Iberiabank (IBKC) 10-K 23 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Jan. 31, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
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		53,912,254
Entity Public Float			$ 4,200,000,000

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets
Cash and due from banks	$ 319,156	$ 295,896
Interest-bearing deposits in banks	306,568	1,066,230
Total cash and cash equivalents	625,724	1,362,126
Securities available for sale, at fair value	4,590,062	3,446,097
Securities held to maturity (fair values of $227,964 and $89,932, respectively)	227,318	89,216
Mortgage loans held for sale, at fair value	134,916	157,041
Loans, net of unearned income	20,078,181	15,064,971
Allowance for loan losses	(140,891)	(144,719)
Loans, net	19,937,290	14,920,252
Premises and equipment, net	331,413	306,373
Goodwill	1,188,902	726,856
Other intangible assets	88,562	32,967
Other assets	779,942	618,262
Total Assets	27,904,129	21,659,190
Deposits:
Non-interest-bearing	6,209,925	4,928,878
Interest-bearing	15,256,792	12,479,405
Total deposits	21,466,717	17,408,283
Short-term borrowings	991,297	509,136
Long-term debt	1,495,835	628,953
Other liabilities	253,489	173,124
Total Liabilities	24,207,338	18,719,496
Shareholders’ Equity
Carrying Amount	132,097	132,097
Common stock, $1 par value - 100,000,000 shares authorized; 53,872,272 and 44,795,386 shares issued and outstanding, respectively	53,872	44,795
Additional paid-in capital	2,787,484	2,084,446
Retained earnings	769,226	704,391
Accumulated other comprehensive income (loss)	(45,888)	(26,035)
Total Shareholders’ Equity	3,696,791	2,939,694
Total Liabilities and Shareholders’ Equity	$ 27,904,129	$ 21,659,190

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Securities held to maturity, fair values	$ 227,964	$ 89,932
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	53,872,272	44,795,386
Common stock, shares outstanding	53,872,272	44,795,386

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest and Dividend Income
Loans, including fees	$ 802,947	$ 663,036	$ 606,966
Mortgage loans held for sale, including fees	4,679	6,564	6,164
Investment securities:
Taxable interest	87,359	52,150	47,380
Tax-exempt interest	8,835	7,004	5,785
Amortization of FDIC loss share receivable	0	(16,023)	(23,500)
Other	9,963	4,208	4,063
Total interest and dividend income	913,783	716,939	646,858
Deposits:
NOW and MMDA	57,283	32,396	27,226
Savings	1,455	1,145	740
Time deposits	21,095	18,040	19,137
Short-term borrowings	7,557	2,452	797
Long-term debt	17,547	13,668	11,200
Total interest expense	104,937	67,701	59,100
Net interest income	808,846	649,238	587,758
Provision for loan losses	51,111	44,424	30,908
Net interest income after provision for loan losses	757,735	604,814	556,850
Non-interest Income
Mortgage income	63,570	83,853	80,662
Service charges on deposit accounts	47,678	44,135	42,197
Title revenue	21,972	22,213	22,837
Broker commissions	9,902	15,338	17,592
ATM/debit card fee income	14,822	14,240	13,989
Credit card and merchant-related income	14,433	12,171	10,675
(Loss) gain on sale of available for sale securities	(148)	2,001	1,575
Other non-interest income	38,811	39,870	30,866
Total non-interest income	211,040	233,821	220,393
Non-interest Expense
Salaries and employee benefits	379,527	331,686	322,586
Net occupancy and equipment	70,663	65,797	68,541
Communication and delivery	14,252	12,383	13,506
Marketing and business development	13,999	12,332	13,176
Data processing	39,176	25,091	34,424
Professional services	48,545	19,153	22,368
Credit and other loan related expense	19,008	10,937	16,653
Insurance	21,815	17,270	16,670
Loss on early termination of loss share agreements	0	17,798	0
Travel and entertainment	11,287	8,481	9,525
Amortization of acquisition intangibles	12,590	8,415	7,811
Errors, fines, and losses	12,246	6,111	12,116
Other non-interest expense	32,788	31,211	32,929
Total non-interest expense	675,896	566,665	570,305
Income before income tax expense	292,879	271,970	206,938
Income tax expense	150,466	85,193	64,094
Net Income	142,413	186,777	142,844
Less: Preferred stock dividends	9,095	7,977	0
Net Income Available to Common Shareholders	133,318	178,800	142,844
Less: Earnings Allocated to Unvested Restricted Stock	(1,210)	(1,872)	(1,680)
Earnings Allocated to Common Shareholders	$ 132,108	$ 176,928	$ 141,164
Earnings per common share - Basic (in usd per share)	$ 2.61	$ 4.32	$ 3.69
Earnings per common share - Diluted (in usd per share)	2.59	4.30	3.68
Cash dividends declared per common share (in usd per share)	$ 1.46	$ 1.4	$ 1.36
Comprehensive Income
Net income	$ 142,413	$ 186,777	$ 142,844
Unrealized gains (losses) on securities:
Unrealized holding gains (losses) arising during the period (net of tax effects of $6,244 $12,261, and $4,374, respectively)	(11,596)	(22,771)	(8,124)
Less: Reclassification adjustment for (losses) gains included in net income (net of tax effects of $52, $700, and $551, respectively)	96	(1,301)	(1,024)
Unrealized gains (losses) on securities, net of tax	(11,500)	(24,072)	(9,148)
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 $329, $231, and $20, respectively)	(611)	(328)	38
Less: Reclassification adjustment for (losses) gains included in net income (net of tax effects of $210, $27, and $0, respectively)	390	(50)	0
Fair value of derivative instruments designated as cash flow hedges, net of tax	(221)	(378)	38
Other comprehensive income (loss), net of tax	(11,721)	(24,450)	(9,110)
Comprehensive income	$ 130,692	$ 162,327	$ 133,734

Consolidated Statements of Com5

Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Unrealized holding gains (losses), taxes	$ 6,244	$ 12,261	$ 4,374
Reclassification adjustment for gains included in net income , taxes	700	700	551
Change in fair value of derivative instruments designated as cash flow hedges, taxes	329	231	20
Reclassification adjustment for losses included in net income, taxes	$ 210	$ 27	$ 0

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)	Treasury Stock at Cost
Beginning balance (in shares) at Dec. 31, 2014			0	35,262,901
Beginning balance at Dec. 31, 2014		$ 1,852,148	$ 0	$ 35,263	$ 1,398,633	$ 496,573	$ 7,525	$ (85,846)
Increase (Decrease) in Shareholders' Equity
Net income		142,844				142,844
Other comprehensive income/(loss)		(9,110)					(9,110)
Cash dividends declared		(54,931)				(54,931)
Reclassification of treasury stock under the LBCA (in shares)	[1]			(1,809,497)
Reclassification of treasury stock under the LBCA	[1]			$ (1,809)	(84,037)			85,846
Common stock issued under incentive plans, net of shares surrendered in payment, including tax benefit (in shares)				211,729
Common stock issued under incentive plans, net of shares surrendered in payment, including tax benefit		2,413		$ 212	2,201			0
Preferred stock issued (in shares)			8,000
Preferred stock issued		76,812	$ 76,812		0			0
Common stock issued for acquisitions (in shares)				7,474,404
Common stock issued for acquisitions		474,753		$ 7,474	467,279
Share-based compensation cost		13,906			13,906
Ending balance (in shares) at Dec. 31, 2015			8,000	41,139,537
Ending balance at Dec. 31, 2015		2,498,835	$ 76,812	$ 41,140	1,797,982	584,486	(1,585)	0
Increase (Decrease) in Shareholders' Equity
Net income		186,777				186,777
Other comprehensive income/(loss)		(24,450)					(24,450)
Cash dividends declared		(58,895)				(58,895)
Preferred stock dividends		(7,977)				(7,977)
Common stock issued under incentive plans, net of shares surrendered in payment, including tax benefit (in shares)				264,605
Common stock issued under incentive plans, net of shares surrendered in payment, including tax benefit		8,020		$ 264	7,756
Preferred stock issued (in shares)			5,750
Preferred stock issued		55,285	$ 55,285
Common stock issued (in shares)				3,593,750
Common stock issued		279,242		$ 3,594	275,648
Common stock repurchases (in shares)				(202,506)
Common stock repurchases		(11,666)		$ (203)	(11,463)
Share-based compensation cost		14,523			14,523
Ending balance (in shares) at Dec. 31, 2016			13,750	44,795,386
Ending balance at Dec. 31, 2016		2,939,694	$ 132,097	$ 44,795	2,084,446	704,391	(26,035)	0
Increase (Decrease) in Shareholders' Equity
Net income		142,413				142,413
Other comprehensive income/(loss)		(11,721)					(11,721)
Cash dividends declared		(76,615)				(76,615)
Reclassification of AOCI to RE due to TJCA	[2]	0				8,132	(8,132)
Preferred stock dividends		(9,095)				(9,095)
Common stock issued under incentive plans, net of shares surrendered in payment, including tax benefit (in shares)				366,582
Common stock issued under incentive plans, net of shares surrendered in payment, including tax benefit		(515)		$ 367	(882)
Common stock issued (in shares)				6,100,000
Common stock issued		485,151		$ 6,100	479,051
Common stock issued for acquisitions (in shares)				2,610,304
Common stock issued for acquisitions		211,043		$ 2,610	208,433
Share-based compensation cost		16,436			16,436
Ending balance (in shares) at Dec. 31, 2017			13,750	53,872,272
Ending balance at Dec. 31, 2017		$ 3,696,791	$ 132,097	$ 53,872	$ 2,787,484	$ 769,226	$ (45,888)	$ 0
[1]	Effective January 1, 2015, companies incorporated in Louisiana became subject to the Louisiana Business Corporation Act (“LBCA”), which eliminates the concept of treasury stock and provides that shares reacquired by a company are to be treated as authorized but unissued. Refer to Note 1 for further discussion.
[2]	One-time reclassification from accumulated other comprehensive income ("AOCI") to retained earnings ("RE") for stranded tax effects resulting from the Tax Cuts and Jobs Act ("TCJA"), enacted on December 22, 2017.

Consolidated Statements of Sha7

Consolidated Statements of Shareholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash dividends declared per common share (in usd per share)	$ 1.46	$ 1.4	$ 1.36
Retained Earnings
Cash dividends declared per common share (in usd per share)	$ 1.46	$ 1.4	$ 1.36

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash Flows from Operating Activities
Net income	$ 142,413	$ 186,777	$ 142,844
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	(4,113)	10,633	12,017
Provision for loan losses	51,111	44,424	30,908
Share-based compensation cost - equity awards	16,436	14,523	13,906
(Gain)/loss on sale of OREO and long-lived assets, net of impairment	1,581	14,500	(1,137)
(Gain)/loss on sale of available for sale securities	148	(2,001)	(1,575)
Expense/(benefit) for deferred income taxes	71,257	(16,654)	4,551
Originations of mortgage loans held for sale	(1,844,358)	(2,460,033)	(2,464,588)
Proceeds from sales of mortgage loans held for sale	1,922,003	2,525,945	2,516,936
Realized and unrealized (gain)/loss on mortgage loans held for sale, net	(62,438)	(74,486)	(83,957)
Other operating activities, net	(30,394)	64,460	26,798
Net Cash Provided by Operating Activities	263,646	308,088	196,703
Cash Flows from Investing Activities
Proceeds from sales of available for sale securities	682,349	197,733	228,604
Proceeds from maturities, prepayments and calls of available for sale securities	568,250	484,138	473,142
Purchases of available for sale securities, net of available for sale securities acquired	(1,475,008)	(1,384,525)	(1,063,460)
Proceeds from maturities, prepayments and calls of held to maturity securities	8,687	8,791	22,939
Purchases of held to maturity securities	(148,234)	0	(5,833)
Purchases of equity securities, net of equity securities acquired	(71,684)	(31,530)	(16,362)
Proceeds from Sale and Maturity of Available-for-sale Securities	21,532	0	0
Increase in loans, net of loans acquired	(976,488)	(704,025)	(703,946)
Proceeds from sale of premises and equipment	354	1,941	13,309
Purchases of premises and equipment, net of premises and equipment acquired	(37,763)	(12,840)	(19,502)
Proceeds from disposition of OREO	25,624	33,236	55,025
Cash paid for additional investment in tax credit entities	(16,401)	(19,208)	(9,671)
Payments to Acquire Businesses, Net of Cash Acquired	(490,435)	0	425,581
Other investing activities, net	636	1,892	29,202
Net Cash Used in Investing Activities	(1,908,581)	(1,424,397)	(570,972)
Cash Flows from Financing Activities
Increase/(decrease) in deposits, net of deposits acquired	(323,257)	1,230,008	968,746
Net change in short-term borrowings, net of borrowings acquired	(38,377)	182,518	(520,653)
Proceeds from long-term debt	964,974	304,728	63,198
Repayments of long-term debt	(97,259)	(15,025)	(201,259)
Cash dividends paid on common stock	(72,772)	(56,793)	(52,318)
Cash dividends paid on preferred stock	(9,095)	(7,028)	0
Net share-based compensation stock transactions	(832)	6,899	1,915
Payments to repurchase common stock	0	(11,666)	0
Net proceeds from issuance of common stock	485,151	279,242	0
Net proceeds from issuance of preferred stock	0	55,285	76,812
Net Cash Provided by Financing Activities	908,533	1,968,168	336,441
Net Increase (Decrease) In Cash and Cash Equivalents	(736,402)	851,859	(37,828)
Cash and Cash Equivalents at Beginning of Period	1,362,126	510,267	548,095
Cash and Cash Equivalents at End of Period	625,724	1,362,126	510,267
Supplemental Schedule of Non-cash Activities
Acquisition of real estate in settlement of loans	18,170	9,743	21,690
Common stock issued in acquisition	211,043	0	474,753
Cash paid for:
Interest on deposits and borrowings	102,558	70,084	58,556
Income taxes, net	$ 77,034	$ 79,784	$ 53,476

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES GENERAL IBERIABANK Corporation is a regional financial holding company with offices in Louisiana, Arkansas, Tennessee, Alabama, Texas, Florida, Georgia, and South Carolina, offering commercial, private banking, consumer, small business, wealth and trust management, retail brokerage, mortgage, and title insurance services. The accompanying consolidated financial statements have been prepared in accordance with GAAP and practices generally accepted in the banking industry. The consolidated financial statements include the accounts of the Company and its subsidiaries. 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 Acronyms at the end of this Report for terms used throughout this Report. 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. PRINCIPLES OF CONSOLIDATION All significant intercompany balances and transactions have been eliminated in consolidation. The Company’s consolidated financial statements include all entities in which the Company has a controlling financial interest under either the voting interest or variable interest model. The assessment of whether or not the Company has a controlling interest (i.e., the primary beneficiary) in a variable interest entity ("VIE") is performed on an on-going basis. All equity investments in non-consolidated VIEs are included in "other assets" in the Company’s consolidated balance sheets. The Company’s maximum exposure to loss as a result of its involvement with non-consolidated VIEs was approximately $160 million and $91 million at December 31, 2017 and 2016, respectively. The Company's maximum exposure to loss was equivalent to the carrying value of its investments and any related outstanding loans to the non-consolidated VIEs. Investments in entities that are not consolidated are accounted for under either the equity, cost, or proportional amortization method of accounting. Investments for which the Company has the ability to exercise significant influence over the operating and financing decisions of the entity are accounted for under the equity method. Investments for which the Company does not hold such ability are accounted for under the cost method. Investments in qualified affordable housing projects, which meet certain criteria, are accounted for under the proportional amortization method. USE OF ESTIMATES The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Actual results could differ from those estimates. Material estimates that are susceptible to significant change in the near term are the allowance for credit losses, valuation of and accounting for acquired loans, goodwill and other intangible assets, and income taxes. CONCENTRATION OF CREDIT RISKS 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. BUSINESS COMBINATIONS Assets and liabilities acquired in business combinations are recorded at their acquisition date fair values. In accordance with ASC Topic 805, Business Combinations , the Company generally records provisional amounts at the time of acquisition based on the information available to the Company. The provisional estimates of fair values may be adjusted for a period of up to one year (“measurement period”) from the date of acquisition if new information is obtained about facts and circumstances that existed as of the acquisition date that, if known, would have affected the measurement of the amounts recognized as of that date. Subsequently, adjustments recorded during the measurement period are recognized in the current reporting period. Loans generally represent a significant portion of the assets acquired in the Company’s business acquisitions. If the Company discovers that it has materially underestimated the credit losses expected in the loan portfolio based on information available at the acquisition date within the measurement period, it will reduce or eliminate the gain and/or increase goodwill recorded on the acquisition in the period the adjustment is recorded. If the Company determines that losses arose subsequent to the acquisition date, such losses are reflected as a provision for credit losses. CASH AND CASH EQUIVALENTS For purposes of presentation in the consolidated statements of cash flows, cash and cash equivalents are defined as cash on hand, interest-bearing deposits, and non-interest-bearing demand deposits at other financial institutions with original maturities less than three months . IBERIABANK may be required to maintain average cash balances on hand or with the Federal Reserve Bank to meet regulatory reserve and clearing requirements. At December 31, 2017 and 2016, IBERIABANK had sufficient cash deposited with the Federal Reserve Bank to cover the required reserve balance. INVESTMENT SECURITIES Management determines the appropriate accounting classification of debt and equity securities at the time of acquisition and re-evaluates such designations at least quarterly. Debt securities that management has the ability and intent to hold to maturity are classified as HTM and carried at cost, adjusted for amortization of premiums and accretion of discounts using methods approximating the interest method. Securities acquired with the intention of recognizing short-term profits or which are actively bought and sold are classified as trading securities and reported at fair value, with unrealized gains and losses recognized in earnings. Securities not classified as HTM or trading, including equity securities with readily determinable fair values, are classified as AFS and recorded at fair value, with unrealized gains and losses excluded from earnings and reported in OCI. Credit-related declines in the fair value of debt and marketable equity securities that are considered OTTI are recorded in earnings. The Company evaluates its investment securities portfolio on a quarterly basis for indicators of OTTI. Declines in the fair value of individual HTM and AFS securities below their amortized cost basis are reviewed to determine whether the declines are other than temporary. In estimating OTTI losses, management considers 1) the length of time and the extent to which the fair value has been less than the amortized cost basis, 2) the financial condition and near-term prospects of the issuer, 3) its intent to sell and whether it is more likely than not that the Company would be required to sell those securities before the anticipated recovery of the amortized cost basis, and 4) for debt securities, the recovery of contractual principal and interest. For securities that the Company does not expect to sell, or it is not more likely than not it will be required to sell prior to recovery of its amortized cost basis, the credit component of an OTTI is recognized in earnings and the non-credit component is recognized in OCI. For securities that the Company does expect to sell, or it is more likely than not that it will be required to sell prior to recovery of its amortized cost basis, both the credit and non-credit component of an OTTI are recognized in earnings. Subsequent to recognition of OTTI, an increase in expected cash flows is recognized as a yield adjustment over the remaining expected life of the security based on an evaluation of the nature of the increase. Nonmarketable equity securities include stock acquired for regulatory purposes, such as Federal Home Loan Bank stock and Federal Reserve Bank stock. These securities are accounted for at amortized cost, evaluated for impairment at least quarterly, and included in "other assets." Gains or losses on securities sold are recorded on the trade date, using the specific identification method. LOANS HELD FOR SALE Loans and loan commitments which the Company does not have the intent and ability to hold for the foreseeable future or until maturity or payoff are classified as loans held for sale at the time of origination or acquisition. Subsequent to origination or acquisition, if the Company no longer has the intent or ability to hold a loan for the foreseeable future, generally a decision has been made to sell the loan, and it is classified within loans held for sale. Unless the fair value option has been elected at origination or acquisition, loans classified as held for sale are carried at the lower of cost or fair value. Amortization/accretion of remaining unamortized net deferred loan fees or costs and discounts or premiums (if applicable) ceases when a loan is classified as held for sale. Loans held for sale primarily consist of fixed rate single-family residential mortgage loans originated and committed to be sold in the secondary market. Mortgage loans originated and held for sale are recorded at fair value under the fair value option, unless otherwise noted. For mortgage loans for which the Company has elected the fair value option, gains and losses are included in mortgage income. For any other loans held for sale, net unrealized losses, if any, are recognized through a valuation allowance that is recorded as a charge to non-interest income. See Note 19 for further discussion of the determination of fair value for loans held for sale. In most cases, loans in this category are sold within thirty days and are generally sold with the mortgage servicing rights released. Buyers generally have recourse to return a purchased loan or request reimbursement for the loan premium or consideration transferred for servicing rights under limited circumstances. Recourse conditions may include prepayment, payment default, breach of representations or warranties, and documentation deficiencies. During 2017 and 2016, an insignificant number of loans were returned to the Company. At December 31, 2017 and 2016, the recorded repurchase liability associated with transferred loans was not material. LOANS Legacy (Loans originated or renewed and underwritten by the Company) The Company originates mortgage, commercial, and consumer loans for customers. Loans that management has the intent and ability to hold for the foreseeable future or until maturity or payoff are reported at the unpaid principal balances, less the ALL, charge-offs, and unamortized net loan origination fees and direct costs, except for loans carried at fair value. Interest income is accrued as earned over the term of the loans based on the principal balance outstanding. Loan origination fees, net of certain direct origination costs, are deferred and recognized as an adjustment of the related loan yield. Acquired (Loans acquired through Business Combinations) Acquired loans are recorded at fair value on the acquisition date in accordance with ASC Topic 820, Fair Value Measurement , consistent with the exit price concept on the date of acquisition. Credit risk assumptions and any resulting credit discounts are included in the determination of fair value. Therefore, an ALL is not recorded at the acquisition date. The determination of fair value includes estimates related to discount rates, expected prepayments, and the amount and timing of undiscounted expected principal, interest, and other cash flows. Acquired loans are evaluated at acquisition and classified as purchased impaired (“acquired impaired”) or purchased non-impaired (“acquired non-impaired”). Acquired impaired loans reflect credit deterioration since origination to the extent that it is probable at the time of acquisition that the Company will be unable to collect all contractually required payments. At the time of acquisition, acquired impaired loans are accounted for individually or aggregated into loan pools with similar characteristics, which include: • whether the loan is performing according to contractual terms at the time of acquisition, • the loan type based on regulatory reporting guidelines, namely whether the loan was a mortgage, consumer, or commercial loan, • the nature of collateral, • the interest rate type, whether fixed or variable rate, and • the loan payment type, primarily whether the loan is amortizing or interest-only. From these pools, the Company uses certain loan information, including outstanding principal balance, estimated expected losses, weighted average maturity, weighted average term to re-price (if a variable rate loan), weighted average margin, and weighted average interest rate to estimate the expected cash flows for each loan pool. For acquired impaired loans, expected cash flows at the acquisition date in excess of the fair value of loans are recorded as interest income over the life of the loans using a level yield method if the timing and amount of future cash flows is reasonably estimable. For acquired non-impaired loans, the difference between the fair value and unpaid principal balance of the loan at acquisition, referred to as a purchase premium or discount, is amortized or accreted to income over the estimated life of the loans as an adjustment to yield. Subsequent to acquisition, the Company performs cash flow re-estimations at least quarterly for each acquired impaired loan and/or loan pool. Increases in estimated cash flows above those expected at acquisition are recognized on a prospective basis as interest income over the remaining life of the loan and/or pool. Decreases in expected cash flows subsequent to acquisition generally result in recognition of a provision for credit loss. The measurement of cash flows involves several assumptions and judgments (i.e., prepayments, default rates, loss severity, etc.). All of these factors are inherently subjective and significant changes in the cash flow estimations can result over the life of the loan. Classification The Company’s loan portfolio is disaggregated into portfolio segments for purposes of determining the ACL. The Company’s portfolio segments include commercial, residential mortgage, and consumer and other loans, bifurcated between legacy and acquired (non-impaired). The Company further disaggregates each commercial, residential mortgage, and consumer and other loans portfolio segment into classes for purposes of monitoring and assessing credit quality based on certain risk characteristics. Classes within the commercial loan portfolio segment include commercial real estate-construction, commercial real estate-owner-occupied, commercial real estate-non-owner occupied, and commercial and industrial. Classes within the consumer and other loans portfolio segment include home equity, indirect automobile, credit card and other. Troubled Debt Restructurings The Company periodically grants concessions to its customers in an attempt to protect as much of its investment as possible and minimize risk of loss. These concessions may include restructuring the terms of a loan to alleviate the burden of the customer’s near-term cash requirements. In order to be classified as a TDR, the Company must conclude that the restructuring constitutes a concession and the customer is experiencing financial difficulties. The Company defines a concession to the customer as a modification of existing terms for economic or legal reasons that it would otherwise not consider. The concession is either granted through an agreement with the customer or is imposed by a court of law. Concessions include modifying original loan terms to reduce or defer cash payments required as part of the loan agreement, including but not limited to: • a reduction of the stated interest rate for the remaining original life of the loan, • extension of the maturity date or dates at a stated interest rate lower than the current market rate for new loans with similar risk characteristics, • reduction of the face amount or maturity amount of the loan as stated in the agreement, or • reduction of accrued interest receivable on the loan. In its determination of whether the customer is experiencing financial difficulties, the Company considers numerous indicators, including, but not limited to: • whether the customer is currently in default on its existing loan(s), or is in an economic position where it is probable the customer will be in default on its loan(s) in the foreseeable future without a modification, • whether the customer has declared or is in the process of declaring bankruptcy, • whether there is substantial doubt about the customer’s ability to continue as a going concern, • whether, based on its projections of the customer’s current capabilities, the Company believes the customer’s future cash flows will be insufficient to service the loan, including interest, in accordance with the contractual terms of the existing agreement for the foreseeable future, and • whether, without modification, the customer cannot obtain sufficient funds from other sources at an effective interest rate equal to the current market rate for a similar loan for a non-troubled debtor. If the Company concludes that both a concession has been granted and the customer is experiencing financial difficulties, the Company identifies the loan as a TDR. All TDRs are considered impaired loans. NON-ACCRUAL AND PAST DUE LOANS (INCLUDING LOAN CHARGE-OFFS) Loans are generally considered past due when contractual payments of principal and interest have not been received within 30 days from the contractual due date. Residential mortgage loans are considered past due when contractual payments have not been received for two consecutive payment dates. Legacy and acquired non-impaired loans are placed on non-accrual status when any of the following occur: 1) the loan is maintained on a cash basis because of deterioration in the financial condition of the borrower; 2) collection of the full contractual amount of principal and interest is not expected (even if the loan is currently paying as agreed); or 3) when principal or interest has been in default for a period of 90 days or more, unless the loan is both well-secured and in the process of collection. Factors considered in determining the collection of the full contractual amount of principal and interest include assessment of the borrower’s cash flow, valuation of underlying collateral, and the ability and willingness of guarantors to provide credit support. Certain commercial loans are also placed on non-accrual status when payment is not past due and full payment of principal and interest is expected, but we have doubt about the borrower’s ability to comply with existing repayment terms. Consideration will be given to placing a loan on non-accrual due to the deterioration of the debtor’s repayment ability, the repayment of the loan becoming dependent on the liquidation of collateral, an existing collateral deficiency, the loan being classified as "Doubtful" or "Loss," the client filing for bankruptcy, and/or foreclosure being initiated. Regarding all classes within the C&I and CRE portfolios, the determination of a borrower’s ability to make the required principal and interest payments is based on an examination of the borrower’s current financial statements, industry, management capabilities, and other qualitative factors. Acquired impaired loans are placed on non-accrual status when the Company cannot reasonably estimate cash flows on a loan or loan pool. Legacy and acquired non-impaired loans are evaluated for potential charge-off in accordance with the parameters discussed in the following paragraph or when the loan is placed on non-accrual status, whichever is earlier. Loans within the commercial portfolio (except for acquired impaired) are generally evaluated for charge-off at 90 days past due, unless both well-secured and in the process of collection. Closed and open-end residential mortgage and consumer loans (except for acquired impaired) are evaluated for charge-off no later than 120 days past due. Any outstanding loan balance in excess of the fair value of the collateral less costs to sell is charged-off no later than 120 days past due for loans secured by real estate. For non-real estate secured loans, in lieu of charging off the entire loan balance, loans may be written down to the fair value of the collateral less costs to sell if repossession of collateral is assured and in process. The accrual of interest, as well as the amortization/accretion of any remaining unamortized net deferred fees or costs and discount or premium, is discontinued at the time the loan is placed on non-accrual status. All accrued but uncollected interest for loans that are placed on non-accrual status is reversed through interest income. Cash receipts received on non-accrual loans are generally applied against principal until the loan has been collected in full, after which time any additional cash receipts are recognized as interest income (i.e., cost recovery method). However, interest may be accounted for under the cash-basis method as long as the remaining recorded investment in the loan is deemed fully collectible. Loans are returned to accrual status when the borrower has demonstrated a capacity to continue payment of the debt (generally a minimum of six months of payment history) and collection of contractually required principal and interest associated with the debt is reasonably assured. At such time, the accrual of interest and amortization/accretion of any remaining unamortized net deferred fees or costs and discount or premium shall resume. Any interest income which was applied to the principal balance shall not be reversed and subsequently will be recognized as an adjustment to yield over the remaining life of the loan. IMPAIRED LOANS For all classes within the commercial portfolio, all loans with an outstanding commitment balance above a specific threshold are evaluated on a quarterly basis for potential impairment. Generally, residential mortgage and consumer loans within any class are not individually evaluated on a regular basis for impairment. All TDRs, regardless of the outstanding balance amount or portfolio classification, and all acquired impaired loans are considered to be impaired. A loan is considered impaired when, based on current information and events, it is probable that the Company will be unable to collect the scheduled payments of principal and/or interest when due, according to the contractual terms of the loan agreement. Factors considered by management in determining impairment include payment status, collateral value, and the likelihood of collecting scheduled principal and interest payments when due. Loans that experience insignificant payment delays and payment shortfalls generally are not classified as impaired. Impairment losses are measured on a loan-by-loan basis for commercial and certain residential mortgage or consumer loans, based on either the present value of expected future cash flows discounted at the loan’s effective interest rate, the loan’s observable market price, or the fair value of the collateral if the loan is collateral-dependent. This measurement requires significant judgment and use of estimates, and the actual loss ultimately recognized by the Company may differ significantly from the estimates. ALLOWANCE FOR CREDIT LOSSES The Company maintains the ACL at a level that management believes appropriate to absorb estimated probable credit losses incurred in the loan portfolios (including unfunded commitments) as of the consolidated balance sheet date. The ACL consists of the allowance for loan losses (contra asset) and the reserve for unfunded commitments (liability). The manner in which the ACL is determined is based on 1) the accounting method applied to the underlying loans and 2) whether the loan is required to be measured for impairment. The Company delineates between loans accounted for under the contractual yield method, legacy and acquired non-impaired loans, and acquired impaired loans. Further, for legacy and acquired non-impaired loans, the Company attributes portions of the ACL to loans and loan commitments that it measures individually, and groups of homogeneous loans and loan commitments that it measures collectively for impairment. Determination of the appropriate ACL involves a high degree of complexity and requires significant judgment regarding the credit quality of the loan portfolio. Several factors are taken into consideration in the determination of the overall ACL, including a qualitative component. These factors include, but are not limited to, the overall risk profiles of the loan portfolios, net charge-off experience, the extent of impaired loans, the level of non-accrual loans, the level of 90 days past due loans, the value of collateral, the ability to monetize guarantor support, and the overall percentage level of the allowance relative to the loan portfolio, amongst other factors. The Company also considers overall asset quality trends, changes in lending practices and procedures, trends in the nature and volume of the loan portfolio, including the existence and effect of any portfolio concentrations, changes in experience and depth of lending staff, the Company’s legal, regulatory and competitive environment, national and regional economic trends, data availability and applicability that might impact the portfolio or the manner in which it estimates losses, and risk rating accuracy and risk identification. The allowance for loan losses for all impaired loans (excluding acquired impaired) is determined on an individual loan basis, considering the facts and circumstances specific to each borrower. The allowance is based on the difference between the recorded investment in the loan and generally either the estimated net present value of projected cash flows or the estimated value of the collateral associated with the loan, if the loan is deemed collateral-dependent. For non-impaired loans (excluding acquired impaired), the allowance for loan losses is calculated based on pools of loans with similar characteristics. The pool-level allowance is calculated through the application of PD (i.e., probability of default) and LGD (i.e., loss given default) factors for each individual loan. PDs and LGDs are determined based on historical default and loss information for similar loans. For purposes of establishing estimated loss percentages for pools of loans that share common risk characteristics, the Company’s loan portfolio is segmented by various loan characteristics including loan type, risk rating (commercial), Vantage or FICO score (residential mortgage and consumer), past due status (residential mortgage and consumer) and call report code. The default and loss information is measured over an appropriate period for each loan pool and adjusted as deemed appropriate. Qualitative adjustments are incorporated into the pool-level analysis to accommodate for the imprecision of certain assumptions and uncertainties inherent in the calculation. See the "Loans" section of this footnote for discussion of the determination of the ACL for acquired impaired loans. Certain inherent, but unconfirmed losses are probable within the loan portfolio. The Company’s current methodology for determining the level of inherent losses is based on historical loss rates, current credit grades, specific allocation, and other qualitative adjustments. In a stable or deteriorating credit environment, heavy reliance on historical loss rates and the credit grade rating process results in model-derived reserves that tend to slightly lag behind portfolio deterioration. Similar lags can occur in an improving credit environment whereby required reserves can lag slightly behind portfolio improvement. Given these and other model limitations, qualitative adjustment factors may be incremental or decremental to the quantitative model results. In periods prior to 2015, the Company estimated incurred losses on its Exploration and Production and its Oil Field Services portfolios as an aggregate portfolio. Beginning in 2015, as the performance of these two portfolios began to diverge, the Company disaggregated the analysis of incurred losses within these portfolios, which included modifying its LGD estimates for the portfolios to more closely align with published historical industry data and other factors. Absent this change, the Company would have recorded an additional $10.0 million , or 17 cents per share, in provision expense for the year ended December 31, 2015. The reserve for unfunded commitments is determined using similar methodologies described above for non-impaired loans. The loss factors used in the reserve for unfunded commitments are equivalent to the loss factors used in the allowance for loan losses, while also considering utilization of unused commitments. PREMISES AND EQUIPMENT Land is carried at cost. Buildings, furniture, fixtures, and equipment are carried at cost, less accumulated depreciation computed on a straight-line basis over the estimated useful lives of 10 to 40 years for buildings and related improvements and generally 3 to 20 years for furniture, fixtures, and equipment. Leasehold improvements are amortized over the lease term, including any renewal periods that are reasonably assured, or the asset’s useful life, whichever is shorter. Premises and equipment are evaluated for impairment whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. SOFTWARE Software is amortized on a straight-line basis over its estimated useful life. The estimated useful life of software is generally three years , but can vary depending on the specific facts and circumstances. Software is evaluated for impairment whenever events or changes in circumstances indicate that the carrying amount of the software may not be recoverable. Software is recorded within "other assets" on the Company’s consolidated balance sheets with carrying amounts at December 31, 2017 and 2016 of $5.2 million and $5.6 million , respectively. GOODWILL AND OTHER INTANGIBLE ASSETS Goodwill Goodwill represents the excess of the consideration paid in a business combination over the fair value of the identifiable net assets acquired. Goodwill is not amortized, but is assessed for potential impairment at a reporting unit level on an annual basis, as of October 1 st , or whenever events or changes in circumstances indicate that it is more likely than not the fair value of a reporting unit is less than its respective carrying amount. For the annual October 1, 2017 impairment evaluation, management elected to bypass the qualitative assessment for each respective reporting unit (IBERIABANK, Mortgage, and LTC) and performed Step 1 of the goodwill impairment test. Step 1 of the goodwill impairment test requires the Company to compare the fair value of each reporting unit with its carrying amount, including goodwill. Accordingly, the Company determined the fair value of each reporting unit and compared the fair value to each respective reporting unit’s carrying amount. The Company determined that none of the reporting units’ fair values were below their respective carrying amounts. The Company concluded goodwill was not impaired as of October 1, 2017. Further, no events or changes in circumstances between October 1, 2017 and December 31, 2017 indicated that it was more likely than not the fair value of any reporting unit had been reduced below its carrying value. Based on the testing performed in 2017 and 2016, management concluded that for the IBERIABANK, Mortgage, and LTC reporting units, goodwill was not impaired at any time during those periods. Title Plant Costs incurred to construct a title plant, including the costs incurred to obtain, organize, and summarize historical information, are capitalized until the title plant can be used to perform title searches. A purchased title plant, including a purchased undivided

Recent Accounting Pronouncement

Recent Accounting Pronouncements	12 Months Ended
	Dec. 31, 2017
Accounting Changes and Error Corrections [Abstract]
Recent Accounting Pronouncements	RECENT ACCOUNTING PRONOUNCEMENTS Pronouncements adopted during the year ended December 31, 2017: ASU No. 2016-09 The Company adopted the amendments of ASU No. 2016-09, Compensation-Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting , effective January 1, 2017 as follows: (i) prospective adoption of the recognition of excess tax benefits associated with vested or settled awards in the statement of comprehensive income; (ii) prospective adoption of the exclusion of excess tax benefits from assumed proceeds for the calculation of diluted EPS; (iii) modified retrospective adoption of the minimum statutory withholdings requirements; (iv) modified retrospective adoption of the accounting policy election to account for forfeitures as they occur; and (v) prospective adoption of the classifications of certain cash flows associated with stock compensation. The adoption of these amendments did not, either individually or in aggregate, have a significant impact on the Company’s consolidated financial statements. ASU No. 2017-01 In January 2017, the FASB issued ASU No. 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business , which introduces amendments that are intended to clarify the definition of a business to assist companies and other reporting organizations in evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. The Company early-adopted the amendments effective January 1, 2017. The adoption of this ASU did not have a significant impact on the Company’s consolidated financial statements. ASU No. 2018-02 In February 2018, the FASB issued ASU No. 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income , which allows a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the newly enacted corporate tax rate on December 22, 2017. ASU No. 2018-02 is effective for annual reporting periods beginning after December 15, 2018, including interim reporting periods within those periods. Early adoption is permitted for financial statements of fiscal years or interim periods which have not yet been issued. The Company elected to early adopt the standard for the fiscal year ending December 31, 2017. The adjustment from accumulated other comprehensive income to retained earnings did not have a significant impact on the Company’s consolidated financial statements. Pronouncements issued but not yet adopted: 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. The amendments in ASU No. 2014-09 will be effective for annual reporting periods beginning after December 15, 2017, including interim reporting periods within that reporting period. The Company will adopt the amendments beginning January 1, 2018 through the modified-retrospective transition method. A significant amount of the Company’s revenues are derived from net interest income on financial assets and liabilities, which are excluded from the scope of the amended guidance. The Company does not expect to recognize a cumulative adjustment to equity upon implementation of the standard, but does anticipate an insignificant adjustment to its consolidated statements of comprehensive income related to the net presentation of certain costs associated with interchange fees and rewards programs, as well as some additional disclosure. 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 . This ASU will impact how the Company measures certain equity investments and discloses and presents certain financial instruments through the application of the “exit price” notion. ASU No. 2016-01 is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2017. The Company will adopt the amendments beginning January 1, 2018 through an insignificant cumulative-effect adjustment to equity at adoption related to its current equity investments with readily determinable fair values. The Company will also modify its fair value methodology for financial instruments measured at amortized cost whose fair values are disclosed under the “entry price” notion to an “exit price” notion. The Company anticipates the fair value of these financial instruments will be lower under the exit price methodology in comparison to the entry price methodology. ASU No. 2016-02 In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 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 (Topic 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 ALL 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 standard and has developed an implementation plan. ASU No. 2016-15 In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 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. ASU 2016-15 will be effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. Early adoption is permitted, including adoption in an interim period. The amendments should be applied using a retrospective transition method to each period presented. The Company is currently evaluating the impact of the ASU on the Company’s consolidated statement of cash flows, but does not anticipate significant changes in presentation. ASU No. 2017-04 In January 2017, the FASB issued ASU No. 2017-04, Intangibles-Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment , which simplifies how an entity is required to test goodwill for impairment by eliminating Step 2 from the goodwill impairment test. Therefore, any carrying amount which exceeds the reporting unit’s fair value (up to the amount of goodwill recorded) will be recognized as an impairment loss. ASU No. 2017-04 will be effective for annual reporting periods beginning after December 15, 2019, including interim reporting periods within those periods. The amendments will be applied prospectively on or after the effective date. Early adoption is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. Based on recent goodwill impairments tests, which did not require the application of Step 2, the Company does not expect the adoption of this ASU to have an immediate impact. ASU No. 2017-12 In August 2017, the FASB issued ASU No. 2017-12, Derivatives and Hedging (Topic 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 amendments within ASU 2017-12 include: • Elimination of the requirement to separately measure and report periodic hedge ineffectiveness for cash flow and net investment hedges. • Recognition and presentation of changes in the fair value of the hedging instrument. • Recognition and presentation of components excluded from an entity’s hedge effectiveness assessment. • Addition of the ability to elect to perform subsequent effectiveness assessments qualitatively. • Elimination of the benchmark interest rate concept for variable-rate instruments in cash flow hedges by allowing the designation of the contractually specified interest rate as the hedged risk. • Addition of the Securities Industry and Financial Markets Association Municipal Swap Rate as a benchmark interest rate. • Addition of the ability to define a long-haul methodology to employ in the event a hedge ceases to qualify under the shortcut method. • Addition of the ability to apply the shortcut method to partial-term fair value hedges of interest rate risk. • Enhancement of the ability to use the critical-terms-match method for a cash flow hedge of groups of forecasted transactions when the timing of the hedged transactions does not perfectly match the hedging instrument’s maturity date. • Addition of new, and amendments to existing, disclosure requirements. ASU No. 2017-12 will be effective for annual reporting periods beginning after December 15, 2018, including interim reporting periods within those periods. Early adoption is permitted in any interim period or fiscal year before the effective date. The implementation of the amendments will not have a significant impact on the Company’s consolidated financial statements based upon its current hedging strategies.

