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Financial Instrument [Axis] Notes To Financial Statements Notes To Financial Statements [Abstract] optt_ClassOfWarrantOrRightExpirationPeriod Class of Warrant or Right, Expiration Period Period from date of issuance that the warrant or right expires. Reimbursement of Out of Pocket and Legal Expenses [Member] Represents the amount reimbursed to the placement agents for their out of pocket and legal expenses in connection with the offering. Proceeds from issuance of common stock and related warrants, net of costs Proceeds from Issuance or Sale of Equity us-gaap_PaymentsForRepurchaseOfCommonStock Acquisition of treasury stock Placement Agents [Member] Represents the persons in connection with the securities purchase agreement. Adoption of accounting standard update related to stock compensation accounting (ASU 2016-09) Cumulative Effect of New Accounting Principle in Period of Adoption Fair Value, Inputs, Level 2 [Member] Fair Value, Inputs, Level 1 [Member] Placement Agent Fees [Member] Represents the fees associated with the placement agents in the securities purchase agreement. optt_LitigationSettlementAmountPaidByInsurer Litigation Settlement, Amount Paid by Insurer Amount of judgment or settlement paid by the entity's insurer in respect of litigation. Retained Earnings [Member] Stipulation [Member] Represents the Stipulation and Agreement of Class Settlement. Fair Value, Inputs, Level 3 [Member] Santander Bank [Member] Cash on deposit at Santander Bank which serves as security for letter of credit. us-gaap_LineOfCredit Long-term Line of Credit Additional Paid-in Capital [Member] Treasury Stock [Member] us-gaap_MarketableSecuritiesCurrent Marketable securities Fair Value Hierarchy [Domain] Cash flows from investing activities: Fair Value, Hierarchy [Axis] Interim Period, Costs Not Allocable [Domain] Proceeds from issuance of common stock, net of costs Nature of Expense [Axis] Reported Value Measurement [Member] Marketable Securities, Policy [Policy Text Block] Equity Component [Domain] Concentration Risk, Credit Risk, Policy [Policy Text Block] Common Stock [Member] Equity Components [Axis] Accounts Payable and Accrued Liabilities [Member] Cash and Cash Equivalents [Domain] Unearned revenues Cash and Cash Equivalents [Axis] us-gaap_LineOfCreditFacilityCommitmentFeePercentage Line of Credit Facility, Commitment Fee Percentage Supplemental Balance Sheet Disclosures [Text Block] us-gaap_IncreaseDecreaseInAccruedLiabilities Accrued expenses Restrictions on Cash and Cash Equivalents [Table Text Block] optt_PricePerCommonStockAndWarrant Price Per Common Stock and Warrant Per unit amount of common stock and warrant issued. Restricted Cash and Cash Equivalents [Axis] us-gaap_TreasuryStockSharesAcquired Treasury Stock, Shares, Acquired Acquisition of treasury stock (in shares) Preferred stock, shares outstanding (in shares) Use of Estimates, Policy [Policy Text Block] New Accounting Pronouncements, Policy [Policy Text Block] Schedule of Cash and Cash Equivalents [Table Text Block] Product Development [Member] Primary financial statement caption encompassing product development. us-gaap_SharesOutstanding Balance (in shares) Balance (in shares) us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount us-gaap_IncreaseDecreaseInAccountsPayable Accounts payable Weighted average shares used to compute basic and diluted net loss per share (in shares) Basic and diluted net loss per share (in dollars per share) us-gaap_SharePrice Share Price us-gaap_IncomeTaxExaminationPenaltiesExpense Income Tax Examination, Penalties Expense Restricted cash Consolidation, Policy [Policy Text Block] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Offering Agreement [Member] Offering-agreement. Tax Authority, Spain [Member] us-gaap_RepaymentsOfLongTermCapitalLeaseObligations Payment of capital lease obligations Schedule of Cash, Cash Equivalents, and Restricted Cash [Table Text Block] Tabular disclosure of the components of cash, cash equivalents, and restricted cash. Restatement Adjustment [Member] Checking and Savings Accounts [Member] Checking and savings accounts [member] Barclays Bank Agreement [Member] Barclays bank agreement [member] U.S. Department of Defense Office of Naval Research [Member] Related to the customer U.S. Department of Defense Office of Naval Research. Balance Sheet Location [Domain] Balance Sheet Location [Axis] Scenario, Unspecified [Domain] Selling, General and Administrative Expenses [Member] Mitsui Engineering and Ship Building [Member] Related to the customer Mitsui Engineering and Ship Building. 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Revenues, percentage Income Statement Location [Domain] Income Statement Location [Axis] us-gaap_TreasuryStockValueAcquiredCostMethod Acquisition of treasury stock Maximum [Member] Customer Concentration Risk [Member] Basis of Accounting, Policy [Policy Text Block] Range [Domain] Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block] Minimum [Member] us-gaap_TreasuryStockValue Treasury stock, at cost; 70,081 and 48,065 shares, respectively Customer [Axis] us-gaap_StockholdersEquityNoteStockSplitConversionRatio1 Stockholders' Equity Note, Stock Split, Conversion Ratio us-gaap_IncreaseDecreaseInOtherOperatingAssets Other assets Concentration Risk Type [Domain] Significant Accounting Policies [Text Block] Range [Axis] us-gaap_UnrecognizedTaxBenefits Unrecognized Tax Benefits Accounting Policies [Abstract] Customer [Domain] us-gaap_LitigationSettlementAmountAwardedToOtherParty Litigation Settlement, Amount Awarded to Other Party Statement of Financial Position [Abstract] Concentration Risk Type [Axis] optt_InputTax Input Tax Input tax. Sales