Basis of Presentation (Policies)	6 Months Ended
Jun. 30, 2018
Accounting Policies [Abstract]
Principles of Consolidation	The consolidated financial statements include the accounts of the Company and its subsidiaries. All significant intercompany balances and transactions have been eliminated in consolidation.
Reclassification	Certain amounts reported in prior periods have been reclassified to conform to the current period presentation. These reclassifications did not have a material effect on previously reported consolidated financial statements.
Concentration of Credit Risks	Concentrations of Credit Risk Most of the Company’s business activity is with customers located in the southeastern United States. The Company’s lending activity is concentrated in its market areas within those states. The Company has emphasized originations of commercial loans and private banking loans, defined as loans to higher net worth clients. Repayments on loans are expected to come from cash flows of the borrower and/or guarantor. Losses on secured loans are limited by the net realizable value of the collateral upon default of the borrowers and guarantor support. The Company believes it does not have any excessive concentrations to any one industry, loan type, or customer.
Recent Accounting Pronouncements	RECENT ACCOUNTING PRONOUNCEMENTS Pronouncements adopted during the six months ended June 30, 2018: ASU No. 2014-09 In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers, which implements a common revenue standard and clarifies the principles used for recognizing revenue. The amendments in the ASU clarify that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. Revenue from Contracts with Customers The majority of the Company’s income streams (e.g., interest and dividend income and mortgage income) are accounted for in accordance with GAAP literature outside the scope of ASC 606, Revenue from Contracts with Customers. Details regarding income recognition for interest and non-interest streams can be found throughout the Company’s 2017 10-K (including Note 1 - Summary of Significant Accounting Policies). Impairment losses recognized against certain receivables (e.g., NSF fees) and capitalized costs (e.g., sales commissions) associated with contracts within the scope of ASC 606 are immaterial. Non-interest income from service charges on deposit accounts, broker commissions, ATM/debit card fee income, credit card and merchant-related income (e.g., interchange fees), and transactional income from traditional banking services (part of other non-interest income) are the significant income streams within the scope of ASC 606 associated with the IBERIABANK reportable segment. Non-interest income from title revenue is associated with the LTC reportable segment. Recognition of Revenue from Contracts with Customers The Company enters into various contracts with customers to provide traditional banking services, including asset management, on a routine basis. The Company’s performance obligations are generally service-related and provided on a daily or monthly basis. The Company does not typically have performance obligations which extend beyond a reporting period. The performance obligations are generally satisfied upon completion of service (i.e., as services are rendered) and the fees are collected at such time, or shortly thereafter. The fees are readily determinable and allocated individually to each service. It is not typical for contracts to require significant judgment to determine the transaction price. Some contracts contain variable consideration; however, the variable consideration is generally constrained (not estimable) as it is based on the occurrence or nonoccurence of a contingent event (or another constraint in some circumstances). The Company generally records the variable consideration when the contingent event occurs and the fee is determinable. The Company provides some services for customers in which it acts in an agent capacity, but generally acts in a principal capacity. Payment terms and conditions vary slightly amongst services; however, amounts are generally invoiced and due or collected by the Company within 30 days, although some fees may be prepaid. The Company bills the customer periodically as performance obligations are satisfied for most services. Therefore, revenue for services provided is generally recognized in the amount invoiced (except in circumstances of prepayment) as that amount corresponds directly to the value of the Company’s performance. In the normal course of business, the Company does not generally grant refunds for services provided. As such, the Company does not establish provisions for estimated returns. Title revenue associated with services provided by LTC, as well as broker commissions, ATM/debit card fee income, credit card and merchant-related income (e.g., interchange fees), and transactional fees from traditional banking services generated within IBERIABANK are generally recognized at the point-in-time the services are provided. The Company has determined this recognition to be appropriate as, upon completion of services, the Company has completed its performance obligations, has a present right to payment (or has collected the cash), and the customer is able to obtain (or has obtained) substantially all of the benefits from the performance obligation (i.e., the provided services). Revenues from service charges on deposit accounts are recognized at the end of the monthly service period (e.g., account service charges) or the date the performance obligation is satisfied (e.g., NSF, stop payment, wire transfer, etc.), except for deposit account services performed by Treasury Management which are recognized on a monthly basis, as these services are performed over that time. Asset management fees (e.g., trust fees) are generally recognized at the end of the monthly service period, but fees are not collected until the beginning of the subsequent month, although some contracts may have quarterly terms and/or be prepaid. NSF fees which are not initially paid are subsequently recorded as “loans” (along with the overdraft balance) and remain classified as such until the amount is paid or charged-off (generally after 60 days). Adoption of ASC 606 The Company adopted ASC 606 as of January 1, 2018 for all contracts as of the effective date. Prior period amounts have been reclassified to conform to current guidance requirements related to the net presentation of certain costs associated with interchange fees and rewards programs. The reclassification of prior period amounts reduced non-interest income and non-interest expense by an immaterial amount (approximately $2.1 million and $4.3 million for the three and six months ended June 30, 2017, respectively) and had no impact on net income. There was no cumulative adjustment made to opening retained earnings as of January 1, 2018. ASU No. 2016-01 In January 2016, the FASB issued ASU No. 2016-01, Financial Statements - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities, which impacts how the Company measures certain equity investments and discloses and presents certain financial instruments through the application of the “exit price” notion. The Company adopted the amendments beginning January 1, 2018. Under the new guidance, equity investments can no longer be classified as trading or available for sale (AFS), and related unrealized holding gains and losses can no longer be recognized in OCI. Per the ASU, such equity investments should be measured at fair value, with adjustments recognized in earnings at