Acquisition Activity

Acquisition Activity	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Acquisition Activity	ACQUISITION ACTIVITY 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 added $4.0 billion in loans and $4.4 billion in deposits after preliminary 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. 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 determination of estimated fair values requires management to make certain estimates about discount rates, future expected cash flows, market conditions, and other future events that are highly subjective in nature and may require adjustments. Upon receipt of final fair value estimates during the measurement period, which must be within one year of the acquisition date, the Company will record any adjustments to the preliminary fair value estimates in the reporting period in which the adjustments are determined. Fair value adjustments based on updated estimates could materially affect the goodwill recorded on the acquisition. The Company may incur losses on the acquired loans that are materially different from losses the Company originally projected. During the third quarter of 2017, the Company recorded preliminary purchase price allocations related to Sabadell United, which resulted in goodwill of $431.8 million . Throughout the fourth quarter of 2017, 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 $30.2 million to $462.0 million . This increase is primarily a result of a change in the estimated fair value of the acquired core deposit intangible assets. As of December 31, 2017, 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 acquired identifiable assets and liabilities assumed as of the acquisition date. Acquisition of Sabadell United (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 558,156 Goodwill $ 462,046 (Dollars in thousands) Sabadell United Fair Value (Preliminary) Assets Cash and cash equivalents $ 318,724 Investment securities 964,123 Loans 4,026,240 Core deposit intangible assets 66,600 Deferred tax asset, net 35,129 Other assets 89,745 Total assets acquired $ 5,500,561 Liabilities Deposit liabilities $ 4,383,049 Short-term borrowings 520,539 Other liabilities 38,817 Total liabilities assumed $ 4,942,405 Information regarding the preliminary allocation of goodwill recorded as a result of the acquisition to the Company's reportable segments is provided in Note 9 "Goodwill and Other Acquired Intangible Assets." The goodwill recorded as a result of the acquisition is not deductible for tax purposes. The following is a description of the methods used to determine the fair values of significant assets acquired and liabilities assumed presented above as well as any material measurement period adjustments applied. 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. 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 cost 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. The fair value for CDI was adjusted during the fourth quarter of 2017. Through review of the fair value calculation and consultation with third party experts, refinements were made to the original core deposit balance valued as well as the average life assumptions applied. These refinements in the discounted cash flow methodology resulted in a decrease to the fair value of the acquired CDI of approximately $30 million with a corresponding adjustment to goodwill. These changes are gross of taxes and reflected in the following table: Acquired Asset Balance Sheet Line Item Provisional Estimate September 30, 2017 Revised Provisional Estimate December 31, 2017 Increase (Decrease) CDI Other intangible assets $ 96,607 $ 66,600 $ (30,007 ) The change in the estimated fair value for CDI also had an immaterial impact on the income statement. 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. Short-term Borrowings: The carrying amount of short-term borrowings is a reasonable estimate of fair value based on the short-term nature of these liabilities. All other measurement period adjustments not discussed above have been deemed immaterial either individually or in the aggregate. The Company’s consolidated financial statements as of and for the year ended December 31, 2017 include the operating results of the acquired assets and liabilities assumed for the period subsequent to the July 31, 2017 acquisition date. Due to the system conversion of Sabadell United in October of 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" columns. 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 Year Ended December 31, (Dollars in thousands) 2017 2016 Net interest income $ 924,348 $ 842,945 Non-interest income 219,021 255,022 Net income 174,246 246,799 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 $20.3 million and $38.8 million for the years ended December 31, 2017 and 2016, respectively, 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 $1.3 million and $4.1 million for the years ended December 31, 2017 and 2016, respectively, 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 $6.4 million and $5.9 million for the years ended December 31, 2017 and 2016, respectively, 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 periods presented. Amortization of acquired intangibles: Pro forma adjustment to non-interest expense of $5.9 million and $10.1 million for the years ended December 31, 2017 and 2016, respectively, 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. Merger-related costs: Pro forma results include IBERIABANK merger-related costs which primarily included, but were not limited to, compensation/benefits, professional services, data processing fees, and legal expenses totaling $41.0 million for the year ended December 31, 2017.

Investment Securities

Investment Securities	12 Months Ended
	Dec. 31, 2017
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: 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 December 31, 2016 (Dollars in thousands) Amortized Gross Gross Estimated Securities available for sale: U.S. Government-sponsored enterprise obligations $ 212,662 $ 245 $ (549 ) $ 212,358 Obligations of state and political subdivisions 286,458 1,948 (5,207 ) 283,199 Mortgage-backed securities 2,888,180 4,820 (41,291 ) 2,851,709 Other securities 98,974 361 (504 ) 98,831 Total securities available for sale $ 3,486,274 $ 7,374 $ (47,551 ) $ 3,446,097 Securities held to maturity: Obligations of state and political subdivisions $ 64,726 $ 1,609 $ (133 ) $ 66,202 Mortgage-backed securities 24,490 57 (817 ) 23,730 Total securities held to maturity $ 89,216 $ 1,666 $ (950 ) $ 89,932 Securities with carrying values of $2.1 billion and $1.5 billion were pledged to secure public deposits and other borrowings at December 31, 2017 and 2016 , respectively. 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: 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 December 31, 2016 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 $ (549 ) $ 150,554 $ — $ — $ (549 ) $ 150,554 Obligations of state and political subdivisions (5,207 ) 148,059 — — (5,207 ) 148,059 Mortgage-backed securities (38,667 ) 2,191,563 (2,624 ) 98,912 (41,291 ) 2,290,475 Other securities (451 ) 36,484 (53 ) 3,850 (504 ) 40,334 Total securities available for sale $ (44,874 ) $ 2,526,660 $ (2,677 ) $ 102,762 $ (47,551 ) $ 2,629,422 Securities held to maturity: Obligations of state and political subdivisions $ (133 ) $ 10,602 $ — $ — $ (133 ) $ 10,602 Mortgage-backed securities (330 ) 12,288 (487 ) 10,960 (817 ) 23,248 Total securities held to maturity $ (463 ) $ 22,890 $ (487 ) $ 10,960 $ (950 ) $ 33,850 The Company assessed the nature of the unrealized losses in its portfolio as of December 31, 2017 and 2016 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 December 31, 2017 or 2016 . At December 31, 2017 , 544 debt securities had unrealized losses of 1.52% of the securities’ amortized cost basis. At December 31, 2016 , 397 debt securities had unrealized losses of 1.79% 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 December 31 is presented in the following table. (Dollars in thousands) 2017 2016 Number of securities Mortgage-backed securities 181 28 Obligations of state and political subdivisions 28 — Other 1 3 210 31 Amortized Cost Basis Mortgage-backed securities $ 1,280,739 $ 112,983 Obligations of state and political subdivisions 72,820 — Other 10,000 3,903 $ 1,363,559 $ 116,886 Unrealized Loss Mortgage-backed securities $ 35,412 $ 3,111 Obligations of state and political subdivisions 1,180 — Other 152 53 $ 36,744 $ 3,164 The securities noted above carry a rating of AA+/AA- by S&P and Aaa/Aa3 by Moodys. The amortized cost and estimated fair value of investment securities by maturity at December 31, 2017 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 0.60 % $ 37,907 $ 37,563 2.79 % $ 1,119 $ 1,125 One through five years 2.04 124,350 123,589 3.01 8,718 8,756 After five through ten years 2.35 867,799 863,931 2.81 34,970 35,418 Over ten years 2.32 3,617,875 3,564,979 2.55 182,511 182,665 2.30 % $ 4,647,931 $ 4,590,062 2.61 % $ 227,318 $ 227,964 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. Years Ended December 31 (Dollars in thousands) 2017 2016 2015 Realized gains $ 1,651 $ 2,949 $ 1,834 Realized losses (1,799 ) (948 ) (259 ) $ (148 ) $ 2,001 $ 1,575 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 amortized cost, which approximates fair value, in “other assets” on the consolidated balance sheets at December 31: (Dollars in thousands) 2017 2016 Federal Home Loan Bank (FHLB) stock $ 95,171 $ 42,326 Federal Reserve Bank (FRB) stock 79,191 48,584 Other investments 3,008 2,808 $ 177,370 $ 93,718

Loans

Loans	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Loans	LOANS Loans consist of the following at December 31: (Dollars in thousands) 2017 2016 Commercial loans: Real estate - construction $ 1,240,396 $ 802,242 Real estate - owner-occupied 2,529,885 2,277,749 Real estate - non-owner-occupied 5,167,949 3,766,558 Commercial and industrial 5,135,067 4,060,032 14,073,297 10,906,581 Residential mortgage loans: 3,056,352 1,267,400 Consumer loans: Home equity 2,292,275 2,155,926 Indirect automobile 62,693 131,052 Credit card 96,368 82,992 Other 497,196 521,020 2,948,532 2,890,990 Total $ 20,078,181 $ 15,064,971 Net deferred loan origination fees were $29.3 million and $22.6 million at December 31, 2017 and 2016, respectively. Total net discount on the Company's loans was $159.3 million and $89.5 million at December 31, 2017 and 2016, respectively, of which $94.7 million and $12.9 million was related to non-impaired loans. Net loan discounts include preliminary discounts recorded on Sabadell United loans which are subject to change upon receipt of final fair value estimates during the measurement period. 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 December 31, 2017 and 2016, overdrafts of $7.4 million and $4.2 million , respectively, have been reclassified to loans. Loans with carrying values of $6.6 billion and $4.5 billion were pledged as collateral for borrowings at December 31, 2017 and 2016, respectively. Aging Analysis The following tables provide an analysis of the aging of loans as of December 31, 2017 and 2016. 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. 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 Loans Acquired Impaired Loans Total Loans Commercial 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 December 31, 2016 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 Loans Acquired Impaired Loans Total Loans Commercial real estate - construction $ 767,305 $ — $ — $ — $ — $ 1,946 $ 32,991 $ 802,242 Real estate - owner-occupied 2,123,014 1,452 1,712 — 3,164 25,950 125,621 2,277,749 Real estate - non-owner-occupied 3,633,472 1,123 224 32 1,379 9,651 122,056 3,766,558 Commercial and industrial 3,857,375 4,071 920 — 4,991 164,934 32,732 4,060,032 Residential mortgage 1,124,463 2,334 2,565 1,353 6,252 13,733 122,952 1,267,400 Consumer - home equity 2,050,204 6,314 1,615 — 7,929 9,374 88,419 2,155,926 Consumer - indirect automobile 127,054 2,551 405 — 2,956 1,038 4 131,052 Consumer - credit card 82,070 199 99 — 298 624 — 82,992 Consumer - other 511,105 2,538 714 — 3,252 1,252 5,411 521,020 Total $ 14,276,062 $ 20,582 $ 8,254 $ 1,385 $ 30,221 $ 228,502 $ 530,186 $ 15,064,971 Loans Acquired As discussed in Note 3, during 2017, the Company acquired loans with fair values of $4.0 billion from Sabadell United. Certain loans that were acquired in the Sabadell United transaction were covered by loss share agreements between the FDIC and Sabadell United. These FDIC loss share agreements were assumed in connection with the Company's acquisition of Sabadell United, and provide IBERIABANK loss protection. Covered loans were $158.6 million at December 31, 2017. Certain acquired loans from Sabadell United were to customers with addresses outside of the United States. Foreign loans totaled $325.5 million at December 31, 2017. Of the total loans acquired, $3.96 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 $65.9 million were determined to exhibit deteriorated credit quality since origination under ASC 310-30. The tables below show the balances acquired during 2017 for these two subsections of the acquired 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 $ 4,914,185 Expected losses and foregone interest (54,226 ) Cash flows expected to be collected at acquisition 4,859,959 Fair value of acquired loans at acquisition $ 3,960,308 (Dollars in thousands) Acquired Impaired Loans Contractually required principal and interest at acquisition $ 111,114 Non-accretable difference (expected losses and foregone interest) (12,245 ) Cash flows expected to be collected at acquisition 98,869 Accretable yield (32,937 ) Basis in acquired loans at acquisition $ 65,932 The following is a summary of changes in the accretable difference for all loans accounted for under ASC 310-30 during the years ended December 31: (Dollars in thousands) 2017 2016 2015 Balance at beginning of period $ 175,054 $ 227,502 $ 287,651 Additions 32,937 — 6,823 Transfers from non-accretable difference to accretable yield 4,912 5,490 9,916 Accretion (56,337 ) (68,211 ) (80,479 ) Changes in expected cash flows not affecting non-accretable differences (1) (3,943 ) 10,273 3,591 Balance at end of period $ 152,623 $ 175,054 $ 227,502 (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") 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 $70.5 million , $222.4 million , and $57.0 million occurred during the twelve months ended December 31, 2017, 2016, and 2015, respectively, through modification of the original loan terms. The following table provides information on how the TDRs were modified during the years ended December 31: (Dollars in thousands) 2017 2016 2015 Extended maturities $ 26,561 $ 75,315 $ 15,594 Interest rate adjustment 24 193 — Maturity and interest rate adjustment 4,932 2,470 23,374 Movement to or extension of interest-rate only payments 4,161 27,931 241 Forbearance 7,226 76,819 122 Other concession(s) (1) 27,555 39,708 17,710 Total $ 70,459 $ 222,436 $ 57,041 (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 $70.5 million of TDRs occurring during the twelve months ended December 31, 2017, $46.3 million are on accrual status and $24.2 million are on non-accrual status. Of the $222.4 million of TDRs occurring during the twelve months ended December 31, 2016, $85.9 million were on accrual status and $136.5 million were on non-accrual status. Of the $57.0 million of TDRs occuring during the twelve months ended December 31, 2015, $34.5 million were on accrual status and $22.5 million were on non-accrual status. The following table presents the end of period balance for loans modified in a TDR during the years ended December 31: 2017 2016 2015 (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 Number of Loans Pre-modification Outstanding Recorded Investment Post-modification Outstanding Recorded Investment Commercial real estate - construction 4 $ 9,404 $ 9,628 3 $ 3,024 $ 3,035 — $ — $ — Commercial real estate - owner-occupied 11 5,779 5,706 20 18,223 18,239 6 15,403 13,889 Commercial real estate - non-owner-occupied 19 11,974 13,738 25 16,644 10,093 5 11,361 11,361 Commercial and industrial 57 21,651 20,883 79 163,265 169,893 28 31,030 27,598 Residential mortgage 24 1,897 1,771 43 5,141 4,946 1 70 68 Consumer - home equity 123 16,346 15,862 158 13,273 12,568 50 4,440 3,865 Consumer - indirect 43 511 371 79 983 792 6 79 79 Consumer - other 78 2,671 2,500 116 3,087 2,870 17 248 181 Total 359 $ 70,233 $ 70,459 523 $ 223,640 $ 222,436 113 $ 62,631 $ 57,041 Information detailing TDRs that defaulted during the years ended December 31, 2017, 2016, and 2015 and were modified in the previous twelve months (i.e., the twelve months prior to the default) is presented in the following table. The Company has defined a default as any loan with a loan payment that is currently past due greater than 30 days , or was past due greater than 30 days at any point during the previous twelve months, or since the date of modification, whichever is shorter. 2017 2016 2015 (In thousands, except number of loans) Number of Loans Recorded Investment Number of Loans Recorded Investment Number of Loans Recorded Investment Commercial real estate - construction 2 $ 3,572 1 $ 116 — $ — Commercial real estate - owner-occupied 6 4,668 3 3,473 2 10,956 Commercial real estate - non-owner-occupied 13 8,060 6 201 4 11,119 Commercial and industrial 32 6,550 22 14,707 21 12,090 Residential mortgage 16 1,218 8 405 — — Consumer - home equity 32 3,285 25 1,379 20 1,547 Consumer - indirect 33 323 37 338 6 79 Consumer - other 29 1,058 22 606 9 2 Total 163 $ 28,734 124 $ 21,225 62 $ 35,793

Allowance for Credit Losses and

Allowance for Credit Losses and Credit Quality	12 Months Ended
	Dec. 31, 2017
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 years ended December 31 is as follows: (Dollars in thousands) 2017 2016 2015 Allowance for credit losses Allowance for loan losses at beginning of period $ 144,719 $ 138,378 $ 130,131 Provision for loan losses before adjustment attributable to FDIC loss share agreements 51,111 42,927 29,548 Adjustment attributable to FDIC loss share arrangements — 1,497 1,360 Net provision for loan losses 51,111 44,424 30,908 Adjustment attributable to FDIC loss share arrangements — (1,497 ) (1,360 ) Transfer of balance to OREO and other 934 (2,781 ) (10,419 ) Loans charged-off (62,466 ) (39,839 ) (17,301 ) Recoveries 6,593 6,034 6,419 Allowance for loan losses at end of period $ 140,891 $ 144,719 $ 138,378 Reserve for unfunded commitments at beginning of period $ 11,241 $ 14,145 $ 11,801 Balance created in acquisition accounting 1,370 — — Provision for (Reversal of) unfunded lending commitments 597 (2,904 ) 2,344 Reserve for unfunded commitments at end of period $ 13,208 $ 11,241 $ 14,145 Allowance for credit losses at end of period $ 154,099 $ 155,960 $ 152,523 A summary of changes in the allowance for credit losses, by loan portfolio type, for the years ended December 31 is as follows: 2017 (Dollars in thousands) Commercial Commercial Residential 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 losses 10,433 31,891 (2,206 ) 10,993 51,111 Transfer of balance to OREO and other 853 (68 ) 2 147 934 Loans charged off (7,433 ) (40,015 ) (365 ) (14,653 ) (62,466 ) Recoveries 1,117 1,169 437 3,870 6,593 Allowance for loan losses at end of period $ 54,201 $ 53,916 $ 9,117 $ 23,657 $ 140,891 Reserve for unfunded commitments at beginning of period $ 3,207 $ 4,537 $ 657 $ 2,840 $ 11,241 Balance created in acquisition accounting 253 783 327 7 1,370 Provision for (Reversal of) unfunded commitments 1,071 (11 ) (429 ) (34 ) 597 Reserve for unfunded commitments at end of period $ 4,531 $ 5,309 $ 555 $ 2,813 $ 13,208 Allowance on loans individually evaluated for impairment $ 1,588 $ 12,736 $ 172 $ 2,856 $ 17,352 Allowance on loans collectively evaluated for impairment 30,360 38,944 3,141 17,210 89,655 Allowance on loans acquired with deteriorated credit quality 22,253 2,236 5,804 3,591 33,884 Loans, net of unearned income: Balance at end of period $ 8,938,230 $ 5,135,067 $ 3,056,352 $ 2,948,532 $ 20,078,181 Balance at end of period individually evaluated for impairment 91,785 102,416 6,749 37,177 238,127 Balance at end of period collectively evaluated for impairment 8,616,924 5,001,505 2,911,222 2,828,848 19,358,499 Balance at end of period acquired with deteriorated credit quality 229,521 31,146 138,381 82,507 481,555 2016 (Dollars in thousands) Commercial Commercial Residential Consumer Total Allowance for loan losses at beginning of period $ 51,372 $ 49,355 $ 11,789 $ 25,862 $ 138,378 Provision for loan losses 1,958 32,296 824 9,346 44,424 Decrease in FDIC loss share receivable (34 ) (50 ) (1,090 ) (323 ) (1,497 ) Transfer of balance to OREO and other (868 ) (519 ) (141 ) (1,253 ) (2,781 ) Loans charged off (4,338 ) (21,645 ) (313 ) (13,543 ) (39,839 ) Recoveries 1,141 1,502 180 3,211 6,034 Allowance for loan losses at end of period $ 49,231 $ 60,939 $ 11,249 $ 23,300 $ 144,719 Reserve for unfunded commitments at beginning of period $ 4,167 $ 6,106 $ 830 $ 3,042 $ 14,145 Reversal of provision for unfunded commitments (960 ) (1,569 ) (173 ) (202 ) (2,904 ) Reserve for unfunded commitments at end of period $ 3,207 $ 4,537 $ 657 $ 2,840 $ 11,241 Allowance on loans individually evaluated for impairment $ 1,378 $ 21,413 $ 144 $ 1,358 $ 24,293 Allowance on loans collectively evaluated for impairment 25,248 37,206 4,223 17,537 84,214 Allowance on loans acquired with deteriorated credit quality 22,605 2,320 6,882 4,405 36,212 Loans, net of unearned income: Balance at end of period $ 6,846,549 $ 4,060,032 $ 1,267,400 $ 2,890,990 $ 15,064,971 Balance at end of period individually evaluated for impairment 61,006 220,995 4,312 16,467 302,780 Balance at end of period collectively evaluated for impairment 6,504,875 3,806,305 1,140,136 2,780,689 14,232,005 Balance at end of period acquired with deteriorated credit quality 280,668 32,732 122,952 93,834 530,186 2015 (Dollars in thousands) Commercial Commercial Residential Consumer Total Allowance for loan losses at beginning of period $ 57,093 $ 33,328 $ 9,162 $ 30,548 $ 130,131 Provision for loan losses 1,059 17,423 3,620 8,806 30,908 Increase (Decrease) in FDIC loss share receivable 757 (49 ) (235 ) (1,833 ) (1,360 ) Transfer of balance to OREO and other (6,849 ) (275 ) (491 ) (2,804 ) (10,419 ) Loans charged off (2,806 ) (1,279 ) (362 ) (12,854 ) (17,301 ) Recoveries 2,118 207 95 3,999 6,419 Allowance for loan losses at end of period $ 51,372 $ 49,355 $ 11,789 $ 25,862 $ 138,378 Reserve for unfunded commitments at beginning of period $ 3,439 $ 5,260 $ 168 $ 2,934 $ 11,801 Provision for unfunded commitments 728 846 662 108 2,344 Reserve for unfunded commitments at end of period $ 4,167 $ 6,106 $ 830 $ 3,042 $ 14,145 Allowance on loans individually evaluated for impairment $ 1,287 $ 2,394 $ 1 $ 397 $ 4,079 Allowance on loans collectively evaluated for impairment 24,186 44,080 4,150 17,839 90,255 Allowance on loans acquired with deteriorated credit quality 25,899 2,881 7,638 7,626 44,044 Loans, net of unearned income: Balance at end of period $ 6,125,927 $ 4,072,928 $ 1,195,319 $ 2,933,254 $ 14,327,428 Balance at end of period individually evaluated for impairment 29,578 33,270 70 5,066 67,984 Balance at end of period collectively evaluated for impairment 5,685,272 3,987,665 1,054,669 2,807,119 13,534,725 Balance at end of period acquired with deteriorated credit quality 411,077 51,993 140,580 121,069 724,719 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 represent loans to commercial customers to finance general working capital needs, equipment purchases 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 where known information about possible credit problems of the borrower cause management to have some doubt as to the ability of these borrowers to comply with the present loan repayment terms and which may result in future disclosure of these loans as non-performing. For assets with identified credit issues, the Company has two primary classifications for problem assets: “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 based on currently existing facts, conditions, and values higher. Loans classified as "Loss" have been identified as uncollectible and in most cases these loans will be charged off in the subsequent reporting period. Loans classified as “Pass” do not meet the criteria set forth for special mention, substandard, doubtful, or loss 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 reflect the classification as of December 31, 2017 and 2016, respectively. 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 December 31, 2017 and 2016. 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 delinquency is the primary credit quality indicator that the Company utilizes to monitor consumer asset quality. December 31, 2017 December 31, 2016 (Dollars in thousands) Pass Special Mention Sub- Doubtful Loss Total Pass Special Mention Sub- Doubtful Loss Total Commercial real estate - construction $ 1,189,490 $ 20,351 $ 30,541 $ 14 $ — $ 1,240,396 $ 775,387 $ 2,694 $ 22,026 $ 2,135 $ — $ 802,242 Commercial real estate - owner-occupied 2,388,715 82,114 56,590 2,466 — 2,529,885 2,180,201 29,039 66,816 1,670 23 2,277,749 Commercial real estate - non-owner-occupied 5,104,074 19,311 42,702 1,744 118 5,167,949 3,687,439 23,004 55,576 539 — 3,766,558 Commercial and industrial 4,882,554 88,149 128,961 35,403 — 5,135,067 3,660,080 104,482 266,553 28,917 — 4,060,032 Total $ 13,564,833 $ 209,925 $ 258,794 $ 39,627 $ 118 $ 14,073,297 $ 10,303,107 $ 159,219 $ 410,971 $ 33,261 $ 23 $ 10,906,581 December 31, 2017 December 31, 2016 (Dollars in thousands) Current 30+ Days Past Due Total Current 30+ Days Past Due Total Residential mortgage $ 2,962,043 $ 94,309 $ 3,056,352 $ 1,229,761 $ 37,639 $ 1,267,400 Consumer - home equity 2,250,205 42,070 2,292,275 2,129,110 26,816 2,155,926 Consumer - indirect automobile 59,836 2,857 62,693 127,047 4,005 131,052 Consumer - credit card 95,263 1,105 96,368 82,052 940 82,992 Consumer - other 490,399 6,797 497,196 515,857 5,163 521,020 Total $ 5,857,746 $ 147,138 $ 6,004,884 $ 4,083,827 $ 74,563 $ 4,158,390 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 allowance for loan losses, is presented in the following tables as of and for the periods indicated. December 31, 2017 (Dollars in thousands) Unpaid Principal Balance Recorded Investment Related Average Interest With no related allowance recorded: Commercial real estate - construction $ 13,763 $ 13,013 $ — $ 9,104 $ 441 Commercial real estate - owner-occupied 50,867 44,482 — 53,282 1,389 Commercial real estate - non-owner-occupied 15,370 14,975 — 15,127 692 Commercial and industrial 103,013 70,254 — 92,312 2,279 Residential mortgage 2,004 2,001 — 2,044 85 Consumer - home equity 5,906 5,634 — 5,747 231 Consumer - other 75 75 — 11 1 With an allowance recorded: Commercial real estate - construction 238 156 (19 ) 197 6 Commercial real estate - owner-occupied 13,314 13,287 (949 ) 13,498 414 Commercial real estate - non-owner-occupied 6,051 5,872 (620 ) 6,196 154 Commercial and industrial 35,306 32,162 (12,736 ) 42,874 1,220 Residential mortgage 5,179 4,748 (172 ) 4,861 180 Consumer - home equity 27,189 26,575 (2,358 ) 23,546 1,007 Consumer - indirect automobile 1,034 679 (79 ) 873 38 Consumer - other 4,320 4,214 (419 ) 3,582 231 Total $ 283,629 $ 238,127 $ (17,352 ) $ 273,254 $ 8,368 Total commercial loans $ 237,922 $ 194,201 $ (14,324 ) $ 232,590 $ 6,595 Total mortgage loans 7,183 6,749 (172 ) 6,905 265 Total consumer loans 38,524 37,177 (2,856 ) 33,759 1,508 December 31, 2016 (Dollars in thousands) Unpaid Principal Balance Recorded Investment Related Average Interest With no related allowance recorded: Commercial real estate - construction $ 38 $ 38 $ — $ 28 $ — Commercial real estate - owner-occupied 25,180 25,074 — 25,890 647 Commercial real estate - non-owner-occupied 15,654 14,794 — 19,587 879 Commercial and industrial 148,311 138,202 — 111,261 3,418 Consumer - home equity — — — — — Consumer - other — — — — — With an allowance recorded: Commercial real estate - construction 1,946 1,946 (649 ) 1,839 54 Commercial real estate - owner-occupied 17,580 17,429 (640 ) 16,668 493 Commercial real estate - non-owner-occupied 1,743 1,725 (89 ) 1,782 95 Commercial and industrial 84,197 82,793 (21,413 ) 78,270 2,858 Residential mortgage 4,628 4,312 (144 ) 4,377 161 Consumer - home equity 13,916 13,267 (993 ) 10,237 435 Consumer - indirect automobile 1,037 758 (114 ) 956 49 Consumer - other 2,448 2,442 (251 ) 1,469 102 Total $ 316,678 $ 302,780 $ (24,293 ) $ 272,364 $ 9,191 Total commercial loans $ 294,649 $ 282,001 $ (22,791 ) $ 255,325 $ 8,444 Total mortgage loans 4,628 4,312 (144 ) 4,377 161 Total consumer loans 17,401 16,467 (1,358 ) 12,662 586 December 31, 2015 (Dollars in thousands) Unpaid Principal Balance Recorded Investment Related Average Interest With no related allowance recorded: Commercial real estate - construction $ 54 $ 51 $ — $ 55 $ 1 Commercial real estate - owner-occupied 3,630 3,495 — 2,928 106 Commercial real estate - non-owner-occupied 13,318 12,600 — 12,881 209 Commercial and industrial 14,571 14,340 — 18,839 1,148 Consumer - home equity 730 730 — 533 22 Consumer - other 66 66 — 66 5 With an allowance recorded: Commercial real estate - construction 3 3 (2 ) 57 1 Commercial real estate - owner-occupied 12,744 12,691 (1,244 ) 12,908 527 Commercial real estate - non-owner-occupied 738 738 (41 ) 1,027 62 Commercial and industrial 18,958 18,930 (2,394 ) 20,055 776 Residential mortgage 70 70 (1 ) 70 5 Consumer - home equity 3,859 3,683 (338 ) 2,454 73 Consumer - other 588 587 (59 ) 488 3 Total $ 69,329 $ 67,984 $ (4,079 ) $ 72,361 $ 2,938 Total commercial loans $ 64,016 $ 62,848 $ (3,681 ) $ 68,750 $ 2,830 Total mortgage loans 70 70 (1 ) 70 5 Total consumer loans 5,243 5,066 (397 ) 3,541 103 As of December 31, 2017 and 2016, 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.

Transfers and Servicing of Fina

Transfers and Servicing of Financial Assets (Including Mortgage Banking Activity)	12 Months Ended
	Dec. 31, 2017
Transfers and Servicing [Abstract]
Transfers and Servicing of Financial Assets (Including Mortgage Banking Activity)	TRANSFERS AND SERVICING OF FINANCIAL ASSETS (INCLUDING MORTGAGE BANKING ACTIVITY) Commercial Banking Activity The unpaid principal balances of loans serviced for others were $1.3 billion and $1.0 billion at December 31, 2017 and 2016, respectively. Custodial escrow balances maintained in connection with the foregoing portfolio of loans serviced for others, and included in demand deposits, were not significant at December 31, 2017 and 2016. Mortgage Banking Activity IBERIABANK through one of its reportable segments, Mortgage, originates mortgage loans for sale into the secondary market. The loans originated primarily consist of residential first mortgages that conform to standards established by the GSEs, but can also consist of junior lien loans secured by residential property. These sales are primarily to private companies that are unaffiliated with the GSEs on a servicing-released basis. Changes to the carrying amount of mortgage loans held for sale at December 31 are presented in the following table. (Dollars in thousands) 2017 2016 2015 Balance at beginning of period $ 157,041 $ 166,247 $ 140,072 Originations and purchases 1,844,358 2,460,033 2,464,588 Sales, net of gains (1,859,565 ) (2,451,459 ) (2,432,979 ) Mortgage loans transferred to held for investment (6,918 ) (14,017 ) — Other — (3,763 ) (5,434 ) Balance at end of period $ 134,916 $ 157,041 $ 166,247 The following table details the components of mortgage income for the years ended December 31: (Dollars in thousands) 2017 2016 2015 Fair value changes of derivatives and mortgage loans held for sale: Mortgage loans held for sale and derivatives $ (7,047 ) $ 1,361 $ 2,216 Derivative settlements, net 1,229 (6,640 ) (5,017 ) Gains on sales 68,255 87,925 82,671 Servicing and other income, net 1,133 1,207 792 $ 63,570 $ 83,853 $ 80,662 Servicing Rights Servicing rights are recorded at the lower of cost or market value in “other 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: December 31, 2017 December 31, 2016 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount (Dollars in thousands) Mortgage servicing rights $ 9,588 $ (3,931 ) $ 5,657 $ 7,202 $ (3,144 ) $ 4,058 In addition, there was an insignificant amount of non-mortgage servicing rights related to SBA loans as of December 31, 2017 and 2016.

Premises and Equipment

Premises and Equipment	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Premises and Equipment	PREMISES AND EQUIPMENT Premises and equipment consisted of the following at December 31: (Dollars in thousands) 2017 2016 Land $ 89,137 $ 84,616 Buildings 261,994 239,626 Furniture, fixtures and equipment 129,866 115,775 Total premises and equipment 480,997 440,017 Accumulated depreciation (149,584 ) (133,644 ) Total premises and equipment, net $ 331,413 $ 306,373 Depreciation expense was $21.0 million , $20.8 million , and $22.2 million , for the years ended December 31, 2017, 2016, and 2015, respectively. The Company actively engages in leasing office space available in buildings it owns. Leases have various terms, generally ranging up to 5 years . Total lease income for the years ended December 31, 2017, 2016, and 2015 was $2.4 million , $2.8 million , and $2.4 million , respectively. Income from leases is reported as a reduction in occupancy and equipment expense. The total allocated cost of the portion of the buildings held for lease at December 31, 2017 and 2016 was $6.9 million and $8.7 million , respectively, with related accumulated depreciation of $2.5 million and $3.1 million , respectively. The Company leases certain branch and corporate offices, land and ATM facilities through operating leases with terms that range from less than one year to 50 years , some of which contain renewal options and escalation clauses under various terms. In addition, some have early termination clauses. Rent expense for the years ended December 31, 2017, 2016, and 2015 totaled $19.1 million , $16.6 million , and $15.4 million , respectively. Minimum future annual rent commitments under lease agreements for the periods indicated are as follows: (Dollars in thousands) 2018 $ 20,697 2019 19,466 2020 17,733 2021 14,437 2022 11,393 2023 and thereafter 36,744 $ 120,470

Goodwill and Other Acquired Int

Goodwill and Other Acquired Intangible Assets	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Acquired Intangible Assets	GOODWILL AND OTHER ACQUIRED INTANGIBLE ASSETS Goodwill Changes to the carrying amount of goodwill by reporting unit for the years ended December 31, 2017 and 2016 are provided in the following table. (Dollars in thousands) IBERIABANK Mortgage LTC Total Balance, December 31, 2015 $ 696,260 $ 23,178 $ 5,165 $ 724,603 Goodwill adjustments during the year 2,253 — — 2,253 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 On July 31, 2017, the Company completed its acquisition of Sabadell United. In connection with the acquisition, the Company has recorded $462.0 million of goodwill based on preliminary fair value estimates. See Note 3 for additional information regarding this acquisition. The goodwill adjustments during 2016 were the result of the finalization of fair value estimates related to the 2015 acquisitions of Florida Bank Group, Old Florida, and Georgia Commerce during the respective measurement periods. 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 test was not necessary. Title Plant The Company held title plant assets recorded in “other intangible assets” on the Company's consolidated balance sheets totaling $6.7 million at both December 31, 2017 and 2016. No events or changes in circumstances occurred during 2017 to suggest the carrying value of the title plant was not recoverable. Intangible assets subject to amortization In connection with the acquisition of Sabadell United, the Company recorded $66.6 million of core deposit intangible assets. Core deposit intangible assets are subject to amortization over a ten year period. See Note 3 for additional information regarding the acquired core deposit 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 December 31: 2017 2016 (Dollars in thousands) Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Core deposit intangible assets $ 127,957 $ (51,971 ) $ 75,986 $ 74,001 $ (52,165 ) $ 21,836 Customer relationship intangible asset 1,143 (996 ) 147 1,348 (1,064 ) 284 Non-compete agreement 63 (39 ) 24 63 (22 ) 41 Total $ 129,163 $ (53,006 ) $ 76,157 $ 75,412 $ (53,251 ) $ 22,161 The related amortization expense of intangible assets is as follows: (Dollars in thousands) Amount Aggregate amortization expense for the years ended December 31: 2015 $ 7,811 2016 8,415 2017 12,590 (Dollars in thousands) Estimated amortization expense for the years ended December 31: 2018 $ 18,415 2019 14,900 2020 11,771 2021 7,988 2022 5,903 2023 and thereafter 17,180

Derivative Instruments and Othe

Derivative Instruments and Other Hedging Activities	12 Months Ended
	Dec. 31, 2017
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 . 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) December 31, 2017 December 31, 2016 December 31, 2017 December 31, 2016 Derivatives designated as hedging instruments under ASC Topic 815: Interest rate contracts Other assets $ — $ — Other liabilities $ — $ 525 Total derivatives designated as hedging instruments under ASC Topic 815 $ — $ — $ — $ 525 Derivatives not designated as hedging instruments under ASC Topic 815: Interest rate contracts Other assets $ 20,446 $ 20,719 Other liabilities $ 16,191 $ 20,719 Foreign exchange contracts Other assets 7 27 Other liabilities 7 26 Forward sales contracts Other assets 136 6,014 Other liabilities 279 794 Written and purchased options Other assets 10,654 12,125 Other liabilities 8,656 8,098 Other contracts Other assets 22 1 Other liabilities 21 47 Total derivatives not designated as hedging instruments under ASC Topic 815 $ 31,265 $ 38,886 $ 25,154 $ 29,684 Total $ 31,265 $ 38,886 $ 25,154 $ 30,209 Derivative Assets - Notional Amount Derivative Liabilities - Notional Amount (Dollars in thousands) December 31, 2017 December 31, 2016 December 31, 2017 December 31, 2016 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 $ 1,218,464 $ 1,033,955 $ 1,218,464 $ 1,033,955 Foreign exchange contracts 268 4,474 268 4,474 Forward sales contracts 82,347 229,181 142,578 120,567 Written and purchased options 278,638 289,115 165,198 154,170 Other contracts 29,755 8,784 86,744 106,518 Total derivatives not designated as hedging instruments under ASC Topic 815 $ 1,609,472 $ 1,565,509 $ 1,613,252 $ 1,419,684 Total $ 1,609,472 $ 1,565,509 $ 1,721,752 $ 1,528,184 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 $86.7 million and $106.5 million at December 31, 2017 and 2016, respectively. Assuming all underlying third party customers referenced in the swap contracts defaulted at December 31, 2017 and December 31, 2016, 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 December 31, 2017 and 2016, the Company was required to post $552 thousand and $1.9 million , respectively, in cash or securities as collateral for its derivative transactions, which are 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 December 31, 2017, the Company was required to post $5.1 million 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 December 31, 2017. 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. 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 . December 31, 2016 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 $ 20,719 $ (9,677 ) $ — $ 11,042 Written and purchased options 8,085 — — 8,085 Total derivative assets subject to master netting arrangements $ 28,804 $ (9,677 ) $ — $ 19,127 Derivative liabilities Interest rate contracts designated as hedging instruments $ 525 $ — $ (181 ) $ 344 Interest rate contracts not designated as hedging instruments 20,719 (9,677 ) (1,711 ) 9,331 Total derivative liabilities subject to master netting arrangements $ 21,244 $ (9,677 ) $ (1,892 ) $ 9,675 (1) Consists of cash collateral recorded at cost, which approximates fair value, and investment securities. During the years ended December 31, 2017 and 2016, 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 December 31, 2017, 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 December 31, 2017, 2016, and 2015, and for the years 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 (Ineffective Portion and Amount Excluded from Effectiveness Testing) Amount of Gain (Loss) Recognized in Income on Derivative (Ineffective Portion and Amount Excluded from Effectiveness Testing) Amount of Gain (Loss) Recognized in OCI net of taxes (Effective Portion) Location of Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion) Amount of Gain (Loss) Reclassified from Accumulated OCI into Income net of taxes (Effective Portion) (Dollars in thousands) For the Years Ended December 31 Derivatives in ASC Topic 815 Cash Flow Hedging Relationships 2017 2016 2015 2017 2016 2015 2017 2016 2015 Interest rate contracts $ (611 ) $ (328 ) $ 38 Interest expense $ (390 ) $ 50 $ — Interest expense $ — $ — $ — Total $ (611 ) $ (328 ) $ 38 $ (390 ) $ 50 $ — $ — $ — $ — Information pertaining to the effect of derivatives not designated as hedging instruments on the consolidated financial statements as of December 31, is as follows: Location of Gain (Loss) Recognized in Income on Derivatives Amount of Gain (Loss) Recognized in Income on Derivatives (Dollars in thousands) 2017 2016 2015 Interest rate contracts (1) Other income $ 4,750 $ 8,830 $ 4,143 Foreign exchange contracts Other income 43 15 22 Forward sales contracts Mortgage income (4,115 ) (1,731 ) (2,947 ) Written and purchased options Mortgage income (2,028 ) (327 ) 274 Other contracts Other income 51 17 — Total $ (1,299 ) $ 6,804 $ 1,492 (1) Includes fees associated with customer interest rate contracts.

