Organization and Basis of Presentation (Policies)	9 Months Ended
Organization and Basis of Presentation (Policies)	Sep. 30, 2018
Organization and Basis of Presentation
Organization and Basis of Presentation	Organization and Basis of Presentation First Hawaiian, Inc. (“FHI” or the “Parent”), a bank holding company, owns 100% of the outstanding common stock of First Hawaiian Bank (“FHB” or the “Bank”), its only direct, wholly owned subsidiary. FHB offers a comprehensive suite of banking services to consumer and commercial customers including loans, deposit products, wealth management, insurance, trust, retirement planning, credit card and merchant processing services. The accompanying unaudited interim consolidated financial statements of First Hawaiian, Inc. and Subsidiary (the “Company”) have been prepared in accordance with generally accepted accounting principles in the United States of America (“GAAP”) for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. The accompanying unaudited interim consolidated financial statements and notes thereto should be read in conjunction with the Company’s audited consolidated financial statements and related notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017. In the opinion of management, all adjustments, which consist of normal recurring adjustments necessary for a fair presentation of the interim period consolidated financial information, have been made. Results of operations for interim periods are not necessarily indicative of results to be expected for the entire year. Intercompany account balances and transactions have been eliminated in consolidation.
Reorganization Transactions	Reorganization Transactions In connection with FHI’s initial public offering (“IPO”) in August 2016 in which BNP Paribas (“BNPP”) sold approximately 17% of its interest in FHI, BNPP announced its intent to sell a controlling interest in FHI, including FHI’s wholly owned subsidiary FHB, over time, subject to market conditions and other considerations. On April 1, 2016, a series of reorganization transactions (the “Reorganization Transactions”) were undertaken to facilitate the IPO. As part of the Reorganization Transactions, FHI, which was then known as BancWest Corporation (“BancWest”), formed a new bank holding company, BancWest Holding Inc. (“BWHI”), a Delaware corporation and a direct wholly owned subsidiary of BancWest, and contributed 100% of its interest in Bank of the West (“BOW”), as well as other assets and liabilities not related to FHB, to BWHI. Following the contribution of BOW to BWHI, BancWest distributed its interest in BWHI to BNPP. As part of these transactions, BancWest amended its certificate of incorporation to change its name to “First Hawaiian, Inc.”, with First Hawaiian Bank remaining as the only direct wholly owned subsidiary of FHI. On July 1, 2016, in order to comply with the Board of Governors of the Federal Reserve System’s requirement (under Regulation YY) applicable to BNPP that a foreign banking organization with $50 billion or more in U.S. non-branch assets as of June 30, 2015 establish a U.S. intermediate holding company and hold its interest in the substantial majority of its U.S. subsidiaries through the intermediate holding company by July 1, 2016, FHI became an indirect subsidiary of BNP Paribas USA, Inc. (“BNP Paribas USA”), BNPP’s U.S. intermediate holding company. As part of that reorganization, FHI became a direct wholly owned subsidiary of BancWest Corporation (“BWC”), a direct wholly owned subsidiary of BNP Paribas USA. As used herein, “BWC” refers, for all periods beginning April 1, 2016, to BancWest Corporation, a Delaware corporation and indirect wholly owned subsidiary of BNPP. On August 4, 2016, FHI’s common stock began trading on the NASDAQ Global Select Market (“NASDAQ”) under the ticker symbol “FHB”. On August 9, 2016, the IPO of 24,250,000 shares of FHI common stock, which included the full exercise of the underwriters’ option to purchase an additional 3,163,043 shares, at a price to the public of $23.00 per share was completed. On February 17, 2017, a secondary offering of 28,750,000 shares of FHI common stock, which included the full exercise of the underwriters’ option to purchase an additional 3,750,000 shares, at a price to the public of $32.00 per share was completed. On May 10, 2018, a secondary offering of 15,300,000 shares of FHI common stock at a price to the public of $27.75 per share was completed. Concurrently with the secondary offering completed on May 10, 2018, FHI entered into a share repurchase agreement with BWC and completed the repurchase of 2,968,069 shares of FHI common stock at $27.56 per share, the per share price paid by the underwriters to BWC in the concurrent public offering. On June 8, 2018, the underwriters’ exercised their full option to purchase an additional 1,530,000 shares of FHI common stock at $27.56 per share. On August 1, 2018, a secondary offering of 20,000,000 shares of FHI common stock at a price to the public of $27.90 per share was completed. Concurrently with the secondary offering completed on August 1, 2018, FHI entered into a share repurchase agreement with BWC and completed the repurchase of 1,801,801 shares of FHI common stock at $27.75 per share, the per share price paid by the underwriters to BWC in the concurrent public offering. Lastly, on September 10, 2018, in a secondary offering, BWC sold 20,000,000 shares of FHI common stock at a variable price to the public. The per share price paid in the offering to BWC by the underwriters was $28.70. FHI did not receive any of the proceeds from the sales of shares of FHI common stock in the secondary offerings completed on September 10, 2018, August 1, 2018, May 10, 2018 or February 17, 2017 or the IPO on August 9, 2016. As of September 30, 2018, BNPP remained the beneficial owner of approximately 18% of FHI’s outstanding common stock.
