Basis of Presentation (Policies)	3 Months Ended
Basis of Presentation (Policies)	Mar. 31, 2018
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 March 31, 2018, East West also has six wholly-owned subsidiaries that are statutory business trusts (the “Trusts”). In accordance with Financial Accounting Standards Board (“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.
New Accounting Pronouncements Adopted and Recent Accounting Pronouncements	New Accounting Pronouncements Adopted 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. ASU 2014-09 also requires new quantitative and qualitative disclosures including the disaggregation of revenues and descriptions of performance obligations. The Company’s revenue is comprised of net interest income and noninterest income. The scope of this new guidance explicitly excludes net interest income, as well as other revenues from financial instruments including loans, leases, securities and derivatives. Accordingly, the majority of the Company’s revenues will not be affected. In addition, the new standard does not materially impact the timing or measurement of the Company’s revenue recognition as it is consistent with the Company’s existing accounting for contracts within the scope of the new standard. The Company adopted this guidance as of January 1, 2018 using the modified retrospective method where there was no cumulative effect adjustment to retained earnings as a result of adopting this new standard. In addition, the standard did not have a material impact on our consolidated financial statements. The Company has provided a disaggregation of the significant categories of revenues within the scope of this guidance and expanded the qualitative disclosures of the Company’s noninterest income. See Note 12 — Revenue from Contracts with Customers for additional information. In January 2016, the FASB issued ASU 2016-01, Financial Instruments — Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities. With the exception of the amendments related to equity investments without readily determinable fair values and the use of exit price to measure the fair value of financial instruments for disclosure purposes that will be adopted prospectively, the Company adopted all the other amendments of the standard effective January 1, 2018 on a modified retrospective basis. ASU 2016-01 requires investments in marketable equity securities to be accounted for at fair value with unrealized gains or losses reflected in earnings. As of the date of adoption, the Company reclassified approximately $31.9 million of marketable equity securities that were previously classified as Available-for-sale investment securities, at fair value to Investment in tax credits and other investments, net. In addition, the Company recorded a cumulative-effect adjustment as of January 1, 2018 that reduced retained earnings by $545 thousand and increased AOCI by $385 thousand. The guidance also provides a measurement alternative for equity securities without readily determinable fair values to be measured at cost less impairment (if any), plus or minus observable price changes from an identical or similar investment of the same issuer. Such price changes (if any) are reflected in earnings beginning in the period of adoption. The Company elected the measurement alternative for its privately held cost method investments of $11.4 million. No cumulative-effect adjustment to retained earnings was recorded related to the adoption of this guidance. The Company’s investments in the Federal Reserve Bank of San Francisco (“FRB”) and FHLB stock are not subject to this guidance and continue to be accounted for at cost. In addition, ASU 2016-01 eliminated the requirement to disclose methods and significant assumptions used to estimate the fair value of financial instruments measured at amortized cost on the Consolidated Balance Sheet. Furthermore, for purposes of disclosing the fair value of financial instruments carried at amortized cost, the Company has updated its valuation methods as necessary to conform to an exit price concept as required by ASU 2016-01. 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 Statement of Cash Flows. 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; and beneficial interests received in securitization transactions. The guidance also clarifies that in instances of cash flows with multiple aspects that cannot be separately identified, the classification should be based on the activity that is likely to be the predominant source or use of the cash flows. The Company adopted this guidance in the first quarter of 2018 on a retrospective basis. The adoption of this guidance did not have a material impact on the Company’s 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 equivalents balances on the Consolidated Statement 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 Statement of Cash Flows. The Company adopted this guidance in the first quarter of 2018 on a retrospective basis. The adoption of this guidance did not have an impact on the Company’s Consolidated Financial Statements. In January 2017, the FASB issued ASU 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business. ASU 2017-01 narrows the definition of a business by adding an initial screen to determine if substantially all of the fair value of the gross assets acquired is concentrated in a single asset or group of similar assets. If the screen is met, the set is not a business. ASU 2017-01 also specifies the minimum required inputs and processes necessary to be a business, and it removes the requirement to evaluate a market participant’s ability to replace missing elements when all of the inputs or processes that the seller used in operating a business were not obtained. ASU 2017-01 became effective on January 1, 2018. The Company adopted this guidance in the first quarter of 2018. This guidance is to be applied prospectively and did not have a material impact on the Company’s 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 has elected to early adopt this guidance in the first quarter of 2018. The adoption of this guidance did not have an impact on the Company’s 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 was effective on January 1, 2018, with early adoption permitted. The Company adopted the guidance in the first quarter of 2018 prospectively. The adoption did not have an impact on the Company’s Consolidated