Document And Entity Information Note To Financial Statement Details Textual Significant Accounting Policies Note 2 - Significant Accounting Policies Note 3 - Inventories Customer Number 3 [Member] Information pertaining to customer number 3 accounting for a percentage of accounts receivable. Note 4 - Equipment and Leasehold Improvements Note 6 - Accrued Expenses Note 7 - Long-term Debt Note 9 - Share-based Compensation Note 11 - (Loss) Earnings Per Share Note 2 - Significant Accounting Polices - Reconciliation of Cash and Restricted Cash (Details) Income Tax Disclosure [Text Block] Note 2 - Significant Accounting Policies - Revenue By Product (Details) Note 3 - Inventories - Components of Inventory (Details) Note 4 - Equipment and Leasehold Improvements, Net - Components of Equipment and Leasehold Improvements (Details) Other assets Note 6 - Accrued Expenses - Components of Accrued Expenses (Details) Share-based compensation expense us-gaap_LiabilitiesCurrent Total current liabilities Note 7 - Long-term Debt - Summary of Long-term Debt (Details) Note 9 - Share-based Compensation - Shares Authorized, Available for Future Grant and Outstanding Under Each Plan (Details) Title of Individual [Axis] Note 9 - Share-based Compensation - Summary of Option Activity Under Stock Plans (Details) Relationship to Entity [Domain] Note 9 - Share-based Compensation - Summary of Non-vested Options (Details) Note 9 - Share-based Compensation - Restricted Stock Units (Details) Note 11 - (Loss) Earnings Per Share - Summary of Reconciliations Between the Numerator and the Denominator of the Basic and Diluted Earnings Per Share Computations (Details) Notes To Financial Statements Notes To Financial Statements [Abstract] OPERATING EXPENSES: Share-based Compensation, Stock Options, Activity [Table Text Block] Granted, weighted average grant price (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Vested, weighted average grant price (in dollars per share) Forfeited, weighted average grant price (in dollars per share) Nonvested restricted stock units, weighted average grant price (in dollars per share) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod Forfeited (in shares) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber Outstanding (in shares) Nonvested restricted stock units (in shares) Nonvested restricted stock units (in shares) Schedule of Nonvested Share Activity [Table Text Block] Current maturities of long-term debt Less current maturities cyan_LongTermDebtAndCapitalLeaseObligationsCurrentAndNoncurrent Long-term Debt and Capital Lease Obligations, Current and Noncurrent Sum of the carrying values as of the balance sheet date of both current and noncurrent portions of long-term debt and capital lease obligations. Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod Vested (in shares) Depreciation and amortization 2014 Directors Plan [Member] Represents the "2014 Directors Plan." The 2005 Plan [Member] Represents the "2005 Plan." Schedule of Nonvested Restricted Stock Units Activity [Table Text Block] 2004 Directors Plan [Member] Represents the "2004 Directors Plan." cyan_DebtCovenantMinimumCurrentRatio Debt Covenant, Minimum Current Ratio The minimum current ratio (current assets divided by current liabilities, expressed as a ratio) as required under a debt covenant. us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice Exercisable, weighted average exercise price (in dollars per share) us-gaap_AssetsCurrent Total current assets us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1 Exercisable, weighted average remaining contractual term (Year) us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1 Exercisable, aggregate intrinsic value us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber Exercisable (in shares) Line of credit Line of Credit, Current us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2 Outstanding, weighted average remaining contractual term (Year) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue Outstanding, aggregate intrinsic value Granted (in dollars per share) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedWeightedAverageGrantDateFairValue Vested (in dollars per share) us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedOptionsForfeitedWeightedAverageGrantDateFairValue Forfeited (in dollars per share) Nonvested (in dollars per share) us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares Vested (in shares) us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedOptionsForfeitedNumberOfShares Forfeited (in shares) Interest expense, net Common stock of $0.02 par value, shares authorized 50,000,000; 5,836,110 