Iberiabank (IBKC) 10-Q 8 May 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	Apr. 30, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
Trading Symbol	IBKC
Entity Registrant Name	IBERIABANK CORP
Entity Central Index Key	933,141
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		56,648,939

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Assets
Cash and due from banks	$ 253,527	$ 319,156
Interest-bearing deposits in banks	310,565	306,568
Total cash and cash equivalents	564,092	625,724
Securities available for sale, at fair value	4,542,486	4,590,062
Securities held to maturity (fair values of $219,868 and $227,964, respectively)	224,241	227,318
Mortgage loans held for sale, at fair value	110,348	134,916
Loans and leases, net of unearned income	21,706,090	20,078,181
Allowance for loan and lease losses	(144,527)	(140,891)
Loans and leases, net	21,561,563	19,937,290
Premises and equipment, net	329,454	331,413
Goodwill	1,236,169	1,188,902
Other intangible assets	102,404	88,562
Other assets	801,880	779,942
Total Assets	29,472,637	27,904,129
Deposits:
Non-interest-bearing	6,595,495	6,209,925
Interest-bearing	16,375,697	15,256,792
Total deposits	22,971,192	21,466,717
Short-term borrowings	900,496	991,297
Long-term debt	1,449,302	1,495,835
Other liabilities	250,740	253,489
Total Liabilities	25,571,730	24,207,338
Shareholders’ Equity
Preferred stock	132,097	132,097
Common stock, $1 par value - 100,000,000 shares authorized; 56,778,841 and 53,872,272 shares issued and outstanding, respectively	56,779	53,872
Additional paid-in capital	3,001,389	2,787,484
Retained earnings	807,325	769,226
Accumulated other comprehensive income (loss)	(96,683)	(45,888)
Total Shareholders’ Equity	3,900,907	3,696,791
Total Liabilities and Shareholders’ Equity	$ 29,472,637	$ 27,904,129

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Securities held to maturity, fair values	$ 219,868	$ 227,964
Preferred stock, par value (in usd per share)	$ 1	$ 1
Preferred stock, shares authorized	5,000,000	5,000,000
Liquidation preference (per share)	$ 10,000	$ 10,000
Preferred stock, shares issued	13,750	13,750
Preferred stock, shares outstanding	13,750	13,750
Common stock, par value (in usd per share)	$ 1	$ 1
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	56,778,841	53,872,272
Common stock, shares outstanding	56,778,841	53,872,272

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Interest and Dividend Income
Loans, including fees	$ 238,069	$ 168,976
Mortgage loans held for sale, including fees	1,154	971
Investment securities:
Taxable interest	25,328	17,864
Tax-exempt interest	2,766	2,063
Other	3,226	2,659
Total interest and dividend income	270,543	192,533
Deposits:
NOW and MMDA	21,228	11,100
Savings	432	320
Time deposits	6,584	4,638
Short-term borrowings	2,524	277
Long-term debt	6,886	3,380
Total interest expense	37,654	19,715
Net interest income	232,889	172,818
Provision for loan and lease losses	7,986	6,154
Net interest income after provision for loan and lease losses	224,903	166,664
Non-interest Income
Mortgage income	9,595	14,115
Service charges on deposit accounts	12,908	11,153
Title revenue	5,027	4,741
Broker commissions	2,221	2,547
ATM/debit card fee income	2,633	2,483
Credit card and merchant-related income	2,907	2,298
Trust Department Income	3,426	1,912
Income from bank owned life insurance	1,282	1,311
Gain (loss) on sale of available for sale securities	(59)	0
Other non-interest income	4,626	4,564
Total non-interest income	44,566	45,124
Non-interest Expense
Salaries and employee benefits	104,586	81,853
Net occupancy and equipment	20,047	16,021
Communication and delivery	3,902	3,044
Marketing and business development	4,752	3,424
Data processing	12,393	6,362
Professional services	7,391	5,335
Credit and other loan related expense	4,618	4,526
Insurance	7,105	4,529
Travel and entertainment	3,237	2,484
Amortization of Intangible Assets	5,102	1,770
Errors, fines, and losses	8,757	2,658
Other non-interest expense	6,406	6,790
Total non-interest expense	188,296	138,796
Income before income tax expense	81,173	72,992
Income tax expense	17,552	22,519
Net Income	63,621	50,473
Less: Preferred stock dividends	3,598	3,599
Net Income Available to Common Shareholders	60,023	46,874
Less: Earnings allocated to unvested restricted stock	639	346
Earnings allocated to common shareholders	$ 59,384	$ 46,528
Earnings per common share - Basic (in usd per share)	$ 1.11	$ 1.01
Earnings per common share - Diluted (in usd per share)	1.10	1
Cash dividends declared per common share (in usd per share)	$ 0.38	$ 0.36
Comprehensive Income
Net income	$ 63,621	$ 50,473
Unrealized gains (losses) on securities:
Unrealized holding gains (losses) arising during the period (net of tax effects of $14,223 and $2,421, respectively)	(53,506)	4,496
Less: Reclassification adjustment for gains (losses) included in net income (net of tax effects of $13 and $0, respectively)	(46)	0
Unrealized gains (losses) on securities, net of tax	(53,460)	4,496
Fair value of derivative instruments designated as cash flow hedges:
Change in fair value of derivative instruments designated as cash flow hedges during the period (net of tax effects of $678 and $39, respectively)	2,549	73
Less: Reclassification adjustment for gains (losses) included in net income (net of tax effects of $31 and $24, respectively)	(116)	(45)
Fair value of derivative instruments designated as cash flow hedges, net of tax	2,665	118
Other comprehensive income (loss), net of tax	(50,795)	4,614
Comprehensive income	$ 12,826	$ 55,087

Consolidated Statements of Com5

Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Unrealized holding gains (losses), taxes	$ 14,223	$ 2,421
Reclassification adjustment for gains (losses) included in net income, taxes	13	0
Change in fair value of derivative instruments designated as cash flow hedges, taxes	678	39
Reclassification adjustment for gains (losses) included in net income, taxes	$ 31	$ 24

Consolidated Statements of Shar

Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Preferred Stock	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2016		13,750	44,795,386
Beginning balance at Dec. 31, 2016	$ 2,939,694	$ 132,097	$ 44,795	$ 2,084,446	$ 704,391	$ (26,035)
Increase (Decrease) in Shareholders' Equity
Net income	50,473				50,473
Other comprehensive income/(loss)	4,614					4,614
Cash dividends declared	(18,271)				(18,271)
Preferred stock dividends	(3,599)				(3,599)
Common stock issued under incentive plans, net of shares surrendered in payment, including tax benefit (in shares)			74,522
Common stock issued under incentive plans, net of shares surrendered in payment	(3,851)		$ 75	(3,926)
Shares issued (in shares)			6,100,000
Common stock issued			$ 6,100	479,094
Preferred Stock Issued During Period, Value, New Issues	485,194
Share-based compensation cost	3,721			3,721
Ending balance (in shares) at Mar. 31, 2017		13,750	50,969,908
Ending balance at Mar. 31, 2017	3,457,975	$ 132,097	$ 50,970	2,563,335	732,994	(21,421)
Beginning balance (in shares) at Dec. 31, 2017		13,750	53,872,272
Beginning balance at Dec. 31, 2017	3,696,791	$ 132,097	$ 53,872	2,787,484	769,226	(45,888)
Increase (Decrease) in Shareholders' Equity
Net income	63,621				63,621
Other comprehensive income/(loss)	(50,795)					(50,795)
Cash dividends declared	(21,579)				(21,579)
Preferred stock dividends	(3,598)				(3,598)
Common stock issued under incentive plans, net of shares surrendered in payment, including tax benefit (in shares)			118,796
Common stock issued under incentive plans, net of shares surrendered in payment	(2,581)		$ 119	(2,700)
Stock Issued During Period, Shares, Acquisitions			2,787,773
Stock Issued During Period, Value, Acquisitions	214,659		$ 2,788	211,871
Share-based compensation cost	4,734			4,734
Ending balance (in shares) at Mar. 31, 2018		13,750	56,778,841
Ending balance at Mar. 31, 2018	$ 3,900,907	$ 132,097	$ 56,779	$ 3,001,389	$ 807,325	$ (96,683)

Consolidated Statements of Sha7

Consolidated Statements of Shareholders' Equity (Parenthetical) - $ / shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash dividends declared per common share (in usd per share)	$ 0.38	$ 0.36
Retained Earnings
Cash dividends declared per common share (in usd per share)	$ 0.38	$ 0.36

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash Flows from Operating Activities
Net income	$ 63,621	$ 50,473
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, amortization, and accretion, including amortization of purchase accounting adjustments and market value adjustments	(309)	1,646
Provision for loan and lease losses	7,986	6,154
Share-based compensation cost - equity awards	4,734	3,721
Loss/(gain) on sale of OREO and long-lived assets, net of impairment	670	(746)
Loss/(gain) on sale of available for sale securities	59	0
Expense/(benefit) for deferred income taxes	10,992	(10,565)
Originations of mortgage loans held for sale	(336,400)	(393,924)
Proceeds from sales of mortgage loans held for sale	367,487	440,337
Realized and unrealized (gain)/loss on mortgage loans held for sale, net	(9,320)	(13,689)
Other operating activities, net	(13,113)	(20,933)
Net Cash Provided by Operating Activities	96,407	62,474
Cash Flows from Investing Activities
Proceeds from maturities, prepayments and calls of available for sale securities	149,987	113,940
Purchases of available for sale securities, net of available for sale securities acquired	(194,543)	(491,055)
Proceeds from maturities, prepayments and calls of held to maturity securities	2,288	2,968
Purchases of equity securities, net of equity securities acquired	(2,452)	(200)
Proceeds from sales of equity securities	61,038	0
Increase in loans, net of loans acquired	(145,201)	(60,609)
Proceeds from sales of premises and equipment	1,408	7
Purchases of premises and equipment, net of premises and equipment acquired	(5,798)	(2,761)
Proceeds from dispositions of OREO	5,318	4,374
Cash paid for additional investment in tax credit entities	(750)	(795)
Payments to Acquire Businesses, Net of Cash Acquired	99,312	0
Other investing activities, net	(745)	6,327
Net Cash Used in Investing Activities	(30,138)	(427,804)
Cash Flows from Financing Activities
Increase/(decrease) in deposits, net of deposits acquired	440,470	(95,916)
Net change in short-term borrowings	(90,802)	(60,440)
Proceeds from long-term debt, net of long-term debt acquired	200,227	0
Repayments of long-term debt	(651,684)	(622)
Cash dividends paid on common stock	(19,933)	(16,126)
Cash dividends paid on preferred stock	(3,598)	(3,599)
Net share-based compensation stock transactions	(2,581)	(4,169)
Net proceeds from issuance of common stock	0	485,194
Net Cash Used in Financing Activities	(127,901)	304,322
Net Increase (Decrease) In Cash and Cash Equivalents	(61,632)	(61,008)
Cash and Cash Equivalents at Beginning of Period	625,724	1,362,126
Cash and Cash Equivalents at End of Period	564,092	1,301,118
Supplemental Schedule of Non-cash Activities
Acquisition of real estate in settlement of loans	1,757	2,733
Common stock issued in acquisitions	214,659	0
Cash paid for:
Interest on deposits and borrowings	37,035	19,850
Income taxes, net	$ 101	$ 39,609

Basis of Presentation

Basis of Presentation	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	BASIS OF PRESENTATION General IBERIABANK Corporation is a regional financial holding company with offices in Louisiana, Arkansas, Tennessee, Alabama, Texas, Florida, Georgia, South Carolina, North Carolina, and New York offering commercial, private banking, consumer, small business, wealth and trust management, retail brokerage, mortgage, and title insurance services. The consolidated financial statements include the accounts of the Company and its subsidiaries. All significant intercompany balances and transactions have been eliminated in consolidation. Certain amounts reported in prior periods have been reclassified to conform to the current period presentation. These reclassifications did not have a material effect on previously reported consolidated financial statements. The accompanying unaudited consolidated financial statements have been prepared in accordance with GAAP for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all information or footnotes required by GAAP for complete financial statements. In the opinion of management, all adjustments, consisting of normal and recurring items, necessary for a fair presentation of the consolidated financial statements have been made. These interim financial statements should be read in conjunction with the audited consolidated financial statements and footnote disclosures for the Company previously filed with the SEC in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017. Operating results for the period ended March 31, 2018 are not necessarily indicative of the results that may be expected for the year ending December 31, 2018. When we refer to the “Company,” “we,” “our,” or “us” in this Report, we mean IBERIABANK Corporation and subsidiaries (consolidated). When we refer to the “Parent,” we mean IBERIABANK Corporation. See the Glossary of Defined Terms at the end of this Report for terms used throughout this Report. Concentrations of Credit Risk Most of the Company’s business activity is with customers located in the southeastern United States. The Company’s lending activity is concentrated in its market areas within those states. The Company has emphasized originations of commercial loans and private banking loans, defined as loans to higher net worth clients. Repayments on loans are expected to come from cash flows of the borrower and/or guarantor. Losses on secured loans are limited by the net realizable value of the collateral upon default of the borrowers and guarantor support. The Company believes it does not have any excessive concentrations to any one industry, loan type, or customer.

Recent Accounting Pronouncement

Recent Accounting Pronouncements (Notes)	3 Months Ended
	Mar. 31, 2018
Accounting Changes and Error Corrections [Abstract]
New Accounting Pronouncements and Changes in Accounting Principles [Text Block]	RECENT ACCOUNTING PRONOUNCEMENTS Pronouncements adopted during the three months ended March 31, 2018: ASU No. 2014-09 In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers , which implements a common revenue standard and clarifies the principles used for recognizing revenue. The amendments in the ASU clarify that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. Revenue from Contracts with Customers The majority of the Company’s income streams (e.g., interest and dividend income and mortgage income) are accounted for in accordance with GAAP literature outside the scope of ASC 606, Revenue from Contracts with Customers . Details regarding income recognition for interest and non-interest streams can be found throughout the Company’s 2017 10-K (including Note 1 - Summary of Significant Accounting Policies). Impairment losses recognized against certain receivables (e.g., NSF fees) and capitalized costs (e.g., sales commissions) associated with contracts within the scope of ASC 606 are immaterial. Non-interest income from service charges on deposit accounts, broker commissions, ATM/debit card fee income, credit card and merchant-related income (e.g., interchange fees), and transactional income from traditional banking services (part of other non-interest income) are the significant income streams within the scope of ASC 606 associated with the IBERIABANK reportable segment. Non-interest income from title revenue is associated with the LTC reportable segment. Recognition of Revenue from Contracts with Customers The Company enters into various contracts with customers to provide traditional banking services, including asset management, on a routine basis. The Company’s performance obligations are generally service-related and provided on a daily or monthly basis. The Company does not typically have performance obligations which extend beyond a reporting period. The performance obligations are generally satisfied upon completion of service (i.e., as services are rendered) and the fees are collected at such time, or shortly thereafter. The fees are readily determinable and allocated individually to each service. It is not typical for contracts to require significant judgment to determine the transaction price. Some contracts contain variable consideration; however, the variable consideration is generally constrained (not estimable) as it is based on the occurrence or nonoccurence of a contingent event (or another constraint in some circumstances). The Company generally records the variable consideration when the contingent event occurs and the fee is determinable. The Company provides some services for customers in which it acts in an agent capacity, but generally acts in a principal capacity. Payment terms and conditions vary slightly amongst services; however, amounts are generally invoiced and due or collected by the Company within 30 days, although some fees may be prepaid. The Company bills the customer periodically as performance obligations are satisfied for most services. Therefore, revenue for services provided is generally recognized in the amount invoiced (except in circumstances of prepayment) as that amount corresponds directly to the value of the Company’s performance. In the normal course of business, the Company does not generally grant refunds for services provided. As such, the Company does not establish provisions for estimated returns. Title revenue associated with services provided by LTC, as well as broker commissions, ATM/debit card fee income, credit card and merchant-related income (e.g., interchange fees), and transactional fees from traditional banking services generated within IBERIABANK are generally recognized at the point-in-time the services are provided. The Company has determined this recognition to be appropriate as, upon completion of services, the Company has completed its performance obligations, has a present right to payment (or has collected the cash), and the customer is able to obtain (or has obtained) substantially all of the benefits from the performance obligation (i.e., the provided services). Revenues from service charges on deposit accounts are recognized at the end of the monthly service period (e.g., account service charges) or the date the performance obligation is satisfied (e.g., NSF, stop payment, wire transfer, etc.), except for deposit account services performed by Treasury Management which are recognized on a monthly basis, as these services are performed over that time. Asset management fees (e.g., trust fees) are generally recognized at the end of the monthly service period, but fees are not collected until the beginning of the subsequent month, although some contracts may have quarterly terms and/or be prepaid. NSF fees which are not initially paid are subsequently recorded as “loans” (along with the overdraft balance) and remain classified as such until the amount is paid or charged-off (generally after 60 days). Adoption of ASC 606 The Company adopted ASC 606 as of January 1, 2018 for all contracts as of the effective date. Prior period amounts have been reclassified to conform to current guidance requirements related to the net presentation of certain costs associated with interchange fees and rewards programs. The reclassification of prior period amounts reduced non-interest income and non-interest expense by an immaterial amount (approximately $2.2 million for the three months ended March 31, 2017) and had no impact on net income. There was no cumulative adjustment made to opening retained earnings as of January 1, 2018. ASU No. 2016-01 In January 2016, the FASB issued ASU No. 2016-01, Financial Statements - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities , which impacts how the Company measures certain equity investments and discloses and presents certain financial instruments through the application of the “exit price” notion. The Company adopted the amendments beginning January 1, 2018. Under the new guidance, equity investments can no longer be classified as trading or available for sale (AFS), and related unrealized holding gains and losses can no longer be recognized in OCI. Per the ASU, such equity investments should be measured at fair value, with adjustments recognized in earnings at the end of each reporting period. As such, the Company reclassified its portfolio of equity investments (approximately $9.8 million at March 31, 2018) previously classified as AFS investment securities to “other assets.” As these equity investments were previously measured at fair value, implementation of the ASU did not impact the Company’s valuation method. In accordance with the ASU, the cumulative-effect adjustment from AOCI to retained earnings for previously recorded fair value adjustments related to these equity investments at adoption was insignificant. The Company elected the practical expedient measurement alternative to prospectively account for other equity investments that do not have readily determinable fair values at cost less impairment plus or minus observable price changes in orderly transactions for an identical or similar investment of the same issuer. These investments are immaterial overall and are classified within “other assets” on the Company’s consolidated balance sheets. The Company also modified its fair value methodology for loans measured at amortized cost whose fair values were previously disclosed using an “entry price” methodology to an “exit price” methodology, in accordance with the ASU. The Company’s “exit price” methodology estimates the fair value of these loans based on the present value of the future cash flows using the interest rate that would be charged for a similar loan to a borrower with similar risk at the indicated balance sheet date, adjusted for a liquidity discount based on the estimated time period to complete a sale transaction with a market participant. This change in methodology solely impacted the Company’s disclosures, and had no impact to the Company’s consolidated financial statements. ASU No. 2016-15 In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (ASC 230): Classification of Certain Cash Receipts and Cash Payments , in order to reduce current diversity in practice in how certain cash receipts and cash payments are presented and classified in the statement of cash flows. The Company retrospectively adopted the amendments effective January 1, 2018. The adoption of these amendments did not impact the Company’s consolidated statements of cash flows. ASU No. 2017-12 In August 2017, the FASB issued ASU No. 2017-12, Derivatives and Hedging (ASC 815): Targeted Improvements to Accounting for Hedging Activities, which amends the hedge accounting model to enable entities to better portray the economics of their risk management activities in the financial statements and enhance the transparency and understandability of hedge results. The Company elected to early adopt the amendments effective January 1, 2018. The modified-retrospective adoption of the amendments did not impact the Company’s consolidated financial statements in the current or prior periods. Pronouncements issued but not yet adopted: ASU No. 2016-02 In February 2016, the FASB issued ASU No. 2016-02, Leases (ASC 842) . A significant amendment to existing GAAP from this ASU is the recognition of lease assets (i.e., right of use assets) and liabilities on the balance sheet for leases that are classified as operating leases by lessees. The lessor model remains similar to the current accounting model in existing GAAP. Additional amendments include, but are not limited to, the elimination of leveraged leases; modification to the definition of a lease; amendments on sale and leaseback transactions; and disclosure of additional quantitative and qualitative information. ASU 2016-02 will be effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years, with early adoption permitted. Lessees and lessors are required to recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach. The Company will adopt the amendments on January 1, 2019. The Company occupies certain banking offices and equipment under operating lease agreements, which currently are not recognized on the consolidated balance sheets. Based on the Company’s preliminary analysis of its current portfolio, the impact to the Company’s consolidated balance sheets is estimated to result in less than a 1% increase in assets and liabilities. The Company is also currently assessing the practical expedients it may elect at adoption, the final determination of the incremental borrowing rate, and the impact to regulatory capital ratios, amongst other matters associated with the ASU. The adjustment to retained earnings is not expected to be significant based on the transition guidance associated with current sale-leaseback agreements. The Company also anticipates additional disclosures to be provided at adoption. ASU No. 2016-13 In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (ASC 326): Measurement of Credit Losses on Financial Instruments . The amendments introduce an impairment model that is based on expected credit losses (“ECL”), rather than incurred losses, to estimate credit losses on certain types of financial instruments (e.g., loans and held-to-maturity securities), including certain off-balance sheet financial instruments (e.g., loan commitments). The measurement of ECL should consider historical information, current information, and reasonable and supportable forecasts, including estimates of prepayments, over the contractual term. Financial instruments with similar risk characteristics may be grouped together when estimating ECL. The ASU also amends the current AFS security impairment model for debt securities. The new model will require an estimate of ECL when the fair value is below the amortized cost of the asset through the use of an allowance to record estimated credit losses (and subsequent recoveries). Non-credit related losses will continue to be recognized through OCI. In addition, the amendments provide for a simplified accounting model for purchased financial assets with a more-than-insignificant amount of credit deterioration since their origination. The initial estimate of expected credit losses would be recognized through an ALLL with an offset (i.e., increase) to the cost basis of the related financial asset at acquisition. ASU 2016-13 will be effective for fiscal years beginning after December 15, 2019, including interim periods. The amendments will be applied through a modified-retrospective approach, resulting in a cumulative-effect adjustment to retained earnings as of the beginning of the first reporting period in which the guidance is effective. A prospective transition approach is required for debt securities for which OTTI had been recognized before the effective date. Amounts previously recognized in AOCI as of the date of adoption that relate to improvements in cash flows expected to be collected should continue to be accreted into income over the remaining life of the asset. Recoveries of amounts previously written off relating to improvements in cash flows after the date of adoption should be recorded in earnings when received. The Company is currently evaluating the impact of the ASU on the Company’s consolidated financial statements; however, the Company has engaged third-party consultants to assist with the ASU and has developed an implementation plan.

Loans

Loans	3 Months Ended
	Mar. 31, 2018
Receivables [Abstract]
Loans	LOANS AND LEASES Loans and leases consist of the following for the periods indicated: (Dollars in thousands) March 31, 2018 December 31, 2017 Commercial loans and leases: Real estate- construction $ 1,199,625 $ 1,240,396 Real estate- owner-occupied 2,612,244 2,529,885 Real estate- non-owner-occupied 5,437,082 5,167,949 Commercial and industrial (1) 5,325,682 5,135,067 14,574,633 14,073,297 Residential mortgage loans: 3,971,067 3,056,352 Consumer loans: Home equity 2,421,186 2,292,275 Indirect automobile 50,671 62,693 Credit card 93,261 96,368 Other 595,272 497,196 3,160,390 2,948,532 Total $ 21,706,090 $ 20,078,181 (1) Includes equipment financing leases. Net deferred loan origination fees were $31.4 million and $29.3 million at March 31, 2018 and December 31, 2017, respectively. Total net discount on the Company's loans was $158.1 million and $159.3 million at March 31, 2018 and December 31, 2017, respectively, of which $100.8 million and $94.7 million was related to non-impaired loans. Net loan discounts include preliminary discounts recorded on Sabadell United and Gibraltar loans, which are subject to change upon receipt of final fair value estimates during the respective measurement periods. In addition to loans issued in the normal course of business, the Company considers overdrafts on customer deposit accounts to be loans and reclassifies these overdrafts as loans in its consolidated balance sheets. At March 31, 2018 and December 31, 2017, overdrafts of $7.3 million and $7.4 million , respectively, have been reclassified to loans. Loans with carrying values of $6.8 billion and $6.6 billion were pledged as collateral for borrowings at March 31, 2018 and December 31, 2017, respectively. Aging Analysis The following tables provide an analysis of the aging of loans as of March 31, 2018 and December 31, 2017. Past due and non-accrual loan amounts exclude acquired impaired loans, even if contractually past due or if the Company does not expect to receive payment in full, as the Company is currently accreting interest income over the expected life of the loans. March 31, 2018 Accruing (Dollars in thousands) Current or Less Than 30 days Past Due 30-59 days 60-89 days > 90 days Total Past Due Non-accrual Acquired Impaired Total Real estate- construction $ 1,157,115 $ 842 $ 129 $ — $ 971 $ 2,634 $ 38,905 $ 1,199,625 Real estate- owner-occupied 2,474,611 4,767 3,461 — 8,228 35,144 94,261 2,612,244 Real estate- non-owner-occupied 5,319,962 7,269 2,526 6,789 16,584 9,378 91,158 5,437,082 Commercial and industrial 5,212,390 7,755 3,406 273 11,434 66,637 35,221 5,325,682 Residential mortgage 3,783,309 25,640 2,655 1,226 29,521 19,932 138,305 3,971,067 Consumer - home equity 2,309,222 11,860 3,191 — 15,051 16,383 80,530 2,421,186 Consumer - indirect automobile 48,581 1,166 175 — 1,341 743 6 50,671 Consumer - credit card 92,497 173 88 — 261 503 — 93,261 Consumer - other 585,969 2,484 706 — 3,190 2,621 3,492 595,272 Total $ 20,983,656 $ 61,956 $ 16,337 $ 8,288 $ 86,581 $ 153,975 $ 481,878 $ 21,706,090 December 31, 2017 Accruing (Dollars in thousands) Current or Less Than 30 days Past Due 30-59 days 60-89 days > 90 days Total Past Due Non-accrual Acquired Impaired Total Real estate- construction $ 1,197,766 $ 269 $ — $ 458 $ 727 $ 2,635 $ 39,268 $ 1,240,396 Real estate- owner-occupied 2,398,487 1,631 659 74 2,364 24,457 104,577 2,529,885 Real estate- non-owner-occupied 5,066,084 2,086 6,405 887 9,378 6,811 85,676 5,167,949 Commercial and industrial 5,014,438 5,788 5,726 146 11,660 77,823 31,146 5,135,067 Residential mortgage 2,877,048 10,083 8,136 5,317 23,536 17,387 138,381 3,056,352 Consumer - home equity 2,186,554 11,675 2,947 18 14,640 12,365 78,716 2,292,275 Consumer - indirect automobile 59,830 1,796 177 — 1,973 884 6 62,693 Consumer - credit card 95,264 140 374 — 514 590 — 96,368 Consumer - other 487,150 3,350 475 — 3,825 2,436 3,785 497,196 Total $ 19,382,621 $ 36,818 $ 24,899 $ 6,900 $ 68,617 $ 145,388 $ 481,555 $ 20,078,181 Acquired Loans As discussed in Note 3, during the third quarter of 2017, the Company acquired loans with fair values of $4.0 billion from Sabadell United. Certain loans that were acquired in this transaction were covered by loss share agreements between the FDIC and Sabadell United, which were assumed in connection with the Company's acquisition of Sabadell United and afford IBERIABANK loss protection. Covered loans were $150.0 million and $158.6 million at March 31, 2018 and December 31, 2017, respectively. Certain acquired loans from Sabadell United were to customers with addresses outside of the United States. Foreign loans, denominated in U.S. dollars, totaled $336.1 million and $325.5 million at March 31, 2018 and December 31, 2017, respectively. During the first quarter of 2018, the Company acquired loans with fair values of $1.5 billion from Gibraltar. Of the total loans acquired from Gibraltar, $1.46 billion were determined to have no evidence of deteriorated credit quality and are accounted for under ASC Topics 310-10 and 310-20. The remaining $10.2 million were determined to exhibit deteriorated credit quality since origination under ASC 310-30. The tables below show the balances acquired during the first quarter of 2018 for these two subsections of the portfolio as of the acquisition date. These amounts are subject to change due to the finalization of purchase accounting adjustments. (Dollars in thousands) Acquired Non-Impaired Loans Contractually required principal and interest at acquisition $ 1,695,918 Expected losses and foregone interest (19,952 ) Cash flows expected to be collected at acquisition 1,675,966 Fair value of acquired loans at acquisition $ 1,455,085 (Dollars in thousands) Acquired Impaired Loans Contractually required principal and interest at acquisition $ 43,779 Non-accretable difference (expected losses and foregone interest) (31,174 ) Cash flows expected to be collected at acquisition 12,605 Accretable yield (2,371 ) Basis in acquired loans at acquisition $ 10,234 The following is a summary of changes in the accretable difference for all loans accounted for under ASC 310-30 during the three months ended March 31: (Dollars in thousands) 2018 2017 Balance at beginning of period $ 152,623 $ 175,054 Additions 2,371 — Transfers from non-accretable difference to accretable yield (279 ) 2,071 Accretion (13,154 ) (14,596 ) Changes in expected cash flows not affecting non-accretable differences (1) 9,687 1,060 Balance at end of period $ 151,248 $ 163,589 (1) Includes changes in cash flows expected to be collected due to the impact of changes in actual or expected timing of liquidation events, modifications, changes in interest rates and changes in prepayment assumptions. Troubled Debt Restructurings Information about the Company’s troubled debt restructurings ("TDRs") at March 31, 2018 and 2017 is presented in the following tables. Modifications of loans that are accounted for within a pool under ASC Topic 310-30 are excluded as TDRs. Accordingly, such modifications do not result in the removal of those loans from the pool, even if the modification of those loans would otherwise be considered a TDR. As a result, all such acquired loans that would otherwise meet the criteria for classification as a TDR are excluded from the tables below. TDRs totaling $27.2 million and $13.2 million occurred during the three months ended March 31, 2018 and March 31, 2017, respectively, through modification of the original loan terms. The following table provides information on how the TDRs were modified during the periods indicated: Three Months Ended March 31, (Dollars in thousands) 2018 2017 Extended maturities $ 5,619 $ 7,199 Maturity and interest rate adjustment 108 3,224 Movement to or extension of interest-rate only payments 48 1,290 Interest rate adjustment 105 — Forbearance 12,886 1,220 Other concession(s) (1) 8,434 232 Total $ 27,200 $ 13,165 (1) Other concessions may include covenant waivers, forgiveness of principal or interest associated with a customer bankruptcy, or a combination of any of the above concessions. Of the $27.2 million of TDRs occurring during the three months ended March 31, 2018, $12.9 million are on accrual status and $14.3 million are on non-accrual status. Of the $13.2 million of TDRs occurring during the three months ended March 31, 2017, $11.8 million were on accrual status and $1.4 million were on non-accrual status. The following table presents the end of period balance for loans modified in a TDR during the periods indicated: Three Months Ended March 31, 2018 2017 (In thousands, except number of loans) 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 Real estate- construction 1 $ 1,950 $ 1,049 — $ — $ — Real estate- owner-occupied 2 10,691 9,324 3 3,004 2,999 Real estate- non-owner-occupied 9 1,089 1,091 7 1,867 1,855 Commercial and industrial 18 14,429 13,314 15 435 427 Residential mortgage — — — 4 259 241 Consumer - home equity 14 1,809 1,795 37 6,622 6,607 Consumer - indirect 11 137 119 13 184 174 Consumer - other 10 511 508 22 867 862 Total 65 $ 30,616 $ 27,200 101 $ 13,238 $ 13,165 Information detailing TDRs that defaulted during the three-month periods ended March 31, 2018 and 2017, and were modified in the previous twelve months (i.e., the twelve months prior to the default) is presented in the following tables. The Company has defined a default as any loan with a payment that is currently past due greater than 30 days , or was past due greater than 30 days at any point during the respective periods, or since the date of modification, whichever is shorter. Three Months Ended March 31, 2018 2017 (In thousands, except number of loans) Number of Loans Recorded Investment Number of Loans Recorded Investment Real estate- construction — $ — 1 $ 117 Real estate- owner-occupied 3 10,187 9 14,732 Real estate- non-owner-occupied 9 492 10 5,041 Commercial and industrial 29 9,708 21 4,186 Residential mortgage 6 598 22 1,793 Consumer - home equity 24 2,331 31 1,337 Consumer - indirect automobile 34 322 43 517 Consumer - other 17 1,035 25 693 Total 122 $ 24,673 162 $ 28,416

