Prosperity Bancshares (PB) 10-Q 2 Aug 19 2019 Q2 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	6 Months Ended
	Jun. 30, 2019	Jul. 30, 2019
Document And Entity Information [Abstract]
Entity Registrant Name	PROSPERITY BANCSHARES INC
Entity Central Index Key	0001068851
Trading Symbol	PB
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Jun. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Amendment Flag	false
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding (in shares)		69,053,368
Entity Current Reporting Status	Yes
Entity File Number	001-35388
Entity Incorporation, State or Country Name	TEXAS
Entity Tax Identification Number	742331986
Entity Address, Address Line One	Prosperity Bank Plaza
Entity Address, Address Line Two	4295 San Felipe
Entity Address, City or Town	Houston
Entity Address, State or Province	Texas
Entity Address, Postal Zip Code	77027
City Area Code	281
Local Phone Number	269-7199
Entity Shell Company	false

Consolidated Balance Sheets (Un

Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
ASSETS
Cash and due from banks	$ 302,069	$ 410,575
Federal funds sold	555	552
Total cash and cash equivalents	302,624	411,127
Available for sale securities, at fair value	306,777	84,155
Held to maturity securities, at cost (fair value of $8,656,409 and $9,081,236, respectively)	8,645,163	9,324,811
Total securities	8,951,940	9,408,966
Loans held for sale	20,315	29,367
Loans held for investment	10,567,060	10,340,946
Total loans	10,587,375	10,370,313
Less: allowance for credit losses	(87,006)	(86,440)
Loans, net	10,500,369	10,283,873
Accrued interest receivable	57,382	56,532
Goodwill	1,900,845	1,900,845
Core deposit intangibles, net	30,299	32,883
Bank premises and equipment, net	262,479	257,046
Other real estate owned	2,005	1,805
Bank owned life insurance (BOLI)	261,372	260,335
Federal Home Loan Bank of Dallas stock	56,459	55,959
Other assets	49,447	24,031
TOTAL ASSETS	22,375,221	22,693,402
Deposits:
Noninterest-bearing	5,691,236	5,666,115
Interest-bearing	11,196,393	11,590,443
Total deposits	16,887,629	17,256,558
Other borrowings	940,874	1,031,126
Securities sold under repurchase agreements	313,825	284,720
Accrued interest payable	5,171	4,201
Other liabilities	99,827	63,973
Total liabilities	18,247,326	18,640,578
COMMITMENTS AND CONTINGENCIES
SHAREHOLDERS’ EQUITY:
Preferred stock, $1 par value; 20,000,000 shares authorized; none issued or outstanding
Common stock, $1 par value; 200,000,000 shares authorized; 69,261,431 shares issued and outstanding at June 30, 2019; 69,846,825 shares issued and outstanding at December 31, 2018	69,261	69,847
Capital surplus	2,012,665	2,045,351
Retained earnings	2,044,696	1,937,316
Accumulated other comprehensive income —net unrealized gain on available for sale securities, net of tax expense of $338 and $82, respectively	1,273	310
Total shareholders’ equity	4,127,895	4,052,824
TOTAL LIABILITIES AND SHAREHOLDERS’ EQUITY	$ 22,375,221	$ 22,693,402

Consolidated Balance Sheets (_2

Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Held to maturity securities, fair value	$ 8,656,409	$ 9,081,236
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Preferred stock, shares authorized (in shares)	20,000,000	20,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	69,261,431	69,846,825
Common stock, shares outstanding (in shares)	69,261,431	69,846,825
Accumulated other comprehensive income (loss)—net unrealized gain (loss) on available for sale securities, tax expense (benefit)	$ 338	$ 82

Consolidated Statements of Inco

Consolidated Statements of Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
INTEREST INCOME:
Loans, including fees	$ 133,525	$ 128,445	$ 263,590	$ 244,691
Securities	53,944	55,577	109,592	110,034
Federal funds sold and other earning assets	318	299	720	614
Total interest income	187,787	184,321	373,902	355,339
INTEREST EXPENSE:
Deposits	26,562	16,061	51,690	30,533
Other borrowings	5,556	6,046	10,873	9,019
Securities sold under repurchase agreements	831	411	1,590	761
Total interest expense	32,949	22,518	64,153	40,313
NET INTEREST INCOME	154,838	161,803	309,749	315,026
PROVISION FOR CREDIT LOSSES	800	4,000	1,500	13,000
NET INTEREST INCOME AFTER PROVISION FOR CREDIT LOSSES	154,038	157,803	308,249	302,026
NONINTEREST INCOME:
Nonsufficient funds (NSF) fees	7,973	7,828	15,789	15,655
Credit card, debit card and ATM card income	6,480	6,335	12,451	12,296
Service charges on deposit accounts	4,989	5,150	9,987	10,425
Trust income	2,558	2,251	5,153	4,979
Mortgage income	990	1,109	1,712	1,872
Brokerage income	541	687	1,214	1,312
Gain (loss) on sale of assets	2	(44)	60	(44)
Net loss on sale of securities	0	(13)	0	(13)
Other	6,425	5,068	11,736	9,827
Total noninterest income	29,958	28,371	58,102	56,309
NONINTEREST EXPENSE:
Salaries and employee benefits	52,941	53,360	104,014	103,759
Net occupancy and equipment	5,492	5,692	10,958	11,301
Credit and debit card, data processing and software amortization	4,904	4,356	9,477	8,804
Regulatory assessments and FDIC insurance	2,325	3,575	4,699	7,150
Core deposit intangibles amortization	1,265	1,501	2,584	3,069
Depreciation	3,111	3,054	6,215	6,087
Communications	2,183	2,606	4,453	5,186
Other real estate expense, net	66	93	(28)	304
Other	8,534	9,365	17,020	17,996
Total noninterest expense	80,821	83,602	159,392	163,656
INCOME BEFORE INCOME TAXES	103,175	102,572	206,959	194,679
PROVISION FOR INCOME TAXES	20,917	20,975	42,299	38,721
NET INCOME	$ 82,258	$ 81,597	$ 164,660	$ 155,958
EARNINGS PER SHARE:
Basic	$ 1.18	$ 1.17	$ 2.36	$ 2.23
Diluted	$ 1.18	$ 1.17	$ 2.36	$ 2.23

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 82,258	$ 81,597	$ 164,660	$ 155,958
Securities available for sale:
Change in unrealized gain during the period	716	380	1,219	580
Total other comprehensive income	716	380	1,219	580
Deferred taxes related to other comprehensive income	(150)	(80)	(256)	(122)
Other comprehensive income, net of tax	566	300	963	458
Comprehensive income	$ 82,824	$ 81,897	$ 165,623	$ 156,416

Consolidated Statements of Chan

Consolidated Statements of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Capital Surplus [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]
BALANCE at Dec. 31, 2017	$ 3,824,154	$ 69,491	$ 2,035,219	$ 1,719,557	$ (113)
BALANCE (in shares) at Dec. 31, 2017		69,490,910
Net income	155,958			155,958
Other comprehensive income	458				458
Common stock issued in connection with the issuance of restricted stock awards, net		$ 347	(347)
Common stock issued in connection with the issuance of restricted stock awards, net (in shares)		347,276
Stock based compensation expense	5,160		5,160
Cash dividends declared	(50,278)			(50,278)
BALANCE at Jun. 30, 2018	3,935,452	$ 69,838	2,040,032	1,825,237	345
BALANCE (in shares) at Jun. 30, 2018		69,838,186
BALANCE at Mar. 31, 2018	3,876,145	$ 69,819	2,037,498	1,768,783	45
BALANCE (in shares) at Mar. 31, 2018		69,819,286
Net income	81,597			81,597
Other comprehensive income	300				300
Common stock issued in connection with the issuance of restricted stock awards, net		$ 19	(19)
Common stock issued in connection with the issuance of restricted stock awards, net (in shares)		18,900
Stock based compensation expense	2,553		2,553
Cash dividends declared	(25,143)			(25,143)
BALANCE at Jun. 30, 2018	3,935,452	$ 69,838	2,040,032	1,825,237	345
BALANCE (in shares) at Jun. 30, 2018		69,838,186
BALANCE at Dec. 31, 2018	4,052,824	$ 69,847	2,045,351	1,937,316	310
BALANCE (in shares) at Dec. 31, 2018		69,846,825
Net income	164,660			164,660
Other comprehensive income	963				963
Common stock issued in connection with the issuance of restricted stock awards, net		$ 13	(13)
Common stock issued in connection with the issuance of restricted stock awards, net (in shares)		13,434
Common stock repurchase	(38,421)	$ (599)	(37,822)
Common stock repurchase (in shares)		(598,828)
Stock based compensation expense	5,149		5,149
Cash dividends declared	(57,280)			(57,280)
BALANCE at Jun. 30, 2019	4,127,895	$ 69,261	2,012,665	2,044,696	1,273
BALANCE (in shares) at Jun. 30, 2019		69,261,431
BALANCE at Mar. 31, 2019	4,109,790	$ 69,846	2,048,156	1,991,081	707
BALANCE (in shares) at Mar. 31, 2019		69,845,925
Net income	82,258			82,258
Other comprehensive income	566				566
Common stock issued in connection with the issuance of restricted stock awards, net		$ 14	(14)
Common stock issued in connection with the issuance of restricted stock awards, net (in shares)		14,334
Common stock repurchase	(38,421)	$ (599)	(37,822)
Common stock repurchase (in shares)		(598,828)
Stock based compensation expense	2,345		2,345
Cash dividends declared	(28,643)			(28,643)
BALANCE at Jun. 30, 2019	$ 4,127,895	$ 69,261	$ 2,012,665	$ 2,044,696	$ 1,273
BALANCE (in shares) at Jun. 30, 2019		69,261,431

Consolidated Statements of Ch_2

Consolidated Statements of Changes in Shareholders' Equity (Unaudited) (Parenthetical) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Retained Earnings [Member]
Cash dividend declared, per share (in dollars per share)	$ 0.41	$ 0.36	$ 0.82	$ 0.72

Consolidated Statements of Cash

Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 164,660	$ 155,958
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and core deposit intangibles amortization	8,799	9,156
Provision for credit losses	1,500	13,000
Net amortization of premium on investments	14,196	16,203
Net (gain) loss on sale of other real estate	(231)	132
Net loss on sale of investment securities	0	13
Net (gain) loss on sale of assets	(60)	44
Net accretion of discount on loans	(3,020)	(7,549)
Net amortization of premium on deposits		(106)
Gain on sale of loans	(1,639)	(1,761)
Proceeds from sale of loans held for sale	94,650	100,620
Originations of loans held for sale	(83,959)	(95,237)
Stock based compensation expense	5,149	5,160
Increase in accrued interest receivable and other assets	(14,998)	(32,554)
Increase (decrease) in accrued interest payable and other liabilities	21,442	(5,206)
Net cash provided by operating activities	206,489	157,873
CASH FLOWS FROM INVESTING ACTIVITIES:
Proceeds from maturities and principal paydowns of held to maturity securities	837,003	862,987
Purchase of held to maturity securities	(171,656)	(940,595)
Proceeds from maturities and principal paydowns of available for sale securities	7,013,362	8,113,160
Purchase of available for sale securities	(7,234,660)	(7,999,686)
Net increase in loans held for investment	(226,664)	(134,124)
Purchase of bank premises and equipment	(11,738)	(6,280)
Proceeds from sale of bank premises, equipment and other real estate	2,505	2,647
Proceeds from insurance claims	2,633	1,701
Net cash provided by (used in) investing activities	210,785	(100,190)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net increase in noninterest-bearing deposits	25,121	34,267
Net decrease in interest-bearing deposits	(394,050)	(877,017)
Net (repayments of) proceeds from other short-term borrowings	(90,000)	750,000
Repayments of other long-term borrowings	(252)	(374)
Net increase (decrease) in securities sold under repurchase agreements	29,105	(31,115)
Repurchase of common stock	(38,421)
Payments of cash dividends	(57,280)	(50,278)
Net cash used in financing activities	(525,777)	(174,517)
NET DECREASE IN CASH AND CASH EQUIVALENTS	(108,503)	(116,834)
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	411,127	392,313
CASH AND CASH EQUIVALENTS, END OF PERIOD	302,624	275,479
NONCASH ACTIVITIES:
Acquisition of real estate through foreclosure of collateral	1,940	153
SUPPLEMENTAL INFORMATION:
Income taxes paid	42,850	94,610
Interest paid	$ 63,183	$ 39,710

Basis of Presentation

Basis of Presentation	6 Months Ended
	Jun. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Basis of Presentation	PROSPERITY BANCSHARES, INC.® AND SUBSIDIARIES NOTES TO CONSOLIDATED FINANCIAL STATEMENTS JUNE 30, 2019 (UNAUDITED) 1. BASIS OF PRESENTATION The consolidated financial statements include the accounts of Prosperity Bancshares, Inc. ® ® The accompanying unaudited consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for financial information and with the rules and regulations of the Securities and Exchange Commission. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of management, the statements reflect all adjustments necessary for a fair presentation of the financial position, results of operations and cash flows of the Company on a consolidated basis; and all such adjustments are of a normal recurring nature. These financial statements and the notes thereto should be read in conjunction with the Company’s Annual Report on Form 10-K for the year ended December 31, 2018. Operating results for the six-month period ended June 30, 2019 are not necessarily indicative of the results that may be expected for the year ending December 31, 2019 or any other period.

Income Per Common Share

Income Per Common Share	6 Months Ended
	Jun. 30, 2019
Earnings Per Share [Abstract]
Income Per Common Share	2. INCOME PER COMMON SHARE The following table illustrates the computation of basic and diluted earnings per share: Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 Amount Per Share Amount Amount Per Share Amount Amount Per Share Amount Amount Per Share Amount (Amounts in thousands, except per share data) Net income $ 82,258 $ 81,597 $ 164,660 $ 155,958 Basic: Weighted average shares outstanding 69,806 $ 1.18 69,839 $ 1.17 69,832 $ 2.36 69,803 $ 2.23 Diluted: Weighted average shares outstanding 69,806 $ 1.18 69,839 $ 1.17 69,832 $ 2.36 69,803 $ 2.23 As of June 30, 2019, all stock options have been exercised and there are no options outstanding. There were no stock options exercisable during the three and six months ended June 30, 2019 or 2018 that would have had an anti-dilutive effect on the above computation.

New Accounting Standards

New Accounting Standards	6 Months Ended
	Jun. 30, 2019
New Accounting Pronouncements And Changes In Accounting Principles [Abstract]
New Accounting Standards	3. NEW ACCOUNTING STANDARDS Accounting Standards Updates (“ASU”) ASU 2016-13, “Financial Instruments – Credit Losses (Topic 326)—Measurement of Credit Losses on Financial Instruments.” ASU 2016-13 requires a financial asset (or a group of financial assets) measured at amortized cost basis to be presented at the net amount expected to be collected. The measurement of current expected credit losses (“CECL”) is based on relevant information about past events, including historical experience, current conditions, and reasonable and supportable forecasts that affect the collectability of the reported amount. An entity must use judgment in determining the relevant information and estimation methods that are appropriate in its circumstances. Additionally, available for sale debt securities may realize value either through collection of contractual cash flows or through sale of the security at fair value. Therefore, the amendments limit the amount of the allowance for credit losses to the difference between amortized cost and fair value. ASU 2016-13 will be effective for the Company as of January 1, 2020. The Company’s implementation workgroup is comprised of individuals from various functional areas including credit, risk management, finance and information technology, among others, and meets periodically to discuss the latest developments and monitor implementation progress. The Company is currently working through an implementation plan that includes assessment of processes, portfolio segmentation and model development. The Company is working with a third-party vendor to assist with implementation and model development. CECL compliant models are currently in the development stage, with model testing and documentation being performed concurrently. The Company is assessing CECL disclosure requirements and developing appropriate internal controls around the CECL process. While the Company continues to evaluate the potential impact of ASU 2016‑13 on the Company’s financial statements, the adoption of ASU 2016-13 may result in an increase in the allowance for loan losses as a result of changing from an incurred loss methodology to an expected loss methodology. ASU 2016-02, "Leases (Topic 842)." ASU 2016-02 requires that lessees recognize lease assets and lease liabilities on the balance sheet and disclose key information about leasing arrangements. The requirements for lessors under ASU 2016-02 are largely unchanged from existing guidance, however certain necessary changes have been made to align with specific changes to lessee accounting and key aspects of the revenue recognition guidance (Topic 606). The Company’s leases relate primarily to office space and banking centers. The Company identified and reviewed existing leases applicable to ASU 2016-02 and elected certain optional practical expedients: 1) not to reassess whether any expired or existing contracts are or contain leases, 2) not to reassess the lease classification for any expired or existing lease, 3) not to reassess initial direct cost for any existing leases and 4) not to separately identify lease and non-lease components. Additionally, the Company elected the short-term lease exemption for lease terms less than 12 months. The Company adopted ASU 2016-02 on January 1, 2019 using a modified retrospective transition approach without adjusting comparative periods. With the adoption of the new standard, the Company recognized right-of-use assets and lease liabilities of $17.3 million as of January 1, 2019. See Note 9 “Contractual Obligations and Off-Balance Sheet Items — Contractual Obligations — Leases” for additional information.

