Equity Components [Axis] Common Stock [Member] Treasury Stock [Member] Additional Paid-In Capital [Member] Accumulated Deficit [Member] Accumulated Other Comprehensive Loss [Member] Type of Arrangement and Non-arrangement Transactions [Axis] Securities Purchase Agreement [Member] Counterparty Name [Axis] Placement Agents [Member] Nature of Expense [Axis] Placement Agent Fees [Member] Pocket and Legal Expenses [Member] Second Amended Purchase Agreement [Member] One Agreement [Member] Legal Entity of Counterparty, Type [Axis] Barclays Bank [Member] Currency [Axis] Euro [Member] Cash and Cash Equivalents [Axis] Checking and Savings Accounts [Member] Money Market Account [Member] Restricted Cash and Cash Equivalents [Axis] Barclays Bank Agreement [Member] Concentration Risk Benchmark [Axis] Sales Revenue, Net [Member] Concentration Risk Type [Axis] Customer Concentration Risk [Member] Customer [Axis] Mitsui Engineering & Shipbuilding [Member] U.S. Department of Defense Office of Naval Research [Member] Income Statement Location [Axis] Product Development [Member] Selling, General and Administrative [Member] Award Type [Axis] Employee Stock Option [Member] Non-vested Restricted Stock [Member] Measurement Frequency [Axis] Fair Value, Measurements, Recurring [Member] Fair Value, Hierarchy [Axis] Fair Value, Inputs, Level 1 [Member] Fair Value, Inputs, Level 2 [Member] Fair Value, Inputs, Level 3 [Member] Financial Instrument [Axis] Warrant Liability [Member] Nonmonetary Transaction Type [Axis] Reverse Stock Split [Member] Geographical [Axis] Monore Township [Member] Plan Name [Axis] Stock Incentive Plan 2006 [Member] 2018 Inducement Plan [Member] Litigation Case [Axis] Stipulation [Member] Restricted Cash [Member] Santander Bank [Member] Eni S.p.A [Member] Premier Oil UK Limited [Member] Range [Axis] Minimum [Member] Maximum [Member] Contract with Customer, Basis of Pricing [Axis] Fixed Price [Member] Firm Fixed Price [Member] Cost Sharing [Member] Cost Plus [Member] Warrant [Member] Measurement Input Type [Axis] Dividend Rate [Member] Risk Free Interest Rate [Member] Expected Life (Years) [Member] Expected Volatility [Member] 2015 Omnibus Incentive Plan [Member] Restricted Stock [Member] Non-Vested Restricted Stock [Member] Legal Entity [Axis] Tide Runner Marine, Inc. Income Tax Authority, Name [Axis] Tax Authority, Spain [Member] Adjustments for New Accounting Pronouncements [Axis] Effect of Adoption [Member] Amounts Excluding Effect of Adoption [Member] Subsequent Event Type [Axis] Subsequent Event [Member] Related Party [Axis] Aspire Capital Fund, LLC [Member] Purchase Agreement [Member] Report Date [Axis] August 28, 2018 [Member] Charles F. Dunleavy [Member] Document And Entity Information Entity Registrant Name Entity Central Index Key Document Type Document Period End Date Amendment Flag Current Fiscal Year End Date Entity Filer Category Entity Common Stock, Shares Outstanding Trading Symbol Document Fiscal Period Focus Document Fiscal Year Focus Statement of Financial Position [Abstract] ASSETS Current assets: Cash and cash equivalents Marketable securities Restricted cash- short-term Accounts receivable Unbilled receivables Contract assets Litigation receivable Other current assets Total current assets Property and equipment, net Restricted cash- long-term Total assets LIABILITIES AND STOCKHOLDERS' EQUITY Current liabilities: Accounts payable Accrued expenses Litigation payable Unearned revenue Contract liabilities Warrant liabilities Current portion of capital lease obligations Deferred credits payable current Total current liabilities Deferred rent Total liabilities Commitments and contingencies Ocean Power Technologies, Inc. stockholders' equity: Preferred stock, $0.001 par value; authorized 5,000,000 shares, none issued or outstanding Common stock, $0.001 par value; authorized 50,000,000 shares, issued 18,442,298 and 18,424,939 shares, respectively Treasury stock, at cost; 74,012 and 74,012 shares, respectively Additional paid-in capital Accumulated deficit Accumulated other comprehensive loss Total stockholders' equity Total liabilities and stockholders' equity Preferred stock, par value Preferred stock, shares authorized Preferred stock, shares issued Preferred stock, shares outstanding Common stock, par value Common stock, shares authorized Common stock, shares issued Treasury stock, shares Income Statement [Abstract] Revenues Cost of revenues Gross loss Operating expenses: Engineering and product development costs Selling, general and administrative costs Total