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] Offering Agreement [Member] Sale of Stock [Axis] Over-Allotment Option [Member] One Agreement [Member] Legal Entity of Counterparty, Type [Axis] Barclays Bank [Member] Currency [Axis] Euro [Member] Range [Axis] Minimum [Member] Maximum [Member] Adjustments for New Accounting Pronouncements [Axis] Accounting Standards Update 2016-18 [Member] Scenario [Axis] Restatement Adjustment [Member] Cash and Cash Equivalents [Axis] Checking and Savings Accounts [Member] Overnight Repurchase Account [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] Warrant [Member] Award Type [Axis] Employee Stock Option [Member] Restricted Stock [Member] Vesting [Axis] Service-based Vesting [Member] Performance-based Vesting [Member] Non-vested Restricted Stock [Member] Measurement Frequency [Axis] Fair Value, Measurements, Nonrecurring [Member] 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] Litigation Case [Axis] Stipulation [Member] Nonmonetary Transaction Type [Axis] Reverse Stock Split [Member] Income Tax Authority [Axis] Foreign Tax Authority [Member] Income Tax Authority, Name [Axis] Tax Authority, Spain [Member] Balance Sheet Location [Axis] Accounts Payable and Accrued Liabilities [Member] Geographical [Axis] Monore Township [Member] Plan Name [Axis] Stock Incentive Plan 2006 [Member] Stock Incentive Plan 2015 [Member] 2018 Inducement Plan [Member] New Jersey Division of Taxation [Member] Restricted Cash [Member] Santander Bank [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 Litigation receivable Other current assets Total current assets Property and equipment, net Restricted cash- long-term Other noncurrent assets Total assets LIABILITIES AND STOCKHOLDERS' EQUITY Current liabilities: Accounts payable Accrued expenses Litigation payable Warrant liabilities Current portion of capital lease obligations Deferred credits payable current Total current liabilities Long-term portion of capital lease obligations 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 18,424,939 and 6,313,996 shares, respectively Treasury stock, at cost; 74,012 and 48,065 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 profit/(loss) Operating expenses: Product development costs Selling, general and administrative costs Total operating expenses Operating loss Gain/(loss) due to the change in fair value of warrant liabilities Interest income, net Other income Foreign exchange gain/(loss) Loss before income taxes Income tax benefit 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 Sale of stock, net of financing costs Sale of stock, net of financing costs, shares Acquisition of treasury stock Acquisition of treasury stock, shares Adoption of accounting standard update related to stock compensation accounting (ASU 2016-09) 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 (gain)/loss Depreciation Loss on disposal of property, plant and equipment Compensation expense related to stock option grants and restricted stock Change in fair value of warrant liabilities Payment for litigation settlement Changes in operating assets and liabilities: Accounts receivable Unbilled receivable Other assets Accounts payable Accrued expenses Deferred rent Unearned revenues 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) provided by investing activities Cash flows from financing activities: Proceeds from issuance of common stock and related warrants, net of costs Payment of capital lease obligations Acquisition of treasury stock Net cash provided by financing activities Effect of exchange rate changes on cash, cash equivalents and restricted cash Net 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 accounts payable Acquisition of leasehold improvements and equipment through accrued expenses Noncash investing and financing activities Accounting Policies [Abstract] Background, Basis of Presentation and Liquidity Summary of Significant Accounting Policies Investments, Debt and Equity Securities [Abstract] Marketable Securities Organization, Consolidation and Presentation of Financial Statements [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 Consolidation Use of Estimates Revenue Recognition 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 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 Marketable Securities Schedule of Accrued Expenses Warrants Tables Schedule of Fair Value Assumptions Used Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions 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 Accumulated deficit Cash and cash equivalents, 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 Share price Public offering price Long-term line of credit Line of credit facility, commitment fee percentage Letters of credit outstanding, amount Property, plant and equipment, useful life Antidilutive securities excluded from computation of earnings per share, shares Term of lease Area of land Tenant improvement work Cumulative effect of new accounting principle in period of adoption Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents RestrictedCash Cash and Cash