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Plan assets at January 1, 2020 Plan assets at September 30, 2020 Defined Benefit Plan, Plan Assets, Amount Trade names and trademarks Trade names and trademarks (Finite lived) Trademarks and Trade Names [Member] Right of use assets under finance leases, gross Property and equipment, gross Finance Lease, Right-of-Use Asset, before Accumulated Amortization Selling and marketing expenses Selling and Marketing Expense [Member] Proceeds from borrowings Proceeds from Issuance of Long-term Debt Income from operations Operating Income (Loss) Long-lived Assets Based on Geographical Information Long-lived Assets by Geographic Areas [Table Text Block] Payment of debt issuance costs Payments of Debt Issuance Costs Entity Address, Postal Zip Code Entity Address, Postal Zip Code Total current liabilities Liabilities, Current Deposits with statutory authorities Deposit Assets (Loss)/gain on foreign currency exchange contracts Reclassification out of Accumulated Other Comprehensive Income [Member] Contracts with Customer, Receivables, Liabilities and Revenue Recognized Contract with Customer, Contract Asset, Contract Liability, and Receivable [Table Text Block] Weighted-average fair value, outstanding, at beginning balance (in dollars per share) Weighted-average fair value, outstanding, at ending balance (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Commitments and contingencies (Refer to Note 24) Commitments and Contingencies Total lease payments Finance Lease, Liability, Payment, Due Discretionary contributions towards 401(k) plan, maximum percentage Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent Other Income, net Interest and Other Income [Text Block] Acquisition of treasury stock Payments for Repurchase of Common Stock Assets Assets [Abstract] Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Accounting Policies [Abstract] Accounting Policies [Abstract] After year five Lessee, Operating Lease, Liability, to be Paid, after Year Five Office furniture and equipment Furniture and Fixtures [Member] Entity Shell Company Entity Shell Company Number, vested (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Cover [Abstract] Cover [Abstract] Operating cash outflows for operating leases Operating Lease, Payments Accounts payable Accounts Payable, Current Currency translation adjustments Goodwill, Foreign Currency Translation Gain (Loss) Document Type Document Type Sublease income Sublease Income Expected return on plan assets, percentage Defined Benefit Plan Expected Return On Plan Assets Percentage Defined Benefit Plan Expected Return On Plan Assets Percentage 2023 Long-Term Debt, Maturity, Year Three Notes Notes Convertible Notes Payable [Member] Accumulated Other Comprehensive Loss Comprehensive Income (Loss) Note [Text Block] Derivative instruments Derivative Asset, Current Retained earnings Retained Earnings (Accumulated Deficit) Operating lease right-of-use assets Operating Lease, Right-of-Use Asset Other Assets Other Assets Disclosure [Text Block] Unrealized gain/(loss) on cash flow hedges Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, after Tax Unamortized debt discount Debt Instrument, Unamortized Discount Schedule of Purchase of Common Stock from Employees Withholding Tax Payments Related to Vesting of Restricted Stock Schedule Of Purchase Of Common Stock From Employees Withholding Tax Payments [Table Text Block] Schedule of Purchase of Common Stock from Employees Withholding Tax Payments Additions Increase In Capitalized Contract Cost Gross Increase In Capitalized Contract Cost Gross Year one Lessee, Operating Lease, Liability, to be Paid, Year One Acquisition of treasury stock (in shares) Shares repurchased (in shares) Treasury Stock, Shares, Acquired Number of options, outstanding, beginning balance (in shares) Number of options, outstanding, ending Balance (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Year one Finance Lease, Liability, to be Paid, Year One ExlService Holdings, Inc. 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Tax, Attributable to Parent Year three Finance Lease, Liability, to be Paid, Year Three Preferred stock, par value (in dollars per share) Preferred Stock, Par or Stated Value Per Share Income tax (expense)/benefit on: Reclassification from AOCI, Current Period, Tax [Abstract] Change in Plan Assets Schedule of Changes in Fair Value of Plan Assets [Table Text Block] 2021 Long-Term Debt, Maturity, Year One Purchases of property and equipment Payments to Acquire Property, Plant, and Equipment Cash payments for amounts included in the measurement of lease liabilities : Cash Flow, Operating Activities, Lessee [Abstract] Healthcare Health Care [Member] Entity Tax Identification Number Entity Tax Identification Number Interest expense on Notes Interest Expense, Related Party Goodwill and Intangible Assets Goodwill and Intangible Assets Disclosure [Text Block] Property, Plant and Equipment [Abstract] Property, Plant and Equipment [Abstract] Actual return Defined Benefit Plan, Plan Assets, 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Deposits for bank guarantees issued Bank Guarantee Issued Bank Guarantee Issued Weighted-average fair value, granted (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Derivative instruments Derivative Instruments and Hedges, Liabilities, Noncurrent Common stock, issued (in shares) Common Stock, Shares, Issued Cash and cash equivalents Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Revenue from External Customers by Products and Services [Table] Revenue from External Customers by Products and Services [Table] Restricted Stock and Restricted Stock Units Restricted Stock and Restricted Stock Units [Member] Restricted Stock and Restricted Stock Units [Member] Amounts paid on deposits Amounts Paid As Deposits In Respect Of Contingencies Amounts paid as deposits in respect of Contingencies. 