Document And Entity Information Scanner Appliances and Other Computer Equipment Subject To Subscription [Member] Represents information related to scanner appliances and other computer equipment subject to subscription. Dividend yield us-gaap_DerivativeNotionalAmount Derivative, Notional Amount Scanner Appliances and Other Computer Equipment Not Placed In Service [Member] Represents scanner appliances and other computer equipment not placed in service. Note To Financial Statement Details Textual Purchased Intangible Assets qlys_DepreciationDepletionAndAmortizationExcludingIntangibleAssetAmortization Depreciation, Depletion And Amortization, Excluding Intangible Asset Amortization Represents amount of depreciation, depletion and amortization excluding intangible asset amortization. Significant Accounting Policies Note 2 - Fair Value of Financial Instruments Scanner Appliances [Member] Represents information related to scanner appliances. Hedging Relationship [Domain] Note 3 - Accumulated Other Comprehensive Income (Loss) Risk-free interest rate Note 4 - Property and Equipment, Net Cash Flow Hedging [Member] Note 5 - Revenue from Contracts with Customers Contract With Customer, Commission Asset Balances [Table Text Block] Tabular disclosure of commission asset balance of contract with customer. Spell Security [Member] Represents information related to spell security. Note 6 - Acquisitions Not Designated as Hedging Instrument [Member] Note 7 - Intangible Assets, Net Available-for-sale Securities, Debt and Equity Maturities, Year One through Two, Fair Value Represents fair value of debt maturities for available-for-sale securities through year one to year two. Note 8 - Leases Total Cloud [Member] Represents total cloud. Note 9 - Commitment and Contingencies Net change in unrealized gains (losses) on available-for-sale debt securities, net of tax Available-for-sale Securities, Debt and Equity Maturities, Year over two years, Fair Value Represents fair value of available-for-sale for debt maturities after year two. Hedging Relationship [Axis] Income Tax Disclosure [Text Block] Note 10 - Stockholders' Equity and Stock-based Compensation Accumulated Other Comprehensive Income Disclosure [Text Block] The entire note disclosure of accumulated other comprehensive income. Note 12 - Income Taxes Hedging Designation [Axis] Note 13 - Segment and Geographic Area Information Hedging Designation [Domain] Note 14 - Net Income Per Share Volatility Designated as Hedging Instrument [Member] us-gaap_LiabilitiesCurrent Total current liabilities Available-for-sale Securities, Debt and Equity Maturities, Next Twelve Months, Fair Value Represents fair value of available-for-sale securities for debt maturities for next twelve months. Note 2 - Fair Value of Financial Instruments - Cash and Cash Equivalents (Details) Note 2 - Fair Value of Financial Instruments - Fair Value Hierarchy (Details) Note 2 - Fair Value of Financial Instruments - Summary of the Fair Value of Marketable Securities (Details) Note 2 - Fair Value of Financial Instruments - Summary of Derivative Financial Instruments (Details) Expected term (in years) (Year) Asset-backed Securities [Member] Note 2 - Fair Value of Financial Instruments - Amounts Recognized In Statement Of Operations (Details) Note 3 - Accumulated Other Comprehensive Income (Loss) - Accumulated Other Comprehensive Income (Loss) (Details) Note 3 - Accumulated Other Comprehensive Income (Loss) - Amounts Reclassified from AOCI (Details) Purchase Consideration Business Combination, Consideration Transferred, Total Note 4 - Property and Equipment, Net - Property and Equipment, Net (Details) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value Note 5 - Revenue from Contracts with Customers - Expected Revenue from All Remaining Performance Obligations (Details) us-gaap_FinitelivedIntangibleAssetsAcquired1 Finite-lived Intangible Assets Acquired Time based Shared Based Compensation [Member] Represents information related to time based share based compensation. Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions [Table Text Block] Note 5 - Revenue from Contracts with Customers - Expected Revenue from All Remaining Performance Obligations 2 (Details) us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife Acquired Finite-lived Intangible Assets, Weighted Average Useful Life (Year) qlys_SharebasedCompensationTerminationPeriodTrigger Share-based Compensation Termination Period Trigger (Month) Represents termination period trigger for share-based compensation. Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Note 5 - Revenue from Contracts with Customers - Revenue by Sales Channel (Details) qlys_SharebasedCompensationPercentageOfSharesThatWillVestUponTrigger Share-Based Compensation, Percentage Of Shares That Will Vest Upon Trigger Represents percentage of shares that will vest upon trigger for share-based compensation. Note 5 - Revenue from Contracts with Customers - Capitalized Cost to Obtain Contracts, Current and Noncurrent (Details) Note 6 - Acquisitions - Estimated Fair Values of the Acquired Assets (Details) Note 7 - Intangible Assets, Net - Carrying Value of Intangible Assets (Details) Note 7 - Intangible Assets, Net - Expected Amortization Expense in Future Periods (Details) Share-based Payment Arrangement, Option, Activity [Table Text Block] Note 8 - Leases - Supplemental Cash Flow Information (Details) Note 8 - Leases - Weighted Average Remaining Lease Term and Weighted Average Discount Rate (Details) Expected to vest, weighted average grant date fair value (in dollars per share) Represents weighted average exercise for share-based compensation arrangement by share-based payment award for equity instruments other than options, expected to vest. Note 8 - Leases - Minimum Annual Lease Payments (Details) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue Granted, weighted average grant date fair value (in dollars per share) qlys_SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsTargetNumberOfShares Share-Based Compensation Arrangement By Share-based Payment Award, Equity Instruments Other Than Options, Target Number Of Shares (in shares) Represents target number of shares of share-based compensation by share-based payment award for equity instruments other than options. Note 9 - Commitment and Contingencies - Remaining Purchase Commitments (Details) Sales and maturities of marketable securities Vested, weighted average grant date fair value (in dollars per share) qlys_GoodwillDeductibleForTaxPurposePeriod Goodwill, Deductible for Tax Purpose Period (Year) Represents deductible for tax purpose period for goodwill. Cancelled, weighted average grant date fair value (in dollars per share) Note 10 - Stockholders' Equity and Stock-based Compensation - Summary of Stock-based Compensation Expense (Details) Share-based Payment Arrangement, Restricted Stock and Restricted Stock Unit, Activity [Table Text Block] Note 10 - Stockholders' Equity and Stock-based Compensation - Fair Value Assumptions, Stock Options (Details) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue Balance, weighted average grant date fair value (in dollars per share) Balance, weighted average grant date fair value (in dollars per share) Note 10 - Stockholders' Equity and Stock-based Compensation - Share-based Compensation and Stock Options Activity (Details) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod Cancelled, number of shares (in shares) qlys_ShareBasedCompensationArrangementByShareBasedPaymentAwardVestingPeriodNumberOfQuarterlyPeriods Share based Compensation Arrangement by Share based Payment Award, Vesting Period, Number Of Quarterly Periods Represents number of quarterly periods for vesting periods for share based compensation arrangement by share based payment award. Note 10 - Stockholders' Equity and Stock-based Compensation - Share-based Compensation, Restricted Stock and Restricted Stock Units (Details) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber Balance, number of shares (in shares) Balance, number of shares (in shares) Note 10 - Stockholders' Equity and Stock-based Compensation - Employee Stock Purchase Plan, Valuation Assumptions (Details) Other foreign currency transactions gains (losses) Commercial Paper, Not Included with Cash and Cash Equivalents [Member] qlys_SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodAsAPercentageOfTarget Share-Based Compensation Arrangement By Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period As A Percentage Of Target Represents equity instruments other than options vested in period as a percentage of target for share-based compensation arrangement by share-based payment award. Note 10 - Stockholders' Equity and Stock-based Compensation - Schedule of Repurchase Agreements (Details) Schedule of Derivative Instruments [Table Text Block] Exercisable, weighted average remaining contractual life (Year) Note 12 - Income Taxes - Schedule of Income before Income Tax, Domestic and Foreign (Details) US Government Agencies Debt Securities [Member] Note 12 - Income Taxes - Schedule of Components of Income Tax Expense (Benefit) (Details) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) Note 12 - Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period (in shares) Vested, number of shares (in shares) Corporate Debt Securities [Member] Note 12 - Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) Intangible Assets Not Subject to Amortization [Member] Represents intangible assets not subject to amortization. Vested and Expected to vest, weighted average remaining contractual life (Year) Note 12 - Income Taxes - Schedule of Unrecognized Tax Benefits Roll Forward (Details) Exercisable (in shares) Note 13 - Segment and Geographic Area Information - Revenue and Property and Equipment, Net by Geographic Area (Details) Exercisable, Weighted average exercise price (in dollars per share) Note 14 - Net Income Per Share - Basic and Diluted Net Income Per Share (Details) Exercisable, aggregate intrinsic value Note 14 - Net Income Per Share - Anti-dilutive Net Income Per Share (Details) Notes To Financial Statements Vested and expected to vest (in shares) Notes To Financial