Consolidated Balance Sheets Consolidated Balance Sheets [Abstract] ASSETS ASSETS [Abstract] Current assets: Current assets: [Abstract] Cash and cash equivalents Marketable securities Accounts receivable Unbilled receivables Other current assets Total current assets Property and equipment, net Patents, net Restricted cash Other noncurrent assets Total assets LIABILITIES AND STOCKHOLDERS' EQUITY LIABILITIES AND STOCKHOLDERS' EQUITY [Abstract] Current liabilities: Current liabilities: [Abstract] Accounts payable Accrued expenses Deferred credits payable Unearned revenues Current portion of long-term debt Total current liabilities Long-term debt Total liabilities Commitments and contingencies (note 9) Ocean Power Technologies, Inc. Stockholders’ equity: Ocean Power Technologies, Inc. Stockholders’ equity: [Abstract] Common stock, $0.001 par value; authorized 105,000,000 shares, issued 10,405,439 and 10,407,389 shares, respectively Treasury stock, at cost; 27,818 and 23,544 shares, respectively Additional paid-in capital Accumulated deficit Accumulated other comprehensive loss Total Ocean Power Technologies, Inc. stockholders’ equity Noncontrolling interest in Ocean Power Technologies (Australasia) Pty Ltd. Total equity Total liabilities and stockholders’ equity Preferred stock par value (in Dollars per share) Preferred stock, shares authorized Preferred stock, shares issued Preferred stock, shares outstanding Common stock par value (in Dollars per share) Common stock, shares authorized Common stock, shares issued Treasury stock, shares Consolidated Statements of Operations (Unaudited) Consolidated Statements of Operations (Unaudited) [Abstract] Revenues Cost of revenues Gross profit Operating expenses: Operating expenses: [Abstract] Product development costs Selling, general and administrative costs Total operating expenses Operating loss Interest income, net Foreign exchange loss Net loss Less: Net loss attributable to the noncontrolling interest in Ocean Power Technologies (Australasia) Pty Ltd. Net loss attributable to Ocean Power Technologies, Inc. Basic and diluted net loss per share (in Dollars per share) Weighted average shares used to compute basic and diluted net loss per share (in Shares) Consolidated Statements of Comprehensive Loss (Unaudited) Consolidated Statements of Comprehensive Loss (Unaudited) [Abstract] Net loss Foreign currency translation adjustment Total comprehensive loss Comprehensive loss attributable to the noncontrolling interest in Ocean Power Technologies (Australasia) Pty Ltd. Comprehensive loss attributable to Ocean Power Technologies, Inc. Consolidated Statements of Cash Flows (Unaudited) Consolidated Statements of Cash Flows (Unaudited) [Abstract] Cash flows from operating activities: Cash flows from operating activities: [Abstract] Net loss Adjustments to reconcile net loss to net cash used in operating activities: Adjustments to reconcile net loss to net cash used in operating activities: [Abstract] Foreign exchange loss Depreciation and amortization Loss on disposals of property, plant and equipment Treasury note (discount) premium amortization Compensation expense related to stock option grants and restricted stock Changes in operating assets and liabilities: Changes in operating assets and liabilities: [Abstract] Accounts receivable Unbilled receivables Other current assets Other noncurrent assets Accounts payable Accrued expenses Unearned revenues Net cash used in operating activities Cash flows from investing activities: Cash flows from investing activities: [Abstract] Purchases of marketable securities Maturities of marketable securities Restricted cash Purchases of equipment Payments of patent costs Net cash (used in) provided by investing activities Cash flows from financing activities: Cash flows from financing activities: [Abstract] Repayment of debt Acquisition of treasury stock Net cash used in financing activities Effect of exchange rate changes on cash and cash equivalents Net (decrease) increase in cash and cash equivalents Cash and cash equivalents, beginning of period Cash and cash equivalents, end of period Supplemental disclosure of noncash investing and financing activities: Supplemental disclosure of noncash investing and financing activities: [Abstract] Capitalized patent costs financed through accounts payable and accrued espenses expenses Capitalized purchases of equipment financed through accounts payable and accrued expenses Consolidated Statements of Stockholders’ Equity (Unaudited) Consolidated Statements of Stockholders’ Equity (Unaudited) [Abstract] Equity Component [Domain] Balance Balance Balance shares (in Shares) Balance shares (in Shares) Net loss Stock based compensation Issuance (forfeiture) of restricted stock, net Issuance (forfeiture) of restricted stock shares, net (in Shares) Acquisition of treasury stock Acquisition of treasury stock shares (in Shares) Other comprehensive loss Note 1. Background and Basis of Presentation Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Note 2. Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Note 3. Marketable Securities Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Note 4. Balance Sheet Detail Supplemental Balance Sheet Disclosures [Text Block] Note 5. Related Party Transactions Related Party Transactions Disclosure [Text Block] Note 6. Debt Debt Disclosure [Text Block] Note 7. Deferred Credits Payable and Deferred Credits Customer Advances And Deposits Disclosure Customer Advances And Deposits Disclosure [Text Block] Note 8. Stock-Based Compensation Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Note 9. Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Note 10. Income Taxes Income Tax Disclosure [Text Block] Note 11. Operating Segments and Geographic Information Segment Reporting Disclosure [Text Block] Significant Accounting Policies (Abstract) Significant Accounting Policies Basis of Accounting, Policy [Policy Text Block] Consolidation, Policy [Policy Text Block] Use of Estimates, Policy [Policy Text Block] Revenue Recognition, Policy [Policy Text Block] Cash and Cash Equivalents, Policy [Policy Text Block] Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block] Foreign Currency Transactions and Translations Policy [Policy Text Block] Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block] Concentration Risk, Credit Risk, Policy [Policy Text Block] Earnings Per Share, Policy [Policy Text Block] New Accounting Pronouncements, Policy [Policy Text Block] Schedule of foreign exchange gain (loss) Schedule of Cash and Cash Equivalents, Restricted Cash and Marketable Securities Schedule of Cash and Cash Equivalents [Table Text Block] Schedule of Restricted Cash and Cash Equivalents [Table Text Block] Schedule of Cash and Cash Equivalents, Restricted Cash and Marketable Securities [Table Text Block] Schedule of Revenue by Major Customers by Reporting Segments [Table Text Block] Marketable Securities [Table Text Block] Schedule of Other Assets and Other Liabilities [Table Text Block] Title of Individual with Relationship to Entity [Domain] Schedule of Related Party Transactions [Table Text Block] Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Schedule of Share-based Compensation, Activity [Table Text Block] Schedule of Share-based Compensation, Restricted Stock Units Award Activity [Table Text Block] Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas [Table Text Block] Cash and Cash Equivalents Cash and Cash Equivalents [Abstract] CashAndCashEquivalents_ [Domain] Cash Restricted Under Security Agreements Cash Restricted Under Security Agreements [Abstract] Credit Facility [Domain] Cash restricted under security agreements Foreign Exchange Gain (Loss) Foreign Exchange Gain (Loss) [Abstract] Foreign Currency Denominated Certificates of Deposit and Cash Accounts Foreign Currency Denominated Certificates of Deposit and Cash Accounts [Abstract] Cash and Cash Equivalents, Restricted Cash and Marketable Securities Foreign currency denominated certificates of deposit and cash accounts Percentage of the Company’s Revenues Derived From Customers Percentage of the Company’s Revenues Derived From Customers [Abstract] Name of Major Customer [Domain] Customer Marketable Securities That Mature Within One Year Marketable Securities That Mature Within One Year [Abstract] Fair Value by Asset Class [Domain] Marketable Securities Balance Sheet Detail Balance Sheet Detail [Abstract] Investment Holding [Domain] Interim Period, Costs Not Allocable [Domain] Accounts Receivable, net Accounts Receivable, net [Abstract] Accounts receivable Allowance for doubtful accounts Property and Equipment Property and Equipment [Abstract] Property and Equipment Accumulated depreciation and amortization Patents Patents [Abstract] Patents Accumulated amortization Accrued Expenses Accrued Expenses [Abstract] Project costs Contract loss reserves Employee incentive payments Other Accrued Liabilities, Current Employee-related costs Payroll tax withholdings Legal and accounting fees Value-added tax Related Party Transactions Related Party Transactions [Abstract] Related party consulting expense Expenses for services provided by related party company Revenue for services provided to related party company Additional Related Party Transactions Additional Related Party Transactions [Abstract] Consulting fees payable to related party Receivable from related party company Weighted Average Fair Value Assumptions for Stock-Based Compensation Weighted Average Fair Value Assumptions for Stock-Based Compensation [Abstract] Risk-free interest rate Expected dividend yield Expected life Expected volatility Stock Options Under the Plans Stock Options Under the Plans [Abstract] Shares Underlying Options Shares Underlying Options Weighted Average Exercise Price (in Dollars per share) Weighted Average Exercise Price (in Dollars per share) Weighted Average Remaining Contractual Term (In Years) Forfeited Forfeited (in Dollars per share) Granted Granted (in Dollars per share) Exercisable as of July 31, 2012 Exercisable as of July 31, 2012 (in Dollars per share) Exercisable as of July 31, 2012 Non-Vested Restricted Stock Under the Plans Non-Vested Restricted Stock Under the Plans [Abstract] Award Type [Domain] Number of Shares Number of Shares Weighted Average Price Per Share (in Dollars per share) Weighted Average Price Per Share (in Dollars per share) Granted Granted (in Dollars per share) Forfeited Forfeited (in Dollars per share) Vested Vested (in Dollars per share) Geographic Segment Information Geographic Segment Information [Abstract] Segment, Geographical [Domain] Revenues from external customers Operating loss Three months ended July 31, 2011 Three months ended July 31, 2011 [Abstract] July 31, 2012 July 31, 2012 [Abstract] Long-lived assets Total assets Asset Impairment Charge As Percent Of Investment Amount Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners Noncontrolling Interest, Ownership Percentage by Parent Asset Impairment Charges Asset Impairment Charge As Percent Of Investment Amount Accounts Receivable, Gross Accounts Receivable, Net Legal Entity Type of Counterparty [Domain] Contract gross profit Contract Gross Profit (in Dollars) Line of Credit Facility, Current Borrowing Capacity (in Euro) Line of Credit Facility, Interest Rate at Period End Line of Credit Facility, Amount Outstanding (in Euro) Long-term Debt (in Dollars) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in Shares) Related party daily transaction rate Related Party Daily Transaction Rate Long Term Debt Payment Terms Long-term Debt Long Term Debt Payment Terms Long-term Debt, Current Maturities Deferred credits payable option details Deferred Credits Payable Market Discount Rate Deferred Credits Payable Market Liquidated Damages Rate Customer Advances and Deposits (in Dollars) Deferred Credits Payable Option Details (in US Ton) Deferred Credits Payable Market Discount Rate Customer Advances and Deposits, Current (in Dollars) Deferred Credits Payable Market Liquidated Damages Rate Allocated Share-based Compensation Expense Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value (in Dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number (in Shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Aggregate Intrinsic Value Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Weighted Average Remaining Contractual Term Share-based Compensation Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Stock Options Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in Shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in Shares) Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Forfeitures (in Shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number (in Shares) Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized Treasury Stock, Shares, Acquired (in Shares) Number of Operating Segments Number of Reportable Segments Scenario [Axis] Equity Components [Axis] Money Market Funds [Member] Investment Holding [Axis] Noncontrolling Interest [Member] Geographical [Axis] Common Stock [Member] Major Customers [Axis] Additional Paid-in Capital [Member] Title of Individual [Axis] Credit Facility [Axis] Director [Member] Treasury Stock [Member] Restricted Stock [Member] Scenario, Unspecified [Domain] Stock Options [Member] Accumulated Other Comprehensive Income (Loss) [Member] Cash and Cash Equivalents [Axis] Award Type [Axis] Legal Entity of Counterparty, Type [Axis] Nature of Expense [Axis] Asset Class [Axis] Barclays Bank [Member] Barclays Bank [Member] US Departmentof Energy [Member] US Department of Energy [Member] Asiaand Australia [Member] Asia and Australia [Member] Certificatesofdepositsand US Treasuryobligations [Member] Certificates of deposits and US Treasury obligations [Member] European Union [Member] European Union [Member] Unvested [Member] Unvested [Member] US Treasuryobligations [Member] US Treasury obligations [Member] Certificatesofdepositdenominatedin Australiandollars [Member] Certificates of deposit denominated in Australian dollars [Member] Accumulated Deficit [Member] Accumulated Deficit [Member] Other Accrued [Member] Other Accrued [Member] Australia [Member] Australia [Member] Investmentin Joint Venture [Member] Investment in Joint Venture [Member] Performancebasedvesting [Member] Performance-based vesting [Member] Checkingandsavingsaccounts [Member] Checking and savings accounts [Member] United States [Member] United States [Member] New Jersey Boardof Public Utilities [Member] New Jersey Board of Public Utilities [Member] Europe [Member] Europe [Member] United Kingdom [Member] United Kingdom [Member] US Navy [Member] US Navy [Member] North America [Member] North