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Entity Address, Address Line One Entity Address, Address Line One Entity Address, Address Line Two Entity Address, Address Line Two Gross profit Gross Profit Effect of exchange rate changes Defined Benefit Plan, Plan Assets, Foreign Currency Translation Gain (Loss) 2023 Finite-Lived Intangible Asset, Expected Amortization, Year Three Capital work in progress Construction in Progress [Member] Accounting Guidance [Domain] Accounting Guidance [Domain] Stock Based Compensation Share-based Payment Arrangement [Text Block] Net income attributable to ExlService Holdings, Inc. stockholders Net income Net Income (Loss) Attributable to Parent Entity Address, State or Province Entity Address, State or Province Finance lease liabilities Finance lease liabilities - Non-current Finance Lease, Liability, Noncurrent Change in operating assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Other current liabilities Other Liabilities, Current Remainder of fiscal year Lessee, Operating Lease, Liability, to be Paid, Remainder of Fiscal Year Other comprehensive income (loss) Other Comprehensive Income (Loss), Net of Tax Schedule of Supplemental Balance Sheet Information Schedule Of Leases In Statement Of Financial Position [Table Text Block] Schedule Of Leases In Statement Of Financial Position [Table Text Block] Leases [Abstract] Leases [Abstract] Summary of Significant Accounting Policies Organization, Consolidation and Presentation of Financial Statements Disclosure and Significant Accounting Policies [Text Block] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Total current assets Assets, Current Income before earnings from equity affiliates Income (Loss) From Continuing Operations Before Equity Method Investments, Total Income (Loss) From Continuing Operations Before Equity Method Investments, Total Operating expenses: Operating Expenses [Abstract] Authorized increase in repurchase amount, 2019 Stock Repurchase Program, Authorized Increase in Repurchase Amount Per Period, Year Three Stock Repurchase Program, Authorized Increase in Repurchase Amount Per Period, Year Three Owned assets, gross Property, Plant and Equipment, Gross, Excluding Capital Leased Assets Capitalized Contract Cost [Table] Capitalized Contract Cost [Table] Earnings per share attributable to ExlService Holdings, Inc. stockholders: Earnings Per Share [Abstract] Total finance lease liabilities Present value of lease liabilities Finance Lease, Liability Unrealized foreign exchange (gain)/loss, net Foreign Currency Transaction Gain (Loss), Unrealized Retirement benefits Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Reclassification from AOCI, before tax Reclassification from AOCI, Current Period, before Tax, Attributable to Parent Translation adjustment, if any Accounts Receivable, Allowance for Credit Loss, Foreign Currency Translation Accounts Receivable, Allowance for Credit Loss, Foreign Currency Translation Cost Capitalized Computer Software, Gross Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Developed technology Developed technology Developed Technology Rights [Member] Previous U.S. GAAP Standards Previous Accounting Guidance [Member] Entity Interactive Data Current Entity Interactive Data Current Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding After year five Finance Lease, Liability, to be Paid, after Year Five Deferred transition revenue Contract with Customer, Liability, Noncurrent Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Owned assets, net Property, Plant and Equipment, Net, Excluding Capital Leased Assets Employer contribution Defined Benefit Plan, Plan Assets, Contributions by Employer Right-of-use assets under finance leases: Capital Leases, Balance Sheet, Assets by Major Class, Net [Abstract] Other liabilities Other Sundry Liabilities, Noncurrent Schedule of Costs Related to Company's Stock-based Compensation Plan Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block] Common Stock Common Stock [Member] Cumulative foreign currency translation loss Accumulated Foreign Currency Adjustment Attributable to Parent [Member] Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Product and Service [Domain] Product and Service [Domain] Property, Plant and Equipment, Type [Domain] Long-Lived Tangible Asset [Domain] Contributions to the defined benefit plans Defined Contribution Plan, Cost Finance lease Finance Lease, Weighted Average Discount Rate, Percent Schedule of Property and Equipment Property, Plant and Equipment [Table Text Block] Prospective Adoption of New 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Net increase in cash, cash equivalents and restricted cash Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Foreign exchange gain, interest expense and other income, net Nonoperating Income (Expense) Hedging Relationship [Domain] Hedging Relationship [Domain] Finance lease property and equipment, net Finance Lease, Right-of-Use Asset, after Accumulated Amortization Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Schedule of Maturities of Operating Lease Liabilities Lessee, Operating Lease, Liability, Maturity [Table Text Block] Basis of Preparation Basis of Accounting, Policy [Policy Text Block] Equity, Class of Treasury Stock [Line Items] Equity, Class of Treasury Stock [Line Items] Basic (in shares) Basic weighted average common shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Basic Weighted-average exercise price, forfeited (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price Treasury stock (in shares) Treasury Stock, Shares Derivatives in Cash Flow Hedging Relationships Derivatives in cash flow hedging relationships Cash Flow Hedging [Member] Effective interest rate Line of Credit Facility, Interest Rate During Period Revenues, net Revenue from Contract with Customer [Text Block] Payable to statutory authorities Statutory Authority Payables, Current Statutory Authority Payables, Current Total equity Beginning balance Ending balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Right-of-use assets obtained in exchange for new operating lease liabilities Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Less: Accumulated depreciation and amortization Accumulated Depreciation, 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Per Share Earnings Per Share [Text Block] Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Current liabilities: Liabilities, Current [Abstract] Cash flows from financing activities: Net Cash Provided by (Used in) Financing Activities, Continuing Operations [Abstract] Shares repurchased (in shares) Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation Recurring Fair Value, Recurring [Member] All Other Other Operations Management [Member] Other Operations Management [Member] Year two Finance Lease, Liability, to be Paid, Year Two Recent Accounting Pronouncements and Recently Adopted Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Short-term investments Short-term Investments