Equivalents Restricted cash- short term Restricted cash- long term Revenues, percentage Total share-based compensation expense 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 Deferred Credits Payable Details Narrative 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 Customer advances and deposits, current Warrant exercise price per share Derivative liability, current Fair value adjustment of warrants Dividend rate Risk-free rate Expected life (years) Expected volatility 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 Sharebased compensation arrangement by sharebased payment award options outstanding contractual term Common stock, capital shares reserved for future issuance Stock based compensation, shares outstanding Stock based compensation, number of stock options 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 Number of restricted stock shares granted Number of unvested restricted stock shares issued Unrecognized compensation cost related to unvested restricted stock Treasury stock, shares, acquired Risk-free interest rate Expected dividend yield Expected life (in years) Expected volatility 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 Liabilities, fair value adjustment Assets, fair value adjustment Fair value, beginning Issuance Transfers Change in fair value Fair value, ending Litigation settlement, amount awarded to other party Estimated litigation liability, current Insurance settlements receivable Stockholders' equity note, stock split, conversion ratio Input tax Foreign tax examination refund Income tax examination, penalties expense Income tax (expense) benefit Proceed from sale of loss carryforwards and tax credits Corporate tax rate Federal statutory tax rate Income tax rate, description Unrecognized tax benefits Number of operating segments Customer Advances And Deposits Disclosure [Text Block] Warrants [Text Block] The current portion of warrant liability. Adoption of accounting standard update related to stock compensation accounting (ASU 2016-09). Securities Purchase Agreement [Member] Placement Agents [Member] Placement Agent Fees [Member] Pocket and Legal Expenses [Member] Second Amended Purchase Agreement [Member] Offering Agreement [Member] Refers to the number of financing agreements closed by the company. Period from date of issuance that the warrant or right expires. One Agreement [Member] Barclays Bank [Member] Euro [Member] Checking and Savings Accounts [Member] Money Market Account [Member] Barclays bank agreement [member] Cash on deposit at Santander Bank which serves as security for letter of credit. Related to the customer Mitsui Engineering and Ship Building. Related to the customer U.S. Department of Defense Office of Naval Research. Primary financial statement caption encompassing product development. Deferred credits payable option details Deferred Credits Payable Market Discount Rate Deferred Credits Payable Market Liquidated Damages Rate Option fee amount. Service-based Vesting [Member] Performance-based Vesting [Member] Non-vested Restricted Stock [Member] Warrant Liability[Member] Stipulation [Member] Reverse Stock Split [Member] Overnight Repurchase Account [Member] Acquisition of leasehold improvements and equipment through accounts payable. Acquisition of leasehold improvements and equipment through accrued expenses. Noncash investing and financing activities. Monore Township [Member] Stock Incentive Plan 2006 [Member] Stock Incentive Plan 2015 [Member] 2018 Inducement Plan [Member] Contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. 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. Input tax. The amount of tax refund due to the result of a foreign tax examination. Amount received from sale of net operating loss carryforwards and other tax credits. Income tax rate, description. Naval Research [Member] Warrant Liabilities [Policy Text Block] Summary of Changes on Value of Warrant Liability [Table Text Block] Restricted Cash [Member] Assets, Current Assets Liabilities, Current Liabilities Treasury Stock, Value Stockholders' Equity Attributable to Parent Liabilities and Equity Gross Profit Operating Expenses Operating Income (Loss) Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Shares, Outstanding Gain (Loss) on Disposition of Property Plant Equipment Payments for Legal Settlements Increase (Decrease) in Accounts Receivable Increase (Decrease) in Unbilled Receivables Increase (Decrease) in Other Operating Assets Increase (Decrease) in Accounts Payable Increase (Decrease) in Accrued Liabilities Increase (Decrease) in Deferred Liabilities Net Cash Provided by (Used in) Operating Activities 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 Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect CustomerAdvancesAndDepositsDisclosureTextBlock WarrantDisclosureTextBlock Marketable Securities, Policy [Policy Text Block] Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate 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, 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 Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value