Securities

Securities	6 Months Ended
	Jun. 30, 2019
Investments Debt And Equity Securities [Abstract]
Securities	4. SECURITIES The amortized cost and fair value of investment securities were as follows: June 30, 2019 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (Dollars in thousands) Available for Sale States and political subdivisions $ 469 $ 1 $ — $ 470 Collateralized mortgage obligations 244,256 796 (130 ) 244,922 Mortgage-backed securities 60,441 946 (2 ) 61,385 Total $ 305,166 $ 1,743 $ (132 ) $ 306,777 Held to Maturity U.S. Treasury securities and obligations of U.S. Government agencies $ 22,867 $ 43 $ (3 ) $ 22,907 States and political subdivisions 215,871 6,088 (144 ) 221,815 Collateralized mortgage obligations 462 5 (1 ) 466 Mortgage-backed securities 8,405,963 50,480 (45,222 ) 8,411,221 Total $ 8,645,163 $ 56,616 $ (45,370 ) $ 8,656,409 December 31, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (Dollars in thousands) Available for Sale States and political subdivisions $ 1,159 $ 7 $ — $ 1,166 Collateralized mortgage obligations 12,724 69 (37 ) 12,756 Mortgage-backed securities 69,880 553 (200 ) 70,233 Total $ 83,763 $ 629 $ (237 ) $ 84,155 Held to Maturity U.S. Treasury securities and obligations of U.S. Government agencies $ 25,778 $ — $ (100 ) $ 25,678 States and political subdivisions 253,198 3,440 (777 ) 255,861 Collateralized mortgage obligations 509 1 (2 ) 508 Mortgage-backed securities 9,045,326 5,798 (251,935 ) 8,799,189 Total $ 9,324,811 $ 9,239 $ (252,814 ) $ 9,081,236 Management evaluates securities for other-than-temporary impairment (“OTTI”) at least on a quarterly basis, and more frequently when economic or market conditions warrant such an evaluation. The investment securities portfolio is evaluated for OTTI by segregating the portfolio into two general segments and applying the appropriate OTTI analysis. Investment securities classified as available for sale or held to maturity are evaluated for OTTI under Financial Accounting Standards Board (“FASB”): Accounting Standards Codification (“ASC”) Topic 320, “ Investments-Debt and Equity Securities.” In determining OTTI, management considers many factors, including: (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, (3) whether the market decline was affected by macroeconomic conditions and (4) whether the entity has the intent to sell the debt security or more likely than not will be required to sell the debt security before its anticipated recovery. The assessment of whether an other-than-temporary decline exists involves a high degree of subjectivity and judgment and is based on the information available to management at the time of such determination. When OTTI occurs, the amount of the OTTI recognized in earnings depends on whether an entity intends to sell the security or more likely than not will be required to sell the security before recovery of its amortized cost basis less any current-period credit loss. If an entity intends to sell or more likely than not will be required to sell the security before recovery of its amortized cost basis less any current-period credit loss, the OTTI will be recognized in earnings equal to the entire difference between the investment’s amortized cost basis and its fair value at the balance sheet date. If an entity does not intend to sell the security and it is not more likely than not that the entity will be required to sell the security before recovery of its amortized cost basis less any current-period loss, the OTTI will be separated into the amount representing the credit-related portion of the impairment loss (“credit loss”) and the noncredit portion of the impairment loss (“noncredit portion”). The amount of the total OTTI related to the credit loss is determined based on the difference between the present value of cash flows expected to be collected and the amortized cost basis and such difference is recognized in earnings. The amount of the total OTTI related to the noncredit portion is recognized in other comprehensive income, net of applicable taxes. The previous amortized cost basis less the OTTI recognized in earnings will become the new amortized cost basis of the investment. Management has the ability and intent to hold the securities classified as held-to-maturity until they mature, at which time the Company will receive full value for the securities. Furthermore, as of June 30, 2019, management does not have the intent to sell any of the securities classified as available for sale before a recovery of cost. In addition, management believes it is more likely than not that the Company will not be required to sell any of its investment securities before a recovery of cost. The unrealized losses are largely due to increases in market interest rates over the yields available at the time the underlying securities were purchased. The fair value is expected to recover as the securities approach their maturity date or repricing date or if market yields for such investments decline. Management does not believe any of the securities are impaired due to reasons of credit quality. Accordingly, as of June 30, 2019, management believes any impairment in the Company’s securities is temporary, and therefore no impairment loss has been recognized in the Company’s consolidated statement of income. Securities with unrealized losses, segregated by length of time, that have been in a continuous loss position were as follows: June 30, 2019 Less than 12 Months 12 Months or More Total Estimated Fair Value Unrealized Losses Estimated Fair Value Unrealized Losses Estimated Fair Value Unrealized Losses (Dollars in thousands) Available for Sale Collateralized mortgage obligations $ 37,871 $ (106 ) $ 1,899 $ (24 ) $ 39,770 $ (130 ) Mortgage-backed securities 67 (1 ) 48 (1 ) 115 (2 ) Total $ 37,938 $ (107 ) $ 1,947 $ (25 ) $ 39,885 $ (132 ) Held to Maturity U.S. Treasury securities and obligations of U.S. Government agencies $ — $ — $ 8,990 $ (3 ) $ 8,990 $ (3 ) States and political subdivisions 43,370 (87 ) 26,552 (57 ) 69,922 (144 ) Collateralized mortgage obligations 79 (1 ) — — 79 (1 ) Mortgage-backed securities 131,659 (356 ) 4,271,546 (44,866 ) 4,403,205 (45,222 ) Total $ 175,108 $ (444 ) $ 4,307,088 $ (44,926 ) $ 4,482,196 $ (45,370 ) December 31, 2018 Less than 12 Months 12 Months or More Total Estimated Fair Value Unrealized Losses Estimated Fair Value Unrealized Losses Estimated Fair Value Unrealized Losses (Dollars in thousands) Available for Sale Collateralized mortgage obligations $ 12 $ — $ 2,096 $ (37 ) $ 2,108 $ (37 ) Mortgage-backed securities 50,950 (197 ) 2,091 (3 ) 53,041 (200 ) Total $ 50,962 $ (197 ) $ 4,187 $ (40 ) $ 55,149 $ (237 ) Held to Maturity U.S. Treasury securities and obligations of U.S. Government agencies $ 20,720 $ (76 ) $ 4,957 $ (24 ) $ 25,677 $ (100 ) States and political subdivisions 89,407 (328 ) 58,262 (449 ) 147,669 (777 ) Collateralized mortgage obligations — — 292 (2 ) 292 (2 ) Mortgage-backed securities 1,003,089 (8,401 ) 6,873,948 (243,534 ) 7,877,037 (251,935 ) Total $ 1,113,216 $ (8,805 ) $ 6,937,459 $ (244,009 ) $ 8,050,675 $ (252,814 ) At June 30, 2019 and December 31, 2018, there were 287 securities and 731 securities, respectively, in an unrealized loss position for 12 months or more. The amortized cost and fair value of investment securities at June 30, 2019, by contractual maturity, are shown below. Actual maturities will differ from contractual maturities because borrowers may have the right to call or prepay obligations at any time with or without call or prepayment penalties. Held to Maturity Available for Sale Amortized Cost Fair Value Amortized Cost Fair Value (Dollars in thousands) Due in one year or less $ 48,722 $ 48,797 $ 165 $ 165 Due after one year through five years 117,183 118,201 304 305 Due after five years through ten years 68,317 73,134 — — Due after ten years 4,516 4,590 — — Subtotal 238,738 244,722 469 470 Mortgage-backed securities and collateralized mortgage obligations 8,406,425 8,411,687 304,697 306,307 Total $ 8,645,163 $ 8,656,409 $ 305,166 $ 306,777 The Company recorded no gain or loss on the sale of securities for the three and six months ended June 30, 2019. The Company recorded a $13 thousand loss on the sale of securities for the three and six months ended June 30, 2018. As of June 30, 2019, the Company did not own any non-agency collateralized mortgage obligations. At June 30, 2019 and December 31, 2018, the Company did not own securities of any one issuer (other than the U.S. government and its agencies) for which aggregate adjusted cost exceeded 10% of the consolidated shareholders’ equity at such respective dates. Securities with an amortized cost of $5.33 billion and $6.04 billion and a fair value of $5.32 billion and $5.86 billion at June 30, 2019 and December 31, 2018, respectively, were pledged to collateralize public deposits and for other purposes required or permitted by law.

Loans and Allowance for Credit

Loans and Allowance for Credit Losses	6 Months Ended
	Jun. 30, 2019
Receivables [Abstract]
Loans and Allowance for Credit Losses	5. LOANS AND ALLOWANCE FOR CREDIT LOSSES The loan portfolio consists of various types of loans and is categorized by major type as follows: June 30, 2019 December 31, 2018 (Dollars in thousands) Residential mortgage loans held for sale $ 20,315 $ 29,367 Commercial and industrial 1,525,628 1,483,571 Real estate: Construction, land development and other land loans 1,739,308 1,622,289 1-4 family residential (includes home equity) 2,692,963 2,677,542 Commercial real estate (includes multi-family residential) 3,551,668 3,538,557 Farmland 541,469 545,373 Agriculture 195,001 184,128 Consumer and other 321,023 289,486 Total loans held for investment 10,567,060 10,340,946 Total $ 10,587,375 $ 10,370,313 Concentrations of Credit. Most of the Company’s lending activity occurs within the states of Texas and Oklahoma. Commercial real estate loans, 1-4 family residential loans and construction, land development and other land loans make up 75.4% of the Company’s total loan portfolio at June 30, 2019. As of June 30, 2019 and December 31, 2018, there were no concentrations of loans related to any single industry in excess of 10% Related Party Loans. As of June 30, 2019 and December 31, 2018, loans outstanding to directors, officers and their affiliates totaled $1.8 million and $1.9 million, respectively. All transactions between the Company and such related parties are conducted in the ordinary course of business and made on the same terms and conditions as similar transactions with unaffiliated persons. An analysis of activity with respect to these related party loans is as follows: As of and for the six months ended June As of and for the year ended December (Dollars in thousands) Beginning balance on January 1 $ 1,923 $ 2,694 New loans — 5 Repayments (168 ) (776 ) Ending balance $ 1,755 $ 1,923 Nonperforming Assets and Nonaccrual and Past Due Loans. The Company has several procedures in place to assist it in maintaining the overall quality of its loan portfolio. The Company has established underwriting guidelines to be followed by its officers, including requiring appraisals on loans collateralized by real estate. The Company also monitors its delinquency levels for any negative or adverse trends. Nevertheless, the Company’s loan portfolio could become subject to increasing pressures from deteriorating borrower credit due to general economic conditions. The Company generally places a loan on nonaccrual status and ceases accruing interest when the payment of principal or interest is delinquent for 90 days, or earlier in some cases, unless the loan is in the process of collection and the underlying collateral fully supports the carrying value of the loan. With respect to potential problem loans, an evaluation of the borrower’s overall financial condition is made to determine the need, if any, for possible writedowns or appropriate additions to the allowance for credit losses. An aging analysis of past due loans, segregated by category of loan, is presented below: June 30, 2019 Loans Past Due and Still Accruing 30-89 Days 90 or More Days Total Past Due Loans Nonaccrual Loans Current Loans Total Loans (Dollars in thousands) Construction, land development and other land loans $ 5,368 $ 1,153 $ 6,521 $ 659 $ 1,732,128 $ 1,739,308 Agriculture and agriculture real estate (includes farmland) 710 — 710 616 735,144 736,470 1-4 family (includes home equity) (1) 11,107 58 11,165 15,278 2,686,835 2,713,278 Commercial real estate (includes multi-family residential) 14,572 — 14,572 4,135 3,532,961 3,551,668 Commercial and industrial 4,102 383 4,485 16,561 1,504,582 1,525,628 Consumer and other 333 — 333 40 320,650 321,023 Total $ 36,192 $ 1,594 $ 37,786 $ 37,289 $ 10,512,300 $ 10,587,375 December 31, 2018 Loans Past Due and Still Accruing 30-89 Days 90 or More Days Total Past Due Loans Nonaccrual Loans Current Loans Total Loans (Dollars in thousands) Construction, land development and other land loans $ 6,363 $ 788 $ 7,151 $ 1,386 $ 1,613,752 $ 1,622,289 Agriculture and agriculture real estate (includes farmland) 705 — 705 256 728,540 729,501 1-4 family (includes home equity) (1) 10,479 2,995 13,474 4,515 2,688,920 2,706,909 Commercial real estate (includes multi-family residential) 9,063 — 9,063 2,727 3,526,767 3,538,557 Commercial and industrial 6,652 221 6,873 4,215 1,472,483 1,483,571 Consumer and other 1,012 — 1,012 48 288,426 289,486 Total $ 34,274 $ 4,004 $ 38,278 $ 13,147 $ 10,318,888 $ 10,370,313 (1) Includes $20.3 million and $29.4 million of residential mortgage loans held for sale at June 30, 2019 and December 31, 2018, respectively. The following table presents information regarding nonperforming assets as of the dates indicated: June 30, 2019 December 31, 2018 (Dollars in thousands) Nonaccrual loans (1) $ 37,289 $ 13,147 Accruing loans 90 or more days past due 1,594 4,004 Total nonperforming loans 38,883 17,151 Repossessed assets 670 — Other real estate 2,005 1,805 Total nonperforming assets $ 41,558 $ 18,956 Nonperforming assets to total loans and other real estate 0.39 % 0.18 % (1) Includes troubled debt restructurings of $14.3 million and $51 thousand as of June 30, 2019 and December 31, 2018, respectively. The Company had $41.6 million in nonperforming assets at June 30, 2019 compared with $19.0 million at December 31, 2018. Nonperforming assets were 0.39% of total loans and other real estate at June 30, 2019 compared with 0.18% of total loans and other real estate at December 31, 2018. If interest on nonaccrual loans had been accrued under the original loan terms, approximately $1.2 million and $951 thousand would have been recorded as income for the six months ended June 30, 2019 and 2018, respectively. The Company had $37.3 million in nonaccrual loans at June 30, 2019 compared with $20.4 million at June 30, 2018. Acquired Loans. Acquired loans were preliminarily recorded at fair value based on a discounted cash flow valuation methodology that considers, among other things, interest rates, projected default rates, loss given default, and recovery rates. During the valuation process, the Company identified Purchased Credit-Impaired (“PCI”) and Non-PCI loans in the acquired loan portfolios. Loans acquired with evidence of credit quality deterioration at acquisition for which it was probable that the Company would not be able to collect all contractual amounts due were accounted for as PCI. PCI loan identification considers the following factors: payment history and past due status, debt service coverage, loan grading, collateral values and other factors that may indicate deterioration of credit quality since origination. Non-PCI loan identification considers the following factors: account types, remaining terms, annual interest rates or coupons, current market rates, interest types, past delinquencies, timing of principal and interest payments, loan to value ratios, loss exposures and remaining balances. Accretion of purchased discounts on PCI loans will be based on estimated future cash flows, regardless of contractual maturities. Accretion of purchased discounts on Non-PCI loans will be recognized on a level-yield basis based on contractual maturity of individual loans. PCI Loans. The recorded investment in PCI loans included in the consolidated balance sheet and the related outstanding balance as of the dates indicated are presented in the table below. The outstanding balance represents the total amount owed as of June 30, 2019 and December 31, 2018. June 30, 2019 December 31, 2018 (Dollars in thousands) PCI loans: Outstanding balance $ 10,110 $ 11,419 Discount (2,165 ) (2,831 ) Recorded investment $ 7,945 $ 8,588 Changes in the accretable yield for acquired PCI loans for the three and six months ended June 30, 2019 and 2018 were as follows: Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 (Dollars in thousands) Balance at beginning of period $ 1,234 $ 7,685 $ 1,534 $ 8,121 Reclassifications from nonaccretable 17 55 36 305 Accretion (347 ) (3,771 ) (666 ) (4,457 ) Balance at June 30, $ 904 $ 3,969 $ 904 $ 3,969 Income recognition on PCI loans is subject to the Company’s ability to reasonably estimate both the timing and amount of future cash flows. PCI loans for which the Company is accruing interest income are not considered non-performing or impaired. The non-accretable difference represents contractual principal and interest the Company does not expect to collect. Non-PCI Loans. The recorded investment in Non-PCI loans included in the consolidated balance sheet and the related outstanding balance as of the dates indicated are presented in the table below. The outstanding balance represents the total amount owed as of June 30, 2019 and December 31, 2018. June 30, 2019 December 31, 2018 (Dollars in thousands) Non-PCI loans: Outstanding balance $ 467,645 $ 526,840 Discount (12,479 ) (14,833 ) Recorded investment $ 455,166 $ 512,007 Changes in the discount accretion for Non-PCI loans for the three and six months ended June 30, 2019 and 2018 were as follows: Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 (Dollars in thousands) Balance at beginning of period $ 13,359 $ 18,885 $ 14,833 $ 20,533 Accretion charge-offs — (2 ) — (10 ) Accretion (880 ) (1,452 ) (2,354 ) (3,092 ) Balance at June 30, $ 12,479 $ 17,431 $ 12,479 $ 17,431 Impaired Loans. Loans are considered impaired when, based on current information and events, it is probable the Company will be unable to collect all amounts due in accordance with the original contractual terms of the loan agreement, including scheduled principal and interest payments. Impairment is evaluated in total for smaller-balance loans of a similar nature and on an individual loan basis for other loans. If a loan is impaired, a specific valuation allowance is allocated, if necessary, so that the loan is reported net, at the present value of estimated future cash flows using the loan’s existing rate or at the fair value of collateral if repayment is expected solely from the collateral. Interest payments on impaired loans are typically applied to principal unless collectability of the principal amount is reasonably assured, in which case interest is recognized on a cash basis. Impaired loans, or portions thereof, are charged off when deemed uncollectible. Impaired loans are set forth in the following tables. No interest income was recognized on impaired loans subsequent to their classification as impaired. The average recorded investment presented in the tables below is reported on a year-to-date basis. June 30, 2019 Recorded Investment Unpaid Contractual Principal Balance Related Allowance Average Recorded Investment (Dollars in thousands) With no related allowance recorded: Construction, land development and other land loans $ 269 $ 270 $ — $ 631 Agriculture and agriculture real estate (includes farmland) 326 326 — 291 1-4 family (includes home equity) 10,035 10,747 — 7,106 Commercial real estate (includes multi-family residential) 3,162 3,341 — 2,945 Commercial and industrial 15,406 17,610 — 9,138 Consumer and other 40 44 — 44 Total 29,238 32,338 — 20,155 With an allowance recorded: Construction, land development and other land loans 390 390 58 391 Agriculture and agriculture real estate (includes farmland) 290 290 160 145 1-4 family (includes home equity) 5,243 5,272 504 2,754 Commercial real estate (includes multi-family residential) 973 993 283 486 Commercial and industrial 1,155 1,171 329 1,241 Consumer and other — — — — Total 8,051 8,116 1,334 5,017 Total: Construction, land development and other land loans 659 660 58 1,022 Agriculture and agriculture real estate (includes farmland) 616 616 160 436 1-4 family (includes home equity) 15,278 16,019 504 9,860 Commercial real estate (includes multi-family residential) 4,135 4,334 283 3,431 Commercial and industrial 16,561 18,781 329 10,379 Consumer and other 40 44 — 44 $ 37,289 $ 40,454 $ 1,334 $ 25,172 December 31, 2018 Recorded Investment Unpaid Contractual Principal Balance Related Allowance Average Recorded Investment (Dollars in thousands) With no related allowance recorded: Construction, land development and other land loans $ 993 $ 995 $ — $ 788 Agriculture and agriculture real estate (includes farmland) 256 311 — 194 1-4 family (includes home equity) 4,177 4,903 — 4,048 Commercial real estate (includes multi-family residential) 2,727 2,848 — 2,475 Commercial and industrial 2,870 3,810 — 5,358 Consumer and other 48 76 — 135 Total 11,071 12,943 — 12,998 With an allowance recorded: Construction, land development and other land loans 391 391 58 195 Agriculture and agriculture real estate (includes farmland) — — — — 1-4 family (includes home equity) 266 289 56 729 Commercial real estate (includes multi-family residential) — — — 743 Commercial and industrial 1,328 1,332 571 3,740 Consumer and other — — — — Total 1,985 2,012 685 5,407 Total: Construction, land development and other land loans 1,384 1,386 58 983 Agriculture and agriculture real estate (includes farmland) 256 311 — 194 1-4 family (includes home equity) 4,443 5,192 56 4,777 Commercial real estate (includes multi-family residential) 2,727 2,848 — 3,218 Commercial and industrial 4,198 5,142 571 9,098 Consumer and other 48 76 — 135 $ 13,056 $ 14,955 $ 685 $ 18,405 Credit Quality Indicators. As part of the on-going monitoring of the credit quality of the Company’s loan portfolio and methodology for calculating the allowance for credit losses, management assigns and tracks loan grades to be used as credit quality indicators. The following is a general description of the loan grades used: Grade 1— Credits in this category have risk potential that is virtually nonexistent. These loans may be secured by insured certificates of deposit, insured savings accounts, U.S. Government securities and highly rated municipal bonds. Grade 2— Credits in this category are of the highest quality. These borrowers represent top rated companies and individuals with unquestionable financial standing with excellent global cash flow coverage, net worth, liquidity and collateral coverage. Grade 3— Credits in this category are not immune from risk but are well protected by the collateral and paying capacity of the borrower. These loans may exhibit a minor unfavorable credit factor, but the overall credit is sufficiently strong to minimize the possibility of loss. Grade 4— Credits in this category are considered to be of acceptable credit quality with moderately greater risk than Grade 3 and receiving closer monitoring. Loans in this category have sources of repayment that remain sufficient to preclude a larger than normal probability of default and secondary sources are likewise currently of sufficient quantity, quality, and liquidity to protect the Company against loss of principal and interest. These borrowers have specific risk factors, but the overall strength of the credit is acceptable based on other mitigating credit and/or collateral factors and can repay the debt in the normal course of business. Grade 5— Credits in this category constitute an undue and unwarranted credit risk; however, the factors do not rise to a level of substandard. These credits have potential weaknesses and/or declining trends that, if not corrected, could expose the Company to risk at a future date. These loans are monitored on the Company ’s internally-generated watch list and evaluated on a quarterly basis. Grade 6— Credits in this category are considered “substandard” but “non-impaired” loans in accordance with regulatory guidelines. Loans in this category have well-defined weakness that, if not corrected, could make default of principal and interest possible. Loans in this category are still accruing interest and may be dependent upon secondary sources of repayment and/or collateral liquidation. Grade 7— Credits in this category are deemed “substandard” and “impaired” pursuant to regulatory guidelines. As such, the Company has determined that it is probable that less than 100% of the contractual principal and interest will be collected. These loans are individually evaluated for a specific reserve and will typically have the accrual of interest stopped. Grade 8— Credits in this category include “doubtful” loans in accordance with regulatory guidance. Such loans are no longer accruing interest and factors indicate a loss is imminent. These loans are also deemed “impaired.” While a specific reserve may be in place while the loan and collateral is being evaluated, these loans are typically charged down to an amount the Company estimates is collectible. Grade 9— Credits in this category are deemed a “loss” in accordance with regulatory guidelines and have been charged off or charged down. The Company may continue collection efforts and may have partial recovery in the future. The following table presents loans by risk grade and category of loan at June 30, 2019. Impaired loans include loans in risk grades 7, 8 and 9, as well as any PCI loan that has a specific reserve allocated to it. Construction, Land Development and Other Agriculture and Agriculture Real Estate (includes Farmland) 1-4 Family (includes Home (1) Commercial Real Estate (includes Multi-Family Commercial and Industrial Consumer and Other Total (Dollars in thousands) Grade 1 $ — $ 14,322 $ — $ — $ 55,562 $ 35,091 $ 104,975 Grade 2 1,215 3,877 15,430 21,640 12,312 56,519 110,993 Grade 3 1,587,922 647,171 2,600,773 2,892,964 1,102,365 200,582 9,031,777 Grade 4 136,083 64,025 67,445 557,501 265,415 24,325 1,114,794 Grade 5 5,684 5,091 6,486 56,772 61,476 2,827 138,336 Grade 6 7,315 1,029 3,750 15,719 11,814 1,639 41,266 Grade 7 659 326 15,278 4,135 16,543 40 36,981 Grade 8 — 290 — — 18 — 308 Grade 9 — — — — — — — PCI Loans 430 339 4,116 2,937 123 — 7,945 Total $ 1,739,308 $ 736,470 $ 2,713,278 $ 3,551,668 $ 1,525,628 $ 321,023 $ 10,587,375 (1) Includes $20.3 million of residential mortgage loans held for sale at June 30, 2019. The following table presents loans by risk grade and category of loan at December 31, 2018 . Impaired loans include loans in risk grades 7, 8 and 9, as well as any PCI loan that has a specific reserve allocated to it. Construction, Land Development and Other Agriculture and Agriculture Real Estate (includes Farmland) 1-4 Family (includes Home (1) Commercial Real Estate (includes Multi-Family Commercial and Industrial Consumer and Other Total (Dollars in thousands) Grade 1 $ — $ 15,725 $ — $ — $ 59,979 $ 37,135 $ 112,839 Grade 2 1,040 3,974 21,465 22,207 11,003 55,802 115,491 Grade 3 1,509,532 636,674 2,598,600 2,974,474 1,083,328 171,758 8,974,366 Grade 4 99,087 66,650 61,430 481,735 243,743 20,164 972,809 Grade 5 3,673 5,578 12,522 37,942 58,088 2,978 120,781 Grade 6 7,081 282 4,332 16,006 23,081 1,601 52,383 Grade 7 1,384 256 4,395 2,727 4,165 48 12,975 Grade 8 — — 48 — 33 — 81 Grade 9 — — — — — — — PCI Loans 492 362 4,117 3,466 151 — 8,588 Total $ 1,622,289 $ 729,501 $ 2,706,909 $ 3,538,557 $ 1,483,571 $ 289,486 $ 10,370,313 (1) Includes $29.4 million of residential mortgage loans held for sale at December 31, 2018. Allowance for Credit Losses. The allowance for credit losses is established through charges to earnings in the form of a provision for credit losses. Management has established an allowance for credit losses which it believes is adequate as of June 30, 2019 for estimated losses in the Company’s loan portfolio. The amount of the allowance for credit losses is affected by the following: (1) charge-offs of loans that occur when loans are deemed uncollectible and decrease the allowance, (2) recoveries on loans previously charged off that increase the allowance and (3) provisions for credit losses charged to earnings that increase the allowance. Based on an evaluation of the loan portfolio and consideration of the factors listed below, management presents a quarterly review of the allowance for credit losses to the Bank’s Board of Directors, indicating any change in the allowance since the last review and any recommendations as to adjustments in the allowance. Although management believes it uses the best information available to make determinations with respect to the allowance for credit losses, future adjustments may be necessary if economic conditions or the borrower’s performance differ from the assumptions used in making the initial determinations. The Company’s allowance for credit losses consists of two components: (1) a specific valuation allowance based on probable losses on specifically identified loans and (2) a general valuation allowance based on historical loan loss experience, general economic conditions and other qualitative risk factors both internal and external to the Company. In setting the specific valuation allowance, the Company follows a loan review program to evaluate the credit risk in the total loan portfolio and assigns risk grades to each loan. Through this loan review process, the Company maintains an internal list of impaired loans, which along with the delinquency list of loans, helps management assess the overall quality of the loan portfolio and the adequacy of the allowance for credit losses. All loans that have been identified as impaired are reviewed on a quarterly basis in order to determine whether a specific reserve is required. For certain impaired loans, the Company allocates a specific loan loss reserve primarily based on the value of the collateral securing the impaired loan in accordance with ASC Topic 310-10, “ Receivables. In connection with this review of the loan portfolio, the Company considers risk elements attributable to particular loan types or categories in assessing the quality of individual loans. Some of the risk elements include: • for 1-4 family residential mortgage loans, the borrower’s ability to repay the loan, including a consideration of the debt to income ratio and employment and income stability, the loan to value ratio, and the age, condition and marketability of collateral; • for commercial real estate loans and multifamily residential loans, the debt service coverage ratio (income from the property in excess of operating expenses compared to loan payment requirements), operating results of the owner in the case of owner-occupied properties, the loan to value ratio, the age and condition of the collateral and the volatility of income, property value and future operating results typical of properties of that type; • for construction, land development and other land loans, the perceived feasibility of the project including the ability to sell developed lots or improvements constructed for resale or the ability to lease property constructed for lease, the quality and nature of contracts for presale or prelease, if any, experience and ability of the developer and loan to value ratio; • for commercial and industrial loans, the operating results of the commercial, industrial or professional enterprise, the borrower’s business, professional and financial ability and expertise, the specific risks and volatility of income and operating results typical for businesses in that category and the value, nature and marketability of collateral; • for agriculture real estate loans, the experience and financial capability of the borrower, projected debt service coverage of the operations of the borrower and loan to value ratio; and • for non-real estate agriculture loans, the operating results, experience and financial capability of the borrower, historical and expected market conditions and the value, nature and marketability of collateral. In addition, for each category, the Company considers secondary sources of income and the financial strength and credit history of the borrower and any guarantors. In determining the amount of the general valuation allowance, management considers factors such as historical loan loss experience, concentration risk of specific loan types, the volume, growth and composition of the Company’s loan portfolio, current economic conditions that may affect the borrower’s ability to pay and the value of collateral, the evaluation of the Company’s loan portfolio through its internal loan review process, general economic conditions, other qualitative risk factors both internal and external to the Company and other relevant factors in accordance with ASC Topic 450, “ Contingencies. The following table details activity in the allowance for credit losses by category of loan for the three and six months ended June 30, 2019 and 2018. Allocation of a portion of the allowance to one category of loans does not preclude its availability to absorb losses in other categories. Construction, Land Development and Other Land Loans Agriculture and Agriculture Real Estate (includes Farmland) 1-4 Family (includes Home Equity) Commercial Real Estate (includes Multi-Family Residential) Commercial and Industrial Consumer and Other Total (Dollars in thousands) Allowance for credit losses: Three Months Ended Balance March 31, 2019 $ 16,192 $ 3,284 $ 14,455 $ 11,590 $ 39,059 $ 1,511 $ 86,091 Provision for credit losses (299 ) 578 (61 ) 575 (710 ) 717 800 Charge-offs (19 ) (54 ) (16 ) — (125 ) (905 ) (1,119 ) Recoveries 12 8 5 1 953 255 1,234 Net charge-offs (7 ) (46 ) (11 ) 1 828 (650 ) 115 Balance June 30, 2019 $ 15,886 $ 3,816 $ 14,383 $ 12,166 $ 39,177 $ 1,578 $ 87,006 Six Months Ended Balance December 31, 2018 $ 15,582 $ 3,693 $ 14,135 $ 11,220 $ 40,223 $ 1,587 $ 86,440 Provision for credit losses 311 (1,109 ) 256 944 (155 ) 1,253 1,500 Charge-offs (63 ) (64 ) (22 ) — (2,082 ) (1,797 ) (4,028 ) Recoveries 56 1,296 14 2 1,191 535 3,094 Net charge-offs (7 ) 1,232 (8 ) 2 (891 ) (1,262 ) (934 ) Balance June 30, 2019 $ 15,886 $ 3,816 $ 14,383 $ 12,166 $ 39,177 $ 1,578 $ 87,006 Allowance for credit losses: Three Months Ended Balance March 31, 2018 $ 14,622 $ 3,304 $ 13,072 $ 10,853 $ 40,340 $ 1,409 $ 83,600 Provision for credit losses (173 ) 407 395 749 2,161 461 4,000 Charge-offs — — (120 ) (986 ) (1,194 ) (901 ) (3,201 ) Recoveries 1 45 6 — 147 366 565 Net charge-offs 1 45 (114 ) (986 ) (1,047 ) (535 ) (2,636 ) Balance June 30, 2018 $ 14,450 $ 3,756 $ 13,353 $ 10,616 $ 41,454 $ 1,335 $ 84,964 Six Months Ended Balance December 31, 2017 $ 14,815 $ 3,772 $ 14,490 $ 10,628 $ 38,810 $ 1,526 $ 84,041 Provision for credit losses (243 ) (122 ) (766 ) 1,476 11,707 948 13,000 Charge-offs (130 ) — (386 ) (1,489 ) (9,370 ) (1,911 ) (13,286 ) Recoveries 8 106 15 1 307 772 1,209 Net charge-offs (122 ) 106 (371 ) (1,488 ) (9,063 ) (1,139 ) (12,077 ) Balance June 30, 2018 $ 14,450 $ 3,756 $ 13,353 $ 10,616 $ 41,454 $ 1,335 $ 84,964 The following table details the amount of the allowance for credit losses allocated to each category of loan as of June 30, 2019, December 31, 2018 and June 30, 2018, on the basis of the impairment methodology used to determine the allowance for credit losses. Construction, Land Development and Other Land Loans Agriculture and Agriculture Real Estate (includes Farmland) 1-4 Family (includes Home Equity) Commercial Real Estate (includes Multi-Family Residential) Commercial and Industrial Consumer and Other Total (Dollars in thousands) Allowance for credit losses related June 30, 2019 Individually evaluated for impairment $ 58 $ 160 $ 504 $ 283 $ 329 $ — $ 1,334 Collectively evaluated for impairment 15,828 3,656 13,879 11,883 38,848 1,578 85,672 PCI loans — — — — — — — Total allowance for credit losses $ 15,886 $ 3,816 $ 14,383 $ 12,166 $ 39,177 $ 1,578 $ 87,006 December 31, 2018 Individually evaluated for impairment $ 58 $ — $ 56 $ — $ 571 $ — $ 685 Collectively evaluated for impairment 15,524 3,693 14,079 11,220 39,652 1,587 85,755 PCI loans — — — — — — — Total allowance for credit losses $ 15,582 $ 3,693 $ 14,135 $ 11,220 $ 40,223 $ 1,587 $ 86,440 June 30, 2018 Individually evaluated for impairment $ — $ 25 $ 61 $ — $ 2,741 $ — $ 2,827 Collectively evaluated for impairment 14,450 3,731 13,292 10,616 38,713 1,335 82,137 PCI loans — — — — — — — Total allowance for credit losses $ 14,450 $ 3,756 $ 13,353 $ 10,616 $ 41,454 $ 1,335 $ 84,964 The following table details the recorded investment in loans by category of loan on the basis of the impairment methodology used to determine the allowance for credit losses as of June 30, 2019, December 31, 2018 and June 30, 2018, excluding $20.3 million, $29.4 million and $27.8 million, respectively, of residential mortgage loans held for sale. Construction, Land Development and Other Land Loans Agriculture and Agriculture Real Estate (includes Farmland) 1-4 Family (includes Home Equity) Commercial Real Estate (includes Multi-Family Residential) Commercial and Industrial Consumer and Other Total (Dollars in thousands) Recorded investment in June 30, 2019 Individually evaluated for impairment $ 659 $ 616 $ 15,278 $ 4,135 $ 16,561 $ 40 $ 37,289 Collectively evaluated for impairment 1,738,219 735,515 2,673,569 3,544,596 1,508,944 320,983 10,521,826 PCI loans 430 339 4,116 2,937 123 — 7,945 Total loans evaluated for impairment $ 1,739,308 $ 736,470 $ 2,692,963 $ 3,551,668 $ 1,525,628 $ 321,023 $ 10,567,060 December 31, 2018 Individually evaluated for impairment $ 1,384 $ 256 $ 4,443 $ 2,727 $ 4,198 $ 48 $ 13,056 Collectively evaluated for impairment 1,620,413 728,883 2,668,982 3,532,364 1,479,222 289,438 10,319,302 PCI loans 492 362 4,117 3,466 151 — 8,588 Total loans evaluated for impairment $ 1,622,289 $ 729,501 $ 2,677,542 $ 3,538,557 $ 1,483,571 $ 289,486 $ 10,340,946 June 30, 2018 Individually evaluated for impairment $ 508 $ 519 $ 4,665 $ 2,291 $ 12,111 $ 81 $ 20,175 Collectively evaluated for impairment 1,541,567 708,721 2,658,656 3,398,158 1,508,509 271,643 10,087,254 PCI loans 696 377 4,380 5,017 899 — 11,369 Total loans evaluated for impairment $ 1,542,771 $ 709,617 $ 2,667,701 $ 3,405,466 $ 1,521,519 $ 271,724 $ 10,118,798 Troubled Debt Restructurings. 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, restructuring amortization schedules and other actions intended to minimize potential losses. Under ASC Topic 310-40 “ the Company evaluates all loan modifications to identify whether the restructuring constitutes a troubled debt restructuring. As of June 30, 2019 and 2018, the Company had $14.3 million and $208 thousand, respectively, in outstanding troubled debt restructurings. The following table presents information regarding the recorded investment of loans modified as troubled debt restructurings during the six months ended June 30, 2019 and 2018. Six Months Ended June 30, 2019 2018 Number of Loans Pre-Modification Outstanding Recorded Investment Post-Modification Outstanding Recorded Investment Number of Loans Pre-Modification Outstanding Recorded Investment Post-Modification Outstanding Recorded Investment (Dollars in thousands) Troubled Debt Restructurings Construction, land development and other land loans — $ — $ — — $ — $ — Agriculture and agriculture real estate (includes farmland) — — — — — — 1-4 Family (includes home equity) — — — — — — Commercial real estate (includes multi-family residential) — — — — — — Commercial and industrial 1 14,783 14,258 2 198 162 Consumer and other — — — — — — Total 1 $ 14,783 $ 14,258 2 $ 198 $ 162 As of June 30, 2019, there have been no defaults on any loans that were modified as troubled debt restructurings during the preceding twelve months. Default is determined at 90 or more days past due. For the six months ended June 30, 2019, the Company added one loan totaling $14.8 million as a new troubled debt restructuring, of which $14.3 million remained outstanding at June 30, 2019. For the six months ended June 30, 2018, the Company added two loans totaling $198 thousand as new troubled debt restructurings, of which $162 thousand remained outstanding at June 30, 2018. The modifications generally related to extending the amortization periods of the loans, which includes loans modified during bankruptcy. The Company did not grant principal reductions on any restructured loans at the time of modification. These modifications did not have a material impact on the Company’s determination of the allowance for credit losses.