Deposits

Deposits	12 Months Ended
	Dec. 31, 2017
Banking and Thrift [Abstract]
Deposits	DEPOSITS Deposits at December 31 are summarized as follows: (Dollars in thousands) 2017 2016 Non-interest-bearing deposits $ 6,209,925 $ 4,928,878 Negotiable order of withdrawal (NOW) 4,348,939 3,314,281 Money market deposits accounts (MMDA) 7,674,291 6,219,532 Savings deposits 846,074 814,385 Certificates of deposit and other time deposits 2,387,488 2,131,207 $ 21,466,717 $ 17,408,283 Total time deposits summarized by denomination at December 31 are as follows: (Dollars in thousands) 2017 2016 Time deposits less than $250,000 $ 1,768,047 $ 1,661,631 Time deposits greater than $250,000 619,441 469,576 $ 2,387,488 $ 2,131,207 A schedule of maturities of all time deposits as of December 31, 2017 is as follows: (Dollars in thousands) Years ending December 31 2018 $ 1,670,503 2019 401,855 2020 158,555 2021 65,885 2022 78,500 2023 and thereafter 12,190 $ 2,387,488

Short-Term Borrowings

Short-Term Borrowings	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Short-Term Borrowings	SHORT-TERM BORROWINGS Short-term borrowings at December 31 are summarized as follows: (Dollars in thousands) 2017 2016 Federal Home Loan Bank advances $ 475,000 $ 175,000 Securities sold under agreements to repurchase 516,297 334,136 $ 991,297 $ 509,136 The levels of securities sold under agreements to repurchase and FHLB advances can fluctuate significantly on a day-to-day basis, depending on funding needs and which sources are used to satisfy those needs. All such arrangements are considered typical of the banking and brokerage industries and are accounted for as borrowings. Securities sold under agreements to repurchase, which are classified as secured borrowings, generally mature daily and are reflected at the amount of cash received in connection with the transaction. The Company may be required to provide additional collateral based on the fair value of the underlying securities. Additional information on the Company’s short-term borrowings for the years indicated is as follows: (Dollars in thousands) 2017 2016 2015 Outstanding at December 31 $ 991,297 $ 509,136 $ 326,617 Maximum month-end outstanding balance 2,197,105 807,993 798,933 Average daily outstanding balance 905,755 614,073 426,011 Average rate during the year 0.83 % 0.40 % 0.19 % Average rate at year end 0.82 % 0.30 % 0.20 %

Long-Term Debt

Long-Term Debt	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Long-Term Debt	LONG-TERM DEBT Long-term debt at December 31 is summarized as follows: (Dollars in thousands) 2017 2016 IBERIABANK: Federal Home Loan Bank notes, 0.864% to 7.040% $ 1,331,579 $ 480,118 Notes payable - Investment fund contribution, 7 to 30 year term, 1.28% to 6.82% fixed, 7 to 40 year term, 0.50% to 3.60% fixed, respectively 44,146 28,725 1,375,725 508,843 IBERIABANK Corporation (junior subordinated debt): Statutory Trust I, 3 month LIBOR (1) , plus 3.25%, issued November 2002 10,310 10,310 Statutory Trust II, 3 month LIBOR (1) , plus 3.15%, issued June 2003 10,310 10,310 Statutory Trust III, 3 month LIBOR (1) , plus 2.00%, issued September 2004 10,310 10,310 Statutory Trust IV, 3 month LIBOR (1) , plus 1.60%, issued October 2006 15,464 15,464 American Horizons Statutory Trust I, 3 month LIBOR (1) , plus 3.15%, assumed January 2005 6,186 6,186 Statutory Trust V, 3 month LIBOR (1) , plus 1.435%, issued June 2007 10,310 10,310 Statutory Trust VI, 3 month LIBOR (1) , plus 2.75%, issued November 2007 12,372 12,372 Statutory Trust VII, 3 month LIBOR (1) , plus 2.54%, issued November 2007 13,403 13,403 Statutory Trust VIII, 3 month LIBOR (1) , plus 3.50%, issued March 2008 7,217 7,217 OMNI Trust I, 3 month LIBOR (1) , plus 3.30%, assumed May 2011 8,248 8,248 OMNI Trust II, 3 month LIBOR (1) , plus 2.79%, assumed May 2011 7,732 7,732 GA Commerce Trust II, 3 month LIBOR (1) , plus 1.64%, assumed May 2015 8,248 8,248 120,110 120,110 $ 1,495,835 $ 628,953 (1) The interest rate on the Company’s long-term debt indexed to LIBOR is based on the 3-month LIBOR rate. The 3-month LIBOR rate w as 1.69% and 1.00% at December 31, 2017 and 2016, respectively. Outstanding FHLB advances are a mix of bullet and amortizing structures. Amortizing FHLB advances are amortized over periods ranging from 1.5 to 30 years , a nd have a balloon feature at maturity. Advances are collateralized by a blanket pledge of eligible loans, subject to contractual adjustments which reduce the borrowing base, as well as a secondary pledge of FHLB stock and FHLB demand deposits, the amount of which can exceed the amounts borrowed based on contractually required adjustments. Total additional FHLB advances for both short-term borrowings and long-term debt at December 31, 2017 w ere $6.4 billion und er the blanket floating lien including $2.1 billion from pledges of investment securities. The weighted average advance rate was 1.48% an d 1.76% at December 31, 2017 and 2016, respectively. Junior subordinated debt consists of a total of $120.1 million in Junior Subordinated Deferrable Interest Debentures of the Company issued to statutory trusts that were funded by the issuance of floating rate capital securities of the trusts. The terms of the junior subordinated debt are 30 years , and they are callable at par by the Company any time after 5 years . Interest is payable quarterly and may be deferred at any time at the election of the Company for up to 20 consecutive quarterly periods. During a deferral period, the Company is subject to certain restrictions, including being prohibited from declaring and paying dividends to its common shareholders. Advances and long-term debt at December 31, 2017 have maturities or call dates in future years as follows: (Dollars in thousands) 2018 $ 235,944 2019 506,231 2020 114,241 2021 55,441 2022 410,800 2023 and thereafter 173,178 $ 1,495,835

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES The provision for income tax expense consists of the following for the years ended December 31: (Dollars in thousands) 2017 2016 2015 Current expense $ 84,827 $ 103,335 $ 67,025 Deferred expense (benefit) 71,257 (16,654 ) 4,551 Tax credits (10,845 ) (7,112 ) (11,268 ) Amortization on qualified affordable housing tax credits 5,227 4,185 2,023 Tax benefits attributable to items charged to equity and goodwill — 1,439 1,763 $ 150,466 $ 85,193 $ 64,094 There was a balance receivable of $4.5 million and a balance payable of $2 million for federal and state income taxes at December 31, 2017 and 2016, respectively. The provision for federal income taxes differs from the amount computed by applying the federal income tax statutory rate of 35 percent on income before income tax expense as indicated in the following analysis for the years ended December 31: (Dollars in thousands) 2017 2016 2015 Federal tax based on statutory rate $ 102,508 $ 95,189 $ 72,428 Increase (decrease) resulting from: Effect of tax-exempt income (9,435 ) (8,203 ) (6,919 ) Interest and other nondeductible expenses 9,605 3,250 5,899 State taxes, net of federal benefit 6,970 4,770 3,955 Tax credits (10,845 ) (7,112 ) (11,268 ) Amortization on qualified affordable housing tax credits 5,227 4,185 2,023 Other (1) 46,436 (6,886 ) (2,024 ) $ 150,466 $ 85,193 $ 64,094 Effective tax rate 51.4 % 31.3 % 31.0 % (1) The composition of other items resulting in a net tax expense of $46.4 million for the year ending December 31, 2017 included $51.0 million related to the estimated net impact from the remeasurement of deferred tax assets and liabilities as a result of the passage of the Tax Cuts and Jobs Act (the "Tax Act") in December 2017. This was partially offset by $3.0 million related to equity based compensation, $1.0 million resulting from the reversal of a prior year deferred tax asset impairment, and a $600 thousand benefit due to a deferred REIT distribution. The net deferred tax asset at December 31 is as follows: (Dollars in thousands) 2017 2016 Deferred tax asset: NOL carryforward $ 8,364 $ 19,584 Allowance for credit losses 38,402 58,036 Deferred compensation 5,876 10,852 Basis difference in acquired assets and liabilities 43,391 32,957 Unrealized loss on securities available for sale 12,198 14,019 OREO 2,639 4,498 Other 22,719 14,720 133,589 154,666 Deferred tax liability: Basis difference in acquired assets and liabilities (31,309 ) (13,150 ) FHLB stock (300 ) (270 ) Premises and equipment (3,723 ) (6,132 ) Acquisition intangibles (8,151 ) (8,134 ) Deferred loan costs (3,114 ) (4,702 ) Other (4,885 ) (9,196 ) (51,482 ) (41,584 ) Net deferred tax asset $ 82,107 $ 113,082 Net operating loss carryforwards arising from acquisitions during 2015 expire over a 20 -year period and will be utilized subject to annual Internal Revenue Code Section 382 limitations. No benefit was recognized at acquisition for net operating losses that will expire unused due to the IRS limitations. The Company determined that the net deferred tax asset is more likely than not to be realized based on an assessment of all available positive and negative evidence, and therefore no valuation allowance has been recorded as of December 31, 2017 or 2016. The Company does not believe it has any unrecognized tax benefits included in its consolidated financial statements. The Company has not had any settlements in the current period with taxing authorities, nor has it recognized tax benefits as a result of a lapse of the applicable statute of limitations. During the year ended December 31, 2017, an immaterial amount of interest and penalty expense associated with one state filing jurisdiction was recorded. During the years ended December 31, 2016 and 2015, the Company did not recognize any interest or penalties in its consolidated financial statements. 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 due to a re-measurement of deferred tax assets and liabilities resulting from the decrease in the corporate income tax rate. This one-time provision increased the 2017 effective tax rate by 17.4% from 34.0% to 51.4% . 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. 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. In addition, the Company early adopted ASU No. 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income , for the fiscal year ending December 31, 2017, which allowed a one-time reclassification of $8.1 million from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Act.

Shareholders' Equity, Capital R

Shareholders' Equity, Capital Ratios and Other Regulatory Matters	12 Months Ended
	Dec. 31, 2017
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 at December 31: 2017 2016 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 Dividends will accrue and be payable on the Series B Preferred Stock, if declared by the Company's Board of Directors, and will be paid semi-annually, in arrears, at an annual rate equal to 6.625% for each period from the issuance date up to and including August 1, 2025 and will be paid quarterly, in arrears, at an annual rate equal to three-month LIBOR plus 4.262% for each period after August 1, 2025. The Company may redeem the Series B Preferred Stock at its option, subject to regulatory approval, as described in the Company’s Registration Statement on Form 8-A, filed with the Securities and Exchange Commission on August 5, 2015. Dividends will accrue and be payable on the Series C Preferred Stock, if declared by the Company's Board of Directors, and will be paid quarterly, in arrears, at an annual rate equal to (i) 6.600% for each period from the issuance date to May 1, 2026 and (ii) three-month LIBOR plus 4.920% for each period on or after May 1, 2026. The Company may redeem the Series C Preferred Stock at its option, subject to regulatory approval, as described in the Company’s Registration Statement on Form 8-A, filed with the Securities and Exchange Commission on May 9, 2016. 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. During 2016, the Company repurchased 202,506 common shares at a weighted average price of $57.61 per common share. The Company did not repurchase any common shares during 2017. At December 31, 2017, the remaining shares that could be repurchased under the plan approved by the Board was 747,494 shares. On December 7, 2016, the Company issued 3,593,750 shares of its common stock at a price of $81.50 per common share. On March 7, 2017, the Company issued 6,100,000 shares of its common stock at a price of $83.00 per common share. Net proceeds from the offerings, after deduction of underwriting discounts, commissions, and direct issuance costs, were $279.2 million and $485.2 million , respectively. The proceeds from these issuances were used to finance the cash portion of the purchase price for the acquisition of Sabadell United. The acquisition, which closed on July 31, 2017, provided for Banco de Sabadell, S.A. to receive 2,610,304 shares of the Company's common stock ( $211.0 million based on the Company's closing stock price of $80.85 on that date) and $809.2 million in cash from the two stock issuances. Banco de Sabadell, S.A. sold the 2.6 million shares received as part of acquisition proceeds early in the fourth quarter of 2017. Refer to Note 3, Acquisition Activity, for further detail regarding the Sabadell United 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 December 31, 2017, the Company and IBERIABANK met all capital adequacy requirements to which they are subject. As of December 31, 2017, 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 December 31 are presented in the following table. (Dollars in thousands) 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 2016 Minimum Well-Capitalized Actual Amount Ratio Amount Ratio Amount Ratio Tier 1 Leverage Consolidated $ 818,440 4.00 % N/A N/A $ 2,221,528 10.86 % IBERIABANK 816,152 4.00 $ 1,020,190 5.00 1,878,703 9.21 Common Equity Tier 1 (CET1) (1) Consolidated $ 794,334 4.50 % N/A N/A $ 2,089,431 11.84 % IBERIABANK 792,111 4.50 $ 1,144,160 6.50 1,878,703 10.67 Tier 1 Risk-Based Capital (1) Consolidated $ 1,059,112 6.00 % N/A N/A $ 2,221,528 12.59 % IBERIABANK 1,056,147 6.00 $ 1,408,197 8.00 1,878,703 10.67 Total Risk-Based Capital (1) Consolidated $ 1,412,149 8.00 % N/A N/A $ 2,493,988 14.13 % IBERIABANK 1,408,197 8.00 $ 1,760,246 10.00 2,034,663 11.56 (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 December 31, 2017, the required minimum capital conservation buffer was 1.250% , and will increase in subsequent years by 0.625% until it is fully phased in on January 1, 2019 at 2.50% . At December 31, 2017, the capital conservation buffers of the Company and IBERIABANK were 4.37% and 3.55% , respectively. Restrictions on Dividends, Loans and Advances IBERIABANK is restricted under applicable laws in the payment of dividends to an amount equal to current year earnings plus undistributed earnings for the immediately preceding year, unless prior permission is received from the Commissioner of Financial Institutions for the State of Louisiana. Dividends payable by IBERIABANK in 2018 without permission will be limited to 2018 earnings plus an additional $160.2 million . Funds available for loans or advances by IBERIABANK to the Parent amounted to $259.1 million . In addition, any dividends that may be paid by IBERIABANK to the Parent would be restricted if IBERIABANK did not comply with the above-described capital conservation buffer requirements and would be prohibited if the effect thereof would cause IBERIABANK’s capital to be reduced below applicable minimum capital requirements. During any deferral period under the Company’s junior subordinated debt, the Company would be prohibited from declaring and paying dividends to preferred and common shareholders. See Note 13 to the consolidated financial statements for additional information. In addition, so long as any shares of Series B Preferred Stock or Series C Preferred Stock remain outstanding, we are prohibited from paying dividends on any of our common stock if the required payments on our Series B Preferred Stock and Series C Preferred Stock have not been made.

Earnings Per Share

Earnings Per Share	12 Months Ended
	Dec. 31, 2017
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. For the Years Ended December 31, (In thousands, except per share data) 2017 2016 2015 Earnings per common share - basic Net income $ 142,413 $ 186,777 $ 142,844 Preferred stock dividends (9,095 ) (7,977 ) — Dividends and undistributed earnings allocated to unvested restricted shares (1,210 ) (1,872 ) (1,680 ) Net income allocated to common shareholders - basic $ 132,108 $ 176,928 $ 141,164 Weighted average common shares outstanding 50,640 40,948 38,214 Earnings per common share - basic 2.61 4.32 3.69 Earnings per common share - diluted Net income allocated to common shareholders - basic $ 132,108 $ 176,928 $ 141,164 Dividends and undistributed earnings allocated to unvested restricted shares (1 ) (37 ) (48 ) Net income allocated to common shareholders - diluted $ 132,107 $ 176,891 $ 141,116 Weighted average common shares outstanding 50,640 40,948 38,214 Dilutive potential common shares 352 158 96 Weighted average common shares outstanding - diluted 50,992 41,106 38,310 Earnings per common share - diluted $ 2.59 $ 4.30 $ 3.68 For the years ended December 31, 2017 , 2016 , and 2015 , the calculations for basic shares outstanding exclude the weighted average shares owned by the Recognition and Retention Plan (“RRP”) of 467,601 , 447,818 , and 607,608 , respectively. The effects from the assumed exercises of 71,260 ; 155,969 ; and 159,236 stock options were not included in the computation of diluted earnings per share for the years ended December 31, 2017 , 2016 , and 2015 , respectively, because such amounts would have had an antidilutive effect on earnings per common share.

Share-Based Compensation

Share-Based Compensation	12 Months Ended
	Dec. 31, 2017
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, phantom stock and performance units. 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 December 31, 2017, awards of 1,602,890 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 December 31, 2017, 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 Aggregate Intrinsic Value (Dollars in thousands) Weighted Average Remaining Contract Life (in years) Outstanding options, December 31, 2014 867,682 $ 55.92 Granted 82,001 62.50 Exercised (119,917 ) 51.71 $ 1,516 Forfeited or expired (15,989 ) 66.52 Outstanding options, December 31, 2015 813,777 $ 56.99 Granted 160,624 48.65 Exercised (196,769 ) 55.39 3,597 Forfeited or expired (56,094 ) 59.49 Outstanding options, December 31, 2016 721,538 $ 55.38 Granted 80,557 84.78 Exercised (85,221 ) 55.45 2,098 Forfeited or expired (30,508 ) 68.46 Outstanding options, December 31, 2017 686,366 $ 58.24 $ 13,767 5.6 Exercisable options, December 31, 2015 546,842 $ 56.54 Exercisable options, December 31, 2016 415,376 56.66 Exercisable options, December 31, 2017 455,010 55.77 $ 9,891 4.4 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 years ended December 31: 2017 2016 2015 Expected dividends 1.7 % 2.8 % 2.2 % Expected volatility 25.0 % 29.0 % 35.6 % Risk-free interest rate 2.1 % 1.4 % 2.0 % Expected term (in years) 5.8 6.5 7.5 Weighted-average grant-date fair value $ 18.86 $ 10.46 $ 19.57 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 years ended December 31: (Dollars in thousands) 2017 2016 2015 Compensation expense related to stock options $ 1,470 $ 2,010 $ 1,861 Income tax benefit related to stock options 124 331 317 At December 31, 2017, there was $1.9 million of unrecognized compensation expense related to stock options that is expected to be recognized over a weighted-average period of 2.7 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 seven years). As of December 31, 2017 and 2016, unrecognized share-based compensation expense associated with these awards totaled $31.9 million and $16.0 million , respectively. The unrecognized compensation expense related to restricted stock awards at December 31, 2017 is expected to be recognized over a weighted-average period of 1.4 years . Restricted share units In 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 performance conditions set forth in the restricted share unit agreement. 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 for further discussion of restricted share units with 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 years ended December 31: (Dollars in thousands) 2017 2016 2015 Compensation expense related to restricted stock awards and restricted share units $ 14,966 $ 12,513 $ 12,045 Income tax benefit related to restricted stock awards and restricted share units 2,809 4,380 4,215 The following table represents unvested restricted stock award and restricted share unit activity for the years ended December 31: 2017 2016 2015 Number of shares at beginning of period 543,261 507,130 506,289 Granted 421,198 254,276 207,575 Forfeited (31,699 ) (28,855 ) (26,970 ) Vested (194,573 ) (189,290 ) (179,764 ) Number of shares at end of period 738,187 543,261 507,130 The weighted average grant date fair value of restricted stock awards and restricted share units granted was $82.49 , $48.84 , and $63.16 for the years ended December 31, 2017, 2016, and 2015, respectively. The total fair value of restricted stock awards and restricted share units vested during the years ended December 31, 2017, 2016, and 2015 was $16.4 million , $10.7 million , and $11.3 million , respectively. 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. Performance units Performance units are tied to the value of shares of the Company's common stock, are payable in cash, and vest in increments of one-third per year after attainment of one or more performance measures. The value of performance units is the same as the value of the corresponding number of shares of common stock. There were no performance units granted in 2017 or 2016. The following table indicates compensation expense recorded for phantom stock and performance units based on the number of share equivalents vested at December 31 of the years indicated and the current market price of the Company’s stock at that time: (Dollars in thousands) 2017 2016 2015 Compensation expense related to phantom stock and performance units $ 10,756 $ 12,933 $ 12,109 The following table represents phantom stock award and performance unit activity during the periods indicated. (Dollars in thousands) Number of share equivalents (1) Value of share equivalents (2) Balance, December 31, 2014 475,347 $ 30,826 Granted 167,573 9,228 Forfeited share equivalents (34,681 ) 1,910 Vested share equivalents (145,809 ) 9,288 Balance, December 31, 2015 462,430 $ 25,466 Granted 215,745 18,069 Forfeited share equivalents (42,051 ) 3,522 Vested share equivalents (163,294 ) 8,509 Balance, December 31, 2016 472,830 $ 39,600 Granted 118,408 9,177 Forfeited share equivalents (34,968 ) 2,710 Vested share equivalents (162,426 ) 15,206 Balance, December 31, 2017 393,844 $ 30,523 (1) Number of share equivalents includes all reinvested dividend equivalents for the years 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 $77.50 , $83.75 and $55.07 on December 31, 2017, 2016 and 2015, respectively. 401(k) defined contribution plan The Company has a 401(k) Profit Sharing Plan covering substantially all of its employees. Annual employer contributions to the Plan are set by the Board of Directors. The Company made contributions of $3.5 million , $1.9 million , and $1.7 million for the years ended December 31, 2017, 2016, and 2015, respectively. The Plan provides, among other things, that participants in the Plan be able to direct the investment of their account balances within the Profit Sharing Plan into alternative investment funds. Participant deferrals under the salary reduction election may be matched by the employer based on a percentage to be determined annually by the employer.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
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 December 31, 2017 and 2016, the fair value of guarantees under commercial and standby letters of credit was $2.1 million and $1.6 million , respectively. This fair value will decrease as the existing commercial and standby letters of credit approach their expiration dates. At December 31, 2017 and 2016, respectively, the Company had the following financial instruments outstanding and related reserves, whose contract amounts represent credit risk: (Dollars in thousands) December 31, 2017 December 31, 2016 Commitments to grant loans $ 342,305 $ 355,558 Unfunded commitments under lines of credit 6,060,034 4,899,930 Commercial and standby letters of credit 210,002 163,560 Reserve for unfunded lending commitments 13,208 11,241 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 , which the Company previously accrued for in the second and third quarters of 2017 in the amount of $6.0 million and $5.7 million , respectively. IBERIABANK has filed a lawsuit in federal district court in New Orleans against the insurers in an effort to recover the $11.7 million it paid to settle the HUD matter. 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.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
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, for a description of how fair value measurements are determined. December 31, 2017 (Dollars in thousands) 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 December 31, 2016 Level 1 Level 2 Level 3 Total Assets Securities available for sale $ — $ 3,446,097 $ — $ 3,446,097 Mortgage loans held for sale — 157,041 — 157,041 Derivative instruments — 38,886 — 38,886 Total $ — $ 3,642,024 $ — $ 3,642,024 Liabilities Derivative instruments $ — $ 30,209 $ — $ 30,209 Total $ — $ 30,209 $ — $ 30,209 During 2017 and 2016, there were no transfers between the Level 1 and Level 2 fair value categories. Gains and losses (realized and unrealized) included in earnings (or accumulated other comprehensive income) during 2017 related to assets and liabilities measured at fair value on a recurring basis are reported in non-interest income or other comprehensive income as follows: (Dollars in thousands) Non-interest income Other comprehensive income (loss), net of tax Total gains (losses) included in earnings $ (1,166 ) $ — Change in unrealized gains (losses) relating to assets still held at December 31, 2017 — (11,721 ) 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. 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 December 31, 2016 (Dollars in thousands) Level 1 Level 2 Level 3 Total Assets Loans $ — $ — $ 93,485 $ 93,485 OREO, net — — 185 185 Total $ — $ — $ 93,670 $ 93,670 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. 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 acquisition. 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 December 31, 2017 and 2016. 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 $15.0 million and $12.7 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 December 31, 2017 and 2016, 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 years ended December 31, 2017 and 2016 totaled $(204) thousand and $(1.1) million , 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: December 31, 2017 December 31, 2016 (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 $ 134,916 $ 131,276 $ 3,640 $ 157,041 $ 153,801 $ 3,240 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 totaled $944 thousand and $(2.5) million for the years ended December 31, 2017 and 2016, 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	12 Months Ended
	Dec. 31, 2017
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, for a description of how fair value measurements are determined. December 31, 2017 (Dollars in thousands) Carrying Amount Fair Value Level 1 Level 2 Level 3 Financial Assets Cash and cash equivalents $ 625,724 $ 625,724 $ 625,724 $ — $ — Investment securities 4,817,380 4,818,026 — 4,818,026 — Loans and loans held for sale, net of unearned income and allowance for loan losses 20,072,206 19,961,773 — 134,916 19,826,857 Derivative instruments 31,265 31,265 — 31,265 — 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 Derivative instruments 25,154 25,154 — 25,154 — December 31, 2016 (Dollars in thousands) Carrying Amount Fair Value Level 1 Level 2 Level 3 Financial Assets Cash and cash equivalents $ 1,362,126 $ 1,362,126 $ 1,362,126 $ — $ — Investment securities 3,535,313 3,536,029 — 3,536,029 — Loans and loans held for sale, net of unearned income and allowance for loan losses 15,077,293 15,066,055 — 157,041 14,909,014 Derivative instruments 38,886 38,886 — 38,886 — Financial Liabilities Deposits 17,408,283 16,762,475 — 16,762,475 — Short-term borrowings 509,136 509,136 334,136 175,000 — Long-term debt 628,953 617,656 — — 617,656 Derivative instruments 30,209 30,209 — 30,209 — The fair value estimates presented herein are based upon pertinent information available to management as of December 31, 2017 and 2016. 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.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2017
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. These transactions are consummated at terms equivalent to the prevailing market rates and terms at the time. 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 December 31, 2017 and 2016. None of the related party loans were classified as non-accrual, past due, troubled debt restructurings, or potential problem loans at December 31, 2017 and 2016, with the exception of the loan discussed below. IBERIABANK and several other financial institutions previously extended credit (the “Credit Facility”) under a multi-bank syndicated credit facility to Stone Energy Corporation (the “Borrower"). At the time of origination and subsequent restructure, one of the Company’s directors, David H. Welch, was the Chairman, President and Chief Executive Officer of the Borrower. IBERIABANK held approximately 6 percent of the total commitments from twelve banks under the Credit Facility. On December 14, 2016, the Borrower filed for Chapter 11 Bankruptcy with the U.S. Bankruptcy Court in the Southern District of Texas. On February 28, 2017, the Borrower’s confirmed Amended Joint Prepackaged Plan of Reorganization became effective, and the Borrower satisfied the entire amount due and owing to the financial institutions, which was the principal amount outstanding under the Credit Facility at the time of the bankruptcy filing. On that date, the Borrower emerged from the Chapter 11 Bankruptcy and entered into a new Exit Facility with the lenders, including IBERIABANK. The new Exit Facility, which replaced the Credit Facility, provides for a $200 million reserve-based credit facility with a maturity date of February 21, 2021. Interest on advances under the Exit Facility is calculated using LIBOR or the base rate, at the election of the Borrower, plus, in each case an applicable margin. IBERIABANK holds a 5.9 percent pro-rata share, or $11.8 million , of the $200 million

Business Segments

Business Segments	12 Months Ended
	Dec. 31, 2017
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. Year Ended December 31, 2017 (Dollars in thousands) IBERIABANK Mortgage LTC Consolidated Interest and dividend income $ 906,521 $ 7,260 $ 2 $ 913,783 Interest expense 104,937 — — 104,937 Net interest income 801,584 7,260 2 808,846 Provision for/(reversal of) loan losses 51,200 (89 ) — 51,111 Mortgage income — 63,570 — 63,570 Title revenue — — 21,972 21,972 Other non-interest income 125,552 (42 ) (12 ) 125,498 Allocated expenses (13,293 ) 10,041 3,252 — Non-interest expense 585,355 73,587 16,954 675,896 Income/(loss) before income tax expense 303,874 (12,751 ) 1,756 292,879 Income tax expense/(benefit) 156,407 (5,771 ) (170 ) 150,466 Net income/(loss) $ 147,467 $ (6,980 ) $ 1,926 $ 142,413 Total loans and loans held for sale, net of unearned income $ 20,028,840 $ 184,257 $ — $ 20,213,097 Total assets 27,672,906 208,710 22,513 27,904,129 Total deposits 21,462,776 3,941 — 21,466,717 Average assets 24,228,436 229,364 22,856 24,480,656 Year Ended December 31, 2016 (Dollars in thousands) IBERIABANK Mortgage LTC Consolidated Interest and dividend income $ 707,676 $ 9,261 $ 2 $ 716,939 Interest expense 64,068 3,633 — 67,701 Net interest income 643,608 5,628 2 649,238 Provision for loan losses 44,336 88 — 44,424 Mortgage income 405 83,448 — 83,853 Title revenue — — 22,213 22,213 Other non-interest income 127,751 4 — 127,755 Allocated expenses (13,972 ) 10,686 3,286 — Non-interest expense 484,099 65,133 17,433 566,665 Income before income tax expense 257,301 13,173 1,496 271,970 Income tax expense 79,565 5,023 605 85,193 Net income $ 177,736 $ 8,150 $ 891 $ 186,777 Total loans and loans held for sale, net of unearned income $ 15,004,360 $ 217,652 $ — $ 15,222,012 Total assets 21,319,267 315,057 24,866 21,659,190 Total deposits 17,402,742 5,541 — 17,408,283 Average assets 19,959,261 335,913 26,060 20,321,234 Year Ended December 31, 2015 (Dollars in thousands) IBERIABANK Mortgage LTC Consolidated Interest and dividend income $ 639,793 $ 7,062 $ 3 $ 646,858 Interest expense 56,222 2,878 — 59,100 Net interest income 583,571 4,184 3 587,758 Provision for loan losses 30,908 — — 30,908 Mortgage income 966 79,696 — 80,662 Title revenue — — 22,837 22,837 Other non-interest income 116,903 (2 ) (7 ) 116,894 Allocated expenses (16,253 ) 12,036 4,217 — Non-interest expense 495,158 57,784 17,363 570,305 Income before income tax expense 191,627 14,058 1,253 206,938 Income tax expense 58,006 5,581 507 64,094 Net income $ 133,621 $ 8,477 $ 746 $ 142,844 Total loans and loans held for sale, net of unearned income $ 14,305,663 $ 188,012 $ — $ 14,493,675 Total assets 19,220,085 256,888 27,095 19,504,068 Total deposits 16,173,831 4,917 — 16,178,748 Average assets 18,146,216 230,819 25,671 18,402,706

Condensed Parent Company Only F

Condensed Parent Company Only Financial Statements	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Parent Company Only Financial Statements	CONDENSED PARENT COMPANY ONLY FINANCIAL STATEMENTS Condensed financial statements of the Parent are shown below. The Parent has no significant operating activities. Condensed Balance Sheets (Dollars in thousands) December 31 2017 2016 Assets Cash in bank $ 168,873 $ 436,792 Investments in subsidiaries 3,661,808 2,635,682 Other assets 49,207 40,423 $ 3,879,888 $ 3,112,897 Liabilities and Shareholders’ Equity Liabilities $ 183,097 $ 173,203 Shareholders’ equity 3,696,791 2,939,694 $ 3,879,888 $ 3,112,897 Condensed Statements of Income Year Ended December 31 (Dollars in thousands) 2017 2016 2015 Operating income Reimbursement of management expenses $ 76,177 $ 65,104 $ 59,255 Other income 146,796 829 (329 ) Total operating income 222,973 65,933 58,926 Operating expenses Interest expense 5,168 3,948 3,393 Salaries and employee benefits expense 55,013 45,623 41,689 Other expenses 32,965 19,566 17,492 Total operating expenses 93,146 69,137 62,574 Income (loss) before income tax benefit and increase in equity in undistributed earnings of subsidiaries 129,827 (3,204 ) (3,648 ) Income tax expense (benefit) 3,123 530 800 Income (loss) before equity in undistributed earnings of subsidiaries 126,704 (3,734 ) (4,448 ) Equity in undistributed earnings of subsidiaries 15,709 190,511 147,292 Net Income 142,413 186,777 142,844 Less: Preferred stock dividends 9,095 7,977 — Net Income Available to Common Shareholders $ 133,318 $ 178,800 $ 142,844 Condensed Statements of Cash Flows (Dollars in thousands) Year Ended December 31 2017 2016 2015 Cash Flow from Operating Activities Net income $ 142,413 $ 186,777 $ 142,844 Adjustments to reconcile net income to net cash provided by operating activities: Depreciation and amortization 62 98 416 Net income of subsidiaries (160,206 ) (190,511 ) (147,292 ) Share-based compensation cost 16,436 14,523 13,906 Gain on sale of assets — — (110 ) Other operating activities, net (4,256 ) 12,417 82,105 Net Cash Provided by (Used in) Operating Activities (5,551 ) 23,304 91,869 Cash Flow from Investing Activities Cash paid in excess of cash received for acquisitions (809,159 ) — (5,054 ) Proceeds from sale of premises and equipment — — 12 Purchases of premises and equipment (105 ) — (2 ) Return of capital from (Capital contributed to) subsidiary 144,500 (6,000 ) 5,000 Other investing activities, net — (749 ) — Net Cash (Used in) Investing Activities (664,764 ) (6,749 ) (44 ) Cash Flow from Financing Activities Cash dividends paid on common stock (72,772 ) (56,793 ) (52,318 ) Cash dividends paid on preferred stock (9,095 ) (7,028 ) — Net share-based compensation stock transactions (832 ) 6,899 1,915 Payments to repurchase common stock — (11,666 ) — Net proceeds from issuance of common stock 485,151 279,242 — Net proceeds from issuance of preferred stock — 55,285 76,812 Other financing activities, net (56 ) — — Net Cash Provided by (Used In) Financing Activities 402,396 265,939 26,409 Net Increase (Decrease) in Cash and Cash Equivalents (267,919 ) 282,494 118,234 Cash and Cash Equivalents at Beginning of Period 436,792 154,298 36,064 Cash and Cash Equivalents at End of Period $ 168,873 $ 436,792 $ 154,298