Acquisition Activity

Acquisition Activity	3 Months Ended
	Mar. 31, 2018
Business Combinations [Abstract]
Acquisition Activity	ACQUISITION ACTIVITY The acquisitions discussed below qualify as business combinations. The Company accounts for business combinations under the acquisition method in accordance with ASC Topic 805, Business Combinations . See Note 1, Summary of Significant Accounting Policies, in the 2017 Annual Report on Form 10-K for the year ended December 31, 2017, for further discussion of the Company's accounting for business combinations. 2018 Acquisitions Acquisition of Gibraltar The Company completed the acquisition of Gibraltar Private Bank & Trust Co. ("Gibraltar") on March 23, 2018. The acquisition added $1.5 billion in loans and $1.1 billion in deposits, based on preliminary purchase accounting adjustments. Gibraltar operated eight offices in total, with seven located in the Florida metropolitan statistical areas of Miami, Key West, and Naples and one in New York City. Under the terms of the Agreement and Plan of Merger, Gibraltar common shareholders received 1.9749 shares of IBERIABANK Corporation common stock for each outstanding share of Gibraltar common stock. Based on the Company's closing common stock price of $77.00 per share on March 23, 2018, the aggregate value of the acquisition consideration paid at the time of closing was approximately $214.7 million . During the first quarter of 2018, the Company recorded preliminary purchase price allocations related to Gibraltar, which resulted in goodwill of $42.5 million . The following table summarizes the consideration paid for Gibraltar's net assets and the preliminary fair value estimates of the identifiable assets acquired and liabilities assumed as of the acquisition date. (Dollars in thousands) Number of Shares Amount Equity consideration Common stock issued 2,787,773 $ 214,659 Total equity consideration 214,659 Non-equity consideration Cash 7 Total consideration paid 214,666 Fair value of net assets assumed including identifiable intangible assets 172,136 Goodwill $ 42,530 (Dollars in thousands) Gibraltar Fair Value (Preliminary) Assets Cash and cash equivalents $ 102,570 Investment securities 19,169 Equity securities 27,519 Loans 1,465,319 Core deposit intangible assets 18,529 Deferred tax asset, net 689 Other assets 14,382 Total assets acquired $ 1,648,177 Liabilities Deposit liabilities $ 1,064,803 Long-term borrowings 405,107 Other liabilities 6,131 Total liabilities assumed $ 1,476,041 The following is a description of the methods used to determine the fair values of significant assets acquired and liabilities assumed presented above. Cash and Cash Equivalents: The carrying amount of these assets is a reasonable estimate of fair value based on the short-term nature of these assets. Investment Securities: Fair values for securities were based on quoted market prices from multiple bond dealers. The simple average of the prices received was used to calculate the adjustments. Equity Securities: The carrying amount of these securities is a reasonable estimate of fair value based on the short-term nature of these assets. Loans: Fair values for loans were based on a discounted cash flow methodology that considered factors including loan type, classification status, remaining term of the loan, fixed or variable interest rate, amortization status and current discount rates. The discount rates used for loans were based on current market rates for new originations of comparable loans and included adjustments for any liquidity concerns. The discount rate did not include an explicit factor for credit losses, as that was included as a reduction to the estimated cash flows. Core Deposit Intangible Assets ("CDI"): The fair value for CDI was estimated based on a discounted cash flow methodology that gave appropriate consideration to expected customer attrition rates, net maintenance cost of the deposit base, alternative costs of funds, and the interest costs associated with the customer deposits. The CDI is being amortized over its estimated useful life of approximately ten years utilizing an accelerated method. Deposit Liabilities: The fair values used for the demand and savings deposits by definition equal the amount payable on demand at the acquisition date. Fair values for time deposits were estimated using a discounted cash flow analysis, that applied interest rates currently being offered to the contractual interest rates on such time deposits. Long-term Borrowings: The carrying amount of long-term borrowings at the acquisition date approximated fair value, as the Company immediately paid off the debt upon acquisition. Acquisition of SolomonParks On January 12, 2018, the Company's subsidiary, Lenders Title Company ("LTC"), acquired SolomonParks Title & Escrow, LLC ("SolomonParks"). Under the terms of the Agreement, LTC paid $3.3 million in cash to acquire eight title offices in the Nashville, Tennessee area, which resulted in goodwill of $3.4 million . In addition, the agreement provides for potential additional cash consideration based on gross revenues over a two-year period after the acquisition. The following table summarizes the preliminary fair value estimates of the identifiable assets acquired and liabilities assumed as of the acquisition date. (Dollars in thousands) SolomonParks Fair Value (Preliminary) Assets Premise and equipment, net $ 42 Non-compete agreement 156 Title Plant investment 15 Total assets acquired $ 213 Liabilities Contingent consideration $ 343 Total liabilities assumed $ 343 Information regarding the preliminary allocation of goodwill recorded as a result of these acquisitions to the Company's reportable segments is provided in Note 7 "Goodwill and Other Intangible Assets." The goodwill recorded as a result of these acquisitions is not deductible for tax purposes. 2017 Acquisition Acquisition of Sabadell United The Company completed the acquisition of Sabadell United Bank, N.A. ("Sabadell United") from Banco de Sabadell, S.A. on July 31, 2017. The acquisition of Sabadell United constituted a business combination. Accordingly, assets acquired, liabilities assumed, and consideration exchanged were recorded at their estimated fair value on the acquisition date. The acquisition added $4.0 billion in loans and $4.4 billion in deposits after fair value adjustments. The acquisition expanded our presence in Southeast Florida adding 25 offices serving the Miami metropolitan area and three offices in Naples, Sarasota and Tampa. Under the terms of the Stock Purchase Agreement, Banco de Sabadell, S.A. received $809.2 million in cash and 2,610,304 shares of IBERIABANK Corporation common stock in exchange for 100 percent of Sabadell United's common stock. The cash consideration was financed through two public common stock offerings completed on December 7, 2016, and March 7, 2017. During the third quarter of 2017, the Company recorded preliminary purchase price allocations related to Sabadell United. Throughout the remainder of 2017 and the first quarter of 2018, the Company continued to analyze the valuations assigned to the acquired assets and liabilities assumed. Based on new information relating to events or circumstances existing at the acquisition date and revised valuations, the Company updated estimated fair values increasing goodwill by $1.4 million to $463.4 million during the first quarter of 2018. This increase is primarily a result of a change in the estimated fair value of the deferred tax asset. As of March 31, 2018, the Company continues to review its fair value estimates and additional adjustments may be required. The following table summarizes the consideration paid for Sabadell United's net assets and the preliminary fair value estimates of identifiable assets acquired and liabilities assumed as of the acquisition date. (Dollars in thousands) Number of Shares Amount Equity consideration Common stock issued 2,610,304 $ 211,043 Total equity consideration 211,043 Non-equity consideration Cash 809,159 Total consideration paid 1,020,202 Fair value of net assets assumed including identifiable intangible assets 556,799 Goodwill $ 463,403 (Dollars in thousands) Sabadell United Fair Value (Preliminary) Assets Cash and cash equivalents $ 318,834 Investment securities 964,123 Loans 4,025,946 Core deposit intangible assets 66,600 Deferred tax asset, net 33,469 Other assets 89,745 Total assets acquired $ 5,498,717 Liabilities Deposit liabilities $ 4,382,780 Short-term borrowings 520,539 Other liabilities 38,599 Total liabilities assumed $ 4,941,918 Information regarding the preliminary allocation of goodwill recorded as a result of the acquisition to the Company's reportable segments is provided in Note 7 "Goodwill and Other Intangible Assets." The goodwill recorded as a result of the acquisition is not deductible for tax purposes. All measurement period adjustments made during the first three months of 2018 have been deemed insignificant individually and in the aggregate. The Company will finalize its valuation of the Sabadell United acquisition within the measurement period (i.e., no later than July 31, 2018). See Note 3, Acquisition Activity, in the 2017 Annual Report on Form 10-K for the year ended December 31, 2017, for a description of the methods used to determine the fair values of significant assets acquired and liabilities assumed presented above. The Company's consolidated financial statements as of and for the period ended March 31, 2018 include the operating results of the acquired assets and liabilities assumed. Due to the system conversion of Sabadell United in October 2017 and subsequent streamlining and integration of the operating activities into those of the Company, historical reporting for the former Sabadell United operations is impracticable and thus disclosure of the revenue from the assets acquired and income before income taxes is impracticable for the period subsequent to acquisition. The following table presents unaudited pro forma information as if the acquisition occurred on January 1, 2016 under the "Unaudited Pro Forma" column. The pro forma information does not necessarily reflect the results of operations that would have occurred had the Company acquired Sabadell United on January 1, 2016. Furthermore, cost savings and other business synergies related to the acquisition are not reflected in the pro forma amounts. Unaudited Pro Forma for (Dollars in thousands) Three months ended March 31, 2017 Net interest income $ 231,087 Non-interest income 54,755 Net income 43,562 This pro forma information combines the historical consolidated results of operations of IBERIABANK and Sabadell United for the periods presented and gives effect to the following non recurring adjustments: Fair value adjustments: Pro forma adjustment to net interest income of $5.1 million for the three months ended March 31, 2017 to record estimated amortization of premiums and accretion of discounts on acquired loans, securities, and deposits. Sabadell United accretion / amortization: Pro forma adjustment to net interest income of $318.5 thousand for the three months ended March 31, 2017 to eliminate Sabadell United's amortization of premiums and accretion of discounts on previously acquired loans, securities, FDIC indemnification asset, and deposits. Sabadell United provision for loan losses: Pro forma adjustments were made to provision for loan losses of $1.6 million for the three months ended March 31, 2017 to eliminate the reversal (benefit) of Sabadell United's release of provision for loan losses and to account for the provision for loan losses on new loans originated during the period presented. Amortization of acquired intangibles: Pro forma adjustment to non-interest expense of $1.5 million for the three months ended March 31, 2017 to record estimated amortization of acquired intangible assets. Other adjustments: Pro forma results also include adjustments related to the removal of benefit from release of reserve for unfunded lending commitments, removal of FDIC clawback liability expense, adjustments to FDIC insurance and other regulatory assessment expenses and related income tax effects.

Investment Securities

Investment Securities	3 Months Ended
	Mar. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Investment Securities	INVESTMENT SECURITIES The amortized cost and fair values of investment securities, with gross unrealized gains and losses, consist of the following: March 31, 2018 (Dollars in thousands) Amortized Gross Gross Estimated Securities available for sale: U.S. Treasury securities $ 6,824 $ — $ — $ 6,824 U.S. Government-sponsored enterprise obligations 41,001 11 (654 ) 40,358 Obligations of state and political subdivisions 267,962 1,228 (4,156 ) 265,034 Mortgage-backed securities 4,277,033 279 (121,215 ) 4,156,097 Other securities 75,205 106 (1,138 ) 74,173 Total securities available for sale $ 4,668,025 $ 1,624 $ (127,163 ) $ 4,542,486 Securities held to maturity: Obligations of state and political subdivisions $ 204,404 $ 726 $ (4,120 ) $ 201,010 Mortgage-backed securities 19,837 35 (1,014 ) 18,858 Total securities held to maturity $ 224,241 $ 761 $ (5,134 ) $ 219,868 December 31, 2017 (Dollars in thousands) Amortized Gross Gross Estimated Securities available for sale: U.S. Government-sponsored enterprise obligations $ 41,003 $ 18 $ (406 ) $ 40,615 Obligations of state and political subdivisions 271,451 4,246 (1,493 ) 274,204 Mortgage-backed securities 4,221,472 1,461 (61,028 ) 4,161,905 Other securities 114,005 247 (914 ) 113,338 Total securities available for sale $ 4,647,931 $ 5,972 $ (63,841 ) $ 4,590,062 Securities held to maturity: Obligations of state and political subdivisions $ 206,736 $ 1,530 $ (275 ) $ 207,991 Mortgage-backed securities 20,582 41 (650 ) 19,973 Total securities held to maturity $ 227,318 $ 1,571 $ (925 ) $ 227,964 Securities with carrying values of $2.1 billion were pledged to secure public deposits and other borrowings at both March 31, 2018 and December 31, 2017 . Information pertaining to securities with gross unrealized losses, aggregated by investment category and length of time that individual securities have been in a continuous loss position, is as follows: March 31, 2018 Less Than Twelve Months Twelve Months or More Total (Dollars in thousands) Gross Unrealized Losses Estimated Fair Value Gross Unrealized Losses Estimated Fair Value Gross Unrealized Losses Estimated Fair Value Securities available for sale: U.S. Treasury securities $ — $ 693 $ — $ — $ — $ 693 U.S. Government-sponsored enterprise obligations (419 ) 29,580 (235 ) 9,765 (654 ) 39,345 Obligations of state and political subdivisions (1,147 ) 96,138 (3,009 ) 66,404 (4,156 ) 162,542 Mortgage-backed securities (68,161 ) 2,847,244 (53,054 ) 1,191,233 (121,215 ) 4,038,477 Other securities (1,138 ) 60,304 — — (1,138 ) 60,304 Total securities available for sale $ (70,865 ) $ 3,033,959 $ (56,298 ) $ 1,267,402 $ (127,163 ) $ 4,301,361 Securities held to maturity: Obligations of state and political subdivisions $ (4,066 ) $ 150,188 $ (54 ) $ 2,976 $ (4,120 ) $ 153,164 Mortgage-backed securities (11 ) 323 (1,003 ) 18,187 (1,014 ) 18,510 Total securities held to maturity $ (4,077 ) $ 150,511 $ (1,057 ) $ 21,163 $ (5,134 ) $ 171,674 December 31, 2017 Less Than Twelve Months Twelve Months or More Total (Dollars in thousands) Gross Unrealized Losses Estimated Fair Value Gross Unrealized Losses Estimated Fair Value Gross Unrealized Losses Estimated Fair Value Securities available for sale: U.S. Government-sponsored enterprise obligations $ (254 ) $ 29,744 $ (152 ) $ 9,848 $ (406 ) $ 39,592 Obligations of state and political subdivisions (326 ) 31,601 (1,167 ) 68,609 (1,493 ) 100,210 Mortgage-backed securities (26,263 ) 2,677,338 (34,765 ) 1,226,058 (61,028 ) 3,903,396 Other securities (914 ) 75,302 — — (914 ) 75,302 Total securities available for sale $ (27,757 ) $ 2,813,985 $ (36,084 ) $ 1,304,515 $ (63,841 ) $ 4,118,500 Securities held to maturity: Obligations of state and political subdivisions $ (263 ) $ 65,817 $ (12 ) $ 3,031 $ (275 ) $ 68,848 Mortgage-backed securities (2 ) 333 (648 ) 19,269 (650 ) 19,602 Total securities held to maturity $ (265 ) $ 66,150 $ (660 ) $ 22,300 $ (925 ) $ 88,450 The Company assessed the nature of the unrealized losses in its portfolio as of March 31, 2018 and December 31, 2017 to determine if there are losses that should be deemed other-than-temporary. In its analysis of these securities, management considered numerous factors to determine whether there were instances where the amortized cost basis of the debt securities would not be fully recoverable, including, but not limited to: • The length of time and extent to which the estimated fair value of the securities was less than their amortized cost; • Whether adverse conditions were present in the operations, geographic area, or industry of the issuer; • The payment structure of the security, including scheduled interest and principal payments, including the issuer’s failures to make scheduled payments, if any, and the likelihood of failure to make scheduled payments in the future; • Changes to the rating of the security by a rating agency; and • Subsequent recoveries or additional declines in fair value after the balance sheet date. Management believes it has considered these factors, as well as all relevant information available, when determining the expected future cash flows of the securities in question. In each instance, management has determined the cost basis of the securities would be fully recoverable. Management also has the intent to hold debt securities until their maturity or anticipated recovery if the security is classified as available for sale. In addition, management does not believe the Company will be required to sell debt securities before the anticipated recovery of the amortized cost basis of the security. As a result of the Company's analysis, no declines in the estimated fair value of the Company's investment securities were deemed to be other-than-temporary at March 31, 2018 or December 31, 2017 . At March 31, 2018 , 635 debt securities had unrealized losses of 2.87% of the securities’ amortized cost basis. At December 31, 2017 , 544 debt securities had unrealized losses of 1.52% of the securities’ amortized cost basis. The unrealized losses for each of the securities related to market interest rate changes and not credit concerns of the issuers. Additional information on securities that have been in a continuous loss position for over twelve months at March 31, 2018 and December 31, 2017 is presented in the following table. (Dollars in thousands) March 31, 2018 December 31, 2017 Number of securities: Mortgage-backed securities 184 181 Obligations of state and political subdivisions 28 28 Other 1 1 213 210 Amortized Cost Basis: Mortgage-backed securities $ 1,263,477 $ 1,280,739 Obligations of state and political subdivisions 72,443 72,820 Other 10,000 10,000 $ 1,345,920 $ 1,363,559 Unrealized Loss: Mortgage-backed securities $ 54,057 $ 35,412 Obligations of state and political subdivisions 3,063 1,180 Other 235 152 $ 57,355 $ 36,744 The securities noted above carry a rating of AA+/Aaa by S&P and Moody's. The amortized cost and estimated fair value of investment securities by maturity at March 31, 2018 are presented in the following table. Securities are classified according to their contractual maturities without consideration of principal amortization, potential prepayments or call options. Accordingly, actual maturities may differ from contractual maturities. Weighted average yields are calculated on the basis of the yield to maturity based on the amortized cost of each security. Securities Available for Sale Securities Held to Maturity (Dollars in thousands) Weighted Amortized Estimated Weighted Amortized Estimated Within one year or less 2.06 % $ 6,667 $ 6,670 3.04 % $ 1,445 $ 1,448 One through five years 2.04 134,449 132,594 2.98 8,369 8,370 After five through ten years 2.36 887,796 868,090 2.66 45,690 45,450 Over ten years 2.38 3,639,113 3,535,132 2.56 168,737 164,600 2.38 % $ 4,668,025 $ 4,542,486 2.60 % $ 224,241 $ 219,868 The following is a summary of realized gains and losses from the sale of securities classified as available for sale. Gains or losses on securities sold are recorded on the trade date, using the specific identification method. Three Months Ended March 31, (Dollars in thousands) 2018 2017 Realized gains $ 9 $ — Realized losses (68 ) — $ (59 ) $ — In addition to the gains above, the Company realized certain gains on calls of securities held to maturity that were not significant to the consolidated financial statements. Other Equity Securities The Company accounts for the following securities at cost less impairment plus or minus any observable price changes, which approximates fair value, with the exception of CRA and Community Development Investment Funds, which are recorded at fair value. Other Equity Securities, which are presented in “other assets” on the consolidated balance sheets, are as follows: (Dollars in thousands) March 31, 2018 December 31, 2017 Federal Home Loan Bank (FHLB) stock $ 90,561 $ 95,171 Federal Reserve Bank (FRB) stock 79,191 79,191 CRA and Community Development Investment Funds 9,801 — Other investments 9,705 3,008 $ 189,258 $ 177,370

Allowance for Credit Losses and

Allowance for Credit Losses and Credit Quality	3 Months Ended
	Mar. 31, 2018
Receivables [Abstract]
Allowance for Credit Losses and Credit Quality	ALLOWANCE FOR CREDIT LOSSES AND CREDIT QUALITY Allowance for Credit Losses Activity A summary of changes in the allowance for credit losses for the three months ended March 31 is as follows: (Dollars in thousands) 2018 2017 Allowance for credit losses Allowance for loan and lease losses at beginning of period $ 140,891 $ 144,719 Provision for loan and lease losses 7,986 6,154 Transfer of balance to OREO and other (47 ) 73 Charge-offs (9,116 ) (7,291 ) Recoveries 4,813 1,235 Allowance for loan and lease losses at end of period $ 144,527 $ 144,890 Reserve for unfunded commitments at beginning of period $ 13,208 $ 11,241 Provision for unfunded lending commitments 224 419 Reserve for unfunded commitments at end of period $ 13,432 $ 11,660 Allowance for credit losses at end of period $ 157,959 $ 156,550 A summary of changes in the allowance for credit losses, by loan portfolio type, for the three months ended March 31 is as follows: 2018 (Dollars in thousands) Commercial Real Estate Commercial and Industrial Residential Mortgage Consumer Total Allowance for loan and lease losses at beginning of period $ 54,201 $ 53,916 $ 9,117 $ 23,657 $ 140,891 Provision for (Reversal of) loan and lease losses 6,377 294 (686 ) 2,001 7,986 Transfer of balance to OREO and other (47 ) — — — (47 ) Charge-offs (114 ) (5,378 ) (105 ) (3,519 ) (9,116 ) Recoveries 191 3,698 22 902 4,813 Allowance for loan and lease losses at end of period $ 60,608 $ 52,530 $ 8,348 $ 23,041 $ 144,527 Reserve for unfunded commitments at beginning of period $ 4,531 $ 5,309 $ 555 $ 2,813 $ 13,208 Provision for (Reversal of) unfunded commitments 1,476 (1,004 ) (15 ) (233 ) 224 Reserve for unfunded commitments at end of period $ 6,007 $ 4,305 $ 540 $ 2,580 $ 13,432 Allowance on loans individually evaluated for impairment $ 2,506 $ 14,040 $ 178 $ 2,974 $ 19,698 Allowance on loans collectively evaluated for impairment 35,871 36,208 2,073 16,544 90,696 Allowance on loans acquired with deteriorated credit quality 22,231 2,282 6,097 3,523 34,133 Loans and leases, net of unearned income: Balance at end of period $ 9,248,951 $ 5,325,682 $ 3,971,067 $ 3,160,390 $ 21,706,090 Balance at end of period individually evaluated for impairment 78,489 78,725 6,041 33,277 196,532 Balance at end of period collectively evaluated for impairment 8,946,138 5,211,736 3,826,721 3,043,085 21,027,680 Balance at end of period acquired with deteriorated credit quality 224,324 35,221 138,305 84,028 481,878 2017 (Dollars in thousands) Commercial Real Estate Commercial and Industrial Residential Mortgage Consumer Total Allowance for loan losses at beginning of period $ 49,231 $ 60,939 $ 11,249 $ 23,300 $ 144,719 Provision for (Reversal of) loan and lease losses 1,786 2,557 (1,060 ) 2,871 6,154 Transfer of balance to OREO and other 377 (350 ) 2 44 73 Charge-offs (95 ) (3,762 ) (22 ) (3,412 ) (7,291 ) Recoveries 196 84 43 912 1,235 Allowance for loan losses at end of period $ 51,495 $ 59,468 $ 10,212 $ 23,715 $ 144,890 Reserve for unfunded commitments at beginning of period $ 3,207 $ 4,537 $ 657 $ 2,840 $ 11,241 Provision for (Reversal of) unfunded commitments 1,379 (885 ) (49 ) (26 ) 419 Reserve for unfunded commitments at end of period $ 4,586 $ 3,652 $ 608 $ 2,814 $ 11,660 Allowance on loans individually evaluated for impairment $ 1,916 $ 25,056 $ 113 $ 1,724 $ 28,809 Allowance on loans collectively evaluated for impairment 26,872 32,383 3,907 17,764 80,926 Allowance on loans acquired with deteriorated credit quality 22,707 2,029 6,192 4,227 35,155 Loans, net of unearned income: Balance at end of period $ 7,021,341 $ 3,975,734 $ 1,296,358 $ 2,838,769 $ 15,132,202 Balance at end of period individually evaluated for impairment 74,351 164,405 5,048 25,308 269,112 Balance at end of period collectively evaluated for impairment 6,687,651 3,778,775 1,176,017 2,723,308 14,365,751 Balance at end of period acquired with deteriorated credit quality 259,339 32,554 115,293 90,153 497,339 Portfolio Segment Risk Factors Commercial real estate loans include loans to commercial customers for long-term financing of land and buildings or for land development or construction of a building. These loans are repaid through revenues from operations of the businesses, rents of properties, sales of properties and refinances. Commercial and industrial loans and leases represent loans to commercial customers to finance general working capital needs, equipment purchases and leases and other projects where repayment is derived from cash flows resulting from business operations. The Company originates commercial business loans on a secured and, to a lesser extent, unsecured basis. Residential mortgage loans consist of loans to consumers to finance a primary residence. The vast majority of the residential mortgage loan portfolio is comprised of non-conforming 1-4 family mortgage loans secured by properties located in the Company's market areas and originated under terms and documentation that permit their sale in a secondary market. Consumer loans are offered by the Company in order to provide a full range of retail financial services to its customers and include home equity, credit card and other direct consumer installment loans. The Company originates substantially all of its consumer loans in its primary market areas. Loans in the consumer segment are sensitive to unemployment and other key consumer economic measures. Credit Quality The Company utilizes an asset risk classification system in accordance with guidelines established by the Federal Reserve Board as part of its efforts to monitor commercial asset quality. “Special mention” loans are defined as loans with potential weaknesses that may, if not corrected, result in future deterioration of the loan. Special mention loans do not expose the Company to sufficient risk to warrant adverse classification. For problem assets with identified credit issues, the Company has two primary classifications: “substandard” and “doubtful.” Substandard assets have one or more defined weaknesses and are characterized by the distinct possibility that the Company will sustain some loss if the deficiencies are not corrected. Doubtful assets have the weaknesses of substandard assets with the additional characteristic that the weaknesses make collection or liquidation in full satisfaction of the loan balance outstanding questionable, which makes probability of loss higher based on currently existing facts, conditions, and values. Loans classified as “Pass” do not meet the criteria set forth for special mention, substandard, or doubtful classification and are not considered criticized. Asset risk classifications are determined at origination or acquisition and reviewed on an ongoing basis. Risk classifications are changed if, in the opinion of management, the risk profile of the customer has changed since the last review of the loan relationship. The Company’s investment in loans by credit quality indicator is presented in the following tables. Asset risk classifications for commercial loans and leases reflect the classification as of March 31, 2018 and December 31, 2017. Credit quality information in the tables below includes total loans acquired (including acquired impaired loans) at the net loan balance, after the application of premiums/discounts, at March 31, 2018 and December 31, 2017. Loan premiums/discounts represent the adjustment of acquired loans to fair value at the acquisition date, as adjusted for income accretion and changes in cash flow estimates in subsequent periods. Loan premiums/discounts include preliminary discounts recorded on acquired Sabadell United and Gibraltar loans, which are subject to change upon receipt of final fair value estimates during the measurement period. Loan delinquency is the primary credit quality indicator that the Company utilizes to monitor consumer asset quality. March 31, 2018 December 31, 2017 (Dollars in thousands) Pass Special Mention Sub- Doubtful Total Pass Special Mention Sub- Doubtful Loss Total Commercial real estate - construction $ 1,153,604 $ 16,399 $ 29,610 $ 12 $ 1,199,625 $ 1,189,490 $ 20,351 $ 30,541 $ 14 $ — $ 1,240,396 Commercial real estate - owner-occupied 2,464,072 83,356 56,409 8,407 2,612,244 2,388,715 82,114 56,590 2,466 — 2,529,885 Commercial real estate- non-owner-occupied 5,335,816 45,905 51,089 4,272 5,437,082 5,104,074 19,311 42,702 1,744 118 5,167,949 Commercial and industrial 5,124,676 55,041 107,126 38,839 5,325,682 4,882,554 88,149 128,961 35,403 — 5,135,067 Total $ 14,078,168 $ 200,701 $ 244,234 $ 51,530 $ 14,574,633 $ 13,564,833 $ 209,925 $ 258,794 $ 39,627 $ 118 $ 14,073,297 March 31, 2018 December 31, 2017 (Dollars in thousands) Current 30+ Days Past Due Total Current 30+ Days Past Due Total Residential mortgage $ 3,859,751 $ 111,316 $ 3,971,067 $ 2,962,043 $ 94,309 $ 3,056,352 Consumer - home equity 2,376,171 45,015 2,421,186 2,250,205 42,070 2,292,275 Consumer - indirect automobile 48,587 2,084 50,671 59,836 2,857 62,693 Consumer - credit card 92,497 764 93,261 95,263 1,105 96,368 Consumer - other 589,098 6,174 595,272 490,399 6,797 497,196 Total $ 6,966,104 $ 165,353 $ 7,131,457 $ 5,857,746 $ 147,138 $ 6,004,884 Impaired Loans Information on the Company’s investment in impaired loans, which include all TDRs and all other non-accrual loans evaluated or measured individually for impairment for purposes of determining the ALLL, is presented in the following tables as of and for the periods indicated. March 31, 2018 December 31, 2017 Unpaid Principal Balance Recorded Investment Related Allowance Unpaid Principal Balance Recorded Investment Related Allowance (Dollars in thousands) With no related allowance recorded: Commercial real estate- construction $ 11,153 $ 11,153 $ — $ 13,763 $ 13,013 $ — Commercial real estate- owner-occupied 43,562 36,042 — 50,867 44,482 — Commercial real estate- non-owner-occupied 10,575 10,449 — 15,370 14,975 — Commercial and industrial 45,720 36,829 — 103,013 70,254 — Residential mortgage 1,083 1,083 — 2,004 2,001 — Consumer - home equity 31 31 — 5,906 5,634 — Consumer -other — — — 75 75 — With an allowance recorded: Commercial real estate- construction 236 154 (18 ) 238 156 (19 ) Commercial real estate- owner-occupied 17,536 17,419 (1,860 ) 13,314 13,287 (949 ) Commercial real estate- non-owner-occupied 3,399 3,272 (628 ) 6,051 5,872 (620 ) Commercial and industrial 46,705 41,896 (14,040 ) 35,306 32,162 (12,736 ) Residential mortgage 5,357 4,958 (178 ) 5,179 4,748 (172 ) Consumer - home equity 28,917 28,187 (2,435 ) 27,189 26,575 (2,358 ) Consumer - indirect automobile 1,004 656 (75 ) 1,034 679 (79 ) Consumer - other 4,493 4,403 (464 ) 4,320 4,214 (419 ) Total $ 219,771 $ 196,532 $ (19,698 ) $ 283,629 $ 238,127 $ (17,352 ) Total commercial loans and leases $ 178,886 $ 157,214 $ (16,546 ) $ 237,922 $ 194,201 $ (14,324 ) Total mortgage loans 6,440 6,041 (178 ) 7,183 6,749 (172 ) Total consumer loans 34,445 33,277 (2,974 ) 38,524 37,177 (2,856 ) Three Months Ended March 31, 2018 Three Months Ended March 31, 2017 Average Interest Average Interest (Dollars in thousands) With no related allowance recorded: Commercial real estate- construction $ 10,470 $ 144 $ — $ — Commercial real estate- owner-occupied 36,277 334 37,197 339 Commercial real estate- non-owner-occupied 10,557 98 5,988 17 Commercial and industrial 27,832 385 90,664 448 Residential mortgage 1,090 12 735 5 Consumer - home equity 32 — 4,158 40 With an allowance recorded: Commercial real estate- construction 153 1 1,984 1 Commercial real estate- owner-occupied 17,608 112 20,980 79 Commercial real estate- non-owner-occupied 3,302 10 8,587 94 Commercial and industrial 44,056 196 78,695 220 Residential mortgage 4,974 44 4,335 42 Consumer - home equity 28,203 292 16,713 179 Consumer - indirect automobile 717 5 767 7 Consumer - other 4,483 62 3,328 52 Total $ 189,754 $ 1,695 $ 274,131 $ 1,523 Total commercial loans and leases $ 150,255 $ 1,280 $ 244,095 $ 1,198 Total mortgage loans 6,064 56 5,070 47 Total consumer loans 33,435 359 24,966 278 As of March 31, 2018 and December 31, 2017, the Company was not committed to lend a material amount of additional funds to any customer whose loan was classified as impaired or as a troubled debt restructuring.