Fair Value

Fair Value	6 Months Ended
	Jun. 30, 2019
Fair Value Disclosures [Abstract]
Fair Value	6. FAIR VALUE The Company uses fair value measurements to record fair value adjustments to certain assets and to determine fair value disclosures. Fair values represent the estimated price that would be received from selling an asset or paid to transfer a liability, otherwise known as an “exit price.” Securities available for sale are recorded at fair value on a recurring basis. Additionally, from time to time, the Company may be required to record other assets at fair value on a nonrecurring basis such as certain loans including residential mortgage loans held for sale, goodwill and other intangible assets and other real estate owned. These nonrecurring fair value adjustments typically involve application of lower-of-cost-or-market accounting or write downs of individual assets. ASC Topic 820 “ Fair Value Measurements and Disclosures Fair Value Hierarchy The Company groups financial assets and financial liabilities measured at fair value in three levels, based on the markets in which the assets and liabilities are traded and the reliability of the assumptions used to determine fair value. These levels are: • Level 1—Quoted prices in active markets for identical assets or liabilities. • Level 2—Other significant observable inputs (including quoted prices in active markets for similar assets or liabilities) or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. • Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. 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. The fair value disclosures below represent the Company’s estimates based on relevant market information and information about the financial instruments. Fair value estimates are based on judgments regarding current economic conditions, risk characteristics of the various instruments and other factors. These estimates are subjective in nature and involve uncertainties and matters of significant judgment and therefore cannot be determined with precision. Changes in the above methodologies and assumptions could significantly affect the estimates. The following tables present fair values for assets and liabilities measured at fair value on a recurring basis: As of June 30, 2019 Level 1 Level 2 Level 3 Total (Dollars in thousands) Assets: Available for sale securities: States and political subdivisions $ — $ 470 $ — $ 470 Collateralized mortgage obligations — 244,922 — 244,922 Mortgage-backed securities — 61,385 — 61,385 Total $ — $ 306,777 $ — $ 306,777 As of December 31, 2018 Level 1 Level 2 Level 3 Total (Dollars in thousands) Assets: Available for sale securities: States and political subdivisions $ — $ 1,166 $ — $ 1,166 Collateralized mortgage obligations — 12,756 — 12,756 Mortgage-backed securities — 70,233 — 70,233 Total $ — $ 84,155 $ — $ 84,155 Certain assets and liabilities are measured at fair value on a nonrecurring basis; that is, the instruments are not measured at fair value on an ongoing basis but are subject to fair value adjustments in certain circumstances (for example, when there is evidence of impairment). These instruments include other real estate owned, repossessed assets, held to maturity debt securities, loans held for sale and impaired loans, which are included as loans held for investment. For the three and six months ended June 30, 2019, the Company had additions to other real estate owned of $569 thousand and $1.9 million, respectively, of which $569 thousand and $1.7 million, respectively, were outstanding as of June 30, 2019. For the three and six months ended June 30, 2019, the Company had additions to impaired loans of $2.1 million and $30.4 million, respectively, of which $2.1 million and $29.0 million, respectively, were outstanding as of June 30, 2019. The remaining financial assets and liabilities measured at fair value on a non-recurring basis that were recorded in 2019 and remained outstanding at June 30, 2019 were not significant. The following tables present carrying and fair value information of financial instruments as of the dates indicated: As of June 30, 2019 Carrying Estimated Fair Value Amount Level 1 Level 2 Level 3 Total Assets (Dollars in thousands) Cash and due from banks $ 302,069 $ 302,069 $ — $ — $ 302,069 Federal funds sold 555 555 — — 555 Held to maturity securities 8,645,163 — 8,656,409 — 8,656,409 Loans held for sale 20,315 — 20,315 — 20,315 Loans held for investment, net of allowance 10,480,054 — — 10,378,010 10,378,010 Other real estate owned 2,005 — 2,005 — 2,005 Liabilities Deposits: Noninterest-bearing $ 5,691,236 $ — $ 5,691,236 $ — $ 5,691,236 Interest-bearing 11,196,393 — 11,188,468 — 11,188,468 Other borrowings 940,874 — 940,915 — 940,915 Securities sold under repurchase agreements 313,825 — 313,821 — 313,821 As of December 31, 2018 Carrying Estimated Fair Value Amount Level 1 Level 2 Level 3 Total Assets (Dollars in thousands) Cash and due from banks $ 410,575 $ 410,575 $ — $ — $ 410,575 Federal funds sold 552 552 — — 552 Held to maturity securities 9,324,811 — 9,081,236 — 9,081,236 Loans held for sale 29,367 — 29,367 — 29,367 Loans held for investment, net of allowance 10,254,506 — — 10,144,556 10,144,556 Other real estate owned 1,805 — 1,805 — 1,805 Liabilities Deposits: Noninterest-bearing $ 5,666,115 $ — $ 5,666,115 $ — $ 5,666,115 Interest-bearing 11,590,443 — 11,564,521 — 11,564,521 Other borrowings 1,031,126 — 1,031,161 — 1,031,161 Securities sold under repurchase agreements 284,720 — 284,685 — 284,685 The following is a description of the fair value estimates, methods and assumptions that are used by the Company in estimating the fair values of financial instruments. Loans held for sale — Loans held for sale are carried at the lower of cost or estimated fair value. Fair value for consumer mortgages held for sale is based on commitments on hand from investors or prevailing market prices. As such, the Company classifies loans held for sale subjected to nonrecurring fair value adjustments as Level 2. Loans held for investment — The Company does not record loans at fair value on a recurring basis. As such, valuation techniques discussed herein for loans are primarily for estimating fair value disclosures. The Company refined the calculation to estimate fair value for loans held for investment to be in accordance with ASU 2016-01. The refined discounted cash flow calculation to determine fair value considers internal and market-based information such as prepayment risk, cost of funds and liquidity. From time to time, the Company records nonrecurring fair value adjustments to impaired loans to reflect (1) partial write downs that are based on the observable market price or current appraised value of the collateral, or (2) the full charge-off of the loan carrying value. Where appraisals are not available, estimated cash flows are discounted using a rate commensurate with the credit risk associated with those cash flows. Assumptions regarding credit risk, cash flows and discount rates are judgmentally determined using available market information and specific borrower information. The Company classifies the estimated fair value of loans held for investment as Level 3. Other real estate owned — Other real estate owned is primarily foreclosed properties securing residential loans and commercial real estate. Foreclosed assets are adjusted to fair value less estimated costs to sell upon transfer of the loans to other real estate owned. Subsequently, these assets are carried at the lower of carrying value or fair value less estimated costs to sell. Other real estate carried at fair value based on an observable market price or a current appraised value is classified by the Company as Level 2. When management determines that the fair value of other real estate requires additional adjustments, either as a result of a non-current appraisal or when there is no observable market price, the Company classifies the other real estate as Level 3. The fair value estimates presented herein are based on pertinent information available to management at June 30, 2019. Although management is not aware of any factors that would significantly affect the estimated fair value amounts, such amounts have not been comprehensively revalued for purposes of these financial statements since those dates and, therefore, current estimates of fair value may differ significantly from the amounts presented herein.