the end of each reporting period. As such, the Company reclassified its portfolio of equity investments (which were insignificant at the adoption date and at June 30, 2018) previously classified as AFS investment securities to “other assets.” As these equity investments were previously measured at fair value, implementation of the ASU did not impact the Company’s valuation method. In accordance with the adoption of the ASU, the Company recorded a cumulative-effect adjustment to retained earnings for previously recorded fair value adjustments related to these equity investments, which was insignificant. The Company elected the practical expedient measurement alternative to prospectively account for other equity investments that do not have readily determinable fair values at cost less impairment plus or minus observable price changes in orderly transactions for an identical or similar investment of the same issuer. These investments are insignificant overall and are classified within “other assets” on the Company’s consolidated balance sheets. The Company also modified its fair value methodology for loans measured at amortized cost whose fair values were previously disclosed using an “entry price” methodology to an “exit price” methodology, in accordance with the ASU. The Company’s “exit price” methodology estimates the fair value of these loans based on the present value of the future cash flows using the interest rate that would be charged for a similar loan to a borrower with similar risk at the indicated balance sheet date, adjusted for a liquidity discount based on the estimated time period to complete a sale transaction with a market participant. This change in methodology solely impacted the Company’s disclosures, and had no impact to the Company’s consolidated financial statements. ASU No. 2016-15 In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (ASC 230): Classification of Certain Cash Receipts and Cash Payments, in order to reduce current diversity in practice in how certain cash receipts and cash payments are presented and classified in the statement of cash flows. The Company retrospectively adopted the amendments effective January 1, 2018. The adoption of these amendments did not impact the Company’s consolidated statements of cash flows. ASU No. 2017-12 In August 2017, the FASB issued ASU No. 2017-12, Derivatives and Hedging (ASC 815): Targeted Improvements to Accounting for Hedging Activities, which amends the hedge accounting model to enable entities to better portray the economics of their risk management activities in the financial statements and enhance the transparency and understandability of hedge results. The Company elected to early adopt the amendments effective January 1, 2018. The modified-retrospective adoption of the amendments did not impact the Company’s consolidated financial statements in the current or prior periods. Pronouncements issued but not yet adopted: ASU No. 2016-02 and ASU No. 2018-11 In February 2016, the FASB issued ASU No. 2016-02, Leases (ASC 842). A significant amendment to existing GAAP from this ASU is the recognition of lease assets (i.e., right of use assets) and liabilities on the balance sheet for leases that are classified as operating leases by lessees. The lessor model remains similar to the current accounting model in existing GAAP. Additional amendments include, but are not limited to, the elimination of leveraged leases; modification to the definition of a lease; amendments on sale and leaseback transactions; and disclosure of additional quantitative and qualitative information. ASU 2016-02 will be effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years, with early adoption permitted. In July 2018, the FASB issued ASU No. 2018-11, Leases (ASC 842): Targeted Improvements. The amendments include an optional transition method to apply ASU 2016-02 on a prospective basis as of the effective date, with a cumulative effect adjustment to retained earnings in the period of adoption, instead of applying the guidance using a modified retrospective approach as originally required under ASU 2016-02. ASU 2018-11 also provides lessors with a practical expedient, by class of underlying asset, to not separate nonlease components from the associated lease component under certain circumstances, and clarifies which guidance (ASC 842 or ASC 606) to apply to combined lease and nonlease components. 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 has developed an implementation plan and selected a third-party vendor to assist in the implementation and subsequent accounting for leases under the ASUs. The Company will elect the optional transition method and adopt ASU 2016-02 and ASU No. 2018-11 on January 1, 2019. The Company is still assessing other 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 ASUs. The adjustment to retained earnings is not expected to be significant based on the transition guidance associated with current sale-leaseback agreements. The Company also anticipates additional disclosures to be provided at adoption. ASU No. 2016-13 In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (ASC 326): Measurement of Credit Losses on Financial Instruments. The amendments introduce an impairment model that is based on expected credit losses (“ECL”), rather than incurred losses, to estimate credit losses on certain types of financial instruments (e.g., loans and held-to-maturity securities), including certain off-balance sheet financial instruments (e.g., loan commitments). The measurement of ECL should consider historical information, current information, and reasonable and supportable forecasts, including estimates of prepayments, over the contractual term. Financial instruments with similar risk characteristics must be grouped together when estimating ECL. The ASU also amends the current AFS security impairment model for debt securities. The new model will require an estimate of ECL when the fair value is below the amortized cost of the asset through the use of an allowance to record estimated credit losses (and subsequent recoveries). Non-credit related losses will continue to be recognized through OCI. In addition, the amendments provide for a simplified accounting model for purchased financial assets with a more-than-insignificant amount of credit deterioration since their origination. The initial estimate of expected credit losses would be recognized through an ALLL with an offset (i.e., increase) to the cost basis of the related financial asset at acquisition. ASU 2016-13 will be effective for fiscal years beginning after December 15, 2019, including interim periods. The amendments will be applied through a modified-retrospective approach, resulting in a cumulative-effect adjustment to retained earnings as of the beginning of the first reporting period in which the guidance is effective. A prospective transition approach is required for debt securities for which OTTI had been recognized before the effective date. Amounts previously recognized in AOCI as of the date of adoption that relate to improvements in cash flows expected to be collected should continue to be accreted into income over the remaining life of the asset. Recoveries of amounts previously written off relating to improvements in cash flows after the date of adoption should be recorded in earnings when received. The Company is currently evaluating the impact of the ASU on the Company’s consolidated financial statements; however, the Company has engaged third-party consultants to assist with the ASU and has developed an implementation plan.