Statements [Abstract] Vested and Expected to vest, weighted average exercise price (in dollars per share) Vested and Expected to vest, aggregate intrinsic value Foreign Exchange Contract [Member] us-gaap_PaymentsForAdvanceToAffiliate Payments for Advance to Affiliate us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value Weighted Average Remaining Contractual Life Balance (Year) Aggregate intrinsic value us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share) Cash and Cash Equivalents and Debt Securities, Available-for-sale, Amortized Cost to Fair Value [Table Text Block] Tabular disclosure of cash and cash equivalents and debt securities available-for-sale amortized cost to fair value. Lessee, Operating Leases and Finance Lease [Text Block] The entire disclosure of operating lease and finance lease for lessee. Short-term marketable securities, amortization cost Represents current amortized cost basis for available-for-sale debt. us-gaap_PaymentsToAcquireMarketableSecurities Purchases of marketable securities Financial Instruments [Domain] qlys_AvailableforsaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTaxCurrent Short-term marketable securities, unrealized loss Represents accumulated unrealized loss before tax current for available for sale debt securities. qlys_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTaxNoncurrent Long-term marketable securities, unrealized loss Represents accumulated gross unrealized loss before tax noncurrent for debt securities available for sale. us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice Weighted average exercise price, balance (in dollars per share) Weighted average exercise price, balance (in dollars per share) Cash and cash equivalents and short-term and long-term Marketable Securities, fair value Represents fair value disclosure for cash and cash equivalents and short-term and long-term debt securities available for sale. Long-term marketable securities, amortization cost Represents noncurrent amortized cost basis for available for sale debt securities. Cash and cash equivalents and marketable securities, amortization cost Represents amortized cost of cash and cash equivalents and available-for-sale debt securities. Accrued liabilities and other noncurrent liabilities increase(decrease) in accrued liabilities and other noncurrent liabilities. Deferred revenues, current Unrealized gains, short-term securities Represents accumulated gross unrealized gain before tax current for debt securities available for sale. Weighted average exercise price, canceled (in dollars per share) Financial Instrument [Axis] Unrealized gains, long-term securities Represents unrealized gain before tax for non current debt securities available for sale. Weighted average exercise price, granted (in dollars per share) Weighted average exercise price, exercised (in dollars per share) Accrued liabilities Accounts payable us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber Balance (in shares) Balance (in shares) Retirement Plan Type [Axis] Retirement Plan Type [Domain] Purchases of property and equipment recorded in accounts payable and accrued liabilities us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod Canceled (in shares) Proceeds from disposal of property and equipment us-gaap_PolicyTextBlockAbstract Accounting Policies us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAcceleratedCompensationCost Share-based Payment Arrangement, Accelerated Cost Property and equipment, net and Operating leases - right of use asset Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale and right-of-use assets under operating leases. Restricted stock units (in shares) us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAcceleratedVestingNumber Share-based Compensation Arrangement by Share-based Payment Award, Accelerated Vesting, Number (in shares) qlys_PaymentsToAcquireMaturitiesOfNotesReceivable Maturity (purchase) of note receivable The amount of cash outflow (inflow) from the acquisition and maturities of notes receivable. us-gaap_PaymentsToAcquireIntangibleAssets Payments to Acquire Intangible Assets us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent Indefinite-lived Intangible Assets [Axis] Indefinite-lived Intangible Assets, Major Class Name [Domain] Employee stock purchase plan (in shares) us-gaap_PaymentsToAcquirePropertyPlantAndEquipment Purchases of property and equipment Stock options (in shares) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized (in shares) Non-cash investing and financing activities us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in shares) Share Repurchase Program [Table Text Block] Tabular disclosure of share repurchase program. us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1 Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year) Weighted average shares used in computing net income per share: Noncompete Agreements [Member] Cash paid for income taxes, net of refunds us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage Current liabilities: Developed Technology Rights [Member] Vesting [Axis] October 