Goodwill and Core Deposit Intan

Goodwill and Core Deposit Intangibles	6 Months Ended
	Jun. 30, 2019
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill and Core Deposit Intangibles	7. GOODWILL AND CORE DEPOSIT INTANGIBLES Changes in the carrying amount of the Company’s goodwill and core deposit intangibles for the six months ended June 30, 2019 and the year ended December 31, 2018 were as follows: Goodwill Core Deposit Intangibles (Dollars in thousands) Balance as of December 31, 2017 $ 1,900,845 $ 38,842 Less: Amortization — (5,959 ) Balance as of December 31, 2018 1,900,845 32,883 Less: Amortization — (2,584 ) Balance as of June 30, 2019 $ 1,900,845 $ 30,299 Goodwill is recorded on the acquisition date of each entity. The Company may record subsequent adjustments to goodwill for amounts undeterminable at acquisition date, such as deferred taxes and real estate valuations, and therefore the goodwill amounts may change accordingly. The Company initially records the total premium paid on acquisitions as goodwill. After finalizing the valuation, core deposit intangibles are identified and reclassified from goodwill to core deposit intangibles on the balance sheet. This reclassification has no effect on total assets, liabilities, shareholders’ equity, net income or cash flows. Management performs an evaluation annually, and more frequently if a triggering event occurs, of whether any impairment of the goodwill and core deposit intangibles has occurred. If any such impairment is determined, a write-down is recorded. As of June 30, 2019, there was no impairment recorded on goodwill and core deposit intangibles. The measurement period for the Company to determine the fair value of acquired identifiable assets and assumed liabilities will be at the end of the earlier of (1) twelve months from the date of acquisition or (2) as soon as the Company receives the information it was seeking about facts and circumstances that existed as of the date of acquisition. Core deposit intangibles are being amortized on a non-pro rata basis over their estimated lives, which the Company believes is between 10 and 15 years. Amortization expense related to intangible assets totaled $1.3 million and $1.5 million for the three months ended June 30, 2019 and 2018, respectively, and $2.6 million and $3.1 million for the six months ended June 30, 2019 and 2018, respectively. The estimated aggregate future amortization expense for core deposit intangibles remaining as of June 30, 2019 is as follows (dollars in thousands): Remaining 2019 $ 2,467 2020 4,483 2021 4,022 2022 3,664 2023 3,350 Thereafter 12,313 Total $ 30,299

Stock-Based Compensation

Stock-Based Compensation	6 Months Ended
	Jun. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	8. STOCK–BASED COMPENSATION At June 30, 2019, the Company had one stock-based employee compensation plan with awards outstanding. During 2012, Bancshares’ Board of Directors established the Prosperity Bancshares, Inc. 2012 Stock Incentive Plan (the “2012 Plan”), which was approved by Bancshares’ shareholders and authorized the issuance of up to 1,250,000 shares of common stock upon the exercise of options granted under the 2012 Plan or pursuant to the grant or exercise, as the case may be, of other awards granted under the 2012 Plan, including restricted stock, stock appreciation rights, phantom stock awards and performance awards. As of June 30, 2019, a total of 344,500 shares of common stock have been issued pursuant to vested awards and 390,782 shares of unvested restricted stock have been granted under the 2012 Plan. As of June 30, 2019, the Company had no stock options outstanding. Stock-based compensation expense related to restricted stock was $2.3 million and $2.6 million during the three months ended June 30, 2019 and 2018, respectively, and $5.1 million and $5.2 million during the six months ended June 30, 2019 and 2018, respectively. As of June 30, 2019, there was $14.7 million of total unrecognized compensation expense related to stock-based compensation arrangements. That cost is expected to be recognized over a weighted average period of 1.68 years.

Contractual Obligations and Off

Contractual Obligations and Off-Balance Sheet Items	6 Months Ended
	Jun. 30, 2019
Commitments And Contingencies Disclosure [Abstract]
Contractual Obligations and Off-Balance Sheet Items	9. CONTRACTUAL OBLIGATIONS AND OFF-BALANCE SHEET ITEMS Contractual Obligations The Company’s contractual obligations and other commitments to make future payments as of June 30, 2019 (other than deposit obligations and securities sold under repurchase agreements) are summarized below. Federal Home Loan Bank Borrowings The Company’s future cash payments associated with its contractual obligations pursuant to its Federal Home Loan Bank (“FHLB”) advances and notes payable as of June 30, 2019 are summarized below. Payments for FHLB notes payable include interest of $75 thousand that will be paid over the future periods. The payments do not include pre-payment options that may be available to the Company. 1 year or less More than 1 year but less than 3 years 3 years or more but less than 5 years 5 years or more Total (Dollars in thousands) Federal Home Loan Bank advances and notes payable $ 940,323 $ 448 $ 125 $ 53 $ 940,949 Leases The Company’s leases relate primarily to operating leases for office space and banking centers. The Company determines if an arrangement is a lease or contains a lease at inception. The Company’s leases have remaining lease terms of 1 to 13 years, which may include the option to extend the lease when it is reasonably certain for the Company to exercise that option. Operating lease right-of-use (ROU) assets and liabilities are recognized at the commencement date based on the present value of lease payments over the lease term. The Company uses its incremental collateralized borrowing rate to determine the present value of lease payments. Short-term leases and leases with variable lease costs are immaterial and the Company does not have any sublease arrangements. As of June 30, 2019, operating lease ROU assets and lease liabilities were approximately $15 million. ROU assets and lease liabilities were classified as other assets and other liabilities, respectively. As of June 30, 2019, the weighted average remaining lease terms of the Company’s operating leases were 5.2 years. The weighted average discount rate used to determine the lease liabilities as of June 30, 2019 for the Company’s operating leases was 3.43%. Cash paid for the Company’s operating leases for the three and six months ended June 30, 2019 was $1.4 million and $2.8 million, respectively. The Company’s future undiscounted cash payments associated with its operating leases as of June 30, 2019 are summarized below (dollars in thousands). Remaining 2019 $ 2,412 2020 4,158 2021 3,129 2022 2,639 2023 2,066 2024 1,287 Thereafter 4,057 Total undiscounted lease payments $ 19,748 The following table presents a summary of non-cancelable future operating lease commitments as of December 31, 2018 (dollars in thousands): 2019 $ 4,897 2020 4,088 2021 3,013 2022 2,319 2023 2,025 Thereafter 3,597 Total non-cancelable lease payments $ 19,939 Off-Balance Sheet Items In the normal course of business, the Company enters into various transactions that, in accordance with GAAP, are not included in its consolidated balance sheets. The Company enters into these transactions to meet the financing needs of its customers. These transactions include commitments to extend credit and standby letters of credit, which involve, to varying degrees, elements of credit risk and interest rate risk in excess of the amounts recognized in the consolidated balance sheets. The Company’s commitments associated with outstanding standby letters of credit and commitments to extend credit expiring by period as of June 30, 2019 are summarized below. Since commitments associated with letters of credit and commitments to extend credit may expire unused, the amounts shown do not necessarily reflect the actual future cash funding requirements. 1 year or less More than 1 year but less than 3 years 3 years or more but less than 5 years 5 years or more Total (Dollars in thousands) Standby letters of credit $ 59,278 $ 6,892 $ 1,540 $ — $ 67,710 Commitments to extend credit 1,079,334 423,900 109,412 1,027,608 2,640,254 Total $ 1,138,612 $ 430,792 $ 110,952 $ 1,027,608 $ 2,707,964

Other Comprehensive Income

Other Comprehensive Income	6 Months Ended
	Jun. 30, 2019
Equity [Abstract]
Other Comprehensive Income	10. OTHER COMPREHENSIVE INCOME The tax effects allocated to each component of other comprehensive income were as follows: Three Months Ended June 30, 2019 2018 Before Tax Amount Tax Effect Net of Tax Amount Before Tax Amount Tax Effect Net of Tax Amount (Dollars in thousands) Other comprehensive income: Securities available for sale: Change in unrealized gain during period $ 716 $ (150 ) $ 566 $ 380 $ (80 ) $ 300 Total securities available for sale 716 (150 ) 566 380 (80 ) 300 Total other comprehensive income $ 716 $ (150 ) $ 566 $ 380 $ (80 ) $ 300 Six Months Ended June 30, 2019 2018 Before Tax Amount Tax Effect Net of Tax Amount Before Tax Amount Tax Effect Net of Tax Amount (Dollars in thousands) Other comprehensive income: Securities available for sale: Change in unrealized gain during period $ 1,219 $ (256 ) $ 963 $ 580 $ (122 ) $ 458 Total securities available for sale 1,219 (256 ) 963 580 (122 ) 458 Total other comprehensive income $ 1,219 $ (256 ) $ 963 $ 580 $ (122 ) $ 458 Activity in accumulated other comprehensive income associated with securities available for sale, net of tax, was as follows: Securities Available for Sale Accumulated Other Comprehensive Income (Dollars in thousands) Balance at December 31, 2018 $ 310 $ 310 Other comprehensive income 963 963 Balance at June 30, 2019 $ 1,273 $ 1,273 Balance at December 31, 2017 $ (113 ) $ (113 ) Other comprehensive income 458 458 Balance at June 30, 2018 $ 345 $ 345

Acquisitions

Acquisitions	6 Months Ended
	Jun. 30, 2019
Business Combinations [Abstract]
Acquisitions	11. ACQUISITIONS On June 17, 2019, Bancshares and LegacyTexas Financial Group, Inc. (“LegacyTexas”) jointly announced the signing of a definitive agreement whereby LegacyTexas, the parent company of LegacyTexas Bank, will merge into Bancshares. LegacyTexas Bank operates 42 locations in 19 North Texas cities in and around the Dallas-Fort Worth area. As of June 30, 2019, LegacyTexas, on a consolidated basis, reported total assets of $9.9 billion, total gross loans of $8.7 billion and total deposits of $7.1 billion. Under the terms of the merger agreement, stockholders of LegacyTexas will receive 0.5280 shares of Bancshares common stock and $6.28 cash for each LegacyTexas share. Consummation of the merger is subject to certain conditions, including the approval by the shareholders of Bancshares and LegacyTexas and customary regulatory approvals. Based on Bancshares’ closing price of $67.24 on June 14, 2019, the total consideration was valued at approximately $2.1 billion, or approximately $41.78 per share. The merger is expected to close during the fourth quarter of 2019, although delays could occur.

New Accounting Standards (Polic

New Accounting Standards (Policies)	6 Months Ended
	Jun. 30, 2019
New Accounting Pronouncements And Changes In Accounting Principles [Abstract]
Accounting Standards Updates (''ASU'')	Accounting Standards Updates (“ASU”) ASU 2016-13, “Financial Instruments – Credit Losses (Topic 326)—Measurement of Credit Losses on Financial Instruments.” ASU 2016-13 requires a financial asset (or a group of financial assets) measured at amortized cost basis to be presented at the net amount expected to be collected. The measurement of current expected credit losses (“CECL”) is based on relevant information about past events, including historical experience, current conditions, and reasonable and supportable forecasts that affect the collectability of the reported amount. An entity must use judgment in determining the relevant information and estimation methods that are appropriate in its circumstances. Additionally, available for sale debt securities may realize value either through collection of contractual cash flows or through sale of the security at fair value. Therefore, the amendments limit the amount of the allowance for credit losses to the difference between amortized cost and fair value. ASU 2016-13 will be effective for the Company as of January 1, 2020. The Company’s implementation workgroup is comprised of individuals from various functional areas including credit, risk management, finance and information technology, among others, and meets periodically to discuss the latest developments and monitor implementation progress. The Company is currently working through an implementation plan that includes assessment of processes, portfolio segmentation and model development. The Company is working with a third-party vendor to assist with implementation and model development. CECL compliant models are currently in the development stage, with model testing and documentation being performed concurrently. The Company is assessing CECL disclosure requirements and developing appropriate internal controls around the CECL process. While the Company continues to evaluate the potential impact of ASU 2016‑13 on the Company’s financial statements, the adoption of ASU 2016-13 may result in an increase in the allowance for loan losses as a result of changing from an incurred loss methodology to an expected loss methodology. ASU 2016-02, "Leases (Topic 842)." ASU 2016-02 requires that lessees recognize lease assets and lease liabilities on the balance sheet and disclose key information about leasing arrangements. The requirements for lessors under ASU 2016-02 are largely unchanged from existing guidance, however certain necessary changes have been made to align with specific changes to lessee accounting and key aspects of the revenue recognition guidance (Topic 606). The Company’s leases relate primarily to office space and banking centers. The Company identified and reviewed existing leases applicable to ASU 2016-02 and elected certain optional practical expedients: 1) not to reassess whether any expired or existing contracts are or contain leases, 2) not to reassess the lease classification for any expired or existing lease, 3) not to reassess initial direct cost for any existing leases and 4) not to separately identify lease and non-lease components. Additionally, the Company elected the short-term lease exemption for lease terms less than 12 months. The Company adopted ASU 2016-02 on January 1, 2019 using a modified retrospective transition approach without adjusting comparative periods. With the adoption of the new standard, the Company recognized right-of-use assets and lease liabilities of $17.3 million as of January 1, 2019. See Note 9 “Contractual Obligations and Off-Balance Sheet Items — Contractual Obligations — Leases” for additional information.

Income Per Common Share (Tables

Income Per Common Share (Tables)	6 Months Ended
	Jun. 30, 2019
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	The following table illustrates the computation of basic and diluted earnings per share: Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 Amount Per Share Amount Amount Per Share Amount Amount Per Share Amount Amount Per Share Amount (Amounts in thousands, except per share data) Net income $ 82,258 $ 81,597 $ 164,660 $ 155,958 Basic: Weighted average shares outstanding 69,806 $ 1.18 69,839 $ 1.17 69,832 $ 2.36 69,803 $ 2.23 Diluted: Weighted average shares outstanding 69,806 $ 1.18 69,839 $ 1.17 69,832 $ 2.36 69,803 $ 2.23

Securities (Tables)

Securities (Tables)	6 Months Ended
	Jun. 30, 2019
Investments Debt And Equity Securities [Abstract]
Schedule of Amortized Cost and Fair Value of Investment Securities	The amortized cost and fair value of investment securities were as follows: June 30, 2019 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (Dollars in thousands) Available for Sale States and political subdivisions $ 469 $ 1 $ — $ 470 Collateralized mortgage obligations 244,256 796 (130 ) 244,922 Mortgage-backed securities 60,441 946 (2 ) 61,385 Total $ 305,166 $ 1,743 $ (132 ) $ 306,777 Held to Maturity U.S. Treasury securities and obligations of U.S. Government agencies $ 22,867 $ 43 $ (3 ) $ 22,907 States and political subdivisions 215,871 6,088 (144 ) 221,815 Collateralized mortgage obligations 462 5 (1 ) 466 Mortgage-backed securities 8,405,963 50,480 (45,222 ) 8,411,221 Total $ 8,645,163 $ 56,616 $ (45,370 ) $ 8,656,409 December 31, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (Dollars in thousands) Available for Sale States and political subdivisions $ 1,159 $ 7 $ — $ 1,166 Collateralized mortgage obligations 12,724 69 (37 ) 12,756 Mortgage-backed securities 69,880 553 (200 ) 70,233 Total $ 83,763 $ 629 $ (237 ) $ 84,155 Held to Maturity U.S. Treasury securities and obligations of U.S. Government agencies $ 25,778 $ — $ (100 ) $ 25,678 States and political subdivisions 253,198 3,440 (777 ) 255,861 Collateralized mortgage obligations 509 1 (2 ) 508 Mortgage-backed securities 9,045,326 5,798 (251,935 ) 8,799,189 Total $ 9,324,811 $ 9,239 $ (252,814 ) $ 9,081,236
Securities in Continuous Loss Position	Securities with unrealized losses, segregated by length of time, that have been in a continuous loss position were as follows: June 30, 2019 Less than 12 Months 12 Months or More Total Estimated Fair Value Unrealized Losses Estimated Fair Value Unrealized Losses Estimated Fair Value Unrealized Losses (Dollars in thousands) Available for Sale Collateralized mortgage obligations $ 37,871 $ (106 ) $ 1,899 $ (24 ) $ 39,770 $ (130 ) Mortgage-backed securities 67 (1 ) 48 (1 ) 115 (2 ) Total $ 37,938 $ (107 ) $ 1,947 $ (25 ) $ 39,885 $ (132 ) Held to Maturity U.S. Treasury securities and obligations of U.S. Government agencies $ — $ — $ 8,990 $ (3 ) $ 8,990 $ (3 ) States and political subdivisions 43,370 (87 ) 26,552 (57 ) 69,922 (144 ) Collateralized mortgage obligations 79 (1 ) — — 79 (1 ) Mortgage-backed securities 131,659 (356 ) 4,271,546 (44,866 ) 4,403,205 (45,222 ) Total $ 175,108 $ (444 ) $ 4,307,088 $ (44,926 ) $ 4,482,196 $ (45,370 ) December 31, 2018 Less than 12 Months 12 Months or More Total Estimated Fair Value Unrealized Losses Estimated Fair Value Unrealized Losses Estimated Fair Value Unrealized Losses (Dollars in thousands) Available for Sale Collateralized mortgage obligations $ 12 $ — $ 2,096 $ (37 ) $ 2,108 $ (37 ) Mortgage-backed securities 50,950 (197 ) 2,091 (3 ) 53,041 (200 ) Total $ 50,962 $ (197 ) $ 4,187 $ (40 ) $ 55,149 $ (237 ) Held to Maturity U.S. Treasury securities and obligations of U.S. Government agencies $ 20,720 $ (76 ) $ 4,957 $ (24 ) $ 25,677 $ (100 ) States and political subdivisions 89,407 (328 ) 58,262 (449 ) 147,669 (777 ) Collateralized mortgage obligations — — 292 (2 ) 292 (2 ) Mortgage-backed securities 1,003,089 (8,401 ) 6,873,948 (243,534 ) 7,877,037 (251,935 ) Total $ 1,113,216 $ (8,805 ) $ 6,937,459 $ (244,009 ) $ 8,050,675 $ (252,814 )
Investment Securities by Contractual Maturity	The amortized cost and fair value of investment securities at June 30, 2019, by contractual maturity, are shown below. Actual maturities will differ from contractual maturities because borrowers may have the right to call or prepay obligations at any time with or without call or prepayment penalties. Held to Maturity Available for Sale Amortized Cost Fair Value Amortized Cost Fair Value (Dollars in thousands) Due in one year or less $ 48,722 $ 48,797 $ 165 $ 165 Due after one year through five years 117,183 118,201 304 305 Due after five years through ten years 68,317 73,134 — — Due after ten years 4,516 4,590 — — Subtotal 238,738 244,722 469 470 Mortgage-backed securities and collateralized mortgage obligations 8,406,425 8,411,687 304,697 306,307 Total $ 8,645,163 $ 8,656,409 $ 305,166 $ 306,777