RECENT ACCOUNTING PRONOUNCEMENTS

Pronouncements adopted during the six months ended June 30, 2018:

ASU No. 2014-09

In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers, which implements a common revenue standard and clarifies the principles used for recognizing revenue. The amendments in the ASU clarify that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services.

Revenue from Contracts with Customers

The majority of the Company’s income streams (e.g., interest and dividend income and mortgage income) are accounted for in accordance with GAAP literature outside the scope of ASC 606, Revenue from Contracts with Customers. Details regarding income recognition for interest and non-interest streams can be found throughout the Company’s 2017 10-K (including Note 1 - Summary of Significant Accounting Policies). Impairment losses recognized against certain receivables (e.g., NSF fees) and capitalized costs (e.g., sales commissions) associated with contracts within the scope of ASC 606 are immaterial.

Non-interest income from service charges on deposit accounts, broker commissions, ATM/debit card fee income, credit card and merchant-related income (e.g., interchange fees), and transactional income from traditional banking services (part of other non-interest income) are the significant income streams within the scope of ASC 606 associated with the IBERIABANK reportable segment. Non-interest income from title revenue is associated with the LTC reportable segment.

Recognition of Revenue from Contracts with Customers

The Company enters into various contracts with customers to provide traditional banking services, including asset management, on a routine basis. The Company’s performance obligations are generally service-related and provided on a daily or monthly basis. The Company does not typically have performance obligations which extend beyond a reporting period. The performance obligations are generally satisfied upon completion of service (i.e., as services are rendered) and the fees are collected at such time, or shortly thereafter. The fees are readily determinable and allocated individually to each service. It is not typical for contracts to require significant judgment to determine the transaction price. Some contracts contain variable consideration; however, the variable consideration is generally constrained (not estimable) as it is based on the occurrence or nonoccurence of a contingent event (or another constraint in some circumstances). The Company generally records the variable consideration when the contingent event occurs and the fee is determinable.

