
Restricted stock granted	0		$ 1	(1)
Stock based compensation expense	4,688			4,688
Exercise of warrants (in shares)			3,203
Exercise of warrants	55			55
Cash dividends ($1.00 in 2019, $0.54 per share in 2018 and $0.40 per share in 2017)	(10,231)				(10,231)
Ending balance (in shares) at Dec. 31, 2017			28,254,893
Ending balance at Dec. 31, 2017	1,336,018	0	$ 283	1,151,990	184,232	(487)
Cumulative effect of change in accounting principles	0				233	(233)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	128,259				128,259
Other comprehensive income (loss), net of tax	(7,585)					(7,585)
Stock issued for acquisition of bank, net of offering costs (in shares)			2,071,981
Stock issued for acquisition of bank, net of offering costs of $804 for 2019, $209 for 2018 and $942 for 2017	157,054		$ 21	157,033
Restricted stock forfeited (in shares)			(3,845)
Restricted stock forfeited	0		$ 0
Restricted stock granted (in shares)			130,212
Restricted stock granted	0		$ 1	(1)
Stock based compensation expense	6,062			6,062
Exercise of warrants (in shares)			147,341
Exercise of warrants	2,533		$ 1	2,532
Cash dividends ($1.00 in 2019, $0.54 per share in 2018 and $0.40 per share in 2017)	(15,908)				(15,908)
Ending balance (in shares) at Dec. 31, 2018			30,600,582
Ending balance at Dec. 31, 2018	1,606,433	0	$ 306	1,317,616	296,816	(8,305)
Cumulative effect of change in accounting principles	(926)				(926)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	192,736				192,736
Other comprehensive income (loss), net of tax	27,615					27,615
Stock issued for acquisition of bank, net of offering costs (in shares)			13,179,748
Stock issued for acquisition of bank, net of offering costs of $804 for 2019, $209 for 2018 and $942 for 2017	601,068		$ 132	600,936
Common stock repurchased (shares)			(952,844)
Common stock repurchased	(51,659)		$ (9)		(51,650)
Restricted stock forfeited (in shares)			(15,866)
Restricted stock forfeited	0
Restricted stock granted (in shares)			138,608
Restricted stock granted	0		$ 1	(1)
Stock based compensation expense	7,808			7,808
Cash dividends ($1.00 in 2019, $0.54 per share in 2018 and $0.40 per share in 2017)	(43,302)				(43,302)
Ending balance (in shares) at Dec. 31, 2019			42,950,228
Ending balance at Dec. 31, 2019	$ 2,339,773	$ 0	$ 430	$ 1,926,359	$ 393,674	$ 19,310

Consolidated Statements of Ch_2

Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Stockholders' Equity [Abstract]
Cash dividends paid (usd per share)	$ 1	$ 0.54	$ 0.4
Stock issued for acquisition of bank, net of offering costs	$ 804	$ 209	$ 942
Common stock issued, net of offering costs			$ 525
Common stock, par value (usd per share)	$ 0.01	$ 0.01	$ 0.01
Common stock shares authorized (shares)	100,000,000	100,000,000	100,000,000
Preferred stock par value (in usd per share)	$ 0.01	$ 0.01	$ 0.01
Preferred stock shares authorized (shares)	10,000,000	10,000,000	10,000,000

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net income	$ 192,736	$ 128,259	$ 76,512
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation expense	11,783	8,391	8,196
Accretion of income recognized on acquired loans	(46,071)	(13,523)	(7,833)
Amortization of other intangibles assets	12,880	5,739	4,639
Amortization of premium on securities, net	2,671	3,316	3,629
Amortization of discount and origination costs on borrowings	633	633	505
Stock based compensation expense	7,808	6,062	4,688
Excess tax expense (benefit) on restricted stock vested	21	(646)	(1,323)
FHLB stock dividends	(854)	(791)	(448)
Loss (gain) on sale of premises and equipment	585	(123)	21
Gain on sale of loans	(6,779)	0	(351)
Gain on sale of branches	(1,549)	0	(2,917)
Gain on sale of trust business	(1,319)	0	0
(Gain) loss on sale of securities available for sale	(275)	581	(124)
(Gain) loss on sale of other real estate owned	(875)	(269)	160
Gain on sale of repossessed assets	0	0	(1,010)
Impairment of other real estate	1,801	85	1,412
Impairment of other assets	1,173	0	0
Deferred tax expense	14,102	1,937	17,054
Provision for loan losses	14,805	9,860	8,265
Increase in cash surrender value of BOLI	(5,525)	(3,170)	(2,748)
Net gain on mortgage loans held for sale	(15,133)	(13,794)	(9,160)
Originations of loans held for sale	(435,076)	(384,178)	(429,874)
Proceeds from sale of loans held for sale	447,291	404,447	422,409
Net change in other assets	(5,878)	(14,352)	(5,987)
Net change in other liabilities	(15,636)	20,277	(2,920)
Net cash provided by operating activities	173,319	158,741	82,795
Cash flows from investing activities:
Proceeds from maturities, calls and pay downs of securities available for sale	5,400,634	3,660,624	2,328,843
Proceeds from sale of securities available for sale	192,417	102,647	31,367
Purchases of securities available for sale	(5,390,543)	(3,674,396)	(2,472,799)
Purchases of certificates of deposit held in other banks	(5,705)	0	0
Proceeds from maturities of certificates of deposit held in other banks	1,473	11,760	747
Proceeds from surrender of bank owned life insurance contracts	802	0	0
Purchase of bank owned life insurance contracts	0	(5,000)	0
Purchases of FHLB stock and other restricted stock	(9,397)	(6,144)	(48)
Proceeds from redemptions of FHLB stock and other restricted stock	34,863	12,606	8,958
Proceeds from sale of loans	90,025	0	3,867
Net loans originated held for investment	(469,023)	(746,804)	(566,881)
Originations of mortgage warehouse purchase loans	(12,835,522)	(5,128,767)	(3,640,235)
Proceeds from pay-offs of mortgage warehouse purchase loans	12,318,495	5,123,171	3,575,863
Additions to premises and equipment	(31,680)	(38,110)	(13,193)
Proceeds from sale of premises and equipment	2,100	14,479	16
Proceeds from sale of other real estate owned	8,207	3,520	9,433
Proceeds from sale of repossessed assets	0	0	1,010
Capitalized additions to other real estate	0	0	(1,030)
Cash acquired in connection with acquisition	39,913	44,723	148,444
Cash paid in connection with acquisition	(9)	(31,016)	(17,773)
Selling costs paid in connection with branch sale	(144)	0	(235)
Net cash transferred in branch sale	(25,163)	0	(58,687)
Proceeds from sale of trust business	4,269	0	0
Net cash used in investing activities	(673,988)	(656,707)	(662,333)
Cash flows from financing activities:
Net increase in demand deposits, money market and savings accounts	876,842	363,003	610,279
Net increase (decrease) in time deposits	237,136	148,891	(210,382)
Repayments of FHLB advances	(1,807,653)	(1,985,667)	(130,079)
Proceeds from FHLB advances	1,700,000	1,685,000	200,000
Net change in repurchase agreements	0	0	(9,158)
Proceeds from other borrowings	65,000	0	29,255
Repayments of other borrowings	(40,500)	0	0
Proceeds from exercise of common stock warrants	0	2,533	55
Offering costs paid in connection with acquired bank	(804)	(209)	(942)
Proceeds from sale of common stock, net	0	0	26,816
Repurchase of common stock	(51,659)	0	0
Dividends paid	(43,302)	(15,908)	(10,231)
Net cash (used in) provided by financing activities	935,060	197,643	505,613
Net change in cash and cash equivalents	434,391	(300,323)	(73,925)
Cash and cash equivalents at beginning of year	130,779	431,102	505,027
Cash and cash equivalents at end of year	$ 565,170	$ 130,779	$ 431,102

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Nature of operations: Independent Bank Group, Inc. (IBG) through its subsidiary, Independent Bank, a Texas state banking corporation (Bank) (collectively known as the Company), provides a full range of banking services to individual and corporate customers in the North, Central and Southeast, Texas areas and along the Colorado Front Range, through its various branch locations in those areas. The Company is engaged in traditional community banking activities, which include commercial and retail lending, deposit gathering, investment and liquidity management activities. The Company’s primary deposit products are demand deposits, money market accounts and certificates of deposit, and its primary lending products are commercial business and real estate, real estate mortgage and consumer loans. Proposed merger with Texas Capital Bancshares, Inc.: The Company and Texas Capital Bancshares, Inc. (TCBI) have entered into an Agreement and Plan of Merger, dated as of December 9, 2019, which is referred to as the "merger agreement". Under the merger agreement, the Company and TCBI have agreed to combine their respective companies in an all stock merger of equals, pursuant to which TCBI will merge with and into the Company, with the Company continuing as the surviving entity, in a transaction referred to as "the merger." Immediately following the merger or at such later time as the parties may mutually agree, Texas Capital Bank will merge with and into Independent Bank, with Independent Bank as the surviving bank. The merger agreement was unanimously approved by each company's board of directors. The transaction is anticipated to close in mid-2020, subject to customary closing conditions, including receipt of shareholder and regulatory approvals. The transaction is discussed in more detail in Note 22 , Business Combinations. Basis of presentation: The accompanying consolidated financial statements include the accounts of IBG and all other entities in which IBG has controlling financial interest. All material intercompany transactions and balances have been eliminated in consolidation. In addition, the Company wholly-owns nine statutory business trusts that were formed for the purpose of issuing trust preferred securities and do not meet the criteria for consolidation (See Note 12 , Junior Subordinated Debentures). On January 1, 2019, the Company acquired Guaranty Bancorp (Guaranty) and its wholly owned subsidiary, Guaranty Bank and Trust Company (Guaranty Bank) and its wholly owned subsidiary, Private Capital Management, LLC. Guaranty was merged into the Company and dissolved and Guaranty Bank and its subsidiary was merged with the Bank as of acquisition date. The Company also acquired two statutory business trusts in connection with the acquisition as disclosed in Note 12 , Junior Subordinated Debentures. See Note 22 , Business Combinations, for more details of the Guaranty acquisition. Accounting standards codification: The Financial Accounting Standards Board's (FASB) Accounting Standards Codification (ASC) is the officially recognized source of authoritative U.S. generally accepted accounting principles (GAAP) applicable to all public and non-public non-governmental entities. Rules and interpretive releases of the SEC under the authority of federal securities laws are also sources of authoritative GAAP for SEC registrants. All other accounting literature is considered non-authoritative. Citing particular content in the ASC involves specifying the unique numeric path to the content through the Topic, Subtopic, Section and Paragraph structure. Segment reporting: The Company has one reportable segment. The Company’s chief operating decision-maker uses consolidated results to make operating and strategic decisions. Reclassifications: Certain prior period financial statement and disclosure amounts have been reclassified to conform to current period presentation. The reclassifications have no effect on net income or stockholders' equity as previously reported. Use of estimates: The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions that affect certain reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. Accordingly, actual results could differ from those estimates. The material estimates included in the financial statements relate to the allowance for loan losses, the valuation of goodwill and valuation of assets and liabilities acquired in business combinations. Cash and cash equivalents: For the purposes of reporting cash flows, cash and cash equivalents include cash on hand, amounts due from banks and federal funds sold. All highly liquid investments with an initial maturity of less than ninety days are considered to be cash equivalents. The Company maintains deposits with other financial institutions in amounts that exceed FDIC insurance coverage. The Company's management monitors the balance in these accounts and periodically assesses the financial condition of the other financial institutions. The Company has not experienced any losses in such accounts and believes it is not exposed to any significant credit risks on cash or cash equivalents. Certificates of deposit: Certificates of deposit are FDIC insured deposits in other financial institutions that mature within 18 months and are carried at cost. Securities: Securities classified as available for sale are those debt securities that the Company intends to hold for an indefinite period of time, but not necessarily to maturity. Any decision to sell a security classified as available for sale would be based on various factors, including significant movements in interest rates, changes in the maturity mix of the Company's assets and liabilities, liquidity needs, regulatory capital considerations and other similar factors. Securities available for sale are reported at fair value with unrealized gains or losses reported as a separate component of other comprehensive income, net of tax. The amortization of premiums and accretion of discounts, computed by the interest method generally over their contractual lives, are recognized in interest income. Premiums on callable securities are amortized to their earliest call date. Prior to the adoption of a new accounting standard in 2019, as further discussed in Note 2 , Recent Accounting Pronouncements, premiums on callable securities were amortized to their respective maturity dates unless such securities were included in pools for the purposes of assessing prepayment expectations. Realized gains or losses, determined on the basis of the cost of specific securities sold, are included in earnings on the trade date. In estimating other than temporary impairment losses, management considers (1) the length of time and the extent to which the fair value has been less than cost, (2) the financial condition and near-term prospects of the issuer, and (3) the intent of the Company to retain its investment and whether it is more likely than not the Company will be required to sell its investment before its anticipated recovery in fair value. When the Company does not intend to sell the security, and it is more likely than not that it will not have to sell the security before recovery of its cost basis, it will recognize the credit component of an other than temporary impairment of a debt security in earnings and the remaining portion in other comprehensive income. Loans held for sale: The Company originates residential mortgage loans that may subsequently be sold to unaffiliated third parties. The Company elected the fair value option for certain residential mortgage loans held for sale originated after July 1, 2018 in accordance with ASC 825, Financial Instruments. This election allows for a more effective offset of the changes in fair values of the loans and the derivative instruments used to economically hedge them without the burden of complying with the requirements for hedge accounting under ASC 815, Derivatives and Hedging . The Company has not elected the fair value option for other residential mortgage loans held for sale primarily because they are not economically hedged using derivative instruments. Mortgage loans originated and intended for sale not recorded under the fair value option are carried at the lower of aggregate cost or fair value, as determined by aggregate outstanding commitments from investors. Net unrealized losses, if any, are recognized through a valuation allowance by charges to income. All mortgage loans held for sale are sold without servicing rights retained. Gains and losses on sales of loans are recognized in noninterest income at settlement dates and are determined by the difference between the sales proceeds and the carrying value of the loans. Acquired loans: Acquired loans from the transactions accounted for as a business combination include both nonperforming loans with evidence of credit deterioration since their origination date and performing loans. The Company is accounting for the nonperforming loans acquired in accordance with ASC 310-30, Loans and Debt Securities Acquired with Deteriorated Credit Quality . The performing loans are being accounted for under ASC 310-20, Nonrefundable Fees and Other Costs , with the related difference in the initial fair value and unpaid principal balance (the discount) recognized as interest income on a level yield basis over the life of the loan. At the date of the acquisition, the acquired loans are recorded at their fair value with no valuation allowance. Purchased credit impaired loans are accounted for individually. The Company estimates the amount and timing of undiscounted expected cash flows for each loan, and the expected cash flows in excess of fair value is recorded as interest income over the remaining life of the loan (accretable yield). The excess of the loan's contractual principal and interest over expected cash flows is not recorded (nonaccretable difference). Over the life of the loan, expected cash flows continue to be estimated. If the expected cash flows decrease, an impairment loss is recorded. If the expected cash flows increase, it is recognized as part of future interest income. Loans, net: Loans that management has the intent and ability to hold for the foreseeable future or until maturity or pay-off are reported at their outstanding principal balance, net of unearned interest, purchase premiums and discounts, deferred loan fees or costs and an allowance for loan losses. Loan origination fees, net of direct origination costs, are deferred and recognized as an adjustment to the related loan yield using the effective interest method without anticipating prepayments. Prior to the year ended December 31, 2019, fees and costs associated with originating loans were generally recognized in the period they were incurred, except in the Houston market, former Grand Bank and Carlile branches, which fees were deferred. Management believes that not deferring such fees and costs did not materially affect the financial position or results of operations of the Company. Allowance for loan losses: The allowance for loan losses is maintained at a level considered adequate by management to provide for probable loan losses. The allowance is increased by provisions charged to expense. Loans are charged against the allowance for loan losses when management believes that collectability of the principal is unlikely. Subsequent recoveries, if any, are credited to the allowance. The provision for loan losses is the amount, which, in the judgment of management, is necessary to establish the allowance for loan losses at a level that is adequate to absorb known and inherent risks in the loan portfolio. See Note 6 , Loans, Net and Allowance for Loan Losses, for further information on the Company's policies and methodology used to estimate the allowance for loan losses. Premises and equipment, net: Land is carried at cost. Bank premises, furniture and equipment and aircraft are carried at cost, less accumulated depreciation computed principally by the straight-line method over the estimated useful lives of the assets, which range from three to thirty years . Real property acquired after January 1, 2019, accounts for depreciation using the straight-line method over the estimated useful lives of the assets considering the salvage value of the real property. Leasehold improvements are carried at cost and are depreciated over the shorter of the estimated useful life or the lease period. Leases: The Company leases certain office facilities and office equipment under operating leases. The Company also owns certain office facilities which it leases to outside parties under operating lessor leases; however, such leases are not significant. On January 1, 2019, the Company adopted ASU 2016-02, Leases (Topic 842), as further explained below and in Note 2 , Recent Accounting Pronouncements. Under the new standard, for operating leases other than those considered to be short-term, the Company recognizes operating lease right-of-use (ROU) assets and operating lease liabilities, which are recorded in other assets and other liabilities, respectively, in the consolidated balance sheets. The Company determines if an arrangement is a lease at inception. Operating lease ROU assets and liabilities are recognized at commencement date based on the present value of lease payments over the lease term. As the Company's leases do not provide an implicit rate, the Company uses its incremental borrowing rate referenced to the Federal Home Loan Bank Secure Connect advance rates for borrowings of similar terms in determining the present value of lease payments. The operating lease ROU asset also includes any lease pre-payments made and excludes lease incentives. The Company's lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Lease expense for lease payments is recognized on a straight-line basis over the lease term. The Company has lease agreements with lease and non-lease components, which the Company has elected to account for separately as the non-lease component amounts are readily determinable under most leases. Long-term assets: Premises and equipment and other long-term assets are reviewed for impairment when events indicate that their carrying amount may not be recoverable from future undiscounted cash flows. If impaired, the assets are recorded at fair value. Other real estate owned: Real estate properties acquired through, or in lieu of, loan foreclosure are initially recorded at fair value less estimated selling costs at the date of foreclosure, establishing a new cost basis. After foreclosure, valuations are periodically performed by management and the real estate is carried at the lower of carrying amount or fair value less cost to sell. Revenue and expenses from operations of other real estate owned and impairment charges on other real estate are included in noninterest expense. Gains and losses on sale of other real estate are included in noninterest income. Goodwill and other intangible assets, net: Goodwill represents the excess of costs over fair value of net assets of businesses acquired. Goodwill is tested for impairment annually on December 31 or on an interim basis if an event triggering impairment may have occurred. Core deposit intangibles and other acquired customer relationship intangibles arising from bank acquisitions are amortized on a straight-line basis over their estimated useful lives of ten years and thirteen years , respectively. Other intangible assets are tested for impairment whenever events or changes in circumstances indicate the carrying amount of the assets may not be recoverable from future undiscounted cash flows. Restricted stock : The Bank is a member of the FHLB system. Members are required to own a certain amount of stock based on the level of borrowings and other factors, and may invest in additional amounts. FHLB of Dallas and other restricted stock do not have readily determinable fair values as ownership is restricted and they lack a ready market. As a result, these stocks are carried at cost and evaluated periodically by management for impairment. Both cash and stock dividends are reported as income. Bank-owned life insurance: Bank-owned life insurance is recorded at the amount that can be realized under the insurance contracts at the balance sheet date, which is the cash surrender value adjusted for other charges or other amounts due that are probable at settlement. Changes in the net cash surrender value of the policies, as well as insurance proceeds received are reflected in noninterest income. Income taxes: Income tax expense is the total of the current year income tax due or refundable and the change in deferred tax assets and liabilities (excluding deferred tax assets and liabilities related to business combinations or components of other comprehensive income). Deferred tax assets and liabilities are the expected future tax amounts for the temporary differences between carrying amounts and tax bases of assets and liabilities, computed using enacted tax rates. The effect of a change in tax rates on deferred assets and liabilities is recognized in income taxes during the period that includes the enactment date. A valuation allowance, if needed, reduces deferred tax assets to the expected amount more likely than not to be realized. Realization of deferred tax assets is dependent upon the level of historical income, prudent and feasible tax planning strategies, reversals of deferred tax liabilities and estimates of future taxable income. The Company evaluates uncertain tax positions at the end of each reporting period. The Company may recognize the tax benefit from an uncertain tax position only if it is more likely than not that the tax position will be sustained on examination by the taxing authorities, based on the technical merits of the position. The tax benefit recognized in the financial statements from any such position is measured based on the largest benefit that has a greater than fifty percent likelihood of being realized upon ultimate settlement. For tax positions not meeting the "more likely than not" test, no tax benefit is recorded. Any interest and/or penalties related to income taxes are reported as a component of income tax expense. Loan commitments and related financial instruments: In the ordinary course of business, the Company has entered into certain off-balance-sheet financial instruments consisting of commitments to extend credit, commercial letters of credit, and standby letters of credit. Such financial instruments are recorded in the financial statements when they are funded or related fees are incurred or received. Management estimates losses on off-balance-sheet financial instruments using the same methodology as for portfolio loans. Estimated losses on off-balance-sheet financial instruments are recorded by charges to the provision for losses and credits to other liabilities in the Company's consolidated balance sheet. There were no estimated losses on off-balance sheet financial instruments as of December 31, 2019 or 2018 . Stock based compensation: Compensation cost is recognized for restricted stock awards issued to employees based on the market price of the Company's common stock on the grant date. Stock-based compensation expense is generally recognized using the straight-line method over the requisite service period for all awards. The impact of forfeitures of stock-based payment awards on compensation expense is recognized as forfeitures occur. Transfers of financial assets: Transfers of financial assets are accounted for as sales, when control over the assets has been relinquished. Control over transferred assets is deemed to be surrendered when the assets have been isolated from the Company, the transferee obtains the right (free of conditions that constrain it from taking advantage of that right) to pledge or exchange the transferred assets, and the Company does not maintain effective control over the transferred assets through an agreement to repurchase them before their maturity. Advertising costs: Advertising costs are expensed as incurred. Business combinations: The Company applies the acquisition method of accounting for business combinations. Under the acquisition method, the acquiring entity in a business combination recognizes 100% of the assets acquired and liabilities assumed at their acquisition date fair values. Management utilizes valuation techniques appropriate for the asset or liability being measured in determining these fair values. Any excess of the purchase price over amounts allocated to assets acquired, including identifiable intangible assets, and liabilities assumed is recorded as goodwill. Where amounts allocated to assets acquired and liabilities assumed is greater than the purchase price, a bargain purchase gain is recognized. Adjustments identified during the measurement period are recognized in the reporting period in which the adjustment amounts are determined. Acquisition-related costs are expensed as incurred. Comprehensive income: Accounting principles generally require that recognized revenue, expenses, gains and losses be included in net income. Although certain changes in assets and liabilities, such as unrealized gains and losses on available for sale securities, are reported as a separate component of the equity section of the balance sheet, such items, along with net income, are components of comprehensive income. Gains and losses on available for sale securities are reclassified to net income as the gains or losses are realized upon sale of the securities. The credit component of other than temporary impairment charges are reclassified to net income at the time of the charge. Fair values of financial instruments: Accounting standards define fair value, establish a framework for measuring fair value in U.S. generally accepted accounting principles, and require certain disclosures about fair value measurements (see Note 18 , Fair Value Measurements). In general, fair values of financial instruments are based upon quoted market prices, where available. If such quoted market prices are not available, fair value is based upon 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. Derivative financial instruments: The Company enters into certain derivative financial instruments: interest rate lock commitments, forward mortgage-backed securities trades and interest rate swaps. These financial instruments are not designated as hedging instruments and are used for asset and liability management related to the Company's mortgage banking activities and commercial customers' financing needs. All derivatives are carried at fair value in either other assets or other liabilities (see Note 19 , Derivative Financial Instruments ) . Mortgage banking: This revenue category reflects the Company's mortgage production revenue, including fees and income derived from mortgages originated with the intent to sell, gains on sales of mortgage loans and the initial and subsequent changes in the fair value of the mortgage derivatives. Interest earned on mortgage loans is recorded in interest income. Revenue recognition: ASC Topic 606, R evenue from Contracts with Customers (ASC 606) , establishes principles for reporting information about the nature, amount, timing and uncertainty of revenue and cash flows arising from the entity's contracts to provide goods or services to customers. The core principle requires an entity to recognize revenue to depict the transfer of goods or services to customers in an amount that reflects the consideration that it expects to be entitled to receive in exchange for those goods or services recognized as performance obligations are satisfied. The majority of the Company's revenue-generating transactions are not subject to ASC 606, including revenue generated from financial instruments, such as loans, letters of credit, and investment securities, as well as revenue related to mortgage banking activities, and BOLI, as these activities are subject to other accounting guidance. Descriptions of revenue-generating activities that are within the scope of ASC 606, and are presented in the accompanying Consolidated Statements of Income as components of noninterest income, are as follows: • Service charges on deposit accounts - these represent general service fees for monthly account maintenance and activity or transaction-based fees and consist of transaction-based revenue, time-based revenue (service period), item-based revenue or some other individual attribute-based revenue. Revenue is recognized when the performance obligation is completed which is generally monthly for account maintenance services or when a transaction has been completed (such as a wire transfer). Payment for such performance obligations are generally received at the time the performance obligations are satisfied. • Investment management and trust - includes income related to providing investment management and trust services to customers under investment management and trust contracts. Also included are fees received from a third party broker-dealer as part of a revenue-sharing agreement for fees earned from customers that are referred to a third party. The investment management fees and referral fees are billed and paid on a quarterly basis and recognized ratably throughout the quarter as performance obligations are satisfied. • Gains/losses on the sale of other real estate owned - generally recognized when the performance obligation is complete which is typically at delivery of control over the property to the buyer at time of each real estate closing. • Other noninterest income - includes the Company's correspondent bank earnings credit, mortgage warehouse purchase program fees, acquired loan recoveries, other deposit fees, and merchant interchange income. The majority of these fees in other noninterest income are not subject to the requirements of ASC 606. The other deposit fees and merchant interchange income are in the scope of ASC 606, and payment for such performance obligations are generally received at the time the performance obligations are satisfied. The Company has made no significant judgments in applying the revenue guidance prescribed in ASC 606 that affect the determination of the amount and timing of revenue from the above-described contracts with customers. Share repurchase program: The Company established share repurchase programs in prior years which would allow the Company to purchase its common stock in the open market or in privately negotiated transactions. In general, share repurchase programs allow the Company to proactively manage its capital position and return excess capital to shareholders. On October 24, 2018, the Company announced the reestablishment of its share repurchase program. The program authorizes the purchase by the Company of up to $75,000 of its common stock. The repurchase program was authorized to continue through October 1, 2019. On October 17, 2019, the repurchase program was renewed and authorized to continue through December 31, 2020. The Company has approval from the Federal Reserve to repurchase up to $60,000 in shares for 2019, of which $10,952 is remaining. The Company intends to request additional approvals, as necessary, for share buybacks in 2020. As of December 31, 2019 , the Company has repurchased a total of 897,738 shares of Company stock at a total cost of $49,048 under this program. Shares of Company stock repurchased to settle employee tax withholding related to vesting of stock awards during the period ended December 31, 2019 totaled 55,106 at a total cost of $2,611 and were not included under this program. No shares of Company stock were repurchased by the Company under this program during 2018. Subsequent events: Companies are required to evaluate events and transactions that occur after the balance sheet date but before the date the financial statements are issued. They must recognize in the financial statements the effect of all events or transactions that provide additional evidence of conditions that existed at the balance sheet date, including the estimates inherent in the financial statement preparation process. Entities shall not recognize the impact of events or transactions that provide evidence about conditions that did not exist at the balance sheet date but arose after that date. The Company has evaluated subsequent events through the date of filing these financial statements with the Securities and Exchange Commission (SEC) and noted no subsequent events requiring financial statement recognition or disclosure, except as disclosed in Note 24 . Earnings per share: Basic earnings per common share is calculated as net income available to common shareholders divided by the weighted average number of common shares outstanding during the period. The unvested share-based payment awards that contain rights to nonforfeitable dividends are considered participating securities for this calculation. Diluted earnings per common share include the dilutive effect of additional potential common shares issuable under stock warrants. The participating nonvested common stock was not included in dilutive shares as it was anti-dilutive for the years ended December 31, 2019 , 2018 and 2017 . The Company's outstanding stock warrants were all exercised prior to December 31, 2018. For the year ended December 31, 2017, proceeds from the assumed exercise of dilutive stock warrants are assumed to be used to repurchase common stock at the average market price. The following table presents a reconciliation of net income available to common shareholders and the number of shares used in the calculation of basic and diluted earnings per common share. Years Ended December 31, 2019 2018 2017 Basic earnings per share: Net income $ 192,736 $ 128,259 $ 76,512 Less: Undistributed earnings allocated to participating securities 971 976 626 Dividends paid on participating securities 281 139 97 Net income available to common shareholders $ 191,484 $ 127,144 $ 75,789 Weighted average basic shares outstanding 42,964,393 29,341,843 25,394,079 Basic earnings per share $ 4.46 $ 4.33 $ 2.98 Diluted earnings per share: Net income available to common shareholders $ 191,484 $ 127,144 $ 75,789 Total weighted average basic shares outstanding 42,964,393 29,341,843 25,394,079 Add dilutive stock warrants — — 106,070 Total weighted average diluted shares outstanding 42,964,393 29,341,843 25,500,149 Diluted earnings per share $ 4.46 $ 4.33 $ 2.97 Anti-dilutive participating securities 73,546 114,087 123,564

Recent Accounting Pronouncement

Recent Accounting Pronouncements	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements Adoption of new accounting standards ASU 2016-02, Leases (Topic 842). This ASU, among other things, requires lessees to recognize a lease liability, which is a lessee’s obligation to make lease payments arising from a lease, measured on a discounted basis; and a right-of-use asset, which is an asset that represents the lessee’s right to use, or control the use of, a specified asset for the lease term. Under this guidance, lessor accounting is largely unchanged. This ASU became effective for annual and interim periods for the Company on January 1, 2019. The Company adopted the standard by applying the alternative transition method whereby comparative periods were not restated, and an immaterial cumulative effect adjustment to the opening balance of retained earnings was recognized as of January 1, 2019. The Company also elected the ASU’s package of three practical expedients, which allowed the Company to forego a reassessment of (i) whether any expired or existing contracts are or contain leases, (ii) the lease classification for any expired or existing leases and (iii) the initial direct costs for any existing leases. The Company also elected not to apply the recognition requirements of the ASU to any short-term leases (as defined by related accounting guidance) and will account for lease and non-lease components separately because such amounts are readily determinable under most lease contracts and because this election results in a lower impact on the Company's balance sheet. The Company has implemented a lease management system to assist in centralizing, maintaining and accounting for all leases and implemented additional processes and internal controls to ensure the Company meets the ASU’s reporting and disclosure requirements. The adoption of this standard resulted in the Company recognizing lease right-of-use assets and related lease liabilities totaling $38,812 and $33,953 , respectively, as of January 1, 2019. The difference between the lease assets and the lease liabilities was $4,949 of prepaid rent, which was reclassified to lease assets, and the remainder, net of the deferred tax impact, was recorded as an adjustment reducing retained earnings in the amount of $70 . In addition, the right-of-use assets and related lease liabilities recognized on January 1, 2019 include the leases assumed with the Guaranty acquisition. The adoption of this ASU did not have a significant impact on the Company’s consolidated statement of income. See Note 1 , Summary of Significant Accounting Policies, and Note 13 , Leases, for required disclosures. ASU 2017-08, Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20), Premium Amortization on Purchased Callable Debt Securities . This ASU requires certain premiums on callable debt securities to be amortized to the earliest call date. The amortization period for callable debt securities purchased at a discount is not impacted. Under current GAAP, premiums on callable debt securities are generally amortized over the contractual life of the security. ASU 2017-08 became effective for the Company on January 1, 2019 and, upon adoption, the Company recognized a cumulative effect adjustment reducing retained earnings by $856 , net of the deferred tax impact, but otherwise did not have a significant impact to the Company's consolidated financial statements and disclosures. ASU 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities. This ASU refines and expands hedge accounting for both financial and commodity risks. Its provisions create more transparency around how economic results are presented, both on the face of the financial statements and in the footnotes. It also makes certain targeted improvements to simplify the application of hedge accounting guidance. ASU 2017-12 became effective for the Company on January 1, 2019. The adoption of this ASU did not have a significant impact on the Company's consolidated financial statements and disclosures. ASU 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220) - Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. The amendments in this update allow reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act (TCJA) which was signed into law on December 22, 2017. The Company elected to early adopt ASU 2018-02 in the first quarter of 2018 and apply the guidance to the beginning of the period, effective January 1, 2018 . The impact of adopting the amendment resulted in a cumulative effect adjustment to the consolidated balance sheet as of January 1, 2018 to reclassify approximately $233 of tax expense from accumulated other comprehensive loss to retained earnings as reflected in the accompanying Consolidated Statements of Changes in Stockholders' Equity. ASU 2018-07, Improvements to Nonemployee Share-Based Payment Accounting . This ASU aligns much of the guidance on measuring and classifying nonemployee awards with that of awards to employees. The guidance applies to nonemployee awards issued in exchange for goods or services used or consumed in an entity’s own operations and to awards granted by an investor to employees and nonemployees of an equity method investee for goods or services used or consumed in the investee’s operations. There are no new disclosure requirements. This ASU became effective for the Company on January 1, 2019. The adoption of this ASU did not have a significant impact on the Company’s financial statements and disclosures. Newly issued but not yet effective accounting standards ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. ASU 2016-13 along with several other subsequent codification updates related to accounting for credit losses, requires the measurement of all expected credit losses for financial assets held at the reporting date based on historical experience, current conditions, and reasonable and supportable forecasts and requires enhanced disclosures related to the significant estimates and judgments used in estimating credit losses, as well as the credit quality and underwriting standards of an organization’s portfolio. In addition, ASU 2016-13 amends the credit loss measurement guidance for available for sale debt securities and purchased financial assets with credit deterioration. Under prior US GAAP, companies generally recognized credit losses when it was probable that the loss has been incurred (incurred loss model). ASU 2016-13 requires a new credit loss methodology, the current expected credit loss (CECL) model, which requires the recognition of an allowance for lifetime expected credit losses on loans, held-to-maturity debt securities and other receivables measured at amortized cost at the time the financial asset is originated or acquired. Credit losses will be immediately recognized through net income; the amount recognized will be based on the current estimate of contractual cash flows not expected to be collected over the financial asset’s contractual term. The Company currently expects the adoption of ASU 2016-13 will result in an increase of its combined allowance for loan losses and reserves for unfunded commitments of approximately $68,000 to $80,000 , of which $20,000 to $22,000 is attributable to purchase credit deteriorated loans. As the Company currently finalizes the execution of its implementation controls and processes, the ultimate impact of the adoption of ASU 2016-13 as of January 1, 2020 could differ from the current expectation. The expected increase in the allowance for loan losses is a result of changing from an incurred loss model, which encompasses allowances for current known and inherent losses within the portfolio, to a CECL model, which encompasses allowances for losses expected to be incurred over the life of the portfolio. The majority of the increase is attributable to applying the CECL model to the Company's acquired loans, which, under prior guidance, were recorded at fair value without an allowance at acquisition date. Furthermore, ASU 2016-13 will necessitate that the Company establish an allowance for expected credit losses for certain debt securities and other financial assets; however, allowances are not expected to be significant. The Company will apply the standard's provisions as a cumulative-effect adjustment to retained earnings. ASU 2017-04, Intangibles - Goodwill and Other (Topic 350) - Simplifying the Test for Goodwill Impairment. This ASU simplifies the accounting for goodwill impairment for all entities by requiring impairment charges to be based on the first step in today’s two-step impairment test. Under the new guidance, if a reporting unit’s carrying amount exceeds its fair value, an entity will record an impairment charge based on that difference. The impairment charge will be limited to the amount of goodwill allocated to that reporting unit. The standard eliminates today’s requirement to calculate a goodwill impairment charge using Step 2, which requires an entity to calculate any impairment charge by comparing the implied fair value of goodwill with its carrying amount. ASU 2017-04 will be effective for the Company on January 1, 2020, with earlier adoption permitted and is not expected to have a significant impact on its financial statements. ASU 2018-13, Fair Value Measurement (Topic 820) - Changes to the Disclosure Requirements for Fair Value Measurement . This ASU modifies the disclosure requirements on fair value measurements by requiring that Level 3 fair value disclosures include the range and weighted average of significant unobservable inputs used to develop those fair value measurements. For certain unobservable inputs, an entity may disclose other quantitative information in lieu of the weighted average if the entity determines that other quantitative information would be a more reasonable and rational method to reflect the distribution of unobservable inputs used to develop Level 3 fair value measurements. ASU 2018-13 will be effective for the Company on January 1, 2020, with early adoption permitted, and is not expected to have a significant impact on its financial statements and disclosures. ASU 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. This ASU aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal use software license). The accounting for the service element of a hosting arrangement that is a service contract is not affected by these amendments. This ASU will be effective for the Company on January 1, 2020, with early adoption permitted, and is not expected to have a significant impact on its financial statements and disclosures. ASU 2019-12, Income Taxes (Topic 740) - Simplifying the Accounting for Income Taxes. The guidance issued in this update simplifies the accounting for income taxes by eliminating certain exceptions to the guidance in ASC 740 related to the approach for intraperiod tax allocation, the methodology for calculating income taxes in an interim period and the recognition for deferred tax liabilities for outside basis differences. ASU 2019-12 also simplifies aspects of the accounting for franchise taxes and enacted changes in tax laws or rates and clarifies the accounting for transactions that result in a step-up in the tax basis of goodwill. ASU 2019-12 will be effective for the Company on January 1, 2021, with early adoption permitted, and is not expected to have a significant impact on our financial statements.

Restrictions on Cash and Due fr

Restrictions on Cash and Due from Banks	12 Months Ended
	Dec. 31, 2019
Cash and Cash Equivalents [Abstract]
Restrictions on Cash and Due From Banks	Restrictions on Cash and Due From Banks At December 31, 2019 and 2018 , the Company had a reserve requirement of $63,739 and $35,952 , respectively, with the Federal Reserve Bank.