Summary of Significant Accoun32

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Reclassification	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.
Principles of Consolidation	PRINCIPLES OF CONSOLIDATION All significant intercompany balances and transactions have been eliminated in consolidation. The Company’s consolidated financial statements include all entities in which the Company has a controlling financial interest under either the voting interest or variable interest model. The assessment of whether or not the Company has a controlling interest (i.e., the primary beneficiary) in a variable interest entity ("VIE") is performed on an on-going basis. All equity investments in non-consolidated VIEs are included in "other assets" in the Company’s consolidated balance sheets. The Company’s maximum exposure to loss as a result of its involvement with non-consolidated VIEs was approximately $160 million and $91 million at December 31, 2017 and 2016, respectively. The Company's maximum exposure to loss was equivalent to the carrying value of its investments and any related outstanding loans to the non-consolidated VIEs. Investments in entities that are not consolidated are accounted for under either the equity, cost, or proportional amortization method of accounting. Investments for which the Company has the ability to exercise significant influence over the operating and financing decisions of the entity are accounted for under the equity method. Investments for which the Company does not hold such ability are accounted for under the cost method. Investments in qualified affordable housing projects, which meet certain criteria, are accounted for under the proportional amortization method.
Use of Estimates	USE OF ESTIMATES The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Actual results could differ from those estimates. Material estimates that are susceptible to significant change in the near term are the allowance for credit losses, valuation of and accounting for acquired loans, goodwill and other intangible assets, and income taxes.
Concentration of Credit Risk	CONCENTRATION OF CREDIT RISKS 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.
Business Combinations	BUSINESS COMBINATIONS Assets and liabilities acquired in business combinations are recorded at their acquisition date fair values. In accordance with ASC Topic 805, Business Combinations , the Company generally records provisional amounts at the time of acquisition based on the information available to the Company. The provisional estimates of fair values may be adjusted for a period of up to one year (“measurement period”) from the date of acquisition if new information is obtained about facts and circumstances that existed as of the acquisition date that, if known, would have affected the measurement of the amounts recognized as of that date. Subsequently, adjustments recorded during the measurement period are recognized in the current reporting period. Loans generally represent a significant portion of the assets acquired in the Company’s business acquisitions. If the Company discovers that it has materially underestimated the credit losses expected in the loan portfolio based on information available at the acquisition date within the measurement period, it will reduce or eliminate the gain and/or increase goodwill recorded on the acquisition in the period the adjustment is recorded. If the Company determines that losses arose subsequent to the acquisition date, such losses are reflected as a provision for credit losses.
Cash and Cash Equivalents	CASH AND CASH EQUIVALENTS For purposes of presentation in the consolidated statements of cash flows, cash and cash equivalents are defined as cash on hand, interest-bearing deposits, and non-interest-bearing demand deposits at other financial institutions with original maturities less than three months . IBERIABANK may be required to maintain average cash balances on hand or with the Federal Reserve Bank to meet regulatory reserve and clearing requirements. At December 31, 2017 and 2016, IBERIABANK had sufficient cash deposited with the Federal Reserve Bank to cover the required reserve balance.
Investment Securities	INVESTMENT SECURITIES Management determines the appropriate accounting classification of debt and equity securities at the time of acquisition and re-evaluates such designations at least quarterly. Debt securities that management has the ability and intent to hold to maturity are classified as HTM and carried at cost, adjusted for amortization of premiums and accretion of discounts using methods approximating the interest method. Securities acquired with the intention of recognizing short-term profits or which are actively bought and sold are classified as trading securities and reported at fair value, with unrealized gains and losses recognized in earnings. Securities not classified as HTM or trading, including equity securities with readily determinable fair values, are classified as AFS and recorded at fair value, with unrealized gains and losses excluded from earnings and reported in OCI. Credit-related declines in the fair value of debt and marketable equity securities that are considered OTTI are recorded in earnings. The Company evaluates its investment securities portfolio on a quarterly basis for indicators of OTTI. Declines in the fair value of individual HTM and AFS securities below their amortized cost basis are reviewed to determine whether the declines are other than temporary. In estimating OTTI losses, management considers 1) the length of time and the extent to which the fair value has been less than the amortized cost basis, 2) the financial condition and near-term prospects of the issuer, 3) its intent to sell and whether it is more likely than not that the Company would be required to sell those securities before the anticipated recovery of the amortized cost basis, and 4) for debt securities, the recovery of contractual principal and interest. For securities that the Company does not expect to sell, or it is not more likely than not it will be required to sell prior to recovery of its amortized cost basis, the credit component of an OTTI is recognized in earnings and the non-credit component is recognized in OCI. For securities that the Company does expect to sell, or it is more likely than not that it will be required to sell prior to recovery of its amortized cost basis, both the credit and non-credit component of an OTTI are recognized in earnings. Subsequent to recognition of OTTI, an increase in expected cash flows is recognized as a yield adjustment over the remaining expected life of the security based on an evaluation of the nature of the increase. Nonmarketable equity securities include stock acquired for regulatory purposes, such as Federal Home Loan Bank stock and Federal Reserve Bank stock. These securities are accounted for at amortized cost, evaluated for impairment at least quarterly, and included in "other assets." Gains or losses on securities sold are recorded on the trade date, using the specific identification method.
Loans Held for Sale	LOANS HELD FOR SALE Loans and loan commitments which the Company does not have the intent and ability to hold for the foreseeable future or until maturity or payoff are classified as loans held for sale at the time of origination or acquisition. Subsequent to origination or acquisition, if the Company no longer has the intent or ability to hold a loan for the foreseeable future, generally a decision has been made to sell the loan, and it is classified within loans held for sale. Unless the fair value option has been elected at origination or acquisition, loans classified as held for sale are carried at the lower of cost or fair value. Amortization/accretion of remaining unamortized net deferred loan fees or costs and discounts or premiums (if applicable) ceases when a loan is classified as held for sale. Loans held for sale primarily consist of fixed rate single-family residential mortgage loans originated and committed to be sold in the secondary market. Mortgage loans originated and held for sale are recorded at fair value under the fair value option, unless otherwise noted. For mortgage loans for which the Company has elected the fair value option, gains and losses are included in mortgage income. For any other loans held for sale, net unrealized losses, if any, are recognized through a valuation allowance that is recorded as a charge to non-interest income. See Note 19 for further discussion of the determination of fair value for loans held for sale. In most cases, loans in this category are sold within thirty days and are generally sold with the mortgage servicing rights released. Buyers generally have recourse to return a purchased loan or request reimbursement for the loan premium or consideration transferred for servicing rights under limited circumstances. Recourse conditions may include prepayment, payment default, breach of representations or warranties, and documentation deficiencies. During 2017 and 2016, an insignificant number of loans were returned to the Company. At December 31, 2017 and 2016, the recorded repurchase liability associated with transferred loans was not material.
Loans	LOANS Legacy (Loans originated or renewed and underwritten by the Company) The Company originates mortgage, commercial, and consumer loans for customers. Loans that management has the intent and ability to hold for the foreseeable future or until maturity or payoff are reported at the unpaid principal balances, less the ALL, charge-offs, and unamortized net loan origination fees and direct costs, except for loans carried at fair value. Interest income is accrued as earned over the term of the loans based on the principal balance outstanding. Loan origination fees, net of certain direct origination costs, are deferred and recognized as an adjustment of the related loan yield. Acquired (Loans acquired through Business Combinations) Acquired loans are recorded at fair value on the acquisition date in accordance with ASC Topic 820, Fair Value Measurement , consistent with the exit price concept on the date of acquisition. Credit risk assumptions and any resulting credit discounts are included in the determination of fair value. Therefore, an ALL is not recorded at the acquisition date. The determination of fair value includes estimates related to discount rates, expected prepayments, and the amount and timing of undiscounted expected principal, interest, and other cash flows. Acquired loans are evaluated at acquisition and classified as purchased impaired (“acquired impaired”) or purchased non-impaired (“acquired non-impaired”). Acquired impaired loans reflect credit deterioration since origination to the extent that it is probable at the time of acquisition that the Company will be unable to collect all contractually required payments. At the time of acquisition, acquired impaired loans are accounted for individually or aggregated into loan pools with similar characteristics, which include: • whether the loan is performing according to contractual terms at the time of acquisition, • the loan type based on regulatory reporting guidelines, namely whether the loan was a mortgage, consumer, or commercial loan, • the nature of collateral, • the interest rate type, whether fixed or variable rate, and • the loan payment type, primarily whether the loan is amortizing or interest-only. From these pools, the Company uses certain loan information, including outstanding principal balance, estimated expected losses, weighted average maturity, weighted average term to re-price (if a variable rate loan), weighted average margin, and weighted average interest rate to estimate the expected cash flows for each loan pool. For acquired impaired loans, expected cash flows at the acquisition date in excess of the fair value of loans are recorded as interest income over the life of the loans using a level yield method if the timing and amount of future cash flows is reasonably estimable. For acquired non-impaired loans, the difference between the fair value and unpaid principal balance of the loan at acquisition, referred to as a purchase premium or discount, is amortized or accreted to income over the estimated life of the loans as an adjustment to yield. Subsequent to acquisition, the Company performs cash flow re-estimations at least quarterly for each acquired impaired loan and/or loan pool. Increases in estimated cash flows above those expected at acquisition are recognized on a prospective basis as interest income over the remaining life of the loan and/or pool. Decreases in expected cash flows subsequent to acquisition generally result in recognition of a provision for credit loss. The measurement of cash flows involves several assumptions and judgments (i.e., prepayments, default rates, loss severity, etc.). All of these factors are inherently subjective and significant changes in the cash flow estimations can result over the life of the loan. Classification The Company’s loan portfolio is disaggregated into portfolio segments for purposes of determining the ACL. The Company’s portfolio segments include commercial, residential mortgage, and consumer and other loans, bifurcated between legacy and acquired (non-impaired). The Company further disaggregates each commercial, residential mortgage, and consumer and other loans portfolio segment into classes for purposes of monitoring and assessing credit quality based on certain risk characteristics. Classes within the commercial loan portfolio segment include commercial real estate-construction, commercial real estate-owner-occupied, commercial real estate-non-owner occupied, and commercial and industrial. Classes within the consumer and other loans portfolio segment include home equity, indirect automobile, credit card and other.
Troubled Debt Restructurings	Troubled Debt Restructurings The Company periodically grants concessions to its customers in an attempt to protect as much of its investment as possible and minimize risk of loss. These concessions may include restructuring the terms of a loan to alleviate the burden of the customer’s near-term cash requirements. In order to be classified as a TDR, the Company must conclude that the restructuring constitutes a concession and the customer is experiencing financial difficulties. The Company defines a concession to the customer as a modification of existing terms for economic or legal reasons that it would otherwise not consider. The concession is either granted through an agreement with the customer or is imposed by a court of law. Concessions include modifying original loan terms to reduce or defer cash payments required as part of the loan agreement, including but not limited to: • a reduction of the stated interest rate for the remaining original life of the loan, • extension of the maturity date or dates at a stated interest rate lower than the current market rate for new loans with similar risk characteristics, • reduction of the face amount or maturity amount of the loan as stated in the agreement, or • reduction of accrued interest receivable on the loan. In its determination of whether the customer is experiencing financial difficulties, the Company considers numerous indicators, including, but not limited to: • whether the customer is currently in default on its existing loan(s), or is in an economic position where it is probable the customer will be in default on its loan(s) in the foreseeable future without a modification, • whether the customer has declared or is in the process of declaring bankruptcy, • whether there is substantial doubt about the customer’s ability to continue as a going concern, • whether, based on its projections of the customer’s current capabilities, the Company believes the customer’s future cash flows will be insufficient to service the loan, including interest, in accordance with the contractual terms of the existing agreement for the foreseeable future, and • whether, without modification, the customer cannot obtain sufficient funds from other sources at an effective interest rate equal to the current market rate for a similar loan for a non-troubled debtor. If the Company concludes that both a concession has been granted and the customer is experiencing financial difficulties, the Company identifies the loan as a TDR. All TDRs are considered impaired loans.
Non-accrual and Past Due Loans (Including Loan Charge-offs)	NON-ACCRUAL AND PAST DUE LOANS (INCLUDING LOAN CHARGE-OFFS) Loans are generally considered past due when contractual payments of principal and interest have not been received within 30 days from the contractual due date. Residential mortgage loans are considered past due when contractual payments have not been received for two consecutive payment dates. Legacy and acquired non-impaired loans are placed on non-accrual status when any of the following occur: 1) the loan is maintained on a cash basis because of deterioration in the financial condition of the borrower; 2) collection of the full contractual amount of principal and interest is not expected (even if the loan is currently paying as agreed); or 3) when principal or interest has been in default for a period of 90 days or more, unless the loan is both well-secured and in the process of collection. Factors considered in determining the collection of the full contractual amount of principal and interest include assessment of the borrower’s cash flow, valuation of underlying collateral, and the ability and willingness of guarantors to provide credit support. Certain commercial loans are also placed on non-accrual status when payment is not past due and full payment of principal and interest is expected, but we have doubt about the borrower’s ability to comply with existing repayment terms. Consideration will be given to placing a loan on non-accrual due to the deterioration of the debtor’s repayment ability, the repayment of the loan becoming dependent on the liquidation of collateral, an existing collateral deficiency, the loan being classified as "Doubtful" or "Loss," the client filing for bankruptcy, and/or foreclosure being initiated. Regarding all classes within the C&I and CRE portfolios, the determination of a borrower’s ability to make the required principal and interest payments is based on an examination of the borrower’s current financial statements, industry, management capabilities, and other qualitative factors. Acquired impaired loans are placed on non-accrual status when the Company cannot reasonably estimate cash flows on a loan or loan pool. Legacy and acquired non-impaired loans are evaluated for potential charge-off in accordance with the parameters discussed in the following paragraph or when the loan is placed on non-accrual status, whichever is earlier. Loans within the commercial portfolio (except for acquired impaired) are generally evaluated for charge-off at 90 days past due, unless both well-secured and in the process of collection. Closed and open-end residential mortgage and consumer loans (except for acquired impaired) are evaluated for charge-off no later than 120 days past due. Any outstanding loan balance in excess of the fair value of the collateral less costs to sell is charged-off no later than 120 days past due for loans secured by real estate. For non-real estate secured loans, in lieu of charging off the entire loan balance, loans may be written down to the fair value of the collateral less costs to sell if repossession of collateral is assured and in process. The accrual of interest, as well as the amortization/accretion of any remaining unamortized net deferred fees or costs and discount or premium, is discontinued at the time the loan is placed on non-accrual status. All accrued but uncollected interest for loans that are placed on non-accrual status is reversed through interest income. Cash receipts received on non-accrual loans are generally applied against principal until the loan has been collected in full, after which time any additional cash receipts are recognized as interest income (i.e., cost recovery method). However, interest may be accounted for under the cash-basis method as long as the remaining recorded investment in the loan is deemed fully collectible. Loans are returned to accrual status when the borrower has demonstrated a capacity to continue payment of the debt (generally a minimum of six months of payment history) and collection of contractually required principal and interest associated with the debt is reasonably assured. At such time, the accrual of interest and amortization/accretion of any remaining unamortized net deferred fees or costs and discount or premium shall resume. Any interest income which was applied to the principal balance shall not be reversed and subsequently will be recognized as an adjustment to yield over the remaining life of the loan.
Impaired Loans	IMPAIRED LOANS For all classes within the commercial portfolio, all loans with an outstanding commitment balance above a specific threshold are evaluated on a quarterly basis for potential impairment. Generally, residential mortgage and consumer loans within any class are not individually evaluated on a regular basis for impairment. All TDRs, regardless of the outstanding balance amount or portfolio classification, and all acquired impaired loans are considered to be impaired. A loan is considered impaired when, based on current information and events, it is probable that the Company will be unable to collect the scheduled payments of principal and/or interest when due, according to the contractual terms of the loan agreement. Factors considered by management in determining impairment include payment status, collateral value, and the likelihood of collecting scheduled principal and interest payments when due. Loans that experience insignificant payment delays and payment shortfalls generally are not classified as impaired. Impairment losses are measured on a loan-by-loan basis for commercial and certain residential mortgage or consumer loans, based on either the present value of expected future cash flows discounted at the loan’s effective interest rate, the loan’s observable market price, or the fair value of the collateral if the loan is collateral-dependent. This measurement requires significant judgment and use of estimates, and the actual loss ultimately recognized by the Company may differ significantly from the estimates.
Allowance for Credit Losses	ALLOWANCE FOR CREDIT LOSSES The Company maintains the ACL at a level that management believes appropriate to absorb estimated probable credit losses incurred in the loan portfolios (including unfunded commitments) as of the consolidated balance sheet date. The ACL consists of the allowance for loan losses (contra asset) and the reserve for unfunded commitments (liability). The manner in which the ACL is determined is based on 1) the accounting method applied to the underlying loans and 2) whether the loan is required to be measured for impairment. The Company delineates between loans accounted for under the contractual yield method, legacy and acquired non-impaired loans, and acquired impaired loans. Further, for legacy and acquired non-impaired loans, the Company attributes portions of the ACL to loans and loan commitments that it measures individually, and groups of homogeneous loans and loan commitments that it measures collectively for impairment. Determination of the appropriate ACL involves a high degree of complexity and requires significant judgment regarding the credit quality of the loan portfolio. Several factors are taken into consideration in the determination of the overall ACL, including a qualitative component. These factors include, but are not limited to, the overall risk profiles of the loan portfolios, net charge-off experience, the extent of impaired loans, the level of non-accrual loans, the level of 90 days past due loans, the value of collateral, the ability to monetize guarantor support, and the overall percentage level of the allowance relative to the loan portfolio, amongst other factors. The Company also considers overall asset quality trends, changes in lending practices and procedures, trends in the nature and volume of the loan portfolio, including the existence and effect of any portfolio concentrations, changes in experience and depth of lending staff, the Company’s legal, regulatory and competitive environment, national and regional economic trends, data availability and applicability that might impact the portfolio or the manner in which it estimates losses, and risk rating accuracy and risk identification. The allowance for loan losses for all impaired loans (excluding acquired impaired) is determined on an individual loan basis, considering the facts and circumstances specific to each borrower. The allowance is based on the difference between the recorded investment in the loan and generally either the estimated net present value of projected cash flows or the estimated value of the collateral associated with the loan, if the loan is deemed collateral-dependent. For non-impaired loans (excluding acquired impaired), the allowance for loan losses is calculated based on pools of loans with similar characteristics. The pool-level allowance is calculated through the application of PD (i.e., probability of default) and LGD (i.e., loss given default) factors for each individual loan. PDs and LGDs are determined based on historical default and loss information for similar loans. For purposes of establishing estimated loss percentages for pools of loans that share common risk characteristics, the Company’s loan portfolio is segmented by various loan characteristics including loan type, risk rating (commercial), Vantage or FICO score (residential mortgage and consumer), past due status (residential mortgage and consumer) and call report code. The default and loss information is measured over an appropriate period for each loan pool and adjusted as deemed appropriate. Qualitative adjustments are incorporated into the pool-level analysis to accommodate for the imprecision of certain assumptions and uncertainties inherent in the calculation. See the "Loans" section of this footnote for discussion of the determination of the ACL for acquired impaired loans. Certain inherent, but unconfirmed losses are probable within the loan portfolio. The Company’s current methodology for determining the level of inherent losses is based on historical loss rates, current credit grades, specific allocation, and other qualitative adjustments. In a stable or deteriorating credit environment, heavy reliance on historical loss rates and the credit grade rating process results in model-derived reserves that tend to slightly lag behind portfolio deterioration. Similar lags can occur in an improving credit environment whereby required reserves can lag slightly behind portfolio improvement. Given these and other model limitations, qualitative adjustment factors may be incremental or decremental to the quantitative model results. In periods prior to 2015, the Company estimated incurred losses on its Exploration and Production and its Oil Field Services portfolios as an aggregate portfolio. Beginning in 2015, as the performance of these two portfolios began to diverge, the Company disaggregated the analysis of incurred losses within these portfolios, which included modifying its LGD estimates for the portfolios to more closely align with published historical industry data and other factors. Absent this change, the Company would have recorded an additional $10.0 million , or 17 cents per share, in provision expense for the year ended December 31, 2015. The reserve for unfunded commitments is determined using similar methodologies described above for non-impaired loans. The loss factors used in the reserve for unfunded commitments are equivalent to the loss factors used in the allowance for loan losses, while also considering utilization of unused commitments.
Premises and Equipment	PREMISES AND EQUIPMENT Land is carried at cost. Buildings, furniture, fixtures, and equipment are carried at cost, less accumulated depreciation computed on a straight-line basis over the estimated useful lives of 10 to 40 years for buildings and related improvements and generally 3 to 20 years for furniture, fixtures, and equipment. Leasehold improvements are amortized over the lease term, including any renewal periods that are reasonably assured, or the asset’s useful life, whichever is shorter. Premises and equipment are evaluated for impairment whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. SOFTWARE Software is amortized on a straight-line basis over its estimated useful life. The estimated useful life of software is generally three years , but can vary depending on the specific facts and circumstances. Software is evaluated for impairment whenever events or changes in circumstances indicate that the carrying amount of the software may not be recoverable. Software is recorded within "other assets" on the Company’s consolidated balance sheets with carrying amounts at December 31, 2017 and 2016 of $5.2 million and $5.6 million , respectively.
Goodwill and Other Intangible Assets	GOODWILL AND OTHER INTANGIBLE ASSETS Goodwill Goodwill represents the excess of the consideration paid in a business combination over the fair value of the identifiable net assets acquired. Goodwill is not amortized, but is assessed for potential impairment at a reporting unit level on an annual basis, as of October 1 st , or whenever events or changes in circumstances indicate that it is more likely than not the fair value of a reporting unit is less than its respective carrying amount. For the annual October 1, 2017 impairment evaluation, management elected to bypass the qualitative assessment for each respective reporting unit (IBERIABANK, Mortgage, and LTC) and performed Step 1 of the goodwill impairment test. Step 1 of the goodwill impairment test requires the Company to compare the fair value of each reporting unit with its carrying amount, including goodwill. Accordingly, the Company determined the fair value of each reporting unit and compared the fair value to each respective reporting unit’s carrying amount. The Company determined that none of the reporting units’ fair values were below their respective carrying amounts. The Company concluded goodwill was not impaired as of October 1, 2017. Further, no events or changes in circumstances between October 1, 2017 and December 31, 2017 indicated that it was more likely than not the fair value of any reporting unit had been reduced below its carrying value. Based on the testing performed in 2017 and 2016, management concluded that for the IBERIABANK, Mortgage, and LTC reporting units, goodwill was not impaired at any time during those periods. Title Plant Costs incurred to construct a title plant, including the costs incurred to obtain, organize, and summarize historical information, are capitalized until the title plant can be used to perform title searches. A purchased title plant, including a purchased undivided interest in a title plant, is recorded at cost at the date of acquisition. For a title plant acquired separately or as part of a business acquisition, cost is measured as the fair value of the consideration paid. Capitalized costs of a title plant are not depreciated or charged to income unless circumstances indicate that the carrying amount of the title plant has been impaired. Impairment indicators include a change in legal requirements or statutory practices, identification of obsolescence, or abandonment of the title plant, among other indicators. Capitalized storage and retrieval costs (e.g., costs to convert from one storage retrieval system to another or to modernize the storage and retrieval systems) incurred after a title plant is operational are charged to expense in a systematic and rational manner. Title plant is recorded within "other assets" on the Company’s consolidated balance sheets. Intangible assets subject to amortization The Company’s acquired intangible assets that are subject to amortization include (amongst other ancillary intangibles described in Note 9) core deposit intangibles, amortized on a straight-line or accelerated basis, and a customer relationship intangible asset, amortized on an accelerated basis, over average lives not to exceed 10 years. The Company reviews intangible assets for impairment whenever events or changes in circumstances indicate that their carrying amounts may not be recoverable. Impairment is identified if the sum of the undiscounted estimated future cash flows is less than the carrying value of the asset. Intangible assets are recorded within "other assets" on the Company’s consolidated balance sheets.
Other Real Estate Owned	OTHER REAL ESTATE OWNED Other real estate owned includes all real estate, other than bank premises used in bank operations, owned or controlled by the Company, including real estate acquired in settlement of loans. Properties are initially recognized at the recorded investment of the loan (which is the pro-rata carrying value of loans accounted for in accordance with ASC Topic 310-30, Receivables - Loans and Debt Securities Acquired with Deteriorated Credit Quality ) or at estimated fair value less costs to sell, whichever is less, generally when the Company has received physical possession (legal title is not required for non-consumer residential property). The amount by which the recorded investment of the loan exceeds the fair value less costs to sell of the property is charged to the ALL. Subsequent to foreclosure, the assets are carried at the lower of cost or fair value less costs to sell. Former bank properties transferred to OREO are recorded at the lower of cost or market. Subsequent declines in the fair value of other real estate are recorded as adjustments to the carrying amount through a valuation allowance. Revenue and expenses from operations, gain or loss on sale, and changes in the valuation allowance are included in net expenses from foreclosed assets. OREO is recorded within "other assets" on the Company’s consolidated balance sheets.
Derivative Financial Instruments	DERIVATIVE FINANCIAL INSTRUMENTS The Company enters into various derivative financial instruments to manage interest rate risk, asset sensitivity, and other exposures such as liquidity and credit risk, as well as to facilitate customer transactions. The primary types of derivatives utilized by the Company for its risk management strategies include interest rate swap agreements, interest rate lock commitments, forward sales commitments, and written and purchased options. All derivative instruments are recognized on the consolidated balance sheets as "other assets" or "other liabilities" at fair value, regardless of whether a right of offset exists. Changes in the fair value (i.e., gains or losses) of a derivative instrument are recorded based on whether it has been designated and qualifies as part of a hedging relationship. Interest rate swap and foreign exchange contracts are entered into by the Company to allow its commercial customers to manage their exposure to market rate fluctuations. To mitigate the Company's exposure to the rate risk associated with customer contracts, offsetting derivative positions are entered into with reputable counterparties. The Company manages its credit risk, or potential risk of default, from the customer contracts through credit limit approval and monitoring procedures. These contracts are not designated for hedge accounting (i.e., treated as economic hedges). Derivatives Designated in Hedging Relationships For cash flow hedges, the effective portion of the gain or loss related to the derivative instrument is initially reported as a component of OCI and subsequently reclassified into earnings when the forecasted transaction affects earnings or when the hedge is terminated. The ineffective portion of the gain or loss, if any, is reported in earnings immediately, in either "other income" or "other expense", respectively. In applying hedge accounting for derivatives (ASC Topic 815-30 Derivatives and Hedging - Cash Flow Hedges ), 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. Derivatives Not Designated in Hedging Relationships For derivative instruments that are not designated as hedging instruments, changes in the fair value of the derivatives are recognized in earnings immediately. Common Types of Derivatives Interest rate swap agreements Interest rate swaps are agreements to exchange interest payments based upon notional amounts. The exchange of payments typically involves paying a fixed rate and receiving a variable rate or vice versa. As part of its activities to manage interest rate risk (i.e., the exposure to the variability of future cash flows or other forecasted transactions due to fluctuating market rates), the Company enters into interest rate contracts, which typically include interest rate swap agreements. The Company primarily utilizes these instruments, which the Company designates as cash flow hedges, to convert a portion of its variable-rate loans or debt to a fixed rate. Interest rate lock commitments The Company enters into commitments to originate mortgage loans intended for sale whereby the interest rate on the prospective loan is determined prior to funding (“rate lock”). A rate lock is provided to a borrower, subject to conditional performance obligations, for a specified period of time that typically does not exceed 60 days. Rate lock commitments on mortgage loans that are intended to be sold are recognized as derivatives. Accordingly, such commitments are recorded at fair value as derivative assets or liabilities, with changes in fair value recorded in mortgage income on the consolidated statements of comprehensive income. Forward sales commitments The Company uses forward sales commitments to protect the value of its rate locks and mortgage loans held for sale from changes in interest rates and pricing between the origination of the rate lock and sale of these loans, as changes in interest rates have the potential to cause a decline in value of rate locks and mortgage loans included in the held for sale portfolio. These commitments are recognized as derivatives and recorded at fair value as derivative assets or liabilities, with changes in fair value recorded in mortgage income on the consolidated statements of comprehensive income. Equity-indexed certificates of deposit IBERIABANK offers its customers a certificate of deposit that provides the purchaser a guaranteed return of principal at maturity plus a potential return, which allows IBERIABANK to identify a known cost of funds. The rate of return is based on the performance of a group of publicly traded stocks that represent a variety of industry segments. Because it is based on an equity index, the rate of return represents an embedded derivative that is not clearly and closely related to the host instrument and is to be accounted for separately. Accordingly, the certificate of deposit is separated into two components: a zero coupon certificate of deposit (the host instrument) and a written option purchased by the depositor (an embedded derivative). The discount on the zero coupon deposit is amortized over the life of the deposit, and the written option is carried at fair value on the Company’s consolidated balance sheets, with changes in fair value recorded through earnings. IBERIABANK offsets the risks of the written option by purchasing an option with terms that mirror the written option, which is also carried at fair value on the Company’s consolidated balance sheets.
Off-balance-Sheet Credit-related Financial Instruments	OFF-BALANCE SHEET CREDIT-RELATED FINANCIAL INSTRUMENTS In the ordinary course of business, the Company executes various commitments to extend credit, including commitments under commercial construction arrangements, commercial and home equity lines of credit, credit card arrangements, commercial letters of credit, and standby letters of credit. Such financial instruments are recorded on the funding date.
Transfers of Financial Assets	TRANSFERS OF FINANCIAL ASSETS Transfers of financial assets, or portions thereof which meet the definition of a participating interest, are accounted for as sales when control over the assets has been surrendered. Control over transferred assets is deemed to be surrendered when 1) the assets have been legally isolated from the Company, 2) the transferee has the right to pledge or exchange the assets with no conditions that constrain the transferee and provide more than a trivial benefit to the Company, and 3) the Company does not maintain effective control over the transferred assets. Should the transfer not satisfy all three criteria, the transaction is recorded as a secured borrowing. If the transfer is accounted for as a sale, the transferred assets are derecognized from the Company’s balance sheet and a gain or loss on sale is recognized. If the transfer is accounted for as a secured borrowing, the transferred assets remain on the Company’s balance sheet and the proceeds from the transaction are recognized as a liability. Servicing Rights The Company recognizes the rights to service mortgage and other loans as separate assets, which are recorded in "other assets" in the consolidated balance sheets, when purchased or when servicing is contractually separated from the underlying loans by sale with servicing rights retained. For loan sales with servicing retained, a servicing right (generally an asset) is recorded at fair value for the right to service the loans sold. All servicing rights are identified by class and subsequently accounted for under the amortization method.
Income Taxes	INCOME TAXES The Company and all subsidiaries file a consolidated Federal income tax return on a calendar year basis. The Company files income tax returns in the U.S. Federal jurisdiction and various state and local jurisdictions through IBERIABANK Corporation (Parent), IBERIABANK, and their respective subsidiaries. In lieu of Louisiana state income tax, IBERIABANK is subject to the Louisiana bank shares tax, portions of which are included in both "non-interest expense" and "income tax expense" in the Company’s consolidated statements of comprehensive income. With few exceptions, the Company is no longer subject to U.S. federal, state or local income tax examinations for years before 2014. Deferred income tax assets and liabilities are determined using the liability (or balance sheet) method. Under this method, the net deferred tax asset or liability is determined based on the tax effects of the temporary differences between the book and tax bases of the various balance sheet assets and liabilities and gives current recognition to changes in tax rates and laws. The measurement of deferred tax assets is reduced, if necessary, by the amount of any tax benefits that, based on available evidence, are not expected to be realized. The Company recognizes interest and penalties accrued related to unrecognized tax benefits, if applicable, in "non-interest expense." Investments in qualified affordable housing projects that meet the applicable GAAP criteria are accounted for under the proportional amortization method. Under this method, the expense associated with the investments is recognized in income tax expense rather than non-interest expense. The Company has also elected to utilize the deferral method for investments that generate investment tax credits. Under this approach, the investment tax credits are recognized as a reduction of the related asset rather than income tax expense. In December 2017, the SEC staff issued Staff Accounting Bulletin No. 118 ("SAB 118"), Income Tax Accounting Implications of the Tax Cuts and Jobs Act (the "Tax Act"), which allows the Company to record provisional amounts during the measurement period. The measurement period is prohibited from extending beyond one year of the enactment date of the Tax Act, or December 22, 2018. Any provisional amounts or adjustments to provisional amounts included in the Company’s consolidated financial statements during the measurement period will be included in the consolidated statements of comprehensive income as an adjustment to income tax expense in the reporting period the amounts are determined. Refer to Note 14, Income Taxes, for further details of the impact of the Tax Act on the Company.
Share-based Compensation Plans	SHARE-BASED COMPENSATION PLANS The Company issues stock options, restricted stock awards, restricted share units, performance units, and phantom stock awards under various plans to directors, officers, and other key employees. Compensation cost for all awards is recognized on a straight-line basis over the requisite service period, which is generally the vesting period, taking into account retirement eligibility. The majority of the Company's share-based awards qualify for equity accounting and contain service conditions. Under equity accounting, the fair value of the award is measured at the grant date and not subsequently remeasured. The Company accounts for share-based forfeitures as they occur. For awards that contain a market condition, the Company includes the market condition in the determination of the grant date fair value of the award. Compensation cost for an award with a market condition is recognized regardless of whether the market condition is satisfied, assuming the requisite service is met. The Company does not include performance conditions in the determination of the grant date fair value of the award. Compensation cost for an award with a performance condition is not recognized if the performance condition is not satisfied. Phantom stock awards and performance units, accounted for as liability awards, are remeasured at each reporting period based on their fair value until the date of settlement. Compensation cost for each reporting period until settlement is based on the change (or a portion of the change, depending on the percentage of the requisite service that has been rendered at the reporting date) in the fair value of the phantom stock award and performance unit for each reporting period. Compensation expense relating to share-based awards is recognized in net income as part of “salaries and employee benefits” on the consolidated statements of comprehensive income for employees and “professional services” for non-employee directors. The exercise price for the options granted by the Company is not less than the fair market value of the underlying stock at the grant date.
Earnings Per Common Share	EARNINGS PER COMMON SHARE Basic earnings per share represents income available to common shareholders divided by the weighted average number of common shares outstanding during the period. Diluted earnings per share reflects additional common shares that would have been outstanding if dilutive potential common shares, in the form of stock options or restricted stock units, had been issued, as well as any adjustment to income that would result from the assumed issuance. Participating common shares issued by the Company relate to unvested outstanding restricted stock awards, the earnings allocated to which are used in determining income available to common shareholders under the two-class method. The two-class method allocates earnings for the period between common shareholders and other participating securities holders. The participating awards receiving dividends are allocated the same percentage of income as if they were outstanding shares.
Share Repurchases	SHARE REPURCHASES The Company classifies repurchased shares, as required for companies incorporated in Louisiana, as a reduction to issued shares of common stock, and accordingly, adjusts the stated value of common stock and paid-in-capital.
Comprehensive Income	COMPREHENSIVE INCOME Accounting principles generally require that recognized revenue, expenses, gains, and losses be included in net income. Although certain changes in assets and liabilities, such as unrealized gains and losses on available for sale securities and cash flow hedges, are reported as a separate component of the shareholders’ equity section of the consolidated balance sheets, such items, along with net income, are components of comprehensive income.
Fair Value Measurements	FAIR VALUE MEASUREMENTS Fair value is the exchange price that would be received for an asset or paid to transfer a liability (exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The Company estimates fair value based on the assumptions market participants would use when selling an asset or transferring a liability and characterizes such measurements within the fair value hierarchy based on the inputs used to develop those assumptions and measure fair value. The hierarchy requires the Company to maximize the use of observable inputs and minimize the use of unobservable inputs. The three levels of inputs used to measure fair value are as follows: • Level 1 - Quoted prices in active markets for identical assets or liabilities. • Level 2 - Observable inputs other than quoted prices included in Level 1, such as quoted prices for similar assets and liabilities in active markets; quoted prices for identical or similar assets and liabilities in markets that are not active; or other inputs that are observable or can be corroborated by observable market data. • Level 3 - Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. This includes certain pricing models, discounted cash flow methodologies, and similar techniques that use significant unobservable inputs. A description of the valuation methodologies used for instruments measured at fair value follows, as well as the classification of such instruments within the valuation hierarchy. The descriptions below are exclusive of assets or liabilities acquired in business combinations, as all such instruments are required to initially be measured at fair value. Cash and cash equivalents The carrying amounts of cash and cash equivalents approximate their fair value. Investment securities Securities are classified within Level 1 where quoted market prices are available in an active market. If quoted market prices are unavailable, fair value is estimated using quoted prices of securities with similar characteristics, at which point the securities are classified within Level 2 of the hierarchy. Mortgage loans held for sale Mortgage loans originated and held for sale are recorded at fair value under the fair value option, unless otherwise noted. When determining the fair value of loans held for sale, the Company obtains quotes or bids on these loans directly from the purchasing financial institutions (Level 2). Loans The fair values of mortgage loans are estimated based on present values using entry-value rates (the interest rate that would be charged for a similar loan to a borrower with similar risk at the indicated balance sheet date) at December 31, 2017 and 2016, weighted for varying maturity dates. Other loans are valued based on present values using entry-value interest rates at December 31, 2017 and 2016 applicable to each category of loans, which are classified within Level 3 of the hierarchy. Impaired loans Loans are measured for impairment using the methods permitted by ASC Topic 310, Receivables . Fair value measurements are used in determining impairment using either the loan’s observable market price (Level 1), if available, or the fair value of the collateral, if the loan is collateral-dependent (Level 3). Fair value of the collateral is determined by appraisals or independent valuation less costs to sell. Impaired loans for which the fair value of the collateral is higher than the recorded investment in the loan are not adjusted to fair value and therefore not recorded in the Company’s non-recurring fair value measurements section of the Fair Value Measurements footnote. Measuring the impairment of loans using the present value of expected future cash flows, discounted at the loan’s effective interest rate, is not considered a fair value measurement under GAAP as the interest rate used to discount the cash flows does not necessarily reflect current credit or market conditions for such loans. Other real estate owned Fair values of OREO are determined by sales agreement or appraisal and costs to sell are based on estimation per the terms and conditions of the sales agreement or amounts commonly used in real estate transactions. Inputs include appraisal values on the properties or recent sales activity for similar assets in the property’s market, and thus OREO measured at fair value is classified within Level 3 of the hierarchy. Derivative financial instruments Fair values of interest rate swaps, interest rate locks, foreign exchange contracts, forward sales contracts, and written and purchased options are estimated using prices of financial instruments with similar characteristics and thus are classified within Level 2 of the fair value hierarchy. Deposits The fair value of non-interest-bearing deposits, NOW accounts, money market deposits and savings accounts are the amounts payable on demand at the reporting date. Certificates of deposit and other time deposits are valued using a discounted cash flow model based on the weighted-average rate at December 31, 2017 and 2016 for deposits with similar remaining maturities. The Company evaluated the inputs to the fair value estimate and based on our use of quoted prices for similar liabilities determined that the fair value of deposits should be categorized within Level 2 of the fair value hierarchy. Short-term borrowings Securities sold under agreements to repurchase, which are classified as secured borrowings, generally mature daily and are reflected at the amount of cash received in connection with the transaction within Level 1 of the fair value hierarchy. The carrying amounts of other short-term borrowings maturing within ninety days approximate their fair values and are considered Level 2 measurements as similar instruments are traded in active markets. Long-term debt The fair values of long-term debt are estimated using discounted cash flow analyses based on the Company’s current incremental borrowing rates for similar types of borrowing arrangements. The fair value of the Company’s long-term debt is categorized within Level 3 of the fair value hierarchy. Off-balance sheet items The Company has outstanding commitments to extend credit and standby letters of credit. These off-balance sheet financial instruments are generally exercisable at the market rate prevailing at the date the underlying transaction will be completed. At December 31, 2017 and 2016, the fair value of guarantees under commercial and standby letters of credit was not material.
Recent Accounting Pronouncements	NOTE 2 - RECENT ACCOUNTING PRONOUNCEMENTS Pronouncements adopted during the year ended December 31, 2017: ASU No. 2016-09 The Company adopted the amendments of ASU No. 2016-09, Compensation-Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting , effective January 1, 2017 as follows: (i) prospective adoption of the recognition of excess tax benefits associated with vested or settled awards in the statement of comprehensive income; (ii) prospective adoption of the exclusion of excess tax benefits from assumed proceeds for the calculation of diluted EPS; (iii) modified retrospective adoption of the minimum statutory withholdings requirements; (iv) modified retrospective adoption of the accounting policy election to account for forfeitures as they occur; and (v) prospective adoption of the classifications of certain cash flows associated with stock compensation. The adoption of these amendments did not, either individually or in aggregate, have a significant impact on the Company’s consolidated financial statements. ASU No. 2017-01 In January 2017, the FASB issued ASU No. 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business , which introduces amendments that are intended to clarify the definition of a business to assist companies and other reporting organizations in evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. The Company early-adopted the amendments effective January 1, 2017. The adoption of this ASU did not have a significant impact on the Company’s consolidated financial statements. ASU No. 2018-02 In February 2018, the FASB issued ASU No. 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income , which allows a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the newly enacted corporate tax rate on December 22, 2017. ASU No. 2018-02 is effective for annual reporting periods beginning after December 15, 2018, including interim reporting periods within those periods. Early adoption is permitted for financial statements of fiscal years or interim periods which have not yet been issued. The Company elected to early adopt the standard for the fiscal year ending December 31, 2017. The adjustment from accumulated other comprehensive income to retained earnings did not have a significant impact on the Company’s consolidated financial statements. Pronouncements issued but not yet adopted: 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. The amendments in ASU No. 2014-09 will be effective for annual reporting periods beginning after December 15, 2017, including interim reporting periods within that reporting period. The Company will adopt the amendments beginning January 1, 2018 through the modified-retrospective transition method. A significant amount of the Company’s revenues are derived from net interest income on financial assets and liabilities, which are excluded from the scope of the amended guidance. The Company does not expect to recognize a cumulative adjustment to equity upon implementation of the standard, but does anticipate an insignificant adjustment to its consolidated statements of comprehensive income related to the net presentation of certain costs associated with interchange fees and rewards programs, as well as some additional disclosure. 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 . This ASU will impact how the Company measures certain equity investments and discloses and presents certain financial instruments through the application of the “exit price” notion. ASU No. 2016-01 is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2017. The Company will adopt the amendments beginning January 1, 2018 through an insignificant cumulative-effect adjustment to equity at adoption related to its current equity investments with readily determinable fair values. The Company will also modify its fair value methodology for financial instruments measured at amortized cost whose fair values are disclosed under the “entry price” notion to an “exit price” notion. The Company anticipates the fair value of these financial instruments will be lower under the exit price methodology in comparison to the entry price methodology. ASU No. 2016-02 In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 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 (Topic 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 ALL 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 standard and has developed an implementation plan. ASU No. 2016-15 In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 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. ASU 2016-15 will be effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. Early adoption is permitted, including adoption in an interim period. The amendments should be applied using a retrospective transition method to each period presented. The Company is currently evaluating the impact of the ASU on the Company’s consolidated statement of cash flows, but does not anticipate significant changes in presentation. ASU No. 2017-04 In January 2017, the FASB issued ASU No. 2017-04, Intangibles-Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment , which simplifies how an entity is required to test goodwill for impairment by eliminating Step 2 from the goodwill impairment test. Therefore, any carrying amount which exceeds the reporting unit’s fair value (up to the amount of goodwill recorded) will be recognized as an impairment loss. ASU No. 2017-04 will be effective for annual reporting periods beginning after December 15, 2019, including interim reporting periods within those periods. The amendments will be applied prospectively on or after the effective date. Early adoption is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. Based on recent goodwill impairments tests, which did not require the application of Step 2, the Company does not expect the adoption of this ASU to have an immediate impact. ASU No. 2017-12 In August 2017, the FASB issued ASU No. 2017-12, Derivatives and Hedging (Topic 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 amendments within ASU 2017-12 include: • Elimination of the requirement to separately measure and report periodic hedge ineffectiveness for cash flow and net investment hedges. • Recognition and presentation of changes in the fair value of the hedging instrument. • Recognition and presentation of components excluded from an entity’s hedge effectiveness assessment. • Addition of the ability to elect to perform subsequent effectiveness assessments qualitatively. • Elimination of the benchmark interest rate concept for variable-rate instruments in cash flow hedges by allowing the designation of the contractually specified interest rate as the hedged risk. • Addition of the Securities Industry and Financial Markets Association Municipal Swap Rate as a benchmark interest rate. • Addition of the ability to define a long-haul methodology to employ in the event a hedge ceases to qualify under the shortcut method. • Addition of the ability to apply the shortcut method to partial-term fair value hedges of interest rate risk. • Enhancement of the ability to use the critical-terms-match method for a cash flow hedge of groups of forecasted transactions when the timing of the hedged transactions does not perfectly match the hedging instrument’s maturity date. • Addition of new, and amendments to existing, disclosure requirements. ASU No. 2017-12 will be effective for annual reporting periods beginning after December 15, 2018, including interim reporting periods within those periods. Early adoption is permitted in any interim period or fiscal year before the effective date. The implementation of the amendments will not have a significant impact on the Company’s consolidated financial statements based upon its current hedging strategies.