The Company provides some services for customers in which it acts in an agent capacity, but generally acts in a principal capacity. Payment terms and conditions vary slightly amongst services; however, amounts are generally invoiced and due or collected by the Company within 30 days, although some fees may be prepaid. The Company bills the customer periodically as performance obligations are satisfied for most services. Therefore, revenue for services provided is generally recognized in the amount invoiced (except in circumstances of prepayment) as that amount corresponds directly to the value of the Company’s performance. In the normal course of business, the Company does not generally grant refunds for services provided. As such, the Company does not establish provisions for estimated returns.

Title revenue associated with services provided by LTC, as well as broker commissions, ATM/debit card fee income, credit card and merchant-related income (e.g., interchange fees), and transactional fees from traditional banking services generated within IBERIABANK are generally recognized at the point-in-time the services are provided. The Company has determined this recognition to be appropriate as, upon completion of services, the Company has completed its performance obligations, has a present right to payment (or has collected the cash), and the customer is able to obtain (or has obtained) substantially all of the benefits from the performance obligation (i.e., the provided services). Revenues from service charges on deposit accounts are recognized at the end of the monthly service period (e.g., account service charges) or the date the performance obligation is satisfied (e.g., NSF, stop payment, wire transfer, etc.), except for deposit account services performed by Treasury Management which are recognized on a monthly basis, as these services are performed over that time. Asset management fees (e.g., trust fees) are generally recognized at the end of the monthly service period, but fees are not collected until the beginning of the subsequent month, although some contracts may have quarterly terms and/or be prepaid. NSF fees which are not initially paid are subsequently recorded as “loans” (along with the overdraft balance) and remain classified as such until the amount is paid or charged-off (generally after 60 days).

Adoption of ASC 606

The Company adopted ASC 606 as of January 1, 2018 for all contracts as of the effective date. Prior period amounts have been reclassified to conform to current guidance requirements related to the net presentation of certain costs associated with interchange fees and rewards programs. The reclassification of prior period amounts reduced non-interest income and non-interest expense by an immaterial amount (approximately $2.1 million and $4.3 million for the three and six months ended June 30, 2017, respectively) and had no impact on net income. There was no cumulative adjustment made to opening retained earnings as of January 1, 2018.

ASU No. 2016-01

In January 2016, the FASB issued ASU No. 2016-01, Financial Statements - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities, which impacts how the Company measures certain equity investments and discloses and presents certain financial instruments through the application of the “exit price” notion.

The Company adopted the amendments beginning January 1, 2018. Under the new guidance, equity investments can no longer be classified as trading or available for sale (AFS), and related unrealized holding gains and losses can no longer be recognized in OCI. Per the ASU, such equity investments should be measured at fair value, with adjustments recognized in earnings at the end of each reporting period. As such, the Company reclassified its portfolio of equity investments (which were insignificant at the adoption date and at June 30, 2018) previously classified as AFS investment securities to “other assets.” As these equity investments were previously measured at fair value, implementation of the ASU did not impact the Company’s valuation method. In accordance with the adoption of the ASU, the Company recorded a cumulative-effect adjustment to retained earnings for previously recorded fair value adjustments related to these equity investments, which was insignificant.

The Company elected the practical expedient measurement alternative to prospectively account for other equity investments that do not have readily determinable fair values at cost less impairment plus or minus observable price changes in orderly transactions for an identical or similar investment of the same issuer. These investments are insignificant overall and are classified within “other assets” on the Company’s consolidated balance sheets.

The Company also modified its fair value methodology for loans measured at amortized cost whose fair values were previously disclosed using an “entry price” methodology to an “exit price” methodology, in accordance with the ASU. The Company’s “exit price” methodology estimates the fair value of these loans based on the present value of the future cash flows using the interest rate that would be charged for a similar loan to a borrower with similar risk at the indicated balance sheet date, adjusted for a liquidity discount based on the estimated time period to complete a sale transaction with a market participant. This change in methodology solely impacted the Company’s disclosures, and had no impact to the Company’s consolidated financial statements.