Statement of Cash Flows

Statement of Cash Flows	12 Months Ended
	Dec. 31, 2019
Supplemental Cash Flow Elements [Abstract]
Statement of Cash Flows	Statement of Cash Flows As allowed by the accounting standards, the Company has chosen to report, on a net basis, its cash receipts and cash payments for time deposits accepted and repayments of those deposits, and loans made to customers and principal collections on those loans. The Company uses the indirect method to present cash flows from operating activities. Other supplemental cash flow information is presented below: Years Ended December 31, 2019 2018 2017 Cash transactions: Interest expense paid $ 144,775 $ 79,509 $ 41,802 Income taxes paid $ 40,504 $ 25,109 $ 34,161 Noncash transactions: Transfers of loans to other real estate owned $ 544 $ 410 $ 1,201 Loans to facilitate the sale of other real estate owned $ 517 $ — $ — Securities purchased, not yet settled $ 9,975 $ — $ — Transfers of loans held for investment to loans held for sale $ 83,526 $ — $ — Right-of-use assets obtained in exchange for lease liabilities $ 35,553 $ — $ — Transfer of bank premises to other real estate $ 7,896 $ — $ 2,716 Transfer of repurchase agreements to deposits $ 8,475 $ — $ 8,845 Supplemental schedule of noncash investing activities from branch sales is as follows: Years ended December 31, 2019 2018 2017 Noncash assets transferred: Loans, including accrued interest $ 796 $ — $ 106,008 Premises and equipment 94 — 7,473 Core deposit intangible assets, net — — 3,011 Other assets 2 — 74 Total assets $ 892 $ — $ 116,566 Noncash liabilities transferred: Deposits, including interest $ 27,721 $ — $ 178,279 Other liabilities 27 — 129 Total liabilities $ 27,748 $ — $ 178,408 Cash and cash equivalents transferred in branch sales $ 206 $ — $ 1,712 Deposit premium received $ 1,386 $ — $ 7,107 Cash paid to buyer, net of deposit premium $ 24,957 $ — $ 56,975 Supplemental schedule of noncash investing activities from sale of trust business during 2019 is as follows: Year ended December 31, 2019 Noncash assets transferred: Customer relationship intangible assets, net $ 2,939 Other assets 11 Total assets $ 2,950 Net cash received from sale $ 4,269 Supplemental schedule of noncash investing activities from acquisitions is as follows: Years ended December 31, 2019 2018 2017 Noncash assets acquired Certificates of deposit held in other banks $ 262 $ — $ 11,025 Securities available for sale 561,052 24,721 336,540 Restricted stock 27,794 3,357 11,110 Loans 2,789,868 651,769 1,384,210 Premises and equipment 65,786 4,863 63,166 Other real estate owned 1,829 — 11,212 Goodwill 272,224 100,339 363,139 Other intangible assets 71,518 7,537 36,717 Bank owned life insurance 80,837 8,181 53,213 Other assets 31,987 6,385 25,379 Total assets acquired $ 3,903,157 $ 807,152 $ 2,295,711 Noncash liabilities assumed: Deposits $ 3,108,810 $ 593,078 $ 1,825,181 Repurchase agreements 8,475 — 18,003 FHLB advances 142,653 60,000 — Other borrowings 40,000 — — Junior subordinated debentures 25,774 — 9,359 Other liabilities 15,477 10,518 7,697 Total liabilities assumed $ 3,341,189 $ 663,596 $ 1,860,240 Cash and cash equivalents acquired from acquisitions $ 39,913 $ 44,723 $ 148,444 Cash paid to shareholders of acquired banks $ 9 $ 31,016 $ 17,773 Fair value of common stock issued to shareholders of acquired banks $ 601,872 $ 157,263 $ 566,142

Securities Available for Sale

Securities Available for Sale	12 Months Ended
	Dec. 31, 2019
Debt Securities, Available-for-sale [Abstract]
Securities Available for Sale	Securities Available for Sale Securities available for sale have been classified in the consolidated balance sheets according to management’s intent. The amortized cost of securities and their approximate fair values at December 31, 2019 and 2018 , are as follows: Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Securities Available for Sale December 31, 2019 U.S. treasuries $ 48,060 $ 743 $ (7 ) $ 48,796 Government agency securities 178,953 926 (583 ) 179,296 Obligations of state and municipal subdivisions 332,715 11,150 (6 ) 343,859 Corporate bonds 7,011 207 — 7,218 Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 493,915 11,981 (329 ) 505,567 Other securities 1,200 — — 1,200 $ 1,061,854 $ 25,007 $ (925 ) $ 1,085,936 December 31, 2018 U.S. treasuries $ 30,110 $ — $ (467 ) $ 29,643 Government agency securities 152,969 80 (2,819 ) 150,230 Obligations of state and municipal subdivisions 187,366 727 (3,086 ) 185,007 Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 326,168 128 (5,826 ) 320,470 $ 696,613 $ 935 $ (12,198 ) $ 685,350 Securities with a carrying amount of approximately $571,843 and $219,927 at December 31, 2019 and 2018 , respectively, were pledged primarily to secure deposits. Proceeds from sale of securities available for sale and gross gains and gross losses for the years ended December 31, 2019 , 2018 and 2017 were as follows: Years Ended December 31, 2019 2018 2017 Proceeds from sale $ 192,417 $ 102,647 $ 31,367 Gross gains $ 306 $ 268 $ 176 Gross losses $ 31 $ 849 $ 52 The amortized cost and estimated fair value of securities available for sale at December 31, 2019 , by contractual maturity, are shown below. Maturities of mortgage-backed securities will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. December 31, 2019 Securities Available for Sale Amortized Cost Fair Value Due in one year or less $ 34,050 $ 34,088 Due from one year to five years 181,742 184,903 Due from five to ten years 162,396 166,337 Thereafter 189,751 195,041 567,939 580,369 Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 493,915 505,567 $ 1,061,854 $ 1,085,936 The number of securities, unrealized losses and fair value, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, as of December 31, 2019 and 2018 , are summarized as follows: Less Than 12 Months Greater Than 12 Months Total Description of Securities Number of Securities Estimated Fair Value Unrealized Losses Number of Securities Estimated Fair Value Unrealized Losses Estimated Fair Value Unrealized Losses Securities Available for Sale December 31, 2019 U.S. treasuries — $ — $ — 2 $ 8,097 $ (7 ) $ 8,097 $ (7 ) Government agency securities 13 52,790 (495 ) 6 15,911 (88 ) 68,701 (583 ) Obligations of state and municipal subdivisions 5 2,793 (1 ) 1 423 (5 ) 3,216 (6 ) Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 13 46,512 (317 ) 1 1,193 (12 ) 47,705 (329 ) 31 $ 102,095 $ (813 ) 10 $ 25,624 $ (112 ) $ 127,719 $ (925 ) December 31, 2018 U.S. treasuries 1 $ 9,749 $ (6 ) 5 $ 19,894 $ (461 ) $ 29,643 $ (467 ) Government agency securities 4 6,068 (32 ) 43 126,745 (2,787 ) 132,813 (2,819 ) Obligations of state and municipal subdivisions 88 32,493 (326 ) 218 105,817 (2,760 ) 138,310 (3,086 ) Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 56 112,114 (1,031 ) 101 186,713 (4,795 ) 298,827 (5,826 ) 149 $ 160,424 $ (1,395 ) 367 $ 439,169 $ (10,803 ) $ 599,593 $ (12,198 ) Unrealized losses are generally due to changes in interest rates. The Company has the intent to hold these securities until maturity or a forecasted recovery and it is more likely than not that the Company will not have to sell the securities before the recovery of their cost basis. As such, the losses are deemed to be temporary.

Loans, Net and Allowance for Lo

Loans, Net and Allowance for Loan Losses	12 Months Ended
	Dec. 31, 2019
Receivables [Abstract]
Loans, Net and Allowance for Loan Losses	Loans, Net and Allowance for Loan Losses Loans, net at December 31, 2019 and 2018 , consisted of the following: December 31, 2019 2018 Commercial $ 2,482,356 $ 1,361,104 Real estate: Commercial 5,872,653 4,141,356 Commercial construction, land and land development 1,236,623 905,421 Residential 1,515,227 1,049,521 Single-family interim construction 378,120 331,748 Agricultural 97,767 66,638 Consumer 32,603 31,759 Other 621 253 11,615,970 7,887,800 Deferred loan fees (1,695 ) (3,303 ) Allowance for loan losses (51,461 ) (44,802 ) $ 11,562,814 $ 7,839,695 The Company has certain lending policies and procedures in place that are designed to maximize loan income within an acceptable level of risk. Management reviews and approves these policies and procedures on a regular basis. A reporting system supplements the review process by providing management with frequent reports related to loan production, loan quality, concentrations of credit, loan delinquencies and nonperforming and potential problem loans. Commercial loans are underwritten after evaluating and understanding the borrower’s ability to operate profitably and prudently expand its business. The Company’s management examines current and projected cash flows to determine the ability of the borrower to repay their obligations as agreed. Commercial loans are primarily made based on the identified cash flows of the borrower and secondarily on the underlying collateral provided by the borrower. These cash flows, however, may not be as expected and the value of collateral securing the loans may fluctuate. Most commercial loans are secured by the assets being financed or other business assets such as accounts receivable or inventory and may incorporate a personal guarantee; however, some short term loans may be made on an unsecured basis. Additionally, our commercial loan portfolio includes loans made to customers in the energy industry, which is a complex, technical and cyclical industry. Experienced bankers with specialized energy lending experience originate our energy loans. Companies in this industry produce, extract, develop, exploit and explore for oil and natural gas. Loans are primarily collateralized with proven producing oil and gas reserves based on a technical evaluation of these reserves. At December 31, 2019 and 2018 , there were approximately $189,781 and $135,034 of energy-related loans outstanding, respectively. The Company has a mortgage warehouse purchase program providing mortgage inventory financing for residential mortgage loans originated by mortgage banker clients across a broad geographic scale. Proceeds from the sale of mortgages is the primary source of repayment for warehouse inventory financing via approved investor takeout commitments. These loans typically have a very short duration ranging between a few days to 15 days . In some cases, loans to larger mortgage originators may be financed for up to 60 days . These loans are reported as commercial loans since the loans are secured by notes receivable, not real estate. As of December 31, 2019 and 2018 , mortgage warehouse purchase loans outstanding totaled $687,317 and $170,290 , respectively. Commercial real estate loans are subject to underwriting standards and processes similar to commercial loans. These loans are viewed primarily as cash flow loans and secondarily as loans secured by real estate. Commercial real estate lending typically involves higher loan principal amounts and the repayment of these loans is generally largely dependent on the successful operation of the property or the business conducted on the property securing the loan. Commercial real estate loans may be more adversely affected by conditions in the real estate markets or in the general economy. The properties securing the Company’s commercial real estate portfolio are diverse in terms of type and geographic location. Management monitors the diversification of the portfolio on a quarterly basis by type and geographic location. Management also tracks the level of owner- occupied property versus non owner-occupied property. At December 31, 2019 , the portfolio consisted of approximately 30% of owner-occupied property. Land and commercial land development loans are underwritten using feasibility studies, independent appraisal reviews and financial analysis of the developers or property owners. Generally, borrowers must have a proven track record of success. Commercial construction loans are generally based upon estimates of cost and value of the completed project. These estimates may not be accurate. Commercial construction loans often involve the disbursement of substantial funds with the repayment dependent on the success of the ultimate project. Sources of repayment for these loans may be pre-committed permanent financing or sale of the developed property. The loans in this portfolio are geographically diverse and due to the increased risk are monitored closely by management and the board of directors on a quarterly basis. Residential real estate and single-family interim construction loans are underwritten primarily based on borrowers’ credit scores, documented income and minimum collateral values. Relatively small loan amounts are spread across many individual borrowers which minimizes risk in the residential portfolio. In addition, management evaluates trends in past dues and current economic factors on a regular basis. Agricultural loans are collateralized by real estate and/or agricultural-related assets. Agricultural real estate loans are primarily comprised of loans for the purchase of farmland. Loan-to-value ratios on loans secured by farmland generally do not exceed 80% and have amortization periods limited to twenty years . Agricultural non-real estate loans are generally comprised of term loans to fund the purchase of equipment, livestock and seasonal operating lines to grain farmers to plant and harvest corn and soybeans. Specific underwriting standards have been established for agricultural-related loans including the establishment of projections for each operating year based on industry developed estimates of farm input costs and expected commodity yields and prices. Operating lines are typically written for one year and secured by the crop and other farm assets as considered necessary. Agricultural loans carry significant credit risks as they involve larger balances concentrated with single borrowers or groups of related borrowers. In addition, repayment of such loans depends on the successful operation or management of the farm property securing the loan or for which an operating loan is utilized. Farming operations may be affected by adverse weather conditions such as drought, hail or floods that can severely limit crop yields. Consumer loans represent less than 1% of the outstanding total loan portfolio. Collateral consists primarily of automobiles and other personal assets. Credit score analysis is used to supplement the underwriting process. Most of the Company’s lending activity occurs within the State of Texas, primarily in the north, central and southeast Texas regions and the State of Colorado, specifically along the Front Range area. As of December 31, 2019 , loans in the Colorado region represented about 27% of the total portfolio. A large percentage of the Company’s portfolio consists of commercial and residential real estate loans. As of December 31, 2019 and 2018 , there were no concentrations of loans related to a single industry in excess of 10% of total loans. The allowance for loan losses is an amount that management believes will be adequate to absorb estimated losses relating to specifically identified loans, as well as probable credit losses inherent in the balance of the loan portfolio. The allowance is derived from the following two components: 1) allowances established on individual impaired loans, which are based on a review of the individual characteristics of each loan, including the customer’s ability to repay the loan, the underlying collateral values and the industry the customer operates and 2) allowances based on actual historical loss experience for the last three years for similar types of loans in the Company’s loan portfolio adjusted for primarily changes in the lending policies and procedures; collection, charge-off and recovery practices; nature and volume of the loan portfolio; change in value of underlying collateral; volume and severity of nonperforming loans; existence and effect of any concentrations of credit and the level of such concentrations and current, national and local economic and business conditions. This second component also includes an unallocated allowance to cover uncertainties that could affect management’s estimate of probable losses. The unallocated allowance reflects the imprecision inherent in the underlying assumptions used in the methodologies for estimating this component. The Company’s management continually evaluates the allowance for loan losses determined from the allowances established on individual loans and the amounts determined from historical loss percentages adjusted for the qualitative factors above. Should any of the factors considered by management change, the Company’s estimate of loan losses could also change and would affect the level of future provision expense. While the calculation of the allowance for loan losses utilizes management’s best judgment and all the information available, the adequacy of the allowance for loan losses is dependent on a variety of factors beyond the Company’s control, including, among other things, the performance of the entire loan portfolio, the economy, changes in interest rates and the view of regulatory authorities towards loan classifications. In addition, regulatory agencies, as an integral part of their examination process, periodically review the Bank’s allowance for loan losses, and may require the Bank to make additions to the allowance based on their judgment about information available to them at the time of their examinations. Loans requiring an allocated loan loss provision are generally identified at the servicing officer level based on review of weekly past due reports and/or the loan officer’s communication with borrowers. In addition, past due loans are discussed at weekly officer loan committee meetings to determine if classification is warranted. The Company’s credit department has implemented an internal risk based loan review process to identity potential internally classified loans that supplements the annual independent external loan review. External loan reviews cover a wide range of the loan portfolio, including large lending relationships and recently acquired loan portfolios. As such, the external loan review generally covers loans exceeding $3,500 . These reviews include analysis of borrower’s financial condition, payment histories and collateral values to determine if a loan should be internally classified. Generally, once classified, an impaired loan analysis is completed by the credit department to determine if the loan is impaired and the amount of allocated allowance required. The Texas economy, specifically the Company’s lending area of north, central and southeast Texas area, continued to expand at a moderate pace while the Colorado economy remained flat during the fourth quarter of 2019. The Texas economy, which is the second largest in the nation, and the Colorado economy have exceeded the average U.S. economy in job creation and employment growth. Overall, the forecast is positive with continued moderate growth in the retail and service sectors. The Texas and Colorado economies are expected to continue to grow into 2020 at a slower pace with an improved outlook, though uncertainties, including slowing U.S. and global economies, trade uncertainty and a significant oil-price decline, remain elevated. The risk of loss associated with all segments of the portfolio could increase due to these factors. The economy and other risk factors are minimized by the Company’s underwriting standards which include the following principles: 1) financial strength of the borrower including strong earnings, high net worth, significant liquidity and acceptable debt to worth ratio, 2) managerial business competence, 3) ability to repay, 4) loan to value, 5) projected cash flow and 6) guarantor financial statements as applicable. The following is a summary of the activity in the allowance for loan losses by loan class for the years ended December 31, 2019 , 2018 and 2017 : Commercial Commercial Real Estate, Construction, Land and Land Development Residential Real Estate Single-Family Interim Construction Agricultural Consumer Other Unallocated Total Year ended December 31, 2019 Balance at beginning of year $ 11,793 $ 27,795 $ 3,320 $ 1,402 $ 241 $ 186 $ 3 $ 62 $ 44,802 Provision for loan losses 8,670 5,289 498 207 91 71 356 (377 ) 14,805 Charge-offs (7,709 ) (3 ) (140 ) (3 ) — (79 ) (430 ) — (8,364 ) Recoveries 90 4 — — — 48 76 — 218 Balance at end of year $ 12,844 $ 33,085 $ 3,678 $ 1,606 $ 332 $ 226 $ 5 $ (315 ) $ 51,461 Year ended December 31, 2018 Balance at beginning of year $ 10,599 $ 23,301 $ 3,447 $ 1,583 $ 250 $ 205 $ (32 ) $ 49 $ 39,402 Provision for loan losses 4,973 4,909 (124 ) (181 ) (9 ) 69 210 13 9,860 Charge-offs (3,863 ) (435 ) (6 ) — — (93 ) (228 ) — (4,625 ) Recoveries 84 20 3 — — 5 53 — 165 Balance at end of year $ 11,793 $ 27,795 $ 3,320 $ 1,402 $ 241 $ 186 $ 3 $ 62 $ 44,802 Year ended December 31, 2017 Balance at beginning of year $ 8,593 $ 18,399 $ 2,760 $ 1,301 $ 207 $ 242 $ 29 $ 60 $ 31,591 Provision for loan losses 2,059 4,886 683 416 43 99 90 (11 ) 8,265 Charge-offs (81 ) (15 ) — (134 ) — (182 ) (190 ) — (602 ) Recoveries 28 31 4 — — 46 39 — 148 Balance at end of year $ 10,599 $ 23,301 $ 3,447 $ 1,583 $ 250 $ 205 $ (32 ) $ 49 $ 39,402 The following table details the amount of the allowance for loan losses and recorded investment in loans by class as of December 31, 2019 and 2018 : Commercial Commercial Residential Real Estate Single-Family Interim Construction Agricultural Consumer Other Unallocated Total December 31, 2019 Allowance for losses: Individually evaluated for impairment $ 357 $ — $ — $ — $ — $ 1 $ — $ — $ 358 Collectively evaluated for impairment 12,108 32,615 3,678 1,606 332 225 5 (315 ) 50,254 Loans acquired with deteriorated credit quality 379 470 — — — — — — 849 Ending balance $ 12,844 $ 33,085 $ 3,678 $ 1,606 $ 332 $ 226 $ 5 $ (315 ) $ 51,461 Loans: Individually evaluated for impairment $ 3,130 $ 6,813 $ 2,008 $ — $ 114 $ 22 $ — $ — $ 12,087 Collectively evaluated for impairment 2,416,569 6,883,639 1,505,896 378,120 93,837 32,556 621 — 11,311,238 Acquired with deteriorated credit quality 62,657 218,824 7,323 — 3,816 25 — — 292,645 Ending balance $ 2,482,356 $ 7,109,276 $ 1,515,227 $ 378,120 $ 97,767 $ 32,603 $ 621 $ — $ 11,615,970 December 31, 2018 Allowance for losses: Individually evaluated for impairment $ 2,633 $ — $ 92 $ — $ — $ 2 $ — $ — $ 2,727 Collectively evaluated for impairment 9,115 27,795 3,228 1,402 241 184 3 62 42,030 Loans acquired with deteriorated credit quality 45 — — — — — — — 45 Ending balance $ 11,793 $ 27,795 $ 3,320 $ 1,402 $ 241 $ 186 $ 3 $ 62 $ 44,802 Loans: Individually evaluated for impairment $ 7,288 $ 1,734 $ 1,943 $ 3,578 $ — $ 32 $ — $ — $ 14,575 Collectively evaluated for impairment 1,335,194 4,955,178 1,044,265 328,170 66,032 31,699 253 — 7,760,791 Acquired with deteriorated credit quality 18,622 89,865 3,313 — 606 28 — — 112,434 Ending balance $ 1,361,104 $ 5,046,777 $ 1,049,521 $ 331,748 $ 66,638 $ 31,759 $ 253 $ — $ 7,887,800 Nonperforming loans by loan class (excluding loans acquired with deteriorated credit quality) at December 31, 2019 and 2018 , are summarized as follows: Commercial Commercial Residential Real Estate Single-Family Interim Construction Agricultural Consumer Other Total December 31, 2019 Nonaccrual loans $ 3,130 $ 6,461 $ 1,820 $ — $ 114 $ 22 $ — $ 11,547 Loans past due 90 days and still accruing 14,529 — — — — — — 14,529 Troubled debt restructurings (not included in nonaccrual or loans past due and still accruing) — 352 188 — — — — 540 $ 17,659 $ 6,813 $ 2,008 $ — $ 114 $ 22 $ — $ 26,616 December 31, 2018 Nonaccrual loans $ 5,224 $ 1,329 $ 1,775 $ 3,578 $ — $ 32 $ — $ 11,938 Loans past due 90 days and still accruing — — — — — 5 — 5 Troubled debt restructurings (not included in nonaccrual or loans past due and still accruing) 114 405 168 — — — — 687 $ 5,338 $ 1,734 $ 1,943 $ 3,578 $ — $ 37 $ — $ 12,630 The accrual of interest is discontinued on a loan when management believes, after considering collection efforts and other factors, that the borrower's financial condition is such that collection of interest is doubtful. All interest accrued but not collected for loans that are placed on nonaccrual status or charged-off is reversed against interest income. Cash collections on nonaccrual loans are generally credited to the loan receivable balance, and no interest income is recognized on those loans until the principal balance has been collected. Loans are returned to accrual status when all the principal and interest amounts contractually due are brought current and future payments are reasonably assured. Impaired loans are those loans where it is probable that all amounts due according to contractual terms of the loan agreement will not be collected. The Company has identified these loans through its normal loan review procedures. Impaired loans are measured based on 1) the present value of expected future cash flows discounted at the loan's effective interest rate; 2) the loan's observable market price; or 3) the fair value of collateral if the loan is collateral dependent. Substantially all of the Company’s impaired loans are measured at the fair value of the collateral. In limited cases, the Company may use other methods to determine the level of impairment of a loan if such loan is not collateral dependent. All commercial, real estate, agricultural loans and troubled debt restructurings are considered for individual impairment analysis. Smaller balance consumer loans are collectively evaluated for impairment. Impaired loans by loan class (excluding loans acquired with deteriorated credit quality) at December 31, 2019 and 2018 and for the years ended December 31, 2019 , 2018 and 2017 , are summarized as follows: Commercial Commercial Residential Real Estate Single-Family Interim Construction Agricultural Consumer Other Total December 31, 2019 Recorded investment in impaired loans: Impaired loans with an allowance for loan losses $ 1,580 $ — $ — $ — $ — $ 1 $ — $ 1,581 Impaired loans with no allowance for loan losses 1,550 6,813 2,008 — 114 21 — 10,506 Total $ 3,130 $ 6,813 $ 2,008 $ — $ 114 $ 22 $ — $ 12,087 Unpaid principal balance of impaired loans $ 8,580 $ 6,967 $ 2,197 $ — $ 123 $ 24 $ — $ 17,891 Allowance for loan losses on impaired loans $ 357 $ — $ — $ — $ — $ 1 $ — $ 358 December 31, 2018 Recorded investment in impaired loans: Impaired loans with an allowance for loan losses $ 6,416 $ — $ 134 $ — $ — $ 1 $ — $ 6,551 Impaired loans with no allowance for loan losses 872 1,734 1,809 3,578 — 31 — 8,024 Total $ 7,288 $ 1,734 $ 1,943 $ 3,578 $ — $ 32 $ — $ 14,575 Unpaid principal balance of impaired loans $ 9,822 $ 1,860 $ 2,056 $ 3,579 $ — $ 38 $ — $ 17,355 Allowance for loan losses on impaired loans $ 2,633 $ — $ 92 $ — $ — $ 2 $ — $ 2,727 For the year ended December 31, 2019 Average recorded investment in impaired loans $ 6,266 $ 3,979 $ 1,746 $ 716 $ 57 $ 30 $ — $ 12,794 Interest income recognized on impaired loans $ 30 $ 39 $ 39 $ 119 $ — $ 6 $ — $ 233 For the year ended December 31, 2018 Average recorded investment in impaired loans $ 8,919 $ 2,667 $ 2,033 $ 716 $ — $ 46 $ — $ 14,381 Interest income recognized on impaired loans $ 119 $ 65 $ 81 $ 1 $ — $ 2 $ — $ 268 For the year ended December 31, 2017 Average recorded investment in impaired loans $ 8,524 $ 3,690 $ 2,431 $ 177 $ — $ 218 $ — $ 15,040 Interest income recognized on impaired loans $ 8 $ 428 $ 58 $ — $ — $ 5 $ — $ 499 Certain impaired loans have adequate collateral and do not require a related allowance for loan loss. The Company will charge-off that portion of any loan which management considers a loss. Commercial and real estate loans are generally considered for charge-off when exposure beyond collateral coverage is apparent and when no further collection of the loss portion is anticipated based on the borrower’s financial condition. The restructuring of a loan is considered a “troubled debt restructuring” if both 1) the borrower is experiencing financial difficulties and 2) the creditor has granted a concession. Concessions may include interest rate reductions or below market interest rates, principal forgiveness, extending amortization and other actions intended to minimize potential losses. A “troubled debt restructured” loan is identified as impaired and measured for credit impairment as of each reporting period in accordance with the guidance in ASC 310-10-35. Modifications primarily relate to extending the amortization periods of the loans and interest rate concessions. The majority of these loans were identified as impaired prior to restructuring; therefore, the modifications did not materially impact the Company’s determination of the allowance for loan losses. The recorded investment in troubled debt restructurings, including those on nonaccrual, was $1,208 and $1,925 as of December 31, 2019 and 2018 , respectively. Following is a summary of loans modified under troubled debt restructurings during the years ended December 31, 2019 and 2018 : Commercial Commercial Residential Real Estate Single-Family Interim Construction Agricultural Consumer Other Total Troubled debt restructurings during the year ended December 31, 2019 Number of contracts — — 1 — — — — 1 Pre-restructuring outstanding recorded investment $ — $ — $ 29 $ — $ — $ — $ — $ 29 Post-restructuring outstanding recorded investment $ — $ — $ 29 $ — $ — $ — $ — $ 29 Troubled debt restructurings during the year ended December 31, 2018 Number of contracts 1 — — — — — — 1 Pre-restructuring outstanding recorded investment $ 114 $ — $ — $ — $ — $ — $ — $ 114 Post-restructuring outstanding recorded investment $ 114 $ — $ — $ — $ — $ — $ — $ 114 At December 31, 2019 and 2018 , there were no loans modified under troubled debt restructurings during the previous twelve month period that subsequently defaulted during the years ended December 31, 2019 and 2018 . At December 31, 2019 and 2018 , the Company had no commitments to lend additional funds to any borrowers with loans whose terms have been modified under troubled debt restructurings. Loans are considered past due if the required principal and interest payments have not been received as of the date such payments were due. The following table presents information regarding the aging of past due loans by loan class as of December 31, 2019 and 2018 : Loans 30-89 Days Past Due Loans 90 Days or More Past Due Total Past Due Loans Current Loans Total Loans December 31, 2019 Commercial $ 4,512 $ 17,656 $ 22,168 $ 2,397,531 $ 2,419,699 Commercial real estate, construction, land and land development 9,153 2,905 12,058 6,878,394 6,890,452 Residential real estate 3,242 642 3,884 1,504,020 1,507,904 Single-family interim construction 2,836 — 2,836 375,284 378,120 Agricultural 22 114 136 93,815 93,951 Consumer 167 22 189 32,389 32,578 Other — — — 621 621 19,932 21,339 41,271 11,282,054 11,323,325 Acquired with deteriorated credit quality 2,556 6,766 9,322 283,323 292,645 $ 22,488 $ 28,105 $ 50,593 $ 11,565,377 $ 11,615,970 December 31, 2018 Commercial $ 15,426 $ 4,366 $ 19,792 $ 1,322,690 $ 1,342,482 Commercial real estate, construction, land and land development 3,435 — 3,435 4,953,477 4,956,912 Residential real estate 4,199 1,035 5,234 1,040,974 1,046,208 Single-family interim construction 774 3,578 4,352 327,396 331,748 Agricultural — — — 66,032 66,032 Consumer 135 35 170 31,561 31,731 Other — — — 253 253 23,969 9,014 32,983 7,742,383 7,775,366 Acquired with deteriorated credit quality 2,939 957 3,896 108,538 112,434 $ 26,908 $ 9,971 $ 36,879 $ 7,850,921 $ 7,887,800 The Company’s internal classified report is segregated into the following categories: 1) Pass/Watch, 2) Special Mention, 3) Substandard and 4) Doubtful. The loans placed in the Pass/Watch category reflect the Company’s opinion that the loans reflect potential weakness that requires monitoring on a more frequent basis. The loans in the Special Mention category reflect the Company’s opinion that the credit contains weaknesses which represent a greater degree of risk and warrant extra attention. These loans are reviewed monthly by officers and senior management to determine if a change in category is warranted. The loans placed in the Substandard category are considered to be potentially inadequately protected by the current debt service capacity of the borrower and/or the pledged collateral. These credits, even if apparently protected by collateral value, have shown weakness related to adverse financial, managerial, economic, market or political conditions which may jeopardize repayment of principal and interest. There is a possibility that some future loss could be sustained by the Company if such weakness is not corrected. The Doubtful category includes loans that are in default or principal exposure is probable. Substandard and Doubtful loans are individually evaluated to determine if they should be classified as impaired and an allowance is allocated if deemed necessary under ASC 310-10. The loans that are not impaired are included with the remaining “pass” credits in determining the portion of the allowance for loan loss based on historical loss experience and other qualitative factors. The portfolio is segmented into categories including: commercial loans, consumer loans, commercial real estate loans, residential real estate loans and agricultural loans. The adjusted historical loss percentage is applied to each category. Each category is then added together to determine the allowance allocated under ASC 450-20. A summary of loans by credit quality indicator by class as of December 31, 2019 and 2018 , is as follows: Pass Pass/ Watch Special Mention Substandard Doubtful Total December 31, 2019 Commercial $ 2,332,611 $ 71,642 $ 37,739 $ 40,364 $ — $ 2,482,356 Commercial real estate, construction, land and land development 6,814,780 184,720 46,889 62,887 — 7,109,276 Residential real estate 1,501,019 4,850 994 8,364 — 1,515,227 Single-family interim construction 376,887 1,233 — — — 378,120 Agricultural 88,044 5,287 1,864 2,572 — 97,767 Consumer 32,459 33 2 109 — 32,603 Other 621 — — — — 621 $ 11,146,421 $ 267,765 $ 87,488 $ 114,296 $ — $ 11,615,970 December 31, 2018 Commercial $ 1,279,024 $ 18,378 $ 30,783 $ 32,919 $ — $ 1,361,104 Commercial real estate, construction, land and land development 4,895,217 81,693 40,601 29,266 — 5,046,777 Residential real estate 1,038,283 3,617 707 6,914 — 1,049,521 Single-family interim construction 327,939 — 231 3,578 — 331,748 Agricultural 61,055 2,918 2,093 572 — 66,638 Consumer 31,559 67 — 133 — 31,759 Other 253 — — — — 253 $ 7,633,330 $ 106,673 $ 74,415 $ 73,382 $ — $ 7,887,800 The Company has acquired certain loans which experienced credit deterioration since origination (purchased credit impaired (PCI) loans). The Company has included PCI loans in the above grading tables. The following provides additional detail on the grades applied to those loans at December 31, 2019 and 2018: Pass Pass/ Special Mention Substandard Doubtful Total December 31, 2019 $ 232,095 $ 21,284 $ 4,502 $ 34,764 $ — $ 292,645 December 31, 2018 40,940 32,427 14,817 24,250 — 112,434 PCI loans may remain on accrual status to the extent the company can reasonably estimate the amount and timing of expected future cash flows. At December 31, 2019 and 2018, nonaccrual PCI loans were $10,850 and $6,996 , respectively. Accretion on PCI loans is based on estimated future cash flows, regardless of contractual maturity. The following table summarizes the outstanding balance and related carrying amount of purchased credit impaired loans by acquired bank as of the acquisition date for the acquisitions occurring in 2019 and 2018 . Acquisition Date January 1, 2019 June 1, 2018 Guaranty Bancorp Integrity Bancshares, Inc. Outstanding balance $ 341,645 $ 57,317 Nonaccretable difference (16,622 ) (9,969 ) Accretable yield (13,299 ) (128 ) Carrying amount $ 311,724 $ 47,220 The carrying amount of all acquired PCI loans included in the consolidated balance sheet and the related outstanding balance at December 31, 2019 and 2018 , were as follows: December 31, 2019 2018 Outstanding balance $ 326,077 $ 129,333 Carrying amount 292,645 112,434 There was an allocation of $849 and $45 established in the allowance for loan losses relating to PCI loans at December 31, 2019 and 2018 , respectively. The changes in accretable yield during the years ended December 31, 2019 and 2018 in regard to loans transferred at acquisition for which it was probable that all contractually required payments would not be collected are presented in the table below. 2019 2018 Balance at January 1 $ 1,436 $ 1,546 Additions 13,299 128 Accretion (5,830 ) (1,557 ) Transfers from nonaccretable — 1,319 Balance at December 31 $ 8,905 $ 1,436

Premises and Equipment, Net

Premises and Equipment, Net	12 Months Ended
	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Premises and Equipment, Net	Premises and Equipment, Net Premises and equipment, net at December 31, 2019 and 2018 consisted of the following: December 31, 2019 2018 Land $ 58,643 $ 43,746 Building 184,589 93,793 Furniture, fixtures and equipment 39,855 34,602 Aircraft 8,947 8,947 Leasehold and tenant improvements 5,466 4,638 Construction in progress 834 32,399 298,334 218,125 Less accumulated depreciation (55,460 ) (50,259 ) $ 242,874 $ 167,866 Depreciation expense amounted to $ 11,783 , $ 8,391 and $ 8,196 for the years ended December 31, 2019 , 2018 and 2017 , respectively.

Goodwill and Core Deposit Intan

Goodwill and Core Deposit Intangible, Net	12 Months Ended
	Dec. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Core Deposit Intangible, Net	Goodwill and Other Intangible Assets, Net At December 31, 2019 and 2018 , goodwill totaled $994,021 and $721,797 , respectively. The Company recorded goodwill of $272,224 relating to the Guaranty Bancorp acquisition in 2019 (see Note 22 , Business Combinations). The following is a summary of other intangible assets activity: December 31, 2019 2018 Core deposit intangible: Balance at beginning of the year $ 63,891 $ 56,354 Additions: Guaranty and Integrity acquisitions 61,993 7,537 Balance at end of the year 125,884 63,891 Less accumulated amortization (31,057 ) (18,849 ) Total core deposit intangible, net 94,827 45,042 Customer relationship intangible: Balance at beginning of the year — — Additions: Guaranty acquisition 9,525 — Deletions: sale of trust business (3,118 ) — Balance at end of the year 6,407 — Less accumulated amortization (493 ) — Total customer relationship intangible, net 5,914 — Total other intangible assets, net $ 100,741 $ 45,042 Amortization expense related to intangible assets amounted to $12,880 , $5,739 and $4,639 for the years ended December 31, 2019 , 2018 and 2017 , respectively. The remaining weighted average amortization period for intangible assets is 8.4 years as of December 31, 2019. The future amortization expense related to other intangible assets remaining at December 31, 2019 is as follows: First year $ 12,671 Second year 12,580 Third year 12,492 Fourth year 12,439 Fifth year 11,752 Thereafter 38,807 $ 100,741

Deposits

Deposits	12 Months Ended
	Dec. 31, 2019
Banking and Thrift [Abstract]
Deposits	Deposits Deposits at December 31, 2019 and 2018 consisted of the following: December 31, 2019 2018 Amount Percent Amount Percent Noninterest-bearing demand accounts $ 3,240,185 27.1 % $ 2,145,930 27.7 % Interest-bearing checking accounts 4,198,772 35.2 2,892,318 37.4 Savings accounts 552,585 4.6 293,108 3.8 Limited access money market accounts 2,119,878 17.8 1,286,135 16.6 Certificates of deposit and individual retirement accounts (IRA), less than $250,000 892,639 7.5 559,016 7.2 Certificates of deposit and individual retirement accounts (IRA), $250,000 and greater 937,277 7.8 561,287 7.3 $ 11,941,336 100.0 % $ 7,737,794 100.0 % At December 31, 2019 , the scheduled maturities of certificates of deposit, including IRAs, were as follows: First year $ 1,531,507 Second year 245,339 Third year 32,216 Fourth year 15,373 Fifth year 5,481 Thereafter — $ 1,829,916 Brokered deposits at December 31, 2019 and 2018 totaled $894,131 and $356,282

Federal Home Loan Bank Advances

Federal Home Loan Bank Advances	12 Months Ended
	Dec. 31, 2019
Banking and Thrift [Abstract]
Federal Home Loan Bank Advances	Federal Home Loan Bank Advances At December 31, 2019 , the Company has advances from the FHLB of Dallas under note payable arrangements with maturities which range from January 7, 2020 to July 6, 2021 . Interest payments on these notes are made monthly. The weighted average interest rate of all notes was 2.17% at both December 31, 2019 and 2018 . The balances outstanding on these advances were $325,000 and $290,000 at December 31, 2019 and 2018 , respectively. Contractual maturities of FHLB advances at December 31, 2019 were as follows: First year $ 300,000 Second year 25,000 Third year — Fourth year — Fifth year — Thereafter — $ 325,000 The advances are secured by $26,901 of FHLB stock owned by the Company and a blanket lien on certain loans with an aggregate available carrying value of $4,454,852 at December 31, 2019 . The Company had remaining credit available under the FHLB advance program of $3,664,617 at December 31, 2019 . At December 31, 2019 , the Company had $1,057,129 in undisbursed advance commitments (letters of credit) with the FHLB. As of December 31, 2019 , these commitments mature on various dates from January 2020 through November 2021. The FHLB letters of credit were obtained in lieu of pledging securities to secure public fund deposits that are over the FDIC insurance limit. At December 31, 2019 , there were no disbursements against the advance commitments.