shares issued and outstanding at September 30, 2018 and 5,772,032 shares at March 31, 2018 us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares Nonvested (in shares) Nonvested (in shares) Adjustments to reconcile net (loss) income to net cash (used in) provided by operating activities: Outstanding, weighted average exercise price (in dollars per share) Common stock, shares authorized (in shares) us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice Forfeited, weighted average exercise price (in dollars per share) Common stock, shares issued (in shares) Common stock, par value (in dollars per share) us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice Granted, weighted average exercise price (in dollars per share) us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice Exercised, weighted average exercise price (in dollars per share) Capital Lease Asses Payable in 36 Equal Monthly Payments [Member] Represents information regarding to capital lease assets which are payable in 36 equal payments. Accrued expenses Total accrued expenses The 2016 Plan [Member] Represents the 2016 Cyanotech Equity Incentive Plan (the “2016 Plan”). Range [Domain] Maximum [Member] Minimum [Member] Accounts payable Product and Service [Axis] Revolving Credit Facility [Member] us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber Outstanding (in shares) Outstanding (in shares) Product and Service [Domain] Range [Axis] Credit Facility [Axis] Credit Facility [Domain] Preferred stock of $0.01 par value, authorized 10,000,000 shares; no shares issued and outstanding Other accrued expenses Preferred, issued shares (in shares) Long-term debt, less current maturities Total long-term debt, net of current maturities and unamortized debt issuance costs Amount of long-term debt and capital lease obligation net of issuance costs, due after one year or beyond the normal operating cycle, if longer. Wages, commissions, bonus and profit sharing Interest us-gaap_PolicyTextBlockAbstract Accounting Policies Property, Plant and Equipment Disclosure [Text Block] Property, Plant and Equipment [Table Text Block] Preferred, authorized shares (in shares) Inventories, net Inventories, net us-gaap_PaymentsToAcquireProductiveAssets Investment in equipment and leasehold improvements Available (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Preferred stock, par value (in dollars per share) Customer [Axis] us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period Customer [Domain] Authorized (in shares) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1 Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period SHARES USED IN CALCULATION OF NET (LOSS) INCOME PER SHARE: Income taxes Current liabilities: us-gaap_IncreaseDecreaseInCustomerDeposits Customer deposits us-gaap_Assets Total assets SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION: Plan Name [Axis] Plan Name [Domain] us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Total CASH FLOWS FROM OPERATING ACTIVITIES: us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1 Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Revenue Recognition, Policy [Policy Text Block] Statement [Line Items] Accounts receivable, allowance for doubtful accounts Accounts receivable, net of allowance for doubtful accounts of $27 at September 30, 2018 and $27 at March 31, 2018 Furniture and Fixtures [Member] us-gaap_DilutiveSecurities Effect of dilutive securities on net income Additional paid-in capital Bank of the West Finance [Member] Finance agreements with Bank of the West. Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Stockholders’ equity: Leasehold Improvements [Member] Equipment Finance Agreement [Member] A financing agreement that allows for the purchase of equipment by the reporting entity. Packaged Astaxanthin [Member] Refers to information regarding packaged Astaxanthin. Bulk Products [Member] Refers to information regarding bulk products. Property, Plant and Equipment, Type [Axis] Packaged Products [Member] Refers to information regarding the packaged products. Property, Plant and Equipment, Type [Domain] Business Description and Basis of Presentation [Text Block] Deposit Account [Member] Equity Award [Domain] Bulk Spirulina [Member] Refers to information regarding bulk Spirulina. cyan_DebtAgreementMaximumBorrowingCapacity Debt Agreement, Maximum Borrowing Capacity Maximum borrowing capacity under a debt agreement on the amount that could be borrowed with a combination of, but not limited to, a line of credit and term loan. Bulk Astaxanthin [Member] Refers to information regarding bulk Astaxanthin. Packaged Spirulina [Member] Refers to information regarding packaged Spirulina. Current assets: us-gaap_CustomerDepositsCurrent Customer deposits Restricted Cash Spirulina [Member] Refers to information regarding Spirulina. Award Type [Axis] Astaxanthin [Member] Refers to information regarding Astaxanthin. Net (loss) income NET (LOSS) INCOME Net income (loss) Cash and restricted cash at beginning of period Cash and restricted cash at beginning of period Cash at end of period Restricted Stock Units (RSUs) [Member] us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect Net (decrease) increase in cash First Foundation Bank [Member] Represents information about First Foundation Bank. 