Revenue, Net [Member] Statement of Cash Flows [Abstract] Statement of Stockholders' Equity [Abstract] us-gaap_AllocatedShareBasedCompensationExpense Allocated Share-based Compensation Expense Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Axis] Issuance of restricted stock, net (in shares) Legal Entity Type of Counterparty [Domain] us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised Exercised (in shares) Issuance of restricted stock, net us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest Total comprehensive loss Legal Entity of Counterparty, Type [Axis] us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings Change in fair value Net loss Net loss us-gaap_IncreaseDecreaseInUnbilledReceivables Unbilled receivable us-gaap_IncreaseDecreaseInAccountsReceivable Accounts receivable us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod Cancelled/forfeited (in shares) Granted (in shares) Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] us-gaap_RepaymentsOfDebt Payment of debt Sale of stock, net of financing costs (in shares) Stock Issued During Period, Shares, New Issues Schedule of Revenue by Major Customers by Reporting Segments [Table Text Block] Sale of stock, net of financing costs us-gaap_LiabilitiesAndStockholdersEquity Total liabilities and stockholders’ equity us-gaap_IncomeTaxExpenseBenefit Income Tax Expense (Benefit) Accumulated deficit Retained Earnings (Accumulated Deficit) Accumulated other comprehensive loss us-gaap_CustomerAdvancesOrDepositsNoncurrent Customer Advances or Deposits, Noncurrent us-gaap_PolicyTextBlockAbstract Accounting Policies Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue Fair value Fair value Marketable Securities [Table Text Block] Major Types of Debt and Equity Securities [Domain] Transfers Statement [Table] Major Types of Debt and Equity Securities [Axis] Issuance Foreign exchange gain Foreign exchange gain Cash flows from financing activities: Income Statement [Abstract] Long-term portion of capital lease obligations Contract loss reserve us-gaap_NumberOfOperatingSegments Number of Operating Segments Class of Stock [Axis] Award Type [Axis] Equity Award [Domain] Interest income, net Segment Reporting Disclosure [Text Block] us-gaap_FairValueAssumptionsExpectedDividendRate Dividend rate us-gaap_DisclosureTextBlockAbstract Notes to Financial Statements us-gaap_FairValueAssumptionsRiskFreeInterestRate Risk-free rate Foreign Currency Transactions and Translations Policy [Policy Text Block] Deferred credits payable current Customer Advances and Deposits, Current 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Compensation, Restricted Stock Units Award Activity [Table Text Block] us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate Expected dividend yield us-gaap_DerivativeLiabilitiesCurrent Derivative Liability, Current us-gaap_LiabilitiesFairValueAdjustment Liabilities, Fair Value Adjustment us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate Risk-free interest rate us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate Expected volatility us-gaap_OperatingIncomeLoss Operating loss Cost of revenues us-gaap_GrossProfit Gross profit (loss) us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1 Expected life (in years) (Year) Litigation Case [Domain] Current portion of capital lease obligations Treasury stock (in shares) Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block] Amendment Flag Warrant Liability, Policy [Policy Text Block] Disclosure of accounting policy for warrant liability. Litigation Case [Axis] Warrant Disclosure [Text Block] The entire disclosure for warrants. Common stock, $0.001 par value; authorized 50,000,000 shares, issued 12,621,205 and 6,313,996 shares, respectively Change in fair value of warrant liabilities Fair Value Adjustment of Warrants Change in fair value of warrant liabilities Commitments and Contingencies Disclosure [Text Block] us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue Cancelled/forfeited (in dollars per share) Common stock, shares authorized (in shares) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue Vested (in dollars per share) Changes on Value of Warrant Liability [Table Text Block] Tabular disclosure of pertinent information about the changes on the value of the warrant liability. Common stock, shares issued (in shares) Other noncurrent assets us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue Beginning Balance, issued and unvested (in dollars per share) Ending Balance, issued and unvested (in dollars per share) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Beginning Balance, issued and unvested (in shares) Ending Balance, issued and unvested (in shares) Common stock, par value (in dollars per share) Income Tax Disclosure [Text Block] us-gaap_GainLossOnSaleOfPropertyPlantEquipment Loss on disposal of property, plant and equipment Compensation expense related to stock option grants and restricted stock us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue Granted (in dollars per share) us-gaap_InsuranceSettlementsReceivable Insurance Settlements Receivable us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod Cancelled/forfeited (in shares) Current Fiscal Year End Date us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod Vested (in shares) us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageRemainingContractualTerm1 Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Weighted Average Remaining Contractual Term Document Fiscal Period Focus Document Fiscal Year Focus Warrant liabilities The current portion of warrant liability. us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1 Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value Litigation receivable