Acquisition Activity (Tables)

Acquisition Activity (Tables)	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Schedule of Business Acquisitions	Acquisition of Sabadell United (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 558,156 Goodwill $ 462,046 (Dollars in thousands) Sabadell United Fair Value (Preliminary) Assets Cash and cash equivalents $ 318,724 Investment securities 964,123 Loans 4,026,240 Core deposit intangible assets 66,600 Deferred tax asset, net 35,129 Other assets 89,745 Total assets acquired $ 5,500,561 Liabilities Deposit liabilities $ 4,383,049 Short-term borrowings 520,539 Other liabilities 38,817 Total liabilities assumed $ 4,942,405
Business Acquisition, Pro Forma Information, Nonrecurring Adjustments [Table Text Block]	These changes are gross of taxes and reflected in the following table: Acquired Asset Balance Sheet Line Item Provisional Estimate September 30, 2017 Revised Provisional Estimate December 31, 2017 Increase (Decrease) CDI Other intangible assets $ 96,607 $ 66,600 $ (30,007 )
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" columns. 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 Year Ended December 31, (Dollars in thousands) 2017 2016 Net interest income $ 924,348 $ 842,945 Non-interest income 219,021 255,022 Net income 174,246 246,799

Investment Securities (Tables)

Investment Securities (Tables)	12 Months Ended
	Dec. 31, 2017
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: 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 December 31, 2016 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 $ (549 ) $ 150,554 $ — $ — $ (549 ) $ 150,554 Obligations of state and political subdivisions (5,207 ) 148,059 — — (5,207 ) 148,059 Mortgage-backed securities (38,667 ) 2,191,563 (2,624 ) 98,912 (41,291 ) 2,290,475 Other securities (451 ) 36,484 (53 ) 3,850 (504 ) 40,334 Total securities available for sale $ (44,874 ) $ 2,526,660 $ (2,677 ) $ 102,762 $ (47,551 ) $ 2,629,422 Securities held to maturity: Obligations of state and political subdivisions $ (133 ) $ 10,602 $ — $ — $ (133 ) $ 10,602 Mortgage-backed securities (330 ) 12,288 (487 ) 10,960 (817 ) 23,248 Total securities held to maturity $ (463 ) $ 22,890 $ (487 ) $ 10,960 $ (950 ) $ 33,850 The amortized cost and fair values of investment securities, with gross unrealized gains and losses, consist of the following: 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 December 31, 2016 (Dollars in thousands) Amortized Gross Gross Estimated Securities available for sale: U.S. Government-sponsored enterprise obligations $ 212,662 $ 245 $ (549 ) $ 212,358 Obligations of state and political subdivisions 286,458 1,948 (5,207 ) 283,199 Mortgage-backed securities 2,888,180 4,820 (41,291 ) 2,851,709 Other securities 98,974 361 (504 ) 98,831 Total securities available for sale $ 3,486,274 $ 7,374 $ (47,551 ) $ 3,446,097 Securities held to maturity: Obligations of state and political subdivisions $ 64,726 $ 1,609 $ (133 ) $ 66,202 Mortgage-backed securities 24,490 57 (817 ) 23,730 Total securities held to maturity $ 89,216 $ 1,666 $ (950 ) $ 89,932
Held-to-maturity Securities	The amortized cost and fair values of investment securities, with gross unrealized gains and losses, consist of the following: 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 December 31, 2016 (Dollars in thousands) Amortized Gross Gross Estimated Securities available for sale: U.S. Government-sponsored enterprise obligations $ 212,662 $ 245 $ (549 ) $ 212,358 Obligations of state and political subdivisions 286,458 1,948 (5,207 ) 283,199 Mortgage-backed securities 2,888,180 4,820 (41,291 ) 2,851,709 Other securities 98,974 361 (504 ) 98,831 Total securities available for sale $ 3,486,274 $ 7,374 $ (47,551 ) $ 3,446,097 Securities held to maturity: Obligations of state and political subdivisions $ 64,726 $ 1,609 $ (133 ) $ 66,202 Mortgage-backed securities 24,490 57 (817 ) 23,730 Total securities held to maturity $ 89,216 $ 1,666 $ (950 ) $ 89,932 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: 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 December 31, 2016 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 $ (549 ) $ 150,554 $ — $ — $ (549 ) $ 150,554 Obligations of state and political subdivisions (5,207 ) 148,059 — — (5,207 ) 148,059 Mortgage-backed securities (38,667 ) 2,191,563 (2,624 ) 98,912 (41,291 ) 2,290,475 Other securities (451 ) 36,484 (53 ) 3,850 (504 ) 40,334 Total securities available for sale $ (44,874 ) $ 2,526,660 $ (2,677 ) $ 102,762 $ (47,551 ) $ 2,629,422 Securities held to maturity: Obligations of state and political subdivisions $ (133 ) $ 10,602 $ — $ — $ (133 ) $ 10,602 Mortgage-backed securities (330 ) 12,288 (487 ) 10,960 (817 ) 23,248 Total securities held to maturity $ (463 ) $ 22,890 $ (487 ) $ 10,960 $ (950 ) $ 33,850
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 December 31 is presented in the following table. (Dollars in thousands) 2017 2016 Number of securities Mortgage-backed securities 181 28 Obligations of state and political subdivisions 28 — Other 1 3 210 31 Amortized Cost Basis Mortgage-backed securities $ 1,280,739 $ 112,983 Obligations of state and political subdivisions 72,820 — Other 10,000 3,903 $ 1,363,559 $ 116,886 Unrealized Loss Mortgage-backed securities $ 35,412 $ 3,111 Obligations of state and political subdivisions 1,180 — Other 152 53 $ 36,744 $ 3,164
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 December 31, 2017 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 0.60 % $ 37,907 $ 37,563 2.79 % $ 1,119 $ 1,125 One through five years 2.04 124,350 123,589 3.01 8,718 8,756 After five through ten years 2.35 867,799 863,931 2.81 34,970 35,418 Over ten years 2.32 3,617,875 3,564,979 2.55 182,511 182,665 2.30 % $ 4,647,931 $ 4,590,062 2.61 % $ 227,318 $ 227,964
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. Years Ended December 31 (Dollars in thousands) 2017 2016 2015 Realized gains $ 1,651 $ 2,949 $ 1,834 Realized losses (1,799 ) (948 ) (259 ) $ (148 ) $ 2,001 $ 1,575
Schedule of Securities in Other Assets on Company's Consolidated Balance Sheets	The Company accounts for the following securities at amortized cost, which approximates fair value, in “other assets” on the consolidated balance sheets at December 31: (Dollars in thousands) 2017 2016 Federal Home Loan Bank (FHLB) stock $ 95,171 $ 42,326 Federal Reserve Bank (FRB) stock 79,191 48,584 Other investments 3,008 2,808 $ 177,370 $ 93,718

Loans (Tables)

Loans (Tables)	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Schedule of Non-Covered and Covered Loans	Loans consist of the following at December 31: (Dollars in thousands) 2017 2016 Commercial loans: Real estate - construction $ 1,240,396 $ 802,242 Real estate - owner-occupied 2,529,885 2,277,749 Real estate - non-owner-occupied 5,167,949 3,766,558 Commercial and industrial 5,135,067 4,060,032 14,073,297 10,906,581 Residential mortgage loans: 3,056,352 1,267,400 Consumer loans: Home equity 2,292,275 2,155,926 Indirect automobile 62,693 131,052 Credit card 96,368 82,992 Other 497,196 521,020 2,948,532 2,890,990 Total $ 20,078,181 $ 15,064,971
Schedule of Aging of Loans	The following tables provide an analysis of the aging of loans as of December 31, 2017 and 2016. 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. 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 Loans Acquired Impaired Loans Total Loans Commercial 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 December 31, 2016 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 Loans Acquired Impaired Loans Total Loans Commercial real estate - construction $ 767,305 $ — $ — $ — $ — $ 1,946 $ 32,991 $ 802,242 Real estate - owner-occupied 2,123,014 1,452 1,712 — 3,164 25,950 125,621 2,277,749 Real estate - non-owner-occupied 3,633,472 1,123 224 32 1,379 9,651 122,056 3,766,558 Commercial and industrial 3,857,375 4,071 920 — 4,991 164,934 32,732 4,060,032 Residential mortgage 1,124,463 2,334 2,565 1,353 6,252 13,733 122,952 1,267,400 Consumer - home equity 2,050,204 6,314 1,615 — 7,929 9,374 88,419 2,155,926 Consumer - indirect automobile 127,054 2,551 405 — 2,956 1,038 4 131,052 Consumer - credit card 82,070 199 99 — 298 624 — 82,992 Consumer - other 511,105 2,538 714 — 3,252 1,252 5,411 521,020 Total $ 14,276,062 $ 20,582 $ 8,254 $ 1,385 $ 30,221 $ 228,502 $ 530,186 $ 15,064,971
Schedule of Carrying Amount of Loans Acquired	The tables below show the balances acquired during 2017 for these two subsections of the acquired 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 $ 4,914,185 Expected losses and foregone interest (54,226 ) Cash flows expected to be collected at acquisition 4,859,959 Fair value of acquired loans at acquisition $ 3,960,308 (Dollars in thousands) Acquired Impaired Loans Contractually required principal and interest at acquisition $ 111,114 Non-accretable difference (expected losses and foregone interest) (12,245 ) Cash flows expected to be collected at acquisition 98,869 Accretable yield (32,937 ) Basis in acquired loans at acquisition $ 65,932
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 years ended December 31: (Dollars in thousands) 2017 2016 2015 Balance at beginning of period $ 175,054 $ 227,502 $ 287,651 Additions 32,937 — 6,823 Transfers from non-accretable difference to accretable yield 4,912 5,490 9,916 Accretion (56,337 ) (68,211 ) (80,479 ) Changes in expected cash flows not affecting non-accretable differences (1) (3,943 ) 10,273 3,591 Balance at end of period $ 152,623 $ 175,054 $ 227,502 (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 years ended December 31: (Dollars in thousands) 2017 2016 2015 Extended maturities $ 26,561 $ 75,315 $ 15,594 Interest rate adjustment 24 193 — Maturity and interest rate adjustment 4,932 2,470 23,374 Movement to or extension of interest-rate only payments 4,161 27,931 241 Forbearance 7,226 76,819 122 Other concession(s) (1) 27,555 39,708 17,710 Total $ 70,459 $ 222,436 $ 57,041 (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 years ended December 31: 2017 2016 2015 (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 Number of Loans Pre-modification Outstanding Recorded Investment Post-modification Outstanding Recorded Investment Commercial real estate - construction 4 $ 9,404 $ 9,628 3 $ 3,024 $ 3,035 — $ — $ — Commercial real estate - owner-occupied 11 5,779 5,706 20 18,223 18,239 6 15,403 13,889 Commercial real estate - non-owner-occupied 19 11,974 13,738 25 16,644 10,093 5 11,361 11,361 Commercial and industrial 57 21,651 20,883 79 163,265 169,893 28 31,030 27,598 Residential mortgage 24 1,897 1,771 43 5,141 4,946 1 70 68 Consumer - home equity 123 16,346 15,862 158 13,273 12,568 50 4,440 3,865 Consumer - indirect 43 511 371 79 983 792 6 79 79 Consumer - other 78 2,671 2,500 116 3,087 2,870 17 248 181 Total 359 $ 70,233 $ 70,459 523 $ 223,640 $ 222,436 113 $ 62,631 $ 57,041 Information detailing TDRs that defaulted during the years ended December 31, 2017, 2016, and 2015 and were modified in the previous twelve months (i.e., the twelve months prior to the default) is presented in the following table. The Company has defined a default as any loan with a loan payment that is currently past due greater than 30 days , or was past due greater than 30 days at any point during the previous twelve months, or since the date of modification, whichever is shorter. 2017 2016 2015 (In thousands, except number of loans) Number of Loans Recorded Investment Number of Loans Recorded Investment Number of Loans Recorded Investment Commercial real estate - construction 2 $ 3,572 1 $ 116 — $ — Commercial real estate - owner-occupied 6 4,668 3 3,473 2 10,956 Commercial real estate - non-owner-occupied 13 8,060 6 201 4 11,119 Commercial and industrial 32 6,550 22 14,707 21 12,090 Residential mortgage 16 1,218 8 405 — — Consumer - home equity 32 3,285 25 1,379 20 1,547 Consumer - indirect 33 323 37 338 6 79 Consumer - other 29 1,058 22 606 9 2 Total 163 $ 28,734 124 $ 21,225 62 $ 35,793

Allowance for Credit Losses a36

Allowance for Credit Losses and Credit Quality (Tables)	12 Months Ended
	Dec. 31, 2017
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 years ended December 31 is as follows: (Dollars in thousands) 2017 2016 2015 Allowance for credit losses Allowance for loan losses at beginning of period $ 144,719 $ 138,378 $ 130,131 Provision for loan losses before adjustment attributable to FDIC loss share agreements 51,111 42,927 29,548 Adjustment attributable to FDIC loss share arrangements — 1,497 1,360 Net provision for loan losses 51,111 44,424 30,908 Adjustment attributable to FDIC loss share arrangements — (1,497 ) (1,360 ) Transfer of balance to OREO and other 934 (2,781 ) (10,419 ) Loans charged-off (62,466 ) (39,839 ) (17,301 ) Recoveries 6,593 6,034 6,419 Allowance for loan losses at end of period $ 140,891 $ 144,719 $ 138,378 Reserve for unfunded commitments at beginning of period $ 11,241 $ 14,145 $ 11,801 Balance created in acquisition accounting 1,370 — — Provision for (Reversal of) unfunded lending commitments 597 (2,904 ) 2,344 Reserve for unfunded commitments at end of period $ 13,208 $ 11,241 $ 14,145 Allowance for credit losses at end of period $ 154,099 $ 155,960 $ 152,523 A summary of changes in the allowance for credit losses, by loan portfolio type, for the years ended December 31 is as follows: 2017 (Dollars in thousands) Commercial Commercial Residential 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 losses 10,433 31,891 (2,206 ) 10,993 51,111 Transfer of balance to OREO and other 853 (68 ) 2 147 934 Loans charged off (7,433 ) (40,015 ) (365 ) (14,653 ) (62,466 ) Recoveries 1,117 1,169 437 3,870 6,593 Allowance for loan losses at end of period $ 54,201 $ 53,916 $ 9,117 $ 23,657 $ 140,891 Reserve for unfunded commitments at beginning of period $ 3,207 $ 4,537 $ 657 $ 2,840 $ 11,241 Balance created in acquisition accounting 253 783 327 7 1,370 Provision for (Reversal of) unfunded commitments 1,071 (11 ) (429 ) (34 ) 597 Reserve for unfunded commitments at end of period $ 4,531 $ 5,309 $ 555 $ 2,813 $ 13,208 Allowance on loans individually evaluated for impairment $ 1,588 $ 12,736 $ 172 $ 2,856 $ 17,352 Allowance on loans collectively evaluated for impairment 30,360 38,944 3,141 17,210 89,655 Allowance on loans acquired with deteriorated credit quality 22,253 2,236 5,804 3,591 33,884 Loans, net of unearned income: Balance at end of period $ 8,938,230 $ 5,135,067 $ 3,056,352 $ 2,948,532 $ 20,078,181 Balance at end of period individually evaluated for impairment 91,785 102,416 6,749 37,177 238,127 Balance at end of period collectively evaluated for impairment 8,616,924 5,001,505 2,911,222 2,828,848 19,358,499 Balance at end of period acquired with deteriorated credit quality 229,521 31,146 138,381 82,507 481,555 2016 (Dollars in thousands) Commercial Commercial Residential Consumer Total Allowance for loan losses at beginning of period $ 51,372 $ 49,355 $ 11,789 $ 25,862 $ 138,378 Provision for loan losses 1,958 32,296 824 9,346 44,424 Decrease in FDIC loss share receivable (34 ) (50 ) (1,090 ) (323 ) (1,497 ) Transfer of balance to OREO and other (868 ) (519 ) (141 ) (1,253 ) (2,781 ) Loans charged off (4,338 ) (21,645 ) (313 ) (13,543 ) (39,839 ) Recoveries 1,141 1,502 180 3,211 6,034 Allowance for loan losses at end of period $ 49,231 $ 60,939 $ 11,249 $ 23,300 $ 144,719 Reserve for unfunded commitments at beginning of period $ 4,167 $ 6,106 $ 830 $ 3,042 $ 14,145 Reversal of provision for unfunded commitments (960 ) (1,569 ) (173 ) (202 ) (2,904 ) Reserve for unfunded commitments at end of period $ 3,207 $ 4,537 $ 657 $ 2,840 $ 11,241 Allowance on loans individually evaluated for impairment $ 1,378 $ 21,413 $ 144 $ 1,358 $ 24,293 Allowance on loans collectively evaluated for impairment 25,248 37,206 4,223 17,537 84,214 Allowance on loans acquired with deteriorated credit quality 22,605 2,320 6,882 4,405 36,212 Loans, net of unearned income: Balance at end of period $ 6,846,549 $ 4,060,032 $ 1,267,400 $ 2,890,990 $ 15,064,971 Balance at end of period individually evaluated for impairment 61,006 220,995 4,312 16,467 302,780 Balance at end of period collectively evaluated for impairment 6,504,875 3,806,305 1,140,136 2,780,689 14,232,005 Balance at end of period acquired with deteriorated credit quality 280,668 32,732 122,952 93,834 530,186 2015 (Dollars in thousands) Commercial Commercial Residential Consumer Total Allowance for loan losses at beginning of period $ 57,093 $ 33,328 $ 9,162 $ 30,548 $ 130,131 Provision for loan losses 1,059 17,423 3,620 8,806 30,908 Increase (Decrease) in FDIC loss share receivable 757 (49 ) (235 ) (1,833 ) (1,360 ) Transfer of balance to OREO and other (6,849 ) (275 ) (491 ) (2,804 ) (10,419 ) Loans charged off (2,806 ) (1,279 ) (362 ) (12,854 ) (17,301 ) Recoveries 2,118 207 95 3,999 6,419 Allowance for loan losses at end of period $ 51,372 $ 49,355 $ 11,789 $ 25,862 $ 138,378 Reserve for unfunded commitments at beginning of period $ 3,439 $ 5,260 $ 168 $ 2,934 $ 11,801 Provision for unfunded commitments 728 846 662 108 2,344 Reserve for unfunded commitments at end of period $ 4,167 $ 6,106 $ 830 $ 3,042 $ 14,145 Allowance on loans individually evaluated for impairment $ 1,287 $ 2,394 $ 1 $ 397 $ 4,079 Allowance on loans collectively evaluated for impairment 24,186 44,080 4,150 17,839 90,255 Allowance on loans acquired with deteriorated credit quality 25,899 2,881 7,638 7,626 44,044 Loans, net of unearned income: Balance at end of period $ 6,125,927 $ 4,072,928 $ 1,195,319 $ 2,933,254 $ 14,327,428 Balance at end of period individually evaluated for impairment 29,578 33,270 70 5,066 67,984 Balance at end of period collectively evaluated for impairment 5,685,272 3,987,665 1,054,669 2,807,119 13,534,725 Balance at end of period acquired with deteriorated credit quality 411,077 51,993 140,580 121,069 724,719
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 reflect the classification as of December 31, 2017 and 2016, respectively. 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 December 31, 2017 and 2016. 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 delinquency is the primary credit quality indicator that the Company utilizes to monitor consumer asset quality. December 31, 2017 December 31, 2016 (Dollars in thousands) Pass Special Mention Sub- Doubtful Loss Total Pass Special Mention Sub- Doubtful Loss Total Commercial real estate - construction $ 1,189,490 $ 20,351 $ 30,541 $ 14 $ — $ 1,240,396 $ 775,387 $ 2,694 $ 22,026 $ 2,135 $ — $ 802,242 Commercial real estate - owner-occupied 2,388,715 82,114 56,590 2,466 — 2,529,885 2,180,201 29,039 66,816 1,670 23 2,277,749 Commercial real estate - non-owner-occupied 5,104,074 19,311 42,702 1,744 118 5,167,949 3,687,439 23,004 55,576 539 — 3,766,558 Commercial and industrial 4,882,554 88,149 128,961 35,403 — 5,135,067 3,660,080 104,482 266,553 28,917 — 4,060,032 Total $ 13,564,833 $ 209,925 $ 258,794 $ 39,627 $ 118 $ 14,073,297 $ 10,303,107 $ 159,219 $ 410,971 $ 33,261 $ 23 $ 10,906,581 December 31, 2017 December 31, 2016 (Dollars in thousands) Current 30+ Days Past Due Total Current 30+ Days Past Due Total Residential mortgage $ 2,962,043 $ 94,309 $ 3,056,352 $ 1,229,761 $ 37,639 $ 1,267,400 Consumer - home equity 2,250,205 42,070 2,292,275 2,129,110 26,816 2,155,926 Consumer - indirect automobile 59,836 2,857 62,693 127,047 4,005 131,052 Consumer - credit card 95,263 1,105 96,368 82,052 940 82,992 Consumer - other 490,399 6,797 497,196 515,857 5,163 521,020 Total $ 5,857,746 $ 147,138 $ 6,004,884 $ 4,083,827 $ 74,563 $ 4,158,390
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 allowance for loan losses, is presented in the following tables as of and for the periods indicated. December 31, 2017 (Dollars in thousands) Unpaid Principal Balance Recorded Investment Related Average Interest With no related allowance recorded: Commercial real estate - construction $ 13,763 $ 13,013 $ — $ 9,104 $ 441 Commercial real estate - owner-occupied 50,867 44,482 — 53,282 1,389 Commercial real estate - non-owner-occupied 15,370 14,975 — 15,127 692 Commercial and industrial 103,013 70,254 — 92,312 2,279 Residential mortgage 2,004 2,001 — 2,044 85 Consumer - home equity 5,906 5,634 — 5,747 231 Consumer - other 75 75 — 11 1 With an allowance recorded: Commercial real estate - construction 238 156 (19 ) 197 6 Commercial real estate - owner-occupied 13,314 13,287 (949 ) 13,498 414 Commercial real estate - non-owner-occupied 6,051 5,872 (620 ) 6,196 154 Commercial and industrial 35,306 32,162 (12,736 ) 42,874 1,220 Residential mortgage 5,179 4,748 (172 ) 4,861 180 Consumer - home equity 27,189 26,575 (2,358 ) 23,546 1,007 Consumer - indirect automobile 1,034 679 (79 ) 873 38 Consumer - other 4,320 4,214 (419 ) 3,582 231 Total $ 283,629 $ 238,127 $ (17,352 ) $ 273,254 $ 8,368 Total commercial loans $ 237,922 $ 194,201 $ (14,324 ) $ 232,590 $ 6,595 Total mortgage loans 7,183 6,749 (172 ) 6,905 265 Total consumer loans 38,524 37,177 (2,856 ) 33,759 1,508 December 31, 2016 (Dollars in thousands) Unpaid Principal Balance Recorded Investment Related Average Interest With no related allowance recorded: Commercial real estate - construction $ 38 $ 38 $ — $ 28 $ — Commercial real estate - owner-occupied 25,180 25,074 — 25,890 647 Commercial real estate - non-owner-occupied 15,654 14,794 — 19,587 879 Commercial and industrial 148,311 138,202 — 111,261 3,418 Consumer - home equity — — — — — Consumer - other — — — — — With an allowance recorded: Commercial real estate - construction 1,946 1,946 (649 ) 1,839 54 Commercial real estate - owner-occupied 17,580 17,429 (640 ) 16,668 493 Commercial real estate - non-owner-occupied 1,743 1,725 (89 ) 1,782 95 Commercial and industrial 84,197 82,793 (21,413 ) 78,270 2,858 Residential mortgage 4,628 4,312 (144 ) 4,377 161 Consumer - home equity 13,916 13,267 (993 ) 10,237 435 Consumer - indirect automobile 1,037 758 (114 ) 956 49 Consumer - other 2,448 2,442 (251 ) 1,469 102 Total $ 316,678 $ 302,780 $ (24,293 ) $ 272,364 $ 9,191 Total commercial loans $ 294,649 $ 282,001 $ (22,791 ) $ 255,325 $ 8,444 Total mortgage loans 4,628 4,312 (144 ) 4,377 161 Total consumer loans 17,401 16,467 (1,358 ) 12,662 586 December 31, 2015 (Dollars in thousands) Unpaid Principal Balance Recorded Investment Related Average Interest With no related allowance recorded: Commercial real estate - construction $ 54 $ 51 $ — $ 55 $ 1 Commercial real estate - owner-occupied 3,630 3,495 — 2,928 106 Commercial real estate - non-owner-occupied 13,318 12,600 — 12,881 209 Commercial and industrial 14,571 14,340 — 18,839 1,148 Consumer - home equity 730 730 — 533 22 Consumer - other 66 66 — 66 5 With an allowance recorded: Commercial real estate - construction 3 3 (2 ) 57 1 Commercial real estate - owner-occupied 12,744 12,691 (1,244 ) 12,908 527 Commercial real estate - non-owner-occupied 738 738 (41 ) 1,027 62 Commercial and industrial 18,958 18,930 (2,394 ) 20,055 776 Residential mortgage 70 70 (1 ) 70 5 Consumer - home equity 3,859 3,683 (338 ) 2,454 73 Consumer - other 588 587 (59 ) 488 3 Total $ 69,329 $ 67,984 $ (4,079 ) $ 72,361 $ 2,938 Total commercial loans $ 64,016 $ 62,848 $ (3,681 ) $ 68,750 $ 2,830 Total mortgage loans 70 70 (1 ) 70 5 Total consumer loans 5,243 5,066 (397 ) 3,541 103

Transfers and Servicing of Fi37

Transfers and Servicing of Financial Assets (Including Mortgage Banking Activity) (Tables)	12 Months Ended
	Dec. 31, 2017
Transfers and Servicing [Abstract]
Changes in Carrying Amount of Mortgage Loans Held-for-sale	Changes to the carrying amount of mortgage loans held for sale at December 31 are presented in the following table. (Dollars in thousands) 2017 2016 2015 Balance at beginning of period $ 157,041 $ 166,247 $ 140,072 Originations and purchases 1,844,358 2,460,033 2,464,588 Sales, net of gains (1,859,565 ) (2,451,459 ) (2,432,979 ) Mortgage loans transferred to held for investment (6,918 ) (14,017 ) — Other — (3,763 ) (5,434 ) Balance at end of period $ 134,916 $ 157,041 $ 166,247
Components of Mortgage Income	The following table details the components of mortgage income for the years ended December 31: (Dollars in thousands) 2017 2016 2015 Fair value changes of derivatives and mortgage loans held for sale: Mortgage loans held for sale and derivatives $ (7,047 ) $ 1,361 $ 2,216 Derivative settlements, net 1,229 (6,640 ) (5,017 ) Gains on sales 68,255 87,925 82,671 Servicing and other income, net 1,133 1,207 792 $ 63,570 $ 83,853 $ 80,662
Schedule of Mortgage Servicing Rights at Carrying Value	Mortgage servicing rights had the following carrying values as of the periods indicated: December 31, 2017 December 31, 2016 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount (Dollars in thousands) Mortgage servicing rights $ 9,588 $ (3,931 ) $ 5,657 $ 7,202 $ (3,144 ) $ 4,058

Premises and Equipment (Tables)

Premises and Equipment (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Schedule of Premises and Equipment	Premises and equipment consisted of the following at December 31: (Dollars in thousands) 2017 2016 Land $ 89,137 $ 84,616 Buildings 261,994 239,626 Furniture, fixtures and equipment 129,866 115,775 Total premises and equipment 480,997 440,017 Accumulated depreciation (149,584 ) (133,644 ) Total premises and equipment, net $ 331,413 $ 306,373
Schedule of Minimum Future Annual Rent Commitments	Minimum future annual rent commitments under lease agreements for the periods indicated are as follows: (Dollars in thousands) 2018 $ 20,697 2019 19,466 2020 17,733 2021 14,437 2022 11,393 2023 and thereafter 36,744 $ 120,470

Goodwill and Other Acquired I39

Goodwill and Other Acquired Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Carrying Amount of Goodwill	Changes to the carrying amount of goodwill by reporting unit for the years ended December 31, 2017 and 2016 are provided in the following table. (Dollars in thousands) IBERIABANK Mortgage LTC Total Balance, December 31, 2015 $ 696,260 $ 23,178 $ 5,165 $ 724,603 Goodwill adjustments during the year 2,253 — — 2,253 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
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 December 31: 2017 2016 (Dollars in thousands) Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Core deposit intangible assets $ 127,957 $ (51,971 ) $ 75,986 $ 74,001 $ (52,165 ) $ 21,836 Customer relationship intangible asset 1,143 (996 ) 147 1,348 (1,064 ) 284 Non-compete agreement 63 (39 ) 24 63 (22 ) 41 Total $ 129,163 $ (53,006 ) $ 76,157 $ 75,412 $ (53,251 ) $ 22,161 The related amortization expense of intangible assets is as follows: (Dollars in thousands) Amount Aggregate amortization expense for the years ended December 31: 2015 $ 7,811 2016 8,415 2017 12,590
Schedule of Amortization Expense of Intangible Assets	(Dollars in thousands) Estimated amortization expense for the years ended December 31: 2018 $ 18,415 2019 14,900 2020 11,771 2021 7,988 2022 5,903 2023 and thereafter 17,180

Derivative Instruments and Ot40

Derivative Instruments and Other Hedging Activities (Tables)	12 Months Ended
	Dec. 31, 2017
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) December 31, 2017 December 31, 2016 December 31, 2017 December 31, 2016 Derivatives designated as hedging instruments under ASC Topic 815: Interest rate contracts Other assets $ — $ — Other liabilities $ — $ 525 Total derivatives designated as hedging instruments under ASC Topic 815 $ — $ — $ — $ 525 Derivatives not designated as hedging instruments under ASC Topic 815: Interest rate contracts Other assets $ 20,446 $ 20,719 Other liabilities $ 16,191 $ 20,719 Foreign exchange contracts Other assets 7 27 Other liabilities 7 26 Forward sales contracts Other assets 136 6,014 Other liabilities 279 794 Written and purchased options Other assets 10,654 12,125 Other liabilities 8,656 8,098 Other contracts Other assets 22 1 Other liabilities 21 47 Total derivatives not designated as hedging instruments under ASC Topic 815 $ 31,265 $ 38,886 $ 25,154 $ 29,684 Total $ 31,265 $ 38,886 $ 25,154 $ 30,209 Derivative Assets - Notional Amount Derivative Liabilities - Notional Amount (Dollars in thousands) December 31, 2017 December 31, 2016 December 31, 2017 December 31, 2016 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 $ 1,218,464 $ 1,033,955 $ 1,218,464 $ 1,033,955 Foreign exchange contracts 268 4,474 268 4,474 Forward sales contracts 82,347 229,181 142,578 120,567 Written and purchased options 278,638 289,115 165,198 154,170 Other contracts 29,755 8,784 86,744 106,518 Total derivatives not designated as hedging instruments under ASC Topic 815 $ 1,609,472 $ 1,565,509 $ 1,613,252 $ 1,419,684 Total $ 1,609,472 $ 1,565,509 $ 1,721,752 $ 1,528,184
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. 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 . December 31, 2016 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 $ 20,719 $ (9,677 ) $ — $ 11,042 Written and purchased options 8,085 — — 8,085 Total derivative assets subject to master netting arrangements $ 28,804 $ (9,677 ) $ — $ 19,127 Derivative liabilities Interest rate contracts designated as hedging instruments $ 525 $ — $ (181 ) $ 344 Interest rate contracts not designated as hedging instruments 20,719 (9,677 ) (1,711 ) 9,331 Total derivative liabilities subject to master netting arrangements $ 21,244 $ (9,677 ) $ (1,892 ) $ 9,675 (1) Consists of cash collateral recorded at cost, which approximates fair value, and investment securities.
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. 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 . December 31, 2016 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 $ 20,719 $ (9,677 ) $ — $ 11,042 Written and purchased options 8,085 — — 8,085 Total derivative assets subject to master netting arrangements $ 28,804 $ (9,677 ) $ — $ 19,127 Derivative liabilities Interest rate contracts designated as hedging instruments $ 525 $ — $ (181 ) $ 344 Interest rate contracts not designated as hedging instruments 20,719 (9,677 ) (1,711 ) 9,331 Total derivative liabilities subject to master netting arrangements $ 21,244 $ (9,677 ) $ (1,892 ) $ 9,675 (1) Consists of cash collateral recorded at cost, which approximates fair value, and investment securities.
Effect of Derivatives on the Consolidated Financial Statements	At December 31, 2017, 2016, and 2015, and for the years 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 (Ineffective Portion and Amount Excluded from Effectiveness Testing) Amount of Gain (Loss) Recognized in Income on Derivative (Ineffective Portion and Amount Excluded from Effectiveness Testing) Amount of Gain (Loss) Recognized in OCI net of taxes (Effective Portion) Location of Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion) Amount of Gain (Loss) Reclassified from Accumulated OCI into Income net of taxes (Effective Portion) (Dollars in thousands) For the Years Ended December 31 Derivatives in ASC Topic 815 Cash Flow Hedging Relationships 2017 2016 2015 2017 2016 2015 2017 2016 2015 Interest rate contracts $ (611 ) $ (328 ) $ 38 Interest expense $ (390 ) $ 50 $ — Interest expense $ — $ — $ — Total $ (611 ) $ (328 ) $ 38 $ (390 ) $ 50 $ — $ — $ — $ — Information pertaining to the effect of derivatives not designated as hedging instruments on the consolidated financial statements as of December 31, is as follows: Location of Gain (Loss) Recognized in Income on Derivatives Amount of Gain (Loss) Recognized in Income on Derivatives (Dollars in thousands) 2017 2016 2015 Interest rate contracts (1) Other income $ 4,750 $ 8,830 $ 4,143 Foreign exchange contracts Other income 43 15 22 Forward sales contracts Mortgage income (4,115 ) (1,731 ) (2,947 ) Written and purchased options Mortgage income (2,028 ) (327 ) 274 Other contracts Other income 51 17 — Total $ (1,299 ) $ 6,804 $ 1,492

Deposits (Tables)

Deposits (Tables)	12 Months Ended
	Dec. 31, 2017
Banking and Thrift [Abstract]
Schedule of Deposits by Type	Deposits at December 31 are summarized as follows: (Dollars in thousands) 2017 2016 Non-interest-bearing deposits $ 6,209,925 $ 4,928,878 Negotiable order of withdrawal (NOW) 4,348,939 3,314,281 Money market deposits accounts (MMDA) 7,674,291 6,219,532 Savings deposits 846,074 814,385 Certificates of deposit and other time deposits 2,387,488 2,131,207 $ 21,466,717 $ 17,408,283
Schedule of Time Deposits	Total time deposits summarized by denomination at December 31 are as follows: (Dollars in thousands) 2017 2016 Time deposits less than $250,000 $ 1,768,047 $ 1,661,631 Time deposits greater than $250,000 619,441 469,576 $ 2,387,488 $ 2,131,207
Schedule of Maturities of Certificates of Deposit	A schedule of maturities of all time deposits as of December 31, 2017 is as follows: (Dollars in thousands) Years ending December 31 2018 $ 1,670,503 2019 401,855 2020 158,555 2021 65,885 2022 78,500 2023 and thereafter 12,190 $ 2,387,488