Other Borrowings

Other Borrowings	12 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
Other Borrowings	Other Borrowings Other borrowings at December 31, 2019 and 2018 consisted of the following: December 31, 2019 2018 Unsecured fixed rate subordinated debentures in the amount of $110,000. The balance of borrowings at December 31, 2019 and 2018 is net of discount and origination costs of $1,628 and $1,986, respectively. Interest payments of 5.875% are made semiannually on February 1 and August 1. The maturity date is August 1, 2024. The notes may not be redeemed prior to maturity and meet the criteria to be recognized as Tier 2 capital for regulatory purposes. (1)(2) $ 108,372 $ 108,014 Unsecured fixed-to-floating subordinated debentures in the amount of $30,000. The balance of borrowings at December 31, 2019 and 2018 is net of origination costs of $621 and $698, respectively. Interest payments initially of 5.00% fixed rate are made semiannually on June 30 and December 31 through December 31, 2022. Thereafter, floating rate payments of 3 month LIBOR plus 2.83% are made quarterly in arrears on March 31, June 30, September 30, and December 31 through March 31, 2028. The maturity date is December 31, 2027 with an optional redemption at December 31, 2022. The notes meet the criteria to be recognized as Tier 2 capital for regulatory purposes. (2) 29,379 29,302 Unsecured fixed-to-floating subordinated debentures in the original amount of $40,000. Interest payments initially of 5.75% are made semiannually on January 20 and July 20 through July 20, 2021. Thereafter, floating rate payments of 3 month LIBOR plus 4.73% are made quarterly in arrears on October 20, January 20, April 20 and July 20 through October 20, 2026. The maturity date is July 20, 2026 with an optional redemption at July 20, 2021. The notes meet the criteria to be recognized as Tier 2 capital for regulatory purposes. (2)(3) 40,000 — Unsecured revolving line of credit with an unrelated commercial bank in the amount of $100,000. The line bears interest at LIBOR plus 1.75% and matures January 17, 2020. The Company is required to meet certain financial covenants on a quarterly basis, which includes certain restrictions on cash at IBG and meeting minimum capital ratios. (4) 24,500 — $ 202,251 $ 137,316 ____________ (1) At December 31, 2019 and 2018 , other borrowings included amounts owed to related parties of $50 . (2) The permissible portion of qualified subordinated notes decreases 20% per year during the final five years of the term of the notes. (3) Assumed on January 1, 2019 with the Guaranty acquisition (see Note 22 , Business Combinations). (4) Subsequent to December 31, 2019 , the Company renewed the line (see Note 24 , Subsequent Events). The Company has established federal funds lines of credit notes with ten unaffiliated banks totaling $375,000 and $365,000 of borrowing capacity at December 31, 2019 and 2018 , respectively. At December 31, 2019 , two of the lines totaling $30,000 have stated maturity dates in August and September 2020 . The remaining lines have no stated maturity dates and the lenders may terminate the lines at any time without notice. The lines are provided on an unsecured basis and must be repaid the following business day from when the funds are borrowed. There were no borrowings against the lines at December 31, 2019 and 2018 . In addition, the Company maintains a secured line of credit with the Federal Reserve Bank with an availability to borrow approximately $895,110 and $738,919 at December 31, 2019 and 2018 , respectively. Approximately $1,196,491 and $978,266 of commercial loans were pledged as collateral at December 31, 2019 and 2018 , respectively. There were no borrowings against this line as of December 31, 2019 and 2018 . The Company also participates in an exchange that provides direct overnight borrowings with other financial institutions. The funds are provided on an unsecured basis. Borrowing availability totaled $484,000 and $204,000 at December 31, 2019 and 2018 , respectively. There were no borrowings as of December 31, 2019 and 2018

Junior Subordinated Debentures

Junior Subordinated Debentures	12 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
Junior Subordinated Debentures	Junior Subordinated Debentures The Company has formed or acquired nine statutory business trusts (the Trusts) for the purpose of issuing trust preferred securities. Each of the Trusts have issued capital and common securities and invested the proceeds thereof in an equivalent amount of junior subordinated debentures (the Debentures) issued by the Company. The interest rate payable on, and the payment terms of the Debentures are the same as the distribution rate and payment terms of the respective issues of capital and common securities issued by the Trusts. The Debentures are subordinated and junior in right of payment to all present and future senior indebtedness. The Company has fully and unconditionally guaranteed the obligations of each of the Trusts with respect to the capital and common securities. Except under certain circumstances, the common securities issued to the Company by the trusts possess sole voting rights with respect to matters involving those entities. Under certain circumstances, the Company may, from time to time, defer the debentures' interest payments, which would result in a deferral of distribution payments on the related trust preferred securities and, with certain exceptions, prevent the Company from declaring or paying cash distributions on the Company's common stock and any other future debt ranking equally with or junior to the debentures. The Company may redeem the debentures, which are intended to qualify as Tier 1 capital, at the Company’s option, subject to approval of the Federal Reserve. As of December 31, 2019 and 2018 , the carrying amount of debentures outstanding totaled $53,824 and $27,852 , respectively. Information regarding the Debentures as of December 31, 2019 are summarized in the table below: Trust Preferred Securities Issued Debentures Carrying Value Repricing Frequency Interest Rate Interest Rate Index Maturity Date IB Trust I $ 5,155 $ 5,155 Quarterly 5.16% LIBOR + 3.25% March 2033 Guaranty Trust III (1) 10,310 10,310 Quarterly 5.09 LIBOR + 3.10 July 2033 IB Trust II 3,093 3,093 Quarterly 4.84 LIBOR + 2.85 March 2034 Cenbank Trust III (1) 15,464 15,464 Quarterly 4.65 LIBOR + 2.65 April 2034 IB Trust III 3,712 3,712 Quarterly 4.31 LIBOR + 2.40 December 2035 IB Centex Trust I 2,578 2,578 Quarterly 5.16 LIBOR + 3.25 February 2035 Community Group Statutory Trust I 3,609 3,609 Quarterly 3.49 LIBOR + 1.60 June 2037 Northstar Trust II (2) 5,155 3,815 Quarterly 3.56 LIBOR + 1.67 June 2037 Northstar Trust III (2) 8,248 6,088 Quarterly 3.56 LIBOR + 1.67 September 2037 $ 57,324 $ 53,824 ____________ (1) Assumed on January 1, 2019 with the Guaranty acquisition (see Note 22 , Business Combinations). (2) Assumed in 2017 with a recorded fair value discount of $3,500

Leases Leases (Notes)

Leases Leases (Notes)	12 Months Ended
	Dec. 31, 2019
Leases [Abstract]
Leases	Leases On January 1, 2019, the Company adopted ASU 2016-02, Leases (Topic 842), as further explained in Note 1 , Summary of Significant Accounting Policies, and Note 2 , Recent Accounting Pronouncements. The Company’s primary leasing activities relate to certain real estate operating leases entered into in support of the Company’s branch operations and back office operations. The Company leases 21 of its 93 branches. The Company’s branch locations operated under lease agreements have all been designated as operating leases. Rent expense related to these leases amounted to $7,025 , $3,758 , and $3,073 for the years ended December 31, 2019, 2018, and 2017, respectively. In addition, the Company leases certain equipment under operating leases. The Company does not have leases designated as finance leases. As of December 31, 2019 the Company’s lease ROU assets and related lease liabilities were $31,813 and $28,978 , respectively, and have remaining terms ranging from 1 to 31 years , including extension options that the Company is reasonably certain will be exercised. The table below summarizes net lease cost: Year Ended December 31, 2019 Operating lease cost $ 7,128 Variable lease cost 1,829 Sublease income (228 ) Net lease cost $ 8,729 The table below summarizes other information related to operating leases: Year Ended December 31, 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ 6,965 Weighted average remaining lease term - operating leases, in years 7.58 Weighted average discount rate - operating leases 3.35 % The following table outlines lease payment obligations as outlined in the Company’s lease agreements for each of the next five years and thereafter in addition to a reconcilement to the Company’s current lease liability as of December 31, 2019 . 2020 $ 5,964 2021 5,784 2022 4,990 2023 4,213 2024 3,437 Thereafter 8,454 Total lease payments 32,842 Less imputed interest (3,864 ) $ 28,978 As of December 31, 2019 , the Company had not entered into any material leases that have not yet commenced.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Tax Cuts and Jobs Act, which was enacted on December 22, 2017, made significant changes to the U.S. tax law, including the reduction of the corporate income tax rate from 35% to 21%. Income tax expense for the years ended December 31, 2019 , 2018 and 2017 was as follows: Years Ended December 31, 2019 2018 2017 Current income tax expense $ 39,426 $ 29,801 $ 28,121 Deferred income tax expense 14,102 2,000 11,526 Deferred income tax (benefit) expense related to remeasurement of deferred taxes — (63 ) 5,528 Income tax expense, as reported $ 53,528 $ 31,738 $ 45,175 A reconciliation between reported income tax expense and the amounts computed by applying the U.S. federal statutory income tax rate of 21% for the years ended December 31, 2019 and 2018 and 35% for the year ended December 31, 2017 to income before income taxes is presented below: Years Ended December 31, 2019 2018 2017 Income tax expense computed at the statutory rate $ 51,715 $ 33,599 $ 42,590 Tax-exempt interest income from municipal securities (1,781 ) (962 ) (1,357 ) Tax-exempt loan income (1,174 ) (490 ) (435 ) Bank owned life insurance income (1,288 ) (666 ) (962 ) Non-deductible acquisition expenses 281 142 491 State taxes, net of federal benefit 3,455 375 241 Non-deductible compensation 2,017 — — Net tax expense (benefit) from stock based compensation 21 (646 ) (1,323 ) Deferred tax adjustment related to reduction in U.S. Federal statutory income tax rate — (63 ) 5,528 Other 282 449 402 $ 53,528 $ 31,738 $ 45,175 As ASC 740, Income Taxes , requires the effects of changes in tax rates and laws on deferred tax balances to be recognized in the period in which the legislation is enacted, the Company remeasured its deferred tax assets and liabilities based upon the newly enacted U.S. statutory federal income tax rate of 21%, which is the tax rate at which these assets and liabilities are expected to reverse in the future and, as noted above, recognized a tax expense related to the remeasurement of $5,528 in 2017. In accordance with the SEC Staff Accounting Bulletin No. 118 (SAB 118), which provides for a one year measurement period from the Tax Act enactment date for companies to complete the accounting under ASC 740, Income Taxes , an additional net tax benefit resulting from the finalization of those calculations of $63 was recorded in 2018. Components of deferred tax assets and liabilities are presented in the table below. Deferred taxes as of December 31, 2019 and 2018 are based on the U.S. statutory federal income tax rate of 21%. December 31, 2019 2018 Deferred tax assets: Allowance for loan losses $ 11,466 $ 9,496 Lease liabilities under operating leases 6,457 — NOL and tax credit carryforwards from acquisitions 4,209 4,810 Net unrealized loss on available for sale securities — 2,365 Acquired loan fair market value adjustments 21,645 6,090 Stock-based compensation 1,218 987 Reserve for bonuses and other accrued expenses 2,773 1,646 Deferred loan fees 378 700 Acquisition costs 416 — Acquired Securities 2,529 273 Acquired intangibles 1,546 — Start up costs 230 274 Other real estate owned 362 273 Unearned income 774 160 Deferred compensation 1,101 1,266 Noncompete agreements 663 552 Nonaccrual loans 390 470 Other 407 303 56,564 29,665 Deferred tax liabilities: Premises and equipment (13,170 ) (5,242 ) Right-of-use assets under operating leases (6,233 ) — Net unrealized gain on available for sale securities (5,367 ) — Intangible assets (22,447 ) (9,547 ) Acquired junior subordinated debentures fair value adjustment (780 ) (777 ) Restricted stock (673 ) (250 ) Prepaids (281 ) (190 ) Acquired tax goodwill (413 ) (232 ) Other (257 ) (247 ) (49,621 ) (16,485 ) Net deferred tax asset $ 6,943 $ 13,180 At December 31, 2019 , the Company had federal net operating loss carryforwards of approximately $17,293 which expire in various years from 2022 to 2032, federal tax credit carryovers of approximately $132 which will never expire and state net operating loss carryforwards of approximately $12,155 which expire in various years from 2030 to 2036. Deferred tax assets are recognized for net operating losses because the benefit is more likely than not to be realized. No valuation allowance for deferred tax assets was recorded at December 31, 2019 or 2018 as management believes it is more likely than not that all of the deferred tax assets will be realized. The Company does not have any material uncertain tax positions and does not have any interest and penalties recorded in the income statement for the years ended December 31, 2019 , 2018 and 2017 . The Company files a consolidated income tax return in the US federal tax jurisdiction. The Company is no longer subject to examination by the US federal tax jurisdiction for years prior to 2016.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Financial Instruments with Off-Balance Sheet Risk The Company is a party to financial instruments with off-balance sheet risk in the normal course of business to meet the financing needs of its customers. The commitments involve, to varying degrees, elements of credit and interest rate risk in excess of the amount recognized in the balance sheet. The Company’s exposure to credit loss in the event of nonperformance by the other party to the financial instrument for commitments to extend credit is represented by the contractual amount of this instrument. The Company uses the same credit policies in making commitments and conditional obligations as it does for on-balance sheet instruments. At December 31, 2019 and 2018 , the approximate amounts of these financial instruments were as follows: December 31, 2019 2018 Commitments to extend credit $ 2,337,385 $ 1,761,724 Standby letters of credit 23,406 14,997 $ 2,360,791 $ 1,776,721 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 many of the commitments are expected to expire without being drawn upon, the total commitment amounts do not necessarily represent future cash requirements. The Company evaluates each customer’s credit worthiness on a case-by-case basis. The amount of collateral obtained if deemed necessary by the Company upon extension of credit is based on management’s credit evaluation of the counterparty. Collateral held varies but may include accounts receivable, inventory, farm crops, property, plant and equipment and income-producing commercial properties. Letters of credit are written conditional commitments used by the Company to guarantee the performance of a customer to a third party. The Company’s policies generally require that letter of credit arrangements contain security and debt covenants similar to those contained in loan arrangements. In the event the customer does not perform in accordance with the terms of the agreement with the third party, the Company would be required to fund the commitment. The maximum potential amount of future payments the Company could be required to make is represented by the contractual amount shown in the table above. If the commitment is funded, the Company would be entitled to seek recovery from the customer. As of December 31, 2019 and 2018 , no amounts have been recorded as liabilities for the Company’s potential obligations under these guarantees. Change in Control Agreements The Company has change-in-control agreements with each of its named executive officers. Under these agreements, each executive could receive, upon the effectiveness of a change-in-control and subsequent termination of employment, as defined in the agreement, a lump sum cash payment in an amount equal to two to three times (depending upon the executive) the sum, of the executive’s current annual base salary, plus the executive’s prorated target annual bonus for the year of termination. In addition all of the executive’s unvested grants of restricted stock will immediately vest and the executive will continue to be a participant in the Independent Bank Survivor Benefit Plan. Litigation The Company is involved in certain legal actions arising from normal business activities. Management believes that the outcome of such proceedings will not materially affect the financial position, results of operations or cash flows of the Company. A legal proceeding that the Company believes could become material is described below. Independent Bank is a party to a legal proceeding inherited by Independent Bank in connection with its acquisition of BOH Holdings, Inc. and its subsidiary, Bank of Houston (BOH). The plaintiffs in the case are alleging that Independent Bank aided and abetted or participated in a fraudulent scheme. Independent Bank is pursuing insurance coverage for these claims, including reimbursement for defense costs. The Company believes the claims made in this lawsuit are without merit and is vigorously defending the lawsuit. The Company is unable to predict when the matter will be resolved, the ultimate outcome or potential costs or damages to be incurred.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2019
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions In the ordinary course of business, the Company has and expects to continue to have transactions, including loans to its officers, directors and their affiliates. In the opinion of management, such transactions are on the same terms as those prevailing at the time for comparable transactions with unaffiliated persons. Loan activity for officers, directors and their affiliates for the year ended December 31, 2019 is as follows: Balance at beginning of year $ 58,967 New loans 14,185 Repayments (31,366 ) Changes in affiliated persons (2,990 ) Balance at end of year $ 38,796 See Note 11 , Other Borrowings, for related party borrowings.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2019
Retirement Benefits [Abstract]
Employee Benefit Plans	Employee Benefit Plans The Company has a 401(k) profit sharing plan (Plan) which covers employees over the age of eighteen who have completed ninety days of credited service, as defined by the Plan. The Plan provides for “before tax” employee contributions through salary reduction contributions under Section 401(k) of the Internal Revenue Code. A participant may choose a salary reduction not to exceed the dollar limit set by law each year ( $19 in 2019 ). Contributions by the Company and by participants are immediately fully vested. In July 2018, the Plan was modified to provide for the Company to make 401(k) matching contributions of 100% , but limited to 6% of the participant's eligible salary. Previously, the Plan provided for the Company to make 401(k) matching contributions ranging from 50% to 100% depending upon the employee's years of service, but limited to 6% of the participant's eligible salary. The Plan also provides for the Company to make additional discretionary contributions to the Plan. The Company made contributions of approximately $6,343 , $3,280 and $2,070 for the years ended December 31, 2019 , 2018 and 2017 , respectively.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The fair value of an asset or liability is the price that would be received to sell that asset or paid to transfer that liability in an orderly transaction occurring in the principal market (or most advantageous market in the absence of a principal market) for such asset or liability. In estimating fair value, the Company utilizes valuation techniques that are consistent with the market approach, the income approach and/or the cost approach. Such valuation techniques are consistently applied. Inputs to valuation techniques include the assumptions that market participants would use in pricing an asset or liability. ASC Topic 820, Fair Value Measurements and Disclosures , establishes a fair value hierarchy for valuation inputs that gives the highest priority to quoted prices in active markets for identical assets or liabilities and the lowest priority to unobservable inputs. The fair value hierarchy is as follows: Level 1 Inputs – Unadjusted quoted prices in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. Level 2 Inputs – Inputs other than quoted prices included in Level 1 that are observable for the asset or liability, either directly or indirectly. These might include quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability (such as interest rates, volatilities, prepayment speeds, credit risks, etc.) or inputs that are derived principally from or corroborated by market data by correlation or other means. Level 3 Inputs – Unobservable inputs for determining the fair values of assets or liabilities that reflect an entity’s own assumptions about the assumptions that market participants would use in pricing the assets or liabilities. The Company elected the fair value option for certain residential mortgage loans held for sale originated after July 1, 2018 in accordance with ASC 825, Financial Instruments. This election allows for a more effective offset of the changes in fair values of the loans and the derivative instruments used to economically hedge them without the burden of complying with the requirements for hedge accounting under ASC 815, Derivatives and Hedging . The Company has not elected the fair value option for other residential mortgage loans held for sale primarily because they are not economically hedged using derivative instruments. See below and Note 19 , Derivative Financial Instruments, for additional information. Assets and Liabilities Measured on a Recurring Basis The following table represents assets and liabilities reported on the consolidated balance sheets at their fair value on a recurring basis as of December 31, 2019 and 2018 by level within the ASC Topic 820 fair value measurement hierarchy: Fair Value Measurements at Reporting Date Using Assets/ Liabilities Measured at Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) December 31, 2019 Assets: Investment securities available for sale: U.S. treasuries $ 48,796 $ — $ 48,796 $ — Government agency securities 179,296 — 179,296 — Obligations of state and municipal subdivisions 343,859 — 343,859 — Corporate bonds 7,218 — 7,218 — Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 505,567 — 505,567 — Other securities 1,200 — 1,200 — Loans held for sale, fair value option elected (1) 29,204 — 29,204 — Derivative financial instruments: Interest rate lock commitments 847 — 847 — Forward mortgage-backed securities trades 6 — 6 — Loan customer counterparty 6,104 — 6,104 — Liabilities: Derivative financial instruments: Forward mortgage-backed securities trades 69 — 69 — Financial institution counterparty 6,566 — 6,566 — December 31, 2018 Assets: Investment securities available for sale: U.S. treasuries $ 29,643 $ — $ 29,643 $ — Government agency securities 150,230 — 150,230 — Obligations of state and municipal subdivisions 185,007 — 185,007 — Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 320,470 — 320,470 — Loans held for sale, fair value option elected (1) 27,871 — 27,871 — Derivative financial instruments: Interest rate lock commitments 822 — 822 — Loan customer counterparty 360 — 360 — Financial institution counterparty 109 — 109 — Liabilities: Derivative financial instruments: Forward mortgage-backed securities trades 226 — 226 — Loan customer counterparty 108 — 108 — Financial institution counterparty 406 — 406 — ____________ (1) At December 31, 2019 and 2018 , loans held for sale for which the fair value option was elected had an aggregate outstanding principal balance of $28,166 and $26,594 , respectively. There were no mortgage loans held for sale under the fair value option that were 90 days or greater past due or on nonaccrual at December 31, 2019 . A description of the valuation methodologies used for instruments measured at fair value, as well as the general classification of such instruments pursuant to the valuation hierarchy, is set forth below. Securities classified as available for sale are reported at fair value utilizing Level 1 and Level 2 inputs. Securities are classified within Level 1 when quoted market prices are available in an active market. Inputs include securities that have quoted prices in active markets for identical assets. For securities utilizing Level 2 inputs, 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 and other yield curves, live trading levels, trade execution data, market consensus prepayment speeds, credit information and the security’s terms and conditions, among other things. Certain mortgage loans held for sale are measured at fair value on a recurring basis due to the Company's election to adopt fair value accounting treatment for those loans originated for which the Company has entered into certain derivative financial instruments as part of its mortgage banking and related risk management activities. These instruments include interest rate lock commitments and mandatory forward commitments to sell these loans to investors known as forward mortgage-backed securities trades. This election allows for a more effective offset of the changes in fair values of the assets and the mortgage related derivative instruments used to economically hedge them without the burden of complying with the requirements for hedge accounting under ASC 815, Derivatives and Hedging. Mortgage loans held for sale, for which the fair value option was elected, which are sold on a servicing released basis, are valued using a market approach by utilizing either: (i) the fair value of securities backed by similar mortgage loans, adjusted for certain factors to approximate the fair value of a whole mortgage loan, including the value attributable to mortgage servicing and credit risk, (ii) current commitments to purchase loans or (iii) recent observable market trades for similar loans, adjusted to credit risk and other individual loan characteristics. As these prices are derived from market observable inputs, the Company classifies these valuations as Level 2 in the fair value disclosures. For mortgage loans held for sale for which the fair value option was elected, the earned current contractual interest payment is recognized in interest income, loan origination costs and fees on fair value option loans are recognized in earnings as incurred and not deferred. The Company has no continuing involvement in any residential mortgage loans sold. The estimated fair values of interest rate lock commitments utilize current secondary market prices for underlying loans and estimated servicing value with similar coupons, maturity and credit quality, subject to the anticipated loan funding probability (pull-through rate). The fair value of interest rate lock commitments is subject to change primarily due to changes in interest rates and the estimated pull-through rate. These commitments are classified as Level 2 in the fair value disclosures, as the valuations are based on observable market inputs. Forward mortgage-backed securities trades are exchange-traded or traded within highly active dealer markets. In order to determine the fair value of these instruments, the Company utilized the exchange price or dealer market price for the particular derivative contract; therefore these contracts are classified as Level 2. The estimated fair values are subject to change primarily due to changes in interest rates. The Company also enters into certain interest rate derivative positions that are not designated as hedging instruments. The estimated fair value of these commercial loan interest rate swaps are obtained from a pricing service that provides the swaps' unwind value (Level 2 inputs). See Note 19 , Derivative Financial Instruments, for more information. Assets and Liabilities Measured on a Nonrecurring Basis In accordance with ASC Topic 820, certain assets and liabilities are measured at fair value on a nonrecurring basis; that is, the assets and liabilities 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). The following table presents the assets carried on the consolidated balance sheet by caption and by level in the fair value hierarchy at December 31, 2019 and 2018 , for which a nonrecurring change in fair value has been recorded: Fair Value Measurements at Reporting Date Using Assets Measured at Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Period Ended Total Losses December 31, 2019 Assets: Impaired loans $ 2,276 $ — $ — $ 2,276 $ 1,806 Other real estate owned 4,618 — — 4,618 749 December 31, 2018 Assets: Impaired loans $ 3,824 $ — $ — $ 3,824 $ 2,227 Impaired loans (loans which are not expected to repay all principal and interest amounts due in accordance with the original contractual terms) are measured at an observable market price (if available) or at the fair value of the loan’s collateral (if collateral dependent). Fair value of the loan’s collateral is determined by appraisals or independent valuation, which is then adjusted for the estimated costs related to liquidation of the collateral. Management’s ongoing review of appraisal information may result in additional discounts or adjustments to valuation based upon more recent market sales activity or more current appraisal information derived from properties of similar type and/or locale. Therefore, the Company has categorized its impaired loans as Level 3. Other real estate is measured at fair value on a nonrecurring basis (upon initial recognition or subsequent impairment). Other real estate is classified within Level 3 of the valuation hierarchy. When transferred from the loan portfolio, other real estate is adjusted to fair value less estimated selling costs and is subsequently carried at the lower of carrying value or fair value less estimated selling costs. The fair value is determined using an external appraisal process, discounted based on internal criteria. Therefore, the Company has categorized its other real estate as Level 3. In addition, mortgage loans held for sale not recorded under the fair value option are required to be measured at the lower of cost or fair value. The fair value of these loans is based upon binding quotes or bids from third party investors. As of December 31, 2019 and 2018 , all mortgage loans held for sale not recorded under the fair value option were recorded at cost. Fair Value of Financial Instruments not Recorded at Fair Value The carrying amount, estimated fair value and the level of the fair value hierarchy of the Company’s financial instruments that are reported at amortized cost on the Company's consolidated balance sheets were as follows at December 31, 2019 and 2018 : Fair Value Measurements at Reporting Date Using Carrying Amount Estimated Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) December 31, 2019 Financial assets: Cash and cash equivalents $ 565,170 $ 565,170 $ 565,170 $ — $ — Certificates of deposit held in other banks 5,719 5,951 — 5,951 — Loans held for sale, at cost 6,441 6,554 — 6,554 — Loans, net 11,562,814 11,689,672 — — 11,689,672 FHLB of Dallas stock and other restricted stock 30,052 30,052 — 30,052 — Accrued interest receivable 35,860 35,860 — 35,860 — Financial liabilities: Deposits 11,941,336 11,958,939 — 11,958,939 — Accrued interest payable 9,583 9,583 — 9,583 — FHLB advances 325,000 325,210 — 325,210 — Other borrowings 202,251 209,050 — 209,050 — Junior subordinated debentures 53,824 48,879 — 48,879 — Off-balance sheet assets (liabilities): Commitments to extend credit — — — — — Standby letters of credit — — — — — December 31, 2018 Financial assets: Cash and cash equivalents $ 130,779 $ 130,779 $ 130,779 $ — $ — Certificates of deposit held in other banks 1,225 1,224 — 1,224 — Loans held for sale, at cost 4,856 4,974 — 4,974 — Loans, net 7,839,695 7,807,823 — — 7,807,823 FHLB of Dallas stock and other restricted stock 26,870 26,870 — 26,870 — Accrued interest receivable 24,253 24,253 — 24,253 — Financial liabilities: Deposits 7,737,794 7,750,059 — 7,750,059 — Accrued interest payable 6,183 6,183 — 6,183 — FHLB advances 290,000 287,450 — 287,450 — Other borrowings 137,316 138,450 — 138,450 — Junior subordinated debentures 27,852 31,370 — 31,370 — Off-balance sheet assets (liabilities): Commitments to extend credit — — — — — Standby letters of credit — — — — — The methods and assumptions used by the Company in estimating fair values of financial instruments as disclosed herein in accordance with ASC Topic 825, Financial Instruments, other than for those measured at fair value on a recurring and nonrecurring basis discussed above, are as follows: Cash and cash equivalents: The carrying amounts of cash and cash equivalents approximate their fair value. Certificates of deposit held in other banks: The fair value of certificates of deposit held in other banks is based upon current market rates. Loans held for sale, at cost: The fair value of loans held for sale is determined based upon commitments on hand from investors. Loans: A discounted cash flow model is used to estimate the fair value of the loans. The discounted cash flow approach models the credit losses directly in the projected cash flows, applying various assumptions regarding credit, interest and prepayment risks for the loans based on loan types, payment types and fixed or variable classifications. Federal Home Loan Bank of Dallas and other restricted stock: The carrying value of restricted securities such as stock in the Federal Home Loan Bank of Dallas and Independent Bankers Financial Corporation approximates fair value. Deposits: The fair values disclosed for demand deposits are, by definition, equal to the amount payable on demand at the reporting date (that is their carrying amounts). The carrying amounts of variable-rate certificates of deposit (CDs) approximate their fair values at the reporting date. Fair values for fixed-rate CDs are estimated using a discounted cash flow calculation that applies interest rates currently being offered on certificates to a schedule of aggregated expected monthly maturities on time deposits. Federal Home Loan Bank advances, line of credit and federal funds purchased: The fair value of advances maturing within 90 days approximates carrying value. Fair value of other advances is based on the Company’s current borrowing rate for similar arrangements. Other borrowings: The carrying value of repurchase agreements approximates fair value due to the short term nature. The fair value of private subordinated debentures are based upon prevailing rates on similar debt in the market place. The subordinated debentures that are publicly traded are valued based on indicative bid prices based upon market pricing observations in the current market. Junior subordinated debentures: The fair value of junior subordinated debentures is estimated using discounted cash flow analyses based on the Company’s current incremental borrowing rates for similar types of borrowing arrangements. Accrued interest: The carrying amounts of accrued interest approximate their fair values. Off-balance sheet instruments: Fair values for off-balance sheet, credit-related financial instruments are based on fees currently charged to enter into similar agreements, taking into account the remaining terms of the agreements and the counterparties' credit standing. The fair value of commitments is not material.

Derivative Financial Instrument

Derivative Financial Instruments	12 Months Ended
	Dec. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments	Derivative Financial Instruments The Company enters into certain derivative financial instruments as part of its hedging strategy. These financial instruments are not designated as hedging instruments and are used for asset and liability management related to the Company's mortgage banking activities and commercial customers' financing needs. All derivatives are carried at fair value in either other assets or other liabilities. Through the normal course of business, the Company enters into interest rate lock commitments with consumers to originate mortgage loans at a specified interest rate. These commitments, which contain fixed expiration dates, offer the borrower an interest rate guarantee provided the loan meets underwriting guidelines and closes within the timeframe established by the Company. During July 2018, the Company began managing the changes in fair value associated with changes in interest rates related to interest rate lock commitments by using forward sold commitments known as forward mortgage-backed securities trades. These instruments are typically entered into at the time the interest rate lock commitment is made. The Company also offers certain derivatives products, primarily interest rate swaps, directly to qualified commercial banking customers to facilitate their risk management strategies. The interest rate swap derivative positions relate to transactions in which the Company enters into an interest rate swap with a customer, while at the same time entering into an offsetting interest rate swap with another financial institution. An interest rate swap transaction allows customers to effectively convert a variable rate loan to a fixed rate. In connection with each swap, the Company agrees to pay interest to the customer on a notional amount at a variable interest rate and receive interest from the customer on a similar notional amount at a fixed interest rate. At the same time, the Company agrees to pay another financial institution the same fixed interest rate on the same notional amount and receive the same variable interest rate on the same notional amount. The following table provides the outstanding notional balances and fair values of outstanding derivative positions at December 31, 2019 and 2018 : Outstanding Notional Balance Asset Derivative Fair Value Liability Derivative Fair Value December 31, 2019 Interest rate lock commitments $ 28,434 $ 847 $ — Forward mortgage-backed securities trades 42,500 6 69 Commercial loan interest rate swaps: Loan customer counterparty 280,751 6,104 — Financial institution counterparty 280,751 — 6,566 December 31, 2018 Interest rate lock commitments $ 20,306 $ 822 $ — Forward mortgage-backed securities trades 27,500 — 226 Commercial loan interest rate swaps: Loan customer counterparty 25,055 360 108 Financial institution counterparty 25,055 109 406 The commercial loan customer counterparty weighted average received and paid interest rates for interest rate swaps outstanding were as follows: Weighted Average Interest Rate December 31, 2019 December 31, 2018 Received Paid Received Paid Loan customer counterparty 4.23 % 3.77 % 4.67 % 4.46 % The credit exposure related to interest rate swaps is limited to the net favorable value of all swaps by each counterparty, which was approximately $6,104 at December 31, 2019 . In some cases collateral may be required from the counterparties involved if the net value of the derivative instruments exceeds a nominal amount. Collateral levels are monitored and adjusted on a regular basis for changes in interest rate swap values. At December 31, 2019 , cash of $4,350 and securities of $3,645 were pledged as collateral for these derivatives. During 2019, the Company entered into a credit risk participation agreement with a financial institution counterparty for interest rate swaps related to loans in which the Company is the lead bank. This agreement provides credit protection to the Company should the borrower fail to perform on its interest rate derivative contract. The agreement has a notional amount of $9,850 at December 31, 2019 . The changes in the fair value of interest rate lock commitments and the forward sales of mortgage-back securities are recorded in mortgage banking revenue. These gains and losses were not attributable to instrument-specific credit risk. For interest rate swaps, because the Company acts as an intermediary for our customer, changes in the fair value of the underlying derivative contracts substantially offset each other and do not have a material impact on the results of operations. Income (loss) for the years ended December 31, 2019 and 2018 was as follows: Years Ended December 31, 2019 2018 Derivatives not designated as hedging instruments Interest rate lock commitments $ 25 $ 822 Forward mortgage-backed securities trades 163 (226 )

Stock Awards

Stock Awards	12 Months Ended
	Dec. 31, 2019
Share-based Payment Arrangement [Abstract]
Stock Awards	Stock Awards The Company grants common stock awards to certain employees of the Company. In connection with the Company's initial public offering in April 2013, the Board of Directors adopted the 2013 Equity Incentive Plan. Under this plan, the Compensation Committee may grant awards to certain employees of the Company in the form of restricted stock, restricted stock rights, restricted stock units, qualified and nonqualified stock options, performance-based share awards and other equity-based awards. All stock awards issued under expired plans prior to 2013 are fully vested. In May 2018, the shareholders of the Company voted to amend the plan to increase the reserved shares of common stock to be awarded by the Company's compensation committee by 1,500,000 for a total of 2,300,000 reserved shares. As of December 31, 2019 , there were 1,452,124 shares remaining available for grant for future awards. The shares currently issued under the 2013 Plan are restricted stock awards and will vest evenly over the required employment period, generally ranging from three to five years . As defined in the plan, outstanding awards may immediately vest upon a change-in-control in the Company. Shares granted under the 2013 Equity Incentive Plan were issued at the date of grant and receive dividends. In connection with the acquisition of Guaranty, as further described in Note 22 , Business Combinations, unvested awards of restricted Guaranty common stock granted under Guaranty’s 2015 Long-Term Incentive Plan (Guaranty 2015 RSA), as amended, that were outstanding as of January 1, 2019, the acquisition date, were converted into awards of restricted shares of Independent common stock (Replacement RSA) with the same terms and conditions as were applicable under such Guaranty 2015 RSA, except with respect to any performance-vesting Guaranty 2015 RSA, which became a service-vesting RSA only. The Replacement RSA will vest over the remaining service period, generally in two years , and do not receive dividends. The following table summarizes the activity in nonvested shares for the years ended December 31, 2019 and 2018 : Number of Shares Weighted Average Grant Date Fair Value Nonvested shares, December 31, 2018 252,903 $ 62.81 Acquired awards replaced during the period 70,248 45.77 Granted during the period 138,608 51.14 Vested during the period (161,032 ) 54.76 Forfeited during the period (15,866 ) 46.95 Nonvested shares, December 31, 2019 284,861 $ 58.63 Nonvested shares, December 31, 2017 242,056 $ 49.17 Granted during the period 130,212 71.85 Vested during the period (115,520 ) 44.36 Forfeited during the period (3,845 ) 64.47 Nonvested shares, December 31, 2018 252,903 $ 62.81 Compensation expense related to these awards is recorded based on the fair value of the award at the date of grant and totaled $7,808 , $6,062 and $4,688 for the years ended December 31, 2019 , 2018 and 2017 , respectively. Compensation expense is recorded in salaries and employee benefits in the accompanying consolidated statements of income. At December 31, 2019 , future compensation expense is estimated to be $11,263 and will be recognized over a remaining weighted average period of 2.40 years. The fair value of common stock awards that vested during the years ended December 31, 2019 , 2018 and 2017 was $8,725 , $8,206 and $8,597 , respectively. The Company has recorded $21 , $(646) and $(1,323) in excess tax expense (benefits) on vested restricted stock to income tax expense for the years ended December 31, 2019 , 2018 and 2017 , respectively. There were no modifications of stock agreements during 2019 , 2018 and 2017 that resulted in significant additional incremental compensation costs. At December 31, 2019 , the future vesting schedule of the nonvested shares is as follows: First year 105,390 Second year 96,125 Third year 62,006 Fourth year 19,260 Fifth year 2,080 Total nonvested shares 284,861

Regulatory Matters

Regulatory Matters	12 Months Ended
	Dec. 31, 2019
Regulated Operations [Abstract]
Regulatory Matters	Regulatory Matters Under banking law, there are legal restrictions limiting the amount of dividends the Bank can declare. Approval of the regulatory authorities is required if the effect of dividends declared would cause the regulatory capital of the Bank to fall below specified minimum levels. For state banks, subject to regulatory capital requirements, payment of dividends is generally allowed to the extent of net profits. The Company (on a consolidated basis) and the Bank are subject to various regulatory capital requirements administered by federal and state banking agencies. Failure to meet minimum capital requirements can initiate certain mandatory and possibly additional discretionary actions by regulators that, if undertaken, could have a direct material effect on the Company’s consolidated financial statements. Under capital adequacy guidelines and the regulatory framework for prompt corrective action, the Company and the Bank must meet specific capital guidelines that involve quantitative measures of assets, liabilities and certain off-balance sheet items as calculated under regulatory accounting practices. The capital amounts and classification are also subject to qualitative judgments by the regulators about components, risk weightings and other factors. Tier 2 capital for the Company includes permissible portions of the Company's subordinated notes. The permissible portion of qualified subordinated notes decreases 20% per year during the final five years of the term of the notes. The Company is subject to the Basel III regulatory capital framework (the "Basel III Capital Rules"). The implementation of the capital conservation buffer was effective for the Company on January 1, 2016 at the 0.625% level and was phased in over a four-year period increasing by 0.625% each year, until it reached 2.5% on January 1, 2019. The capital conservation buffer is designed to absorb losses during periods of economic stress and requires increased capital levels for the purpose of capital distributions and other payments. Failure to meet the full amount of the buffer will result in restrictions on the Company's ability to make capital distributions, including dividend payments and stock repurchases and to pay discretionary bonuses to executive officers. Fully phased in on January 1, 2019, the Basel III Capital Rules require the Company and Bank to maintain (i) a minimum ratio of Common Equity Tier 1 ("CET1") capital to risk-weighted assets of at least 4.5%, plus the 2.5% capital conservation buffer (7.0%), (ii) a minimum ratio of Tier 1 capital to risk-weighted assets of at least 6.0%, plus the 2.5% capital conservation buffer (8.5%), (iii) a minimum ratio of Total capital (that is, Tier 1 plus Tier 2) to risk-weighted assets of at least 8.0%, plus the 2.5% capital conservation buffer (10.5%) and (iv) a minimum leverage ratio of 4.0%, calculated as the ratio of Tier 1 capital to average quarterly assets. Quantitative measures established by regulation to ensure capital adequacy require the Company and the Bank to maintain minimum amounts and ratios (set forth in the table below) of total, CET1 and Tier 1 capital (as defined in the regulations) to risk weighted assets (as defined), and of Tier 1 capital (as defined) to average assets (as defined). Management believes, as of December 31, 2019 and 2018, the Company and the Bank meet all capital adequacy requirements to which they are subject, including the capital buffer requirement. As of December 31, 2019 and 2018, the Bank’s capital ratios exceeded those levels necessary to be categorized as “well capitalized” under the regulatory framework for prompt corrective action. To be categorized as “well capitalized,” the Bank must maintain minimum total risk based, CET1, Tier 1 risk based and Tier 1 leverage ratios as set forth in the table. There are no conditions or events that management believes have changed the Bank’s category. The following table presents the actual capital amounts and required ratios of the Company and Bank as of December 31, 2019 and 2018. The minimum required capital amounts presented as of December 31, 2019 include the minimum required capital levels as of January 1, 2019 when the Basel III Capital Rules have been fully phased-in. Actual Minimum for Capital Adequacy Purposes To Be Well Capitalized Under Prompt Corrective Action Provisions Amount Ratio Amount Ratio Amount Ratio December 31, 2019 Total capital to risk weighted assets: Consolidated $ 1,513,209 11.83 % $ 1,343,114 10.50 % N/A N/A Bank 1,548,103 12.11 1,342,595 10.50 $ 1,278,662 10.00 % Tier 1 capital to risk weighted assets: Consolidated 1,303,748 10.19 1,087,282 8.50 N/A N/A Bank 1,496,642 11.70 1,086,863 8.50 1,022,930 8.00 Common equity tier 1 to risk weighted assets: Consolidated 1,248,148 9.76 895,409 7.00 N/A N/A Bank 1,496,642 11.70 895,064 7.00 831,130 6.50 Tier 1 capital to average assets: Consolidated 1,303,748 9.32 559,758 4.00 N/A N/A Bank 1,496,642 10.70 559,584 4.00 699,480 5.00 December 31, 2018 Total capital to risk weighted assets: Consolidated $ 1,072,156 12.58 % $ 681,686 8.00 % N/A N/A Bank 1,054,783 12.39 681,004 8.00 $ 851,255 10.00 % Tier 1 capital to risk weighted assets: Consolidated 887,354 10.41 511,264 6.00 N/A N/A Bank 1,009,981 11.86 510,753 6.00 681,004 8.00 Common equity tier 1 to risk weighted assets: Consolidated 856,754 10.05 383,448 4.50 N/A N/A Bank 1,009,981 11.86 383,065 4.50 553,316 6.50 Tier 1 capital to average assets: Consolidated 887,354 9.57 370,727 4.00 N/A N/A Bank 1,009,981 10.91 370,412 4.00 463,015 5.00