Use of Estimates in the Preparation of Financial Statements	Use of Estimates in the Preparation of Financial Statements The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Management bases its estimates on historical experience and various other assumptions believed to be reasonable. Although these estimates are based on management’s best knowledge of current events, actual results may differ from these estimates.
Correction of an Immaterial Error to the Financial Statements	Correction of an Immaterial Error to the Financial Statements Subsequent to the issuance of the Company’s unaudited interim September 30, 2017 consolidated financial statements, the Company’s management determined that certain expenses related to the Company’s card rewards program were incorrectly offset against credit and debit card fee income and credit card interchange assessment fees were incorrectly classified in card rewards program expense instead of credit and debit card fee income in the consolidated statements of income for the three and nine months ended September 30, 2017. For the three and nine months ended September 30, 2017, income from service charges on deposit accounts was overstated by $0.2 million and $0.5 million, respectively, credit and debit card fee income was understated by $1.3 million and $5.0 million, respectively, occupancy expense was understated by $0.4 million and $1.2 million, respectively, and card rewards program expense was understated by $0.7 million and $3.3 million, respectively. As a result, certain noninterest income and noninterest expense amounts have been restated from the amounts previously reported to correct the classification errors. There was no change to net income or earnings per share as previously reported as a result of these errors. Management has evaluated the materiality of these errors on its prior period financial statements from a quantitative and qualitative perspective, and has concluded that these errors were not material to the prior periods.
Accounting Standard Adopted in 2018 and Recent Accounting Pronouncements	Accounting Standards Adopted in 2018 In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers (Topic 606). This guidance requires entities to recognize revenues when they transfer 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 Company adopted the provisions of ASU No. 2014-09 on January 1, 2018. The Company adopted the new guidance using the modified retrospective transition approach, in which the guidance would only be applied to existing contracts in effect at January 1, 2018 and new contracts entered into after this date. Most of the Company’s revenue is comprised of net interest income on loans, leases, investment securities and deposits, all of which is explicitly out of scope of the new revenue recognition guidance. Management conducted an assessment of the revenue streams that were potentially affected by the new guidance and reviewed contracts in scope to ensure compliance with the new guidance. These contracts included those related to credit and debit card fees, service charges and fees on deposit accounts, and trust and investment services fees. The adoption of ASU No. 2014-09 did not have a material impact on the Company’s consolidated financial statements. However, additional disclosures required by the standard have been included in “Note 15. Revenue from Contracts with Customers” to the Company’s consolidated financial statements. In March 2017, the FASB issued ASU No. 2017-07, Compensation – Retirement Benefits (Topic 715), Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. This guidance requires entities to report the service cost component of net periodic benefit cost in the same line item as other compensation costs arising from services rendered by pertinent employees during the reporting period. The other components of net periodic benefit costs are to be presented in the income statement separately from the service cost component. The Company adopted the provisions of ASU No. 2017-07 on January 1, 2018 and applied the guidance retrospectively to all periods for which a statement of income is presented. The Company continues to record the service cost component of net periodic benefit cost in salaries and employee benefits expense; however, all other components of net periodic benefit cost are now recorded in other noninterest expense. The Company elected to use the practical expedient which permits entities to estimate amounts for comparative periods using the information previously disclosed in the Company’s pension and other postretirement benefit plan disclosure as such amounts are not material. The adoption of ASU No. 2017-07 did not have a material impact on the Company’s consolidated financial statements. See “Note 17. Benefit Plans” for required disclosures. In May 2017, the FASB issued ASU No. 2017-09, Compensation – Stock Compensation (Topic 718), Scope of Modification Accounting. This guidance applies to entities that change the terms or conditions of a share-based payment award. This guidance clarifies when an entity should account for a change as a modification. Modification accounting will be required only if the fair value, the vesting conditions or the classification of the award (as equity or liability) changes as a result of the change in terms or conditions. The Company adopted the provisions of ASU No. 2017-09 on January 1, 2018. The adoption of ASU No. 2017-09 did not have a material impact on the Company’s consolidated financial statements. 