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	3 Months Ended
	Mar. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangible Assets	GOODWILL AND OTHER INTANGIBLE ASSETS Goodwill Changes to the carrying amount of goodwill by reporting unit for the three months ended March 31, 2018, and the year ended December 31, 2017 are provided in the following table. (Dollars in thousands) IBERIABANK Mortgage LTC Total Balance, December 31, 2016 $ 698,513 $ 23,178 $ 5,165 $ 726,856 Goodwill acquired during the year (preliminary allocation) 462,046 — — 462,046 Balance, December 31, 2017 $ 1,160,559 $ 23,178 $ 5,165 $ 1,188,902 Goodwill acquired during the year (preliminary allocation) and adjustments 43,887 — 3,380 47,267 Balance, March 31, 2018 $ 1,204,446 $ 23,178 $ 8,545 $ 1,236,169 On March 23, 2018 the Company completed its acquisition of Gibraltar. In connection with the acquisition, the Company recorded $42.5 million of goodwill based on preliminary adjustments. On January 12, 2018, the Company's subsidiary, LTC, completed its acquisition of SolomonParks. In connection with the acquisition, LTC recorded $3.4 million of goodwill based on preliminary adjustments. In addition, goodwill adjustments were made during the first three months of 2018 as a result of measurement period updates to the preliminary fair value estimates related to the 2017 acquisition of Sabadell United. See Note 3 for additional information regarding these acquisitions. The Company performed the required annual goodwill impairment test as of October 1, 2017. The Company’s annual impairment test did not indicate impairment in any of the Company’s reporting units as of the testing date. Following the testing date, management evaluated the events and changes that could indicate that goodwill might be impaired and concluded that a subsequent interim test was not necessary. Mortgage Servicing Rights Mortgage servicing rights are recorded at the lower of cost or market value in “other intangible assets” on the Company's consolidated balance sheets and amortized over the remaining servicing life of the loans, with consideration given to prepayment assumptions. Mortgage servicing rights had the following carrying values as of the periods indicated: March 31, 2018 December 31, 2017 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount (Dollars in thousands) Mortgage servicing rights $ 10,030 $ (4,128 ) $ 5,902 $ 9,588 $ (3,931 ) $ 5,657 In addition, there was an insignificant amount of non-mortgage servicing rights related to SBA loans as of March 31, 2018 and December 31, 2017, respectively. Title Plant The Company held title plant assets recorded in “other intangible assets” on the Company's consolidated balance sheets totaling $6.8 million on March 31, 2018 and $6.7 million on December 31, 2017. The increase in title plant assets was the result of the SolomonParks acquisition during the first quarter of 2018. No events or changes in circumstances occurred during the three months ended March 31, 2018 to suggest the carrying value of the title plant was not recoverable. Intangible assets subject to amortization In connection with the acquisition of Gibraltar, the Company recorded $18.5 million of core deposit intangible assets. Core deposit intangible assets are subject to amortization over a ten year period. In connection with the acquisition of SolomonParks, the Company recorded $155.9 thousand of non-compete agreement intangible assets. Non-compete agreement intangible assets are subject to amortization over a five year period. Definite-lived intangible assets had the following carrying values included in “other intangible assets” on the Company’s consolidated balance sheets as of the periods indicated: March 31, 2018 December 31, 2017 (Dollars in thousands) Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Core deposit intangible assets $ 136,183 $ (46,736 ) $ 89,447 $ 127,957 $ (51,971 ) $ 75,986 Customer relationship intangible asset 1,385 (1,262 ) 123 1,143 (996 ) 147 Non-compete agreement 206 (36 ) 170 63 (39 ) 24 Total $ 137,774 $ (48,034 ) $ 89,740 $ 129,163 $ (53,006 ) $ 76,157

Derivative Instruments and Othe

Derivative Instruments and Other Hedging Activities	3 Months Ended
	Mar. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments and Other Hedging Activities	DERIVATIVE INSTRUMENTS AND OTHER HEDGING ACTIVITIES The Company enters into derivative financial instruments to manage interest rate risk, exposures related to liquidity and credit risk, and to facilitate customer transactions. The primary types of derivatives used by the Company include interest rate swap agreements, foreign exchange contracts, interest rate lock commitments, forward sales commitments, written and purchased options and credit derivatives. All derivative instruments are recognized on the consolidated balance sheets as "other assets" or "other liabilities" at fair value, as required by ASC Topic 815, Derivatives and Hedging . For cash flow hedges, the effective and ineffective portions of the gain or loss related to the derivative instrument is initially reported as a component of other comprehensive income and subsequently reclassified into earnings when the forecasted transaction affects earnings or when the hedge is terminated, per the Company’s early adoption of ASU No. 2017-12, Derivatives and Hedging (ASC 815): Targeted Improvements to Accounting for Hedging Activities, as of January 1, 2018. In applying hedge accounting for derivatives, the Company establishes and documents a method for assessing the effectiveness of the hedging derivative and a measurement approach for determining the ineffective aspect of the hedge upon the inception of the hedge. The Company has designated interest rate swaps in a cash flow hedge to convert forecasted variable interest payments to a fixed rate on its junior subordinated debt and has concluded that the forecasted transactions are probable of occurring. For derivative instruments that are not designated as hedging instruments, changes in the fair value of the derivatives are recognized in earnings immediately. Information pertaining to outstanding derivative instruments is as follows: Balance Sheet Location Derivative Assets - Fair Value Balance Sheet Location Derivative Liabilities - Fair Value (Dollars in thousands) March 31, 2018 December 31, 2017 March 31, 2018 December 31, 2017 Derivatives designated as hedging instruments under ASC Topic 815: Interest rate contracts Other assets $ — $ — Other liabilities $ — $ — Total derivatives designated as hedging instruments under ASC Topic 815 $ — $ — $ — $ — Derivatives not designated as hedging instruments under ASC Topic 815: Interest rate contracts Other assets $ 5,827 $ 20,446 Other liabilities $ 25,771 $ 16,191 Foreign exchange contracts Other assets 2 7 Other liabilities 2 7 Forward sales contracts Other assets 2,851 136 Other liabilities 703 279 Written and purchased options Other assets 8,383 10,654 Other liabilities 5,667 8,656 Other contracts Other assets 9 22 Other liabilities 11 21 Total derivatives not designated as hedging instruments under ASC Topic 815 $ 17,072 $ 31,265 $ 32,154 $ 25,154 Total $ 17,072 $ 31,265 $ 32,154 $ 25,154 Derivative Assets - Notional Amount Derivative Liabilities - Notional Amount (Dollars in thousands) March 31, 2018 December 31, 2017 March 31, 2018 December 31, 2017 Derivatives designated as hedging instruments under ASC Topic 815: Interest rate contracts $ 108,500 $ — $ — $ 108,500 Total derivatives designated as hedging instruments under ASC Topic 815 $ 108,500 $ — $ — $ 108,500 Derivatives not designated as hedging instruments under ASC Topic 815: Interest rate contracts $ 1,356,990 $ 1,218,464 $ 1,276,990 $ 1,218,464 Foreign exchange contracts 628 268 628 268 Forward sales contracts 96,810 82,347 215,918 142,578 Written and purchased options 339,852 278,638 164,341 165,198 Other contracts 29,676 29,755 71,889 86,744 Total derivatives not designated as hedging instruments under ASC Topic 815 $ 1,823,956 $ 1,609,472 $ 1,729,766 $ 1,613,252 Total $ 1,932,456 $ 1,609,472 $ 1,729,766 $ 1,721,752 The Company has entered into risk participation agreements with counterparties to transfer or assume credit exposures related to interest rate derivatives. The notional amounts of risk participation agreements sold were $71.9 million and $86.7 million at March 31, 2018 and December 31, 2017, respectively. Assuming all underlying third party customers referenced in the swap contracts defaulted at March 31, 2018 and December 31, 2017, the exposure from these agreements would not be material based on the fair value of the underlying swaps. The Company is party to collateral agreements with certain derivative counterparties. Such agreements require that the Company maintain collateral based on the fair values of individual derivative transactions. In the event of default by the Company, the counterparty would be entitled to the collateral. At March 31, 2018, the Company was not required to post collateral due to the Company's derivative position at the balance sheet date. At December 31, 2017, the Company was required to post $552 thousand in cash or securities as collateral for its derivative transactions, which is included in "interest-bearing deposits in banks" on the Company’s consolidated balance sheets. Effective January 3, 2017, the Chicago Mercantile Exchange and LCH.Clearnet Limited amended their rulebooks to legally characterize variation margin payments for over-the-counter derivatives they clear as settlements of the derivatives' exposure rather than collateral against the exposures. In light of changes to the aforementioned rulebooks, the Board of Governors of the Federal Reserve System, the Office of the Comptroller of the Currency (OCC) and the FDIC issued guidance effective August 14, 2017, which is consistent with the SEC's accounting guidance, that allows institutions to treat centrally-cleared derivatives as settled for purposes of the capital rule. At March 31, 2018 and December 31, 2017, the Company was required to post $28.8 million and $5.1 million , respectively, in variation margin payments for its derivative transactions, which is now required to be netted against the fair value of the derivatives in "other assets/other liabilities" on the consolidated balance sheets. The Company does not anticipate additional assets will be required to be posted as collateral, nor does it believe additional assets would be required to settle its derivative instruments immediately if contingent features were triggered at March 31, 2018. The Company’s master netting agreements represent written, legally enforceable bilateral agreements that (1) create a single legal obligation for all individual transactions covered by the master agreement and (2) in the event of default, provide the non-defaulting counterparty the right to accelerate, terminate, and close-out on a net basis all transactions under the agreement and to promptly liquidate or set-off collateral posted by the defaulting counterparty. As permitted by U.S. GAAP, the Company does not offset fair value amounts recognized for the right to reclaim cash collateral or the obligation to return cash collateral against recognized fair value amounts of derivatives executed with the same counterparty under a master netting agreement. The following table reconciles the gross amounts presented in the consolidated balance sheets to the net amounts that would result in the event of offset. March 31, 2018 Gross Amounts Presented in the Balance Sheet Gross Amounts Not Offset in the Balance Sheet Net (Dollars in thousands) Derivatives Collateral (1) Derivatives subject to master netting arrangements Derivative assets Interest rate contracts not designated as hedging instruments $ 5,827 $ (548 ) $ — $ 5,279 Written and purchased options 5,656 — — 5,656 Total derivative assets subject to master netting arrangements $ 11,483 $ (548 ) $ — $ 10,935 Derivative liabilities Interest rate contracts designated as hedging instruments $ — $ — $ — $ — Interest rate contracts not designated as hedging instruments 25,771 (548 ) — 25,223 Written and purchased options 5,587 — — 5,587 Total derivative liabilities subject to master netting arrangements $ 31,358 $ (548 ) $ — $ 30,810 (1) Consists of cash collateral recorded at cost, which approximates fair value, and investment securities. December 31, 2017 Gross Amounts Presented in the Balance Sheet Gross Amounts Not Offset in the Balance Sheet Net (Dollars in thousands) Derivatives Collateral (1) Derivatives subject to master netting arrangements Derivative assets Interest rate contracts not designated as hedging instruments $ 20,446 $ (12,469 ) $ — $ 7,977 Written and purchased options 8,610 — — 8,610 Total derivative assets subject to master netting arrangements $ 29,056 $ (12,469 ) $ — $ 16,587 Derivative liabilities Interest rate contracts designated as hedging instruments $ — $ — $ — $ — Interest rate contracts not designated as hedging instruments 16,191 (12,469 ) (552 ) 3,170 Total derivative liabilities subject to master netting arrangements $ 16,191 $ (12,469 ) $ (552 ) $ 3,170 (1) Consists of cash collateral recorded at cost, which approximates fair value, and investment securities. During the three months ended March 31, 2018 and 2017 , the Company has not reclassified into earnings any gain or loss as a result of the discontinuance of cash flow hedges, because it was probable the original forecasted transaction would not occur by the end of the originally specified term. At March 31, 2018 , the Company does not expect to reclassify a material amount from accumulated other comprehensive income into interest income over the next twelve months for derivatives that will be settled. At March 31, 2018 and 2017 , and for the three months then ended, information pertaining to the effect of the hedging instruments on the consolidated financial statements is as follows: Location of Gain (Loss) Recognized in Income on Derivative (Amount Excluded from Effectiveness Testing) Amount of Gain (Loss) Recognized in Income on Derivative (Amount Excluded from Effectiveness Testing) Amount of Gain (Loss) Recognized in OCI, net of taxes Location of Gain (Loss) Reclassified from Accumulated OCI into Income Amount of Gain (Loss) Reclassified from Accumulated OCI into Income, net of taxes (Dollars in thousands) For the Three Months Ended March 31 Derivatives in ASC Topic 815 Cash Flow Hedging Relationships 2018 2017 2018 2017 2018 2017 Interest rate contracts $ 2,549 $ 73 Interest expense $ (116 ) $ (45 ) Interest expense $ — $ — Total $ 2,549 $ 73 $ (116 ) $ (45 ) $ — $ — Information pertaining to the effect of derivatives not designated as hedging instruments on the consolidated financial statements as of March 31, is as follows: Location of Gain (Loss) Recognized in Income on Derivatives Amount of Gain (Loss) Recognized in Income on Derivatives For the Three Months Ended March 31 (Dollars in thousands) 2018 2017 Interest rate contracts (1) Other income $ 1,049 $ 1,117 Foreign exchange contracts Other income 5 7 Forward sales contracts Mortgage income 3,387 (360 ) Written and purchased options Mortgage income 648 655 Other contracts Other income (3 ) 4 Total $ 5,086 $ 1,423 (1) Includes fees associated with customer interest rate contracts.

Income Taxes (Notes)

Income Taxes (Notes)	3 Months Ended
	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income Tax Disclosure [Text Block]	INCOME TAXES The Company's provision for income taxes for the three months ended March 31, 2018 and 2017 is based on the estimated annual effective tax rate, plus discrete items. The following table presents the provision for income taxes and the effective tax rates for the three months ended March 31, 2018 and 2017: Three Months Ended March 31, (Dollars in thousands) 2018 2017 Income before income tax expense $ 81,173 $ 72,992 Income tax expense 17,552 22,519 Effective tax rate 21.6 % 30.9 % The difference between the Company's effective tax rates for the three months ended March 31, 2018 and 2017 and the U.S. statutory tax rates of 21% and 35%, respectively, primarily relates to tax-exempt income, non-deductible expenses, state income taxes (net of federal income tax benefit), and the recognition of tax credits. The effective tax rate may vary significantly due to fluctuations in the amount and source of pretax income, changes in amounts of non-deductible expenses, and timing of the recognition of tax credits. Provisional amounts in effective tax rate On December 22, 2017, President Trump signed the Tax Cuts and Jobs Act (the "Tax Act") into law. Under ASC 740, the effects of changes in tax rates and laws are recognized in the period in which the new legislation is enacted. In the case of U.S. federal income taxes, the enactment date is the date the bill becomes law (i.e., upon presidential signature). Among other provisions, the most significant to the Company is the reduction of the corporate income tax rate from 35% to 21%. With respect to the legislation, the Company recognized a provisional one-time increase in tax expense of $51.0 million as of December 31, 2017 due to a re-measurement of deferred tax assets and liabilities resulting from the decrease in the corporate income tax rate. During the three months ended March 31, 2018, the Company made no adjustment to the provisional amounts recorded at December 31, 2017, and the accounting for the tax effects of the Tax Act remain incomplete as of March 31, 2018. The Company is in the process of analyzing certain aspects of the Tax Act, obtaining additional information, and refining its calculations, which could potentially affect the measurement of these balances. Information which could result in adjustment to the provisional amount includes, but is not limited to, provisional deferred tax amounts acquired in the Sabadell United acquisition, elections or changes in IRS tax methods, and further analysis of tax positions. Our estimates may also be affected as we gain a more thorough understanding of the Tax Act. Consistent with the guidance provided under ASC 740, the Company recorded impacts from enactment of the Tax Act in the fourth quarter of 2017 subject to Staff Accounting Bulletin 118, Income Tax Accounting Implications of the Tax Cuts and Jobs Act ("SAB 118"). SAB 118 provides a measurement period not to extend beyond one year of the enactment date to adjust the accounting for certain elements of the tax reform.

Shareholders' Equity, Capital R

Shareholders' Equity, Capital Ratios and Other Regulatory Matters	3 Months Ended
	Mar. 31, 2018
Banking and Thrift [Abstract]
Shareholders' Equity, Capital Ratios and Other Regulatory Matters	SHAREHOLDERS' EQUITY, CAPITAL RATIOS AND OTHER REGULATORY MATTERS Preferred Stock The following table presents a summary of the Company's non-cumulative perpetual preferred stock: March 31, 2018 December 31, 2017 Issuance Date Earliest Redemption Date Annual Dividend Rate Liquidation Amount Carrying Amount Carrying Amount (Dollars in thousands) Series B Preferred Stock 8/5/2015 8/1/2025 6.625 % $ 80,000 $ 76,812 $ 76,812 Series C Preferred Stock 5/9/2016 5/1/2026 6.600 % 57,500 55,285 55,285 $ 137,500 $ 132,097 $ 132,097 Common Stock During the second quarter of 2016, the Company's Board of Directors authorized the repurchase of up to 950,000 shares of IBERIABANK Corporation's outstanding common stock. Stock repurchases under this program will be made from time to time, on the open market or in privately negotiated transactions. The timing of these repurchases will depend on market conditions and other requirements. The share repurchase program does not obligate the Company to repurchase any dollar amount or number of shares, and expires during the second quarter of 2018. The program may be extended, modified, suspended, or discontinued at any time. The Company did not repurchase any shares during the quarter ended March 31, 2018. At March 31, 2018, the remaining common shares that could be repurchased under the plan approved by the Board was 747,494 shares. Subsequent to quarter end and through May 7, 2018, the Company repurchased 180,000 common shares for approximately $13.7 million . On March 23, 2018, as part of the Gibraltar acquisition, the Company issued 2,787,773 shares of common stock. The aggregate value of the acquisition consideration paid by the Company at the time of closing was approximately $214.7 million based on the Company's closing common stock price of $77.00 per share on March 23, 2018. Gibraltar common shareholders received 1.9749 shares of IBERIABANK Corporation common stock for each outstanding share of Gibraltar common stock. Refer to Note 3, Acquisition Activity, for further detail regarding the Gibraltar acquisition. Regulatory Capital The Company and IBERIABANK are subject to various regulatory capital requirements administered by the federal and state banking agencies. Failure to meet minimum capital requirements can initiate certain mandatory and possibly additional discretionary actions by regulators that, if undertaken, could have a direct material effect on the Company’s consolidated financial statements. Under capital adequacy regulations and the regulatory framework for prompt corrective action, the Company and IBERIABANK, as applicable, must meet specific capital guidelines that involve quantitative measures of their assets, liabilities and certain off-balance sheet items as calculated under regulatory accounting practices. The capital amounts and classification are also subject to qualitative judgments by the regulators about components, risk weightings and other factors. Management believes that, as of March 31, 2018, the Company and IBERIABANK met all capital adequacy requirements to which they are subject. As of March 31, 2018, the most recent notification from the FRB categorized IBERIABANK as well-capitalized under the regulatory framework for prompt corrective action (the prompt corrective action requirements are not applicable to the Company). To be categorized as well-capitalized, an institution must maintain minimum total risk-based, Tier 1 risk-based and Tier 1 leverage ratios as set forth in the following table. There are no conditions or events since the notification that management believes have changed that categorization. The Company’s and IBERIABANK’s actual capital amounts and ratios as of March 31, 2018 and December 31, 2017 are presented in the following tables. (Dollars in thousands) March 31, 2018 Minimum Well-Capitalized Actual Amount Ratio Amount Ratio Amount Ratio Tier 1 Leverage Consolidated $ 1,076,933 4.00 % N/A N/A $ 2,685,315 9.97 % IBERIABANK 1,074,579 4.00 1,343,223 5.00 2,640,916 9.83 Common Equity Tier 1 (CET1) (1) Consolidated $ 1,067,284 4.50 % N/A N/A $ 2,553,218 10.77 % IBERIABANK 1,065,059 4.50 1,538,418 6.50 2,640,916 11.16 Tier 1 Risk-Based Capital (1) Consolidated $ 1,423,046 6.00 % N/A N/A $ 2,685,315 11.32 % IBERIABANK 1,420,078 6.00 1,893,437 8.00 2,640,916 11.16 Total Risk-Based Capital (1) Consolidated $ 1,897,394 8.00 % N/A N/A $ 2,959,774 12.48 % IBERIABANK 1,893,437 8.00 2,366,797 10.00 2,798,875 11.83 December 31, 2017 Minimum Well-Capitalized Actual Amount Ratio Amount Ratio Amount Ratio Tier 1 Leverage Consolidated $ 1,073,381 4.00 % N/A N/A $ 2,509,496 9.35 % IBERIABANK 1,070,789 4.00 1,338,487 5.00 2,437,275 9.10 Common Equity Tier 1 (CET1) (1) Consolidated $ 1,011,732 4.50 % N/A N/A $ 2,377,398 10.57 % IBERIABANK 1,009,553 4.50 1,458,243 6.50 2,437,275 10.86 Tier 1 Risk-Based Capital (1) Consolidated $ 1,348,977 6.00 % N/A N/A $ 2,509,496 11.16 % IBERIABANK 1,346,070 6.00 1,794,760 8.00 2,437,275 10.86 Total Risk-Based Capital (1) Consolidated $ 1,798,635 8.00 % N/A N/A $ 2,780,095 12.37 % IBERIABANK 1,794,760 8.00 2,243,450 10.00 2,591,374 11.55 (1) Minimum capital ratios are subject to a capital conservation buffer. In order to avoid limitations on distributions, including dividend payments, and certain discretionary bonus payments to executive officers, an institution must hold a capital conservation buffer above its minimum risk-based capital requirements. This capital conservation buffer is calculated as the lowest of the differences between the actual CET1 ratio, Tier 1 Risk-Based Capital Ratio, and Total Risk-Based Capital ratio and the corresponding minimum ratios. At March 31, 2018, the required minimum capital conservation buffer was 1.875% , and will increase by 0.625% and be fully phased-in on January 1, 2019 at 2.50% . At March 31, 2018, the capital conservation buffers of the Company and IBERIABANK were 4.48% and 3.83% , respectively.

Earnings Per Share

Earnings Per Share	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Earnings Per Share	EARNINGS PER SHARE Share-based payment awards that entitle holders to receive non-forfeitable dividends before vesting are considered participating securities that are included in the calculation of earnings per share using the two-class method. The two-class method is an earnings allocation formula under which earnings per share is calculated for common stock and participating securities according to dividends declared and participating rights in undistributed earnings. Under this method, all earnings, distributed and undistributed, are allocated to common shares and participating securities based on their respective rights to receive dividends. The following table presents the calculation of basic and diluted earnings per share for the periods indicated. Three Months Ended March 31, (In thousands, except per share data) 2018 2017 Earnings per common share - basic: Net income $ 63,621 $ 50,473 Less: Preferred stock dividends 3,598 3,599 Less: Dividends and undistributed earnings allocated to unvested restricted shares 639 346 Net income allocated to common shareholders - basic $ 59,384 $ 46,528 Weighted average common shares outstanding 53,616 46,123 Earnings per common share - basic 1.11 1.01 Earnings per common share - diluted: Net income allocated to common shareholders - basic $ 59,384 $ 46,528 Adjustment for undistributed earnings allocated to unvested restricted shares (18 ) (37 ) Net income allocated to common shareholders - diluted $ 59,366 $ 46,491 Weighted average common shares outstanding 53,616 46,123 Dilutive potential common shares 351 373 Weighted average common shares outstanding - diluted 53,967 46,496 Earnings per common share - diluted $ 1.10 $ 1.00 For the three months ended March 31, 2018 , and 2017 , the calculations for basic shares outstanding exclude the weighted average shares owned by the Recognition and Retention Plan (“RRP”) of 606,442 and 406,896 , respectively. The effects from the assumed exercises of 156,737 and 70,456 stock options were not included in the computation of diluted earnings per share for the three months ended March 31, 2018 and 2017 , respectively, because such amounts would have had an antidilutive effect on earnings per common share.

Share-Based Compensation

Share-Based Compensation	3 Months Ended
	Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation	SHARE-BASED COMPENSATION The Company has various types of share-based compensation plans that permit the granting of awards in the form of stock options, restricted stock, restricted share units and phantom stock. These plans are administered by the Compensation Committee of the Board of Directors, which selects persons eligible to receive awards and determines the terms, conditions and other provisions of the awards. At March 31, 2018, awards of 1,166,797 shares could be made under approved incentive compensation plans. The Company issues shares to fulfill stock option exercises and restricted share units and restricted stock awards vesting from available authorized common shares. At March 31, 2018, the Company believes there are adequate authorized shares to satisfy anticipated stock option exercises and restricted share unit and restricted stock award vesting. Stock option awards The Company issues stock options under various plans to directors, officers and other key employees. The option exercise price cannot be less than the fair value of the underlying common stock as of the date of the option grant and the maximum option term cannot exceed ten years . The following table represents the activity related to stock options during the periods indicated: Number of Shares Weighted Average Exercise Price Outstanding options, December 31, 2016 721,538 $ 55.38 Granted 70,433 85.52 Exercised (24,457 ) 53.85 Forfeited or expired (12,539 ) 75.77 Outstanding options, March 31, 2017 754,975 $ 57.90 Exercisable options, March 31, 2017 509,347 $ 55.78 Outstanding options, December 31, 2017 686,366 $ 58.24 Granted 92,162 82.20 Exercised (21,212 ) 52.10 Forfeited or expired (14,513 ) 65.27 Outstanding options, March 31, 2018 742,803 $ 61.25 Exercisable options, March 31, 2018 519,496 $ 56.53 The Company uses the Black-Scholes option pricing model to estimate the fair value of stock option awards. The following weighted-average assumptions were used for option awards issued during the following periods: For the Three Months Ended March 31, 2018 2017 Expected dividends 1.8 % 1.7 % Expected volatility 24.3 % 24.9 % Risk-free interest rate 2.7 % 2.1 % Expected term (in years) 5.7 5.6 Weighted-average grant-date fair value $ 18.36 $ 18.75 The assumptions above are based on multiple factors, including historical stock option exercise patterns and post-vesting employment termination behaviors, expected future exercise patterns and the expected volatility of the Company’s stock price. The following table represents the compensation expense that is included in non-interest expense and related income tax benefits in the accompanying consolidated statements of comprehensive income related to stock options for the following periods: For the Three Months Ended March 31, (Dollars in thousands) 2018 2017 Compensation expense related to stock options $ 312 $ 444 Income tax benefit related to stock options 23 68 At March 31, 2018, there was $2.8 million of unrecognized compensation expense related to stock options that is expected to be recognized over a weighted-average period of 3.2 years . Restricted stock awards The Company issues restricted stock under various plans for certain officers and directors. The restricted stock awards may not be sold or otherwise transferred until certain restrictions have lapsed. The holders of the restricted stock receive dividends and have the right to vote the shares. The compensation expense for these awards is determined based on the market price of the Company's common stock at the date of grant applied to the total number of shares granted and is recognized over the vesting period (generally three to five years). As of March 31, 2018 and 2017, unrecognized share-based compensation expense associated with these awards totaled $39.0 million and $21.4 million , respectively. The unrecognized compensation expense related to restricted stock awards at March 31, 2018 is expected to be recognized over a weighted-average period of 1.5 years . Restricted share units During the first three months of 2018 and 2017, the Company issued restricted share units to certain of its executive officers. Restricted share units vest after the end of a three year performance period, based on satisfaction of the market and performance conditions set forth in the restricted share unit agreements. Recipients do not possess voting or investment power over the common stock underlying such units until vesting. The grant date fair value of these restricted share units is the same as the value of the corresponding number of shares of common stock, adjusted for assumptions surrounding the market-based conditions contained in the respective agreements. See Note 1, Summary of Significant Accounting Policies, in the 2017 Annual Report on Form 10-K for the year ended December 31, 2017, for further discussion of restricted share units with market or performance conditions. The following table represents the compensation expense that was included in non-interest expense and related income tax benefits in the accompanying consolidated statements of comprehensive income related to restricted stock awards and restricted share units for the periods indicated: For the Three Months Ended March 31, (Dollars in thousands) 2018 2017 Compensation expense related to restricted stock awards and restricted share units $ 4,422 $ 3,277 Income tax benefit related to restricted stock awards and restricted share units 929 1,147 The following table represents unvested restricted stock award and restricted share unit activity for the following periods: For the Three Months Ended March 31, 2018 2017 Number of shares at beginning of period 738,187 543,258 Granted 199,958 146,175 Forfeited (43,405 ) (4,105 ) Vested (115,877 ) (157,753 ) Number of shares at end of period 778,863 527,575 Phantom stock awards The Company issues phantom stock awards to certain key officers and employees. The awards are subject to a vesting period of five years and are paid out in cash upon vesting. The amount paid per vesting period is calculated as the number of vested “share equivalents” multiplied by the closing market price of a share of the Company’s common stock on the vesting date. Share equivalents are calculated on the date of grant as the total award’s dollar value divided by the closing market price of a share of the Company’s common stock on the grant date. Award recipients are also entitled to a “dividend equivalent” on each unvested share equivalent held by the award recipient. A dividend equivalent is a dollar amount equal to the cash dividends that the participant would have been entitled to receive if the participant’s share equivalents were issued in shares of common stock. Dividend equivalents are reinvested as share equivalents that will vest and be paid out on the same date as the underlying share equivalents on which the dividend equivalents were paid. The number of share equivalents accumulated with a dividend equivalent is determined by dividing the aggregate of dividend equivalents paid on the unvested share equivalents by the closing price of a share of the Company’s common stock on the dividend payment date. The following table indicates compensation expense recorded for phantom stock based on the number of share equivalents vested at March 31 of the periods indicated and the current market price of the Company’s stock at that time: For the Three Months Ended March 31, (Dollars in thousands) 2018 2017 Compensation expense related to phantom stock $ 2,996 $ 3,053 The following table represents phantom stock award activity during the periods indicated. (Dollars in thousands) Number of share equivalents (1) Value of share equivalents (2) Balance, December 31, 2016 472,830 $ 39,600 Granted 96,897 7,665 Forfeited share equivalents (5,330 ) 422 Vested share equivalents (143,643 ) 12,024 Balance, March 31, 2017 420,754 $ 33,282 Balance, December 31, 2017 393,844 $ 30,523 Granted 129,234 10,080 Forfeited share equivalents (24,460 ) 1,908 Vested share equivalents (121,758 ) 10,187 Balance, March 31, 2018 376,860 $ 29,395 (1) Number of share equivalents includes all reinvested dividend equivalents for the periods indicated. (2) Except for share equivalents at the beginning of each period, which are based on the value at that time, and vested share payments, which are based on the cash paid at the time of vesting, the value of share equivalents is calculated based on the market price of the Company’s stock at the end of the respective periods. The market price of the Company’s stock was $78.00 and $79.10 on March 31, 2018, and 2017, respectively.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	FAIR VALUE MEASUREMENTS Recurring fair value measurements The Company has segregated all financial assets and liabilities that are measured at fair value on a recurring basis into the most appropriate level within the fair value hierarchy based on the inputs used to estimate the fair value at the measurement date in the tables below. See Note 1, Summary of Significant Accounting Policies, in the Annual Report on Form 10-K for the year ended December 31, 2017, for a description of how fair value measurements are determined. March 31, 2018 (Dollars in thousands) Level 1 Level 2 Level 3 Total Assets Securities available for sale $ — $ 4,542,486 $ — $ 4,542,486 CRA and Community Development Investment Funds — 9,801 — 9,801 Mortgage loans held for sale — 110,348 — 110,348 Derivative instruments — 17,072 — 17,072 Total $ — $ 4,679,707 $ — $ 4,679,707 Liabilities Derivative instruments $ — $ 32,154 $ — $ 32,154 Total $ — $ 32,154 $ — $ 32,154 December 31, 2017 Level 1 Level 2 Level 3 Total Assets Securities available for sale $ — $ 4,590,062 $ — $ 4,590,062 Mortgage loans held for sale — 134,916 — 134,916 Derivative instruments — 31,265 — 31,265 Total $ — $ 4,756,243 $ — $ 4,756,243 Liabilities Derivative instruments $ — $ 25,154 $ — $ 25,154 Total $ — $ 25,154 $ — $ 25,154 During the three months ended March 31, 2018 , there were no transfers between the Level 1 and Level 2 fair value categories. Non-recurring fair value measurements The Company has segregated all assets and liabilities that are measured at fair value on a non-recurring basis into the most appropriate level within the fair value hierarchy based on the inputs used to determine the fair value at the measurement date in the tables below. March 31, 2018 (Dollars in thousands) Level 1 Level 2 Level 3 Total Assets Loans $ — $ — $ 85,269 $ 85,269 OREO, net — — 2,234 2,234 Total $ — $ — $ 87,503 $ 87,503 December 31, 2017 (Dollars in thousands) Level 1 Level 2 Level 3 Total Assets Loans $ — $ — $ 71,210 $ 71,210 OREO, net — — 3,029 3,029 Total $ — $ — $ 74,239 $ 74,239 The tables above exclude the initial measurement of assets and liabilities that were acquired as part of the Sabadell United acquisition in July of 2017 and the Gibraltar acquisition in March of 2018. These assets and liabilities were recorded at their fair value upon acquisition in accordance with U.S. GAAP and were not re-measured during the periods presented unless specifically required by U.S. GAAP. Acquisition date fair values represent either Level 2 fair value measurements (investment securities, deposits, property, equipment, and debt) or Level 3 fair value measurements (loans and core deposit intangible assets.) Refer to Note 3, Acquisition Activity, for further detail regarding the Sabadell United and Gibraltar acquisitions. In accordance with the provisions of ASC Topic 310, the Company records certain loans considered impaired at their estimated fair value. A loan is considered impaired if it is probable the Company will be unable to collect all amounts due according to the contractual terms of the loan agreement. Fair value is measured at the estimated fair value of the collateral for collateral-dependent loans. The Company did not record any liabilities at fair value for which measurement of the fair value was made on a non-recurring basis as of March 31, 2018 and December 31, 2017 . Fair value option The Company has elected the fair value option for certain originated residential mortgage loans held for sale, which allows for a more effective offset of the changes in fair values of the loans and the derivative instruments used to hedge them without the burden of complying with the requirements for hedge accounting. The Company has $17.0 million and $15.0 million of mortgage loans held for investment for which the fair value option was elected upon origination and continue to be accounted for at fair value at March 31, 2018 and December 31, 2017, respectively. Net gains (losses) resulting from the change in fair value of these loans that were recorded in mortgage income in the consolidated statements of comprehensive income for the three months ended March 31, 2018 and 2017 totaled $(749) thousand and $(409) thousand , respectively. The following table summarizes the difference between the aggregate fair value and the aggregate unpaid principal balance for mortgage loans held for sale measured at fair value: March 31, 2018 December 31, 2017 (Dollars in thousands) Aggregate Fair Value Aggregate Unpaid Principal Aggregate Fair Value Less Unpaid Principal Aggregate Fair Value Aggregate Unpaid Principal Aggregate Fair Value Less Unpaid Principal Mortgage loans held for sale, at fair value $ 110,348 $ 107,849 $ 2,499 $ 134,916 $ 131,276 $ 3,640 Interest income on mortgage loans held for sale is recognized based on contractual rates and is reflected in interest income on loans held for sale in the consolidated statements of comprehensive income. Net gains (losses) resulting from the change in fair value of these loans that were recorded in mortgage income in the consolidated statements of comprehensive income for the three months ended March 31, 2018 and 2017 totaled $(1.1) million and $839 thousand , respectively. The changes in fair value are mostly offset by economic hedging activities, with an insignificant portion of these changes attributable to changes in instrument-specific credit risk.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	FAIR VALUE OF FINANCIAL INSTRUMENTS The estimated fair value of a financial instrument is the current amount that would be exchanged between willing parties, other than in a forced liquidation. Fair value is best determined based upon quoted market prices. However, in many instances, there are no quoted market prices for the Company’s various financial instruments. In cases where quoted market prices are not available, fair values are based on estimates using present value or other valuation techniques. Those techniques are significantly affected by the assumptions used, including the discount rate and estimates of future cash flows. Accordingly, the fair value estimates may not be realized in an immediate settlement of the instrument. ASC Topic 825, Financial Instruments , excludes certain financial instruments and all non-financial instruments from its disclosure requirements. Consequently, the aggregate fair value amounts presented may not necessarily represent the underlying fair value of the Company. The carrying amount and estimated fair values, as well as the level within the fair value hierarchy, of the Company’s financial instruments are included in the tables below. See Note 1, Summary of Significant Accounting Policies, in the 2017 Annual Report on Form 10-K for the year ended December 31, 2017 for a description of how fair value measurements are determined, except for loans, amended upon implementation of ASU 2016-01, Financial Statements - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities. See Note 2, Recent Accounting Pronouncements, in this Report for a description of how the fair value measurement is determined for loans beginning January 1, 2018. March 31, 2018 (Dollars in thousands) Carrying Amount Fair Value Level 1 Level 2 Level 3 Measurement Category Fair Value Financial Assets Securities available for sale $ 4,542,486 $ 4,542,486 $ — $ 4,542,486 $ — CRA and Community Development Investment Funds 9,801 9,801 — 9,801 — Mortgage loans held for sale 110,348 110,348 — 110,348 — Derivative instruments 17,072 17,072 — 17,072 — Financial Liabilities Derivative instruments 32,154 32,154 — 32,154 — Amortized Cost Financial Assets Cash and cash equivalents $ 564,092 $ 564,092 $ 564,092 $ — $ — Securities held to maturity 224,241 219,868 — 219,868 — Loans and leases, net of unearned income and allowance for loan and lease losses 21,561,563 21,495,639 — — 21,495,639 Financial Liabilities Deposits 22,971,192 22,970,554 — 22,970,554 — Short-term borrowings 900,496 900,496 525,496 375,000 — Long-term debt 1,449,302 1,429,335 — — 1,429,335 December 31, 2017 (Dollars in thousands) Carrying Amount Fair Value Level 1 Level 2 Level 3 Measurement Category Fair Value Financial Assets Securities available for sale $ 4,590,062 $ 4,590,062 $ — $ 4,590,062 $ — Mortgage loans held for sale 134,916 134,916 — 134,916 — Derivative instruments 31,265 31,265 — 31,265 — Financial Liabilities Derivative instruments 25,154 25,154 — 25,154 — Amortized Cost Financial Assets Cash and cash equivalents $ 625,724 $ 625,724 $ 625,724 $ — $ — Securities held to maturity 227,318 227,964 — 227,964 — Loans and leases, net of unearned income and allowance for loan and lease losses 19,937,290 19,826,857 — — 19,826,857 Financial Liabilities Deposits 21,466,717 21,460,782 — 21,460,782 — Short-term borrowings 991,297 991,297 516,297 475,000 — Long-term debt 1,495,835 1,476,899 — — 1,476,899 The fair value estimates presented herein are based upon pertinent information available to management as of March 31, 2018 and December 31, 2017 . 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 that date and, therefore, current estimates of fair value may differ significantly from the amounts presented herein.

