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Accounting Policies [Abstract] ng_DebtInstrumentPrepaymentOption Debt Instrument, Prepayment Option The amount of cash outflow needed to prepay the debt instrument in full. May 2025 Offering [Member] Represents the May 2025 Offering. NovaGold Resources Alaska [Member] Represents NovaGold Resources Alaska. Other Liabilities Disclosure [Text Block] Donlin Gold Holdings [Member] Represents Donlin Gold Holdings. ng_WarrantsAndRightsOutstandingFairValuePerShare Warrants and Rights Outstanding, Fair Value Per Share Value of outstanding derivative securities, per share, that permit the holder the right to purchase securities (usually equity) from the issuer at a specified price. Offering to Fund Dublin Gold Transaction [Member] Represents the offering used to fund the Dublin Gold transaction. Electrum [Member] Represents Electrum. Fuel tax credit The amount of income related to a fuel tax credit. ng_ClassOfWarrantOrRightIssuedDuringPeriodExercisePrice Class of Warrant or Right, Issued During Period, Exercise Price Exercise price per share of warrants or rights issued during period. Measurement Input Type [Axis] Income Statement [Abstract] Counterparty Name [Domain] Issued during period (in shares) Class of Warrant or Right, Issued During Period The number of warrants or rights issued during period. ng_EquityOfferingMaximumOfferingAmount Equity Offering, Maximum Offering Amount Maximum value of company's equity authorized for issuance under equity offering. Backstop Warrants [Member] Represents the Backstop Warrants. May 31, 2025 (in shares) Balance (in shares) Balance (in shares) ng_EquityOfferingOptionSharesAvailable Equity Offering, Option, Shares Available (in shares) Represents the overallotment option to purchase additional shares. ng_EquityOfferingOptionPeriod Equity Offering, Option Period (Day) Represents the equity offering, option period. ng_EquityOfferingOptionPricePerShare Equity Offering, Option, Price Per Share Represents the price share for the overallotment option. ng_EquityMethodInvestmentPercentageSold Equity Method Investment, Percentage Sold The percentage amount of an equity method investment which has been sold. Public Equity Offering [Member] Represents a public equity offering. Segment Reporting [Text Block] Measurement Input, Expected Term [Member] Measurement Input, Exercise Price [Member] Net loss Net loss Net loss Adjustments: Award Type [Axis] Measurement Input, Price Volatility [Member] us-gaap_Liabilities Liabilities LIABILITIES us-gaap_LiabilitiesAndStockholdersEquity Liabilities and Equity Share-based Compensation Expense Measurement Input Type [Domain] Segment Reporting [Table] Measurement Input, Risk Free Interest Rate [Member] Share-based compensation (Note 14) Share-based compensation (Note 13) Equity Method Investment, Nonconsolidated Investee [Axis] ng_EquityMethodInvestmentPercentageAcquired Equity Method Investment, Percentage Acquired Percentage of equity method investment acquired. Equity Method Investment, Nonconsolidated Investee [Domain] us-gaap_WarrantsAndRightsOutstandingMeasurementInput Warrants and Rights Outstanding, Measurement Input Share-Based Payment Arrangement [Text Block] Change in operating assets and liabilities Accounting Standards Update and Change in Accounting Principle [Table] Note Receivable Upon Approval of Galore Creek Project Construction Plan [Member] Related to the note receivable upon approval of Galore Creek project construction plan. Note Receivable Upon Completion of Galore Creek Project Feasibility [Member] Related to the note receivable upon completion of the Galore Creek project feasibility stud. Note Receivable Upon Completion of Galore Creek Project Pre-feasibility [Member] Related to the note receivable upon completion of Galore Creek project pre-feasiblity study. Fair Value, by Balance Sheet Grouping [Table] us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect Net change in cash and cash equivalents us-gaap_RelatedPartyTransactionAmountsOfTransaction Related Party Transaction, Amounts of Transaction ng_WorkingCapitalAdjustment Working Capital Adjustment Represents the amount of working capital adjustment paid during the period. Related and Nonrelated Parties [Domain] Cashless exercise – options cancelled (in shares) The number of equity-based payment instruments, excluding stock (or unit) options, that were cancelled during the reporting period. us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations Effect of exchange rate changes on cash and cash equivalents ng_ShareBasedCompensationArrangementBySharebasedPaymentAwardPerformancePeriod Share-Based Compensation Arrangement by Share-based Payment Award, Performance Period The length of the performance period between the grant date and the maturity date when a vesting determination is made. Related Party Transaction [Table] ng_DebtInstrumentPaymentsPercentageOfCertainNetProceeds Debt Instrument, Payments, Percentage of Certain Net Proceeds Amount of payments of debt as percentage of certain net proceeds. Related Party Transactions Disclosure [Text Block] New Accounting Pronouncements, Policy [Policy Text Block] Cashless exercise – options cancelled, weighted average exercise price (in dollars per share) Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were cancelled. us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations Cash and cash equivalents at beginning of period Cash and cash equivalents at end of period Warrants (Note 9) Statement [Table] Warrants exercised (Note 9) (in shares) Number of shares issued during period for exercise of warrants. ng_ClassOfWarrantOrRightCancelledDuringPeriod Cashless exercise – warrants cancelled (in shares) The number of warrants or rights cancelled during period. ng_ClassOfWarrantOrRightExercisedDuringPeriod Exercised – shares issued (in shares) The number of warrants or rights exercised during period. Effect of exchange rate changes on cash and cash equivalents Warrants exercised (Note 9) The value of shares issued on exercise of warrants. us-gaap_PrepaidExpenseCurrent Prepaid expenses Corporate communications and regulatory The amount of expense in the period for communications and regulatory. Other (expense) income: us-gaap_EquityMethodInvestments Balance – beginning of period Balance – end of period us-gaap_DebtInstrumentBasisSpreadOnVariableRate1 Debt Instrument, Basis Spread on Variable Rate Statement of Financial Position [Abstract] us-gaap_NonoperatingIncomeExpense Nonoperating Income (Expense) us-gaap_EquitySecuritiesFvNi Equity Securities, FV-NI, Current Line of Credit Facility, Lender [Domain] us-gaap_EquityMethodInvestmentOwnershipPercentage Equity Method Investment, Ownership Percentage us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number Balance, PSU awards (in shares) Balance, PSU awards (in shares) Lender Name [Axis] us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue Balance, PSU award, weighted-average grant day fair value (in dollars per share) Balance, PSU award, weighted-average grant day day value (in dollars per share) ng_EquityMethodInvestmentTransactionCosts Equity Method Investment, Transaction Costs This element represents the transaction costs of investments accounted for under the equity method of accounting. Granted (in shares) Granted, weighted-average grant day fair value (in dollars per share) Long-Term Debt, Type [Axis] us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod Forfeited (in shares) Change in fair market value of marketable equity securities Change in fair value of marketable securities (Note 12) Professional fees us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount Line of Credit Facility [Table] Other Assets, Noncurrent Other assets (Note 6) Other Assets, Noncurrent Other assets us-gaap_WarrantsAndRightsOutstanding Warrants and Rights Outstanding dei_DocumentType Document Type Weighted-average grant-date fair value (in dollars per share) Operating expenses: Document Information [Line Items] dei_DocumentQuarterlyReport Document Quarterly Report Contingent Note Receivable, Policy [Policy Text Block] Disclosure of accounting policy for contingent note receivable. Intrinsic value of options exercised Document Information [Table] Vested and exercisable as of November 30, 2024 (in shares) dei_EntityInteractiveDataCurrent Entity Interactive Data Current Vested and exercisable as of November 30, 2024 (in dollars per share) ASSETS us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber Balance shares (in shares) Balance shares (in shares) dei_DocumentTransitionReport Document Transition Report us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice Weighted average exercise price outstanding, balance (in dollars per share) Weighted average exercise price outstanding, balance (in dollars per share) Statement [Line Items] us-gaap_OperatingExpenses Operating Expenses Private Placement [Member] May 31, 2026 Award Type [Domain] Risk-free