Short-Term Borrowings (Tables)

Short-Term Borrowings (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Summary of Short-Term Borrowings	Short-term borrowings at December 31 are summarized as follows: (Dollars in thousands) 2017 2016 Federal Home Loan Bank advances $ 475,000 $ 175,000 Securities sold under agreements to repurchase 516,297 334,136 $ 991,297 $ 509,136 The levels of securities sold under agreements to repurchase and FHLB advances can fluctuate significantly on a day-to-day basis, depending on funding needs and which sources are used to satisfy those needs. All such arrangements are considered typical of the banking and brokerage industries and are accounted for as borrowings. Securities sold under agreements to repurchase, which are classified as secured borrowings, generally mature daily and are reflected at the amount of cash received in connection with the transaction. The Company may be required to provide additional collateral based on the fair value of the underlying securities. Additional information on the Company’s short-term borrowings for the years indicated is as follows: (Dollars in thousands) 2017 2016 2015 Outstanding at December 31 $ 991,297 $ 509,136 $ 326,617 Maximum month-end outstanding balance 2,197,105 807,993 798,933 Average daily outstanding balance 905,755 614,073 426,011 Average rate during the year 0.83 % 0.40 % 0.19 % Average rate at year end 0.82 % 0.30 % 0.20 %

Long-Term Debt (Tables)

Long-Term Debt (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Schedule of Long-Term Debt	Long-term debt at December 31 is summarized as follows: (Dollars in thousands) 2017 2016 IBERIABANK: Federal Home Loan Bank notes, 0.864% to 7.040% $ 1,331,579 $ 480,118 Notes payable - Investment fund contribution, 7 to 30 year term, 1.28% to 6.82% fixed, 7 to 40 year term, 0.50% to 3.60% fixed, respectively 44,146 28,725 1,375,725 508,843 IBERIABANK Corporation (junior subordinated debt): Statutory Trust I, 3 month LIBOR (1) , plus 3.25%, issued November 2002 10,310 10,310 Statutory Trust II, 3 month LIBOR (1) , plus 3.15%, issued June 2003 10,310 10,310 Statutory Trust III, 3 month LIBOR (1) , plus 2.00%, issued September 2004 10,310 10,310 Statutory Trust IV, 3 month LIBOR (1) , plus 1.60%, issued October 2006 15,464 15,464 American Horizons Statutory Trust I, 3 month LIBOR (1) , plus 3.15%, assumed January 2005 6,186 6,186 Statutory Trust V, 3 month LIBOR (1) , plus 1.435%, issued June 2007 10,310 10,310 Statutory Trust VI, 3 month LIBOR (1) , plus 2.75%, issued November 2007 12,372 12,372 Statutory Trust VII, 3 month LIBOR (1) , plus 2.54%, issued November 2007 13,403 13,403 Statutory Trust VIII, 3 month LIBOR (1) , plus 3.50%, issued March 2008 7,217 7,217 OMNI Trust I, 3 month LIBOR (1) , plus 3.30%, assumed May 2011 8,248 8,248 OMNI Trust II, 3 month LIBOR (1) , plus 2.79%, assumed May 2011 7,732 7,732 GA Commerce Trust II, 3 month LIBOR (1) , plus 1.64%, assumed May 2015 8,248 8,248 120,110 120,110 $ 1,495,835 $ 628,953 (1) The interest rate on the Company’s long-term debt indexed to LIBOR is based on the 3-month LIBOR rate. The 3-month LIBOR rate w as 1.69% and 1.00% at December 31, 2017 and 2016, respectively.
Maturities of Long-Term Debt	Advances and long-term debt at December 31, 2017 have maturities or call dates in future years as follows: (Dollars in thousands) 2018 $ 235,944 2019 506,231 2020 114,241 2021 55,441 2022 410,800 2023 and thereafter 173,178 $ 1,495,835

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of Provision for Income Tax Expense	The provision for income tax expense consists of the following for the years ended December 31: (Dollars in thousands) 2017 2016 2015 Current expense $ 84,827 $ 103,335 $ 67,025 Deferred expense (benefit) 71,257 (16,654 ) 4,551 Tax credits (10,845 ) (7,112 ) (11,268 ) Amortization on qualified affordable housing tax credits 5,227 4,185 2,023 Tax benefits attributable to items charged to equity and goodwill — 1,439 1,763 $ 150,466 $ 85,193 $ 64,094
Reconciliation of Effective Tax Rate	The provision for federal income taxes differs from the amount computed by applying the federal income tax statutory rate of 35 percent on income before income tax expense as indicated in the following analysis for the years ended December 31: (Dollars in thousands) 2017 2016 2015 Federal tax based on statutory rate $ 102,508 $ 95,189 $ 72,428 Increase (decrease) resulting from: Effect of tax-exempt income (9,435 ) (8,203 ) (6,919 ) Interest and other nondeductible expenses 9,605 3,250 5,899 State taxes, net of federal benefit 6,970 4,770 3,955 Tax credits (10,845 ) (7,112 ) (11,268 ) Amortization on qualified affordable housing tax credits 5,227 4,185 2,023 Other (1) 46,436 (6,886 ) (2,024 ) $ 150,466 $ 85,193 $ 64,094 Effective tax rate 51.4 % 31.3 % 31.0 %
Deferred Tax Assets and Liabilities	The net deferred tax asset at December 31 is as follows: (Dollars in thousands) 2017 2016 Deferred tax asset: NOL carryforward $ 8,364 $ 19,584 Allowance for credit losses 38,402 58,036 Deferred compensation 5,876 10,852 Basis difference in acquired assets and liabilities 43,391 32,957 Unrealized loss on securities available for sale 12,198 14,019 OREO 2,639 4,498 Other 22,719 14,720 133,589 154,666 Deferred tax liability: Basis difference in acquired assets and liabilities (31,309 ) (13,150 ) FHLB stock (300 ) (270 ) Premises and equipment (3,723 ) (6,132 ) Acquisition intangibles (8,151 ) (8,134 ) Deferred loan costs (3,114 ) (4,702 ) Other (4,885 ) (9,196 ) (51,482 ) (41,584 ) Net deferred tax asset $ 82,107 $ 113,082

Shareholders' Equity, Capital45

Shareholders' Equity, Capital Ratios and Other Regulatory Matters (Tables)	12 Months Ended
	Dec. 31, 2017
Banking and Thrift [Abstract]
Schedule of Preferred Stock	The following table presents a summary of the Company's non-cumulative perpetual preferred stock at December 31: 2017 2016 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 December 31 are presented in the following table. (Dollars in thousands) 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 2016 Minimum Well-Capitalized Actual Amount Ratio Amount Ratio Amount Ratio Tier 1 Leverage Consolidated $ 818,440 4.00 % N/A N/A $ 2,221,528 10.86 % IBERIABANK 816,152 4.00 $ 1,020,190 5.00 1,878,703 9.21 Common Equity Tier 1 (CET1) (1) Consolidated $ 794,334 4.50 % N/A N/A $ 2,089,431 11.84 % IBERIABANK 792,111 4.50 $ 1,144,160 6.50 1,878,703 10.67 Tier 1 Risk-Based Capital (1) Consolidated $ 1,059,112 6.00 % N/A N/A $ 2,221,528 12.59 % IBERIABANK 1,056,147 6.00 $ 1,408,197 8.00 1,878,703 10.67 Total Risk-Based Capital (1) Consolidated $ 1,412,149 8.00 % N/A N/A $ 2,493,988 14.13 % IBERIABANK 1,408,197 8.00 $ 1,760,246 10.00 2,034,663 11.56

Earnings Per Share (Tables)

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2017
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. For the Years Ended December 31, (In thousands, except per share data) 2017 2016 2015 Earnings per common share - basic Net income $ 142,413 $ 186,777 $ 142,844 Preferred stock dividends (9,095 ) (7,977 ) — Dividends and undistributed earnings allocated to unvested restricted shares (1,210 ) (1,872 ) (1,680 ) Net income allocated to common shareholders - basic $ 132,108 $ 176,928 $ 141,164 Weighted average common shares outstanding 50,640 40,948 38,214 Earnings per common share - basic 2.61 4.32 3.69 Earnings per common share - diluted Net income allocated to common shareholders - basic $ 132,108 $ 176,928 $ 141,164 Dividends and undistributed earnings allocated to unvested restricted shares (1 ) (37 ) (48 ) Net income allocated to common shareholders - diluted $ 132,107 $ 176,891 $ 141,116 Weighted average common shares outstanding 50,640 40,948 38,214 Dilutive potential common shares 352 158 96 Weighted average common shares outstanding - diluted 50,992 41,106 38,310 Earnings per common share - diluted $ 2.59 $ 4.30 $ 3.68

Share-Based Compensation (Table

Share-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2017
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 years ended December 31: 2017 2016 2015 Number of shares at beginning of period 543,261 507,130 506,289 Granted 421,198 254,276 207,575 Forfeited (31,699 ) (28,855 ) (26,970 ) Vested (194,573 ) (189,290 ) (179,764 ) Number of shares at end of period 738,187 543,261 507,130 The following table represents phantom stock award and performance unit activity during the periods indicated. (Dollars in thousands) Number of share equivalents (1) Value of share equivalents (2) Balance, December 31, 2014 475,347 $ 30,826 Granted 167,573 9,228 Forfeited share equivalents (34,681 ) 1,910 Vested share equivalents (145,809 ) 9,288 Balance, December 31, 2015 462,430 $ 25,466 Granted 215,745 18,069 Forfeited share equivalents (42,051 ) 3,522 Vested share equivalents (163,294 ) 8,509 Balance, December 31, 2016 472,830 $ 39,600 Granted 118,408 9,177 Forfeited share equivalents (34,968 ) 2,710 Vested share equivalents (162,426 ) 15,206 Balance, December 31, 2017 393,844 $ 30,523 (1) Number of share equivalents includes all reinvested dividend equivalents for the years 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 $77.50 , $83.75 and $55.07 on December 31, 2017, 2016 and 2015, respectively. The following table represents the activity related to stock options during the periods indicated: Number of Shares Weighted Average Exercise Price Aggregate Intrinsic Value (Dollars in thousands) Weighted Average Remaining Contract Life (in years) Outstanding options, December 31, 2014 867,682 $ 55.92 Granted 82,001 62.50 Exercised (119,917 ) 51.71 $ 1,516 Forfeited or expired (15,989 ) 66.52 Outstanding options, December 31, 2015 813,777 $ 56.99 Granted 160,624 48.65 Exercised (196,769 ) 55.39 3,597 Forfeited or expired (56,094 ) 59.49 Outstanding options, December 31, 2016 721,538 $ 55.38 Granted 80,557 84.78 Exercised (85,221 ) 55.45 2,098 Forfeited or expired (30,508 ) 68.46 Outstanding options, December 31, 2017 686,366 $ 58.24 $ 13,767 5.6 Exercisable options, December 31, 2015 546,842 $ 56.54 Exercisable options, December 31, 2016 415,376 56.66 Exercisable options, December 31, 2017 455,010 55.77 $ 9,891 4.4
Schedule of Valuation Assumptions	The following weighted-average assumptions were used for option awards issued during the years ended December 31: 2017 2016 2015 Expected dividends 1.7 % 2.8 % 2.2 % Expected volatility 25.0 % 29.0 % 35.6 % Risk-free interest rate 2.1 % 1.4 % 2.0 % Expected term (in years) 5.8 6.5 7.5 Weighted-average grant-date fair value $ 18.86 $ 10.46 $ 19.57
Schedule of Allocation for Share-based Compensation Expense	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 years ended December 31: (Dollars in thousands) 2017 2016 2015 Compensation expense related to stock options $ 1,470 $ 2,010 $ 1,861 Income tax benefit related to stock options 124 331 317 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 years ended December 31: (Dollars in thousands) 2017 2016 2015 Compensation expense related to restricted stock awards and restricted share units $ 14,966 $ 12,513 $ 12,045 Income tax benefit related to restricted stock awards and restricted share units 2,809 4,380 4,215 The following table indicates compensation expense recorded for phantom stock and performance units based on the number of share equivalents vested at December 31 of the years indicated and the current market price of the Company’s stock at that time: (Dollars in thousands) 2017 2016 2015 Compensation expense related to phantom stock and performance units $ 10,756 $ 12,933 $ 12,109

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Summary of Financial Instruments Outstanding	At December 31, 2017 and 2016, respectively, the Company had the following financial instruments outstanding and related reserves, whose contract amounts represent credit risk: (Dollars in thousands) December 31, 2017 December 31, 2016 Commitments to grant loans $ 342,305 $ 355,558 Unfunded commitments under lines of credit 6,060,034 4,899,930 Commercial and standby letters of credit 210,002 163,560 Reserve for unfunded lending commitments 13,208 11,241

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
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, for a description of how fair value measurements are determined. December 31, 2017 (Dollars in thousands) 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 December 31, 2016 Level 1 Level 2 Level 3 Total Assets Securities available for sale $ — $ 3,446,097 $ — $ 3,446,097 Mortgage loans held for sale — 157,041 — 157,041 Derivative instruments — 38,886 — 38,886 Total $ — $ 3,642,024 $ — $ 3,642,024 Liabilities Derivative instruments $ — $ 30,209 $ — $ 30,209 Total $ — $ 30,209 $ — $ 30,209
Gains and Losses Included in Earnings Related to Asset and Liabilities Measured at Fair Value on Recurring Basis	Gains and losses (realized and unrealized) included in earnings (or accumulated other comprehensive income) during 2017 related to assets and liabilities measured at fair value on a recurring basis are reported in non-interest income or other comprehensive income as follows: (Dollars in thousands) Non-interest income Other comprehensive income (loss), net of tax Total gains (losses) included in earnings $ (1,166 ) $ — Change in unrealized gains (losses) relating to assets still held at December 31, 2017 — (11,721 )
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. 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 December 31, 2016 (Dollars in thousands) Level 1 Level 2 Level 3 Total Assets Loans $ — $ — $ 93,485 $ 93,485 OREO, net — — 185 185 Total $ — $ — $ 93,670 $ 93,670
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: December 31, 2017 December 31, 2016 (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 $ 134,916 $ 131,276 $ 3,640 $ 157,041 $ 153,801 $ 3,240

Fair Value of Financial Instr50

Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2017
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, for a description of how fair value measurements are determined. December 31, 2017 (Dollars in thousands) Carrying Amount Fair Value Level 1 Level 2 Level 3 Financial Assets Cash and cash equivalents $ 625,724 $ 625,724 $ 625,724 $ — $ — Investment securities 4,817,380 4,818,026 — 4,818,026 — Loans and loans held for sale, net of unearned income and allowance for loan losses 20,072,206 19,961,773 — 134,916 19,826,857 Derivative instruments 31,265 31,265 — 31,265 — 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 Derivative instruments 25,154 25,154 — 25,154 — December 31, 2016 (Dollars in thousands) Carrying Amount Fair Value Level 1 Level 2 Level 3 Financial Assets Cash and cash equivalents $ 1,362,126 $ 1,362,126 $ 1,362,126 $ — $ — Investment securities 3,535,313 3,536,029 — 3,536,029 — Loans and loans held for sale, net of unearned income and allowance for loan losses 15,077,293 15,066,055 — 157,041 14,909,014 Derivative instruments 38,886 38,886 — 38,886 — Financial Liabilities Deposits 17,408,283 16,762,475 — 16,762,475 — Short-term borrowings 509,136 509,136 334,136 175,000 — Long-term debt 628,953 617,656 — — 617,656 Derivative instruments 30,209 30,209 — 30,209 —

Business Segments (Tables)

Business Segments (Tables)	12 Months Ended
	Dec. 31, 2017
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. Year Ended December 31, 2017 (Dollars in thousands) IBERIABANK Mortgage LTC Consolidated Interest and dividend income $ 906,521 $ 7,260 $ 2 $ 913,783 Interest expense 104,937 — — 104,937 Net interest income 801,584 7,260 2 808,846 Provision for/(reversal of) loan losses 51,200 (89 ) — 51,111 Mortgage income — 63,570 — 63,570 Title revenue — — 21,972 21,972 Other non-interest income 125,552 (42 ) (12 ) 125,498 Allocated expenses (13,293 ) 10,041 3,252 — Non-interest expense 585,355 73,587 16,954 675,896 Income/(loss) before income tax expense 303,874 (12,751 ) 1,756 292,879 Income tax expense/(benefit) 156,407 (5,771 ) (170 ) 150,466 Net income/(loss) $ 147,467 $ (6,980 ) $ 1,926 $ 142,413 Total loans and loans held for sale, net of unearned income $ 20,028,840 $ 184,257 $ — $ 20,213,097 Total assets 27,672,906 208,710 22,513 27,904,129 Total deposits 21,462,776 3,941 — 21,466,717 Average assets 24,228,436 229,364 22,856 24,480,656 Year Ended December 31, 2016 (Dollars in thousands) IBERIABANK Mortgage LTC Consolidated Interest and dividend income $ 707,676 $ 9,261 $ 2 $ 716,939 Interest expense 64,068 3,633 — 67,701 Net interest income 643,608 5,628 2 649,238 Provision for loan losses 44,336 88 — 44,424 Mortgage income 405 83,448 — 83,853 Title revenue — — 22,213 22,213 Other non-interest income 127,751 4 — 127,755 Allocated expenses (13,972 ) 10,686 3,286 — Non-interest expense 484,099 65,133 17,433 566,665 Income before income tax expense 257,301 13,173 1,496 271,970 Income tax expense 79,565 5,023 605 85,193 Net income $ 177,736 $ 8,150 $ 891 $ 186,777 Total loans and loans held for sale, net of unearned income $ 15,004,360 $ 217,652 $ — $ 15,222,012 Total assets 21,319,267 315,057 24,866 21,659,190 Total deposits 17,402,742 5,541 — 17,408,283 Average assets 19,959,261 335,913 26,060 20,321,234 Year Ended December 31, 2015 (Dollars in thousands) IBERIABANK Mortgage LTC Consolidated Interest and dividend income $ 639,793 $ 7,062 $ 3 $ 646,858 Interest expense 56,222 2,878 — 59,100 Net interest income 583,571 4,184 3 587,758 Provision for loan losses 30,908 — — 30,908 Mortgage income 966 79,696 — 80,662 Title revenue — — 22,837 22,837 Other non-interest income 116,903 (2 ) (7 ) 116,894 Allocated expenses (16,253 ) 12,036 4,217 — Non-interest expense 495,158 57,784 17,363 570,305 Income before income tax expense 191,627 14,058 1,253 206,938 Income tax expense 58,006 5,581 507 64,094 Net income $ 133,621 $ 8,477 $ 746 $ 142,844 Total loans and loans held for sale, net of unearned income $ 14,305,663 $ 188,012 $ — $ 14,493,675 Total assets 19,220,085 256,888 27,095 19,504,068 Total deposits 16,173,831 4,917 — 16,178,748 Average assets 18,146,216 230,819 25,671 18,402,706

Condensed Parent Company Only52

Condensed Parent Company Only Financial Statements (Tables)	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Balance Sheets	Condensed Balance Sheets (Dollars in thousands) December 31 2017 2016 Assets Cash in bank $ 168,873 $ 436,792 Investments in subsidiaries 3,661,808 2,635,682 Other assets 49,207 40,423 $ 3,879,888 $ 3,112,897 Liabilities and Shareholders’ Equity Liabilities $ 183,097 $ 173,203 Shareholders’ equity 3,696,791 2,939,694 $ 3,879,888 $ 3,112,897
Condensed Statements of Income	Condensed Statements of Income Year Ended December 31 (Dollars in thousands) 2017 2016 2015 Operating income Reimbursement of management expenses $ 76,177 $ 65,104 $ 59,255 Other income 146,796 829 (329 ) Total operating income 222,973 65,933 58,926 Operating expenses Interest expense 5,168 3,948 3,393 Salaries and employee benefits expense 55,013 45,623 41,689 Other expenses 32,965 19,566 17,492 Total operating expenses 93,146 69,137 62,574 Income (loss) before income tax benefit and increase in equity in undistributed earnings of subsidiaries 129,827 (3,204 ) (3,648 ) Income tax expense (benefit) 3,123 530 800 Income (loss) before equity in undistributed earnings of subsidiaries 126,704 (3,734 ) (4,448 ) Equity in undistributed earnings of subsidiaries 15,709 190,511 147,292 Net Income 142,413 186,777 142,844 Less: Preferred stock dividends 9,095 7,977 — Net Income Available to Common Shareholders $ 133,318 $ 178,800 $ 142,844
Condensed Statements of Cash Flows	Condensed Statements of Cash Flows (Dollars in thousands) Year Ended December 31 2017 2016 2015 Cash Flow from Operating Activities Net income $ 142,413 $ 186,777 $ 142,844 Adjustments to reconcile net income to net cash provided by operating activities: Depreciation and amortization 62 98 416 Net income of subsidiaries (160,206 ) (190,511 ) (147,292 ) Share-based compensation cost 16,436 14,523 13,906 Gain on sale of assets — — (110 ) Other operating activities, net (4,256 ) 12,417 82,105 Net Cash Provided by (Used in) Operating Activities (5,551 ) 23,304 91,869 Cash Flow from Investing Activities Cash paid in excess of cash received for acquisitions (809,159 ) — (5,054 ) Proceeds from sale of premises and equipment — — 12 Purchases of premises and equipment (105 ) — (2 ) Return of capital from (Capital contributed to) subsidiary 144,500 (6,000 ) 5,000 Other investing activities, net — (749 ) — Net Cash (Used in) Investing Activities (664,764 ) (6,749 ) (44 ) Cash Flow from Financing Activities Cash dividends paid on common stock (72,772 ) (56,793 ) (52,318 ) Cash dividends paid on preferred stock (9,095 ) (7,028 ) — Net share-based compensation stock transactions (832 ) 6,899 1,915 Payments to repurchase common stock — (11,666 ) — Net proceeds from issuance of common stock 485,151 279,242 — Net proceeds from issuance of preferred stock — 55,285 76,812 Other financing activities, net (56 ) — — Net Cash Provided by (Used In) Financing Activities 402,396 265,939 26,409 Net Increase (Decrease) in Cash and Cash Equivalents (267,919 ) 282,494 118,234 Cash and Cash Equivalents at Beginning of Period 436,792 154,298 36,064 Cash and Cash Equivalents at End of Period $ 168,873 $ 436,792 $ 154,298

Summary of Significant Accoun53

Summary of Significant Accounting Policies - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2015	Dec. 31, 2016
Accounting Policies [Abstract]
Maximum loss exposure	$ 160		$ 91
Fair value adjustment period	1 year
Maturity period for cash and cash equivalents	3 months
Threshold period of past due status of financing receivable	30 days
Period due to be considered for accrual of interest on loans Is discontinued	90 days
Accounts, Notes, Loans and Financing Receivable
Past due loans threshold period for write-off	120 days
Effect of change in method on allowance for credit losses		$ 10
Effect of change in method on allowance for credit losses on per share		$ 0.17
Rate lock period	60 days
Commercial Loans
Accounts, Notes, Loans and Financing Receivable
Past due loans threshold period for write-off	90 days
Residential and Consumer Portfolio
Accounts, Notes, Loans and Financing Receivable
Past due loans threshold period evaluation for charge-off	120 days

Summary of Significant Accoun54

Summary of Significant Accounting Policies - Useful Lives (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Other assets	$ 779,942	$ 618,262
Buildings | Minimum
Property, Plant and Equipment [Line Items]
Useful life of property and equipment	10 years
Buildings | Maximum
Property, Plant and Equipment [Line Items]
Useful life of property and equipment	40 years
Furniture, fixtures and equipment | Minimum
Property, Plant and Equipment [Line Items]
Useful life of property and equipment	3 years
Furniture, fixtures and equipment | Maximum
Property, Plant and Equipment [Line Items]
Useful life of property and equipment	20 years
Software
Property, Plant and Equipment [Line Items]
Other assets	$ 5,200	$ 5,600
Software | Weighted Average
Property, Plant and Equipment [Line Items]
Useful life of property and equipment	3 years
Customer relationship intangible asset | Maximum
Finite-Lived Intangible Assets, Net [Abstract]
Useful life of finite-lived intangible asset	10 years

Acquisition Activity - Addition

Acquisition Activity - Additional Information (Details) $ in Thousands	Jul. 31, 2017USD ($)bankshares	Dec. 31, 2017USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Sep. 30, 2017USD ($)
Business Acquisition [Line Items]
Goodwill		$ 1,188,902	$ 1,188,902	$ 726,856	$ 724,603
Increase (decrease) in goodwill due to adjustments			462,046
Amortization of acquisition intangibles			12,590	8,415	$ 7,811
Sabadell United
Business Acquisition [Line Items]
Loans acquired	$ 4,000,000	4,026,240	4,026,240
Interest-bearing deposits acquired	$ 4,400,000	4,383,049	4,383,049
Number of offices acquired | bank	25
Cash consideration	$ 809,159
Percentage of voting interests acquired	100.00%
Goodwill	$ 462,046	462,000	462,000			$ 431,800
Increase (decrease) in goodwill due to adjustments		30,200	462,000
Merger related costs			41,000
Sabadell United | Fair Value Adjustments
Business Acquisition [Line Items]
Amortization of premiums and accretion of discounts on acquired loans, securities, and deposits			20,300	38,800
Elimination of amortization of premiums and accretion of discounts on previously acquired loans, securities, FDIC indemnification asset, and deposits			1,300	4,100
Allowance for loan and lease losses acquired			6,400	5,900
Amortization of acquisition intangibles			5,900	$ 10,100
Sabadell United | Common Stock
Business Acquisition [Line Items]
Common stock issued (shares) | shares	2,610,304
Sabadell United | Core deposit intangible assets
Business Acquisition [Line Items]
Intangible assets acquired	$ 96,607	66,600	$ 66,600
Increase (decrease) in goodwill due to adjustments		30,000
Decrease in intangible assets recognized due to adjustments		$ (30,007)

Acquisition Activity - Consider

Acquisition Activity - Consideration (Details) - USD ($) $ in Thousands	Jul. 31, 2017	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Goodwill		$ 1,188,902		$ 726,856	$ 724,603
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	558,156
Goodwill	$ 462,046	$ 462,000	$ 431,800
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) - Sabadell United - USD ($) $ in Thousands	Dec. 31, 2017	Jul. 31, 2017
Assets
Cash and cash equivalents	$ 318,724
Investment securities	964,123
Loans	4,026,240	$ 4,000,000
Deferred tax asset, net	35,129
Other assets	89,745
Total assets acquired	5,500,561
Liabilities
Deposit liabilities	4,383,049	4,400,000
Short-term borrowings	520,539
Other liabilities	38,817
Total liabilities assumed	4,942,405
Core deposit intangible assets
Assets
Core deposit intangible assets	$ 66,600	$ 96,607

Acquisition Activity - Pro Form

Acquisition Activity - Pro Forma Information (Details) - Sabadell United - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Net interest income	$ 924,348	$ 842,945
Non-interest income	219,021	255,022
Net income	$ 174,246	$ 246,799

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	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities
Amortized cost	$ 4,647,931	$ 3,486,274
Gross unrealized gain	5,972	7,374
Gross unrealized losses	(63,841)	(47,551)
Estimated fair value	4,590,062	3,446,097
Schedule of Held-to-maturity Securities
Amortized cost	227,318	89,216
Gross unrealized gains	1,571	1,666
Gross unrealized losses	(925)	(950)
Estimated fair value	227,964	89,932
Fair value of securities held as collateral	2,100,000	1,500,000
U.S. Government-Sponsored Enterprise Obligations
Schedule of Available-for-sale Securities
Amortized cost	41,003	212,662
Gross unrealized gain	18	245
Gross unrealized losses	(406)	(549)
Estimated fair value	40,615	212,358
Obligations of State and Political Subdivisions
Schedule of Available-for-sale Securities
Amortized cost	271,451	286,458
Gross unrealized gain	4,246	1,948
Gross unrealized losses	(1,493)	(5,207)
Estimated fair value	274,204	283,199
Schedule of Held-to-maturity Securities
Amortized cost	206,736	64,726
Gross unrealized gains	1,530	1,609
Gross unrealized losses	(275)	(133)
Estimated fair value	207,991	66,202
Mortgage-Backed Securities
Schedule of Available-for-sale Securities
Amortized cost	4,221,472	2,888,180
Gross unrealized gain	1,461	4,820
Gross unrealized losses	(61,028)	(41,291)
Estimated fair value	4,161,905	2,851,709
Schedule of Held-to-maturity Securities
Amortized cost	20,582	24,490
Gross unrealized gains	41	57
Gross unrealized losses	(650)	(817)
Estimated fair value	19,973	23,730
Other Securities
Schedule of Available-for-sale Securities
Amortized cost	114,005	98,974
Gross unrealized gain	247	361
Gross unrealized losses	(914)	(504)
Estimated fair value	$ 113,338	$ 98,831

Investment Securities - Sched60

Investment Securities - Schedule of Securities with Gross Unrealized Losses Aggregated by Investment Category (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Gross Unrealized Losses
Less than twelve months	$ (27,757)	$ (44,874)
Over twelve months	(36,084)	(2,677)
Total	(63,841)	(47,551)
Estimated Fair Value
Less than twelve months	2,813,985	2,526,660
Over twelve months	1,304,515	102,762
Total	4,118,500	2,629,422
Gross Unrealized Losses
Less than twelve months	(265)	(463)
Over twelve months	(660)	(487)
Total	(925)	(950)
Estimated Fair Value
Less than twelve months	66,150	22,890
Over twelve months	22,300	10,960
Total	88,450	33,850
U.S. Government-Sponsored Enterprise Obligations
Gross Unrealized Losses
Less than twelve months	(254)	(549)
Over twelve months	(152)	0
Total	(406)	(549)
Estimated Fair Value
Less than twelve months	29,744	150,554
Over twelve months	9,848	0
Total	39,592	150,554
Obligations of State and Political Subdivisions
Gross Unrealized Losses
Less than twelve months	(326)	(5,207)
Over twelve months	(1,167)	0
Total	(1,493)	(5,207)
Estimated Fair Value
Less than twelve months	31,601	148,059
Over twelve months	68,609	0
Total	100,210	148,059
Mortgage-Backed Securities
Gross Unrealized Losses
Less than twelve months	(26,263)	(38,667)
Over twelve months	(34,765)	(2,624)
Total	(61,028)	(41,291)
Estimated Fair Value
Less than twelve months	2,677,338	2,191,563
Over twelve months	1,226,058	98,912
Total	3,903,396	2,290,475
Other Securities
Gross Unrealized Losses
Less than twelve months	(914)	(451)
Over twelve months	0	(53)
Total	(914)	(504)
Estimated Fair Value
Less than twelve months	75,302	36,484
Over twelve months	0	3,850
Total	75,302	40,334
Obligations of State and Political Subdivisions
Gross Unrealized Losses
Less than twelve months	(263)	(133)
Over twelve months	(12)	0
Total	(275)	(133)
Estimated Fair Value
Less than twelve months	65,817	10,602
Over twelve months	3,031	0
Total	68,848	10,602
Mortgage-Backed Securities
Gross Unrealized Losses
Less than twelve months	(2)	(330)
Over twelve months	(648)	(487)
Total	(650)	(817)
Estimated Fair Value
Less than twelve months	333	12,288
Over twelve months	19,269	10,960
Total	$ 19,602	$ 23,248

Investment Securities - Additio

Investment Securities - Additional Information on Securities in a Continuous Loss Position (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)Security	Dec. 31, 2016USD ($)Security
Schedule of Available-for-sale Securities
Number of debt securities with unrealized losses | Security	544	397
Debt securities with unrealized losses (percentage of amortized cost)	1.52%	1.79%
Number of securities | Security	210	31
Amortized cost basis	$ 1,363,559	$ 116,886
Unrealized loss	$ 36,744	$ 3,164
Fannie Mae, Freddie Mac, or Ginnie Mae
Schedule of Available-for-sale Securities
Number of securities | Security	181	28
Amortized cost basis	$ 1,280,739	$ 112,983
Unrealized loss	$ 35,412	$ 3,111
Political Subdivisions
Schedule of Available-for-sale Securities
Number of securities | Security	28	0
Amortized cost basis	$ 72,820	$ 0
Unrealized loss	$ 1,180	$ 0
Other
Schedule of Available-for-sale Securities
Number of securities | Security	1	3
Amortized cost basis	$ 10,000	$ 3,903
Unrealized loss	$ 152	$ 53

Investment Securities - Sched62

Investment Securities - Schedule of Amortized Cost and Estimated Fair Value of Investment Securities by Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Weighted Average Yield
Within one year or less	0.60%
One through five years	2.04%
After five through ten years	2.35%
Over ten years	2.32%
Weighted average yield	2.30%
Amortized Cost
Within one year or less	$ 37,907
One through five years	124,350
After five through ten years	867,799
Over ten years	3,617,875
Amortized cost	4,647,931
Estimated Fair Value
Within one year or less	37,563
One through five years	123,589
After five through ten years	863,931
Over ten years	3,564,979
Estimated fair value	$ 4,590,062	$ 3,446,097
Weighted Average Yield
Within one year or less	2.79%
One through five years	3.01%
After five through ten years	2.81%
Over ten years	2.55%
Weighted average yield	2.61%
Amortized Cost
Within one year or less	$ 1,119
One through five years	8,718
After five through ten years	34,970
Over ten years	182,511
Amortized cost	227,318	89,216
Estimated Fair Value
Within one year or less	1,125
One through five years	8,756
After five through ten years	35,418
Over ten years	182,665
Estimated fair value	$ 227,964	$ 89,932

Investment Securities - Sched63

Investment Securities - Schedule of Realized Gains and Losses from Sale of Securities Classified as Available for Sale (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Realized gains	$ 1,651	$ 2,949	$ 1,834
Realized losses	(1,799)	(948)	(259)
Net realized gains (losses)	$ (148)	$ 2,001	$ 1,575

Investment Securities - Sched64

Investment Securities - Schedule of Securities in Other Assets on Company's Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Federal Home Loan Bank (FHLB) stock	$ 95,171	$ 42,326
Federal Reserve Bank Stock	79,191	48,584
Other Investments	3,008	2,808
Marketable Securities, Equity Securities	$ 177,370	$ 93,718

Loans - Schedule of Non-Covered

Loans - Schedule of Non-Covered Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable
Total loans, net of unearned income	$ 20,078,181	$ 15,064,971
Commercial Loans
Accounts, Notes, Loans and Financing Receivable
Total loans, net of unearned income	14,073,297	10,906,581
Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Total loans, net of unearned income	1,240,396	802,242
Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Total loans, net of unearned income	2,529,885	2,277,749
Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Total loans, net of unearned income	5,167,949	3,766,558
Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Total loans, net of unearned income	5,135,067	4,060,032
Residential Mortgage
Accounts, Notes, Loans and Financing Receivable
Total loans, net of unearned income	3,056,352	1,267,400
Consumer and Other Loans
Accounts, Notes, Loans and Financing Receivable
Total loans, net of unearned income	2,948,532	2,890,990
Consumer and Other Loans | Home Equity
Accounts, Notes, Loans and Financing Receivable
Total loans, net of unearned income	2,292,275	2,155,926
Consumer and Other Loans | Consumer - Indirect automobile
Accounts, Notes, Loans and Financing Receivable
Total loans, net of unearned income	62,693	131,052
Consumer and Other Loans | Other
Accounts, Notes, Loans and Financing Receivable
Total loans, net of unearned income	$ 497,196	$ 521,020

Loans (Detail)

Loans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jul. 31, 2017
Accounts, Notes, Loans and Financing Receivable
Net deferred loan origination fees	$ 29,300	$ 22,600
Net discount	159,300	89,500
Deposit liabilities reclassified as loans receivable	7,400	4,200
Loans with carrying value pledged to secure public deposits and other borrowings	6,600,000	4,500,000
Loans acquired with no evidence of deteriorated credit quality	15,000	12,700
Acquired Loans
Accounts, Notes, Loans and Financing Receivable
Net discount	94,700	12,900
Sabadell United
Accounts, Notes, Loans and Financing Receivable
Loans acquired	4,026,240			$ 4,000,000
Covered loans acquired	158,600
Loans acquired with no evidence of deteriorated credit quality	3,960,308
Loans acquired with deteriorated credit quality	65,932
Sabadell United | Foreign
Accounts, Notes, Loans and Financing Receivable
Covered loans acquired	325,500
Troubled Debt Restructurings [Member]
Accounts, Notes, Loans and Financing Receivable
TDRs during period	70,459	222,436	$ 57,041
TDRs during period on accrual status	46,300	85,900	34,500
TDRs during period on non-accrual status	$ 24,200	$ 136,500	$ 22,500

Loans - Schedule of Aging of Lo

Loans - Schedule of Aging of Loans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable
Accruing	$ 68,617	$ 30,221
Non-accrual Loans	145,388	228,502
Acquired Impaired Loans	238,127	302,780	$ 62,848
Total Loans	$ 20,078,181	15,064,971
Past due loans threshold period	120 days
Commercial Loans
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	$ 194,201	282,001	70
Total Loans	$ 14,073,297	10,906,581
Past due loans threshold period	90 days
Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Accruing	$ 727	0
Non-accrual Loans	2,635	1,946
Total Loans	1,240,396	802,242
Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	2,364	3,164
Non-accrual Loans	24,457	25,950
Total Loans	2,529,885	2,277,749
Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	9,378	1,379
Non-accrual Loans	6,811	9,651
Total Loans	5,167,949	3,766,558
Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	11,660	4,991
Non-accrual Loans	77,823	164,934
Total Loans	5,135,067	4,060,032
Residential Mortgage
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	6,749	4,312	$ 5,066
Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Current	2,962,043	1,229,761
Accruing	23,536	6,252
Non-accrual Loans	17,387	13,733
Total Loans	3,056,352	1,267,400
Consumer and Other Loans
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	37,177	16,467
Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Current	2,250,205	2,129,110
Accruing	14,640	7,929
Non-accrual Loans	12,365	9,374
Total Loans	2,292,275	2,155,926
Consumer and Other Loans | Consumer - Indirect automobile
Accounts, Notes, Loans and Financing Receivable
Current	59,836	127,047
Accruing	1,973	2,956
Non-accrual Loans	884	1,038
Total Loans	62,693	131,052
Consumer and Other Loans | Consumer - Credit card
Accounts, Notes, Loans and Financing Receivable
Current	95,263	82,052
Accruing	514	298
Non-accrual Loans	590	624
Total Loans	96,368	82,992
Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Current	490,399	515,857
Accruing	3,825	3,252
Non-accrual Loans	2,436	1,252
Total Loans	497,196	521,020
Current or Less Than 30 days past due
Accounts, Notes, Loans and Financing Receivable
Current	19,382,621	14,276,062
Current or Less Than 30 days past due | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Current	1,197,766	767,305
Current or Less Than 30 days past due | Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Current	2,398,487	2,123,014
Current or Less Than 30 days past due | Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Current	5,066,084	3,633,472
Current or Less Than 30 days past due | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Current	5,014,438	3,857,375
Current or Less Than 30 days past due | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Current	2,877,048	1,124,463
Current or Less Than 30 days past due | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Current	2,186,554	2,050,204
Current or Less Than 30 days past due | Consumer and Other Loans | Consumer - Indirect automobile
Accounts, Notes, Loans and Financing Receivable
Current	59,830	127,054
Current or Less Than 30 days past due | Consumer and Other Loans | Consumer - Credit card
Accounts, Notes, Loans and Financing Receivable
Current	95,264	82,070
Current or Less Than 30 days past due | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Current	487,150	511,105
30-59 days
Accounts, Notes, Loans and Financing Receivable
Accruing	36,818	20,582
30-59 days | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Accruing	269	0
30-59 days | Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	1,631	1,452
30-59 days | Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	2,086	1,123
30-59 days | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	5,788	4,071
30-59 days | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	10,083	2,334
30-59 days | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Accruing	11,675	6,314
30-59 days | Consumer and Other Loans | Consumer - Indirect automobile
Accounts, Notes, Loans and Financing Receivable
Accruing	1,796	2,551
30-59 days | Consumer and Other Loans | Consumer - Credit card
Accounts, Notes, Loans and Financing Receivable
Accruing	140	199
30-59 days | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	3,350	2,538
60-89 days
Accounts, Notes, Loans and Financing Receivable
Accruing	24,899	8,254
60-89 days | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
60-89 days | Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	659	1,712
60-89 days | Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	6,405	224
60-89 days | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	5,726	920
60-89 days | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	8,136	2,565
60-89 days | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Accruing	2,947	1,615
60-89 days | Consumer and Other Loans | Consumer - Indirect automobile
Accounts, Notes, Loans and Financing Receivable
Accruing	177	405
60-89 days | Consumer and Other Loans | Consumer - Credit card
Accounts, Notes, Loans and Financing Receivable
Accruing	374	99
60-89 days | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	475	714
Greater than 90 days
Accounts, Notes, Loans and Financing Receivable
Accruing	6,900	1,385
Greater than 90 days | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Accruing	458	0
Greater than 90 days | Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	74	0
Greater than 90 days | Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	887	32
Greater than 90 days | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	146	0
Greater than 90 days | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	5,317	1,353
Greater than 90 days | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Accruing	18	0
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	481,555	530,186
Acquired Loans | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	39,268	32,991
Acquired Loans | Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	104,577	125,621
Acquired Loans | Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	85,676	122,056
Acquired Loans | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	31,146	32,732
Acquired Loans | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	138,381	122,952
Acquired Loans | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	78,716	88,419
Acquired Loans | Consumer and Other Loans | Consumer - Indirect automobile
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	6	4
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	$ 3,785	$ 5,411