Business Combinations

Business Combinations	12 Months Ended
	Dec. 31, 2019
Business Combinations [Abstract]
Business Combinations	Business Combinations Proposed Merger with Texas Capital Bancshares, Inc. On December 9, 2019, The Company and TCBI jointly announced the signing of a definitive merger agreement under which, the companies will combine in an all-stock merger of equals transaction. TCBI is headquartered in Dallas, Texas and has full-service locations in Austin, Dallas, Fort Worth, Houston, and San Antonio. Under the terms of the agreement, TCBI will merge into the Company and Texas Capital Bank will merge into Independent Bank. The combined holding company will operate under the Company name, Independent Bank Group, Inc. The name of the combined bank will be Texas Capital Bank and will operate under the name Independent Financial in Colorado and Texas Capital Bank in Texas. Under the terms of the merger agreement, TCBI shareholders will receive 1.0311 shares of the Company's common stock for each share of TCBI common stock based on a fixed exchange ratio. Following the completion of the merger, the Company estimates that former holders of TCBI common stock will own approximately fifty-five percent ( 55% ) and holders of the Company common stock will own approximately forty-five percent ( 45% ) of the common stock of the combined company. In addition, each share of TCBI series A preferred stock issued and outstanding immediately prior to the effective time of the merger will be converted into the right to receive one ( 1 ) share of the Company's series B preferred stock having substantially the same terms as the TCBI series A preferred stock. The merger agreement was unanimously approved by the boards of directors of both companies and is anticipated to close in mid-2020, although delays may occur. The transaction is subject to receipt of regulatory approvals and satisfaction of other customary closing conditions, including approval of both Independent Bank Group and TCBI shareholders. The Company has incurred expenses related to the proposed merger of approximately $5,835 for the year ended December 31, 2019 , of which $813 is included in salaries and benefits and $5,022 is included in acquisition expense in the consolidated statements of income. Guaranty Bancorp On January 1, 2019, the Company acquired 100% of the outstanding stock of Guaranty Bancorp (Guaranty) and its subsidiary, Guaranty Bank and Trust Company (Guaranty Bank), Denver, Colorado. As a result of the acquisition, the Company added 32 full service branch locations along the Colorado Front Range, including locations throughout the Denver metropolitan area and along I-25 to Fort Collins expanding the Company's footprint in Colorado. The Company issued 13,179,748 shares of Company stock for the outstanding shares of Guaranty common stock, including restricted stock replacement awards. The Company has recognized total goodwill of $272,224 which is calculated as the excess of both the consideration exchanged and liabilities assumed compared to the estimated fair market value of identifiable assets acquired. The goodwill in this acquisition resulted from a combination of expected synergies and expansion into desirable Colorado markets. None of the goodwill recognized is expected to be deductible for income tax purposes. The Company has incurred expenses related to the acquisition of approximately $33,622 for the year ended December 31, 2019 , of which $5,328 is included in salaries and benefits and $28,294 is included in acquisition expense in the consolidated statements of income. The Company incurred expense of $1,560 during the year ended December 31, 2018. In addition, for the year ended December 31, 2019 , the Company paid offering costs totaling $804 which were recorded as a reduction to stock issuance proceeds through additional paid in capital. The following table summarizes the final fair values of the assets acquired and liabilities assumed in this transaction as of the closing date and subsequent measurement period adjustments are as follows: Initially Recorded at Acquisition Date Measurement Period Adjustments Adjusted Values as of December 31, 2019 Assets of acquired bank: Cash and cash equivalents $ 39,913 $ — $ 39,913 Certificates of deposit held in other banks 262 — 262 Securities available for sale 561,052 — 561,052 Restricted stock 27,794 — 27,794 Loans 2,788,159 1,709 2,789,868 Premises and equipment 65,786 — 65,786 Other real estate owned 1,710 119 1,829 Goodwill 270,583 1,641 272,224 Other intangible assets 71,518 — 71,518 Bank owned life insurance 80,837 — 80,837 Other assets 31,517 470 31,987 Total assets acquired $ 3,939,131 $ 3,939 $ 3,943,070 Liabilities of acquired bank: Deposits $ 3,108,810 $ — $ 3,108,810 Repurchase agreements 8,475 — 8,475 FHLB advances 142,653 — 142,653 Other borrowings 40,000 — 40,000 Junior subordinated debentures 25,774 — 25,774 Other liabilities 11,538 3,939 15,477 Total liabilities assumed $ 3,337,250 $ 3,939 $ 3,341,189 Common stock of 13,109,500 issued at $45.77 per share $ 600,022 $ — $ 600,022 Consideration attributable to 70,248 shares of restricted stock replacement awards $ 1,850 $ — $ 1,850 Cash paid $ 9 $ — $ 9 The nature of the measurement period adjustments noted in the table above was a result of information obtained subsequent to our initial reporting of provisional fair values but prior to finalizing our fair values in accordance with ASC 805, Business Combinations . Such information was determined to be a condition in existence as of acquisition date. The income effects resulting from the recorded measurement period adjustments during the period ending December 31, 2019 are immaterial for separate disclosure. Non-credit impaired loans had a fair value of $2,478,144 at acquisition date and contractual balance of $2,573,355 . As of acquisition date, the Company expects that an insignificant amount of the contractual balance of these loans will be uncollectible. The difference of $95,211 will be recognized into interest income as an adjustment to yield over the life of the loans. The following table presents pro-forma information as if the Guaranty acquisition was completed as of January 1, 2018. The pro-forma results combine the historical results of Guaranty into the Company's consolidated statement of income including the impact of certain purchase accounting adjustments including loan and investment discount accretion and intangible assets amortization. The pro-forma results have been prepared for comparative purposes only and are not necessarily indicative of the results that would have been obtained had the acquisition actually occurred on January 1, 2018: Year Ended December 31, 2018 Interest income $ 585,412 Noninterest income 71,983 Total revenue $ 657,395 Net income (1) $ 203,542 Basic earnings per share $ 4.76 Diluted earnings per share $ 4.74 ____________ (1) Excludes nonrecurring costs attributable to the acquisition including advisory, legal, other professional fees, and, integration costs, incurred by the Company and Guaranty of $1,560 and $2,034 , and the related tax effects, respectively. Revenues and earnings of the acquired company since the acquisition date have not been disclosed as Guaranty was merged into the Company and separate financial information is not readily available. Integrity Bancshares, Inc. On June 1, 2018, the Company acquired 100% of the outstanding stock of Integrity Bancshares, Inc. and its subsidiary, Integrity Bank, SSB, Houston, Texas (Integrity) with four branches located in Houston, TX. The Company issued 2,071,981 shares of Company stock and paid $31,016 in cash for the outstanding shares and options of Integrity common stock. The Company recognized total goodwill of $100,339 , which is calculated as the excess of both the consideration exchanged and liabilities assumed compared to the fair market value of identifiable assets acquired. The fair value of consideration exchanged related to the Company's stock was calculated based upon the closing market price of the Company's stock as of June 1, 2018. The goodwill in this acquisition resulted from a combination of expected synergies and expansion in the Houston market. None of the goodwill recognized is expected to be deductible for income tax purposes. The Company has incurred expenses related to the acquisition of approximately $4,074 and $360 during the years ended December 31, 2018 and 2017, which are included in acquisition expense in the consolidated statements of income. In addition, as of December 31, 2018, the Company paid offering costs totaling $209 which were recorded as a reduction to stock issuance proceeds through additional paid in capital. The following table summarizes the final fair values of the assets acquired and liabilities in this transaction: Final Value as reported at December 31, 2018 Assets of acquired bank: Cash and cash equivalents $ 44,723 Securities available for sale 24,721 Restricted stock 3,357 Loans 651,769 Premises and equipment 4,863 Goodwill 100,339 Core deposit intangible 7,537 Bank owned life insurance 8,181 Other assets 6,385 Total assets acquired $ 851,875 Liabilities of acquired bank: Deposits $ 593,078 FHLB advances 60,000 Other liabilities 10,518 Total liabilities assumed $ 663,596 Common stock issued at $75.90 per share $ 157,263 Cash paid $ 31,016 Non-credit impaired loans had a fair value of $604,549 at acquisition date and contractual balance of $609,675 . As of acquisition date, the Company expects that an insignificant amount of the contractual balance of these loans will be uncollectible. The difference of $5,126 will be recognized into interest income as an adjustment to yield over the life of the loans.

Parent Company Only Financial S

Parent Company Only Financial Statements	12 Months Ended
	Dec. 31, 2019
Condensed Financial Information Disclosure [Abstract]
Parent Company Only Financial Statements	Parent Company Only Financial Statements The following balance sheets, statements of income and statements of cash flows for Independent Bank Group, Inc. should be read in conjunction with the consolidated financial statements and the notes thereto. Balance Sheets December 31, 2019 2018 Assets Cash and cash equivalents $ 8,277 $ 8,355 Investment in subsidiaries 2,588,857 1,764,698 Investment in trusts 1,724 950 Other assets 3,355 2,189 Total assets $ 2,602,213 $ 1,776,192 Liabilities and Stockholders' Equity Other borrowings $ 202,251 $ 137,316 Junior subordinated debentures 53,824 27,852 Other liabilities 6,365 4,591 Total liabilities 262,440 169,759 Stockholders' equity: Preferred stock — — Common stock 430 306 Additional paid-in capital 1,926,359 1,317,616 Retained earnings 393,674 296,816 Accumulated other comprehensive loss 19,310 (8,305 ) Total stockholders' equity 2,339,773 1,606,433 Total liabilities and stockholders' equity $ 2,602,213 $ 1,776,192 Statements of Income Years Ended December 31, 2019 2018 2017 Interest expense: Interest on other borrowings $ 11,561 $ 8,390 $ 6,873 Interest on junior subordinated debentures 3,028 1,609 1,162 Total interest expense 14,589 9,999 8,035 Noninterest income: Dividends from subsidiaries 105,877 39,841 29,563 Other 1 14 32 Total noninterest income 105,878 39,855 29,595 Noninterest expense: Salaries and employee benefits 7,653 6,318 5,175 Professional fees 264 332 546 Acquisition expense, including legal 33,445 6,157 12,767 Other 2,562 1,611 1,614 Total noninterest expense 43,924 14,418 20,102 Income before income tax benefit and equity in undistributed income of subsidiaries 47,365 15,438 1,458 Income tax benefit 11,066 5,541 8,890 Income before equity in undistributed income of subsidiaries 58,431 20,979 10,348 Equity in undistributed income of subsidiaries 134,305 107,280 66,164 Net income $ 192,736 $ 128,259 $ 76,512 Statements of Cash Flows Years Ended December 31, 2019 2018 2017 Cash flows from operating activities: Net income $ 192,736 $ 128,259 $ 76,512 Adjustments to reconcile net income to net cash provided by operating activities: Equity in undistributed net income of subsidiaries (134,305 ) (107,280 ) (66,164 ) Amortization of discount and origination costs on borrowings 633 633 505 Stock based compensation expense 7,808 6,062 4,688 Excess tax expense (benefit) on restricted stock vested 21 (646 ) (1,323 ) Deferred tax expense 2,165 1,054 11,782 Net change in other assets 1,863 6,918 (6,750 ) Net change in other liabilities (64 ) 1,130 (1,663 ) Net cash provided by operating activities 70,857 36,130 17,587 Cash flows from investing activities: Capital investment in subsidiaries — — (50,050 ) Cash acquired in connection with acquisition 339 7,425 5,418 Cash paid in connection with acquisition (9 ) (31,016 ) (17,773 ) Net cash provided by (used in) financing activities 330 (23,591 ) (62,405 ) Cash flows from financing activities: Proceeds from other borrowings 65,000 — 29,255 Repayments of other borrowings (40,500 ) — — Proceeds from exercise of common stock warrants — 2,533 55 Offering costs paid in connection with acquired bank (804 ) (209 ) (942 ) Proceeds from sale of common stock, net — — 26,816 Repurchase of common stock (51,659 ) — — Dividends paid (43,302 ) (15,908 ) (10,231 ) Net cash (used in) provided by financing activities (71,265 ) (13,584 ) 44,953 Net change in cash and cash equivalents (78 ) (1,045 ) 135 Cash and cash equivalents at beginning of year 8,355 9,400 9,265 Cash and cash equivalents at end of year $ 8,277 $ 8,355 $ 9,400

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2019
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events Line of credit agreement On January 17, 2020, the Company's $100,000 unsecured revolving line of credit was renewed and matures on January 17, 2021. As of March 2, 2020 , the Company has no borrowings against its revolving line of credit. Declaration of dividends On January 29, 2020, the Company declared a quarterly cash dividend in the amount of $0.25 per share of common stock to the stockholders of record on February 10, 2020. The dividend totaling $10,754 was paid on February 20, 2020.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Nature of Operations	Nature of operations: Independent Bank Group, Inc. (IBG) through its subsidiary, Independent Bank, a Texas state banking corporation (Bank) (collectively known as the Company), provides a full range of banking services to individual and corporate customers in the North, Central and Southeast, Texas areas and along the Colorado Front Range, through its various branch locations in those areas. The Company is engaged in traditional community banking activities, which include commercial and retail lending, deposit gathering, investment and liquidity management activities. The Company’s primary deposit products are demand deposits, money market accounts and certificates of deposit, and its primary lending products are commercial business and real estate, real estate mortgage and consumer loans. Proposed merger with Texas Capital Bancshares, Inc.: The Company and Texas Capital Bancshares, Inc. (TCBI) have entered into an Agreement and Plan of Merger, dated as of December 9, 2019, which is referred to as the "merger agreement". Under the merger agreement, the Company and TCBI have agreed to combine their respective companies in an all stock merger of equals, pursuant to which TCBI will merge with and into the Company, with the Company continuing as the surviving entity, in a transaction referred to as "the merger." Immediately following the merger or at such later time as the parties may mutually agree, Texas Capital Bank will merge with and into Independent Bank, with Independent Bank as the surviving bank. The merger agreement was unanimously approved by each company's board of directors. The transaction is anticipated to close in mid-2020, subject to customary closing conditions, including receipt of shareholder and regulatory approvals. The transaction is discussed in more detail in Note 22 , Business Combinations.
Basis of Presentation	Basis of presentation: The accompanying consolidated financial statements include the accounts of IBG and all other entities in which IBG has controlling financial interest. All material intercompany transactions and balances have been eliminated in consolidation. In addition, the Company wholly-owns nine statutory business trusts that were formed for the purpose of issuing trust preferred securities and do not meet the criteria for consolidation (See Note 12 , Junior Subordinated Debentures). On January 1, 2019, the Company acquired Guaranty Bancorp (Guaranty) and its wholly owned subsidiary, Guaranty Bank and Trust Company (Guaranty Bank) and its wholly owned subsidiary, Private Capital Management, LLC. Guaranty was merged into the Company and dissolved and Guaranty Bank and its subsidiary was merged with the Bank as of acquisition date. The Company also acquired two statutory business trusts in connection with the acquisition as disclosed in Note 12 , Junior Subordinated Debentures. See Note 22 , Business Combinations, for more details of the Guaranty acquisition. Accounting standards codification: The Financial Accounting Standards Board's (FASB) Accounting Standards Codification (ASC) is the officially recognized source of authoritative U.S. generally accepted accounting principles (GAAP) applicable to all public and non-public non-governmental entities. Rules and interpretive releases of the SEC under the authority of federal securities laws are also sources of authoritative GAAP for SEC registrants. All other accounting literature is considered non-authoritative. Citing particular content in the ASC involves specifying the unique numeric path to the content through the Topic, Subtopic, Section and Paragraph structure.
Segment Reporting	Segment reporting: The Company has one reportable segment. The Company’s chief operating decision-maker uses consolidated results to make operating and strategic decisions.
Reclassifications	Reclassifications: Certain prior period financial statement and disclosure amounts have been reclassified to conform to current period presentation. The reclassifications have no effect on net income or stockholders' equity as previously reported.
Use of estimates	Use of estimates: The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions that affect certain reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. Accordingly, actual results could differ from those estimates. The material estimates included in the financial statements relate to the allowance for loan losses, the valuation of goodwill and valuation of assets and liabilities acquired in business combinations.
Cash and cash equivalents	Cash and cash equivalents: For the purposes of reporting cash flows, cash and cash equivalents include cash on hand, amounts due from banks and federal funds sold. All highly liquid investments with an initial maturity of less than ninety days are considered to be cash equivalents. The Company maintains deposits with other financial institutions in amounts that exceed FDIC insurance coverage. The Company's management monitors the balance in these accounts and periodically assesses the financial condition of the other financial institutions. The Company has not experienced any losses in such accounts and believes it is not exposed to any significant credit risks on cash or cash equivalents.
Certificates of deposit	Certificates of deposit: Certificates of deposit are FDIC insured deposits in other financial institutions that mature within 18 months and are carried at cost.
Securities	Securities: Securities classified as available for sale are those debt securities that the Company intends to hold for an indefinite period of time, but not necessarily to maturity. Any decision to sell a security classified as available for sale would be based on various factors, including significant movements in interest rates, changes in the maturity mix of the Company's assets and liabilities, liquidity needs, regulatory capital considerations and other similar factors. Securities available for sale are reported at fair value with unrealized gains or losses reported as a separate component of other comprehensive income, net of tax. The amortization of premiums and accretion of discounts, computed by the interest method generally over their contractual lives, are recognized in interest income. Premiums on callable securities are amortized to their earliest call date. Prior to the adoption of a new accounting standard in 2019, as further discussed in Note 2 , Recent Accounting Pronouncements, premiums on callable securities were amortized to their respective maturity dates unless such securities were included in pools for the purposes of assessing prepayment expectations. Realized gains or losses, determined on the basis of the cost of specific securities sold, are included in earnings on the trade date. In estimating other than temporary impairment losses, management considers (1) the length of time and the extent to which the fair value has been less than cost, (2) the financial condition and near-term prospects of the issuer, and (3) the intent of the Company to retain its investment and whether it is more likely than not the Company will be required to sell its investment before its anticipated recovery in fair value. When the Company does not intend to sell the security, and it is more likely than not that it will not have to sell the security before recovery of its cost basis, it will recognize the credit component of an other than temporary impairment of a debt security in earnings and the remaining portion in other comprehensive income.
Loans held for sale	Loans held for sale: The Company originates residential mortgage loans that may subsequently be sold to unaffiliated third parties. The Company elected the fair value option for certain residential mortgage loans held for sale originated after July 1, 2018 in accordance with ASC 825, Financial Instruments. This election allows for a more effective offset of the changes in fair values of the loans and the derivative instruments used to economically hedge them without the burden of complying with the requirements for hedge accounting under ASC 815, Derivatives and Hedging . The Company has not elected the fair value option for other residential mortgage loans held for sale primarily because they are not economically hedged using derivative instruments. Mortgage loans originated and intended for sale not recorded under the fair value option are carried at the lower of aggregate cost or fair value, as determined by aggregate outstanding commitments from investors. Net unrealized losses, if any, are recognized through a valuation allowance by charges to income. All mortgage loans held for sale are sold without servicing rights retained. Gains and losses on sales of loans are recognized in noninterest income at settlement dates and are determined by the difference between the sales proceeds and the carrying value of the loans.
Acquired loans	Acquired loans: Acquired loans from the transactions accounted for as a business combination include both nonperforming loans with evidence of credit deterioration since their origination date and performing loans. The Company is accounting for the nonperforming loans acquired in accordance with ASC 310-30, Loans and Debt Securities Acquired with Deteriorated Credit Quality . The performing loans are being accounted for under ASC 310-20, Nonrefundable Fees and Other Costs , with the related difference in the initial fair value and unpaid principal balance (the discount) recognized as interest income on a level yield basis over the life of the loan. At the date of the acquisition, the acquired loans are recorded at their fair value with no valuation allowance. Purchased credit impaired loans are accounted for individually. The Company estimates the amount and timing of undiscounted expected cash flows for each loan, and the expected cash flows in excess of fair value is recorded as interest income over the remaining life of the loan (accretable yield). The excess of the loan's contractual principal and interest over expected cash flows is not recorded (nonaccretable difference). Over the life of the loan, expected cash flows continue to be estimated. If the expected cash flows decrease, an impairment loss is recorded. If the expected cash flows increase, it is recognized as part of future interest income.
Loans, net	Loans, net: Loans that management has the intent and ability to hold for the foreseeable future or until maturity or pay-off are reported at their outstanding principal balance, net of unearned interest, purchase premiums and discounts, deferred loan fees or costs and an allowance for loan losses. Loan origination fees, net of direct origination costs, are deferred and recognized as an adjustment to the related loan yield using the effective interest method without anticipating prepayments. Prior to the year ended December 31, 2019, fees and costs associated with originating loans were generally recognized in the period they were incurred, except in the Houston market, former Grand Bank and Carlile branches, which fees were deferred. Management believes that not deferring such fees and costs did not materially affect the financial position or results of operations of the Company.
Allowance for loan losses	Allowance for loan losses: The allowance for loan losses is maintained at a level considered adequate by management to provide for probable loan losses. The allowance is increased by provisions charged to expense. Loans are charged against the allowance for loan losses when management believes that collectability of the principal is unlikely. Subsequent recoveries, if any, are credited to the allowance. The provision for loan losses is the amount, which, in the judgment of management, is necessary to establish the allowance for loan losses at a level that is adequate to absorb known and inherent risks in the loan portfolio. See Note 6 , Loans, Net and Allowance for Loan Losses, for further information on the Company's policies and methodology used to estimate the allowance for loan losses. The allowance is derived from the following two components: 1) allowances established on individual impaired loans, which are based on a review of the individual characteristics of each loan, including the customer’s ability to repay the loan, the underlying collateral values and the industry the customer operates and 2) allowances based on actual historical loss experience for the last three years for similar types of loans in the Company’s loan portfolio adjusted for primarily changes in the lending policies and procedures; collection, charge-off and recovery practices; nature and volume of the loan portfolio; change in value of underlying collateral; volume and severity of nonperforming loans; existence and effect of any concentrations of credit and the level of such concentrations and current, national and local economic and business conditions. This second component also includes an unallocated allowance to cover uncertainties that could affect management’s estimate of probable losses. The unallocated allowance reflects the imprecision inherent in the underlying assumptions used in the methodologies for estimating this component. The Company’s management continually evaluates the allowance for loan losses determined from the allowances established on individual loans and the amounts determined from historical loss percentages adjusted for the qualitative factors above. Should any of the factors considered by management change, the Company’s estimate of loan losses could also change and would affect the level of future provision expense. While the calculation of the allowance for loan losses utilizes management’s best judgment and all the information available, the adequacy of the allowance for loan losses is dependent on a variety of factors beyond the Company’s control, including, among other things, the performance of the entire loan portfolio, the economy, changes in interest rates and the view of regulatory authorities towards loan classifications. In addition, regulatory agencies, as an integral part of their examination process, periodically review the Bank’s allowance for loan losses, and may require the Bank to make additions to the allowance based on their judgment about information available to them at the time of their examinations. Loans requiring an allocated loan loss provision are generally identified at the servicing officer level based on review of weekly past due reports and/or the loan officer’s communication with borrowers. In addition, past due loans are discussed at weekly officer loan committee meetings to determine if classification is warranted. The Company’s credit department has implemented an internal risk based loan review process to identity potential internally classified loans that supplements the annual independent external loan review. External loan reviews cover a wide range of the loan portfolio, including large lending relationships and recently acquired loan portfolios. As such, the external loan review generally covers loans exceeding $3,500 . These reviews include analysis of borrower’s financial condition, payment histories and collateral values to determine if a loan should be internally classified. Generally, once classified, an impaired loan analysis is completed by the credit department to determine if the loan is impaired and the amount of allocated allowance required. The Texas economy, specifically the Company’s lending area of north, central and southeast Texas area, continued to expand at a moderate pace while the Colorado economy remained flat during the fourth quarter of 2019. The Texas economy, which is the second largest in the nation, and the Colorado economy have exceeded the average U.S. economy in job creation and employment growth. Overall, the forecast is positive with continued moderate growth in the retail and service sectors. The Texas and Colorado economies are expected to continue to grow into 2020 at a slower pace with an improved outlook, though uncertainties, including slowing U.S. and global economies, trade uncertainty and a significant oil-price decline, remain elevated. The risk of loss associated with all segments of the portfolio could increase due to these factors.
Premises and equipment, net	Premises and equipment, net: Land is carried at cost. Bank premises, furniture and equipment and aircraft are carried at cost, less accumulated depreciation computed principally by the straight-line method over the estimated useful lives of the assets, which range from three to thirty years . Real property acquired after January 1, 2019, accounts for depreciation using the straight-line method over the estimated useful lives of the assets considering the salvage value of the real property. Leasehold improvements are carried at cost and are depreciated over the shorter of the estimated useful life or the lease period.
Leases	Leases: The Company leases certain office facilities and office equipment under operating leases. The Company also owns certain office facilities which it leases to outside parties under operating lessor leases; however, such leases are not significant. On January 1, 2019, the Company adopted ASU 2016-02, Leases (Topic 842), as further explained below and in Note 2 , Recent Accounting Pronouncements. Under the new standard, for operating leases other than those considered to be short-term, the Company recognizes operating lease right-of-use (ROU) assets and operating lease liabilities, which are recorded in other assets and other liabilities, respectively, in the consolidated balance sheets. The Company determines if an arrangement is a lease at inception. Operating lease ROU assets and liabilities are recognized at commencement date based on the present value of lease payments over the lease term. As the Company's leases do not provide an implicit rate, the Company uses its incremental borrowing rate referenced to the Federal Home Loan Bank Secure Connect advance rates for borrowings of similar terms in determining the present value of lease payments. The operating lease ROU asset also includes any lease pre-payments made and excludes lease incentives. The Company's lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Lease expense for lease payments is recognized on a straight-line basis over the lease term. The Company has lease agreements with lease and non-lease components, which the Company has elected to account for separately as the non-lease component amounts are readily determinable under most leases. The Company’s primary leasing activities relate to certain real estate operating leases entered into in support of the Company’s branch operations and back office operations. The Company leases 21 of its 93 branches. The Company’s branch locations operated under lease agreements have all been designated as operating leases. Rent expense related to these leases amounted to $7,025 , $3,758 , and $3,073 for the years ended December 31, 2019, 2018, and 2017, respectively. In addition, the Company leases certain equipment under operating leases. The Company does not have leases designated as finance leases. As of December 31, 2019 the Company’s lease ROU assets and related lease liabilities were $31,813 and $28,978 , respectively, and have remaining terms ranging from 1 to 31 years , including extension options that the Company is reasonably certain will be exercised.
Long-term assets	Long-term assets: Premises and equipment and other long-term assets are reviewed for impairment when events indicate that their carrying amount may not be recoverable from future undiscounted cash flows. If impaired, the assets are recorded at fair value.
Other real estate owned	Other real estate owned: Real estate properties acquired through, or in lieu of, loan foreclosure are initially recorded at fair value less estimated selling costs at the date of foreclosure, establishing a new cost basis. After foreclosure, valuations are periodically performed by management and the real estate is carried at the lower of carrying amount or fair value less cost to sell. Revenue and expenses from operations of other real estate owned and impairment charges on other real estate are included in noninterest expense. Gains and losses on sale of other real estate are included in noninterest income.
Goodwill and core deposit intangible, net	Goodwill and other intangible assets, net: Goodwill represents the excess of costs over fair value of net assets of businesses acquired. Goodwill is tested for impairment annually on December 31 or on an interim basis if an event triggering impairment may have occurred. Core deposit intangibles and other acquired customer relationship intangibles arising from bank acquisitions are amortized on a straight-line basis over their estimated useful lives of ten years and thirteen years , respectively. Other intangible assets are tested for impairment whenever events or changes in circumstances indicate the carrying amount of the assets may not be recoverable from future undiscounted cash flows.
Restricted stock	Restricted stock : The Bank is a member of the FHLB system. Members are required to own a certain amount of stock based on the level of borrowings and other factors, and may invest in additional amounts. FHLB of Dallas and other restricted stock do not have readily determinable fair values as ownership is restricted and they lack a ready market. As a result, these stocks are carried at cost and evaluated periodically by management for impairment. Both cash and stock dividends are reported as income.
Bank-owned life insurance	Bank-owned life insurance: Bank-owned life insurance is recorded at the amount that can be realized under the insurance contracts at the balance sheet date, which is the cash surrender value adjusted for other charges or other amounts due that are probable at settlement. Changes in the net cash surrender value of the policies, as well as insurance proceeds received are reflected in noninterest income.
Income taxes	Income taxes: Income tax expense is the total of the current year income tax due or refundable and the change in deferred tax assets and liabilities (excluding deferred tax assets and liabilities related to business combinations or components of other comprehensive income). Deferred tax assets and liabilities are the expected future tax amounts for the temporary differences between carrying amounts and tax bases of assets and liabilities, computed using enacted tax rates. The effect of a change in tax rates on deferred assets and liabilities is recognized in income taxes during the period that includes the enactment date. A valuation allowance, if needed, reduces deferred tax assets to the expected amount more likely than not to be realized. Realization of deferred tax assets is dependent upon the level of historical income, prudent and feasible tax planning strategies, reversals of deferred tax liabilities and estimates of future taxable income. The Company evaluates uncertain tax positions at the end of each reporting period. The Company may recognize the tax benefit from an uncertain tax position only if it is more likely than not that the tax position will be sustained on examination by the taxing authorities, based on the technical merits of the position. The tax benefit recognized in the financial statements from any such position is measured based on the largest benefit that has a greater than fifty percent likelihood of being realized upon ultimate settlement. For tax positions not meeting the "more likely than not" test, no tax benefit is recorded. Any interest and/or penalties related to income taxes are reported as a component of income tax expense.
Loan commitments and related financial instruments	Loan commitments and related financial instruments: In the ordinary course of business, the Company has entered into certain off-balance-sheet financial instruments consisting of commitments to extend credit, commercial letters of credit, and standby letters of credit. Such financial instruments are recorded in the financial statements when they are funded or related fees are incurred or received. Management estimates losses on off-balance-sheet financial instruments using the same methodology as for portfolio loans. Estimated losses on off-balance-sheet financial instruments are recorded by charges to the provision for losses and credits to other liabilities in the Company's consolidated balance sheet. There were no estimated losses on off-balance sheet financial instruments as of December 31, 2019 or 2018 .
Stock based compensation	Stock based compensation: Compensation cost is recognized for restricted stock awards issued to employees based on the market price of the Company's common stock on the grant date. Stock-based compensation expense is generally recognized using the straight-line method over the requisite service period for all awards. The impact of forfeitures of stock-based payment awards on compensation expense is recognized as forfeitures occur.
Transfers of financial assets	Transfers of financial assets: Transfers of financial assets are accounted for as sales, when control over the assets has been relinquished. Control over transferred assets is deemed to be surrendered when the assets have been isolated from the Company, the transferee obtains the right (free of conditions that constrain it from taking advantage of that right) to pledge or exchange the transferred assets, and the Company does not maintain effective control over the transferred assets through an agreement to repurchase them before their maturity.
Advertising costs	Advertising costs: Advertising costs are expensed as incurred.
Business combinations	Business combinations: The Company applies the acquisition method of accounting for business combinations. Under the acquisition method, the acquiring entity in a business combination recognizes 100% of the assets acquired and liabilities assumed at their acquisition date fair values. Management utilizes valuation techniques appropriate for the asset or liability being measured in determining these fair values. Any excess of the purchase price over amounts allocated to assets acquired, including identifiable intangible assets, and liabilities assumed is recorded as goodwill. Where amounts allocated to assets acquired and liabilities assumed is greater than the purchase price, a bargain purchase gain is recognized. Adjustments identified during the measurement period are recognized in the reporting period in which the adjustment amounts are determined. Acquisition-related costs are expensed as incurred.
Comprehensive income	Comprehensive income: Accounting principles generally require that recognized revenue, expenses, gains and losses be included in net income. Although certain changes in assets and liabilities, such as unrealized gains and losses on available for sale securities, are reported as a separate component of the equity section of the balance sheet, such items, along with net income, are components of comprehensive income. Gains and losses on available for sale securities are reclassified to net income as the gains or losses are realized upon sale of the securities. The credit component of other than temporary impairment charges are reclassified to net income at the time of the charge.
Fair value measurements	Fair values of financial instruments: Accounting standards define fair value, establish a framework for measuring fair value in U.S. generally accepted accounting principles, and require certain disclosures about fair value measurements (see Note 18 , Fair Value Measurements). In general, fair values of financial instruments are based upon quoted market prices, where available. If such quoted market prices are not available, fair value is based upon 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 fair value of an asset or liability is the price that would be received to sell that asset or paid to transfer that liability in an orderly transaction occurring in the principal market (or most advantageous market in the absence of a principal market) for such asset or liability. In estimating fair value, the Company utilizes valuation techniques that are consistent with the market approach, the income approach and/or the cost approach. Such valuation techniques are consistently applied. Inputs to valuation techniques include the assumptions that market participants would use in pricing an asset or liability. ASC Topic 820, Fair Value Measurements and Disclosures , establishes a fair value hierarchy for valuation inputs that gives the highest priority to quoted prices in active markets for identical assets or liabilities and the lowest priority to unobservable inputs. The fair value hierarchy is as follows: Level 1 Inputs – Unadjusted quoted prices in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. Level 2 Inputs – Inputs other than quoted prices included in Level 1 that are observable for the asset or liability, either directly or indirectly. These might include quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability (such as interest rates, volatilities, prepayment speeds, credit risks, etc.) or inputs that are derived principally from or corroborated by market data by correlation or other means. Level 3 Inputs – Unobservable inputs for determining the fair values of assets or liabilities that reflect an entity’s own assumptions about the assumptions that market participants would use in pricing the assets or liabilities. The Company elected the fair value option for certain residential mortgage loans held for sale originated after July 1, 2018 in accordance with ASC 825, Financial Instruments. This election allows for a more effective offset of the changes in fair values of the loans and the derivative instruments used to economically hedge them without the burden of complying with the requirements for hedge accounting under ASC 815, Derivatives and Hedging . The Company has not elected the fair value option for other residential mortgage loans held for sale primarily because they are not economically hedged using derivative instruments. See below and Note 19 , Derivative Financial Instruments, for additional information. Securities classified as available for sale are reported at fair value utilizing Level 1 and Level 2 inputs. Securities are classified within Level 1 when quoted market prices are available in an active market. Inputs include securities that have quoted prices in active markets for identical assets. For securities utilizing Level 2 inputs, 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 and other yield curves, live trading levels, trade execution data, market consensus prepayment speeds, credit information and the security’s terms and conditions, among other things. Certain mortgage loans held for sale are measured at fair value on a recurring basis due to the Company's election to adopt fair value accounting treatment for those loans originated for which the Company has entered into certain derivative financial instruments as part of its mortgage banking and related risk management activities. These instruments include interest rate lock commitments and mandatory forward commitments to sell these loans to investors known as forward mortgage-backed securities trades. This election allows for a more effective offset of the changes in fair values of the assets and the mortgage related derivative instruments used to economically hedge them without the burden of complying with the requirements for hedge accounting under ASC 815, Derivatives and Hedging. Mortgage loans held for sale, for which the fair value option was elected, which are sold on a servicing released basis, are valued using a market approach by utilizing either: (i) the fair value of securities backed by similar mortgage loans, adjusted for certain factors to approximate the fair value of a whole mortgage loan, including the value attributable to mortgage servicing and credit risk, (ii) current commitments to purchase loans or (iii) recent observable market trades for similar loans, adjusted to credit risk and other individual loan characteristics. As these prices are derived from market observable inputs, the Company classifies these valuations as Level 2 in the fair value disclosures. For mortgage loans held for sale for which the fair value option was elected, the earned current contractual interest payment is recognized in interest income, loan origination costs and fees on fair value option loans are recognized in earnings as incurred and not deferred. The Company has no continuing involvement in any residential mortgage loans sold. The estimated fair values of interest rate lock commitments utilize current secondary market prices for underlying loans and estimated servicing value with similar coupons, maturity and credit quality, subject to the anticipated loan funding probability (pull-through rate). The fair value of interest rate lock commitments is subject to change primarily due to changes in interest rates and the estimated pull-through rate. These commitments are classified as Level 2 in the fair value disclosures, as the valuations are based on observable market inputs. Forward mortgage-backed securities trades are exchange-traded or traded within highly active dealer markets. In order to determine the fair value of these instruments, the Company utilized the exchange price or dealer market price for the particular derivative contract; therefore these contracts are classified as Level 2. The estimated fair values are subject to change primarily due to changes in interest rates. The Company also enters into certain interest rate derivative positions that are not designated as hedging instruments. The estimated fair value of these commercial loan interest rate swaps are obtained from a pricing service that provides the swaps' unwind value (Level 2 inputs). See Note 19 , Derivative Financial Instruments, for more information. Assets and Liabilities Measured on a Nonrecurring Basis Impaired loans (loans which are not expected to repay all principal and interest amounts due in accordance with the original contractual terms) are measured at an observable market price (if available) or at the fair value of the loan’s collateral (if collateral dependent). Fair value of the loan’s collateral is determined by appraisals or independent valuation, which is then adjusted for the estimated costs related to liquidation of the collateral. Management’s ongoing review of appraisal information may result in additional discounts or adjustments to valuation based upon more recent market sales activity or more current appraisal information derived from properties of similar type and/or locale. Therefore, the Company has categorized its impaired loans as Level 3. Other real estate is measured at fair value on a nonrecurring basis (upon initial recognition or subsequent impairment). Other real estate is classified within Level 3 of the valuation hierarchy. When transferred from the loan portfolio, other real estate is adjusted to fair value less estimated selling costs and is subsequently carried at the lower of carrying value or fair value less estimated selling costs. The fair value is determined using an external appraisal process, discounted based on internal criteria. Therefore, the Company has categorized its other real estate as Level 3. The methods and assumptions used by the Company in estimating fair values of financial instruments as disclosed herein in accordance with ASC Topic 825, Financial Instruments, other than for those measured at fair value on a recurring and nonrecurring basis discussed above, are as follows: Cash and cash equivalents: The carrying amounts of cash and cash equivalents approximate their fair value. Certificates of deposit held in other banks: The fair value of certificates of deposit held in other banks is based upon current market rates. Loans held for sale, at cost: The fair value of loans held for sale is determined based upon commitments on hand from investors. Loans: A discounted cash flow model is used to estimate the fair value of the loans. The discounted cash flow approach models the credit losses directly in the projected cash flows, applying various assumptions regarding credit, interest and prepayment risks for the loans based on loan types, payment types and fixed or variable classifications. Federal Home Loan Bank of Dallas and other restricted stock: The carrying value of restricted securities such as stock in the Federal Home Loan Bank of Dallas and Independent Bankers Financial Corporation approximates fair value. Deposits: The fair values disclosed for demand deposits are, by definition, equal to the amount payable on demand at the reporting date (that is their carrying amounts). The carrying amounts of variable-rate certificates of deposit (CDs) approximate their fair values at the reporting date. Fair values for fixed-rate CDs are estimated using a discounted cash flow calculation that applies interest rates currently being offered on certificates to a schedule of aggregated expected monthly maturities on time deposits. Federal Home Loan Bank advances, line of credit and federal funds purchased: The fair value of advances maturing within 90 days approximates carrying value. Fair value of other advances is based on the Company’s current borrowing rate for similar arrangements. Other borrowings: The carrying value of repurchase agreements approximates fair value due to the short term nature. The fair value of private subordinated debentures are based upon prevailing rates on similar debt in the market place. The subordinated debentures that are publicly traded are valued based on indicative bid prices based upon market pricing observations in the current market. Junior subordinated debentures: The fair value of junior subordinated debentures is estimated using discounted cash flow analyses based on the Company’s current incremental borrowing rates for similar types of borrowing arrangements. Accrued interest: The carrying amounts of accrued interest approximate their fair values. Off-balance sheet instruments: Fair values for off-balance sheet, credit-related financial instruments are based on fees currently charged to enter into similar agreements, taking into account the remaining terms of the agreements and the counterparties' credit standing. The fair value of commitments is not material.
Derivative financial instruments	Derivative financial instruments: The Company enters into certain derivative financial instruments: interest rate lock commitments, forward mortgage-backed securities trades and interest rate swaps. These financial instruments are not designated as hedging instruments and are used for asset and liability management related to the Company's mortgage banking activities and commercial customers' financing needs. All derivatives are carried at fair value in either other assets or other liabilities (see Note 19 , Derivative Financial Instruments ) . Through the normal course of business, the Company enters into interest rate lock commitments with consumers to originate mortgage loans at a specified interest rate. These commitments, which contain fixed expiration dates, offer the borrower an interest rate guarantee provided the loan meets underwriting guidelines and closes within the timeframe established by the Company. During July 2018, the Company began managing the changes in fair value associated with changes in interest rates related to interest rate lock commitments by using forward sold commitments known as forward mortgage-backed securities trades. These instruments are typically entered into at the time the interest rate lock commitment is made. The Company also offers certain derivatives products, primarily interest rate swaps, directly to qualified commercial banking customers to facilitate their risk management strategies. The interest rate swap derivative positions relate to transactions in which the Company enters into an interest rate swap with a customer, while at the same time entering into an offsetting interest rate swap with another financial institution. An interest rate swap transaction allows customers to effectively convert a variable rate loan to a fixed rate. In connection with each swap, the Company agrees to pay interest to the customer on a notional amount at a variable interest rate and receive interest from the customer on a similar notional amount at a fixed interest rate. At the same time, the Company agrees to pay another financial institution the same fixed interest rate on the same notional amount and receive the same variable interest rate on the same notional amount.
Mortgage banking	Mortgage banking: 15 days . In some cases, loans to larger mortgage originators may be financed for up to 60 days
Revenue recognition	Revenue recognition: ASC Topic 606, R evenue from Contracts with Customers (ASC 606) , establishes principles for reporting information about the nature, amount, timing and uncertainty of revenue and cash flows arising from the entity's contracts to provide goods or services to customers. The core principle requires an entity to recognize revenue to depict the transfer of goods or services to customers in an amount that reflects the consideration that it expects to be entitled to receive in exchange for those goods or services recognized as performance obligations are satisfied. The majority of the Company's revenue-generating transactions are not subject to ASC 606, including revenue generated from financial instruments, such as loans, letters of credit, and investment securities, as well as revenue related to mortgage banking activities, and BOLI, as these activities are subject to other accounting guidance. Descriptions of revenue-generating activities that are within the scope of ASC 606, and are presented in the accompanying Consolidated Statements of Income as components of noninterest income, are as follows: • Service charges on deposit accounts - these represent general service fees for monthly account maintenance and activity or transaction-based fees and consist of transaction-based revenue, time-based revenue (service period), item-based revenue or some other individual attribute-based revenue. Revenue is recognized when the performance obligation is completed which is generally monthly for account maintenance services or when a transaction has been completed (such as a wire transfer). Payment for such performance obligations are generally received at the time the performance obligations are satisfied. • Investment management and trust - includes income related to providing investment management and trust services to customers under investment management and trust contracts. Also included are fees received from a third party broker-dealer as part of a revenue-sharing agreement for fees earned from customers that are referred to a third party. The investment management fees and referral fees are billed and paid on a quarterly basis and recognized ratably throughout the quarter as performance obligations are satisfied. • Gains/losses on the sale of other real estate owned - generally recognized when the performance obligation is complete which is typically at delivery of control over the property to the buyer at time of each real estate closing. • Other noninterest income - includes the Company's correspondent bank earnings credit, mortgage warehouse purchase program fees, acquired loan recoveries, other deposit fees, and merchant interchange income. The majority of these fees in other noninterest income are not subject to the requirements of ASC 606. The other deposit fees and merchant interchange income are in the scope of ASC 606, and payment for such performance obligations are generally received at the time the performance obligations are satisfied. The Company has made no significant judgments in applying the revenue guidance prescribed in ASC 606 that affect the determination of the amount and timing of revenue from the above-described contracts with customers.
Share repurchase plan	Share repurchase program: The Company established share repurchase programs in prior years which would allow the Company to purchase its common stock in the open market or in privately negotiated transactions. In general, share repurchase programs allow the Company to proactively manage its capital position and return excess capital to shareholders. On October 24, 2018, the Company announced the reestablishment of its share repurchase program. The program authorizes the purchase by the Company of up to $75,000 of its common stock. The repurchase program was authorized to continue through October 1, 2019. On October 17, 2019, the repurchase program was renewed and authorized to continue through December 31, 2020. The Company has approval from the Federal Reserve to repurchase up to $60,000 in shares for 2019, of which $10,952 is remaining. The Company intends to request additional approvals, as necessary, for share buybacks in 2020. As of December 31, 2019 , the Company has repurchased a total of 897,738 shares of Company stock at a total cost of $49,048 under this program. Shares of Company stock repurchased to settle employee tax withholding related to vesting of stock awards during the period ended December 31, 2019 totaled 55,106 at a total cost of $2,611 and were not included under this program. No shares of Company stock were repurchased by the Company under this program during 2018.
Subsequent events	Subsequent events: Companies are required to evaluate events and transactions that occur after the balance sheet date but before the date the financial statements are issued. They must recognize in the financial statements the effect of all events or transactions that provide additional evidence of conditions that existed at the balance sheet date, including the estimates inherent in the financial statement preparation process. Entities shall not recognize the impact of events or transactions that provide evidence about conditions that did not exist at the balance sheet date but arose after that date. The Company has evaluated subsequent events through the date of filing these financial statements with the Securities and Exchange Commission (SEC) and noted no subsequent events requiring financial statement recognition or disclosure, except as disclosed in Note 24 .
Earnings per share	Earnings per share: Basic earnings per common share is calculated as net income available to common shareholders divided by the weighted average number of common shares outstanding during the period. The unvested share-based payment awards that contain rights to nonforfeitable dividends are considered participating securities for this calculation. Diluted earnings per common share include the dilutive effect of additional potential common shares issuable under stock warrants. The participating nonvested common stock was not included in dilutive shares as it was anti-dilutive for the years ended December 31, 2019 , 2018 and 2017 . The Company's outstanding stock warrants were all exercised prior to December 31, 2018. For the year ended December 31, 2017, proceeds from the assumed exercise of dilutive stock warrants are assumed to be used to repurchase common stock at the average market price.
Recent accounting pronouncements	Recent Accounting Pronouncements Adoption of new accounting standards ASU 2016-02, Leases (Topic 842). This ASU, among other things, requires lessees to recognize a lease liability, which is a lessee’s obligation to make lease payments arising from a lease, measured on a discounted basis; and a right-of-use asset, which is an asset that represents the lessee’s right to use, or control the use of, a specified asset for the lease term. Under this guidance, lessor accounting is largely unchanged. This ASU became effective for annual and interim periods for the Company on January 1, 2019. The Company adopted the standard by applying the alternative transition method whereby comparative periods were not restated, and an immaterial cumulative effect adjustment to the opening balance of retained earnings was recognized as of January 1, 2019. The Company also elected the ASU’s package of three practical expedients, which allowed the Company to forego a reassessment of (i) whether any expired or existing contracts are or contain leases, (ii) the lease classification for any expired or existing leases and (iii) the initial direct costs for any existing leases. The Company also elected not to apply the recognition requirements of the ASU to any short-term leases (as defined by related accounting guidance) and will account for lease and non-lease components separately because such amounts are readily determinable under most lease contracts and because this election results in a lower impact on the Company's balance sheet. The Company has implemented a lease management system to assist in centralizing, maintaining and accounting for all leases and implemented additional processes and internal controls to ensure the Company meets the ASU’s reporting and disclosure requirements. The adoption of this standard resulted in the Company recognizing lease right-of-use assets and related lease liabilities totaling $38,812 and $33,953 , respectively, as of January 1, 2019. The difference between the lease assets and the lease liabilities was $4,949 of prepaid rent, which was reclassified to lease assets, and the remainder, net of the deferred tax impact, was recorded as an adjustment reducing retained earnings in the amount of $70 . In addition, the right-of-use assets and related lease liabilities recognized on January 1, 2019 include the leases assumed with the Guaranty acquisition. The adoption of this ASU did not have a significant impact on the Company’s consolidated statement of income. See Note 1 , Summary of Significant Accounting Policies, and Note 13 , Leases, for required disclosures. ASU 2017-08, Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20), Premium Amortization on Purchased Callable Debt Securities . This ASU requires certain premiums on callable debt securities to be amortized to the earliest call date. The amortization period for callable debt securities purchased at a discount is not impacted. Under current GAAP, premiums on callable debt securities are generally amortized over the contractual life of the security. ASU 2017-08 became effective for the Company on January 1, 2019 and, upon adoption, the Company recognized a cumulative effect adjustment reducing retained earnings by $856 , net of the deferred tax impact, but otherwise did not have a significant impact to the Company's consolidated financial statements and disclosures. ASU 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities. This ASU refines and expands hedge accounting for both financial and commodity risks. Its provisions create more transparency around how economic results are presented, both on the face of the financial statements and in the footnotes. It also makes certain targeted improvements to simplify the application of hedge accounting guidance. ASU 2017-12 became effective for the Company on January 1, 2019. The adoption of this ASU did not have a significant impact on the Company's consolidated financial statements and disclosures. ASU 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220) - Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. The amendments in this update allow reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act (TCJA) which was signed into law on December 22, 2017. The Company elected to early adopt ASU 2018-02 in the first quarter of 2018 and apply the guidance to the beginning of the period, effective January 1, 2018 . The impact of adopting the amendment resulted in a cumulative effect adjustment to the consolidated balance sheet as of January 1, 2018 to reclassify approximately $233 of tax expense from accumulated other comprehensive loss to retained earnings as reflected in the accompanying Consolidated Statements of Changes in Stockholders' Equity. ASU 2018-07, Improvements to Nonemployee Share-Based Payment Accounting . This ASU aligns much of the guidance on measuring and classifying nonemployee awards with that of awards to employees. The guidance applies to nonemployee awards issued in exchange for goods or services used or consumed in an entity’s own operations and to awards granted by an investor to employees and nonemployees of an equity method investee for goods or services used or consumed in the investee’s operations. There are no new disclosure requirements. This ASU became effective for the Company on January 1, 2019. The adoption of this ASU did not have a significant impact on the Company’s financial statements and disclosures. Newly issued but not yet effective accounting standards ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. ASU 2016-13 along with several other subsequent codification updates related to accounting for credit losses, requires the measurement of all expected credit losses for financial assets held at the reporting date based on historical experience, current conditions, and reasonable and supportable forecasts and requires enhanced disclosures related to the significant estimates and judgments used in estimating credit losses, as well as the credit quality and underwriting standards of an organization’s portfolio. In addition, ASU 2016-13 amends the credit loss measurement guidance for available for sale debt securities and purchased financial assets with credit deterioration. Under prior US GAAP, companies generally recognized credit losses when it was probable that the loss has been incurred (incurred loss model). ASU 2016-13 requires a new credit loss methodology, the current expected credit loss (CECL) model, which requires the recognition of an allowance for lifetime expected credit losses on loans, held-to-maturity debt securities and other receivables measured at amortized cost at the time the financial asset is originated or acquired. Credit losses will be immediately recognized through net income; the amount recognized will be based on the current estimate of contractual cash flows not expected to be collected over the financial asset’s contractual term. The Company currently expects the adoption of ASU 2016-13 will result in an increase of its combined allowance for loan losses and reserves for unfunded commitments of approximately $68,000 to $80,000 , of which $20,000 to $22,000 is attributable to purchase credit deteriorated loans. As the Company currently finalizes the execution of its implementation controls and processes, the ultimate impact of the adoption of ASU 2016-13 as of January 1, 2020 could differ from the current expectation. The expected increase in the allowance for loan losses is a result of changing from an incurred loss model, which encompasses allowances for current known and inherent losses within the portfolio, to a CECL model, which encompasses allowances for losses expected to be incurred over the life of the portfolio. The majority of the increase is attributable to applying the CECL model to the Company's acquired loans, which, under prior guidance, were recorded at fair value without an allowance at acquisition date. Furthermore, ASU 2016-13 will necessitate that the Company establish an allowance for expected credit losses for certain debt securities and other financial assets; however, allowances are not expected to be significant. The Company will apply the standard's provisions as a cumulative-effect adjustment to retained earnings. ASU 2017-04, Intangibles - Goodwill and Other (Topic 350) - Simplifying the Test for Goodwill Impairment. This ASU simplifies the accounting for goodwill impairment for all entities by requiring impairment charges to be based on the first step in today’s two-step impairment test. Under the new guidance, if a reporting unit’s carrying amount exceeds its fair value, an entity will record an impairment charge based on that difference. The impairment charge will be limited to the amount of goodwill allocated to that reporting unit. The standard eliminates today’s requirement to calculate a goodwill impairment charge using Step 2, which requires an entity to calculate any impairment charge by comparing the implied fair value of goodwill with its carrying amount. ASU 2017-04 will be effective for the Company on January 1, 2020, with earlier adoption permitted and is not expected to have a significant impact on its financial statements. ASU 2018-13, Fair Value Measurement (Topic 820) - Changes to the Disclosure Requirements for Fair Value Measurement . This ASU modifies the disclosure requirements on fair value measurements by requiring that Level 3 fair value disclosures include the range and weighted average of significant unobservable inputs used to develop those fair value measurements. For certain unobservable inputs, an entity may disclose other quantitative information in lieu of the weighted average if the entity determines that other quantitative information would be a more reasonable and rational method to reflect the distribution of unobservable inputs used to develop Level 3 fair value measurements. ASU 2018-13 will be effective for the Company on January 1, 2020, with early adoption permitted, and is not expected to have a significant impact on its financial statements and disclosures. ASU 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. This ASU aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal use software license). The accounting for the service element of a hosting arrangement that is a service contract is not affected by these amendments. This ASU will be effective for the Company on January 1, 2020, with early adoption permitted, and is not expected to have a significant impact on its financial statements and disclosures. ASU 2019-12, Income Taxes (Topic 740) - Simplifying the Accounting for Income Taxes. The guidance issued in this update simplifies the accounting for income taxes by eliminating certain exceptions to the guidance in ASC 740 related to the approach for intraperiod tax allocation, the methodology for calculating income taxes in an interim period and the recognition for deferred tax liabilities for outside basis differences. ASU 2019-12 also simplifies aspects of the accounting for franchise taxes and enacted changes in tax laws or rates and clarifies the accounting for transactions that result in a step-up in the tax basis of goodwill. ASU 2019-12 will be effective for the Company on January 1, 2021, with early adoption permitted, and is not expected to have a significant impact on our financial statements.
Nonaccrual loan and lease status	The accrual of interest is discontinued on a loan when management believes, after considering collection efforts and other factors, that the borrower's financial condition is such that collection of interest is doubtful. All interest accrued but not collected for loans that are placed on nonaccrual status or charged-off is reversed against interest income. Cash collections on nonaccrual loans are generally credited to the loan receivable balance, and no interest income is recognized on those loans until the principal balance has been collected. Loans are returned to accrual status when all the principal and interest amounts contractually due are brought current and future payments are reasonably assured.
Impaired loan and lease receivable	Impaired loans are those loans where it is probable that all amounts due according to contractual terms of the loan agreement will not be collected. The Company has identified these loans through its normal loan review procedures. Impaired loans are measured based on 1) the present value of expected future cash flows discounted at the loan's effective interest rate; 2) the loan's observable market price; or 3) the fair value of collateral if the loan is collateral dependent. Substantially all of the Company’s impaired loans are measured at the fair value of the collateral. In limited cases, the Company may use other methods to determine the level of impairment of a loan if such loan is not collateral dependent.
Loan charge off amounts	The Company will charge-off that portion of any loan which management considers a loss. Commercial and real estate loans are generally considered for charge-off when exposure beyond collateral coverage is apparent and when no further collection of the loss portion is anticipated based on the borrower’s financial condition.
Trouble debt restructuring	The restructuring of a loan is considered a “troubled debt restructuring” if both 1) the borrower is experiencing financial difficulties and 2) the creditor has granted a concession. Concessions may include interest rate reductions or below market interest rates, principal forgiveness, extending amortization and other actions intended to minimize potential losses.
Loans past due	Loans are considered past due if the required principal and interest payments have not been received as of the date such payments were due.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Earnings Per Share	The following table presents a reconciliation of net income available to common shareholders and the number of shares used in the calculation of basic and diluted earnings per common share. Years Ended December 31, 2019 2018 2017 Basic earnings per share: Net income $ 192,736 $ 128,259 $ 76,512 Less: Undistributed earnings allocated to participating securities 971 976 626 Dividends paid on participating securities 281 139 97 Net income available to common shareholders $ 191,484 $ 127,144 $ 75,789 Weighted average basic shares outstanding 42,964,393 29,341,843 25,394,079 Basic earnings per share $ 4.46 $ 4.33 $ 2.98 Diluted earnings per share: Net income available to common shareholders $ 191,484 $ 127,144 $ 75,789 Total weighted average basic shares outstanding 42,964,393 29,341,843 25,394,079 Add dilutive stock warrants — — 106,070 Total weighted average diluted shares outstanding 42,964,393 29,341,843 25,500,149 Diluted earnings per share $ 4.46 $ 4.33 $ 2.97 Anti-dilutive participating securities 73,546 114,087 123,564