Business Segments

Business Segments	3 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
Business Segments	BUSINESS SEGMENTS Each of the Company’s reportable operating segments serves the specific needs of the Company’s customers based on the products and services it offers. The reportable segments are based upon those revenue-producing components for which separate financial information is produced internally and primarily reflect the manner in which resources are allocated and performance is assessed. Further, the reportable operating segments are also determined based on the quantitative thresholds prescribed within ASC Topic 280, Segment Reporting , and consideration of the usefulness of the information to the users of the consolidated financial statements. The Company reports the results of its operations through three reportable segments: IBERIABANK, Mortgage, and LTC. The IBERIABANK segment represents the Company’s commercial and retail banking functions, including its lending, investment, and deposit activities. IBERIABANK also includes the Company’s wealth management, capital markets, and other corporate functions. The Mortgage segment represents the Company’s origination, funding, and subsequent sale of one-to-four family residential mortgage loans. The LTC segment represents the Company’s title insurance and loan closing services. Certain expenses not directly attributable to a specific reportable segment are allocated to segments based on pre-determined methods that reflect utilization. Also within IBERIABANK are certain reconciling items that translate reportable segment results into consolidated results. The following tables present certain information regarding our operations by reportable segment, including a reconciliation of segment results to reported consolidated results for the periods presented. Reconciling items between segment results and reported results include: • Elimination of interest income and interest expense representing interest earned by IBERIABANK on interest-bearing checking accounts held by related companies, as well as the elimination of the related deposit balances at the IBERIABANK segment; • Elimination of investment in subsidiary balances on certain operating segments included in total and average segment assets; and • Elimination of intercompany due to and due from balances on certain operating segments that are included in total and average segment assets. Three Months Ended March 31, 2018 (Dollars in thousands) IBERIABANK Mortgage LTC Consolidated Interest and dividend income $ 268,775 $ 1,767 $ 1 $ 270,543 Interest expense 37,654 — — 37,654 Net interest income 231,121 1,767 1 232,889 Provision for/(reversal of) loan and lease losses 7,991 (5 ) — 7,986 Mortgage income — 9,595 — 9,595 Title revenue — — 5,027 5,027 Other non-interest income 29,906 38 — 29,944 Allocated expenses (1,479 ) 1,166 313 — Non-interest expense 171,816 11,916 4,564 188,296 Income/(loss) before income tax expense 82,699 (1,677 ) 151 81,173 Income tax expense/(benefit) 18,540 (410 ) (578 ) 17,552 Net income/(loss) $ 64,159 $ (1,267 ) $ 729 $ 63,621 Total loans, leases, and loans held for sale, net of unearned income $ 21,652,223 $ 164,215 $ — $ 21,816,438 Total assets 29,243,983 205,497 23,157 29,472,637 Total deposits 22,959,061 12,131 — 22,971,192 Average assets 27,924,587 185,742 21,890 28,132,219 Three Months Ended March 31, 2017 (Dollars in thousands) IBERIABANK Mortgage LTC Consolidated Interest and dividend income $ 190,823 $ 1,709 $ 1 $ 192,533 Interest expense 19,715 — — 19,715 Net interest income 171,108 1,709 1 172,818 Provision for/(reversal of) loan and lease losses 6,158 (4 ) — 6,154 Mortgage income — 14,115 — 14,115 Title revenue — — 4,741 4,741 Other non-interest income 26,284 (10 ) (6 ) 26,268 Allocated expenses (2,174 ) 1,656 518 — Non-interest expense 119,429 15,167 4,200 138,796 Income/(loss) before income tax expense 73,979 (1,005 ) 18 72,992 Income tax expense/(benefit) 22,829 (322 ) 12 22,519 Net income/(loss) $ 51,150 $ (683 ) $ 6 $ 50,473 Total loans, leases, and loans held for sale, net of unearned income $ 15,072,661 $ 181,874 $ — $ 15,254,535 Total assets 21,774,586 209,911 23,982 22,008,479 Total deposits 17,306,328 5,937 — 17,312,265 Average assets 21,550,930 286,694 23,877 21,861,501

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	COMMITMENTS AND CONTINGENCIES Off-balance sheet commitments In the normal course of business, to meet the financing needs of its customers, the Company is a party to credit-related financial instruments, with risk not reflected in the consolidated financial statements. These financial instruments include commitments to extend credit, standby letters of credit, and commercial letters of credit. Such commitments involve, to varying degrees, elements of credit and interest rate risk in excess of the amount recognized in the consolidated balance sheets. The credit policies used for these commitments are consistent with those used for on-balance sheet instruments. The Company’s exposure to credit loss in the event of non-performance by its customers under such commitments or letters of credit represents the contractual amount of the financial instruments as indicated in the table below. At both March 31, 2018 and December 31, 2017, the fair value of guarantees under commercial and standby letters of credit was $2.1 million . This fair value will decrease as the existing commercial and standby letters of credit approach their expiration dates. At March 31, 2018 and December 31, 2017, respectively, the Company had the following financial instruments outstanding and related reserves, whose contract amounts represent credit risk: (Dollars in thousands) March 31, 2018 December 31, 2017 Commitments to grant loans $ 319,318 $ 342,305 Unfunded commitments under lines of credit 6,340,135 6,060,034 Commercial and standby letters of credit 211,070 210,002 Reserve for unfunded lending commitments 13,432 13,208 Commitments to extend credit are agreements to lend to a customer as long as there is no violation of any condition established in the contract. Commitments generally have fixed expiration dates or other termination clauses and may require payment of a fee by the borrower. Since many of the commitments are expected to be drawn upon, the total commitment amounts generally represent future cash requirements. The Company evaluates each customer’s creditworthiness on a case-by-case basis. The amount of collateral, if any, is based on management’s credit evaluation of the customer. Unfunded commitments under commercial lines of credit, revolving credit lines, and overdraft protection agreements are commitments for possible future extensions of credit to existing customers. Many of these types of commitments do not contain a specified maturity date and may not be drawn upon to the total extent to which the Company is committed. See Note 6, Allowance for Credit Losses and Credit Quality, for additional information related to the Company’s reserve for unfunded lending commitments. Commercial and standby letters of credit are conditional commitments issued by the Company to guarantee the performance of a customer to a third party. These guarantees are primarily issued to support public and private borrowing arrangements, including commercial paper issuance, bond financing, and similar transactions. The credit risk involved in issuing letters of credit is essentially the same as that involved in extending loan facilities to customers. When necessary they are collateralized, generally in the form of marketable securities and cash equivalents. Legal proceedings The nature of the business of the Company’s banking and other subsidiaries ordinarily results in a certain amount of claims, litigation, investigations, and legal and administrative cases and proceedings, which are considered incidental to the normal conduct of business. Some of these claims are against entities or assets of which the Company is a successor or acquired in business acquisitions. The Company has asserted defenses to these claims and, with respect to such legal proceedings, intends to continue to defend itself vigorously, litigating or settling cases according to management’s judgment as to what is in the best interest of the Company and its shareholders. In July of 2016, the Company received a subpoena from the Office of Inspector General of the U.S. Department of Housing and Urban Development (“HUD”) requesting information on certain previously originated loans insured by the Federal Housing Administration ("FHA") as well as other documents regarding the Company's FHA-related policies and practices. After the Company complied with the subpoena, attorneys from the Department of Justice (“DOJ”) informed the Company in late March of 2017 that a civil qui tam suit had been filed against the Company in federal court involving the subject matter of the HUD subpoena. The HUD lawsuit was settled on December 11, 2017 in the amount of $11.7 million . On February 2, 2018, IBERIABANK filed a lawsuit in the United States District Court for the Eastern District of Louisiana (New Orleans) against Illinois Union Insurance Company and Travelers Casualty and Surety Company of America in an effort to recover the $11.7 million it paid to settle the HUD matter. IBERIABANK filed that lawsuit to recover the insurance proceeds to which it claims to be entitled under certain Bankers’ Professional Liability insurance policies issued by defendants Illinois Union and Travelers. More Specifically, IBERIABANK alleges that the insurers have failed to honor their obligations under the policies to pay IBERIABANK’s losses in connection with the $11.7 million settlement of disputed allegations relating to IBERIABANK’s professional services in connection with certain mortgage loans insured by the FHA. The Company assesses its liabilities and contingencies in connection with outstanding legal proceedings utilizing the latest information available. Where it is probable that the Company will incur a loss and the amount of the loss can be reasonably estimated, the Company records a liability in its consolidated financial statements. These legal reserves may be increased or decreased to reflect any relevant developments on a quarterly basis. Where a loss is not probable or the amount of loss is not estimable, the Company does not accrue legal reserves. While the outcome of legal proceedings is inherently uncertain, based on information currently available and available insurance coverage, the Company’s management believes that it has established appropriate legal reserves. Any incremental liabilities arising from pending legal proceedings are not expected to have a material adverse effect on the Company’s consolidated financial position, consolidated results of operations, or consolidated cash flows. However, it is possible that the ultimate resolution of these matters, if unfavorable, may be material to the Company’s consolidated financial position, consolidated results of operations, or consolidated cash flows. As of the date of this filing, the Company believes the amount of losses associated with legal proceedings that it is reasonably possible to incur above amounts already accrued is not material.

Related Party Transactions

Related Party Transactions	3 Months Ended
	Mar. 31, 2018
Related Party Transactions [Abstract]
Related Party Transactions	RELATED PARTY TRANSACTIONS In the ordinary course of business, the Company may execute transactions with various related parties. Examples of such transactions may include lending or deposit arrangements, transfers of financial assets, services for administrative support, and other miscellaneous items. The Company has granted loans to executive officers and directors and their affiliates. These loans, including the related principal additions, principal payments, and unfunded commitments are not material to the consolidated financial statements at March 31, 2018 and December 31, 2017. There were no outstanding loans to related parties classified as non-accrual, past due, or troubled debt restructurings at March 31, 2018. Deposits from related parties held by the Company were not material at March 31, 2018 and December 31, 2017.

Basis of Presentation (Policies

Basis of Presentation (Policies)	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Principles of Consolidation	The consolidated financial statements include the accounts of the Company and its subsidiaries. All significant intercompany balances and transactions have been eliminated in consolidation.
Reclassification	Certain amounts reported in prior periods have been reclassified to conform to the current period presentation. These reclassifications did not have a material effect on previously reported consolidated financial statements.
Concentration of Credit Risks	Concentrations of Credit Risk Most of the Company’s business activity is with customers located in the southeastern United States. The Company’s lending activity is concentrated in its market areas within those states. The Company has emphasized originations of commercial loans and private banking loans, defined as loans to higher net worth clients. Repayments on loans are expected to come from cash flows of the borrower and/or guarantor. Losses on secured loans are limited by the net realizable value of the collateral upon default of the borrowers and guarantor support. The Company believes it does not have any excessive concentrations to any one industry, loan type, or customer.
Recent Accounting Pronouncements	RECENT ACCOUNTING PRONOUNCEMENTS Pronouncements adopted during the three months ended March 31, 2018: ASU No. 2014-09 In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers , which implements a common revenue standard and clarifies the principles used for recognizing revenue. The amendments in the ASU clarify that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. Revenue from Contracts with Customers The majority of the Company’s income streams (e.g., interest and dividend income and mortgage income) are accounted for in accordance with GAAP literature outside the scope of ASC 606, Revenue from Contracts with Customers . Details regarding income recognition for interest and non-interest streams can be found throughout the Company’s 2017 10-K (including Note 1 - Summary of Significant Accounting Policies). Impairment losses recognized against certain receivables (e.g., NSF fees) and capitalized costs (e.g., sales commissions) associated with contracts within the scope of ASC 606 are immaterial. Non-interest income from service charges on deposit accounts, broker commissions, ATM/debit card fee income, credit card and merchant-related income (e.g., interchange fees), and transactional income from traditional banking services (part of other non-interest income) are the significant income streams within the scope of ASC 606 associated with the IBERIABANK reportable segment. Non-interest income from title revenue is associated with the LTC reportable segment. Recognition of Revenue from Contracts with Customers The Company enters into various contracts with customers to provide traditional banking services, including asset management, on a routine basis. The Company’s performance obligations are generally service-related and provided on a daily or monthly basis. The Company does not typically have performance obligations which extend beyond a reporting period. The performance obligations are generally satisfied upon completion of service (i.e., as services are rendered) and the fees are collected at such time, or shortly thereafter. The fees are readily determinable and allocated individually to each service. It is not typical for contracts to require significant judgment to determine the transaction price. Some contracts contain variable consideration; however, the variable consideration is generally constrained (not estimable) as it is based on the occurrence or nonoccurence of a contingent event (or another constraint in some circumstances). The Company generally records the variable consideration when the contingent event occurs and the fee is determinable. The Company provides some services for customers in which it acts in an agent capacity, but generally acts in a principal capacity. Payment terms and conditions vary slightly amongst services; however, amounts are generally invoiced and due or collected by the Company within 30 days, although some fees may be prepaid. The Company bills the customer periodically as performance obligations are satisfied for most services. Therefore, revenue for services provided is generally recognized in the amount invoiced (except in circumstances of prepayment) as that amount corresponds directly to the value of the Company’s performance. In the normal course of business, the Company does not generally grant refunds for services provided. As such, the Company does not establish provisions for estimated returns. Title revenue associated with services provided by LTC, as well as broker commissions, ATM/debit card fee income, credit card and merchant-related income (e.g., interchange fees), and transactional fees from traditional banking services generated within IBERIABANK are generally recognized at the point-in-time the services are provided. The Company has determined this recognition to be appropriate as, upon completion of services, the Company has completed its performance obligations, has a present right to payment (or has collected the cash), and the customer is able to obtain (or has obtained) substantially all of the benefits from the performance obligation (i.e., the provided services). Revenues from service charges on deposit accounts are recognized at the end of the monthly service period (e.g., account service charges) or the date the performance obligation is satisfied (e.g., NSF, stop payment, wire transfer, etc.), except for deposit account services performed by Treasury Management which are recognized on a monthly basis, as these services are performed over that time. Asset management fees (e.g., trust fees) are generally recognized at the end of the monthly service period, but fees are not collected until the beginning of the subsequent month, although some contracts may have quarterly terms and/or be prepaid. NSF fees which are not initially paid are subsequently recorded as “loans” (along with the overdraft balance) and remain classified as such until the amount is paid or charged-off (generally after 60 days). Adoption of ASC 606 The Company adopted ASC 606 as of January 1, 2018 for all contracts as of the effective date. Prior period amounts have been reclassified to conform to current guidance requirements related to the net presentation of certain costs associated with interchange fees and rewards programs. The reclassification of prior period amounts reduced non-interest income and non-interest expense by an immaterial amount (approximately $2.2 million for the three months ended March 31, 2017) and had no impact on net income. There was no cumulative adjustment made to opening retained earnings as of January 1, 2018. ASU No. 2016-01 In January 2016, the FASB issued ASU No. 2016-01, Financial Statements - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities , which impacts how the Company measures certain equity investments and discloses and presents certain financial instruments through the application of the “exit price” notion. The Company adopted the amendments beginning January 1, 2018. Under the new guidance, equity investments can no longer be classified as trading or available for sale (AFS), and related unrealized holding gains and losses can no longer be recognized in OCI. Per the ASU, such equity investments should be measured at fair value, with adjustments recognized in earnings at the end of each reporting period. As such, the Company reclassified its portfolio of equity investments (approximately $9.8 million at March 31, 2018) previously classified as AFS investment securities to “other assets.” As these equity investments were previously measured at fair value, implementation of the ASU did not impact the Company’s valuation method. In accordance with the ASU, the cumulative-effect adjustment from AOCI to retained earnings for previously recorded fair value adjustments related to these equity investments at adoption was insignificant. The Company elected the practical expedient measurement alternative to prospectively account for other equity investments that do not have readily determinable fair values at cost less impairment plus or minus observable price changes in orderly transactions for an identical or similar investment of the same issuer. These investments are immaterial overall and are classified within “other assets” on the Company’s consolidated balance sheets. The Company also modified its fair value methodology for loans measured at amortized cost whose fair values were previously disclosed using an “entry price” methodology to an “exit price” methodology, in accordance with the ASU. The Company’s “exit price” methodology estimates the fair value of these loans based on the present value of the future cash flows using the interest rate that would be charged for a similar loan to a borrower with similar risk at the indicated balance sheet date, adjusted for a liquidity discount based on the estimated time period to complete a sale transaction with a market participant. This change in methodology solely impacted the Company’s disclosures, and had no impact to the Company’s consolidated financial statements. ASU No. 2016-15 In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (ASC 230): Classification of Certain Cash Receipts and Cash Payments , in order to reduce current diversity in practice in how certain cash receipts and cash payments are presented and classified in the statement of cash flows. The Company retrospectively adopted the amendments effective January 1, 2018. The adoption of these amendments did not impact the Company’s consolidated statements of cash flows. ASU No. 2017-12 In August 2017, the FASB issued ASU No. 2017-12, Derivatives and Hedging (ASC 815): Targeted Improvements to Accounting for Hedging Activities, which amends the hedge accounting model to enable entities to better portray the economics of their risk management activities in the financial statements and enhance the transparency and understandability of hedge results. The Company elected to early adopt the amendments effective January 1, 2018. The modified-retrospective adoption of the amendments did not impact the Company’s consolidated financial statements in the current or prior periods. Pronouncements issued but not yet adopted: ASU No. 2016-02 In February 2016, the FASB issued ASU No. 2016-02, Leases (ASC 842) . A significant amendment to existing GAAP from this ASU is the recognition of lease assets (i.e., right of use assets) and liabilities on the balance sheet for leases that are classified as operating leases by lessees. The lessor model remains similar to the current accounting model in existing GAAP. Additional amendments include, but are not limited to, the elimination of leveraged leases; modification to the definition of a lease; amendments on sale and leaseback transactions; and disclosure of additional quantitative and qualitative information. ASU 2016-02 will be effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years, with early adoption permitted. Lessees and lessors are required to recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach. The Company will adopt the amendments on January 1, 2019. The Company occupies certain banking offices and equipment under operating lease agreements, which currently are not recognized on the consolidated balance sheets. Based on the Company’s preliminary analysis of its current portfolio, the impact to the Company’s consolidated balance sheets is estimated to result in less than a 1% increase in assets and liabilities. The Company is also currently assessing the practical expedients it may elect at adoption, the final determination of the incremental borrowing rate, and the impact to regulatory capital ratios, amongst other matters associated with the ASU. The adjustment to retained earnings is not expected to be significant based on the transition guidance associated with current sale-leaseback agreements. The Company also anticipates additional disclosures to be provided at adoption. ASU No. 2016-13 In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (ASC 326): Measurement of Credit Losses on Financial Instruments . The amendments introduce an impairment model that is based on expected credit losses (“ECL”), rather than incurred losses, to estimate credit losses on certain types of financial instruments (e.g., loans and held-to-maturity securities), including certain off-balance sheet financial instruments (e.g., loan commitments). The measurement of ECL should consider historical information, current information, and reasonable and supportable forecasts, including estimates of prepayments, over the contractual term. Financial instruments with similar risk characteristics may be grouped together when estimating ECL. The ASU also amends the current AFS security impairment model for debt securities. The new model will require an estimate of ECL when the fair value is below the amortized cost of the asset through the use of an allowance to record estimated credit losses (and subsequent recoveries). Non-credit related losses will continue to be recognized through OCI. In addition, the amendments provide for a simplified accounting model for purchased financial assets with a more-than-insignificant amount of credit deterioration since their origination. The initial estimate of expected credit losses would be recognized through an ALLL with an offset (i.e., increase) to the cost basis of the related financial asset at acquisition. ASU 2016-13 will be effective for fiscal years beginning after December 15, 2019, including interim periods. The amendments will be applied through a modified-retrospective approach, resulting in a cumulative-effect adjustment to retained earnings as of the beginning of the first reporting period in which the guidance is effective. A prospective transition approach is required for debt securities for which OTTI had been recognized before the effective date. Amounts previously recognized in AOCI as of the date of adoption that relate to improvements in cash flows expected to be collected should continue to be accreted into income over the remaining life of the asset. Recoveries of amounts previously written off relating to improvements in cash flows after the date of adoption should be recorded in earnings when received. The Company is currently evaluating the impact of the ASU on the Company’s consolidated financial statements; however, the Company has engaged third-party consultants to assist with the ASU and has developed an implementation plan.

Loans (Tables)

Loans (Tables)	3 Months Ended
	Mar. 31, 2018
Receivables [Abstract]
Schedule of Non-Covered and Covered Loans	Loans and leases consist of the following for the periods indicated: (Dollars in thousands) March 31, 2018 December 31, 2017 Commercial loans and leases: Real estate- construction $ 1,199,625 $ 1,240,396 Real estate- owner-occupied 2,612,244 2,529,885 Real estate- non-owner-occupied 5,437,082 5,167,949 Commercial and industrial (1) 5,325,682 5,135,067 14,574,633 14,073,297 Residential mortgage loans: 3,971,067 3,056,352 Consumer loans: Home equity 2,421,186 2,292,275 Indirect automobile 50,671 62,693 Credit card 93,261 96,368 Other 595,272 497,196 3,160,390 2,948,532 Total $ 21,706,090 $ 20,078,181 (1) Includes equipment financing leases.
Schedule of Aging of Loans	The following tables provide an analysis of the aging of loans as of March 31, 2018 and December 31, 2017. Past due and non-accrual loan amounts exclude acquired impaired loans, even if contractually past due or if the Company does not expect to receive payment in full, as the Company is currently accreting interest income over the expected life of the loans. March 31, 2018 Accruing (Dollars in thousands) Current or Less Than 30 days Past Due 30-59 days 60-89 days > 90 days Total Past Due Non-accrual Acquired Impaired Total Real estate- construction $ 1,157,115 $ 842 $ 129 $ — $ 971 $ 2,634 $ 38,905 $ 1,199,625 Real estate- owner-occupied 2,474,611 4,767 3,461 — 8,228 35,144 94,261 2,612,244 Real estate- non-owner-occupied 5,319,962 7,269 2,526 6,789 16,584 9,378 91,158 5,437,082 Commercial and industrial 5,212,390 7,755 3,406 273 11,434 66,637 35,221 5,325,682 Residential mortgage 3,783,309 25,640 2,655 1,226 29,521 19,932 138,305 3,971,067 Consumer - home equity 2,309,222 11,860 3,191 — 15,051 16,383 80,530 2,421,186 Consumer - indirect automobile 48,581 1,166 175 — 1,341 743 6 50,671 Consumer - credit card 92,497 173 88 — 261 503 — 93,261 Consumer - other 585,969 2,484 706 — 3,190 2,621 3,492 595,272 Total $ 20,983,656 $ 61,956 $ 16,337 $ 8,288 $ 86,581 $ 153,975 $ 481,878 $ 21,706,090 December 31, 2017 Accruing (Dollars in thousands) Current or Less Than 30 days Past Due 30-59 days 60-89 days > 90 days Total Past Due Non-accrual Acquired Impaired Total Real estate- construction $ 1,197,766 $ 269 $ — $ 458 $ 727 $ 2,635 $ 39,268 $ 1,240,396 Real estate- owner-occupied 2,398,487 1,631 659 74 2,364 24,457 104,577 2,529,885 Real estate- non-owner-occupied 5,066,084 2,086 6,405 887 9,378 6,811 85,676 5,167,949 Commercial and industrial 5,014,438 5,788 5,726 146 11,660 77,823 31,146 5,135,067 Residential mortgage 2,877,048 10,083 8,136 5,317 23,536 17,387 138,381 3,056,352 Consumer - home equity 2,186,554 11,675 2,947 18 14,640 12,365 78,716 2,292,275 Consumer - indirect automobile 59,830 1,796 177 — 1,973 884 6 62,693 Consumer - credit card 95,264 140 374 — 514 590 — 96,368 Consumer - other 487,150 3,350 475 — 3,825 2,436 3,785 497,196 Total $ 19,382,621 $ 36,818 $ 24,899 $ 6,900 $ 68,617 $ 145,388 $ 481,555 $ 20,078,181
Schedule of Carrying Amount of Loans Acquired	The tables below show the balances acquired during the first quarter of 2018 for these two subsections of the portfolio as of the acquisition date. These amounts are subject to change due to the finalization of purchase accounting adjustments. (Dollars in thousands) Acquired Non-Impaired Loans Contractually required principal and interest at acquisition $ 1,695,918 Expected losses and foregone interest (19,952 ) Cash flows expected to be collected at acquisition 1,675,966 Fair value of acquired loans at acquisition $ 1,455,085 (Dollars in thousands) Acquired Impaired Loans Contractually required principal and interest at acquisition $ 43,779 Non-accretable difference (expected losses and foregone interest) (31,174 ) Cash flows expected to be collected at acquisition 12,605 Accretable yield (2,371 ) Basis in acquired loans at acquisition $ 10,234
Summary of Changes in Accretable Yields of Acquired Loans	The following is a summary of changes in the accretable difference for all loans accounted for under ASC 310-30 during the three months ended March 31: (Dollars in thousands) 2018 2017 Balance at beginning of period $ 152,623 $ 175,054 Additions 2,371 — Transfers from non-accretable difference to accretable yield (279 ) 2,071 Accretion (13,154 ) (14,596 ) Changes in expected cash flows not affecting non-accretable differences (1) 9,687 1,060 Balance at end of period $ 151,248 $ 163,589 (1) Includes changes in cash flows expected to be collected due to the impact of changes in actual or expected timing of liquidation events, modifications, changes in interest rates and changes in prepayment assumptions.
Schedule of Modified TDRs	The following table provides information on how the TDRs were modified during the periods indicated: Three Months Ended March 31, (Dollars in thousands) 2018 2017 Extended maturities $ 5,619 $ 7,199 Maturity and interest rate adjustment 108 3,224 Movement to or extension of interest-rate only payments 48 1,290 Interest rate adjustment 105 — Forbearance 12,886 1,220 Other concession(s) (1) 8,434 232 Total $ 27,200 $ 13,165 (1) Other concessions may include covenant waivers, forgiveness of principal or interest associated with a customer bankruptcy, or a combination of any of the above concessions.
Schedule of Subsequently Defaulted TDRs	The following table presents the end of period balance for loans modified in a TDR during the periods indicated: Three Months Ended March 31, 2018 2017 (In thousands, except number of loans) 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 Real estate- construction 1 $ 1,950 $ 1,049 — $ — $ — Real estate- owner-occupied 2 10,691 9,324 3 3,004 2,999 Real estate- non-owner-occupied 9 1,089 1,091 7 1,867 1,855 Commercial and industrial 18 14,429 13,314 15 435 427 Residential mortgage — — — 4 259 241 Consumer - home equity 14 1,809 1,795 37 6,622 6,607 Consumer - indirect 11 137 119 13 184 174 Consumer - other 10 511 508 22 867 862 Total 65 $ 30,616 $ 27,200 101 $ 13,238 $ 13,165 Information detailing TDRs that defaulted during the three-month periods ended March 31, 2018 and 2017, and were modified in the previous twelve months (i.e., the twelve months prior to the default) is presented in the following tables. The Company has defined a default as any loan with a payment that is currently past due greater than 30 days , or was past due greater than 30 days at any point during the respective periods, or since the date of modification, whichever is shorter. Three Months Ended March 31, 2018 2017 (In thousands, except number of loans) Number of Loans Recorded Investment Number of Loans Recorded Investment Real estate- construction — $ — 1 $ 117 Real estate- owner-occupied 3 10,187 9 14,732 Real estate- non-owner-occupied 9 492 10 5,041 Commercial and industrial 29 9,708 21 4,186 Residential mortgage 6 598 22 1,793 Consumer - home equity 24 2,331 31 1,337 Consumer - indirect automobile 34 322 43 517 Consumer - other 17 1,035 25 693 Total 122 $ 24,673 162 $ 28,416