Loans - Schedule of Carrying Am

Loans - Schedule of Carrying Amount of Loans Acquired (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Jul. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable
Expected losses and foregone interest	$ (154,099)		$ (155,960)	$ (152,523)
Loans acquired with no evidence of deteriorated credit quality	15,000		12,700
Related allowance	2,856		$ 24,293
Sabadell United
Accounts, Notes, Loans and Financing Receivable
Loans acquired	4,026,240	$ 4,000,000
Covered loans acquired	158,600
Contractually required principal and interest at acquisition	4,914,185
Expected losses and foregone interest	(54,226)
Cash flows expected to be collected at acquisition	4,859,959
Loans acquired with no evidence of deteriorated credit quality	3,960,308
Impaired Financing Receivable, with Related Allowance, Recorded Investment	111,114
Related allowance	12,245
Impaired Financing Receivable, Expected Cash Flow	98,869
Accretable yield	32,937
Loans acquired with deteriorated credit quality	$ 65,932

Loans - Summary of Changes in A

Loans - Summary of Changes in Accretable Yields of Acquired Loans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	$ 175,054	$ 227,502	$ 287,651
Additions	32,937	0	6,823
Transfers from non-accretable difference to accretable yield	4,912	5,490	9,916
Accretion	(56,337)	(68,211)	(80,479)
Changes in expected cash flows not affecting non-accretable differences	(3,943)	10,273	3,591
Balance at end of period	$ 152,623	$ 175,054	$ 227,502

Loans - Schedule of Modified TD

Loans - Schedule of Modified TDRs (Detail) - Troubled Debt Restructurings [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Modifications
TDRs during period on accrual status	$ 46,300	$ 85,900	$ 34,500
TDRs during period on non-accrual status	24,200	136,500	22,500
Extended maturities	26,561	75,315	15,594
Interest rate adjustment	24	193	0
Maturity and interest rate adjustment	4,932	2,470	23,374
Movement to or extension of interest-rate only payments	4,161	27,931	241
Forbearance	7,226	76,819	122
Other concession(s)	27,555	39,708	17,710
TDRs during period	$ 70,459	$ 222,436	$ 57,041

Loans - Schedule of Subsequentl

Loans - Schedule of Subsequently Defaulted TDRs (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)SecurityLoan	Dec. 31, 2016USD ($)SecurityLoan	Dec. 31, 2015USD ($)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	359	523	113
Pre-modification Outstanding Recorded Investment	$ 70,233	$ 223,640	$ 62,631
Post-modification Outstanding Recorded Investment	$ 70,459	$ 222,436	$ 57,041
Number of loans | SecurityLoan	163	124	62
Recorded investment	$ 28,734	$ 21,225	$ 35,793
Non-Covered TDRs | Commercial Loans | Commercial real estate - Construction | TDRs Occurring during the Period
Accounts, Notes, Loans and Financing Receivable
Number of Loans | SecurityLoan	4	3	0
Pre-modification Outstanding Recorded Investment	$ 9,404	$ 3,024	$ 0
Post-modification Outstanding Recorded Investment	$ 9,628	$ 3,035	$ 0
Number of loans | SecurityLoan	2	1	0
Recorded investment	$ 3,572	$ 116	$ 0
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	11	20	6
Pre-modification Outstanding Recorded Investment	$ 5,779	$ 18,223	$ 15,403
Post-modification Outstanding Recorded Investment	$ 5,706	$ 18,239	$ 13,889
Number of loans | SecurityLoan	6	3	2
Recorded investment	$ 4,668	$ 3,473	$ 10,956
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	19	25	5
Pre-modification Outstanding Recorded Investment	$ 11,974	$ 16,644	$ 11,361
Post-modification Outstanding Recorded Investment	$ 13,738	$ 10,093	$ 11,361
Number of loans | SecurityLoan	13	6	4
Recorded investment	$ 8,060	$ 201	$ 11,119
Non-Covered TDRs | Commercial Loans | Commercial and industrial | TDRs Occurring during the Period
Accounts, Notes, Loans and Financing Receivable
Number of Loans | SecurityLoan	57	79	28
Pre-modification Outstanding Recorded Investment	$ 21,651	$ 163,265	$ 31,030
Post-modification Outstanding Recorded Investment	$ 20,883	$ 169,893	$ 27,598
Number of loans | SecurityLoan	32	22	21
Recorded investment	$ 6,550	$ 14,707	$ 12,090
Non-Covered TDRs | Residential Mortgage | Residential mortgage | TDRs Occurring during the Period
Accounts, Notes, Loans and Financing Receivable
Number of Loans | SecurityLoan	24	43	1
Pre-modification Outstanding Recorded Investment	$ 1,897	$ 5,141	$ 70
Post-modification Outstanding Recorded Investment	$ 1,771	$ 4,946	$ 68
Number of loans | SecurityLoan	16	8	0
Recorded investment	$ 1,218	$ 405	$ 0
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	123	158	50
Pre-modification Outstanding Recorded Investment	$ 16,346	$ 13,273	$ 4,440
Post-modification Outstanding Recorded Investment	$ 15,862	$ 12,568	$ 3,865
Number of loans | SecurityLoan	32	25	20
Recorded investment	$ 3,285	$ 1,379	$ 1,547
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	43	79	6
Pre-modification Outstanding Recorded Investment	$ 511	$ 983	$ 79
Post-modification Outstanding Recorded Investment	$ 371	$ 792	$ 79
Number of loans | SecurityLoan	33	37	6
Recorded investment	$ 323	$ 338	$ 79
Non-Covered TDRs | Consumer and Other Loans | Consumer - Other | TDRs Occurring during the Period
Accounts, Notes, Loans and Financing Receivable
Number of Loans | SecurityLoan	78	116	17
Pre-modification Outstanding Recorded Investment	$ 2,671	$ 3,087	$ 248
Post-modification Outstanding Recorded Investment	$ 2,500	$ 2,870	$ 181
Number of loans | SecurityLoan	29	22	9
Recorded investment	$ 1,058	$ 606	$ 2

Allowance for Credit Losses a72

Allowance for Credit Losses and Credit Quality - Schedule of Allowance for Loan Losses for Covered and Non-Covered Loan Portfolios (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for credit losses
Allowance for loan losses at beginning of period	$ 144,719	$ 138,378	$ 130,131
Provision for loan losses before benefit attributable to FDIC loss share agreements	51,111	42,927	29,548
Adjustment attributable to FDIC loss share arrangements	0	(1,497)	(1,360)
Net provision for loan losses	51,111	44,424	30,908
Transfer of balance to OREO and other	934	(2,781)	(10,419)
Loans charged-off	(62,466)	(39,839)	(17,301)
Recoveries	6,593	6,034	6,419
Allowance for loan losses at end of period	140,891	144,719	138,378
Reserve For Unfunded Commitments
Reserve for unfunded commitments at beginning of period	11,241	14,145	11,801
Balance created in acquisition accounting	1,370	0	0
Provision for (Reversal of) unfunded lending commitments	597	(2,904)	2,344
Reserve for unfunded commitments at end of period	13,208	11,241	14,145
Allowance for credit losses at end of period	$ 154,099	$ 155,960	$ 152,523

Allowance for Credit Losses a73

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	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses
Allowance for loan losses at beginning of period	$ 144,719	$ 138,378	$ 130,131
Provision for (Reversal of) loan losses	51,111	44,424	30,908
Decrease in FDIC loss share receivable		(1,497)	(1,360)
Transfer of balance to OREO and other	934	(2,781)	(10,419)
Loans charged-off	(62,466)	(39,839)	(17,301)
Recoveries	6,593	6,034	6,419
Allowance for loan losses at end of period	140,891	144,719	138,378
Financing Receivable, Reserve For Unfunded Commitments
Reserve for unfunded commitments at beginning of period	11,241	14,145	11,801
Balance created in acquisition accounting	1,370	0	0
Provision for (Reversal of) unfunded commitments	597	(2,904)	2,344
Reserve for unfunded commitments at end of period	13,208	11,241	14,145
Allowance on loans individually evaluated for impairment	17,352	24,293	4,079
Allowance on loans collectively evaluated for impairment	89,655	84,214	90,255
Allowance on loans acquired with deteriorated credit quality	154,099	155,960	152,523
Loans, net of unearned income:
Loans, net of unearned income	20,078,181	15,064,971	14,327,428
Balance at end of period individually evaluated for impairment	238,127	302,780	67,984
Balance at end of period collectively evaluated for impairment	19,358,499	14,232,005	13,534,725
Commercial Loans | Real Estate
Financing Receivable, Allowance for Credit Losses
Allowance for loan losses at beginning of period	49,231	51,372	57,093
Provision for (Reversal of) loan losses	10,433	1,958	1,059
Decrease in FDIC loss share receivable		(34)	757
Transfer of balance to OREO and other	853	(868)	(6,849)
Loans charged-off	(7,433)	(4,338)	(2,806)
Recoveries	1,117	1,141	2,118
Allowance for loan losses at end of period	54,201	49,231	51,372
Financing Receivable, Reserve For Unfunded Commitments
Reserve for unfunded commitments at beginning of period	3,207	4,167	3,439
Balance created in acquisition accounting	253
Provision for (Reversal of) unfunded commitments	1,071	(960)	728
Reserve for unfunded commitments at end of period	4,531	3,207	4,167
Allowance on loans individually evaluated for impairment	1,588	1,378	1,287
Allowance on loans collectively evaluated for impairment	30,360	25,248	24,186
Loans, net of unearned income:
Loans, net of unearned income	8,938,230	6,846,549	6,125,927
Balance at end of period individually evaluated for impairment	91,785	61,006	29,578
Balance at end of period collectively evaluated for impairment	8,616,924	6,504,875	5,685,272
Commercial Loans | Commercial and industrial
Financing Receivable, Allowance for Credit Losses
Allowance for loan losses at beginning of period	60,939	49,355	33,328
Provision for (Reversal of) loan losses	31,891	32,296	17,423
Decrease in FDIC loss share receivable		(50)	(49)
Transfer of balance to OREO and other	(68)	(519)	(275)
Loans charged-off	(40,015)	(21,645)	(1,279)
Recoveries	1,169	1,502	207
Allowance for loan losses at end of period	53,916	60,939	49,355
Financing Receivable, Reserve For Unfunded Commitments
Reserve for unfunded commitments at beginning of period	4,537	6,106	5,260
Balance created in acquisition accounting	783
Provision for (Reversal of) unfunded commitments	(11)	(1,569)	846
Reserve for unfunded commitments at end of period	5,309	4,537	6,106
Allowance on loans individually evaluated for impairment	12,736	21,413	2,394
Allowance on loans collectively evaluated for impairment	38,944	37,206	44,080
Loans, net of unearned income:
Loans, net of unearned income	5,135,067	4,060,032	4,072,928
Balance at end of period individually evaluated for impairment	102,416	220,995	33,270
Balance at end of period collectively evaluated for impairment	5,001,505	3,806,305	3,987,665
Residential Mortgage
Financing Receivable, Allowance for Credit Losses
Allowance for loan losses at beginning of period	11,249	11,789	9,162
Provision for (Reversal of) loan losses	(2,206)	824	3,620
Decrease in FDIC loss share receivable		(1,090)	(235)
Transfer of balance to OREO and other	2	(141)	(491)
Loans charged-off	(365)	(313)	(362)
Recoveries	437	180	95
Allowance for loan losses at end of period	9,117	11,249	11,789
Financing Receivable, Reserve For Unfunded Commitments
Reserve for unfunded commitments at beginning of period	657	830	168
Balance created in acquisition accounting	327
Provision for (Reversal of) unfunded commitments	(429)	(173)	662
Reserve for unfunded commitments at end of period	555	657	830
Allowance on loans individually evaluated for impairment	172	144	1
Allowance on loans collectively evaluated for impairment	3,141	4,223	4,150
Loans, net of unearned income:
Loans, net of unearned income	3,056,352	1,267,400	1,195,319
Balance at end of period individually evaluated for impairment	6,749	4,312	70
Balance at end of period collectively evaluated for impairment	2,911,222	1,140,136	1,054,669
Consumer and Other Loans
Financing Receivable, Allowance for Credit Losses
Allowance for loan losses at beginning of period	23,300	25,862	30,548
Provision for (Reversal of) loan losses	10,993	9,346	8,806
Decrease in FDIC loss share receivable		(323)	(1,833)
Transfer of balance to OREO and other	147	(1,253)	(2,804)
Loans charged-off	(14,653)	(13,543)	(12,854)
Recoveries	3,870	3,211	3,999
Allowance for loan losses at end of period	23,657	23,300	25,862
Financing Receivable, Reserve For Unfunded Commitments
Reserve for unfunded commitments at beginning of period	2,840	3,042	2,934
Balance created in acquisition accounting	7
Provision for (Reversal of) unfunded commitments	(34)	(202)	108
Reserve for unfunded commitments at end of period	2,813	2,840	3,042
Allowance on loans individually evaluated for impairment	2,856	1,358	397
Allowance on loans collectively evaluated for impairment	17,210	17,537	17,839
Loans, net of unearned income:
Loans, net of unearned income	2,948,532	2,890,990	2,933,254
Balance at end of period individually evaluated for impairment	37,177	16,467	5,066
Balance at end of period collectively evaluated for impairment	2,828,848	2,780,689	2,807,119
Receivables Acquired with Deteriorated Credit Quality
Financing Receivable, Reserve For Unfunded Commitments
Allowance on loans acquired with deteriorated credit quality	33,884	36,212	44,044
Loans, net of unearned income:
Balance at end of period acquired with deteriorated credit quality	481,555	530,186	724,719
Receivables Acquired with Deteriorated Credit Quality | Commercial Loans | Real Estate
Financing Receivable, Reserve For Unfunded Commitments
Allowance on loans acquired with deteriorated credit quality	22,253	22,605	25,899
Loans, net of unearned income:
Balance at end of period acquired with deteriorated credit quality	229,521	280,668	411,077
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	2,236	2,320	2,881
Loans, net of unearned income:
Balance at end of period acquired with deteriorated credit quality	31,146	32,732	51,993
Receivables Acquired with Deteriorated Credit Quality | Residential Mortgage
Financing Receivable, Reserve For Unfunded Commitments
Allowance on loans acquired with deteriorated credit quality	5,804	6,882	7,638
Loans, net of unearned income:
Balance at end of period acquired with deteriorated credit quality	138,381	122,952	140,580
Receivables Acquired with Deteriorated Credit Quality | Consumer and Other Loans
Financing Receivable, Reserve For Unfunded Commitments
Allowance on loans acquired with deteriorated credit quality	3,591	4,405	7,626
Loans, net of unearned income:
Balance at end of period acquired with deteriorated credit quality	$ 82,507	$ 93,834	$ 121,069

Allowance for Credit Losses a74

Allowance for Credit Losses and Credit Quality - Investment in Legacy and Acquired Loans by Credit Quality Indicator (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses
Total Loans	$ 20,078,181	$ 15,064,971
Commercial Loans
Financing Receivable, Allowance for Credit Losses
Total Loans	14,073,297	10,906,581
Commercial Loans | Commercial real estate - Construction
Financing Receivable, Allowance for Credit Losses
Total Loans	1,240,396	802,242
Commercial Loans | Commercial real estate - owner-occupied
Financing Receivable, Allowance for Credit Losses
Total Loans	2,529,885	2,277,749
Commercial Loans | Commercial real estate - non-owner-occupied
Financing Receivable, Allowance for Credit Losses
Total Loans	5,167,949	3,766,558
Commercial Loans | Commercial and industrial
Financing Receivable, Allowance for Credit Losses
Total Loans	5,135,067	4,060,032
Residential and Consumer Portfolio
Financing Receivable, Allowance for Credit Losses
Current	5,857,746	4,083,827
30 or more days past due	147,138	74,563
Total Loans	6,004,884	4,158,390
Residential Mortgage | Residential mortgage
Financing Receivable, Allowance for Credit Losses
Current	2,962,043	1,229,761
30 or more days past due	94,309	37,639
Total Loans	3,056,352	1,267,400
Consumer and Other Loans | Consumer - Home equity
Financing Receivable, Allowance for Credit Losses
Current	2,250,205	2,129,110
30 or more days past due	42,070	26,816
Total Loans	2,292,275	2,155,926
Consumer and Other Loans | Consumer - Indirect Automobile
Financing Receivable, Allowance for Credit Losses
Current	59,836	127,047
30 or more days past due	2,857	4,005
Total Loans	62,693	131,052
Consumer and Other Loans | Consumer - Credit card
Financing Receivable, Allowance for Credit Losses
Current	95,263	82,052
30 or more days past due	1,105	940
Total Loans	96,368	82,992
Consumer and Other Loans | Consumer - Other
Financing Receivable, Allowance for Credit Losses
Current	490,399	515,857
30 or more days past due	6,797	5,163
Total Loans	497,196	521,020
Pass | Commercial Loans
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	13,564,833	10,303,107
Pass | Commercial Loans | Commercial real estate - Construction
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	1,189,490	775,387
Pass | Commercial Loans | Commercial real estate - owner-occupied
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	2,388,715	2,180,201
Pass | Commercial Loans | Commercial real estate - non-owner-occupied
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	5,104,074	3,687,439
Pass | Commercial Loans | Commercial and industrial
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	4,882,554	3,660,080
Special Mention | Commercial Loans
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	209,925	159,219
Special Mention | Commercial Loans | Commercial real estate - Construction
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	20,351	2,694
Special Mention | Commercial Loans | Commercial real estate - owner-occupied
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	82,114	29,039
Special Mention | Commercial Loans | Commercial real estate - non-owner-occupied
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	19,311	23,004
Special Mention | Commercial Loans | Commercial and industrial
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	88,149	104,482
Substandard | Commercial Loans
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	258,794	410,971
Substandard | Commercial Loans | Commercial real estate - Construction
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	30,541	22,026
Substandard | Commercial Loans | Commercial real estate - owner-occupied
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	56,590	66,816
Substandard | Commercial Loans | Commercial real estate - non-owner-occupied
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	42,702	55,576
Substandard | Commercial Loans | Commercial and industrial
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	128,961	266,553
Doubtful | Commercial Loans
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	39,627	33,261
Doubtful | Commercial Loans | Commercial real estate - Construction
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	14	2,135
Doubtful | Commercial Loans | Commercial real estate - owner-occupied
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	2,466	1,670
Doubtful | Commercial Loans | Commercial real estate - non-owner-occupied
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	1,744	539
Doubtful | Commercial Loans | Commercial and industrial
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	35,403	28,917
Loss | Commercial Loans
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	118	23
Loss | Commercial Loans | Commercial real estate - Construction
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	0	0
Loss | Commercial Loans | Commercial real estate - owner-occupied
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	0	23
Loss | Commercial Loans | Commercial real estate - non-owner-occupied
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	118	0
Loss | Commercial Loans | Commercial and industrial
Financing Receivable, Allowance for Credit Losses
Gross loans and leases receivable	$ 0	$ 0

Allowance for Credit Losses a75

Allowance for Credit Losses and Credit Quality - Schedule of Investment in Legacy Impaired Loans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Impaired
Unpaid Principal Balance	$ 283,629	$ 316,678	$ 64,016
Recorded Investment	238,127	302,780	62,848
Related Allowance	(2,856)	(24,293)
Average Recorded Investment	273,254	272,364	68,750
Interest Income Recognized	8,368	9,191	2,830
Commercial Loans
Financing Receivable, Impaired
Unpaid Principal Balance	237,922	294,649	70
Recorded Investment	194,201	282,001	70
Related Allowance	(17,352)	(22,791)	(3,681)
Average Recorded Investment	232,590	255,325	70
Interest Income Recognized	6,595	8,444	5
Residential Mortgage
Financing Receivable, Impaired
Unpaid Principal Balance	7,183	4,628	5,243
Recorded Investment	6,749	4,312	5,066
Related Allowance	(14,324)	(144)	(1)
Average Recorded Investment	6,905	4,377	3,541
Interest Income Recognized	265	161	103
Consumer and Other Loans
Financing Receivable, Impaired
Unpaid Principal Balance	38,524	17,401
Recorded Investment	37,177	16,467
Related Allowance	(172)	(1,358)	(397)
Average Recorded Investment	33,759	12,662
Interest Income Recognized	1,508	586
With No Related Allowance Recorded | Commercial Loans | Commercial real estate - Construction
Financing Receivable, Impaired
Unpaid Principal Balance	13,763	38	54
Recorded Investment	13,013	38	51
Average Recorded Investment	9,104	28	55
Interest Income Recognized	441	0	1
With No Related Allowance Recorded | Commercial Loans | Commercial real estate - owner-occupied
Financing Receivable, Impaired
Unpaid Principal Balance	50,867	25,180	3,630
Recorded Investment	44,482	25,074	3,495
Average Recorded Investment	53,282	25,890	2,928
Interest Income Recognized	1,389	647	106
With No Related Allowance Recorded | Commercial Loans | Commercial real estate - non-owner-occupied
Financing Receivable, Impaired
Unpaid Principal Balance	15,370	15,654	13,318
Recorded Investment	14,975	14,794	12,600
Average Recorded Investment	15,127	19,587	12,881
Interest Income Recognized	692	879	209
With No Related Allowance Recorded | Commercial Loans | Commercial and industrial
Financing Receivable, Impaired
Unpaid Principal Balance	103,013	148,311	14,571
Recorded Investment	70,254	138,202	14,340
Average Recorded Investment	92,312	111,261	18,839
Interest Income Recognized	2,279	3,418	1,148
With No Related Allowance Recorded | Commercial Loans | Residential mortgage
Financing Receivable, Impaired
Unpaid Principal Balance	2,004
Recorded Investment	2,001
Average Recorded Investment	2,044
Interest Income Recognized	85
With No Related Allowance Recorded | Consumer and Other Loans | Consumer - Home equity
Financing Receivable, Impaired
Unpaid Principal Balance	5,906	0	730
Recorded Investment	5,634	0	730
Average Recorded Investment	5,747	0	533
Interest Income Recognized	231	0	22
With No Related Allowance Recorded | Consumer and Other Loans | Consumer - Other
Financing Receivable, Impaired
Unpaid Principal Balance	75	0	66
Recorded Investment	75	0	66
Average Recorded Investment	11	0	66
Interest Income Recognized	1	0	5
With An Allowance Recorded | Commercial Loans | Commercial real estate - Construction
Financing Receivable, Impaired
Unpaid Principal Balance	238	1,946	3
Recorded Investment	156	1,946	3
Related Allowance	(19)	(649)	(2)
Average Recorded Investment	197	1,839	57
Interest Income Recognized	6	54	1
With An Allowance Recorded | Commercial Loans | Commercial real estate - owner-occupied
Financing Receivable, Impaired
Unpaid Principal Balance	13,314	17,580	12,744
Recorded Investment	13,287	17,429	12,691
Related Allowance	(949)	(640)	(1,244)
Average Recorded Investment	13,498	16,668	12,908
Interest Income Recognized	414	493	527
With An Allowance Recorded | Commercial Loans | Commercial real estate - non-owner-occupied
Financing Receivable, Impaired
Unpaid Principal Balance	6,051	1,743	738
Recorded Investment	5,872	1,725	738
Related Allowance	(620)	(89)	(41)
Average Recorded Investment	6,196	1,782	1,027
Interest Income Recognized	154	95	62
With An Allowance Recorded | Commercial Loans | Commercial and industrial
Financing Receivable, Impaired
Unpaid Principal Balance	35,306	84,197	18,958
Recorded Investment	32,162	82,793	18,930
Related Allowance	(12,736)	(21,413)	(2,394)
Average Recorded Investment	42,874	78,270	20,055
Interest Income Recognized	1,220	2,858	776
With An Allowance Recorded | Residential Mortgage | Residential mortgage
Financing Receivable, Impaired
Unpaid Principal Balance	5,179	4,628	70
Recorded Investment	4,748	4,312	70
Related Allowance	(172)	(144)	(1)
Average Recorded Investment	4,861	4,377	70
Interest Income Recognized	180	161	5
With An Allowance Recorded | Consumer and Other Loans | Consumer - Home equity
Financing Receivable, Impaired
Unpaid Principal Balance	27,189	13,916	3,859
Recorded Investment	26,575	13,267	3,683
Related Allowance	(2,358)	(993)	(338)
Average Recorded Investment	23,546	10,237	2,454
Interest Income Recognized	1,007	435	73
With An Allowance Recorded | Consumer and Other Loans | Consumer - Indirect Automobile
Financing Receivable, Impaired
Unpaid Principal Balance	1,034	1,037	588
Recorded Investment	679	758	587
Related Allowance	(79)	(114)	(59)
Average Recorded Investment	873	956	488
Interest Income Recognized	38	49	3
With An Allowance Recorded | Consumer and Other Loans | Consumer - Other
Financing Receivable, Impaired
Unpaid Principal Balance	4,320	2,448	69,329
Recorded Investment	4,214	2,442	67,984
Related Allowance	(419)	(251)	(4,079)
Average Recorded Investment	3,582	1,469	72,361
Interest Income Recognized	$ 231	$ 102	$ 2,938

Transfers and Servicing of Fi76

Transfers and Servicing of Financial Assets (Including Mortgage Banking Activity) (Detail) - USD ($) $ in Billions	Dec. 31, 2017	Dec. 31, 2016
Transfers and Servicing [Abstract]
Unpaid principal balances of loans serviced	$ 1.3	$ 1

Transfers and Servicing of Fi77

Transfers and Servicing of Financial Assets (including Mortgage Banking Activity) - Changes in Carrying Amount of Mortgage Loans Held-for-sale (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Loans Receivable Held-for-sale, Net, Reconciliation to Cash Flow [Roll Forward]
Balance at beginning of period	$ 157,041	$ 166,247	$ 140,072
Originations and purchases	1,844,358	2,460,033	2,464,588
Sales, net of gains	(1,859,565)	(2,451,459)	(2,432,979)
Mortgage loans transferred to held for investment	(6,918)	(14,017)	0
Other	0	(3,763)	(5,434)
Balance at end of period	$ 134,916	$ 157,041	$ 166,247

Transfers and Servicing of Fi78

Transfers and Servicing of Financial Assets (including Mortgage Banking Activity) - Components of Mortgage Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Participating Mortgage Loans
Gains on sales	$ 62,438	$ 74,486	$ 83,957
Total mortgage income	63,570	83,853	80,662
Mortgage income
Participating Mortgage Loans
Mortgage loans held for sale and derivatives	(7,047)	1,361	2,216
Derivative settlements, net	1,229	(6,640)	(5,017)
Gains on sales	68,255	87,925	82,671
Servicing and other income, net	1,133	1,207	792
Total mortgage income	$ 63,570	$ 83,853	$ 80,662

- Schedule of Mortgage Servicin

- Schedule of Mortgage Servicing Rights at Carrying Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Acquired Finite-Lived Intangible Assets
Gross Carrying Amount	$ 129,163	$ 75,412
Accumulated Amortization	(53,006)	(53,251)
Net Carrying Amount	76,157	22,161
Mortgage servicing rights
Acquired Finite-Lived Intangible Assets
Gross Carrying Amount	9,588	7,202
Accumulated Amortization	(3,931)	(3,144)
Net Carrying Amount	$ 5,657	$ 4,058

Premises and Equipment - Schedu

Premises and Equipment - Schedule of Premises and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Land	$ 89,137	$ 84,616
Buildings	261,994	239,626
Furniture, fixtures and equipment	129,866	115,775
Total premises and equipment	480,997	440,017
Accumulated depreciation	(149,584)	(133,644)
Total premises and equipment, net	$ 331,413	$ 306,373

Premises and Equipment (Detail)

Premises and Equipment (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 21	$ 20.8	$ 22.2
Maximum lease term	5 years
Total lease income	$ 2.4	2.8	2.4
Rent expense	$ 19.1	16.6	$ 15.4
Minimum
Property, Plant and Equipment [Line Items]
Operating lease term (in years)	1 year
Maximum
Property, Plant and Equipment [Line Items]
Operating lease term (in years)	50 years
Buildings
Property, Plant and Equipment [Line Items]
Total allocated cost of portion of buildings held for lease	$ 6.9	8.7
Accumulated depreciation	$ 2.5	$ 3.1

Premises and Equipment - Sche82

Premises and Equipment - Schedule of Minimum Future Annual Rent Commitments (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Property, Plant and Equipment [Abstract]
2,018	$ 20,697
2,019	19,466
2,020	17,733
2,021	14,437
2,022	11,393
2023 and thereafter	36,744
Total	$ 120,470

Goodwill and Other Acquired I83

Goodwill and Other Acquired Intangible Assets - Schedule of Carrying Amount of Goodwill (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Goodwill
Balance at beginning of the period		$ 726,856	$ 724,603
Goodwill adjustments during the year			2,253
Goodwill acquired during the year (preliminary allocation)		462,046
Balance at end of the period	$ 1,188,902	1,188,902	726,856
Operating Segments | IBERIABANK
Goodwill
Balance at beginning of the period		698,513	696,260
Goodwill adjustments during the year			2,253
Goodwill acquired during the year (preliminary allocation)		462,046
Balance at end of the period	1,160,559	1,160,559	698,513
Operating Segments | Mortgage
Goodwill
Balance at beginning of the period		23,178	23,178
Goodwill adjustments during the year			0
Goodwill acquired during the year (preliminary allocation)		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 adjustments during the year			0
Goodwill acquired during the year (preliminary allocation)		0
Balance at end of the period	5,165	5,165	$ 5,165
Sabadell United
Goodwill
Balance at beginning of the period	431,800
Goodwill acquired during the year (preliminary allocation)	30,200	462,000
Balance at end of the period	$ 462,000	$ 462,000

Goodwill and Other Acquired I84

Goodwill and Other Acquired Intangible Assets Goodwill and Other Acquired Intangible Assets (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Jul. 31, 2017	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Title plant assets	$ 6,700	$ 6,700		$ 6,700
Business Acquisition [Line Items]
Goodwill acquired during the year (preliminary allocation)		462,046
Sabadell United
Business Acquisition [Line Items]
Goodwill acquired during the year (preliminary allocation)	30,200	462,000
Core deposit intangible assets | Sabadell United
Business Acquisition [Line Items]
Goodwill acquired during the year (preliminary allocation)	30,000
Intangible assets acquired	$ 66,600	$ 66,600	$ 96,607

Goodwill and Other Acquired I85

Goodwill and Other Acquired Intangible Assets - Schedule of Definite-Lived Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Acquired Finite-Lived Intangible Assets
Gross Carrying Amount	$ 129,163	$ 75,412
Accumulated Amortization	(53,006)	(53,251)
Net Carrying Amount	76,157	22,161
Core deposit intangible assets
Acquired Finite-Lived Intangible Assets
Gross Carrying Amount	127,957	74,001
Accumulated Amortization	(51,971)	(52,165)
Net Carrying Amount	75,986	21,836
Customer relationship intangible asset
Acquired Finite-Lived Intangible Assets
Gross Carrying Amount	1,143	1,348
Accumulated Amortization	(996)	(1,064)
Net Carrying Amount	147	284
Non-compete agreement
Acquired Finite-Lived Intangible Assets
Gross Carrying Amount	63	63
Accumulated Amortization	(39)	(22)
Net Carrying Amount	$ 24	$ 41

Goodwill and Other Acquired I86

Goodwill and Other Acquired Intangible Assets - Schedule of Amortization Expense of Intangible Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Aggregate amortization expense	$ 12,590	$ 8,415	$ 7,811
Estimated amortization expense for the years ended December 31:
2,018	18,415
2,019	14,900
2,020	11,771
2,021	7,988
2,022	5,903
2023 and thereafter	$ 17,180

Derivative Instruments and Ot87

Derivative Instruments and Other Hedging Activities - Schedule of Outstanding Derivative Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value of Derivatives
Derivative Asset	$ 31,265	$ 38,886
Derivative Liability	25,154	30,209
Notional Amount of Derivatives
Derivative assets	1,609,472	1,565,509
Derivative liabilities	1,721,752	1,528,184
Designated as Hedging Instruments
Fair Value of Derivatives
Derivative Asset	0	0
Derivative Liability	0	525
Notional Amount of Derivatives
Derivative assets	0	0
Derivative liabilities	108,500	108,500
Designated as Hedging Instruments | Interest rate contracts
Notional Amount of Derivatives
Derivative assets	0	0
Derivative liabilities	108,500	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	525
Not Designated as Hedging Instruments
Notional Amount of Derivatives
Derivative assets	1,609,472	1,565,509
Derivative liabilities	1,613,252	1,419,684
Not Designated as Hedging Instruments | Other Assets
Fair Value of Derivatives
Derivative Asset	31,265	38,886
Not Designated as Hedging Instruments | Other Liabilities
Fair Value of Derivatives
Derivative Liability	25,154	29,684
Not Designated as Hedging Instruments | Interest rate contracts
Notional Amount of Derivatives
Derivative assets	1,218,464	1,033,955
Derivative liabilities	1,218,464	1,033,955
Not Designated as Hedging Instruments | Interest rate contracts | Other Assets
Fair Value of Derivatives
Derivative Asset	20,446	20,719
Not Designated as Hedging Instruments | Interest rate contracts | Other Liabilities
Fair Value of Derivatives
Derivative Liability	16,191	20,719
Not Designated as Hedging Instruments | Foreign exchange contracts
Notional Amount of Derivatives
Derivative assets	268	4,474
Derivative liabilities	268	4,474
Not Designated as Hedging Instruments | Foreign exchange contracts | Other Assets
Fair Value of Derivatives
Derivative Asset	7	27
Not Designated as Hedging Instruments | Foreign exchange contracts | Other Liabilities
Fair Value of Derivatives
Derivative Liability	7	26
Not Designated as Hedging Instruments | Forward sales contracts
Notional Amount of Derivatives
Derivative assets	82,347	229,181
Derivative liabilities	142,578	120,567
Not Designated as Hedging Instruments | Forward sales contracts | Other Assets
Fair Value of Derivatives
Derivative Asset	136	6,014
Not Designated as Hedging Instruments | Forward sales contracts | Other Liabilities
Fair Value of Derivatives
Derivative Liability	279	794
Not Designated as Hedging Instruments | Written and purchased options
Notional Amount of Derivatives
Derivative assets	278,638	289,115
Derivative liabilities	165,198	154,170
Not Designated as Hedging Instruments | Written and purchased options | Other Assets
Fair Value of Derivatives
Derivative Asset	10,654	12,125
Not Designated as Hedging Instruments | Written and purchased options | Other Liabilities
Fair Value of Derivatives
Derivative Liability	8,656	8,098
Not Designated as Hedging Instruments | Other contracts
Notional Amount of Derivatives
Derivative assets	29,755	8,784
Derivative liabilities	86,744	106,518
Not Designated as Hedging Instruments | Other contracts | Other Assets
Fair Value of Derivatives
Derivative Asset	22	1
Not Designated as Hedging Instruments | Other contracts | Other Liabilities
Fair Value of Derivatives
Derivative Liability	$ 21	$ 47

Derivative Instruments and Ot88

Derivative Instruments and Other Hedging Activities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Notional amount of derivative liabilities	$ 1,721,752	$ 1,528,184
Cash as collateral for derivative transactions	552	1,900
Cash Posted As Variation Margin for Derivatives	5,100
Not Designated as Hedging Instruments
Derivative [Line Items]
Notional amount of derivative liabilities	1,613,252	1,419,684
Not Designated as Hedging Instruments | Other contracts
Derivative [Line Items]
Notional amount of derivative liabilities	$ 86,744	$ 106,518

Derivative Instruments and Ot89

Derivative Instruments and Other Hedging Activities - Reconciliation of Gross Amounts in Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Derivative assets
Gross derivative assets	$ 29,056	$ 28,804
Gross amounts not offset in the Balance Sheet, derivatives	(12,469)	(9,677)
Gross amounts not offset in the Balance Sheet, collateral	0	0
Net derivative assets	16,587	19,127
Derivative liabilities
Gross derivative liabilities	16,191	21,244
Gross amounts not offset in the Balance Sheet, derivatives	(12,469)	(9,677)
Gross amounts not offset in the Balance Sheet, collateral	(552)	(1,892)
Net derivative liabilities	3,170	9,675
Written and purchased options
Derivative assets
Gross derivative assets	8,610	8,085
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	8,610	8,085
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	0	525
Gross amounts not offset in the Balance Sheet, derivatives	0	0
Gross amounts not offset in the Balance Sheet, collateral	0	(181)
Net derivative liabilities	0	344
Not Designated as Hedging Instruments | Interest rate contracts
Derivative assets
Gross derivative assets		20,719
Gross amounts not offset in the Balance Sheet, derivatives		(9,677)
Gross amounts not offset in the Balance Sheet, collateral		0
Net derivative assets		11,042
Derivative liabilities
Gross derivative liabilities	16,191	20,719
Gross amounts not offset in the Balance Sheet, derivatives	(12,469)	(9,677)
Gross amounts not offset in the Balance Sheet, collateral	(552)	(1,711)
Net derivative liabilities	$ 3,170	$ 9,331