Statement of Cash Flows (Tables

Statement of Cash Flows (Tables)	12 Months Ended
	Dec. 31, 2019
Supplemental Cash Flow Elements [Abstract]
Other Supplemental Cash Flow Information	Other supplemental cash flow information is presented below: Years Ended December 31, 2019 2018 2017 Cash transactions: Interest expense paid $ 144,775 $ 79,509 $ 41,802 Income taxes paid $ 40,504 $ 25,109 $ 34,161 Noncash transactions: Transfers of loans to other real estate owned $ 544 $ 410 $ 1,201 Loans to facilitate the sale of other real estate owned $ 517 $ — $ — Securities purchased, not yet settled $ 9,975 $ — $ — Transfers of loans held for investment to loans held for sale $ 83,526 $ — $ — Right-of-use assets obtained in exchange for lease liabilities $ 35,553 $ — $ — Transfer of bank premises to other real estate $ 7,896 $ — $ 2,716 Transfer of repurchase agreements to deposits $ 8,475 $ — $ 8,845 Supplemental schedule of noncash investing activities from branch sales is as follows: Years ended December 31, 2019 2018 2017 Noncash assets transferred: Loans, including accrued interest $ 796 $ — $ 106,008 Premises and equipment 94 — 7,473 Core deposit intangible assets, net — — 3,011 Other assets 2 — 74 Total assets $ 892 $ — $ 116,566 Noncash liabilities transferred: Deposits, including interest $ 27,721 $ — $ 178,279 Other liabilities 27 — 129 Total liabilities $ 27,748 $ — $ 178,408 Cash and cash equivalents transferred in branch sales $ 206 $ — $ 1,712 Deposit premium received $ 1,386 $ — $ 7,107 Cash paid to buyer, net of deposit premium $ 24,957 $ — $ 56,975 Supplemental schedule of noncash investing activities from sale of trust business during 2019 is as follows: Year ended December 31, 2019 Noncash assets transferred: Customer relationship intangible assets, net $ 2,939 Other assets 11 Total assets $ 2,950 Net cash received from sale $ 4,269 Supplemental schedule of noncash investing activities from acquisitions is as follows: Years ended December 31, 2019 2018 2017 Noncash assets acquired Certificates of deposit held in other banks $ 262 $ — $ 11,025 Securities available for sale 561,052 24,721 336,540 Restricted stock 27,794 3,357 11,110 Loans 2,789,868 651,769 1,384,210 Premises and equipment 65,786 4,863 63,166 Other real estate owned 1,829 — 11,212 Goodwill 272,224 100,339 363,139 Other intangible assets 71,518 7,537 36,717 Bank owned life insurance 80,837 8,181 53,213 Other assets 31,987 6,385 25,379 Total assets acquired $ 3,903,157 $ 807,152 $ 2,295,711 Noncash liabilities assumed: Deposits $ 3,108,810 $ 593,078 $ 1,825,181 Repurchase agreements 8,475 — 18,003 FHLB advances 142,653 60,000 — Other borrowings 40,000 — — Junior subordinated debentures 25,774 — 9,359 Other liabilities 15,477 10,518 7,697 Total liabilities assumed $ 3,341,189 $ 663,596 $ 1,860,240 Cash and cash equivalents acquired from acquisitions $ 39,913 $ 44,723 $ 148,444 Cash paid to shareholders of acquired banks $ 9 $ 31,016 $ 17,773 Fair value of common stock issued to shareholders of acquired banks $ 601,872 $ 157,263 $ 566,142

Securities Available for Sale (

Securities Available for Sale (Tables)	12 Months Ended
	Dec. 31, 2019
Debt Securities, Available-for-sale [Abstract]
Amortized Cost of Securities and Approximate Fair Values	The amortized cost of securities and their approximate fair values at December 31, 2019 and 2018 , are as follows: Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Securities Available for Sale December 31, 2019 U.S. treasuries $ 48,060 $ 743 $ (7 ) $ 48,796 Government agency securities 178,953 926 (583 ) 179,296 Obligations of state and municipal subdivisions 332,715 11,150 (6 ) 343,859 Corporate bonds 7,011 207 — 7,218 Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 493,915 11,981 (329 ) 505,567 Other securities 1,200 — — 1,200 $ 1,061,854 $ 25,007 $ (925 ) $ 1,085,936 December 31, 2018 U.S. treasuries $ 30,110 $ — $ (467 ) $ 29,643 Government agency securities 152,969 80 (2,819 ) 150,230 Obligations of state and municipal subdivisions 187,366 727 (3,086 ) 185,007 Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 326,168 128 (5,826 ) 320,470 $ 696,613 $ 935 $ (12,198 ) $ 685,350
Proceeds from Sale, Gross Gains and Losses of Securities Available for Sale	Proceeds from sale of securities available for sale and gross gains and gross losses for the years ended December 31, 2019 , 2018 and 2017 were as follows: Years Ended December 31, 2019 2018 2017 Proceeds from sale $ 192,417 $ 102,647 $ 31,367 Gross gains $ 306 $ 268 $ 176 Gross losses $ 31 $ 849 $ 52
Amortized Cost and Estimated Fair Value of Securities Available for Sale by Contractual Maturity	The amortized cost and estimated fair value of securities available for sale at December 31, 2019 , by contractual maturity, are shown below. Maturities of mortgage-backed securities will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. December 31, 2019 Securities Available for Sale Amortized Cost Fair Value Due in one year or less $ 34,050 $ 34,088 Due from one year to five years 181,742 184,903 Due from five to ten years 162,396 166,337 Thereafter 189,751 195,041 567,939 580,369 Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 493,915 505,567 $ 1,061,854 $ 1,085,936
Summary of Unrealized Losses and Fair Value Securities in Continuous Unrealized Loss Position	The number of securities, unrealized losses and fair value, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, as of December 31, 2019 and 2018 , are summarized as follows: Less Than 12 Months Greater Than 12 Months Total Description of Securities Number of Securities Estimated Fair Value Unrealized Losses Number of Securities Estimated Fair Value Unrealized Losses Estimated Fair Value Unrealized Losses Securities Available for Sale December 31, 2019 U.S. treasuries — $ — $ — 2 $ 8,097 $ (7 ) $ 8,097 $ (7 ) Government agency securities 13 52,790 (495 ) 6 15,911 (88 ) 68,701 (583 ) Obligations of state and municipal subdivisions 5 2,793 (1 ) 1 423 (5 ) 3,216 (6 ) Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 13 46,512 (317 ) 1 1,193 (12 ) 47,705 (329 ) 31 $ 102,095 $ (813 ) 10 $ 25,624 $ (112 ) $ 127,719 $ (925 ) December 31, 2018 U.S. treasuries 1 $ 9,749 $ (6 ) 5 $ 19,894 $ (461 ) $ 29,643 $ (467 ) Government agency securities 4 6,068 (32 ) 43 126,745 (2,787 ) 132,813 (2,819 ) Obligations of state and municipal subdivisions 88 32,493 (326 ) 218 105,817 (2,760 ) 138,310 (3,086 ) Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 56 112,114 (1,031 ) 101 186,713 (4,795 ) 298,827 (5,826 ) 149 $ 160,424 $ (1,395 ) 367 $ 439,169 $ (10,803 ) $ 599,593 $ (12,198 )

Loans, Net and Allowance for _2

Loans, Net and Allowance for Loan Losses (Tables)	12 Months Ended
	Dec. 31, 2019
Receivables [Abstract]
Compositions of Loans	Loans, net at December 31, 2019 and 2018 , consisted of the following: December 31, 2019 2018 Commercial $ 2,482,356 $ 1,361,104 Real estate: Commercial 5,872,653 4,141,356 Commercial construction, land and land development 1,236,623 905,421 Residential 1,515,227 1,049,521 Single-family interim construction 378,120 331,748 Agricultural 97,767 66,638 Consumer 32,603 31,759 Other 621 253 11,615,970 7,887,800 Deferred loan fees (1,695 ) (3,303 ) Allowance for loan losses (51,461 ) (44,802 ) $ 11,562,814 $ 7,839,695
Summary of Activity in Allowance for Loan Losses by Loan Class	The following is a summary of the activity in the allowance for loan losses by loan class for the years ended December 31, 2019 , 2018 and 2017 : Commercial Commercial Real Estate, Construction, Land and Land Development Residential Real Estate Single-Family Interim Construction Agricultural Consumer Other Unallocated Total Year ended December 31, 2019 Balance at beginning of year $ 11,793 $ 27,795 $ 3,320 $ 1,402 $ 241 $ 186 $ 3 $ 62 $ 44,802 Provision for loan losses 8,670 5,289 498 207 91 71 356 (377 ) 14,805 Charge-offs (7,709 ) (3 ) (140 ) (3 ) — (79 ) (430 ) — (8,364 ) Recoveries 90 4 — — — 48 76 — 218 Balance at end of year $ 12,844 $ 33,085 $ 3,678 $ 1,606 $ 332 $ 226 $ 5 $ (315 ) $ 51,461 Year ended December 31, 2018 Balance at beginning of year $ 10,599 $ 23,301 $ 3,447 $ 1,583 $ 250 $ 205 $ (32 ) $ 49 $ 39,402 Provision for loan losses 4,973 4,909 (124 ) (181 ) (9 ) 69 210 13 9,860 Charge-offs (3,863 ) (435 ) (6 ) — — (93 ) (228 ) — (4,625 ) Recoveries 84 20 3 — — 5 53 — 165 Balance at end of year $ 11,793 $ 27,795 $ 3,320 $ 1,402 $ 241 $ 186 $ 3 $ 62 $ 44,802 Year ended December 31, 2017 Balance at beginning of year $ 8,593 $ 18,399 $ 2,760 $ 1,301 $ 207 $ 242 $ 29 $ 60 $ 31,591 Provision for loan losses 2,059 4,886 683 416 43 99 90 (11 ) 8,265 Charge-offs (81 ) (15 ) — (134 ) — (182 ) (190 ) — (602 ) Recoveries 28 31 4 — — 46 39 — 148 Balance at end of year $ 10,599 $ 23,301 $ 3,447 $ 1,583 $ 250 $ 205 $ (32 ) $ 49 $ 39,402 The following table details the amount of the allowance for loan losses and recorded investment in loans by class as of December 31, 2019 and 2018 : Commercial Commercial Residential Real Estate Single-Family Interim Construction Agricultural Consumer Other Unallocated Total December 31, 2019 Allowance for losses: Individually evaluated for impairment $ 357 $ — $ — $ — $ — $ 1 $ — $ — $ 358 Collectively evaluated for impairment 12,108 32,615 3,678 1,606 332 225 5 (315 ) 50,254 Loans acquired with deteriorated credit quality 379 470 — — — — — — 849 Ending balance $ 12,844 $ 33,085 $ 3,678 $ 1,606 $ 332 $ 226 $ 5 $ (315 ) $ 51,461 Loans: Individually evaluated for impairment $ 3,130 $ 6,813 $ 2,008 $ — $ 114 $ 22 $ — $ — $ 12,087 Collectively evaluated for impairment 2,416,569 6,883,639 1,505,896 378,120 93,837 32,556 621 — 11,311,238 Acquired with deteriorated credit quality 62,657 218,824 7,323 — 3,816 25 — — 292,645 Ending balance $ 2,482,356 $ 7,109,276 $ 1,515,227 $ 378,120 $ 97,767 $ 32,603 $ 621 $ — $ 11,615,970 December 31, 2018 Allowance for losses: Individually evaluated for impairment $ 2,633 $ — $ 92 $ — $ — $ 2 $ — $ — $ 2,727 Collectively evaluated for impairment 9,115 27,795 3,228 1,402 241 184 3 62 42,030 Loans acquired with deteriorated credit quality 45 — — — — — — — 45 Ending balance $ 11,793 $ 27,795 $ 3,320 $ 1,402 $ 241 $ 186 $ 3 $ 62 $ 44,802 Loans: Individually evaluated for impairment $ 7,288 $ 1,734 $ 1,943 $ 3,578 $ — $ 32 $ — $ — $ 14,575 Collectively evaluated for impairment 1,335,194 4,955,178 1,044,265 328,170 66,032 31,699 253 — 7,760,791 Acquired with deteriorated credit quality 18,622 89,865 3,313 — 606 28 — — 112,434 Ending balance $ 1,361,104 $ 5,046,777 $ 1,049,521 $ 331,748 $ 66,638 $ 31,759 $ 253 $ — $ 7,887,800
Summary of Nonperforming Loans by Loan Class	Nonperforming loans by loan class (excluding loans acquired with deteriorated credit quality) at December 31, 2019 and 2018 , are summarized as follows: Commercial Commercial Residential Real Estate Single-Family Interim Construction Agricultural Consumer Other Total December 31, 2019 Nonaccrual loans $ 3,130 $ 6,461 $ 1,820 $ — $ 114 $ 22 $ — $ 11,547 Loans past due 90 days and still accruing 14,529 — — — — — — 14,529 Troubled debt restructurings (not included in nonaccrual or loans past due and still accruing) — 352 188 — — — — 540 $ 17,659 $ 6,813 $ 2,008 $ — $ 114 $ 22 $ — $ 26,616 December 31, 2018 Nonaccrual loans $ 5,224 $ 1,329 $ 1,775 $ 3,578 $ — $ 32 $ — $ 11,938 Loans past due 90 days and still accruing — — — — — 5 — 5 Troubled debt restructurings (not included in nonaccrual or loans past due and still accruing) 114 405 168 — — — — 687 $ 5,338 $ 1,734 $ 1,943 $ 3,578 $ — $ 37 $ — $ 12,630
Impaired Loans by Loan Class	Impaired loans by loan class (excluding loans acquired with deteriorated credit quality) at December 31, 2019 and 2018 and for the years ended December 31, 2019 , 2018 and 2017 , are summarized as follows: Commercial Commercial Residential Real Estate Single-Family Interim Construction Agricultural Consumer Other Total December 31, 2019 Recorded investment in impaired loans: Impaired loans with an allowance for loan losses $ 1,580 $ — $ — $ — $ — $ 1 $ — $ 1,581 Impaired loans with no allowance for loan losses 1,550 6,813 2,008 — 114 21 — 10,506 Total $ 3,130 $ 6,813 $ 2,008 $ — $ 114 $ 22 $ — $ 12,087 Unpaid principal balance of impaired loans $ 8,580 $ 6,967 $ 2,197 $ — $ 123 $ 24 $ — $ 17,891 Allowance for loan losses on impaired loans $ 357 $ — $ — $ — $ — $ 1 $ — $ 358 December 31, 2018 Recorded investment in impaired loans: Impaired loans with an allowance for loan losses $ 6,416 $ — $ 134 $ — $ — $ 1 $ — $ 6,551 Impaired loans with no allowance for loan losses 872 1,734 1,809 3,578 — 31 — 8,024 Total $ 7,288 $ 1,734 $ 1,943 $ 3,578 $ — $ 32 $ — $ 14,575 Unpaid principal balance of impaired loans $ 9,822 $ 1,860 $ 2,056 $ 3,579 $ — $ 38 $ — $ 17,355 Allowance for loan losses on impaired loans $ 2,633 $ — $ 92 $ — $ — $ 2 $ — $ 2,727 For the year ended December 31, 2019 Average recorded investment in impaired loans $ 6,266 $ 3,979 $ 1,746 $ 716 $ 57 $ 30 $ — $ 12,794 Interest income recognized on impaired loans $ 30 $ 39 $ 39 $ 119 $ — $ 6 $ — $ 233 For the year ended December 31, 2018 Average recorded investment in impaired loans $ 8,919 $ 2,667 $ 2,033 $ 716 $ — $ 46 $ — $ 14,381 Interest income recognized on impaired loans $ 119 $ 65 $ 81 $ 1 $ — $ 2 $ — $ 268 For the year ended December 31, 2017 Average recorded investment in impaired loans $ 8,524 $ 3,690 $ 2,431 $ 177 $ — $ 218 $ — $ 15,040 Interest income recognized on impaired loans $ 8 $ 428 $ 58 $ — $ — $ 5 $ — $ 499
Summary of Troubled Debt Restructurings	Following is a summary of loans modified under troubled debt restructurings during the years ended December 31, 2019 and 2018 : Commercial Commercial Residential Real Estate Single-Family Interim Construction Agricultural Consumer Other Total Troubled debt restructurings during the year ended December 31, 2019 Number of contracts — — 1 — — — — 1 Pre-restructuring outstanding recorded investment $ — $ — $ 29 $ — $ — $ — $ — $ 29 Post-restructuring outstanding recorded investment $ — $ — $ 29 $ — $ — $ — $ — $ 29 Troubled debt restructurings during the year ended December 31, 2018 Number of contracts 1 — — — — — — 1 Pre-restructuring outstanding recorded investment $ 114 $ — $ — $ — $ — $ — $ — $ 114 Post-restructuring outstanding recorded investment $ 114 $ — $ — $ — $ — $ — $ — $ 114
Aging of Past Due Loans by Loan Class	The following table presents information regarding the aging of past due loans by loan class as of December 31, 2019 and 2018 : Loans 30-89 Days Past Due Loans 90 Days or More Past Due Total Past Due Loans Current Loans Total Loans December 31, 2019 Commercial $ 4,512 $ 17,656 $ 22,168 $ 2,397,531 $ 2,419,699 Commercial real estate, construction, land and land development 9,153 2,905 12,058 6,878,394 6,890,452 Residential real estate 3,242 642 3,884 1,504,020 1,507,904 Single-family interim construction 2,836 — 2,836 375,284 378,120 Agricultural 22 114 136 93,815 93,951 Consumer 167 22 189 32,389 32,578 Other — — — 621 621 19,932 21,339 41,271 11,282,054 11,323,325 Acquired with deteriorated credit quality 2,556 6,766 9,322 283,323 292,645 $ 22,488 $ 28,105 $ 50,593 $ 11,565,377 $ 11,615,970 December 31, 2018 Commercial $ 15,426 $ 4,366 $ 19,792 $ 1,322,690 $ 1,342,482 Commercial real estate, construction, land and land development 3,435 — 3,435 4,953,477 4,956,912 Residential real estate 4,199 1,035 5,234 1,040,974 1,046,208 Single-family interim construction 774 3,578 4,352 327,396 331,748 Agricultural — — — 66,032 66,032 Consumer 135 35 170 31,561 31,731 Other — — — 253 253 23,969 9,014 32,983 7,742,383 7,775,366 Acquired with deteriorated credit quality 2,939 957 3,896 108,538 112,434 $ 26,908 $ 9,971 $ 36,879 $ 7,850,921 $ 7,887,800
Summary of Loans by Credit Quality Indicator by Class	The Company has included PCI loans in the above grading tables. The following provides additional detail on the grades applied to those loans at December 31, 2019 and 2018: Pass Pass/ Special Mention Substandard Doubtful Total December 31, 2019 $ 232,095 $ 21,284 $ 4,502 $ 34,764 $ — $ 292,645 December 31, 2018 40,940 32,427 14,817 24,250 — 112,434 A summary of loans by credit quality indicator by class as of December 31, 2019 and 2018 , is as follows: Pass Pass/ Watch Special Mention Substandard Doubtful Total December 31, 2019 Commercial $ 2,332,611 $ 71,642 $ 37,739 $ 40,364 $ — $ 2,482,356 Commercial real estate, construction, land and land development 6,814,780 184,720 46,889 62,887 — 7,109,276 Residential real estate 1,501,019 4,850 994 8,364 — 1,515,227 Single-family interim construction 376,887 1,233 — — — 378,120 Agricultural 88,044 5,287 1,864 2,572 — 97,767 Consumer 32,459 33 2 109 — 32,603 Other 621 — — — — 621 $ 11,146,421 $ 267,765 $ 87,488 $ 114,296 $ — $ 11,615,970 December 31, 2018 Commercial $ 1,279,024 $ 18,378 $ 30,783 $ 32,919 $ — $ 1,361,104 Commercial real estate, construction, land and land development 4,895,217 81,693 40,601 29,266 — 5,046,777 Residential real estate 1,038,283 3,617 707 6,914 — 1,049,521 Single-family interim construction 327,939 — 231 3,578 — 331,748 Agricultural 61,055 2,918 2,093 572 — 66,638 Consumer 31,559 67 — 133 — 31,759 Other 253 — — — — 253 $ 7,633,330 $ 106,673 $ 74,415 $ 73,382 $ — $ 7,887,800
Outstanding balance and related carrying amount of purchased credit impaired loans	The following table summarizes the outstanding balance and related carrying amount of purchased credit impaired loans by acquired bank as of the acquisition date for the acquisitions occurring in 2019 and 2018 . Acquisition Date January 1, 2019 June 1, 2018 Guaranty Bancorp Integrity Bancshares, Inc. Outstanding balance $ 341,645 $ 57,317 Nonaccretable difference (16,622 ) (9,969 ) Accretable yield (13,299 ) (128 ) Carrying amount $ 311,724 $ 47,220 The carrying amount of all acquired PCI loans included in the consolidated balance sheet and the related outstanding balance at December 31, 2019 and 2018 , were as follows: December 31, 2019 2018 Outstanding balance $ 326,077 $ 129,333 Carrying amount 292,645 112,434
Accretable yield rollforward	The changes in accretable yield during the years ended December 31, 2019 and 2018 in regard to loans transferred at acquisition for which it was probable that all contractually required payments would not be collected are presented in the table below. 2019 2018 Balance at January 1 $ 1,436 $ 1,546 Additions 13,299 128 Accretion (5,830 ) (1,557 ) Transfers from nonaccretable — 1,319 Balance at December 31 $ 8,905 $ 1,436