Financial Statements. In August 2017, the FASB issued ASU 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities. This guidance 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. The guidance also changes 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 by modified retrospective method, with early adoption permitted. The Company has elected to early adopt this guidance in the first quarter of 2018, and the adoption of this guidance did not have a material impact on the Company’s Consolidated Financial Statements. In February 2018, the FASB issued ASU 2018-02, Income Statement — Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. On December 22, 2017, the Tax Cuts and Jobs Act (the “Tax Act”) was signed into law. Under current U.S. GAAP, deferred tax assets and liabilities are to be adjusted for the effect of a change in tax laws or rates included in net income of the reporting period that includes the enactment date. This accounting treatment resulted in the tax effect of items within AOCI not reflecting the appropriate tax rate. This guidance permits companies to reclassify the stranded tax effects resulting from the Tax Act from AOCI to retained earnings. The guidance is effective on January 1, 2019 with early adoption permitted. The Company has elected to early adopt this guidance in the first quarter of 2018 retrospectively. The Company has identified the unrealized losses for available-for-sale securities to be the only item in AOCI with stranded tax effects, and made a policy election to reclassify the related stranded tax effects using the “investment-by-investment” approach. The adoption of the guidance resulted in a cumulative-effect adjustment as of January 1, 2018 that increased retained earnings by $6.7 million and reduced AOCI by the same amount. Recent Accounting Pronouncements 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 Sheet, 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 has completed its review of its existing lease contracts and service contracts that may include embedded leases and is in the process of implementing a new system to address this guidance. 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 Sheet. The Company does not expect a material impact to its recognition of operating lease expense on its Consolidated Statement of Income and is in the process of evaluating 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. The new current expected credit loss (“CECL”) impairment model applies 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. The CECL model utilizes a lifetime “expected credit loss” measurement objective for the recognition of credit losses at the time the financial asset is originated or acquired. The expected credit losses are adjusted in each period for changes in expected lifetime credit losses. 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 debt securities. 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. The implementation efforts also involve, but are not limited to, assessing potential macroeconomic factors that will be used to determine the reasonable and supportable forecast period. 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. Under this guidance, 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 requirement to perform a qualitative assessment for any reporting units with a zero or negative carrying amount. 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 Company’s Consolidated Financial Statements.
Held-For-Sale Classification	The Company reports a business as held-for-sale when management has approved or received approval to sell the business and is committed to a formal plan, the business is available for immediate sale, the business is being actively marketed, the sale is anticipated to occur during the next 12 months and certain other specific criteria are met. A business classified as held-for-sale is recorded at the lower of its carrying amount or estimated fair value less costs to sell. If the carrying amount of the business exceeds its estimated fair value, a loss is recognized. Depreciation and amortization expense are not recorded with respect to the assets of a business after it is classified as held-for-sale.
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 classifies loans 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 loans that have sufficient sources of repayment in order to repay the loan in full in accordance with all terms and conditions. Special Mention loans are loans that have potential weaknesses that warrant closer attention by management. Special Mention is 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 loans that 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 remains classified as Substandard grade. Doubtful loans have insufficient sources of repayment and a high probability of loss. Loss loans are loans that are 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.
Loans held-for-sale	Loans held-for-sale are carried at the lower of cost or fair value. When a determination is made at the time of commitment to originate or purchase loans as held-for-investment, it is the Company’s intent to hold these loans to maturity or for the “foreseeable future,” subject to periodic reviews under the Company’s management evaluation processes, including asset/liability management and credit risk management. When the Company subsequently changes its intent to hold certain loans, the loans are transferred from held-for-investment to held-for-sale at the lower of cost or fair value. From time to time, the Company purchases and sells loans in the secondary market. Certain purchased loans are transferred from held-for-investment to held-for-sale; and write-downs to allowance for loan losses are recorded, when appropriate.
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 Statement of Income.
Goodwill and Core Deposit Intangibles	Goodwill is tested for impairment on an annual basis as of December 31, 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. Core deposit intangibles represent the intangible value of depositor relationships resulting from deposit liabilities assumed in various acquisitions and are included in Other assets on the Consolidated Balance Sheet. These intangibles are tested for impairment on an annual basis, or more frequently as events occur or current circumstances and conditions warrant.
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.