Exercisable, weighted average remaining contractual term (Year) Document Period End Date Preferred stock, $0.001 par value; authorized 5,000,000 shares, none issued or outstanding Preferred stock, shares issued (in shares) Overnight Repurchase Account [Member] Represents overnight repurchase account. Exercisable, weighted average exercise price (in dollars per share) Document Type Exercisable, shares underlying options (in shares) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value Accrued taxes payable Depreciation and amortization us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2 Balance, weighted average remaining contractual term (Year) Preferred stock, shares authorized (in shares) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value Accounts payable Document Information [Line Items] Document Information [Table] Preferred stock par value (in dollars per share) us-gaap_AssetsCurrent Total current assets us-gaap_AccruedLiabilitiesCurrent Accrued expenses Accrued expenses total Estimate of Fair Value Measurement [Member] Entity Filer Category Employee incentive payments Entity Current Reporting Status Counterparty Name [Domain] Entity Voluntary Filers Counterparty Name [Axis] us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares Entity Well-known Seasoned Issuer Measurement Basis [Axis] us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice Beginning Balance, weighted average exercise price (in dollars per share) Ending Balance, weighted average exercise price (in dollars per share) Portion at Fair Value Measurement [Member] optt_NumberOfFinancingAgreementsClosed Number of Financing Agreements Closed Refers to the number of financing agreements closed by the company. Accrued salary and benefits us-gaap_PaymentsToAcquireMarketableSecurities Purchases of marketable securities Cancelled/forfeited (in dollars per share) Granted (in dollars per share) Adjustments to reconcile net loss to net cash used in operating activities: us-gaap_OtherAccruedLiabilitiesCurrent Other Exercised (in dollars per share) Legal and accounting fees Entity Central Index Key Entity Registrant Name us-gaap_AssetsFairValueAdjustment Assets, Fair Value Adjustment Entity [Domain] Legal Entity [Axis] us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber Beginning Balance, shares underlying options (in shares) Ending Balance, shares underlying options (in shares) us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1 Class of Warrant or Right, Exercise Price of Warrants or Rights us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight Class of Warrant or Right, Number of Securities Called by Each Warrant or Right us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights Class of Warrant or Right, Number of Securities Called by Warrants or Rights Barclays Bank [Member] The entity of Barclays bank. Project costs Other current assets Entity Common Stock, Shares Outstanding (in shares) Cash paid for interest LIABILITIES AND STOCKHOLDERS' EQUITY us-gaap_Assets Total assets Additional paid-in capital optt_ForeignTaxExaminationRefund Foreign Tax Examination Refund The amount of tax refund due to the result of a foreign tax examination. Ocean Power Technologies, Inc. stockholders’ equity: Revenue Recognition, Policy [Policy Text Block] Trading Symbol us-gaap_LettersOfCreditOutstandingAmount Letters of Credit Outstanding, Amount Non-vested Restricted Stock [Member] Business Description and Basis of Presentation [Text Block] us-gaap_PaymentsToAcquireMachineryAndEquipment Purchases of equipment Liquidity, Policy [Policy Text Block] Disclosure of liquidity accounting policy. Vesting [Domain] Selling, general and administrative costs Vesting [Axis] Commitments and contingencies Service-based Vesting [Member] Shares which will vest based on service. us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options us-gaap_Liabilities Total liabilities us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1 Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options Restricted Stock [Member] Warrant [Member] Cash flows from operating activities: Employee Stock Option [Member] Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block] Accounts Receivable Statement [Line Items] Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Statement of Comprehensive Income [Abstract] Product development costs Supplemental schedule of cash flows information: AOCI Attributable to Parent [Member] us-gaap_PropertyPlantAndEquipmentUsefulLife Property, Plant and Equipment, Useful Life Fair Value Disclosures [Text Block] Restricted cash- short-term Restricted cash- short term Property and equipment, net us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Cash, cash equivalents and restricted cash, beginning of period Cash, cash equivalents and restricted cash, end of period ASSETS Accounting Standards Update 2016-09 [Member] Effect of exchange rate changes on cash and cash equivalents us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect Net increase in cash, cash equivalents and restricted cash us-gaap_NetCashProvidedByUsedInFinancingActivities Net cash provided by financing activities Foreign currency translation adjustment Over-Allotment Option [Member] us-gaap_NetCashProvidedByUsedInInvestingActivities Net cash used in investing activities us-gaap_NetCashProvidedByUsedInOperatingActivities Net cash used in operating activities Sale of Stock [Domain] us-gaap_TableTextBlock Notes Tables Sale of Stock [Axis] Other comprehensive loss Property, Plant and Equipment, Policy [Policy Text Block] Accounting Standards Update 2016-18 [Member] us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest Total stockholders' equity Balance Balance Unbilled receivables