Basis of Presentation (Policies)	9 Months Ended
Basis of Presentation (Policies)	Sep. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Consolidation	East West Bancorp, Inc. (referred to herein on an unconsolidated basis as “East West” and on a consolidated basis as the “Company”) is a registered bank holding company that offers a full range of banking services to individuals and businesses through its subsidiary bank, East West Bank and its subsidiaries (“East West Bank” or the “Bank”). The unaudited interim Consolidated Financial Statements in this Form 10-Q include the accounts of East West, East West Bank and East West’s various subsidiaries. Intercompany transactions and accounts have been eliminated in consolidation. As of September 30, 2017, East West also has six wholly-owned subsidiaries that are statutory business trusts (the “Trusts”). In accordance with FASB Accounting Standards Codification (“ASC”) Topic 810, the Trusts are not included on the Consolidated Financial Statements.
Basis of Presentation	The unaudited interim Consolidated Financial Statements presented in accordance with United States Generally Accepted Accounting Principles (“U.S. GAAP”), applicable guidelines prescribed by regulatory authorities, and general practices in the banking industry, reflect all adjustments that, in the opinion of management, are necessary for fair statement of the interim period Consolidated Financial Statements. Certain items on the Consolidated Financial Statements and notes for the prior periods have been reclassified to conform to the current period presentation.
Current Accounting Developments	New Accounting Pronouncements Adopted In March 2016, the FASB issued Accounting Standards Update (“ASU”) 2016-05, Derivatives and Hedging (Topic 815): Effect of Derivative Contract Novations on Existing Hedge Accounting Relationships, to clarify that a change in the counterparty to a derivative instrument that has been designated as the hedging instrument in an existing hedging relationship would not be considered a termination of the derivative instrument or a change in a critical term of the hedging relationship provided that all other hedge accounting criteria in ASC 815 continue to be met. This clarification applies to both cash flow and fair value hedging relationships. The Company adopted this guidance prospectively in the first quarter of 2017. The adoption of this guidance did not have an impact on the Company’s Consolidated Financial Statements. In March 2016, the FASB issued ASU 2016-06, Derivatives and Hedging (Topic 815): Contingent Put and Call Options in Debt Instruments, which requires an entity to use a four-step decision model when assessing contingent call (put) options that can accelerate the payment of principal on debt instruments to determine whether they are clearly and closely related to their debt hosts. The Company adopted this guidance on a modified retrospective basis in the first quarter of 2017. The adoption of this guidance did not have an impact on the Company’s Consolidated Financial Statements. In March 2016, the FASB issued ASU 2016-07, Investments — Equity Method and Joint Ventures (Topic 323): Simplifying the Transition to the Equity Method of Accounting, to eliminate the requirement for an investor to retroactively apply the equity method when its increase in ownership interest (or degree of influence) in an investee triggers equity method accounting. The amendments in ASU 2016-07 also require that an entity that has an available-for-sale equity security that becomes qualified for the equity method of accounting recognize through earnings the unrealized holding gain or loss in accumulated other comprehensive income (loss) (“AOCI”) at the date the investment becomes qualified for use of the equity method. The Company adopted this guidance prospectively in the first quarter of 2017. The adoption of this guidance did not have an impact on the Company’s Consolidated Financial Statements. In March 2016, the FASB issued ASU 2016-09, Compensation — Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting, to simplify several aspects of the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities and classification in the statements of cash flows. The Company adopted this guidance in the first quarter of 2017. The changes that impacted the Company included a requirement that excess tax benefits and deficiencies be recognized as a component of Income tax expense on the Consolidated Statements of Income rather than Additional paid-in capital on the Consolidated Statements of Changes in Stockholders’ Equity as required in the previous guidance. The adoption of this guidance results in increased volatility to the Company’s income tax expense, but does not have a material impact on the Consolidated Balance Sheets or the Consolidated Statements of Changes in Stockholders’ Equity. The income tax expense volatility is dependent on the Company’s stock price on the dates the restricted stock units (“RSUs”) vest, which occur primarily in the first quarter of each year. Net excess tax benefits for RSUs of $4.6 million have been recognized by the Company as a component of Income tax expense on the Consolidated Statements of Income during the nine months ended September 30, 2017. The guidance also removes the impact of the excess tax benefits and deficiencies from the calculation of diluted EPS. In addition, ASU 2016-09 no longer requires a presentation of excess tax benefits and deficiencies as both an operating outflow and a financing inflow on the Consolidated Statements of Cash Flows. Instead, excess tax benefits and deficiencies are recorded along with other income tax cash flows as an operating activity. These changes to the guidance were applied on a prospective basis. The Company has also elected to retain its existing accounting policy election to estimate award forfeitures. Recent Accounting Pronouncements In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606), which clarifies the principles for recognizing revenue for contracts to provide goods or services to customers and will replace most existing revenue recognition guidance in the U.S. GAAP when it becomes effective. Quantitative and qualitative disclosures regarding the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers are also required. ASU 2014-09 is effective on January 1, 2018. The guidance should be applied on either a modified retrospective or full retrospective basis. The Company’s revenue is mainly