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. This guidance provided entities with an option to reclassify tax effects that were stranded in accumulated other comprehensive income, pursuant to the Tax Cuts and Jobs Act of 2017 (the “Tax Act”), to retained earnings. This guidance is effective for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. However, this guidance may be early adopted in any interim or annual period for which financial statements have not yet been issued and applied either in the period of adoption or retrospectively to each period in which the effect of the change in the corporate tax rate in the Tax Act is recognized. The Company elected to early adopt the provisions of ASU No. 2018-02 on January 1, 2018 and reflected the reclassification related to the Tax Act in the period of adoption. The amount of the reclassification reflected the impact of the Tax Act that was signed into law on December 22, 2017 which reduced the corporate tax rate from 35% to 21%. The result of the early adoption of ASU No. 2018-02 was to reclassify a credit balance of $20.1 million from accumulated other comprehensive loss to retained earnings as of January 1, 2018. The Company utilizes a security-by-security approach to releasing income tax effects from accumulated other comprehensive loss. The adoption of ASU No. 2018-02 did not have a material impact on the Company’s consolidated financial statements. Recent Accounting Pronouncements The following ASUs have been issued by the FASB and are applicable to the Company in future reporting periods. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). This guidance provides that lessees will be required to recognize the following for all operating leases (with the exception of short-term leases): 1) a lease liability, which is the present value of a lessee's obligation to make lease payments, and 2) a right-of-use asset, which is an asset that represents the lessee's right to use, or control the use of, a specified asset for the lease term. Lessor accounting under the new guidance remains largely unchanged as it is substantially equivalent to existing guidance for sales-type leases, direct financing leases and operating leases. This guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. In July 2018, the FASB issued ASU No. 2018-11, Targeted Improvements to Topic 842, Leases. Specifically, entities may elect not to recast comparative periods presented when transitioning to Topic 842 and lessors may elect not to separate lease and nonlease components when certain conditions are met. The Company expects to elect the practical expedient to not recast comparative periods upon the adoption of ASU No. 2016-02 on January 1, 2019. As lessee, the Company has lease agreements for branch premises, ATM locations and information technology equipment that are currently considered operating leases, and therefore, are not recognized on the Company’s consolidated balance sheets. The Company has formed a working group comprised of teams from different disciplines, including finance, bank properties and information technology. The Company has also engaged a software vendor to assist in complying with the new lease accounting requirements. The FASB has made available several practical expedients to assist entities with adoption. In addition to the transition practical expedient noted above, the Company expects to elect the package of practical expedients which among other things, would require no reassessment of whether existing contracts are or contain leases as well as no reassessment of lease classification for existing leases. Additionally, the Company does not plan to elect the practical expedient to use hindsight in determining the lease term and in assessing impairment of right-of-use assets. While the Company has not yet quantified the impact to the consolidated balance sheet upon the adoption of this new guidance, the Company expects to report increased assets and liabilities as a result of recognizing right-of-use assets and lease liabilities related to the Company’s operating lease agreements noted above. However, the Company does not expect the adoption of ASU No. 2016-02 will have a material impact on its consolidated statements of income as the majority of its leases will remain operating in nature. As such, the expense recognition will be similar to previously required straight-line expense treatment. In conjunction with the Company’s adoption of ASU No. 2016-02, management is also assessing internal controls to ensure that complete, accurate and up-to-date records of all lease agreements are not only available at commencement of a lease, but also throughout the term of the lease agreement. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326), Measurement of Credit Losses on Financial Instruments. This guidance eliminates the probable recognition threshold for credit losses on financial assets measured at amortized cost. For loans and held-to-maturity debt securities, this update requires a current expected credit loss (“CECL”) approach to determine the allowance for credit losses. CECL requires loss estimates for the remaining estimated life of the financial asset using historical experience, current conditions, and reasonable and supportable forecasts. In addition, this guidance modifies the other-than-temporary impairment model for available-for-sale debt securities to require an allowance for credit impairment instead of a direct write-down, which allows for a reversal of credit losses in future periods. This guidance requires entities to record a cumulative effect adjustment to the consolidated balance sheet as of the beginning of the first reporting period in which the guidance is effective. This update is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019, with earlier adoption permitted. The new guidance will require significant operational changes, particularly in data collection and analysis. The Company has formed a working group comprised of teams from different disciplines, including credit, finance and information technology, to evaluate the requirements of the new standard and the impact it will have on the Company’s current processes. Management has evaluated the Company’s existing credit loss forecasting models to determine their appropriateness for CECL, has performed a data gap analysis, and is developing analytical approaches to determine CECL model inputs. The Company has also engaged a software vendor to assist in implementing a CECL production