operating expenses Operating loss Gain due to the change in fair value of warrant liabilities Interest income, net Foreign exchange gain/(loss) Net loss Basic and diluted net loss per share Weighted average shares used to compute basic and diluted net loss per share Statement of Comprehensive Income [Abstract] Net loss Foreign currency translation adjustment Total comprehensive loss Statement [Table] Statement [Line Items] Balance Balance, shares Stock based compensation Issuance of restricted stock, net Issuance of restricted stock, net, shares Other comprehensive loss Balance Balance, shares Statement of Cash Flows [Abstract] Cash flows from operating activities: Adjustments to reconcile net loss to net cash used in operating activities: Foreign exchange loss/(gain) Depreciation Loss on disposal of property, plant and equipment Compensation expense related to stock option grants and restricted stock Gain due to the change in fair value of warrant liabilities Changes in operating assets and liabilities: Accounts receivable Unbilled receivables Contract assets Other assets Accounts payable Accrued expenses Deferred rent Deferred credit payable Unearned revenue Contract liabilities Net cash used in operating activities Cash flows from investing activities: Purchases of marketable securities Maturities of marketable securities Leasehold improvements and purchase of equipment Net cash used in investing activities Cash flows from financing activities: Proceeds from issuance of common stock, net of costs Payment of capital lease obligations Acquisition of treasury stock Net cash (used in) provided by financing activities Effect of exchange rate changes on cash, cash equivalents and restricted cash Net (decrease)/increase in cash, cash equivalents and restricted cash Cash, cash equivalents and restricted cash, beginning of period Cash, cash equivalents and restricted cash, end of period Supplemental schedule of cash flows information: Cash paid for interest Supplemental disclosure of noncash investing activities: Acquisition of leasehold improvements and equipment through accrued expenses Accounting Policies [Abstract] Background, Basis of Presentation and Liquidity Summary of Significant Accounting Policies Account Receivable Contract Assets And Contract Liabilities Account Receivable, Contract Assets, and Contract Liabilities Investments, Debt and Equity Securities [Abstract] Marketable Securities Payables and Accruals [Abstract] Accrued Expenses Deferred Credits Payable Deferred Credits Payable Warrants Warrants Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Stock-Based Compensation Fair Value Disclosures [Abstract] Fair Value Measurements Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Income Tax Disclosure [Abstract] Income Taxes Segment Reporting [Abstract] Operating Segments and Geographic Information Adoption Of Revenue Recognition Guidance Adoption of Revenue Recognition Guidance Subsequent Events [Abstract] Subsequent Events Consolidation Use of Estimates Cash, Cash Equivalents, Restricted Cash and Security Agreements Marketable Securities Foreign Exchange Gains and Losses Property and Equipment Concentration of Credit Risk Warrant Liabilities Net Loss Per Common Share Share-Based Compensation Deferred Rent Revenue Recognition Recently Issued Accounting Standards Schedule of Cash and Cash Equivalents Schedule of Cash and Cash Equivalents and Restricted Cash Schedule of Revenue by Major Customers by Reporting Segments Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs Schedule of Percentages of Revenues by Contract Schedule of Accounts Receivable Schedule of Contract Assets and Contract Liabilities Schedule of Accrued Expenses Schedule of Fair Value Assumptions Used Schedule of Stock Option Activity Schedule of Non-vested Restricted Stock Activity Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis Summary of Changes on Value of Warrant Liability Schedule of Condensed Consolidated Financial Statements Accumulated deficit Cash and cash equivalents, restricted cash and marketable securities, at carrying value Number of financing agreements closed Number of common stock shares sold Warrant to purchase shares common stock Class of warrant or right, number of securities called by each warrant or right Combined purchase price per share Proceeds from issuance or sale of equity Class of warrant or right, exercise price of warrants or rights Class of warrant or right, expiration period Payments of stock issuance costs Scenario [Axis] Restatement [Axis] Investment