comprised of net interest income and noninterest income. The scope of the guidance explicitly excludes net interest income, as well as other revenues from financial instruments such as loans, leases, securities and derivatives. The Company has completed a comprehensive scoping exercise to determine the revenue streams that are in the scope of the guidance and the review of its contracts to ascertain whether certain noninterest income revenue items are within the scope of the new guidance. Based on the completed contract reviews thus far, the adoption of this guidance is not expected to have a material impact on its Consolidated Balance Sheets or Consolidated Statements of Income. The next phase of the Company’s implementation work will be to evaluate any changes that may be required to its applicable disclosures. In January 2016, the FASB issued ASU 2016-01, Financial Instruments — Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities, which requires equity investments, except those accounted for under the equity method of accounting or consolidated, to be measured at fair value with changes recognized in net income, thus eliminating eligibility for the current available-for-sale category. If there is no readily determinable fair value, the guidance allows entities to measure equity investments at cost less impairment, whereby impairment is based on a qualitative assessment. Furthermore, investments in Federal Reserve Bank and FHLB stock are not subject to this guidance and will continue to be presented at cost. The guidance eliminates the requirement to disclose the methods and significant assumptions used to estimate the fair value of financial instruments measured at amortized cost and changes the presentation of financial assets and financial liabilities on the Consolidated Balance Sheets or in the footnotes. If an entity has elected the fair value option to measure liabilities, the guidance requires the portion of the change in the fair value of a liability resulting from credit risk to be presented in Other comprehensive income. ASU 2016-01 is effective on January 1, 2018. Early adoption is not permitted except for certain specific changes under the fair value option guidance. The amendments related to equity securities without readily determinable fair values (including disclosure requirements) should be applied prospectively to equity investments that exist as of the adoption date. The Company does not have a significant amount of equity securities classified as available-for-sale. Additionally, the Company does not have any financial liabilities accounted for under the fair value option. For the guidance that is applicable to us, the accounting will be implemented on a modified retrospective basis through a cumulative-effect adjustment to the Consolidated Balance Sheets as of January 1, 2018, except for the guidance related to equity securities without readily determinable fair values, which should be applied on a prospective basis. The adoption of this guidance is not expected to have a material impact on the Company’s Consolidated Balance Sheets or Consolidated Statements of Income. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which is intended to increase transparency and comparability in the accounting for lease transactions. The guidance requires lessees to recognize right-of-use assets and related lease liabilities for all leases with lease terms of more than 12 months on the Consolidated Balance Sheets, and provide quantitative and qualitative disclosures regarding key information about the leasing arrangements. For short-term leases with a term of 12 months or less, lessees can make a policy election not to recognize lease assets and lease liabilities. Lessor accounting is largely unchanged. ASU 2016-02 is effective on January 1, 2019, with early adoption permitted. The guidance should be applied using a modified retrospective transition method through a cumulative-effect adjustment. The Company is currently evaluating the potential impact on its Consolidated Financial Statements by reviewing its existing lease contracts and service contracts that may include embedded leases. The Company expects the adoption of ASU 2016-02 to result in additional assets and liabilities, as the Company will be required to recognize operating leases on its Consolidated Balance Sheets. The Company does not expect a material impact to its recognition of operating lease expense on its Consolidated Statements of Income. Upon completion of the contract reviews and consideration of system requirements, the Company will evaluate the impacts of adopting the new accounting guidance on its disclosures. In June 2016, the FASB issued ASU 2016-13, Financial Instruments — Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, to introduce a new approach based on expected losses to estimate credit losses on certain types of financial instruments, which modifies the impairment model for available-for-sale debt securities and provides for a simplified accounting model for purchased financial assets with credit deterioration since their origination. The new “expected credit loss” impairment model will apply to most financial assets measured at amortized cost and certain other instruments, including trade and other receivables, loan receivables, available-for-sale and held-to-maturity debt securities, net investments in leases and off-balance sheet credit exposures. For available-for-sale debt securities with unrealized losses, ASU 2016-13 does not change the measurement method of credit losses, except that the losses will be recognized as allowances rather than reductions in the amortized cost of the securities. ASU 2016-13 also expands the disclosure requirements regarding an entity’s assumptions, models and methods for estimating the allowance for loan and lease losses, and requires disclosure of the amortized cost balance for each class of financial asset by credit quality indicator, disaggregated by the year of origination (i.e., by vintage year). ASU 2016-13 is effective on January 1, 2020, with early adoption permitted on January 1, 2019. The guidance should be applied using a modified retrospective approach through a cumulative-effect adjustment to retained earnings as of the beginning of the reporting period of adoption. While the Company is still evaluating the impact on its Consolidated Financial Statements, the Company expects that ASU 2016-13 may result in an increase in the allowance for credit losses due to the following factors: 1) the allowance for credit losses provides for expected credit losses over the remaining expected life of the loan portfolio, and will consider expected future changes in macroeconomic conditions; 2) the nonaccretable difference on the purchased credit impaired (“PCI”) loans will be recognized as an allowance, offset by an increase in the carrying value of the PCI loans; and 3) an allowance may be established for estimated credit losses on available-for-sale and held-to-maturity debt securities. The amount of the increase will be impacted by the portfolio composition and quality, as well as the economic conditions and forecasts as of the adoption date. The Company has begun its implementation efforts by identifying key interpretive issues, assessing its processes and identifying the system requirements against the new guidance to determine what modifications may be required. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments, to provide guidance on eight specific issues related to classification on the Consolidated Statements of Cash Flows in order to reduce diversity in practice. The specific issues cover cash payments for debt prepayment or debt extinguishment costs; cash outflows for settlement of zero-coupon debt instruments or other debt instruments with coupon interest rates that are insignificant in relation to the effective interest rate of the borrowing; contingent consideration payments that are not made soon after a business combination; proceeds from the settlement of insurance claims; proceeds from the settlement of corporate-owned life insurance policies, including bank-owned life insurance policies; distributions received from equity method investees; beneficial interests received in securitization transactions; and clarification regarding when no specific U.S. GAAP guidance exists and the sources of the cash flows are not separately identifiable, the classification should be based on the activity that is likely to be the predominant source or use of the cash flows. ASU 2016-15 is effective on January 1, 2018, with early adoption permitted. The guidance should be applied using a retrospective transition method. The Company does not expect the adoption of this guidance to have a material impact on its Consolidated Financial Statements. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash, which requires the Company to include those amounts that are deemed to be restricted cash and restricted cash equivalents in its cash and cash equivalent balances on the Consolidated Statements of Cash Flows. In addition, the Company is required to explain the changes in the combined total of restricted and unrestricted balances on the Consolidated Statements of Cash Flows. ASU 2016-18 is effective on January 1, 2018, with early adoption permitted. The guidance should be applied using a retrospective transition method to each period presented. The Company does not expect the adoption of this guidance to have a material impact on its Consolidated Financial Statements. In January 2017, the FASB issued ASU 2017-04, Intangibles — Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment, to simplify the accounting for goodwill impairment. An entity will no longer perform a hypothetical purchase price allocation to measure goodwill impairment. Instead, impairment will be measured using the difference between the carrying amount and the fair value of the reporting unit. The guidance also eliminates the requirements for any reporting units with a zero or negative carrying amount to perform a qualitative assessment. ASU 2017-04 is effective on January 1, 2020 and should be applied prospectively. Early adoption is permitted for interim or annual goodwill impairment tests with measurement dates after January 1, 2017. The Company does not expect the adoption of this guidance to have a material impact on the Consolidated Financial Statements. In March 2017, the FASB issued ASU 2017-08, Receivables — Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities, which amends the amortization period for certain purchased callable debt securities held at a premium, shortening such period to the earliest call date. The guidance does not require any accounting changes for debt securities held at a discount; the discount continues to be amortized as an adjustment of yield over the contractual life (to maturity) of the instrument. ASU 2017-08 is effective on January 1, 2019, with early adoption permitted. The guidance should be applied using a modified retrospective transition method, with the cumulative-effect adjustment recognized to retained earnings as of the beginning of the period of adoption. The Company is currently evaluating the impact on its Consolidated Financial Statements. In May 2017, the FASB issued ASU 2017-09, Compensation — Stock Compensation (Topic 718): Scope of Modification Accounting, which amends the scope of modification accounting for share-based payment arrangements. Specifically, an entity would not apply modification accounting if the fair value, vesting conditions and classification of the awards are the same immediately before and after the modification. ASU 2017-09 is effective on January 1, 2018, with early adoption permitted. The guidance should be applied prospectively to awards modified on or after the adoption date. The Company plans to adopt this guidance in the first quarter of 2018 prospectively. In August 2017, the FASB issued ASU 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities, which better aligns the Company’s risk management activities and financial reporting for hedging relationships through changes to both the description and measurement guidance for qualifying hedging relationships and the presentation of hedge results, expands and refines hedge accounting for both nonfinancial and financial risk components, and aligns the recognition and presentation of the effects of the hedging instrument and the hedged item on the Consolidated Financial Statements. ASU 2017-12 is effective on January 1, 2019, with early adoption permitted. Upon adoption, the guidance should be applied using a retrospective transition method to any existing cash flows or net investment hedges through a cumulative-effect adjustment to AOCI to eliminate the separate measurement of ineffectiveness. The amended presentation and disclosure guidance is applied prospectively. The Company is currently evaluating the impact on its Consolidated Financial Statements.