platform. However, as the impact of adopting the new guidance is expected to be heavily influenced by an assessment of the composition, characteristics, and credit quality of the Company’s loan and investment securities portfolio as well as the economic conditions in effect at the adoption date, management is currently unable to reasonably estimate the impact of adopting the new standard. In January 2017, the FASB issued ASU No. 2017-04, Intangibles – Goodwill and Other (Topic 350), Simplifying the Test for Goodwill Impairment. This guidance simplifies the subsequent measurement of goodwill by eliminating Step 2 from the current two-step goodwill impairment test. This guidance provides that a goodwill impairment test be conducted by comparing the fair value of a reporting unit with its carrying amount. Entities are to recognize an impairment charge for goodwill by the amount by which the carrying amount exceeds the reporting unit’s fair value. Entities will continue to have the option to perform the qualitative assessment for a reporting unit to determine if the quantitative impairment test is necessary. This update is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. The adoption of ASU No. 2017-04 is not expected to have a material impact on the Company’s consolidated financial statements. In March 2017, the FASB issued ASU No. 2017-08, Receivables – Nonrefundable Fees and Other Costs (Subtopic 310-20), Premium Amortization on Purchased Callable Debt Securities. Under current GAAP, entities normally amortize the premium as an adjustment of yield over the contractual life of the instrument. This guidance shortens the amortization period for certain callable debt securities held at a premium to the earliest call date. This update is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. The adoption of ASU No. 2017-08 is not expected to have a material impact on the Company’s consolidated financial statements. In August 2017, the FASB issued ASU No. 2017-12, Derivatives and Hedging (Topic 815), Targeted Improvements to Accounting for Hedging Activities. The objectives of the new guidance are to: (1) improve the transparency and understandability of information conveyed to financial statement users about an entity’s risk management activities by better aligning the entity’s financial reporting for hedging relationships with those risk management activities, and (2) reduce the complexity of and simplify the application of hedge accounting by preparers. This update is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. Historically, the Company has participated in limited activities in fair value and cash flow hedging relationships. As a result, the adoption of ASU No. 2017-12 is not expected to have a material impact on the Company’s consolidated financial statements. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820), Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement. This guidance is a part of the FASB’s disclosure framework project to improve disclosure effectiveness. This guidance eliminates certain disclosure requirements for fair value measurements: the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy, an entity’s policy for the timing of transfers between levels of the fair value hierarchy and an entity’s valuation processes for Level 3 fair value measurements. This guidance also adds new disclosure requirements for public entities: changes in unrealized gains and losses for the period included in other comprehensive income for recurring Level 3 fair value measurements of instruments held at the end of the reporting period, and the range and weighted average of significant unobservable inputs used to develop recurring and nonrecurring Level 3 fair value measurements, including how the weighted average is calculated. Furthermore, this guidance modifies certain requirements which will involve disclosing: transfers into and out of Level 3 of the fair value hierarchy, purchases and issuances of Level 3 assets and liabilities, and information about the measurement uncertainty of Level 3 fair value measurements as of the reporting date. This update is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. The adoption of ASU No. 2018-13 is not expected to have a material impact on the Company’s consolidated financial statements. In August 2018, the FASB issued ASU No. 2018-15, Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That is a Service Contract. This guidance aligns the accounting for implementation costs related to a hosting arrangement that is a service contract with the guidance on capitalizing costs associated with developing or obtaining internal-use software. Common examples of hosting arrangements include software as a service, platform or infrastructure as a service and other similar types of hosting arrangements. While capitalized costs related to internal-use software is generally considered an intangible asset, costs incurred to implement a cloud computing arrangement that is a service contract would typically be characterized in the company’s financial statements in the same manner as other service costs (e.g., prepaid expense). The new guidance provides that an entity would be required to amortize capitalized implementation costs over the term of the hosting arrangement on a straight-line basis unless another systematic and rational basis is more representative of the pattern in which the entity expects to benefit from access to the hosted software. This update is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019, with earlier adoption permitted in any annual or interim period for which financial statements have not yet been issued or made available for issuance. The Company expects to early adopt the provisions of ASU No. 2018-15 on January 1, 2019 due to the Company’s shift towards utilizing more hosting arrangements that is a service contract. Management is currently evaluating the impact that the adoption of ASU No. 2018-15 will have on the Company’s consolidated financial statements.