Loans and Allowance for Credi_2

Loans and Allowance for Credit Losses (Tables)	6 Months Ended
	Jun. 30, 2019
Receivables [Abstract]
Types of Loans in Loan Portfolio	The loan portfolio consists of various types of loans and is categorized by major type as follows: June 30, 2019 December 31, 2018 (Dollars in thousands) Residential mortgage loans held for sale $ 20,315 $ 29,367 Commercial and industrial 1,525,628 1,483,571 Real estate: Construction, land development and other land loans 1,739,308 1,622,289 1-4 family residential (includes home equity) 2,692,963 2,677,542 Commercial real estate (includes multi-family residential) 3,551,668 3,538,557 Farmland 541,469 545,373 Agriculture 195,001 184,128 Consumer and other 321,023 289,486 Total loans held for investment 10,567,060 10,340,946 Total $ 10,587,375 $ 10,370,313
Related Party Loans	An analysis of activity with respect to these related party loans is as follows: As of and for the six months ended June As of and for the year ended December (Dollars in thousands) Beginning balance on January 1 $ 1,923 $ 2,694 New loans — 5 Repayments (168 ) (776 ) Ending balance $ 1,755 $ 1,923
Aging Analysis of Past Due Loans	An aging analysis of past due loans, segregated by category of loan, is presented below: June 30, 2019 Loans Past Due and Still Accruing 30-89 Days 90 or More Days Total Past Due Loans Nonaccrual Loans Current Loans Total Loans (Dollars in thousands) Construction, land development and other land loans $ 5,368 $ 1,153 $ 6,521 $ 659 $ 1,732,128 $ 1,739,308 Agriculture and agriculture real estate (includes farmland) 710 — 710 616 735,144 736,470 1-4 family (includes home equity) (1) 11,107 58 11,165 15,278 2,686,835 2,713,278 Commercial real estate (includes multi-family residential) 14,572 — 14,572 4,135 3,532,961 3,551,668 Commercial and industrial 4,102 383 4,485 16,561 1,504,582 1,525,628 Consumer and other 333 — 333 40 320,650 321,023 Total $ 36,192 $ 1,594 $ 37,786 $ 37,289 $ 10,512,300 $ 10,587,375 December 31, 2018 Loans Past Due and Still Accruing 30-89 Days 90 or More Days Total Past Due Loans Nonaccrual Loans Current Loans Total Loans (Dollars in thousands) Construction, land development and other land loans $ 6,363 $ 788 $ 7,151 $ 1,386 $ 1,613,752 $ 1,622,289 Agriculture and agriculture real estate (includes farmland) 705 — 705 256 728,540 729,501 1-4 family (includes home equity) (1) 10,479 2,995 13,474 4,515 2,688,920 2,706,909 Commercial real estate (includes multi-family residential) 9,063 — 9,063 2,727 3,526,767 3,538,557 Commercial and industrial 6,652 221 6,873 4,215 1,472,483 1,483,571 Consumer and other 1,012 — 1,012 48 288,426 289,486 Total $ 34,274 $ 4,004 $ 38,278 $ 13,147 $ 10,318,888 $ 10,370,313 (1) Includes $20.3 million and $29.4 million of residential mortgage loans held for sale at June 30, 2019 and December 31, 2018, respectively.
Non-performing Assets	The following table presents information regarding nonperforming assets as of the dates indicated: June 30, 2019 December 31, 2018 (Dollars in thousands) Nonaccrual loans (1) $ 37,289 $ 13,147 Accruing loans 90 or more days past due 1,594 4,004 Total nonperforming loans 38,883 17,151 Repossessed assets 670 — Other real estate 2,005 1,805 Total nonperforming assets $ 41,558 $ 18,956 Nonperforming assets to total loans and other real estate 0.39 % 0.18 % (1) Includes troubled debt restructurings of $14.3 million and $51 thousand as of June 30, 2019 and December 31, 2018, respectively.
Recorded Investment and Outstanding Balance for Purchased Credit Impaired Loans and Non Purchased Credit Impaired Loans	The recorded investment in PCI loans included in the consolidated balance sheet and the related outstanding balance as of the dates indicated are presented in the table below. The outstanding balance represents the total amount owed as of June 30, 2019 and December 31, 2018. June 30, 2019 December 31, 2018 (Dollars in thousands) PCI loans: Outstanding balance $ 10,110 $ 11,419 Discount (2,165 ) (2,831 ) Recorded investment $ 7,945 $ 8,588 June 30, 2019 December 31, 2018 (Dollars in thousands) Non-PCI loans: Outstanding balance $ 467,645 $ 526,840 Discount (12,479 ) (14,833 ) Recorded investment $ 455,166 $ 512,007
Summary of Changes in Accretable Yields of Acquired Loans	Changes in the accretable yield for acquired PCI loans for the three and six months ended June 30, 2019 and 2018 were as follows: Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 (Dollars in thousands) Balance at beginning of period $ 1,234 $ 7,685 $ 1,534 $ 8,121 Reclassifications from nonaccretable 17 55 36 305 Accretion (347 ) (3,771 ) (666 ) (4,457 ) Balance at June 30, $ 904 $ 3,969 $ 904 $ 3,969 Changes in the discount accretion for Non-PCI loans for the three and six months ended June 30, 2019 and 2018 were as follows: Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 (Dollars in thousands) Balance at beginning of period $ 13,359 $ 18,885 $ 14,833 $ 20,533 Accretion charge-offs — (2 ) — (10 ) Accretion (880 ) (1,452 ) (2,354 ) (3,092 ) Balance at June 30, $ 12,479 $ 17,431 $ 12,479 $ 17,431
Summary of Impaired Loans	Impaired loans are set forth in the following tables. No interest income was recognized on impaired loans subsequent to their classification as impaired. The average recorded investment presented in the tables below is reported on a year-to-date basis. June 30, 2019 Recorded Investment Unpaid Contractual Principal Balance Related Allowance Average Recorded Investment (Dollars in thousands) With no related allowance recorded: Construction, land development and other land loans $ 269 $ 270 $ — $ 631 Agriculture and agriculture real estate (includes farmland) 326 326 — 291 1-4 family (includes home equity) 10,035 10,747 — 7,106 Commercial real estate (includes multi-family residential) 3,162 3,341 — 2,945 Commercial and industrial 15,406 17,610 — 9,138 Consumer and other 40 44 — 44 Total 29,238 32,338 — 20,155 With an allowance recorded: Construction, land development and other land loans 390 390 58 391 Agriculture and agriculture real estate (includes farmland) 290 290 160 145 1-4 family (includes home equity) 5,243 5,272 504 2,754 Commercial real estate (includes multi-family residential) 973 993 283 486 Commercial and industrial 1,155 1,171 329 1,241 Consumer and other — — — — Total 8,051 8,116 1,334 5,017 Total: Construction, land development and other land loans 659 660 58 1,022 Agriculture and agriculture real estate (includes farmland) 616 616 160 436 1-4 family (includes home equity) 15,278 16,019 504 9,860 Commercial real estate (includes multi-family residential) 4,135 4,334 283 3,431 Commercial and industrial 16,561 18,781 329 10,379 Consumer and other 40 44 — 44 $ 37,289 $ 40,454 $ 1,334 $ 25,172 December 31, 2018 Recorded Investment Unpaid Contractual Principal Balance Related Allowance Average Recorded Investment (Dollars in thousands) With no related allowance recorded: Construction, land development and other land loans $ 993 $ 995 $ — $ 788 Agriculture and agriculture real estate (includes farmland) 256 311 — 194 1-4 family (includes home equity) 4,177 4,903 — 4,048 Commercial real estate (includes multi-family residential) 2,727 2,848 — 2,475 Commercial and industrial 2,870 3,810 — 5,358 Consumer and other 48 76 — 135 Total 11,071 12,943 — 12,998 With an allowance recorded: Construction, land development and other land loans 391 391 58 195 Agriculture and agriculture real estate (includes farmland) — — — — 1-4 family (includes home equity) 266 289 56 729 Commercial real estate (includes multi-family residential) — — — 743 Commercial and industrial 1,328 1,332 571 3,740 Consumer and other — — — — Total 1,985 2,012 685 5,407 Total: Construction, land development and other land loans 1,384 1,386 58 983 Agriculture and agriculture real estate (includes farmland) 256 311 — 194 1-4 family (includes home equity) 4,443 5,192 56 4,777 Commercial real estate (includes multi-family residential) 2,727 2,848 — 3,218 Commercial and industrial 4,198 5,142 571 9,098 Consumer and other 48 76 — 135 $ 13,056 $ 14,955 $ 685 $ 18,405
Risk Grade and Category of Loan	The following table presents loans by risk grade and category of loan at June 30, 2019. Impaired loans include loans in risk grades 7, 8 and 9, as well as any PCI loan that has a specific reserve allocated to it. Construction, Land Development and Other Agriculture and Agriculture Real Estate (includes Farmland) 1-4 Family (includes Home (1) Commercial Real Estate (includes Multi-Family Commercial and Industrial Consumer and Other Total (Dollars in thousands) Grade 1 $ — $ 14,322 $ — $ — $ 55,562 $ 35,091 $ 104,975 Grade 2 1,215 3,877 15,430 21,640 12,312 56,519 110,993 Grade 3 1,587,922 647,171 2,600,773 2,892,964 1,102,365 200,582 9,031,777 Grade 4 136,083 64,025 67,445 557,501 265,415 24,325 1,114,794 Grade 5 5,684 5,091 6,486 56,772 61,476 2,827 138,336 Grade 6 7,315 1,029 3,750 15,719 11,814 1,639 41,266 Grade 7 659 326 15,278 4,135 16,543 40 36,981 Grade 8 — 290 — — 18 — 308 Grade 9 — — — — — — — PCI Loans 430 339 4,116 2,937 123 — 7,945 Total $ 1,739,308 $ 736,470 $ 2,713,278 $ 3,551,668 $ 1,525,628 $ 321,023 $ 10,587,375 (1) Includes $20.3 million of residential mortgage loans held for sale at June 30, 2019. The following table presents loans by risk grade and category of loan at December 31, 2018 . Impaired loans include loans in risk grades 7, 8 and 9, as well as any PCI loan that has a specific reserve allocated to it. Construction, Land Development and Other Agriculture and Agriculture Real Estate (includes Farmland) 1-4 Family (includes Home (1) Commercial Real Estate (includes Multi-Family Commercial and Industrial Consumer and Other Total (Dollars in thousands) Grade 1 $ — $ 15,725 $ — $ — $ 59,979 $ 37,135 $ 112,839 Grade 2 1,040 3,974 21,465 22,207 11,003 55,802 115,491 Grade 3 1,509,532 636,674 2,598,600 2,974,474 1,083,328 171,758 8,974,366 Grade 4 99,087 66,650 61,430 481,735 243,743 20,164 972,809 Grade 5 3,673 5,578 12,522 37,942 58,088 2,978 120,781 Grade 6 7,081 282 4,332 16,006 23,081 1,601 52,383 Grade 7 1,384 256 4,395 2,727 4,165 48 12,975 Grade 8 — — 48 — 33 — 81 Grade 9 — — — — — — — PCI Loans 492 362 4,117 3,466 151 — 8,588 Total $ 1,622,289 $ 729,501 $ 2,706,909 $ 3,538,557 $ 1,483,571 $ 289,486 $ 10,370,313 (1) Includes $29.4 million of residential mortgage loans held for sale at December 31, 2018.
Allowance for Credit Losses by Category of Loan	The following table details activity in the allowance for credit losses by category of loan for the three and six months ended June 30, 2019 and 2018. Allocation of a portion of the allowance to one category of loans does not preclude its availability to absorb losses in other categories. Construction, Land Development and Other Land Loans Agriculture and Agriculture Real Estate (includes Farmland) 1-4 Family (includes Home Equity) Commercial Real Estate (includes Multi-Family Residential) Commercial and Industrial Consumer and Other Total (Dollars in thousands) Allowance for credit losses: Three Months Ended Balance March 31, 2019 $ 16,192 $ 3,284 $ 14,455 $ 11,590 $ 39,059 $ 1,511 $ 86,091 Provision for credit losses (299 ) 578 (61 ) 575 (710 ) 717 800 Charge-offs (19 ) (54 ) (16 ) — (125 ) (905 ) (1,119 ) Recoveries 12 8 5 1 953 255 1,234 Net charge-offs (7 ) (46 ) (11 ) 1 828 (650 ) 115 Balance June 30, 2019 $ 15,886 $ 3,816 $ 14,383 $ 12,166 $ 39,177 $ 1,578 $ 87,006 Six Months Ended Balance December 31, 2018 $ 15,582 $ 3,693 $ 14,135 $ 11,220 $ 40,223 $ 1,587 $ 86,440 Provision for credit losses 311 (1,109 ) 256 944 (155 ) 1,253 1,500 Charge-offs (63 ) (64 ) (22 ) — (2,082 ) (1,797 ) (4,028 ) Recoveries 56 1,296 14 2 1,191 535 3,094 Net charge-offs (7 ) 1,232 (8 ) 2 (891 ) (1,262 ) (934 ) Balance June 30, 2019 $ 15,886 $ 3,816 $ 14,383 $ 12,166 $ 39,177 $ 1,578 $ 87,006 Allowance for credit losses: Three Months Ended Balance March 31, 2018 $ 14,622 $ 3,304 $ 13,072 $ 10,853 $ 40,340 $ 1,409 $ 83,600 Provision for credit losses (173 ) 407 395 749 2,161 461 4,000 Charge-offs — — (120 ) (986 ) (1,194 ) (901 ) (3,201 ) Recoveries 1 45 6 — 147 366 565 Net charge-offs 1 45 (114 ) (986 ) (1,047 ) (535 ) (2,636 ) Balance June 30, 2018 $ 14,450 $ 3,756 $ 13,353 $ 10,616 $ 41,454 $ 1,335 $ 84,964 Six Months Ended Balance December 31, 2017 $ 14,815 $ 3,772 $ 14,490 $ 10,628 $ 38,810 $ 1,526 $ 84,041 Provision for credit losses (243 ) (122 ) (766 ) 1,476 11,707 948 13,000 Charge-offs (130 ) — (386 ) (1,489 ) (9,370 ) (1,911 ) (13,286 ) Recoveries 8 106 15 1 307 772 1,209 Net charge-offs (122 ) 106 (371 ) (1,488 ) (9,063 ) (1,139 ) (12,077 ) Balance June 30, 2018 $ 14,450 $ 3,756 $ 13,353 $ 10,616 $ 41,454 $ 1,335 $ 84,964 The following table details the amount of the allowance for credit losses allocated to each category of loan as of June 30, 2019, December 31, 2018 and June 30, 2018, on the basis of the impairment methodology used to determine the allowance for credit losses. Construction, Land Development and Other Land Loans Agriculture and Agriculture Real Estate (includes Farmland) 1-4 Family (includes Home Equity) Commercial Real Estate (includes Multi-Family Residential) Commercial and Industrial Consumer and Other Total (Dollars in thousands) Allowance for credit losses related June 30, 2019 Individually evaluated for impairment $ 58 $ 160 $ 504 $ 283 $ 329 $ — $ 1,334 Collectively evaluated for impairment 15,828 3,656 13,879 11,883 38,848 1,578 85,672 PCI loans — — — — — — — Total allowance for credit losses $ 15,886 $ 3,816 $ 14,383 $ 12,166 $ 39,177 $ 1,578 $ 87,006 December 31, 2018 Individually evaluated for impairment $ 58 $ — $ 56 $ — $ 571 $ — $ 685 Collectively evaluated for impairment 15,524 3,693 14,079 11,220 39,652 1,587 85,755 PCI loans — — — — — — — Total allowance for credit losses $ 15,582 $ 3,693 $ 14,135 $ 11,220 $ 40,223 $ 1,587 $ 86,440 June 30, 2018 Individually evaluated for impairment $ — $ 25 $ 61 $ — $ 2,741 $ — $ 2,827 Collectively evaluated for impairment 14,450 3,731 13,292 10,616 38,713 1,335 82,137 PCI loans — — — — — — — Total allowance for credit losses $ 14,450 $ 3,756 $ 13,353 $ 10,616 $ 41,454 $ 1,335 $ 84,964 Construction, Land Development and Other Land Loans Agriculture and Agriculture Real Estate (includes Farmland) 1-4 Family (includes Home Equity) Commercial Real Estate (includes Multi-Family Residential) Commercial and Industrial Consumer and Other Total (Dollars in thousands) Recorded investment in June 30, 2019 Individually evaluated for impairment $ 659 $ 616 $ 15,278 $ 4,135 $ 16,561 $ 40 $ 37,289 Collectively evaluated for impairment 1,738,219 735,515 2,673,569 3,544,596 1,508,944 320,983 10,521,826 PCI loans 430 339 4,116 2,937 123 — 7,945 Total loans evaluated for impairment $ 1,739,308 $ 736,470 $ 2,692,963 $ 3,551,668 $ 1,525,628 $ 321,023 $ 10,567,060 December 31, 2018 Individually evaluated for impairment $ 1,384 $ 256 $ 4,443 $ 2,727 $ 4,198 $ 48 $ 13,056 Collectively evaluated for impairment 1,620,413 728,883 2,668,982 3,532,364 1,479,222 289,438 10,319,302 PCI loans 492 362 4,117 3,466 151 — 8,588 Total loans evaluated for impairment $ 1,622,289 $ 729,501 $ 2,677,542 $ 3,538,557 $ 1,483,571 $ 289,486 $ 10,340,946 June 30, 2018 Individually evaluated for impairment $ 508 $ 519 $ 4,665 $ 2,291 $ 12,111 $ 81 $ 20,175 Collectively evaluated for impairment 1,541,567 708,721 2,658,656 3,398,158 1,508,509 271,643 10,087,254 PCI loans 696 377 4,380 5,017 899 — 11,369 Total loans evaluated for impairment $ 1,542,771 $ 709,617 $ 2,667,701 $ 3,405,466 $ 1,521,519 $ 271,724 $ 10,118,798
Troubled Debt Restructurings	The following table presents information regarding the recorded investment of loans modified as troubled debt restructurings during the six months ended June 30, 2019 and 2018. Six Months Ended June 30, 2019 2018 Number of Loans Pre-Modification Outstanding Recorded Investment Post-Modification Outstanding Recorded Investment Number of Loans Pre-Modification Outstanding Recorded Investment Post-Modification Outstanding Recorded Investment (Dollars in thousands) Troubled Debt Restructurings Construction, land development and other land loans — $ — $ — — $ — $ — Agriculture and agriculture real estate (includes farmland) — — — — — — 1-4 Family (includes home equity) — — — — — — Commercial real estate (includes multi-family residential) — — — — — — Commercial and industrial 1 14,783 14,258 2 198 162 Consumer and other — — — — — — Total 1 $ 14,783 $ 14,258 2 $ 198 $ 162

Fair Value (Tables)

Fair Value (Tables)	6 Months Ended
	Jun. 30, 2019
Fair Value Disclosures [Abstract]
Fair Value Assets and Liabilities Measured on Recurring Basis	The following tables present fair values for assets and liabilities measured at fair value on a recurring basis: As of June 30, 2019 Level 1 Level 2 Level 3 Total (Dollars in thousands) Assets: Available for sale securities: States and political subdivisions $ — $ 470 $ — $ 470 Collateralized mortgage obligations — 244,922 — 244,922 Mortgage-backed securities — 61,385 — 61,385 Total $ — $ 306,777 $ — $ 306,777 As of December 31, 2018 Level 1 Level 2 Level 3 Total (Dollars in thousands) Assets: Available for sale securities: States and political subdivisions $ — $ 1,166 $ — $ 1,166 Collateralized mortgage obligations — 12,756 — 12,756 Mortgage-backed securities — 70,233 — 70,233 Total $ — $ 84,155 $ — $ 84,155
Summary of Carrying and Fair Value Information of Financial Instruments	The following tables present carrying and fair value information of financial instruments as of the dates indicated: As of June 30, 2019 Carrying Estimated Fair Value Amount Level 1 Level 2 Level 3 Total Assets (Dollars in thousands) Cash and due from banks $ 302,069 $ 302,069 $ — $ — $ 302,069 Federal funds sold 555 555 — — 555 Held to maturity securities 8,645,163 — 8,656,409 — 8,656,409 Loans held for sale 20,315 — 20,315 — 20,315 Loans held for investment, net of allowance 10,480,054 — — 10,378,010 10,378,010 Other real estate owned 2,005 — 2,005 — 2,005 Liabilities Deposits: Noninterest-bearing $ 5,691,236 $ — $ 5,691,236 $ — $ 5,691,236 Interest-bearing 11,196,393 — 11,188,468 — 11,188,468 Other borrowings 940,874 — 940,915 — 940,915 Securities sold under repurchase agreements 313,825 — 313,821 — 313,821 As of December 31, 2018 Carrying Estimated Fair Value Amount Level 1 Level 2 Level 3 Total Assets (Dollars in thousands) Cash and due from banks $ 410,575 $ 410,575 $ — $ — $ 410,575 Federal funds sold 552 552 — — 552 Held to maturity securities 9,324,811 — 9,081,236 — 9,081,236 Loans held for sale 29,367 — 29,367 — 29,367 Loans held for investment, net of allowance 10,254,506 — — 10,144,556 10,144,556 Other real estate owned 1,805 — 1,805 — 1,805 Liabilities Deposits: Noninterest-bearing $ 5,666,115 $ — $ 5,666,115 $ — $ 5,666,115 Interest-bearing 11,590,443 — 11,564,521 — 11,564,521 Other borrowings 1,031,126 — 1,031,161 — 1,031,161 Securities sold under repurchase agreements 284,720 — 284,685 — 284,685

Goodwill and Core Deposit Int_2

Goodwill and Core Deposit Intangibles (Tables)	6 Months Ended
	Jun. 30, 2019
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill and Core Deposit Intangibles	Changes in the carrying amount of the Company’s goodwill and core deposit intangibles for the six months ended June 30, 2019 and the year ended December 31, 2018 were as follows: Goodwill Core Deposit Intangibles (Dollars in thousands) Balance as of December 31, 2017 $ 1,900,845 $ 38,842 Less: Amortization — (5,959 ) Balance as of December 31, 2018 1,900,845 32,883 Less: Amortization — (2,584 ) Balance as of June 30, 2019 $ 1,900,845 $ 30,299
Estimated Aggregate Future Amortization Expense for Core Deposit Intangibles	The estimated aggregate future amortization expense for core deposit intangibles remaining as of June 30, 2019 is as follows (dollars in thousands): Remaining 2019 $ 2,467 2020 4,483 2021 4,022 2022 3,664 2023 3,350 Thereafter 12,313 Total $ 30,299

