Basis of Presentation (Policies)	3 Months Ended
Basis of Presentation (Policies)	Mar. 31, 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, East West Insurance Services, Inc., and various subsidiaries. Intercompany transactions and accounts have been eliminated in consolidation. As of March 31, 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 financial statements. Certain items on the Consolidated Financial Statements and notes for the prior years 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 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 statement of cash flows. The Company adopted ASU 2016-09 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. Net excess tax benefits for restricted stock units (“RSUs”) of approximately $4.4 million were recognized by the Company as a component of Income tax expense on the Consolidated Statements of Income during the first quarter of 2017. This change 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 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 on the Consolidated Statements of Cash Flows. These changes were applied on a prospective basis. The adoption of ASU 2016-09 will result in increased volatility to the Company’s income tax expense but is not expected to 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 RSUs vest, which occur primarily in the first quarter of each year. The Company has 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). The new guidance replaces existing revenue recognition guidance for contracts to provide goods or services to customers. ASU 2014-09 clarifies the principles for recognizing revenue and replaces nearly all existing revenue recognition guidance in U.S. GAAP. 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 as amended by ASU 2015-14, ASU 2016-08, ASU 2016-10, ASU 2016-12 and ASU 2016-20, is effective for interim and annual periods beginning after December 15, 2017 and is applied on either a modified retrospective or full retrospective basis. Early adoption is permitted for interim and annual periods beginning after December 15, 2016. 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 conducted a comprehensive scoping exercise to determine the revenue streams that are in the scope of these updates. Preliminary results indicate that certain noninterest income financial statement line items may contain revenue streams that are in the scope of these updates. The Company’s next implementation efforts include identifying contracts within the scope of the new guidance and assessing the related noninterest income revenues to determine if any accounting or internal control changes will be required under the provisions of the new guidance. The Company continues to evaluate the impact of ASU 2014-09 on our noninterest income and on our presentation and 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. ASU 2016-01 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. If there is no readily determinable fair value, the guidance allows entities the ability to measure investments at cost less impairment, whereby impairment is based on a qualitative assessment. 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 new accounting 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. The Company has not elected to measure any of its liabilities at fair value, and therefore, this aspect of the guidance is not applicable to us. ASU 2016-01 is effective for interim and annual reporting periods beginning after December 15, 2017. Early adoption is not permitted except for certain specific changes under the fair value option guidance. To adopt the amendments, the Company is required to make a cumulative effect adjustment to the Consolidated Balance Sheets as of the beginning of the fiscal year in which the guidance is effective. However, 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 is currently evaluating the impact on its Consolidated Financial Statements. 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. ASU 2016-02 requires lessees to recognize all leases longer than 12 months on the Consolidated Balance Sheet as lease assets and lease liabilities and provide quantitative and qualitative disclosures regarding key information about 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 for interim and annual reporting periods beginning after December 15, 2018 with modified retrospective application. Early adoption is permitted. 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. 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, loans, 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 loans 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 for the fiscal years beginning after December 15, 2019, including interim periods within those fiscal years using a modified retrospective approach through a cumulative effect adjustment to retained earnings as of the beginning of the first reporting period in which the guidance is effective. Earlier adoption is permitted as of the fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. 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 began its implementation efforts by identifying key interpretive issues, and 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 Flow (Topic 230): Classification of Certain Cash Receipts and Cash Payments, to provide guidance on the classification of certain cash receipts and payments on the Consolidated Statements of Cash Flows in order to reduce diversity in practice. ASU 2016-15 is effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. The guidance requires application using a retrospective transition method. Early adoption is permitted. 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 in its cash and cash equivalents balances on the Statements of Cash Flows those amounts that are deemed to be restricted cash and restricted cash equivalents. In addition, the Company is required to explain the changes in the combined total of restricted and unrestricted balances on the Statements of Cash Flows. ASU 2016-18 is effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years, where the guidance should be applied using a retrospective transition method to each period presented. Early adoption is permitted. The Company is currently evaluating the 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. ASU 2017-04 also eliminates the requirements for any reporting unit with a zero or negative carrying amount to perform a qualitative assessment. ASU 2017-04 is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years 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 is currently evaluating the impact on its 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. Therefore, entities will no longer recognize a loss in earnings upon the debtor’s exercise of a call on a purchased callable debt security held at a premium. The ASU does not require any accounting change 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 for interim and annual reporting periods beginning after December 15, 2018. Early adoption is permitted. Entities must apply a modified retrospective approach, with the cumulative effect adjustment recognized to retained earnings as of the beginning of the period of adoption. Entities are also required to provide disclosures about a change in accounting principle in the period of adoption. 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 on the Consolidated Statements of Income as a component of income tax expense.
Goodwill and Other Intangible Assets	Core deposit intangibles represent the intangible value of depositor relationships resulting from deposit liabilities assumed in various acquisitions. 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	The Company amortizes the core deposit intangibles based on the projected useful lives of the related deposits.
Earnings Per Share	EPS — 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.