Acquisition Activity (Tables)

Acquisition Activity (Tables)	3 Months Ended
	Mar. 31, 2018
Gibraltar Private Bank & Trust Company [Member]
Business Acquisition [Line Items]
Schedule of Business Acquisitions	(Dollars in thousands) Number of Shares Amount Equity consideration Common stock issued 2,787,773 $ 214,659 Total equity consideration 214,659 Non-equity consideration Cash 7 Total consideration paid 214,666 Fair value of net assets assumed including identifiable intangible assets 172,136 Goodwill $ 42,530 (Dollars in thousands) Gibraltar Fair Value (Preliminary) Assets Cash and cash equivalents $ 102,570 Investment securities 19,169 Equity securities 27,519 Loans 1,465,319 Core deposit intangible assets 18,529 Deferred tax asset, net 689 Other assets 14,382 Total assets acquired $ 1,648,177 Liabilities Deposit liabilities $ 1,064,803 Long-term borrowings 405,107 Other liabilities 6,131 Total liabilities assumed $ 1,476,041
Solomon Parks Title & Escrow [Member]
Business Acquisition [Line Items]
Schedule of Business Acquisitions	(Dollars in thousands) SolomonParks Fair Value (Preliminary) Assets Premise and equipment, net $ 42 Non-compete agreement 156 Title Plant investment 15 Total assets acquired $ 213 Liabilities Contingent consideration $ 343 Total liabilities assumed $ 343
Sabadell United
Business Acquisition [Line Items]
Schedule of Business Acquisitions	(Dollars in thousands) Number of Shares Amount Equity consideration Common stock issued 2,610,304 $ 211,043 Total equity consideration 211,043 Non-equity consideration Cash 809,159 Total consideration paid 1,020,202 Fair value of net assets assumed including identifiable intangible assets 556,799 Goodwill $ 463,403 (Dollars in thousands) Sabadell United Fair Value (Preliminary) Assets Cash and cash equivalents $ 318,834 Investment securities 964,123 Loans 4,025,946 Core deposit intangible assets 66,600 Deferred tax asset, net 33,469 Other assets 89,745 Total assets acquired $ 5,498,717 Liabilities Deposit liabilities $ 4,382,780 Short-term borrowings 520,539 Other liabilities 38,599 Total liabilities assumed $ 4,941,918
Schedule of Pro Forma Information	The following table presents unaudited pro forma information as if the acquisition occurred on January 1, 2016 under the "Unaudited Pro Forma" column. The pro forma information does not necessarily reflect the results of operations that would have occurred had the Company acquired Sabadell United on January 1, 2016. Furthermore, cost savings and other business synergies related to the acquisition are not reflected in the pro forma amounts. Unaudited Pro Forma for (Dollars in thousands) Three months ended March 31, 2017 Net interest income $ 231,087 Non-interest income 54,755 Net income 43,562

Investment Securities (Tables)

Investment Securities (Tables)	3 Months Ended
	Mar. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Available-for-sale Securities	Information pertaining to securities with gross unrealized losses, aggregated by investment category and length of time that individual securities have been in a continuous loss position, is as follows: March 31, 2018 Less Than Twelve Months Twelve Months or More Total (Dollars in thousands) Gross Unrealized Losses Estimated Fair Value Gross Unrealized Losses Estimated Fair Value Gross Unrealized Losses Estimated Fair Value Securities available for sale: U.S. Treasury securities $ — $ 693 $ — $ — $ — $ 693 U.S. Government-sponsored enterprise obligations (419 ) 29,580 (235 ) 9,765 (654 ) 39,345 Obligations of state and political subdivisions (1,147 ) 96,138 (3,009 ) 66,404 (4,156 ) 162,542 Mortgage-backed securities (68,161 ) 2,847,244 (53,054 ) 1,191,233 (121,215 ) 4,038,477 Other securities (1,138 ) 60,304 — — (1,138 ) 60,304 Total securities available for sale $ (70,865 ) $ 3,033,959 $ (56,298 ) $ 1,267,402 $ (127,163 ) $ 4,301,361 Securities held to maturity: Obligations of state and political subdivisions $ (4,066 ) $ 150,188 $ (54 ) $ 2,976 $ (4,120 ) $ 153,164 Mortgage-backed securities (11 ) 323 (1,003 ) 18,187 (1,014 ) 18,510 Total securities held to maturity $ (4,077 ) $ 150,511 $ (1,057 ) $ 21,163 $ (5,134 ) $ 171,674 December 31, 2017 Less Than Twelve Months Twelve Months or More Total (Dollars in thousands) Gross Unrealized Losses Estimated Fair Value Gross Unrealized Losses Estimated Fair Value Gross Unrealized Losses Estimated Fair Value Securities available for sale: U.S. Government-sponsored enterprise obligations $ (254 ) $ 29,744 $ (152 ) $ 9,848 $ (406 ) $ 39,592 Obligations of state and political subdivisions (326 ) 31,601 (1,167 ) 68,609 (1,493 ) 100,210 Mortgage-backed securities (26,263 ) 2,677,338 (34,765 ) 1,226,058 (61,028 ) 3,903,396 Other securities (914 ) 75,302 — — (914 ) 75,302 Total securities available for sale $ (27,757 ) $ 2,813,985 $ (36,084 ) $ 1,304,515 $ (63,841 ) $ 4,118,500 Securities held to maturity: Obligations of state and political subdivisions $ (263 ) $ 65,817 $ (12 ) $ 3,031 $ (275 ) $ 68,848 Mortgage-backed securities (2 ) 333 (648 ) 19,269 (650 ) 19,602 Total securities held to maturity $ (265 ) $ 66,150 $ (660 ) $ 22,300 $ (925 ) $ 88,450 The amortized cost and fair values of investment securities, with gross unrealized gains and losses, consist of the following: March 31, 2018 (Dollars in thousands) Amortized Gross Gross Estimated Securities available for sale: U.S. Treasury securities $ 6,824 $ — $ — $ 6,824 U.S. Government-sponsored enterprise obligations 41,001 11 (654 ) 40,358 Obligations of state and political subdivisions 267,962 1,228 (4,156 ) 265,034 Mortgage-backed securities 4,277,033 279 (121,215 ) 4,156,097 Other securities 75,205 106 (1,138 ) 74,173 Total securities available for sale $ 4,668,025 $ 1,624 $ (127,163 ) $ 4,542,486 Securities held to maturity: Obligations of state and political subdivisions $ 204,404 $ 726 $ (4,120 ) $ 201,010 Mortgage-backed securities 19,837 35 (1,014 ) 18,858 Total securities held to maturity $ 224,241 $ 761 $ (5,134 ) $ 219,868 December 31, 2017 (Dollars in thousands) Amortized Gross Gross Estimated Securities available for sale: U.S. Government-sponsored enterprise obligations $ 41,003 $ 18 $ (406 ) $ 40,615 Obligations of state and political subdivisions 271,451 4,246 (1,493 ) 274,204 Mortgage-backed securities 4,221,472 1,461 (61,028 ) 4,161,905 Other securities 114,005 247 (914 ) 113,338 Total securities available for sale $ 4,647,931 $ 5,972 $ (63,841 ) $ 4,590,062 Securities held to maturity: Obligations of state and political subdivisions $ 206,736 $ 1,530 $ (275 ) $ 207,991 Mortgage-backed securities 20,582 41 (650 ) 19,973 Total securities held to maturity $ 227,318 $ 1,571 $ (925 ) $ 227,964
Held-to-maturity Securities	Information pertaining to securities with gross unrealized losses, aggregated by investment category and length of time that individual securities have been in a continuous loss position, is as follows: March 31, 2018 Less Than Twelve Months Twelve Months or More Total (Dollars in thousands) Gross Unrealized Losses Estimated Fair Value Gross Unrealized Losses Estimated Fair Value Gross Unrealized Losses Estimated Fair Value Securities available for sale: U.S. Treasury securities $ — $ 693 $ — $ — $ — $ 693 U.S. Government-sponsored enterprise obligations (419 ) 29,580 (235 ) 9,765 (654 ) 39,345 Obligations of state and political subdivisions (1,147 ) 96,138 (3,009 ) 66,404 (4,156 ) 162,542 Mortgage-backed securities (68,161 ) 2,847,244 (53,054 ) 1,191,233 (121,215 ) 4,038,477 Other securities (1,138 ) 60,304 — — (1,138 ) 60,304 Total securities available for sale $ (70,865 ) $ 3,033,959 $ (56,298 ) $ 1,267,402 $ (127,163 ) $ 4,301,361 Securities held to maturity: Obligations of state and political subdivisions $ (4,066 ) $ 150,188 $ (54 ) $ 2,976 $ (4,120 ) $ 153,164 Mortgage-backed securities (11 ) 323 (1,003 ) 18,187 (1,014 ) 18,510 Total securities held to maturity $ (4,077 ) $ 150,511 $ (1,057 ) $ 21,163 $ (5,134 ) $ 171,674 December 31, 2017 Less Than Twelve Months Twelve Months or More Total (Dollars in thousands) Gross Unrealized Losses Estimated Fair Value Gross Unrealized Losses Estimated Fair Value Gross Unrealized Losses Estimated Fair Value Securities available for sale: U.S. Government-sponsored enterprise obligations $ (254 ) $ 29,744 $ (152 ) $ 9,848 $ (406 ) $ 39,592 Obligations of state and political subdivisions (326 ) 31,601 (1,167 ) 68,609 (1,493 ) 100,210 Mortgage-backed securities (26,263 ) 2,677,338 (34,765 ) 1,226,058 (61,028 ) 3,903,396 Other securities (914 ) 75,302 — — (914 ) 75,302 Total securities available for sale $ (27,757 ) $ 2,813,985 $ (36,084 ) $ 1,304,515 $ (63,841 ) $ 4,118,500 Securities held to maturity: Obligations of state and political subdivisions $ (263 ) $ 65,817 $ (12 ) $ 3,031 $ (275 ) $ 68,848 Mortgage-backed securities (2 ) 333 (648 ) 19,269 (650 ) 19,602 Total securities held to maturity $ (265 ) $ 66,150 $ (660 ) $ 22,300 $ (925 ) $ 88,450 The amortized cost and fair values of investment securities, with gross unrealized gains and losses, consist of the following: March 31, 2018 (Dollars in thousands) Amortized Gross Gross Estimated Securities available for sale: U.S. Treasury securities $ 6,824 $ — $ — $ 6,824 U.S. Government-sponsored enterprise obligations 41,001 11 (654 ) 40,358 Obligations of state and political subdivisions 267,962 1,228 (4,156 ) 265,034 Mortgage-backed securities 4,277,033 279 (121,215 ) 4,156,097 Other securities 75,205 106 (1,138 ) 74,173 Total securities available for sale $ 4,668,025 $ 1,624 $ (127,163 ) $ 4,542,486 Securities held to maturity: Obligations of state and political subdivisions $ 204,404 $ 726 $ (4,120 ) $ 201,010 Mortgage-backed securities 19,837 35 (1,014 ) 18,858 Total securities held to maturity $ 224,241 $ 761 $ (5,134 ) $ 219,868 December 31, 2017 (Dollars in thousands) Amortized Gross Gross Estimated Securities available for sale: U.S. Government-sponsored enterprise obligations $ 41,003 $ 18 $ (406 ) $ 40,615 Obligations of state and political subdivisions 271,451 4,246 (1,493 ) 274,204 Mortgage-backed securities 4,221,472 1,461 (61,028 ) 4,161,905 Other securities 114,005 247 (914 ) 113,338 Total securities available for sale $ 4,647,931 $ 5,972 $ (63,841 ) $ 4,590,062 Securities held to maturity: Obligations of state and political subdivisions $ 206,736 $ 1,530 $ (275 ) $ 207,991 Mortgage-backed securities 20,582 41 (650 ) 19,973 Total securities held to maturity $ 227,318 $ 1,571 $ (925 ) $ 227,964
Additional Information on Securities in a Continuous Loss Position	Additional information on securities that have been in a continuous loss position for over twelve months at March 31, 2018 and December 31, 2017 is presented in the following table. (Dollars in thousands) March 31, 2018 December 31, 2017 Number of securities: Mortgage-backed securities 184 181 Obligations of state and political subdivisions 28 28 Other 1 1 213 210 Amortized Cost Basis: Mortgage-backed securities $ 1,263,477 $ 1,280,739 Obligations of state and political subdivisions 72,443 72,820 Other 10,000 10,000 $ 1,345,920 $ 1,363,559 Unrealized Loss: Mortgage-backed securities $ 54,057 $ 35,412 Obligations of state and political subdivisions 3,063 1,180 Other 235 152 $ 57,355 $ 36,744
Schedule of Amortized Cost and Estimated Fair Value of Investment Securities by Maturity	The amortized cost and estimated fair value of investment securities by maturity at March 31, 2018 are presented in the following table. Securities are classified according to their contractual maturities without consideration of principal amortization, potential prepayments or call options. Accordingly, actual maturities may differ from contractual maturities. Weighted average yields are calculated on the basis of the yield to maturity based on the amortized cost of each security. Securities Available for Sale Securities Held to Maturity (Dollars in thousands) Weighted Amortized Estimated Weighted Amortized Estimated Within one year or less 2.06 % $ 6,667 $ 6,670 3.04 % $ 1,445 $ 1,448 One through five years 2.04 134,449 132,594 2.98 8,369 8,370 After five through ten years 2.36 887,796 868,090 2.66 45,690 45,450 Over ten years 2.38 3,639,113 3,535,132 2.56 168,737 164,600 2.38 % $ 4,668,025 $ 4,542,486 2.60 % $ 224,241 $ 219,868
Schedule of Realized Gains and Losses from Sale of Securities Classified as Available for Sale	The following is a summary of realized gains and losses from the sale of securities classified as available for sale. Gains or losses on securities sold are recorded on the trade date, using the specific identification method. Three Months Ended March 31, (Dollars in thousands) 2018 2017 Realized gains $ 9 $ — Realized losses (68 ) — $ (59 ) $ —
Schedule of Securities in Other Assets on Company's Consolidated Balance Sheets	The Company accounts for the following securities at cost less impairment plus or minus any observable price changes, which approximates fair value, with the exception of CRA and Community Development Investment Funds, which are recorded at fair value. Other Equity Securities, which are presented in “other assets” on the consolidated balance sheets, are as follows: (Dollars in thousands) March 31, 2018 December 31, 2017 Federal Home Loan Bank (FHLB) stock $ 90,561 $ 95,171 Federal Reserve Bank (FRB) stock 79,191 79,191 CRA and Community Development Investment Funds 9,801 — Other investments 9,705 3,008 $ 189,258 $ 177,370

Allowance for Credit Losses a30

Allowance for Credit Losses and Credit Quality (Tables)	3 Months Ended
	Mar. 31, 2018
Receivables [Abstract]
Schedule of Allowance for Loan Losses for Covered and Non-Covered Loan Portfolios	A summary of changes in the allowance for credit losses for the three months ended March 31 is as follows: (Dollars in thousands) 2018 2017 Allowance for credit losses Allowance for loan and lease losses at beginning of period $ 140,891 $ 144,719 Provision for loan and lease losses 7,986 6,154 Transfer of balance to OREO and other (47 ) 73 Charge-offs (9,116 ) (7,291 ) Recoveries 4,813 1,235 Allowance for loan and lease losses at end of period $ 144,527 $ 144,890 Reserve for unfunded commitments at beginning of period $ 13,208 $ 11,241 Provision for unfunded lending commitments 224 419 Reserve for unfunded commitments at end of period $ 13,432 $ 11,660 Allowance for credit losses at end of period $ 157,959 $ 156,550 A summary of changes in the allowance for credit losses, by loan portfolio type, for the three months ended March 31 is as follows: 2018 (Dollars in thousands) Commercial Real Estate Commercial and Industrial Residential Mortgage Consumer Total Allowance for loan and lease losses at beginning of period $ 54,201 $ 53,916 $ 9,117 $ 23,657 $ 140,891 Provision for (Reversal of) loan and lease losses 6,377 294 (686 ) 2,001 7,986 Transfer of balance to OREO and other (47 ) — — — (47 ) Charge-offs (114 ) (5,378 ) (105 ) (3,519 ) (9,116 ) Recoveries 191 3,698 22 902 4,813 Allowance for loan and lease losses at end of period $ 60,608 $ 52,530 $ 8,348 $ 23,041 $ 144,527 Reserve for unfunded commitments at beginning of period $ 4,531 $ 5,309 $ 555 $ 2,813 $ 13,208 Provision for (Reversal of) unfunded commitments 1,476 (1,004 ) (15 ) (233 ) 224 Reserve for unfunded commitments at end of period $ 6,007 $ 4,305 $ 540 $ 2,580 $ 13,432 Allowance on loans individually evaluated for impairment $ 2,506 $ 14,040 $ 178 $ 2,974 $ 19,698 Allowance on loans collectively evaluated for impairment 35,871 36,208 2,073 16,544 90,696 Allowance on loans acquired with deteriorated credit quality 22,231 2,282 6,097 3,523 34,133 Loans and leases, net of unearned income: Balance at end of period $ 9,248,951 $ 5,325,682 $ 3,971,067 $ 3,160,390 $ 21,706,090 Balance at end of period individually evaluated for impairment 78,489 78,725 6,041 33,277 196,532 Balance at end of period collectively evaluated for impairment 8,946,138 5,211,736 3,826,721 3,043,085 21,027,680 Balance at end of period acquired with deteriorated credit quality 224,324 35,221 138,305 84,028 481,878 2017 (Dollars in thousands) Commercial Real Estate Commercial and Industrial Residential Mortgage Consumer Total Allowance for loan losses at beginning of period $ 49,231 $ 60,939 $ 11,249 $ 23,300 $ 144,719 Provision for (Reversal of) loan and lease losses 1,786 2,557 (1,060 ) 2,871 6,154 Transfer of balance to OREO and other 377 (350 ) 2 44 73 Charge-offs (95 ) (3,762 ) (22 ) (3,412 ) (7,291 ) Recoveries 196 84 43 912 1,235 Allowance for loan losses at end of period $ 51,495 $ 59,468 $ 10,212 $ 23,715 $ 144,890 Reserve for unfunded commitments at beginning of period $ 3,207 $ 4,537 $ 657 $ 2,840 $ 11,241 Provision for (Reversal of) unfunded commitments 1,379 (885 ) (49 ) (26 ) 419 Reserve for unfunded commitments at end of period $ 4,586 $ 3,652 $ 608 $ 2,814 $ 11,660 Allowance on loans individually evaluated for impairment $ 1,916 $ 25,056 $ 113 $ 1,724 $ 28,809 Allowance on loans collectively evaluated for impairment 26,872 32,383 3,907 17,764 80,926 Allowance on loans acquired with deteriorated credit quality 22,707 2,029 6,192 4,227 35,155 Loans, net of unearned income: Balance at end of period $ 7,021,341 $ 3,975,734 $ 1,296,358 $ 2,838,769 $ 15,132,202 Balance at end of period individually evaluated for impairment 74,351 164,405 5,048 25,308 269,112 Balance at end of period collectively evaluated for impairment 6,687,651 3,778,775 1,176,017 2,723,308 14,365,751 Balance at end of period acquired with deteriorated credit quality 259,339 32,554 115,293 90,153 497,339
Investment in Legacy and Acquired Loans by Credit Quality Indicator	The Company’s investment in loans by credit quality indicator is presented in the following tables. Asset risk classifications for commercial loans and leases reflect the classification as of March 31, 2018 and December 31, 2017. Credit quality information in the tables below includes total loans acquired (including acquired impaired loans) at the net loan balance, after the application of premiums/discounts, at March 31, 2018 and December 31, 2017. Loan premiums/discounts represent the adjustment of acquired loans to fair value at the acquisition date, as adjusted for income accretion and changes in cash flow estimates in subsequent periods. Loan premiums/discounts include preliminary discounts recorded on acquired Sabadell United and Gibraltar loans, which are subject to change upon receipt of final fair value estimates during the measurement period. Loan delinquency is the primary credit quality indicator that the Company utilizes to monitor consumer asset quality. March 31, 2018 December 31, 2017 (Dollars in thousands) Pass Special Mention Sub- Doubtful Total Pass Special Mention Sub- Doubtful Loss Total Commercial real estate - construction $ 1,153,604 $ 16,399 $ 29,610 $ 12 $ 1,199,625 $ 1,189,490 $ 20,351 $ 30,541 $ 14 $ — $ 1,240,396 Commercial real estate - owner-occupied 2,464,072 83,356 56,409 8,407 2,612,244 2,388,715 82,114 56,590 2,466 — 2,529,885 Commercial real estate- non-owner-occupied 5,335,816 45,905 51,089 4,272 5,437,082 5,104,074 19,311 42,702 1,744 118 5,167,949 Commercial and industrial 5,124,676 55,041 107,126 38,839 5,325,682 4,882,554 88,149 128,961 35,403 — 5,135,067 Total $ 14,078,168 $ 200,701 $ 244,234 $ 51,530 $ 14,574,633 $ 13,564,833 $ 209,925 $ 258,794 $ 39,627 $ 118 $ 14,073,297 March 31, 2018 December 31, 2017 (Dollars in thousands) Current 30+ Days Past Due Total Current 30+ Days Past Due Total Residential mortgage $ 3,859,751 $ 111,316 $ 3,971,067 $ 2,962,043 $ 94,309 $ 3,056,352 Consumer - home equity 2,376,171 45,015 2,421,186 2,250,205 42,070 2,292,275 Consumer - indirect automobile 48,587 2,084 50,671 59,836 2,857 62,693 Consumer - credit card 92,497 764 93,261 95,263 1,105 96,368 Consumer - other 589,098 6,174 595,272 490,399 6,797 497,196 Total $ 6,966,104 $ 165,353 $ 7,131,457 $ 5,857,746 $ 147,138 $ 6,004,884
Schedule of Investment in Legacy Impaired Loans	Information on the Company’s investment in impaired loans, which include all TDRs and all other non-accrual loans evaluated or measured individually for impairment for purposes of determining the ALLL, is presented in the following tables as of and for the periods indicated. March 31, 2018 December 31, 2017 Unpaid Principal Balance Recorded Investment Related Allowance Unpaid Principal Balance Recorded Investment Related Allowance (Dollars in thousands) With no related allowance recorded: Commercial real estate- construction $ 11,153 $ 11,153 $ — $ 13,763 $ 13,013 $ — Commercial real estate- owner-occupied 43,562 36,042 — 50,867 44,482 — Commercial real estate- non-owner-occupied 10,575 10,449 — 15,370 14,975 — Commercial and industrial 45,720 36,829 — 103,013 70,254 — Residential mortgage 1,083 1,083 — 2,004 2,001 — Consumer - home equity 31 31 — 5,906 5,634 — Consumer -other — — — 75 75 — With an allowance recorded: Commercial real estate- construction 236 154 (18 ) 238 156 (19 ) Commercial real estate- owner-occupied 17,536 17,419 (1,860 ) 13,314 13,287 (949 ) Commercial real estate- non-owner-occupied 3,399 3,272 (628 ) 6,051 5,872 (620 ) Commercial and industrial 46,705 41,896 (14,040 ) 35,306 32,162 (12,736 ) Residential mortgage 5,357 4,958 (178 ) 5,179 4,748 (172 ) Consumer - home equity 28,917 28,187 (2,435 ) 27,189 26,575 (2,358 ) Consumer - indirect automobile 1,004 656 (75 ) 1,034 679 (79 ) Consumer - other 4,493 4,403 (464 ) 4,320 4,214 (419 ) Total $ 219,771 $ 196,532 $ (19,698 ) $ 283,629 $ 238,127 $ (17,352 ) Total commercial loans and leases $ 178,886 $ 157,214 $ (16,546 ) $ 237,922 $ 194,201 $ (14,324 ) Total mortgage loans 6,440 6,041 (178 ) 7,183 6,749 (172 ) Total consumer loans 34,445 33,277 (2,974 ) 38,524 37,177 (2,856 ) Three Months Ended March 31, 2018 Three Months Ended March 31, 2017 Average Interest Average Interest (Dollars in thousands) With no related allowance recorded: Commercial real estate- construction $ 10,470 $ 144 $ — $ — Commercial real estate- owner-occupied 36,277 334 37,197 339 Commercial real estate- non-owner-occupied 10,557 98 5,988 17 Commercial and industrial 27,832 385 90,664 448 Residential mortgage 1,090 12 735 5 Consumer - home equity 32 — 4,158 40 With an allowance recorded: Commercial real estate- construction 153 1 1,984 1 Commercial real estate- owner-occupied 17,608 112 20,980 79 Commercial real estate- non-owner-occupied 3,302 10 8,587 94 Commercial and industrial 44,056 196 78,695 220 Residential mortgage 4,974 44 4,335 42 Consumer - home equity 28,203 292 16,713 179 Consumer - indirect automobile 717 5 767 7 Consumer - other 4,483 62 3,328 52 Total $ 189,754 $ 1,695 $ 274,131 $ 1,523 Total commercial loans and leases $ 150,255 $ 1,280 $ 244,095 $ 1,198 Total mortgage loans 6,064 56 5,070 47 Total consumer loans 33,435 359 24,966 278

Goodwill and Other Intangible31

Goodwill and Other Intangible Assets (Tables)	3 Months Ended
	Mar. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Carrying Amount of Goodwill	Changes to the carrying amount of goodwill by reporting unit for the three months ended March 31, 2018, and the year ended December 31, 2017 are provided in the following table. (Dollars in thousands) IBERIABANK Mortgage LTC Total Balance, December 31, 2016 $ 698,513 $ 23,178 $ 5,165 $ 726,856 Goodwill acquired during the year (preliminary allocation) 462,046 — — 462,046 Balance, December 31, 2017 $ 1,160,559 $ 23,178 $ 5,165 $ 1,188,902 Goodwill acquired during the year (preliminary allocation) and adjustments 43,887 — 3,380 47,267 Balance, March 31, 2018 $ 1,204,446 $ 23,178 $ 8,545 $ 1,236,169
Schedule of Mortgage Servicing Rights	Mortgage Servicing Rights Mortgage servicing rights are recorded at the lower of cost or market value in “other intangible assets” on the Company's consolidated balance sheets and amortized over the remaining servicing life of the loans, with consideration given to prepayment assumptions. Mortgage servicing rights had the following carrying values as of the periods indicated: March 31, 2018 December 31, 2017 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount (Dollars in thousands) Mortgage servicing rights $ 10,030 $ (4,128 ) $ 5,902 $ 9,588 $ (3,931 ) $ 5,657
Schedule of Definite-Lived Intangible Assets	Definite-lived intangible assets had the following carrying values included in “other intangible assets” on the Company’s consolidated balance sheets as of the periods indicated: March 31, 2018 December 31, 2017 (Dollars in thousands) Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Core deposit intangible assets $ 136,183 $ (46,736 ) $ 89,447 $ 127,957 $ (51,971 ) $ 75,986 Customer relationship intangible asset 1,385 (1,262 ) 123 1,143 (996 ) 147 Non-compete agreement 206 (36 ) 170 63 (39 ) 24 Total $ 137,774 $ (48,034 ) $ 89,740 $ 129,163 $ (53,006 ) $ 76,157

Derivative Instruments and Ot32

Derivative Instruments and Other Hedging Activities (Tables)	3 Months Ended
	Mar. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Outstanding Derivative Instruments	Information pertaining to outstanding derivative instruments is as follows: Balance Sheet Location Derivative Assets - Fair Value Balance Sheet Location Derivative Liabilities - Fair Value (Dollars in thousands) March 31, 2018 December 31, 2017 March 31, 2018 December 31, 2017 Derivatives designated as hedging instruments under ASC Topic 815: Interest rate contracts Other assets $ — $ — Other liabilities $ — $ — Total derivatives designated as hedging instruments under ASC Topic 815 $ — $ — $ — $ — Derivatives not designated as hedging instruments under ASC Topic 815: Interest rate contracts Other assets $ 5,827 $ 20,446 Other liabilities $ 25,771 $ 16,191 Foreign exchange contracts Other assets 2 7 Other liabilities 2 7 Forward sales contracts Other assets 2,851 136 Other liabilities 703 279 Written and purchased options Other assets 8,383 10,654 Other liabilities 5,667 8,656 Other contracts Other assets 9 22 Other liabilities 11 21 Total derivatives not designated as hedging instruments under ASC Topic 815 $ 17,072 $ 31,265 $ 32,154 $ 25,154 Total $ 17,072 $ 31,265 $ 32,154 $ 25,154 Derivative Assets - Notional Amount Derivative Liabilities - Notional Amount (Dollars in thousands) March 31, 2018 December 31, 2017 March 31, 2018 December 31, 2017 Derivatives designated as hedging instruments under ASC Topic 815: Interest rate contracts $ 108,500 $ — $ — $ 108,500 Total derivatives designated as hedging instruments under ASC Topic 815 $ 108,500 $ — $ — $ 108,500 Derivatives not designated as hedging instruments under ASC Topic 815: Interest rate contracts $ 1,356,990 $ 1,218,464 $ 1,276,990 $ 1,218,464 Foreign exchange contracts 628 268 628 268 Forward sales contracts 96,810 82,347 215,918 142,578 Written and purchased options 339,852 278,638 164,341 165,198 Other contracts 29,676 29,755 71,889 86,744 Total derivatives not designated as hedging instruments under ASC Topic 815 $ 1,823,956 $ 1,609,472 $ 1,729,766 $ 1,613,252 Total $ 1,932,456 $ 1,609,472 $ 1,729,766 $ 1,721,752
Offsetting Assets	The following table reconciles the gross amounts presented in the consolidated balance sheets to the net amounts that would result in the event of offset. March 31, 2018 Gross Amounts Presented in the Balance Sheet Gross Amounts Not Offset in the Balance Sheet Net (Dollars in thousands) Derivatives Collateral (1) Derivatives subject to master netting arrangements Derivative assets Interest rate contracts not designated as hedging instruments $ 5,827 $ (548 ) $ — $ 5,279 Written and purchased options 5,656 — — 5,656 Total derivative assets subject to master netting arrangements $ 11,483 $ (548 ) $ — $ 10,935 Derivative liabilities Interest rate contracts designated as hedging instruments $ — $ — $ — $ — Interest rate contracts not designated as hedging instruments 25,771 (548 ) — 25,223 Written and purchased options 5,587 — — 5,587 Total derivative liabilities subject to master netting arrangements $ 31,358 $ (548 ) $ — $ 30,810 (1) Consists of cash collateral recorded at cost, which approximates fair value, and investment securities. December 31, 2017 Gross Amounts Presented in the Balance Sheet Gross Amounts Not Offset in the Balance Sheet Net (Dollars in thousands) Derivatives Collateral (1) Derivatives subject to master netting arrangements Derivative assets Interest rate contracts not designated as hedging instruments $ 20,446 $ (12,469 ) $ — $ 7,977 Written and purchased options 8,610 — — 8,610 Total derivative assets subject to master netting arrangements $ 29,056 $ (12,469 ) $ — $ 16,587 Derivative liabilities Interest rate contracts designated as hedging instruments $ — $ — $ — $ — Interest rate contracts not designated as hedging instruments 16,191 (12,469 ) (552 ) 3,170 Total derivative liabilities subject to master netting arrangements $ 16,191 $ (12,469 ) $ (552 ) $ 3,170
Offsetting Liabilities	The following table reconciles the gross amounts presented in the consolidated balance sheets to the net amounts that would result in the event of offset. March 31, 2018 Gross Amounts Presented in the Balance Sheet Gross Amounts Not Offset in the Balance Sheet Net (Dollars in thousands) Derivatives Collateral (1) Derivatives subject to master netting arrangements Derivative assets Interest rate contracts not designated as hedging instruments $ 5,827 $ (548 ) $ — $ 5,279 Written and purchased options 5,656 — — 5,656 Total derivative assets subject to master netting arrangements $ 11,483 $ (548 ) $ — $ 10,935 Derivative liabilities Interest rate contracts designated as hedging instruments $ — $ — $ — $ — Interest rate contracts not designated as hedging instruments 25,771 (548 ) — 25,223 Written and purchased options 5,587 — — 5,587 Total derivative liabilities subject to master netting arrangements $ 31,358 $ (548 ) $ — $ 30,810 (1) Consists of cash collateral recorded at cost, which approximates fair value, and investment securities. December 31, 2017 Gross Amounts Presented in the Balance Sheet Gross Amounts Not Offset in the Balance Sheet Net (Dollars in thousands) Derivatives Collateral (1) Derivatives subject to master netting arrangements Derivative assets Interest rate contracts not designated as hedging instruments $ 20,446 $ (12,469 ) $ — $ 7,977 Written and purchased options 8,610 — — 8,610 Total derivative assets subject to master netting arrangements $ 29,056 $ (12,469 ) $ — $ 16,587 Derivative liabilities Interest rate contracts designated as hedging instruments $ — $ — $ — $ — Interest rate contracts not designated as hedging instruments 16,191 (12,469 ) (552 ) 3,170 Total derivative liabilities subject to master netting arrangements $ 16,191 $ (12,469 ) $ (552 ) $ 3,170
Effect of Derivatives on the Consolidated Financial Statements	At March 31, 2018 and 2017 , and for the three months then ended, information pertaining to the effect of the hedging instruments on the consolidated financial statements is as follows: Location of Gain (Loss) Recognized in Income on Derivative (Amount Excluded from Effectiveness Testing) Amount of Gain (Loss) Recognized in Income on Derivative (Amount Excluded from Effectiveness Testing) Amount of Gain (Loss) Recognized in OCI, net of taxes Location of Gain (Loss) Reclassified from Accumulated OCI into Income Amount of Gain (Loss) Reclassified from Accumulated OCI into Income, net of taxes (Dollars in thousands) For the Three Months Ended March 31 Derivatives in ASC Topic 815 Cash Flow Hedging Relationships 2018 2017 2018 2017 2018 2017 Interest rate contracts $ 2,549 $ 73 Interest expense $ (116 ) $ (45 ) Interest expense $ — $ — Total $ 2,549 $ 73 $ (116 ) $ (45 ) $ — $ — Information pertaining to the effect of derivatives not designated as hedging instruments on the consolidated financial statements as of March 31, is as follows: Location of Gain (Loss) Recognized in Income on Derivatives Amount of Gain (Loss) Recognized in Income on Derivatives For the Three Months Ended March 31 (Dollars in thousands) 2018 2017 Interest rate contracts (1) Other income $ 1,049 $ 1,117 Foreign exchange contracts Other income 5 7 Forward sales contracts Mortgage income 3,387 (360 ) Written and purchased options Mortgage income 648 655 Other contracts Other income (3 ) 4 Total $ 5,086 $ 1,423