30, 2018 Amount of additional stock repurchase plan authorized 1. Vesting [Domain] Supplemental disclosures of cash flow information us-gaap_Assets Total assets Patents [Member] Plan Name [Axis] Shareholders' Equity and Share-based Payments [Text Block] Plan Name [Domain] Compensation and Employee Benefit Plans [Text Block] us-gaap_OperatingLeaseExpense Operating Lease, Expense us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1 Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year) us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense Share-based Payment Arrangement, Expense, Tax Benefit Deferred tax assets, net Computer Software, Intangible Asset [Member] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets, Major Class Name [Domain] Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block] us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation Taxes related to net share settlement of equity awards Award Type [Domain] Basis of Presentation and Significant Accounting Policies [Text Block] Award Type [Axis] Net income Net income us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization Amortization of intangible assets Net Book Value Total expected future amortization expense Total intangible assets, net Restricted Stock Units (RSUs) [Member] Cost Performance Shares [Member] Share-based Payment Arrangement, Option [Member] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block] Antidilutive Securities [Axis] Antidilutive Securities, Name [Domain] Intangible assets not subject to amortization Commitments and Contingencies Disclosure [Text Block] Business Combination Disclosure [Text Block] us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment Less: accumulated depreciation and amortization Property and equipment, net Property, Plant and Equipment, Net, Ending Balance Property and equipment and finance lease, net Schedule of Business Acquisitions, by Acquisition [Table Text Block] Goodwill Goodwill us-gaap_PropertyPlantAndEquipmentGross Property and equipment and finance lease Net gains (losses) from non-designated forward contracts us-gaap_Investments Investments, Total Derivative Instrument [Axis] Derivative Contract [Domain] Cash flow from investing activities: Debt Securities, Available-for-sale Net income per share: Earnings Per Share [Text Block] us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments Total Income tax provision Income tax provision us-gaap_ForeignCurrencyCashFlowHedgeGainLossToBeReclassifiedDuringNext12Months Foreign Currency Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months us-gaap_IncreaseDecreaseInAccountsPayable Accounts payable ESPP Shares [Member] Represents information regarding ESPP shares. qlys_EmployeeStockPurchasePlanPercentageOfEligibleCompensationContributable Employee Stock Purchase Plan, Percentage of Eligible Compensation Contributable Represents the percentage of employee's eligible compensation that can be used to contribute, through payroll withholding, to an employee stock purchase plan. us-gaap_OperatingExpenses Total operating expenses Restricted cash us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount Defined Contribution Plan, Employer Discretionary Contribution Amount us-gaap_RestrictedCash Restricted Cash, Total General and administrative Cash and cash equivalents Cash, Cash Equivalents and Short-Term and Long-Term Investments Policy [Policy Text Block] Accounting policies disclosure for cash, cash equivalent and short-term and long-term investments. Stock-based compensation us-gaap_AllocatedShareBasedCompensationExpense Share-based Payment Arrangement, Expense U.S. Treasury and government agencies Commercial paper Money market funds Asset-backed securities Amendment Flag Auditor Name Auditor Location Auditor Firm ID ICFR Auditor Attestation Flag Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract] us-gaap_ComprehensiveIncomeNetOfTax Comprehensive income City Area Code Use of Estimates, Policy [Policy Text Block] Total New Accounting Pronouncements, Policy [Policy Text Block] qlys_SharebasedCompensationArrangementBySharebasedPaymentAwardNumberOfSharesAuthorizedAnnualIncreasePercentOfSharesOutstanding Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized, Annual Increase, Percent of Shares Outstanding Represents percentage of shares outstanding for member of shares authorized for shared-based compensation arrangement by share-based compensation. qlys_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardStrikePriceAsAPercentageOfMarketValue Share-based Compensation Arrangement by Share-based Payment Award, Award Strike Price as a Percentage of Market Value Represents awards strike price as a percentage for share based compensation arrangement by share based payment award. us-gaap_GainLossOnSaleOfPropertyPlantEquipment Loss on disposal of property and equipment INDIA us-gaap_IncreaseDecreaseInContractWithCustomerLiability Deferred revenues Foreign government us-gaap_SharesOutstanding Balances (in shares) Balances (in shares) Common stock, shares outstanding (in shares) Corporate bonds Preferred stock, shares