interest rate Expected volatility Basic and diluted (thousands) (in shares) Expected dividend rate us-gaap_NotesReceivableNet Financing Receivable, after Allowance for Credit Loss Net loss per common share – basic and diluted (in dollars per share) us-gaap_NotesPayable Notes Payable Balance – beginning of period Balance – end of period Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table] Notes Payable, Other Payables [Member] Common shares Promissory note (Note 7) us-gaap_ProceedsFromDivestitureOfInterestInSubsidiariesAndAffiliates Proceeds from Divestiture of Interest in Subsidiaries and Affiliates Proceeds from issuance of equity (Note 9) us-gaap_ProceedsFromIssuanceOfCommonStock Proceeds from Issuance of Common Stock us-gaap_InterestPayableCurrentAndNoncurrent Interest Payable us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent Accounts payable and accrued liabilities Current liabilities: Accounts payable, accrued liabilities and lease obligations us-gaap_PolicyTextBlockAbstract Accounting Policies us-gaap_DisclosureTextBlockAbstract Notes to Financial Statements us-gaap_TableTextBlock Notes Tables Document Fiscal Period Focus Document Fiscal Year Focus us-gaap_ComprehensiveIncomeNetOfTax Comprehensive loss Investment, Name [Domain] Amendment Flag Common Stock [Member] Financing Receivables [Text Block] us-gaap_ProceedsFromSaleAndMaturityOfMarketableSecurities Proceeds from sale of marketable securities dei_DocumentPeriodEndDate Document Period End Date Nonrelated Party [Member] Legal Entity [Axis] us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross Granted (in shares) us-gaap_EmployeeRelatedLiabilitiesCurrent Accrued payroll and related benefits Related Party [Member] Significant Accounting Policies [Text Block] Financing Receivable, Allowance for Credit Loss [Table] dei_EntityFileNumber Entity File Number May 31, 2026 (Year) us-gaap_ProceedsFromCollectionOfNotesReceivable Proceeds from Collection of Notes Receivable Entity [Domain] Entity Central Index Key PSU, Awards, Aggregate intrinsic value dei_EntityRegistrantName Entity Registrant Name Schedule of Other Nonoperating Income (Expense) [Table Text Block] dei_EntityCurrentReportingStatus Entity Current Reporting Status dei_EntityIncorporationStateCountryCode Entity Incorporation, State or Country Code Expected term of options (years) (Year) Current Fiscal Year End Date Vested and exercisable as of November 30, 2024 (Year) dei_EntityFilerCategory Entity Filer Category dei_EntityShellCompany Entity Shell Company dei_EntityEmergingGrowthCompany Entity Emerging Growth Company us-gaap_EquityMethodInvestmentAggregateCost Equity Method Investment, Aggregate Cost dei_EntitySmallBusiness Entity Small Business us-gaap_OperatingIncomeLoss Loss from operations Schedule of Stockholders' Equity Note, Warrants or Rights [Table Text Block] Class of Warrant or Right [Table] us-gaap_ProceedsFromInterestAndDividendsReceived Interest and dividends received us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Nonvested, Number of Shares us-gaap_Revenues Revenues Interest expense on promissory note Interest expense - promissory note (Note 7) dei_EntityAddressStateOrProvince Entity Address, State or Province Statement of Stockholders' Equity [Abstract] Loss Contingencies [Table] dei_EntityAddressCityOrTown Entity Address, City or Town Accumulated deficit dei_EntityAddressAddressLine1 Entity Address, Address Line One Class of Warrant or Right [Axis] Statement of Cash Flows [Abstract] Class of Warrant or Right [Domain] dei_CityAreaCode City Area Code us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation Payments of withholding tax on share-based compensation dei_LocalPhoneNumber Local Phone Number dei_EntityAddressPostalZipCode Entity Address, Postal Zip Code Equity Method Investment [Table] us-gaap_OperatingLeaseRightOfUseAssetStatementOfFinancialPositionExtensibleList Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] Other comprehensive income Long-Term Debt, Type [Domain] dei_Security12bTitle Title of 12(b) Security Equity Components [Axis] Expired, weighted average exercise price (in dollars per share) Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were expired. dei_SecurityExchangeName Security Exchange Name Donlin Gold [Member] Represents information pertaining to the Donlin Gold project in Alaska, U.S.A. Expired (in shares) Expired (in shares) The number of equity-based payment instruments, excluding stock (or unit) options, that were expired