Contractual Obligations and O_2

Contractual Obligations and Off-Balance Sheet Items (Tables)	6 Months Ended
	Jun. 30, 2019
Commitments And Contingencies Disclosure [Abstract]
Schedule of Contractual Obligations and Other Commitments	The Company’s future cash payments associated with its contractual obligations pursuant to its Federal Home Loan Bank (“FHLB”) advances and notes payable as of June 30, 2019 are summarized below. 1 year or less More than 1 year but less than 3 years 3 years or more but less than 5 years 5 years or more Total (Dollars in thousands) Federal Home Loan Bank advances and notes payable $ 940,323 $ 448 $ 125 $ 53 $ 940,949
Future Undiscounted Cash Payments Associated with its Operating Leases	The Company’s future undiscounted cash payments associated with its operating leases as of June 30, 2019 are summarized below (dollars in thousands). Remaining 2019 $ 2,412 2020 4,158 2021 3,129 2022 2,639 2023 2,066 2024 1,287 Thereafter 4,057 Total undiscounted lease payments $ 19,748
Summary of Non-Cancelable Future Operating Lease Commitments	The following table presents a summary of non-cancelable future operating lease commitments as of December 31, 2018 (dollars in thousands): 2019 $ 4,897 2020 4,088 2021 3,013 2022 2,319 2023 2,025 Thereafter 3,597 Total non-cancelable lease payments $ 19,939
Summary of Commitments Associated with Outstanding Standby Letters of Credit and Commitments to Extend Credit	The Company’s commitments associated with outstanding standby letters of credit and commitments to extend credit expiring by period as of June 30, 2019 are summarized below. Since commitments associated with letters of credit and commitments to extend credit may expire unused, the amounts shown do not necessarily reflect the actual future cash funding requirements. 1 year or less More than 1 year but less than 3 years 3 years or more but less than 5 years 5 years or more Total (Dollars in thousands) Standby letters of credit $ 59,278 $ 6,892 $ 1,540 $ — $ 67,710 Commitments to extend credit 1,079,334 423,900 109,412 1,027,608 2,640,254 Total $ 1,138,612 $ 430,792 $ 110,952 $ 1,027,608 $ 2,707,964

Other Comprehensive Income (Tab

Other Comprehensive Income (Tables)	6 Months Ended
	Jun. 30, 2019
Equity [Abstract]
Tax Effects Allocated to Each Component of Other Comprehensive Income	The tax effects allocated to each component of other comprehensive income were as follows: Three Months Ended June 30, 2019 2018 Before Tax Amount Tax Effect Net of Tax Amount Before Tax Amount Tax Effect Net of Tax Amount (Dollars in thousands) Other comprehensive income: Securities available for sale: Change in unrealized gain during period $ 716 $ (150 ) $ 566 $ 380 $ (80 ) $ 300 Total securities available for sale 716 (150 ) 566 380 (80 ) 300 Total other comprehensive income $ 716 $ (150 ) $ 566 $ 380 $ (80 ) $ 300 Six Months Ended June 30, 2019 2018 Before Tax Amount Tax Effect Net of Tax Amount Before Tax Amount Tax Effect Net of Tax Amount (Dollars in thousands) Other comprehensive income: Securities available for sale: Change in unrealized gain during period $ 1,219 $ (256 ) $ 963 $ 580 $ (122 ) $ 458 Total securities available for sale 1,219 (256 ) 963 580 (122 ) 458 Total other comprehensive income $ 1,219 $ (256 ) $ 963 $ 580 $ (122 ) $ 458
Activity in Accumulated Other Comprehensive Income Associated with Securities Available for Sale, Net of Tax	Activity in accumulated other comprehensive income associated with securities available for sale, net of tax, was as follows: Securities Available for Sale Accumulated Other Comprehensive Income (Dollars in thousands) Balance at December 31, 2018 $ 310 $ 310 Other comprehensive income 963 963 Balance at June 30, 2019 $ 1,273 $ 1,273 Balance at December 31, 2017 $ (113 ) $ (113 ) Other comprehensive income 458 458 Balance at June 30, 2018 $ 345 $ 345

Income Per Common Share - Sched

Income Per Common Share - Schedule of Earnings Per Share, Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net income	$ 82,258	$ 81,597	$ 164,660	$ 155,958
Basic, Weighted average shares outstanding (in shares)	69,806	69,839	69,832	69,803
Weighted average shares outstanding, per share amount	$ 1.18	$ 1.17	$ 2.36	$ 2.23
Diluted, Weighted average shares outstanding (in shares)	69,806	69,839	69,832	69,803
Diluted	$ 1.18	$ 1.17	$ 2.36	$ 2.23

Income Per Common Share - Addit

Income Per Common Share - Additional Information (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Number of options outstanding	0		0
Antidilutive Securities excluded from computation of earnings per share, amount	0	0	0	0

New Accounting Standards - Addi

New Accounting Standards - Additional Information (Details) - USD ($) $ in Millions	Jun. 30, 2019	Jan. 01, 2019
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Operating lease, right-of-use asset	$ 15
Operating lease, liability	$ 15
Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Operating lease, right-of-use asset		$ 17.3
Operating lease, liability		$ 17.3

Securities - Schedule of Amorti

Securities - Schedule of Amortized Cost and Fair Value of Investment Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Available for Sale, Amortized Cost	$ 305,166	$ 83,763
Available for Sale, Gross Unrealized Gains	1,743	629
Available for Sale, Gross Unrealized Losses	(132)	(237)
Available for Sale	306,777	84,155
Held to Maturity, Amortized Cost	8,645,163	9,324,811
Held to Maturity, Gross Unrealized Gains	56,616	9,239
Held to Maturity, Gross Unrealized Losses	(45,370)	(252,814)
Held to Maturity	8,656,409	9,081,236
US States and Political Subdivisions [Member]
Schedule Of Available For Sale Securities [Line Items]
Available for Sale, Amortized Cost	469	1,159
Available for Sale, Gross Unrealized Gains	1	7
Available for Sale	470	1,166
Held to Maturity, Amortized Cost	215,871	253,198
Held to Maturity, Gross Unrealized Gains	6,088	3,440
Held to Maturity, Gross Unrealized Losses	(144)	(777)
Held to Maturity	221,815	255,861
Collateralized Mortgage Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Available for Sale, Amortized Cost	244,256	12,724
Available for Sale, Gross Unrealized Gains	796	69
Available for Sale, Gross Unrealized Losses	(130)	(37)
Available for Sale	244,922	12,756
Held to Maturity, Amortized Cost	462	509
Held to Maturity, Gross Unrealized Gains	5	1
Held to Maturity, Gross Unrealized Losses	(1)	(2)
Held to Maturity	466	508
Collateralized Mortgage Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available for Sale, Amortized Cost	60,441	69,880
Available for Sale, Gross Unrealized Gains	946	553
Available for Sale, Gross Unrealized Losses	(2)	(200)
Available for Sale	61,385	70,233
Held to Maturity, Amortized Cost	8,405,963	9,045,326
Held to Maturity, Gross Unrealized Gains	50,480	5,798
Held to Maturity, Gross Unrealized Losses	(45,222)	(251,935)
Held to Maturity	8,411,221	8,799,189
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]
Schedule Of Available For Sale Securities [Line Items]
Held to Maturity, Amortized Cost	22,867	25,778
Held to Maturity, Gross Unrealized Gains	43
Held to Maturity, Gross Unrealized Losses	(3)	(100)
Held to Maturity	$ 22,907	$ 25,678

Securities - Additional Informa

Securities - Additional Information (Details) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019USD ($)Security	Jun. 30, 2018USD ($)	Jun. 30, 2019USD ($)SegmentSecurity	Jun. 30, 2018USD ($)	Dec. 31, 2018USD ($)Security
Schedule Of Held To Maturity Securities [Line Items]
Number of Investment Securities Segments | Segment			2
Other than Temporary Impairment Losses, Investments			$ 0
Securities in Unrealized Loss Positions Qualitative Disclosure Number of Positions Greater Than or Equal to One Year | Security	287		287		731
Gain (loss) on sale of securities	$ 0	$ (13)	$ 0	$ (13)
Available for sale securities, at fair value	306,777		306,777		$ 84,155
Collateralized Securities [Member]
Schedule Of Held To Maturity Securities [Line Items]
Available for Sale Securities, Amortized Cost Basis	5,330,000		5,330,000		6,040,000
Available for sale securities, at fair value	$ 5,320,000		$ 5,320,000		$ 5,860,000
Securities Concentration Risk [Member] | Stockholders' Equity, Total [Member]
Schedule Of Held To Maturity Securities [Line Items]
Concentration Risk, Percentage			10.00%		10.00%

Securities - Securities in Cont

Securities - Securities in Continuous Loss Position (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Available for Sale, Estimated Fair Value, Less than 12 Months	$ 37,938	$ 50,962
Available for Sale, Unrealized Losses, Less than 12 Months	(107)	(197)
Available for Sale, Estimated Fair Value, 12 Months or More	1,947	4,187
Available for Sale, Unrealized Losses, 12 Months or More	(25)	(40)
Available for Sale, Estimated Fair Value, Total	39,885	55,149
Available for Sale, Unrealized Losses, Total	(132)	(237)
Held to Maturity, Estimated Fair Value, Less than 12 Months	175,108	1,113,216
Held to Maturity, Unrealized Losses, Less than 12 Months	(444)	(8,805)
Held to Maturity, Estimated Fair Value, 12 Months or More	4,307,088	6,937,459
Held to Maturity, Unrealized Losses, 12 Months or More	(44,926)	(244,009)
Held to Maturity, Estimated Fair Value, Total	4,482,196	8,050,675
Held to Maturity, Unrealized Losses, Total	(45,370)	(252,814)
Collateralized Mortgage Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Available for Sale, Estimated Fair Value, Less than 12 Months	37,871	12
Available for Sale, Unrealized Losses, Less than 12 Months	(106)
Available for Sale, Estimated Fair Value, 12 Months or More	1,899	2,096
Available for Sale, Unrealized Losses, 12 Months or More	(24)	(37)
Available for Sale, Estimated Fair Value, Total	39,770	2,108
Available for Sale, Unrealized Losses, Total	(130)	(37)
Held to Maturity, Estimated Fair Value, Less than 12 Months	79
Held to Maturity, Unrealized Losses, Less than 12 Months	(1)
Held to Maturity, Estimated Fair Value, 12 Months or More		292
Held to Maturity, Unrealized Losses, 12 Months or More		(2)
Held to Maturity, Estimated Fair Value, Total	79	292
Held to Maturity, Unrealized Losses, Total	(1)	(2)
Collateralized Mortgage Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available for Sale, Estimated Fair Value, Less than 12 Months	67	50,950
Available for Sale, Unrealized Losses, Less than 12 Months	(1)	(197)
Available for Sale, Estimated Fair Value, 12 Months or More	48	2,091
Available for Sale, Unrealized Losses, 12 Months or More	(1)	(3)
Available for Sale, Estimated Fair Value, Total	115	53,041
Available for Sale, Unrealized Losses, Total	(2)	(200)
Held to Maturity, Estimated Fair Value, Less than 12 Months	131,659	1,003,089
Held to Maturity, Unrealized Losses, Less than 12 Months	(356)	(8,401)
Held to Maturity, Estimated Fair Value, 12 Months or More	4,271,546	6,873,948
Held to Maturity, Unrealized Losses, 12 Months or More	(44,866)	(243,534)
Held to Maturity, Estimated Fair Value, Total	4,403,205	7,877,037
Held to Maturity, Unrealized Losses, Total	(45,222)	(251,935)
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]
Schedule Of Available For Sale Securities [Line Items]
Held to Maturity, Estimated Fair Value, Less than 12 Months		20,720
Held to Maturity, Unrealized Losses, Less than 12 Months		(76)
Held to Maturity, Estimated Fair Value, 12 Months or More	8,990	4,957
Held to Maturity, Unrealized Losses, 12 Months or More	(3)	(24)
Held to Maturity, Estimated Fair Value, Total	8,990	25,677
Held to Maturity, Unrealized Losses, Total	(3)	(100)
US States and Political Subdivisions [Member]
Schedule Of Available For Sale Securities [Line Items]
Held to Maturity, Estimated Fair Value, Less than 12 Months	43,370	89,407
Held to Maturity, Unrealized Losses, Less than 12 Months	(87)	(328)
Held to Maturity, Estimated Fair Value, 12 Months or More	26,552	58,262
Held to Maturity, Unrealized Losses, 12 Months or More	(57)	(449)
Held to Maturity, Estimated Fair Value, Total	69,922	147,669
Held to Maturity, Unrealized Losses, Total	$ (144)	$ (777)

Securities - Investment Securit

Securities - Investment Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Investments Debt And Equity Securities [Abstract]
Held to Maturity, amortized cost, due in one year or less	$ 48,722
Held to Maturity, amortized cost, due after one year through five years	117,183
Held to Maturity, amortized cost, due after five years through ten years	68,317
Held to Maturity, amortized cost, due after ten years	4,516
Held to Maturity, amortized cost, subtotal	238,738
Held to Maturity, amortized cost, mortgage-backed securities and collateralized mortgage obligations	8,406,425
Held to Maturity, Amortized Cost	8,645,163	$ 9,324,811
Held to Maturity, fair value, due in one year or less	48,797
Held to Maturity, fair value, due after one year through five years	118,201
Held to Maturity, fair value, due after five years through ten years	73,134
Held to Maturity, fair value, due after ten years	4,590
Held to Maturity, fair value, subtotal	244,722
Held to Maturity, fair value, mortgage-backed securities and collateralized mortgage obligations	8,411,687
Held to Maturity, fair value, total	8,656,409	9,081,236
Available for Sale, amortized cost, due in one year or less	165
Available for Sale, amortized cost, due after one year through five years	304
Available for Sale, amortized cost, subtotal	469
Available for Sale, amortized cost, mortgage-backed securities and collateralized mortgage obligations	304,697
Available for Sale, Amortized Cost	305,166	83,763
Available for Sale, fair value, due in one year or less	165
Available for Sale, fair value, due after one year through five years	305
Available for Sale, fair value, subtotal	470
Available for Sale, fair value, mortgage-backed securities and collateralized mortgage obligations	306,307
Available for Sale securities, at fair value	$ 306,777	$ 84,155

Loans and Allowance for Credi_3

Loans and Allowance for Credit Losses - Types of Loans in Loan Portfolio (Details) - USD ($) $ in Thousands		Jun. 30, 2019		Dec. 31, 2018		Jun. 30, 2018
Accounts Notes And Loans Receivable [Line Items]
Loans held for sale		$ 20,315		$ 29,367
Total loans held for investment		10,567,060		10,340,946		$ 10,118,798
Total		10,587,375		10,370,313
Residential Mortgage Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans held for sale		20,315		29,367
Commercial and Industrial [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans held for investment		1,525,628		1,483,571		1,521,519
Total		1,525,628		1,483,571
Real Estate [Member] | Construction, Land Development and Other Land Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans held for investment		1,739,308		1,622,289		1,542,771
Total		1,739,308		1,622,289
Real Estate [Member] | 1-4 Family Residential (Includes Home Equity) [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans held for investment		2,692,963		2,677,542		2,667,701
Total	[1]	2,713,278	[2]	2,706,909	[3]
Real Estate [Member] | Commercial Real Estate (Includes Multi-Family Residential) [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans held for investment		3,551,668		3,538,557		3,405,466
Total		3,551,668		3,538,557
Real Estate [Member] | Farmland [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans held for investment		541,469		545,373
Agriculture [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans held for investment		195,001		184,128
Consumer and Other [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans held for investment		321,023		289,486		$ 271,724
Total		$ 321,023		$ 289,486
[1]	Includes $20.3 million and $29.4 million of residential mortgage loans held for sale at June 30, 2019 and December 31, 2018, respectively.
[2]	Includes $20.3 million of residential mortgage loans held for sale at June 30, 2019.
[3]	Includes $29.4 million of residential mortgage loans held for sale at December 31, 2018.

Loans and Allowance for Credi_4

Loans and Allowance for Credit Losses - Additional Information (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2019USD ($)contract	Jun. 30, 2018USD ($)contract	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Accounts Notes And Loans Receivable [Line Items]
Percentage of Loans Related to Single Industry on Loans	10.00%		10.00%
Percentage of real estate loans aggregating to company loan portfolio	75.40%
Loans and Leases Receivable, Related Parties	$ 1,755		$ 1,923	$ 2,694
Loans held for investment	$ 10,567,060	$ 10,118,798	$ 10,340,946
Financing Receivable Ratio of Nonperforming Loans to All Loans and Other Real Estate	0.39%		0.18%
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans	$ 1,200	951
Loans and leases receivable, nonaccrual loans	37,300	20,400
Financing Receivable, Allowance for Credit Losses	$ 87,000		$ 86,400
Allowance for Credit Losses as Percentage of Loans	0.82%		0.83%
Loans held for sale	$ 20,300	$ 27,800	$ 29,400
Nonaccrual loans	$ 37,289		13,147
Troubled debt restructurings, number of loans | contract	1	2
Financing receivable, number of loans with default | contract	0
Financing receivable, modifications, recorded investment	$ 14,300	$ 162
Troubled debt restructurings, recorded investment at date of restructure	$ 14,783	198
Loan to be Considered as Payment Default in Period	90 days
Troubled Debt Restructuring [Member]
Accounts Notes And Loans Receivable [Line Items]
Nonaccrual loans	$ 14,300	$ 208
Nonperforming Financial Instruments [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans held for investment	$ 41,600		$ 19,000

Loans and Allowance for Credi_5

Loans and Allowance for Credit Losses - Related Party Loans (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Receivables [Abstract]
Beginning balance on January 1	$ 1,923	$ 2,694
New loans		5
Repayments	(168)	(776)
Ending balance	$ 1,755	$ 1,923

Loans and Allowance for Credi_6

Loans and Allowance for Credit Losses - Aging Analysis of Past Due Loans (Details) - USD ($) $ in Thousands		Jun. 30, 2019		Dec. 31, 2018
Accounts Notes And Loans Receivable [Line Items]
Loans past due and still accruing		$ 37,786		$ 38,278
Nonaccrual loans		37,289		13,147
Current loans		10,512,300		10,318,888
Total loans		10,587,375		10,370,313
Financing Receivables, 30 to 89 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans past due and still accruing		36,192		34,274
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans past due and still accruing		1,594		4,004
Agriculture and Agriculture Real Estate (Includes Farmland) [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans past due and still accruing		710		705
Nonaccrual loans		616		256
Current loans		735,144		728,540
Total loans		736,470		729,501
Agriculture and Agriculture Real Estate (Includes Farmland) [Member] | Financing Receivables, 30 to 89 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans past due and still accruing		710		705
Real Estate [Member] | Construction, Land Development and Other Land Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans past due and still accruing		6,521		7,151
Nonaccrual loans		659		1,386
Current loans		1,732,128		1,613,752
Total loans		1,739,308		1,622,289
Real Estate [Member] | Construction, Land Development and Other Land Loans [Member] | Financing Receivables, 30 to 89 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans past due and still accruing		5,368		6,363
Real Estate [Member] | Construction, Land Development and Other Land Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans past due and still accruing		1,153		788
Real Estate [Member] | 1-4 Family Residential (Includes Home Equity) [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans past due and still accruing	[1]	11,165		13,474
Nonaccrual loans	[1]	15,278		4,515
Current loans	[1]	2,686,835		2,688,920
Total loans	[1]	2,713,278	[2]	2,706,909	[3]
Real Estate [Member] | 1-4 Family Residential (Includes Home Equity) [Member] | Financing Receivables, 30 to 89 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans past due and still accruing	[1]	11,107		10,479
Real Estate [Member] | 1-4 Family Residential (Includes Home Equity) [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans past due and still accruing	[1]	58		2,995
Real Estate [Member] | Commercial Real Estate (Includes Multi-Family Residential) [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans past due and still accruing		14,572		9,063
Nonaccrual loans		4,135		2,727
Current loans		3,532,961		3,526,767
Total loans		3,551,668		3,538,557
Real Estate [Member] | Commercial Real Estate (Includes Multi-Family Residential) [Member] | Financing Receivables, 30 to 89 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans past due and still accruing		14,572		9,063
Commercial and Industrial [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans past due and still accruing		4,485		6,873
Nonaccrual loans		16,561		4,215
Current loans		1,504,582		1,472,483
Total loans		1,525,628		1,483,571
Commercial and Industrial [Member] | Financing Receivables, 30 to 89 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans past due and still accruing		4,102		6,652
Commercial and Industrial [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans past due and still accruing		383		221
Consumer and Other [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans past due and still accruing		333		1,012
Nonaccrual loans		40		48
Current loans		320,650		288,426
Total loans		321,023		289,486
Consumer and Other [Member] | Financing Receivables, 30 to 89 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans past due and still accruing		$ 333		$ 1,012
[1]	Includes $20.3 million and $29.4 million of residential mortgage loans held for sale at June 30, 2019 and December 31, 2018, respectively.
[2]	Includes $20.3 million of residential mortgage loans held for sale at June 30, 2019.
[3]	Includes $29.4 million of residential mortgage loans held for sale at December 31, 2018.