Income Taxes Income Taxes (Tabl

Income Taxes Income Taxes (Tables)	3 Months Ended
	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	The following table presents the provision for income taxes and the effective tax rates for the three months ended March 31, 2018 and 2017: Three Months Ended March 31, (Dollars in thousands) 2018 2017 Income before income tax expense $ 81,173 $ 72,992 Income tax expense 17,552 22,519 Effective tax rate 21.6 % 30.9 %

Shareholders' Equity, Capital34

Shareholders' Equity, Capital Ratios and Other Regulatory Matters (Tables)	3 Months Ended
	Mar. 31, 2018
Banking and Thrift [Abstract]
Schedule of Preferred Stock	The following table presents a summary of the Company's non-cumulative perpetual preferred stock: March 31, 2018 December 31, 2017 Issuance Date Earliest Redemption Date Annual Dividend Rate Liquidation Amount Carrying Amount Carrying Amount (Dollars in thousands) Series B Preferred Stock 8/5/2015 8/1/2025 6.625 % $ 80,000 $ 76,812 $ 76,812 Series C Preferred Stock 5/9/2016 5/1/2026 6.600 % 57,500 55,285 55,285 $ 137,500 $ 132,097 $ 132,097
Actual Capital Amounts and Ratios	The Company’s and IBERIABANK’s actual capital amounts and ratios as of March 31, 2018 and December 31, 2017 are presented in the following tables. (Dollars in thousands) March 31, 2018 Minimum Well-Capitalized Actual Amount Ratio Amount Ratio Amount Ratio Tier 1 Leverage Consolidated $ 1,076,933 4.00 % N/A N/A $ 2,685,315 9.97 % IBERIABANK 1,074,579 4.00 1,343,223 5.00 2,640,916 9.83 Common Equity Tier 1 (CET1) (1) Consolidated $ 1,067,284 4.50 % N/A N/A $ 2,553,218 10.77 % IBERIABANK 1,065,059 4.50 1,538,418 6.50 2,640,916 11.16 Tier 1 Risk-Based Capital (1) Consolidated $ 1,423,046 6.00 % N/A N/A $ 2,685,315 11.32 % IBERIABANK 1,420,078 6.00 1,893,437 8.00 2,640,916 11.16 Total Risk-Based Capital (1) Consolidated $ 1,897,394 8.00 % N/A N/A $ 2,959,774 12.48 % IBERIABANK 1,893,437 8.00 2,366,797 10.00 2,798,875 11.83 December 31, 2017 Minimum Well-Capitalized Actual Amount Ratio Amount Ratio Amount Ratio Tier 1 Leverage Consolidated $ 1,073,381 4.00 % N/A N/A $ 2,509,496 9.35 % IBERIABANK 1,070,789 4.00 1,338,487 5.00 2,437,275 9.10 Common Equity Tier 1 (CET1) (1) Consolidated $ 1,011,732 4.50 % N/A N/A $ 2,377,398 10.57 % IBERIABANK 1,009,553 4.50 1,458,243 6.50 2,437,275 10.86 Tier 1 Risk-Based Capital (1) Consolidated $ 1,348,977 6.00 % N/A N/A $ 2,509,496 11.16 % IBERIABANK 1,346,070 6.00 1,794,760 8.00 2,437,275 10.86 Total Risk-Based Capital (1) Consolidated $ 1,798,635 8.00 % N/A N/A $ 2,780,095 12.37 % IBERIABANK 1,794,760 8.00 2,243,450 10.00 2,591,374 11.55 (1) Minimum capital ratios are subject to a capital conservation buffer. In order to avoid limitations on distributions, including dividend payments, and certain discretionary bonus payments to executive officers, an institution must hold a capital conservation buffer above its minimum risk-based capital requirements. This capital conservation buffer is calculated as the lowest of the differences between the actual CET1 ratio, Tier 1 Risk-Based Capital Ratio, and Total Risk-Based Capital ratio and the corresponding minimum ratios. At March 31, 2018, the required minimum capital conservation buffer was 1.875% , and will increase by 0.625% and be fully phased-in on January 1, 2019 at 2.50% . At March 31, 2018, the capital conservation buffers of the Company and IBERIABANK were 4.48% and 3.83% , respectively.

Earnings Per Share (Tables)

Earnings Per Share (Tables)	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Schedule of Calculation of Basic and Diluted Earnings Per Share	The following table presents the calculation of basic and diluted earnings per share for the periods indicated. Three Months Ended March 31, (In thousands, except per share data) 2018 2017 Earnings per common share - basic: Net income $ 63,621 $ 50,473 Less: Preferred stock dividends 3,598 3,599 Less: Dividends and undistributed earnings allocated to unvested restricted shares 639 346 Net income allocated to common shareholders - basic $ 59,384 $ 46,528 Weighted average common shares outstanding 53,616 46,123 Earnings per common share - basic 1.11 1.01 Earnings per common share - diluted: Net income allocated to common shareholders - basic $ 59,384 $ 46,528 Adjustment for undistributed earnings allocated to unvested restricted shares (18 ) (37 ) Net income allocated to common shareholders - diluted $ 59,366 $ 46,491 Weighted average common shares outstanding 53,616 46,123 Dilutive potential common shares 351 373 Weighted average common shares outstanding - diluted 53,967 46,496 Earnings per common share - diluted $ 1.10 $ 1.00

Share-Based Compensation (Table

Share-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Share-based Compensation Arrangements by Share-based Payment Award	The following table represents unvested restricted stock award and restricted share unit activity for the following periods: For the Three Months Ended March 31, 2018 2017 Number of shares at beginning of period 738,187 543,258 Granted 199,958 146,175 Forfeited (43,405 ) (4,105 ) Vested (115,877 ) (157,753 ) Number of shares at end of period 778,863 527,575 The following table represents phantom stock award activity during the periods indicated. (Dollars in thousands) Number of share equivalents (1) Value of share equivalents (2) Balance, December 31, 2016 472,830 $ 39,600 Granted 96,897 7,665 Forfeited share equivalents (5,330 ) 422 Vested share equivalents (143,643 ) 12,024 Balance, March 31, 2017 420,754 $ 33,282 Balance, December 31, 2017 393,844 $ 30,523 Granted 129,234 10,080 Forfeited share equivalents (24,460 ) 1,908 Vested share equivalents (121,758 ) 10,187 Balance, March 31, 2018 376,860 $ 29,395 (1) Number of share equivalents includes all reinvested dividend equivalents for the periods indicated. (2) Except for share equivalents at the beginning of each period, which are based on the value at that time, and vested share payments, which are based on the cash paid at the time of vesting, the value of share equivalents is calculated based on the market price of the Company’s stock at the end of the respective periods. The market price of the Company’s stock was $78.00 and $79.10 on March 31, 2018, and 2017, respectively. The following table represents the activity related to stock options during the periods indicated: Number of Shares Weighted Average Exercise Price Outstanding options, December 31, 2016 721,538 $ 55.38 Granted 70,433 85.52 Exercised (24,457 ) 53.85 Forfeited or expired (12,539 ) 75.77 Outstanding options, March 31, 2017 754,975 $ 57.90 Exercisable options, March 31, 2017 509,347 $ 55.78 Outstanding options, December 31, 2017 686,366 $ 58.24 Granted 92,162 82.20 Exercised (21,212 ) 52.10 Forfeited or expired (14,513 ) 65.27 Outstanding options, March 31, 2018 742,803 $ 61.25 Exercisable options, March 31, 2018 519,496 $ 56.53
Schedule of Valuation Assumptions	The following weighted-average assumptions were used for option awards issued during the following periods: For the Three Months Ended March 31, 2018 2017 Expected dividends 1.8 % 1.7 % Expected volatility 24.3 % 24.9 % Risk-free interest rate 2.7 % 2.1 % Expected term (in years) 5.7 5.6 Weighted-average grant-date fair value $ 18.36 $ 18.75
Schedule of Allocation for Share-based Compensation Expense	The following table represents the compensation expense that was included in non-interest expense and related income tax benefits in the accompanying consolidated statements of comprehensive income related to restricted stock awards and restricted share units for the periods indicated: For the Three Months Ended March 31, (Dollars in thousands) 2018 2017 Compensation expense related to restricted stock awards and restricted share units $ 4,422 $ 3,277 Income tax benefit related to restricted stock awards and restricted share units 929 1,147 The following table represents the compensation expense that is included in non-interest expense and related income tax benefits in the accompanying consolidated statements of comprehensive income related to stock options for the following periods: For the Three Months Ended March 31, (Dollars in thousands) 2018 2017 Compensation expense related to stock options $ 312 $ 444 Income tax benefit related to stock options 23 68 The following table indicates compensation expense recorded for phantom stock based on the number of share equivalents vested at March 31 of the periods indicated and the current market price of the Company’s stock at that time: For the Three Months Ended March 31, (Dollars in thousands) 2018 2017 Compensation expense related to phantom stock $ 2,996 $ 3,053

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Financial Asset and Liabilities Measured at Fair Value on Recurring Basis	The Company has segregated all financial assets and liabilities that are measured at fair value on a recurring basis into the most appropriate level within the fair value hierarchy based on the inputs used to estimate the fair value at the measurement date in the tables below. See Note 1, Summary of Significant Accounting Policies, in the Annual Report on Form 10-K for the year ended December 31, 2017, for a description of how fair value measurements are determined. March 31, 2018 (Dollars in thousands) Level 1 Level 2 Level 3 Total Assets Securities available for sale $ — $ 4,542,486 $ — $ 4,542,486 CRA and Community Development Investment Funds — 9,801 — 9,801 Mortgage loans held for sale — 110,348 — 110,348 Derivative instruments — 17,072 — 17,072 Total $ — $ 4,679,707 $ — $ 4,679,707 Liabilities Derivative instruments $ — $ 32,154 $ — $ 32,154 Total $ — $ 32,154 $ — $ 32,154 December 31, 2017 Level 1 Level 2 Level 3 Total Assets Securities available for sale $ — $ 4,590,062 $ — $ 4,590,062 Mortgage loans held for sale — 134,916 — 134,916 Derivative instruments — 31,265 — 31,265 Total $ — $ 4,756,243 $ — $ 4,756,243 Liabilities Derivative instruments $ — $ 25,154 $ — $ 25,154 Total $ — $ 25,154 $ — $ 25,154
Financial Asset and Liabilities Measured at Fair Value on Nonrecurring Basis	The Company has segregated all assets and liabilities that are measured at fair value on a non-recurring basis into the most appropriate level within the fair value hierarchy based on the inputs used to determine the fair value at the measurement date in the tables below. March 31, 2018 (Dollars in thousands) Level 1 Level 2 Level 3 Total Assets Loans $ — $ — $ 85,269 $ 85,269 OREO, net — — 2,234 2,234 Total $ — $ — $ 87,503 $ 87,503 December 31, 2017 (Dollars in thousands) Level 1 Level 2 Level 3 Total Assets Loans $ — $ — $ 71,210 $ 71,210 OREO, net — — 3,029 3,029 Total $ — $ — $ 74,239 $ 74,239
Summary of Difference Between the Aggregate Fair Value and the Aggregate Unpaid Principal Balance for Mortgage Loans Held for Sale	The following table summarizes the difference between the aggregate fair value and the aggregate unpaid principal balance for mortgage loans held for sale measured at fair value: March 31, 2018 December 31, 2017 (Dollars in thousands) Aggregate Fair Value Aggregate Unpaid Principal Aggregate Fair Value Less Unpaid Principal Aggregate Fair Value Aggregate Unpaid Principal Aggregate Fair Value Less Unpaid Principal Mortgage loans held for sale, at fair value $ 110,348 $ 107,849 $ 2,499 $ 134,916 $ 131,276 $ 3,640

Fair Value of Financial Instr38

Fair Value of Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Estimated Fair Values and Carrying Amounts of Financial Instruments	The carrying amount and estimated fair values, as well as the level within the fair value hierarchy, of the Company’s financial instruments are included in the tables below. See Note 1, Summary of Significant Accounting Policies, in the 2017 Annual Report on Form 10-K for the year ended December 31, 2017 for a description of how fair value measurements are determined, except for loans, amended upon implementation of ASU 2016-01, Financial Statements - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities. See Note 2, Recent Accounting Pronouncements, in this Report for a description of how the fair value measurement is determined for loans beginning January 1, 2018. March 31, 2018 (Dollars in thousands) Carrying Amount Fair Value Level 1 Level 2 Level 3 Measurement Category Fair Value Financial Assets Securities available for sale $ 4,542,486 $ 4,542,486 $ — $ 4,542,486 $ — CRA and Community Development Investment Funds 9,801 9,801 — 9,801 — Mortgage loans held for sale 110,348 110,348 — 110,348 — Derivative instruments 17,072 17,072 — 17,072 — Financial Liabilities Derivative instruments 32,154 32,154 — 32,154 — Amortized Cost Financial Assets Cash and cash equivalents $ 564,092 $ 564,092 $ 564,092 $ — $ — Securities held to maturity 224,241 219,868 — 219,868 — Loans and leases, net of unearned income and allowance for loan and lease losses 21,561,563 21,495,639 — — 21,495,639 Financial Liabilities Deposits 22,971,192 22,970,554 — 22,970,554 — Short-term borrowings 900,496 900,496 525,496 375,000 — Long-term debt 1,449,302 1,429,335 — — 1,429,335 December 31, 2017 (Dollars in thousands) Carrying Amount Fair Value Level 1 Level 2 Level 3 Measurement Category Fair Value Financial Assets Securities available for sale $ 4,590,062 $ 4,590,062 $ — $ 4,590,062 $ — Mortgage loans held for sale 134,916 134,916 — 134,916 — Derivative instruments 31,265 31,265 — 31,265 — Financial Liabilities Derivative instruments 25,154 25,154 — 25,154 — Amortized Cost Financial Assets Cash and cash equivalents $ 625,724 $ 625,724 $ 625,724 $ — $ — Securities held to maturity 227,318 227,964 — 227,964 — Loans and leases, net of unearned income and allowance for loan and lease losses 19,937,290 19,826,857 — — 19,826,857 Financial Liabilities Deposits 21,466,717 21,460,782 — 21,460,782 — Short-term borrowings 991,297 991,297 516,297 475,000 — Long-term debt 1,495,835 1,476,899 — — 1,476,899

Business Segments (Tables)

Business Segments (Tables)	3 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
Schedule of Segment Reporting Information	The following tables present certain information regarding our operations by reportable segment, including a reconciliation of segment results to reported consolidated results for the periods presented. Reconciling items between segment results and reported results include: • Elimination of interest income and interest expense representing interest earned by IBERIABANK on interest-bearing checking accounts held by related companies, as well as the elimination of the related deposit balances at the IBERIABANK segment; • Elimination of investment in subsidiary balances on certain operating segments included in total and average segment assets; and • Elimination of intercompany due to and due from balances on certain operating segments that are included in total and average segment assets. Three Months Ended March 31, 2018 (Dollars in thousands) IBERIABANK Mortgage LTC Consolidated Interest and dividend income $ 268,775 $ 1,767 $ 1 $ 270,543 Interest expense 37,654 — — 37,654 Net interest income 231,121 1,767 1 232,889 Provision for/(reversal of) loan and lease losses 7,991 (5 ) — 7,986 Mortgage income — 9,595 — 9,595 Title revenue — — 5,027 5,027 Other non-interest income 29,906 38 — 29,944 Allocated expenses (1,479 ) 1,166 313 — Non-interest expense 171,816 11,916 4,564 188,296 Income/(loss) before income tax expense 82,699 (1,677 ) 151 81,173 Income tax expense/(benefit) 18,540 (410 ) (578 ) 17,552 Net income/(loss) $ 64,159 $ (1,267 ) $ 729 $ 63,621 Total loans, leases, and loans held for sale, net of unearned income $ 21,652,223 $ 164,215 $ — $ 21,816,438 Total assets 29,243,983 205,497 23,157 29,472,637 Total deposits 22,959,061 12,131 — 22,971,192 Average assets 27,924,587 185,742 21,890 28,132,219 Three Months Ended March 31, 2017 (Dollars in thousands) IBERIABANK Mortgage LTC Consolidated Interest and dividend income $ 190,823 $ 1,709 $ 1 $ 192,533 Interest expense 19,715 — — 19,715 Net interest income 171,108 1,709 1 172,818 Provision for/(reversal of) loan and lease losses 6,158 (4 ) — 6,154 Mortgage income — 14,115 — 14,115 Title revenue — — 4,741 4,741 Other non-interest income 26,284 (10 ) (6 ) 26,268 Allocated expenses (2,174 ) 1,656 518 — Non-interest expense 119,429 15,167 4,200 138,796 Income/(loss) before income tax expense 73,979 (1,005 ) 18 72,992 Income tax expense/(benefit) 22,829 (322 ) 12 22,519 Net income/(loss) $ 51,150 $ (683 ) $ 6 $ 50,473 Total loans, leases, and loans held for sale, net of unearned income $ 15,072,661 $ 181,874 $ — $ 15,254,535 Total assets 21,774,586 209,911 23,982 22,008,479 Total deposits 17,306,328 5,937 — 17,312,265 Average assets 21,550,930 286,694 23,877 21,861,501

Commitments and Contingencies (

Commitments and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Summary of Financial Instruments Outstanding	At March 31, 2018 and December 31, 2017, respectively, the Company had the following financial instruments outstanding and related reserves, whose contract amounts represent credit risk: (Dollars in thousands) March 31, 2018 December 31, 2017 Commitments to grant loans $ 319,318 $ 342,305 Unfunded commitments under lines of credit 6,340,135 6,060,034 Commercial and standby letters of credit 211,070 210,002 Reserve for unfunded lending commitments 13,432 13,208

Recent Accounting Pronounceme41

Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands		Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Mar. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	[1]		$ (345)
Equity Securities, FV-NI		$ 9,801		$ 0
ASU 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption					$ 2,200
[1]	Cumulative-effect adjustment to beginning retained earnings for fair value adjustments related to the reclassification of certain equity investments in accordance with ASU 2016-01, adopted as of January 1, 2018.

Loans - Schedule of Non-Covered

Loans - Schedule of Non-Covered Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable
Loans and leases, net of unearned income	$ 21,706,090	$ 20,078,181
Commercial Loans
Accounts, Notes, Loans and Financing Receivable
Loans and leases, net of unearned income	14,574,633	14,073,297
Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Loans and leases, net of unearned income	1,199,625	1,240,396
Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Loans and leases, net of unearned income	2,612,244	2,529,885
Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Loans and leases, net of unearned income	5,437,082	5,167,949
Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Loans and leases, net of unearned income	5,325,682	5,135,067
Residential Mortgage
Accounts, Notes, Loans and Financing Receivable
Loans and leases, net of unearned income	3,971,067	3,056,352
Consumer and Other Loans
Accounts, Notes, Loans and Financing Receivable
Loans and leases, net of unearned income	3,160,390	2,948,532
Consumer and Other Loans | Home Equity
Accounts, Notes, Loans and Financing Receivable
Loans and leases, net of unearned income	2,421,186	2,292,275
Consumer and Other Loans | Consumer - Indirect automobile
Accounts, Notes, Loans and Financing Receivable
Loans and leases, net of unearned income	50,671	62,693
Consumer and Other Loans | Other
Accounts, Notes, Loans and Financing Receivable
Loans and leases, net of unearned income	$ 595,272	$ 497,196

Loans (Detail)

Loans (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 23, 2018	Dec. 31, 2017	Jul. 31, 2017
Accounts, Notes, Loans and Financing Receivable
Net deferred loan origination fees	$ 31,400			$ 29,300
Net discount	158,100			159,300
Deposit liabilities reclassified as loans receivable	7,300			7,400
Loans with carrying value pledged to secure public deposits and other borrowings	6,800,000			6,600,000
Loans acquired with no evidence of deteriorated credit quality	17,000			15,000
Acquired Loans
Accounts, Notes, Loans and Financing Receivable
Net discount	100,800			94,700
Sabadell United
Accounts, Notes, Loans and Financing Receivable
Loans acquired					$ 4,025,946
Covered loans acquired	150,000			158,600
Sabadell United | Non-US [Member]
Accounts, Notes, Loans and Financing Receivable
Covered loans acquired	336,100			$ 325,500
Gibraltar Private Bank & Trust Company [Member]
Accounts, Notes, Loans and Financing Receivable
Loans acquired	1,500,000		$ 1,465,319
Loans acquired with no evidence of deteriorated credit quality	1,455,085
Loans acquired with deteriorated credit quality	10,234
Troubled Debt Restructurings [Member]
Accounts, Notes, Loans and Financing Receivable
TDRs during period	27,200	$ 13,165
TDRs during period on accrual status	12,900	11,800
TDRs during period on non-accrual status	$ 14,300	$ 1,400

Loans - Schedule of Aging of Lo

Loans - Schedule of Aging of Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable
Accruing	$ 86,581	$ 68,617
Non-accrual Loans	153,975	145,388
Acquired Impaired Loans	196,532	238,127
Total Loans	21,706,090	20,078,181
Commercial Loans
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	157,214	194,201
Total Loans	14,574,633	14,073,297
Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Accruing	971	727
Non-accrual Loans	2,634	2,635
Total Loans	1,199,625	1,240,396
Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	8,228	2,364
Non-accrual Loans	35,144	24,457
Total Loans	2,612,244	2,529,885
Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	16,584	9,378
Non-accrual Loans	9,378	6,811
Total Loans	5,437,082	5,167,949
Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	11,434	11,660
Non-accrual Loans	66,637	77,823
Total Loans	5,325,682	5,135,067
Residential Mortgage
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	6,041	6,749
Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Current	3,859,751	2,962,043
Accruing	29,521	23,536
Non-accrual Loans	19,932	17,387
Total Loans	3,971,067	3,056,352
Consumer and Other Loans
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	33,277	37,177
Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Current	2,376,171	2,250,205
Accruing	15,051	14,640
Non-accrual Loans	16,383	12,365
Total Loans	2,421,186	2,292,275
Consumer and Other Loans | Consumer - Indirect automobile
Accounts, Notes, Loans and Financing Receivable
Current	48,587	59,836
Accruing	1,341	1,973
Non-accrual Loans	743	884
Total Loans	50,671	62,693
Consumer and Other Loans | Consumer - Credit card
Accounts, Notes, Loans and Financing Receivable
Current	92,497	95,263
Accruing	261	514
Non-accrual Loans	503	590
Total Loans	93,261	96,368
Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Current	589,098	490,399
Accruing	3,190	3,825
Non-accrual Loans	2,621	2,436
Total Loans	595,272	497,196
Current or Less Than 30 days past due
Accounts, Notes, Loans and Financing Receivable
Current	20,983,656	19,382,621
Current or Less Than 30 days past due | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Current	1,157,115	1,197,766
Current or Less Than 30 days past due | Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Current	2,474,611	2,398,487
Current or Less Than 30 days past due | Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Current	5,319,962	5,066,084
Current or Less Than 30 days past due | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Current	5,212,390	5,014,438
Current or Less Than 30 days past due | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Current	3,783,309	2,877,048
Current or Less Than 30 days past due | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Current	2,309,222	2,186,554
Current or Less Than 30 days past due | Consumer and Other Loans | Consumer - Indirect automobile
Accounts, Notes, Loans and Financing Receivable
Current	48,581	59,830
Current or Less Than 30 days past due | Consumer and Other Loans | Consumer - Credit card
Accounts, Notes, Loans and Financing Receivable
Current	92,497	95,264
Current or Less Than 30 days past due | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Current	585,969	487,150
30-59 days
Accounts, Notes, Loans and Financing Receivable
Accruing	61,956	36,818
30-59 days | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Accruing	842	269
30-59 days | Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	4,767	1,631
30-59 days | Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	7,269	2,086
30-59 days | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	7,755	5,788
30-59 days | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	25,640	10,083
30-59 days | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Accruing	11,860	11,675
30-59 days | Consumer and Other Loans | Consumer - Indirect automobile
Accounts, Notes, Loans and Financing Receivable
Accruing	1,166	1,796
30-59 days | Consumer and Other Loans | Consumer - Credit card
Accounts, Notes, Loans and Financing Receivable
Accruing	173	140
30-59 days | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	2,484	3,350
60-89 days
Accounts, Notes, Loans and Financing Receivable
Accruing	16,337	24,899
60-89 days | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Accruing	129	0
60-89 days | Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	3,461	659
60-89 days | Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	2,526	6,405
60-89 days | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	3,406	5,726
60-89 days | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	2,655	8,136
60-89 days | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Accruing	3,191	2,947
60-89 days | Consumer and Other Loans | Consumer - Indirect automobile
Accounts, Notes, Loans and Financing Receivable
Accruing	175	177
60-89 days | Consumer and Other Loans | Consumer - Credit card
Accounts, Notes, Loans and Financing Receivable
Accruing	88	374
60-89 days | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	706	475
Greater than 90 days
Accounts, Notes, Loans and Financing Receivable
Accruing	8,288	6,900
Greater than 90 days | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Accruing	0	458
Greater than 90 days | Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	0	74
Greater than 90 days | Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	6,789	887
Greater than 90 days | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	273	146
Greater than 90 days | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	1,226	5,317
Greater than 90 days | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Accruing	0	18
Greater than 90 days | Consumer and Other Loans | Consumer - Indirect automobile
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Greater than 90 days | Consumer and Other Loans | Consumer - Credit card
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Greater than 90 days | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Acquired Loans
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	481,878	481,555
Acquired Loans | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	38,905	39,268
Acquired Loans | Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	94,261	104,577
Acquired Loans | Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	91,158	85,676
Acquired Loans | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	35,221	31,146
Acquired Loans | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	138,305	138,381
Acquired Loans | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	80,530	78,716
Acquired Loans | Consumer and Other Loans | Consumer - Indirect automobile
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	6	6
Acquired Loans | Consumer and Other Loans | Consumer - Credit card
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	0	0
Acquired Loans | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	$ 3,492	$ 3,785

Loans - Schedule of Carrying Am

Loans - Schedule of Carrying Amount of Loans Acquired (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 23, 2018	Dec. 31, 2017	Jul. 31, 2017	Mar. 31, 2017
Accounts, Notes, Loans and Financing Receivable
Expected losses and foregone interest	$ (157,959)				$ (156,550)
Loans acquired with no evidence of deteriorated credit quality	17,000		$ 15,000
Related allowance	(2,974)		(2,856)
Sabadell United
Accounts, Notes, Loans and Financing Receivable
Loans acquired				$ 4,025,946
Covered loans acquired	150,000		$ 158,600
Gibraltar Private Bank & Trust Company [Member]
Accounts, Notes, Loans and Financing Receivable
Loans acquired	1,500,000	$ 1,465,319
Contractually required principal and interest at acquisition	1,695,918
Expected losses and foregone interest	(19,952)
Cash flows expected to be collected at acquisition	1,675,966
Loans acquired with no evidence of deteriorated credit quality	1,455,085
Impaired Financing Receivable, with Related Allowance, Recorded Investment	43,779
Related allowance	(31,174)
Impaired Financing Receivable, Expected Cash Flow	12,605
Accretable yield	(2,371)
Loans acquired with deteriorated credit quality	$ 10,234

Loans - Summary of Changes in A

Loans - Summary of Changes in Accretable Yields of Acquired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	$ 152,623	$ 175,054
Additions	2,371	0
Transfers from non-accretable difference to accretable yield	(279)	2,071
Accretion	(13,154)	(14,596)
Changes in expected cash flows not affecting non-accretable differences	9,687	1,060
Balance at end of period	$ 151,248	$ 163,589

Loans - Schedule of Modified TD

Loans - Schedule of Modified TDRs (Detail) - Troubled Debt Restructurings [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Financing Receivable, Modifications
TDRs during period on accrual status	$ 12,900	$ 11,800
TDRs during period on non-accrual status	14,300	1,400
Extended maturities	5,619	7,199
Maturity and interest rate adjustment	108	3,224
Movement to or extension of interest-rate only payments	48	1,290
Interest rate adjustment	105	0
Financing Receivable Modifications Forbearance	12,886	1,220
Other concession(s)	8,434	232
TDRs during period	$ 27,200	$ 13,165