Type [Axis] Long-term line of credit Line of credit facility, commitment fee percentage Letters of credit outstanding, amount Estimated useful life of asset Concentration risk percentage Antidilutive securities excluded from computation of earnings per share, shares Term of lease Area of land Tenant improvement work Revenue remaining performance obligation Revenue remaining performance obligation, percentage Performance obligation revenue of next twelve months Additional performance obligation revenue of next twelve months Restricted Cash Cash and Cash Equivalents Restricted cash- short term Restricted cash- long term Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Revenues, percentage Total share-based compensation expense Percentages of revenues by contract Revenue related to performance obligations Account Receivable Contract Assets And Contract Liabilities - Schedule Of Accounts Receivable Opening balance Amount invoiced to customer Collections Ending balance Account Receivable Contract Assets And Contract Liabilities - Schedule Of Contract Assets And Contract Liabilities Contract (liability)/assets, net Certificate of Deposit Project costs Contract loss reserve Employee incentive payments Accrued salary and benefits Legal and accounting fees Accrued taxes payable Other Accrued expenses total Customer advances or deposits, noncurrent Deferred credits payable option details Deferred credits payable market discount rate Deferred credits payable market liquidated damages rate Option fee amount Payments on deferred credits Customer advances and deposits, current Warrant exercise price per share Class of warrant or right, expiration period Fair value adjustment of warrants Fair value measurement percent Fair value measurement expected life Vesting [Axis] Share-based compensation arrangement by share-based payment award, number of shares authorized Share-based compensation arrangement by share-based payment award, number of additional shares authorized Stock based compensation shares, available for grant Number of restricted shares granted Share-based compensation intrinsic value of outstanding Share-based compensation options, exercisable intrinsic value Share-based compensation unvested shares of stock options Share-based compensation weighted average remaining contractual term Share-based compensation expense Unrecognized compensation cost related to non-vested stock options Share-based compensation cost expected to recognize weighted-average term Unrecognized compensation cost related to unvested restricted stock Treasury stock, shares, acquired Shares Underlying Options Outstanding, Beginning Shares Underlying Options Outstanding, Granted Shares Underlying Options Outstanding, Exercised Shares Underlying Options Outstanding, Cancelled/forfeited Shares Underlying Options Outstanding, Ending Shares Underlying Options Outstanding, Exercisable Weighted Average Exercise Price, Beginning Balance Weighted Average Exercise Price, Granted Weighted Average Exercise Price, Exercised Weighted Average Exercise Price, Cancelled/forfeited Weighted Average Exercise Price, Ending Balance Weighted Average Exercise Price, Exercisable Weighted Average Remaining Contractual Term (In Years), Beginning Weighted Average Remaining Contractual Term (In Years), Ending Weighted Average Remaining Contractual Term (In Years), Exercisable Number of Shares, Issued and unvested, Beginning Number of Shares, Granted Number of Shares, Vested Number of Shares, Cancelled/forfeited Number of Shares, Issued and Unvested, Ending Weighted Average Price per Share, Issued and Unvested, Beginning Weighted Average Price per Share, Granted Weighted Average Price per Share, Vested Weighted Average Price per Share, Cancelled/forfeited Weighted Average Price per Share, Issued and Unvested, Ending Fair Value Hierarchy and NAV [Axis] Warrant liabilities Fair value, beginning Change in fair value Fair value, ending Litigation settlement, amount awarded to other party Loss Contingency Accrual Loss contingency, receivable Reverse stock split Damages sought value Income tax examination, penalties and interest accrued Income tax benefit (expense) Number of reportable segments Operating loss Total comprehensive loss Total assets Contract liability Stockholders' equity Total liabilities and stockholders' equity Contract liability Net cash used in operating activities Net increase in cash, cash equivalents and restricted cash Cash, cash equivalents and restricted cash, end of period Common stock, price per share Common