Loans and Allowance for Credi_7

Loans and Allowance for Credit Losses - Aging Analysis of Past Due Loans (Parenthetical) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Accounts Notes And Loans Receivable [Line Items]
Loans held for sale	$ 20,315	$ 29,367
Residential Mortgage Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans held for sale	$ 20,315	$ 29,367

Loans and Allowance for Credi_8

Loans and Allowance for Credit Losses - Nonperforming Assets (Details) - USD ($) $ in Thousands		Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Accounts Notes And Loans Receivable [Line Items]
Loans held for investment		$ 10,567,060	$ 10,340,946	$ 10,118,798
Other real estate owned		$ 2,005	$ 1,805
Nonperforming assets to total loans and other real estate		0.39%	0.18%
Nonperforming Financial Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans held for investment		$ 38,883	$ 17,151
Repossessed assets		670
Other real estate owned		2,005	1,805
Total nonperforming assets		41,558	18,956
Nonperforming Financial Loans [Member] | Finance Receivable Nonaccrual Status [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans held for investment	[1]	37,289	13,147
Nonperforming Financial Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans held for investment		$ 1,594	$ 4,004
[1]	Includes troubled debt restructurings of $14.3 million and $51 thousand as of June 30, 2019 and December 31, 2018, respectively.

Loans and Allowance for Credi_9

Loans and Allowance for Credit Losses - Nonperforming Assets (Parenthetical) (Details) - USD ($) $ in Thousands		Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Accounts Notes And Loans Receivable [Line Items]
Loans held for investment		$ 10,567,060	$ 10,340,946	$ 10,118,798
Nonperforming Financial Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans held for investment		38,883	17,151
Nonperforming Financial Loans [Member] | Finance Receivable Nonaccrual Status [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans held for investment	[1]	37,289	13,147
Troubled Debt Restructuring [Member] | Nonperforming Financial Loans [Member] | Finance Receivable Nonaccrual Status [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans held for investment		$ 14,300	$ 51
[1]	Includes troubled debt restructurings of $14.3 million and $51 thousand as of June 30, 2019 and December 31, 2018, respectively.

Loans and Allowance for Cred_10

Loans and Allowance for Credit Losses - Recorded Investment and Outstanding Balance for Purchased Credit Impaired Loans and Non Purchased Credit Impaired Loans (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Purchased And Non Purchased Credit Impaired Loans [Line Items]
Recorded investment	$ 7,945	$ 8,588	$ 11,369
PCI Loans [Member]
Purchased And Non Purchased Credit Impaired Loans [Line Items]
Outstanding balance	10,110	11,419
Discount	(2,165)	(2,831)
Recorded investment	7,945	8,588
Non PCI Loans [Member]
Purchased And Non Purchased Credit Impaired Loans [Line Items]
Outstanding balance	467,645	526,840
Discount	(12,479)	(14,833)
Recorded investment	$ 455,166	$ 512,007

Loans and Allowance for Cred_11

Loans and Allowance for Credit Losses - Summary of Changes in Accretable Yields of Acquired Loans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
PCI Loans [Member]
Changes In Accretable Yield for PCI And Non PCI Loans [Line Items]
Balance at beginning of period	$ 1,234	$ 7,685	$ 1,534	$ 8,121
Reclassifications from nonaccretable	17	55	36	305
Accretion	(347)	(3,771)	(666)	(4,457)
Balance at June 30,	904	3,969	904	3,969
Non PCI Loans [Member]
Changes In Accretable Yield for PCI And Non PCI Loans [Line Items]
Balance at beginning of period	13,359	18,885	14,833	20,533
Accretion charge-offs		(2)		(10)
Accretion	(880)	(1,452)	(2,354)	(3,092)
Balance at June 30,	$ 12,479	$ 17,431	$ 12,479	$ 17,431

Loans and Allowance for Cred_12

Loans and Allowance for Credit Losses - Impaired Loans (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable Impaired [Line Items]
Impaired loans with no related allowance, recorded investment	$ 29,238	$ 11,071
Impaired loans with no related allowance, unpaid contractual principal balance	32,338	12,943
Impaired loans with no related allowance, average recorded investment	20,155	12,998
Impaired loans with related allowance, recorded investment	8,051	1,985
Impaired loans with related allowance, unpaid contractual principal balance	8,116	2,012
Impaired loans with related allowance, related allowance	1,334	685
Impaired loans with related allowance, average recorded investment	5,017	5,407
Impaired loans, recorded investment	37,289	13,056
Impaired loans, unpaid contractual principal balance	40,454	14,955
Impaired loans with an allowance recorded, related allowance	1,334	685
Impaired loans, average recorded investment	25,172	18,405
Agriculture and Agriculture Real Estate (Includes Farmland) [Member]
Financing Receivable Impaired [Line Items]
Impaired loans with no related allowance, recorded investment	326	256
Impaired loans with no related allowance, unpaid contractual principal balance	326	311
Impaired loans with no related allowance, average recorded investment	291	194
Impaired loans with related allowance, recorded investment	290
Impaired loans with related allowance, unpaid contractual principal balance	290
Impaired loans with related allowance, related allowance	160
Impaired loans with related allowance, average recorded investment	145
Impaired loans, recorded investment	616	256
Impaired loans, unpaid contractual principal balance	616	311
Impaired loans, average recorded investment	436	194
Real Estate [Member] | Construction, Land Development and Other Land Loans [Member]
Financing Receivable Impaired [Line Items]
Impaired loans with no related allowance, recorded investment	269	993
Impaired loans with no related allowance, unpaid contractual principal balance	270	995
Impaired loans with no related allowance, average recorded investment	631	788
Impaired loans with related allowance, recorded investment	390	391
Impaired loans with related allowance, unpaid contractual principal balance	390	391
Impaired loans with related allowance, related allowance	58	58
Impaired loans with related allowance, average recorded investment	391	195
Impaired loans, recorded investment	659	1,384
Impaired loans, unpaid contractual principal balance	660	1,386
Impaired loans, average recorded investment	1,022	983
Real Estate [Member] | 1-4 Family Residential (Includes Home Equity) [Member]
Financing Receivable Impaired [Line Items]
Impaired loans with no related allowance, recorded investment	10,035	4,177
Impaired loans with no related allowance, unpaid contractual principal balance	10,747	4,903
Impaired loans with no related allowance, average recorded investment	7,106	4,048
Impaired loans with related allowance, recorded investment	5,243	266
Impaired loans with related allowance, unpaid contractual principal balance	5,272	289
Impaired loans with related allowance, related allowance	504	56
Impaired loans with related allowance, average recorded investment	2,754	729
Impaired loans, recorded investment	15,278	4,443
Impaired loans, unpaid contractual principal balance	16,019	5,192
Impaired loans, average recorded investment	9,860	4,777
Real Estate [Member] | Commercial Real Estate (Includes Multi-Family Residential) [Member]
Financing Receivable Impaired [Line Items]
Impaired loans with no related allowance, recorded investment	3,162	2,727
Impaired loans with no related allowance, unpaid contractual principal balance	3,341	2,848
Impaired loans with no related allowance, average recorded investment	2,945	2,475
Impaired loans with related allowance, recorded investment	973
Impaired loans with related allowance, unpaid contractual principal balance	993
Impaired loans with related allowance, related allowance	283
Impaired loans with related allowance, average recorded investment	486	743
Impaired loans, recorded investment	4,135	2,727
Impaired loans, unpaid contractual principal balance	4,334	2,848
Impaired loans, average recorded investment	3,431	3,218
Commercial and Industrial [Member]
Financing Receivable Impaired [Line Items]
Impaired loans with no related allowance, recorded investment	15,406	2,870
Impaired loans with no related allowance, unpaid contractual principal balance	17,610	3,810
Impaired loans with no related allowance, average recorded investment	9,138	5,358
Impaired loans with related allowance, recorded investment	1,155	1,328
Impaired loans with related allowance, unpaid contractual principal balance	1,171	1,332
Impaired loans with related allowance, related allowance	329	571
Impaired loans with related allowance, average recorded investment	1,241	3,740
Impaired loans, recorded investment	16,561	4,198
Impaired loans, unpaid contractual principal balance	18,781	5,142
Impaired loans, average recorded investment	10,379	9,098
Consumer and Other [Member]
Financing Receivable Impaired [Line Items]
Impaired loans with no related allowance, recorded investment	40	48
Impaired loans with no related allowance, unpaid contractual principal balance	44	76
Impaired loans with no related allowance, average recorded investment	44	135
Impaired loans, recorded investment	40	48
Impaired loans, unpaid contractual principal balance	44	76
Impaired loans, average recorded investment	$ 44	$ 135

Loans and Allowance for Cred_13

Loans and Allowance for Credit Losses - Risk Grade and Category of Loan (Details) - USD ($) $ in Thousands		Jun. 30, 2019		Dec. 31, 2018
Financing Receivable Impaired [Line Items]
Loans		$ 10,587,375		$ 10,370,313
Agriculture and Agriculture Real Estate (Includes Farmland) [Member]
Financing Receivable Impaired [Line Items]
Loans		736,470		729,501
Real Estate [Member] | Construction, Land Development and Other Land Loans [Member]
Financing Receivable Impaired [Line Items]
Loans		1,739,308		1,622,289
Real Estate [Member] | 1-4 Family Residential (Includes Home Equity) [Member]
Financing Receivable Impaired [Line Items]
Loans	[1]	2,713,278	[2]	2,706,909	[3]
Real Estate [Member] | Commercial Real Estate (Includes Multi-Family Residential) [Member]
Financing Receivable Impaired [Line Items]
Loans		3,551,668		3,538,557
Commercial and Industrial [Member]
Financing Receivable Impaired [Line Items]
Loans		1,525,628		1,483,571
Consumer and Other [Member]
Financing Receivable Impaired [Line Items]
Loans		321,023		289,486
Grade 1 [Member]
Financing Receivable Impaired [Line Items]
Loans		104,975		112,839
Grade 1 [Member] | Agriculture and Agriculture Real Estate (Includes Farmland) [Member]
Financing Receivable Impaired [Line Items]
Loans		14,322		15,725
Grade 1 [Member] | Real Estate [Member] | Construction, Land Development and Other Land Loans [Member]
Financing Receivable Impaired [Line Items]
Loans		0		0
Grade 1 [Member] | Real Estate [Member] | 1-4 Family Residential (Includes Home Equity) [Member]
Financing Receivable Impaired [Line Items]
Loans		0	[2]	0	[3]
Grade 1 [Member] | Real Estate [Member] | Commercial Real Estate (Includes Multi-Family Residential) [Member]
Financing Receivable Impaired [Line Items]
Loans		0		0
Grade 1 [Member] | Commercial and Industrial [Member]
Financing Receivable Impaired [Line Items]
Loans		55,562		59,979
Grade 1 [Member] | Consumer and Other [Member]
Financing Receivable Impaired [Line Items]
Loans		35,091		37,135
Grade 2 [Member]
Financing Receivable Impaired [Line Items]
Loans		110,993		115,491
Grade 2 [Member] | Agriculture and Agriculture Real Estate (Includes Farmland) [Member]
Financing Receivable Impaired [Line Items]
Loans		3,877		3,974
Grade 2 [Member] | Real Estate [Member] | Construction, Land Development and Other Land Loans [Member]
Financing Receivable Impaired [Line Items]
Loans		1,215		1,040
Grade 2 [Member] | Real Estate [Member] | 1-4 Family Residential (Includes Home Equity) [Member]
Financing Receivable Impaired [Line Items]
Loans		15,430	[2]	21,465	[3]
Grade 2 [Member] | Real Estate [Member] | Commercial Real Estate (Includes Multi-Family Residential) [Member]
Financing Receivable Impaired [Line Items]
Loans		21,640		22,207
Grade 2 [Member] | Commercial and Industrial [Member]
Financing Receivable Impaired [Line Items]
Loans		12,312		11,003
Grade 2 [Member] | Consumer and Other [Member]
Financing Receivable Impaired [Line Items]
Loans		56,519		55,802
Grade 3 [Member]
Financing Receivable Impaired [Line Items]
Loans		9,031,777		8,974,366
Grade 3 [Member] | Agriculture and Agriculture Real Estate (Includes Farmland) [Member]
Financing Receivable Impaired [Line Items]
Loans		647,171		636,674
Grade 3 [Member] | Real Estate [Member] | Construction, Land Development and Other Land Loans [Member]
Financing Receivable Impaired [Line Items]
Loans		1,587,922		1,509,532
Grade 3 [Member] | Real Estate [Member] | 1-4 Family Residential (Includes Home Equity) [Member]
Financing Receivable Impaired [Line Items]
Loans		2,600,773	[2]	2,598,600	[3]
Grade 3 [Member] | Real Estate [Member] | Commercial Real Estate (Includes Multi-Family Residential) [Member]
Financing Receivable Impaired [Line Items]
Loans		2,892,964		2,974,474
Grade 3 [Member] | Commercial and Industrial [Member]
Financing Receivable Impaired [Line Items]
Loans		1,102,365		1,083,328
Grade 3 [Member] | Consumer and Other [Member]
Financing Receivable Impaired [Line Items]
Loans		200,582		171,758
Grade 4 [Member]
Financing Receivable Impaired [Line Items]
Loans		1,114,794		972,809
Grade 4 [Member] | Agriculture and Agriculture Real Estate (Includes Farmland) [Member]
Financing Receivable Impaired [Line Items]
Loans		64,025		66,650
Grade 4 [Member] | Real Estate [Member] | Construction, Land Development and Other Land Loans [Member]
Financing Receivable Impaired [Line Items]
Loans		136,083		99,087
Grade 4 [Member] | Real Estate [Member] | 1-4 Family Residential (Includes Home Equity) [Member]
Financing Receivable Impaired [Line Items]
Loans		67,445	[2]	61,430	[3]
Grade 4 [Member] | Real Estate [Member] | Commercial Real Estate (Includes Multi-Family Residential) [Member]
Financing Receivable Impaired [Line Items]
Loans		557,501		481,735
Grade 4 [Member] | Commercial and Industrial [Member]
Financing Receivable Impaired [Line Items]
Loans		265,415		243,743
Grade 4 [Member] | Consumer and Other [Member]
Financing Receivable Impaired [Line Items]
Loans		24,325		20,164
Grade 5 [Member]
Financing Receivable Impaired [Line Items]
Loans		138,336		120,781
Grade 5 [Member] | Agriculture and Agriculture Real Estate (Includes Farmland) [Member]
Financing Receivable Impaired [Line Items]
Loans		5,091		5,578
Grade 5 [Member] | Real Estate [Member] | Construction, Land Development and Other Land Loans [Member]
Financing Receivable Impaired [Line Items]
Loans		5,684		3,673
Grade 5 [Member] | Real Estate [Member] | 1-4 Family Residential (Includes Home Equity) [Member]
Financing Receivable Impaired [Line Items]
Loans		6,486	[2]	12,522	[3]
Grade 5 [Member] | Real Estate [Member] | Commercial Real Estate (Includes Multi-Family Residential) [Member]
Financing Receivable Impaired [Line Items]
Loans		56,772		37,942
Grade 5 [Member] | Commercial and Industrial [Member]
Financing Receivable Impaired [Line Items]
Loans		61,476		58,088
Grade 5 [Member] | Consumer and Other [Member]
Financing Receivable Impaired [Line Items]
Loans		2,827		2,978
Grade 6 [Member]
Financing Receivable Impaired [Line Items]
Loans		41,266		52,383
Grade 6 [Member] | Agriculture and Agriculture Real Estate (Includes Farmland) [Member]
Financing Receivable Impaired [Line Items]
Loans		1,029		282
Grade 6 [Member] | Real Estate [Member] | Construction, Land Development and Other Land Loans [Member]
Financing Receivable Impaired [Line Items]
Loans		7,315		7,081
Grade 6 [Member] | Real Estate [Member] | 1-4 Family Residential (Includes Home Equity) [Member]
Financing Receivable Impaired [Line Items]
Loans		3,750	[2]	4,332	[3]
Grade 6 [Member] | Real Estate [Member] | Commercial Real Estate (Includes Multi-Family Residential) [Member]
Financing Receivable Impaired [Line Items]
Loans		15,719		16,006
Grade 6 [Member] | Commercial and Industrial [Member]
Financing Receivable Impaired [Line Items]
Loans		11,814		23,081
Grade 6 [Member] | Consumer and Other [Member]
Financing Receivable Impaired [Line Items]
Loans		1,639		1,601
Grade 7 [Member]
Financing Receivable Impaired [Line Items]
Loans		36,981		12,975
Grade 7 [Member] | Agriculture and Agriculture Real Estate (Includes Farmland) [Member]
Financing Receivable Impaired [Line Items]
Loans		326		256
Grade 7 [Member] | Real Estate [Member] | Construction, Land Development and Other Land Loans [Member]
Financing Receivable Impaired [Line Items]
Loans		659		1,384
Grade 7 [Member] | Real Estate [Member] | 1-4 Family Residential (Includes Home Equity) [Member]
Financing Receivable Impaired [Line Items]
Loans		15,278	[2]	4,395	[3]
Grade 7 [Member] | Real Estate [Member] | Commercial Real Estate (Includes Multi-Family Residential) [Member]
Financing Receivable Impaired [Line Items]
Loans		4,135		2,727
Grade 7 [Member] | Commercial and Industrial [Member]
Financing Receivable Impaired [Line Items]
Loans		16,543		4,165
Grade 7 [Member] | Consumer and Other [Member]
Financing Receivable Impaired [Line Items]
Loans		40		48
Grade 8 [Member]
Financing Receivable Impaired [Line Items]
Loans		308		81
Grade 8 [Member] | Agriculture and Agriculture Real Estate (Includes Farmland) [Member]
Financing Receivable Impaired [Line Items]
Loans		290		0
Grade 8 [Member] | Real Estate [Member] | Construction, Land Development and Other Land Loans [Member]
Financing Receivable Impaired [Line Items]
Loans		0		0
Grade 8 [Member] | Real Estate [Member] | 1-4 Family Residential (Includes Home Equity) [Member]
Financing Receivable Impaired [Line Items]
Loans		0	[2]	48	[3]
Grade 8 [Member] | Real Estate [Member] | Commercial Real Estate (Includes Multi-Family Residential) [Member]
Financing Receivable Impaired [Line Items]
Loans		0		0
Grade 8 [Member] | Commercial and Industrial [Member]
Financing Receivable Impaired [Line Items]
Loans		18		33
Grade 8 [Member] | Consumer and Other [Member]
Financing Receivable Impaired [Line Items]
Loans		0		0
Grade 9 [Member]
Financing Receivable Impaired [Line Items]
Loans		0		0
Grade 9 [Member] | Agriculture and Agriculture Real Estate (Includes Farmland) [Member]
Financing Receivable Impaired [Line Items]
Loans		0		0
Grade 9 [Member] | Real Estate [Member] | Construction, Land Development and Other Land Loans [Member]
Financing Receivable Impaired [Line Items]
Loans		0		0
Grade 9 [Member] | Real Estate [Member] | 1-4 Family Residential (Includes Home Equity) [Member]
Financing Receivable Impaired [Line Items]
Loans		0	[2]	0	[3]
Grade 9 [Member] | Real Estate [Member] | Commercial Real Estate (Includes Multi-Family Residential) [Member]
Financing Receivable Impaired [Line Items]
Loans		0		0
Grade 9 [Member] | Commercial and Industrial [Member]
Financing Receivable Impaired [Line Items]
Loans		0		0
Grade 9 [Member] | Consumer and Other [Member]
Financing Receivable Impaired [Line Items]
Loans		0		0
PCI Loans [Member]
Financing Receivable Impaired [Line Items]
Loans		7,945		8,588
PCI Loans [Member] | Agriculture and Agriculture Real Estate (Includes Farmland) [Member]
Financing Receivable Impaired [Line Items]
Loans		339		362
PCI Loans [Member] | Real Estate [Member] | Construction, Land Development and Other Land Loans [Member]
Financing Receivable Impaired [Line Items]
Loans		430		492
PCI Loans [Member] | Real Estate [Member] | 1-4 Family Residential (Includes Home Equity) [Member]
Financing Receivable Impaired [Line Items]
Loans		4,116	[2]	4,117	[3]
PCI Loans [Member] | Real Estate [Member] | Commercial Real Estate (Includes Multi-Family Residential) [Member]
Financing Receivable Impaired [Line Items]
Loans		2,937		3,466
PCI Loans [Member] | Commercial and Industrial [Member]
Financing Receivable Impaired [Line Items]
Loans		123		151
PCI Loans [Member] | Consumer and Other [Member]
Financing Receivable Impaired [Line Items]
Loans		$ 0		$ 0
[1]	Includes $20.3 million and $29.4 million of residential mortgage loans held for sale at June 30, 2019 and December 31, 2018, respectively.
[2]	Includes $20.3 million of residential mortgage loans held for sale at June 30, 2019.
[3]	Includes $29.4 million of residential mortgage loans held for sale at December 31, 2018.