during the reporting period. dei_TradingSymbol Trading Symbol Galore Creek [Member] Represents information pertaining to the Galore Creek project in British Columbia, Canada. Payments for costs related to equity issuance (Note 9) Payments of Stock Issuance Costs Share-Based Payment Arrangement [Policy Text Block] Cash received from options exercised Class of Stock [Axis] Proceeds from term deposits Amount of cash inflow for receipts of term deposits. Equity Component [Domain] Prime Rate [Member] Variable Rate [Domain] Management and Administrative Services Provided [Member] Information pertaining to provided management and administrative services. Related Party Transaction [Domain] AOCI Attributable to Parent [Member] Equity [Text Block] dei_EntityCommonStockSharesOutstanding Entity Common Stock, Shares Outstanding (in shares) Additional Paid-in Capital [Member] us-gaap_ClassOfWarrantOrRightOutstanding Balance – beginning of year (in shares) Balance – end of period (in shares) Retained Earnings [Member] Related Party Transaction [Axis] Other assets (Note 6) Other Assets, Current Term deposits Other operating adjustments Barrick [Member] Represents information pertaining to Barrick Gold Corporation. ng_UnconsolidatedVenturesNumberOfDirectorsSelectedByVenturePartners Unconsolidated Ventures, Number of Directors Selected By Venture Partners Represents the number of directors on the board of unconsolidated ventures, which directors are selected by the reporting entity's venture partners. Weighted average shares outstanding Non-current assets: Right-of-use assets, property and equipment ng_UnconsolidatedVenturesNumberOfDirectors Unconsolidated Ventures, Number of Directors Represents the total number of directors on the board of an unconsolidated venture, including those selected by the reporting entity and/or the venture partner. ng_UnconsolidatedVenturesNumberOfDirectorsSelectedByTheReportingEntity Unconsolidated Ventures, Number of Directors, Selected By the Reporting Entity Represents the number of directors on the board of unconsolidated ventures, which directors are selected by the reporting entity. ng_EquityMethodInvestmentSummarizedFinancialInformationMineralPropertyExpenditures Mineral property expenditures The Company's share of the cost of mineral property expenditures reported by an equity method investment. Remediation liability The increase (decrease) during the reporting period in remediation liability. Salaries and benefits Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table] ng_EquityMethodInvestmentSummarizedFinancialInformationDepreciation Depreciation The Company's share of the depreciation expense reported by an equity method investment of the entity. Other Income and Other Expense Disclosure [Text Block] Office expense Sale of Stock [Axis] Vested and exercisable as of November 30, 2024 Income taxes payable Investment, Name [Axis] Share-based compensation Share-based compensation ng_EquityMethodInvestmentSummarizedFinancialInformationAccretion Accretion The Company's share of the accretion expense reported by an equity method investment of the entity. EQUITY (DEFICIT) Schedule of Nonvested Performance-Based Units Activity [Table Text Block] Other Other (expense) income, net (Note 12) Foreign currency translation adjustments us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax Receivable [Domain] Sale of Stock [Domain] Share-Based Payment Arrangement, Option, Activity [Table Text Block] us-gaap_Assets Assets Cash and cash equivalents us-gaap_InterestReceivableCurrent Interest receivable Fair Value Disclosures [Text Block] Share-Based Payment Arrangement, Option [Member] Schedule of Share-Based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Supplemental disclosures of cash flow information: Expected volatility of TSX index The estimated measure of the percentage by which a TSX index share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period. ng_ReclamationAndLeaseLiability Non-current liabilities: Reclamation and lease obligations The amount reclamation and lease liability. Remediation liabilities, current Represents current remediation liabilities. us-gaap_AccountsReceivableNet Accounts Receivable, after Allowance for Credit Loss Remediation liabilities, noncurrent Represents noncurrent remediation liabilities. Lease obligations, current Represents current lease obligations. us-gaap_LiabilitiesCurrent Current liabilities us-gaap_DebtInstrumentVariableInterestRateTypeExtensibleEnumeration