outstanding (in shares) Preferred Stock, Shares Outstanding, Ending Balance (in shares) qlys_SharebasedCompensationArrangementBySharebasedPaymentAwardNumberOfSharesAuthorizedAnnualIncreaseShares Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized, Annual Increase, Shares (in shares) Represents number of shares authorized for share-based compensation arrangement by share-based compensation. Current Fiscal Year End Date us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets Prepaid expenses and other assets Weighted average discount rate Document Fiscal Period Focus Document Fiscal Year Focus Document Period End Date Lease liabilities arising from obtaining right-of-use assets us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability Weighted average remaining lease term (Year) Entity File Number Entity Emerging Growth Company Document Type Entity Small Business Entity Shell Company Document Information [Line Items] Document Information [Table] Entity Public Float Entity Filer Category Entity Current Reporting Status Entity Voluntary Filers Entity Well-known Seasoned Issuer Write off of noncurrent asset us-gaap_ImpairmentOfLongLivedAssetsHeldForUse Impairment, Long-Lived Asset, Held-for-Use, Total us-gaap_CapitalizedContractCostImpairmentLoss Capitalized Contract Cost, Impairment Loss us-gaap_IncreaseDecreaseInAccountsReceivable Accounts receivable Stock-based compensation Entity Tax Identification Number Entity Central Index Key Entity Registrant Name Entity [Domain] us-gaap_CapitalizedContractCostAmortizationPeriod Capitalized Contract Cost, Amortization Period (Year) Legal Entity [Axis] Entity Address, Address Line One us-gaap_AmortizationOfIntangibleAssets Amortization of Intangible Assets, Total Entity Address, City or Town us-gaap_AmortizationOfDeferredSalesCommissions Amortization of Deferred Sales Commissions Entity Address, Postal Zip Code Entity Address, State or Province Allowance for doubtful accounts receivable us-gaap_StockRepurchasedDuringPeriodShares Repurchase of common stock (in shares) Entity Common Stock, Shares Outstanding us-gaap_StockRepurchasedAndRetiredDuringPeriodValue Stock Repurchased and Retired During Period, Value us-gaap_StockRepurchasedAndRetiredDuringPeriodShares Stock Repurchased and Retired During Period, Shares (in shares) us-gaap_StockRepurchasedDuringPeriodValue Repurchase of common stock us-gaap_AdvertisingExpense Advertising Expense Investments [Domain] Trading Symbol Investment Type [Axis] Local Phone Number Issuance of common stock upon exercise of stock options (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period (in shares) Exercised (in shares) us-gaap_TableTextBlock Notes Tables qlys_DeferredLiabilitiesRightofuseAssets Operating leases - right of use asset Represents the deferred liabilities right-of-use-assets. Issuance of common stock upon exercise of stock options qlys_DeferredTaxLiabilitiesDeferredCommission Deferred commissions Represents the deferred tax liabilities deferred commission. Bad debt expense us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross Granted (in shares) Sales and marketing us-gaap_LiabilitiesAndStockholdersEquity Total liabilities and stockholders’ equity UNITED STATES Provident Fund Plan and Gratuity Plan [Member] Represents the provident fund plan and gratuity plan Research and development Retained earnings (accumulated deficit) Accumulated other comprehensive income (loss) Money Market Funds [Member] 401(k) Plan [Member] Represents a 401(k) Plan. Cash and Cash Equivalents [Axis] Derivative Instruments, Gain (Loss) [Table Text Block] us-gaap_InterestExpense Interest expense Cash and Cash Equivalents [Domain] Cash [Member] Changes in operating assets and liabilities: us-gaap_DisclosureTextBlockAbstract Notes to Financial Statements Lease liabilities, noncurrent us-gaap_OperatingLeaseLiability Present value of net minimum lease payments Deferred income taxes Securities Owned Not Readily Marketable, Policy [Policy Text Block] Operating lease liabilities, current Less: lease liabilities, current Operating leases - right of use asset us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue Total minimum lease payments, operating leases us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount Less: interest us-gaap_FinanceLeasePrincipalPayments Principal payments under finance lease obligations us-gaap_DeferredIncomeTaxExpenseBenefit Deferred income tax provision (benefit) 2024, operating leases 2025, operating leases 2026, operating leases 2025 and thereafter, operating leases us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo 2023 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree 2024 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour 2025 2022, operating leases us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive 2026 2023, operating leases Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths 2022 Schedule of Acquired Finite-Lived Intangible Assets by Major Class [Table Text Block] Foreign Currency Transactions and Translations Policy [Policy Text Block] Noncurrent Lessee, Operating