stock bid price, description Purchase of common stock Acquisition of leasehold improvements and equipment through accrued expenses. Barclays bank agreement [member] Barclays Bank [Member] Checking and Savings Accounts [Member] Customer Advances And Deposits Disclosure [Text Block] Related to the customer Mitsui Engineering and Ship Building. Money Market Account [Member] Monore Township [Member] Naval Research [Member] Non-vested Restricted Stock [Member] Offering Agreement [Member] One Agreement [Member] Overnight Repurchase Account [Member] Performance-based Vesting [Member] Placement Agent Fees [Member] Placement Agents [Member] Pocket and Legal Expenses [Member] Primary financial statement caption encompassing product development. Restricted Cash [Member] Reverse Stock Split [Member] Cash on deposit at Santander Bank which serves as security for letter of credit. Second Amended Purchase Agreement [Member] Securities Purchase Agreement [Member] Service-based Vesting [Member] Stipulation [Member] Stock Incentive Plan 2015 [Member] Stock Incentive Plan 2006 [Member] Summary of Changes on Value of Warrant Liability [Table Text Block] 2018 Inducement Plan [Member] Related to the customer U.S. Department of Defense Office of Naval Research. Warrants [Text Block] Warrant Liabilities [Policy Text Block] Warrant Liability[Member] Represents office furniture and equipment. OPTA [Member] New Jersey Board of Public Utilities 1 [Member] Equipment Under Capitalized Lease [Member] George W. Taylor [Member] Monroe Lease [Member] Stern Lawsuit [Member] Asia and australia [member] Period from date of issuance that the warrant or right expires. 2015 Omnibus Incentive Plan [Member] August 30, 2018 [Member] Refers to the number of financing agreements closed by the company. Eni S.p.A [Member] Premier Oil UK Limited [Member] Deferred credits payable option details Deferred Credits Payable Market Discount Rate Deferred Credits Payable Market Liquidated Damages Rate Option fee amount. Computer Equipment & Software [Member] Office Furniture & Fixtures [Member] Income Tax Reforms [Member] Account Receivable, Contract Assets, and Contract Liabilities [Text Block] Schedule of Percentages of Revenues by Contract [Table Text Block] Fixed Price [Member] Firm Fixed Price [Member] Cost Sharing [Member] Cost Plus [Member] Fair value measurement percent. Fair value measurement expected life. Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. The current portion of warrant liability. Effect of Adoption [Member] Amounts Excluding Effect of Adoption [Member] Purchase Agreement [Member] Common stock bid price, description. Euro [Member] Contract (liability)/assets, net. Payments on deferred credits. Aspire Capital Fund, LLC [Member] Tide Runner Marine, Inc. [Member] September 11th, 2018 [Member] Cash and cash equivalents, restricted cash and marketable securities, at carrying value. Unearned revenue. Increase decrease in unearned revenue. August 28, 2018 [Member] Charles F. Dunleavy [Member] Assets, Current Liabilities, Current Liabilities Treasury Stock, Value Gross Profit Operating Expenses Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Shares, Outstanding Gain (Loss) on Disposition of Property Plant Equipment Increase (Decrease) in Accounts Receivable Increase (Decrease) in Unbilled Receivables Increase (Decrease) in Contract with Customer, Asset Increase (Decrease) in Other Operating Assets Increase (Decrease) in Accounts Payable Increase (Decrease) in Accrued Liabilities Increase (Decrease) in Deferred Liabilities IncreaseDecreaseInUnearnedRevenue Payments to Acquire Marketable Securities Payments to Acquire Machinery and Equipment Net Cash Provided by (Used in) Investing Activities Repayments of Long-term Capital Lease Obligations Payments for Repurchase of Common Stock Net Cash Provided by (Used in) Financing Activities CustomerAdvancesAndDepositsDisclosureTextBlock WarrantDisclosureTextBlock Marketable Securities, Policy [Policy Text Block] Proceeds from Sale and Collection of Receivables optt_ClassOfWarrantOrRightExpirationPeriod Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number 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, Exercisable, Weighted Average Exercise Price Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number 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, Equity Instruments Other than Options, Forfeited in Period Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value WarrantLiabilityCurrent Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value