Credit Quality Indicators	All loans are subject to the Company’s internal and external credit review and monitoring. Loans are risk rated based on an analysis of the current state of the borrower’s credit quality. The analysis of credit quality includes a review of all repayment sources, the borrower’s current payment performance/delinquency, current financial and liquidity status and all other relevant information. For single-family residential loans, payment performance/delinquency is the driving indicator for the risk ratings. Risk ratings are the overall credit quality indicator for the Company and the credit quality indicator utilized for estimating the appropriate allowance for loan losses. The Company utilizes a risk rating system, which can be classified within the following categories: Pass, Watch, Special Mention, Substandard, Doubtful and Loss. The risk ratings reflect the relative strength of the repayment sources. Pass and Watch loans are generally considered to have sufficient sources of repayment in order to repay the loan in full in accordance with all terms and conditions. Special Mention loans are considered to have potential weaknesses that warrant closer attention by management. Special Mention is considered a transitory grade. If potential weaknesses are resolved, the loan is upgraded to a Pass or Watch grade. If negative trends in the borrower’s financial status or other information indicate that the repayment sources may become inadequate, the loan is downgraded to a Substandard grade. Substandard loans are considered to have well-defined weaknesses that jeopardize the full and timely repayment of the loan. Substandard loans have a distinct possibility of loss, if the deficiencies are not corrected. Additionally, when management has assessed a potential for loss but a distinct possibility of loss is not recognizable, the loan is still classified as Substandard. Doubtful loans have insufficient sources of repayment and a high probability of loss. Loss loans are considered to be uncollectible and of such little value that they are no longer considered bankable assets. These internal risk ratings are reviewed routinely and adjusted based on changes in the borrowers’ financial status and the loans’ collectability.
Impaired Loans	The Company’s loans are grouped into heterogeneous and homogeneous (mostly consumer loans) categories. Classified loans in the heterogeneous category are identified and evaluated for impairment on an individual basis. A loan is considered impaired when, based on current information and events, it is probable that the Company will not be able to collect all scheduled payments of principal or interest due in accordance with the original contractual terms. Impaired loans are measured based on the present value of expected future cash flows discounted at the loan’s effective interest rate or, as expedient, at the loan’s observable market price or the fair value of the collateral, if the loan is collateral dependent, less costs to sell. When the value of an impaired loan is less than the recorded investment and the loan is classified as nonperforming and uncollectible, the deficiency is charged-off against the allowance for loan losses. Impaired loans exclude the homogeneous consumer loan portfolio, which is evaluated collectively for impairment. The Company’s impaired loans include predominantly non-PCI loans held-for-investment on nonaccrual status and any non-PCI loans modified in a TDR, which may be on accrual or nonaccrual status.
Investments in Qualified Affordable Housing Partnerships, Net	The Company records its investments in qualified affordable housing partnerships, net, using the proportional amortization method. Under the proportional amortization method, the Company amortizes the initial cost of the investment in proportion to the tax credits and other tax benefits received, and recognizes the amortization in Income tax expense on the Consolidated Statements of Income.
Goodwill and Core Deposit Intangibles	Core deposit intangibles represent the intangible value of depositor relationships resulting from deposit liabilities assumed in various acquisitions and were included in Other assets on the Consolidated Balance Sheets. These intangibles are tested for impairment on an annual basis, or more frequently as events occur, or as current circumstances and conditions warrant. Goodwill is tested for impairment on an annual basis as of December 31^st, or more frequently as events occur or circumstances change that would more likely than not reduce the fair value of a reporting unit below its carrying amount.
Amortization Expense of Core Deposit Intangibles	The Company amortizes the core deposit intangibles based on the projected useful lives of the related deposits.
Earnings Per Share	Basic EPS is computed by dividing net income available to common stockholders by the weighted average number of common shares outstanding during each period. Diluted EPS is computed by dividing net income available to common stockholders by the weighted average number of common shares outstanding during each period, plus common share equivalents calculated for warrants and RSUs outstanding using the treasury stock method.