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diluted Concentration Risk, Credit Risk, Policy [Policy Text Block] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation Withholding on restricted stock unit vesting us-gaap_CapitalLeasedAssetsNumberOfUnits Capital Leased Assets, Number of Units CASH FLOWS FROM INVESTING ACTIVITIES: us-gaap_RelatedPartyTransactionSellingGeneralAndAdministrativeExpensesFromTransactionsWithRelatedParty Related Party Transaction, Selling, General and Administrative Expenses from Transactions with Related Party us-gaap_IncomeTaxExpenseBenefitContinuingOperationsAdjustmentOfDeferredTaxAssetLiability Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability NET (LOSS) INCOME PER SHARE: Earnings Per Share [Text Block] NET SALES Revenue Proceeds from stock options exercised Related Party Transactions Disclosure [Text Block] Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Table Text Block] Tabular disclosure of the components of cash and cash equivalents, and cash and cash equivalents restricted to withdrawal or usage. us-gaap_IncreaseDecreaseInAccruedLiabilities Accrued expenses INCOME TAX (BENEFIT) EXPENSE Equity Components [Axis] Equity Component [Domain] Long-term debt Long-term Debt, Total Capital lease obligations Capital Lease Obligations, Total cyan_RelatedPartyTransactionPaymentsToRelatedParty Related Party Transaction, Payments to Related Party Represents the amount of payments to related party during the period. us-gaap_IncreaseDecreaseInAccountsPayable Accounts payable The 2015 Loan Agreement [Member] Represents the 2015 Loan Agreement with a lender. us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest (Loss) income before income taxes us-gaap_OperatingExpenses Total operating expenses General and administrative Cash us-gaap_DeferredFinanceCostsNet Less unamortized debt issuance costs us-gaap_IncreaseDecreaseInOtherNoncurrentLiabilities Other long-term liabilities Disaggregation of Revenue [Table Text Block] us-gaap_AllocatedShareBasedCompensationExpense Allocated Share-based Compensation Expense, Total us-gaap_RepaymentsOfLongTermDebt Principal payments on long-term debt Equipment [Member] us-gaap_RepaymentsOfLongTermCapitalLeaseObligations Payments on capitalized leases Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block] Amendment Flag us-gaap_UnrecognizedTaxBenefits Unrecognized Tax Benefits, Ending Balance Accounting Policies [Abstract] Significant Accounting Policies [Text Block] Use of Estimates, Policy [Policy Text Block] New Accounting Pronouncements, Policy [Policy Text Block] Reclassification, Policy [Policy Text Block] Common stock, shares outstanding (in shares) Preferred outstanding, shares (in shares) us-gaap_DebtInstrumentInterestRateDuringPeriod Debt Instrument, Interest Rate During Period Long-term debt, excluding current maturities Current Fiscal Year End Date us-gaap_DebtInstrumentBasisSpreadOnVariableRate1 Debt Instrument, Basis Spread on Variable Rate Net increase (decrease) in liabilities: us-gaap_DebtInstrumentInterestRateStatedPercentage Debt Instrument, Interest Rate, Stated Percentage us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets Prepaid expenses and other assets Document Fiscal Period Focus Document Fiscal Year Focus Consolidation, Policy [Policy Text Block] Document Period End Date Entity Emerging Growth Company Document Type Customer Number 1 [Member] Information pertaining to customer number 1 accounting for a percentage of accounts receivable. us-gaap_AssetImpairmentCharges Asset Impairment Charges, Total Entity Small Business Customer Number 2 [Member] Information pertaining to customer number 2 accounting for a percentage of accounts receivable. Document Information [Line Items] Document Information [Table] Non-employee Directors [Member] Represents the information pertaining to non-employee directors. Entity Filer Category Debt Instrument [Axis] Entity Current Reporting Status Debt Instrument, Name [Domain] Employees [Member] Refers to information regarding employees. 