Loans - Schedule of Subsequentl

Loans - Schedule of Subsequently Defaulted TDRs (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)SecurityLoan	Mar. 31, 2017USD ($)SecurityLoan
Accounts, Notes, Loans and Financing Receivable
Threshold period for loans in default (in days)	30 days
Non-Covered TDRs | TDRs Occurring during the Period
Accounts, Notes, Loans and Financing Receivable
Number of Loans | SecurityLoan	65	101
Pre-modification Outstanding Recorded Investment	$ 30,616	$ 13,238
Post-modification Outstanding Recorded Investment	$ 27,200	$ 13,165
Number of loans | SecurityLoan	122	162
Recorded investment	$ 24,673	$ 28,416
Non-Covered TDRs | Commercial Loans | Commercial real estate - Construction | TDRs Occurring during the Period
Accounts, Notes, Loans and Financing Receivable
Number of Loans | SecurityLoan	1	0
Pre-modification Outstanding Recorded Investment	$ 1,950	$ 0
Post-modification Outstanding Recorded Investment	$ 1,049	$ 0
Number of loans | SecurityLoan	0	1
Recorded investment	$ 0	$ 117
Non-Covered TDRs | Commercial Loans | Commercial real estate - owner-occupied | TDRs Occurring during the Period
Accounts, Notes, Loans and Financing Receivable
Number of Loans | SecurityLoan	2	3
Pre-modification Outstanding Recorded Investment	$ 10,691	$ 3,004
Post-modification Outstanding Recorded Investment	$ 9,324	$ 2,999
Number of loans | SecurityLoan	3	9
Recorded investment	$ 10,187	$ 14,732
Non-Covered TDRs | Commercial Loans | Commercial real estate - non-owner-occupied | TDRs Occurring during the Period
Accounts, Notes, Loans and Financing Receivable
Number of Loans | SecurityLoan	9	7
Pre-modification Outstanding Recorded Investment	$ 1,089	$ 1,867
Post-modification Outstanding Recorded Investment	$ 1,091	$ 1,855
Number of loans | SecurityLoan	9	10
Recorded investment	$ 492	$ 5,041
Non-Covered TDRs | Commercial Loans | Commercial and industrial | TDRs Occurring during the Period
Accounts, Notes, Loans and Financing Receivable
Number of Loans | SecurityLoan	18	15
Pre-modification Outstanding Recorded Investment	$ 14,429	$ 435
Post-modification Outstanding Recorded Investment	$ 13,314	$ 427
Number of loans | SecurityLoan	29	21
Recorded investment	$ 9,708	$ 4,186
Non-Covered TDRs | Residential Mortgage | Residential mortgage | TDRs Occurring during the Period
Accounts, Notes, Loans and Financing Receivable
Number of Loans | SecurityLoan	0	4
Pre-modification Outstanding Recorded Investment	$ 0	$ 259
Post-modification Outstanding Recorded Investment	$ 0	$ 241
Number of loans | SecurityLoan	6	22
Recorded investment	$ 598	$ 1,793
Non-Covered TDRs | Consumer and Other Loans | Consumer - Home equity | TDRs Occurring during the Period
Accounts, Notes, Loans and Financing Receivable
Number of Loans | SecurityLoan	14	37
Pre-modification Outstanding Recorded Investment	$ 1,809	$ 6,622
Post-modification Outstanding Recorded Investment	$ 1,795	$ 6,607
Number of loans | SecurityLoan	24	31
Recorded investment	$ 2,331	$ 1,337
Non-Covered TDRs | Consumer and Other Loans | Consumer - Indirect Automobile | TDRs Occurring during the Period
Accounts, Notes, Loans and Financing Receivable
Number of Loans | SecurityLoan	11	13
Pre-modification Outstanding Recorded Investment	$ 137	$ 184
Post-modification Outstanding Recorded Investment	$ 119	$ 174
Number of loans | SecurityLoan	34	43
Recorded investment	$ 322	$ 517
Non-Covered TDRs | Consumer and Other Loans | Consumer - Other | TDRs Occurring during the Period
Accounts, Notes, Loans and Financing Receivable
Number of Loans | SecurityLoan	10	22
Pre-modification Outstanding Recorded Investment	$ 511	$ 867
Post-modification Outstanding Recorded Investment	$ 508	$ 862
Number of loans | SecurityLoan	17	25
Recorded investment	$ 1,035	$ 693

Acquisition Activity - Addition

Acquisition Activity - Additional Information (Details)	Mar. 31, 2018USD ($)	Mar. 23, 2018USD ($)$ / sharesshares	Jul. 31, 2017USD ($)bankshares	Mar. 31, 2018USD ($)	Mar. 31, 2018USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Business Acquisition [Line Items]
Increase in goodwill due to adjustments				$ 47,267,000
Amortization of intangible assets acquired				5,102,000		$ 1,770,000
Goodwill	$ 1,236,169,000			1,236,169,000	$ 1,236,169,000		$ 1,188,902,000	$ 726,856,000
Gibraltar Private Bank & Trust Company
Business Acquisition [Line Items]
Loans acquired	1,500,000,000	$ 1,465,319,000		1,500,000,000	1,500,000,000
Interest-bearing deposits acquired		1,064,803,000
Cash consideration	214,700,000	7,000
Increase in goodwill due to adjustments	42,500,000
Goodwill		$ 42,530,000
Gibraltar Private Bank & Trust Company | Common Stock
Business Acquisition [Line Items]
Common stock issued (in dollars per share) | $ / shares		$ 77
Number of shares issued per share acquired | $ / shares		$ 1.9749
Common stock issued (shares) | shares		2,787,773
Solomon Parks Title & Escrow
Business Acquisition [Line Items]
Cash consideration					3,300,000
Increase in goodwill due to adjustments					3,400,000
Sabadell United
Business Acquisition [Line Items]
Loans acquired			$ 4,025,946,000
Interest-bearing deposits acquired			$ 4,382,780,000
Number of offices acquired | bank			25
Cash consideration			$ 809,159,000
Percentage of voting interests acquired			100.00%
Increase in goodwill due to adjustments				1,400,000
Goodwill	$ 463,400,000		$ 463,403,000	$ 463,400,000	$ 463,400,000
Sabadell United | Fair Value Adjustments
Business Acquisition [Line Items]
amortization of premiums and accretion of discounts on acquired loans, securities, and deposits						5,100,000
Elimination of amortization of premiums and accretion of discounts on previously acquired loans, securities, FDIC indemnification asset, and deposits						318,500
Allowance for loan and lease losses acquired						1,600,000
Amortization of intangible assets acquired						$ 1,500,000
Sabadell United | Common Stock
Business Acquisition [Line Items]
Common stock issued (shares) | shares			2,610,304

Acquisition Activity - Consider

Acquisition Activity - Consideration (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 23, 2018	Jul. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Total equity consideration				$ 214,659	$ 0
Goodwill	$ 1,236,169			1,236,169		$ 1,188,902	$ 726,856
Gibraltar Private Bank & Trust Company
Business Acquisition [Line Items]
Total equity consideration		$ 214,659
Cash	214,700	7
Total consideration paid		214,666
Fair value of net assets assumed including identifiable intangible assets		172,136
Goodwill		$ 42,530
Gibraltar Private Bank & Trust Company | Common Stock
Business Acquisition [Line Items]
Common stock issued (shares)		2,787,773
Common stock issued		$ 214,659
Sabadell United
Business Acquisition [Line Items]
Total equity consideration			$ 211,043
Cash			809,159
Total consideration paid			1,020,202
Fair value of net assets assumed including identifiable intangible assets			556,799
Goodwill	$ 463,400		$ 463,403	$ 463,400
Sabadell United | Common Stock
Business Acquisition [Line Items]
Common stock issued (shares)			2,610,304
Common stock issued			$ 211,043

Acquisition Activity - Assets A

Acquisition Activity - Assets Acquired and Liabilities Assumed (Details) - USD ($)	Mar. 31, 2018	Mar. 23, 2018	Jan. 12, 2018	Jul. 31, 2017
Assets
Non-compete agreement			$ 155,900
Gibraltar Private Bank & Trust Company
Assets
Cash and cash equivalents		$ 102,570,000
Investment securities		19,169,000
Equity securities		27,519,000
Loans	$ 1,500,000,000	1,465,319,000
Core deposit intangible assets		18,529,000
Deferred tax asset, net		689,000
Other assets		14,382,000
Total assets acquired		1,648,177,000
Liabilities
Deposit liabilities		1,064,803,000
Long-term borrowings		405,107,000
Other liabilities		6,131,000
Total liabilities assumed		$ 1,476,041,000
Solomon Parks Title & Escrow
Assets
Premise and equipment, net			42,000
Non-compete agreement			156,000
Title Plant investment			15,000
Total assets acquired			213,000
Liabilities
Contingent consideration			343,000
Total liabilities assumed			$ 343,000
Sabadell United
Assets
Cash and cash equivalents				$ 318,834,000
Investment securities				964,123,000
Loans				4,025,946,000
Core deposit intangible assets				66,600,000
Deferred tax asset, net				33,469,000
Other assets				89,745,000
Total assets acquired				5,498,717,000
Liabilities
Deposit liabilities				4,382,780,000
Short-term borrowings				520,539,000
Other liabilities				38,599,000
Total liabilities assumed				$ 4,941,918,000

Acquisition Activity - Pro Form

Acquisition Activity - Pro Forma Information (Details) - Sabadell United $ in Thousands	3 Months Ended
	Mar. 31, 2017USD ($)
Business Acquisition [Line Items]
Net interest income	$ 231,087
Non-interest income	54,755
Net income	$ 43,562

Investment Securities - Schedul

Investment Securities - Schedule of Amortized Cost and Fair Values of Investment Securities, with Gross Unrealized Gains and Losses (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities
Amortized cost	$ 4,668,025	$ 4,647,931
Gross unrealized gain	1,624	5,972
Gross unrealized losses	(127,163)	(63,841)
Estimated fair value	4,542,486	4,590,062
Schedule of Held-to-maturity Securities
Amortized cost	224,241	227,318
Gross unrealized gains	761	1,571
Gross unrealized losses	(5,134)	(925)
Estimated fair value	219,868	227,964
Fair value of securities held as collateral	2,100,000	0
US Treasury Securities
Schedule of Available-for-sale Securities
Amortized cost	6,824
Gross unrealized gain	0
Gross unrealized losses	0
Estimated fair value	6,824
U.S. Government-Sponsored Enterprise Obligations
Schedule of Available-for-sale Securities
Amortized cost	41,001	41,003
Gross unrealized gain	11	18
Gross unrealized losses	(654)	(406)
Estimated fair value	40,358	40,615
Obligations of State and Political Subdivisions
Schedule of Available-for-sale Securities
Amortized cost	267,962	271,451
Gross unrealized gain	1,228	4,246
Gross unrealized losses	(4,156)	(1,493)
Estimated fair value	265,034	274,204
Schedule of Held-to-maturity Securities
Amortized cost	204,404	206,736
Gross unrealized gains	726	1,530
Gross unrealized losses	(4,120)	(275)
Estimated fair value	201,010	207,991
Mortgage-Backed Securities
Schedule of Available-for-sale Securities
Amortized cost	4,277,033	4,221,472
Gross unrealized gain	279	1,461
Gross unrealized losses	(121,215)	(61,028)
Estimated fair value	4,156,097	4,161,905
Schedule of Held-to-maturity Securities
Amortized cost	19,837	20,582
Gross unrealized gains	35	41
Gross unrealized losses	(1,014)	(650)
Estimated fair value	18,858	19,973
Other Securities
Schedule of Available-for-sale Securities
Amortized cost	75,205	114,005
Gross unrealized gain	106	247
Gross unrealized losses	(1,138)	(914)
Estimated fair value	$ 74,173	$ 113,338

Investment Securities - Sched54

Investment Securities - Schedule of Securities with Gross Unrealized Losses Aggregated by Investment Category (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Gross Unrealized Losses
Less than twelve months	$ (70,865)	$ (27,757)
Over twelve months	(56,298)	(36,084)
Total	(127,163)	(63,841)
Estimated Fair Value
Less than twelve months	3,033,959	2,813,985
Over twelve months	1,267,402	1,304,515
Total	4,301,361	4,118,500
Gross Unrealized Losses
Less than twelve months	(4,077)	(265)
Over twelve months	(1,057)	(660)
Total	(5,134)	(925)
Estimated Fair Value
Less than twelve months	150,511	66,150
Over twelve months	21,163	22,300
Total	171,674	88,450
US Treasury Securities
Gross Unrealized Losses
Less than twelve months	0
Over twelve months	0
Total	0
Estimated Fair Value
Less than twelve months	693
Over twelve months	0
Total	693
U.S. Government-Sponsored Enterprise Obligations
Gross Unrealized Losses
Less than twelve months	(419)	(254)
Over twelve months	(235)	(152)
Total	(654)	(406)
Estimated Fair Value
Less than twelve months	29,580	29,744
Over twelve months	9,765	9,848
Total	39,345	39,592
Obligations of State and Political Subdivisions
Gross Unrealized Losses
Less than twelve months	(1,147)	(326)
Over twelve months	(3,009)	(1,167)
Total	(4,156)	(1,493)
Estimated Fair Value
Less than twelve months	96,138	31,601
Over twelve months	66,404	68,609
Total	162,542	100,210
Mortgage-Backed Securities
Gross Unrealized Losses
Less than twelve months	(68,161)	(26,263)
Over twelve months	(53,054)	(34,765)
Total	(121,215)	(61,028)
Estimated Fair Value
Less than twelve months	2,847,244	2,677,338
Over twelve months	1,191,233	1,226,058
Total	4,038,477	3,903,396
Other Securities
Gross Unrealized Losses
Less than twelve months	(1,138)	(914)
Over twelve months	0	0
Total	(1,138)	(914)
Estimated Fair Value
Less than twelve months	60,304	75,302
Over twelve months	0	0
Total	60,304	75,302
Obligations of State and Political Subdivisions
Gross Unrealized Losses
Less than twelve months	(4,066)	(263)
Over twelve months	(54)	(12)
Total	(4,120)	(275)
Estimated Fair Value
Less than twelve months	150,188	65,817
Over twelve months	2,976	3,031
Total	153,164	68,848
Mortgage-Backed Securities
Gross Unrealized Losses
Less than twelve months	(11)	(2)
Over twelve months	(1,003)	(648)
Total	(1,014)	(650)
Estimated Fair Value
Less than twelve months	323	333
Over twelve months	18,187	19,269
Total	$ 18,510	$ 19,602

Investment Securities - Additio

Investment Securities - Additional Information on Securities in a Continuous Loss Position (Detail) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018USD ($)Security	Dec. 31, 2017USD ($)Security
Schedule of Available-for-sale Securities
Number of debt securities with unrealized losses | Security	635	544
Debt securities with unrealized losses (percentage of amortized cost)	2.87%	1.52%
Number of securities | Security	213	210
Amortized cost basis	$ 1,345,920	$ 1,363,559
Unrealized loss	$ 57,355	$ 36,744
Mortgage-backed securities
Schedule of Available-for-sale Securities
Number of securities | Security	184	181
Amortized cost basis	$ 1,263,477	$ 1,280,739
Unrealized loss	$ 54,057	$ 35,412
Obligations of state and political subdivisions
Schedule of Available-for-sale Securities
Number of securities | Security	28	28
Amortized cost basis	$ 72,443	$ 72,820
Unrealized loss	$ 3,063	$ 1,180
Other
Schedule of Available-for-sale Securities
Number of securities | Security	1	1
Amortized cost basis	$ 10,000	$ 10,000
Unrealized loss	$ 235	$ 152

Investment Securities - Sched56

Investment Securities - Schedule of Amortized Cost and Estimated Fair Value of Investment Securities by Maturity (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Weighted Average Yield
Within one year or less	2.06%
One through five years	2.04%
After five through ten years	2.36%
Over ten years	2.38%
Weighted average yield	2.38%
Amortized Cost
Within one year or less	$ 6,667
One through five years	134,449
After five through ten years	887,796
Over ten years	3,639,113
Amortized cost	4,668,025
Estimated Fair Value
Within one year or less	6,670
One through five years	132,594
After five through ten years	868,090
Over ten years	3,535,132
Estimated fair value	$ 4,542,486	$ 4,590,062
Weighted Average Yield
Within one year or less	3.04%
One through five years	2.98%
After five through ten years	2.66%
Over ten years	2.56%
Weighted average yield	2.60%
Amortized Cost
Within one year or less	$ 1,445
One through five years	8,369
After five through ten years	45,690
Over ten years	168,737
Amortized cost	224,241	227,318
Estimated Fair Value
Within one year or less	1,448
One through five years	8,370
After five through ten years	45,450
Over ten years	164,600
Estimated fair value	$ 219,868	$ 227,964

Investment Securities - Sched57

Investment Securities - Schedule of Realized Gains and Losses from Sale of Securities Classified as Available for Sale (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Realized gains	$ 9	$ 0
Realized losses	(68)	0
Net realized gains (losses)	$ (59)	$ 0

Investment Securities - Sched58

Investment Securities - Schedule of Securities in Other Assets on Company's Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Federal Home Loan Bank (FHLB) stock	$ 90,561	$ 95,171
Federal Reserve Bank Stock	79,191	79,191
Equity Securities, FV-NI	9,801	0
Other Investments	9,705	3,008
Marketable Securities, Equity Securities	$ 189,258	$ 177,370

Allowance for Credit Losses a59

Allowance for Credit Losses and Credit Quality - Schedule of Allowance for Loan Losses for Covered and Non-Covered Loan Portfolios (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Allowance for credit losses
Allowance for loan losses at beginning of period	$ 140,891	$ 144,719
Provision for loan and lease losses	7,986	6,154
Transfer of balance to OREO and other	(47)	73
Loans charged-off	(9,116)	(7,291)
Recoveries	4,813	1,235
Allowance for loan losses at end of period	144,527	144,890
Reserve For Unfunded Commitments
Reserve for unfunded commitments at beginning of period	13,208	11,241
Provision for (Reversal of) unfunded lending commitments	224	419
Reserve for unfunded commitments at end of period	13,432	11,660
Allowance for credit losses at end of period	$ 157,959	$ 156,550

Allowance for Credit Losses a60

Allowance for Credit Losses and Credit Quality - Schedule of Allowance for Loan Losses for Legacy and Acquired Loans, by Loan Portfolio (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Financing Receivable, Allowance for Credit Losses
Allowance for loan losses at beginning of period	$ 140,891	$ 144,719
Provision for (Reversal of) loan losses	7,986	6,154
Transfer of balance to OREO and other	(47)	73
Loans charged-off	(9,116)	(7,291)
Recoveries	4,813	1,235
Allowance for loan losses at end of period	144,527	144,890
Financing Receivable, Reserve For Unfunded Commitments
Reserve for unfunded commitments at beginning of period	13,208	11,241
Provision for (Reversal of) unfunded commitments	224	419
Reserve for unfunded commitments at end of period	13,432	11,660
Allowance on loans individually evaluated for impairment	19,698	28,809
Allowance on loans collectively evaluated for impairment	90,696	80,926
Allowance on loans acquired with deteriorated credit quality	157,959	156,550
Loans, net of unearned income:
Loans, net of unearned income	21,706,090	15,132,202
Balance at end of period individually evaluated for impairment	196,532	269,112
Balance at end of period collectively evaluated for impairment	21,027,680	14,365,751
Commercial Loans | Real Estate
Financing Receivable, Allowance for Credit Losses
Allowance for loan losses at beginning of period	54,201	49,231
Provision for (Reversal of) loan losses	6,377	1,786
Transfer of balance to OREO and other	(47)	377
Loans charged-off	(114)	(95)
Recoveries	191	196
Allowance for loan losses at end of period	60,608	51,495
Financing Receivable, Reserve For Unfunded Commitments
Reserve for unfunded commitments at beginning of period	4,531	3,207
Provision for (Reversal of) unfunded commitments	1,476	1,379
Reserve for unfunded commitments at end of period	6,007	4,586
Allowance on loans individually evaluated for impairment	2,506	1,916
Allowance on loans collectively evaluated for impairment	35,871	26,872
Loans, net of unearned income:
Loans, net of unearned income	9,248,951	7,021,341
Balance at end of period individually evaluated for impairment	78,489	74,351
Balance at end of period collectively evaluated for impairment	8,946,138	6,687,651
Commercial Loans | Commercial and industrial
Financing Receivable, Allowance for Credit Losses
Allowance for loan losses at beginning of period	53,916	60,939
Provision for (Reversal of) loan losses	294	2,557
Transfer of balance to OREO and other	0	(350)
Loans charged-off	(5,378)	(3,762)
Recoveries	3,698	84
Allowance for loan losses at end of period	52,530	59,468
Financing Receivable, Reserve For Unfunded Commitments
Reserve for unfunded commitments at beginning of period	5,309	4,537
Provision for (Reversal of) unfunded commitments	(1,004)	(885)
Reserve for unfunded commitments at end of period	4,305	3,652
Allowance on loans individually evaluated for impairment	14,040	25,056
Allowance on loans collectively evaluated for impairment	36,208	32,383
Loans, net of unearned income:
Loans, net of unearned income	5,325,682	3,975,734
Balance at end of period individually evaluated for impairment	78,725	164,405
Balance at end of period collectively evaluated for impairment	5,211,736	3,778,775
Residential Mortgage
Financing Receivable, Allowance for Credit Losses
Allowance for loan losses at beginning of period	9,117	11,249
Provision for (Reversal of) loan losses	(686)	(1,060)
Transfer of balance to OREO and other	0	2
Loans charged-off	(105)	(22)
Recoveries	22	43
Allowance for loan losses at end of period	8,348	10,212
Financing Receivable, Reserve For Unfunded Commitments
Reserve for unfunded commitments at beginning of period	555	657
Provision for (Reversal of) unfunded commitments	(15)	(49)
Reserve for unfunded commitments at end of period	540	608
Allowance on loans individually evaluated for impairment	178	113
Allowance on loans collectively evaluated for impairment	2,073	3,907
Loans, net of unearned income:
Loans, net of unearned income	3,971,067	1,296,358
Balance at end of period individually evaluated for impairment	6,041	5,048
Balance at end of period collectively evaluated for impairment	3,826,721	1,176,017
Consumer and Other Loans
Financing Receivable, Allowance for Credit Losses
Allowance for loan losses at beginning of period	23,657	23,300
Provision for (Reversal of) loan losses	2,001	2,871
Transfer of balance to OREO and other	0	44
Loans charged-off	(3,519)	(3,412)
Recoveries	902	912
Allowance for loan losses at end of period	23,041	23,715
Financing Receivable, Reserve For Unfunded Commitments
Reserve for unfunded commitments at beginning of period	2,813	2,840
Provision for (Reversal of) unfunded commitments	(233)	(26)
Reserve for unfunded commitments at end of period	2,580	2,814
Allowance on loans individually evaluated for impairment	2,974	1,724
Allowance on loans collectively evaluated for impairment	16,544	17,764
Loans, net of unearned income:
Loans, net of unearned income	3,160,390	2,838,769
Balance at end of period individually evaluated for impairment	33,277	25,308
Balance at end of period collectively evaluated for impairment	3,043,085	2,723,308
Receivables Acquired with Deteriorated Credit Quality
Financing Receivable, Reserve For Unfunded Commitments
Allowance on loans acquired with deteriorated credit quality	34,133	35,155
Loans, net of unearned income:
Balance at end of period acquired with deteriorated credit quality	481,878	497,339
Receivables Acquired with Deteriorated Credit Quality | Commercial Loans | Real Estate
Financing Receivable, Reserve For Unfunded Commitments
Allowance on loans acquired with deteriorated credit quality	22,231	22,707
Loans, net of unearned income:
Balance at end of period acquired with deteriorated credit quality	224,324	259,339
Receivables Acquired with Deteriorated Credit Quality | Commercial Loans | Commercial and industrial
Financing Receivable, Reserve For Unfunded Commitments
Allowance on loans acquired with deteriorated credit quality	2,282	2,029
Loans, net of unearned income:
Balance at end of period acquired with deteriorated credit quality	35,221	32,554
Receivables Acquired with Deteriorated Credit Quality | Residential Mortgage
Financing Receivable, Reserve For Unfunded Commitments
Allowance on loans acquired with deteriorated credit quality	6,097	6,192
Loans, net of unearned income:
Balance at end of period acquired with deteriorated credit quality	138,305	115,293
Receivables Acquired with Deteriorated Credit Quality | Consumer and Other Loans
Financing Receivable, Reserve For Unfunded Commitments
Allowance on loans acquired with deteriorated credit quality	3,523	4,227
Loans, net of unearned income:
Balance at end of period acquired with deteriorated credit quality	$ 84,028	$ 90,153

Allowance for Credit Losses a61

Allowance for Credit Losses and Credit Quality - Investment in Legacy and Acquired Loans by Credit Quality Indicator (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses
Total Loans	$ 21,706,090	$ 20,078,181
Commercial Loans
Financing Receivable, Allowance for Credit Losses
Total Loans	14,574,633	14,073,297
Commercial Loans | Commercial real estate - Construction
Financing Receivable, Allowance for Credit Losses
Total Loans	1,199,625	1,240,396
Commercial Loans | Commercial real estate - owner-occupied
Financing Receivable, Allowance for Credit Losses
Total Loans	2,612,244	2,529,885
Commercial Loans | Commercial real estate - non-owner-occupied
Financing Receivable, Allowance for Credit Losses
Total Loans	5,437,082	5,167,949
Commercial Loans | Commercial and industrial
Financing Receivable, Allowance for Credit Losses
Total Loans	5,325,682	5,135,067
Residential and Consumer Portfolio
Financing Receivable, Allowance for Credit Losses
Current	6,966,104	5,857,746
30 or more days past due	165,353	147,138
Total Loans	7,131,457	6,004,884
Residential Mortgage | Residential mortgage
Financing Receivable, Allowance for Credit Losses
Current	3,859,751	2,962,043
30 or more days past due	111,316	94,309
Total Loans	3,971,067	3,056,352
Consumer and Other Loans | Consumer - Home equity
Financing Receivable, Allowance for Credit Losses
Current	2,376,171	2,250,205
30 or more days past due	45,015	42,070
Total Loans	2,421,186	2,292,275
Consumer and Other Loans | Consumer - Indirect Automobile
Financing Receivable, Allowance for Credit Losses
Current	48,587	59,836
30 or more days past due	2,084	2,857
Total Loans	50,671	62,693
Consumer and Other Loans | Consumer - Credit card
Financing Receivable, Allowance for Credit Losses
Current	92,497	95,263
30 or more days past due	764	1,105
Total Loans	93,261	96,368
Consumer and Other Loans | Consumer - Other
Financing Receivable, Allowance for Credit Losses
Current	589,098	490,399
30 or more days past due	6,174	6,797
Total Loans	595,272	497,196
Pass | Commercial Loans
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	14,078,168	13,564,833
Pass | Commercial Loans | Commercial real estate - Construction
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	1,153,604	1,189,490
Pass | Commercial Loans | Commercial real estate - owner-occupied
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	2,464,072	2,388,715
Pass | Commercial Loans | Commercial real estate - non-owner-occupied
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	5,335,816	5,104,074
Pass | Commercial Loans | Commercial and industrial
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	5,124,676	4,882,554
Special Mention | Commercial Loans
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	200,701	209,925
Special Mention | Commercial Loans | Commercial real estate - Construction
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	16,399	20,351
Special Mention | Commercial Loans | Commercial real estate - owner-occupied
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	83,356	82,114
Special Mention | Commercial Loans | Commercial real estate - non-owner-occupied
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	45,905	19,311
Special Mention | Commercial Loans | Commercial and industrial
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	55,041	88,149
Substandard | Commercial Loans
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	244,234	258,794
Substandard | Commercial Loans | Commercial real estate - Construction
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	29,610	30,541
Substandard | Commercial Loans | Commercial real estate - owner-occupied
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	56,409	56,590
Substandard | Commercial Loans | Commercial real estate - non-owner-occupied
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	51,089	42,702
Substandard | Commercial Loans | Commercial and industrial
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	107,126	128,961
Doubtful | Commercial Loans
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	51,530	39,627
Doubtful | Commercial Loans | Commercial real estate - Construction
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	12	14
Doubtful | Commercial Loans | Commercial real estate - owner-occupied
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	8,407	2,466
Doubtful | Commercial Loans | Commercial real estate - non-owner-occupied
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	4,272	1,744
Doubtful | Commercial Loans | Commercial and industrial
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	$ 38,839	35,403
Loss | Commercial Loans
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable		118
Loss | Commercial Loans | Commercial real estate - Construction
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable		0
Loss | Commercial Loans | Commercial real estate - owner-occupied
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable		0
Loss | Commercial Loans | Commercial real estate - non-owner-occupied
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable		118
Loss | Commercial Loans | Commercial and industrial
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable		$ 0

Allowance for Credit Losses a62

Allowance for Credit Losses and Credit Quality - Schedule of Investment in Legacy Impaired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Financing Receivable, Impaired
Unpaid Principal Balance	$ 219,771		$ 283,629
Recorded Investment	196,532		238,127
Related allowance	(2,974)		(2,856)
Average Recorded Investment	189,754	$ 274,131
Interest Income Recognized	1,695	1,523
Commercial Loans
Financing Receivable, Impaired
Unpaid Principal Balance	178,886		237,922
Recorded Investment	157,214		194,201
Related allowance	(19,698)		(17,352)
Average Recorded Investment	150,255	244,095
Interest Income Recognized	1,280	1,198
Residential Mortgage
Financing Receivable, Impaired
Unpaid Principal Balance	6,440		7,183
Recorded Investment	6,041		6,749
Related allowance	(16,546)		(14,324)
Average Recorded Investment	6,064	5,070
Interest Income Recognized	56	47
Consumer and Other Loans
Financing Receivable, Impaired
Unpaid Principal Balance	34,445		38,524
Recorded Investment	33,277		37,177
Related allowance	(178)		(172)
Average Recorded Investment	33,435	24,966
Interest Income Recognized	359	278
With No Related Allowance Recorded | Commercial Loans | Commercial real estate - Construction
Financing Receivable, Impaired
Unpaid Principal Balance	11,153		13,763
Recorded Investment	11,153		13,013
Average Recorded Investment	10,470	0
Interest Income Recognized	144	0
With No Related Allowance Recorded | Commercial Loans | Commercial real estate - owner-occupied
Financing Receivable, Impaired
Unpaid Principal Balance	43,562		50,867
Recorded Investment	36,042		44,482
Average Recorded Investment	36,277	37,197
Interest Income Recognized	334	339
With No Related Allowance Recorded | Commercial Loans | Commercial real estate - non-owner-occupied
Financing Receivable, Impaired
Unpaid Principal Balance	10,575		15,370
Recorded Investment	10,449		14,975
Average Recorded Investment	10,557	5,988
Interest Income Recognized	98	17
With No Related Allowance Recorded | Commercial Loans | Commercial and industrial
Financing Receivable, Impaired
Unpaid Principal Balance	45,720		103,013
Recorded Investment	36,829		70,254
Average Recorded Investment	27,832	90,664
Interest Income Recognized	385	448
With No Related Allowance Recorded | Commercial Loans | Residential mortgage
Financing Receivable, Impaired
Unpaid Principal Balance	1,083		2,004
Recorded Investment	1,083		2,001
Average Recorded Investment	1,090	735
Interest Income Recognized	12	5
With No Related Allowance Recorded | Consumer and Other Loans | Consumer - Home equity
Financing Receivable, Impaired
Unpaid Principal Balance	31		5,906
Recorded Investment	31		5,634
Average Recorded Investment	32	4,158
Interest Income Recognized	0	40
With No Related Allowance Recorded | Consumer and Other Loans | Consumer - Other
Financing Receivable, Impaired
Unpaid Principal Balance	0		75
Recorded Investment	0		75
With An Allowance Recorded | Commercial Loans | Commercial real estate - Construction
Financing Receivable, Impaired
Unpaid Principal Balance	236		238
Recorded Investment	154		156
Related allowance	(18)		(19)
Average Recorded Investment	153	1,984
Interest Income Recognized	1	1
With An Allowance Recorded | Commercial Loans | Commercial real estate - owner-occupied
Financing Receivable, Impaired
Unpaid Principal Balance	17,536		13,314
Recorded Investment	17,419		13,287
Related allowance	(1,860)		(949)
Average Recorded Investment	17,608	20,980
Interest Income Recognized	112	79
With An Allowance Recorded | Commercial Loans | Commercial real estate - non-owner-occupied
Financing Receivable, Impaired
Unpaid Principal Balance	3,399		6,051
Recorded Investment	3,272		5,872
Related allowance	(628)		(620)
Average Recorded Investment	3,302	8,587
Interest Income Recognized	10	94
With An Allowance Recorded | Commercial Loans | Commercial and industrial
Financing Receivable, Impaired
Unpaid Principal Balance	46,705		35,306
Recorded Investment	41,896		32,162
Related allowance	(14,040)		(12,736)
Average Recorded Investment	44,056	78,695
Interest Income Recognized	196	220
With An Allowance Recorded | Residential Mortgage | Residential mortgage
Financing Receivable, Impaired
Unpaid Principal Balance	5,357		5,179
Recorded Investment	4,958		4,748
Related allowance	(178)		(172)
Average Recorded Investment	4,974	4,335
Interest Income Recognized	44	42
With An Allowance Recorded | Consumer and Other Loans | Consumer - Home equity
Financing Receivable, Impaired
Unpaid Principal Balance	28,917		27,189
Recorded Investment	28,187		26,575
Related allowance	(2,435)		(2,358)
Average Recorded Investment	28,203	16,713
Interest Income Recognized	292	179
With An Allowance Recorded | Consumer and Other Loans | Consumer - Indirect Automobile
Financing Receivable, Impaired
Unpaid Principal Balance	1,004		1,034
Recorded Investment	656		679
Related allowance	(75)		(79)
Average Recorded Investment	717	767
Interest Income Recognized	5	7
With An Allowance Recorded | Consumer and Other Loans | Consumer - Other
Financing Receivable, Impaired
Unpaid Principal Balance	4,493		4,320
Recorded Investment	4,403		4,214
Related allowance	(464)		$ (419)
Average Recorded Investment	4,483	3,328
Interest Income Recognized	$ 62	$ 52