ASU No. 2016-15

In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (ASC 230): Classification of Certain Cash Receipts and Cash Payments, in order to reduce current diversity in practice in how certain cash receipts and cash payments are presented and classified in the statement of cash flows.

The Company retrospectively adopted the amendments effective January 1, 2018. The adoption of these amendments did not impact the Company’s consolidated statements of cash flows.

ASU No. 2017-12

In August 2017, the FASB issued ASU No. 2017-12, Derivatives and Hedging (ASC 815): Targeted Improvements to Accounting for Hedging Activities, which amends the hedge accounting model to enable entities to better portray the economics of their risk management activities in the financial statements and enhance the transparency and understandability of hedge results.

The Company elected to early adopt the amendments effective January 1, 2018. The modified-retrospective adoption of the amendments did not impact the Company’s consolidated financial statements in the current or prior periods.

Pronouncements issued but not yet adopted:

ASU No. 2016-02 and ASU No. 2018-11

In February 2016, the FASB issued ASU No. 2016-02, Leases (ASC 842). A significant amendment to existing GAAP from this ASU is the recognition of lease assets (i.e., right of use assets) and liabilities on the balance sheet for leases that are classified as operating leases by lessees. The lessor model remains similar to the current accounting model in existing GAAP. Additional amendments include, but are not limited to, the elimination of leveraged leases; modification to the definition of a lease; amendments on sale and leaseback transactions; and disclosure of additional quantitative and qualitative information.

ASU 2016-02 will be effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years, with early adoption permitted.

In July 2018, the FASB issued ASU No. 2018-11, Leases (ASC 842): Targeted Improvements. The amendments include an optional transition method to apply ASU 2016-02 on a prospective basis as of the effective date, with a cumulative effect adjustment to retained earnings in the period of adoption, instead of applying the guidance using a modified retrospective approach as originally required under ASU 2016-02. ASU 2018-11 also provides lessors with a practical expedient, by class of underlying asset, to not separate nonlease components from the associated lease component under certain circumstances, and clarifies which guidance (ASC 842 or ASC 606) to apply to combined lease and nonlease components.

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 has developed an implementation plan and selected a third-party vendor to assist in the implementation and subsequent accounting for leases under the ASUs. The Company will elect the optional transition method and adopt ASU 2016-02 and ASU No. 2018-11 on January 1, 2019. The Company is still assessing other 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 ASUs.

The adjustment to retained earnings is not expected to be significant based on the transition guidance associated with current sale-leaseback agreements. The Company also anticipates additional disclosures to be provided at adoption.

ASU No. 2016-13

In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (ASC 326): Measurement of Credit Losses on Financial Instruments. The amendments introduce an impairment model that is based on expected credit losses (“ECL”), rather than incurred losses, to estimate credit losses on certain types of financial instruments (e.g., loans and held-to-maturity securities), including certain off-balance sheet financial instruments (e.g., loan commitments). The measurement of ECL should consider historical information, current information, and reasonable and supportable forecasts, including estimates of prepayments, over the contractual term. Financial instruments with similar risk characteristics must be grouped together when estimating ECL.

The ASU also amends the current AFS security impairment model for debt securities. The new model will require an estimate of ECL when the fair value is below the amortized cost of the asset through the use of an allowance to record estimated credit losses (and subsequent recoveries). Non-credit related losses will continue to be recognized through OCI.

In addition, the amendments provide for a simplified accounting model for purchased financial assets with a more-than-insignificant amount of credit deterioration since their origination. The initial estimate of expected credit losses would be recognized through an ALLL with an offset (i.e., increase) to the cost basis of the related financial asset at acquisition.

ASU 2016-13 will be effective for fiscal years beginning after December 15, 2019, including interim periods. The amendments will be applied through a modified-retrospective approach, resulting in a cumulative-effect adjustment to retained earnings as of the beginning of the first reporting period in which the guidance is effective. A prospective transition approach is required for debt securities for which OTTI had been recognized before the effective date. Amounts previously recognized in AOCI as of the date of adoption that relate to improvements in cash flows expected to be collected should continue to be accreted into income over the remaining life of the asset. Recoveries of amounts previously written off relating to improvements in cash flows after the date of adoption should be recorded in earnings when received.

The Company is currently evaluating the impact of the ASU on the Company’s consolidated financial statements; however, the Company has engaged third-party consultants to assist with the ASU and has developed an implementation plan.