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Entity [Domain] Customer Concentration Risk [Member] Legal Entity [Axis] Statement [Table] Scenario [Axis] Statement of Financial Position [Abstract] Diluted (in dollars per share) Earnings per share - diluted (in dollars per share) Scenario, Unspecified [Domain] cyan_DebtInstrumentReferenceRate Debt Instrument Reference Rate Represents the reference rate used to compute the variable rate on the debt instrument. Basic (in shares) Shares outstanding - basic (in shares) Accounts Payable and Accrued Liabilities Disclosure [Text Block] cyan_DebtInstrumentPrepaymentPenaltyPercentage Debt Instrument, Prepayment Penalty Percentage Represents the prepayment penalty rate applicable, if any prepayment is made prior to the first anniversary. cyan_NumberOfMajorCustomers Number of Major Customers Represents the number of major customers accounting for 10% or more of the specified concentration risk benchmark, which includes, but not limited to, sales revenue, accounts receivable, etc cyan_DebtInstrumentPrepaymentPenaltyPercentageReductionDuringEachYear Debt Instrument, Prepayment Penalty Percentage Reduction During Each Year Represents the percentage of reduction in prepayment penalty rate each year. cyan_DebtInstrumentOneTimeOriginationAndGuarantyFees Debt Instrument One Time Origination and Guaranty Fees Amount of one-time origination and guaranty fees on the debt instrument. us-gaap_EffectiveIncomeTaxRateContinuingOperations Effective Income Tax Rate Reconciliation, Percent, Total cyan_DebtInstrumentAnnualRenewalFeePayablePercentage Debt Instrument Annual Renewal Fee Payable Percentage Represents the percentage of annual renewal fee payable on the debt instrument. cyan_DebtInstrumentGuaranteedPortion Debt Instrument Guaranteed Portion Represents the guaranteed portion of the debt instrument. Basic (in dollars per share) Earnings per share - basic (in dollars per share) Concentration Risk Type [Axis] Net draws (payments) on line of credit Concentration Risk Type [Domain] cyan_DebtInstrumentPeriodicPaymentsNumber Debt Instrument Periodic Payments Number Represents the number of required periodic payments. Statement of Cash Flows [Abstract] Entity Common Stock, Shares Outstanding (in shares) Income Statement [Abstract] Sales Revenue, Net [Member] Accounts Receivable [Member] us-gaap_ProceedsFromIssuanceOfDebt Proceeds from Issuance of Debt Schedule of Accrued Liabilities [Table Text Block] Long-term Debt [Text Block] us-gaap_IncreaseDecreaseInInventories Inventories Trading Symbol Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Domain] Schedule of Share-based Compensation Shares Authorized Available and Outstanding by Plan [Table Text Block] Tabular disclosure of shares authorized, available for future grant and outstanding under each stock-based compensation plan. us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity Line of Credit Facility, Remaining Borrowing Capacity us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised Exercised (in shares) us-gaap_GainLossOnDispositionOfAssets Loss on disposal of assets us-gaap_TableTextBlock Notes Tables us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity Line of Credit Facility, Maximum Borrowing Capacity Director [Member] Related Party [Axis] Related Party [Domain] Granted (in shares) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross Granted (in shares) CASH FLOWS FROM FINANCING ACTIVITIES: us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod Forfeited (in shares) us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Sales and marketing Line of Credit Facility, Lender [Domain] cyan_NumberOfShareholderApprovedSharebasedCompensationPlans Number of Shareholder Approved Share-based Compensation Plans Represents the number of shareholder approved plans under which shares were available for equity based awards. Raw materials Supplies Lender Name [Axis] us-gaap_LiabilitiesAndStockholdersEquity Total liabilities and stockholders’ equity Finished goods Work in process Accumulated deficit Research and development Short-term Debt [Text Block] Net (increase) decrease in assets: us-gaap_StockholdersEquity Total stockholders’ equity Amortization of debt issue costs and other assets us-gaap_DisclosureTextBlockAbstract Notes to Financial Statements Inventory Disclosure [Text Block] Schedule of Inventory, Current [Table Text Block] Class of Stock [Axis] Other long-term liabilities us-gaap_RestrictedCashNoncurrent Restricted cash Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Subsequent Events [Text Block]