Premises and Equipment, Net (Ta

Premises and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Components of Premises and Equipment, Net	Premises and equipment, net at December 31, 2019 and 2018 consisted of the following: December 31, 2019 2018 Land $ 58,643 $ 43,746 Building 184,589 93,793 Furniture, fixtures and equipment 39,855 34,602 Aircraft 8,947 8,947 Leasehold and tenant improvements 5,466 4,638 Construction in progress 834 32,399 298,334 218,125 Less accumulated depreciation (55,460 ) (50,259 ) $ 242,874 $ 167,866

Goodwill and Core Deposit Int_2

Goodwill and Core Deposit Intangible, Net (Tables)	12 Months Ended
	Dec. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Summary of Other Intangible Assets Activity	The following is a summary of other intangible assets activity: December 31, 2019 2018 Core deposit intangible: Balance at beginning of the year $ 63,891 $ 56,354 Additions: Guaranty and Integrity acquisitions 61,993 7,537 Balance at end of the year 125,884 63,891 Less accumulated amortization (31,057 ) (18,849 ) Total core deposit intangible, net 94,827 45,042 Customer relationship intangible: Balance at beginning of the year — — Additions: Guaranty acquisition 9,525 — Deletions: sale of trust business (3,118 ) — Balance at end of the year 6,407 — Less accumulated amortization (493 ) — Total customer relationship intangible, net 5,914 — Total other intangible assets, net $ 100,741 $ 45,042
Future Amortization Expense Related to Other Intangible Assets	The future amortization expense related to other intangible assets remaining at December 31, 2019 is as follows: First year $ 12,671 Second year 12,580 Third year 12,492 Fourth year 12,439 Fifth year 11,752 Thereafter 38,807 $ 100,741

Deposits (Tables)

Deposits (Tables)	12 Months Ended
	Dec. 31, 2019
Banking and Thrift [Abstract]
Components of Deposits	Deposits at December 31, 2019 and 2018 consisted of the following: December 31, 2019 2018 Amount Percent Amount Percent Noninterest-bearing demand accounts $ 3,240,185 27.1 % $ 2,145,930 27.7 % Interest-bearing checking accounts 4,198,772 35.2 2,892,318 37.4 Savings accounts 552,585 4.6 293,108 3.8 Limited access money market accounts 2,119,878 17.8 1,286,135 16.6 Certificates of deposit and individual retirement accounts (IRA), less than $250,000 892,639 7.5 559,016 7.2 Certificates of deposit and individual retirement accounts (IRA), $250,000 and greater 937,277 7.8 561,287 7.3 $ 11,941,336 100.0 % $ 7,737,794 100.0 %
Maturities of Certificates of Deposit	At December 31, 2019 , the scheduled maturities of certificates of deposit, including IRAs, were as follows: First year $ 1,531,507 Second year 245,339 Third year 32,216 Fourth year 15,373 Fifth year 5,481 Thereafter — $ 1,829,916

Federal Home Loan Bank Advanc_2

Federal Home Loan Bank Advances (Tables)	12 Months Ended
	Dec. 31, 2019
Banking and Thrift [Abstract]
Contractual Maturities of FHLB Advances	Contractual maturities of FHLB advances at December 31, 2019 were as follows: First year $ 300,000 Second year 25,000 Third year — Fourth year — Fifth year — Thereafter — $ 325,000

Other Borrowings (Tables)

Other Borrowings (Tables)	12 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
Other borrowings	Other borrowings at December 31, 2019 and 2018 consisted of the following: December 31, 2019 2018 Unsecured fixed rate subordinated debentures in the amount of $110,000. The balance of borrowings at December 31, 2019 and 2018 is net of discount and origination costs of $1,628 and $1,986, respectively. Interest payments of 5.875% are made semiannually on February 1 and August 1. The maturity date is August 1, 2024. The notes may not be redeemed prior to maturity and meet the criteria to be recognized as Tier 2 capital for regulatory purposes. (1)(2) $ 108,372 $ 108,014 Unsecured fixed-to-floating subordinated debentures in the amount of $30,000. The balance of borrowings at December 31, 2019 and 2018 is net of origination costs of $621 and $698, respectively. Interest payments initially of 5.00% fixed rate are made semiannually on June 30 and December 31 through December 31, 2022. Thereafter, floating rate payments of 3 month LIBOR plus 2.83% are made quarterly in arrears on March 31, June 30, September 30, and December 31 through March 31, 2028. The maturity date is December 31, 2027 with an optional redemption at December 31, 2022. The notes meet the criteria to be recognized as Tier 2 capital for regulatory purposes. (2) 29,379 29,302 Unsecured fixed-to-floating subordinated debentures in the original amount of $40,000. Interest payments initially of 5.75% are made semiannually on January 20 and July 20 through July 20, 2021. Thereafter, floating rate payments of 3 month LIBOR plus 4.73% are made quarterly in arrears on October 20, January 20, April 20 and July 20 through October 20, 2026. The maturity date is July 20, 2026 with an optional redemption at July 20, 2021. The notes meet the criteria to be recognized as Tier 2 capital for regulatory purposes. (2)(3) 40,000 — Unsecured revolving line of credit with an unrelated commercial bank in the amount of $100,000. The line bears interest at LIBOR plus 1.75% and matures January 17, 2020. The Company is required to meet certain financial covenants on a quarterly basis, which includes certain restrictions on cash at IBG and meeting minimum capital ratios. (4) 24,500 — $ 202,251 $ 137,316 ____________ (1) At December 31, 2019 and 2018 , other borrowings included amounts owed to related parties of $50 . (2) The permissible portion of qualified subordinated notes decreases 20% per year during the final five years of the term of the notes. (3) Assumed on January 1, 2019 with the Guaranty acquisition (see Note 22 , Business Combinations). (4) Subsequent to December 31, 2019 , the Company renewed the line (see Note 24 , Subsequent Events).

Junior Subordinated Debentures

Junior Subordinated Debentures (Tables)	12 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
Schedule of Subordinated Borrowing	Information regarding the Debentures as of December 31, 2019 are summarized in the table below: Trust Preferred Securities Issued Debentures Carrying Value Repricing Frequency Interest Rate Interest Rate Index Maturity Date IB Trust I $ 5,155 $ 5,155 Quarterly 5.16% LIBOR + 3.25% March 2033 Guaranty Trust III (1) 10,310 10,310 Quarterly 5.09 LIBOR + 3.10 July 2033 IB Trust II 3,093 3,093 Quarterly 4.84 LIBOR + 2.85 March 2034 Cenbank Trust III (1) 15,464 15,464 Quarterly 4.65 LIBOR + 2.65 April 2034 IB Trust III 3,712 3,712 Quarterly 4.31 LIBOR + 2.40 December 2035 IB Centex Trust I 2,578 2,578 Quarterly 5.16 LIBOR + 3.25 February 2035 Community Group Statutory Trust I 3,609 3,609 Quarterly 3.49 LIBOR + 1.60 June 2037 Northstar Trust II (2) 5,155 3,815 Quarterly 3.56 LIBOR + 1.67 June 2037 Northstar Trust III (2) 8,248 6,088 Quarterly 3.56 LIBOR + 1.67 September 2037 $ 57,324 $ 53,824 ____________ (1) Assumed on January 1, 2019 with the Guaranty acquisition (see Note 22 , Business Combinations). (2) Assumed in 2017 with a recorded fair value discount of $3,500

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2019
Leases [Abstract]
Schedule of Net Lease Cost and Other Information Related to Operating Leases	The table below summarizes net lease cost: Year Ended December 31, 2019 Operating lease cost $ 7,128 Variable lease cost 1,829 Sublease income (228 ) Net lease cost $ 8,729 The table below summarizes other information related to operating leases: Year Ended December 31, 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ 6,965 Weighted average remaining lease term - operating leases, in years 7.58 Weighted average discount rate - operating leases 3.35 %
Summary of Lease Payment Obligations	The following table outlines lease payment obligations as outlined in the Company’s lease agreements for each of the next five years and thereafter in addition to a reconcilement to the Company’s current lease liability as of December 31, 2019 . 2020 $ 5,964 2021 5,784 2022 4,990 2023 4,213 2024 3,437 Thereafter 8,454 Total lease payments 32,842 Less imputed interest (3,864 ) $ 28,978

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Schedule of Income Tax Expense	Income tax expense for the years ended December 31, 2019 , 2018 and 2017 was as follows: Years Ended December 31, 2019 2018 2017 Current income tax expense $ 39,426 $ 29,801 $ 28,121 Deferred income tax expense 14,102 2,000 11,526 Deferred income tax (benefit) expense related to remeasurement of deferred taxes — (63 ) 5,528 Income tax expense, as reported $ 53,528 $ 31,738 $ 45,175
Schedule of Effective Income Tax Rate Reconciliation	A reconciliation between reported income tax expense and the amounts computed by applying the U.S. federal statutory income tax rate of 21% for the years ended December 31, 2019 and 2018 and 35% for the year ended December 31, 2017 to income before income taxes is presented below: Years Ended December 31, 2019 2018 2017 Income tax expense computed at the statutory rate $ 51,715 $ 33,599 $ 42,590 Tax-exempt interest income from municipal securities (1,781 ) (962 ) (1,357 ) Tax-exempt loan income (1,174 ) (490 ) (435 ) Bank owned life insurance income (1,288 ) (666 ) (962 ) Non-deductible acquisition expenses 281 142 491 State taxes, net of federal benefit 3,455 375 241 Non-deductible compensation 2,017 — — Net tax expense (benefit) from stock based compensation 21 (646 ) (1,323 ) Deferred tax adjustment related to reduction in U.S. Federal statutory income tax rate — (63 ) 5,528 Other 282 449 402 $ 53,528 $ 31,738 $ 45,175
Schedule of Deferred Tax Assets and Liabilities	Components of deferred tax assets and liabilities are presented in the table below. Deferred taxes as of December 31, 2019 and 2018 are based on the U.S. statutory federal income tax rate of 21%. December 31, 2019 2018 Deferred tax assets: Allowance for loan losses $ 11,466 $ 9,496 Lease liabilities under operating leases 6,457 — NOL and tax credit carryforwards from acquisitions 4,209 4,810 Net unrealized loss on available for sale securities — 2,365 Acquired loan fair market value adjustments 21,645 6,090 Stock-based compensation 1,218 987 Reserve for bonuses and other accrued expenses 2,773 1,646 Deferred loan fees 378 700 Acquisition costs 416 — Acquired Securities 2,529 273 Acquired intangibles 1,546 — Start up costs 230 274 Other real estate owned 362 273 Unearned income 774 160 Deferred compensation 1,101 1,266 Noncompete agreements 663 552 Nonaccrual loans 390 470 Other 407 303 56,564 29,665 Deferred tax liabilities: Premises and equipment (13,170 ) (5,242 ) Right-of-use assets under operating leases (6,233 ) — Net unrealized gain on available for sale securities (5,367 ) — Intangible assets (22,447 ) (9,547 ) Acquired junior subordinated debentures fair value adjustment (780 ) (777 ) Restricted stock (673 ) (250 ) Prepaids (281 ) (190 ) Acquired tax goodwill (413 ) (232 ) Other (257 ) (247 ) (49,621 ) (16,485 ) Net deferred tax asset $ 6,943 $ 13,180

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	At December 31, 2019 and 2018 , the approximate amounts of these financial instruments were as follows: December 31, 2019 2018 Commitments to extend credit $ 2,337,385 $ 1,761,724 Standby letters of credit 23,406 14,997 $ 2,360,791 $ 1,776,721

Related Party Transactions (Tab

Related Party Transactions (Tables)	12 Months Ended
	Dec. 31, 2019
Related Party Transactions [Abstract]
Loan Activity for Officers, Directors and Affiliates	Loan activity for officers, directors and their affiliates for the year ended December 31, 2019 is as follows: Balance at beginning of year $ 58,967 New loans 14,185 Repayments (31,366 ) Changes in affiliated persons (2,990 ) Balance at end of year $ 38,796

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Assets and Liabilities at Fair Value on Recurring Basis	The following table represents assets and liabilities reported on the consolidated balance sheets at their fair value on a recurring basis as of December 31, 2019 and 2018 by level within the ASC Topic 820 fair value measurement hierarchy: Fair Value Measurements at Reporting Date Using Assets/ Liabilities Measured at Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) December 31, 2019 Assets: Investment securities available for sale: U.S. treasuries $ 48,796 $ — $ 48,796 $ — Government agency securities 179,296 — 179,296 — Obligations of state and municipal subdivisions 343,859 — 343,859 — Corporate bonds 7,218 — 7,218 — Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 505,567 — 505,567 — Other securities 1,200 — 1,200 — Loans held for sale, fair value option elected (1) 29,204 — 29,204 — Derivative financial instruments: Interest rate lock commitments 847 — 847 — Forward mortgage-backed securities trades 6 — 6 — Loan customer counterparty 6,104 — 6,104 — Liabilities: Derivative financial instruments: Forward mortgage-backed securities trades 69 — 69 — Financial institution counterparty 6,566 — 6,566 — December 31, 2018 Assets: Investment securities available for sale: U.S. treasuries $ 29,643 $ — $ 29,643 $ — Government agency securities 150,230 — 150,230 — Obligations of state and municipal subdivisions 185,007 — 185,007 — Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 320,470 — 320,470 — Loans held for sale, fair value option elected (1) 27,871 — 27,871 — Derivative financial instruments: Interest rate lock commitments 822 — 822 — Loan customer counterparty 360 — 360 — Financial institution counterparty 109 — 109 — Liabilities: Derivative financial instruments: Forward mortgage-backed securities trades 226 — 226 — Loan customer counterparty 108 — 108 — Financial institution counterparty 406 — 406 — ____________ (1) At December 31, 2019 and 2018 , loans held for sale for which the fair value option was elected had an aggregate outstanding principal balance of $28,166 and $26,594 , respectively. There were no mortgage loans held for sale under the fair value option that were 90 days or greater past due or on nonaccrual at December 31, 2019 .
Assets and Liabilities at Fair Value on Nonrecurring Basis	The following table presents the assets carried on the consolidated balance sheet by caption and by level in the fair value hierarchy at December 31, 2019 and 2018 , for which a nonrecurring change in fair value has been recorded: Fair Value Measurements at Reporting Date Using Assets Measured at Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Period Ended Total Losses December 31, 2019 Assets: Impaired loans $ 2,276 $ — $ — $ 2,276 $ 1,806 Other real estate owned 4,618 — — 4,618 749 December 31, 2018 Assets: Impaired loans $ 3,824 $ — $ — $ 3,824 $ 2,227
Carrying Amount and Estimated Fair Value of Financial Instruments	The carrying amount, estimated fair value and the level of the fair value hierarchy of the Company’s financial instruments that are reported at amortized cost on the Company's consolidated balance sheets were as follows at December 31, 2019 and 2018 : Fair Value Measurements at Reporting Date Using Carrying Amount Estimated Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) December 31, 2019 Financial assets: Cash and cash equivalents $ 565,170 $ 565,170 $ 565,170 $ — $ — Certificates of deposit held in other banks 5,719 5,951 — 5,951 — Loans held for sale, at cost 6,441 6,554 — 6,554 — Loans, net 11,562,814 11,689,672 — — 11,689,672 FHLB of Dallas stock and other restricted stock 30,052 30,052 — 30,052 — Accrued interest receivable 35,860 35,860 — 35,860 — Financial liabilities: Deposits 11,941,336 11,958,939 — 11,958,939 — Accrued interest payable 9,583 9,583 — 9,583 — FHLB advances 325,000 325,210 — 325,210 — Other borrowings 202,251 209,050 — 209,050 — Junior subordinated debentures 53,824 48,879 — 48,879 — Off-balance sheet assets (liabilities): Commitments to extend credit — — — — — Standby letters of credit — — — — — December 31, 2018 Financial assets: Cash and cash equivalents $ 130,779 $ 130,779 $ 130,779 $ — $ — Certificates of deposit held in other banks 1,225 1,224 — 1,224 — Loans held for sale, at cost 4,856 4,974 — 4,974 — Loans, net 7,839,695 7,807,823 — — 7,807,823 FHLB of Dallas stock and other restricted stock 26,870 26,870 — 26,870 — Accrued interest receivable 24,253 24,253 — 24,253 — Financial liabilities: Deposits 7,737,794 7,750,059 — 7,750,059 — Accrued interest payable 6,183 6,183 — 6,183 — FHLB advances 290,000 287,450 — 287,450 — Other borrowings 137,316 138,450 — 138,450 — Junior subordinated debentures 27,852 31,370 — 31,370 — Off-balance sheet assets (liabilities): Commitments to extend credit — — — — — Standby letters of credit — — — — —

Derivative Financial Instrume_2

Derivative Financial Instruments - (Tables)	12 Months Ended
	Dec. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Notional Balances and Fair Values of Outstanding Positions	The following table provides the outstanding notional balances and fair values of outstanding derivative positions at December 31, 2019 and 2018 : Outstanding Notional Balance Asset Derivative Fair Value Liability Derivative Fair Value December 31, 2019 Interest rate lock commitments $ 28,434 $ 847 $ — Forward mortgage-backed securities trades 42,500 6 69 Commercial loan interest rate swaps: Loan customer counterparty 280,751 6,104 — Financial institution counterparty 280,751 — 6,566 December 31, 2018 Interest rate lock commitments $ 20,306 $ 822 $ — Forward mortgage-backed securities trades 27,500 — 226 Commercial loan interest rate swaps: Loan customer counterparty 25,055 360 108 Financial institution counterparty 25,055 109 406
Schedule of Weighted Average Interest Rate Received and Paid	The commercial loan customer counterparty weighted average received and paid interest rates for interest rate swaps outstanding were as follows: Weighted Average Interest Rate December 31, 2019 December 31, 2018 Received Paid Received Paid Loan customer counterparty 4.23 % 3.77 % 4.67 % 4.46 %
Income (Loss) on Derivatives Not Designated as Hedging Instruments	Income (loss) for the years ended December 31, 2019 and 2018 was as follows: Years Ended December 31, 2019 2018 Derivatives not designated as hedging instruments Interest rate lock commitments $ 25 $ 822 Forward mortgage-backed securities trades 163 (226 )

Stock Awards (Tables)

Stock Awards (Tables)	12 Months Ended
	Dec. 31, 2019
Share-based Payment Arrangement [Abstract]
Nonvested Shares Activity	The following table summarizes the activity in nonvested shares for the years ended December 31, 2019 and 2018 : Number of Shares Weighted Average Grant Date Fair Value Nonvested shares, December 31, 2018 252,903 $ 62.81 Acquired awards replaced during the period 70,248 45.77 Granted during the period 138,608 51.14 Vested during the period (161,032 ) 54.76 Forfeited during the period (15,866 ) 46.95 Nonvested shares, December 31, 2019 284,861 $ 58.63 Nonvested shares, December 31, 2017 242,056 $ 49.17 Granted during the period 130,212 71.85 Vested during the period (115,520 ) 44.36 Forfeited during the period (3,845 ) 64.47 Nonvested shares, December 31, 2018 252,903 $ 62.81
Future Vesting Schedule of Nonvested Shares Activity	At December 31, 2019 , the future vesting schedule of the nonvested shares is as follows: First year 105,390 Second year 96,125 Third year 62,006 Fourth year 19,260 Fifth year 2,080 Total nonvested shares 284,861

Regulatory Matters (Tables)

Regulatory Matters (Tables)	12 Months Ended
	Dec. 31, 2019
Regulated Operations [Abstract]
Schedule of Compliance with Regulatory Capital Requirements	The following table presents the actual capital amounts and required ratios of the Company and Bank as of December 31, 2019 and 2018. The minimum required capital amounts presented as of December 31, 2019 include the minimum required capital levels as of January 1, 2019 when the Basel III Capital Rules have been fully phased-in. Actual Minimum for Capital Adequacy Purposes To Be Well Capitalized Under Prompt Corrective Action Provisions Amount Ratio Amount Ratio Amount Ratio December 31, 2019 Total capital to risk weighted assets: Consolidated $ 1,513,209 11.83 % $ 1,343,114 10.50 % N/A N/A Bank 1,548,103 12.11 1,342,595 10.50 $ 1,278,662 10.00 % Tier 1 capital to risk weighted assets: Consolidated 1,303,748 10.19 1,087,282 8.50 N/A N/A Bank 1,496,642 11.70 1,086,863 8.50 1,022,930 8.00 Common equity tier 1 to risk weighted assets: Consolidated 1,248,148 9.76 895,409 7.00 N/A N/A Bank 1,496,642 11.70 895,064 7.00 831,130 6.50 Tier 1 capital to average assets: Consolidated 1,303,748 9.32 559,758 4.00 N/A N/A Bank 1,496,642 10.70 559,584 4.00 699,480 5.00 December 31, 2018 Total capital to risk weighted assets: Consolidated $ 1,072,156 12.58 % $ 681,686 8.00 % N/A N/A Bank 1,054,783 12.39 681,004 8.00 $ 851,255 10.00 % Tier 1 capital to risk weighted assets: Consolidated 887,354 10.41 511,264 6.00 N/A N/A Bank 1,009,981 11.86 510,753 6.00 681,004 8.00 Common equity tier 1 to risk weighted assets: Consolidated 856,754 10.05 383,448 4.50 N/A N/A Bank 1,009,981 11.86 383,065 4.50 553,316 6.50 Tier 1 capital to average assets: Consolidated 887,354 9.57 370,727 4.00 N/A N/A Bank 1,009,981 10.91 370,412 4.00 463,015 5.00

Business Combinations (Tables)

Business Combinations (Tables)	12 Months Ended
	Dec. 31, 2019
Business Combinations [Abstract]
Estimated Fair Values of Assets Acquired and Liabilities Assumed	The following table summarizes the final fair values of the assets acquired and liabilities assumed in this transaction as of the closing date and subsequent measurement period adjustments are as follows: Initially Recorded at Acquisition Date Measurement Period Adjustments Adjusted Values as of December 31, 2019 Assets of acquired bank: Cash and cash equivalents $ 39,913 $ — $ 39,913 Certificates of deposit held in other banks 262 — 262 Securities available for sale 561,052 — 561,052 Restricted stock 27,794 — 27,794 Loans 2,788,159 1,709 2,789,868 Premises and equipment 65,786 — 65,786 Other real estate owned 1,710 119 1,829 Goodwill 270,583 1,641 272,224 Other intangible assets 71,518 — 71,518 Bank owned life insurance 80,837 — 80,837 Other assets 31,517 470 31,987 Total assets acquired $ 3,939,131 $ 3,939 $ 3,943,070 Liabilities of acquired bank: Deposits $ 3,108,810 $ — $ 3,108,810 Repurchase agreements 8,475 — 8,475 FHLB advances 142,653 — 142,653 Other borrowings 40,000 — 40,000 Junior subordinated debentures 25,774 — 25,774 Other liabilities 11,538 3,939 15,477 Total liabilities assumed $ 3,337,250 $ 3,939 $ 3,341,189 Common stock of 13,109,500 issued at $45.77 per share $ 600,022 $ — $ 600,022 Consideration attributable to 70,248 shares of restricted stock replacement awards $ 1,850 $ — $ 1,850 Cash paid $ 9 $ — $ 9 The following table summarizes the final fair values of the assets acquired and liabilities in this transaction: Final Value as reported at December 31, 2018 Assets of acquired bank: Cash and cash equivalents $ 44,723 Securities available for sale 24,721 Restricted stock 3,357 Loans 651,769 Premises and equipment 4,863 Goodwill 100,339 Core deposit intangible 7,537 Bank owned life insurance 8,181 Other assets 6,385 Total assets acquired $ 851,875 Liabilities of acquired bank: Deposits $ 593,078 FHLB advances 60,000 Other liabilities 10,518 Total liabilities assumed $ 663,596 Common stock issued at $75.90 per share $ 157,263 Cash paid $ 31,016
Business Acquisition, Pro Forma Information	The following table presents pro-forma information as if the Guaranty acquisition was completed as of January 1, 2018. The pro-forma results combine the historical results of Guaranty into the Company's consolidated statement of income including the impact of certain purchase accounting adjustments including loan and investment discount accretion and intangible assets amortization. The pro-forma results have been prepared for comparative purposes only and are not necessarily indicative of the results that would have been obtained had the acquisition actually occurred on January 1, 2018: Year Ended December 31, 2018 Interest income $ 585,412 Noninterest income 71,983 Total revenue $ 657,395 Net income (1) $ 203,542 Basic earnings per share $ 4.76 Diluted earnings per share $ 4.74 ____________ (1) Excludes nonrecurring costs attributable to the acquisition including advisory, legal, other professional fees, and, integration costs, incurred by the Company and Guaranty of $1,560 and $2,034 , and the related tax effects, respectively.

Parent Company Only Financial_2

Parent Company Only Financial Statements (Tables)	12 Months Ended
	Dec. 31, 2019
Condensed Financial Information Disclosure [Abstract]
Balance Sheet for the Parent Company	The following balance sheets, statements of income and statements of cash flows for Independent Bank Group, Inc. should be read in conjunction with the consolidated financial statements and the notes thereto. Balance Sheets December 31, 2019 2018 Assets Cash and cash equivalents $ 8,277 $ 8,355 Investment in subsidiaries 2,588,857 1,764,698 Investment in trusts 1,724 950 Other assets 3,355 2,189 Total assets $ 2,602,213 $ 1,776,192 Liabilities and Stockholders' Equity Other borrowings $ 202,251 $ 137,316 Junior subordinated debentures 53,824 27,852 Other liabilities 6,365 4,591 Total liabilities 262,440 169,759 Stockholders' equity: Preferred stock — — Common stock 430 306 Additional paid-in capital 1,926,359 1,317,616 Retained earnings 393,674 296,816 Accumulated other comprehensive loss 19,310 (8,305 ) Total stockholders' equity 2,339,773 1,606,433 Total liabilities and stockholders' equity $ 2,602,213 $ 1,776,192
Statement of Income for the Parent Company	Statements of Income Years Ended December 31, 2019 2018 2017 Interest expense: Interest on other borrowings $ 11,561 $ 8,390 $ 6,873 Interest on junior subordinated debentures 3,028 1,609 1,162 Total interest expense 14,589 9,999 8,035 Noninterest income: Dividends from subsidiaries 105,877 39,841 29,563 Other 1 14 32 Total noninterest income 105,878 39,855 29,595 Noninterest expense: Salaries and employee benefits 7,653 6,318 5,175 Professional fees 264 332 546 Acquisition expense, including legal 33,445 6,157 12,767 Other 2,562 1,611 1,614 Total noninterest expense 43,924 14,418 20,102 Income before income tax benefit and equity in undistributed income of subsidiaries 47,365 15,438 1,458 Income tax benefit 11,066 5,541 8,890 Income before equity in undistributed income of subsidiaries 58,431 20,979 10,348 Equity in undistributed income of subsidiaries 134,305 107,280 66,164 Net income $ 192,736 $ 128,259 $ 76,512
Statement of Cash Flows for the Parent Company	Statements of Cash Flows Years Ended December 31, 2019 2018 2017 Cash flows from operating activities: Net income $ 192,736 $ 128,259 $ 76,512 Adjustments to reconcile net income to net cash provided by operating activities: Equity in undistributed net income of subsidiaries (134,305 ) (107,280 ) (66,164 ) Amortization of discount and origination costs on borrowings 633 633 505 Stock based compensation expense 7,808 6,062 4,688 Excess tax expense (benefit) on restricted stock vested 21 (646 ) (1,323 ) Deferred tax expense 2,165 1,054 11,782 Net change in other assets 1,863 6,918 (6,750 ) Net change in other liabilities (64 ) 1,130 (1,663 ) Net cash provided by operating activities 70,857 36,130 17,587 Cash flows from investing activities: Capital investment in subsidiaries — — (50,050 ) Cash acquired in connection with acquisition 339 7,425 5,418 Cash paid in connection with acquisition (9 ) (31,016 ) (17,773 ) Net cash provided by (used in) financing activities 330 (23,591 ) (62,405 ) Cash flows from financing activities: Proceeds from other borrowings 65,000 — 29,255 Repayments of other borrowings (40,500 ) — — Proceeds from exercise of common stock warrants — 2,533 55 Offering costs paid in connection with acquired bank (804 ) (209 ) (942 ) Proceeds from sale of common stock, net — — 26,816 Repurchase of common stock (51,659 ) — — Dividends paid (43,302 ) (15,908 ) (10,231 ) Net cash (used in) provided by financing activities (71,265 ) (13,584 ) 44,953 Net change in cash and cash equivalents (78 ) (1,045 ) 135 Cash and cash equivalents at beginning of year 8,355 9,400 9,265 Cash and cash equivalents at end of year $ 8,277 $ 8,355 $ 9,400

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details)	Jan. 01, 2019business_trust	Dec. 31, 2019USD ($)segmentbusiness_trustshares	Dec. 31, 2018shares	Oct. 24, 2018USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of wholly owned statutory business trusts | business_trust		9
Number of reportable segments | segment		1
Common stock repurchased		$ 51,659,000
October 2018 Share Repurchase Program
Summary Of Significant Accounting Policies [Line Items]
Stock repurchase authorized amount				$ 75,000,000
Common stock repurchased (shares) | shares		897,738
Common stock repurchased		$ 49,048,000
Common stock purchased to settle employee tax withholding related to vesting of stock awards (shares) | shares		55,106
Common stock purchased to settle employee tax withholding related to vesting of stock awards		$ 2,611,000
Stock repurchased shares acquired (in shares) | shares			0
October 2018 Share Repurchase Program, Authorized By Federal Reserve
Summary Of Significant Accounting Policies [Line Items]
Stock repurchase authorized amount				60,000,000
Share repurchase program, remaining authorized repurchase amount				$ 10,952,000
Core deposit intangibles
Summary Of Significant Accounting Policies [Line Items]
Finite-lived intangible assets, useful life		10 years
Customer relationship intangibles
Summary Of Significant Accounting Policies [Line Items]
Finite-lived intangible assets, useful life		13 years
Minimum
Summary Of Significant Accounting Policies [Line Items]
Premises and equipment, useful life		3 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Premises and equipment, useful life		30 years
Guaranty Bancorp
Summary Of Significant Accounting Policies [Line Items]
Number of wholly owned statutory business trusts | business_trust	2

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Basic earnings per share:
Net income	$ 192,736	$ 128,259	$ 76,512
Undistributed earnings allocated to participating securities	971	976	626
Dividends paid on participating securities	281	139	97
Net income available to common shareholders	$ 191,484	$ 127,144	$ 75,789
Weighted-average basic shares outstanding (shares)	42,964,393	29,341,843	25,394,079
Basic earnings per share (usd per share)	$ 4.46	$ 4.33	$ 2.98
Diluted earnings per share:
Net income available to common shareholders	$ 191,484	$ 127,144	$ 75,789
Weighted-average basic shares outstanding (shares)	42,964,393	29,341,843	25,394,079
Add dilutive stock warrants (shares)	0	0	106,070
Total weighted-average diluted shares outstanding (shares)	42,964,393	29,341,843	25,500,149
Diluted earnings per share (usd per share)	$ 4.46	$ 4.33	$ 2.97
Anti-dilutive participating securities (shares)	73,546	114,087	123,564

Recent Accounting Pronounceme_2

Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	Jan. 01, 2020	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use assets		$ 31,813
Operating Lease, Liability		28,978
Cumulative effect adjustment				$ 926		$ 0
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use assets			$ 38,812
Operating Lease, Liability			33,953
Prepaid Rent			4,949
Accumulated other comprehensive loss
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment						233
Accumulated other comprehensive loss | Accounting Standards Update 2018-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment					$ 233
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment				926		$ (233)
Retained Earnings | Accounting Standards Update 2018-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment					$ (233)
Retained Earnings | Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment			(70)
Retained Earnings | Accounting Standards Update 2017-08
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment			$ 856
Receivables Acquired with Deteriorated Credit Quality
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans acquired with deteriorated credit quality		$ 849		$ 45
Unfunded Loan Commitment [Member] | Minimum | Forecast | Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans acquired with deteriorated credit quality	$ 68,000
Unfunded Loan Commitment [Member] | Maximum | Forecast | Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans acquired with deteriorated credit quality	80,000
Unfunded Loan Commitment [Member] | Receivables Acquired with Deteriorated Credit Quality | Minimum | Forecast | Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans acquired with deteriorated credit quality	20,000
Unfunded Loan Commitment [Member] | Receivables Acquired with Deteriorated Credit Quality | Maximum | Forecast | Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans acquired with deteriorated credit quality	$ 22,000

Restrictions on Cash and Due _2

Restrictions on Cash and Due from Banks (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Cash and Cash Equivalents [Abstract]
Deposit reserve requirement	$ 63,739	$ 35,952

Statement of Cash Flows - Other

Statement of Cash Flows - Other Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash transactions:
Interest expense paid	$ 144,775	$ 79,509	$ 41,802
Income taxes paid	40,504	25,109	34,161
Noncash transactions:
Transfers of loans to other real estate owned	544	410	1,201
Loans to facilitate the sale of other real estate owned	517	0	0
Securities purchased, not yet settled	9,975	0	0
Transfers of loans held for investment to loans held for sale	83,526	0	0
Right-of-use assets obtained in exchange for lease liabilities	35,553	0	0
Transfer of bank premises to other real estate	7,896	0	2,716
Transfer of repurchase agreements to deposits	$ 8,475	$ 0	$ 8,845

Statement of Cash Flows - Nonca

Statement of Cash Flows - Noncash Investing from Branch Sale (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Noncash liabilities transferred:
Deposit premium received	$ 1,386	$ 0	$ 7,107
Cash paid to buyer, net of deposit premium	24,957	0	56,975
Sale of Branch
Noncash assets transferred:
Loans, including accrued interest	796	0	106,008
Premises and equipment	94	0	7,473
Core deposit intangible assets, net	0	0	3,011
Other assets	2	0	74
Total assets	892	0	116,566
Noncash liabilities transferred:
Deposits, including interest	27,721	0	178,279
Other liabilities	27	0	129
Total liabilities	27,748	0	178,408
Sale of Branch | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Noncash liabilities transferred:
Cash and cash equivalents transferred in branch sales	$ 206	$ 0	$ 1,712

Statement of Cash Flows - Non_2

Statement of Cash Flows - Noncash Investing from Sale of Trust Business (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Noncash assets transferred:
Proceeds from sale of trust business	$ 4,269	$ 0	$ 0
Trust Business Sale | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Trust Business Sale
Noncash assets transferred:
Customer relationship intangible assets, net	2,939
Other assets	11
Total assets	$ 2,950

Statement of Cash Flows - Non_3

Statement of Cash Flows - Noncash Investing Activities from Acquisitions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Noncash assets acquired
Certificates of deposit held in other banks	$ 262	$ 0	$ 11,025
Securities available for sale	561,052	24,721	336,540
Restricted stock	27,794	3,357	11,110
Loans	2,789,868	651,769	1,384,210
Premises and equipment	65,786	4,863	63,166
Other real estate owned	1,829	0	11,212
Goodwill	272,224	100,339	363,139
Other intangible assets	71,518	7,537	36,717
Bank owned life insurance	80,837	8,181	53,213
Other assets	31,987	6,385	25,379
Total assets acquired	3,903,157	807,152	2,295,711
Noncash liabilities assumed:
Deposits	3,108,810	593,078	1,825,181
Repurchase agreements	8,475	0	18,003
FHLB advances	142,653	60,000	0
Other borrowings	40,000	0	0
Junior subordinated debentures	25,774	0	9,359
Other liabilities	15,477	10,518	7,697
Total liabilities assumed	3,341,189	663,596	1,860,240
Cash and cash equivalents acquired from acquisitions	39,913	44,723	148,444
Cash paid to shareholders of acquired banks	9	31,016	17,773
Fair value of common stock issued to shareholders of acquired banks	$ 601,872	$ 157,263	$ 566,142

Securities Available for Sale -

Securities Available for Sale - Amortized Cost of Securities and Approximate Fair Values (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,061,854	$ 696,613
Gross Unrealized Gains	25,007	935
Gross Unrealized Losses	(925)	(12,198)
Fair Value	1,085,936	685,350
U.S. treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	48,060	30,110
Gross Unrealized Gains	743	0
Gross Unrealized Losses	(7)	(467)
Fair Value	48,796	29,643
Government agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	178,953	152,969
Gross Unrealized Gains	926	80
Gross Unrealized Losses	(583)	(2,819)
Fair Value	179,296	150,230
Obligations of state and municipal subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	332,715	187,366
Gross Unrealized Gains	11,150	727
Gross Unrealized Losses	(6)	(3,086)
Fair Value	343,859	185,007
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	7,011
Gross Unrealized Gains	207
Gross Unrealized Losses	0
Fair Value	7,218
Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	493,915	326,168
Gross Unrealized Gains	11,981	128
Gross Unrealized Losses	(329)	(5,826)
Fair Value	505,567	$ 320,470
Other securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,200
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	$ 1,200

Securities Available for Sale_2

Securities Available for Sale - Additional Information (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Abstract]
Carrying value of securities pledged	$ 571,843	$ 219,927

Securities Available for Sale_3

Securities Available for Sale - Proceeds from Sale, Gross Gains and Losses of Securities Available for Sale (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Abstract]
Proceeds from sale	$ 192,417	$ 102,647	$ 31,367
Gross gains	306	268	176
Gross losses	$ 31	$ 849	$ 52

Securities Available for Sale_4

Securities Available for Sale - Amortized Cost and Estimated Fair Value of Securities Available for Sale by Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Amortized Cost
Due in one year or less	$ 34,050
Due from one year to five years	181,742
Due from five to ten years	162,396
Thereafter	189,751
Single maturity dates, amortized cost basis	567,939
Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA	493,915
Amortized Cost	1,061,854	$ 696,613
Fair Value
Due in one year or less	34,088
Due from one year to five years	184,903
Due from five to ten years	166,337
Thereafter	195,041
Single maturity dates, fair value	580,369
Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA	505,567
Fair value, total	$ 1,085,936	$ 685,350