Goodwill and Other Intangible63

Goodwill and Other Intangible Assets - Schedule of Carrying Amount of Goodwill (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2018	Mar. 31, 2018	Mar. 31, 2017
Goodwill
Balance at beginning of the period		$ 1,188,902		$ 726,856
Goodwill acquired during the year (preliminary allocation)				462,046
Goodwill acquired during the year (preliminary allocation) and adjustments		47,267
Balance at end of the period	$ 1,236,169	1,236,169	$ 1,236,169
Operating Segments | IBERIABANK
Goodwill
Balance at beginning of the period		1,160,559		698,513
Goodwill acquired during the year (preliminary allocation)				462,046
Goodwill acquired during the year (preliminary allocation) and adjustments		43,887
Balance at end of the period	1,204,446	1,204,446	1,204,446
Operating Segments | IMC
Goodwill
Balance at beginning of the period		23,178		23,178
Goodwill acquired during the year (preliminary allocation)				0
Goodwill acquired during the year (preliminary allocation) and adjustments		0
Balance at end of the period	23,178	23,178	23,178
Operating Segments | LTC
Goodwill
Balance at beginning of the period		5,165		5,165
Goodwill acquired during the year (preliminary allocation)				$ 0
Goodwill acquired during the year (preliminary allocation) and adjustments		3,380
Balance at end of the period	8,545	$ 8,545	8,545
Gibraltar Private Bank & Trust Company
Goodwill
Goodwill acquired during the year (preliminary allocation) and adjustments	$ 42,500
Solomon Parks Title & Escrow
Goodwill
Goodwill acquired during the year (preliminary allocation) and adjustments			$ 3,400

Goodwill and Other Intangible64

Goodwill and Other Intangible Assets - Narrative (Detail) - USD ($)	Mar. 31, 2018	Mar. 31, 2018	Mar. 23, 2018	Jan. 12, 2018	Dec. 31, 2017	Jul. 31, 2017
Goodwill
Goodwill acquired during the year (preliminary allocation) and adjustments		$ 47,267,000
Non-compete agreement				$ 155,900
Title plant assets	$ 6,800,000	6,800,000			$ 6,700,000
Gibraltar Private Bank & Trust Company [Member]
Goodwill
Goodwill acquired during the year (preliminary allocation) and adjustments	$ 42,500,000
Core deposit intangible assets			$ 18,529,000
Sabadell United
Goodwill
Goodwill acquired during the year (preliminary allocation) and adjustments		$ 1,400,000
Core deposit intangible assets						$ 66,600,000

Goodwill and Other Intangible65

Goodwill and Other Intangible Assets - Schedule of Mortgage Servicing Rights at Carrying Value (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 137,774	$ 129,163
Accumulated Amortization	(48,034)	(53,006)
Net Carrying Amount	89,740	76,157
Mortgage servicing rights
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	10,030	9,588
Accumulated Amortization	(4,128)	(3,931)
Net Carrying Amount	$ 5,902	$ 5,657

Goodwill and Other Intangible66

Goodwill and Other Intangible Assets - Schedule of Definite-Lived Intangible Assets (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 137,774	$ 129,163
Accumulated Amortization	(48,034)	(53,006)
Net Carrying Amount	89,740	76,157
Core deposit intangible assets
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	136,183	127,957
Accumulated Amortization	(46,736)	(51,971)
Net Carrying Amount	89,447	75,986
Customer relationship intangible asset
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,385	1,143
Accumulated Amortization	(1,262)	(996)
Net Carrying Amount	123	147
Non-compete agreement
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	206	63
Accumulated Amortization	(36)	(39)
Net Carrying Amount	$ 170	$ 24

Derivative Instruments and Ot67

Derivative Instruments and Other Hedging Activities - Schedule of Outstanding Derivative Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Fair Value of Derivatives
Derivative Asset	$ 17,072	$ 31,265
Derivative Liability	32,154	25,154
Notional Amount of Derivatives
Derivative assets	1,932,456	1,609,472
Derivative liabilities	1,729,766	1,721,752
Designated as Hedging Instruments
Fair Value of Derivatives
Derivative Asset	0	0
Derivative Liability	0	0
Notional Amount of Derivatives
Derivative assets	108,500	0
Derivative liabilities	0	108,500
Designated as Hedging Instruments | Interest rate contracts
Notional Amount of Derivatives
Derivative assets	108,500	0
Derivative liabilities	0	108,500
Designated as Hedging Instruments | Interest rate contracts | Other Assets
Fair Value of Derivatives
Derivative Asset	0	0
Designated as Hedging Instruments | Interest rate contracts | Other Liabilities
Fair Value of Derivatives
Derivative Liability	0	0
Not Designated as Hedging Instruments
Notional Amount of Derivatives
Derivative assets	1,823,956	1,609,472
Derivative liabilities	1,729,766	1,613,252
Not Designated as Hedging Instruments | Other Assets
Fair Value of Derivatives
Derivative Asset	17,072	31,265
Not Designated as Hedging Instruments | Other Liabilities
Fair Value of Derivatives
Derivative Liability	32,154	25,154
Not Designated as Hedging Instruments | Interest rate contracts
Notional Amount of Derivatives
Derivative assets	1,356,990	1,218,464
Derivative liabilities	1,276,990	1,218,464
Not Designated as Hedging Instruments | Interest rate contracts | Other Assets
Fair Value of Derivatives
Derivative Asset	5,827	20,446
Not Designated as Hedging Instruments | Interest rate contracts | Other Liabilities
Fair Value of Derivatives
Derivative Liability	25,771	16,191
Not Designated as Hedging Instruments | Foreign exchange contracts
Notional Amount of Derivatives
Derivative assets	628	268
Derivative liabilities	628	268
Not Designated as Hedging Instruments | Foreign exchange contracts | Other Assets
Fair Value of Derivatives
Derivative Asset	2	7
Not Designated as Hedging Instruments | Foreign exchange contracts | Other Liabilities
Fair Value of Derivatives
Derivative Liability	2	7
Not Designated as Hedging Instruments | Forward sales contracts
Notional Amount of Derivatives
Derivative assets	96,810	82,347
Derivative liabilities	215,918	142,578
Not Designated as Hedging Instruments | Forward sales contracts | Other Assets
Fair Value of Derivatives
Derivative Asset	2,851	136
Not Designated as Hedging Instruments | Forward sales contracts | Other Liabilities
Fair Value of Derivatives
Derivative Liability	703	279
Not Designated as Hedging Instruments | Written and purchased options
Notional Amount of Derivatives
Derivative assets	339,852	278,638
Derivative liabilities	164,341	165,198
Not Designated as Hedging Instruments | Written and purchased options | Other Assets
Fair Value of Derivatives
Derivative Asset	8,383	10,654
Not Designated as Hedging Instruments | Written and purchased options | Other Liabilities
Fair Value of Derivatives
Derivative Liability	5,667	8,656
Not Designated as Hedging Instruments | Other contracts
Notional Amount of Derivatives
Derivative assets	29,676	29,755
Derivative liabilities	71,889	86,744
Not Designated as Hedging Instruments | Other contracts | Other Assets
Fair Value of Derivatives
Derivative Asset	9	22
Not Designated as Hedging Instruments | Other contracts | Other Liabilities
Fair Value of Derivatives
Derivative Liability	$ 11	$ 21

Derivative Instruments and Ot68

Derivative Instruments and Other Hedging Activities - Narrative (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Notional amount of derivative liabilities	$ 1,729,766	$ 1,721,752
Cash as collateral for derivative transactions	0	(552)
Cash Posted As Variation Margin for Derivatives	28,800	5,100
Not Designated as Hedging Instruments
Derivative [Line Items]
Notional amount of derivative liabilities	1,729,766	1,613,252
Not Designated as Hedging Instruments | Other contracts
Derivative [Line Items]
Notional amount of derivative liabilities	$ 71,889	$ 86,744

Derivative Instruments and Ot69

Derivative Instruments and Other Hedging Activities - Reconciliation of Gross Amounts in Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Derivative assets
Gross derivative assets	$ 11,483	$ 29,056
Gross amounts not offset in the Balance Sheet, derivatives	(548)	(12,469)
Gross amounts not offset in the Balance Sheet, collateral	0	0
Net derivative assets	10,935	16,587
Derivative liabilities
Gross derivative liabilities	31,358	16,191
Gross amounts not offset in the Balance Sheet, derivatives	(548)	(12,469)
Gross amounts not offset in the Balance Sheet, collateral	0	(552)
Net derivative liabilities	30,810	3,170
Written and purchased options
Derivative assets
Gross derivative assets	5,656	8,610
Gross amounts not offset in the Balance Sheet, derivatives	0	0
Gross amounts not offset in the Balance Sheet, collateral	0	0
Net derivative assets	5,656	8,610
Derivative liabilities
Gross derivative liabilities	5,587
Gross amounts not offset in the Balance Sheet, derivatives	0
Gross amounts not offset in the Balance Sheet, collateral	0
Net derivative liabilities	5,587
Designated as Hedging Instruments | Interest rate contracts
Derivative assets
Gross derivative assets	5,827
Gross amounts not offset in the Balance Sheet, derivatives	(548)
Gross amounts not offset in the Balance Sheet, collateral	0
Net derivative assets	5,279
Derivative liabilities
Gross derivative liabilities	0	0
Gross amounts not offset in the Balance Sheet, derivatives	0	0
Gross amounts not offset in the Balance Sheet, collateral	0	0
Net derivative liabilities	0	0
Not Designated as Hedging Instruments | Interest rate contracts
Derivative assets
Gross derivative assets		20,446
Gross amounts not offset in the Balance Sheet, derivatives		(12,469)
Gross amounts not offset in the Balance Sheet, collateral		0
Net derivative assets		7,977
Derivative liabilities
Gross derivative liabilities	25,771	16,191
Gross amounts not offset in the Balance Sheet, derivatives	(548)	(12,469)
Gross amounts not offset in the Balance Sheet, collateral	0	(552)
Net derivative liabilities	$ 25,223	$ 3,170

Derivative Instruments and Ot70

Derivative Instruments and Other Hedging Activities - Effect of Hedging Instruments on Consolidated Financial Statements (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Designated as Hedging Instruments | Cash Flow Hedging | Interest rate contracts | Interest expense
Derivative Instruments and Hedging Activities Disclosures
Amount of Gain (Loss) Recognized in OCI, net of taxes	$ 2,549	$ 73
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income, net of taxes	(116)	(45)
Amount of Gain (Loss) Recognized in Income on Derivative (Amount Excluded from Effectiveness Testing)	0	0
Not Designated as Hedging Instruments
Derivative Instruments and Hedging Activities Disclosures
Amount of Gain (Loss) Recognized in Income on Derivatives	5,086	1,423
Not Designated as Hedging Instruments | Interest rate contracts | Other income
Derivative Instruments and Hedging Activities Disclosures
Amount of Gain (Loss) Recognized in Income on Derivatives	1,049	1,117
Not Designated as Hedging Instruments | Foreign exchange contracts | Other income
Derivative Instruments and Hedging Activities Disclosures
Amount of Gain (Loss) Recognized in Income on Derivatives	5	7
Not Designated as Hedging Instruments | Forward sales contracts | Mortgage income
Derivative Instruments and Hedging Activities Disclosures
Amount of Gain (Loss) Recognized in Income on Derivatives	3,387	(360)
Not Designated as Hedging Instruments | Written and purchased options | Mortgage income
Derivative Instruments and Hedging Activities Disclosures
Amount of Gain (Loss) Recognized in Income on Derivatives	648	655
Not Designated as Hedging Instruments | Other contracts | Other income
Derivative Instruments and Hedging Activities Disclosures
Amount of Gain (Loss) Recognized in Income on Derivatives	$ (3)	$ 4

Income Taxes Schedule of Effect

Income Taxes Schedule of Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	$ 81,173	$ 72,992
Income Tax Expense (Benefit)	$ 17,552	$ 22,519
Effective Income Tax Rate Reconciliation, Percent	21.60%	30.90%
Tax Cuts and Jobs Act of 2017, Change in Tax Rate, Deferred Tax Asset, Income Tax Expense (Benefit)	$ 51,000

Income Taxes Income Taxes (Deta

Income Taxes Income Taxes (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)
Income Tax Disclosure [Abstract]
Tax Cuts and Jobs Act of 2017, Change in Tax Rate, Deferred Tax Asset, Income Tax Expense (Benefit)	$ 51

Shareholders' Equity, Capital73

Shareholders' Equity, Capital Ratios and Other Regulatory Matters - Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	May 07, 2018	Mar. 31, 2018	Mar. 23, 2018	May 09, 2016	Aug. 05, 2015	Dec. 31, 2017	Jun. 30, 2016
Class of Stock [Line Items]
Liquidation preference value				$ 137,500
Carrying Amount		$ 132,097				$ 132,097
Number of shares authorized to be repurchased							950,000
Shares authorized to be repurchased		747,494
Series B Preferred Stock
Class of Stock [Line Items]
Ownership per share					6.625%
Liquidation preference value					$ 80,000
Carrying Amount		$ 76,812				76,812
Series C Preferred Stock
Class of Stock [Line Items]
Ownership per share				6.60%
Liquidation preference value				$ 57,500
Carrying Amount		55,285				$ 55,285
Gibraltar Private Bank & Trust Company
Class of Stock [Line Items]
Cash consideration		$ 214,700	$ 7
Gibraltar Private Bank & Trust Company | Common Stock
Class of Stock [Line Items]
Common stock issued (shares)			2,787,773
Common stock issued			$ 214,659
Common stock issued (in dollars per share)			$ 77
Number of shares issued per share acquired			$ 1.9749
Subsequent Event
Class of Stock [Line Items]
Treasury stock acquired (shares)	180,000
Treasury stock acquired	$ 13,700

Shareholders' Equity, Capital74

Shareholders' Equity, Capital Ratios and Other Regulatory Matters - Actual Capital Amounts and Ratios (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Consolidated
Tier 1 Leverage
Minimum amount	$ 1,076,933	$ 1,073,381
Minimum ratio	4.00%	4.00%
Actual amount	$ 2,685,315	$ 2,509,496
Actual ratio	9.97%	9.35%
Common Equity Tier 1 (CET1)
Minimum amount	$ 1,067,284	$ 1,011,732
Minimum ratio	4.50%	4.50%
Actual amount	$ 2,553,218	$ 2,377,398
Actual ratio	10.77%	10.57%
Tier 1 Risk-Based Capital (1)
Minimum amount	$ 1,423,046	$ 1,348,977
Minimum ratio	6.00%	6.00%
Actual amount	$ 2,685,315	$ 2,509,496
Actual ratio	11.32%	11.16%
Total Risk-Based Capital (1)
Minimum amount	$ 1,897,394	$ 1,798,635
Minimum ratio	8.00%	8.00%
Actual amount	$ 2,959,774	$ 2,780,095
Actual ratio	12.48%	12.37%
IBERIABANK
Tier 1 Leverage
Minimum amount	$ 1,074,579	$ 1,070,789
Minimum ratio	4.00%	4.00%
Well capitalized amount	$ 1,343,223	$ 1,338,487
Well capitalized ratio	5.00%	5.00%
Actual amount	$ 2,640,916	$ 2,437,275
Actual ratio	9.83%	9.10%
Common Equity Tier 1 (CET1)
Minimum amount	$ 1,065,059	$ 1,009,553
Minimum ratio	4.50%	4.50%
Well capitalized amount	$ 1,538,418	$ 1,458,243
Well capitalized ratio	6.50%	6.50%
Actual amount	$ 2,640,916	$ 2,437,275
Actual ratio	11.16%	10.86%
Tier 1 Risk-Based Capital (1)
Minimum amount	$ 1,420,078	$ 1,346,070
Minimum ratio	6.00%	6.00%
Well capitalized amount	$ 1,893,437	$ 1,794,760
Well capitalized ratio	8.00%	8.00%
Actual amount	$ 2,640,916	$ 2,437,275
Actual ratio	11.16%	10.86%
Total Risk-Based Capital (1)
Minimum amount	$ 1,893,437	$ 1,794,760
Minimum ratio	8.00%	8.00%
Well capitalized amount	$ 2,366,797	$ 2,243,450
Well capitalized ratio	10.00%	10.00%
Actual amount	$ 2,798,875	$ 2,591,374
Actual ratio	11.83%	11.55%

Earnings Per Share - Schedule o

Earnings Per Share - Schedule of Calculation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings per common share - basic:
Net income	$ 63,621	$ 50,473
Less: Preferred stock dividends	3,598	3,599
Less: Dividends and undistributed earnings allocated to unvested restricted shares	639	346
Net income allocated to common shareholders - basic	$ 59,384	$ 46,528
Weighted average common shares outstanding	53,616	46,123
Earnings per common share - basic (in usd per share)	$ 1.11	$ 1.01
Earnings per common share - diluted:
Net income allocated to common shareholders - basic	$ 59,384	$ 46,528
Adjustment for undistributed earnings allocated to unvested restricted shares	(18)	(37)
Earnings Allocated to Common Shareholders	$ 59,366	$ 46,491
Weighted average common shares outstanding	53,616	46,123
Dilutive potential common shares	351	373
Weighted average common shares outstanding - diluted	53,967	46,496
Earnings per common share - diluted (in usd per share)	$ 1.10	$ 1

Earnings Per Share - Narrative

Earnings Per Share - Narrative (Detail) - shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share
Weighted average number of shares held by Recognition and Retention Plan excluded from the calculation for basic shares outstanding	606,442	406,896
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive securities excluded from the computation of earnings per share	156,737	70,456

Share-Based Compensation - Narr

Share-Based Compensation - Narrative (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Future awards shares under approved incentive compensation plans	1,166,797
Share-based compensation maximum option term (in years)	10 years
Stock Option Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unearned share-based compensation associated with awards	$ 2.8
Unrecognized compensation cost related to stock options expected to be recognized over a weighted-average period	3 years 2 months 18 days
Restricted Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unearned share-based compensation associated with awards	$ 39	$ 21.4
Unrecognized compensation cost related to stock options expected to be recognized over a weighted-average period	1 year 6 months
Restricted Share Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)	3 years
Phantom Stock Awards | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)	5 years

Share-Based Compensation - Acti

Share-Based Compensation - Activity Related to Stock Options (Detail) - Stock Option Awards - $ / shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Number of shares
Balance at beginning of the period (in shares)	686,366,000	721,538,000
Granted (in shares)	92,162,000	70,433,000
Exercised (in shares)	(21,212,000)	(24,457,000)
Forfeited or expired (in shares)	(14,513,000)	(12,539,000)
Balance at end of the period (in shares)	742,803,000	754,975,000
Exercisable at period end (in shares)	519,496,000	509,347,000
Weighted Average Exercise Price
Balance at beginning of the period (in usd per share)	$ 58.24	$ 55.38
Granted (in usd per share)	82.20	85.52
Exercised (in usd per share)	52.10	53.85
Forfeited or expired (in usd per share)	65.27	75.77
Balance at end of the period (in usd per share)	61.25	57.90
Exercisable at period end (in usd per share)	$ 56.53	$ 55.78

Share-Based Compensation - Esti

Share-Based Compensation - Estimate Fair Value of Stock Option Awards with Weighted-Average Assumptions (Detail) - Stock Option Awards - $ / shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividends	1.80%	1.70%
Expected volatility	24.30%	24.90%
Risk-free interest rate	2.70%	2.10%
Expected term (in years)	5 years 8 months 18 days	5 years 7 months
Weighted-average grant-date fair value	$ 18.36	$ 18.75

Share-Based Compensation - Comp

Share-Based Compensation - Compensation Expense Included in Non-Interest Expense and Related Income Tax Benefits (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Stock Option Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	$ 312	$ 444
Income tax benefit	23	68
Restricted Stock And Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	4,422	3,277
Income tax benefit	929	1,147
Phantom Stock and Performance Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	$ 2,996	$ 3,053

Share-Based Compensation - Unve

Share-Based Compensation - Unvested Restricted Stock Award Activity (Detail) - Restricted Stock And Restricted Stock Units - shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Balance at beginning of the period (in shares)	738,187,000	543,258,000
Granted (in shares)	199,958,000	146,175,000
Forfeited (in shares)	(43,405,000)	(4,105,000)
Earned and issued (in shares)	(115,877,000)	(157,753,000)
Balance at end of the period (in shares)	778,863,000	527,575,000

Share-Based Compensation - Sche

Share-Based Compensation - Schedule of Share and Dividend Equivalent Share Award Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Value of share equivalents
Market price of Company's stock	$ 78	$ 79.10
Phantom Stock and Performance Stock Units
Number of share equivalents
Balance at beginning of the period (in shares)	393,844,000	472,830,000
Granted (in shares)	129,234,000	96,897,000
Forfeited share equivalents (in shares)	(24,460,000)	(5,330,000)
Vested share equivalents (in shares)	(121,758,000)	(143,643,000)
Balance at end of the period (in shares)	376,860,000	420,754,000
Value of share equivalents
Balance at beginning of the period (in shares)	$ 30,523	$ 39,600
Granted (in shares)	10,080	7,665
Forfeited share equivalents (in shares)	(1,908)	(422)
Vested share equivalents (in shares)	(10,187)	(12,024)
Balance at end of the period (in shares)	$ 29,395	$ 33,282

Fair Value Measurements - Finan

Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Assets
Securities available for sale, at fair value	$ 4,542,486,000	$ 4,590,062,000
Equity Securities, FV-NI	9,801,000	0
Mortgage loans held for sale	110,348,000	134,916,000
Derivative instruments	11,483,000	29,056,000
Liabilities
Derivative instruments	31,358,000	16,191,000
Fair value assets transferred from Level 1 to Level 2	0
Level 1
Assets
Securities available for sale, at fair value	0	0
Equity Securities, FV-NI	0
Level 2
Assets
Securities available for sale, at fair value	4,542,486,000	4,590,062,000
Equity Securities, FV-NI	9,801,000
Level 3
Assets
Securities available for sale, at fair value	0	0
Equity Securities, FV-NI	0
Recurring
Assets
Securities available for sale, at fair value	4,542,486,000	4,590,062,000
Equity Securities, FV-NI	9,801,000
Mortgage loans held for sale	110,348,000	134,916,000
Derivative instruments	17,072,000	31,265,000
Total, Assets	4,679,707,000	4,756,243,000
Liabilities
Derivative instruments	32,154,000	25,154,000
Total	32,154,000	25,154,000
Recurring | Level 1
Assets
Securities available for sale, at fair value	0	0
Equity Securities, FV-NI	0
Mortgage loans held for sale	0	0
Derivative instruments	0	0
Total, Assets	0	0
Liabilities
Derivative instruments	0	0
Total	0	0
Recurring | Level 2
Assets
Securities available for sale, at fair value	4,542,486,000	4,590,062,000
Equity Securities, FV-NI	9,801,000
Mortgage loans held for sale	110,348,000	134,916,000
Derivative instruments	17,072,000	31,265,000
Total, Assets	4,679,707,000	4,756,243,000
Liabilities
Derivative instruments	32,154,000	25,154,000
Total	32,154,000	25,154,000
Recurring | Level 3
Assets
Securities available for sale, at fair value	0	0
Equity Securities, FV-NI	0
Mortgage loans held for sale	0	0
Derivative instruments	0	0
Total, Assets	0	0
Liabilities
Derivative instruments	0	0
Total	$ 0	$ 0

Fair Value Measurements - Fin84

Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on Nonrecurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Assets
Unpaid Principal Balance	$ 219,771	$ 283,629
Related allowance	2,974	2,856
Nonrecurring
Assets
Loans	85,269	71,210
OREO, net	2,234	3,029
Total	87,503	74,239
Nonrecurring | Level 1
Assets
Loans	0	0
OREO, net	0	0
Total	0	0
Nonrecurring | Level 2
Assets
Loans	0	0
OREO, net	0	0
Total	0	0
Nonrecurring | Level 3
Assets
Loans	85,269	71,210
OREO, net	2,234	3,029
Total	$ 87,503	$ 74,239

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Difference Between the Aggregate Fair Value and the Aggregate Unpaid Principal Balance for Mortgage Loans Held for Sale (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair value of acquired loans at acquisition	$ 17,000		$ 15,000
Net gains (losses) resulting from change in fair value of loans held-for-investment	(749)	$ (409)
Mortgages Held For Sale at Fair Value
Aggregate fair value	110,348		134,916
Aggregate unpaid principal	107,849		131,276
Aggregate fair value less unpaid principal	2,499		$ 3,640
Net gains (losses) resulting from change in fair value of loans held-for-sale	$ (1,100)	$ 839

Fair Value of Financial Instr86

Fair Value of Financial Instruments - Estimated Fair Values and Carrying Amounts of Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Financial Assets
Securities available for sale, at fair value	$ 4,542,486	$ 4,590,062
Equity Securities, FV-NI	9,801	0
Financial Assets	110,348	134,916
Derivative Asset	17,072	31,265
Cash and cash equivalents	564,092	625,724	$ 1,301,118	$ 1,362,126
Securities held to maturity (fair values of $219,868 and $227,964, respectively)	224,241	227,318
Financial Liabilities
Financial Liabilities	22,971,192	21,466,717	$ 17,312,265
Short-term Debt	900,496	991,297
Long-term debt	1,449,302	1,495,835
Derivative instruments	32,154	25,154
Level 1
Financial Assets
Securities available for sale, at fair value	0	0
Equity Securities, FV-NI	0
Financial Assets	0	0
Derivative Asset	0	0
Cash and cash equivalents	564,092	625,724
Securities held to maturity (fair values of $219,868 and $227,964, respectively)	0	0
Loans and Leases Receivable, Net Amount	0	0
Financial Liabilities
Financial Liabilities	0	0
Short-term Debt	525,496	516,297
Long-term debt	0	0
Derivative instruments	0	0
Level 2
Financial Assets
Securities available for sale, at fair value	4,542,486	4,590,062
Equity Securities, FV-NI	9,801
Financial Assets	110,348	134,916
Derivative Asset	17,072	31,265
Cash and cash equivalents	0	0
Securities held to maturity (fair values of $219,868 and $227,964, respectively)	219,868	227,964
Loans and Leases Receivable, Net Amount	0	0
Financial Liabilities
Financial Liabilities	22,970,554	21,460,782
Short-term Debt	375,000	475,000
Long-term debt	0	0
Derivative instruments	32,154	25,154
Level 3
Financial Assets
Securities available for sale, at fair value	0	0
Equity Securities, FV-NI	0
Financial Assets	0	0
Derivative Asset	0	0
Cash and cash equivalents	0	0
Securities held to maturity (fair values of $219,868 and $227,964, respectively)	0	0
Loans and Leases Receivable, Net Amount	21,495,639	19,826,857
Financial Liabilities
Financial Liabilities	0	0
Short-term Debt	0	0
Long-term debt	1,429,335	1,476,899
Derivative instruments	0	0
Carrying Amount
Financial Assets
Securities available for sale, at fair value	4,542,486	4,590,062
Equity Securities, FV-NI	9,801
Financial Assets	110,348	134,916
Derivative Asset	17,072	31,265
Cash and cash equivalents	564,092	625,724
Securities held to maturity (fair values of $219,868 and $227,964, respectively)	224,241	227,318
Loans and Leases Receivable, Net Amount	21,561,563	19,937,290
Financial Liabilities
Financial Liabilities	22,971,192	21,466,717
Short-term Debt	900,496	991,297
Long-term debt	1,449,302	1,495,835
Derivative instruments	32,154	25,154
Fair Value
Financial Assets
Securities available for sale, at fair value	4,542,486	4,590,062
Equity Securities, FV-NI	9,801
Financial Assets	110,348	134,916
Derivative Asset	17,072	31,265
Cash and cash equivalents	564,092	625,724
Securities held to maturity (fair values of $219,868 and $227,964, respectively)	219,868	227,964
Loans and Leases Receivable, Net Amount	21,495,639	19,826,857
Financial Liabilities
Financial Liabilities	22,970,554	21,460,782
Short-term Debt	900,496	991,297
Long-term debt	1,429,335	1,476,899
Derivative instruments	$ 32,154	$ 25,154

Business Segments (Detail)

Business Segments (Detail)	3 Months Ended
	Mar. 31, 2018Segment
Segment Reporting [Abstract]
Number of business segments	3

Business Segments - Schedule of

Business Segments - Schedule of Segment Reporting Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Segment Reporting Information
Interest and dividend income	$ 270,543	$ 192,533
Interest expense	37,654	19,715
Net interest income	232,889	172,818
Provision for loan and lease losses	7,986	6,154
Mortgage income	9,595	14,115
Service charges on deposit accounts	12,908	11,153
Title revenue	5,027	4,741
Other non-interest income	29,944	26,268
Allocated expenses	0	0
Non-interest expense	188,296	138,796
Income before income tax expense	81,173	72,992
Income tax expense	17,552	22,519
Net income	63,621	50,473
Total loans, leases, and loans held for sale, net of unearned income	21,816,438	15,254,535
Total assets	29,472,637	22,008,479	$ 27,904,129
Total deposits	22,971,192	17,312,265	$ 21,466,717
Average assets	28,132,219	21,861,501
Operating Segments | IBERIABANK
Segment Reporting Information
Interest and dividend income	268,775	190,823
Interest expense	37,654	19,715
Net interest income	231,121	171,108
Provision for loan and lease losses	7,991	6,158
Mortgage income	0	0
Title revenue	0	0
Other non-interest income	29,906	26,284
Allocated expenses	(1,479)	(2,174)
Non-interest expense	171,816	119,429
Income before income tax expense	82,699	73,979
Income tax expense	18,540	22,829
Net income	64,159	51,150
Total loans, leases, and loans held for sale, net of unearned income	21,652,223	15,072,661
Total assets	29,243,983	21,774,586
Total deposits	22,959,061	17,306,328
Average assets	27,924,587	21,550,930
Operating Segments | IMC
Segment Reporting Information
Interest and dividend income	1,767	1,709
Interest expense	0	0
Net interest income	1,767	1,709
Provision for loan and lease losses	(5)	(4)
Mortgage income	9,595	14,115
Title revenue	0	0
Other non-interest income	38	(10)
Allocated expenses	1,166	1,656
Non-interest expense	11,916	15,167
Income before income tax expense	(1,677)	(1,005)
Income tax expense	(410)	(322)
Net income	(1,267)	(683)
Total loans, leases, and loans held for sale, net of unearned income	164,215	181,874
Total assets	205,497	209,911
Total deposits	12,131	5,937
Average assets	185,742	286,694
Operating Segments | LTC
Segment Reporting Information
Interest and dividend income	1	1
Interest expense	0	0
Net interest income	1	1
Provision for loan and lease losses	0	0
Mortgage income	0	0
Title revenue	5,027	4,741
Other non-interest income	0	(6)
Allocated expenses	313	518
Non-interest expense	4,564	4,200
Income before income tax expense	151	18
Income tax expense	(578)	12
Net income	729	6
Total loans, leases, and loans held for sale, net of unearned income	0	0
Total assets	23,157	23,982
Total deposits	0	0
Average assets	$ 21,890	$ 23,877

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Detail) - USD ($) $ in Millions	Dec. 11, 2017	Mar. 31, 2018	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Fair value of guarantees under commercial and standby letters of credit		$ 2.1	$ 2.1
Settled Litigation [Member]
Loss Contingencies [Line Items]
Settlement amount	$ 11.7
Pending Litigation [Member]
Loss Contingencies [Line Items]
Damages sought		$ 11.7

Commitments and Contingencies90

Commitments and Contingencies - Summary of Financial Instruments Outstanding (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Commitments to grant loans	$ 319,318	$ 342,305
Unfunded commitments under lines of credit	6,340,135	6,060,034
Commercial and standby letters of credit	211,070	210,002
Reserve for unfunded lending commitments	$ 13,432	$ 13,208	$ 11,660	$ 11,241

Uncategorized Items - ibkc-2018

Label	Element	Value
Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ (345,000)	[1]
[1]	Cumulative-effect adjustment to beginning retained earnings for fair value adjustments related to the reclassification of certain equity investments in accordance with ASU 2016-01, adopted as of January 1, 2018.