Loans and Allowance for Cred_14

Loans and Allowance for Credit Losses - Risk Grade and Category of Loan (Parenthetical) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable Impaired [Line Items]
Loans held for sale	$ 20,315	$ 29,367
Residential Mortgage Loans [Member]
Financing Receivable Impaired [Line Items]
Loans held for sale	$ 20,315	$ 29,367

Loans and Allowance for Cred_15

Loans and Allowance for Credit Losses - Allowance for Credit Losses by Category of Loan (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Allowance for credit losses:
Allowance for credit losses, beginning balance	$ 86,091	$ 83,600	$ 86,440	$ 84,041
Provision for credit losses	800	4,000	1,500	13,000
Charge-offs	(1,119)	(3,201)	(4,028)	(13,286)
Recoveries	1,234	565	3,094	1,209
Net charge-offs	115	(2,636)	(934)	(12,077)
Allowance for credit losses, ending balance	87,006	84,964	87,006	84,964
Allowance for credit losses related to:
Allowance for credit losses, individually evaluated for impairment					$ 1,334	$ 685	$ 2,827
Allowance for credit losses, collectively evaluated for impairment					85,672	85,755	82,137
Total allowance for credit losses	87,006	83,600	87,006	84,964	87,006	86,440	84,964
Recorded investment in loans:
Loans, individually evaluated for impairment					37,289	13,056	20,175
Loans, collectively evaluated for impairment					10,521,826	10,319,302	10,087,254
PCI loans					7,945	8,588	11,369
Total loans evaluated for impairment					10,567,060	10,340,946	10,118,798
Agriculture and Agriculture Real Estate (Includes Farmland) [Member]
Allowance for credit losses:
Allowance for credit losses, beginning balance	3,284	3,304	3,693	3,772
Provision for credit losses	578	407	(1,109)	(122)
Charge-offs	(54)		(64)
Recoveries	8	45	1,296	106
Net charge-offs	(46)	45	1,232	106
Allowance for credit losses, ending balance	3,816	3,756	3,816	3,756
Allowance for credit losses related to:
Allowance for credit losses, individually evaluated for impairment					160		25
Allowance for credit losses, collectively evaluated for impairment					3,656	3,693	3,731
Total allowance for credit losses	3,284	3,304	3,816	3,756	3,816	3,693	3,756
Recorded investment in loans:
Loans, individually evaluated for impairment					616	256	519
Loans, collectively evaluated for impairment					735,515	728,883	708,721
PCI loans					339	362	377
Total loans evaluated for impairment					736,470	729,501	709,617
Real Estate [Member] | Construction, Land Development and Other Land Loans [Member]
Allowance for credit losses:
Allowance for credit losses, beginning balance	16,192	14,622	15,582	14,815
Provision for credit losses	(299)	(173)	311	(243)
Charge-offs	(19)		(63)	(130)
Recoveries	12	1	56	8
Net charge-offs	(7)	1	(7)	(122)
Allowance for credit losses, ending balance	15,886	14,450	15,886	14,450
Allowance for credit losses related to:
Allowance for credit losses, individually evaluated for impairment					58	58
Allowance for credit losses, collectively evaluated for impairment					15,828	15,524	14,450
Total allowance for credit losses	16,192	14,622	15,886	14,450	15,886	15,582	14,450
Recorded investment in loans:
Loans, individually evaluated for impairment					659	1,384	508
Loans, collectively evaluated for impairment					1,738,219	1,620,413	1,541,567
PCI loans					430	492	696
Total loans evaluated for impairment					1,739,308	1,622,289	1,542,771
Real Estate [Member] | 1-4 Family Residential (Includes Home Equity) [Member]
Allowance for credit losses:
Allowance for credit losses, beginning balance	14,455	13,072	14,135	14,490
Provision for credit losses	(61)	395	256	(766)
Charge-offs	(16)	(120)	(22)	(386)
Recoveries	5	6	14	15
Net charge-offs	(11)	(114)	(8)	(371)
Allowance for credit losses, ending balance	14,383	13,353	14,383	13,353
Allowance for credit losses related to:
Allowance for credit losses, individually evaluated for impairment					504	56	61
Allowance for credit losses, collectively evaluated for impairment					13,879	14,079	13,292
Total allowance for credit losses	14,455	13,072	14,383	13,353	14,383	14,135	13,353
Recorded investment in loans:
Loans, individually evaluated for impairment					15,278	4,443	4,665
Loans, collectively evaluated for impairment					2,673,569	2,668,982	2,658,656
PCI loans					4,116	4,117	4,380
Total loans evaluated for impairment					2,692,963	2,677,542	2,667,701
Real Estate [Member] | Commercial Real Estate (Includes Multi-Family Residential) [Member]
Allowance for credit losses:
Allowance for credit losses, beginning balance	11,590	10,853	11,220	10,628
Provision for credit losses	575	749	944	1,476
Charge-offs		(986)		(1,489)
Recoveries	1		2	1
Net charge-offs	1	(986)	2	(1,488)
Allowance for credit losses, ending balance	12,166	10,616	12,166	10,616
Allowance for credit losses related to:
Allowance for credit losses, individually evaluated for impairment					283
Allowance for credit losses, collectively evaluated for impairment					11,883	11,220	10,616
Total allowance for credit losses	11,590	10,853	12,166	10,616	12,166	11,220	10,616
Recorded investment in loans:
Loans, individually evaluated for impairment					4,135	2,727	2,291
Loans, collectively evaluated for impairment					3,544,596	3,532,364	3,398,158
PCI loans					2,937	3,466	5,017
Total loans evaluated for impairment					3,551,668	3,538,557	3,405,466
Commercial and Industrial [Member]
Allowance for credit losses:
Allowance for credit losses, beginning balance	39,059	40,340	40,223	38,810
Provision for credit losses	(710)	2,161	(155)	11,707
Charge-offs	(125)	(1,194)	(2,082)	(9,370)
Recoveries	953	147	1,191	307
Net charge-offs	828	(1,047)	(891)	(9,063)
Allowance for credit losses, ending balance	39,177	41,454	39,177	41,454
Allowance for credit losses related to:
Allowance for credit losses, individually evaluated for impairment					329	571	2,741
Allowance for credit losses, collectively evaluated for impairment					38,848	39,652	38,713
Total allowance for credit losses	39,059	40,340	39,177	41,454	39,177	40,223	41,454
Recorded investment in loans:
Loans, individually evaluated for impairment					16,561	4,198	12,111
Loans, collectively evaluated for impairment					1,508,944	1,479,222	1,508,509
PCI loans					123	151	899
Total loans evaluated for impairment					1,525,628	1,483,571	1,521,519
Consumer and Other [Member]
Allowance for credit losses:
Allowance for credit losses, beginning balance	1,511	1,409	1,587	1,526
Provision for credit losses	717	461	1,253	948
Charge-offs	(905)	(901)	(1,797)	(1,911)
Recoveries	255	366	535	772
Net charge-offs	(650)	(535)	(1,262)	(1,139)
Allowance for credit losses, ending balance	1,578	1,335	1,578	1,335
Allowance for credit losses related to:
Allowance for credit losses, collectively evaluated for impairment					1,578	1,587	1,335
Total allowance for credit losses	$ 1,511	$ 1,409	$ 1,578	$ 1,335	1,578	1,587	1,335
Recorded investment in loans:
Loans, individually evaluated for impairment					40	48	81
Loans, collectively evaluated for impairment					320,983	289,438	271,643
Total loans evaluated for impairment					$ 321,023	$ 289,486	$ 271,724

Loans and Allowance for Cred_16

Loans and Allowance for Credit Losses - Troubled Debt Restructurings (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2019USD ($)contract	Jun. 30, 2018USD ($)contract
Financing Receivable Modifications [Line Items]
Troubled debt restructurings, number of loans | contract	1	2
Troubled debt restructurings, pre-modification outstanding recorded investment	$ 14,783	$ 198
Troubled debt restructurings, post-modification outstanding recorded investment	$ 14,258	$ 162
Commercial and Industrial [Member]
Financing Receivable Modifications [Line Items]
Troubled debt restructurings, number of loans | contract	1	2
Troubled debt restructurings, pre-modification outstanding recorded investment	$ 14,783	$ 198
Troubled debt restructurings, post-modification outstanding recorded investment	$ 14,258	$ 162

Fair Value - Fair Value Assets

Fair Value - Fair Value Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Available for sale securities:
Available for sale securities, at fair value	$ 306,777	$ 84,155
Fair Value, Measurements, Recurring [Member]
Available for sale securities:
Available for sale securities, at fair value	306,777	84,155
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Available for sale securities:
Available for sale securities, at fair value	306,777	84,155
Fair Value, Measurements, Recurring [Member] | States and Political Subdivisions [Member]
Available for sale securities:
Available for sale securities, at fair value	470	1,166
Fair Value, Measurements, Recurring [Member] | States and Political Subdivisions [Member] | Level 2 [Member]
Available for sale securities:
Available for sale securities, at fair value	470	1,166
Fair Value, Measurements, Recurring [Member] | Collateralized Mortgage Obligations [Member]
Available for sale securities:
Available for sale securities, at fair value	244,922	12,756
Fair Value, Measurements, Recurring [Member] | Collateralized Mortgage Obligations [Member] | Level 2 [Member]
Available for sale securities:
Available for sale securities, at fair value	244,922	12,756
Fair Value, Measurements, Recurring [Member] | Mortgage-backed Securities [Member]
Available for sale securities:
Available for sale securities, at fair value	61,385	70,233
Fair Value, Measurements, Recurring [Member] | Mortgage-backed Securities [Member] | Level 2 [Member]
Available for sale securities:
Available for sale securities, at fair value	$ 61,385	$ 70,233

Fair Value - Additional Informa

Fair Value - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Fair Value Disclosures [Abstract]
Other real estate, additions	$ 569	$ 1,900
Real estate owned outstanding	569	1,700
Additions to impaired loans	2,100	30,400
Impaired loans outstanding	$ 2,100	$ 29,000

Fair Value - Summary of Carryin

Fair Value - Summary of Carrying and Fair Value Information of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Assets
Cash and due from banks	$ 302,069	$ 410,575
Federal funds sold	555	552
Held to maturity securities	8,656,409	9,081,236
Loans held for sale	20,315	29,367
Other real estate owned	2,005	1,805
Liabilities
Noninterest-bearing	5,691,236	5,666,115
Interest-bearing	11,196,393	11,590,443
Other borrowings	940,874	1,031,126
Securities sold under repurchase agreements	313,825	284,720
Carrying Amount [Member]
Assets
Cash and due from banks	302,069	410,575
Federal funds sold	555	552
Held to maturity securities	8,645,163	9,324,811
Loans held for sale	20,315	29,367
Loans held for investment, net of allowance	10,480,054	10,254,506
Other real estate owned	2,005	1,805
Liabilities
Noninterest-bearing	5,691,236	5,666,115
Interest-bearing	11,196,393	11,590,443
Other borrowings	940,874	1,031,126
Securities sold under repurchase agreements	313,825	284,720
Estimated Fair Value [Member]
Assets
Cash and due from banks	302,069	410,575
Federal funds sold	555	552
Held to maturity securities	8,656,409	9,081,236
Loans held for sale	20,315	29,367
Loans held for investment, net of allowance	10,378,010	10,144,556
Other real estate owned	2,005	1,805
Liabilities
Noninterest-bearing	5,691,236	5,666,115
Interest-bearing	11,188,468	11,564,521
Other borrowings	940,915	1,031,161
Securities sold under repurchase agreements	313,821	284,685
Estimated Fair Value [Member] | Level 1 [Member]
Assets
Cash and due from banks	302,069	410,575
Federal funds sold	555	552
Estimated Fair Value [Member] | Level 2 [Member]
Assets
Held to maturity securities	8,656,409	9,081,236
Loans held for sale	20,315	29,367
Other real estate owned	2,005	1,805
Liabilities
Noninterest-bearing	5,691,236	5,666,115
Interest-bearing	11,188,468	11,564,521
Other borrowings	940,915	1,031,161
Securities sold under repurchase agreements	313,821	284,685
Estimated Fair Value [Member] | Level 3 [Member]
Assets
Loans held for investment, net of allowance	$ 10,378,010	$ 10,144,556

Goodwill and Core Deposit Int_3

Goodwill and Core Deposit Intangibles - Goodwill and Core Deposit Intangibles (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill, Beginning balance			$ 1,900,845	$ 1,900,845	$ 1,900,845
Goodwill, Ending balance	$ 1,900,845		1,900,845		1,900,845
Core Deposit Intangibles, Beginning balance			32,883	38,842	38,842
Core Deposit Intangibles, Amortization	(1,265)	$ (1,501)	(2,584)	$ (3,069)	(5,959)
Core Deposit Intangibles, Ending balance	$ 30,299		$ 30,299		$ 32,883

Goodwill and Core Deposit Int_4

Goodwill and Core Deposit Intangibles - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Schedule Of Intangible Assets And Goodwill [Line Items]
Impairment recorded on goodwill and core deposit intangibles			$ 0
Amortization expense related to intangible assets	$ 1,265,000	$ 1,501,000	$ 2,584,000	$ 3,069,000	$ 5,959,000
Minimum [Member]
Schedule Of Intangible Assets And Goodwill [Line Items]
Finite-lived intangible assets, useful life			10 years
Maximum [Member]
Schedule Of Intangible Assets And Goodwill [Line Items]
Finite-lived intangible assets, useful life			15 years

Goodwill and Core Deposit Int_5

Goodwill and Core Deposit Intangibles - Estimated Aggregate Future Amortization Expense for Core Deposit Intangibles (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Goodwill And Intangible Assets Disclosure [Abstract]
Remaining 2019	$ 2,467
2020	4,483
2021	4,022
2022	3,664
2023	3,350
Thereafter	12,313
Total	$ 30,299	$ 32,883	$ 38,842

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019USD ($)Planshares	Jun. 30, 2018USD ($)	Jun. 30, 2019USD ($)Planshares	Jun. 30, 2018USD ($)	Dec. 31, 2012shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of stock-based employee compensation plans | Plan	1		1
Total unrecognized compensation expense related to stock-based compensation arrangements | $	$ 14.7		$ 14.7
Weighted-average period of cost expected to be recognized			1 year 8 months 4 days
Number of shares outstanding	0		0
Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense | $	$ 2.3	$ 2.6	$ 5.1	$ 5.2
2012 Stock Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common shares authorized for issuance					1,250,000
Shares issued			344,500
Number of restricted shares granted			390,782

Contractual Obligations and O_3

Contractual Obligations and Off-Balance Sheet Items - Additional Information (Details) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019USD ($)	Jun. 30, 2019USD ($)
Contractual Obligations And Off Balance Sheet Items [Line Items]
Operating lease, right-of-use asset	$ 15,000	$ 15,000
Operating lease, liability	$ 15,000	$ 15,000
Operating lease, weighted average remaining lease term	5 years 2 months 12 days	5 years 2 months 12 days
Operating lease weighted average discount rate, percent	3.43%	3.43%
Operating lease, payments	$ 1,400	$ 2,800
Minimum [Member]
Contractual Obligations And Off Balance Sheet Items [Line Items]
Lessee operating lease remaining lease term		1 year
Maximum [Member]
Contractual Obligations And Off Balance Sheet Items [Line Items]
Lessee operating lease remaining lease term		13 years
Federal Home Loan Bank Advance And Notes Payable [Member]
Contractual Obligations And Off Balance Sheet Items [Line Items]
Interest payable	$ 75	$ 75

Contractual Obligations and O_4

Contractual Obligations and Off-Balance Sheet Items - Contractual Obligations and Other Commitments (Details) - Federal Home Loan Bank Advance And Notes Payable [Member] $ in Thousands	Jun. 30, 2019USD ($)
Contractual Obligations And Off Balance Sheet Items [Line Items]
1 year or less	$ 940,323
More than 1 year but less than 3 years	448
3 years or more but less than 5 years	125
5 years or more	53
Total	$ 940,949

Contractual Obligations and O_5

Contractual Obligations and Off-Balance Sheet Items - Future Undiscounted Cash Payments Associated with its Operating Leases (Details) $ in Thousands	Jun. 30, 2019USD ($)
Leases [Abstract]
Remaining 2019	$ 2,412
2020	4,158
2021	3,129
2022	2,639
2023	2,066
2024	1,287
Thereafter	4,057
Total undiscounted lease payments	$ 19,748

Contractual Obligations and O_6

Contractual Obligations and Off-Balance Sheet Items - Summary of Non-Cancelable Future Operating Lease Commitments (Details) $ in Thousands	Dec. 31, 2018USD ($)
Leases [Abstract]
2019	$ 4,897
2020	4,088
2021	3,013
2022	2,319
2023	2,025
Thereafter	3,597
Total non-cancelable lease payments	$ 19,939

Contractual Obligations and O_7

Contractual Obligations and Off-Balance Sheet Items - Summary of Commitments Associated with Outstanding Standby Letters of Credit and Commitments to Extend Credit (Details) - Guarantee Obligations [Member] $ in Thousands	Jun. 30, 2019USD ($)
Contractual Obligations And Off Balance Sheet Items [Line Items]
1 year or less	$ 1,138,612
More than 1 year but less than 3 years	430,792
3 years or more but less than 5 years	110,952
5 years or more	1,027,608
Total	2,707,964
Standby Letters of Credit [Member]
Contractual Obligations And Off Balance Sheet Items [Line Items]
1 year or less	59,278
More than 1 year but less than 3 years	6,892
3 years or more but less than 5 years	1,540
5 years or more	0
Total	67,710
Commitments to Extend Credit [Member]
Contractual Obligations And Off Balance Sheet Items [Line Items]
1 year or less	1,079,334
More than 1 year but less than 3 years	423,900
3 years or more but less than 5 years	109,412
5 years or more	1,027,608
Total	$ 2,640,254

Other Comprehensive Income - Ta

Other Comprehensive Income - Tax Effects Allocated to Each Component of Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Equity [Abstract]
Change in unrealized gain during period, before tax amount	$ 716	$ 380	$ 1,219	$ 580
Change in unrealized gain during period, tax effect	(150)	(80)	(256)	(122)
Change in unrealized gain during period, net of tax amount	566	300	963	458
Total securities available for sale, before tax amount	716	380	1,219	580
Total securities available for sale, tax effect	(150)	(80)	(256)	(122)
Total securities available for sale, net of tax amount	566	300	963	458
Total other comprehensive income, before tax amount	716	380	1,219	580
Total other comprehensive income, tax effect	(150)	(80)	(256)	(122)
Other comprehensive income, net of tax	$ 566	$ 300	$ 963	$ 458

Other Comprehensive Income - Ac

Other Comprehensive Income - Activity in Accumulated Other Comprehensive Income Associated with Securities Available for Sale, Net of Tax (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Beginning balance, accumulated other comprehensive income			$ 310	$ (113)
Other comprehensive income	$ 566	$ 300	963	458
Ending balance, accumulated other comprehensive income	1,273	345	1,273	345
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Beginning balance, accumulated other comprehensive income			310	(113)
Other comprehensive income			963	458
Ending balance, accumulated other comprehensive income	$ 1,273	$ 345	$ 1,273	$ 345

Acquisitions - Additional Infor

Acquisitions - Additional Information (Details) $ / shares in Units, $ in Thousands	Jun. 17, 2019LocationCity$ / shares	Jun. 14, 2019USD ($)$ / shares	Jun. 30, 2019USD ($)	Dec. 31, 2018USD ($)
Business Acquisition [Line Items]
Total assets			$ 22,375,221	$ 22,693,402
Total deposits			16,887,629	$ 17,256,558
Closing price per share | $ / shares		$ 67.24
LegacyTexas [Member]
Business Acquisition [Line Items]
Total assets			9,900,000
Total gross loans			8,700,000
Total deposits			$ 7,100,000
LegacyTexas [Member]
Business Acquisition [Line Items]
Business acquisition, share consideration per share, percentage	52.80%
Business acquisition, cash for each share | $ / shares	$ 6.28
Total consideration		$ 2,100,000
Business acquisition, share price | $ / shares		$ 41.78
LegacyTexas [Member] | North Texas [Member]
Business Acquisition [Line Items]
Number of bank operating locations | Location	42
Number of bank operating cities | City	19