Debt Instrument, Variable Interest Rate, Type [Extensible Enumeration] Schedule of Share-Based Payment Award, Performance Share Units, Valuation Assumptions [Table Text Block] Tabular disclosure of the significant assumptions used during the year to estimate the fair value of performance share units, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions. Lease obligations, noncurrent Represents noncurrent lease obligations. Equity Method Investments and Joint Ventures Disclosure [Text Block] us-gaap_AccountsReceivableNetCurrent Accounts receivable Equity Method Investments [Table Text Block] us-gaap_MarketableSecuritiesNoncurrent Marketable equity securities Withholding tax on PSUs Withholding tax on PSUs Expected correlation between Company shares and TSX The estimated measure of the percentage by which the share price of the company shares is expected to be correlated with the TSX Index. us-gaap_MarketableSecuritiesCurrent Marketable equity securities Other Liabilities [Table Text Block] us-gaap_IncomeTaxesPaid Income taxes paid us-gaap_AssetsNet Net assets ng_OfficeEquipment Office equipment Represents the carrying value of office equipment as of the balance sheet date. Interest income Disposal Group Name [Domain] Receivable Type [Axis] General and Administrative Expenses [Text Block] The entire disclosure for general and administrative expense items. Funding ng_PercentageOfSpecifiedRevenueFromWhichThePromissoryNoteAndAccruedInterestArePayable Percentage of Specified Revenue from Which the Promissory Note and Accrued Interest Are Payable Represents the percentage of revenue from future mine production or from any net proceeds resulting from a reduction of the reporting entity's interest in the specified equity method investment, from which the promissory note and accrued interest are payable. Other Commitments [Table] General and Administrative Expenses [Table Text Block] Tabular disclosure of each detailed component of general and administrative expenses. Accumulated other comprehensive loss us-gaap_PaymentsToAcquireInvestments Purchases of term deposits us-gaap_PaymentsToAcquireInterestInSubsidiariesAndAffiliates Funding of Donlin Gold Non-current assets: Mineral property us-gaap_MineralPropertiesNet Disposal Group Name [Axis] General & administrative (Note 11) General and Administrative Expense ng_PolicyTable Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block] Contributed surplus May 31, 2025 Equity, Attributable to Parent Balance Balance Debt Disclosure [Text Block] Forfeited, weighted average exercise price (in dollars per share) Performance Share Units [Member] Represents information pertaining to performance share units. ng_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfCommonSharesPerAwardAdjustedMultiplier Share-based Compensation Arrangement by Share-based Payment Award, Number of Common Shares Per Award, Adjusted, Multiplier Represents the percentage multiplier that may be used in order to determine the adjusted number of common shares to be granted per share-based payment award, based on the achievement of certain performance criteria. Other Assets Disclosure [Text Block] us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1 Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Deferred Share Units [Member] Represents information pertaining to deferred share units. Private placement, net (Note 9) Other comprehensive income (loss): Performance share units (PSUs) settled in shares Stock, Class of Stock [Table] us-gaap_DebtInstrumentFairValue Debt Instrument, Fair Value Disclosure Nature of Operation, Product Information, Concentration of Risk [Table] us-gaap_DebtInstrumentFaceAmount Debt Instrument, Face Amount Schedule of Other Assets [Table Text Block] Stock options exercised us-gaap_OperatingLeaseRightOfUseAsset Right-of-use assets Other liabilities (Note 8) Other Liabilities, Current, Total Schedule of Debt [Table Text Block] Current assets: Cash, prepaid expenses, and other receivables us-gaap_AssetsCurrent Current assets us-gaap_OtherLiabilitiesNoncurrent Other liabilities (Note 8) Other Liabilities, Noncurrent, Total Performance share units (PSUs) settled in shares (in shares) ecd_Rule10b51ArrTrmntdFlag Rule 10b5-1 Arrangement Terminated [Flag] ecd_Rule10b51ArrAdoptedFlag Rule 10b5-1 Arrangement Adopted [Flag] Expected forfeiture rate The estimated forfeiture rate over the option's term. Private placement, net (Note 9) (in shares) Stock Issued During Period, Shares, New Issues