America [Member] NJBPU [Member] NJBPU [Member] UK Governments Technology Strategy Board [Member] UK Government's Technology Strategy Board [Member] Certificateofdepositdenominatedin U Sdollars [Member] Certificate of deposit denominated in US dollars [Member] Document and Entity Information [Abstract] CustomerAdvancesAndDepositsDisclosureTextBlock ContractGrossProfit RelatedPartyDailyTransactionRate DeferredCreditsPayableMarketDiscountRate LongTermDebtPaymentTerms AssetImpairmentChargeAsPercentOfInvestmentAmount DeferredCreditsPayableMarketLiquidatedDamagesRate ScheduleOfForeignExchangeGainLossTableTextBlock ScheduleofCashandCashEquivalentsRestrictedCashandMarketableSecuritiesTableTextBlock DeferredCreditsPayableOptionDetails Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Net Cash Provided by (Used in) Investing Activities Document Period End Date Payments to Acquire Intangible Assets Increase (Decrease) in Deferred Revenue Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Stock Options Revenue Recognition, Policy [Policy Text Block] Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value Amendment Flag Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Increase (Decrease) in Accounts Receivable Entity Central Index Key Net Cash Provided by (Used in) Financing Activities Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price Line of Credit Facility, Current Borrowing Capacity Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block] Line of Credit Facility, Interest Rate at Period End Increase (Decrease) in Accounts Payable Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Weighted Average Remaining Contractual Term Document Fiscal Year Focus Net Income (Loss) Attributable to Noncontrolling Interest Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block] Increase (Decrease) in Other Current Assets Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Liabilities and Equity Entity Current Reporting Status Allowance for Doubtful Accounts Receivable, Current Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest New Accounting Pronouncements, Policy [Policy Text Block] Net Income (Loss) Attributable to Parent Payments to Acquire Machinery and Equipment Long-term Debt Payments for Repurchase of Common Stock Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Aggregate Intrinsic Value Cash and Cash Equivalents, Policy [Policy Text Block] Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures Increase (Decrease) in Contract Receivables, Net Stockholders' Equity Attributable to Parent Allocated Share-based Compensation Expense Amendment Description Basis of Accounting, Policy [Policy Text Block] Document Type Accounts Receivable, Net Customer Advances and Deposits Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Treasury Stock, Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners Asset Impairment Charges Liabilities, Current Operating Expenses Repayments of Debt Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Concentration Risk, Credit Risk, Policy [Policy Text Block] Net Cash Provided by (Used in) Operating Activities Use of Estimates, Policy [Policy Text Block] Payments to Acquire Marketable Securities Cash and Cash Equivalents, Period Increase (Decrease) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Assets, Current Marketable Securities, Current Noncontrolling Interest, Ownership Percentage by Parent Shares, Outstanding Consolidation, Policy [Policy Text Block] Earnings Per Share, Policy [Policy Text Block] Finite-Lived Intangible Assets, Accumulated Amortization Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized Accounts Receivable, Gross Entity Common Stock, Shares Outstanding Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Increase (Decrease) in Other Noncurrent Assets Comprehensive Income (Loss), Net of Tax, Attributable to Parent Accounts Receivable, Gross, Current Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Forfeitures Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Number of Operating Segments Entity Filer Category Entity Public Float Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Foreign Currency Transactions and Translations Policy [Policy Text Block] Entity Voluntary Filers Operating Income (Loss) Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price Treasury Stock, Shares, Acquired Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value Assets Entity Registrant Name Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Line of Credit Facility, Amount Outstanding Entity Well-known Seasoned Issuer Increase (Decrease) in Accrued Liabilities Number of Reportable Segments Gross Profit Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Increase (Decrease) in Restricted Cash Liabilities Accrued Professional Fees, Current Current Fiscal Year End Date Property, Plant and Equipment, Gross Document Fiscal Period Focus Statement [Table] Statement [Line Items]