Derivative Instruments and Ot90

Derivative Instruments and Other Hedging Activities - Effect of Hedging Instruments on Consolidated Financial Statements (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
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 (Effective Portion)	$ (611)	$ (328)	$ 38
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income net of taxes (Effective Portion)	(390)	50	0
Amount of Gain (Loss) Recognized in Income on Derivative (Ineffective Portion and Amount Excluded from Effectiveness Testing)	0	0	0
Not Designated as Hedging Instruments
Derivative Instruments and Hedging Activities Disclosures
Amount of Gain (Loss) Recognized in Income on Derivatives	(1,299)	6,804	1,492
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	4,750	8,830	4,143
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	43	15	22
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	(4,115)	(1,731)	(2,947)
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	(2,028)	(327)	274
Not Designated as Hedging Instruments | Other contracts | Other income
Derivative Instruments and Hedging Activities Disclosures
Amount of Gain (Loss) Recognized in Income on Derivatives	$ 51	$ 17	$ 0

Deposits - Schedule of Deposits

Deposits - Schedule of Deposits by Type (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Banking and Thrift [Abstract]
Non-interest-bearing deposits	$ 6,209,925	$ 4,928,878
Negotiable order of withdrawal (NOW)	4,348,939	3,314,281
Money market deposits accounts (MMDA)	7,674,291	6,219,532
Savings deposits	846,074	814,385
Certificates of deposit and other time deposits	2,387,488	2,131,207
Total deposits	$ 21,466,717	$ 17,408,283	$ 16,178,748

Deposits - Schedule of Time Dep

Deposits - Schedule of Time Deposits (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Banking and Thrift [Abstract]
Time Deposits, Less than $250,000	$ 1,768,047	$ 1,661,631
Time Deposits, $250,000 or More	619,441	469,576
Total time deposits	$ 2,387,488	$ 2,131,207

Deposits - Schedule of Maturiti

Deposits - Schedule of Maturities of Certificates of Deposit (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Banking and Thrift [Abstract]
2,018	$ 1,670,503
2,019	401,855
2,020	158,555
2,021	65,885
2,022	78,500
2023 and thereafter	12,190
Total time deposits	$ 2,387,488	$ 2,131,207

Short-Term Borrowings - Summary

Short-Term Borrowings - Summary of Short-Term Borrowings (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Disclosure [Abstract]
Federal Home Loan Bank advances	$ 475,000	$ 175,000
Securities sold under agreements to repurchase	516,297	334,136
Total short-term borrowings	991,297	509,136	$ 326,617
Short-term Debt, Other Disclosures
Outstanding at December 31	991,297	509,136	326,617
Maximum month-end outstanding balance	2,197,105	807,993	798,933
Average daily outstanding balance	$ 905,755	$ 614,073	$ 426,011
Average rate during the year	0.83%	0.40%	0.19%
Average rate at year end	0.82%	0.30%	0.20%

Long-Term Debt - Schedule of Lo

Long-Term Debt - Schedule of Long-Term Debt (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument
Long-term debt	$ 1,495,835	$ 628,953
IBERIABANK
Debt Instrument
Long-term debt	1,375,725	508,843
IBERIABANK | Federal Home Loan Bank Notes
Debt Instrument
Long-term debt	$ 1,331,579	$ 480,118
IBERIABANK | Federal Home Loan Bank Notes | Minimum
Debt Instrument
Interest rate	0.864%	0.864%
IBERIABANK | Federal Home Loan Bank Notes | Maximum
Debt Instrument
Interest rate	7.04%	7.04%
IBERIABANK | Notes Payable
Debt Instrument
Long-term debt	$ 44,146	$ 28,725
IBERIABANK | Notes Payable | Minimum
Debt Instrument
Interest rate	1.28%	0.50%
Debt Instrument term	7 years	7 years
IBERIABANK | Notes Payable | Maximum
Debt Instrument
Interest rate	6.82%	3.60%
Debt Instrument term	30 years	40 years
IBERIABANK Corporation | Junior Subordinated Debt
Debt Instrument
Long-term debt	$ 120,110	$ 120,110
Debt Instrument term	30 years
IBERIABANK Corporation | Junior Subordinated Debt | Statutory Trust I, 3 month LIBOR, plus 3.25%
Debt Instrument
Long-term debt	$ 10,310	10,310
IBERIABANK Corporation | Junior Subordinated Debt | Statutory Trust II, 3 month LIBOR, plus 3.15%
Debt Instrument
Long-term debt	10,310	10,310
IBERIABANK Corporation | Junior Subordinated Debt | Statutory Trust III, 3 month LIBOR, plus 2.00%
Debt Instrument
Long-term debt	10,310	10,310
IBERIABANK Corporation | Junior Subordinated Debt | Statutory Trust IV, 3 month LIBOR, plus 1.60%
Debt Instrument
Long-term debt	15,464	15,464
IBERIABANK Corporation | Junior Subordinated Debt | American Horizons Statutory Trust I, 3 month LIBOR, plus 3.15%
Debt Instrument
Long-term debt	6,186	6,186
IBERIABANK Corporation | Junior Subordinated Debt | Statutory Trust V, 3 month LIBOR, plus 1.435%
Debt Instrument
Long-term debt	10,310	10,310
IBERIABANK Corporation | Junior Subordinated Debt | Statutory Trust VI, 3 month LIBOR, plus 2.75%
Debt Instrument
Long-term debt	12,372	12,372
IBERIABANK Corporation | Junior Subordinated Debt | Statutory Trust VII, 3 month LIBOR, plus 2.54%
Debt Instrument
Long-term debt	13,403	13,403
IBERIABANK Corporation | Junior Subordinated Debt | Statutory Trust VIII, 3 month LIBOR, plus 3.50%
Debt Instrument
Long-term debt	7,217	7,217
IBERIABANK Corporation | Junior Subordinated Debt | OMNI Trust I, 3 month LIBOR, plus 3.30%
Debt Instrument
Long-term debt	8,248	8,248
IBERIABANK Corporation | Junior Subordinated Debt | OMNI Trust II, 3 Month LIBOR, plus 2.79%
Debt Instrument
Long-term debt	7,732	7,732
IBERIABANK Corporation | Junior Subordinated Debt | GA Commerce Trust II, 3 Month LIBOR, plus 1.64%
Debt Instrument
Long-term debt	$ 8,248	$ 8,248
IBERIABANK Corporation | Junior Subordinated Debt | 3 Month LIBOR Rate
Debt Instrument
Three month LIBOR rate during period	1.69%	1.00%
IBERIABANK Corporation | Junior Subordinated Debt | 3 Month LIBOR Rate | Statutory Trust I, 3 month LIBOR, plus 3.25%
Debt Instrument
Basis spread on variable rate	3.25%	3.25%
IBERIABANK Corporation | Junior Subordinated Debt | 3 Month LIBOR Rate | Statutory Trust II, 3 month LIBOR, plus 3.15%
Debt Instrument
Basis spread on variable rate	3.15%	3.15%
IBERIABANK Corporation | Junior Subordinated Debt | 3 Month LIBOR Rate | Statutory Trust III, 3 month LIBOR, plus 2.00%
Debt Instrument
Basis spread on variable rate	2.00%	2.00%
IBERIABANK Corporation | Junior Subordinated Debt | 3 Month LIBOR Rate | Statutory Trust IV, 3 month LIBOR, plus 1.60%
Debt Instrument
Basis spread on variable rate	1.60%	1.60%
IBERIABANK Corporation | Junior Subordinated Debt | 3 Month LIBOR Rate | American Horizons Statutory Trust I, 3 month LIBOR, plus 3.15%
Debt Instrument
Basis spread on variable rate	3.15%	3.15%
IBERIABANK Corporation | Junior Subordinated Debt | 3 Month LIBOR Rate | Statutory Trust V, 3 month LIBOR, plus 1.435%
Debt Instrument
Basis spread on variable rate	1.435%	1.435%
IBERIABANK Corporation | Junior Subordinated Debt | 3 Month LIBOR Rate | Statutory Trust VI, 3 month LIBOR, plus 2.75%
Debt Instrument
Basis spread on variable rate	2.75%	2.75%
IBERIABANK Corporation | Junior Subordinated Debt | 3 Month LIBOR Rate | Statutory Trust VII, 3 month LIBOR, plus 2.54%
Debt Instrument
Basis spread on variable rate	2.54%	2.54%
IBERIABANK Corporation | Junior Subordinated Debt | 3 Month LIBOR Rate | Statutory Trust VIII, 3 month LIBOR, plus 3.50%
Debt Instrument
Basis spread on variable rate	3.50%	3.50%
IBERIABANK Corporation | Junior Subordinated Debt | 3 Month LIBOR Rate | OMNI Trust I, 3 month LIBOR, plus 3.30%
Debt Instrument
Basis spread on variable rate	3.30%	3.30%
IBERIABANK Corporation | Junior Subordinated Debt | 3 Month LIBOR Rate | OMNI Trust II, 3 Month LIBOR, plus 2.79%
Debt Instrument
Basis spread on variable rate	2.79%	2.79%
IBERIABANK Corporation | Junior Subordinated Debt | 3 Month LIBOR Rate | GA Commerce Trust II, 3 Month LIBOR, plus 1.64%
Debt Instrument
Basis spread on variable rate	1.64%	1.64%

Long-Term Debt (Detail)

Long-Term Debt (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument
Long-term debt	$ 1,495,835	$ 628,953
IBERIABANK
Debt Instrument
Long-term debt	$ 1,375,725	508,843
IBERIABANK | Federal Home Loan Bank Notes
Debt Instrument
Minimum FHLB advance amortization period	1 year 6 months
Maximum FHLB advance amortization period	30 years
Long-term debt	$ 1,331,579	480,118
IBERIABANK | Federal Home Loan Bank Notes | Blanket Floating Lien
Debt Instrument
Additional advances available from FHLB	6,400,000
IBERIABANK | Federal Home Loan Bank Notes | Pledge of Investment Securities
Debt Instrument
Additional advances available from FHLB	2,100,000
IBERIABANK Corporation | Junior Subordinated Debt
Debt Instrument
Long-term debt	$ 120,110	$ 120,110
Debt Instrument term	30 years
Earliest call date after issue	5 years
Earliest interest payment deferral date (in years or 20 consecutive quarters)	5 years
Weighted Average | IBERIABANK | Federal Home Loan Bank Notes
Debt Instrument
Weighted average advance rate on FHLB advances	1.48%	1.76%

Long-Term Debt - Maturities of

Long-Term Debt - Maturities of Long-Term Debt (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
2,018	$ 235,944
2,019	506,231
2,020	114,241
2,021	55,441
2,022	410,800
2023 and thereafter	173,178
Total long-term debt	$ 1,495,835	$ 628,953

- Schedule of Provision for Inc

- Schedule of Provision for Income Tax Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Current expense	$ 84,827	$ 103,335	$ 67,025
Deferred expense (benefit)	71,257	(16,654)	4,551
Tax credits	(10,845)	(7,112)	(11,268)
Amortization on qualified affordable housing tax credits	5,227	4,185	2,023
Tax benefits attributable to items charged to equity and goodwill	0	1,439	1,763
Total income tax expense	$ 150,466	$ 85,193	$ 64,094

Income Taxes (Detail)

Income Taxes (Detail) - USD ($)		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income taxes receivable		$ 4,500,000
Income taxes payable			$ 2,000,000
Operating loss carryforwards expiration period		20 years
Deferred tax assets valuation allowance		$ 0	$ 0
Remeasurement of deferred tax assets and liabilities due to TCJA		$ 51,000,000
Remeasurement of deferred tax assets and liabilities due to TCJA percentage		17.40%
Effective tax rate before impact of TCJA		34.00%
Effective tax rate		51.40%	31.30%	31.00%
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of AOCI to RE due to TJCA	[1]	$ 0
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of AOCI to RE due to TJCA	[1]	$ 8,132,000
[1]	One-time reclassification from accumulated other comprehensive income ("AOCI") to retained earnings ("RE") for stranded tax effects resulting from the Tax Cuts and Jobs Act ("TCJA"), enacted on December 22, 2017.

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Effective Tax Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Federal tax based on statutory rate	$ 102,508	$ 95,189	$ 72,428
Effect of tax-exempt income	(9,435)	(8,203)	(6,919)
Interest and other nondeductible expenses	9,605	3,250	5,899
State taxes, net of federal benefit	6,970	4,770	3,955
Tax credits	(10,845)	(7,112)	(11,268)
Amortization on qualified affordable housing tax credits	5,227	4,185	2,023
Other	46,436	(6,886)	(2,024)
Total income tax expense	$ 150,466	$ 85,193	$ 64,094
Effective tax rate	51.40%	31.30%	31.00%
Remeasurement of deferred tax assets and liabilities due to TCJA	$ 51,000
Equity based compensation	3,000
Reversal of prior year deferred tax asset impairment	1,000
Deferred REIT distribution	$ 600

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax asset:
NOL carryforward	$ 8,364	$ 19,584
Allowance for credit losses	38,402	58,036
Deferred compensation	5,876	10,852
Basis difference in acquired assets and liabilities	43,391	32,957
Unrealized loss on securities available for sale	12,198	14,019
OREO	2,639	4,498
Other	22,719	14,720
Deferred tax assets	133,589	154,666
Deferred tax liability:
Basis difference in acquired assets and liabilities	(31,309)	(13,150)
FHLB stock	(300)	(270)
Premises and equipment	(3,723)	(6,132)
Acquisition intangibles	(8,151)	(8,134)
Deferred loan costs	(3,114)	(4,702)
Other	(4,885)	(9,196)
Deferred tax liabilities	(51,482)	(41,584)
Net deferred tax asset	$ 82,107	$ 113,082

Shareholders' Equity, Capita102

Shareholders' Equity, Capital Ratios and Other Regulatory Matters - Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	Jul. 31, 2017	Mar. 07, 2017	Dec. 07, 2016	May 09, 2016	Aug. 05, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jun. 30, 2017
Class of Stock [Line Items]
Liquidation preference value				$ 137,500
Carrying Amount						$ 132,097	$ 132,097
Number of shares authorized to be repurchased							202,506		950,000
Average price per share of common stock repurchased							$ 57.61
Remaining number of shares authorized to be repurchased						747,494
Proceeds from common stock issued						$ 485,151	$ 279,242	$ 0
Series B Preferred Stock
Class of Stock [Line Items]
Dividend rate per share					6.625%
Liquidation preference value					$ 80,000
Carrying Amount						76,812	76,812
Series B Preferred Stock | 3 Month LIBOR Rate
Class of Stock [Line Items]
Variable dividend rate per share					4.262%
Series C Preferred Stock
Class of Stock [Line Items]
Dividend rate per share				6.60%
Liquidation preference value				$ 57,500
Carrying Amount						55,285	$ 55,285
Series C Preferred Stock | 3 Month LIBOR Rate
Class of Stock [Line Items]
Variable dividend rate per share				4.92%
Common Stock
Class of Stock [Line Items]
Common stock issued (in shares)		6,100,000	3,593,750
Price per share of stock of issued		$ 83	$ 81.50
Proceeds from common stock issued		$ 485,200	$ 279,200
Sabadell United
Class of Stock [Line Items]
Cash consideration	$ 809,159
Sabadell United | Common Stock
Class of Stock [Line Items]
Common stock issued (shares)	2,610,304
Common stock issued	$ 211,043
Price per share of common stock issued	$ 80.85
IBERIABANK
Class of Stock [Line Items]
Additional amount of dividends after annual earnings						160,200
Funds available for loans or advances by parent						$ 259,100

Shareholders' Equity, Capita103

Shareholders' Equity, Capital Ratios and Other Regulatory Matters - Actual Capital Amounts and Ratios (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Consolidated
Tier 1 Leverage
Minimum amount	$ 1,073,381	$ 818,440
Minimum ratio	4.00%	4.00%
Actual amount	$ 2,509,496	$ 2,221,528
Actual ratio	9.35%	10.86%
Common Equity Tier 1 (CET1)
Minimum amount	$ 1,011,732	$ 794,334
Minimum ratio	4.50%	4.50%
Actual amount	$ 2,377,398	$ 2,089,431
Actual ratio	10.57%	11.84%
Tier 1 Risk-Based Capital (1)
Minimum amount	$ 1,348,977	$ 1,059,112
Minimum ratio	6.00%	6.00%
Actual amount	$ 2,509,496	$ 2,221,528
Actual ratio	11.16%	12.59%
Total Risk-Based Capital (1)
Minimum amount	$ 1,798,635	$ 1,412,149
Minimum ratio	8.00%	8.00%
Actual amount	$ 2,780,095	$ 2,493,988
Actual ratio	12.37%	14.13%
IBERIABANK
Tier 1 Leverage
Minimum amount	$ 1,070,789	$ 816,152
Minimum ratio	4.00%	4.00%
Well capitalized amount	$ 1,338,487	$ 1,020,190
Well capitalized ratio	5.00%	5.00%
Actual amount	$ 2,437,275	$ 1,878,703
Actual ratio	9.10%	9.21%
Common Equity Tier 1 (CET1)
Minimum amount	$ 1,009,553	$ 792,111
Minimum ratio	4.50%	4.50%
Well capitalized amount	$ 1,458,243	$ 1,144,160
Well capitalized ratio	6.50%	6.50%
Actual amount	$ 2,437,275	$ 1,878,703
Actual ratio	10.86%	10.67%
Tier 1 Risk-Based Capital (1)
Minimum amount	$ 1,346,070	$ 1,056,147
Minimum ratio	6.00%	6.00%
Well capitalized amount	$ 1,794,760	$ 1,408,197
Well capitalized ratio	8.00%	8.00%
Actual amount	$ 2,437,275	$ 1,878,703
Actual ratio	10.86%	10.67%
Total Risk-Based Capital (1)
Minimum amount	$ 1,794,760	$ 1,408,197
Minimum ratio	8.00%	8.00%
Well capitalized amount	$ 2,243,450	$ 1,760,246
Well capitalized ratio	10.00%	10.00%
Actual amount	$ 2,591,374	$ 2,034,663
Actual ratio	11.55%	11.56%

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	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings per common share - basic
Net income	$ 142,413	$ 186,777	$ 142,844
Preferred stock dividends	(9,095)	(7,977)	0
Dividends and undistributed earnings allocated to unvested restricted shares	(1,210)	(1,872)	(1,680)
Net income allocated to common shareholders - basic	$ 132,108	$ 176,928	$ 141,164
Weighted average common shares outstanding	50,640	40,948	38,214
Earnings per common share - basic (in usd per share)	$ 2.61	$ 4.32	$ 3.69
Earnings per common share - diluted
Net income allocated to common shareholders - basic	$ 132,108	$ 176,928	$ 141,164
Dividends and undistributed earnings allocated to unvested restricted shares	(1)	(37)	(48)
Earnings Allocated to Common Shareholders	$ 132,107	$ 176,891	$ 141,116
Weighted average common shares outstanding	50,640	40,948	38,214
Dilutive potential common shares	352	158	96
Weighted average common shares outstanding - diluted	50,992	41,106	38,310
Earnings per common share - diluted (in usd per share)	$ 2.59	$ 4.30	$ 3.68

Earnings Per Share (Detail)

Earnings Per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
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	467,601	447,818	607,608
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive securities excluded from the computation of earnings per share	71,260	155,969	159,236

Share-Based Compensation (Detai

Share-Based Compensation (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Future awards shares under approved incentive compensation plans	1,602,890
Share-based compensation maximum option term (in years)	10 years
Contributions made by the company to 401(k) plan	$ 3.5	$ 1.9	$ 1.7
Stock Option Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unearned share-based compensation associated with awards	$ 1.9
Unrecognized compensation cost related to stock options expected to be recognized over a weighted-average period	2 years 8 months
Restricted Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unearned share-based compensation associated with awards	$ 31.9	$ 16
Unrecognized compensation cost related to stock options expected to be recognized over a weighted-average period	1 year 5 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 - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of shares
Balance at beginning of the period (in shares)	721,538	813,777	867,682
Granted (in shares)	80,557	160,624	82,001
Exercised (in shares)	(85,221)	(196,769)	(119,917)
Forfeited or expired (in shares)	(30,508)	(56,094)	(15,989)
Balance at end of the period (in shares)	686,366	721,538	813,777
Exercisable at period end (in shares)	455,010	415,376	546,842
Weighted Average Exercise Price
Balance at beginning of the period (in usd per share)	$ 55.38	$ 56.99	$ 55.92
Granted (in usd per share)	84.78	48.65	62.50
Exercised (in usd per share)	55.45	55.39	51.71
Forfeited or expired (in usd per share)	68.46	59.49	66.52
Balance at end of the period (in usd per share)	58.24	55.38	56.99
Exercisable at period end (in usd per share)	$ 55.77	$ 56.66	$ 56.54
Aggregate Intrinsic Value (Dollars in thousands)
Exercised	$ 2,098	$ 3,597	$ 1,516
Balance at end of period	13,767
Exercisable at period end	$ 9,891
Weighted Average Remaining Contract Life (in years)
Weighted average remaining contract life at period end	5 years 7 months 10 days
Exercisable at period end	4 years 4 months 24 days

Share-Based Compensation - Esti

Share-Based Compensation - Estimate Fair Value of Stock Option Awards with Weighted-Average Assumptions (Detail) - Stock Option Awards - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividends	1.70%	2.80%	2.20%
Expected volatility	25.00%	29.00%	35.60%
Risk-free interest rate	2.10%	1.40%	2.00%
Expected term (in years)	5 years 10 months 5 days	6 years 6 months	7 years 6 months
Weighted-average grant-date fair value	$ 18.86	$ 10.46	$ 19.57

Share-Based Compensation - Comp

Share-Based Compensation - Compensation Expense Included in Non-Interest Expense and Related Income Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock Option Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	$ 1,470	$ 2,010	$ 1,861
Income tax benefit	124	331	317
Restricted Stock And Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	14,966	12,513	12,045
Income tax benefit	2,809	4,380	4,215
Phantom Stock and Performance Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	$ 10,756	$ 12,933	$ 12,109

Share-Based Compensation - Unve

Share-Based Compensation - Unvested Restricted Stock Award Activity (Detail) - Restricted Stock And Restricted Stock Units - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Balance at beginning of the period (in shares)	543,261	507,130	506,289
Granted (in shares)	421,198	254,276	207,575
Forfeited (in shares)	(31,699)	(28,855)	(26,970)
Earned and issued (in shares)	(194,573)	(189,290)	(179,764)
Balance at end of the period (in shares)	738,187	543,261	507,130
Weighted average grant date fair value (in usd per share)	$ 82.49	$ 48.84	$ 63.16
Fair value of restricted stock and restricted share units vested during the period	$ 16.4	$ 10.7	$ 11.3

Share-Based Compensation - Sche

Share-Based Compensation - Schedule of Share and Dividend Equivalent Share Award Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Value of share equivalents
Market price of Company's stock	$ 77.50	$ 83.75	$ 55.07
Phantom Stock and Performance Stock Units
Number of share equivalents
Balance at beginning of the period (in shares)	472,830	462,430	475,347
Granted (in shares)	118,408	215,745	167,573
Forfeited share equivalents (in shares)	(34,968)	(42,051)	(34,681)
Vested share equivalents (in shares)	(162,426)	(163,294)	(145,809)
Balance at end of the period (in shares)	393,844	472,830	462,430
Value of share equivalents
Balance at beginning of the period (in shares)	$ 39,600	$ 25,466	$ 30,826
Granted (in shares)	9,177	18,069	9,228
Forfeited share equivalents (in shares)	2,710	3,522	1,910
Vested share equivalents (in shares)	15,206	8,509	9,288
Balance at end of the period (in shares)	$ 30,523	$ 39,600	$ 25,466

Commitments and Contingencie112

Commitments and Contingencies (Detail) - USD ($) $ in Millions	Dec. 11, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Fair value of guarantees under commercial and standby letters of credit				$ 2.1	$ 1.6
Loss Contingencies [Line Items]
Loss recognized				$ 11.7
Settled Litigation
Loss Contingencies [Line Items]
Loss recognized	$ 11.7
Pending Litigation
Loss Contingencies [Line Items]
Accrual for potential loss		$ 5.7	$ 6

Commitments and Contingencies -

Commitments and Contingencies - Summary of Financial Instruments Outstanding (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Commitments to grant loans	$ 342,305	$ 355,558
Unfunded commitments under lines of credit	6,060,034	4,899,930
Commercial and standby letters of credit	210,002	163,560
Reserve for unfunded lending commitments	$ 13,208	$ 11,241	$ 14,145	$ 11,801

Fair Value Measurements - Finan

Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Assets
Securities available for sale, at fair value	$ 4,590,062,000	$ 3,446,097,000
Mortgage loans held for sale	134,916,000	157,041,000
Derivative instruments	29,056,000	28,804,000
Liabilities
Derivative instruments	16,191,000	21,244,000
Fair value assets transferred from Level 1 to Level 2	0	0
Recurring
Assets
Securities available for sale, at fair value	4,590,062,000	3,446,097,000
Mortgage loans held for sale	134,916,000	157,041,000
Derivative instruments	31,265,000	38,886,000
Total, Assets	4,756,243,000	3,642,024,000
Liabilities
Derivative instruments	25,154,000	30,209,000
Total	25,154,000	30,209,000
Recurring | Level 1
Assets
Securities available for sale, at fair value	0	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	4,590,062,000	3,446,097,000
Mortgage loans held for sale	134,916,000	157,041,000
Derivative instruments	31,265,000	38,886,000
Total, Assets	4,756,243,000	3,642,024,000
Liabilities
Derivative instruments	25,154,000	30,209,000
Total	25,154,000	30,209,000
Recurring | Level 3
Assets
Securities available for sale, at fair value	0	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 - Gains

Fair Value Measurements - Gains and Losses Included in Earnings Related to Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Non-interest Income
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation
Total gains (losses) included in earnings	$ (1,166)
Change in unrealized gains (losses) relating to assets still held at December 31, 2017	0
Other Comprehensive Income (loss) net of tax
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation
Total gains (losses) included in earnings	0
Change in unrealized gains (losses) relating to assets still held at December 31, 2017	$ (11,721)

Fair Value Measurements - Fi116

Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on Nonrecurring Basis (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assets
Unpaid Principal Balance	$ 283,629,000	$ 316,678,000	$ 64,016,000
Related allowance	2,856,000	24,293,000
Nonrecurring
Assets
Loans	71,210,000	93,485,000
OREO, net	3,029,000	185,000
Total	74,239,000	93,670,000
Fair value of liabilities	0	0
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	71,210,000	93,485,000
OREO, net	3,029,000	185,000
Total	$ 74,239,000	$ 93,670,000

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	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Loans Receivable, Fair Value Disclosure	$ 15,000	$ 12,700
Net Losses from change in fair value of mortgages loans held for investment	(204)	(1,100)
Mortgages Held For Sale at Fair Value
Aggregate fair value	134,916	157,041
Aggregate unpaid principal	131,276	153,801
Aggregate fair value less unpaid principal	3,640	3,240
Total mortgage income (loss) in the Consolidated Statement of Comprehensive Income	$ 944	$ (2,500)

Fair Value of Financial Inst118

Fair Value of Financial Instruments - Estimated Fair Values and Carrying Amounts of Financial Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financial Assets
Cash and cash equivalents	$ 625,724	$ 1,362,126	$ 510,267	$ 548,095
Loans and loans held for sale, net of unearned income and allowance for loan losses	20,213,097	15,222,012	14,493,675
Derivative instruments	31,265	38,886
Financial Liabilities
Deposits	21,466,717	17,408,283	16,178,748
Short-term borrowings	991,297	509,136	$ 326,617
Long-term debt	1,495,835	628,953
Derivative instruments	25,154	30,209
Level 1
Financial Assets
Cash and cash equivalents	625,724	1,362,126
Investment securities	0	0
Loans and loans held for sale, net of unearned income and allowance for loan losses	0	0
Derivative instruments	0	0
Financial Liabilities
Deposits	0	0
Short-term borrowings	516,297	334,136
Long-term debt	0	0
Derivative instruments	0	0
Level 2
Financial Assets
Cash and cash equivalents	0	0
Investment securities	4,818,026	3,536,029
Loans and loans held for sale, net of unearned income and allowance for loan losses	134,916	157,041
Derivative instruments	31,265	38,886
Financial Liabilities
Deposits	21,460,782	16,762,475
Short-term borrowings	475,000	175,000
Long-term debt	0	0
Derivative instruments	25,154	30,209
Level 3
Financial Assets
Cash and cash equivalents	0	0
Investment securities	0	0
Loans and loans held for sale, net of unearned income and allowance for loan losses	19,826,857	14,909,014
Derivative instruments	0	0
Financial Liabilities
Deposits	0	0
Short-term borrowings	0	0
Long-term debt	1,476,899	617,656
Derivative instruments	0	0
Carrying Amount
Financial Assets
Cash and cash equivalents	625,724	1,362,126
Investment securities	4,817,380	3,535,313
Loans and loans held for sale, net of unearned income and allowance for loan losses	20,072,206	15,077,293
Derivative instruments	31,265	38,886
Financial Liabilities
Deposits	21,466,717	17,408,283
Short-term borrowings	991,297	509,136
Long-term debt	1,495,835	628,953
Derivative instruments	25,154	30,209
Fair Value
Financial Assets
Cash and cash equivalents	625,724	1,362,126
Investment securities	4,818,026	3,536,029
Loans and loans held for sale, net of unearned income and allowance for loan losses	19,961,773	15,066,055
Derivative instruments	31,265	38,886
Financial Liabilities
Deposits	21,460,782	16,762,475
Short-term borrowings	991,297	509,136
Long-term debt	1,476,899	617,656
Derivative instruments	$ 25,154	$ 30,209

Related Party Transactions (Det

Related Party Transactions (Details) $ in Thousands	Dec. 31, 2017USD ($)bank	Feb. 28, 2017USD ($)	Dec. 31, 2016USD ($)
Related Party Transaction [Line Items]
Total debt outstanding to all lenders	$ 1,495,835		$ 628,953
Affiliated Entity | Stone Energy Corporation | Credit Facility
Related Party Transaction [Line Items]
Number of banks party to facility | bank	12
Affiliated Entity | Stone Energy Corporation | Exit Facility
Related Party Transaction [Line Items]
Borrowing base		$ 200,000
Affiliated Entity | Stone Energy Corporation | IBERIABANK | Credit Facility
Related Party Transaction [Line Items]
Percent of commitments held under facility	6.00%
Affiliated Entity | Stone Energy Corporation | IBERIABANK | Exit Facility
Related Party Transaction [Line Items]
Percent of commitments held under facility		5.90%
Outstanding balance to IBERIABANK		$ 11,800

Business Segments (Detail)

Business Segments (Detail)	12 Months Ended
	Dec. 31, 2017Segment
Segment Reporting [Abstract]
Number of business segments	3

Business Segments - Schedule of

Business Segments - Schedule of Segment Reporting Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information
Interest and dividend income	$ 913,783	$ 716,939	$ 646,858
Interest expense	104,937	67,701	59,100
Net interest income	808,846	649,238	587,758
Provision for loan losses	51,111	44,424	30,908
Mortgage income	63,570	83,853	80,662
Title revenue	21,972	22,213	22,837
Other non-interest income	125,498	127,755	116,894
Allocated expenses	0	0	0
Non-interest expense	675,896	566,665	570,305
Income before income tax expense	292,879	271,970	206,938
Income tax expense	150,466	85,193	64,094
Net income	142,413	186,777	142,844
Total loans and loans held for sale, net of unearned income	20,213,097	15,222,012	14,493,675
Total assets	27,904,129	21,659,190	19,504,068
Total deposits	21,466,717	17,408,283	16,178,748
Average assets	24,480,656	20,321,234	18,402,706
Operating Segments | IBERIABANK
Segment Reporting Information
Interest and dividend income	906,521	707,676	639,793
Interest expense	104,937	64,068	56,222
Net interest income	801,584	643,608	583,571
Provision for loan losses	51,200	44,336	30,908
Mortgage income	0	405	966
Title revenue	0	0	0
Other non-interest income	125,552	127,751	116,903
Allocated expenses	(13,293)	(13,972)	(16,253)
Non-interest expense	585,355	484,099	495,158
Income before income tax expense	303,874	257,301	191,627
Income tax expense	156,407	79,565	58,006
Net income	147,467	177,736	133,621
Total loans and loans held for sale, net of unearned income	20,028,840	15,004,360	14,305,663
Total assets	27,672,906	21,319,267	19,220,085
Total deposits	21,462,776	17,402,742	16,173,831
Average assets	24,228,436	19,959,261	18,146,216
Operating Segments | IMC
Segment Reporting Information
Interest and dividend income	7,260	9,261	7,062
Interest expense	0	3,633	2,878
Net interest income	7,260	5,628	4,184
Provision for loan losses	(89)	88	0
Mortgage income	63,570	83,448	79,696
Title revenue	0	0	0
Other non-interest income	(42)	4	(2)
Allocated expenses	10,041	10,686	12,036
Non-interest expense	73,587	65,133	57,784
Income before income tax expense	(12,751)	13,173	14,058
Income tax expense	(5,771)	5,023	5,581
Net income	(6,980)	8,150	8,477
Total loans and loans held for sale, net of unearned income	184,257	217,652	188,012
Total assets	208,710	315,057	256,888
Total deposits	3,941	5,541	4,917
Average assets	229,364	335,913	230,819
Operating Segments | LTC
Segment Reporting Information
Interest and dividend income	2	2	3
Interest expense	0	0	0
Net interest income	2	2	3
Provision for loan losses	0	0	0
Mortgage income	0	0	0
Title revenue	21,972	22,213	22,837
Other non-interest income	(12)	0	(7)
Allocated expenses	3,252	3,286	4,217
Non-interest expense	16,954	17,433	17,363
Income before income tax expense	1,756	1,496	1,253
Income tax expense	(170)	605	507
Net income	1,926	891	746
Total loans and loans held for sale, net of unearned income	0	0	0
Total assets	22,513	24,866	27,095
Total deposits	0	0	0
Average assets	$ 22,856	$ 26,060	$ 25,671

Condensed Parent Company Onl122

Condensed Parent Company Only Financial Statements - Condensed Balance Sheets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Assets
Cash in bank	$ 319,156	$ 295,896
Other assets	779,942	618,262
Total Assets	27,904,129	21,659,190	$ 19,504,068
Liabilities and Shareholders’ Equity
Liabilities	24,207,338	18,719,496
Shareholders’ equity	3,696,791	2,939,694	$ 2,498,835	$ 1,852,148
Total Liabilities and Shareholders’ Equity	27,904,129	21,659,190
IBERIABANK Corporation
Assets
Cash in bank	168,873	436,792
Investments in subsidiaries	3,661,808	2,635,682
Other assets	49,207	40,423
Total Assets	3,879,888	3,112,897
Liabilities and Shareholders’ Equity
Liabilities	183,097	173,203
Shareholders’ equity	3,696,791	2,939,694
Total Liabilities and Shareholders’ Equity	$ 3,879,888	$ 3,112,897

Condensed Parent Company Onl123

Condensed Parent Company Only Financial Statements - Condensed Statements of Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating income
Other income	$ 38,811	$ 39,870	$ 30,866
Operating expenses
Interest expense	104,937	67,701	59,100
Salaries and employee benefits expense	379,527	331,686	322,586
Other expenses	32,788	31,211	32,929
Income (loss) before income tax benefit and increase in equity in undistributed earnings of subsidiaries	292,879	271,970	206,938
Income tax benefit	150,466	85,193	64,094
Net Income	142,413	186,777	142,844
Less: Preferred stock dividends	(9,095)	(7,977)	0
Net Income Available to Common Shareholders	133,318	178,800	142,844
IBERIABANK Corporation
Operating income
Reimbursement of management expenses	76,177	65,104	59,255
Other income	146,796	829	(329)
Total operating income	222,973	65,933	58,926
Operating expenses
Interest expense	5,168	3,948	3,393
Salaries and employee benefits expense	55,013	45,623	41,689
Other expenses	32,965	19,566	17,492
Total operating expenses	93,146	69,137	62,574
Income (loss) before income tax benefit and increase in equity in undistributed earnings of subsidiaries	129,827	(3,204)	(3,648)
Income tax benefit	3,123	530	800
Income (loss) before equity in undistributed earnings of subsidiaries	126,704	(3,734)	(4,448)
Equity in undistributed earnings of subsidiaries	15,709	190,511	147,292
Net Income	142,413	186,777	142,844
Less: Preferred stock dividends	9,095	7,977	0
Net Income Available to Common Shareholders	$ 133,318	$ 178,800	$ 142,844

Condensed Parent Company Onl124

Condensed Parent Company Only Financial Statements - Condensed Statements of Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash Flow from Operating Activities
Net income	$ 142,413	$ 186,777	$ 142,844
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	(4,113)	10,633	12,017
Gain on sale of assets	1,581	14,500	(1,137)
Other operating activities, net	(30,394)	64,460	26,798
Net Cash Provided by Operating Activities	263,646	308,088	196,703
Cash Flow from Investing Activities
Proceeds from sale of premises and equipment	354	1,941	13,309
Purchases of premises and equipment, net of premises and equipment acquired	(37,763)	(12,840)	(19,502)
Other investing activities, net	636	1,892	29,202
Net Cash Used in Investing Activities	(1,908,581)	(1,424,397)	(570,972)
Cash Flow from Financing Activities
Cash dividends paid on common stock	(72,772)	(56,793)	(52,318)
Cash dividends paid on preferred stock	(9,095)	(7,028)	0
Net share-based compensation stock transactions	(832)	6,899	1,915
Payments to repurchase common stock	0	(11,666)	0
Net proceeds from issuance of common stock	485,151	279,242	0
Net proceeds from issuance of preferred stock	0	55,285	76,812
Net Cash Provided by Financing Activities	908,533	1,968,168	336,441
Net Increase (Decrease) In Cash and Cash Equivalents	(736,402)	851,859	(37,828)
Cash and Cash Equivalents at Beginning of Period	1,362,126	510,267	548,095
Cash and Cash Equivalents at End of Period	625,724	1,362,126	510,267
IBERIABANK Corporation
Cash Flow from Operating Activities
Net income	142,413	186,777	142,844
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	62	98	416
Net income of subsidiaries	(160,206)	(190,511)	(147,292)
Share-based compensation cost	16,436	14,523	13,906
Gain on sale of assets	0	0	(110)
Other operating activities, net	(4,256)	12,417	82,105
Net Cash Provided by Operating Activities	(5,551)	23,304	91,869
Cash Flow from Investing Activities
Cash paid in excess of cash received for acquisitions	(809,159)	0	(5,054)
Proceeds from sale of premises and equipment	0	0	12
Purchases of premises and equipment, net of premises and equipment acquired	(105)	0	(2)
Return of capital from (Capital contributed to) subsidiary	144,500	(6,000)	5,000
Other investing activities, net	0	(749)	0
Net Cash Used in Investing Activities	(664,764)	(6,749)	(44)
Cash Flow from Financing Activities
Cash dividends paid on common stock	(72,772)	(56,793)	(52,318)
Cash dividends paid on preferred stock	(9,095)	(7,028)	0
Net share-based compensation stock transactions	(832)	6,899	1,915
Payments to repurchase common stock	0	(11,666)	0
Net proceeds from issuance of common stock	485,151	279,242	0
Net proceeds from issuance of preferred stock	0	55,285	76,812
Proceeds from (Payments for) Other Financing Activities	(56)	0	0
Net Cash Provided by Financing Activities	402,396	265,939	26,409
Net Increase (Decrease) In Cash and Cash Equivalents	(267,919)	282,494	118,234
Cash and Cash Equivalents at Beginning of Period	436,792	154,298	36,064
Cash and Cash Equivalents at End of Period	$ 168,873	$ 436,792	$ 154,298