Securities Available for Sale_5

Securities Available for Sale - Summary of Unrealized Losses and Fair Value of Securities in Continuous Unrealized Loss Positions (Details) $ in Thousands	Dec. 31, 2019USD ($)security	Dec. 31, 2018USD ($)security
Debt Securities, Available-for-sale [Line Items]
Less than 12 months: number of securities | security	31	149
Less than 12 months: estimated fair value	$ 102,095	$ 160,424
Less than 12 months: unrealized losses	$ (813)	$ (1,395)
Greater than 12 months: number of securities | security	10	367
Greater than 12 months: estimated fair value	$ 25,624	$ 439,169
Greater than 12 months: unrealized losses	(112)	(10,803)
Total: estimated fair value	127,719	599,593
Total: unrealized losses	$ (925)	$ (12,198)
U.S. treasuries
Debt Securities, Available-for-sale [Line Items]
Less than 12 months: number of securities | security	0	1
Less than 12 months: estimated fair value	$ 0	$ 9,749
Less than 12 months: unrealized losses	$ 0	$ (6)
Greater than 12 months: number of securities | security	2	5
Greater than 12 months: estimated fair value	$ 8,097	$ 19,894
Greater than 12 months: unrealized losses	(7)	(461)
Total: estimated fair value	8,097	29,643
Total: unrealized losses	$ (7)	$ (467)
Government agency securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 months: number of securities | security	13	4
Less than 12 months: estimated fair value	$ 52,790	$ 6,068
Less than 12 months: unrealized losses	$ (495)	$ (32)
Greater than 12 months: number of securities | security	6	43
Greater than 12 months: estimated fair value	$ 15,911	$ 126,745
Greater than 12 months: unrealized losses	(88)	(2,787)
Total: estimated fair value	68,701	132,813
Total: unrealized losses	$ (583)	$ (2,819)
Obligations of state and municipal subdivisions
Debt Securities, Available-for-sale [Line Items]
Less than 12 months: number of securities | security	5	88
Less than 12 months: estimated fair value	$ 2,793	$ 32,493
Less than 12 months: unrealized losses	$ (1)	$ (326)
Greater than 12 months: number of securities | security	1	218
Greater than 12 months: estimated fair value	$ 423	$ 105,817
Greater than 12 months: unrealized losses	(5)	(2,760)
Total: estimated fair value	3,216	138,310
Total: unrealized losses	$ (6)	$ (3,086)
Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA
Debt Securities, Available-for-sale [Line Items]
Less than 12 months: number of securities | security	13	56
Less than 12 months: estimated fair value	$ 46,512	$ 112,114
Less than 12 months: unrealized losses	$ (317)	$ (1,031)
Greater than 12 months: number of securities | security	1	101
Greater than 12 months: estimated fair value	$ 1,193	$ 186,713
Greater than 12 months: unrealized losses	(12)	(4,795)
Total: estimated fair value	47,705	298,827
Total: unrealized losses	$ (329)	$ (5,826)

Loans, Net and Allowance for _3

Loans, Net and Allowance for Loan Losses - Composition of Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounts Notes And Loans Receivable [Line Items]
Loans, gross	$ 11,615,970	$ 7,887,800
Deferred loan fees	(1,695)	(3,303)
Allowance for loan losses	(51,461)	(44,802)	$ (39,402)	$ (31,591)
Loans, net	11,562,814	7,839,695
Commercial
Accounts Notes And Loans Receivable [Line Items]
Loans, gross	2,482,356	1,361,104
Allowance for loan losses	(12,844)	(11,793)	(10,599)	(8,593)
Real estate | Commercial
Accounts Notes And Loans Receivable [Line Items]
Loans, gross	5,872,653	4,141,356
Real estate | Commercial construction, land and land development
Accounts Notes And Loans Receivable [Line Items]
Loans, gross	1,236,623	905,421
Real estate | Residential Real Estate
Accounts Notes And Loans Receivable [Line Items]
Loans, gross	1,515,227	1,049,521
Allowance for loan losses	(3,678)	(3,320)	(3,447)	(2,760)
Real estate | Single-family interim construction
Accounts Notes And Loans Receivable [Line Items]
Loans, gross	378,120	331,748
Allowance for loan losses	(1,606)	(1,402)	(1,583)	(1,301)
Agricultural
Accounts Notes And Loans Receivable [Line Items]
Loans, gross	97,767	66,638
Allowance for loan losses	(332)	(241)	(250)	(207)
Consumer
Accounts Notes And Loans Receivable [Line Items]
Loans, gross	32,603	31,759
Allowance for loan losses	(226)	(186)	(205)	(242)
Other
Accounts Notes And Loans Receivable [Line Items]
Loans, gross	621	253
Allowance for loan losses	$ (5)	$ (3)	$ 32	$ (29)

Loans, Net and Allowance for _4

Loans, Net and Allowance for Loan Losses - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2019USD ($)modified_loancomponent	Dec. 31, 2018USD ($)modified_loan
Accounts Notes And Loans Receivable [Line Items]
Loans, net amount	$ 11,562,814,000	$ 7,839,695,000
Number of components the allowance is derived from | component	2
Troubled debt restructuring modification recorded investment	$ 1,208,000	$ 1,925,000
Number of loans modified under troubled debt restructuring | modified_loan	0	0
Commitments to lend additional funds	$ 0	$ 0
Receivables Acquired with Deteriorated Credit Quality
Accounts Notes And Loans Receivable [Line Items]
Nonaccrual loans	10,850,000	6,996,000
Allowance for loan losses on PCI loans	$ 849,000	45,000
Loans and Leases, Net | COLORADO | Geographic Concentration Risk
Accounts Notes And Loans Receivable [Line Items]
Percentage of portfolio	27.00%
Owner Occupied | Loans and Leases, Net
Accounts Notes And Loans Receivable [Line Items]
Percentage of portfolio	30.00%
Commercial | Receivables Acquired with Deteriorated Credit Quality
Accounts Notes And Loans Receivable [Line Items]
Allowance for loan losses on PCI loans	$ 379,000	45,000
Commercial | Energy Related Loans
Accounts Notes And Loans Receivable [Line Items]
Loans, net amount	189,781,000	135,034,000
Commercial | Warehouse Loans
Accounts Notes And Loans Receivable [Line Items]
Loans, net amount	$ 687,317,000	170,290,000
Duration of the loans to larger mortgage originators	60 days
Agricultural | Receivables Acquired with Deteriorated Credit Quality
Accounts Notes And Loans Receivable [Line Items]
Allowance for loan losses on PCI loans	$ 0	0
Agricultural | Agricultural
Accounts Notes And Loans Receivable [Line Items]
Loan to value ratio (percent)	80.00%
Loan, amortization period	20 years
Agricultural | Non-Real Estate Loan
Accounts Notes And Loans Receivable [Line Items]
Period of operating lines	1 year
Consumer
Accounts Notes And Loans Receivable [Line Items]
Percentage of portfolio	1.00%
Consumer | Receivables Acquired with Deteriorated Credit Quality
Accounts Notes And Loans Receivable [Line Items]
Allowance for loan losses on PCI loans	$ 0	$ 0
Maximum | Commercial | Warehouse Loans
Accounts Notes And Loans Receivable [Line Items]
Duration of the loans to mortgage bankers	15 days
Minimum
Accounts Notes And Loans Receivable [Line Items]
Loans requiring external review	$ 3,500,000

Loans, Net and Allowance for _5

Loans, Net and Allowance for Loan Losses - Rollforward of Activity in Loan Losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	$ 44,802	$ 39,402	$ 31,591
Provision for loan losses	14,805	9,860	8,265
Charge-offs	(8,364)	(4,625)	(602)
Recoveries	218	165	148
Balance at end of year	51,461	44,802	39,402
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	11,793	10,599	8,593
Provision for loan losses	8,670	4,973	2,059
Charge-offs	(7,709)	(3,863)	(81)
Recoveries	90	84	28
Balance at end of year	12,844	11,793	10,599
Real estate | Commercial real estate, construction, land and land development
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	27,795	23,301	18,399
Provision for loan losses	5,289	4,909	4,886
Charge-offs	(3)	(435)	(15)
Recoveries	4	20	31
Balance at end of year	33,085	27,795	23,301
Real estate | Residential Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	3,320	3,447	2,760
Provision for loan losses	498	(124)	683
Charge-offs	(140)	(6)	0
Recoveries	0	3	4
Balance at end of year	3,678	3,320	3,447
Real estate | Single-family interim construction
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	1,402	1,583	1,301
Provision for loan losses	207	(181)	416
Charge-offs	(3)	0	(134)
Recoveries	0	0	0
Balance at end of year	1,606	1,402	1,583
Agricultural
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	241	250	207
Provision for loan losses	91	(9)	43
Charge-offs	0	0	0
Recoveries	0	0	0
Balance at end of year	332	241	250
Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	186	205	242
Provision for loan losses	71	69	99
Charge-offs	(79)	(93)	(182)
Recoveries	48	5	46
Balance at end of year	226	186	205
Other
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	3	(32)	29
Provision for loan losses	356	210	90
Charge-offs	(430)	(228)	(190)
Recoveries	76	53	39
Balance at end of year	5	3	(32)
Unallocated
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	62	49	60
Provision for loan losses	(377)	13	(11)
Charge-offs	0	0	0
Recoveries	0	0	0
Balance at end of year	$ (315)	$ 62	$ 49

Loans, Net and Allowance for _6

Loans, Net and Allowance for Loan Losses - Summary of Activity in Allowance for Loan Losses by Loan Class (Details) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for loan losses:
Individually evaluated for impairment	$ 358	$ 2,727
Collectively evaluated for impairment	50,254	42,030
Ending balance	51,461	44,802	$ 39,402	$ 31,591
Loans:
Individually evaluated for impairment	12,087	14,575
Collectively evaluated for impairment	11,311,238	7,760,791
Ending balance	11,615,970	7,887,800
Receivables Acquired with Deteriorated Credit Quality
Allowance for loan losses:
Loans acquired with deteriorated credit quality	849	45
Loans:
Acquired with deteriorated credit quality	292,645	112,434
Ending balance	292,645	112,434
Commercial
Allowance for loan losses:
Individually evaluated for impairment	357	2,633
Collectively evaluated for impairment	12,108	9,115
Ending balance	12,844	11,793	10,599	8,593
Loans:
Individually evaluated for impairment	3,130	7,288
Collectively evaluated for impairment	2,416,569	1,335,194
Ending balance	2,482,356	1,361,104
Commercial | Receivables Acquired with Deteriorated Credit Quality
Allowance for loan losses:
Loans acquired with deteriorated credit quality	379	45
Loans:
Acquired with deteriorated credit quality	62,657	18,622
Real estate | Commercial real estate, construction, land and land development
Allowance for loan losses:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	32,615	27,795
Ending balance	33,085	27,795	23,301	18,399
Loans:
Individually evaluated for impairment	6,813	1,734
Collectively evaluated for impairment	6,883,639	4,955,178
Ending balance	7,109,276	5,046,777
Real estate | Commercial real estate, construction, land and land development | Receivables Acquired with Deteriorated Credit Quality
Allowance for loan losses:
Loans acquired with deteriorated credit quality	470	0
Loans:
Acquired with deteriorated credit quality	218,824	89,865
Real estate | Residential Real Estate
Allowance for loan losses:
Individually evaluated for impairment	0	92
Collectively evaluated for impairment	3,678	3,228
Ending balance	3,678	3,320	3,447	2,760
Loans:
Individually evaluated for impairment	2,008	1,943
Collectively evaluated for impairment	1,505,896	1,044,265
Ending balance	1,515,227	1,049,521
Real estate | Residential Real Estate | Receivables Acquired with Deteriorated Credit Quality
Allowance for loan losses:
Loans acquired with deteriorated credit quality	0	0
Loans:
Acquired with deteriorated credit quality	7,323	3,313
Real estate | Single-family interim construction
Allowance for loan losses:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	1,606	1,402
Ending balance	1,606	1,402	1,583	1,301
Loans:
Individually evaluated for impairment	0	3,578
Collectively evaluated for impairment	378,120	328,170
Ending balance	378,120	331,748
Real estate | Single-family interim construction | Receivables Acquired with Deteriorated Credit Quality
Allowance for loan losses:
Loans acquired with deteriorated credit quality	0	0
Loans:
Acquired with deteriorated credit quality	0	0
Agricultural
Allowance for loan losses:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	332	241
Ending balance	332	241	250	207
Loans:
Individually evaluated for impairment	114	0
Collectively evaluated for impairment	93,837	66,032
Ending balance	97,767	66,638
Agricultural | Receivables Acquired with Deteriorated Credit Quality
Allowance for loan losses:
Loans acquired with deteriorated credit quality	0	0
Loans:
Acquired with deteriorated credit quality	3,816	606
Consumer
Allowance for loan losses:
Individually evaluated for impairment	1	2
Collectively evaluated for impairment	225	184
Ending balance	226	186	205	242
Loans:
Individually evaluated for impairment	22	32
Collectively evaluated for impairment	32,556	31,699
Ending balance	32,603	31,759
Consumer | Receivables Acquired with Deteriorated Credit Quality
Allowance for loan losses:
Loans acquired with deteriorated credit quality	0	0
Loans:
Acquired with deteriorated credit quality	25	28
Other
Allowance for loan losses:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	5	3
Ending balance	5	3	(32)	29
Loans:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	621	253
Ending balance	621	253
Other | Receivables Acquired with Deteriorated Credit Quality
Allowance for loan losses:
Loans acquired with deteriorated credit quality	0	0
Loans:
Acquired with deteriorated credit quality	0	0
Unallocated
Allowance for loan losses:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	(315)	62
Ending balance	(315)	62	$ 49	$ 60
Loans:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	0	0
Ending balance	0	0
Unallocated | Receivables Acquired with Deteriorated Credit Quality
Allowance for loan losses:
Loans acquired with deteriorated credit quality	0	0
Loans:
Acquired with deteriorated credit quality	$ 0	$ 0

Loans, Net and Allowance for _7

Loans, Net and Allowance for Loan Losses - Summary of Non Performing Loans by Loan Class (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accounts Notes And Loans Receivable [Line Items]
Troubled debt restructurings (not included in nonaccrual or loans past due and still accruing)	$ 1,208	$ 1,925
Nonperforming Loans
Accounts Notes And Loans Receivable [Line Items]
Nonaccrual loans	11,547	11,938
Loans past due 90 days and still accruing	14,529	5
Troubled debt restructurings (not included in nonaccrual or loans past due and still accruing)	540	687
Total nonperforming loans	26,616	12,630
Nonperforming Loans | Commercial
Accounts Notes And Loans Receivable [Line Items]
Nonaccrual loans	3,130	5,224
Loans past due 90 days and still accruing	14,529	0
Troubled debt restructurings (not included in nonaccrual or loans past due and still accruing)	0	114
Total nonperforming loans	17,659	5,338
Nonperforming Loans | Real estate | Commercial real estate, construction, land and land development
Accounts Notes And Loans Receivable [Line Items]
Nonaccrual loans	6,461	1,329
Loans past due 90 days and still accruing	0	0
Troubled debt restructurings (not included in nonaccrual or loans past due and still accruing)	352	405
Total nonperforming loans	6,813	1,734
Nonperforming Loans | Real estate | Residential Real Estate
Accounts Notes And Loans Receivable [Line Items]
Nonaccrual loans	1,820	1,775
Loans past due 90 days and still accruing	0	0
Troubled debt restructurings (not included in nonaccrual or loans past due and still accruing)	188	168
Total nonperforming loans	2,008	1,943
Nonperforming Loans | Real estate | Single-family interim construction
Accounts Notes And Loans Receivable [Line Items]
Nonaccrual loans	0	3,578
Loans past due 90 days and still accruing	0	0
Troubled debt restructurings (not included in nonaccrual or loans past due and still accruing)	0	0
Total nonperforming loans	0	3,578
Nonperforming Loans | Agricultural
Accounts Notes And Loans Receivable [Line Items]
Nonaccrual loans	114	0
Loans past due 90 days and still accruing	0	0
Troubled debt restructurings (not included in nonaccrual or loans past due and still accruing)	0	0
Total nonperforming loans	114	0
Nonperforming Loans | Consumer
Accounts Notes And Loans Receivable [Line Items]
Nonaccrual loans	22	32
Loans past due 90 days and still accruing	0	5
Troubled debt restructurings (not included in nonaccrual or loans past due and still accruing)	0	0
Total nonperforming loans	22	37
Nonperforming Loans | Other
Accounts Notes And Loans Receivable [Line Items]
Nonaccrual loans	0	0
Loans past due 90 days and still accruing	0	0
Troubled debt restructurings (not included in nonaccrual or loans past due and still accruing)	0	0
Total nonperforming loans	$ 0	$ 0

Loans, Net and Allowance for _8

Loans, Net and Allowance for Loan Losses - Impaired Loans by Loan Class (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Recorded investment in impaired loans:
Impaired loans with an allowance for loan losses	$ 1,581	$ 6,551
Impaired loans with no allowance for loan losses	10,506	8,024
Total	12,087	14,575
Unpaid principal balance of impaired loans	17,891	17,355
Allowance for loan losses on impaired loans	358	2,727
Average recorded investment in impaired loans	12,794	14,381	$ 15,040
Interest income recognized on impaired loans	233	268	499
Commercial
Recorded investment in impaired loans:
Impaired loans with an allowance for loan losses	1,580	6,416
Impaired loans with no allowance for loan losses	1,550	872
Total	3,130	7,288
Unpaid principal balance of impaired loans	8,580	9,822
Allowance for loan losses on impaired loans	357	2,633
Average recorded investment in impaired loans	6,266	8,919	8,524
Interest income recognized on impaired loans	30	119	8
Real estate | Commercial real estate, construction, land and land development
Recorded investment in impaired loans:
Impaired loans with an allowance for loan losses	0	0
Impaired loans with no allowance for loan losses	6,813	1,734
Total	6,813	1,734
Unpaid principal balance of impaired loans	6,967	1,860
Allowance for loan losses on impaired loans	0	0
Average recorded investment in impaired loans	3,979	2,667	3,690
Interest income recognized on impaired loans	39	65	428
Real estate | Residential Real Estate
Recorded investment in impaired loans:
Impaired loans with an allowance for loan losses	0	134
Impaired loans with no allowance for loan losses	2,008	1,809
Total	2,008	1,943
Unpaid principal balance of impaired loans	2,197	2,056
Allowance for loan losses on impaired loans	0	92
Average recorded investment in impaired loans	1,746	2,033	2,431
Interest income recognized on impaired loans	39	81	58
Real estate | Single-family interim construction
Recorded investment in impaired loans:
Impaired loans with an allowance for loan losses	0	0
Impaired loans with no allowance for loan losses	0	3,578
Total	0	3,578
Unpaid principal balance of impaired loans	0	3,579
Allowance for loan losses on impaired loans	0	0
Average recorded investment in impaired loans	716	716	177
Interest income recognized on impaired loans	119	1	0
Agricultural
Recorded investment in impaired loans:
Impaired loans with an allowance for loan losses	0	0
Impaired loans with no allowance for loan losses	114	0
Total	114	0
Unpaid principal balance of impaired loans	123	0
Allowance for loan losses on impaired loans	0	0
Average recorded investment in impaired loans	57	0	0
Interest income recognized on impaired loans	0	0	0
Consumer
Recorded investment in impaired loans:
Impaired loans with an allowance for loan losses	1	1
Impaired loans with no allowance for loan losses	21	31
Total	22	32
Unpaid principal balance of impaired loans	24	38
Allowance for loan losses on impaired loans	1	2
Average recorded investment in impaired loans	30	46	218
Interest income recognized on impaired loans	6	2	5
Other
Recorded investment in impaired loans:
Impaired loans with an allowance for loan losses	0	0
Impaired loans with no allowance for loan losses	0	0
Total	0	0
Unpaid principal balance of impaired loans	0	0
Allowance for loan losses on impaired loans	0	0
Average recorded investment in impaired loans	0	0	0
Interest income recognized on impaired loans	$ 0	$ 0	$ 0

Loans, Net and Allowance for _9

Loans, Net and Allowance for Loan Losses - Summary of Troubled Debt Restructurings (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)contract	Dec. 31, 2018USD ($)contract
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of contracts | contract	1	1
Pre-restructuring outstanding recorded investment	$ 29	$ 114
Post-restructuring outstanding recorded investment	$ 29	$ 114
Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of contracts | contract	0	1
Pre-restructuring outstanding recorded investment	$ 0	$ 114
Post-restructuring outstanding recorded investment	$ 0	$ 114
Real estate | Commercial real estate, construction, land and land development
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of contracts | contract	0	0
Pre-restructuring outstanding recorded investment	$ 0	$ 0
Post-restructuring outstanding recorded investment	$ 0	$ 0
Real estate | Residential Real Estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of contracts | contract	1	0
Pre-restructuring outstanding recorded investment	$ 29	$ 0
Post-restructuring outstanding recorded investment	$ 29	$ 0
Real estate | Single-family interim construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of contracts | contract	0	0
Pre-restructuring outstanding recorded investment	$ 0	$ 0
Post-restructuring outstanding recorded investment	$ 0	$ 0
Agricultural
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of contracts | contract	0	0
Pre-restructuring outstanding recorded investment	$ 0	$ 0
Post-restructuring outstanding recorded investment	$ 0	$ 0
Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of contracts | contract	0	0
Pre-restructuring outstanding recorded investment	$ 0	$ 0
Post-restructuring outstanding recorded investment	$ 0	$ 0
Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of contracts | contract	0	0
Pre-restructuring outstanding recorded investment	$ 0	$ 0
Post-restructuring outstanding recorded investment	$ 0	$ 0

Loans, Net and Allowance for_10

Loans, Net and Allowance for Loan Losses - Aging of Past Due Loans by Loan Class (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	$ 50,593	$ 36,879
Current Loans	11,565,377	7,850,921
Ending balance	11,615,970	7,887,800
Loans 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	22,488	26,908
Loans 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	28,105	9,971
Commercial
Financing Receivable, Past Due [Line Items]
Ending balance	2,482,356	1,361,104
Real estate | Commercial real estate, construction, land and land development
Financing Receivable, Past Due [Line Items]
Ending balance	7,109,276	5,046,777
Real estate | Residential Real Estate
Financing Receivable, Past Due [Line Items]
Ending balance	1,515,227	1,049,521
Real estate | Single-family interim construction
Financing Receivable, Past Due [Line Items]
Ending balance	378,120	331,748
Agricultural
Financing Receivable, Past Due [Line Items]
Ending balance	97,767	66,638
Consumer
Financing Receivable, Past Due [Line Items]
Ending balance	32,603	31,759
Other
Financing Receivable, Past Due [Line Items]
Ending balance	621	253
Receivables Acquired with Deteriorated Credit Quality
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	9,322	3,896
Current Loans	283,323	108,538
Ending balance	292,645	112,434
Receivables Acquired with Deteriorated Credit Quality | Loans 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	2,556	2,939
Receivables Acquired with Deteriorated Credit Quality | Loans 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	6,766	957
Financing Receivables, Excluding Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	41,271	32,983
Current Loans	11,282,054	7,742,383
Ending balance	11,323,325	7,775,366
Financing Receivables, Excluding Receivables Acquired with Deteriorated Credit Quality [Member] | Loans 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	19,932	23,969
Financing Receivables, Excluding Receivables Acquired with Deteriorated Credit Quality [Member] | Loans 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	21,339	9,014
Financing Receivables, Excluding Receivables Acquired with Deteriorated Credit Quality [Member] | Commercial
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	22,168	19,792
Current Loans	2,397,531	1,322,690
Ending balance	2,419,699	1,342,482
Financing Receivables, Excluding Receivables Acquired with Deteriorated Credit Quality [Member] | Commercial | Loans 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	4,512	15,426
Financing Receivables, Excluding Receivables Acquired with Deteriorated Credit Quality [Member] | Commercial | Loans 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	17,656	4,366
Financing Receivables, Excluding Receivables Acquired with Deteriorated Credit Quality [Member] | Real estate | Commercial real estate, construction, land and land development
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	12,058	3,435
Current Loans	6,878,394	4,953,477
Ending balance	6,890,452	4,956,912
Financing Receivables, Excluding Receivables Acquired with Deteriorated Credit Quality [Member] | Real estate | Commercial real estate, construction, land and land development | Loans 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	9,153	3,435
Financing Receivables, Excluding Receivables Acquired with Deteriorated Credit Quality [Member] | Real estate | Commercial real estate, construction, land and land development | Loans 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	2,905	0
Financing Receivables, Excluding Receivables Acquired with Deteriorated Credit Quality [Member] | Real estate | Residential Real Estate
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	3,884	5,234
Current Loans	1,504,020	1,040,974
Ending balance	1,507,904	1,046,208
Financing Receivables, Excluding Receivables Acquired with Deteriorated Credit Quality [Member] | Real estate | Residential Real Estate | Loans 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	3,242	4,199
Financing Receivables, Excluding Receivables Acquired with Deteriorated Credit Quality [Member] | Real estate | Residential Real Estate | Loans 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	642	1,035
Financing Receivables, Excluding Receivables Acquired with Deteriorated Credit Quality [Member] | Real estate | Single-family interim construction
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	2,836	4,352
Current Loans	375,284	327,396
Ending balance	378,120	331,748
Financing Receivables, Excluding Receivables Acquired with Deteriorated Credit Quality [Member] | Real estate | Single-family interim construction | Loans 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	2,836	774
Financing Receivables, Excluding Receivables Acquired with Deteriorated Credit Quality [Member] | Real estate | Single-family interim construction | Loans 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	0	3,578
Financing Receivables, Excluding Receivables Acquired with Deteriorated Credit Quality [Member] | Agricultural
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	136	0
Current Loans	93,815	66,032
Ending balance	93,951	66,032
Financing Receivables, Excluding Receivables Acquired with Deteriorated Credit Quality [Member] | Agricultural | Loans 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	22	0
Financing Receivables, Excluding Receivables Acquired with Deteriorated Credit Quality [Member] | Agricultural | Loans 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	114	0
Financing Receivables, Excluding Receivables Acquired with Deteriorated Credit Quality [Member] | Consumer
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	189	170
Current Loans	32,389	31,561
Ending balance	32,578	31,731
Financing Receivables, Excluding Receivables Acquired with Deteriorated Credit Quality [Member] | Consumer | Loans 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	167	135
Financing Receivables, Excluding Receivables Acquired with Deteriorated Credit Quality [Member] | Consumer | Loans 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	22	35
Financing Receivables, Excluding Receivables Acquired with Deteriorated Credit Quality [Member] | Other
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	0	0
Current Loans	621	253
Ending balance	621	253
Financing Receivables, Excluding Receivables Acquired with Deteriorated Credit Quality [Member] | Other | Loans 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	0	0
Financing Receivables, Excluding Receivables Acquired with Deteriorated Credit Quality [Member] | Other | Loans 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	$ 0	$ 0

Loans, Net and Allowance for_11

Loans, Net and Allowance for Loan Losses - Summary of Loans by Credit Quality Indicator (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	$ 11,615,970	$ 7,887,800
Receivables Acquired with Deteriorated Credit Quality
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	292,645	112,434
Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	11,146,421	7,633,330
Pass | Receivables Acquired with Deteriorated Credit Quality
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	232,095	40,940
Pass/ Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	267,765	106,673
Pass/ Watch | Receivables Acquired with Deteriorated Credit Quality
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	21,284	32,427
Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	87,488	74,415
Special Mention | Receivables Acquired with Deteriorated Credit Quality
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	4,502	14,817
Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	114,296	73,382
Substandard | Receivables Acquired with Deteriorated Credit Quality
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	34,764	24,250
Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	0
Doubtful | Receivables Acquired with Deteriorated Credit Quality
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	0
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	2,482,356	1,361,104
Commercial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	2,332,611	1,279,024
Commercial | Pass/ Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	71,642	18,378
Commercial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	37,739	30,783
Commercial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	40,364	32,919
Commercial | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	0
Real estate | Commercial real estate, construction, land and land development
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	7,109,276	5,046,777
Real estate | Commercial real estate, construction, land and land development | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	6,814,780	4,895,217
Real estate | Commercial real estate, construction, land and land development | Pass/ Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	184,720	81,693
Real estate | Commercial real estate, construction, land and land development | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	46,889	40,601
Real estate | Commercial real estate, construction, land and land development | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	62,887	29,266
Real estate | Commercial real estate, construction, land and land development | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	0
Real estate | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	1,515,227	1,049,521
Real estate | Residential Real Estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	1,501,019	1,038,283
Real estate | Residential Real Estate | Pass/ Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	4,850	3,617
Real estate | Residential Real Estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	994	707
Real estate | Residential Real Estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	8,364	6,914
Real estate | Residential Real Estate | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	0
Real estate | Single-family interim construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	378,120	331,748
Real estate | Single-family interim construction | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	376,887	327,939
Real estate | Single-family interim construction | Pass/ Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	1,233	0
Real estate | Single-family interim construction | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	231
Real estate | Single-family interim construction | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	3,578
Real estate | Single-family interim construction | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	0
Agricultural
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	97,767	66,638
Agricultural | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	88,044	61,055
Agricultural | Pass/ Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	5,287	2,918
Agricultural | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	1,864	2,093
Agricultural | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	2,572	572
Agricultural | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	0
Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	32,603	31,759
Consumer | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	32,459	31,559
Consumer | Pass/ Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	33	67
Consumer | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	2	0
Consumer | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	109	133
Consumer | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	0
Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	621	253
Other | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	621	253
Other | Pass/ Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	0
Other | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	0
Other | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	0
Other | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	$ 0	$ 0

Loans, Net and Allowance for_12

Loans, Net and Allowance for Loan Losses - Outstanding Balance and Related Carrying Amount of Purchased Impaired Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Jun. 01, 2018
Business Acquisition [Line Items]
Outstanding balance	$ 326,077		$ 129,333
Carrying amount	$ 292,645		$ 112,434
Guaranty Bancorp
Business Acquisition [Line Items]
Outstanding balance		$ 341,645
Nonaccretable difference		(16,622)
Accretable yield		(13,299)
Carrying amount		$ 311,724
Integrity Bancshares, Inc.
Business Acquisition [Line Items]
Outstanding balance				$ 57,317
Nonaccretable difference				(9,969)
Accretable yield				(128)
Carrying amount				$ 47,220

Loans, Net and Allowance for_13

Loans, Net and Allowance for Loan Losses - Purchased Credit Impaired Loans in Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Receivables [Abstract]
Outstanding balance	$ 326,077	$ 129,333
Carrying amount	$ 292,645	$ 112,434

Loans, Net and Allowance for_14

Loans, Net and Allowance for Loan Losses - Accretable Yield Rollforward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at January 1	$ 1,436	$ 1,546
Additions	13,299	128
Accretion	(5,830)	(1,557)
Transfers from nonaccretable	0	1,319
Balance at December 31	$ 8,905	$ 1,436

Premises and Equipment, Net - C

Premises and Equipment, Net - Components of Premises and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Land	$ 58,643	$ 43,746
Building	184,589	93,793
Furniture, fixtures and equipment	39,855	34,602
Aircraft	8,947	8,947
Leasehold and tenant improvements	5,466	4,638
Construction in progress	834	32,399
Premises and equipment, gross	298,334	218,125
Less accumulated depreciation	(55,460)	(50,259)
Premises and equipment, net	$ 242,874	$ 167,866

Premises and Equipment, Net - A

Premises and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 11,783	$ 8,391	$ 8,196

Goodwill and Core Deposit Int_3

Goodwill and Core Deposit Intangible, Net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
Goodwill And Other Intangible Assets [Line Items]
Goodwill	$ 994,021	$ 721,797
Amortization of other intangible assets	$ 12,880	$ 5,739	$ 4,639
Remaining weighted averaged amortization period	8 years 4 months 24 days
Guaranty Bancorp
Goodwill And Other Intangible Assets [Line Items]
Goodwill	$ 272,224			$ 270,583
Goodwill, acquired during period	$ 272,224

Goodwill and Core Deposit Int_4

Goodwill and Core Deposit Intangible, Net - Gross Carrying Value and Accumulated Amortization of Intangible Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Acquired Finite-Lived Intangible Assets [Line Items]
Total other intangible assets, net	$ 100,741	$ 45,042
Core deposit intangibles
Acquired Finite-Lived Intangible Assets [Line Items]
Balance at beginning of the year	63,891	56,354
Additions: Guaranty and Integrity acquisitions	61,993	7,537
Balance at end of the year	125,884	63,891
Less accumulated amortization	(31,057)	(18,849)
Total other intangible assets, net	94,827	45,042
Customer relationship intangibles
Acquired Finite-Lived Intangible Assets [Line Items]
Balance at beginning of the year	0	0
Additions: Guaranty and Integrity acquisitions	9,525	0
Deletions: sale of trust business	(3,118)	0
Balance at end of the year	6,407	0
Less accumulated amortization	(493)	0
Total other intangible assets, net	$ 5,914	$ 0

Goodwill and Core Deposit Int_5

Goodwill and Core Deposit Intangible, Net - Future Amortization Expense Related to Core Deposit Intangible (Detail) $ in Thousands	Dec. 31, 2019USD ($)
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
First year	$ 12,671
Second year	12,580
Third year	12,492
Fourth year	12,439
Fifth year	11,752
Thereafter	38,807
Future amortization expense	$ 100,741

Deposits - Components of Deposi

Deposits - Components of Deposits (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Amount
Noninterest-bearing demand accounts	$ 3,240,185	$ 2,145,930
Interest-bearing checking accounts	4,198,772	2,892,318
Savings accounts	552,585	293,108
Limited access money market accounts	2,119,878	1,286,135
Certificates of deposit and individual retirement accounts (IRA), less than $250,000	892,639	559,016
Certificates of deposit and individual retirement accounts (IRA), $250,000 and greater	937,277	561,287
Total deposits	$ 11,941,336	$ 7,737,794
Percent
Noninterest-bearing demand accounts (percent)	27.10%	27.70%
Interest-bearing checking accounts (percent)	35.20%	37.40%
Savings accounts (percent)	4.60%	3.80%
Limited access money market accounts (percent)	17.80%	16.60%
Certificates of deposit and individual retirement accounts (IRA), less than $250,000 (percent)	7.50%	7.20%
Certificates of deposit and individual retirement account (IRA), $250,000 and greater (percent)	7.80%	7.30%
Total deposits (percent)	100.00%	100.00%

Deposits - Maturities of Certif

Deposits - Maturities of Certificates of Deposit (Detail) $ in Thousands	Dec. 31, 2019USD ($)
Time Deposits, Fiscal Year Maturity [Abstract]
First year	$ 1,531,507
Second year	245,339
Third year	32,216
Fourth year	15,373
Fifth year	5,481
Thereafter	0
Total	$ 1,829,916

Deposits - Additional Informati

Deposits - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Banking and Thrift [Abstract]
Brokered deposit	$ 894,131	$ 356,282

Federal Home Loan Bank Advanc_3

Federal Home Loan Bank Advances - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Weighted average interest rate on advances (percent)	2.17%	2.17%
Outstanding balances of advances	$ 325,000	$ 290,000
Federal Home Loan Bank Stock	26,901
Carrying value of loans with blanket lien	4,454,852
Remaining credit facility under FHLB advances	3,664,617
Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Undisbursed advance commitments (letter of credit)	$ 1,057,129

Federal Home Loan Bank Advanc_4

Federal Home Loan Bank Advances - Schedule of Outstanding Balances on Advances (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Federal Home Loan Bank, Advances, Fiscal Year Maturity [Abstract]
First year	$ 300,000
Second year	25,000
Third year	0
Fourth year	0
Fifth year	0
Thereafter	0
FHLB advances	$ 325,000	$ 290,000

Other Borrowings - Other Borrow

Other Borrowings - Other Borrowings (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Other borrowings	$ 202,251,000	$ 137,316,000
Other borrowings, related parties	50,000	50,000
5.875% Subordinated Notes Due August 1, 2024
Debt Instrument [Line Items]
Subordinated debt	108,372,000	108,014,000
Debt original amount	$ 110,000,000	110,000,000
Stated interest rate (percent)	5.875%
Discount and origination costs	$ 1,628,000	1,986,000
5.00% Subordinated Debenture Notes Due December 31, 2027
Debt Instrument [Line Items]
Subordinated debt	29,379,000	29,302,000
Debt original amount	$ 30,000,000	30,000,000
Stated interest rate (percent)	5.00%
Origination costs	$ 621,000	698,000
5.75% Subordinated Debenture Notes Due July 20, 2026
Debt Instrument [Line Items]
Subordinated debt	40,000,000	0
Debt original amount	$ 40,000,000	0
Stated interest rate (percent)	5.75%
London Interbank Offered Rate (LIBOR) | 5.00% Subordinated Debenture Notes Due December 31, 2027
Debt Instrument [Line Items]
Basis spread on variable rate	2.83%
London Interbank Offered Rate (LIBOR) | 5.75% Subordinated Debenture Notes Due July 20, 2026
Debt Instrument [Line Items]
Basis spread on variable rate	4.73%
Line of Credit | Line of Credit | Revolving line of credit
Debt Instrument [Line Items]
Line of Credit Facility, Outstanding Balance	$ 24,500,000	$ 0
Line of credit, maximum capacity	$ 100,000,000
Line of Credit | Line of Credit | London Interbank Offered Rate (LIBOR) | Revolving line of credit
Debt Instrument [Line Items]
Basis spread on variable rate	1.75%

Other Borrowings - Additional I

Other Borrowings - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2019USD ($)unaffiliated_bankNumber_of_Lines	Dec. 31, 2018USD ($)unaffiliated_bank
Federal Funds Line of Credit | Line of Credit
Line of Credit Facility [Line Items]
Line of credit, maximum capacity	$ 375,000,000	$ 365,000,000
Outstanding borrowings on line of credit	$ 0	$ 0
Number of unaffiliated banks | unaffiliated_bank	10	10
Secured Debt | Line of Credit
Line of Credit Facility [Line Items]
Line of credit, maximum capacity	$ 895,110,000	$ 738,919,000
Outstanding borrowings on line of credit	0	0
Line of credit, collateral	1,196,491,000	978,266,000
Direct Overnight Borrowings | Unsecured Debt | Line of Credit
Line of Credit Facility [Line Items]
Line of credit, maximum capacity	484,000,000	204,000,000
Outstanding borrowings on line of credit	0	$ 0
Line of Credit | Federal Funds Line of Credit
Line of Credit Facility [Line Items]
Line of credit, maximum capacity	$ 30,000,000
Number of lines | Number_of_Lines	2