Lease, Liability, Maturity [Table Text Block] us-gaap_ShareBasedCompensation Stock-based compensation Other noncurrent assets Lessee, Leases [Policy Text Block] Weighted Average Remaining Life (Year) Business Combinations Policy [Policy Text Block] Weighted Average Life (Year) Finite-Lived Intangible Asset, Useful Life (Year) Earnings Per Share, Policy [Policy Text Block] Operating expenses: Comprehensive Income, Policy [Policy Text Block] Income Tax, Policy [Policy Text Block] us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments Amortization of premiums (accretion of discounts) on marketable securities The 2021 Employee Stock Purchase Plan [Member] Information related to the 2021 Employee Stock Purchase Plan. qlys_SharebasedCompensationArrangementBySharebasedPaymentAwardOfferingPeriod Share-based Compensation Arrangement by Share-based Payment Award, Offering Period (Month) Represents the offering period under a share-based payment arrangement. Long-term marketable securities Depreciation and amortization expense us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation Taxes related to net share settlement of equity awards (in shares) Performance-based Restricted Stock Units [Member] Information related to performance-based restricted stock units. Intangible Assets Disclosure [Text Block] President and Chief Executive Officer [Member] Information related to the President and Chief Executive Officer. us-gaap_ForeignCurrencyContractAssetFairValueDisclosure Foreign currency forward contracts us-gaap_ForeignCurrencyContractsLiabilityFairValueDisclosure Foreign currency forward contracts us-gaap_AssetsCurrent Total current assets us-gaap_CashAndCashEquivalentsFairValueDisclosure Cash and cash equivalents Share-based Payment Arrangement [Policy Text Block] Purchases of intangible assets recorded in accrued liabilities us-gaap_ImpairmentOfInvestments Other than Temporary Impairment Losses, Investments, Total Advertising Cost [Policy Text Block] Common stock: $0.001 par value; 1,000,000 shares authorized, 39,112 and 39,253 shares issued and outstanding as of December 31, 2021 and 2020, respectively Adjustments to reconcile net income to net cash provided by operating activities: Measurement Frequency [Axis] Measurement Frequency [Domain] Fair Value, Recurring [Member] Common stock, shares authorized (in shares) Commercial Paper [Member] Common stock, shares issued (in shares) Common stock, par or stated value per share (in dollars per share) us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount us-gaap_DeferredTaxAssetsValuationAllowance Deferred Tax Assets, Valuation Allowance, Total Valuation allowance Statistical Measurement [Domain] Cash payments included in the measurement of lease liabilities us-gaap_OperatingLeasePayments Maximum [Member] Minimum [Member] Current us-gaap_DeferredTaxAssetsNet Net deferred tax assets Statistical Measurement [Axis] Preferred stock: $0.001 par value; 20,000 shares authorized, no shares issued and outstanding as of December 31, 2021 and 2020 us-gaap_NumberOfReportingUnits Number of Reporting Units us-gaap_DeferredTaxAssetsLiabilitiesNet Net deferred tax assets Preferred stock, shares issued (in shares) Preferred Stock, Shares Issued, Total (in shares) Cash paid for interest expense Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block] Other Property, Plant and Equipment Disclosure [Text Block] Geographical [Axis] Goodwill and Intangible Assets, Policy [Policy Text Block] Property, Plant and Equipment [Table Text Block] Geographical [Domain] us-gaap_DeferredTaxAssetsGross Gross deferred tax assets Preferred stock, shares authorized (in shares) Preferred Stock, Shares Authorized (in shares) us-gaap_DeferredIncomeTaxLiabilities Total deferred tax liabilities Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas [Table Text Block] Preferred stock, par value (in dollars per share) Preferred Stock, Par or Stated Value Per Share (in dollars per share) Total foreign exchange gains (losses), net Deferred revenues Fair Value Hierarchy and NAV [Domain] Fair Value, Inputs, Level 1 [Member] Intangible assets Fair Value, Inputs, Level 2 [Member] 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Attributable to Parent [Member] Stockholders’ equity: Short-term marketable securities Leasehold Improvements [Member] Property, Plant and Equipment, Policy [Policy Text Block] us-gaap_OtherNonoperatingExpense Other expenses Other income (expense), net Other income (expense), net Long-Lived Tangible Asset [Axis] us-gaap_NonoperatingIncomeExpense Total other income, net Long-Lived Tangible Asset [Domain] Segment Reporting Disclosure [Text Block] Research and development credit carryforwards Foreign tax credit carryforwards Current assets: Fair Value Disclosures [Text Block] us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations Cash, cash equivalents and restricted cash at beginning of period Cash, cash equivalents and restricted cash at end of period Contractual Obligation, Fiscal Year Maturity [Table Text Block] Interest income 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