Junior Subordinated Debenture_2

Junior Subordinated Debentures - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)business_trust	Dec. 31, 2018USD ($)
Debt Instrument [Line Items]
Number of wholly owned statutory business trusts | business_trust	9
Junior subordinated debentures, carrying value	$ 53,824	$ 27,852
Trust Preferred Securities Issued	57,324
Junior subordinated debentures, unamortized discount	3,500
IB Trust I
Debt Instrument [Line Items]
Junior subordinated debentures, carrying value	5,155
Trust Preferred Securities Issued	$ 5,155
Interest Rate	5.16%
Guaranty Trust III
Debt Instrument [Line Items]
Junior subordinated debentures, carrying value	$ 10,310
Trust Preferred Securities Issued	$ 10,310
Interest Rate	5.09%
IB Trust II
Debt Instrument [Line Items]
Junior subordinated debentures, carrying value	$ 3,093
Trust Preferred Securities Issued	$ 3,093
Interest Rate	4.84%
Cenbank Trust III
Debt Instrument [Line Items]
Junior subordinated debentures, carrying value	$ 15,464
Trust Preferred Securities Issued	$ 15,464
Interest Rate	4.65%
IB Trust III
Debt Instrument [Line Items]
Junior subordinated debentures, carrying value	$ 3,712
Trust Preferred Securities Issued	$ 3,712
Interest Rate	4.31%
IB Centex Trust I
Debt Instrument [Line Items]
Junior subordinated debentures, carrying value	$ 2,578
Trust Preferred Securities Issued	$ 2,578
Interest Rate	5.16%
Community Group Statutory Trust I
Debt Instrument [Line Items]
Junior subordinated debentures, carrying value	$ 3,609
Trust Preferred Securities Issued	$ 3,609
Interest Rate	3.49%
Northstar Trust II
Debt Instrument [Line Items]
Junior subordinated debentures, carrying value	$ 3,815
Trust Preferred Securities Issued	$ 5,155
Interest Rate	3.56%
Northstar Trust III
Debt Instrument [Line Items]
Junior subordinated debentures, carrying value	$ 6,088
Trust Preferred Securities Issued	$ 8,248
Interest Rate	3.56%
London Interbank Offered Rate (LIBOR) | IB Trust I
Debt Instrument [Line Items]
Description of variable rate basis	LIBOR
Interest Rate Index	3.25%
London Interbank Offered Rate (LIBOR) | Guaranty Trust III
Debt Instrument [Line Items]
Description of variable rate basis	LIBOR
Interest Rate Index	3.10%
London Interbank Offered Rate (LIBOR) | IB Trust II
Debt Instrument [Line Items]
Description of variable rate basis	LIBOR
Interest Rate Index	2.85%
London Interbank Offered Rate (LIBOR) | Cenbank Trust III
Debt Instrument [Line Items]
Description of variable rate basis	LIBOR
Interest Rate Index	2.65%
London Interbank Offered Rate (LIBOR) | IB Trust III
Debt Instrument [Line Items]
Description of variable rate basis	LIBOR
Interest Rate Index	2.40%
London Interbank Offered Rate (LIBOR) | IB Centex Trust I
Debt Instrument [Line Items]
Description of variable rate basis	LIBOR
Interest Rate Index	3.25%
London Interbank Offered Rate (LIBOR) | Community Group Statutory Trust I
Debt Instrument [Line Items]
Description of variable rate basis	LIBOR
Interest Rate Index	1.60%
London Interbank Offered Rate (LIBOR) | Northstar Trust II
Debt Instrument [Line Items]
Description of variable rate basis	LIBOR
Interest Rate Index	1.67%
London Interbank Offered Rate (LIBOR) | Northstar Trust III
Debt Instrument [Line Items]
Description of variable rate basis	LIBOR
Interest Rate Index	1.67%

Leases - Additional Information

Leases - Additional Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)branch	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Lessee, Lease, Description [Line Items]
Number of branches leased | branch	21
Number of branches operated | branch	93
Operating lease expense	$ 7,025	$ 3,758	$ 3,073
Right-of-use assets	31,813
Lease liability	$ 28,978
Minimum
Lessee, Lease, Description [Line Items]
Lease term	1 year
Maximum
Lessee, Lease, Description [Line Items]
Lease term	31 years

Leases - Schedule of Net Lease

Leases - Schedule of Net Lease Cost and Other Information Related to Operating Leases (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
Leases [Abstract]
Operating lease cost	$ 7,128
Variable lease cost	1,829
Sublease income	(228)
Net lease cost	8,729
Operating cash flows from operating leases	$ 6,965
Weighted average remaining lease term - operating leases, in years	7 years 6 months 29 days
Weighted average discount rate - operating leases	3.35%

Leases - Summary of Lease Liabi

Leases - Summary of Lease Liability Maturity (Details) $ in Thousands	Dec. 31, 2019USD ($)
Leases [Abstract]
2020	$ 5,964
2021	5,784
2022	4,990
2023	4,213
2024	3,437
Thereafter	8,454
Total lease payments	32,842
Less imputed interest	(3,864)
Lease liability	$ 28,978

Income Taxes - Tax Expense (Det

Income Taxes - Tax Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Current income tax expense	$ 39,426	$ 29,801	$ 28,121
Deferred income tax expense	14,102	2,000	11,526
Deferred income tax (benefit) expense related to remeasurement of deferred taxes	0	(63)	5,528
Income tax expense, as reported	$ 53,528	$ 31,738	$ 45,175

Income Taxes - Tax Reconciliati

Income Taxes - Tax Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income tax expense computed at the statutory rate	$ 51,715	$ 33,599	$ 42,590
Tax-exempt interest income from municipal securities	(1,781)	(962)	(1,357)
Tax-exempt loan income	(1,174)	(490)	(435)
Bank owned life insurance income	(1,288)	(666)	(962)
Non-deductible acquisition expenses	281	142	491
State taxes, net of federal benefit	3,455	375	241
Non-deductible compensation	2,017	0	0
Net tax expense (benefit) from stock based compensation	21	(646)	(1,323)
Deferred tax adjustment related to reduction in U.S. Federal statutory income tax rate	0	(63)	5,528
Other	282	449	402
Income tax expense, as reported	$ 53,528	$ 31,738	$ 45,175

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019
Operating Loss Carryforwards [Line Items]
Deferred expense related to impact of Tax Cuts and Jobs Act		$ 5,528,000
Tax benefit related to change in tax rate and tax method of accounting	$ 63,000
Valuation allowance	$ 0		$ 0
Federal Tax Authority
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards			17,293,000
Tax credit carryover			132,000
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards			$ 12,155,000

Income Taxes - Components of De

Income Taxes - Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Allowance for loan losses	$ 11,466	$ 9,496
Lease liabilities under operating leases	6,457	0
NOL and tax credit carryforwards from acquisitions	4,209	4,810
Net unrealized loss on available for sale securities	0	2,365
Acquired loan fair market value adjustments	21,645	6,090
Stock-based compensation	1,218	987
Reserve for bonuses and other accrued expenses	2,773	1,646
Deferred loan fees	378	700
Acquisition costs	416	0
Acquired Securities	2,529	273
Acquired intangibles	1,546	0
Start up costs	230	274
Other real estate owned	362	273
Unearned income	774	160
Deferred compensation	1,101	1,266
Noncompete agreements	663	552
Nonaccrual loans	390	470
Other	407	303
Deferred tax assets, gross	56,564	29,665
Deferred tax liabilities:
Premises and equipment	(13,170)	(5,242)
Right-of-use assets under operating leases	(6,233)	0
Net unrealized gain on available for sale securities	5,367	0
Intangible assets	(22,447)	(9,547)
Acquired junior subordinated debentures fair value adjustment	(780)	(777)
Restricted stock	(673)	(250)
Prepaids	(281)	(190)
Acquired tax goodwill	(413)	(232)
Other	(257)	(247)
Deferred tax liabilities, gross	(49,621)	(16,485)
Net deferred tax asset	$ 6,943	$ 13,180

Commitments and Contingencies_2

Commitments and Contingencies (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance sheet risk	$ 2,360,791	$ 1,776,721
Commitments to extend credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance sheet risk	2,337,385	1,761,724
Standby letters of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance sheet risk	$ 23,406	$ 14,997

Related Party Transactions - Lo

Related Party Transactions - Loan Activity for Officers, Directors and Affiliates (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
Loans and Leases Receivable, Related Parties [Roll Forward]
Balance at beginning of year	$ 58,967
New loans	14,185
Repayments	(31,366)
Changes in affiliated persons	(2,990)
Balance at end of year	$ 38,796

Employee Benefit Plans - Additi

Employee Benefit Plans - Additional Information (Detail) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Contribution Plan Disclosure [Line Items]
Minimum age			18 years
Credited service period			90 days
Salary reduction set by law			$ 19
Employer contribution, matching percentage (percent)	100.00%		100.00%
Employer contribution as percentage of participant's eligible salary (percent)	6.00%	6.00%	6.00%
Employer contribution, amount			$ 6,343	$ 3,280	$ 2,070
Minimum
Defined Contribution Plan Disclosure [Line Items]
Employer contribution, matching percentage (percent)		50.00%
Maximum
Defined Contribution Plan Disclosure [Line Items]
Employer contribution, matching percentage (percent)		100.00%

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	$ 1,085,936	$ 685,350
Loans held for sale, fair value option elected	29,204	27,871
Aggregate principal balance of loans held for sale	28,166	26,594
Not designated as hedging | Interest rate lock commitments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Asset Derivative Fair Value	847	822
Liability Derivative Fair Value	0	0
Not designated as hedging | Forward mortgage-backed securities trades
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Asset Derivative Fair Value	6	0
Liability Derivative Fair Value	69	226
Fair Value, Measurements, Recurring | Not designated as hedging
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Loans held for sale, fair value option elected	29,204	27,871
Fair Value, Measurements, Recurring | Not designated as hedging | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Loans held for sale, fair value option elected	0	0
Fair Value, Measurements, Recurring | Not designated as hedging | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Loans held for sale, fair value option elected	29,204	27,871
Fair Value, Measurements, Recurring | Not designated as hedging | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Loans held for sale, fair value option elected	0	0
Fair Value, Measurements, Recurring | Not designated as hedging | Interest rate lock commitments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Asset Derivative Fair Value	847	822
Fair Value, Measurements, Recurring | Not designated as hedging | Interest rate lock commitments | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Asset Derivative Fair Value	0	0
Fair Value, Measurements, Recurring | Not designated as hedging | Interest rate lock commitments | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Asset Derivative Fair Value	847	822
Fair Value, Measurements, Recurring | Not designated as hedging | Interest rate lock commitments | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Asset Derivative Fair Value	0	0
Fair Value, Measurements, Recurring | Not designated as hedging | Forward mortgage-backed securities trades
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Asset Derivative Fair Value	6
Liability Derivative Fair Value	69	226
Fair Value, Measurements, Recurring | Not designated as hedging | Forward mortgage-backed securities trades | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Asset Derivative Fair Value	0
Liability Derivative Fair Value	0	0
Fair Value, Measurements, Recurring | Not designated as hedging | Forward mortgage-backed securities trades | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Asset Derivative Fair Value	6
Liability Derivative Fair Value	69	226
Fair Value, Measurements, Recurring | Not designated as hedging | Forward mortgage-backed securities trades | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Asset Derivative Fair Value	0
Liability Derivative Fair Value	0	0
Fair Value, Measurements, Recurring | Not designated as hedging | Interest rate swap | Loan customer counterparty
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Asset Derivative Fair Value	6,104	360
Liability Derivative Fair Value		108
Fair Value, Measurements, Recurring | Not designated as hedging | Interest rate swap | Loan customer counterparty | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Asset Derivative Fair Value	0	0
Liability Derivative Fair Value		0
Fair Value, Measurements, Recurring | Not designated as hedging | Interest rate swap | Loan customer counterparty | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Asset Derivative Fair Value	6,104	360
Liability Derivative Fair Value		108
Fair Value, Measurements, Recurring | Not designated as hedging | Interest rate swap | Loan customer counterparty | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Asset Derivative Fair Value	0	0
Liability Derivative Fair Value		0
Fair Value, Measurements, Recurring | Not designated as hedging | Interest rate swap | Financial institution counterparty
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Asset Derivative Fair Value		109
Liability Derivative Fair Value	6,566	406
Fair Value, Measurements, Recurring | Not designated as hedging | Interest rate swap | Financial institution counterparty | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Asset Derivative Fair Value		0
Liability Derivative Fair Value	0	0
Fair Value, Measurements, Recurring | Not designated as hedging | Interest rate swap | Financial institution counterparty | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Asset Derivative Fair Value		109
Liability Derivative Fair Value	6,566	406
Fair Value, Measurements, Recurring | Not designated as hedging | Interest rate swap | Financial institution counterparty | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Asset Derivative Fair Value		0
Liability Derivative Fair Value	0	0
U.S. treasuries
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	48,796	29,643
U.S. treasuries | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	48,796	29,643
U.S. treasuries | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	0	0
U.S. treasuries | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	48,796	29,643
U.S. treasuries | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	0	0
Government agency securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	179,296	150,230
Government agency securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	179,296	150,230
Government agency securities | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	0	0
Government agency securities | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	179,296	150,230
Government agency securities | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	0	0
Obligations of state and municipal subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	343,859	185,007
Obligations of state and municipal subdivisions | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	343,859	185,007
Obligations of state and municipal subdivisions | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	0	0
Obligations of state and municipal subdivisions | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	343,859	185,007
Obligations of state and municipal subdivisions | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	0	0
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	7,218
Corporate bonds | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	7,218
Corporate bonds | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	0
Corporate bonds | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	7,218
Corporate bonds | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	0
Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	505,567	320,470
Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	505,567	320,470
Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	0	0
Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	505,567	320,470
Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	0	$ 0
Other securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	1,200
Other securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	1,200
Other securities | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	0
Other securities | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	1,200
Other securities | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Securities available for sale	$ 0

Fair Value Measurements - Ass_2

Fair Value Measurements - Assets and Liabilities at Fair Value on Nonrecurring Basis (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Impaired loans	$ 12,087	$ 14,575
Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Impaired loans	2,276	3,824
Other real estate owned	4,618
Fair Value, Measurements, Nonrecurring | Impaired loans
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Period Ended Total Losses	1,806	2,227
Fair Value, Measurements, Nonrecurring | Other real estate owned
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Period Ended Total Losses	749
Fair Value, Measurements, Nonrecurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Impaired loans	0	0
Other real estate owned	0
Fair Value, Measurements, Nonrecurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Impaired loans	0	0
Other real estate owned	0
Fair Value, Measurements, Nonrecurring | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Impaired loans	2,276	$ 3,824
Other real estate owned	$ 4,618

Fair Value Measurements - Carry

Fair Value Measurements - Carrying Amount and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Off-balance sheet assets (liabilities):
Financial instruments with off-balance sheet risk	$ 2,360,791	$ 1,776,721
Commitments to extend credit
Off-balance sheet assets (liabilities):
Financial instruments with off-balance sheet risk	2,337,385	1,761,724
Standby letters of credit
Off-balance sheet assets (liabilities):
Financial instruments with off-balance sheet risk	23,406	14,997
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and cash equivalents	565,170	130,779
Certificates of deposit held in other banks	0	0
Loans held for sale, at cost	0	0
Loans, net	0	0
FHLB of Dallas stock and other restricted stock	0	0
Accrued interest receivable	0	0
Financial liabilities:
Deposits	0	0
Accrued interest payable	0	0
FHLB advances	0	0
Other borrowings	0	0
Junior subordinated debentures	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Commitments to extend credit
Off-balance sheet assets (liabilities):
Financial instruments with off-balance sheet risk	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Standby letters of credit
Off-balance sheet assets (liabilities):
Financial instruments with off-balance sheet risk	0	0
Significant Other Observable Inputs (Level 2)
Financial assets:
Cash and cash equivalents	0	0
Certificates of deposit held in other banks	5,951	1,224
Loans held for sale, at cost	6,554	4,974
Loans, net	0	0
FHLB of Dallas stock and other restricted stock	30,052	26,870
Accrued interest receivable	35,860	24,253
Financial liabilities:
Deposits	11,958,939	7,750,059
Accrued interest payable	9,583	6,183
FHLB advances	325,210	287,450
Other borrowings	209,050	138,450
Junior subordinated debentures	48,879	31,370
Significant Other Observable Inputs (Level 2) | Commitments to extend credit
Off-balance sheet assets (liabilities):
Financial instruments with off-balance sheet risk	0	0
Significant Other Observable Inputs (Level 2) | Standby letters of credit
Off-balance sheet assets (liabilities):
Financial instruments with off-balance sheet risk	0	0
Significant Unobservable Inputs (Level 3)
Financial assets:
Cash and cash equivalents	0	0
Certificates of deposit held in other banks	0	0
Loans held for sale, at cost	0	0
Loans, net	11,689,672	7,807,823
FHLB of Dallas stock and other restricted stock	0	0
Accrued interest receivable	0	0
Financial liabilities:
Deposits	0	0
Accrued interest payable	0	0
FHLB advances	0	0
Other borrowings	0	0
Junior subordinated debentures	0	0
Significant Unobservable Inputs (Level 3) | Commitments to extend credit
Off-balance sheet assets (liabilities):
Financial instruments with off-balance sheet risk	0	0
Significant Unobservable Inputs (Level 3) | Standby letters of credit
Off-balance sheet assets (liabilities):
Financial instruments with off-balance sheet risk	0	0
Carrying Amount
Financial assets:
Cash and cash equivalents	565,170	130,779
Certificates of deposit held in other banks	5,719	1,225
Loans held for sale, at cost	6,441	4,856
Loans, net	11,562,814	7,839,695
FHLB of Dallas stock and other restricted stock	30,052	26,870
Accrued interest receivable	35,860	24,253
Financial liabilities:
Deposits	11,941,336	7,737,794
Accrued interest payable	9,583	6,183
FHLB advances	325,000	290,000
Other borrowings	202,251	137,316
Junior subordinated debentures	53,824	27,852
Carrying Amount | Commitments to extend credit
Off-balance sheet assets (liabilities):
Financial instruments with off-balance sheet risk	0	0
Carrying Amount | Standby letters of credit
Off-balance sheet assets (liabilities):
Financial instruments with off-balance sheet risk	0	0
Estimated Fair Value
Financial assets:
Cash and cash equivalents	565,170	130,779
Certificates of deposit held in other banks	5,951	1,224
Loans held for sale, at cost	6,554	4,974
Loans, net	11,689,672	7,807,823
FHLB of Dallas stock and other restricted stock	30,052	26,870
Accrued interest receivable	35,860	24,253
Financial liabilities:
Deposits	11,958,939	7,750,059
Accrued interest payable	9,583	6,183
FHLB advances	325,210	287,450
Other borrowings	209,050	138,450
Junior subordinated debentures	48,879	31,370
Estimated Fair Value | Commitments to extend credit
Off-balance sheet assets (liabilities):
Financial instruments with off-balance sheet risk	0	0
Estimated Fair Value | Standby letters of credit
Off-balance sheet assets (liabilities):
Financial instruments with off-balance sheet risk	$ 0	$ 0

Derivative Financial Instrume_3

Derivative Financial Instruments - Notional Balances and Fair Values of Outstanding Positions (Details) - Not designated as hedging - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Interest rate lock commitments
Derivative [Line Items]
Outstanding Notional Balance	$ 28,434	$ 20,306
Asset Derivative Fair Value	847	822
Liability Derivative Fair Value	0	0
Forward mortgage-backed securities trades
Derivative [Line Items]
Outstanding Notional Balance	42,500	27,500
Asset Derivative Fair Value	6	0
Liability Derivative Fair Value	69	226
Commercial loan interest rate swaps | Commercial Loan | Loan customer counterparty
Derivative [Line Items]
Outstanding Notional Balance	280,751	25,055
Asset Derivative Fair Value	6,104	360
Liability Derivative Fair Value	0	108
Commercial loan interest rate swaps | Commercial Loan | Financial institution counterparty
Derivative [Line Items]
Outstanding Notional Balance	280,751	25,055
Asset Derivative Fair Value	0	109
Liability Derivative Fair Value	$ 6,566	$ 406

Derivative Financial Instrume_4

Derivative Financial Instruments - Narrative (Details) $ in Thousands	Dec. 31, 2019USD ($)
Derivative [Line Items]
Cash collateral pledged for derivatives	$ 4,350
Securities collateral pledged for derivatives	3,645
Risk Participation Agreements Lead Bank
Derivative [Line Items]
Credit risk participation	9,850
Loan customer counterparty | Interest rate swap
Derivative [Line Items]
Credit exposure	$ 6,104

Derivative Financial Instrume_5

Derivative Financial Instruments Derivative Financial Instruments - Schedule of Weighted Average Interest Rate Received and Paid (Details) - Not designated as hedging - Commercial Loan - Loan customer counterparty - Interest rate swap	Dec. 31, 2019	Dec. 31, 2018
Interest Rate Received
Derivative [Line Items]
Weighted Average Interest Rate	4.23%	4.67%
Interest Rate Paid
Derivative [Line Items]
Weighted Average Interest Rate	3.77%	4.46%

Derivative Financial Instrume_6

Derivative Financial Instruments - Income (Loss) on Derivatives Not Designated as Hedging Instruments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Interest rate lock commitments
Derivative [Line Items]
Derivatives not designated as hedging instruments	$ 25	$ 822
Forward mortgage-backed securities trades
Derivative [Line Items]
Derivatives not designated as hedging instruments	$ 163	$ (226)

Stock Awards - Additional Infor

Stock Awards - Additional Information (Detail) - USD ($) $ in Thousands	Jan. 01, 2019	May 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense			$ 7,808	$ 6,062	$ 4,688
Estimated future compensation expense			$ 11,263
Period for recognition			2 years 4 months 24 days
Fair value of common stock awards vested			$ 8,725	8,206	8,597
Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Excess tax expense (benefit) on vested restricted stock			$ 21	$ (646)	$ (1,323)
2013 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase in shares reserved for future issuance (shares)		1,500,000
Shares reserved for future issuance (shares)		2,300,000
Remaining available for grant for future awards (shares)			1,452,124
2013 Equity Incentive Plan | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock vesting period			3 years
2013 Equity Incentive Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock vesting period			5 years
Guaranty 2015 RSA
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock vesting period	2 years

Stock Awards - Schedule of Nonv

Stock Awards - Schedule of Nonvested Shares Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Number of Shares
Nonvested shares, beginning balance (shares)	252,903	242,056
Acquired awards replaced during the period (shares)	70,248
Granted during the period (shares)	138,608	130,212
Vested during the period (shares)	(161,032)	(115,520)
Forfeited during the period (shares)	(15,866)	(3,845)
Nonvested shares, ending balance (shares)	284,861	252,903
Weighted Average Grant Date Fair Value
Nonvested shares, beginning balance (usd per share)	$ 62.81	$ 49.17
Acquired awards replaced during the period (usd per share)	45.77
Granted during the period (usd per share)	51.14	71.85
Vested during the period (usd per share)	54.76	44.36
Forfeited during the period (use per share)	46.95	64.47
Nonvested shares, ending balance (usd per share)	$ 58.63	$ 62.81

Stock Awards - Future Vesting S

Stock Awards - Future Vesting Schedule of Nonvested Shares (Detail)	Dec. 31, 2019shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested shares	284,861
First year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested shares	105,390
Second year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested shares	96,125
Third year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested shares	62,006
Fourth year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested shares	19,260
Fifth year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested shares	2,080

Regulatory Matters - Actual Cap

Regulatory Matters - Actual Capital Amounts and Ratios (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Consolidated
Total capital to risk weighted assets:
Actual Amount	$ 1,513,209	$ 1,072,156
Actual Ratio (percent)	11.83%	12.58%
Minimum Required for Capital Adequacy Purposes Amount	$ 1,343,114	$ 681,686
Minimum Required for Capital Adequacy Purposes Ratio (percent)	10.50%	8.00%
Tier 1 capital to risk weighted assets:
Actual Amount	$ 1,303,748	$ 887,354
Actual Ratio (percent)	10.19%	10.41%
Minimum Required for Capital Adequacy Purposes Amount	$ 1,087,282	$ 511,264
Minimum Required for Capital Adequacy Purposes Ratio (percent)	8.50%	6.00%
Common equity tier 1 to risk weighted assets:
Actual Amount	$ 1,248,148	$ 856,754
Actual Ratio (percent)	9.76%	10.05%
Minimum Required for Capital Adequacy Purposes Amount	$ 895,409	$ 383,448
Minimum Required for Capital Adequacy Purposes Ratio (percent)	7.00%	4.50%
Tier 1 capital to average assets:
Actual Amount	$ 1,303,748	$ 887,354
Actual Ratio (percent)	9.32%	9.57%
Minimum Required for Capital Adequacy Purposes Amount	$ 559,758	$ 370,727
Minimum Required for Capital Adequacy Purposes Ratio (percent)	4.00%	4.00%
Bank
Total capital to risk weighted assets:
Actual Amount	$ 1,548,103	$ 1,054,783
Actual Ratio (percent)	12.11%	12.39%
Minimum Required for Capital Adequacy Purposes Amount	$ 1,342,595	$ 681,004
Minimum Required for Capital Adequacy Purposes Ratio (percent)	10.50%	8.00%
To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	$ 1,278,662	$ 851,255
To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (percent)	10.00%	10.00%
Tier 1 capital to risk weighted assets:
Actual Amount	$ 1,496,642	$ 1,009,981
Actual Ratio (percent)	11.70%	11.86%
Minimum Required for Capital Adequacy Purposes Amount	$ 1,086,863	$ 510,753
Minimum Required for Capital Adequacy Purposes Ratio (percent)	8.50%	6.00%
To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	$ 1,022,930	$ 681,004
To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (percent)	8.00%	8.00%
Common equity tier 1 to risk weighted assets:
Actual Amount	$ 1,496,642	$ 1,009,981
Actual Ratio (percent)	11.70%	11.86%
Minimum Required for Capital Adequacy Purposes Amount	$ 895,064	$ 383,065
Minimum Required for Capital Adequacy Purposes Ratio (percent)	7.00%	4.50%
To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	$ 831,130	$ 553,316
To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (percent)	6.50%	6.50%
Tier 1 capital to average assets:
Actual Amount	$ 1,496,642	$ 1,009,981
Actual Ratio (percent)	10.70%	10.91%
Minimum Required for Capital Adequacy Purposes Amount	$ 559,584	$ 370,412
Minimum Required for Capital Adequacy Purposes Ratio (percent)	4.00%	4.00%
To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	$ 699,480	$ 463,015
To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (percent)	5.00%	5.00%

Business Combinations - Additio

Business Combinations - Additional Information (Detail) $ in Thousands	Jan. 01, 2019USD ($)branchshares	Dec. 31, 2018USD ($)	Jun. 01, 2018USD ($)branchshares	Jun. 01, 2020	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Business Acquisition [Line Items]
Acquisition related expenses					$ 33,445	$ 6,157	$ 12,898
Cash paid					9	31,016	17,773
Goodwill acquired		$ 721,797			994,021	721,797
Offering costs paid in connection with acquired banks					804	209	942
Texas Capital Bancshares, Inc.
Business Acquisition [Line Items]
Acquisition related expenses					5,835
Guaranty Bancorp
Business Acquisition [Line Items]
Percentage of outstanding stock acquired (percent)	100.00%
Acquisition related expenses					33,622	1,560
Number of branches acquired | branch	32
Stock issued for acquisition of bank (in shares) | shares	13,179,748
Cash paid	$ 9				9
Goodwill acquired	270,583				272,224
Offering costs paid in connection with acquired banks					804
Estimated fair value of non-credit impaired loans	2,478,144
Contractual balance of non-credit impaired loans	2,573,355
Interest income adjustment for non-credit impaired loans	$ 95,211
Integrity Bancshares, Inc.
Business Acquisition [Line Items]
Percentage of outstanding stock acquired (percent)			100.00%
Acquisition related expenses						4,074	$ 360
Stock issued for acquisition of bank (in shares) | shares			2,071,981
Cash paid		31,016	$ 31,016
Goodwill acquired		$ 100,339	100,339			100,339
Offering costs paid in connection with acquired banks						$ 209
Estimated fair value of non-credit impaired loans			604,549
Contractual balance of non-credit impaired loans			609,675
Interest income adjustment for non-credit impaired loans			$ 5,126
Integrity Bancshares, Inc. | Houston
Business Acquisition [Line Items]
Number of branches acquired | branch			4
Independent Bank Group, Inc. | Forecast | Texas Capital Bancshares, Inc.
Business Acquisition [Line Items]
Percentage of outstanding stock acquired (percent)				45.00%
Texas Capital Bancshares, Inc. | Forecast | Texas Capital Bancshares, Inc.
Business Acquisition [Line Items]
business acquisition, equity interest issued or issuable, number of shares acquired, conversion ratio				103.11%
Percentage of outstanding stock acquired (percent)				55.00%
Salaries and employee benefits | Texas Capital Bancshares, Inc.
Business Acquisition [Line Items]
Acquisition related expenses					813
Salaries and employee benefits | Guaranty Bancorp
Business Acquisition [Line Items]
Acquisition related expenses					5,328
Acquisition expense | Texas Capital Bancshares, Inc.
Business Acquisition [Line Items]
Acquisition related expenses					5,022
Acquisition expense | Guaranty Bancorp
Business Acquisition [Line Items]
Acquisition related expenses					$ 28,294
Preferred Stock | Texas Capital Bancshares, Inc. | Forecast | Texas Capital Bancshares, Inc.
Business Acquisition [Line Items]
business acquisition, equity interest issued or issuable, number of shares acquired, conversion ratio				100.00%

Business Combinations - Estimat

Business Combinations - Estimated Fair Values Of Assets Acquired And Liabilities Assumed (Detail) - USD ($) $ / shares in Units, $ in Thousands	Jan. 01, 2019	Dec. 31, 2018	Jun. 01, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Assets of acquired bank:
Goodwill		$ 721,797		$ 994,021	$ 721,797
Measurement period adjustments:
Common stock issued at $45.77 for Guaranty and $75.90 for Integrity per share				601,872	157,263	$ 566,142
Cash paid				9	31,016	$ 17,773
Guaranty Bancorp
Assets of acquired bank:
Cash and cash equivalents	$ 39,913			39,913
Certificates of deposit held in other banks	262			262
Securities available for sale	561,052			561,052
Restricted stock	27,794			27,794
Loans	2,788,159			2,789,868
Premises and equipment	65,786			65,786
Other real estate owned	1,710			1,829
Goodwill	270,583			272,224
Other intangible assets	71,518			71,518
Bank owned life insurance	80,837			80,837
Other assets	31,517			31,987
Total assets acquired	3,939,131			3,943,070
Liabilities of acquired bank:
Deposits	3,108,810			3,108,810
Repurchase agreements	8,475			8,475
FHLB advances	142,653			142,653
Other borrowings	40,000			40,000
Junior subordinated debentures	25,774			25,774
Other liabilities	11,538			15,477
Total liabilities assumed	3,337,250			3,341,189
Measurement period adjustments:
Loans				1,709
Other real estate owned				119
Goodwill				1,641
Other assets				470
Total assets				3,939
Other liabilities				3,939
Total liabilities				3,939
Common stock issued at $45.77 for Guaranty and $75.90 for Integrity per share	600,022			600,022
Cash paid	$ 9			9
Stock issued for acquisition of bank (in shares)	13,179,748
Share price (in USD per share)	$ 45.77
Integrity Bancshares, Inc.
Assets of acquired bank:
Cash and cash equivalents		44,723			44,723
Securities available for sale		24,721			24,721
Restricted stock		3,357			3,357
Loans		651,769			651,769
Premises and equipment		4,863			4,863
Goodwill		100,339	$ 100,339		100,339
Other intangible assets		7,537			7,537
Bank owned life insurance		8,181			8,181
Other assets		6,385			6,385
Total assets acquired		851,875			851,875
Liabilities of acquired bank:
Deposits		593,078			593,078
FHLB advances		60,000			60,000
Other liabilities		10,518			10,518
Total liabilities assumed		663,596			$ 663,596
Measurement period adjustments:
Common stock issued at $45.77 for Guaranty and $75.90 for Integrity per share		157,263
Cash paid		$ 31,016	$ 31,016
Stock issued for acquisition of bank (in shares)			2,071,981
Share price (in USD per share)			$ 75.90
Common Stock | Guaranty Bancorp
Measurement period adjustments:
Stock issued for acquisition of bank (in shares)	13,109,500
Restricted Stock Replacement Awards | Guaranty Bancorp
Measurement period adjustments:
Common stock issued at $45.77 for Guaranty and $75.90 for Integrity per share	$ 1,850			$ 1,850
Stock issued for acquisition of bank (in shares)	70,248

Business Combinations - Pro For

Business Combinations - Pro Forma Information (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Acquisition related expenses	$ 33,445	$ 6,157	$ 12,898
Guaranty Bancorp
Business Acquisition [Line Items]
Interest income		585,412
Noninterest income		71,983
Total revenue		657,395
Net income		$ 203,542
Basic earnings per share (in usd per share)		$ 4.76
Diluted earnings per share (in usd per share)		$ 4.74
Acquisition related expenses	$ 33,622	$ 1,560
Guaranty Bancorp | Guaranty Bancorp
Business Acquisition [Line Items]
Acquisition related expenses		$ 2,034

Parent Company Only Financial_3

Parent Company Only Financial Statements - Balance Sheet (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Assets
Cash and cash equivalents	$ 565,170	$ 130,779
Other assets	108,392	51,713
Total assets	14,958,207	9,849,965
Liabilities and Stockholders’ Equity
Other borrowings	202,251	137,316
Junior subordinated debentures	53,824	27,852
Other liabilities	96,023	50,570
Total liabilities	12,618,434	8,243,532
Stockholders’ equity:
Preferred stock	0	0
Common stock	430	306
Additional paid-in capital	1,926,359	1,317,616
Retained earnings	393,674	296,816
Accumulated other comprehensive loss	19,310	(8,305)
Total stockholders’ equity	2,339,773	1,606,433	$ 1,336,018	$ 672,365
Total liabilities and stockholders’ equity	14,958,207	9,849,965
Parent
Assets
Cash and cash equivalents	8,277	8,355	$ 9,400	$ 9,265
Investment in subsidiaries	2,588,857	1,764,698
Investment in trusts	1,724	950
Other assets	3,355	2,189
Total assets	2,602,213	1,776,192
Liabilities and Stockholders’ Equity
Other borrowings	202,251	137,316
Junior subordinated debentures	53,824	27,852
Other liabilities	6,365	4,591
Total liabilities	262,440	169,759
Stockholders’ equity:
Preferred stock	0	0
Common stock	430	306
Additional paid-in capital	1,926,359	1,317,616
Retained earnings	393,674	296,816
Accumulated other comprehensive loss	19,310	(8,305)
Total stockholders’ equity	2,339,773	1,606,433
Total liabilities and stockholders’ equity	$ 2,602,213	$ 1,776,192

Parent Company Only Financial_4

Parent Company Only Financial Statements - Statement of Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Interest expense:
Interest on other borrowings	$ 11,590	$ 8,398	$ 6,898
Interest on junior subordinated debentures	3,028	1,609	1,162
Total interest expense	148,175	81,038	42,436
Noninterest income:
Other	13,148	9,507	7,608
Total noninterest income	78,176	42,224	41,287
Noninterest expense:
Salaries and employee benefits	162,683	111,697	95,741
Professional fees	7,936	4,556	4,564
Acquisition expense, including legal	33,445	6,157	12,898
Other	39,207	25,961	17,956
Total noninterest expense	321,864	198,619	176,813
Income before income tax benefit and equity in undistributed income of subsidiaries	246,264	159,997	121,687
Income tax benefit	(53,528)	(31,738)	(45,175)
Net income	192,736	128,259	76,512
Parent
Interest expense:
Interest on other borrowings	11,561	8,390	6,873
Interest on junior subordinated debentures	3,028	1,609	1,162
Total interest expense	14,589	9,999	8,035
Noninterest income:
Dividends from subsidiaries	105,877	39,841	29,563
Other	1	14	32
Total noninterest income	105,878	39,855	29,595
Noninterest expense:
Salaries and employee benefits	7,653	6,318	5,175
Professional fees	264	332	546
Acquisition expense, including legal	33,445	6,157	12,767
Other	2,562	1,611	1,614
Total noninterest expense	43,924	14,418	20,102
Income before income tax benefit and equity in undistributed income of subsidiaries	47,365	15,438	1,458
Income tax benefit	11,066	5,541	8,890
Income before equity in undistributed income of subsidiaries	58,431	20,979	10,348
Equity in undistributed income of subsidiaries	134,305	107,280	66,164
Net income	$ 192,736	$ 128,259	$ 76,512

Parent Company Only Financial_5

Parent Company Only Financial Statements - Statement of Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net income	$ 192,736	$ 128,259	$ 76,512
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of discount and origination costs on borrowings	633	633	505
Stock based compensation expense	7,808	6,062	4,688
Excess tax expense (benefit) on restricted stock vested	21	(646)	(1,323)
Deferred tax expense	14,102	1,937	17,054
Net change in other assets	(5,878)	(14,352)	(5,987)
Net change in other liabilities	(15,636)	20,277	(2,920)
Net cash provided by operating activities	173,319	158,741	82,795
Cash flows from investing activities:
Cash acquired in connection with acquisition	39,913	44,723	148,444
Cash paid in connection with acquisition	(9)	(31,016)	(17,773)
Net cash used in investing activities	(673,988)	(656,707)	(662,333)
Cash flows from financing activities:
Proceeds from other borrowings	65,000	0	29,255
Repayments of other borrowings	(40,500)	0	0
Proceeds from exercise of common stock warrants	0	2,533	55
Offering costs paid in connection with acquired bank	(804)	(209)	(942)
Proceeds from sale of common stock, net	0	0	26,816
Repurchase of common stock	(51,659)	0	0
Dividends paid	(43,302)	(15,908)	(10,231)
Net cash (used in) provided by financing activities	935,060	197,643	505,613
Net change in cash and cash equivalents	434,391	(300,323)	(73,925)
Cash and cash equivalents at beginning of year	130,779
Cash and cash equivalents at end of year	565,170	130,779
Parent
Cash flows from operating activities:
Net income	192,736	128,259	76,512
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed net income of subsidiaries	(134,305)	(107,280)	(66,164)
Amortization of discount and origination costs on borrowings	633	633	505
Stock based compensation expense	7,808	6,062	4,688
Excess tax expense (benefit) on restricted stock vested	21	(646)	(1,323)
Deferred tax expense	2,165	1,054	11,782
Net change in other assets	1,863	6,918	(6,750)
Net change in other liabilities	(64)	1,130	(1,663)
Net cash provided by operating activities	70,857	36,130	17,587
Cash flows from investing activities:
Capital investment in subsidiaries	0	0	(50,050)
Cash acquired in connection with acquisition	339	7,425	5,418
Cash paid in connection with acquisition	(9)	(31,016)	(17,773)
Net cash used in investing activities	330	(23,591)	(62,405)
Cash flows from financing activities:
Proceeds from other borrowings	65,000	0	29,255
Repayments of other borrowings	(40,500)	0	0
Proceeds from exercise of common stock warrants	0	2,533	55
Offering costs paid in connection with acquired bank	(804)	(209)	(942)
Proceeds from sale of common stock, net	0	0	26,816
Repurchase of common stock	(51,659)	0	0
Dividends paid	(43,302)	(15,908)	(10,231)
Net cash (used in) provided by financing activities	(71,265)	(13,584)	44,953
Net change in cash and cash equivalents	(78)	(1,045)	135
Cash and cash equivalents at beginning of year	8,355	9,400	9,265
Cash and cash equivalents at end of year	$ 8,277	$ 8,355	$ 9,400

Subsequent Events - Narrative (

Subsequent Events - Narrative (Details) - Subsequent event - USD ($)	Mar. 02, 2020	Feb. 20, 2020	Jan. 29, 2020	Jan. 17, 2020
Subsequent Event [Line Items]
Dividends declared (in usd per share)			$ 0.25
Dividends paid		$ 10,754,000
Revolving line of credit | Line of Credit
Subsequent Event [Line Items]
Line of credit, maximum capacity				$ 100,000,000
Borrowings against line of credit	$ 0